tity 1 — (V/V) is not far different from zero, whereas for strong shocks in air the same quan- tity is not far different from 1. The density of air relative to soil is in the order of 1079. At Eniwetok, the water table comes within a few feet of the surface, the interstices of soil are water-filled, and the incompressibility of water further favers the propagation of shocksin air over the shock in ground. The greater area of the air shock is indicated in Fig. 1.1, which follows from similar considerations involving the shock velocity, and this area enhances the transfer of energy to the air by another factor of approximately 2. In LA-1529 it was shownthat, over a substantial range of pressures, the relative rate of work of the ground shock to the air shock was around 0.001; something less than 0.1 per cent of the energy of the bomb is transferred to the soil and hence available for crater formation. The situation is somewhat different in very porous soils, such as at Nevada Test Site. There the soil may contain 40 per cent air by volume, so the quan- tity 1 -(V/V,) is not small, but a number more like 6/10. In this case, the relative rate of work in soil to air is still proportional to the square root of the density ratios and is more like a factor of only 100 to 1 in favor of air over soil. In the paper on nuclear explosionsin soil, it was predicted that slightly less than 1 per cent of the energy could be transferred to the soil and hence available for crater formation at Nevada Test Site. Of course, crater formation is not likely to be a uniform or reproducible process in any real soil because of marked inhomogeneity in compressibility as well as in density, which is due in turn to pockets of air or water, rock formations, or differences in particle sizes. At the outset, the most one can hope for is a general description which suits the average condition. © Local variations in crater size by factors of 2 seem entirely reasonable. 1.3.2 Geologic Structure of the Atoll at Eniwetok Crater formation at Eniwetok is further beset by difficulties involving the geologic structure of the Atoll itself, which was shown by geologic investigations under the direction of H. K. Stephenson of LASL and Roger Revelle of the Scripps Institution of Oceanography. The Atoll rests on a consolidated basalt floor which is about 4000 ft below sea level. The overlying 4000 ft are mostly loose, unconsoli- dated sands or coral but interspersed with large pockets of water and presumably local stringers or networks of coral formation. The relatively loose material is contained on the ocean side by a sheath of coral rock of varying thickness which is expected to have numerous weak spots because of joints and fissures characteristic of corai formations. The excess density of this inner material over that of water represents enormous potential energy by virtue of its ele- ‘vation above the ocean floor. The Atoll is con- sidered to be ina metastable state but is presently contained by the structural strength of the coral rock, by rock formations within the sands, and by internal friction in the sand formation. The theory of dilation has been appliedto this geologic structure. The passage of the ground shock may break up the coral sheath and rock formation to an unknown extent and disturb the matrix of sand particles. The theory suggests that the sand formation will momentarily behave as a dense liquid after passage of the shock and flow plastically; the excess hydrostatic pressure may now breach the weakened sheath, permitting the sand material to flow to lower depths. If this structural failure occurred at a sufficient depth, the potential energy released could be-. come comparable to the energy in the destructive oceanwide tsunami, and, by virtue of this trigger mechanism, this energy would greatly exceed the small amount of energy transferred to the soil from the nuclear explosion. The purpose of LA-1529 was in good part to show that a large-scale geologic failure of the Atoll could not be reasonably expected. On the other hand, the theory and the geologic structure suggest the possibility that holes or pockets may occur in or near the crater, which would be more representative of the geologic struc- ture than of the nuclear explosion. Near a structural weakness material could flow through fissures in the ruptured wall, both because of the shock pressures and because of gravity. 1.3.3 Hydrodynamic Variables at the Ground for a Tower Shot Some estimates of the magnitude of the hydrodynamic variables in the air shock with their distribution in space are contained in a study by the author and are reported in the Greenhouse Handbook of Nuclear Explosions.’ This provides rough theoretical estimates for the air pressures near Ground Zero of Greenhouse Easy