32 



COLIN 



tied up in leaf-litter on the soil surface, but relatively little 

 is actually found in the soil. 



The larger islands of the atoll have good freshwater 

 lenses beneath them. All the islands are quite low, so the 

 water table lies very close to the ground's surface. It is not 

 necessary to drill more than about 3 m deep to hit water. 

 The groundwaters of Encwetak have been studied in some 

 detail (Chapter 4 of this volume). 



MAN-MADE FEATURES 

 Quarries 



Areas of reef flat adjacent to several islands at 

 Encwetak were quarried or excavated for building or road 

 construction purposes. A single quarried area is at the 

 rKjrth end of Enewetak Island adjacent to MPRL (Fig. 4). 

 This area was quarried during the Japanese occupation. 

 Because a wide area of reef flat was left seaward to 

 reduce wave swell entering the quarry, the Enewetak 

 quarry is calm during low tides and is an ideal location for 

 snorkling and diving. Numerous investigators at Enewetak 

 have taken advantage of this. The Enewetak quarry covers 

 about 2.75 hectares and averages about 1.5 m in depth, 

 with the deepest sfX)t being 3 m. The biological communi- 

 ties present in it are discussed in Chapters 7 and 8 of this 

 volume. 



The reef flat at the south end of Medren Island was 

 also quarried. Although slightly larger than the Enewetak 

 quarry, little protective reef flat was left seaward of it; 



therefore, it is more open to wave action from the open 

 ocean. A small quarry occurs at the north end of Medren 

 on the reef flat. 



Seven relatively small areas were quarried on the reef 

 flat near the middle portion of Runit Island. All are well 

 inside the seaward margin of the reef flat and are well pro- 

 tected from waves at low tides. 



At Enjebi, there are a few areas toward the north end 

 where the reef flat was quarried. There is one elongate 

 rectangular quarry and two small round ones. Also, on the 

 western side of the island are three irregular areas next to 

 shore, deeper than the adjacent bottom, which were prob- 

 ably quarried for construction of the Japanese airstrip 

 there during World War II. 



Craters 



Six craters remain from nuclear weafwns testing at 

 Enewetak. Three craters are the result of atomic bomb 

 tests. The other three are from thermonuclear weapons 

 tests and are roughly three orders of magnitude larger in 

 area and volume. Two atomic bomb craters are at the 

 north end of Runit Island (Fig. 5). The histories, morphol- 

 ogy, and subsurface geology of the Enewetak craters are 

 extensively discussed by Ristvct (1978), resulting from 

 work done by the Air Force Weapons Laboratory, Albu- 

 querque. Both Runit craters are about 120 m in diameter. 

 The most lagoonward. Cactus crater, was used for con- 

 struction of the Cactus crater crypt during the Enewetak 

 cleanup from 1977 through 1979 in which the crater was 

 filled with cement, contaminated debris, and soil. A 



Fig. 4 Aarlai view ot the north end ot tnewetaK isiana snowing the buildings of the Mid- 

 Pacific Rasearch Laboratory and to the right of them the quarry on the reef fiat. [Photo by 

 E. S. RecM.] 



