Chapter 1 Introduction 1.1 PURPOSE The purposeof this test was to study the general characteristics of the craters formed from nuclear explosions in connection with Operation Greenhouse at Eniwetok and, if possibie, to formulate general rules as to their size and shape. The crater shape, especially at Eniwetok, may well be a dynamic rather than a static problem, as will become apparent in the discussion of results. In general, this report is restricted to the description and study of the craters at a late stage when they were in relatively stable configuration. Data are not available on, nor does the report consider in detail, the intermediate configurations of the craters. 1.2 HISTORICAL This test was performed at the instigation and request of Frederick Reines, Director of Pro- gram 1 for Operation Greenhouse. In his directive, reproduced in Appendix A, detailed pians were given for the array of stakes, as well as for surveys to be made before and after Dog and Easy shots. Edward J. Zadina, then of J-Division, Los Alamos Scientific Laboratory (LASL), was in charge of the project until he left J-Division in the spring of 1952, at which time the responsibility for the report was assigned to the present author. Data for the crater survey were received in the late summerand fall of 1952. The prepara- tion of the report has been delayed, however, in part by preoccupation with other operations. In the meantime, the crater survey for Mike shot of Operation Ivy became available and has been incorporated as part of this report. The author would have liked to make more detailed analyses and study of the results, which the subject deserves. However, some worth-while conclusions appear justified from a cursory study; this, together with his impending trans- fer from LASL, makes it worth while to publish the report in its present form. 1.3 BASIC THEORY 1.3.1 General Characteristics of a Nuclear Explosion at a Soil-Air Interface Some general characteristics of the phenomena involved in a nuclear explosion at an inter- face between soil and air is contained in Report LA-1529.! This was based in turn on a detailed study for the nuclear explosion in soil in preparation for Jangle Underground shot. A principal result of both these studies is the vastly greater material and shock velocities in air relative to those in soil during the extremely high pressure phases of a nuclear explosion. This results in a very small energy transfer to the soil, and in relatively broad and shallow crategs. In LA-1529 methods are suggested and carried out for calculating the peak pressure as a function of distance beneath Ground Zero. The craters from nuclear explosions are expected to be markedly different in size and shape from those of TNT, and no attempt is made here to scale craters between TNT and nuclear explo- sions. Figure 1.1 is reproduced from LA-1529 and showsthe relative shape of the shock configuration for both nuclear explosions and TNT. Although the figures are intended to be qualitative, they are not exaggerated; the pronounced difference in shape of the ground shock is oc- casioned by the very different relative velocities between soil and air at the very high pressures