ocean floor. For this reason, it is considered to be in a metastable state contained by
the structural strungth of its coral jacket, by rock formations within the material, and
by internal friction of the material formation (Reference 1),
4.2
SHOT LACROSSE
The Lacrosse crater presents an example of a relatively unwashed crater from a
large-yield explosion.
The crater lip (Figure 3.2) did not breach, showing that there
was no rapid flow of water into and over the crater.
There appears to be, however, some
evidence of sloughing of the crater side, as shown by the profile (Figure 3.3). Scaled-~
wise, the crater vas smaller in radius and greater in depth than EPG washed craters and
TABLE 4.1
EPG CRATER DATA
~
Shot
“Weapon Burst
Yield
Height
He S44Crater
Ratu
Ho-ft
Redwing
Lacrosse
Zunt
Seminole
Mohawk
Tews
Greenhouse
Dog
Easy
George
Ivy
39.5 xt
3.53 ‘At
.
§.01 Mt
.
.
46.7 <t
1?
9.25
~let
300
20*
300
R - Sealed
Crater
Depth
D,-Scaled
fect?
De-ft
r™
ftfet?
R,-ft
5.00
0.61
202
1,155
59
76
44
103
17.6
13.4
1.19
2,000
_
nl?
129
300
83.5
700
195
200
Ivy Mike
10.5 Mt
35
1.6
2,800
128
Castle
Castle No. 1
14.5 Mt
15.5
0.64
3,000
128
CastleNo. 3
110}
13.6
2.84
400
83.4
.
3
R/D
Site
18.7
_
11.2
_
_16.8
Eniwetok
Bikini
Eniwetok
Eniwetok
Bikinl
_
_
Eniwetok
_
Eniwetok
—
—
Eniwetok
120
11.98
23.4
Eniwetok
240
21.8
12.8
Bikini
_ 40
12.5
10
Bikini
* See diacusgion about ' arst height.
falls between the esults expected for NTS soil and those expected for EPG soil. The La-~
crosse crater als: differed from other EPG craters in that the sides were steep and the
bottom relatively ‘lat. The steep sides of the crater are similar to those observed in
craters formed in rock or concrete by high explosives. The flat bottom is also similar
to those formed ir. hard rock or formed in material above a rock or concrete interface
(Reference 10). In examining the shot site, it was found that Lacrosse was detonated
over a large cemented platform, probably filled with coral, situated on a reef located at
the northwest end of Site Yvonne. A drilling log, to the northeast of ground zero (made
during Operation lardtack) showed layers of hard cemented sand at 16 and 45 feet below
the ground surface.
Since the Lacrosse crater is the first nuclear crater in saturated soil that did not
breach to open water, it is to be expected that it will be compared to NTS craters by
means of a soil factor. However, to obtain such a factor, it is necessary to compare
the Lacrosse crater conditions with those of the standard dry-soil curves for NTS. In
order to adjust the Lacrosse crater radius, it is necessary to apply a correction factor
for hardness, since the Lacrosse site is harder and more rocklike than the NTSsoil
(which is considered to have a factor of 1) but not as hard as granite (for which a factor
of 0.8 is given). If a factor of 0.9 is assumed and the radius adjusted for hardness and
scaled to 1 kt, it is approximately 65.6 feet instead of 59 feet. The equivalent crater
radius obtained fiom TM 23-200 is 45 feet, thereby making the soil factor, presumably
due to moisture content, 1.46.
This would tend to substantiate TM 23-200, which gives
32