sisted of firing a series of 105-mm howitzer HE
Table 1. Predicted apparent scaled radius and
depth of craters.
projectiles with point-detonating fuses, the type
of fuse and projectile normally fired into the ERF
Ice†
Snow*
Frozen silt**
impact area for training. A series of HE projectiles
0.87 Mc1/3
0.71 Mc1/3
0.56 Mc1/3
Ra
with time-delay fuses was also fired to determine
0.30.5 Mc1/3
0.24 Mc1/3
0.28 Mc1/3
Da
if the slight delay before detonation would allow
the projectile to penetrate the ice cover before ex-
Mc is the mass of the explosive charge in kilograms.
ploding. The HE projectiles were fired from M101A1
Radius and depth of craters are in meters.
105-mm howitzers of the 4th Battalion, 11th Field
*Mellor (1965)
†Mellor (1986a)
Artillery. The howitzers were set up at Firing Point
**Mellor and Sellmann (1970)
One (FP1), 4 km east of the impact area (Fig. 1).
The second phase of tests used 81-mm mortar pro-
jectiles, using both point-detonating and delay
of charge mass), allowing comparisons of craters
fuses, into an area just north of the 105-mm im-
formed by explosive charges of various sizes. For
pact area. The 81-mm mortars were set up at FP
surface explosions, that is, explosions with a depth
Fox, 1500 m southeast of the impact area. The
ratio of zero, the predictions in Table 1 can be made
third phase of tests consisted of 60-mm mortar
for the size of craters formed in snow, ice and fro-
projectiles with point-detonating fuses fired into
zen silt using the equations presented in Mellor
an area west of the 105-mm impact area. The 60-
(1965, 1986a) and Mellor and Sellmann (1970).
mm mortars were set up at FP Upper Cole, 1000 m
For example, a 105-mm howitzer M1 projectile,
south of the impact area. The tests were observed
containing 2.3 kg of HE, has predicted apparent
and photgraphed from Observation Point Fagan,
radii of the craters resulting from a contact burst
1000 m east of the impact area. Firing information
for snow, ice and frozen silt of 1.15, 0.94 and 0.74
for the weapons used is presented in Table 2.
m, respectively. The predicted apparent depths
After the firing we photographed and measured
would be 0.400.66, 0.32 and 0.37 m, respectively.
the apparent diameters and apparent depths of the
The differences between the apparent crater formed
craters. Samples of snow were collected from around
by an explosion vs. the true crater may be substan-
the craters to analyze for explosive residues.
tial; they depend on whether the charge depth is
All the dimensions given in this report are ap-
zero (i.e. at the surface) or at some depth below
parent crater diameters and depths. Because of the
the surface. The apparent crater is the excavation
safety constraints and time limitations, none of the
as it appears to an observer immediately after a
craters were excavated to measure true crater di-
blast (Livingston 1960). It often contains fall-back
mensions. However, except for the broken ice ob-
material, defined as the loose material thrown up
served in the bottom of some 105-mm-howitzer
by the explosion that has fallen back into the cra-
craters, most craters appeared to have little loose
ter. Excavation of the fall-back material in the cra-
material in them.
ter reveals the true crater.
The analyses of our crater measurements as-
sume that all explosions were contact bursts. A
contact burst is one in which the center of mass of
ARTILLERY TESTS
the exploding charge is at the surface, giving a
depth ratio of zero. In actuality, the projectile with
The test firing onto the ice of Eagle River Flats
a point-detonating fuse may penetrate the sur-
took place on 20 March 1991. The test firing was
face by some unknown amount before exploding,
conducted in three phases. The first phase con-
Table 2. Firing information for weapons used in the tests.
Weapon
Round
Barrel angle
HE weight
105-mm howitzer
105mm HE M1
350354 mils =
2.3 kg
19.7-19.9
M101A1
(5.0 lb)
81-mm mortar
M374-A-3-81 mm
12171289 mils =
0.95 kg
68.572.5
M252
(2.1 lb)
1166 mils = 65.6
60-mm mortar
M49-A-4-60 mm
0.19 kg
M224
(0.42 lb)
4
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