^ Report of the 

; Hawaiian Volcano 

; Observatory for 

; 1948 and 1949

By R. H. FINCH and GORDON A. MACDONALD

v CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

GEOLOGICAL SURVEY BULLETIN 974-D

Including- sections on the 

1949 eruption of Maun a Loa 

and the bombing of lava flows

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1951

Hf .
UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary

GEOLOGICAL SURVEY 

" W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S; Government Printing Office ** 

Washington 25, D. C. - Price 20 cents (paper cover)

 * 
v CONTENTS

<^- Page

Abstract________________________________________________________ 103

Introduction. ___________________________ __________________________ 103

Physical plant___________________________________________________ 104

Seismographs and tiltmeters-___-----_-___--_______-_________-__ 104

_.._ Shop_____---_--_----_----_-__------- -----------_---__._______ 108

Records and investigations, 1948-49.________________________________ 109

.w Earthquakes.____________-___-_--_-_--__-_-___---__-_____-_-_. 109

Tilting of the ground__________-_-_-----_-__-_________________ 111

W Crack measurements.-____-_-__--_-_-_--__---___-___________--_ 113

Radiation ____________________________________________________ T15

- Temperature. __ ___________________________'____________________ 116

Rainfall.____________-________----_---__-_-__-----_-.____--_ 118

Volcanic conditions___--_____----_------__-_---__--____________ 118

_i__ Kilauea._________________________________________________ 118

Mauna Loa__-_-_-___-_---------------_-_---_---_-______-_ 119

^ Special studies_______-_---__-_-_---------------------___----__-___ 119

Activity of Mauna Loa during 1949_....___________________________ 119

y Bombing to divert lava flows__________________________________ 128

References cited._-____-___-____-__-________-_-__----_--____---____ 132

-> Index.___________________________________________________ 133

ILLUSTRATIONS

FIGURE 32. Map of Kilauea caldera and vicinity, showing location or 

Hawaiian Volcano Observatory, seismographs, and tiltmeters _ ________-__--__-___-____--____--_-_____-____ 105

33. Map of Hawaii, showing location of seismograph stations and

historic lava flows___________________________________ 107

34. Semiportable tiltmeter___-_--_-_____-_____-_-__-______- 109

35. Graph showing number of earthquakes per week during 1948

and 1949__________.-_--_--_____________________ 110

36. Graph showing tilting of the ground during 1948 and 1949. __ 112

37. Map showing lava flows and vents of 1949 eruption.________ 120

38. Mokuaweoweo caldera on January 7, 1949, showing lava

fountains and flows and fuming 1940 cone_-_--_______.__ 121

39. Southwestern part of Mokuaweoweo on January 7, 1949,

showing lava fountains and flows________--_--______-____ 121

40. Large lava fountains at southwest edge of Mokuaweoweo on

January 19, 1949. _____________________________________ 123

41. Cone area of 1949 eruption_____________________________ 125

42. Small lava cone built during late stages of 1949 eruption..... 126

TABLES

TABLE 1. Seismographs and tiltmeters operated by the Hawaiian Volcano

Observatory ___________________________________________ 108

2. Width of cracks at Kilauea caldera, Hawaii....-____-_-_-_--.. 114

' Hi

REPORT OF THE HAWAIIAN VOLCANO OBSERVATORY 

FOR 1948 AND 1949

By R. H. FINCH and GORDON A. MACDONALD

ABSTRACT

*f ' - This report, the first of its kind, summarizes the work of the Hawaiian Volcano

^ Observatory >for,the years 1948 and 1949. A short history of .the observatory 

from its founding in 1912 by the Massachusetts Institute of Technology and the

 4 Hawaiian Volcano Research Association is given.

At the present time five seismograph stations are maintained on the island

v of Hawaii. In addition there are two stations at which tilt only is measured. 

Instruments are repaired and new ones are built in the observatory shop. One 

project of the shop is the building of semiportable tiltrneters that can be housed

_ in a 20-inch cubical box. *TT

Records and investigations during 1948 and 1949 are discussed under the

following headings : earthquakes, tilting of the ground, cracks, radiation, temperature, rainfall, and volcanic conditions. The number of earthquakes per week

** is given by a graph that shows the increase in earthquake frequency preceding 

the January 1949 outbreak of Mauna Loa. Tilt curves for 1948 and 1949 also are 

shown by means of a graph. Measurements on two sorts of cracks are described,

y rainfall statistics summarized, and steam and lava temperatures given. Radiation studies, using both X-ray film and a Geiger-Muller counter, indicate no

^ appreciable radioactivity at either Kilauea or Mauna Loa.

Special sections in the report are devoted to the eruption of Mauna Loa,

/" January 6-June 1,1949, and the possibility of diverting lava flows by bombing.

INTRODUCTION

The Hawaiian Volcano Observatory was founded in 1912 by T. A.

* Jaggar under the joint sponsorship of the Massachusetts Institute of 

Technology and the Hawaiian Volcano Research Association. The 

latter, with headquarters in Honolulu, was organized with the broad 

purpose of promoting volcano investigations and specifically to help 

establish and maintain an observatory at Kilauea volcano. It is com- 

^" posed of members and patrons in Hawaii and elsewhere. Theobserva-

», tory was taken over by the United States Weather Bureau in 1919 

and transferred to the Geological Survey in 1924. In 1935 it was 

transferred to the National Park Service, which supported it until

, the Geological Survey again took it over on December 28, 1947.

This report, the first of its kind, summarizes the work of the

r observatory under Geological Survey sponsorship during 1948 and

 * 103
104 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

1949, when the staff consisted of Ruy H. Finch, volcanologist in -fcharge; Gordon A. Macdonald, geologist; Burton J. Loucks, instrument maker; Brother B. T. Pleimann, seismograph operator, Hilo; 

Howard M. Tatsuno, seismograph operator, Kona; Chester K. Wentworth, geologist, part-time; Ruth C. Loucks, assistant. It is proposed

to issue similar reports, annually, in future years.

-V 

PHYSICAL PLANT

=T'~

From the time it was established until 1941 the Hawaiian Volcano 

Observatory was located in a frame building on the northeast rim of 

Kilauea caldera. In 1941 the old observatory structure was razed to 

make room for a new hotel, and the observatory was moved to newly 

built quarters about 600 feet northeast of the original site (fig. 32). 

In 1948 the building that housed the observatory was taken over for ^_ 

the headquarters of Hawaii National Park, and the observatory was 

moved to the old museum originally built in 1927 by the Hawaiian 

Volcano Research Association at Uwekahuna, on the west rim of Ki- ^ 

lauea caldera. The new location (fig. 32) affords an excellent view of 

Kilauea and, during clear weather, of the entire profile of Mauna Loa. ^

SEISMOGBAPHS AND TILTMETERS ^

The first seismographs installed at the Hawaiian Volcano Observatory were of special design, built in Tokyo. One was intended for « 

recording teleseisms and had only a single horizontal component. The 

other was a three-component instrument for recording local earthquakes. A Bosch-Omori two-component horizontal pendulum seismo- - < 

graph was installed a little later and is still the principal instrument 

of the observatory. Operated with a period of 7.7 seconds and a mag- ** 

nification of 115, it gives satisfactory records of short-period local ^ 

earthquakes and is a sufficiently sensitive tiltmeter.

The seismographs were purchased through an allotment from the 

Whitney fund for geophysical research of the Massachusetts Institute 

of Technology. Consequently the station was named the Whitney Laboratory of Seismology. The laboratory is a cellar, 18 feet square, that 

originally was under the main observatory building (fig. 32). The v 

cellar was dug through 5% feet of volcanic ash and pumice to the upper 

surface of basalt. It is only 20 feet from the cliff that forms the inner 

wall of Kilauea caldera. Steam cracks beneath the concrete floor in -V* 

the badly fissured basalt keep the cellar at a temperature of nearly 

90° F.

A vertical seismograph was installed at the Whitney station late in > 

1929. In 1941, when the original observatory building was torn down, 

the cellar housing the Whitney Laboratory was covered with a concrete 

slab and 18 inches of soil. The vertical seismograph was moved to a 

cellar under the new observatory building (second location, fig. 32),
r I <- 

Observatory,new locatio

a

Observatory.old locatio

Seismograph and tiltme

A 

Tiltmeter

Se

-Fir

Uweikahuna vault

W

Hawaiian^ Volcdnojobservator

lt cellar 

Southeast tilt cellar

Contour interval 250 feet 

Datum is approximately sea level

FIGURE 32. Map of the vicinity of Kilauea caldera, showing the successive sites of the Ha

principal seismograph and tiltmeter installati
106 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

but the Bosch-Omori instrument was left in the Whitney vault. In -f 

1948, when this building was taken over by Hawaii National Park, the 

vertical seismograph was moved to a new vault about 1,000 feet west of 

the present observatory building at Uwekahuna (fig. 32).

During 1948 and 1949 the Hawaiian Volcano Observatory maintained three seismograph stations in addition to the Whitney and Uwekahuna stations, as well as two stations on the floor of Kilauea caldera -V 

at which only tilting of the ground is measured. The locations of the 

seismograph and tiltmeter stations are shown in figures 32 and 33. 

In the Uwekahuna vault, in addition to the vertical seismograph, there ^ 

is a pair of horizontal pendulums for measuring north-south and eastwest tilting of the ground. It is planned to convert these tiltmeters 

into seismographs and install them in the newly constructed building ^- 

of St. Joseph's School in Hilo. Space has been provided in the Uwekahuna vault for installing a high-magnification seismograph with 

photographic registration. *~

The Hilo, Kona, and Mauna Loa stations (fig. 33) are equipped ^ 

with two-component "Hawaiian"-type seismographs. The Hilo station is located at St. Joseph's School, the Kona station at Konawaena -T 

School in Kealakekua, and the Mauna Loa station at an altitude of 

6,600 feet on the eastern slope of Mauna Loa. The heavy mass of the 

Hawaiian-type seismograph is a section of 8-inch pipe 27 inches long, 

which when filled with sand weighs approximately 225 pounds. The A . 

mass is suspended as a horizontal pendulum by means of short pianowire links at the top and bottom.

All the seismographs mentioned record on smoked paper. The 

vertical seismograph has a magnification of 250, and all the others 

have magnifications of approximately 115. The Bosch-Omori recording drum is driven by a synchronous A. C. motor, and the other 

drums by spring-powered clocks. Time control for the Whitney station, and (normally) the Uwekahuna and Mauna Loa stations as well, 

is supplied by a Howard pendulum clock.

The Bosch-Omori seismograph has a fixed stylus used to scratch 

a reference line at the beginning of each record from which tilt of 

the ground is measured. Tilting of the ground is a change in the 

angular relation between a part of the earth's surface and the horizontal (Jaggar and Finch, 1929). Any tilting of the ground causes 

a shift of the position of the pendulum, which in turn results in a 

displacement of the recording stylus. As the instrument is now 

operated, a displacement of the recording stylus of 1 centimeter indicates a tilt of 1.2 seconds of arc. Tilt is measured in a similar manner 

on the Mauna Loa instrument, but the values obtained are much 

smaller than those from the instruments in the vicinity of Kilauea 

caldera. Tilt is not measured at the Hilo and Kona stations because
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 107

KOHAB^MTN

MAUNA KEA

HUALALAI 

VOLCANO

MAUNA/LOA^ 

VOLCAN

Contour interval 1000 feet 

Datum /s mean sea level

FIODRB 33. Map of the island of Hawaii, showing the location of the seismograph stations 

of the Hawaiian Volcano Observatory and the distribution of the historic lava flows 

of Mauna Loa and Kilauea. The lava of 1949 is shown in solid black, and the older 

historic flows are stippled.

experience has shown that they are subject to little tilting other than 

diurnal and seasonal.

Two tiltmeters are housed in vaults on the floor of Kilauea caldera 

near Halemaumau crater (fig. 32). Each of these tiltmeters is a normal pendulum 206 centimeters long, suspended from a tripod resting 

on leveling screws. By means of a pivot arrangement the magnifying 

lever projects vertically upward to a point just below a horizontal 

disk that is graduated in degrees and ruled with concentric circles 

spaced 2 millimeters apart. Readings are obtained by means of a mir939932 51 2
108 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

ror. The instrument indicates both the amount and the direction 

of tilt, a shift of the pointer of 1 millimeter corresponding to a tilt of 

1.3 seconds of arc.

None of the tiltmeters is of the recording type. They are read 

at various intervals, some once a day and others only monthly unless 

rapid tilting indicates the desirability of more frequent readings. 

The accumulation of tilt from day to day, and over longer intervals, as 

shown by plotting on millimeter cross-section paper, has been found 

useful in making correlations with results obtained, by precise leveling 

and in the study of earthquakes and volcanic activity both at the surface and in depth (fig. 36).

A list of the seismographs and tiltmeters operated by the Hawaiian 

Volcano Observatory, with some of their constants, is given in table 1.

TABLE 1. Seismographs and tiltmeters operated by the Hawaiian 

Volcano Observatory

Station

Whitney Laboratory of Seismology 

(northeast rim of Kilauea caldera).

Mauna Loa (altitude of 6,600 feet 

on east slope of Mauna Loa).

Uwekahuna (1,000 feet west of west 

rim of Kilauea caldera).

Hilo (St. Joseph's School) ............

Weft tilt cellar (floor of Kilauea 

caldera west of Halemaumau). 

Kona (Konawaena School, Kealakekua). 

Southeast tilt cellar (floor of Kilauea 

caldera southeast of Halemaumau).

Instrument

Bosch-Omori seismograph and 

tiltmeter. 

Hawaiian-type 

seismograph. 

Vertical seismograph.o 

North-south and 

east-west horizontal pendulum tiltmeters.

seismograph. 

Normal pendulum tiltmeter. 

Hawaiian-type 

seismograph. 

Normal " pendulum tiltmeter.

Period of 

pendulum 

(spconds )

7.7

7.1 

.4

34.0 

7.3

3.0 

7.3 

3.0

Magnification (approximate)

115

115 

250

7 

115

100 

115 

100

Sensitivity to tilt 

(seconds of arc per 

millimeter)

0.12 

.14

.1 

.13

1.3 

.13 

1.3

-f

4-

SHOP

A machine shop for the building and repair of instruments is housed 

in one wing of the observatory building. It is equipped with a 10-inch 

screw cutting lathe, a 9-inch high-speed precision lathe, a jeweler's 

lathe, a milling machine (Van Norman No. 12), a drill press, a 16-inch 

stroke shaper, a power hacksaw, and assorted hand and bench tools. 

Power is obtained from a 25-kilowatt Diesel-driven generator.

The pOAver plant and most of the heavy machinery are loaned to 

the observatory by Hawaii National Park, and appreciation is hereby 

expressed to the park officials for their use.

Several two-component semiportable tiltmeters are being built for 

use locally and in Aleutian volcano investigations. They are designed 

for installation on a concrete base in a 20-inch cubical weatherproof 

box. The small housing requirements and light weight of the instru-
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 109

ments (about 90 pounds each) permit their installation in rather inaccessible places. They have a lever magnification of 15, and when 

they are operated with a period of 20 seconds a 1-millimeter shifting 

of the lever pointer indicates a tilt of 0.08 seconds of arc. The instruments are nonrecording, although a chronograph could be installed 

with only slight modifications. Figure 34 is a photograph of one 

of these instruments.

FIGURE 34. Semiportable tiltmeter designed and built at the Hawaiian Volcano Observatory for use locally and in Aleutian volcano investigations. The height of the upright 

post at the back of the Instrument is 16 inches. Each of the heavy masses weighs 35 

pounds. , - ,

RECORDS AND INVESTIGATIONS, 1948-49

> EARTHQUAKES J i i

The number of earthquakes recorded per week on the Bosch-Omori 

seismograph for the years 1948 and 1949 is shown graphically in 

figure 35. The weekly totals that occur most frequently are four, 

five, and six. Normally about five earthquakes per week can be 

expected. An appreciable excess over this total occurs at times of 

local superficial adjustments along the active rifts of the volcanoes
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PIGDBE 35. Graph the showing number ofearthquakes each theWhitney recorded weekvault ofatHa\ 

1948 and1949. duration oftheThe 1949 eruption Mauna Loaisndicated by thebracket. Duyears 

1949, of 98earthquakes recorded. total awas 
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 111

and may have little volcanic significance. Such earthquakes are shallow-seated. An equal number of quakes, with at least the earlier 

quakes of the group originating at greater depth, especially under 

volcanic vents, commonly is an indication of volcanic uneasiness.

The large totals shown in November and December 1948 were premonitory symptoms preceding the January outbreak of Mauna Loa. 

The number of earthquakes remained large during the first week of 

the eruption. This is common, especially during flank eruptions when 

there is motion along a rift system often several miles long.

The large totals for the weeks starting January 23 and February 20, 

1949, probably accompanied resumption or increase of lava extrusion.

The 24 quakes that were recorded during the week beginning 

October 30, 1949, originated deep under Mauna Kea, a volcano that 

has been quiescent for several thousand years.

During the week beginning December 25, 1949, a total of 98 earthquakes was recorded. Most of these originated at a shallow depth 

beneath the 12,000-foot contour along the northeast rift of Mauna Loa. 

The Mauna Loa seismograph, which is about 9 miles closer to the 

epicentral region than the Whitney station (fig. 33), recorded 274 

tremors during the week. These earthquakes were all small and of 

rather uniform amplitude, suggesting the possibility that they may 

have been caused by a shallow intrusion under the upper end of the 

northeast rift of Mauna Loa.

TILTING OF THE GBOtfND

Tilt curves for the Whitney station for 1948 and 1949 are shown in 

figure 36. Records show that there is a distinct seasonal tilt on the 

northeast rim of Kilauea caldera. The east-west seasonal curve closely 

parallels that of the air temperature. The north-south curve, though 

definitely showing seasonal effects, is somewhat out of phase with 

that of the air temperature. Southward tilting is usual from January to April, inclusive, and northward tilting from May to December. Accordingly, seasonal southward tilting is more rapid than 

the northward tilting. An allowance for normal seasonal tilt must 

be made before estimating the amount of tilt resulting from volcanic 

processes. Northward and eastward tilting in excess of usual seasonal 

amounts means a doming up of the Kilauea edifice. Southward and 

westward tilting means a sinking. The summit of Mauna Loa lies 

nearly west of the Whitney station (fig. 33), and there are some 

indications that Mauna Loa eruptions are preceded by eastward, 

tilting.

The north-south tilt curve for 1948 showed the usual rapid southward tilt for the first 4 months and a northward tilt in about the 

same amount during the next 8 months. Southward tilt at the begin-
112 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

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HAWAIIAN VOLCANO OBSERVATORY, 1948-49 113

^.. ning of 1949 was more rapid than usual; it stopped on February 26, 

about 21/2 months earlier than usual. The reversal followed a strong

"*" earthquake under the east slope of Maima Loa, and the tilt '.during 

the single day February 26-27 amounted to 3.2 seconds of arc, many 

times the amount resulting from instrumental lag. .The accumulation of northward tilt during the rest of 1949 was a little less than 

usual, and the net tilt for the 2 years was 5.6 seconds to the south.

Except for a rapid eastward tilting during the first 2 weeks of 

November 1948 and a nearly compensating westward tilting from 

January 11 to January 30, 1949, the east-west tilt curve shows the 

usual seasonal characteristics. The rapid eastward tilt preceded the 

January 1949 eruption of Mauna Loa by a little more than 2 months.

.4 There was no significant accumulation of tilt in the east-west direction for the 2 years.

"T

CRACK MEASUREMENTS

-V.

Periodic measurements are made of the width of certain cracks in 

and near Kilauea caldera. A brass stud has been set on each side

-T< of the crack at the measuring point, and the top of each stud marked

with an indented point or a cross. Measurement of the distance from

^ the mark on one stud to the mark on the other is made directly with

a steel tape graduated in millimeters, or for longer distances by

means of a large pair of calipers having a span of about 1.5 meters.

At one time more than a hundred such cracks were measured once 

a week. It was found, however, that the number of cracks and fre- 

, quency of measurement were much greater than necessary under ordinary conditions. The number of cracks measured has now been 

V reduced to 13, and.during times of volcanic quiescence measurements 

are made only once a month.

The cracks now being measured are of two sorts. Cracks that lie 

back of blocks of rock on the rim of Halemaumau are measured purely 

as a matter of safety. Any widening of these cracks indicates a movement of the block toward the center of the pit. If such movement 

' becomes large or rapid, warning can be given that the block is likely 

to collapse into the pit. A crack of this sort crosses the platform at 

the Halemaumau tourist lookout, about 20 feet back from the edge 

of the pit. During the interval from July 1948 to December 1949 

the width of this crack at measuring station 5 (table 2) increased 

1.8 centimeters.

Cracks of the second category are of greater significance volcanologically. Some of these cracks lie on the floor of Kilauea caldera 

away from the rim of Halemaumau, and others along the east rift 

zone. Although there are some variations because of differences in 

the movement of individual blocks, in general these cracks open up
TABLE 2. Width of cracks at Kilauea caldera, Hawaii (i

Date

1948 

July 31 -.

Oct. 31 .

Nov. 28... .

1949

Mar. 1- _. 

July 1 

Sept. 30 .

Oct. 31 ____ ... _ .---- __ ..

Nov. 30...-. ... __ . _ ...

Measuring station numbe

Halemaumau rim cracks

5

104.8 

104.9 

105.0 

105.0 

105.1 

105.4

105.4 

105.7 

105.9 

105. 9 . 

106.2 

106.1 

106.2 

106.4 

106.4 

106.5 

106.6 

106.6

6

57.8 

57.8 

57.8 

57.8 

57.7 

57.8

57.8 

58.1 

58.0 

58.2 

58.2 

58.2 

58.3 

58.4 

58.4 

58.5 

58.5 

58.4

7

34.5 

34.5 

34.4 

34.5 

34.5 

34.5

34.5 

34.5 

34.5 

34.5 

34.4 

34.6 

34.6 

34.6 

34.6 

34.6 

34.6 

34.6

8

57.7 

57.7 

57.7 

57.7 

57.7

57.8 

57.7 

57.8 

57.8 

57.8 

57.8 

57.9 

57.9 

57.9 

57.9 

A7.9 

57.9

9

77.8 

77.6 

77.6 

77.6

77.7

77.8 

77.9

77. 8 

77.8 

77.8 

77.9 

77.9 

77.9 

77.9 

77.9

27

64.0.

64.1 

64.1 

64.0 

64.1

64.1 

64.1

64.1 

64.2 

64.1 

64.1 

64.1 

64.1 

64.2 

fn.l

Cracks o

37

N.-S. :

49.6

49.5 

49.5 

 49.5 

49.5

49.4 

49.3

49.3 

49.3 

49.2 

49.2 

49.2 

49.2 

49.2 

49.2

E.-W.

- 44-, 9,

44.8 

44.9 

44.8 

44.8

44.8 

44.8

44.7 

44.7 

44.7 

44.7 

44.6 

44.6 

44.6 

44.6
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 115

during the tumescence that accompanies the subsurface rise of magmu 

and close during the sinking that accompanies a decrease of volcanic 

pressure. Of the cracks on the floor of the caldera, crack 40 is west 

of Halemaumau (about 400 feet west of the West tilt cellar), crack 

41 is south of Halemaumau, and the others are southeast of Halemaumau. All appear to be part of the continuation of the southwest

 f' rift zone across the caldera floor. The interval from July 1948 to 

December 1949 was one of volcanic quiet at Kilauea, and from late 

December 1948 to mid-February 1949 marked southerly tilt at the

 * northeast rim of the caldera (fig. 36) indicated a decrease in volcanic 

pressure. A decrease in pressure and the resultant sinking are indicated, also, by a closing of the cracks southeast of Halemaumau

 * (table 2).

RADIATION *T"

^ A series of experiments was started in August 1948 by Kuth C. 

Loucks in an attempt to determine to what extent X-ra}7 film can 

be used to record radiation from volcanic sources (Loucks, 1949).

., Because X-ray film is affected by radiation both longer and shorter 

than the X-ray range, it appeared possible that it might be of use 

^ in detecting any short-wave radiation that might be present. No 

X-radiation is to be expected, but both ultraviolet and gamma radiation can be recorded on X-ray film. Dental pack film was used be-

< cause of the ease of handling.

To obtain control for the experiment, several series of films Avere 

exposed at times and places where they would not be directly affected 

by volcanic eruption. One series was exposed for 10 weeks, some of

^ the films at Puu Ulaula, 10,000 feet above sea level on the northeast 

rift zone of Mauna Loa, and some at the rim of MokuaAveoAveo caldera,

 more than 13,000 feet above sea level. Of tliL series, unshielded

films showed pronounced fogging, but films that were only slightly

shielded Avere unfogged. Even a strip of masking tape produced

* a shadow on the film, indicating that the radiation that affected the

. rf film was of relatively long Avave .length. Of tAvo films exposed back to

back, the front one Avas fogged, but the one behind, Avhich Avas shielded

by the tAvo lead-foil backing sheets, Avas not fogged.

A second series of films Avas tested in the Kilauea region. Film

tested for tightness of the film pack to visible light shoAved no darkenv-v ing. Cosmic radiation also produced no detectable darkening on any

a of the films tested. Other film exposed for 5 weeks at a distance of

12 to 15 feet from tiltmeter masses, containing slightly radioactive

lead, in the UAvekahuna vault shoAved slight darkening, thus serving

as a check of the sensitivity of the film to gamma radiation.

A third series of films was exposed for nearly 6 months at Puu 

Ulaula, Avith various degrees of shielding. The unshielded film Avas

939932 51 3
116 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

darkened. Films covered respectively by 0.11 millimeter of aluminum 

foil and by sheets of lead 1.75 and 3.5 millimeters thick all were undarkened. It therefore appears that the darkening was caused by 

ultraviolet radiation and that the radiation can be excluded by enclosing the film in even a thin covering of aluminum foil. During future 

eruptions lightly shielded films can be exposed to radiation from the 

lava fountains to see whether any darkening results from gamma 

radiation.

Two series of X-ray films were taped to the stone monument in 

front of the summit rest house on Mauna Loa and exposed for periods 

ranging from 17 hours to 17 days during the high-lava-fountain stage 

of the 1949 eruption. The films, which were unshielded, showed 

darkening that was probably caused by ultraviolet radiation. However, the films were more than a mile from the lava fountains, too far 

away for gamma radiation to be expected. Because of bad weather 

and inaccessibility it was not feasible to place them closer. At that 

time the tests with shielded films at Puu Ulaula had not yet been made.

A Geiger-Miiller counter was received by the Hawaiian Volcano 

Observatory late in January 1949. The instrument is a type SGM18A Survey Meter, manufactured by El-Tronics, Inc. It arrived too 

late to be used in testing for radiation from the high lava fountains 

of the early phase of the 1949 eruption of Mauna Loa. However, 

observations were made on hot lava flows in and near South Pit on 

February 5. The number of clicks in the earphones ranged from 38 

to 45 per minute with the shield on the counter tube both open and 

closed. This is approximately the same number of clicks as was 

obtained on nearby prehistoric lavas and is approximately the number to be expected from cosmic radiation alone. This work was purely 

preliminary and does not constitute a conclusive test of radiation 

associated with volcanic activity. It is especially desirable to test 

for the possible presence of radioactive materials in the gases liberated 

during the early lava-fountain phase. Such tests are planned for 

future eruptions. In the meantime, it is planned to obtain a series 

of counts at various altitudes to determine the background effect of 

cosmic radiation.

TEMPERATURE

Frequent measurements of the temperature of the steam escaping 

from the shallow drilled wells at Sulphur Bank were started on 

September 10, 1949. Sulphur Bank is a solfatara in a small graben 

at the foot of the outermost boundary fault at the northeast edge of 

Kilauea caldera, but outside the main caldera depression. During 

1922, two holes were drilled in the floor of the graben. The more 

westerly of these was drilled to a depth of 50 feet. In 1923 it was 

deepened to 70 feet, and a 15-foot hole was drilled on each side of it,
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 117

about 4 feet away, to increase the output of steam. The three holes 

are cased and are connected above the ground surface by a manifold G 

inches in diameter. After some experimenting a uniform procedure 

of temperature measurement has been adopted. A half-inch plug at 

the top of the east end of the manifold is removed, and the well is 

allowed to blow freely for 10 minutes. A maximum thermometer is 

then inserted all the way into the aperture and allowed to remain 5 

minutes, with steam escaping around it.

Weekly readings made in this way gave a temperature of 96.5° C. 

from September 10 to October 9. On October 15 the temperature was 

found to have dropped to 96.0°, which was maintained until November 13. On November 30 the temperature was 95.5°, and it remained 

the same at each reading for the rest of the year. Other readings at 

natural steam vents in the Sulphur Bank area ranged from 95.0° to 

97.5°.

When the holes at Sulphur Bank were first drilled, in 1922, the temperature was found to average 96.0° C. In 1923 readings with a 

thermocouple gave an average temperature of 95.5°, which is close to 

.the boiling point of pure water at the altitude (3,950 feet) of Sulphur 

Bank.

On November 4, 1949, temperature measurements were made in 

two prominent steaming areas near the Chain of Craters road, on 

the east rift zone of Kilauea. The highest temperature found in 

the steaming area just south of Kokoolau crater was 88° C., and 

that in the Aloi steaming area was 90.0°.

In regions where rainfall is high, such as Sulphur Bank and the 

east rift zone of Kilauea, it is to be expected that ground water will 

almost always be present in excess of the amount that can be converted into steam and therefore that temperatures in the steam 

much in excess of the boiling point of Avater are not commonly to be 

observed. The temperatures measured at Sulphur Bank do not show 

any immediate change in response to variations in the amount of 

rainfall, but this probably indicates merely that the transformation 

of ground water into steam occurs at a depth greater than that to 

which the amount of water present in the rocks is much affected 

by short-term variations in rainfall. However, noteworthy changes 

in the steam temperature do occur. In March 1886 the steam at 

Sulphur Bank became so hot that the steam baths could not be used 

(Brigham, 1909, p. 162). Such changes are most probably the result 

of increases in the amount of subsurface heat and therefore of subsurface volcanic episodes such as shallow intrusions. It is hoped, 

that systematic measurement of temperatures at Sulphur Bank, and 

possibly at .other localities, may aid in the interpretation of subsurface changes: -,- .. 
118 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Little new information was obtained on lava temperatures during 

the 1949 eruption of Mauna Loa. Estimation based on their color 

at night indicates the temperature of the lava fountains to have been ^~ 

in the vicinity of 1,000° C. Temperature measurements with an 

optical pyrometer 'were made on the glowing interior of a thick aa 

flow in South Pit on the afternoon of February 5. The glowing part 

of the flow was well exposed in a large crack. Three observations -y 

were made, all yielding readings close to 760° C. This temperature is 

believed to be accurate within 50°. The flow was essentially motionless but was still creeping ahead a little on a very low slope. Thus > 

aa lava with a temperature in the vicinity of 760° is still capable of

floAving.

RAINFALL

A rain gage was set up approximately 75 feet west of the U.wekahima seismograph vault in October 1948. Since that time daily 

records of rainfall have been kept. The monthly totals are as follows:

Monthly rainfall at Uwekahuna, west rim of Kilauea caldera, Hawaii'

1948: Inches

November ________________ 11. 16

December._________________ 4. 87

1949:

January____________________ 31. 52

February___________________ 6. 04

March_I_________________._ 3. 14

April______________________ .49

Mav_____-_-_----____-_-___ 1. 01

1949 Continued inches

June _____________________ 0. 85

July____.__________________ .81

August___________________ . 63

September__________________ .22

October____________________ 3. 61

November..._______________ 4. 94

December. ______ __._._._... 12. 19

Total for 1949..--______ 65.45

In comparison, the total rainfall for the year 1949 at Hawaii National 

Park headquarters (second site of Hawaiian Volcano Observatory, 

fig. 32) was 95.63 inches.

VOLCANIC CONDITIONS

Kilauea. Kilau '.a volcano erupted in Halemaumau in September 

1934. Since then tAere has been no surface activity, although in 1944 

the pattern of earthquakes and occurrence of harmonic tremor on the 

seismographs indicated the movement of magma underground (Finch. 

1949). Except for occasional small avalanches from the walls of 

Halemanmau, there have been no visible surface changes during 1948 

and 1949.

Solfataric activity has continued with no apparent change at Sulphur Bank, which is at the northeast edge of Kilauea caldera, and 

along the inner boundary cliff of the caldera east of Halemaumau. 

Steam vents have continued active on the flats west of the Whitney 

vault at the north edge of the caldera, on the caldera floor, and at several localities along the east rift zone between the caldera and Makao-
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 119

puhi crater. The two most prominent of the steaming areas along

_, the east rift zone are the one crossed by the Chain of Craters road

at Aloi crater and another that lies southwest of the road just south

of Kokoolau crater. The latter area, which is roughly circular and

about 1,500 feet*across, first appeared in 1938 and almost certainly

can be attributed to the emplacement of a body of magma at a fairly

'" shallow depth beneath it.

Mauna Loa. Mauna Loa was in eruption at the summit from 

January 6 to June 1, 1949. During 1948 and the rest of 1949 it was

* quiescent. A swarm of earthquakes on December 28,1949, may have 

accompanied the .intrusion of magma at a shallow depth along the 

upper part of the northeast rift zone, unaccompanied by surface

"f activity. The eruption of Mauna Loa is described on pages 119-128. 

i Steam vents are constantly active along the northeast rift both 

above and below the prominent cinder cone at an altitude of 11,750 

feet. The conspicuousness of the steam varies greatly, owing in part 

to changing visibility with changing weather conditions but probably also to variation in the abundance of the water supply. The

T^ steam is especially prominent during and just after the melting of 

heavy snowfalls. Steam vents and solfataras are present on the 

southwest rift in the vicinity of Sulphur Cone at an altitude of 11,300 

feet. Comparison of photographs taken at Sulphur Cone by Mac 

donald in October 1949 with others taken by Finch in 1926 shows no 

apparent change in the degree of activity. During October 1948 

Macdonald and Howard A. Powers observed light fume at the 1940

v cinder cone in Mokuaweoweo caldera and light but conspicuous sulfurous fume at fissures on the caldera floor north of the 1940 cone, at

** about the position where the 1949 eruptive fissure later opened. Fume 

continued to issue from numerous secondary fumaroles on the flows 

within Mokuaweoweo caldera for a few weeks after the end of the 

1949 eruption. At the end of 1949 the 1940 cone and the new cone

*i of the 1949 eruption were still fuming lightly, as were fissures on the 

caldera floor half a mile north of the 1940 cone.

SPECIAL STUDIES

ACTIVITY OF MAUNA LOA DURING 1949

^ A summit eruption of Mauna Loa began at about 4 o'clock in the 

afternoon of January 6, 1949. The last previous activity had been

J noted during 1943, when from November 21 to 24 volcanic tremor on 

the seismographs and a fume cloud at the summit of the mountain 

indicated weak activity.

The 1949 eruption has been described in detail elsewhere (Macdonald and Finch, 1949a and 1949b; Macdonald and Orr, 1950). 

Only a brief summary account will be given here.
120 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

The early activity was characterized by explosive violence. Kumbling was audible at the Hawaiian Volcano Observatory, 20 miles 

east of the site of eruption. Fragments of pumice were carried by 

the wind 7 miles northeastward, and Pele's hair was drifted about 

20 miles. Q

The lava broke out along a series of fissures en echelon (fig. 37) that 

crossed the floor of Mokuaweoweo (the caldera at the summit of Mauna 

Loa), split the 1940 cinder cone, cut the cliff-at the southwest edge of 

the caldera, and extended about 1.2 miles down the southwest slope of 

the mountain (fig. 38). The total length of erupting fissure was about 

3 miles. On the morning of January 7 lava fountains were still playing from the fissures at four localities. One of these was near the 

center of Mokuaweoweo (fig. 38), north of the 1940 cone, another 

was at the southwest boundary of the caldera (fig. 39), and the other 

two were on the southwest slope of the mountain outside the caldera. 

The rest of the fissures had become inactive except for the emission 

of fume. On the morning of January 9 very weak intermittent fountaining was still going on at one place outside the caldera, but by that 

evening lava liberation was entirely confined to the caldera.

Cinder cone of 1949 

Eruptive fissure of 1949 

Pumice field of 1949 

Cinder cone of 1940

FIGURE 37. Map showing the approximate outlines of the lava flows and the location of 

the vents of the 1949 eruption of Mauna Loa.
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 121

FIGURE 38. Aerial photograph looking southwestward across Mokuaweoweo caldera, January 1, 1949. In the right foreground a chain of small lava fountains is playing along 

the eruptive fissure and sending a flow of lava to the left across the caldera floor. In 

the middle ground the fissure can be seen crossing the 1940 cone, which is fuming. In 

the left background clouds of fume are rising from the fissure, which cuts the caldera 

wall and extends on down the flank of the mountain. Lava fountains are playing at 

the base of the ealdera wall. Official photograph, United States Navy.

FIGURE 39. A closer view, on January 7, of the southwest wall of Mokuaweoweo caldera 

and the upper flank of the mountain shown in the background in figure 38. Lava fountains are spurting from, the fissure in the wall and on the floor of the caldera close to 

the wall. A pool of molten lava has formed just to the left of the base of the fountains 

and is spilling northward over the escarpment at the edge, of the South Lunate platform 

to form another pool at the right of the picture. The edge of South I'it is visible at 

the left. The white patches on the caldera walls and outer slope of the mountain are 

snow. Official photograph, United States Navy.
122 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

The fountains outside the caldera gave rise to a lava flow down 

the west slope of the mountain, just north of and partly overlying 

the flow of 1851 (figs. 33 and 37). In its first 24 hours this flow 

advanced about 6 miles and occasioned some alarm in the Kona district, despite reassurances from the observatory staff that danger was 

not imminent. With the cessation of fountain activity outside the 

caldera the supply of lava was cut off, and by January 8 the flow 

appeared to be essentially motionless. The total length of the flow 

is about 6.8 miles.

The first ground observers reached the scene on the afternoon of 

January 7. At that time a nearly continuous line of lava fountains 

half a mile long was playing from the fissure near the center of 

Mokuaweoweo. The average height of the fountains was about 50 

feet, but occasional bursts rose as high as 150 feet. Flows of lava 

were spreading both eastward and westward over the caldera floor, but 

the principal flow moved eastward. The other active area was at the 

southwest edge of the caldera. There a small fountain played intermittently from the fissure at the base of the cliff, with occasional 

spurts part way up the wall, and a much larger and steadier fountain 

played a short distance out from the cliff on the caldera floor. The 

larger fountain shot constantly to heights of 150 to 200 feet, with 

occasional bursts as high as 300 feet. From the southwestern fountains a stream of lava flowed northward, west of the 1940 cone, and 

joined the lava from the central fountain chain. Another lava stream 

flowed eastward, then divided, sending one branch northeastward 

across the caldera and another southward into South Pit.

The eruptive fissure split the 1940 cone, which was fuming strongly 

(fig. 38). Later examinations showed that lava had risen in the 

crater of the cone and had issued from the fissure on both sides of 

the cone, but by the afternoon of January 7 all this activity had 

ceased. Early on the morning of January 8 the observing party was 

driven off the summit by a heavy blizzard, and for the next 2 weeks the 

only observations were made from the air.

On January 9 the central fountains had stopped playing. For a 

week or more the southwestern fountains appear to have remained 

small, although variable in size. After that they increased greatly 

in height. On January 19 the larger fountain was reported to be 

400 to 500 feet high (fig. 40). On January 21 Frank Hjort and 

James Orr, of the National Park Service, reached the summit and 

reported that the fountains were playing to heights of 300 to 500 feet. 

On January 23 Orr and D. H. Hubbard estimated the height of the 

larger fountain to be well over 500 feet, with some bursts reaching 800 

feet or more. This great height, possibly the greatest yet observed on 

Mauna Loa, is roughly confirmed by comparison in photographs of 

the height of the fountain with that of the cliff behind it (fig. 40).
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 123

FIGURE 40. Looking nearly west toward the lava fountains and How at the southwest 

edge of Mokuaweoweo caldera on the evening of January 19, 1949. The smaller fountain on the left is issuing from the fissure part way up the wall. The fountain on the 

right is about 500 feet high. Photograph by K. Otaki, Ace Portrait Studio, Hilo.

These very high lava fountains, together with strong shifting 

winds, resulted in a light distribution of Pole's hair all over the 

southern part of the island. The fountains produced, for Mauna 

Loa, exceptionally large amounts of pumice, which accumulated 

around them to form a large cone and was drifted westward to form 

a blanket of pumice a mile long, half a mile wide, and about 20 feet 

thick near the cone (fig. 37).

The lava fountains were inclined somewhat eastward, and most 

of the ejecta fell into a pool at the east edge of the cone. From the 

pool the lava flowed eastward, over the surface of the old South 

Lunate platform. Lava spilling northward almost completely obliterated the scarp that formerly separated the Lunate platform from 

the central pit of Mokuaweoweo (fig. 39). During late January 

flows poured part of the time into the main caldera and part of the 

time into South Pit.
124 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

Lava pouring into South Pit gradually filled it. On January 25 

the lava reached the level of the low southeast rim of the pit, and late 

on the same day the pit overflowed. A new lava stream flowed southeastward down the outer slope of the mountain, and by the evening 

of January 26 it had attained a length of about 2 miles. On the evening of January 31 the flow front was about 5.5 miles from South 

Pit (fig. 37). On January 29 or 30 a new branch of the flow broke 

out near South Pit, and this appears to have robbed the older branch 

of its supply of lava. After January 31 the older branch advanced 

very little. The new stream moved down slope just east of the older 

one and partly overlapped it, eventually attaining a length of about 2 

miles.

During the night of February 4 lava-fountain activity was still 

moderately strong, but by the morning of February 5 it had become 

weak and irregular and on the afternoon of that day it ceased altogether. The cone was climbed on February 6, and the vent was found 

to be completely inactive except for the liberation of fume. On February 7 the flows on the south flank of the mountain were still found 

to be moving slowly. This continuation of movement in the flows 

after the cessation of lava extrusion at the vent probably resulted 

from draining of the still-fluid lava from the feeding tubes in the 

flows on the upper slopes of the mountain.

Thus the first phase of the eruption came to an end on February 5. 

It had buried about two-thirds of the floor of Mokuaweoweo with new 

lava, filled South Pit to the level of its southeast rim, sent two new 

flows down the west and south flanks of the mountain, and built a 

large cone at the southwest margin of the caldera (fig. 41). The cone 

is compound. An outer cone, breached on its east side, consists 

largely of fine cinder and pumice. It rests partly on the outer slope of 

the mountain and partly on the caldera floor and against the boundary 

cliff. The top of the outer cone is about 100 feet above the former 

rim of the caldera, and the maximum diameter of the cone is about 

1,500 feet. At the east edge of the large cone, and partly enclosed 

within it, is a small double cone of coarse cinder and spatter. This 

inner cone probably was built during the stage of reduced gas pressure and lower fountains that directly preceded the end of the first 

phase of the eruption.

The area and volume of each of the major divisions of the 1949 

lava are shown in the accompanying tabulation. Except for that 

in Mokuaweoweo and an almost negligible amount in South Pit, all 

the lava was poured out during the first phase of the eruption. It 

is estimated that, of the 44 million cubic yards of new lava in Mokuaweoweo, less than 4 million was extruded during the second phase of 

the eruption.
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 125

FIGURE 41. View of the cone area of the 1949 eruption on July 26, from the top of the 

caldera wall to the north. In the foreground and on the right can be seen the big 

pumice cone built on and against the caldera rim during early stages of the eruption. 

The fissures are the result of partial collapse and slumping of the cone, and the "white 

areas are the result of alteration of the pumice and deposition of salts by escaping gases. 

In the middle distance can be seen the hollow cinder-and-spatter cone, and to its left 

the lava cone. Photograph by G. A. Macdonald.

Area and volume of 1949 lava of Mauna Loa

;' ' :, *'.'.: ' Division

South Pit-_--_-_-------------------._------

Western (Kona) flow _ _ _ . _

Southern (Kau) flow

TotaL ----- - ----.-----_----_--_---

Area (square 

miles)

1. 5

. 2

3. 1

.8

5. 6

Volume (cubic 

yards)

44, 000, 000

8, 000, 000

16, 000, 000

9, 000, 000

77, 000, 000

Lava fountaining ended on February 5, but fume rising from 

Mokuaweoweo was visible almost constantly during the remainder 

of February and March. It was obvious that the magma column 

must be standing at a very high level in the conduit. On several 

different nights a distinct glow was reported at the summit of the 

mountain. Although at no time when observers were able to see into
126 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

the caldera was there any sign of lava fountaining or flow, there 

can be no doubt that the reported glows were the result of brief, 

quiet outpourings of lava.

During late March or early April the quiet outflow of lava became 

essentially continuous. On April 8 the cinder-and-spatter conelet 

inside the crater of the large pumice-and-cinder cone was emitting 

great puffs of fume, but no lava. About 250 feet east of the fuming 

conelet a small lava cone had been built (fig. 41), about 80 feet high 

and 150 feet across at the base, with a crater 40 feet in diameter 

containing a small surging pond of molten lava. The surface of 

the lava pond heaved slowly up and down, from a few inches to 

15 feet below the rim of the crater. From the vent area liquid 

lava moved through tubes beneath the surface, emerging about a 

mile east-northeast of the cone to 'feed two sluggish flows of aa. 

Another sluggish aa flow was moving southeastward into South Pit.

On May 5 the height of the lava cone had increased to about 95 

feet (fig. 42), and the cinder-and-spatter conelet had liberated some 

short flows of lava that partly veneered its flanks. A small pahoehoe 

flow was spreading near the base of the lava cone. Another, larger 

stream moved through tubes to issue a mile northeast of the cone 

as a moderately active pahoehoe flow.

Fn;ri!K 4L>. The small lava cone built within the crater of the big cinder-and-pumice cone 

during the late stage of the 1949 eruption. The cone is about 100 feet high. The view 

was taken looking nearly east from a point near the summit of the cinder-and-spatter 

conelet on June 3, just after the end of the eruption. Hawaii National Park photograph 

by James B. Orr.
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 127

On May 7, J. B. Orr observed a distinctly cyclic pattern in the 

behavior of the two small cones. Each cycle began with a loud 

hissing and roaring within the cinder-and-spatter conelet, accom-

^ panied by copious liberation of fume. This lasted about 5 minutes 

and was followed by rapid outpouring of gas-rich pahoehoe. The 

lava effusion continued about 45 minutes, the rapidity of extrusion

r gradually decreasing until all flows ceased. . Within about 5 minutes 

after the lava ceased to flow the hissing and roaring within the cone 

began again, and a relatively violent escape of gas continued for about

*** 10 minutes. Immediately afterward the lava cone, which had been 

, quiescent, started to fume copiously, and shortly thereafter fluid lava

entered its crater, which had been empty.,, Within 10 minutes the 

c crater was completely filled. The fluid lava gradually bulged up

above the crater rim; confined within its tough crust, it formed a 

i flat dome a foot or two high. Then the crust ruptured and the lava

* poured down the flanks of the cone. This phase of overflow continued for about an hour. Then the lava in the crater drained away, 

accompanied by liberation of large volumes of fume at the lava cone

 ^ and hissing and roaring in the cinder-and-spatter conelet. This was 

followed by a period of quiet lasting about an hour, after whiqh the 

entire cycle was repeated. 

The eruption ended about the first of June. Flows were still mov-

-* inS actively on the caldera floor on May 19. On June 2 there was 

no further sign of movement in the flows, but a weak glow was still

 *- visible in the cone, which .was fuming strongly. By the afternoon 

of June 3 the fume was very light and contained less sulfur dioxide 

than it had earlier. During the remainder of June no glow, and

+ only weak fuming, were reported. On July 26 the 1949 cones were

^. still hot, and both they and the 1940 cone were fuming weakly.

Later visits, in October 1949 and March 1950, showed no further

~i changes in Mokuaweoweo except partial collapse of both the cinderi and-spatter conelet and the lava cone. The collapse revealed the 

cinder-and-spatter conelet to be partly hollow. In the center of the 

cone is an open chamber, about 25 feet across, with nearly vertical 

walls arching inward to a point at the top. The opening is about 40 

feet high but was formerly higher, as the visible floor is formed of 

loose rubble that resulted from the collapse of the cone. The walls

x of the chamber are lined with a layer of pahoehoe 2 to 4 feet thick, 

in which the flow lines and flow planes are arranged parallel to the

; walls of the chamber and are nearly vertical. At the apex of the

chamber the pahoehoe lining is prolonged upward as a 3-foot dike

leading to two small spatter conelets at the summit. Apparently the

* lava rose into the cone, making room for itself by removing the matej rial that in earlier stages formed the core of the cone. There is no
128 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

evidence whether the removal was by stoping or by redissolving the 

hot cinder, or both. At the end of the eruption the magma column 

withdrew, leaving the center of the cone empty and the walls of the 

cavity veneered with a thin layer of lava.

BOMBING TO DIVERT LAVA FLOWS

Probably the first attempt to alter the course of a lava flow by artificial means occurred during the 1669 eruption of Etna volcano. The 

flow was advancing toward the city of Catania and seemed likely to 

destroy it. In an attempt to save the city, several dozen men covered 

themselves with wet cowhides fpr protection against the heat and dug 

a channel through the Avail of hot lava at one edge of the flow. The 

operation was initially successful. A stream of lava escaped through 

the gap thus created and moved away at a high angle to the direction 

of the original flow, partly relieving the pressure on the stream moving toward Catania. Unfortunately, however, the new flow moved 

toward the town of Paterno, and some 500 irate citizens of that town 

descended upon the men of Catania and drove them away from the 

newly dug lava channel. Left unattended, the gap in the flow wall 

soon clogged up with cooled lava, and the main branch of the flow 

continued toward Catania, partly destroying it (Bittmann, 1929). 

This early attempt, although it ended in failure, demonstrated the 

possibility of diverting part or all of a lava flow to a new course by 

artificially breaking down the confining wall of the flow.

Digging away the edge of the flow, by hand or by machine, is a 

difficult and possibly dangerous procedure. It is easier and quicker 

to blast away the lava by means of explosives. Lorrin A. Thurston 

suggested orally in the early 1920's that, in the case of pahoehoe lava 

flows descending gentle slopes, high explosives might be thrust out 

over the flow on long poles and dropped through windows in the feeding tube near the flow source, shattering the tube, forcing the lava to 

spread out again near the source, and removing the supply of lava 

from the advancing lower end of the flow. He later published the 

suggestion (Thurston, 1929). Similar methods had been under discussion for several years by members of the staff of the Hawaiian Volcano Observatory. Thurston's suggestion was accepted and advocated by Jaggar (1931), and during the Mauna Loa eruption of 1935 

Jaggar introduced the method of emplacing the explosive by dropping military bombs from airplanes (Jaggar, 1936). This generally is the most practical way of transporting and emplacing the 

explosive. In some instances shells from nearby big guns might be 

more effective because of the greater accuracy with which they can be 

directed, but for the most part potential diversion sites are too inaccessible to be reached conveniently or quickly by artillery.
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 129

There are three principal ways in which bombing can bring about 

diversion of the fluid lava, thereby robbing the, older flow front of its 

supply of lava and causing stagnation of the lower end of the flow,. 

These are: (1) bombing of the natural levees along the open lava river 

of an aa flow or a young pahoehoe flow in which tubes have not yet 

formed; (2) bombing of the main feeding channel of a mature 

pahoehoe flow in which tubes have become well developed; and (3) 

bombing of the walls of the cinder cone at the source of the flow.

In well-established lava flows on little-dissected terrain the liquid 

lava of the main feeding channels commonly is confined within tubes 

or between natural levees and is at a level several feet higher than that 

of the land surface adjacent to the flow. Where the lava river is still 

open and confined between levees, the breaking down of the levee therefore will allow the liquid lava to escape to one side and form a new 

flow, robbing the old flow of part or all of its supply of liquid lava. 

If topographic conditions are favorable, the new flow may move off 

at a high angle to the direction of the older flow and reach some entirely different destination. More commonly, however, because the 

older flow was guided by the direction of steepest slope or preexisting 

topographic depressions, the new flow follows the same direction and 

moves down slope along the edge of the older one. If it does so, it 

may eventually reach the same place at which the older flow terminated. However, the advance of the lava as a whole is greatly delayed, because the diverted flow may take days, or even weeks, to reach 

the point attained previously by the older flow. When the second 

flow has reached the danger point, it also can be bombed, thus delaying 

the advance of the lava front still further.

A long stretch of the flow, or several separate points on the flow, 

may be suitable for bombing. If so, in general it appears advisable 

to select the lowest suitable site for bombing first. If it then becomes 

necessary to bomb the flow again at a later date, the higher sites are 

still available. On the other hand, if the higher sites are bombed first 

the new lava streams advancing along the edges of the older one may 

so alter conditions that the lower sites are no longer suitable. Generally speaking, it is wise to wait as long as is safely possible before 

bombing the flow. Every day during which bombing is delayed brings 

the eruption that much closer to an end and, in general, sees the rate 

of lava output diminished. Premature bombing may result in a need 

for repeating the process, whereas a single bombing might have sufficed had it been delayed a little longer. Care must be taken, however, 

to allow a sufficient margin of time to cover the possibility of periods 

of bad weather with low visibility (when bombing is impossible) and 

rapid forward spurts of the flow.
130 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

The practicability of breaking down the levee of an open lava stream -1 

by aerial bombing was demonstrated during the 1942 eruption of 

Mauna Loa (Finch, 1942, p. 4). Disruption of the levee by bombs 

resulted in at least one new lava stream that poured out through the 

break in the wall. Topography was not favorable for directing the ^ 

new flow away from the course of the older one; consequently it flowed 

along the edge of the older one for a short distance and then rejoined 

it. Even such a brief diversion may have some effect, however, in retarding the advance of the front of the major flow, owing to the rapid 

cooling of the channel of the main flow below the point of diversion 

and the consequent chilling of the next lava to enter it, with the ac- ^ 

companying tendency to clog the channel.

The method of bombing the main tubes of a pahoehoe flow was tried 

successfully during the 1935 eruption of Mauna Loa (Jaggar, 1936). -* 

Bombs dropped on the roof of the tube may break in the roof and <± 

cause the tube to become clogged with solid fragments, or bombs 

dropped into the liquid lava within the tubes through the roof or « 

through windows in the roof may cause sufficiently violent stirring of 

the liquid to transform it from pahoehoe to aa, with an increase in 

viscosity or even local congelation. If it is not swept away with the 

current, this mass may cause a plugging of the tube. If in either 

way the tube becomes clogged, the result is an overflow of liquid 

lava from the tube at the point of clogging and a partial or total 4- 

removal of the supply of liquid from the tube farther down slope. 

The lava that overflows at the break forms new tongues, which advance down slope on top of, or alongside, the older flow. If the 

eruption continues long enough, these tongues may develop new major 

tubes and may in time reach or pass the terminus of the older flow, 

but the advance of the lava as a whole will have been delayed and *" 

the end of the eruption will be that much closer. It may be possible 

to repeat the bombing if necessary.

The cinder-and-spatter cones formed at the source of lava flows 

commonly contain pools of lava that are held at levels several feet 

above the surrounding land surface. Likewise, the liquid surface of 

lava flowing in a well-established channel issuing from the cone is v 

generally several feet above the adjacent terrain. The breaking down ^, 

of the cone walls, either naturally or by bombing, therefore will allow 

the liquid in the cone to escape over the surrounding ground, robbing 

the established lava flow of its supply of new lava. Many of the cones 

on the rifts of Mauna Loa have a form especially favorable for bombing. They are built by rows of lava fountains spurting from fissures * 

and are long and narrow, with relatively thin walls that probably 

would be quite easy to break down by bombing. Bombing of the 

walls of the source cone has been suggested (Finch, 1942, p. 6; Mac-
HAWAIIAN VOLCANO OBSERVATORY, 1948-49 131

donald, 1943, p. 255) but has not yet been tried. However, during 

the 1942 eruption of Mauna Loa there occurred a natural breakdown 

of the cone walls, liberating floods of pahoehoe, one of Svhich formed 

a new flow advancing seaward parallel to the older channel. A day 

later, forward movement at the front of the older flow had practically 

ceased.

Successful diversion of lava flows by bombing depends upon a combination of several favorable circumstances, including a lava river 

flowing in a channel or lava held in the source cone at a level higher 

than the adjacent land surface; narrow levees, thin cone walls, or 

thinly roofed tubes that can be broken open by bombs; and favorable 

topography. The first two conditions are commonly present during 

eruptions of basaltic lava, but favorable topography is not so general. 

On the slopes of volcanoes that have been appreciably dissected by 

erosion, flows may be confined within valleys, and diversion may be 

difficult or impossible. Even under those conditions, however, it may 

be possible to delay greatly the advance of the flow front by repeated 

bombing and spreading of the lava in the upper reaches of the valley. 

On the undissected or little-dissected slopes of young volcanoes, where 

erosion has not yet cut valleys, bombing to divert the flow is both 

possible and practical.

It must be pointed out that successful diversion ig possible only 

where the flow has continued long enough to establish well-defined 

channels or build at least moderate-sized cones. Probably little can 

be done with the voluminous bursts that occur during the early hours 

of Mauna Loa eruptions when the flows are spreading rapidly in 

several directions and moving through many shifting and anastomosing channels. Fortunately these early floods are generally high on 

the mountain, where they constitute no danger. It must likewise be 

realized that time is required to prepare the planes and load the 

bombs, as well as to select the targets and put the plan into operation. 

Therefore, diversion by bombing may not be possible in time to avert 

catastrophe where the flow is advancing rapidly down steep slopes 

or where the point of outbreak of the flow is too close to the area whose 

protection is desired. It is difficult to place any definite limit on the 

distance of the vent from the endangered area within which time is 

insufficient to permit bombing to divert the flow. This depends on 

the fluidity of the particular lava stream, on the slope, and on the 

general character of the terrain. For average Hawaiian eruptions, 

with average slope conditions, it may be about 7 miles. Where the 

distance is less than that, or where slopes are steep and flow of the 

lava rapid, only lava barriers such as those suggested by Jaggar (1945) 

can furnish protection.
132 CONTRIBUTIONS TO GENERAL GEOLOGY, 1950

REFERENCES CITED

BRIG HAM, W. T., 1909, The volcanoes of Kilanea and Mauna Loa: Bernice Pauahi

Bishop Mus. Mem., vol. 2, no. 4. 

FINCH, R. H., 1942, The 1942 eruption of Mauna Loa : Volcano Letter 476, pp. 1-6.

 , 1949, Volcanic tremor (pt. 1) : Seismol. Soc. America Bull., vol. 39,

pp. 73-78. 

JAGGAR, T. A., 1931, Preparedness against disaster: Volcano Letter 338, pp. 2-4.

 , 1936, The bombing operation at Mauna Loa: Volcano Letter 431, pp. 4-6.

 , 1945, Protection of harbors from lava flow: Am. Jour. Sci., vol. 243-A

(Daly volume), pp. 333-351. 

JAGGAB, T. A., and FINCH, R. H., 1929, Tilt records for 13 years at the Hawaiian

Volcano Observatory: Seismol. Soc. America Bull., vol. 19, pp. 38-51. 

LOUCKS, R. C., 1949, Report on preliminary work for radiation survey: Volcano

Letter 505, p. 1. 

MACDONALD, G. A., 1943, The 1942 eruption of Mauna Loa, Hawaii: Am. Jour.

Sci., vol. 241, pp. 241-256; 

MACDONALD, G. A., and FINCH, R. H., 1949a, The Mauna Loa eruption of January

1949 : Volcano Letter 503, pp. 1-7.

 , 1949b, Activity of Mauna Loa during April, May, and June 1949:

Volcano Letter 504, pp. 1-4. 

MACDONALD, G. A., and ORE, J. B., 1950, The 1949 summit eruption of Mauna Loa:

U. 'S. Geol. Survey Bull. 974-A. 

RITTMANN, A., 1929, Der Atna und seine Laven: Naturwissenschaften, vol. 17,

pp. 95-96. 

THURSTON, L. A., 1929, On the use of high explosive to divert lava flows:

Honolulu Daily Advertiser, September 27.
INDEX

Aloi crater, steaming area at.

Bombing of lava flows..--------------------

Bosch-Omori seismograph 104,

Chain of Craters road, steaming areas near.. 

Crack measurements.- - . - 

Earthquakes.-----.-----....-------.

Equipment... - - . 

Etna, 1609 attempt to divert lava of.

Page

117,119

128-131 

106,109

117,119 

113-115

109-111 

104-109 

.. 128

Founding. 

Oeiger-Miiller counter, observations with .

103

116

Halemaumau, cracks at-....--------------- 113-115

tiltmeters near----....----.-..- 107-108

"Hawaiian-type" seismographs.--------.----- 106

Hawaiian Volcano Research Association...- 103,104 

Hilo seismograph station.--..---------- 106-107,10g

Housing-........-.....-....-.---------------- 104

Kokoolau crater, steaming area south of-... 117,119 

Kona seismograph station.............. 106-107,108

Lava (historic), distribution of--------.---..- 107

Lava (1949), area and volume of.--.-.-.._._.. 125 

distribution of..---------------------- 107,120

emission of-----..--..----------------- 120-128

observations with Oeiger-Muller counter

on.-..- .......-........-....... 116

temperature of.... -------------------.-- 118

Lava flows, bombing of__ . 128-131

Lava fountains.......-.-.....-... -...-_ 120-124

Location of instruments.................... 104-108

Massachusetts Institute of Technology.._.. 103,104 

Mauna Kea... _... - - . Ill

.cage 

Mauna Loa, 1935eruption of-- .. . 130

1942 eruption of....-.---...-.-..-....... 130,131

1949 eruption of................. Ill, 113,119-128

cones---.......-....-.. 120,124,125,126-128

explosive.activity_. _ .. _ 120 

lava.............-....... .. 118,120-128

Pole's hair............_ ..._ ._. 120,123

pumice--..--.--.-.- 120,123,124,125,126 

vents.... -- --- -- -- - _ 120

Mauna Loa seismograph station. ..... 106,108,111

Puu Ulaula, radiation tests at------. . 115-116

Radiation.__.. ..._____.__....... 115-116

Rainfall-----..------------------------. 118

Seismographs..... --. . .-. 104-107,108

Shop..-.--.....---..- ........... 108-109

Solfataric activity. _-_..--__-_... 116-117,118-119 

Sponsorship ..- --.--................-..... ] 03

Staff......--.-..--.- -.-....-....-. 104

Steam, temperature of. . .. 116-117

Sulphur Bank, steam temperature at ... 116-117 

Temperature, of lava..--....... .._. 116-117

of steam_-..... . . .. . 118

Tilting of ground.-----....----.-.-- 111-113

Tiltmeters. ...-.--... 105,106,107-108,108-109 

Topography, importance in bombing lava

flows. - . -.. -....- 129,130,131

Uwekahuna seismograph station__ _ 105,

106,107,108,115,118

Volcanic conditions.._.... . .____ 118-128

Whitncy seismograph station (Whitney

Laboratory of Seismology). -..- 104- 

106,107,108,110,111,112

X-ray films exposed - _ -- 115-116

133

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