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Cover design by Nancy Polend, 1991
Introduction:

Enewetak Atoll

and the PEACE Program

By THOMAS W. HENRY and BRUCE R. WARDLAW

GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL, 

REPUBLIC OF THE MARSHALL ISLANDS

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1513-A

A compilation of studies originating from the 

Pacific Enewetak Atoll Crater Exploration 

(PEACE) Program, prepared in cooperation 

with the Defense Nuclear Agency

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1990
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government

Library of Congress Cataloging in Publication Data

Introduction : Enewetak Atoll and the PEACE Program / Thomas W. Henry and Bruce R. Wardlaw.

p. cm. (Geologic and geophysical investigations of Enewetak Atoll, Republic of the Marshall Islands ; ch. A) (U.S. Geological

Survey professional paper ; 1513-A) 

"A compilation of studies originating from the Pacific Enewetak Atoll Crater Exploration (PEACE) Program, prepared in

cooperation with the Defense Nuclear Agency." 

Includes bibliographical references. 

Supt.ofDocs.no.: I 19.16: 1513-A 

1. Geology Marshall Islands Enewetak Atoll. 2. Geophysics Marshall Islands Enewetak Atoll. 3. Pacific Enewetak

Atoll Crater Exploration Program. I. Henry, Thomas W. II. Wardlaw, Bruce R. III. Pacific Enewetak Atoll Crater

Exploration Program. IV. Title: Introduction: Enewetak Atoll and the PEACE Program. V. Series. VI. Series: U.S.

Geological Survey professional paper ; 1513A.

QE349.M35I58 1990 90^3314 

559.68'3-dc20 CIP

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
CONTENTS

	Page

Abstract............................................................................ Al

General Remarks................................................................ 1

Basic Problem.................................................................... 3

Pacific Proving Grounds and Enewetak Nuclear Testing ........... 5

Objectives of PEACE Program............................................. 5

Roles, Data Bases, and Data Acquisition................................ 5

Pre-PEACE Program Data Bases ................................... 7

Preparatory Onsite Work............................................... 8

Marine Phase of PEACE Program .................................. 8

Drilling Phase of PEACE Program.................................. 10

PEACE Program Reports.................................................... 10

Current Series of Papers ..................................................... 12

Acknowledgments............................................................... 12

Location and Setting........................................................... 16

Previous Geologic Investigations........................................... A16

Studies from 1946 to 1952 .............................................. 16

First Atoll Boreholes..................................................... 17

AEC-LASL Drilling Program (1950-1951)........................ 18

USGS-AEC Drilling Program (1951-1952)......................... 18

Interim Period (1952-1970)............................................. 21

Air Force Weapons Laboratory Studies (1970-1981)........... 21

PACE Program (1970-1972)..................................... 21

EXPOE Program (1973-1974)................................... 21

EASI Program (1979-1981)...................................... 24

Interim Events (1981-1984) Leading to PEACE

Program................................................................ 25

References Cited................................................................ 25

ILLUSTRATIONS

FIGURE 1. Index and geographic maps of the Republic of the Marshall Islands.......................................................................... A2

2. Map of Enewetak Atoll, Republic of the Marshall Islands....................................................................................... 3

3. Graph showing dimensions of explosion and impact craters ..................................................................................... 4

4. Map showing sites of detonations on Enewetak Atoll............................................................................................. 7

5, 6. Photographs of:

5. DOE research vessel Egabrag II and MARFAB, Inc's, two-man submersible Delta ....................................... 9

6. 237-foot-long drill ship Knut Constructor........ ......................................................................................... 11

7. Maps of KOA and OAK crater areas showing borehole sites and general bathymetric contours..................................... 12

8. Photograph of drill ship H.M.S. Porpoise............................................................................................................. 17

9, 10. Maps of Enewetak Atoll showing locations of:

9. AEC-LASL (1950-1951) boreholes.......................................................................................................... 18

10. USGS-AEC (1951-1952) deep boreholes .................................................................................................. 19

11. Chart showing correlation of USGS-AEC deep boreholes drilled on Enewetak and Bikini Atolls ................................... 20

12, 13. Maps of Enewetak Atoll showing locations of:

12. PACE Program (1970-1972) boreholes .................................................................................................... 22

13. EXPOE Program (1973-1974) boreholes.................................................................................................. 23

14. Subsurface geologic cross section of Enjebi Island................................................................................................. 24

TABLES

TABLE 1. Dates and locations of nuclear detonations on Enewetak Atoll........................................................................................ A6

2. Downhole geophysical logs from PEACE Program drilling ............................................................................................ 13

3. Summary of PEACE Program borehole data from KOA and OAK craters ....................................................................... 14

4. Summary of reports from the PEACE Program .......................................................................................................... 15
IV CONTENTS

METRIC CONVERSION FACTORS

For readers who wish to convert measurements from the inch-pound system of units to the metric 

system of units, the conversion factors are listed below:

Multiply inch-pound units By To obtain metric units

foot (ft) 

nautical mile (nmi)1 

nautical mile2 (nmi2) 1

0.3048 

1.852 

3.430

meter (m) 

kilometer (km) 

kilometer2 (km2)

1U.S. nautical mile.

ALTITUDE DATUM

Sea level: The term "sea level" generally refers to the National Geodetic Vertical Datum of 1929 

(NGVD of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of 

both the United States and Canada, formerly called Sea Level Datum of 1929. The tidal datum used 

in this report was established in 1952 during Operation IVY jointly by the U.S. Coast and Geodetic 

Survey and Holmes and Narver, Inc. (H&N). The datum used is 0.5 ft below the mean-lowwater-spring-tide level (MLWS), which is the datum used on the navigation charts of Enewetak Atoll 

produced by the U.S. Navy Hydrographic Office. Individual tidal datums for several of the northern 

islands were established in 1951 and 1952 by Holmes and Narver. These datums are 0.5 ft below 

approximate-mean-low-water-spring tide (AMLWS). In this report, "sea level" refers to the AMLWS 

datum of 1951-52, also called the H&N datum.
GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL, 

REPUBLIC OF THE MARSHALL ISLANDS

INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM

By THOMAS W. HENRY and BRUCE R. WARDLAW

ABSTRACT

An extensive study was made from June 1984 through August 1985 

of the surface and subsurface configurations of two large nuclear 

craters on the northern side of Enewetak Atoll, Republic of the 

Marshall Islands. These craters, KOA and OAK, resulted from the 

near-surface detonation of two high-yield thermonuclear devices in 

1958, when the atoll was part of the Pacific Proving Grounds. This 

multidisciplinary study was designed to produce a broad, welldocumented geologic, geophysical, and materials-properties data base 

for use in answering critical questions concerning craters formed by 

high-yield bursts. The study was part of a larger research initiative by 

the U.S. Department of Defense to better understand high-yield, 

strategic-scale nuclear bursts and how Pacific Proving Grounds craters 

relate to the basing and targeting of nuclear-weapon systems and 

related national defense issues.

The data gathered during the study of the Enewetak craters are 

applicable to many scientific topics well beyond cratering mechanics 

and other related strategic concerns of the Department of Defense. 

These scientific topics include the geologic evolution of the Pacific 

Basin, the biologic and geologic history of a coral atoll, the fluctuation 

of sea level in response to glaciation and deglaciation, the diagenetic 

history of carbonate rocks in relation to sea-level changes and the 

differing substrate-water geochemistries thus produced, the speciation 

and migration of marine biotas, and the biostratigraphic succession of 

biotas through time and the calibration of these events with an absolute 

isotopic time scale, to name a few. The objective of this U.S. Geological 

Survey Professional Paper series is to provide a forum for these 

studies.

GENERAL REMARKS

From mid-1984 through mid-1985, the U.S. Geological 

Survey (USGS) conducted geologic and geophysical 

investigations of two craters formed by the detonation of 

high-yield, near-surface nuclear devices at Enewetak 

Atoll in the Marshall Islands (figs. 1, 2). These investigations are collectively referred to as the Pacific 

Enewetak Atoll Crater Exploration (PEACE) Program. 

The craters studied, KOA and OAK, resulted from 1.4-

Manuscript approved for publication February 27, 1990.

and 8.9-megaton (Mt)-yield detonations on May 12 and 

June 28, 1958, respectively, near the northern perimeter 

of Enewetak lagoon. At that time, Enewetak was administered by the U.S. Government through the Trust 

Territories of the Pacific Islands and was part of the 

Pacific Proving Grounds (PPG), where, on remote atolls 

and islands from 1946 through 1962, atmospheric nuclear 

testing was carried out. KOA and OAK are among the 

few craters produced by high-yield, near-surface bursts 

that are available for study.

Few sedimentary geologic environments are more 

heterogeneous than a coral atoll. An analogy between a 

Pacific atoll and an inverted bucket filled with sediment 

is appropriate. The reef facies is the hard, competent, 

cemented exterior formed by an organic framework 

dominated by coralline algae and corals. The backreef 

environment, where the islands are generally located, 

consists of a spectrum of carbonate materials ranging 

from uncemented to well cemented. Here, a group of 

generally inorganic (marine) processes acts to cement 

the sediment in selected areas to form what generally is 

referred to as "beachrock." Thus, the reef and backreef 

environments are the hard rim of the bucket. The bucket 

is filled with finer grained, lagoonal sediment that generally is much less cemented or uncemented and consequently is less competent than the rim. Also scattered 

throughout the lagoon of any atoll the size of Enewetak 

are numerous patch or pinnacle reefs. These lagoonal 

reefs are structurally competent edifices. However, 

within the material inside the bucket (that is dominated 

by the finer grained sediment) are layers that have been 

more or less cemented by postdepositional nonmarine 

(ground water) geochemical processes during periods of 

atoll emergence. These periods of emergence were 

believed to have resulted from global lowstands of sea 

level during glacial periods. These cemented layers 

extend some distance inward toward the middle of the

Al
A2 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

140° 180° 140°

V

MARSHALL ISLANDS i HAWAII

INDEX MAP

160° 164° 168° 172°

16'

12'

50 100 150 200 250 300 NAUTICAL MILES

J____I____I____I____I____I

I I I I I I I

0 50 100 150 200 250 300 KILOMETERS

PACIFIC OCEAN

_ ,.-." . Enewetak Atoll Bikini Atoll

.-Toangi Atoll

REPUBLIC OF THE 

MARSHALL ISLANDS

~"~

\

z~. Ujelang Atoll

\ 

\

+ +

-: .--.x.Kwajalein 

^ -^ Atoll

%

\^

\

FEDERATED STATES 

OF MICRONESIA

Kosrae

\

Majuro .- 

Atoll ~'^^

 ~i

REPUBLIC 

OF NAURU

GILBERT ISLANDS 

(UK)

Makin 

Atoll

FIGURE 1. Index map showing location of the Marshall Islands in the Pacific Ocean and geographic map of the Republic of the Marshall Islands.
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A3

162° 162°101

Teiteiripucchi (GENE)

Elugelab (FLORA) 

Bokinwotme (EDNA)

Louj (DAISY) 

Kirunu (CLARA) 

Bokombako (BELLE) 

Bokoluo (ALICE)

162°20'

 I 

162°30'

H°40'

Boken (IRENE)

Enjebi (JANET)

Mijikadrek (KATE)

Kidrinen (LUCY)

Bokeneiab (MARY) 

Elle (NANCY)

Aej (OLIVE)

Lujor (PEARL)

Eleleron (RUBY) 

Aomon (SALLY) 

Bijile (TILDA) 

Lojwa (URSULA) 

-Alerrbel (VERA) 

Billae (WILMA)

Runit (YVONNE)

11 "SO1

IVY /*" 

GRID' 

(FT)

160000

PREVAILING WIND

+ 120000

"M- (ZONA)

Biken (LEROY)

nedrol (ALVIN)

+ 80000

Anaij (BRUCE)

dimini (CLYDE) 

 Japtan (DAVID)

EAST (DEEP) CHANNEL 

Medren (ELMER)

+ 40000

Kidrenen (KEITH) 

Ribewon (JAMES)

Boken (IRWIN)

Mut (HENRY) 

Ikuren (GLENN)

Enewetak (FRED)

5 NAUTICAL MILES 0 10,000

l.lllllllll

30,000 50,000 FEET 0

i I

10 KILOMETERS

FIGURE 2. Enewetak Atoll, Republic of the Marshall Islands, with locations of principal islands and other features (native names followed by 

military site names in parentheses), OAK, KOA, and MIKE craters, and MACK and OSCAR pinnacles. Jieroru is a small sand island inside 

the East Channel that was not given a site name. Magnetic declination (1948) shown in compass.

lagoon. This was the environment in which many of the 

high-yield, near-surface PPG nuclear bursts were detonated.

BASIC PROBLEM

Prior to the PEACE Program, the craters formed 

from near-surface bursts in the PPG were thought to 

differ in several critical ways from craters produced by

both high-explosive and low-yield nuclear bursts in dry 

test beds at the Nevada Test Site1 or, for that matter, 

elsewhere. The craters produced by high-yield bursts in 

the PPG were all formed in wet carbonate substrates. 

They have saucer-shaped apparent-crater profiles that 

are extraordinarily broad and shallow. The apparent

lrThese are generally referred to as continental United States (CONUS) sites.
A4 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

10°

1 fl10 :

10*

Pacific Proving Grounds craters

EXPLANATION

NE HE

x + Dry soil

* A Soft rock

v v Hard rock

4 0 Wet soil/wet soft rock

IMPACT CRATERS 

n Moon

 Mercury

* Terrestrial

10' 10 : 10- 10 1 10° 101 102

DIAMETER (km) 

FIGURE 3. Dimensions of explosion and impact craters (from Cooper, 1977). NE, nuclear explosive; HE, high-yield explosive.

103

craters2 resulting from these high-yield PPG bursts have 

high aspect ratios3 and, consequently, large volumes. 

The data base for PPG craters was extremely small and, 

because of the remoteness of the PPG and political 

considerations, difficult to augment. In contrast, the 

CONUS craters, for which a large data base was easily 

obtained and easily expanded, have bowl-shaped 

apparent-crater profiles that are small and proportionally deeper. These apparent craters have low aspect 

ratios and proportionally small volumes. In this sense, 

the CONUS craters are more similar to some impact 

(meteor) craters than to the PPG craters (see fig. 3).

Research in the PPG undertaken in the 1970's, principally by the Defense Nuclear Agency (DNA), suggested 

that geologic and hydrologic environments influence latetime cratering processes and, therefore, play a funda2Apparent crater is the locus of the zero-difference contour line surrounding a 

crater that is, the locus of points along which the effects of an explosion can no 

longer be detected when the preevent contours are compared with the postevent 

contours (B.L. Ristvet, pers. commun., 1986).

3Aspect ratio is the ratio of crater depth to radius; the PPG craters typically 

have aspect ratios of about 3:5, CONUS craters, 1:2.

mental role in determining the final morphology and size 

of a crater (Knowles and Erode, 1977; Ristvet and 

others, 1978; Erode, 1979). To quote Cooper (1977, p. 

20), "In general, the variation in cratering efficiency 

appears to correlate with media strength, i.e., the 

weaker the medium, the larger the crater." It was 

suggested that processes operating in response to the 

water-saturated, "weak" geologic substrates were 

responsible for significant "late-stage" modifications of 

the PPG craters and that the aspect ratios of the 

excavational craters (not the final apparent craters) 

resulting from PPG high-yield bursts were in fact much 

closer to aspect ratios predicted by first principle calculations and to aspect ratios at CONUS sites.

Computational models capable of simulating a wide 

variety of phenomena associated with high-explosive and 

low-yield nuclear bursts were available by the late 

1970's. However, to summarize, the PPG craters (as 

observed and measured) formed by high-yield bursts and 

scaled to their CONUS counterparts were anomalous in 

shape and volume and could not be modeled confidently 

(Cooper, 1977; Knowles and Erode, 1977). The marked 

difference in crater volume between the predictions from
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A5

modeling and observations of existing PPG craters a 

difference in the realm of an order of magnitude and the 

lack of confidence in the fundamental data base itself 

resulted in considerable uncertainty about the Defense 

community's ability to predict the effectiveness of 

nuclear weapons against targets and the attendant capability of strategic installations to functionally survive a 

nuclear burst. Of particular concern were hardened, 

underground installations.

PACIFIC PROVING GROUNDS AND 

ENEWETAK NUCLEAR TESTING

The U.S. Government conducted atmospheric nuclear 

tests in the Pacific from 1946 through 1962, before the 

Limited Test-Ban Treaty of 1963 mandated that all 

further testing of nuclear weapons be conducted 

underground4 . Enewetak and Bikini Atolls together constituted the western part of the PPG, which was created 

in 1948. The PPG, Amchitka in the Aleutian Islands, and 

Pahute Mesa on the Nevada Test Site were the only sites 

where the U.S. Government tested megaton-range 

nuclear devices. After the residents of Enewetak and 

Bikini Atolls were moved to nearby atolls, nuclear shots 

were conducted from 1946 through 1958 26 on Bikini 

Atoll and 43 on or in the vicinity of Enewetak Atoll 

(Hines, 1962; Defense Nuclear Agency, 1981; Bliss, 

1982). On October 31, 1958, the United States and the 

Soviet Union began a joint moratorium on atmospheric 

testing of nuclear weapons. In fall 1961, however, the 

Soviets resumed atmospheric nuclear testing. The 

United States responded in 1962 with a series of 34 

nuclear tests in the vicinity of Johnston Atoll and Christmas Island in the central Pacific and 4 low-yield tests at 

the Nevada Test Site.

The first PPG nuclear tests were conducted on Bikini 

Atoll in 1946 during Operation CROSSROADS. The first 

nuclear test on Enewetak Atoll was on April 14, 1948, as 

part of Operation SANDSTONE, a three-shot program 

staged from 200-foot (ft)-tall, island-based towers. The 

tests on Enewetak were primarily weapons related, 

although attempts were made to understand explosion 

phenomena and the blast effects on various types of 

manmade structures. Additional studies were conducted 

to measure biologic exposure and responses, to evaluate 

detection instruments, to compare nuclear-yield determinations, and so forth (Bliss, 1982, p. 1).

Table 1 lists the nuclear tests conducted on Enewetak 

Atoll. All but three of the Enewetak detonations 

occurred on or in the vicinity of the northeastern band of 

islands on the atoll (fig. 4).

4The Limited Test-Ban Treaty did allow near-surface nuclear explosions for 

peaceful purposes, such as excavations for harbors and canals.

OBJECTIVES OF PEACE PROGRAM

The PEACE Program was a broad research initiative 

formulated by the DNA for the U.S. Department of 

Defense (DOD) to answer a number of key questions 

about the dynamic properties of strategic-scale nuclear 

bursts and the relevance of the large craters of the PPG 

to strategic issues. The multidisciplinary study of KOA 

and OAK craters conducted by the USGS on Enewetak 

was part of the PEACE Program. These two craters 

were selected because of their accessibility and their 

differing source characteristics (see section on "Interim 

Events (1981-1984) Leading to PEACE Program").

The specific objectives of the DOD for the USGS 

portion of the PEACE Program were (1) formulation of 

a geologic and geophysical framework for the stratigraphic section (substrate or "test beds") in which the 

craters were formed, (2) identification and description of 

crater morphology, physiography, and structure, and 

measurement of the dimensions of primary crater features, (3) acquisition of new material-properties data 

from the PPG substrates, and (4) better understanding of 

the processes that both formed the excavational crater 

and altered that early-stage feature to the crater 

observed today (that is, the apparent crater). Establishment of a geologic framework in which to place the new 

PPG material-properties data was extremely important 

to the DNA for effective testing of computational modeling of a high-yield nuclear event (code validation). As 

stated simply by Cooper (1977, p. 14), the larger of two 

main sources of error in simulating high-yield nuclear 

events is the "state-of-ignorance of the dynamic response 

of geologic media."

ROLES, DATA BASES, AND DATA ACQUISITION

Enewetak Atoll lies in a geographically highly remote 

area. Successful operation of any large-scale research 

program in such an area requires careful thought and 

planning. Acquisition of data from Enewetak and the 

logistics were a collaborative effort between the USGS, 

the DNA, the U.S. Department of Energy (DOE), other 

Federal agencies, private contractors and research laboratories, personnel from several universities, officials of 

the newly formed Republic of the Marshall Islands 

(RMI), and the people of Enewetak.

The USGS conducted the geologic, paleontologic, and 

geophysical investigations of OAK and KOA and worked 

closely with DNA contractors on analysis of the downhole geophysical logging, on the borehole gravimetry, 

and on parts of the other material-properties studies. As 

originally planned, all field operations on Enewetak were 

to be conducted concurrently. However, the fieldwork 

later was divided into two major phases, the Marine
A6 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

TABLE 1. Dates and locations of nuclear detonations on Enewetak Atoll 

[ft, feet; kt, kiloton; Class., classified; Mt, megaton. 1 Mt = 1,000 kt]

Event 

name

X-RAY

YOKE

ZEBRA

DOG

EASY

GEORGE

ITEM

MIKE

KING

NECTAR

LACROSSE

YUMA

ERIE

SEMINOLE

BLACKFOOT

KICKAPOO

OSAGE

INCA

MOHAWK

APACHE

HURON

CACTUS

BUTTERNUT

KOA

WAHOO

HOLLY

YELLOWWOOD

MAGNOLIA

TOBACCO

ROSE

UMBRELLA

WALNUT

LINDEN

ELDER

OAK

SEQUOIA

DOGWOOD

SCAEVOLA

PISONIA

OLIVE

PINE

QUINCE

FIG

Date

1948

Apr. 14

Apr. 30

May 14

1951

Apr. 7

Apr. 20

May 8

May 24

1952

Oct. 31

Nov. 15

1954

May 13

1956

May 4

May 27

May 30

June 6

June 11

June 13

June 16

June 21

July 2

JulyS

July 21

1958

May 5

May 11

May 12

May 16

May 20

May 26

May 26

May 30

June 2

June 8

June 14

June 18

June 27

June 28

July 1

July 5

July 14

July 17

July 22

July 26

Aug. 6

Aug. 18

Burst type/ 

height

Tower, 200 ft

Tower, 200 ft

Tower, 200 ft

Tower, 300 ft

Tower, 300 ft

Tower, 200 ft

Tower, 200 ft

Surface

Airdrop, 1,500 ft

Barge

Surface

Tower, 200 ft

Tower, 300 ft

Surface

Tower, 200 ft

Tower, 300 ft

Airdrop

Tower, 200 ft

Tower, 300 ft

Barge

Barge

Surface

Barge

Surface

Underwater, 500 ft

Barge

Barge

Barge

Barge

Barge

Underwater3

Barge

Barge

Barge

Barge

LCU

LCU

Barge

Barge

LCU

Barge

Surface

Surface

Yield

37 kt

49 kt

18 kt

Class.

47 kt

Class.

Class.

210.4 Mt

500 kt

1.69 Mt

40 kt

Class.

Class.

13.7 kt

Class.

Class.

Class.

Class.

Class.

Class.

Class.

18 kt

Class.

2 1.37 Mt

Class.

Class.

Class.

Class.

Class.

Class.

Class.

Class.

Class.

Class.

28.9 Mt

Class.

Class.

Class.

Class.

Class.

Class.

Class.

Class.

General 

location1

JANET

SALLY

YVONNE

YVONNE

JANET

RUBY

JANET

FLORA

YVONNE

MIKE crater area

YVONNE, N. end

SALLY

YVONNE

IRENE

YVONNE

SALLY

YVONNE

PEARL

RUBY

MIKE crater area

MIKE crater area

YVONNE

SW. of YVONNE

GENE

HENRY, oceanside

SW. of YVONNE

SW. of JANET

SW. of YVONNE

SW. of JANET

SW. of YVONNE

N. of GLENN

SW. of JANET

SW. of YVONNE

SW. of JANET

SW. of ALICE

SW. of YVONNE

SW. of JANET

SW. of YVONNE

W. of YVONNE

SW. of JANET

SW. of JANET

YVONNE, middle

YVONNE, middle

IVY-grid coordinates

147,330 N.

130,907 N.

106,120 N.

106,178 N.

147,382 N.

130,947 N.

148,985 N.

147,754 N.

108,150 N.

147,750 N.

106,885 N.

130,603 N.

102,060 N.

149,897 N.

104,435 N.

132,295 N.

102,851 N.

133,540 N.

132,165 N.

148,063 N.

148,304 N.

106,370 N.

080,812 N.

149,360 N.

029,550 N.

101,834 N.

143,994 N.

101,344 N.

145,137 N.

080,811 N.

042,615 N.

143,996 N.

101,877 N.

145,136 N.

124,981 N.

101,871 N.

145,135 N.

102,638 N.

103,212 N.

145, 138 N.

142,549 N.

103,950 N.

103,950 N.

083,569 E.

111,993 E.

124,364 E.

124,318 E.

083,515 E.

111,929 E.

086,450 E.

067,789 E.

124,130 E.

067,790 E.

124,515 E.

112,155 E.

127,930 E.

075,237 E.

126,080 E.

114,018 E.

126,647 E.

105,300 E.

109,737 E.

069,227 E.

070,015 E.

124,215 E.

123,319 E.

071,120 E.

061,515 E.

124,943 E.

078,161 E.

124,161 E.

079,779 E.

123,315 E.

076,029 E.

078,168 E.

125,012 E.

079,790 E.

036,108 E.

125,000 E.

079,786 E.

126,227 E.

114,678 E.

079,790 E.

076, 110 E.

126,185 E.

126,185 E.

locations shown in figure 4.

2Thermonuclear device.

3Shot 5 ft off bottom in 150 ft of water.
162°

INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM 

162°10' 162°20'

A7

162°30'

rZEBRA

J DOG 

i] CACTUS 

ILACROSS

f BLACKFOOT 

J FIG 

] QUINCE

LOSAGE 

Runit (YVONNE)

YELLOWWOOD 

TOBACCO 

WALNUT

ELDER

DOGWOOD

OLIVE

PINE

(OSCAR)

HOLLY ~]

MAGNOLIA I

LINDEN f

SEQUOIA J

IVY 

GRID 

(FT)

/ 7

+ 160000

+ 120000

+ 80000

SOUTHWEST 

PASSAGE

EAST (DEEP) CHANNEL

+ 40000

WAHOO Enewetak (FRED)

5 NAUTICAL MILES 0 10,000

I.MlllMll

30,000 50,000 FEET 10 KILO METERS

FIGURE 4. Sites of detonations on Enewetak Atoll. Detonations having the same or approximately the same ground-zero location are grouped 

with brackets. Generally, large asterisks indicate thermonuclear bursts, and small asterisks nonthermonuclear nuclear detonations.

Phase and the Drilling Phase. The Marine Phase consisted of geophysical and geologic investigations of surface and subsurface characteristics of the two craters and 

environs. The Drilling Phase consisted of complementary 

geologic and geophysical assessments of borehole data.

PRE-PEACE PROGRAM DATA BASES

A wide array of pre-PEACE Program data from the 

PPG was reexamined during the USGS studies. Included 

were the following:
A8 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

1. Published accounts in the USGS Professional Paper 

260 series (Emery and others, 1954) from the initial 

geologic, geophysical, biologic, and oceanographic 

investigations in the Marshall Islands associated with 

the early phases of nuclear testing. Some of the 

original geologic samples and core were examined 

also.

2. Published reports and raw data from the geologic and 

geophysical studies of the PACE, EXPOE, and EASI 

Programs5, sponsored by the DNA and conducted on 

Enewetak by the Air Force Weapons Laboratory 

(AFWL) (Henny and others, 1974a, 1974b; Couch and 

others, 1975; Ristvet and others, 1978; Tremba and 

others, 1981; Tremba and others, 1982; Tremba, 

1987). Some of the multichannel seismic lines from 

EASI were reprocessed by Grow, Lee, and others 

(1986), and selected PACE/EXPOE boreholes were 

redescribed and analyzed petrographically, biostratigraphically, and isotopically before the Drilling Phase 

started (Cronin and others, 1986; Halley, Major, and 

others, 1986; Henry and others, 1986).

3. Other published scientific (biologic, geologic, oceanographic, radiologic) and general interest articles on 

Enewetak, the Marshall Islands, the PPG, and Pacific 

atolls. Included were the series of papers in the twovolume "The Natural History of Enewetak Atoll" 

edited by Devaney and others (1987) and released by 

the DOE.

4. Unpublished archival material from the PPG made 

available to USGS investigators by the DNA and the 

DOE. These data included pre- and postshot survey 

maps of the OAK and KOA crater areas, both blackand-white and color stereographic aerial photographs, 

other types of aerial photographs, and photographs 

made (both pre- and posttesting) from ground level of 

various crater features and manmade structures. Preand postshot maps of OAK crater prepared by Holmes 

and Narver, Inc., were digitized and form an essential 

part of the volumetric analysis for the PEACE Program (Peterson and Henny, 1987).

PREPARATORY ONSITE WORK

Navigational accuracy for locating point data for the 

PEACE Program was extremely important. The navigation network was controlled by five transponder stations placed on towers on the islands of Biken (LEROY), 

Bokoluo (ALICE), Enjebi (JANET), Lojwa (URSULA), 

and Enewetak (FRED) (fig. 2). Navigation specialists 

from Meridian Ocean Systems of Ventura, Calif., assemBPACE is an acronym for Pacific Atoll Cratering Experiments Program, 

EXPOE for Exploratory Program on Enewetak, and EASI for Enewetak Atoll 

Seismic Investigation Program.

bled the towers, set up the transponders, and tied them 

into the IVY-grid6 net using Motorola Satellite Navigation Systems in January 1984. The tie-in of these stations 

to the IVY-grid was verified by specialists from the 

Defense Mapping Agency by geodetic surveys using a 

laser theodolite (Woodworth and Crothers, 1985; Folger, 

1986a). Meridian Ocean Systems operated the Motorola 

Falcon-IV Miniranger system (accuracy about 10 ft) 

during both phases of the program.

In April 1984, just prior to the arrival of the main 

group of scientists and technicians for the Marine Phase, 

the USGS and the DNA conducted a successful pilot 

borehole-gravity study in an old, deep drill hole (E-l) on 

Medren (ELMER), one of the southern islands of the 

atoll (Beyer and others, 1986; Beyer, 1987).

MARINE PHASE OF PEACE PROGRAM

The Marine Phase (June 17 to September 20,1984) was 

carried out by USGS personnel principally from the 

Office of Energy and Marine Geology. It involved onsite 

observers from the DNA (and their contractors) and 

substantial logistic support from the Pacific Area Support Office of the DOE. Lists of key personnel and 

responsibilities and a detailed discussion of the Marine 

Phase are given in Folger (1986a).

Basically, this phase was designed to study both 

sea-floor and subbottom characteristics of KOA and 

OAK by using overwater geophysical techniques, scuba 

teams, and surveys from a submersible. Studied were (1) 

the bathymetry, physiography, and character and distribution of bottom or near-subsurface materials and (2) the 

depth, distribution, continuity, and disruption of acoustic 

reflectors in the craters and their proximity. Geophysical 

studies generated data from sidescan-sonar surveys, 

single- and multichannel seismic-reflection surveys, and 

a seismic-refraction survey of OAK. Geologic studies 

gathered data from sea-floor observations from the submersible and scuba operations, from six shallow (that is, 

less than 40 ft deep) boreholes drilled by the scuba 

teams, and from lagoonwide benthic sampling.

The primary support vessel for the Marine Phase was 

the DOE research vessel Egabrag II (fig. 5A), operated 

by U.S. Oceanography out of San Diego; the two-man 

submersible was MARFAB, Inc.'s, Delta (fig. 5.6), operating out of Los Angeles.

6The IVY-grid is a second- and third-order plane coordinate system based on 

true meridian and established for the PPG (Holmes and Narver, 1952) for 

operation IVY, a series of nuclear tests conducted in 1952 for the development of 

a hydrogen (thermonuclear) bomb. The origin of coordinates for Enewetak is a 

triangulation station with arbitrarily assigned values of North 100,000 ft and East 

100,000 ft.
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A9

A

B

FIGURE 5. A, DOE research vessel Egabrag II (photographed by authors, June 1985); B, MARFAB, Inc.'s, two-man 

submersible Delta (photograph courtesy of B.L. Ristvet, Defense Nuclear Agency).
A10 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

DRILLING PHASE OF PEACE PROGRAM

The Drilling Phase had three primary field objectives: 

(1) to acquire samples of rock and sediment in as undisturbed condition as possible for geologic studies of the 

litho- and biostratigraphic framework and for materialproperties studies of soil and (or) rock mechanics; (2) to 

conduct downhole geophysical logging for additional geologic, material-properties, and radiologic information on 

the two craters; and (3) to verify and complete the 

description and identification of the major crater features 

and dimensions begun during the Marine Phase.

Detailed discussion of the Drilling Phase (January 14 

through July 25, 1985), including lists of personnel, 

tours, and duties, is given in Henry, Wardlaw, and 

others (1986) and in U.S. Department of Energy (1985). 

Fieldwork was a cooperative effort between three Federal agencies, the USGS, the DNA, and the DOE. The 

drill ship was the North-Sea class Knut Constructor, 

owned by Knutsen O.A.S. Shipping and based out of 

Singapore (figs. 6A, 6B).

The chief scientists and onsite program managers for 

the Drilling Phase were from the DNA, which also 

provided experts in downhole geophysical logging, material properties, and gravimetry.

Logistic and technical support from the DOE was 

through the Pacific Area Support Office of the Nevada 

Operations Office (U.S. Department of Energy, 1985). 

Through DOE's contractors, Holmes and Narver (H&N) 

and Fenix and Sisson, the drilling, downhole geophysical 

logging, borehole gravimetry, navigation, submersible, 

and communications were subcontracted. The DOE also 

arranged the radiologic monitoring, supply and resupply, 

personnel transportation, and core and sample shipment 

stateside.

The role of the USGS during the Drilling Phase was 

essentially geologic, and most of the USGS personnel, 

including the chief geologists, were from the Office of 

Regional Geology. The USGS was solely responsible for 

stratigraphic analysis of the borehole data, including 

description and paleontologic studies of the core and 

samples, and was jointly responsible with the DNA for 

interpretation of the downhole geophysical logging and 

the borehole gravimetry. The USGS assisted the DNA in 

development of the initial drilling plan and worked with 

both the DNA and the DOE in constant onsite modification of that plan, including placement of boreholes, 

geologic and material-properties sampling, downhole 

geophysical logging, and borehole gravimetry.

Thirty-two boreholes were drilled overwater in the 

northern part of the lagoon (fig. 2) from the Knut 

Constructor (fig. 6). These consisted of 27 geologic, 4 

material-properties, and 1 cone-penetrometer borehole. 

Eight boreholes were in the KOA area (fig. 7'A), the rest

in the OAK area (fig. IE). Borehole penetrations below 

the sea floor ranged from 41 to 1,605 ft, and the composite linear footage was 14,189 ft. The deepest borehole 

(the OAK crater ground-zero borehole, OBZ-4), drilled 

in the deepest water (slightly in excess of 200 ft), 

penetrated lower Miocene strata. In addition to the 

integrated suite of conventional geophysical logs that 

was run (table 2), shallow, borehole-gravity surveys 

were done in selected boreholes on the southwestern 

transect of OAK crater (Beyer and others, 1986; Beyer, 

1987). Tables 2 and 3 present technical details of the 

Drilling Phase boreholes, including water depth, total 

footage, and types of logs run.

This group of boreholes formed the primary data base 

for the geologic framework for the program. It also 

formed the ground-truth for interpretation of the singlechannel and multichannel seismic profiles that provided 

the primary three-dimensional subsurface picture of the 

craters and environs.

Two other activities occurred on Enewetak during the 

Drilling Phase: (1) an additional set of benthic samples 

was taken from the drill ship in the vicinity of OAK and 

KOA and (2) because of the value of the information 

obtained from the submersible during the Marine Phase 

the previous summer, the Delta was brought back to 

Enewetak for further sea-floor investigations.

PEACE PROGRAM REPORTS

Table 4 lists the PEACE Program data groups and 

analyses with corresponding references for all the 

reports published by the USGS for the DNA and for 

some additional reports and papers by other groups. 

Most of the Marine Phase information appears in USGS 

Bulletin 1678 (Folger, 1986b), although some is included 

in three of the subsequent four USGS open-file reports 

for the Drilling Phase Open-File Reports 86-159 (Cronin and others, 1986), 86-555 (Henry and Wardlaw, 

1986), and 87-665 (Henry and Wardlaw, 1987). The 

remaining open-file report (86-419; Henry and others, 

1986) documents the drilling operations, strategies for 

selecting borehole locations, rationale for downhole logging, and procedures for core and sample handling and 

sampling and gives detailed lithic descriptions. Also 

included in this volume is an appendix (Holloway and 

Young, 1986) summarizing technical aspects of the drill 

ship and drilling system, strategies for drilling and 

sampling, procedures for core and sample handling, the 

geotechnical (material-properties) investigations conducted onsite by McClelland Engineers, Inc., and engineering rock ("soils") descriptions of the boreholes.

Most of the material-properties studies were not conducted by the USGS, nor was our close collaboration
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM All

A

B

FIGURE 6. 237-foot-long drill ship Knut Constructor. Drill rig is mounted amidship (photographed in OAK crater in June 

1985 by Lt. Col. Robert F. Couch, Jr., Defense Nuclear Agency). A, Port side view from surface; B, Starboard side view 

photographed from air.
A12 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

0 1000 2000 3000 FEET [ii I I

0 200 400 600 800 METERS 152,000 N g

0 200 400 600 800 METERS

FIGURE 7. Borehole sites and general bathymetric contours in (A) 

KOA crater area and (B) OAK crater area. General locations shown 

in figures 2 and 4; specific sites (depicted by letters) described in 

table 3. Contour lines in feet. (Modified from Henry and others, 1986, 

figs. 27, 29.)

requested or required for these. The results of these 

investigations have been reported elsewhere for the 

DNA (Akers, 1986; Borschel and others, 1986; McClelland Engineers, Inc., 1986; Blouin and Timian, 1987; 

Mueller, 1987; Patti and Schatz, 1987). The USGS did 

collaborate closely with the X-ray diffraction (mineralogic), organic-content, and insoluble-residue studies and 

the analyses of the downhole geophysical logs and the 

borehole gravimetry all of which provide primary physical and numeric data for computational modeling. These 

are reported in two of the USGS open-file reports cited 

previously (table 4) and in Oberste-Lehn (1989).

CURRENT SERIES OF PAPERS

In a multidisciplinary investigation of this scope and 

scale, data bases are created that are applicable to 

research activities far beyond the original objectives and 

scope of the program. The PEACE Program is no 

exception. These "spinoffs" include studies of the geologic history and evolution of the Pacific Basin, the 

biologic and geologic evolution of a coral atoll, the 

petrographic and geochemical diagenesis of carbonate 

rocks, fluctuations in sea level as a response of the global 

ocean to major climatic events (glaciation, deglaciation), 

and the speciation (evolution) and migration of marine 

biotas, to name but a few topics of interest. Several 

papers that exploit this new information already have 

been published in other journals (Hudson, 1985; Halley 

and Ludwig, 1987; Ludwig and others, 1988; Quinn and 

others, 1989; Quinn, in press).

In the spirit of Professional Paper 260, "Bikini and 

Nearby Atolls," which marked the first involvement of 

the USGS in the Marshall Islands, the purpose of the 

current series is to provide a forum for more of these 

geologic and biologic studies and for expansion of several 

topics summarized but not completely covered primarily because of time and space constraints in the initial 

USGS reports to the DNA.

ACKNOWLEDGMENTS

We, as editors of this Professional Paper series and 

chief geologists for the Drilling Phase of the PEACE 

Program, extend a special note of appreciation to the 

following people, without whom this program would not 

have been possible. Lt. Col. Robert F. Couch, Jr. (U.S. 

Air Force, Washington, D.C., and DNA manager for the 

PEACE Program), Byron L. Ristvet and Edward L. 

Tremba (both DNA subcontractors from S-Cubed Division of Maxwell Laboratories, Albuquerque, N. Mex., 

during the program and currently with the DNA in 

Las Vegas, Nev., and Alexandria, Va., respectively), and Robert W. Henny (Air Force Weapons Laboratory (AFWL), Kirtland Air Force Base, N. Mex.) were 

full collaborators with us during the PEACE Program. 

All four of these geologists had logged extensive onsite experience in the PPG and with various problems 

of nuclear-weapons effects prior to the current program 

and were principal investigators in all or various phases 

of the earlier AFWL investigations on Enewetak. 

In a real sense, they represent a vital component of 

the record of cratering studies on Enewetak. Their 

expertise and geotechnical knowledge were invaluable 

to the PEACE Program, and we owe them a profound 

debt of gratitude. Couch, Ristvet, and Tremba served
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A13

TABLE 2. Downhole geophysical logs from PEACE Program drilling 

[X indicates that log was made]

Borehole

MCS GR/NU

Log type1

GR/DN/CP TAG SRS GR/CP BHG

KOA crater

KAR-1

KAM-2

KAP-3/KAM-2A

KBZ-4

KCT-5

KDT-6

KET-7

KFT-8

X

-

-

X

X

-

-

-

X

-

-

X

X

X

-

X

X

- -

-

X

X

X

- -

X

X - -

_

_

X - -

X - -

X - -

_

X - -

OAK crater

OAM-l/OAR-2

OAR-2A

OAM-3

OBZ-4

OCT-5

ODT-6

OET-7

OFT^S

OGT-9

OHT-10

OIT-11

OJT-12

OKT-13

OLT-14

OMT-15

ONT-16

OOR-17

OPZ-18

OQT-19

ORT-20

OSR-21

OSM-22

OTG-23

OUT-24

_

X

-

X

X

-

X

X3

-

-

X

_

X

-

-

_

X

_

X

-

_

-

-

X

X

X

X2

X2

-

X

X

X

X

X

X

X2

-

X

X

X

X2

X2

_

-

_

_

X

X X

X

X

X

X

-

X

- -

- -

-

X

_ _

X

-

-

_ _

X

X

X

X

X

_ 

 

-

X - -

_ _

_ _ _

X - -

X - -

_

_ _ _

_ _ _

_

_

_

_ _ _

_ _ _

_

_

_ _ _

X - X4

X4

X4

X4

X4

_ _ _

X4 X4

- - -

JLog type: MCS, multichannel sonic; GR/NU, gamma-ray/neutron-neutron; 

GR/DN/CP, gamma-ray/density/caliper; TAG, three-arm caliper; SRS, seismic 

reference survey; GR/CP, gamma-ray/caliper; BHG, borehole gravimetry.

2Run in open hole only. 

3Run in drill pipe only. 

4Run in casing.

as chief scientists aboard the Knut Constructor during legs of the Drilling Phase of the program, and all 

three were onsite part of the time during the Marine 

Phase.

David J. Roddy (USGS, Flagstaff) set up the initial 

USGS involvement in the PEACE Program and helped 

guide and advise the program through many of its 

stages.

L. Stephen Melzer and John F. Schatz of Science 

Applications International Corporation provided us with 

constructive scientific, engineering, and technical information during the program. Melzer was onsite with us as 

a chief scientist during part of the Drilling Phase fieldwork.

Our appreciation is extended to all the members of the 

Marine Phase, particularly David W. Folger, PEACE 

Program coordinator for the USGS Office of Energy and 

Marine Geology, John A. Grow and his crew for the 

superb multichannel seismic profiles, James C. Robb and 

his group for the single-channel sections, and Folger, 

Robb, and J.C. Hampson and company for the sidescansonar images of both craters. These images, digitally 

processed at the USGS laboratories in Flagstaff, Ariz., 

were enhanced by airbrush techniques and were instrumental in the critical identification of many surficial 

crater features. The sidescan-sonar images and the 

seismic-reflection profiles greatly aided the selection of 

the borehole sites during the Drilling Phase.
A14 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

TABLE 3. Summary of PEACE Program borehole data from KOA and OAK craters

Site1 Borehole2

IVY-grid coordinates 

(feet)

Water depth 

(feet below Holmes 

and Narver datum3)

Borehole depth 

(feet below sea level)

Recovery

Footage Percentage

KOA crater

A

A

A

A

B

C

D

E

F

GZ

KAR-1

KAM-2

KAP-34

KAM-2A4

KBZ^

KCT-5

KDT-6

KET-7

KFT-8

140,851 N.

140,816 N.

140,874 N.

140,874 N.

149,350 N.

148,815 N.

148, 178 N.

148,034 N.

148,490 N.

149,360 N.

071,192 E.

071,157 E.

071,106 E.

071,106 E.

071,113 E.

071,087 E.

071, 140 E.

071,147 E.

071,107 E.

071,120 E.

105.1

105.7

111.1

111.1

109.1

98.9

56.2

51.1

77.8

163.0

1,146.3

80.8

578.0

5482.9

1,045.9

306.6

123.8

41.1

317.9

710.0

(5)

(5)

(5 )

388.8

135.0

55.1

13.1

126.1

62

(5)

(5 )

(5 )

37

44

45

32

40

OAK crater

A

A

A

A

B

C

D

E

F

G

H

I

J

K

L

M

N

0

P

Q

R

S

s

T

U

GZ

OAM-14

OAR-24

OAR-2A

OAM-3

OBZ^

OCT-5

ODT-6

OET-7

OFT-8

OGT-9

OHT-10

OIT-11

OJT-12

OKT-13

OLT-14

OMT-15

ONT-16

OOR-17

OPZ-18

OQT-19

ORT-20

OSR-21

OSM-22

OTG-23

OUT-24

127,784 N.

127,784 N.

127,861 N.

127,873 N.

124,980 N.

125,467 N.

126,140 N.

125,938 N.

125,803 N.

125,754 N.

124,003 N.

124,230 N.

124,053 N.

124,362 N.

123,569 N.

123,974 N.

124,215 N.

119,843 N.

124,789 N.

123,651 N.

123,303 N.

120,320 N.

120,313 N.

124,204 N.

125,499 N.

124,981 N.

039,575 E.

039,575 E.

039,566 E.

039,569 E.

036.115E.

036,552 E.

037,372 E.

037,095 E.

036,882 E.

036,809 E.

037,195 E.

037,051 E.

037,527 E.

036,879 E.

038,473 E.

038,068 E.

037,767 E.

032,899 E.

036,383 E.

035,545 E.

035,339 E.

033,197 E.

033,127 E.

035,899 E.

035,424 E.

036,108 E.

114.2

114.2

110.5

111.0

198.7

163.7

90.1

106.9

130.8

134.8

137.3

155.0

143.8

164.7

139.7

110.9

135.1

75.1

201.9

117.5

101.4

84.0

76.0

164.0

147.0

195.6

5401.6

885.6

410.5

593.0

1,605.2

851.5

164.2

231.7

283.5

75.0

162.5

286.5

97.3

765.3

49.2

76.6

152.3

1,091.1

748.6

701.5

491.8

354.3

5 127.5

5587.3

351.4

...

(5)

366.3

188.1

(5)

967.8

260.6

86.8

113.4

104.0

28.3

64.5

111.5

53.4

248.5

27.1

36.7

73.1

563.5

188.1

126.0

73.3

63.9

(5)

(5)

56.8

(5 )

76

46

(5 )

60

31

53

49

37

38

40

39

57

32

55

48

48

52

26

18

15

18

(5 )

(5 )

16

...

JSite locations shown in figure 7; GZ, ground zero.

2In borehole identifiers, first character stands for the crater area (0, OAK; K, KOA), second character for the site, and third character for the type of borehole 

(R, reference; M, material properties; P, cone penetrometer; Z, ground zero; T, transition zone; and G, borehole gravimetry). The numbers to the right of the hyphen 

designate the sequential number drilled.

3Holmes and Narver datum is 0.5 ft below approximate-mean-low-water-spring tide (AMLWS).

4KAP-3 and KAM-2A are the same hole; OAM-1 and OAR-2 are the same hole.

5Not used in summary for geologic total footage and recovery.

We thank the authors of the chapters of the current 

Professional Paper series and of the previous set of 

open-file reports for their timely response to our needs in 

compiling and editing their chapters for this Professional 

Paper and for their cooperation and stimulation earlier in 

synthesizing the diverse data bases for the open-file 

reports.

A profound debt of gratitude is owed to Thomas R. 

Clark, manager of the Nevada Operations Office (NVO)

of the DOE, and Roger Ray, deputy manager for Pacific 

operations, NVO, and their staff, and to William J. 

Stanley, director of the Pacific Area Support Office of the 

DOE in Honolulu, and his staff, particularly Harry U. 

Brown, DOE program manager for this project, for 

contracting the drilling, downhole logging, navigation, 

and related activities, for arranging for support from a 

number of Government and subcontractor personnel to 

manage the operations and logistics for the fieldwork,
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A15

TABLE 4. Summary of reports from the PEACE Program

Data group

Bathymetric maps

Sidescan sonar and imagery

Single-channel seismic reflection

Multichannel seismic reflection

Seismic refraction

Submersible observations

Debris/ejecta studies

Scuba observations

Benthic samples

Boreholes

Lithostratigraphic framework

Biostratigraphic framework and mixing studies

Geophysical logs

Seismic reference survey

Borehole gravity

Petrography, diagenesis

Sr-isotope framework

X-ray mineralogy

Organic geochemistry

Insoluble residues

Radiation chemistry

Electron-spin resonance

Crater-area benthic samples

Crater synthesis

Phase

Marine

Marine

Marine

Marine

Marine

Marine 

Both

Marine 

Marine 

Drilling

Marine

Both

Drilling

Drilling

Drilling

Drilling

Drilling

Drilling 

Drilling

Drilling 

Drilling 

Drilling

Marine 

Drilling

Drilling

Drilling

Drilling

Drilling

Drilling

Drilling

Marine 

Both 

Both

Publication1

Bull. 1678 

OF-87-665

Bull. 1678

Bull. 1678

Bull. 1678

Bull. 1678

Bull. 1678 

OF-86-555

Bull. 1678 

OF-86-555 

OF-87-665

Bull. 1678

OF-86-555

OF-86-419

OF-86-555

OF-87-665

OF-86-159 

OF-86-555 

OF-87-665 

"Geology"

OF-86-555 

OF-87-665

OF-86-555

OF-86-555 

OF-87-665 

OF-87-665 

TR-161605-002

Brown Univ. 

GSA Abstr. 

"Sedimentology"

Bull. 1678 

OF-86-555 

"Geology"

OF-86-555

OF-86-555

OF-86-555

OF-86-555

OF-87-665

OF-86-555 

OF-86-555

Bull. 1678 

OF-86-555 

OF-87-665

Chapter

A 

5

B

C

D

E

F

13

G 

3

4

H

10

-

2

7

11 

3

v. 17

7 

6

9

8 

2 

6

-

G 

3

v. 16

4

5

6

12

4

4 

10

A

14

7

Reference

Folger, Hampson, and others (1986). 

Peterson and Henny (1987).

Folger, Robb, and others (1986).

Robb and others (1986).

Grow and others (1986).

Ackermann and others (1986).

Halley, Slater, and others (1986). 

Slater and others (1986).

Halley, Major, and others (1986). 

Ludwig and others (1986). 

Polanskey and Ahrens (1987).

Shinn and others (1986).

Wardlaw and others (1986).

Henry and others (1986).

Wardlaw and Henry (1986b). 

Wardlaw (1987).

Cronin and others (1986). 

Brouwers and others (1986). 

Cronin and Gibson (1987). 

Wardlaw (1989).

Melzer (1986). 

Trulio (1987).

Tremba and Ristvet (1986a).

Beyer and others (1986). 

Beyer (1987). 

Trulio (1987). 

Oberste-Lehn (1989).

Quinn (1989). 

Quinn and others (1989). 

Quinn (in press).

Halley, Major, and others (1986). 

Ludwig and others (1986). 

Ludwig and others (1988).

Tremba and Ristvet (1986b).

Ristvet and Tremba (1986c).

Ristvet and Tremba (1986a).

Ristvet and Tremba (1986b).

Polanskey and Ahrens (1987).

Tremba and Ristvet (1986b). 

Wardlaw and others (1986).

Folger (1986a). 

Wardlaw and Henry (1986a). 

Wardlaw (1987).

'Bull., USGS Bulletin; OF, USGS Open-File Report; TR, Technical Report.
A16 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

and for obtaining necessary approval from the U.S. Air 

Force at Hickam Field in Honolulu, from the U.S. Army 

Missile Base at Kwajalein Atoll, and from Government 

officials of the Republic of the Marshall Islands and the 

Trust Territory of the Pacific Islands.

Emit L. Herbst (H&N, Las Vegas) and George Krosnbein, Judy Honda, Jack H. Matthewman, and Pat R. 

Haggerty (all H&N, Honolulu) orchestrated transportation and supply logistics throughout the Drilling Phase. 

In addition, we thank Stan S. Miyasato (H&N) and his 

staff at the University of Hawaii/DOE Mid-Pacific 

Research Laboratory on Enewetak Island for providing 

every assistance throughout the drilling and logging 

operations.

The program is indebted to members of the staff and 

management of McClelland Engineers, Inc., and particularly to McClelland's project director, Alan G. Young, 

and his deputy, Tom Hamilton. Peter Gemeinhardt, 

vice-president for international operations and operations director for this program, served onsite as a 

crewman during mobilization and the early phases of 

drilling. The response of McClelland's field superintendents (Chuck Rivette and Glenn L. Holloway), chief 

drillers (Glen Mooney and Charlie Peltier), multinational 

drilling crew, and support personnel to program needs 

and technical problems was outstanding and often innovative. The program would have not been possible 

without their expertise, enthusiasm, and cooperation.

We also acknowledge the support of the officials of the 

Republic of the Marshall Islands and the people of 

Enewetak, many of whom piloted the whalers and LCM6 

landing craft used as resupply vessels between the 

islands and the drill ship (in all kinds of weather) and 

assisted us in many other project operations. All of these 

individuals freely and warmly extended their hospitality 

to program participants.

Last but not least, we express our appreciation to the 

officers and crew of the drill ship, the Knut Constructor, 

for their role in this program. We salute the "Jolly 

Knut," as she became affectionately known to us, for her 

fine service during the PEACE Program.

LOCATION AND SETTING

Enewetak and Bikini are "coral" atolls in the equatorial Pacific Ocean located roughly 2,500 nautical miles 

(nmi) southwest of Hawaii (fig. 1). Both Enewetak and 

Bikini are part of the Republic of the Marshall Islands, 

formed in 1987. The approximate center of Enewetak 

Atoll is 11°30' N. 162°15' E.; Bikini is about 220 nmi east 

of Enewetak, with a center at about 11°35' N. 165°23' E.

The Marshall Islands are located principally on two 

subparallel chains of extinct volcanoes (the Ralik and 

Ratak Chains) that formed as the Pacific tectonic plate

moved northwestward over a hot spot in the upper 

mantle known as the Darwin Rise. Enewetak Atoll is at 

the northwestern end of a third chain, which is principally submerged. Reefs made primarily from corals and 

coralline algae became established on the volcanic bases 

and, in the cases of atolls such as Enewetak and Bikini, 

reef growth generally kept pace with subsidence and (or) 

eustatic sea-level rises.

Enewetak Atoll is acorn shaped, with a long axis 

approximately 22 nmi long and oriented in a northwestsoutheast direction. The short axis is about 17 nmi long 

(fig. 2). Like most of the Marshall Islands, Enewetak's 

approximately 40 islands are very low lying (maximum 

elevation about 13 ft above sea level) and are restricted 

to the atoll margin. Enewetak thus is dominated by the 

lagoon, which has three principal outlets to the open 

ocean (fig. 2). The islands constitute only about 2.75 

square nautical miles (nmi2) of the atolPs almost 300 nmi2 

and are concentrated primarily on Enewetak's northeastern margin, facing the prevailing trade winds. The 

islands have been called by different names. As many as 

four "native" names or variations in English phonetic 

spellings have been applied to some. To avoid confusion, 

most of the islands were assigned a military site name 

during the period of nuclear testing. In both Folger's 

(1986a) report and the USGS open-file reports, and in the 

current series, the Marshallese names identified by 

Tobin (1973) and reported in Freisen (1982) are used. The 

military site names are given in parentheses in capital 

letters after the preferred island name.

PREVIOUS GEOLOGIC INVESTIGATIONS

Scientific studies were conducted sporadically in the 

Marshall Islands prior to the end of World War II. The 

first geologic observations of the islands were made in 

1816 and 1817 by Albert Chamisso, a naturalist with one 

of the Russian Pacific expeditions. Chamisso described 

the reefs, islands, and lagoons of the Ratak (eastern) 

Chain of the Marshalls. From 1918 through 1944, the 

Marshall Islands were part of the Pacific territories 

controlled by the Japanese. Although the Japanese conducted scientific studies on the atolls during this period, 

most of their data has been lost (Emery and others, 

1954). Some general comments were published by 

Stearns (1945) concerning possible damage to the 

Enewetak reefs during the 1944 American invasion when 

the Japanese were defeated.

STUDIES FROM 1946 TO 1952

Operation CROSSROADS was initiated by the U.S. 

Government in 1946 just prior to the detonation of two 

atomic bombs over and under naval warships in the
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A17

lagoon at Bikini Atoll. This scientific study was conducted to establish a baseline against which to assess the 

impact of the Nuclear Weapons Testing Program in what 

was to become the PPG. The Operation CROSSROADS 

study of Bikini included (1) surficial geologic investigations of the reef complex, the lagoon floor, and the outer 

slopes of the atoll and (2) a seismic-refraction study of the 

subsurface structure of the atoll (Emery and others, 

1954). To paraphrase Hines (1962, p. 31, 32), Operation 

CROSSROADS was unquestionably the most thoroughly documented, reported, and publicized peacetime 

military/scientific program in history. This study set the 

stage for the extensive scientific investigations of the 

northern Marshall Islands that followed. Those of geologic and geophysical importance are the Bikini Resurvey (1947), the Mid-Pacific Expedition (1950), the Atomic 

Energy Commission (AEC)-Los Alamos Scientific Laboratory (LASL) Drilling Program (1950-1951), and the 

USGS/AEC Drilling Program (1951-1952). Under these 

programs from 1946 to 1952, extensive geologic, paleontologic, geophysical, biologic, radiologic, oceanographic, 

and atmospheric studies were conducted by the DOD, 

the USGS, the U.S. Fish and Wildlife Service, the AEC, 

the LASL, the Woods Hole Oceanographic Institution, 

the Scripps Institution of Oceanography, the Smithsonian Institution, other Federal agencies, the Bishop 

Museum, and various American universities. Summaries 

of many of these investigations were published as the 

35-volume USGS Professional Paper 260, beginning in 

1954 (Emery and others, 1954, Professional Paper 260-A) 

and ending in 1969 (Leopold, 1969, Professional Paper 

260-11). To quote Ristvet (1987, p. 39), "This...series 

comprises the most comprehensive single body of geologic, geophysical, and oceanographic data ever assembled on a group of atolls."

FIRST ATOLL BOREHOLES

Coral atolls have been of intensive interest to geologists and biologists since before the publication by 

Charles Darwin of "Voyage of the Beagle?' in 1837. From 

the data base assembled during the expedition to the 

South Pacific (1831-36) of the H.M.S. Beagle, Darwin 

(1837, 1842) constructed a threefold classification of coral 

reefs fringing reefs, barrier reefs, and coral atolls and 

postulated that atolls were formed on the foundation of 

subsiding islands that evolved (with subsidence and 

upward growth of the reef complex) through the 

fringing-reef and barrier-reef stages. This sparked a 

number of alternative theories about atoll formation, as 

well as the scientific impetus to drill into the volcanic 

basement on a coral atoll.

The first major attempt to drill through the carbonate 

cap of a coral atoll was made by the Royal Society of

FIGURE 8. Drill ship H.M.S. Porpoise showing bow and the hydraulic 

(steam) rig used to drill the two overwater boreholes in the lagoon at 

Funafuti Atoll in 1898. (From Halligan, 1904, p. 161, fig. 20.)

London at Funafuti Atoll, in the Ellice Islands (about 

1,300 nmi south of the Marshalls), in 1896-98 (Coral Reef 

Committee, 1904). During this expedition, in 1897-98, 

one borehole was drilled on Funafuti Atoll to a depth of 

973 ft (David, 1904, p. 56), and, in 1898, two boreholes 

were drilled with a steam rig from the H.M.S. Porpoise 

(fig. 8) in the lagoon in about 200 ft of water to depths of 

114 and 113 ft below the bottom (Halligan, 1904). These 

two boreholes were the first ever drilled overwater in a 

coral atoll lagoon. All three boreholes penetrated only 

carbonate sediments, and no volcanic rock, and therefore 

only partly confirmed Darwin's (1837, 1842) subsidence 

theory.

The first conclusive demonstration of deep subsidence 

on open-ocean atolls was made a little more than 50 years 

later in the northern Marshall Islands in conjunction with 

the onset of nuclear testing in the Pacific. Activities in 

1946 on Bikini Atoll under Operation CROSSROADS 

included surficial geologic studies of the reef, lagoon 

floor, and outer slopes and a seismic-refraction study of 

the subsurface of the atoll (Emery, 1948; Dobrin and 

Perkins, 1954; Emery and others, 1954; Raitt, 1954). In 

1947, two boreholes were drilled on Bikini Atoll, borehole 2-A to a depth of 1,346 ft and 2-B to a depth of 2,556 

ft (Ladd and others, 1948; Ladd and others, 1950; Emery 

and others, 1954); neither reached the volcanic basement. In 1950, a few deep-sea cores were obtained from 

the southeastern flank and lower slope of Bikini Atoll and 

one core was obtained from the adjoining guyots and atoll 

slopes (Emery and others, 1954), and volcanic rocks were 

dredged from the southeastern slopes of Bikini from 

depths of 6,000 to 12,060 ft (Ladd and others, 1953).
A18

162°

GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL 

162° 10' 162°20' 162°301

IVY /-160000 GRID 7 

(FT)

+ 120000

+ 80000

SOUTHWEST 

PASSAGE

EAST (DEEP) CHANNEL

+ 40000

SOUTH PASSAGE

5 NAUTICAL MILES 10,000

Illll

30,000 50,000 FEET 10 KILO METERS

FIGURE 9. Location of AEC-LASL (1950-1951) boreholes (modified from Ladd and Schlanger, 1960, fig. 260). On original map and in 

accompanying text, Bokoluo (ALICE) is called Bogallua, Enjebi (JANET) is Engebi, Mijikadrek (KATE) is Mujinkarikku, Eleleron (RUBY) 

is Eberiru, and Aomon (SALLY) is Aranit.

AEC-LASL DRILLING PROGRAM (1950-1951)

Drilling on Enewetak Atoll commenced in 1950, with 

four very shallow boreholes (maximum depth 15.9 ft) 

drilled under the sponsorship of the AEC and the LASL 

and the supervision of the USGS. These holes were 

drilled on the seaward side of Enjebi (JANET), 

Mijikadrek (KATE), Eleleron (RUBY), Aomon 

(SALLY), and Runit (YVONNE) on the northeastern

side of the atoll (fig. 9). These boreholes and subsequent 

ones were described in Ladd and Schlanger (1960).

USGS-AEC DRILLING PROGRAM (1951-1952)

Three deep holes were drilled on Enewetak Atoll in 

1951 and 1952 by the USGS and the AEC (fig. 10) from 

heavy truck- and trailer-mounted rotary rigs. K-1B was
162°

INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM 

162°10- 162°20'

A19

162°30'

1T401

Runit (YVONNE)

IVY /-160000 

GRID 7 

(FT)

+ 120000

+ 80000

SOUTHWEST 

PASSAGE

EAST (DEEP; CHANNEL

+ 40000

SOUTH PASSAGE

5 NAUTICAL MILES

j

10,000

ll.MI

30,000 50,000 FEET 10 KILOMETERS

FIGURE 10.-Location of USGS-AEC (1951-1952) deep boreholes (modified from Ladd and Schlanger, 1960, fig. 261). On original map and in 

accompanying text, Enjebi (JANET) is called Engebi and Medren (ELMER) is called Parry Island.

drilled on Enjebi (JANET) to a depth of 1,280 ft, F-l was 

drilled on Elugelab (FLORA) to 4,630 ft, and E-l was 

drilled on Medren (ELMER) to 4,222 ft (Ladd and 

others, 1953; Ladd and Schlanger, 1960). Boreholes E-l 

and F-l (fig. 10) penetrated through the limestone cap of 

the atoll into the volcanic, olivine-basalt basement at 

depths of 4,610 ft and 4,158 ft, respectively (fig. 11). 

About 15 ft of the basalt was recovered in the latter 

borehole. In general, recovery was poor in these boreholes (see fig. 11), and only relatively small portions of

F-l and E-l were actually cored. However, cuttings 

were carefully evaluated and provided invaluable information about the stratigraphy. Of these three deep 

boreholes, only E-l7 was not destroyed by the direct 

effects of nuclear testing (Couch and others, 1975).

7E-1 was the borehole in which the borehole-gravimetry pilot study was 

conducted for the PEACE Program.
A20 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

FEET METERS 

0 i 0

1000

2000

3000 

4000 

 200

 400

 600

800

 1000

 1200

 1400

r

Enjebi

(JANET)

K-1B

ENEWETAK

____A.____

BIKINI

A

Elugelab

(FLORA)

F-1

Medren

(ELMER)

E-1 2-A

TD 4222 ft

EXPLANATION

No recovery

Limestone (calcite) with solution 

features

Limestone and unlithified sediments 

with primary aragonite

Partly recrystallized and leached 

limestone

Dolomite

Solution unconformity 

(\f\f\J Gradational zone

-------- Correlation between unconformities

 Foraminifer zones

TD 4630 ft

5000^

FIGURE 11. Correlation of USGS-AEC deep boreholes drilled on Enewetak and Bikini Atolls, showing zones of unaltered material and 

recrystallized and partly dolomitized intervals (modified from Schlanger, 1963, fig. 308). Numbers along sides of drill holes F-1 and E-1 

indicate cored intervals. Tertiary g, Tertiary e, and Tertiary b are "standard" biostratigraphic zones based on larger foraminifers, developed 

and picked by Cole (1957). TD, total depth.
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A21

E-l and F-l were the first boreholes on any atoll to 

reach the volcanic "basement." The three deep 

Enewetak holes and the two deep Bikini holes provided 

the first general litho- and biostratigraphic framework 

for these atolls and demonstrated that they had remarkably similar geologic histories. The subsurface sedimentary sequence at both Enewetak and Bikini is characterized by relatively thick intervals of leached, altered, 

cemented (lithified), calcite-rich carbonate rock (predominantly limestone) alternating with generally thick intervals of unleached, unaltered, uncemented (unlithified), 

aragonite-rich carbonate sediments (fig. 11). The 

cemented, altered zones grade downward into unaltered, 

uncemented intervals that in turn sharply overlie 

another cemented zone. Because the tops of the leached 

and cemented zones are sharp and the rocks immediately 

underlying them commonly contain dissolution features, 

they were referred to by Schlanger (1963, p. 994) as 

"solution unconformities," interpreted to have formed 

during periods when sea level was lower and the atolls 

emergent (Ladd and others, 1948; Emery and others, 

1954; Schlanger, 1963). That these unconformities generally coincide with major microfaunal breaks (fig. 11) 

indicated to these geologists that periods of nondeposition or perhaps even erosion had interrupted the formation of the carbonate sequence.

INTERIM PERIOD (1952-1970)

The original experiments, observations, and data base 

that were obtained from the PPG just after World War II 

were oriented toward military application and weapons 

development rather than the physics of ground shock and 

cratering phenomenology. Between 1952 and 1970, after 

the flurry of geologic studies in the early post-World War 

II period, several major problems surfaced that required 

additional information from the PPG. Specifically, additional data were needed to better understand crater 

geometry, material properties, and ground-shock phenomena associated with high-yield nuclear explosions 

(Circeo and Nordyke, 1964; Henny and others, 1974a; 

Couch and others, 1975; Ristvet and others, 1978; 

Tremba and others, 1981; Tremba and others, 1982; and 

Tremba, 1987).

In addition to the problems of geologic heterogeneity, 

the PPG high-yield craters did not scale with their 

high-explosive and low-yield nuclear counterparts at 

other test sites, as discussed in a preceding section. It 

was postulated (at various times) that some of these 

deviations resulted from (1) the differences in the material properties of the test-site environment (for example, 

the water-saturated carbonate environment of the PPG 

versus the air- and gas-saturated silicate environment of 

the other test sites), (2) primarily the yield of the energy

source (device), (3) the manner in which the energy 

source was coupled to the substrate, (4) massive washback of the water evacuated by the explosion in the 

lagoon, or (5) failure of the weak geologic matrix induced 

by the ground shock.

These concerns resulted in four research programs 

based on Enewetak, all funded by the DNA. The first 

three of these-the PACE, EXPOE, and EASI Programs (see Pyrz, 1973; Henny and others, 1974a, 1974b; 

Couch and others, 1975; Tremba, 1987) were directed 

by the AFWL. The last one is the PEACE Program.

AIR FORCE WEAPONS LABORATORY STUDIES 

(1970-1981)

PACE PROGRAM (1970-1972)

As originally formulated, the Pacific Atoll Cratering 

Experiment (PACE) Program consisted of two interrelated subprograms, PACE 1 and PACE 2 (Tremba and 

others, 1982). PACE 1 was designed to examine the 

nuclear craters on Enewetak and to provide information 

on the near-surface geology of the atoll and the physical 

and structural characteristics of selected craters and 

related ejecta fields. PACE 2 was to concentrate on the 

cratering and ground-motion response of the watersaturated carbonate substrate to a series of highexplosive TNT tests, culminating in a 500-ton blast. 

However, the program was terminated prematurely 

through legal and political action before all of the objectives were achieved (see Tremba and others, 1981; Kiste, 

1987). Consequently, PACE 2 yielded little valuable new 

geologic and physical information.

Fieldwork for PACE 1 was conducted in 1971 (Couch 

and others, 1975), when 128 shallow boreholes (total of 

8,200 linear ft of hole) were drilled on seven of the 

northeastern islands (fig. 12). Most boreholes were concentrated on Runit (YVONNE) (35 holes) and Aomon 

(SALLY) (80 holes). In addition to the drilling program, 

60 shallow trenches were dug to determine the distribution of the beachrock beneath six of the islands, and 

50,000 ft of land-based seismic-refraction surveys were 

run, mainly in the vicinity of Aomon (SALLY) and on 

Runit Island (YVONNE) (Henny and others, 1974a, 

1974b).

EXPOE PROGRAM (1973-1974)

To model the geologic and material-properties heterogeneity of the subsurface of Enewetak Atoll, the strategy of the EXPOE Program (the successor of PACE 1) 

was to (1) delimit the general geologic differences 

between the leeward, windward, and transitional islands
A22

162°

GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL 

162°10' 162°20' 162°30'

Bokaidrik 

(HELEN)

8

CO

IVY J160000

Boken (IRENE)

Eleleron (RUBY)

Aomon (SALLY) 

Bijile (TILDA)

Lojwa (URSULA)

Runit (YVONNE)

GRID 

(FT)

+ 120000

+ 80000

SOUTHWEST 

PASSAGE

EAST (DEEPJ CHANNEL

+ 40000

SOUTH PASSAGE

5 NAUTICAL MILES 0 10,000 30,000 50,000 FEET 0 10 KILOMETERS

i . . i

FIGURE 12. Location of PACE Program (1970-1972) boreholes (modified from Couch and others, 1975, fig. 4). Only islands drilled are identified;

for individual sites, see Couch and others (1975).

(fig. 13) and (2) drill groups of boreholes both parallel and 

perpendicular to the reef front in the areas of the 

selected craters. According to Couch and others (1975, p. 

23), (1) the general lack of lithofacies variation in the 

transects parallel to the reef front and (2) the marked 

lateral facies changes between the transects perpendicular to the reef front indicated the validity of modeling 

the entire atoll subsurface on the basis of a few sections 

perpendicular to the reef trend and by comparing the

geology of the reefward area with that of the lagoonward 

area.

During the EXPOE Program, 46 additional shallow 

boreholes were drilled (8,413 linear ft) with truckmounted rotary rigs on Enewetak (FRED), Medren 

(ELMER), Japtan (DAVID), Runit (YVONNE), Lojwa 

(URSULA), Aomon (SALLY), Enjebi (JANET), Boken 

(IRENE), Bokaidrik (HELEN), Bokinwotme (EDNA), 

Kirunu (CLARA), Bokombako (BELLE), and Biken
162°

INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM 

162°10' 162°20'

A23

162°30'

n°30'

SEMINOLE Bokaidrik (HELEN) 

-Boken (IRENE)

§ 

IVY J- 160000

Bokinwotme (EDNA 

Kirunu (CLARA) 

Bokombako (BELLE)

Enjebi (JANET)

PREVAILING WIND

Aomon (SALLY) 

Lojwa (URSULA)

GRID 

(FT)

+ 120000

.CACTUS/LACROSSE 

Runit (YVONNE)

Biken (LEROY)

SOUTHWEST 

PASSAGE

+ 80000

Japtan (DAVID)

EAST (DEEP] CHANNEL

Medren (ELMER)

+ 40000

SOUTH PASSAGE Enewetak (FRED)

5 NAUTICAL MILES 0 10,000 30,000 50,000 FEET 0 10 KILOMETERS

FIGURE 13. Location of EXPOE Program (1973-1974) boreholes (modified from Couch and others, 1975, fig. 8). Only islands drilled are 

identified; for individual sites, see Couch and others (1975). Drilled islands are identified as transitional, windward, or leeward, with respect 

to prevailing wind.

(LEROY) (fig. 13). The deepest of these holes, 298-ft 

XEN-3, located on Enjebi (JANET), is part of the first 

lagoon-to-reef geologic cross section of an atoll island 

(fig. 14). Similar lagoon-to-reef cross sections for Boken 

(IRENE) and Aomon (SALLY) appear in Ristvet, 

Tremba, and others (1978, p. 167, fig. 6.5) and in Szabo, 

Tracey, and Goter (1985, p. 56, fig. 2), respectively.

Because of improved core and sample recovery 

(approximately 80 percent) and more detailed analysis,

five major, gently lagoonward dipping unconformities 

were identified in the upper 300 ft of section on 

Enewetak (FRED) in the PACE/EXPOE stratigraphic 

synthesis (Ristvet and others, 1974; Tracey and Ladd, 

1974; Couch and others, 1975). After analysis of subsequent seismic work, Ristvet, Couch, and Tremba (1980) 

were able to confirm a sixth solution unconformity, 

corresponding to a major unconformity at a depth of 

about 300 ft postulated by Schlanger (1963) and by
A24 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

LAGOON

FEET METERS

ISLAND REEF OCEAN

(MSL) 0-

50-

150-

250-

350 -1

100

EXPLANATION

Boundstone

Limestone, well cemented 

::j::!!!Jji!::j Limestone, moderately cemented 

jrlrjrj Sediments uncemented 

Solution unconformity

5000 FEET

0 1 KILOMETER 

FIGURE 14. Subsurface geologic cross section of Enjebi (JANET) Island (modified from Couch and others, 1975, fig. 15).

Tracey and Ladd (1974) on the basis of correlation with 

the Bikini sections. As in earlier studies, these unconformities were interpreted as former subaerial-exposure 

surfaces marked by terra-rosa types of paleosols 

(reddish-brown stain, reddish-brown fine silty clay, 

light-brown laminated crusts), black manganese coatings 

in pores and cavities, and dissolution features. The 

unconformities were thought to correlate with similar 

unconformities produced during glacial lowstands of sea 

level in other carbonate sections of late Cenozoic age 

elsewhere in the world.

The first attempts to drill boreholes overwater in 

nuclear craters also were made during EXPOE (Couch 

and others, 1975; Ristvet and others, 1978). Although 

sample recovery was poor, two small, water-filled craters were successfully probed to depths of 153.3 ft and 

200.0 ft from a Failing-314 drilling rig mounted on an 

anchored pontoon barge. The craters, SEMINOLE and 

CACTUS (fig. 13), were produced by surface bursts of 

13.7 and 18 kilotons (kt) on Boken (IRENE) and Runit 

(YVONNE) in 1956 and 1958, respectively (table 1). An 

attempt had been made to drill the much larger KOA 

crater, which resulted from the 1.4-Mt device detonated 

in a water tank (fig. 13, table 1). Although water filled, 

SEMINOLE and CACTUS are essentially landlocked 

craters, whereas KOA is in much deeper water, is not 

landlocked, and is exposed to waves and currents generated in the open lagoon. The EXPOE drilling barge 

proved to be unstable and unsafe as a drilling platform in 

KOA, and the effort was abandoned after only setting 

surface casing (Couch and others, 1975, p. 38).

Geophysical studies were an integral part of EXPOE 

(Pyrz, 1973). As summarized by Ristvet, Tremba, and 

others (1978), EXPOE obtained about 280,000 linear ft of 

seismic-refraction profiles for the near-surface section 

(less than 200 ft thick) from the islands, about 100,000 ft 

of overwater seismic-refraction lines for the near-surface 

areas (less than 300 ft) of the large craters OAK, KOA, 

and MIKE, overwater seismic-refraction and seismicreflection profiles for the noncratered areas of the 

lagoon, and downhole geophysical logs for many of the 

boreholes drilled during the program. Unfortunately, 

the seismic-reflection data from the lagoon were not of 

good quality because of high noise levels aboard the ship, 

the data-reduction techniques, and inaccuracies in navigation. Most downhole geophysical logs were also poor 

because of casing problems in the boreholes.

EASI PROGRAM (1979-1981)

Although the PACE and EXPOE Programs provided 

greater understanding of the importance of geologic 

factors controlling crater formation on a coral atoll and 

greater definition of crater parameters and other features for the small craters SEMINOLE, CACTUS, and 

LACROSSE, these programs did not answer fully the 

major questions regarding the large craters OAK, 

KOA, and MIKE and many of the questions about 

material properties presented by the lagoonward location of OAK ground zero.

By 1979, research on nuclear-weapons effects funded 

by the DNA generated renewed interest in resolving the
INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A25

remaining major PPG cratering issues. Another twophase seismic and drilling program was proposed by the 

AFWL in July and August 1979. However, only the 

seismic and geophysical phase of the proposed study 

received funding by the DNA; the funded study was 

designated the EASI Program. About 140 nmi of overwater, high-resolution seismic lines were run in 1980 

(Tremba and others, 1982; Tremba, 1987). These were 

concentrated mainly in grids over OAK, MIKE, and 

KOA craters but included profiles in areas of the lagoon 

not affected by the nuclear detonations. A limited number of dives and traverses in the OAK and KOA areas 

were made in 1981 with the submersible R/V Makalii, 

sponsored jointly by the University of Hawaii and the 

National Oceanic and Atmospheric Administration, the 

Bishop Museum, and the DNA.

The EASI seismic study and associated submersible 

observations, coupled with detailed direct and quantitative calculations of the results, provided the DNA and 

DOE weapons-effects community the first direct evidence that the Pacific high-yield nuclear craters were 

dominated by late-time processes rather than excavation 

and ejection. According to Tremba, Couch, and Ristvet 

(1982, p. 74-80), the evidence strongly suggested that a 

small, bowl-shaped excavational crater existed prior to 

the formation of the much larger, broader, dish-shaped 

crater for OAK, and that the major factors in the 

difference between the excavational crater and the final 

crater could be explained plausibly by a combination of 

shock-induced liquefaction and subsidence responses, 

compaction, and slope failures of the crater walls. They 

also stated that it was essential to verify these tentative 

conclusions with an extensive drilling program.

INTERIM EVENTS (1981-1984) LEADING TO 

PEACE PROGRAM

The DNA embarked on a three-pronged program in 

1981 to better understand near-surface nuclear events. 

This program consisted of computer-calculation efforts 

supporting underground nuclear testing, high-explosive 

simulation, and a detailed site survey of two PPG craters, OAK and KOA, produced by megaton-sized detonations. The two craters were selected for study because 

of their differing high-yield nuclear-source characteristics, the relative isolation of one of them (OAK) from 

other nuclear bursts, accessibility by a shallow-water 

drill ship, and a support base (Mid-Pacific Research 

Laboratory) at Enewetak Island (FRED). In 1983, an 

outline of the program was formulated by David J. 

Roddy of the USGS and Maj. J.B. Jones of the DNA, 

with the assistance of DNA contractors. This program, 

which included a drilling plan, was presented to the DNA

and later to the USGS. Thus, the PEACE Program came 

into being.

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A26 GEOLOGIC AND GEOPHYSICAL INVESTIGATIONS OF ENEWETAK ATOLL

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INTRODUCTION: ENEWETAK ATOLL AND THE PEACE PROGRAM A27

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