Hawaiian Volcanoes 

During 1951

GEOLOGICAL SURVEY BULLETIN 996-D

A CONTRIBUTION TO GENERAL GEOLOGY

HAWAIIAN VOLCANOES DURING 1951

By GORDON A. MACDONALD and CHESTER K. WENTWORTTI

ABSTRACT

The year 1951 produced no eruptive activity of the Hawaiian volcanoes, but 

much subsurface volcanic uneasiness was manifested in tilting of the ground surface and abundant earthquakes. Records of the earthquakes, of magnetic 

changes, of changes in the width of cracks, and of tilting of the ground surface, 

all reveal some of the changes that took place.

In December 1950, rapid south-southwestward tilting of the ground at the 

northeastern rim of Kilauea caldera indicated a sinking of the top of Kilauea 

volcano, in response to a decrease of pressure beneath. Throughout the first 

quarter of 1951 Kilauea was quiet, but in April there began a period of marked 

uneasiness. This was evidenced by a strong earthquake originating on the east 

rift zone on April 22, followed by 108 aftershocks, and on April 24 by the beginning of rapid northward tilting at the northeastern rim of the caldera, apparently 

accompanying an increase of volcanic pressure at depth. The increase of pressure beneath Kilauea continued until early August.

On August 21 the uneasiness was abruptly transferred to Mauna Loa. The 

earthquake at 00b 57m on August 21, in Kona, on the western slope of Mauna Loa, 

was the most severe of any on the island of Hawaii since 1868. In its epicentral 

area, in the vicinity of Napoopoo and Captain Cook in central Kona, it had an 

intensity of 7 on the modified Mercalli scale. The earthquake was felt generally 

and strongly over the island of Hawaii, and weakly by many people in Honolulu, 

200 miles away. The Kona seismograph was severely damaged by the first shock, 

and was only restored to operation 2 days later. The seismographs at the western rim of Kilauea caldera, and on the southeastern slope of Mauna Loa, at an 

altitude of 6,700 feet, were dismantled by the first waves and provided no useful 

records of the main earthquake. The seismograph at the northeastern rim 

of Kilauea caldera recorded the preliminary waves of the quake, but Avas dismantled by the first surface waves. All the instruments were restored to operation as soon as possible after the main quake, and recorded more than 1,000 aftershocks through the next few weeks.

Damage to structures and roads in the Kona district was severe and extensive. 

Several churches and houses and about 150 water tanks were demolished. Many 

houses suffered lesser damage. In every cemetery for a distance of 25 miles 

there was some derangement of headstones, and in those cemeteries near the 

epicenter damage was severe. Many stone walls were thrown down.

A study of the instrumental records and the distribution of damage indicate 

that the epicenter of the earthquake was probably on the Kealakekua fault

141
142 CONTRIBUTIONS TO GENERAL GEOLOGY

beneath the ocean, about 4 miles west of Napoopoo. The submarine origin of the 

quake is confirmed by the generation of a small tsunami.

During September a group of earthquakes originated on the Kaoiki fault zone, 

between Mauna Loa and Kilauea. In October earthquakes originated beneath 

the summit area of Mauna Loa and along both rift zones, as well as on the 

Kaoiki fault, and on the Kealakekua fault in Kona. On November 8 a strong 

quake originated on the southwest rift of Mauna Loa near Kahuku Ranch headquarters, and throughout November earthquakes came from scattered sources 

in Mauna Loa and Kilauea. The uneasiness of both volcanoes continued into 

early December, but the year closed with relative quiet prevailing.

In view of subsequent developments, there is little doubt that the general 

uneasiness throughout most of the year resulted from an increase of volcanic 

pressure beneath both volcanoes, which led eventually to the eruption of Kilauea 

on June 27, 1952.

INTRODUCTION

The offices and shop of the Hawaiian Volcano Observatory occupy a 

building at Uwekahima, on the western rim of Kilauea caldera near the 

highest point of Kilauea mountain. In addition the Observatory operates five seismograph stations and two independent tilt stations on the 

island of Hawaii. The master station for earthquake recording and 

tilt measurement is the Whitney Laboratory of Seismology, located on 

the northeastern rim of Kilauea caldera beneath the western end of the 

Volcano House, at the original site of the Hawaiian Volcano Observatory (fig. 31). The Uwekahuna station, near the western rim of 

Kilauea caldera about a quarter of a mile west of the main Observatory 

building (fig. 31), contains seismographs and tiltmeters.

The Mauna Loa station lies on the southeastern slope of Mauna Loa 

at an altitude of 6,700 feet, 8 miles northwest of the Observatory (fig. 

31). Tilt is measured from the records of the Hawaiian-type seismograph at the Mauna Loa station, but the record has proved of little use. 

Other seismograph stations are located in Hilo, 23 miles northeast, and 

in Kealakekua, Kona, 43 miles 1ST. 80° W., of the Observatory (fig. 41). 

Tilt is not measured at the Hilo and Kona stations. Two tilt-measuring stations are located on the floor of Kilauea caldera, respectively 

southeast and west of Halemaumau crater (fig. 35).

Accounts of the activity of the Hawaiian Volcano Observatory from 

the time it was taken over by the Geological Survey in December 1947, 

until the end of the year 1950 have already been published (Finch and 

Macdonald, 1951; Finch and Macdonald, 1953). The present report 

continues the account of Observatory activities through the year 1951.

The principal change in the organization during the year was the 

retirement on February 28 of Ruy H. Finch as volcanologist in 

charge of the Observatory. He was succeeded by Gordon A. Macdonald. In May, Chester K. Wentworth retired as geologist for the 

Honolulu Board of Water Supply and assumed full-time duties as 

geologist for the Observatory. He returned to part-time status in 

October. John C. Forbes served as instrumentmaker, and LaVieve G.
HAWAIIAN VOLCANOES DURING 1951 143

Forbes served as part-time clerk-stenographer throughout the year. 

During July, Brother Bernard T. Pleimann was succeeded by Sister 

M. Thecla as operator of the seismograph station at St. Joseph's 

School in Hilo.

ACKNOWLEDGMENTS

It is a pleasure to acknowledge the aid of many persons on the island 

of Hawaii in the routine operations of the Hawaiian Volcano Observatory and during the course of special investigations. Although our 

sincere thanks are extended to all, it is impossible to mention all by 

name.

The staff of Hawaii National Park has been constantly helpful and 

we wish to express our appreciation to F. R. Oberhansley, superintendent, for innumerable courtesies and assistance in many ways. D. 

H. Hubbard, naturalist, and V. R. Bender, biologist, have supplied 

information on several occasions. E. Iv. Field, chief ranger, and E. L. 

Bohlin, ranger, made aerial photographs of parts of the caldera of 

Kilauea and the southwest rift zone of Maun a Loa, for use by the 

Observatory in mapping.

Mrs. Alfred E. Hansen of Naalehu, Miss Nancy Wallace of Kealakekua, Robert M. Baldwin of Hilo, Edward G. Wingate of Kapoho, and 

Alien P. Johnston, manager of the Kapapala Ranch, have all aided 

greatly by reporting to the Observatory the time and character of 

earthquakes felt by them and others in their districts.

Copies of the seismograms of the major earthquake of August 21 

recorded at the Honolulu Magnetic Observatory of the U. S. Coast 

and Geodetic Survey, at Barbers Point on Oahu, were kindly loaned 

to us by Roland E. White, the observer in charge. Commander C. A. 

George of the Coast and Geodetic Survey, also kindly supplied us witli 

copies of the tide-gage records from Honolulu and Hilo harbors, showing the small tsunami that followed the earthquake.

Many persons cooperated in supplying information on water tanks 

damaged by the earthquake of August 21. Especially helpful were: 

John I wane, of the Extension Service, University of Hawaii; Masuoka 

Nagai, of Captain Cook Coffee Co.; Mark Sutherland, principal of 

Konawaena School; and George T. Imai, of the Hawaii County Road 

Department; and the Hilo office of the Territorial Department of 

Public Instruction. The Territorial Board of Health supplied data 

on the location and ownership of cemeteries in Kona. Homer A. 

Hayes has aided by supplying information on damage by the August 

21 earthquake, and data on the age of several of the old churches in 

the Kona district.

SEISMOGRAPHS AND 1TLTMETERS

An account of the seismographs and tiltmeters in operation by the 

Hawaiian Volcano Observatory at the close of 1949 was given in an
144 CONTRIBUTIONS TO GENERAL GEOLOGY

earlier report (Finch and Macdonald, 1951). For the most part the 

installations remained the same through 1950-51. Some minor 

changes are described below.

In September 1950, a Sprengnether vertical seismograph was 

installed in the Uwekahuna seismograph vault. However, because of 

the lack of electric power at the Uwekahuna vault, the instrument was 

operated only for short periods, on an experimental basis. During 

this brief period the recorder was operated by means of storage batteries and a dc-ac inverter. In March 1951, the installation of an 

underground power cable was completed from the observatory building to the Uwekahuna vault. It was, however, possible to operate the 

Sprengnether seismograph only during the time the observatory shop 

was in operation, about 8 hours a day, 5 days a week. Operation of a 

Diesel-driven 25-kilowatt generator to supply power for the Sprengnether seismograph proved too expensive, and maintenance of the 

engine was too difficult.

In September 1951, Roland F. White, observer in charge of the 

Honolulu Magnetic Observatory of the Coast and Geodetic Survey, 

installed in the Uwekahuna seismograph vault a Neumann-Labarre 

vibration meter. The instrument has been loaned to the Hawaiian 

Volcano Observatory by the Coast and Geodetic Survey, for experimental purposes. Appreciation is expressed to the Coast and Geodetic Survey for the loan of the instrument, and for the assistance 

of Mr. White in installing it. Appreciation is also expressed to the 

Coast and Geodetic Survey for the earlier aid of Thomas Pearce in 

installing and adjusting the Sprengnether seismograph.

Until the end of 1951 the Neumann-Labarre instrument was operated intermittently, at different periods, to determine the optimum 

conditions for its operation to meet local problems. The boom of the 

instrument is oriented in an east-west position, because the station 

lies nearly west of the center of Kilauea caldera and east rift zone 

of Kilauea, and nearly east of the summit of Mauna Loa.

In April a new tiltmeter was installed in the Uwekahuna vault. 

This instrument consists of two horizontal pendulums, each weighing about 150 pounds, oriented respectively in north-south and eastwest directions. From April until September the pendulums were 

operated at a period of 29 seconds, but on September 25 the period 

was reduced to 20 seconds, and kept at that length for the remainder 

of the year. Until early July the semiportable tiltmeter, installed for 

temporary service in March 1950, was also operated in the Uwekahuna 

vault. There was fairly close agreement in the readings of the semiportable tiltmeter and of the new tiltmeter during the period that 

both were in operation.

Table 1 lists the seismographs and tiltmeters in regular operation 

in the stations of the Hawaiian Volcano Observatory at the end of
HAWAIIAN VOLCANOES DURING 1951

1951. The principal constants of the instruments, and the locations 

of the stations, also are given. The positions of the stations are shown 

in figure 31.

EXPLANATION

Howiion Volcano Observatory

Seismograph station

Magnetometer jtation

*I06 

Crack-measuring station

Topography by U.S. Geological Survey 155 20

FIGUUE 31. Map showing the location of the Hawaiian Volcano Observatory, seismograph 

stations, and magnetometer stations, in the vicinity of Kilauea caldera.

TABLE 1. Seismographs and tiltmeters operated l>y the Haivaiian Volcano

Observatory during 1951

Station

Whitney Laboratory of

Seismology (northeast

rim of Kilauea caldera).

Mauna Loa (altitude of

6,000 feet on east slope of

Mauna Loa).

Uwekahuna (1,000 feet west

of west rim of Kilauea

caldera).

Hilo (St. Joseph's School)..

Kona ( Konawacna School,

Kealakckua).

Southeast tilt cellar floor of

Kilauea caldera southeast

of Halemaumau.

West tilt cellar (floor of

Kilauea caldera west of

Halemaumau).

Latitude 

(north)

19°25'53"

19°29'32"

19°25'26"

19°43'11"

19°30'47"

19°24'20"

19°24'32"

Longitude 

(west)

155°15'40"

155°23'29"

155°17'30"

155°05'20"

155°55'07"

155°16'59"

155°17'33"

Instrument

Bosch-Omori seismograph and tiltmeter.

Hawaiian-type seismograph.

[Jaggar vertical seismograph.

Sprengnether vertical

< seismograph.

North-south and eastwest horizontal pen-

\ duluni tiltmeters.

Modified Bosch-Omori

seismograph.

Hawaiian-type seismograph.

Normal pendulum tiltmeter.

Normal pendulum tiltmeter.

Period of pendulum (seconds)

7.7

7.1

.4

.5

20.0

3.0

7.3

3

3

Magnification (approximate)

115

115

250

1, 750

7

175

115

100

100

Sensitivity to tilt

(seconds 

of arc 

per millimeter)

0.12

.14

None.

None.

.32

.48

.13

1.3

1.3

296333 54-
146 CONTRIBUTIONS TO GENERAL GEOLOGY 

RECORDS AND INVESTIGATIONS 

EARTHQUAKES

A total of 833 earthquakes was recorded on the seismographs at 

Kilauea caldera in 1951. During the same period, the seismograph 

at the Mauna Loa station recorded 704 earthquakes. The total number 

of shocks received at the Kona station is not known, because of incomplete recording during the early part of the year. During the interval from August 23 to December 31 the Kona seismograph recorded 

1,276 earthquakes. If the instrument had not been put out of operation temporarily by tlie heavy earthquake of August 21, it is estimated that the total would have been more than 2,400.

The number of earthquakes recorded per week on the BoschOmori seismograph at the Whitney Laboratory, on the northeastern 

rim of Kilauea caldera, ranged from 0 to 209. The most frequent 

number was 4, followed by 2 and 9. If the weeks having very high 

totals caused by swarms of aftershocks following major earthquakes 

are excluded, the average number per week is 8.9, or slightly more 

than one earthquake a day. The number of earthquakes per week 

recorded at the Whitney Laboratory is shown graphically in figure 32.

Swarms of aftershocks followed the Kilauea earthquake of April 

22 and the Kona earthquake of August 21.' They are discussed in later 

sections of the report dealing specifically with those earthquakes.

Early on the morning of September 16 an earthquake was felt over 

most of the southern part of the island. It was reported strong at 

Kapapala, fairly strong at Naalehu, Pahala, and the Volcano district, 

and weak in Kona and Hilo. The first waves were registered on the 

Bosch-Omori seismograph at the Whitney Laboratory at Ol h42m55s 

Hawaiian time. The time of origin of the quake was Olh42m51s 

(Ilh42m51s G. c. t.) The Bosch-Omori seismograph at the Whitney 

Laboratory, the Jaggar vertical seismograph at the Uwekahuna station, and the Hawaiian-type seismograph at the Mauna Loa station, 

all were dismantled by the P phase of the earthquake. The S-P intervals recorded on the Hilo and Kona seismographs, and the damage 

clone by the earthquake, place the focus of the quake beneath the southeastern slope of Mauna Loa about 10 miles southwest of Kilauea 

caldera and about 3 miles northeast of Kapapala, at approximately 

19° 19' N. and 155° 25' W. The focus of the earthquake probably was 

along the Kaoiki fault zone. The intensity near the epicenter was 

about 5 on the modified Mercalli scale. Three miles southwest of the 

epicenter, at Kapapala Ranch headquarters, objects were thrown from 

shelves and water slopped out of tanks. Rocks were shaken down in 

road cuts along the Mauna Loa truck trail in Hawaii National Park, 

and rock slides started in Halemaumau that continued intermittently
HAWAIIAN VOLCANOES DURING 1951 147

30

; 20

.

orthquok

"o

u 10 

0)

a

Z 

n

-

-

-

1C-1)4

'

,| ||

2C

4

)9

*

5 

4

0

>

4

4

2

>

-

"

-

-

-

-

\i/--L I tl f ID t 10 ween |4 28 M 25 M 2. 

>: storfin« Jon. Feb. Mar.

15 29 13 27 10 24 8 22 5 19 2 16 30 14 28 II 25 9 23 

8 22 6 20 3 17 I 15 29 12 26 9 23 7 21 4 18 2 16 30 

Apr. May June July Aug. Sept. Oct. Nov. Dec.

FIGUUK 32. Gruph showing the number of earthquakes recorded each week during 11)51 lit 

the Whitncy Laboratory of Seismology, on the northeastern rim of Kilauea caldera.

for several days. No serious damage was done, however. The major 

earthquake was followed by 21 small aftershocks, most of which apparently also originated along the Ivaoiki fault zone.

Another swarm of small earthquakes that originated along the 

Kaoiki fault zone between October 1 and 6, bring the total recorded 

at the Whitney Laboratory dining the week starting September 30 to 

26.

An earthquake of about intensity 6 in the modified-Mercalli scale 

occurred on the morning of November 8. The time of arrival of the 

first waves at the Whitney Laboratory was 09h 34m24s, and the time of 

origin of .the quake was approximately 09h34m12s. All the seismographs operating on the island of Hawaii were dismantled by the 

quake, the Mauna Loa instrument being dismantled by the preliminary waves. The earthquake was felt over all the island, and was felt 

strongly over the southwestern part. At Kahuku Ranch headquarters, 9.5 miles north of South Point, dishes were thrown from shelves, 

and stone walls were extensively damaged. The intensity decreased 

rapidly away from the epicenter. At South Point, and at Kaalualu, 

10 miles southeast from Kahuku Ranch headquarters, there was no 

damage to stone walls, and in the homestead area 4 miles southeast of 

ranch headquarters the damage was very small. Westward the decrease was even more rapid. Two and a half miles west of the ranch 

headquarters iStone walls along the highway were undamaged. In-
148 CONTRIBUTIONS TO GENERAL GEOLOGY

strumental data and the field investigation place the epicenter of the 

earthquake on the southwest rift zone of Mauna Loa at an altitude of 

4,500 feet, about 5 miles north of Kahuku Ranch headquarters. The 

Kahuku fault, one of the major fractures in the southwest rift zone, 

trends nearly north and south just west of the ranch headquarters. 

The area of damage to stone walls was distinctly elongated parallel to 

the Kahuku fault, suggesting that the earthquake was caused by 

movement on that fault. The rapid decrease of damage at increasing 

distance from the epicenter suggests a shallow origin of the quake, 

but no surface fault displacement has been found.

At 20h19m on December 6 a strong earthquake was felt over the 

southeastern part of the island of Hawaii. None of the seismographs 

were dismantled and no damage was reported. The earthquake originated on the east rift zone of Kilauea volcano, about 14 miles east of 

the caldera and 7 miles southwest of the town of Pahoa, at a depth 

of 3 or 4 miles.

For more than 20 years the Hawaiian Volcano Observatory has been 

employing a scale of seismicity, designed to give some roughly qualitative measure of the comparative amounts of energy released by local 

earthquakes during given periods (Jones, 1932). The scale is an 

arbitrary one. Seismicity values are derived by assigning a numerical 

value to each earthquake, depending on its intensity, and totaling these 

values for the period in question. The intensity assigned to the earthquake depends largely or entirely on the amplitude of the record 

produced by the earthquake on the seismographs, taking into consideration the magnification of the various instruments. Thus an earthquake producing a record having a double amplitude of 4 to 11 

millimeters on the Bosch-Omori seismograph at the Whitney Laboratory is classified as "feeble," and assigned a seismicity value of 1. 

An earthquake producing a record with a double amplitude of 25 to 

60 millimeters on the same instrument is classified as "moderate," and 

assigned a seismicity value of 3. The grades of earthquake intensity 

and the seismicity value assigned to each grade, are listed in table 2.

Earthquakes of seismicity value 1 to 4 correspond to about the same 

numerical grades in the Rossi-Forel and modified Mercalli scales of 

intensity. Table 2 also indicates the corresponding grades in those 

scales, and gives a brief description of the noninstrumental effects 

produced by earthquakes of each grade from 1 to 4. However, because 

the Hawaiian Volcano Observatory scale is based on instrumental 

effects, and the other scales on noninstrumental effects, the correspondence is far from exact.

All earthquakes producing a double amplitude of oscillation of more 

than 60 millimeters on the Boch-Omori seismograph are classified as 

strong and receive the same seismicity rating.
HAWAIIAN VOLCANOES DURING 1951 

TABLE 2. Comparison of earthquake intensity scales

149

Hawaiian Volcano Observatory scale

Designation

Foeble. ..............

Slight................

Double amplitude of motion 

on BoschOmori seismograph at the 

Whitney 

Laboratory 

(millimeters)

1/2-4

4-11

11-25 

25-00 

- >CO

Seismicity 

value

1/4 

1/2

1 

2 

3

4

Description of noninstrumcntal effects

Not felt......................... .........

Not felt, or only rarely felt by few persons 

in especially favorable positions, usually 

lying down. 

Not felt, or felt only by a few persons in 

favorable positions. 

Felt by many persons at rest. Hanging 

objects may swing. 

Felt generally, in buildings and out of 

doors. Hanging objects swing. 

Felt by nearly everyone. Objects swing. 

Dishes, doors, and windows rattle. 

Minor damage may result.

Approximate 

grade in 

Rossi-Forel 

and modified 

Mercalli 

scales

I 

11 

III 

IV

Figure 33 is a graph of weekly seismicity at the Whitney Laboratory, 

derived in this manner. The 'curve generally follows that of the number of earthquakes per week, given in figure 32. Table 3 lists the number of earthquakes per week, and the weekly seismicity value, for the 

Whitney andMaunaLoa stations.

Seismicity at the Whitney Laboratory indicates the degree of earthquake activity, but not the origin, and giA^es no direct indication of 

which, if either, volcano is the source of the majority of the activity. 

Many of the small earthquakes are not sufficiently well recorded to 

allow positive determination of their origin. However, more of the 

small earthquakes should be recorded near their origin than at more 

distant stations. Quakes recorded at both stations should yield a 

larger record near their origin. Thus the seismicity of stations near 

the points of origin of the majority of the quakes recorded in any 

given period should be higher than that of more distant stations. The 

relative seismicity curve in the upper portion of figure 33 shows graphically the relationship of the Mauna Loa and Whitney stations to the 

location of origin, of the majority of the earthquakes during the year 

1.951. The value for relative seismicity is derived by assigning a plus 

value to the seismicity of the Mauna Loa station and a minus value to 

that of the Whitney Laboratory (Kilauea) station, and adding the two 

algebraically. A positive residue indicates an excess of Mauna Loa 

activity over that of Kilauea, and a negative residue indicates conversely that the majority of the earthquake activity originated at 

Kilauea.

Thus a high total seismicity value combined with a large positive 

value for the relative seismicity indicates a large amount of earthquake
150 CONTRIBUTIONS TO GENERAL GEOLOGY

 5 5

55.75

starting Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

FIGURE 33. Graph in the lower part showing the seismicity at the Whitney Laboratory 

of Seismology each week during 1951; and in the upper part the relative seismicity at 

the Mauna Loa seismograph station and the Whitney (Kilauea) station.

activity originating at Mauna Loa. In figure 33 the high seismicity 

and strongly negative relative seismicity for the week of April 22 indicates that most of the numerous earthquakes during that week were 

of Kilauea origin. On the other hand, the high seismicity combined 

with a low value of relative seismicity during the weeks of August 19 

and September 16 indicate that the abundant earthquakes of those 

weeks were approximately equidistant from the two stations in Kona 

and along the Kaoiki fault between Mauna Loa and Kilauea. The 

relatively very high seismicity during the week of August 19, at the 

Kona station would indicate clearly, without the other evidence, that 

the origin of the quakes was near that station.
HAWAIIAN VOLCANOES DURING 1951 151

Table 4 lists the earthquakes of local origin, larger than tremors, 

recorded during 1951 by seismographs operated on the island of 

Hawaii by the Hawaiian Volcano Observatory. The time given is the 

arrival time of the preliminary phase at the Whitney Laboratory of 

Seismology. It is given to the closest minute in Hawaiian standard 

time, which is 10 hours slower than Greenwich civil time. If the 

earthquake was more intense at one of the other stations than it was 

at the Whitney Laboratory, the intensity rating at the station is given 

in the column under Remarks.

Table 5 lists the earthquakes of distant origin recorded during the 

year. The time given is that of the arrival of the first recognizable 

oscillation at the Whitney Laboratory. The epicenters given in the 

table are taken from the notices of "Preliminary determinations of 

epicenters, 1951," published by the U. S. Coast and Geodetic Survey.

TABLE 3. Number of earthquakes per week and weekly seismicity

Week beginning

January 7

14

21

28

February 4

11

18

25

March 4

11

18

25

April 1

8

15

22

29

May 6

13

20

27

June 3

10

17

24

Whitney station

(Kllauea)

Number of

earthquakes

0

4

6

2

3

9

7

5

9

9

7

1

4

9

4

104

12

4

13

8

3

4

7

12

5

Seismicity

0

1.0

1.75

.5

.75

6.0

3.25

2.0

3.5

5.75

2.75

.25

1.25

3.25

1.25

55.75

3.25

3.0

5.0

2.75

1.25

2.75

3.5

4.25

1.5

Mauna Loa

station

Number of

earthquakes

0

2

3

1

3

5

4

2

2

7

5

0

3

6

2

65

8

5

7

3

2

4

6

14

5

Seismicity

0

.5

.75

.25

.75

6.75

1.0

.5

1.0

3.5

2.0

0

1.0

3.25

.75

35.25

2.0

1.75

5.0

1.0

.5

2.25

2.25

5.75

1.5

Week beginning

July 1

8

15

22

29

August 5

12

19

26

September 2

9

16

23

30

October 7

14

21

28

November 4

11

18

25

December 2

9

16

23

30

Whitnoy station

(Kllauea)

Number of

earthquakes

2

2

11

2

5

4

2

209

50

21

21

42

16

26

12

10

15

21

22

14

18

15

9

12

4

7

10

Seismicity

1.5

.5

3.25

.5

1.75

1.5

.5

120

18.75

7.5

11.0

18.5

7.5

9.0

6.5

5.75

5.0

7.0

11.75

6.5

8.0

4.75

6.75

5.25

3.25

2.75

2.75

Mauna Loa

station

Number of

earthquakes

2

7

5

1

5

3

1

213

49

19

21

42

15

26

10 (')

(')

 (')

16

7

15

9

6

7

1

3

CO

Soismicity

0.75

1.75

1.25

.25

1.5

1.0

.25

121

17. 75

7.0

8.25

19.25

7.0

10. 25

7.0 (')

(')

(0

9.5

3.75

5.5

2.25

3.25

1.75

.25

1.0

(0

1 Record incomplete; drum drive stopped.
CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 4. Local earthquakes recorded at Hawaiian Volcano Observatory during

1951

Serial 

no.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

T"- 25'

"~~ : 26 .

" ' 27"'

28'!

 ' 29

 '30

' "31"

T-*r-f*v

"32"

' 33

r-~"34

|f-«r 

 35

(*W

r ' 

36

37

38

39

40

41

4.2

43

44

45

46

47

48

49

50

51

52

53

54

Date

Jan. 3

6

26

Feb. 14

16

16

20

20

20

21

23

24

26

26

28

Mar. 5

5

5

5

8

14

14

14

15

15

15

20

24

24

Apr. 4

13

13

15

22

22

22

22

22

22

22

22

22

22

22

22

22

22

22

22

22

22

23

23

23

Time (Hawaiian standard)

ft ro 

03 39

04 58

06 40

10 55

07 26

18 58

20 01

20 47

21 47

21 26

03 41

17 39

01 28

09 21

14 13

03 53

03 56

09 33

16 44

16' 30

03 47

03 4&"1

20 50'

04 38T

11 34'

16 43T

06 42

06 28T

22 33

1043"

01 war 19 1

14 53

13 36

04 54

14 52

15 25

15 41

15 49

15 50

15 51

16 08

16 14

16 49

17 19

17 30

18 46

20 30

21 11

23 30

23 40

00 17

02 46

' 03 04

Intensity at Whitney Laboratory

Very feeble..... ...

Slight.- 

Very feeble __ . ...

Slight-- . 

 .do. -----

Very feeble. __ ....

.. do--. --.

 do..--. _

 -do ..

 -do ... -

-.-do - -----

.- do.---- .--.

- do ....-

---do .-.--

- _do ~- -

 do. .. -------

 do. -

- do...- ------

.- do. -----

- do ------

.--do ---------

Slight.-----.--.-.

.---do..- ------

.-.-do.. -------

 do.. 

- do --

Feeble.... -. ...--

---do ---------

- do -

..-..do --------

- do - -

- do ---

 do . 

--.-do ---------

- do.------..--.

Feeble. ---------

 do- 

..--.do ----------

Verv feeble

.... .do... 

-. do- ....... .-

 do ..... ...

--..do ---.....-.

Epicenter

Loa at an altitude of 

about 8,000 feet.

near Puu Ulaula.

Loa.

Kilauea caldera.

miles east-northeast of 

Napau Crater.

near Kealakekua.

miles east of Kulani 

cone.

of Waimea.

miles S. 15° E. of Glenwood. 

East rift of Kilauea near

the caldera.

East rift of Kilauea 7

miles east of the caldera.

Southwest rift of Kilauea

near Mauna Iki.

pala.

Eemarks

erate, Mauna Loa. Felt 

at Kapapala.

erate, Mauna Loa. Felt 

from Hilo to Naalehu.

in Hilo and Volcano 

areas.

..j.i .

in Puuco district of Hilo.

Shallow, felt at Waimea.

21 miles deep. Felt at

Kapapala and from Volcano district to Hilo. 

25 to 30 miles deep. Felt

all over Hawaii Island, 

and on Maul and Oahu.

About 8 miles deep.

About 5 miles deep.

Very feeble, Mauna Loa.

Do.
HAWAIIAN VOLCANOES DURING 1951 153

TABLE 4. Local earthquakes recorded at Hawaiian Volcano Observatory during

195.1. Continued

Serial 

no.

55

50

57

58

59

00

01

02

63

64

05

GO

07

08

09

70

71

72

73

74

75

70

77

78

79

80

81

82

83

84

85

80

87

88

89

90

91

Q9

93

94

95

90

97-

98

99

100

101

103

104

Date

Apr. 23

23

23

23

23

23

23

23

23

23

23

23

24

24

24

25

25

20

20

20

28

29

7

8

10

13

14

15

17

18

20

20

25

30

31

7

11

11

12

14

15

17

19

22

23

27

27

Time 

(Hawaiian 

standard)

h in 

03 27

04 37

04 40

04 41

04 44

05 24

05 48

00 13

00 36

21 53

22 10

22 18

01 14

01 29

11 30

11 41

22 38

00 57

03 58

05 51

07 08

10 19

08 53

12 30

00 38

15 24

00 24

18 41

22 10

12 12

03 00

13 34

10 10

03 10

21 59

09 13

04 45

22 50

08 33

19 23

12 12

13 19

12 01

05 15

08 11

07 27

11 49

Intensity at Whitney Laboratory

Very feeble

Slight.............

-...clo....... ......

Very feeble

Slight.............

Very feeble

.....do.............

-...do.... ...

.....do.............

..... do..... ..... ...

..... do....... .... ..

..... do... ......... .

.....do.. .... .......

Slight............

Very feeble

 do....... ...

J^GCble

 do.. .

Very feeble

 do _ ...

.....do-.... .....

Feeble.............

VCTV feeble

....do.... .... ...

....do ... . ......

....do ...........

 do 

.... do.. ...

ney vault. 

Slight.. 

.... do. ....... ......

. do.... .. 

Very feeble

_ .do.. ______ .

.... do..... ... ...

Tremor _ ....--...

Epicenter

East rift of Kilauea 2 miles

south of Makaopuhi 

Crater. 

Three miles north of Kilauea caldcra.

near Kulani cone.

Kilauea caldera.

Southwest rift of Kilauea 2

miles southwest of 

Maunaiki. 

Southwest rift of Kilauea

near Puu Koae. 

East slope of Mauna Loa

2 miles southwest of 

Kulani cone.

Three miles northwest of

Kilauca caldera.

Makaopuhi Crater.

miles east of Waimea.

cone.

Kulani cone. 

Kaoiki fault zone, 3 miles

southwest of Pahala.

Puu Huluhulu.

Southwest rift of Kilauea

near Maunaiki.

East rift of Kilauca near

Pauahi Crater. 

East rift of Kilauea 6

miles west of Pahoa.

kuaweoweo.

Remarks

About 4 miles deep.

About 5 miles deep.

About 7 miles deep.

About 6 miles deep.

About 5 miles deep.

Do.

Do.

About 11 miles deep.

Very feeble, Mauna Loa.

About 12 miles deep. Felt

in Volcano district.

Felt by 1 person in Volcano district, and some in 

Pahala and Naalehu.

Shallow.

Do.

Very feeble, Mauna Loa.

Shallow. Felt in Volcano

district and by a few in 

Hilo. 

About 7 miles deep. Felt

generally from Hilo to 

Volcano district. 

Very feeble, Mauna Loa.

Do.

About 16 miles deep

Slight, Mauna Loa.

Very feeble, Mauna Loa.

Do.
154 CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 4. Local earthquakes recorded at Hawaiian Volcano Observatory during

1951 Continued

Serial 

no.

'105

inn

107

108

109

110

111

112

113

114

115-135

136

137

1 QQ.14C

149

150-154

155

156-161

164

165-167

168

169

170

171

172-174

175

1 7ft_l Cft

181

182

183

1Q4

185-187

191

192

1 QQ

194

196

197

198

199

200

201

202

203

204

9ne

206

207

208

209

210

211

212

Date

July 1

17

19

6

10

21

21

21

21

21

21

21

21

21

21

91

22

99

99

99

22

22

99

99

99

90

24

OK

OC

oc

26

26

26

27

27

27

28

28

28

98

28

29

29

29

30

QA

31

Time 

(Hawaiian 

standard)

ft m

23 20

no ^9

19 24

m d.n

04 31

00 57

01 29

03 50

04 00

06 03

0803

no QQ

10 12

1Q OO

21 07

99 AQ

02 14

AP. OQ

16 04

16 38

17 1 K

1 7 9Q

00 25

90 CQ

10 22

11 14

AQ 9Q

0804

08 11

19 40

04 31

91 f^S

17 48

18 04

20 28

06 02

19 43

21 25

07 23

14 23

16 08

Intensity at Whitney Laboratory

Feeble -------

 -do.. 

-....do ...........

.. ...do... .......... .

.....do.... ..........

Feeble.. ........ .-..

.....do.... ..........

feeble. 

Slight. .............

feeble. 

Slight..- - 

feeble.

Very feeble

Slight...... 

Feeble find vcrv

feeble.

Fggble jincl vcrv

feeble. 

Slight. .......... ...

Slight. .............

feeble, 

 do........ 

Very feeble

Feeble

Verv feeble

 do... ...... .- 

 do -

...-do.-......- .

..... do... . -------

 do... ... ...

..... do...... ... -----

 do 

..... do.-. . ...

..... do 

Feeble... .. 

Verv feeble

 do 

. do 

 do 

do

..... do.-... ...

.... .do... ... ...-- 

 .do.. 

Epicenter

Southwest rift of Mauna

Loa near Sulphur Cone.

East rift of Kilauea near

Napau Crater. 

About 3 miles WNW of

Napoopoo, probably on 

Kealakekua fault. 

Near no. 113. _ - -. 

Kona... _ ... . _____ .

- do .... ....... .......

.. do. ....... .......

..... do...... ...... 

.. do ..................

.....do. ....... ...

.-..do ................

.-..do . 

-...do ......... .......

.....do. ...... .... ......

 do........ .... ........ '.

..... do. ... ............

.. do..... ................

.....do. ...... ... . ..

-.-do. ....... ... ... ...

-...do ................

 do ... ...... ...

.-..do ................

-...do - - ..

..... do ................

..... do ..... .........

..-.do. ..............

.....do. ..............

 do.. ...

Kona.--.--... -----.--..

.... .do....- . ...... ....

Kona, Pali Kaholo... _ Kealakekua fault....... ...

Kona 2.3 miles S. 75° E. of

Napoopoo. 

Kealakekua fault. ...... ...

.... . do...... .... ...

Kealakekua fault..-.... .

... ..do.... 

About 3 miles east-southeast of Mountain View.

near Kilauea Iki. 

Kealakekua fault. _ ......

 do..... -

Kona. __ ... __ .

. do......... ...... ...

Kealakekua fault. _ __ ..

Remarks

Shallow.

Much damage in Kona.

Intensity 7. 

Felt strongly in Kona.

Felt from Kona to Volcano

district. 

Do.

'

Do.

Do.

Felt from Kona to Kapapala.

Felt from Kona to Volcano

district. 

Felt as far as Naalehu.

Kona feeble.

Kona slight.

Kona feeble.

Kona slight.

Felt in Mountain View and

Volcano district.

Kona feeble.

Do.

Kona slight.

Kona feeble. Felt in

Kona. 

Kona moderate. Felt

strongly in Kona.

Kona strong, intensity 5.

Felt strongly in Kona.
HAWAIIAN VOLCANOES DURING 1951 155

TABLE 4. Local earthquakes recorded at Hawaiian Volcano Observatory during

1951 Continued

Serial 

no.

213

214

215

216

217

218

219

220

221

222

223

224

225

226

228

229

230

231

232

233

234

235

236

237

238

239

240

241-250

251

252

253

254

255

256

257

258

259

261

262

263

264

265

266

267

268

269 

270

271

979

970

274

275

Date

Aug. 31

Sept. 1

2

3

4

4

6

8

8

9

10

10

11

12

12

12

12

12

14

15

15

15

16

16

16

16

17

17

17

18

19

20

20

20

20

21

21

23

24

24

24

24

25

OC

26

26

Qrt

on

30

Time (Hawaiian standard)

ft 771

18 51

12 29

23 21

18 35

00 37

00 48

05 10

14 13

16 16

22 28

01 29

14 50

23.27

13 58

01 50

12 55

nn 9fi

12 44

01 12

01 27

03 26

18 55

18 56

16 49

16 45

21 33

23 48

01 43

21 50

23 19

10 17

15 19

18 17

08 47

19 15

00 11

00 25

03 21

12 30

19 01

03 01

03 13

03 30

23 47

00 56 

01 23

20 20

23 21

06 21

11 17

16 06

Intensity at Whitnoy Laboratory

Feeble..............

.....do.... ......... .

.. ...do... ........ ...

.....do...... ........

 do. 

.....do..............

.....do..............

..... do ... 

.. do.. 

.. do. 

---..do...------.---.

Vcrv feeble

.....do .... ...

Feeble

Vcrv feeble

. -..do-....-. ------

. do. . ..

Vcrv feeble

.... .do - -

.....do ---------

Verv feeble

 ..do 

Vcrv feeble

Vcrv feeble

. do. . ..

..... do......- -...

.... .do 

.....do. ..

Verv feeble

Vcrv feeble

Vcrv feeble

. -...do-.-.. ........

..... do .. 

..... do -------- 

Slight.-. - 

..... do.... ...- ..

... ..do ..... ..

 do... -

.....do. .--.

Epicenter

of Hookena.

of Kealia.

-.-.do.... .................

 .do..... .. ......

.. do..... .

Central Kona ... _

Kona. -...-----------.--..

Puu Huluhulu.

near Pit Craters.

Loa at altitude of about 

9,000 feet.

northeast of Kapapala. 

Kaoiki fault... _ ---------

near summit.

Southwest rift of Mauna

Loa at an altitude of 

about 11,000 feet.

Central Kona :

 ..do.... . .

cast of Ainapo. 

Near summit of Hualalai _.

East rift of Kilauea about

10 miles east of Kapoo. 

Northwest rift of Hualalai 

at an altitude of about 

5,000 feet.

South slope of Hualalai

about 4 miles southeast 

of Holualoa.

.... .do.... . ....

.. do.-.- .

Remarks

Do.

Kona moderate.

Felt strongly in Kona.

Felt as far as Naalchu. 

Kona slight.

Kona feeble. 

Kona moderate.

Kona slight.

Kona feeble. Felt at Naalchu.

Felt at Kapapala.

Intensity 5. Felt from

Kona to Hilo.

Kona feeble.

Kona moderate.

Mauna Loa, very feeble.

Kona feeble.

Kona slight.

Mauna Loa very feeble.

Kona slight.

Do.

Kona feeble.

Kona strong. Felt strongly

in Kona.

Kona slight. Felt in Kona

Kona feeble.

Felt in Hilo.

Kona feeble. Felt in north 

Kona.

Kona moderate. Generally felt In Kona. 

Kona slight. Felt in Kona.
156 CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 4. Local earthquakes recorded at Hawaiian Volcano Observatory during

1951 Continued

Serial 

no.

276

277

278

279

280

281

282

283

284

285

286 

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

QO'J

OOd

00 c

V)R

097

090

Q9Q

oqn

qqi

oq9

Date

Oct. 1

3

4

4

5

5

6

6

6

6

7 

7

' 8

9

9

9

10

11

11

12

12

14

14

15

17

17

19

20

20

20

23

24

24

25

25

27

98

29

29

Nov. 1

3

4

6

6

7

8

g

10

11

Time 

(Hawaiian 

standard)

h m 

09 17

22 56

0601

19 03

02 09

08 42

02 44

04 36

08 35

13 34

01 28 

05 14

07 16

01 40

04 45

05 23

02 31

21 30

16 06

16 37

19 52

08 49

01 00

11 58

19 10

21 01

13 14

13 15

02 42

ni 99

21 05

06 53

23 49

20 48

06 26

19 24

10 44

11 08

20 11

no 3d

10 16

14 10

14 22

16 33

oq 97

00 55

14 16

03 52

07 08

Intensity at Whitney Laboratoiy

Tremor ----------

. -...do. -------------

..-..do .............

-...do ------

Feoblc. -----

Very feeble.- .--... .

-...do -- -

Slight. ......... ....

Feeble. ............ .

.... .do... ........ ...

.....do. ....... ...:.

 _do 

-....do. . ----------

..-.do ---

- do. . 

Vcrv feeble

..... do 

.... .do 

..... do 

..... do. ... ...

-'...do... ..... ---

..-.do . ------

--...do... -------

..-..do ----------

.....do ------

..... do ... ...

.... .do-..---. 

-...do ---

Verv feeble

.... . do .... .-

_ ..do 

 .do 

Slight. .-... --------

Epicenter

. ....do-... ......... .......

.-...do--.. ..... .....

 do.-.... 

.....do..-- --------

Bay.

northeast of Kapapala.

northeast of Kapapala.

Near Hilea. _ 

 do.... ... 

.....do........ ............

Loa near the 3,000-foot 

contour.

Loa(?).

._-.do.--. ------

 do.-.. 

.....do.-.-....-.---.--.

Kaoiki fault about 3 miles

northeast of Hilea.

Northeast of Mauna Loa. .

-...do........ ---..

Near summit of Hualalai 

Loa at an altitude of 

about 4,500 feet.

Kilauea ...................

Kapukapu.

Loa at an altitude of 

about 11,000 feet.

Pauahi Crater.

Remarks

Do.

Do.

ehu.

Naalchu.

Felt at Naalehu. 

Kona very feeble

Do.

Kealakekua. 

Kona very feeble

Kealakekua.

at Volcano and Hilo.

Kealakekua. 

Komi feeble.

Felt at summit of Mauna

Loa.

Intensity 6 at Kahuku.

Felt over the entire 

southern part of island.

Felt in Hilo.
HAWAIIAN VOLCANOES DURING 1951 157

TABLE 4. Local eartliquakes recorded at Hawaiian Volcano Observatory duriny

1951. Continued

Serial 

no.

333

334

335

330

337

338

330

3-10

341

'<<19

343

344

3-15

34(1

347

348

349

350

351

352

353

354

355

350

357

358

359

300

301

302

303

304

305

300

307

308

309

370

371

372

373

374

375 

370

377

DatO

Nov. 12

13

10

10

17

18

18

18

19

20

21

21

21

22

23

25

25

20

20

28

28

Doc. 1

2

3

5

0

9

11

11

12

13

13

14

15

15

17

19

23

25

20

28

29

29 

30

31

Time 

(Hawaiian 

standard)

h m 

07 01

00 41

02 57

20 54

14 50

01 31

02 47

17 43

00 22

10 00

22 23

17 37

08 22

00 17

21 41

91 9^

11 41

08 33

05 20

20 19

10 37

02 12

13 58

10 51

03 00

21 54

19 22

01 30

23 10

15 48

05 30

09 31

09 50

23 00

10 17

08 45

17 32 

02 00

15 49

Intensity at VVhitney Laboratory

.....do. .............

..-..do..............

.....do. ....... ...

.....do..............

Vcrv foohlc

.....do .............

.....do..............

.....do.. ............

.....do..............

Slight. . ............

.....do.... .......

Very feeble

.....do..............

.....do. .............

.....do..............

.....do..............

.....do .............

.. ...do... . ..........

.....do..............

. ....do... ......... ..

.....do..............

.....do..............

.. ...do...... ...... ..

.....do..............

. ....do.... ..........

Very feeble.... .....

Epicenter

.....do... ..................

Uvvekahuna.

ucla P. 0.

about 3 miles east of 

Kulani cone. 

Kealakckua fault about 5

miles west of Napoopoo.

Makaopuhi Crater.

7 miles southwest of 

Pahoa.

.....do. ....................

Kaoiki fault near Pahala..

.....do...... ...............

Remarks

Kealakekua.

Kealakekua.

Kealakekua.

Koni very feeble

Kona to Kahuku. 

Kona very feeble

Do.

and cast Puna.

Do.

Felt at Naalehu and 

Kapapala.

Do.
158 CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 5. Distant earthquakes recorded at Wliitney Laboratory, Hawaiian 

Volcano Observatory, during 1951

Date

Jan. 13

17

Feb. 19

Mar. . 10

Apr. 30

May 19

19

June 16

Aug. 31

Sept. 27

Oct. 21

21

Nov. 6

8

Dec. 7

25

27

30

Time 

(Hawaiian 

standard)

h m 

12 20

11 17

12 38

12 06

05 35

04 59

06 45

23 54

23 16

09 40

11 46

17 41

06 53

04 02

1.8 35

15 03

23 34

12 50

Strength at Whitney 

Laboratory

Slight..........---.

. ....do..... ........ .-

Slight.. -

. ....do.. ........... ..

.--. .do. ........... ....

.... .do....... ... -

- do...... . 

.... .do. ..............

Slight.... ..... ......

- do.. -

-.--do. ._..._ _

Slight..... ---------

. do.. .... .....

. do.. ..... ... .

Epicenter 

(From preliminary determinations of epicenters by IT. S. 

Coast and Geodetic Survey)

Do.

Pacific Ocean, west of Easter Island.

TILTING OF THE GROUND

Tilting of the ground surface, and its relationship to Hawaiian 

volcanism, were discussed at some length in the report of the Hawaiian 

Volcano Observatory for 1950 (Finch and Macdonald, 1953). The 

reader is referred to that report for the discussion, which will not be 

repeated here.

Figure 34 is a graph showing the north-south and east-west components of the tilting of the ground surface measured at the Whitney 

Laboratory of Seismology by means of the Bosch-Omori seismograph. 

The approximate average annual tilt curves in the two components, determined for years in which there was no surficial volcanic activity, also 

are shown in the figure. The vertical position of this average curve 

on the graph may not have any significance. However, any marked 

variation in the general form of the curve of actual measured tilt from 

that of the average curve is probably the result of variations in volcanic 

conditions, presumably largely subsurface magmatic pressure. Thus 

a rise of the north-south tilt curve at a rate much greater than the 

average curve apparently represents an increase of pressure beneath 

Kilauea volcano, with an accompanying rise of the ground surface near 

Halemaumau and a north-northeastward tilting of the surface at the 

Wliitney Laboratory. Conversely, a decline of the north-south tilt 

curve at a rate faster than the average probably reflects a decrease of 

pressure beneath Kilauea.

The significance of the east-west tilt curve is somewhat more difficult to ascertain. As pointed out in the Hawaiian Volcano Observatory report for 1950 (Finch and Macdonald, 1953), there apparently is 

some correlation between east-west tilting at the Wliitney Laboratory 

and volcanic conditions at Mauna Loa. The distance of the station
HAWAIIAN VOLCANOES DURING 1951 159

2-

-8

vA

A

NORTH

f\j

SOUTH

A

8--

leEAST

VA,

^

WEST

'-8

1950 -1951 ^1952

FIGUHB 34. Graph showing ground tilting at the Whitney Laboratory of Seismology, on 

the northeastern rim of Kilauea caldera, in 1951. The solid line shows the tilt as 

measured during the year. The dotted line is the approximate normal annual curve 

for years in which there is no volcanic disturbance.

from the volcano is so great, however, that the expectable tilting from 

that cause is small. Ascertaining the tilt curve is further complicated 

because the Whitney station lies slightly east, as well as north, of the 

center of Kilauea caldera, and tumescence of Kilauea volcano would 

be expected to produce some eastward component of tilt at the Whitney station. The apparent degree of correlation between volcanic 

episodes at Mauna Loa and east-west tilting at the Whitney Laboratory may actually be partly the result of a sympathy of action between 

Mauria Loa and Kilauea, resulting in a simultaneous tumescence and 

detumescence of the two volcanoes. Thus eastward tilting at the 

Whitney Laboratory preceding a Mauna Loa eruption might be caused 

by increase of pressure beneath Kilauea accompanying that beneath 

Mauna Loa. A longer period of record and further analysis of the tilt
160 CONTRIBUTIONS TO GENERAL GEOLOGY

curves are necessary to determine fully the significance of eastward tilting at the Whitney Laboratory.

Table 6 lists the direction and amount of the tilting of the ground 

surface at the Whitney and Uwekahuna stations for each week of 1951.

TABLE 6. Ground lilting at seismograph vaults on the rim of Kilauea caldera,

during 1951

Week beginning

Whitney vault 

(northeast rim)

Direction

Amount

(seconds of

arc)

Uwekahuna vault ] 

(west rim)

Direction

Amount

(seconds of

arc)

Dec. 31... -.....-..- . ---- - S. 45° W. 

Jan. 7...'... ... . N. 38°E.

14 ---. N.

21 ..... S.35°E.

28. -. . . S.37°W.

Feb. 4......... . S.45°W.

11. N. 38°E.

18 .. - S. 35° E.

25 - .- ... .- . .. --------- S. 42°W.

Mar. 4 S. 26° W.

11. S. 5°W.

18. ... . .. .. . S. 16°W.

25 . W.

Apr. I...-.-..... -..-- -- ---.----------- N. 45° W.

8 . S.63°E.

15 . S. 85° W.

22 . _- N. 22° E.

29 ----- N. 27° W. 

May 6. N. 7° W.

13 N.17°E.

20. i\T . 18° E.

27 N.15°E.

June 3.... -.. . --... ---------------- N. 60° E.

10. . S.86°E.

17 N. 56° E.

24. N. 52° E.

July 1_. N. 9°W.

8.. - - -- -- --------- N. 16° E.

15 . N. 6°E.

22 N. 26° W.

29..... N.18°E.

Aug. 5... . - N. 36° E.

12 . .... N. 67° E.

19" . ...-. N. 26° W.

26 N.40°E.

Sept. 2...... -. N. 27° E.

9. . S.34°E.

16.-.. --------------------------------- N. 67° E.

23... . --. N. 10° E.

30 ... -- N. 10° E.

Oct. 7-.-----------.---------------..-.----.------ N.45°E.

14..... - N.

21 N. 6°E.

28 -. S. 31° E.

Nov. 4..._-. . . _ N. 22° E.

11 .. S.45°W.

18 ----------------------- N. 74° E.

25 N. 25° W.

Dec. 2.... . .. S. 5°W.

9....- _ ._ . i _ S.23° E.

16 N. 23° E.

23 .. ... . S. 72° E.

30-...--....- ----...---.........-....---- N.

.7 

2.0

.6 

1.2 

1.5

1.5

1.6 

2.1 

4.1

1.2 

.6 

.5 

.8

1.3

1.4

.4

1.0

1.2

1.1

1.9

1.0

1.6

.4

1.4

.7

.8

2.2

1.1

.8

.6

.9

1.3

.6

1.7

.7

.3

.7

1.2

.7

1.4

4.2

.9

2.8 

.4 

.5

56° W.

26° W. 

. 70° W. 

. 15° W. 

. 27° E.

70° E.

58° W. 

. 58° W. 

. 78° E.

15° E. 

79° E. 

. 63° E. 

74° W. 

. 45° W. 

72° W. 

62° W. 

. 74° W. 

. 81° W.

9° E. 

19° E. 

17° E. 

. 3°W. 

. 17° W. 

. 53° W. 

. 45° E. 9°E.

. 24° E. 

45° E. 

. 32° W.

4° W. 9°W.

5°W. 

. 7°E. 

68° W.

16°W. 

20° E. 

45° E. 

. 18° W. 

. 22° W. 

. 10° W.

S.

S.

S.

S.

N,

N,

N,

S.

S.18°E.

N. 8°W.

S.13°E.

N. 10° W.

N. 10° W.

S. 5°E.

S. 34° E.

N. 7°W.

0.4

.7

1.5

2.4

.2

1.2

1.5

1.8

2.4

1.5

.7

.5

.4

.9

.3

.2

1.4

.6

1.1

2.8

.4

1.4

2.1

1.4

.6

.2

1.1

3.9

2.7

1.9

4.2

2.4

5.0

1.8

2.6

.8

5.0

2.3

2.0

.4

1.0

5.1

5.2 

4.8 

3.0 

2.0 

3.3 

2.0 

2.0 

4.2 

1.2 

5.]

1 Eecord before May 13 is based on a small semiportable tiltmcter. During early May a pair of heavy 

horizontal pendulums was installed, and the record after May 20 is based on this new instrument. The 

record for the week starting May 13 is considered unreliable because of improper operation of the east-west 

pendulum.
HAWAIIAN VOLCANOES DURING 1951 161

Tilt records at the Uwekahuna station are too short for their significance yet to be fully known. By analogy with the records from 

the Whitney station, it is to be expected that an increase of pressure 

beneath Kilauea caldera will cause a westward tilting of the ground at 

the Uwekahuna station, near the western rim of the caldera. Likewise, a decrease of pressure should probably cause an eastward tilting 

at the Uwekahuna station. A marked east\vard tilting at Uwekahuna' 

did accompany the Kilauean subsidence of December 1950, which 

simultaneously produced a south-southwestward tilting at the Whitney Laboratory. Thus it is probable that major changes in volcanic 

pressure beneath Kilauea will be clearly reflected by tilt changes at the 

Uwekahuna station. Since, however, the station lies almost directly 

between Kilauea and Mauna Loa, a simultaneous increase or decrease 

of pressure under the two volcanoes may cause little tilting at the 

Uwekahuna station. This is particularly true if a large change under 

distant Mauna Loa is accompanied by a smaller sympathetic change 

under nearby Kilauea. Kesults to date also suggest that ground tilting at the Uwekahuna station may be much more affected by shortperiod changes in air temperature, and other weather changes, than 

is the tilting at the Whitney Laboratory.

The apparent changes in volcanic pressure indicated by the conf-. 

parison of the tilting actually measured during the year with the average curve, in figure 34, are discussed in a later section of the report, 

under the heading "Volcanic conditions during 1951."

CRACK MEASUREMENTS

Measurements of crack Avidths were made at 13 stations, at monthly 

intervals throughout 1951. The measurements, including those for 

December 1950 for comparison, are given in table 7. The locations of 

the crack-measuring stations are shown in figures 31 and 35.

Crack-measuring stations 5 to 9 lie along a series of cracks near 

and parallel to the southeastern rim of Halemaumau, at the observation area provided for tourists. Station 5, near the northern end of the 

series of cracks, showed consistent opening throughout 1951, the total 

opening from December 31, 1950, to December 31, 1951, being 7.2 

centimeters (2.8 inches). Station 6 showed a net opening of 1.4 centimeters during the year, and station 7 a net opening of 0.3 centimeter. 

Station 8 showed no net change during the year, and station 9, near

296333 54-
162 CONTRIBUTIONS TO GENERAL GEOLOGY

the southern end of the crack, showed a net closing of 0.3 centimeter. 

Thus the block bounded by the series of cracks apparently is moving 

toward the crater at its northern edge, but slightly away from the 

crater at its southern end.

Topography by U.S. Geological Survey 

FIGURE 35. Map of Halemaumau and vicinity, showing the location of tilt-measuring 

stations and crack-measuring stations.

The cracks at stations 37 and 3TA, on the caldera floor east of Halemaumau, showed a small net opening during the year. However, the 

cracks at stations 40 and 41, west and south of Halemaumau, showed 

essentially no change. Along the east rift zone of Kilauea volcano, the
HAWAIIAN VOLCANOES DURING 1951 163

crack at station 101A opened 2.5 centimeters during the year, but those 

at stations 106 and DT-1 showed no significant change.

TABLE 7. Width of cracks at Kilauea during 1951 (in centimeters)

Date

Dec. 31 

Jan. 30 

Mar. 1 

31 

Apr. 23 

May 1 

31 

July 2 

31 

Aug. 21 

31 

Sept. 30 

Nov. 1 

30 

Dec. 31

Measuring station number

Halemaumau^im cracks

5

109.4 

109.6 

109.9 

110.5

111.4 

111.9 

112.2 

112.5 

113.3 

113.7 

114.4 

115.1 

115.9 

116.6

6

59.3 

59.4 

59.5 

59.7 

59.7

59.8 

59.9 

60.1 

60.2 

59.9 

59.9 

60.2 

60.2 

60.5 

60.7

7

34.7 

34.7 

34.7 

34.8 

34.8

34.7 

34.9 

35.0 

35.0 

35.0 

35.2 

35.1 

35.1 

35.0 

35.0

8

58.0 

58.0 

58.0 

58.1 

58.0

58.0 

58.0 

58.1 

58.1 

58.0 

57.9 

58.0 

58.0 

57.9 

58.0

9

77.9 

77.9 

77.8 

77.7 

77.7

77.7 

77.7 

77.6 

77.7 

77.7 

77.7 

77.6 

77.6 

77.7 

77.6

27

64.2 

64.2 

64.2 

64.2

64.5 

64.5 

64.5 

64.6 

64.7 

64.8 

64.9 

64.9 

64.9 

64.9

Cracks on floor of caklera

37

N-S

49.0 

49.0 

49.0 

49.1

49.1 

49.2 

49.3 

49.3 

49.3 

49.3 

49.4 

49.5 

49.5 

49.5

E-W

44.5 

44.5 

44.6 

44.6

44.7 

44.7 

44.9 

44.8 

44.8 

44.9 

45.0 

45.0 

45.1 

45.1

37 A

64.3 

64.3 

64.3 

64.3 

64.3

64.2 

64.3 

64.4 

64.4 

64.4 

64.4 

64.4 

64.5 

64.5 

64.5

40

33.1 

33.1 

33.1 

33.1 

33.1

33.1 

33.0 

33.1 

33.1 

33.1 

33.0 

33.1 

33.1 

33.1 

33.1

41

33.4 

33.4 

33.4 

33.4 

33.4

33.4 

33.4 

33.4 

33.4 

33.4 

33.4 

33.4 

33.4 

33.5 

33.5

Cracks on cast rift

101A

127.6 

128.6 

129.0 

128.6 

129.0

128.6 

129.0 

129.0 

129.0

128.8 

129.2 

128.9 

129.2 

130.1

106

101.5 

101.5 

101.5 

1.01. 5 

101.6

101.5 

101.6 

101.6 

101.7

101.5 

101.4 

101.4 

101.5 

101.6

DT-1

36.0 

36.0 

36.0 

36.0 

36.0

36.0 

36.0 

36.0 

36.0

36.0 

36.0 

36.0 

36.0 

36.0

GEOMAGNETIC OBSERVATIONS

For the past several years the staff of the Hawaiian Volcano Observatory has wanted to start geomagnetic measurements at Kilauea 

and Mauna Loa volcanoes. Results obtained by workers on volcanoes 

in other areas, especially Japan (Kato, 1933-35; Takahasi and 

Hirano, 1941; Rikitake, 1951) have suggested that magnetic measurements in Hawaii might give information on magmatic conditions 

and movements beneath the surface, and might supplement other 

methods in predicting eruptions. Preliminary studies by Omer (1945) 

suggested some correlation between volcanic conditions on the island 

of Hawaii and small variations in the magnetic field at Honolulu, 

nearly 200 miles away.

The opportunity to begin magnetic studies came early in 1950, when 

two Wolf son vertical magnetometers were made available to the Hawaiian Volcano Observatory by the U. S. Geological Survey. H. R. 

Joesting and J. IT. Swartz, accompanied by R. E. Wilcox, spent the 

first three weeks of February at the Observatory setting up procedures, calibrating instruments, and instructing the Observatory 

personnel in their use.

Theoretically, the rise of hot magma beneath the volcano should 

result in a decrease of the strength of the magnetic attraction, and 

consequently a decrease in the strength of the vertical component of 

the earth's magnetic field above the heated area. This effect was observed by Rikitake (1951, p. 180) during the 1950 eruption of Ooshima 

Volcano in Japan.
164 CONTRIBUTIONS TO GENERAL GEOLOGY

Permanent observation stations were established during February 

and March 1950 on Kilauea and the lower slopes of Mauna Loa. The 

location of the stations is shown in figure 31. The number of stations is not as great as might be desired, but is limited by the time 

available for the work.

Each station was set at a point where closely spaced setups of the 

magnetometer showed the magnetic field to be reasonably regular over 

an area of about 100 square feet. At each station three concrete hubs 

were set and small pits drilled in them to receive the ends of the 

magnetometer tripod legs (fig. 36). The tripod legs are kept at a 

fixed length when the stations are occupied, and each leg is placed 

on the same hub in successive readings at each station. The leveling 

screws also are turned out as nearly as possible to the same distance 

for each setup. Thus the position of the instrument, horizontally and

FIGURE 36. Magnetometer set up for observations on one of the permanent stations. 

Concrete cups for tripod legs facilitates achieving the same position of the instrument 

at each reoccupation.
HAWAIIAN VOLCANOES DURING 1951 165

vertically, is as nearly as possible the same for successive readings 

at a given station.

Observations of the intensity of the vertical component of the 

earth's magnetic field were made at each of the stations about once o

a month throughout the remainder of 1950-51. All the readings of 

each set were made on the same day, or on two successive days.

The procedure is as follows: One instrument is set on station 0, 

near the Observatory at the western edge of Kilauea caldera (fig. 31). 

After the reading at station 0 is obtained the instrument is taken to 

each of the other stations and readings obtained. Readings are made 

with the north end of the balance pointed first east and then west, 

and the average of the two sets of readings is used, thus compensating 

for any small errors in orientation and leveling of the instrument. 

Until May 1951, immediately after the first instrument was removed 

from station 0, the second was set up at that station, and read at frequent intervals throughout the time the first instrument was in use at 

the other stations. From the readings at station 0 a curve of diurnal 

variation was constructed which was used in correcting the readings 

at the other stations. At the end of the traverse the first instrument 

was again set on station 0, and after correcting for diurnal variation 

any closing error is distributed linearly throughout the time of operation. The diurnal variation was very small in comparison with the 

changes in values between successive readings at individual stations. 

Consequently, because of shortage of personnel at the Observatory, 

since May, 1951, only one instrument has been used and the correction for diurnal variation has been neglected. The instrument is 

recalibrated for sensitivity in the laboratory every two or three 

months. The corrected scale readings are converted into gammas, 

and the value at each station is recorded in terms of difference in 

gammas from the value at station 0.

The program is not ideal, but it represents the best results that 

can be obtained for the available time and the small size of the Observatory staff. It is hoped that the program can be expanded and 

improved in the future, if results justify it. The values obtained 

thus far are shown in table 8.

Joesting and Swartz again visited the Observatory in June, 1950, 

during the eruption of Manna Loa, for the purpose of checking on 

the progress of the investigation and the operation of the instruments. 

Of the measurements listed in the table, those for June 12 were made 

by them. The others were made by members of the Observatory staff, 

assisted during March and April by J. B. Orr of the National Park 

Service. On March 8-9, 1951, F. C. Farnham of the Geological Survey made measurements with an absolute magnetometer at station 0 

near the Observatory, and at a newly established station near the 

seismograph station at St. Joseph's School in Hilo.
166 CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 8. Difference in vertical intensity of geomagnetism (in gammas) at 

stations on Mauna Loa and Kilauea, compared to that at station 0

All readings for station 0 are actual values. Other values for the month are differences from this reading

Magnetometer station 

no.

0 .............

1 

2. . .........

3 .

4. .......... ...

5. .......... ...

6. .......... ...

7...-. ... ......

8. ........... ..

9. .............

10... ....... ...

11 

12.............

13.... .........

14.............

15....-....--.

16.. ........

17... ...... .

18...........

19.... ....... ..

20. ........... .

21. ...____. ....

22.... ....... ..

23....... ..

24.... .-

25.... 

26...- .-

27... 

28-. 

i--

,0o> 

PR

+234

-681

-171

-677

-35

+416

+786

8

1

+156

-683

-37

-271

-291

+77

-117

-76

-615

-714

I

D,

-4

+163

-744

-54

-303

-345

+57

-141

-107

-659

-758

-669

-204

-676

-536

-69

+433

+177

-663

-418

+287

-273

+257

+784

+1167

-46

+243

May 9-10

+149 -828

-18

-301

-326

_|_AO

-176

-120

-765

-899

-760

-212

-745

-604

-45

+486

+198

-740

-473

+353 -304

+288

+899

+1358

+2547

+288

-872

-927

o> 

o

Hs

+160

-329

4-8'<

-115

-865

19

June 12

+203

-.795

-36

-304

-327

+112

-117

-82

-710

-835

50

July 15-16

-130

-864

-60

-348

-400

+96

-148

-110

-762

-901

-785

-244

-760

-588

-31

+452

+178

-758

-466

+326

-283

+311

+894

+1334

+291

-910

-921

CO

3

bi

«j

-313

-823

-84

-342

+77

-728

-834

-705

-166

-696

-559

-19

+456

+217

-684

-451

-258

+1255

-50

+2550

+289

-850

-925

§

IN

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<u

O3

-307

-806

-1

-300

-326

+131

-136

-79

-697

-793

-676

-143

-658

-541

-21

+437

+217

-685

-411

+313

-258

+319

+845

+1219

-7

+2591

+276

-827

-897

IN

O

0

-381

-847

-35

-364

-371

+26

-121

-75

-692

-834

-676

-155

-676

-541

-26

+437

+217

-732

-454

+352

-310

+294

-896

-957

7 8 

>o

fc

-240

-1003

-228

-508

-551

-85

-336

-339

-976

-1098

-1019

-497

-1053

-919

-443

+73

+209

-672

-791

+16

-581

+67

+697

+1168

-186

+2555

+189

-895

-958

S3

8

Q

+186

-756

-869

-778

-177

-700

-506

-30

+466

+168

-666

 441

+332

-311

+274

+823
HAWAIIAN VOLCANOES DURING 1951 167

TABLE 8. Difference in vertical intensity of geomagnetism (in gammas) at 

stations on Mauna Loa and Kilauea, compared to that at station 0 Continued

[All readings for station 0 are actual values. Other values for the month are differences from this reading]

Magnetometer station 

no.

0..............

I..... .........

2..............

3..............

4..............

5....... .......

6..............

7..............

8..............

9..............

10.............

11. .........

12.............

13.............

14.............

15.............

16.............

17.............

18.............

19.............

20.... .........

21.. ........

22.............

23.............

24.............

25.............

26.............

27.............

28.............

1

d 

£

+212

-821

-87

-348

-368

+73

-139

-724

-912

4-1 QQ

-460

+331 -280

+279

+1108

+1284

__ Q

+2602

+342

-924

-976

S

4

ft

+471

-792

-13

-247

+233

-66

-625

-766

-629

__ 401

-62

+621

+306 -609

-345

+414 -180

+398

-937

-994

8

03

s

+405

-858

-46

-524

-486

-81

-308

-1060

-1179

-1052

-290

-339

-216

+788

+526

-367

-178

+598 -18

+552

+889

+1278

-123

+3843

-825

-920

 *

a 

^

+400

-602

+159

-83

-158

+295

+58

4-99

-836

-924

-761

-224

-748

-484

+40

+524

-712

-374

+414

-228

+352

+863

+291

May 24-25

+249

-853

-9

-293

-297

+111

-138

-129

-715

-880

 849

-347

-871

-738

-253

+182

+267

-1031

-791

+9

-507

+62

+493

+1083

-280

+2718

+320

-821

-874

19

June 26-27

+836

-800

-66

-312

-347

+102

-110

-79

-708

-831

-704

-132

-616

-616

-62

+453

+216

-690

-444

+352

-250

+330

+858

+1170

-110

+2652

+229

-884

-919

51

July 20-21

+418

-862

-84

-339

-378

+35

-185

-172

-774

-893

-717

-114

-651

-427

+5

+511

+216

-783

-440

+299

-286

+264

+871

+1210

-119

+1504

+255

-928

-928

I

tab

3 

<

+471

-854

-58

-374

-278

+210

-119

-18

-766

-898

 77*;

-194

-964

-445

-40

+462

+198

-704

-457

+290

-304

+303

+889

+1201

-79

+2503

+193

-805

-885

!Si

"a

a> 

ra

+370

-891

-90

-337

-346

+123

-166

-71

-763

-853

 654

-204

-687

-592

+5

+517

+308 -640

-337

+497

-157

+559

+1010

+1384

-61

+2768

+303

-740

-778

X

o

fc

+356

-953

-105

-347

-432

+47

-185

-110

-816

-972

 787

-143

-674

-473

+61

+573

+294

-777

-512

+360

-237

+351

+995

+1469

-38

+2839

+284

-976

-882

z

«

a> 

ft

+365

-929

-90

-341

-337

+14

-137

-14

-711

-863

 7'<>;

-209

-877

-588

-38

+526

+204

-810

-450

+408

-265

'+1550

+972

+1427

-171

+2786

+370

'4-285

'+166

8

8 

ft

+294

-868

-66

-356

-384

+80

-147

-176

-664

-711

-56

-747

-510

-28

+536

+327

-706

-427

+397

-261

+351

+953

+1375

-113

+2720

+251

-993

-965

Headings confirmed by repetition.
168 CONTRIBUTIONS TO GENERAL GEOLOGY

Early in July 1950, soon after the end of the Mauna Loa eruption, 

three stations were established. These extended southeastward for 1.5 

miles from a point on the recently active rift at an altitude of about 

8,530 feet. A fourth station was established 8 miles farther southsoutheast, near the upper access road of the Kahuku Ranch. The 

latter station lies about 4 miles east of the southwest rift zone of 

Mauna Loa, but 7.4 miles from the nearest point of eruption during 

1950. The locations are shown in figure 41. Readings at these stations were repeated in November 1950 and February 1951. The 

values obtained are given in table 9, expressed as the difference (in 

gammas) between the value at the station and that at the base station 

near the Observatory. The gradually increasing negativity at stations A, #, G may possibly have resulted from a slow warming up 

of the terrane in the vicinity of the rift by the outward conduction 

of heat from hot intrusive bodies along the rift. Erratic behavior 

was observed at station Z>, located on newly erupted lava only 75 feet 

from the eruptive fissure. This behavior may have resulted from a 

rapid cooling of the new lava directly beneath the station, followed 

by some rewarming of the lava heat conducted upward from intrusive 

masses at depth along the fissure.

TABLE 9. Vertical intensity of geomagnetism (in gammas) at stations near the 

soutMvest rift of Mauna Loa, in comparison with that at station 0, near the 

Hawaiian Volcano Observatory

Date

JulylO-12,1950...-.-- --- ----- ----- 

Station

Kahuku A 

(4 miles 

cast of rift)

+199 

-211 -246

Kahuhu B 

(1 .4 miles 

east of rift)

+365 

+182 

+115

Kahuku C 

(0.4 mile 

cast of rift)

+1080 

+1093 

+423

Kahuku D 

(at rift)

-636 

+136 -242

It is too soon to attempt an interpretation of the results of the geomagnetic measurements at the permanent stations on Kilauea volcano 

and the adjacent southeastern slope of Mauna Loa. Thus far it can 

be stated definitely only that there are marked changes in the vertical 

magnetic field both at individual stations, and at groups of related 

stations as compared with other groups of stations.

Curves A, B, and 0, in figure 37, indicate the changes in the relative 

magnetism between a group of stations (1 to 5) on the slope of Mauna 

Loa, and groups on Kilauea volcano. Group 10 to 14 lies within 

Kilauea caldera, group 16 to 21 lies along the east rift zone of Kilauea, 

and stations 27 and 28 lie on the southern slope of Kilauea about 5 

miles south of the caldera. Curve D indicates a similar variation 

between stations in Kilauea caldera and those on the southern slope 

of Kilauea. The use of groups of related stations minimizes the oc-
800

600

400

200

£-200-

-400

-600

. A

FIGURE 37. Graph showing differences in vertical intensity of geomagnetism, in gammas, at suc

Loa and Kilauea volcanoes. Curve A shows the change in differences of the average of the v

of the values of stations 10 to 14, in the caldera of Kilauea. Curve B shows the change in d

from that of stations 16 to 21, on the east rift zone of Kilauea. Curve C shows the change 

1 to 5 from that of stations 27 and 28, on the south flank of Kilauea. Curve D shows the c

tions 10 to 14, in Kilauea caldera, from that of stations 27 and 28, on the south flank of 

data are complete for both sets of stations. The open circles are points for which the data 

for the adjacent months. 
170 CONTRIBUTIONS TO GENERAL GEOLOGY

casional large, apparently aberrant, changes that occur at single 

stations. In these curves no distinct reflection of the eruption of 

Mauna Loa in June 1950, can be detected. Neither is there any distinct reflection of >the withdrawal of magma which probably accompanied the subsidence at Kilauea caldera in December 1950. The 

sharp jog in the curves caused by the readings in late November 1950, 

may possibly be related to the December subsidence. The change in 

strength of the vertical magnetic field at Kilauea caldera, as compared 

 with the Mauna Loa stations, is'in the right direction (increase) to 

have been caused by withdrawal of heated material in the area beneath 

the caldera. However, the duration of the change was much less than 

would be expected if it was caused by magmatic withdrawal. The 

direction of the change as related to the stations remote from the 

caldera on the southern slope of Mauna Loa is the reverse of that 

which would be expected. The changes in March 1951, and the great 

increase in magnetic attraction at stations 21,.27, and 28 during early 

December 1951, can not be correlated with any known volcanic events. 

Events such as the 1950 eruption of Mauna Loa, and the subsidence 

of Kilauea in December 1950, involve the movement of great 

masses of hot material at depth. At what depths these movements 

occur is not definitely known, but certain earthquake evidence suggests 

that it may occur at depths of 20 miles or more. The total areal spread 

of the permanent magnetometer stations is less than that amount, and 

it may be, therefore, that the resultant differences in magnetism at 

the separate group of stations might be too small to be recognized. 

Too much emphasis should not, therefore, be put on the significance 

of the curves in figure 37.

TEMPERATURE MEASUREMENTS

Measurements of the temperature of steam escaping at Sulphur 

Bank (fig. 31), 0.2 mile northwest of the Whitney Laboratory of 

Seismology, have been continued at monthly intervals throughout 

1951. Measurements were made at natural vents, and at the drilled 

well (Finch and Macdonald, 1951, p. 116). The temperature at the 

steam well showed little variation. On December 30, 1950, and January 30, 1951, it was 95.5 C. On March 1, the temperature had increased slightly to 96 C., and remained at that reading until October 

1, On November 1, December 14, and December 31 it was 95.5 C. 

(Boiling point of water at this altitude is about 95.7 C.) The greater 

abundance of rain during the winter months may, in the absence 

of other factors, cause a slightly lower temperature than during the 

drier summer months. Measurements at the natural vents were much 

more variable than those at the steam Avell, at least partly because 

of changes in external conditions, such as direction and strength of
HAWAIIAN VOLCANOES DURING 1951 171

the wind. It is difficult to obtain uniform conditions of exposure of 

the thermometer in the natural vents.

On December 13, 1951, the temperature of the escaping mixture of 

air and water vapor was measured at several vents in the steaming 

area just south of Kokoolau crater on the east rift zone of Kilauea. 

The temperature at the two hottest vents found was 82 and 89.5 C. 

On December 14 measurements were made of the temperature of the 

escaping gas at se^7 eral vents on the Steaming Flat southwest of 

Sulphur Bank. The temperatures ranged from 71 to 75 C.

Temperature measurements were made on September 9, on the Ohia 

Lodge flow of 1950 where it crosses the highway in south Kona (Finch 

and Macdonald, 1953). Many cracks yielded measurements exceeding 130 C at depths of about a foot beneath the surface. Several 

cracks were found in which the temperature exceeded 230 C, the 

maximum on the available thermometers. In the hottest cracks dry 

sticks ignited within 20 seconds, and lead foil lowered to a point 18 

inches below the surface melted and dripped in about 5 seconds. 

Zinc foil softened, but did not melt. Thus the temperature 18 inches 

below the surface in these hottest cracks, 15 months after the termination of the eruption, still exceeded 327 C, and was probably about 

400 C. These hottest cracks are near the banks of the principal feeding river of the flow, in an area where the thickness of the underlying 

flow is about 50 feet.

RAINFALL RECORDS

Daily readings of rainfall were continued at the gage near the 

Uwekahuna seismograph station throughout 1951. A new gage was 

established at the Mauna Loa seismograph station on September 2, 

1951, and has been read about every other day since. These readings 

are on file at the Hawaiian Volcano Observatory. In addition, a gage 

near the southeastern rim of Halemauman, and another at an altitude 

of 5,500 feet on the Mauna Loa truck trail, 2 miles southeast of the 

Mauna Loa seismograph station, have been read once a month. 

Monthly totals for these four gages are given in table 10.

TABLE 10. Monthly rainfall, in inches, during J.951

Month

July.........

Halomaumau

7.81

10.40

18.35

1.90

.83

1.47

.70

G

Uwekahuna seismograph 

station

11.43

18. CC

19.98

2.14

010

1.16

age

Mauna 

Loa 

truck 

trail

7.91

23.35

19.98

1.10

1.72

Mauna 

Loa seismograph 

station

Month

Total.

Halomaumau

5.07

.47

19.78

5.58

 4.07

Gt

Uwekahuna seismograph 

station

8.38

1.83

19.25

8.11

3.57

99.80

igc

Mauna 

Loa 

truck 

trail

6.37

.61

10. 91

5.37

3.42

83. 98

Mauna 

Loa seismograph 

station

0.62

9.71

8.20

2.36
172 CONTRIBUTIONS TO GENERAL GEOLOGY

VOLCANIC CONDITIONS DURING 1951

General. There was no eruptive activity of Hawaiian volcanoes 

during the year 1951. However, seismic activity was decidedly greater 

than usual. The principal seismic events of the year were the Kilauea 

earthquake of April 22 and its aftershocks, and the intense Kona 

earthquake of August 21 and its aftershocks. These earthquake 

spasms are described in some detail on later pages of this report. 

Another strong earthquake damaged walls and dishes on November 8.

The earthquake on April 22 apparently accompanied a decrease of 

magmatic pressure under Kilauea volcano. It was quickly followed, 

however, by the commencement of rapid northward tilting of the 

ground at the Whitney Laboratory of Seismology, which is interpreted as indicating a resumption of increasing pressure under 

Kilauea. During June the apparent increase of pressure beneath 

Kilauea ceased temporarily, giving way to an apparent increase of 

pressure under Mauna Loa. In July, however, the pressure increase 

apparently shifted back to Kilauea. During August, September, and 

most of October, the rate of ground tilting was about normal for that 

season. Late in October, however, a sudden northeastward tilting may 

have been caused by an increase of pressure under both volcanoes. 

Mauna Loa and Kilauea were uneasy during November and many 

many small earthquakes originated at Kilauea, and oscillation of tilt 

suggested fluctuations of pressure beneath Mauna Loa. Uneasiness 

was less marked during December, and there appears to have been a 

decrease of pressure beneath Kilauea.

From December 31,1950, to December 31, 1951, a net accumulation 

of 9.4 seconds of arc of northward tilt, and 7.2 seconds of eastward 

tilt was recorded. This suggests that at the end of 1951 the pressure 

beneath both Kilauea and Mauna Loa was somewhat higher than at 

the end of 1950.

January. Mauna Loa and Kilauea volcanoes were very quiet 

throughout the month of January. Only 18 earthquakes were recorded 

at the Whitney Laboratory of Seismology, on the northeastern rim of 

Kilauea caldera, and 8 were recorded at the Mauna Loa station. This 

was the smallest number recorded at either station for any month since 

October 1947, when 11 earthquakes were recorded at the Whitney 

station.

During January ground-surface tilting was mainly southward, following the usual seasonal pattern for that time of year. From January 

7 to 17, however, there was a sharp northward tilting of about 2 seconds 

of arc, suggesting a slight increase of magmatic pressure beneath 

Kilauea volcano.

Conspicuous steam clouds rose from Halemaumau crater on January 

22, following heavy rains. This is a fairly common event and occurs
HAWAIIAN VOLCANOES DURING 1951 173

several times each year. Abundant steam is liberated within Halemaumau about 60 to 90 minutes after the beginning of torrential rainfalls. Although there has been no surface eruptive activity at Kilauea 

since 1934, the rain Avater does not have to percolate far beneath, the 

floor of Halemaumau to encounter rock hot enough to evaporate it. 

The steam issues from numerous small vents on the floor of Halemaumau.

February. Manna Loa and Kilauea continued quiet during February. The seismograph at the Whitney Laboratory recorded 25 

earthquakes, but only 16 were recorded on the seismograph at the 

Maim a Loa station. An earthquake felt in the vicinity of Kapapala at 

10h 55m on February 14 originated at a depth of about 7 miles on or near 

the Kaoiki fault zone near Ainapo, on the southeastern flank of Manna 

Loa. At 07h26m on February 16 a stronger earthquake was felt from 

Naalehu to Hilo. It originated about 15 miles below a point on the 

northeast rift zone of Manna Loa near Pun Ulaula. Most of the small 

earthquakes during the month originated in Kilauea volcano.

Tilting of the ground at the northeastern rim of Kilauea caldera 

continued southward, as is normal during that season of the year. 

There was almost no accumulation of east-west tilt during the month. 

However, because there is normally a westward tilting at that time 

of the year, the absence of tilting may indicate a small increase of 

magmatic pressure beneath Manna Loa.

The vents of the 1950 eruption of Mauna Loa were visited on February 9 and 10. Steam was issuing from the vent fissures from an 

altitude of 10,200 to 11,500 feet, and large amounts of sulfurous fumes 

were being liberated at an altitude of about 10,000 feet. The vent 

fissures were still warm, but no heat could be detected in most of the 

thin flows near the vents. Fume along the southwest rift of Mauna 

Loa in the vicinity of the 1950 Agents Avas visible from the HaAvaiian 

Volcano Observatory on the afternoon of February 16.

During and after heavy rains in late February spectacular steam 

clouds rose from Halemaumau, indicating that the principal A^ent of 

Kilauea A^olcano still is very hot a short distance beloAv the surface.

March. Volcanic quiescence continued throughout March. The 

seismograph at the Whitney Laboratory of Seismology recorded 27 

earthquakes, two more than Avere recorded in February, and slightly 

less than the average number recorded per month during times of 

quiet. Only 14 earthquakes Avere recorded at the Mauna Loa station.

An earthquake felt from Kilauea caldera to Hilo at 20h 50m on 

March 14 had its origin at a depth of about 7 miles on the east rift 

zone of Kilauea, 5 miles east-northeast of Makaopuhi Crater. At 

06h41m on March 20 another earthquake Avas felt by a feAv persons in 

the Puueo district of Hilo. This earthquake originated about 6 miles 

beneath the eastern slope of Mauna Loa, 3 miles east of Kulani cone.
174 CONTRIBUTIONS TO GENERAL GEOLOGY

From March 15 to 19 several small earthquakes originated on the 

western slope of Mauna Loa near Kealakekua, possibly on the same 

fault involved in the major earthquake of August 21.

Tilting ^ of. the ground surface at the northeastern rim of Kilauea 

caldera continued southward throughout March, as is normal during 

that season. However, from March 1 to IT the tilting was distinctly 

more rapid than normal, indicating a small decrease of magmatic 

pressure beneath Kilauea caldera. This, like the northward tilting 

during January, indicates fluctuation of pressure and demonstrates 

that the magma column beneath Ivilauea is still mobile. Slight westward tilting also occurred during the month, as is usual at that season.

April. The period of volcanic quiescence that began in late December, 1950, was ended on April 22 by a heavy earthquake followed by 

a swarm of aftershocks. The earthquake and aftershocks are described 

on later pages. The Hawaiian Volcano Observatory seismographs 

recorded 132 earthquakes during the month. Of these, 108 were aftershocks of the major earthquake of April 22. The origin of most of 

the quakes in Kilauea volcano is demonstrated by the fact that 125 

of them were recorded on the instruments at the rim of Ivilauea 

caldera, and only 89 of them at the Mauna Loa station.

Although damage to the tiltmeters, caused by the earthquake, made. 

actual measurements impossible, the writers believe that the major 

earthquake of April 22 accompanied a distinct subsidence of the 

ground surface at Kilauea caldera, probably caused by a decrease of 

magmatic pressure at depth. However, this was quickly followed, on 

April 24, by a fairly rapid tumescence of the volcano, expressed by 

northward tilting of the ground at the Whitney Laboratory. The 

northward tilting was considerably in excess of the rate normal for 

that time of year. It is noteworthy also, that the reversal from southward to northward tilting came nearly a month earlier than usual. 

Ivilauea volcano appeared distinctly uneasy during late April.

May. The rapid northward tilting of the ground at the Whitiiey 

Laboratory, which commenced on April 24, continued throughout 

May. By the end of the month a total of 6 seconds of arc of northward 

tilting had accumulated. The rate of northward tilting was about 

twice as great as normal during that season, and indicated a continued increase of pressure beneath Kilauea. Some cracks on the floor 

of the caldera and along the Chain of Craters Road opened slightly 

during the month, possibly in response to the tumescence of the 

volcanic edifice.

The seismographs of the Hawaiian Volcano Observatory recorded 

41 earthquakes during May. Of these, 36 were recorded at the 

Whitney Laboratory, and 20 at the Mauna Loa station. A feeble 

earthquake felt by a few persons in the Volcano district (2 to 5 miles
HAWAIIAN VOLCANOES DURING 1951 175

northeast of Kilauea caldera) just after noon on May IT, originated 

under Kilauea volcano about 6 miles south of the caldera.

June. The marked northward tilting of the ground at the Whitney 

Laboratory continued into early June. After June 8, however, the 

rate of northward tilting decreased to about normal for that season. 

During late May the rate of eastward tilting had been about normal, 

but beginning on June 3 it became appreciably greater, and continued 

above normal for the remainder of the month. This eastward tilting 

indicated an increase of volcanic pressure beneath the summit area of 

Mauna Loa.

Forty-two earthquakes were recorded on the Hawaiian Volcano 

Observatory seismographs during June. Of these, 28 were recorded 

at the Whitney Laboratory, and 29 at the Mauna Loa station. A series 

of small earthquakes (mostly tremors) on June 18 and 19, which were 

recorded only on the Mauna Loa seismograph, indicated some movement on the northeast rift zone of Mauna Loa.

Slight earthquakes Avere felt by some persons from Kilauea caldera 

to Hilo at 22h49m on June T and OSh32m on June 11. Both earthquakes had their origin on the east rift zone of Kilauea volcano, 

the first near Pauahi Crater, and the second about 6 miles southwest 

of Pahoa.

July. Seismically, Hawaiian volcanoes were quiet during the 

month of July. Only 29 earthquakes were recorded on the Hawaiian 

Volcano Observatory seismographs. Seventeen earthquakes were recorded at the Whitney Laboratory of Seismology, and 15 at the Mauna 

Loa station. A feeble earthquate at 04hOTm on July 1 originated on 

the southwest rift zone of Mauna Loa beneath a point near Sulphur 

Cone, at an altitude of 11,250 feet. Another, at 23h20ra on July 5, 

originated beneath Kilauea caldera, probably within 3 miles of the 

surface.

Northward tilting of the ground surface at the Whitney Laboratory 

continued throughout the month, and totaled nearly 4 seconds of arc. 

That rate of tilting is more than twice the average for that season, 

and indicated a further increase of magmatic pressure beneath 

Kilauea volcano. Tilting in the east-west direction showed minor 

oscillations during the month, but no appreciable net change.

Mokuaweoweo caldera, at the summit of Mauna Loa, was visited on 

July 25. Small amounts of sulfurous fumes were issuing at the 1940 

cinder cone within the caldera, and a little steam was issuing near 

the northern edge of the 1940 cone, and at places on and near the 

1949 cone, both within and just outside of the caldera.

August. The outstanding event of the month was the severe earthquake that took place at OOh5Tm on August 21. This earthquake, and 

the damage caused by it, are described in a later chapter. The major
176 CONTRIBUTIONS TO GENERAL GEOLOGY

earthquake was followed by a large number of aftershocks. Between 

00h 57m and 24hOOm on August 21, the seismographs of the Hawaiian 

Volcano Observatory recorded 135 earthquakes. During this period 

the seismograph at Konawaena School, in Kona, was not operating, 

because of extensive damage to the instrument during the major 

quake. On the basis of the ratio between the number of earthquakes 

of Kona origin recorded at the Kona and Kilauea stations on later 

days, it is estimated that if the Kona instrument had been in operation 

on August 21, it would have recorded about 900 earthquakes during 

that single day. A woman at Keei, about 5 miles from the epicenter 

of the major earthquake, felt 109 earthquakes between 00h57m and 

09hOOm on August 21. The Kona seismograph recorded 494 earthquakes between the time it was restored to operation, at 15h 15m 

on August 23, and midnight on August 31. During August, 264 

earthquakes were recorded on the seismograph at the Whitnej Laboratory and 268 at the Maun a Loa station. Of these, 235 occurred 

after the major earthquake of August 21.

The intense earthquake of August 21 probably had its origin on 

the seaward prolongation of a fault zone that extends into the sea 

just north of Kealakekua Bay. This fault zone consists of normal 

faults along which the lower western slope of Mauna Loa has in the 

past moved downward in relation to the upper part of Mauna Loa 

east of the faults. It is not known whether the fault movement on 

August 21 resulted from rise of the summit of Mauna Loa in response 

to a sudden increase in magmatic pressure beneath it; to a downward 

elastic rebound of the lower slopes after a longer period bulging of 

Mauna Loa possibly associated with the 1949 and 1950 eruptions; or 

to a gravity-impelled downward shifting of the lower, submarine portion of the mountain flank toward the ocean deeps to the west.

At I7h48m on August 28 a small earthquake originated beneath the 

eastern slope of Mauna Loa near Mountain View, and at 18h04m on 

the same day a smaller one originated just east of Kilauea caldera.

Beginning at 06h 02m on August 23 the seismograph at the Whitney 

Laboratory recorded 21 minutes of continuous tremor, of the type that 

indicates subterranean movement of magma. However, there were no 

other indications of magma movement during the month. Northward 

and eastward tilting of the ground at the Whitney Laboratory was at 

a rate about normal for that season.

On August 14, E. K. Field, chief ranger, and Elroy Bohlin, ranger, of 

Hawaii National Park, flew over the summit of Mauna Loa and 

observed fumes issuing mildly from the 1940 cinder cone in 

Mokuaweoweo caldera.

September. Earthquakes continued abundant during September. 

Most of the activity centered in the Kona area. The Kona seismograph recorded 471 earthquakes. Most of these were too small and
HAWAIIAN VOLCANOES DURING 195l' 177

.4 shallow-seated to be recorded on the seismographs at Kilauea caldera, 

f 42 miles away. During September the seismograph at the Whitney 

^ Laboratory recorded 110 earthquakes', and the Mauna Loa seismo- 

}, graph recorded 106.

Most of the earthquakes originated within 10 miles of the Kona

seismograph station, probably along the Kealakekua fault zone. HowA ever, several had their origins beneath points along the southwest rift

i zone of Mauna Loa from an altitude of 9,000 feet to the summit, and a

1 few originated in Kilauea volcano. A small quake felt in Hilo at

^ 23h4Sm on September 24 had its focus on the northeast rift of Mauna

Loa. From September 23 to 26 several earthquakes originated beneath

Hualalai volcano.

*. On September 16 and 17 about 25 earthquakes originated along the 

y Kaoiki fault zone. This zone of normal faults along the southeastern 

slope of Mauna Loa is analogous to the Kealakekua fault zone on the 

^ western slope. The earthquake of intensity 5, at Olh43m on September 

16 was felt over most of the southern part of the island. It has already 

been described on page 146. The quake started rock slides on the walls 

0k. of Halemaumau that continued at intervals for several days. A 

crack parallel to the southeastern rim of Halemaumau opened 8 millimeters during the month of September; most of the opening took place 

during the earthquakes of September 16.

Northeastward tilting of the ground continued throughout September at the Whitney Laboratory. The direction and rate of tilting were 

about average for that season.

October. The uneasiness that was manifest at Mauna Loa during 

September continued throughout October. Earthquakes originated 

( beneath the summit area of the mountain and along the northeast and 

southwest rift zones, as well as on the Kealakekua fault zone on the 

^~ western slope and the Kaoiki fault zone on the southeastern slope of 

the mountain. Starting at 22h03ra on October 8 the Hawaiian Volcano 

Observatory seismographs recorded 16 minutes of continuous volcanic 

tremor, probably caused by subterranean movement of magma. It 

was followed at 04h45ra on October 9 by a moderate earthquake that 

apparently originated at a depth of 25 to 30 miles beneath the summit 

area of Mauna Loa. This earthquake was felt by some persons 

throughout the southern part of the island of Hawaii, from Kealakekua 

in Kona to Hilo. A smaller earthquake at 05h23m on the same morning originated deep beneath the upper end of the southwest rift zone 

of Mauna Loa.

During most of the month the rate of eastward tilting at the Whitney Laboratory was about normal. However, from October 28 to 

30 it was much more rapid than usual. The rapid tilt may have been 

caused by a heavy rainfall that preceded it, or it may have resulted 

from an increase of magmatic pressure beneath Mauna Loa. Abrior-
178 CONTRIBUTIONS TO GENERAL GEOLOGY

mally rapid northward tilting during the same period may have been 

caused by an increase of pressure beneath Kilauea.

On October 24, I. C. Maims, superintendent of construction and 

maintenance for the Kulani project. Territorial Department of Institutions, reported a long period of continuous trembling of the ground 

at the summit of Mauna Loa. This trembling appeared on the seismograms as a series of closely spaced, but separate small earthquakes. Mr. 

Maims also reported an apparent increase in the amount of steam being 

liberated at vents within Mokuaweoweo caldera. On October 31 observers in aircraft reported a large cloud of steam rising from the 

southwest rift of Mauna Loa at an altitude from 8,000 to 12,000 feet. 

This is the area in which are situated the vents of the 1950 eruption. 

Fume liberation at the vents has been continuous since the end of 

the eruption. On October 20,1. J. Castro, acting superintendent, and 

Elroy Bohlin, ranger, of Hawaii National Park, flew over the summit 

and southwest rift of Mauna Loa and reported fume (probably 

largely steam) rising at eight localities along the rift at an altitude 

from 9,000 to 12,000 feet. The reported increase in the size of the 

steam cloud on October 31 probably resulted from the heavy rains on 

October 26-28 coming in contact with still hot lava near the vents, and 

the clear visibility of the steam owing to the unusually high humidity. 

The same heavy rains resulted in large and conspicuous steam clouds 

at Halemaumau. in Kilauea caldera (fig. 38).

During October the seismographs at Kilauea caldera recorded 73 

earthquakes, the Mauna Loa station recorded 65, and the Kona station 

recorded 139.

FIGURE 3S. Clouds of steam rising from IIal<: nitiumaii on October 29. 11)51. following 

heavy rains on the preceding* 2 days. The view is from the Hawaiian Volcano Observatory, at Uwekahuna.
HAWAIIAN VOLCANOES DURING 1951 179

November. Maima Loa and Kilauea volcanoes continued somewhat 

uneasy throughout November. During the month 73 earthquakes were 

recorded at the Whitney Laboratory. This number is more than twice 

the average recorded during times of quiescence. The Mauna Loa seismograph recorded 53 earthquakes, and the Kona seismograph recorded 110. The rate of ground tilting during the month was about 

normal for that season, but moderately strong oscillations of tilt in 

the east-west direction suggest fluctuations in pressure beneath Mauna 

Loa.

At 09h34m on November 8 an earthquake of intensity 6 in the modified Mercalli scale of 1931 broke dishes and did extensive damage to 

stone walls at the Kahuku Ranch, 9.5 miles north of the southernmost 

point of the island of Hawaii. The earthquake was felt over the entire 

island. It originated on the southwest rift zone of Mauna Loa about 

6 miles north of the Kahuku Ranch headquarters, or 15.5 miles north 

from South Point.

Most of the earthquakes recorded by the Kona seismograph had 

their origin within a few miles of the instrument, probably largely 

or entirely on the Kealakeku fault zone. On November 7 at 20h llm 

a small earthquake originated beneath the summit region of Hualalai 

volcano. On November 21, at 09h 59m, another small quake originated 

beneath the Waimea Plain a few miles Avest from Kamuela, 22 miles 

northwest of the summit of Mauna Kea. Nearly all the other earthquakes during the month had their origin in Kilauea and Mauna Loa 

volcanoes.

On the morning of November 23 two observers at different points 

in the Kona area reported what appeared to them to be smoke near 

the summit of Mauna Loa. E. K. Field, chief ranger, and R. L. 

Jeffery, superintendent of construction and maintenance, of Hawaii 

National Park, were at the summit of Mauna Loa at the time. They 

reported conditions in the caldera and the adjacent summit area to be 

normal. The cloud which appeared to the observers in Kona to be 

smoke apparently was steam rising near the vents of the 1950 lava 

flows, probably as a result of heavy rains from November 20 to 22.

December. The uneasiness apparent at Mauna Loa and Kilauea 

during October and November was much less marked during December. Most of the earthquake activity originated at Kilauea volcano, 

but the total of 37 earthquakes recorded during the month at the 

Whitney Laboratory is only slightly more than the average number recorded during times of volcanic quiet. The Mauna Loa seismograph 

recorded only 21 earthquakes. The Kona seismograph .recorded 62 

earthquakes during December, bringing the total recorded since August 23 to 1,276. Most of the quakes recorded in Kona apparently 

originated on the Kealakekua fault zone.
180 CONTRIBUTIONS TO GENERAL GEOLOGY

At 20h 19m on December 6 a strong earthquake was felt over the southeastern part of the island of Hawaii. It originated at a depth of 3 or 4 

miles on the east rift zone of Kilauea volcano, about 14 miles east of 

the caldera. The earthquake had been preceded by 3 days of rapid 

southward tilting at the Whitney Laboratory, presumably caused by 

a decrease of magmatic pressure beneath Kilauea caldera. The quake 

may have reflected a similar decrease of pressure beneath the east rift 

zone, or it may have been caused by an opening of the rift zone which 

allowed the subsurface movement of magma away from the caldera, 

thus reducing the pressure there.

Between December 3 and 7 the ground surface at the Whitney Laboratory, at the northeastern rim of Kilauea caldera, tilted southward 

through an angle of 4.4 seconds of arc. By December 16 an additional 

southward tilting of 0.6 second had taken place. A rapid northward 

tilt of 2.6 seconds of arc followed on December 25. The net southward tilt during the month was 2.2 seconds. This suggests an oscillation, having a net decrease, of pressure beneath Kilauea. Oscillations of the east-Avest tilt likewise suggest some fluctuation of pressure 

beneath Mauna Loa.

SPECIAL INVESTIGATIONS

PNEUMATOLYTIC DEPOSITS

White salts deposited by rising gases are common on recent lava 

flows of Mauna Loa, along the vent fissures and cracks in thick flows. 

A sample was collected on October 4, 1948, from the vent fissure of 

the 1942 lava flow at an altitude of 9,300 feet. Another sample of similar material was collected on October 25, 1949, from cracks in the 

1949 lava flow on the floor of Mokuaweoweo caldera 0.75 mile east of 

the 1940 cinder cone. These samples were tested chemically, optically, 

and by X-ray methods, by Theodore Woodward, of the U. S. Geological Survey. Both samples consisted of thenardite (Na2SO4 ). The 

SO4 radical undoubtedly was formed by oxidation of volatile sulfur 

liberated from the lava. It is uncertain whether the Na radical also 

was carried out of the lava by escaping volatiles, or Avas leached out 

of the lava along the fissures by the sulfuric acid vapors. There is 

no sign of decomposition of the lava directly associated Avith the 

thenardite deposits, but the possibility of decomposition of the lava 

and leaching of sodium deeper in the fissures cannot be ruled out.

White pOAvdery material collected by R. H. Finch from a crack near 

Cone Crater, on the southwest rift zone of Kilauea, on September 15, 

1947, Avas determined by Woodward to be opal. Thin crusts of opal, 

commonly in mammillary and botryoidal forms, are found along 

many cracks Avhere steam is escaping on the floor of Kilauea caldera.
v HAWAIIAN VOLCANOES DURING 1951 181

^ The associated lavas generally are someAvhat decomposed, at least for 

a few millimeters below the opal crust, and it is probable that the 

silica was derived by alteration of the lavas by the rising steam. Some

* transportation of the silica by the rising steam undoubtedly has taken 

. place.

* THE KILAUEA EABTHQUAKE OF APRIL 22, 1951, AND ITS

AFTERSHOCKS

On April 22, at 14h52m Hawaiian time, the southern part of the 

island of HaAvaii experienced the strongest earthquake in this area

fc since 1929, and possibly since 1908. The epicenter of the quake lay 

just east of Kilauea caldera. The intensity of 5 on the modified MerK calli scale was essentially uniform for 30 miles northeast and southwest of the epicenter, to Hilo and Naalehu respectively. This uniformity of intensity over such a broad area indicates that the origin 

of the earthquake was at great depth, probably 25 to 30 miles. It was

* impossible to determine either the epicenter or the depth of origin 

instrumentally, because all the seismographs of the local net were

* dismantled by the preliminary waves. The operator of the Hilo seismograph station, Brother Bernard T. Pleimann of St. Joseph's 

School, reached the dismantled instrument and reassembled it in time 

to record the coda of the earthquake. Shaking continued on the Hilo 

instrument for 16 minutes.

The preliminary determination of the epicenter issued by the U. S. 

Coast and Geodetic Survey on April 24 gives the time at the origin

./ as 00h 52m21s on April 23, Greenwich civil time, and the magnitude on 

the Gutenberg-Richter scale as 6.5 as determined at Pasadena, Calif., 

and 6.0 at Berkeley.

The earthquake was felt generally over the entire island of Hawaii, 

and by many persons on the islands of Maui and Oahu. Damage resulting from the quake was slight. On the southern part of the island 

of HaAvaii many small objects were overturned, and some dishes Avere 

broken. Many, but not all pendulum clocks Avere stopped. A Avater 

pipe Avas broken at the Hawaiian Volcano Observatory, and a plateglass windoAv at Glenwood was cracked. Water slopped over the rims 

of some tanks. Small earth slips occurred in road cuts betAveen 

Kilauea caldera and Hilo, and north of Hilo along the Hamakua

*> coast. Several rock slides occurred on the Avails of Kilauea caldera, 

and many occurred on the unstable walls of Halemaumau crater. The 

latter were small. No large blocks of the crater rim Avere displaced, 

although many cracks near the rim Avere appreciably Avidened. The. 

crack which crosses the tourist area at the southeastern rim of the 

crater opened 6 millimeters at the time of the earthquake, and 3 milli-

* meters more during the period of aftershocks.
182 CONTRIBUTIONS TO GENERAL GEOLOGY

Small slides continued in Halemaumau for about a week after the 

main earthquakes. Small rock avalanches occurred on the walls of 

Alae and Makaopuhi craters, on the east rift zone of Kilauea. Superintendent F. K. Oberhansley of Hawaii National Park reported rock 

falls at the cliffs of Hilina Pali and Puu Kapukapu, at the southern 

shore of the island. Minor cracking of the highway occurred at the

northeastern rim of Kilauea caldera, a quarter of a mile southeast of 

the Whitney Laboratory (fig. 39), apparently caused by settling of a 

thin fill under the pavement when the block at the edge of the caldera 

moved slightly toward the caldera. Cracking in the soil also was 

observed at several places north and east of Kilauea caldera, apparently caused by lurching of the soil. No surface faulting was observed.
*> HAWAIIAN VOLCANOES DURING 1951 183

The Bosch-Omori seismograph at the Whitney Laboratory on the 

northeastern rim of Kilauea caldera (fig. 39), and the vertical seismograph at Uwekahuna, were dismantled. The vertical seismograph was 

restored to operation at 15h 20ra , but resumption of recording on the 

V Bosch-Omori seismograph was delayed until 16h 45m by electricpower failure caused by the earthquake. The wire suspensions on the

*" heavy mass of one component of the HaAvaiian-type seismograph at 

the Maima Loa station were broken, and the mass, weighing 220 

pounds, dropped to the floor of the vault, 3 feet from its proper position. At the Uwekahuna vault the wire suspensions on both com- 

» ponents of a semiportable tiltmeter were broken and the horizontal 

pendulums, each weighing 35 pounds, dropped onto the pier. The 

breaking of the wire suspensions, which have considerable strength 

under normal conditions of lateral swing of the pendulums, suggests 

a vertical dancing of the pendulums. This damage and the dismantling of the vertical seismograph, which is seldom dismantled even

* by strong earthquakes, indicate a high angle of emergence of the earthquake vibrations, consonant with a deep origin nearly beneath Kilauea

* caldera.

Damage to the seismographs and tiltmeters made it impossible to 

determine with certainty the direction of tilt during the earthquake, 

but it probably was southeastward at the Whitney station and eastward at Uwekahuna. The direction of first motion of the earthquake 

was south and east at the Whitney station, and down at the vertical 

seismograph at Uwekahuna. The writers believe that the earthquake 

accompanied a marked subsidence at Kilauea, probably caused by a 

decrease of volcanic pressure at depth. Subsidence is suggested by the 

direction of first motion and the probable direction of tilt, and also by 

the observed generalization that the strongest local earthquakes generally, if not always, accompany subsidence rather than tumescence. 

It was observed that the subsidence was immediately followed by the 

beginning of rapid northward tilting of the ground at the Whitney 

station, apparently indicating restoration of the pressure. This rapid 

northward tilting continued until June 8.

The major earthquake was preceded, at 04h 53 53s H. s. t. on April 

22, by a moderate earthquake which originated at a depth of about 21 

miles on the east rift zone of Kilauea volcano, 10 miles east of the 

caldera (location 34, fig. 39).

During the 7 days following the major shock 108 earthquakes were 

recorded on the Hawaiian Volcano Observatory seismographs. Of 

this number, 71 occurred on April 22 and 23. More than half were 

tremors, too small to permit identification of separate phases in the

* record. Figure 40 is a graph of daily seismicity from April 20 to 30,

* derived by assigning, a numerical value to each earthquake, depending 

on its intensity, and totaling these values for each clay (see page 184).
184 CONTRIBUTIONS TO GENERAL GEOLOGY

25 -

20 21 22 23 24 25 26 27 28 29 30

APRIL

FIGURE 40. Graph showing daily seismicity at the Whitney Laboratory of Seismology

from April 20 to 30, 1951.

All earthquakes producing a double amplitude of oscillation of more 

than 60 millimeters on. the Bosch-Omori seismograph are classified as 

strong, and receive the same seismicity rating. Thus the major earthquake of April 22 received the same seismicity value as the much 

smaller "strong" earthquakes which took place on April 23 and 26. 

If allowance were made for this, the seismicity on April 22 should be 

somewhat increased. The high seismicity on April 22 and 23 results 

principally from the large number of very small aftershocks (tremors 

and very feeble earthquakes) on those days.

Most of the aftershocks were too small to be located. The phase 

arrivals were not recognizable on the seismograms, or recognizable 

only on the record of one station. Nineteen could be located with
HAWAIIAN VOLCANOES DURING 1951 185

v

r reasonable certainty. The epicenters of these are shown in figure 40, 

in which the number accompanying the cross indicating the epicenter 

is the serial number of the earthquake for the current year. The 

date, time, and intensity are given following its serial number in table 

4. All the located aftershocks were of comparatively shallow origin,

*v The deepest was that at 03h 57m on April 26 (serial No. 73), at a 

+ depth of about 11 miles on the east rift zone of Kilauea. Most of the 

others originated at depths ranging from 3 to 8 miles. The aftershocks generally fall into two groups, one distributed along the rift 

zones of Kilauea volcano, and the other associated with the Kaoiki 

fault zone along the southeastern slope of Mauna Loa and the pro-

* longation of the Kaoiki zone northeastward beyond any recognized 

 surface fault offsets. It is of interest to note that the northeastward continuation of the Kaoiki fault was suggested years ago by 

H. 0. Wood (1915, p. 56-57), who also found an apparent clustering 

of earthquakes along this line. The Kaoiki fault zone lies at or 

near the surface contact between Kilauea and Mauna Loa volcanoes, ^ '

and earthquake activity along this zone probably resulted from rela- 

> tive downward movement of Kilauea along the Kaoiki faults in response to decrease of volcanic pressure beneath Kilauea.

Many of the small aftershocks which could not be definitely located apparently originated beneath Kilauea caldera or along one 

of the rift zones in the immediate, vicinity of the caldera. Two of 

the quakes originated along the Hilina fault zone near the southern

* coast of Kilauea.

THE KONA EARTHQUAKE OF AUGUST 21, 1951, AND ITS 

AFTERSHOCKS

Small to moderate-sized earthquakes associated with the volcanoes 

Kilauea and Mauna Loa are numerous, but strong earthquakes are 

t comparatively rare in the Hawaiian Islands. The earthquake of 

August 21 ranks among the strongest on record in the Hawaiian 

region, and probably was the strongest since 1868, when severe earthquakes did extensive damage throughout the southwestern part of 

the island of Hawaii.

The earthquake of August 21, 1951, had its origin a few miles west

* of the western shoreline of the island, and caused much damage in 

the adjacent district of central Kona. In consequence, it has become 

generally known as the "Kona earthquake" (Macdonald and Wentworth, 1951, 1952; Wentworth, 1951, 1953). The quake was felt 

strongly over the entire island of Hawaii, and weakly by many persons on the islands of Maui and Molokai, and in Honolulu, on the

* island of Oah.ii, 180 miles from the focus of the earthquake. The 

principal earthquake was followed by many aftershocks, of lesser 

intensity.
186 CONTRIBUTIONS TO GENERAL GEOLOGY 

NARRATIVE OF THE EARTHQUAKE

At 57 minutes past midnight on August 21, residents of the island ,- 

of Hawaii were awakened by a violent earthquake. The violence was 

greatest in central Kona, from Kealakekua to Hookena (fig. 41). Near

VTopogrophy by U.S. Geologicol Survey

FIGURE 41. Map of the central Kona district showing the location of places mentioned in 

the text, and the approximate locations of the epicenters of the major earthquake of 

August 21, 19'51, and the aftershocks for which reasonably good locations were obtained. 

The inset map of the island of Hawaii shows the location of the area (shaded) covered 

by the other map, and the approximate position of the isftseismal lines for the major 

earthquake.
V HAWAIIAN VOLCANOES DURING 1951 187

* the epicenter the initial movement was reported to be largely up and 

down, with some swaying in an east-west direction. This swaying 

rapidly increased in intensity, and changed to what appeared to several persons to be a vortical motion. A few persons, who were awake

V at the time the earthquake occurred, report that the apparent shaking of the ground was preceded by a dull roar which seemed to come 

from the ground. Observers near the epicenter reported the shaking 

was nearly continuous for an hour or more after the major quake.

Noise during the major earthquake was intense. Dishes, furniture, and canned and bottled goods crashed to the floor, doors and

> windows rattled, water tanks collapsed, rocks rolled from stone walls 

and banks, and landslides and rock falls rushed down cliffs.

11 Within moments, several houses, churches, and a school building 

were partly or entirely destroyed, and many other houses slightly 

damaged. About 200 water tanks collapsed, miles of stone Avail were 

thrown down, roads partly blocked by rock slides, and road pavev ments and shoulders badly cracked. Headstones in cemeteries were 

shifted or overturned, water lines broken, and telephone and electric 

service disrupted. Fortunately, only two small fires broke out, and 

only two persons received minor injuries from broken glass. One of 

the most serious consequences of the earthquake was the loss of water 

supply throughout much of the central Kona district.

The greatest destruction occurred in the 10-mile interval south of 

the village of Captain Cook. However, minor damage extended from 

Holualoa, 10 miles north of the epicenter, to Pahala, 37 miles southeast. As far away as Naalehu (fig. 41), many dishes fell to the floor 

in homes, groceries and bottles toppled from shelves in stores, and 

stone walls collapsed. One house was shifted several inches oif its 

foundation. In the vicinity of Kilauea caldera, 45 miles from the epicenter, a few objects were toppled from shelves, pavements were 

cracked, and many landslides were started.

Macdonald was driving through Naalehu, 36 miles from the epicenter, when the earthquake occurred. The car swerved violently, as 

though it had struck deep mud on the road. Immediate]y afterward 

dead branches snapped from trees overhead and fell on the pavement. 

Suspended signs and electric wires swung violently, the few visible 

lights went out, and blue sparks from broken wires were observed.

At Kealakekua Bay large rock slides were started on the cliff at 

the head of the bay. At Napoopoo, on the southern shore, the ocean 

water was observed withdrawing from shore, and most of the inhabitants of the village were quickly evacuated to higher ground in fear 

of a large tsunami, or "tidal wave." A flood of water entering one 

basement from a collapsed water tank added to the confusion. Actually, a tsunami did occur, but was too small to cause any damage.
188 CONTRIBUTIONS TO GENERAL GEOLOGY

Two small fires broke out as a result of the earthquake. Kerosene 

spilled in the kerosene-power refrigerator caused one fire in south 

Kona. The other was in Naalehu, where the earthquake upset a 

lighted kerosene lamp. But fires were quickly extinguished. The 

only human casualities were in the same house. Mr. and Mrs. W. H. 

Thompson suffered cuts on their feet from broken glass on the kitchen 

floor, while extinguishing the fire started by the refrigerator.

Eesponsible persons at Naalehu and Pahala reported bright flashes 

of white light at the time of the major earthquake. These persons 

believe the flashes were not the result of electric sparks caused by 

broken circuits. The flashes observed by Macdonald at Naalehu, 

caused by electric sparks, were distinctly blue rather than white. Peculiar lights have been reported during some other strong earthquakes.

During the night of August 21, shortly after the major earthquake, persons in the central Kona area reported a distinct odor of 

hydrogen sulfide, apparently coming in intermittent waves. The 

source of that odor is not known. No increase in liberation of fumes 

was detected by aerial observers at the vents of the 1950 lava flows on 

the southwest rift of Mauna Loa.

The main earthquake was followed by a large number of aftershocks. The exact number will never be known, because the seismograph at Konawaena School was badly damaged by the preliminary 

waves and many of the aftershocks were too small to be recorded at 

the stations at Kilauea caldera or at the Mauna Loa station. Mrs. 

H. Masuhara, at Keei, just south of the Keelakekua fault and 5 miles 

east of the epicenter of the major earthquake (fig. 41), counted 109 

earthquakes between the time of the principal shock and 9 o'clock the 

next morning. Between the time of the main earthquake and 15h 15m , 

on August 23, when the Konawaena seismograph was restored to 

operation, the Bosch-Omori seismograph at the northeastern edge of 

Kilauea caldera recorded 171 earthquakes. This record was only a 

small proportion of the number that would have been recorded by the 

Konawaena instrument if it had been in operation. The Konawaena 

seismograph recorded 90 earthquakes the first 24 hours after it 

resumed operation, and by midnight on August 31 had recorded 494 

aftershocks. Most of these were too small to be felt, even near the 

epicenter. Nevertheless, aftershocks sufficiently large> to be felt were 

so numerous that the people of Kona were apprehensive for several 

weeks, and on August 22 it was deemed advisable to hold graduation 

ceremonies at the Konawaena School out of doors instead of in the 

auditorium.

INSTRUMENTAL, DATA

THE MAJOR EARTHQUAKE

The principal earthquake dismantled all seismographs on the island 

of Hawaii. All but the Bosch-Omori seismograph in the Whitney
HAWAIIAN VOLCANOES DURING 1951 189

Laboratory on the northeast rim of Kilauea caldera were dismantled 

by the preliminary waves. Precise time control, and consequently the 

precise time of arrival of the first waves, is lacking on the Kona and 

Hilo instruments. Consequently instrumental data are inadequate 

for the close location of the focus of the earthquake. The interval 

between the arrival of the primary and secondary waves on the northsouth component of the Bosch-Omori instrument was 9.5 seconds, 

corresponding with a distance from the Whitney Laboratory to the 

origin of the quake of about 47 miles.

John C. Forbes, instrument-maker at the Hawaiian Volcano Observatory, repaired the minor damage to the Bosch-Omori seismograph and restored it to operation at Olh 24m , 27 minutes after the earthquake started. At that time the instrument was recording the long 

waves of a large earthquake. The period of these waves ranged from 

about 6 to 8 seconds and averaged about 6.7 seconds. Their double 

amplitude ranged up to 67 millimeters, corresponding to a theoretical 

ground displacement of about half a millimeter. These waves continued with gradually decreasing amplitude until 03h20m a. m. Because no other earthquake at an appropriate time was observed by more 

distant stations, these long-period waves probably were surface waves 

of the major Kona earthquake.

The time of origin of the major earthquake is given in the notice 

of preliminary determination of epicenter issued by the U. S. Coast 

and Geodetic Survey as 00h 56m57.58 Hawaiian standard time 

(10h56m57.5s Greenwich civil time). The time of beginning of registration of the preliminary waves at the Whitney Laboratory at 

Kilauea was 00h 57m09.5s Hawaiian standard time.

The direction of the first ground movement at Kilauea caldera was 

, east-southeast and up, that at the Manna Loa station Avas east-northcast, and that at the Kealakekua station, was east-northeast. At the 

Kealakekua station the north-south component of the seismograph suffered only minor damage, but the suspensions of the east-west component were broken and the weight dropped on the floor 2 feet west 

of the pier.

THE AFTERSHOCKS

The Kona seismograph, at Konawaena School (fig. 41) was restored 

to operation at 15ll15'n on August 23. Before that time location of the 

points of origin of the aftershocks on an instrumental basis was uncertain, because of the very short base of the triangle formed by the 

intersection of lines from the earthquake foci to the other stations. 

Earthquakes after that time are fairly well located because of the 

control given by the Kealakekua seismograph. Most of these aftershocks were located by means of data from four stations: Kealakekua, 

Mauna Loa, Hilo, and Whitney (Kilauea).
190 CONTRIBUTIONS TO GENERAL GEOLOGY

Locations of the epicenters of some of the aftershocks which occurred 

after 15h 15m on August 23 are shown in figure 41. Thirty-three such 

aftershocks have been located with small probable error. Most of them 

fall on or near a fault that extends into the sea in a west-northwesterly 

direction along the northern edge of Kealakekua Bay. The existence 

of this fault, partly buried by subsequent lava flows, has been recognized for many years (Dana, 1890, p. 30; Stearns and Macdonald, 

1946, p. 37, pi. 1). At its eastern end it bends southward, and the 

writers believe that the abnormally steep lower western slope of Mauna 

Loa inland from the highway for 1.5 miles or more south of Captain 

Cook, is a fault scarp deeply buried by later flows. An interesting 

partial confirmation of this theory is furnished by the location of the 

epicenters of several aftershocks along this line (fig. 41).

Especially strong aftershocks occurred at Olh28m, 09h 56m, 10h 12m , 

18h32m, and 22h48m (Hawaiian standard time) on August 21; and at 

I7h15m on August 22. Slightly less strong quakes occurred at 2h 14ra 

and 6h28m on August 22.

The frequency of aftershocks decreased rapidly from August 23 

to September 4. As shown in figure 42, the average frequency then

26 31 1

AUGUST

15 

SEPTEMBER

20 25 30

FIGURE 42. Graph showing the frequency of aftershocks of the earthquake of August 21, 

to the end of September 1951.

decreased very slowly until the end of September. No data are available for September 7, because of mechanical failure in the recorder at 

the Konawaena station.

Table 11 shows the gradual decrease in the number of earthquakes 

recorded on the Konawaena seismograph from the time of the major 

earthquake to the end of the year.
 V HAWAIIAN VOLCANOES DURING 1951 191

TABLE 11. Number of earthquakes recorded on the seismograph at Konawaena 

School from August 23 to December 31,1951

Period

August 23-31.. ..........................................................

Total..............................................................

Number of 

earthquakes 

recorded

494

471

135

.109

02

1,271

Average number per day

01.0

15.7

4.5

3.0

2.0

From the time the instrument was restored to operation until the 

end of August, the Kealakekua seismograph recorded 494 earthquakes, and by the end of September had recorded 965. Nearly all 

are regarded as aftershocks of the major earthquake of August 21. 

Most were too small and shalloAv-seated to be recorded at the other 

stations, and hence their foci could not be closely located. Probably 

most originated along the Kealakekua fault at the northern edge of 

the Kealakekua ernbayment: The apparent depth of origin of the 

located aftershocks ranged from 3 to 12 miles, most of them about 6 or 

7 miles. No progressive change of depth with passage of time is 

apparent.

EFFECTS OF THE EARTHQUAKE

TOPOGRAPHIC AND GEOLOGIC SETTING

The area in which the earthquake originated, and in which the 

effects were strongest, lies on the western slope of Mauna Loa volcano. 

The main highway traverses it from north to south, at altitudes of 

1,000 to 1,300 feet, and side roads lead to the seacoast at Napoopoo, 

Honaunau, Hookena, and Milolii (fig. 41).

Most of the terrane is an initial constructional surface formed by 

lava flows from the summit and southwest rift zone of Mauna Loa, and 

is essentially untouched by erosion. Low sea cliffs cut by wave action 

border much of the coast. The average westward slope is approximately 7-°, or about 650 feet to the mile.

At the northern side of Kealakekua Bay a fault scarp, in large part 

mantled by later lava flows, extends inland in a southeasterly direction. This fault has been named the Kealakekua fault (Stearns and 

Macdonald, 1946, p. 37). It apparently consists not of a single fracture, but of a series of fractures en echelon. About 5 miles southeast 

of Kealakekua Bay the scarp bends southward, and becomes less distinct. However, for more than 10 miles southward there is a narrow 

zone near the higlrsvay in which the surface and the surficial lava flows 

slope westward at an angle of about 10°. Above, and at many places 

below this steep zone, the slope decreases to about 7°. The writers believe that this steep zone is the surficial expression of a zone of fault-
192 CONTRIBUTIONS TO GENERAL GEOLOGY

ing deeply buried by later lava flows. The occurrence of several welllocated aftershocks of the August 21 earthquake along this zone lends 

confirmation to this theory.

One branch of the Kealakekua fault bends northwestward at the 

northern edge of Kealakekua Bay, and is responsible for the cliff, 

known as Pali Kapu o Keoua, at the head of the Kaawaloa peninsula, 

just north of the bay (Stearns and Macdonald, 1946, p. 37). There 

is little doubt, however, that another branch extends nearly westward 

beneath the ocean. Its position is clearly marked by indentations in 

the 500- and 1,000-fathom submarine contours. The hypocenter of 

the Kona earthquake of August 21 probably was on this westward 

continuation of the Kealakekua fault.

Near the shore, from Hookena to Milolii, another line of cliffs 

mantled with younger lava flows apparently is also a fault scarp. 

This has been called the Kaholo fault (Stearns and Macdonald, 1946, 

p. 37, 39). A few of the aftershocks of the Kona earthquake probably 

were associated with this fault.

The steep seaward slope of the entire Kona area results in a distinct 

asymmetry to the terrane, and that asymmetry of necessity extends to 

nearly all structures on the terrane. Buildings rest on foundations 

that are high on one side and low on the other. Roads in many places 

rest on a ciit on one side and fill on the other, or on a fill that has one 

thin side and the other thick. Stone walls parallel to the coast have 

a higher side in the downhill direction. This results in a lesser degree 

of stability than in structures built on flat terranes, and in a favored 

direction of unstability. Partly because of the higher foundations 

and thicker fills on the seaward side, and partly because of the continuous effect of gravity, structures tended to move down hill during 

the earthquake regardless of the direction of the actual shaking. This 

effect must be kept in mind in using the direction of displacement of 

objects in locating the epicenter.

ROCK SLIDES

The Kona earthquake caused many small rock slides in highway 

cuts. Most of them came from cuts on the inland side of the highway, 

probably because the cuts were higher on that side. Most of the slides 

were small, bringing down blocks less than 2 feet across. These 

caused little damage and were easily removed. A few larger slides 

brought down blocks weighing several tons, the removal of which 

required the use of bulldozers or other heavy equipment. The large 

slide farthest from the origin of the earthquake occurred at a high 

road cut just west of Honuapo, 40 miles from the epicenter. Small 

slides and rock falls in road cuts extended as far as Kilauea caldera, 

44 miles from the epicenter. Many small rock avalanches took place
HAWAIIAN VOLCANOES DURING 1951 193

in Halemaumau crater during, and for several days after, the

earthquake.

Many large slides took place on the fault scarp (Pali Kapu o Keoua) 

at the northern edge of Kealakekua Bay. The slides caused a disturbance of the water of the bay just after the earthquake. Many 

residents fled inland from the coastal village of Napoopoo, fearing 

a big tsunami ("tidal wave"). Slides continued on the Napoopoo 

cliff for several days after the earthquake, sending up clouds of yellowish-brown dust, leaving fresh scars on the cliff face, and building talus 

fans at the foot of the cliff.

Less numerous and smaller slides also occurred along the Kaholo 

cliff just inland from the village of Hookena Beach, where many 

fragments of the lava veneer were dislodged during the earthquake.

A large part of the damage to road cuts did not result from 

land slides. Most of it was caused by loose or semiloose material 

rolling down the slope and fraying the banks. Few of the highway 

cuts exceeded 5 feet in height, or were dressed back to any approximation of an equilibrium slope. The earthquake of August 21 greatly 

exceeded in size any previous quake in the affected area since the road 

cuts were made, and dislodged much of the loose material and allowed 

it to roll onto the road.

The distribution of abundance of rock slides in road cuts is shown in 

figure 43, in which it is represented by the portion of the columns 

labeled "bank caving." Like the other damage shown in the graph,

Road crocks 

Bonk caving [/.-. 

Stone wall down

30 Miles

FIOUKB 43. Diagram showing the frequency distribution of three of the principal types 

T* of earthquake damage along the mam highway. The arrows indicate the position on 

the highway of some villages and other features. Note the centering of damage near 

the Kealakekua fault.
194 CONTRIBUTIONS TO GENERAL GEOLOGY

it was greatest in the immediate vicinity of the Kealakekua fault, 

inland and a little south of Kealakekua Bay.

TSUNAMI

The earthquake was accompanied by a small tsunami, or "tidal 

wave." At Napoopoo wharf the water withdrew from shore. The 

tide was low at the time, and withdrawal of the water lowered the 

level to about 4 feet below normal low tide. Immediately afterward 

the water returned shoreward, and the level rose about 2 feet above 

low tide.

At Milolii, Eugene Kaupiko reported that a few minutes after the 

earthquake, which he felt in a canoe anchored offshore, the water 

receded from shore, revealing the sea bottom as far out as the edge 

of the wharf. This represents a lowering of the water level about 

3 feet. Following the withdrawal, the water returned shoreward causing a rise of the water level 3 or 4 feet above normal low tide and 

floating away a canoe which had been drawn up on the beach about 

2.5 feet above high-tide level. One large fall and rise of the water 

level was apparently followed by many small oscillations.

At Honaunau, between Napoopoo and Milolii, Eli Cooper, the caretaker of the City of Kefuge park, observed the water's edge a few 

minutes after the earthquake. He could see no signs of disturbance of 

the water, but a small tsunami could have occurred between the time 

of the earthquake and when he reached the strand. At Hookena no 

tsunami was observed, and there was none large enough to flood the 

floor of the dock, about 4 feet above normal water level. However, it 

cannot be said definitely that no small tsunami occurred.

The Honolulu tide-gage record shows a distinct oscillatory disturbance of the water starting at approximately Olh 35m, 38 minutes after 

the earthquake. Seven or more oscillations are detectable, having an 

average period of about 14 minutes, and reaching an amplitude from 

crest to trough of 3.6 inches. This undoubtedly is the record of a 

seiche set up in Honolulu harbor by the tsunami. Using the time of 

beginning of the disturbance at Honolulu as that of arrival of the 

tsunami, the average speed of travel of the tsunami from the epicenter 

to Honolulu was about 284 miles an hour. The time of beginning of 

the disturbance at Honolulu corresponds with the calculated theoretical arrival time of a tsunami caused by the Kona earthquake, so 

there can be little doubt the disturbance was of that origin. A similar o

disturbance is shown on the record of the Hilo tide gage. The time of 

beginning of the disturbance at Hilo is less definite, but apparently 

was about 02h 38m. This corresponds with a much slower average speed 

of travel of the tsunami, of about 78 miles an hour, as the waves were 

refracted around the island in comparatively shallow water.
HAWAIIAN VOLCANOES DURING 1951 195 

DAMAGE TO BUILDINGS

Shortly after the earthquake the Kona police estimated that about 

200 homes in the area had suffered some degree of damage. Most 

houses in the area near the epicenter are of frame construction, set on 

knee-braced timber underpinnings. Such supports proved capable of 

undergoing the shaking and distortion caused by the earthquake 

without sustaining serious damage. Most of the damage was minor 

and quickly repaired. Some houses shifted from a fraction of an inch 

to 3 or 4 inches on their foundations. Many were sufficiently twisted 

to in alee it difficult or impossible to close windows and doors. In 

nearly all houses dishes and other objects were thrown from shelves. 

Only the more seriously damaged structures are enumerated below.

At Kaimalino, 0.3 miles south of Kealia (fig. 41), a shop building 

collapsed. This building was placed on timber supports level with the 

highway at the front, but 6 feet above ground level at the back, without adequate cross-bracing. Failure of the underpinning allowed the 

building to tilt backward and slump to the ground. A similar situation existed at Keokea, 1.2 miles north of Kealia, where a servicestation building slumped down hill from the highway and partly 

collapsed.

In the Kahauloa area, about 1.7 miles east of Napoopoo village, the 

walls of a store partly collapsed, as result of distortion caused by shifting on its foundation. The warehouse of another store was badly 

damaged.

At Hookena beach two old frame houses were destroyed. The first, 

which had been occupied briefly in 1889 by Robert Louis Stevenson, 

collapsed when its timber underpinning failed. The second one also 

was dropped onto the ground by failure of its underpinning and 

apparently dropped almost straight downward. This building was 

somewhat twisted, but not otherwise seriously damaged. At Kealia, 

and Kiilae, about 0.4 mile south of Kealia, two other frame houses 

were badly damaged by collapse of their timber underpinning. All 

these examples of damage to frame houses appear to have been caused 

by inadequate cross-bracing or poor materials in the underpinning, in 

some instances probably aggravated by insecure footings.

Structural damage most distant from the epicenter occurred at 

Naalehu, 36 miles southeast of Napoopoo. Wallboard in a restaurant 

was cracked and one house was moved several inches off its foundation.

A striking example of the effect of poorly designed underpinning is 

furnished by the Honaunau School. This school was a long, narrow 

frame building placed with its length parallel to the contour of the 

ground surface. The front of the building was about 3 feet above 

ground level and the back about 10 feet above ground. It was supported on timber posts. The posts and the knee-bracing parallel to
196 CONTRIBUTIONS TO GENERAL GEOLOGY

the length of the building; were entirely adequate, but there was comparatively little bracing parallel to the width of the building, and 

some of this bracing was fastened, not to joists, but to floorboards. As 

a result, the underpinning was deficient in stiffness parallel to the 

ground slope. The direction of shaking during the earthquake was 

nearly parallel to this weakness in the structure, and the swaying 

caused the underpinning to fail in part and allow the building to 

slump downhill onto the ground (fig. 44). The building is a total loss.

FreuiiE 44. Honaunau School building from the southwest. All but the south end of this 

building was dropped and moved westward owing to inadequate bracing of the underpinning in an east-west trending direction transverse to the longer dimension. The 

wood-stave water tank collapsed and was thrown westward from its concrete-block 

footings.

Several church buildings in the area near the epicenter were constructed with masonry walls. Most of these walls suffered some cracking, and others were seriously damaged. The masonry consists of 

fragments of lava rock laid with mortar made by calcining coral limestone. In some there was very little mortar in the inside parts of the 

wall. Most of the buildings were more than 95 years old.

In the Central Kona Church at Kealakekiia, interior plaster on the 

eastern and western walls was cracked, but the masonry showed little 

or no cracking. At the back of the church is a small lean-to addition, 

the roof of which is supported by beams with one end set into niches 

in the wall of the main building. During the earthquake there was
HAWAIIAN VOLCANOES DURING 1951 197

enough differential movement of the two parts of the building to pull 

the beams out of their supporting niches and allow the roof of the 

addition to drop a few inches. At the front of the church is a tower 

covered with exterior plaster. The tower and main church buildings 

are essentially separate structures, and apparently moved independently during the earthquate. The plaster of the tower was badly 

cracked.

St. Paul's Church at Honalo, 1.9 miles north of Kealakekua, suffered severe cracking of the masonry, in the main building and in the 

rectory. Kahikolu Church, at ISfapoopoo, suffered little damage. The 

lintels and interior plaster showed some cracking, but the masonry 

was not damaged.

The Pukaana Church at Hookena Beach was bady damaged. The 

building consisted of masonry walls, and a sheet-iron roof supported 

on heavy hand-hewn beams. These were supported by east-west beams 

resting in niches on the upper edge of the front and back walls. During the earthquake most of the front (west) wall was throAvn out, 

some debris falling as much as 25 feet from the building. The other 

Avails were not appreciably damaged, even the interior plaster showing 

little cracking. It is possible that during the quake the roof may 

have moved as a separate unit from the rest of the structure, and by 

its tendency to lag during the initial violent eastward movement of 

the ground may have pushed the front wall out.

A small stone building nearby, which had long been without a roof 

as shown by trees growing within the walls, similarly had the end 

walls thrown outward, to west and east, while the side walls remained 

standing though somewhat cracked.

The church 0.6 mile north of Hookena Beach was heavily damaged. 

The upper portions of the eastern and western walls were thrown down 

(fig. 45) and the interior plaster was cracked. However, the walls 

were built of loose stones laid together, without mortar between them 

except near the faces, where the interior and exterior plaster had penetrated a short distance. Considering the type of construction, probably the most surprising feature is that the building had not collapsed 

previously, in one of the strong earthquakes that occur in Ivona every 

few years.

The lessons to be learned from the structural damage caused by 

the earthquake are those which have been taught by many strong 

earthquakes elsewhere. A large proportion of the damage results 

from poor construction, or inappropriate materials. Masonry structures that are not reinforced are inadvisable in any area subject to 

strong earthquakes. Footings should be firm, and construction materials, particularly the underpinning, should be sound. Cross-bracing, particularly of underpinning, should be adequate in all directions. 

The best insurance against earthquake damage is sound construction.
198 CONTRIBUTIONS TO GENERAL GEOLOGY 

DAMAGE TO WATER TANKS

Most dwellings and public buildings in the Kona area are equipped 

with water tanks for storage of rain caught on the roof. In addition there are many tanks used to store water for cattle. Nearly all

these tanks are of wooden-stave construction. Many of these round 

tub-type tanks were destroyed or damaged by the earthquake. The 

few metal and reinforced masonry tanks were undamaged. Because
HAWAIIAN VOLCANOES DURING 1951 199

of their importance, not only in Kona but in many other Hawaiian 

communities, a special study of the damage to tanks by the earthquake 

was undertaken.

About 200 tanks, of a total probably exceeding 2,000 in the heavily 

shaken area, were damaged or destroyed by the earthquake. Tank 

damage extended from Keauhou at the north to Milolii on the south, 

and was most severe in the area from Captain Cook to Hookena. 

Tanks showed all degrees of failure, from the development of slight 

leaks to complete collapse. Of 90 tanks for which complete data have 

been compiled, 43 were reported demolished or totally destroyed. Of 

the remainder, several had the bottom collapsed, others developed 

general leakage that cause loss of all the water, and many were so 

dislodged and deformed that complete rebuilding was necessary. 

Broken pipe-fittings released all the water at some tanks, but they 

were repaired without great expense. Unless prompt action was 

taken to repair and refill those tanks which lost their water, much 

additional loss would be sustained through drying and further 

deterioration.

The common household tank is erected with its upper edge just 

under the level of the eaves of the building, the roof of which provides the rain catchment. To meet hydraulic requirements within the 

house the bottom of the tank is built 6 or 8 feet, and the top 15 feet 

or more above the ground surface. The tanks contain from 8 (2,000 

gallons) to 20 tons (5,000 gallons), or as much as 40 tons (10,000 

gallons) of water. They are supported on a base which commonly 

is little more than 10 or 12 feet in breadth, with their center of gravity 

10 or 12 feet above the ground. A 2,000-gallon tank on six footings 

exerts a load of about 2,700 pounds on each footing, and a 5,000-gallon tank of 12 footings imposes a load of about 3,300 pounds on each. 

From data gathered during this investigation, many of the tanks 

having capacities of 10,000 to 25,000 gallons impose loads on individual footings of 4, 5, or as much as 6 tons. Such loads are several 

times as great as those commonly carried by the columns under an 

ordinary frame house, and the height of the tank is much greater 

compared with the breadth of the base than is that of most houses.

The types and adequacy of footings varied greatly. Some footings were solid bedrock. Others were concrete blocks or large flat 

blocks of rock. Some of the latter were well embedded in the soil, 

and some were well tied together. Commonly, however, they were 

not securely embedded and were totally untied, so that under the 

stresses induced by the earthquake individual footings could turn or 

shif t in relation to each other with comparative ease.

Tanks that are built near the ground require no legs or columns 

and may have no systematic arrangement of footings under the sills.
200 CONTRIBUTIONS TO GENERAL GEOLOGY

In some tanks the bottom planks rest on joists or beams that in turn 

lie directly on the ground, or on concrete or rock footings having no 

cross members parallel to the bottom planks. Such an arrangement 

leaves the bottom of the tank in a precarious position if there is any 

differential movement of the footings, and poorly protected against 

even ordinary settling, much less a severe earthquake.

Most of the larger tanks require support at the end of the joists 

within the circle of the tank chimes, and are supported on a sill or 

beam pattern that is six- or eight-sided, and the outer columns are 

six or eight, or more. Usually the columns are braced from near the 

bottom to the top of adjacent columns, and they may or may not have 

bracing toward the center of the tank. Most commonly the bracing 

is spiked or bolted to the outside or inside edges of the columns, so 

that its effect is offcenter and tends to develop a torque in the columns.

The chief causes of tank destruction during the earthquake were 

poor footings and inadequate bracing of the supporting structures. 

It is evident that the footings, although adequate to support the 

direct static load, commonly were not sufficiently fixed in position or 

well enough tied to the structure to withstand earthquake. The footing blocks are prone to move during the rocking to which the whole 

frame is subjected in an earthquake, with progressive yielding and 

increase of movement to the point where the frame itself fails. A 

contributing factor undoubtedly was the excessive loads carried on 

individual footings at some tanks. As already pointed out, some of 

the larger tanks, as for example, the one at Honaunau School (fig. 

44), exerted static loads on each footing of more than 6 tons. Lateral 

shaking of a mass imposing such loads on individual columns and 

footings imposed too great a strain on the bracing, and after initial 

displacement of critical bracing or footings the entire structure 

quickly collapsed.

There were few eye-witness accounts of the progressive destruction 

of individual tanks, but it is evident that the interrelated failure of 

bracing and footings was the chief cause. A few persons heard 

slopping of water in and from the tanks for an appreciable interval 

before final collapse. No marked correlation could be shown between 

the age of the tank and the damage, and only in a few instances was 

it proven that preexisting impairment was responsible. So many 

nearly new tanks, in good condition, were destroyed that apparently 

the stresses developed by general shaking could not be met by the 

existing bracing. The lateral components were as much as 0.2 or 0.3 

of the value of gravity. Likewise the footings became progressively 

displaced and hastened the destruction. Such stresses are comparable 

to tilting the tank and understructure to an angle of about 16 degrees 

and submitting it to repeated vertical loading and unloading. Under 

such conditions it is not surprising that many of the structures failed.
HAWAIIAN VOLCANOES DURING 1951 201

It is not likely that any feasible methods of construction will entirely eliminate damage from earthquake in the Kona district. The 

writers believe, however, that marked improvement is possible without 

incurring an additional expense disproportionate to the value of the 

tank. Keeping earthquake risk in mind, the important factors are 

the following:

1. So far as possible, water-storage tanks should be based on the 

ground on a levelled, preferably concrete, surface. Tanks should not 

be based wholly or partly on fill unless the entire filled area is enclosed 

in carefully designed solid retaining walls. These walls should be 

prepared for unit loads two or three times as great as those from 

the tank. Lacking such preparation, the tank should be carried on an 

overall timber crib or mat of adequate size and spacing. Increasing 

availability of electricity to operate pumps, and commoner use of 

pressure installations for domestic service should in the future make 

possible the basing of additional large tanks on the ground.

2. If the understructure consists of sills on columns, the lower ends 

of the columns should be completely tied together for compression and 

tension in amounts up to at least half the unit load. For a simple 

square deck on four columns, the columns should be tied at their feet 

and each of the four sides diagonally braced from column bottom 

to top and similarly diagonally braced through the center between 

opposite columns. So far as possible bracing and cross-tying should 

be kept in the two planes parallel to the sills and joists respectively, 

with secondary truncating sills to approximate the form of a circle 

under large tanks. Without adequate internal bracing in the two 

rectangular directions, the bracing of a six or eight-sided array of 

columns around the periphery results in offcenter reactions and may 

cause structural failure and destruction of the tank.

3. Footings of concrete blocks or large flat stones should be anchored 

in the ground or to the rock by imbedding them to a depth equal to 

their area, or by rods and grouting. This method will give bearing 

resistance against lateral stresses of half the unit vertical load. Concrete piers should be tied to each other unless they are deeply 

imbedded.

4. Wherever possible all footing-surfaces should be at one level. If 

this is not possible the long columns should be tied at the level of the 

footings of the short columns and bracing should be completed at 

this level.

5. Sills should be fastened at the top by drift pins, and bolts and 

timber fasteners should be used in the framing of supports for all 

tanks except the smallest. Braces should be paired or framed into 

the plane of the columns in order not to introduce torque into the 

stresses.
202 CONTRIBUTIONS TO GENERAL GEOLOGY

6. Frequent inspection, painting or creosoting, and repair of defective conditions will provide longer assurance of reasonable safety, as 

with any other structures.

DAMAGE TO STONE WALLS

The loose-stone walls characteristic of the Kona area were extensively damaged by the earthquake. The greatest destruction was in 

the area between Keauhou, 3.5 miles north from Kealakekua, and 

Pahoehoe, 3 miles south from Hookena (fig. 41). However, isolated 

instances of wall derangement were observed as far north as Honokahau, 16 miles north of the epicentral area, and Naalehu, 36 miles 

southeast. The distribution of damage to walls is shown graphically 

in figure 43. Many miles of wall required rebuilding. As the cost 

of contract rebuilding is about a dollar a yard, the total monetary loss 

from the destruction of walls is very appreciable.

At the ancient City of Refuge, at Honaunau, about 20 feet of the 

seaward side of the main outer wall of the enclosure collapsed. The 

damage was restricted to a reconstructed part, whereas the remaining 

parts of the original enclosure wall, and the walls of heiau (temple) 

platforms, were undamaged. Homer Hayes, who has devoted much 

study to the City of Refuge, made a highly plausible suggestion concerning the peculiar construction of the ancient walls. He observed 

that occasional broad slabs extend entirely or largely through the wall, 

and sometimes bridge open spaces beneath. These slabs are responsible for the greater resistance to earthquakes of the old portions of 

the wall.

Most of the stone walls consist of irregular fragments of clinkery 

lava less than a foot across. A few walls have bases of blocks a foot or 

more long reaching half way through them. In the older ones there 

are occasional slabs laid partly or entirely through the wall to help 

tie it together. Because of the rough irregular surfaces of the fragments they can be built nearly vertical, 3 or 4 feet high and about 30 

inches thick at the base. Such walls stand well under ordinary conditions, but because of the shortness of the bonding surfaces of adjacent blocks they are rather unstable under any joggling, as by earthquakes. The earthquake of August 21 caused extensive damage. The 

commonest type of damage was a collapse of the upper part of the 

downslope face, the fragments rolling down and a short distance away 

from the base. Such damage was common in north-south walls and 

near the top. In a few instances those on nearly level ground were 

dislodged about equally in both directions. However the failure was 

preponderantly on the western side and the material was displaced 

westward.
HAWAIIAN VOLCANOES DURING 1951 203

Some of the westward displacement probably resulted from the 

tendency of the loose material in the wall to lag behind during the 

initial strong eastward movement of the ground. Greater failure of 

the western side of the walls was caused by the general westward 

slope of the ground and because that side was higher and commonly 

steeper than the eastern. Likewise, there was a tendency for materials to shift downslope under the influence of gravity.

Well-built walls were surprisingly resistant to earthquake damage. 

Thus the wall along the landward side of the highway from Honaunau to Napoopoo, built of carefully placed rectangular blocks of lava, 

was almost wholly undamaged despite its proximity to the epicenter. 

Likewise, in other parts of the epicentral area, older walls in which 

slabs extending through a large portion of the wall had been used to 

tie the wall together, showed comparatively little damage.

DAMAGE TO ROADS

Damage to paved roads was of three general types: cracking of 

pavement, cracking and slumping of shoulders and separation of 

shoulders from pavement, and collapse of road cuts causing partial 

obstruction of the road. The latter has already been discussed under 

the heading "Kock slides." Minor cracking of shoulders occurred 

over an area extending about 10 miles north and 12 miles south of the 

approximate epicenter, and a few cracks were formed as far away as 

ths northeastern side of Kilauea caldera, 47 miles from the epicenter. 

However, extensive pavement cracking and slumping was restricted 

to the area between Captain Cook and Hookena. The distribution of 

cracks in the road is shown in figure 43.

Cracking or slumping of the pavement or shoulders was entirely 

restricted to portions of the road on fills. Some gullies A\7 ere crossed 

by laying a rock fill having a batter, or departure from the vertical, of 

less than 1 in 4; filling with fine material; and laying asphalt pavement across the top. Such fills were not sufficiently stable to withstand the shaking of a strong earthquake, and in several places the 

downslope face of the fill was dislodged, allowing the material of the 

roadbed to settle, thus cracking the pavement. In other places the 

fill apparently settled a little by compaction during the jostling by 

the earthquake, causing cracks in the pavement.

A common occurrence was the formation of a crack parallel to the 

edge of the pavement on its downslope side, either within the pavement a few inches from its edge, or between it and the shoulder 

(fig. 46). Some of these cracks were as much as 75 feet long and 8 

inches wide. This apparently resulted from a downslope lurching of 

the shoulder that moved as a separate unit from the portion of the fill
204 CONTRIBUTIONS TO GENERAL GEOLOGY

FICUHK -40. (Ji'aek along llic o<lge 01 1110 Highway pavonieiil ^ iniirs south irujn Kuimalino, 

apparently resulting from a downslope lurching of the shoulder, which moved as a 

separate unit from the part of the fill beneath the pavement.

beneath the pavement. The independence of movement of the shoulder and pavement was interestingly shown along the highway about 

2 miles southeast from Captain Cook, where soil and sod on the 

shoulder was overthrust as much as an inch onto the pavement.

DAMAGE IN CEMETERIES

Many headstones in cemeteries in the area near the epicenter were 

deranged by the earthquake. As a part of the investigation these cemeteries were examined and a rough statistical study of the damage was 

made. Unfortunately, owing to shortage of personnel and pressure 

of other duties, we were delayed several days in making the cemetery 

examinations, and some restoration of headstones had already taken 

place. However, in most cemeteries little restoration had been done, 

and the damage remaining probably was a representative sample of 

the original damage. The writers believe that even after the stones 

had been replaced, the derangement could be detected by breaks or 

scratches or by disturbance of the cement bond at the base of the stone.
HAWAIIAN VOLCANOES DURING 1951 205

There are more than 50 cemeteries in the area, but most are small 

family or church plots with few graves, and have not been used in 

recent years. In some cemeteries, burial was in vaults without headstones or the headstones or markers were firmly cemented in place 

and not readily susceptible to damage by an earthquake of the intensity of the one under study. The most valuable information came 

from the investigation of a few of the larger cemeteries. Damage 

at these cemeteries is summarized in table 12, and their locations are 

shown in figures 41 and 48.

Derangement of headstones included overturning of stones 

(fig. 47), and shifting of stones on their bases with or without rotation. 

Many grave caps were broken, some by falling or disturbance of headstones, and some by lurching or slumping of the adjacent subsoil.

FIRDHE 47. Gravestone rotated counterclockwise, in the Daifukuji cemetery at Hoiialo. 

Other stones have been thrown from the vacant bases visible in the photograph and are 

out of sight behind the bases.

Slumping was particularly prevalent on steep slopes where the subsoil is thick and loose. Damage of all sorts was restricted to the area 

between Honalo and Honokua, 5 miles northeast and 10.5 miles southsoutheast of the probable position of the epicenter.

In cemeteries north of Iveauhou no damage or derangement was 

noted. At Lanakihi cemetery, 2 miles south from Keauhou, of 15 

headstones, 4 were dislodged to the west. Inland and slightly northward, at the Daifukuji Mission in Honalo, about 5 miles north from 

Napoopoo, of an estimated total of 150 grave markers, 6 toppled west, 

7 north, 2 east and none south. Six had been shifted north, 16 were 

twisted clockwise, and 2 were twisted counterclockwise; 8 grave
206 CONTRIBUTIONS TO GENERAL GEOLOGY

caps were broken (fig. 47"). It was reported that many more had been 

disturbed but had been restored.

At Hongwanji Mission cemetery, Kealakekua, which has more than 

600 graves, 12 headstones were overthrown to the west, 9 to the east, 

and none north or south. Thirty-four were twisted right (clockwise), 

11 left, one each shifted north, west, and south, and 22 grave caps were 

broken.

At the Central Kona Church cemetery at Kealakekua, 12 headstones 

and one large memorial monument were overturned westward, and 

one eastward. One stone was rotated counterclockwise. In the Christ 

Church cemetery, just across the highway, 5 headstones were overturned westward, one was rotated counterclockwise, and one clockwise.

At Kahikolu Church, about half a mile south of the Kealakekua 

fault line, of a total of 10 headstones, 2 were oA7 erturned to the west and 

one Avas twisted to the right. Two miles farther inland, but only 

about 0.6 mile south of the fault line, is another cemetery of the Hongwanji Mission. Here, of more than 200 headstones, 29 were still down 

on September 7, the majority dislodged to the west, and 10 or more had 

been replaced. Thirteen had been twisted to the right, 4 to the left, 

and 24 grave caps were broken. There was much damage to caps and 

markers in the lower section of the cemetery Avhere the ground is composed of rocky talus.

At St. Benedict Church, 1.5 miles farther south, is a cemetery having nearly 100 markers. About half of these are AArooden crosses Avhich 

Avere not deranged. Several others are light-concrete crosses that liaAre 

Avire reinforcing. Some of these Avere so broken that the Avires Avere 

exposed and the markers Avere supported wholly by one or tAvo of the 

Avires. Of about 20 vertical headstones, 11 Avere displaced or broken.

The most complete derangement Avas found in the Kalahiki Japanese cemetery, a small hillside cemetery 3.8 miles south of Kealia, 

Avhere only 2 markers of 30 Avere found in position 5 days after the 

earthquake. The dislodgment Avas chiefly to the southwest, and to 

a lesser extent to the northeast. Ten markers Avere shifted to the north 

but Avere not throA\7 n down. Seven, including some of the above, Avere 

rotated to the right, and one to the left. Here, on loose steeply sloping ground, many grave caps Avere broken, OAving to poor design and 

and to being placed on the neAvly heaped grave mound. This cemetery 

is about 11 miles south of the probable epicenter. South of this point 

no cemeteries Avith headstone susceptible to overturning or rotation 

Avere found.

The east-Avest azimuth of fall of gravestones throughout the area 

is probably the result of the prevailing westward slope. The orientation of most cemeteries is governed by the general north-south alinement of the principal roads, and in turn most gravestones face the
HAWAIIAN VOLCANOES DURING 1951 207

west or east and the long dimension of their base is oriented northsouth. Therefore the stones rock in an east-west direction much more 

easily than in any other, and the most likely azimuth of fall consequently is an east-west direction. Furthermore, under sustained shaking there is a tendency for all loose objects, including the soil cover, 

to work down slope to the west under the influence of gravity.

TABLE 12. Summary of damage in cemeteries caused l)y the earthquake in

Kona, August 21, 1951

Name of cemetery

Daifukuji. ...................

Christ Church...............

Kahikolu Church...........

Location

Holualoa....

Kainaliu.... 

Kealakekua. 

..... do. ......

.---do.......

Napoo poo...

Honaunau . . 

KalahikL...

Miles from 

Napoo poo 

(and 

direction)

10 N. 

5 N. 

 4.5 N. 

3 N. 

2.5 N. 

2.5 N. 

.58. 

1.5SE. 

3.5 SE. 

7.5 S.

Approximate number of 

headstones

300 

150 

12 

600 

30 

60 

10 

200 

100 

31

Headstones overturned

CJ 

A

B3 

fc

0 

15 

4 

21 

12 

8 

2 

40 

11 

20

.1o 

PH

0 

10 

33 

3.5 

40 

13 

20 

20 

11 

64

Approximate 

direction

N

0 

7 

0 

0 

1 

0 

0 

3 

0 

1

E

0 

2 

0 

9 

0 

3 

1 

22 

0 

G

S

0 

0 

0 

0 

0 

0 

0

1

0

1

w

0 

G 

4 

12 

11 

5 

1 

14 

11 

12

Headstones 

rotated

05 

1

 a

0

O

0 

2 

0 

33 

0 

1 

1 

13 

0 

14

i H> 1! 3 o

0 0

Oo

0 

16 

0 

10 

1 

1 

0 

4 

0 

1

ROTATION OF COLUMNS

Imamura (1937, p. 96) has shown that the direction of rotation 

of short rectangular columns, such as headstones, can be useful in 

determining the direction of motion during an earthquake, and consequently the approximate azimuth of the line toward the epicenter. 

If the earthquake motion is parallel to the sides or to the diagonal 

(A-B, inset figure 48) of the column, rotation probably will not occur. 

HoAvever, if the earthquake motion is in some intermediate direction, 

such as E-E' in figure 48, a rocking of the column will be accompanied 

by a rotational tendency. A ground motion in the direction E' will 

cause the column to rock on the corner B. At the same time, the resultant of the force E' in the direction CD will tend to rotate the 

column about the corner B in a counterclockwise direction. Similarly 

a motion in the direction E will tend to cause a counterclockwise rotation about corner A. In the diagram in the inset, figure 48, directions of earthquake motion in the unshaded octants tend to cause 

counterclockwise rotation of the column, and directions of motion 

in the shaded octants tend to cause clockwise rotation.

However this law of rotation can be, and commonly is, upset by 

other conditions. Inhomogeneity of the terrane may locally cause the 

principal motion to be in a direction other than the azimuth pointing directly to the epicenter. Also, excentric irregularities in the
208 CONTRIBUTIONS TO GENERAL GEOLOGY

FIGURE 48. Map of the central Kona area, showing the prevalent direction of rotation of 

monuments in cemeteries. The cemeteries are indicated on the map by numbers as 

follows: (1) Daifukuji, Honalo ; (2) Hongwanji Mission, Kealakekua; (3) Hongwanji 

Mission, Keei; (4) Kalahiki Japanese. At each cemetery the arrow indicates the 

prevalent direction of rotation. The boundaries of the octants containing the direction 

toward the epicenter are prolonged. The cross-hatched area west of Captain Cook is 

that in which three or more of the octants overlap. The inset in the lower left is a 

diagram (after Imamura, 1937.) of a horizontal cross section of a rectangular column, 

indicating the manner in which horizontal earthquake motion (E-E') brings about rotation of the column.

bottom of the monument or its underlying base, or in the adhesion 

.between the monument and its base, may result in rotation around 

those irregularities independent of the rotation described above.
HAWAIIAN VOLCANOES DURING 1951 209

During our study of the Kona earthquake it soon became evident 

that to be of value the direction of rotation must be considered on 

a statistical basis. Thus two columns only 10 feet apart in the Christ 

Church cemetery at Kealakekua were rotated in approximately equal 

amounts in opposite directions. HoAvever, by using the prevailing 

direction of rotation of a number of columns in a single area, more 

useful results were obtained. The average direction of rotation of 

monuments in each of 6 cemetery areas from 5 miles north to 10 

miles south from Napoopoo all were consistent with an origin of the 

earthquake on or near the Kealakekua fault from 2.5 to 5 miles west 

from Kapoopoo. Cemeteries near the epicenter showed less consistency in the direction of rotation than did those farther away.

In figure 48 is shown the prevalent direction of rotation of monuments in four cemeteries. Four other cemeteries were omitted either 

because no monuments were rotated or because the number was too 

small to yield a reliable statistical result. At each of the four cemeteries plotted the boundaries of the octants containing the direction 

toward the epicenter are prolonged. In an area west of the shoreline, 

from 2 miles south to 2 miles north of the approximate trace of the 

Kealakekua fault, three or more of the four significant octants overlap, and it is within this area of overlap that the epicenter should be 

situated.

LOCATION OF THE EPICENTER

Owing to the dismantling of all but one of the seismographs on the 

island of Hawaii during the preliminary phase of the earthquake, it 

is not possible to locate the origin or epicenter instrumentally. The 

only instrumental datum available is the S-P interval of 9.5 seconds 

given by the Bosch-Omori seismograph at the northeastern rim of 

Kilauea caldera (fig. 31). Using the travel times given by Byerly 

(1942, p. 210), this gives us a distance of origin of the earthquake of 

about 47 miles from the Bosch-Omori instrument. These curves were 

derived for sedimentary and granitic rocks, but over a period of several years of use at the Hawaiian Volcano Observatory have yielded 

more satisfactory and reasonable earthquake locations than any others. 

The use of Jones' (1935, p. 50) curve for duration of the preliminary 

waves increases the distance only to 49 miles. Taking into consideration the area of greatest intensity of the earthquake, these distances 

place the origin of the quake 3 to 5 miles west of the coastline 

in the vicinity of Napoopoo. The depth of origin appears probably 

to have been between 5 and 10 miles.

Some information bearing on the location of the epicenter can be 

derived from the study of damage by the earthquake. The general 

distribution of damage to roads, stone Avails, and road cuts along the 

main highway is shown in figure 43. This is based on a count checked
210 CONTRIBUTIONS TO GENERAL GEOLOGY ~«

against odometer mileage, assigning one unit of damage for each 1 

to 15 feet of collapsed wall or road cut. Despite irregularities, the T ; 

graph shows a distinctly symmetrical bell-shaped distribution curve, 

with its peak about 2.5 miles by road southeast of Captain Cook. '"'^ 

An average of more than 60 items of damage per mile in the central ^, 

5 miles decreases to only one or two per mile more than 9 miles from 

the center. This point of maximum damage coincides closely with 

the position of the buried inland extension of the Kealakekua fault. v 

Other types of damage also were most abundant in the same general area. As most of the aftershocks, located by instrumental means, <>: 

originated on the Kealakekua fault, it leaves little question that the 

origin of the major earthquake lay on or near the Kealakekua fault, 

and that the earthquake almost certainly resulted from movement 

on that fault. « $.

The greatest structural damage was farther south, at Hookena, 

where the destruction of the eastern and western walls of the two 

stone churches suggests an epicenter somewhat farther south. The « 

possibility of a twin earthquake with one epicenter lying offshore 

nearly west of Hookena has been considered, but no other evidence 

suggests it, and no signs of a second earthquake could be detected from -^ 

the seismograms either from the island of Hawaii stations or from 

the Coast and Geodetic Survey's Barbers Point station on Oahu.

Throughout the Kona area the prevalent direction of fall of rock 

slides, stone walls and tombstones, was westward, and the next commonest direction was eastward. The seismograms indicate that the 

first movement of the ground was eastward, and it is probable that 

some of the westward fall of objects was the result of lagging behind 

as the ground moved eastward under them. To some extent also, the 

general east-west azimuth of fall undoubtedly reflects the direction of « 

the epicenter. However, still more important in determining the direction of fall of objects apparently was the prevailing east-west slope. 

Its effects on various types of damage have already been pointed out.

The prevalent direction of rotation of columns in cemeteries indicates a location of the epicenter within the shaded offshore area in 

figure 48. This area contains the seaward extension of the Kealakekua / 

fault.

Consideration of all the evidence indicates that the probable r, 

epicenter of the earthquake is about 3 miles west of Napoopoo, at 

latitude, 19°29' N.; longitude, 155°58' W. ^

INTENSITY OF THE EARTHQUAKE ,

- A

Two methods of determining and expressing the strength of an 

earthquake are in common use. The older method is based on the ! 

observed effects of the earthquake on structures and other objects.
HAWAIIAN VOLCANOES DURING 1951 211

Based on these effects a numerical value is assigned which is termed 

the "intensity" of the earthquake at any one point. Obviously, since 

the eft'ects are less at greater distances from the origin of the quake, 

the intensity decreases away from the epicenter. Various scales of 

intensity have been proposed. The scale used in the present study is 

the modified Mercalli intensity scale of 1931 (Wood and Neumann, 

1931), in which values range from 1, at which the earthquake is not 

felt except by a very few persons under especially favorable conditions, 

to 12 at Avhich damage is total. The second method assigns a value 

called "magnitude" to the earthquake, based on the effect on standard 

seismographs at known distances from the origin of the quake 

(Richter, 1935). The magnitude is a measure of the amount of energy 

in the earthquake at its point of origin, and consequently should be 

essentially the same at all measuring stations.

The notice of preliminary determination of epicenter issued by the 

Coast and Geodetic Survey lists the magnitude of the earthquake of 

August 21 at 6.75 as determined at Pasadena, and 7.0 as determined at 

Berkeley, Calif.

Field studies of the effects of the earthquake indicate an intensity 

of 7 on the modified Mercalli scale in the area near the epicenter, 

decreasing to 6 at Waiohinu and JSTaalehu, 5 in the vicinity of Kilauea 

caldera and in Hilo, and 4 at Honokaa and in the Kohala district at 

the northern end of the island. At Honolulu, 180 miles (288 km) 

from the epicenter, the intensity was 2. Populated areas of the island 

of Hawaii are largely restricted to the periphery of the island. 

Parts of the interior of the island are almost wholly unpopulated, 

making it impossible to draw accurate isoseismal lines. Approximate isoseismals are shown in figure 41.

Given a single impulse, the minimum horizontal acceleration that 

can cause the sliding of a short stone column on a stone base is 71 

percent of the value of gravity, decreasing to 57 percent at an angle 

of emergence of 35° to the horizontal (Imamura, 1937, p. 105). Because the sliding of headstones, and especially base plates, was common in cemeteries during the August 21 earthquake, it might have 

been concluded that the acceleration during the earthquake was at 

least six-tenths that of gravity. However, Imamura (1937, p. 106) 

also has shown that small, short-period vibrations in the epicentral 

areas of strong earthquakes, although they do not themselves cause 

the displacement of objects, may so lower the normal values of the 

coefficients of friction that sliding can be caused by longer period 

vibrations with accelerations much less than six-tenths that of gravity. 

The presence of such vibrations in the Kona area is suggested by local 

vagaries of displacement and other factors. The acceleration which 

caused the lateral displacement of objects during the Kona earth-
212 CONTRIBUTIONS TO GENERAL GEOLOGt

quake is not known, but probably was much, less than six-tenths that 

of gravity.

CONCLUSION

The earthquake of August 21, like most of its aftershocks, probably 

was caused by movement on the Kealakekua fault. This fault is one 

of many along which the lower slopes of Mauna Loa and Kilauea 

volcanoes have moved relatively downward and outward toward the 

ocean. In this sense the earthquake A\r as tectonic in origin.

Although all earthquakes in Hawaii originate in the volcanoes, the 

earthquake of August 21 cannot be directly related to any specific volcanic episode. It is possible that it is related in some way to the great 

extravasation of lava during the 1950 eruption of Mauna Loa, but 

there is no evidence to demonstrate such a relationship. On September 

16 a series of smaller earthquakes originated on the Kaoiki fault 

system, a series of fractures corresponding to the Kealakekua fault, on 

the southeastern slope of Mauna Loa. From mid-May until early July 

abnormally rapid eastward tilting at Kilauea caldera indicated a 

tumescence of Mauna Loa volcano. There -is a possibility that the 

August 21 earthquake and its aftershocks, and the September 16 earthquakes were caused by a slight upward movement of the central portion 

of Mauna Loa in relation to the lower slopes. In view of the eruption 

of Kilauea volcano in June 1952, it appears possible that the numerous 

earthquakes during 1951 (and early 1952) may have accompanied an 

inflation of the entire Kilauea-Mauna Loa system.

The southern part of the island of Hawaii is subject to frequent 

earthquakes, but few are as intense as that of August 21, 1951. The 

great earthquake of April 2, 1868, judging from the descriptions of 

damage, was however, much more severe. Wood (1914) assigned to 

this earthquake (April 2, 1868), an intensity of 10 in the Rossi-Forel 

scale, which would correspond to an intensity of not less than 10 in the 

modified Mercalli scale used in this report. Its epicenter was near 

Waiohinu, in Kau, about 35 miles southeast of that of the Kona earthquake of 1951. Extensive surface faulting took place in the epicentral 

area. The earthquakes of March 28 and April 3, 1868, also probably 

were at least as severe as that of August, 1951. The earthquake of 

October 6, 1929, centered beneath Hualalai volcano, had a magnitude 

of 6.5 (Gutenberg and Richter, 1949, p. 207), and did damage as far 

south as Captain Cook. The Maui earthquake on January 23, 1938, 

had a magnitude of 6.75, about the same as that assigned by the California Institute of Technology Seismological Laboratory in Pasadena 

for the earthquake of August 21, 1951. The earthquake of May 29, 

1950, was assigned a magnitude of 6.25 at Pasadena, and did minor 

damage in central Kona.
HAWAIIAN VOLCANOES DURING 1951 213

During the years 1929-45 Gutenberg and Eichter (1949, table 17) 

list 8 earthquakes of magnitude 5, or more, that originated in the general Hawaiian area. During the same interval they list 58 earthquakes 

in California having magnitude of 5 or more, and 127 in Japan and 

Kamchatka. Thus during those years California had about 7 times 

as many large earthquakes as did the Hawaiian area, and the JapanKamchatka area had about 16 times as many. Based solely on the 

interval 1929-45, the Hawaiian area can expect an average of about 

one earthquake of magnitude 5 or more every 2 years.

On the other hand, during the past century, there have been only six 

earthquakes of intensity comparable to that of the August 21 quake, 

and no other appears to have been quite as severe in central Kona. 

There is no assurance that another earthquake equally, or even more 

severe, will not occur in that area in much less time than a century. It 

might even occur within the next few months, but judging from the 

past, that is quite unlikely.

However, like all the rest of the island of Hawaii except the northernmost part, Kona experiences lesser earthquakes frequently. Wellbuilt structures, with footing of better quality than many of those 

found in Kona now, will minimize and may eliminate the damage 

resulting from such ordinary earthquakes.

It may not be economically feasible to build in such a way as to 

eliminate damage from the infrequent large earthquakes.

LITERATURE CITED

Byerly, P., 1942, Seismology, 256 p., New York. 

Dana, J. D., 1890, Characteristics of volcanoes, 399 p., New York. 

Finch, R. H., and Macdonalcl, G. A., 1951, Report of the Hawaiian Volcano 

Observatory for 1948 and 1949: U. S. Geol. Survey, Bull. 974-D, p. 103-133.

 1953, Hawaiian Volcanoes during 1950: U. S. Geol. Survey, Bull. 996-B,

p. 27-89.

Gutenberg, B., and Richter, C. F., 1949, Seismicity of the earth, 273 p., Priuceton. 

Imamura, A., 1937, Theoretical and applied seismology, 358 p., Tokyo. 

.Tones, A. E., 1932, Chart of Kilauea seismicity: Volcano Letter, 371, p. 1-3.

 1935, Hawaiian travel times: Seismol. Soc. America Bull., v. 25, p. 33-61. 

Kato, Y., 1933-35, Seismic and volcanic activities and changes in the earth's

magnetic field: Japanese Tour, of Astronomy and Geophysics, .v. 10, p. 249-

262,1933; v. 12, p. 1-26,1934; v. 12, p. 237-243,1935. 

Macdonald, G. A., and Wentworth, C. K., 1951, The Kona earthquake of August

21,1951: Volcano Letter 513, p. 1-4.

 1952, The Kona earthquake of August 21,1951, and its aftershocks : Pacific

Sci., v. 6, p. 269-287.

Oruer, G., 1945, On magnetic studies : Volcano Letter, 487, p. 1-4. 

Richter, C. F., 1935, An instrumental earthquake magnitude scale: Seismol. Soc.

America Bull., v. 25, p. 1-32. 

Rikitake, T., 1951, The distribution of magnetic dip in Ooshima (Oo-sima) Island

and its change that accompanied the eruption of volcano Mihara, 1950;

Tokyo Univ., Earthquake Research Inst., Bull., v. 29, pt. 1, p. 161-181.
214 CONTRIBUTIONS TO GENERAL GEOLOGY . 4

Stearns, H. T., and Macdonald, G. A., 1946, Geology and ground-water resources

of the island of Hawaii: Hawaii Div. Hydrog., Bull. 9, 363 p. 

Takahasi, R., and Hirano, K., 1941, Changes in the vertical intensity of geomag- *

netism that accompanied the eruption of Miyake-sima in 1940: Tokyo Univ.,

Earthquake Research Inst, Bull., v. 19, p. 373-380. 

Wentworth, C. K., 1951, Destruction of water tanks during the Kona earthquake .

of August 21,1951: Volcano Letter 514, p. 1-3.

 1953, Construction of water tanks for resistance to earthquake damage: 

Agrictulture Ext. Service, Univ. Hawaii Bull. 60, p. 3-10.

Wood, H. O., 1914, On the earthquakes of 1868 in Hawaii: Seisinol. Soc. America 

Bull., v. 4, p. 169-203.

 1915, A consideration of recent earthquakes local to Hawaii, and of the 

seisinological problem they indicate: Hawaiian Volcano Observatory, Bull., 

v. 3, no. 5, p. 53-64.

Wood, H. O., and Neumann, F., 1931, Modified Mercalli intensity scale of 1931: 

Seismol. Soc. America Bull., v. 21, p. 277-283.
INDEX

A Page 

Abstract.. ..---.------------------------. 141-142

Acknowledgments - - 143,144

Aftershocks of Kilauea earthquake.---.--.--- 184 

of Kona earthquake- ------------ 188,189,210

Ainapo........-....--..-----.--..-----------. 173

Altitude of stations.._--__.--..__-.__._ 142 

Area of destruction, .Kona earthquake -_.. 185-188

Captain Cook, damage at.................. 187,210

Cemeteries, damage in .................... 204

Central Kona Church.................... 200

Christ Church.. ..................... 206, 209

Daifukuji Mission-..--..-........-...- 205-206

Hongwanji Mission__.................. 206

Kalahiki Japanese-----.----------.--.-... 206

Lauakila.._.........._..........__. 205

St. Benedict Church.-................... 206

Central Kona Church, damage to.---.-...... 196

Chain of Craters Road, cracks..-------------- 174

Changes in volcanic pressure---.--.---------- 160

City of Refuge- ------------------------ 202

Comparison of earthquake intensity scales_- 149 

Correlation between volcanic episodes and

tilting----.-----.---.----.-- 158-159

Crack-measuring stations_--------------- 161-163

D

Damage to buildings..........__.__.. 195-197

cemeteries.............._...._..__ 207-209

roads----..--..------------------- 204-207

Stone walls.--...__._._____.__ 202-203 

water tanks--.---...--..--------------- 198-202

Derangement of headstones................... 205

Detumescencc ..-...-.--.....-.-....-... .- 159

Difference in vertical magnetic intensity on

Mauna Loa and Kilauea... .. 160-167 

Distance of rock slides from epicenter. ..... 192

Distribution of cracks in Kona earthquake... 203

E

Earthquake(s). ........-.--.--.-.-.--...... 146

distant- . 158

local. . 153-157

Kilaeua, April 22. 146,172,181,212 

Kona, August 21........... 146,172,192, 209, 212

number recorded-...---.---..--...---.--- 146, 

151,172-180,183,188,190,191

Epicenters . 152,158,181,182,185,187,208,209,210 

Eruption of Mauna Loa, 1950......._ 168,170

F 

Frequency of aftershocks............___... 190

O 

Geology of the area______..._____ 191,192

Page

Geomagnetic measurements.------- 163,166-167,168

stations----.---...-...-.-..-----..---.. 168

Gu ten berg-Richter scale.. _................. 181

H

Hawaiian earthquakes, comparison with number in other areas................. 213

Hilina fault zone.---.--...-..-.-.----.-....-- 185

Pali . 182

Hilo seismograph station.. .,-___..... 142,145 

tide-gage--- - 194

Honalo, damage at..........----------------- 205

Honaunau 194,202,203

School-.---..--..--..-----.--..-...-.... 195

Honolulu. . .. _.-- -.. 194 

harbor__.. . ._ _ .. __ __ _ 194 

tide-gage..-- -. . _... ............ 194

Hookcna.-............................. 186,194,203

Beach........................... 193,195,197

Horizontal acceleration... ._ . _. 211

Hualalai volcano..___........__._..... 177

Instrumental data.............._........... 148

Intensity, of earthquakes........... 146,147,152,181

of geomagnetism ..______ 151,165-167,169 

Intensity scales, earthquake.____... 146,147, 210 

Interpretation of results of geomagnetic measurements------..--...__....... 168

Kaalualu 147,192

Kahauloa area, damage at - .. .--....... 195

Kahikolu Church, damage to.._............. 197

Kaholofault - . 192

Kahukufault..-..--- -.- .-...-. 148,150 

Ranch, damage at ....- -. - -. 147,179

Kaimaliuo, damage at ................... 195

Kaoiki fault, earthquakes on.................. 146,

147,150,173,177,185,212

Kcalakokua.. . . ._ 197,206,209 

Bay-.----.--.---------. 176,187,190,191,193

fault zone ----------- 177,179,191,192,210,212

seismograph........-.......-.. .. - 189,190

Kealia, damage at ..- _ - -. 195 

Keel, earthquakes at....-....-..---...__.. 176,188

Kiilae.. 195

Kilauca caldera.-..-.-. 146,173,174,175,176,181,182,

187,189, 203, 212

volcano . 148,158,163,170,172-180 

station--...-....-..--.......... 142,144,145,159

Kohala district.----------_ .__---------- 211

Kokoolau crater, steaming area._------------ 171

Kona, earthquakes in..---..---.--..-__... 186-212 

station.----------- 142,145,146,176,178,179,189

Konawaena seismograph ..-...-....-. 145,188,189

215
216 INDEX

L Page

Location, magnetometer stations..---------- 145,104

seismographstatioiis-----.----------.--- 144,145

M

Magmaticprcssurc.-------- 158,172,173,176,177,180

Magnetometer investigations _. . - 163

stations,.-_. . 170

MagnitudeofKonacarthquake---------.--- 211,212

Mauna Loa..-.. 159,163,168,172-179,188,190,191, 212

station............. 142,145,146,147,149,183,189

Mercalli scale ......................:. 148,149,211

Milolii.... ....... ....-.......-. .-.- 194

Mokuaweoweocaldera.--.--L.-.-.- 175,176,178,180 

Mountain View, earthquake near............. 176

Movement of shoulder and pavement in

quake.--.-------.------.--------- 204

N

Naalehu.. .- .- - 187,195

Napoopoo.-- - - 187,193,194,203 

Number of earthquakes recorded............. 146

headstones dislodged..................... 205

homes damaged by Kona earthquake...-. 195

0

Ohia Lodge flow.............................. 171

Ooshima Volcano_.-.--..-.----.-..-------- 163

Origin of major earthquake...---------- 174,185,210

Pahala........-.-..- ...-- __.-- - 187

Pali Kapu o Keoua......................... 192,193

Pavement cracking. .-_. . __ .- 203

Pneumatolytic deposits......-.-.-......--.--- 180

Principal types of earthquake damage. --- 193

Procedure for making magnetic measurements. 165

Pukaana Church, damage to.... . ..- . 197

Puu Kapukapu.--.---..- ------------ 182

R

Rainfall..- -- -.- 171,172 

monthly record-.---...---------....---- 172-180

Rock slides-....-.----. 146,181,182,187,192,193, 203

Rossi-Forel scale - - - 148, 212 

Rotation of columns ... 207-209

S Page 

Scismicity - 148-150,183-184

derivation. . _.__. .......__ 148

St. Joseph's School. -._._--------------- 181

St. Paul's Church, damage to.---------___ 197

Seiche----------..-------.----------..-...-- 194

Seismographs:

Bosch-Omori-.--------.-----.-.-.-...-.- 145

Hawaiian-type.----------.-------.----- 145

Jaggar... -_--- ---.-- . ...-_ ._. 145 

Neumann-Labarre .. . 144,145

Sprengnether vertical..-.-----.--...--.. 144,145

Separation of shoulders from pavement....... 203

South Point-...---.-----..-..--.---......-- 147

Steam......-.-----.--.----. 170-171,173,175,178,180

Steaming Flat..._ ......._....... ... 170

Structural damage.-._-_ . -- . 195,197,210 

Subsidence of Kilauea, December 1950-. -- 170 

Sulphur Bank......,.........-------....... 170,171

T

Temperature measurements, gas_... ....;. 171

steam--.-...-..-......-...--...-..-. 170-171

Thenardite _- - -. 180

Tilting, amount of. ............... 158-160,175

direction of....---.---.-..-. -.. 160-161,183

net accumulation of--..---------..-.-.- 172-180

Tiltmeters.............-.-...---.-.-.-.--. 143,144

description............................... 144

Topography of area. -.---.----- ---- -- 191

Tsunami....-..--.....-......--.---.-.. 187,193,194

Tumescence.. .--------.-------.---.-. - 159,212

U

Uwekahuan._. ___ ... _.._. - 171

station............. 142,144,145,146,160,171,183

Value for relative seismicity.----------.. 149,150

Volcanic activity.. _ ._.._. 158,172 

Volcano district----.-.-------.------..-.---.- 174

Waimea Plain................................ 179

Whitney Laboratory of Seismology. 142,145,146,148,

149,158,159,160,172, 174,175,177,179,180,189

Width of cracks...--...-- 161,162,163,177,181,203

Wolfson vertical magnetometers._...._... 163

O