morphology than in dry continental sites. By the end of the last decade, computational models were capable of simulating accurately an array of phenomena associated with high-explosive and low-yield nuclear shots. However, the PPG craters (as observed and measured) formed by the high-yield events and scaled to their continental and meteor-impact counterparts were anomalous and could not be modeled confidently. The marked difference between these simulations and existing observations from the PPG were of considerable concern to the DOD. In fact, the lack of confidence in these data cast doubt on the DOD's ability to predict how effective nuclear weapons would be against hardened targets and how well strategic defense systems would survive in the event of nuclear attack.

Participation of the USGS in fieldwork on Enewetak was divided into two major parts. The first, the marine phase, began in April of 1984 with a pilot borehole-gravity study by the USGS and DNA in a deep borehole drilled in 1952 on Medren Island (fig. 12). Most of the marine phase was conducted during the summer and early fall of 1984 by USGS personnel, but scientific advisors from DNA and logistic support from the Pacific Area Support Office of the Department of Energy (DOE) also participated in the marine phase. The second phase, the drilling phase, was conducted

from late winter through the summer of 1985 and was conducted jointly by personnel from the USGS, DNA, and DOE, which contracted the 245-foot drilling vessel, the Knut Constructor (fig. 13). The DOE also obtained necessary cooperation of the officials of the Republic of the Marshall Islands to conduct the fieldwork on Enewetak and to provide extensive logistic support.

The marine phase concentrated on mapping seafloor features and profiling subbottom characteristics of KOA and OAK using shipboard geophysical techniques and scuba and submersible surveys (figs. 14, 15). Most of these analyses are reported in USGS Bulletin 1678. The geophysical studies incorporated data from sidescan-sonar images, single-channel and multichannel seismic surveys, and refraction surveys; the geologic investigations included seafloor observations, collection of bottom (benthic) samples, and shallow boreholes drilled by scuba teams.

Thirty-two deep boreholes were completed in the vicinity of KOA and OAK during the drilling phase. These provided information on the stratigraphic framework of the upper 1,200 feet of the carbonate cap of the atoll and ground-truth for the geophysical profiles and other marine phase data. The deepest hole was drilled about 1,800 feet below sea level in roughly 200 feet of water near OAK ground zero. Samples of rock and sediment from the

Figure 15. Two-man research submersible Delta, operated by MARFAB, Inc., used extensively for direct observation and photography of crater features and surrounding area during both phases of the Enewetak Program. Photograph taken in OAK crater in June 1985.

• The first borehole gravity measurements made on a coral atoll and the first successful application of a slimline borehole gravity tool from aboard ship. These measurements provided essential bulk density and porosity data for the computational modeling.

The multidisciplinary approach confirmed that the original excavational craters of KOA and OAK were transient features significantly smaller than originally thought and far more compatible with DOD predictions. Processes operating on a scale of hours to years greatly enlarged the size and modified the configuration of the initial craters in the water-saturated test beds. These processes included major failure of the sidewalls of the excavational crater, shock-induced liquefaction, consolidation, upward piping of material (partly from beds far below the excavational crater), and subsidence of the materials below and adjacent to the initial crater.

Federal/State

Cooperative Geologic Mapping 1985-1987

By Wayne L. Newell

COGEOMAP, the Federal/State Cooperative Geologic Mapping program, is proving to be an effective program for providing geologic maps of high-priority areas in a timely manner that meet the varied needs of geologic map users. In its third year of activity in fiscal year 1987, COGEOMAP has grown to encompass 30 Federal/State cooperative projects (fig. 16). When the program began in fiscal year 1985, 18 State-proposed cooperative projects were accepted and funding was at the $1 million level. Congress increased funding to the $1.5 million level in fiscal year 1986 and fiscal year 1987.

During fiscal year 1987, major projects under the program included continuing work on new State geologic maps for Arizona, Hawaii, Montana, New Hampshire, New Jersey, New Mexico, Virginia, and Washington. Detailed mapping projects were carried out in Alabama, Alaska, Arkansas, Idaho, Illinois, Indiana, Maine, Minnesota, Missouri, Nebraska, Nevada, North Carolina, North Dakota, Oklahoma, Oregon, Rhode Island, Tennessee, Texas, Utah, Vermont, Wisconsin, and Wyoming to identify mineral, energy, and water resources and delineate geological hazards. Significant results from the overall program include

Discovery of new high-BTU coal seams and fluorspar exploration targets in Illinois.

• Development of land-use plans for the southern coast of Maine that will protect ground water in this urbanized area.

• Completion of detailed geologic mapping of four mountain ranges in the Phoenix, Arizona, region, which has stimulated mineral exploration and aided in the planning for construction of a major earth-fill dam.

• Stimulation of mineral exploration in the Wind River Mountains area of Wyoming and of petroleum exploration in the Ouachita Mountains of Oklahoma and Arkansas.

Beginning in fiscal year 1988, the COGEOMAP program becomes a major component of the new National Geologic Mapping (NGM) program, which will seek to accelerate geologic mapping to meet the continuing strong demand for modern geologic maps from the public and private sectors. Other major goals of the NGM program are

Identifying, on a province-by-province basis, critical earth-science data needs that require new or additional intermediate- to large-scale geologic mapping.

• Establishing national geologic mapping priorities by province in order to focus future mapping on critical areas.

Increasing the coverage of the United States by intermediate- and large-scale geologic maps in provinces or portions of provinces of highest national priority. • Coordinating and integrating subsurface studies, particularly geophysical, geochemical, and hydrologic investigations, with surface geologic mapping.

• Preparing and maintaining a system for an annual nationwide inventory of current geologic mapping and published map