distance of approximately 28 miles and arrived as though generated close to ground sero,
having travelled across the lagoon at the velocity of shallow water waves. Since Ivy Mike
was an island shot, it was not wholly surprising that it did not generate waves in a manner
analogous to high explosives detonated on water. Although the Mike shot did reach into
the iagoon, the generation and collapse of the cavity was not considered to be identical to
that from a burst on water. Therefore, it was believed that the shot environment cancelled out most of the direct generation region.
In contrast to the Mike results, Castle data indicated that the recorded waves did emanate.from the central region of the detonation. The first arrival. was a short-period,
highly damped series of ground- or water-transmitted shocks. Following these, the
2 &t Free Air
Overpressure , psi
from WT- 710
300
1000
Horizontal Range , Feet
2000
(Scaled to (kt)
Figure 2.11 Averaged pressure-distance data.
records clearly showed the arrival of the air-transmitted shock wave. Next, preceding
the direct water wave, a slow rise in pressure (water) occurred that was postulated to
be caused by large quantities of water and coral debris falling back to the water surface.
This was abruptly lost in the arrival of the direct water wave —the first arrival in all
cases being a crest followed by a trough. These appeared to act as oscillatory waves,
the time of arrival of the first crest showing a propagation velocity fitting the relation
Ve (ghy!/2, where h is an average depth of 170 feet assumed for the Bikini Lagoon.
Refraction and reflection against a reef or shore line may significantly reduce or amplify the destructive capabilities of water waves at termination. At Bikini, How Island
is an example of a protected shore, while Nan is an example of one highly susceptible to
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