because of the small time delay between the im-
pact on the surface and the detonation of the
explosion. In softer material such as mud or deep
snow, where there is no hard surface to initiate
the detonation, the point-detonating fuse will
detonate once it senses a loss of momentum.
Based on the results of the March 1991 test,
Eagle River Flats was reopened as an impact
range in January 1992. Training began again in
ERF on 7 January 1992, when the 4th Battalion,
11th Field Artillery fired a series of 105-mm
howitzer projectiles into the impact range as
part of a training exercise. Most projectiles im-
pacted on the ice-covered levee and mudflats
near the river. Several projectiles impacted on
the ice-covered shallow ponds near the east side
of the impact area. After the firing was com-
pleted we were able to measure several of the
craters formed in the ice of the shallow ponds.
Figure 2. Explosion of a 105-mm HE projectile in the test
We wanted to compare the effects of exploding
area.
105-mm howitzer projectiles on a floating ice
sheet with our previous observations on the ef-
ters no. 16 and 9); all values are for the apparent
fects on grounded ice and frozen ground. We also
craters. All seven measured craters were oblong
compared the measured crater parameters with the
in shape, probably due to a low impact angle caused
predicted parameters for explosives on floating ice.
by the low firing angle (19.719.9). The longest
axis of the craters ranged from 2.26 to 3.63 m, and
the shortest axis ranged from 1.89 to 3.05 m. The
RESULTS
mean lengths for maximum and minimum axes
105-mm howitzer test firing
were 3.17 and 2.45 m, respectively. This gives a
Eight high-explosive 105-mm projectiles with
mean apparent diameter of 2.81 m, or a mean ap-
point-detonating fuses were fired into the impact
parent radius Ra of 1.41 m. The seven measured
area. Seven of the eight projectiles detonated on
craters were shallow, between 0.2 and 0.44 m, with a
contact with the ice (Fig. 2). The impact area had a
mean apparent depth of 0.32 m. In all but one case,
the ice sheet was still intact, with only a 0.6- to 1.0-
20-cm snow cover on the ice sheet, and the ice
m-diameter area of broken ice in the center of the
thickness varied from 0.30 to 0.60 m. The measure-
crater (Fig. 3).
ments of seven craters are included in Table 3 (cra-
Figure 3. Crater formed by a 105-mm HE projectile.
5
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