PHYSKDGRAPHY 



31 



which have the characteristics of typical algal ridge struc- 

 tures, they are covered with fleshy algae. Indications are 

 that these areas were live algal ridges sometime within the 

 relatively recent past, but whether man has played a role 

 in their demise is uncertain. There is one small area of live 

 algal ridge still present at Enewetak, near the island of 

 Ananij, which occurs at the easternmost extension of the 

 reef flat. This and the ecology of the reef flat are discussed 

 in subsequent chapters. 



The Seaward Slope 



The seaward slope from the reef flat to the dropoffs to 

 depths over hundreds of meters is narrow all around 

 Enewetak. The edge of the seaward slop>e is marked by 

 "spur and groove," alternating reef and rubble fingers 

 projecting seaward where the waves break. On leeward 

 reefs, there are no distinct spur and groove formations but 

 a deeper series of promentories and reentrants in the 

 upper 15 m. On windward reefs, a rock bottom then 

 slopes away gradually to a break point at the 18 to 30 m 

 depth where the bottom begins to slope much more 

 steeply. Oceanic depths are quickly reached. 



The width of the seaward shelf varies around the atoll. 

 It is widest off Enewetak Island, being about 400 m wide. 

 Other areas of the windward reefs are narrower so that it 

 is only 100 to 200 m wide on the northeastern reefs 

 between Lojwa and Enjebi. On leeward shores the shelf is 

 very narrow, only a few tens of meters wide. It is literally 

 possible to stand on the reef flat and throw a stone into 

 depths of 100 fathoms. 



The Islands 



There arc approximately 40 islands at Enewetak, 

 excluding a few small sand islands remaining above water 

 at high tide. Two islands (Elugelab and Lidilbut, not shown 

 in Fig. 1) were vaporized by nuclear testing, and three oth- 

 ers were so severely altered that only small remnants 

 remain (located in the northwest part of the atoll). The 

 vegetation of most islands at Enewetak has been progres- 

 sively and increasingly altered compared to the nondis- 

 turbed state. The alterations occurred initially by the estab- 

 lishment of coconut groves, later by wartime construction 

 and damage, and finally by nuclear testing activities and 

 subsequent military activity. Extreme alteration occurred 

 again during the Enewetak cleanup with the aim of re- 

 establishing the coconut groves. The only islands which 

 have essentially undisturbed vegetation are the five south- 

 western islands and Biken (see Chapter 11 of this volume 

 and Chapter 3 of Volume II for further details). 



The islands can be grouped into several reasonably 

 natural units defined by significant gaps between units and 

 identified by direction location. Often these units are identi- 

 fied by compass location and are defined here. 



The "southwest islands" of Enewetak are the five 

 islands from the southerly Kidrenen through Ikuren. They 

 are separated by both distance and intervening passes 

 from isolate Biken, which will be termed the "western 



island," and from Enewetak Island. The islands of 

 Enewetak, Bokandretok, and Medren are called "south- 

 eastern islands"; they share a common reef flat and are 

 separated from all others by passes. The ten "central 

 islands" are those of the windward side from Japtan 

 through Runit, including Jedrol. The "northern islands" are 

 those 15 to 16 islands from Bijire or Billae through the 

 northern Boken. They are separated from the central 

 islands by several kilometers of op)en reef flat. The last 

 group, the "northwest islands," from Bokoluo to Luoj, are 

 separated from the northern islands by the large MIKE and 

 KOA craters and consist of four islands and one sand bar. 



The islands consist largely of coral sand, rubble, and 

 boulders with areas of exposed beach rock and reef flat 

 pavement. In certain areas, large quantities of cement 

 debris are incorporated among coral boulders and rubble. 

 All the islands are low, the highest elevation being approxi- 

 mately 4 m on Enewetak Island. Beaches occur on many 

 lagoon shores, the most extensive and continuous today 

 found on Medren. Enewetak Island in pretesting days pos- 

 sessed an apparently continuous beach, but the lagoon 

 shore has been so altered by the construction of seawalls 

 or by the dumping of riprap that sand beaches occur only 

 in short stretches today. 



The ocean shore of islands on the windward side of 

 the atoll facing the reef flat often have alternating 

 beach-beach-rock shores. Sand beaches here, however, do 

 not extend below the intertidal, merging with the reef flat 

 or rock which extends offshore. 



Vegetation occurs above the high tide line on all 

 shores. There are no mangroves or mangrove-like terres- 

 trial plants extending into salt water at Enewetak. With the 

 exception of Biken and the five southwestern islands, the 

 vegetation has been extremely altered. 



Enewetak, Medren, and Japtan Islands are residence 

 islands. Houses were constructed and other buildings were 

 converted during the Enewetak cleanup. These three 

 residence islands, plus Ananij and the islands from Billae 

 through Aej, were planted with coconut palms between 

 1978 and 1979. Coconut palms have not been planted on 

 Enjebi, the second largest island of the atoll, except for an 

 experimental garden plot that was established in 1975 by 

 Lawrence Livermore National Laboratory and that contains 

 coconuts, pandanus, and breadfruit. 



The soil of Enewetak Atoll islands consists of little 

 more than calcium carbonate sand and rubble (Chapter 11 

 of this volume). This material has virtually all its origin 

 from the sea and is derived from corals, calcareous algae, 

 foraminifera, and a wide variety of organisms producing 

 smaller amounts of carbonate materials. Occasionally, 

 pieces of pumice which have drifted to Enewetak are 

 found near beaches. More rarely, noncarbonate rocks, car- 

 ried by rafting debris such as fallen trees, are found. 



Enewetak soils have very little organic matter or 

 nutrients. This is particularly true for the highly disturbed 

 islands where human activity has eliminated the normal 

 ground cover of vegetation and nesting birds. On normally 

 vegetated islands, a limited amount of organic materia! is 



