mately ‘2000 ft wide. The result is of further interest becausethére presently exists no deep water channel on the north side of Bikini Atoll and the circulation of sea water is confined essentially within the lagoon of the Atoll. The breaching of the reef near Namu will provide the possibility of a deep channel, which may be further deepened by tidal action as the sea water flows in and out of the lagoon. On the other hand, there is also the possibility that the crater will be closed through sand deposition. The result will be interesting, however, because for the first time in history there is a possibility of altering a geographical feature by use of a nuclear explosion. On Operation Castle a number of shots are to be located on barges several thousand yards offshore within the lagoon, where the water depth is about 30 fathoms, or 180 ft. It seems that no substantial craters will be formed in the lagoon floor for shots on the order of 1 Mt unless the bottom is ooze. If the deep hole in the Mike crater has been correctly attributed to a local geologic structure, and its shape peculiar to its close proximity to the outer edge of the reef, then the depths of Fig. 3.6 are applicable, from which the crater depth over soil itself would be only about 75 ft for shots in the order of 5 Mt. Because the hydrodynamics are such a strong function of the relative density between air and either soil or water at the in- terface, it would appear reasonable that the crater “in water” will not extend to a depth which is greatly different from that in soil. Since the depth of the lagoon is considerably beyond the expected depth of the crater in soil, there is a good probability that no crater at all will be observed at the lagoon bottom for these barge shots. In any case, they will be difficult to measure by sounding; the depth will be comparable or small compared with the height of the natural water waves in the Bikini lagoon. REFERENCE 1. F. B. Porzel, Soil Pressures and Energy Transfer on Mike Shot, Los AlamosScientific Laboratory Report LA-1529, October 1952, 21 syS have a crater about 3000 ft in radius. It is proposed to fire it on the reef southwest of Namu in Bikini where the reef itself is only approxi-