PHYSICAL CHARACTERISTICS of CRATERS from NEAR-SURFACE NUCLEAR DETONATIONS OBJECTIVES The objectives of this project were to (1) measure the physical characteristics of the apparent craters and lips from near-surface nuclear detonations; (2) compare and correlate the data so obtained with those already available in order to more firmly establish the capability of predicting craters from surface-burst weapons; and (3) documentthe crater lip, throwout, and permanent vertical ground surface displacement surrounding the apparent craters. BACKGROUND In the last several years, the increased interest in cratering as a primary damage mechanism has resulted in a need for data to improve crater-prediction techniques, particularly for surface detonations. Craters from twelve nuclear detonations in the EPG were documented during Oper- ations Greenhouse, Ivy, Castle, and Redwing (References 1, 2, 3, and 4). Results have been analyzed and used in the prediction curve with factors given in TM 23-200 (Reference 5, Figure 2-20 through 2-26B). * Figures 1 and 2 of this report contain a summary of scaled crater data from past EPG operations as well as cratering curves taken from TM 23-200. The data show considerable scatter which is due primarily to variation in soil structure of the islands, washing action of waves generated by the shots, and washingaction bytidal effects. TM 23-200 suggests multiplication factors be used in conjunction with the TM dry-NTS-soil curves to account for these environmental conditions. In the theory section of this report, results from past EPG craters are compared with TM 23-200 by the use of factors. ° In past operations, unusual weapon-tamping configuration has influenced the crater size (Ref- erences 4 and 6). It would be impossible to assign crater adjustment factors for the many poss- ible types of weapon-tamping configurations. One configuration that has not been fully evaluated is that in which a large water tank encloses a device, i.e., Shot Seminole, Operation Redwing (Reference 4). This configuration became important to this operation because Shot Koa had a Similar tamping configuration. The crater formed from Shot Seminole was larger than expected, and this was attributed to the water enclosure. It was expected that Shot Koa would give addi- tional information on this effect. Reliable data on crater lip dimensions have been limited to a few high explosive cratering series and three nuclear craters. Lip dimensions for these shots have been taken from smoothed, average profiles representing actual lips of rough and irregular shapes. Several methods of pre- dicting lip height are given in test literature; TM 23-200 indicates that the crater lip height is onefourth of the crater depth, while other sources indicate scaling by fractional powers of the yield (Reference 7). Predictions of lip width have included areas large enough to contain all the large throwout fragments. THEORY At the present time predictions of crater dimensions are based largely on empirical curves derived for the most part from data from high explosive charges supplemented by a few nuclear