Chapter 4
DISCUSSION
In order to enhan e the value of the discussion of the Redwing cratering results, a corn-~
parison should be made with crater measurements from other nuclear bursts in the Eniwetok Proving Gr ound. A summary of EPG cratering data is presented in Table 4.1.
Crater radii, sca ed to 1 kt, are plotted against height of burst on Figure 4.1. A similar
plot of crater dep hs is made on Figure 4.2. Cumparing these curves with the curves for
dry soils from Ti! 23-200, it is apparent that some explanations are in order. The larger
radii measured fcr the EPG craters may be attributed to soil factors (Reference 9), but
it is felt that the vashing action was an important contributing factor. This is also reflected in the fact that crater depths are less in the EPG. It appears that some peculiar
burst configurati: n or eavironmental condition influenced the crater dimensions of Shots
Lacrosse, Semir ile, and Zuni to a marked degree.
It should be re-emphasized here
that only apparen or washed crater measurements were taken during Redwing as well as
during all previo s cratering bursts, both at NTS and at EPG, with one exception (Teapot
Shot 7), for whic true crater dimensions were taken. As defined in Section 1.3, the ap~
parent crater is hat deformation of the ground surface that is visible to the eye subsequent to the com; letion of the dynamic effects of the explosion. It should also be remem-
bered that the m. jority of the craters measured in the Pacific had vented to open water
and had undergor : some degree of washing from waves created by the explosion. The
alteration of the crater through washing action is believed to differ for each shot, and it
is felt that the extent by which the waves generated by the explosion removed the material
deposited in the crater lip is a rough measure of the degree of washing.
As mentioned earlier, soil type, energy partition, and height or depth of burst all
play animportan role in determining crater size and shape. The data from this project
give good examp!:s of these effects.
4.1
GEOLOGICAL STRUCTURE
Investigation cf the geologic structure of Eniwetok were made by Scripps Institution of
Oceanography an! summarized by Porze] in Reference 1. Another investigation was made
and the results p :blished in the Bulletin of American Association of Petroleum Geologists
in October 1953 (Reference 6).
Since Bikini Atoll is similar in structure to Eniwetok, a
brief summary o° Eniwetok is felt to be sufficient (References 7 and 8).
The atoll consists of various layers of lenses of material interspersed with large
:
cavities of water and air. With the exception of a few feet of hard rock at a depth of approximately 20 f et, the atoll is composed primarily of soft, unconsolidated sedimentary
beds contained on the ocean side by a sheath of coral rock of varying thickness.
This
container wall is expected to have numerous weak spots because of joints and fissures
characteristic of coral formations. At depths greater than 1,100 feet, hard or firm sedimentary layers become more prevalent and at a depth of 2,900, running up to 1,000 feet
in thickness, the atoll is made up of a soft, chalky limestone. The atoll rests on a consolidated basalt floor, which is about 4,000 feet below sea level.
The excess density of the inner material that makes up the atoll over that of the water
represents an enormous amount of potential energy by virtue of its elevation above the
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