crater. It is felt that the water waves generated by the shot were insignificant since the water over the reef was only a few feet deep. Photographs show that the Cactus crater was filled with water but essentially unwashed. Preshot and postshot photographs are shown in Figures 9, 10, 11, and 12. . The measured crater radius of 170 feet and depth of 34.5 feet were obtained from photugrammetric measurements, Figure 13, and from lead~line soundings. The profile, Figure 15, was plotted from preshot and postshot survey data and lead-line soundings along 6 radii, Figire 14. The photogrammetric measurements were made from aerial photographs. To compare these crater dimensions with those from the dry soil curves of TM 23-200, it was necesSary to obtain factors for adjusting the Shot Cactus dimensions. This can be done by comparing Shot Cactus and NTS environments (soil strength and moisturecondition). The soil at Site Yvonne is interspersed with layers of hard and soft cemented sand, coral, and shells, and is considered to be more cohesive than the NTS soil. Tests conducted under Project 1.8 indicated that cementation at Site Yvonne was much more complete than at Site Irene and, therefore, less crushing would be expected at high stress levels. Drilling logs were made from holes drilled 400 feet southeast of ground zero; results are presented in Table 2. In order to adjust the crater radius for soil strength, an F, factor value of 0.9 is arbitrarily assumed because, as stated above, the Site Yvonne soil is more cohesive than NTS soil, upon which the dry soil curve was based, but not as hard as granite (for which a factor of 0.8 is given). Soil moisture conditions, although slightly different from those existing at the Shot Lacrosse site, are assumedto be fully saturated for the purpose of these calculations, and a Saturation factor of 1.5 is used. The adjusted scaled crater radius is 48.3 feet. The radius given in TM 23-200 for the same crater under NTS conditions is 60 feet. If Shot Cactus height of burst were adjusted to a surface burst by using an HOB factor, the corrected radius would be 51.5 feet to 64 feet given in the TM or a difference of approxinately 24 percent. This percentage is well within the accuracy of the basic TM curve. It is probable, however, that a factor of 1.4 instead of 1.5 should have been used as the saturation factor since the top few feet of the soil around ground zero was above the water table and was‘essentially in a dry state. If this were the case, then the scaled adjusted radius would have been 59 feet giving a difference of only 10 percent of the listed value of 64 feet. Both values are plotted in Figure 3. _ The adjusted crater depth was more a matter of conjecture but it was felt that the underlying formations, acting as interfaces, decreased the depth considerably. The relative flatness of the crater bottom and the steep sides tended to support this theory. Similar craters were formed from high-explosive detonations in soils having cement interfaces at various depths, Reference 8. The Cactus crater depth was predicted by using data from Shot Lacrosse which had‘a depth of only 44 feet. The drilling log also shows a hard cemented interface at approximately this depth. The depth of a crater in saturated soil would normally be predicted as 1.5 times the value in dry sand, as taken from TM 23-200. Crater Dimensions, Shot Koa. The Shot Koa device was detonated inside a 30-foot-diameter water tank on the west end of Site Gene at the edge of the Ivy Mike crater. A preshot photograph with a line indicating the crater edge is shown in Figure 16. A postshot picture of the crater edge is shown in Figure 17. Station 360.01 can be identified in both photographs. Preshot and postshot survey radii are shown in Figure 18. The postshot radii are displaced from the preshot by a distance of 208 feet, making it difficult to relate the preshot overburden to the postshot crater. To better define the crater the lead-line soundings along the postshot radii have been shifted 208 feet to correspond with preshot data and plotted as profiles, Figures 19, 20, and 21. This procedure introduces some error, particularly insofar as depth measurements are concerned; however, the error is slight and no reasonable basis for correction exists. Radii 1 and 4 pass through ground zero and show the true measured crater depth. A crater radius of 1,825 feet was given in the ITR and was found by measuring the distance from ground zero to Station 360.01, which was within 5 feet of the crater edge. A more accurate measurement of the crater profiles would give a radius of slightly in excess of 2,000 feet. 32