Occurrence of 

Diatomaceous Earth 

Near Kenai, Alaska

GEOLOGICAL SURVEY BULLETIN 1039-B

Occurrence of 

Diatomaceous Earth 

Near Kenai, Alaska

By GEORGE PLAFKER

'NVESTIGATIONS OF CONSTRUCTION MATERIALS IN ALASKA

GEOLOGICAL SURVEY BULLETIN 1039-B

A short description of the occurrence 

and formation of diatomaceous earth, 

and its suitability as a construction 

material

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON i 1956
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D. G. - Price 75 cents (paper corer)
CONTENTS

Pag*

Abstract______________.___________-_____-----_ 25

Introduction and acknowledgments___-_____--_--__----_----_-__---_- 25

Geology.___________^________ _ ___________________________________ 27

Glaciofluvial outwash__________________________________________ 27

Older lake sediments_-___--_--_-___-_--__-___--__---_---------- 28

Diatomaceous earth___-__--________-______-_____-__--_---_-- 28

Talus and beach deposits_-___-_______-__----_------__--_- 29

Origin of the diatomaceous earth._______________________________ 29

Factors affecting development_____________________________________ 30

Literature cited.__________________________________________________ 31

ILLUSTRATIONS

, Page 

PLATE 3. Geologic map and section of diatomaceous earth deposits near

Kenai, Alaska__________________________________ In pocket

4.4, View looking north from near south end of meadow underlain 

by diatomaceous earth; B, View of road cut in sea cliff 

showing diatomaceous earth, older lake deposits, and 

glaciofluvial outwash_______________--__-_______ Follows 2&

5, 6. Photomicrographs of diatoms from diatomaceous earth deposit

near Kenai, Alaska____________________________ Follows 28

FIGURE 8. Index map of the Kenai area showing location of diatomaceous

earth deposits--_-_---_-_-_-_-__---_--_- __ 26-

m

INVESTIGATIONS OF CONSTRUCTION MATERIALS IN ALASKA

OCCURRENCE OF DIATOMACEOUS EARTH 

NEAR KENAI, ALASKA

By GEORGE PLAPKEE

ABSTRACT

Diatomaceous earth is an unconsolidated earthy deposit formed by accumulation of the minute siliceous tests (skeletons) of diatoms, a type of algae, and is 

sometimes referred to as diatomite. It occurs in postglacial lake deposits exposed 

along the shore of Cook Inlet north of the village of Kenai, Alaska.

The largest and purest of these deposits was mapped and sampled in detail. 

The diatomaceous earth attains a maximum thickness of 12 feet with the dried 

material averaging between 65 and 75 percent diatoms by weight.

The deposit mapped contains about 200,000 cubic yards of diatomaceous earth 

which is readily accessible and is favorably situated with regard to transportation by sea and road.

INTRODUCTION AND ACKNOWLEDGMENTS

As a part of the U. S. Geological Survey's program of exploration 

for construction materials in Alaska, diatomaceous earth exposed in 

four postglacial lake deposits along the shore of Cook Inlet from 6 to 

12 miles north of the village of Kenai (fig. 8) were examined. The 

deposit described in this report is the only one considered to be of 

sufficient extent and purity to be of possible economic interest. This 

deposit is 10% miles north of Kenai in sec. 21, T. 7 N., R. 12 W. 

Anchorage, the largest city in Alaska, is 65 miles to the northeast by 

sea and 172 miles by an all-weather road.

The climate of the Kenai area is characterized by cool summers 

and mild winters for the latitude. The table (p. 27) compiled from 

the records of the U. S. Weather Bureau shows average monthly 

temperatures at Kenai over a period of 18 years and average monthly 

precipitation for a period of 22 years.

Since the beginning of World War II, Alaska has experienced a 

construction boom, so that today the value of the construction 

industry in Alaska now outranks both mining and fishing. However, 

all of the raw materials for construction, other than natural aggregates 

and some lumber, are imported, with attendant increased costs of

367124 66 25
26 INVESTIGATIONS OF CONSTRUCTION MATERIALS IN ALASKA

DEPOSIT CONSIDERED 

IN THIS REPORT

 r-f i -} h i 

FIGUEE 8. Index map of the Kenai area showing location of diatomaceous earth deposits.

freight and handling charges. In view of the rigorous climate in most 

of Alaska, it is particularly desirable to develop sources of lightweight 

and insulative building materials such as diatomaceous earth, haydite, 

perlite, and pumice. These materials not only serve as thermal 

insulation, but, because of their relatively light weight, also reduce 

the amount of costly framing required for large structures.
OCCURRENCE OF DIATOMACEOUS EARTH NEAR KENAI

Month

January. _ 

February ______________________ ___..__ ___ _ _ _ __

March. ___ _____ __ __________________

April ______

May _________ _ ____ _ _ __ _________ __ _______

June __ ____________ _____ _ __ _ _ __ _

July ______________________ _ _______

August- ___ _ __ _ . _ _ __ ___ . _

September- _ ____ _

October. __ __________________________

November ___________________________

December. _ ______ _ _________________

Yearly average 

Temperature 

(degrees

11.5

17.4

23.7

32.5

, 43.3

49.4

53.6

53.3

46.3

34.5

21.2

13.2

33.3

Precipitation 

(inches)

0.77

.78

.86

.78

.80

.76

2.22

3.10

3.17

2.08

1.62

1.07

18.01

The deposits shown in figure 8 were described briefly in an unpublished administrative report by Thor N. V. Karlstrom of the U. S. 

Geological Survey in November 1951. The present investigation was 

made between July 26 and August 9, 1952, during which time all the 

deposits shown in figure 8 were mapped and sampled. The largest 

deposit was mapped in detail (see pi. 3) by planetable (scale 1:2,400; 

contour interval 10 feet). Twenty sections, clearly exposed along the 

sea cliff, were examined and measured. In addition, 25 hand-auger 

holes shown in plate 3 were drilled throughout the deposit to determine the thickness of the diatomaceous earth.

The author wishes to thank Mr. Ted Meining of Kenai for the 

many courtesies extended during the course of field work, and Dr. 

G. Dallas Hanna of the California Academy of Sciences, who identified 

the diatoms occurring in the deposit.

GEOLOGY

The diatomaceous earth is the youngest deposit in a sequence of 

postglacial lacustrine sediments with a maximum aggregate thickness 

of 18 feet. These sediments were deposited on the surface of a 

glacial outwash plain in one or more small lakes that were subsequently drained and are now exposed in cross section in the sea cliff 

along the east shore of Cook Inlet.

GLACIOFLUVIAL OUTWASH

The entire area shown in figure 8 is underlain by glacial outwash 

of unknown thickness. Maximum local relief on the surface of the 

outwash is 75 feet, with numerous shallow depressions occupied by 

lakes and peat bogs. The outwash is generally well stratified, consisting predominantly of tan to brown subrounded pebble to cobble 

gravel in a silty sand matrix. Where the outwash is close to the
28 INVESTIGATIONS OF CONSTRUCTION MATERIALS IN ALASKA

surface in this area, it characteristically supports a moderately dense 

growth of brush and trees (pi. 4A).

OLDER LAKE SEDIMENTS

Deposited on the glacial outwash is a sequence of fine-grained dark 

thinly laminated clay, silt, and sand as much as 13 feet thick (pi. 4.5). 

The older lake sediments consist predominantly of brown or gray to 

black silt, clayey silt, and sandy silt containing a considerable amount 

of organic matter. Interstratified with, and grading into the silty 

sediments, are subordinate amounts of very fine- to medium-grained 

brown sand or pebbly sand and minor dark-brown clay. Individual 

units average less than 6 inches in thickness and are not persistent 

laterally. Where the poorly drained older lake sediments are exposed 

at the surface, they support a sparse growth of trees.

DIATOMACEOUS EARTH

A surficial layer of diatomaceous earth mantles the older lake 

sediments as shown in plate 4B. The thickness of this deposit is 

extremely variable owing to the irregular configuration of the lake 

floor on which the diatoms were deposited and to stripping after the 

lake was drained and exposed to erosion. Throughout most of the 

deposit the diatomaceous earth averages between 2 and 6 feet in 

thickness and, near the southern margin of the deposit, attains a 

maximum thickness of 12 feet. The contact of the diatomaceous 

earth with the underlying sediments is abrupt with only local 

perceptible downward gradation into the older lake sediments.

Except for a thin veneer of air-dried material exposed along the 

sea cliff, the diatomaceous earth is saturated with as much as 1% 

times its weight of water. When wet, the diatomaceous earth is 

mottled drab brown to green, fetid in odor, and jellylike in consistency. In contrast, the dried material is massive, very light weight, 

chalk white to light buff, and friable. Although the diatomaceous 

earth is extremely homogeneous in appearance and composition, a 

faint varvelike banding is locally discernible in moist samples.

Between 65 and 75 percent by weight of the dried diatomaceous 

earth consists of Recent fresh-water diatom tests ranging hi size from 

0.023 to 0.004 millimeter (plate 5, 6). Genera identified in the 

deposit are given below.

Abundant forms:

Stephanodiscus

Melosira

Cymbella

Less abundant forms: 

Fragillaria 

Navicula 

Pinnularia 

Gomphonema 

Bpithemia 

Tetracyclus 

. Cydotella 

Synedra
GEOLOGICAL SURVEY BULLETIN 1039 PLATE 4

A. VIEW LOOKING NORTH FROM NEAR SOUTH END OF MEADOW UNDERLAIN BY

DIATOMACEOUS EARTH. 

Trees in background mark approximate contact of diatomaceous earth with glaciofluvial outwash.

B. VIEW OF ROAD CUT IN SEA CLIFF.

Outcrop shows 12 feet of diatomaceous earth (d) underlain by 3 feet of older lake deposits (c) and 

glaciofluvial outwash (e). The base of the cliff is covered with talus (t).
GEOLOGICAL PURVEY BULLETIN 1039 PLATE 5

X475 .,-- X'47'6

' >U7S

X475 X475

PHOTOMICROGRAPHS OF DIATOMS FROM DIATOMACEOUS EARTH DEPOSIT NEAR

KENAI, ALASKA.
GEOLOGICAL SURVEY BULLETIN 1039 PLATE 6

X475 X4?§

> r

r X 220

/

X 220 220

PHOTOMICROGRAPHS OF DIATOMS FROM DIATOMACEOUS EARTH DEPOSIT NEAR

KENAI, ALASKA.

OCCURRENCE OF DIATOMACEOUS EARTH NEAR KENAI 29

The remainder of the diatpmaceous earth is composed of about 13 

percent organic matter, minor amounts of siliceous sponge spicules 

about 0.3 millimeter long, and from 10 to 20 percent wind-deposited 

silt and clay less than 0.025 millimeter maximum diameter. The 

chemical composition of a representative sample of diatomaceous 

earth analyzed by the Bureau of Mines is given below.

Composition Pereeid

Si02 _ _______________________.____--_____ ___ -__-_ _ 71.02

A12O3 ________________________________________ 6.96

Fe2O8 --______________________________________ 3.84

TiO2 __________________________________________________________ .37

Others. ____________________________________ 4. 14

Ignition loss___________ _____________________________________ 13. 69

Total____--___________.._____-_____________________ -__- 100.02

Areas underlain by diatomaceous earth are mantled by hummocky 

mounds of weeds and grasses (pi. 4A). Within the root zone, which 

is generally less than 2 feet thick, the diatomaceous earth is stained 

to a yellowish-orange color owing to oxidation of iron contained in 

the impurities.

TALUS AND BEACH DEPOSITS

All but the highest section of the steep sea cliff shown in plate 3 

is mantled with loose outwash gravel and blocks of lake sediments 

that have slumped from the cliff (see pi. 45). The beach deposits 

and road fill consist of loose, rounded sand and gravel derived from 

the glacial outwash.

ORIGIN OF THE DIATOMACEOUS EARTH

According to carbon-14 dating by Karlstrom (PeVe1 and others, 

1953) the outwash underlying this area was deposited between 8,000 

and 14,000 years ago during the Naptowne glaciation by meltwater 

streams from a glacier whose southern margin was about 6 miles 

north of the diatomaceous earth deposit. The depression in which 

the diatomaceous earth occurs was probably formed by melting away 

of a mass of ice that was buried or partly buried in outwash. Subsequently, the depression was filled with water; and the older lake 

deposits, consisting of laminated clay, silt, and sand that underlie the 

diatomaceous earth, were carried into the lake by streams and to a 

lesser extent by wind. After accumulation of as much as 13 feet of 

older lake sediments, deposition abruptly ceased, and the lake water 

cleared. The accumulation of diatoms followed and continued without interruption until the sea cliff along Cook Inlet cut into and 

drained the lake, leaving the deposit exposed as we see it now.

It is unlikely that "normal" geologic processes such as retreat of 

the glacier to the north or postglacial uplift and warping could have
30 INVESTIGATIONS OF CONSTRUCTION MATERIALS IN ALASKA

been responsible for the abrupt change in conditions that cut off 

the supply of clastic sediments and favored relatively pure accumulation of diatoms. More probably the change in environment was 

related to the presence of a beaver dam that now blocks the old intake 

near the east side of this deposit (pi. 3) and to other beaver-dammed 

streams in this area. Construction of a beaver dam upstream from the 

former lake provided a settling basin in which all but the very finest 

particles were deposited, thereby cutting off the supply of clastic 

sediments to down stream areas. The resulting clear lake water was 

an ideal environment for diatoms to accumulate in vast numbers owing 

to the following factors: (1) A plentiful supply of silica (the basic 

constituent of the potential sediments), mainly in the form of finely 

divided siliceous rock flour from the surrounding glacial deposits and 

possibly in part from the wind-deposited volcanic ash derived from 

the chain of active volcanoes to the west and southwest; (2) low 

temperature, which inhibits bacterial activity and increases the capacity of water to absorb both oxygen and carbon dioxide, thereby 

favoring diatom growth; (3) adequate illumination, which is essential 

for the growth of these plants (Conger, 1942). The above conditions 

must have been rigidly maintained over a considerable period of time 

for the minute diatoms to have accumulated to the extent shown in 

this deposit.

Undoubtedly similar environmental conditions prevailed hi some of 

the numerous inland lakes in this same general area, and it is highly 

probable that prospecting might uncover additional deposits of 

diatomaceous earth.

FACTORS AFFECTING DEVELOPMENT

Diatom tests consist of hydrous silicon dioxide containing between 

96 and 97 percent of SiO2 and between 3 and 4 percent of combined 

water, which can be driven off at temperatures between 500° and 800° 

C. Melting point of the silica is over 1,400° C. The diatom skeletons 

are chemically stable, being soluble only in hydrofluoric acid and 

caustic alkalies.

The silica of diatoms has a true specific gravity about the same 

as opal, or 2.1 to 2.2. Individual tests are extremely porous, however, 

so the apparent density of solid dried diatomaceous earth ranges from 

0.4 to 0.5, and the apparent density of loose, powdered material is 

between 0.12 and 0.23.

From the physical and chemical properties, it is apparent that the 

distinguishing characteristics of a material consisting largely of 

diatom tests are high porosity, low apparent density, chemical inertness, and stability over a wide range of temperatures. It is suitable, 

therefore, for use as a filter media, filler, and as an insulative and build-
OCCURRENCE OF DIATOMACEOTJS EARTH NEAR KENAI 31

ing material. Minor amounts of diatomaceous earth are also used in, 

the chemical, abrasives, fertilizer, and many other industries,

The diatomaceous earth in this deposit would probably be suitable 

for use as an insulator and construction material but is not sufficiently 

pure for most of the other uges enumerated above.

For additional information on the uses and processing of diatomaceous earth the reader is referred to Bowles, 1943; EardleyWilmot, 1928; Friberg, 1953; and Mielenz, 1950.

The diatomaceous earth could be readily excavated by employing 

bulldozers, powef shovels, or scrapers. Only a thin mat of vegetation 

must be removed to expose the deposit. Quarrying operations woulcl, 

probably be hampered during winter by subfreezing temperatures 

and snowfall. The material could be loaded directly on barges at the 

beach during periods of favorable tides and weather or trucked to 

Kenai where docking facilities are available.

A minimum calculated volume of diatomaceous earth in this deposit, based on the exposed section along the sea cliff and on the auger 

holes, is 210,000 cubic yards. Using the average apparent specific 

gravity of 0.4, the solid dried material weighs 25 pounds per cubic 

foot, or 0.337 ton per cubic yard. The minimum calculated reserves 

based on these figures would be about 70,000 tons of solid dried 

diatomaceous earth.

LITERATURE CITED

Bowles, Oliver, 1943, Industrial insulation with mineral products: TL S. Bureau 

Mines Inf. Circ. 7263.

Conger, P. S., 1942, Accumulation of diatomaceous deposits: Jour. Sed. Petrology, 

v. 12, no. 2.

Eardley-Wilmot, V. L., 1928, Diatomite, its occurrence, preparation, and uses 1. 

Canada Dept. Mines, Mines Branch Pub. 691, 150 p.

Friberg, W. R., 1953, Woodfibre diatomite concrete: Idaho Univ., Coll. Agriculture Ext. Bull. 179.

Mielenz, R. C., 1950, Materials for pozzolan: U. S. Bur. Reclamation Petrog, 

Rept. 90B.

P6w6, T. L., and others, 1953, Multiple glaciation in Alaska: U. S. Geol. Survey 

Circ. 289.

United States Weather Bureau, 1952, Annual Summary, 1950.

o