SPECIAL REPORT 95-2

Winter Tests of Artillery Firing into

Eagle River Flats, Fort Richardson,

Alaska

Charles M. Collins and Darryl J. Calkins January 1995
Abstract

Winter tests of artillery firing were conducted in the Eagle River Flats impact range

to determine the physical effects of exploding high-explosive (HE) projectiles on

the ice-covered terrain. Eagle River Flats is an estuary at the mouth of the Eagle

River used as the artillery impact range for Ft. Richardson. The Army suspended

use of the impact range following the discovery that white phosphorus (WP)

deposited in the salt marsh was responsible for large numbers of waterfowl

deaths each summer. The purpose of these tests was to assess if seasonal firing

of HE projectiles from 60- and 81-mm mortars and 105-mm howitzers into

Eagle River Flats could be resumed without significantly disturbing the sediments contaminated with WP. The results of the test firings indicated that a

minimum of 25 cm of ice over frozen sediment or a minimum of 30 cm of floating

ice over shallow water was required to prevent disturbance of the WPcontaminated sediment by exploding 105-mm howitzer projectiles. Only 10 cm

of ice was required to prevent disturbance by exploding 60- and 81-mm mortar

projectiles.

For conversion of SI metric units to U.S./British customary units of measurement

consult ASTM Standard E380-89a, Standard Practice for Use of the International

System of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 95-2

Winter Tests of Artillery Firing into

Eagle River Flats, Fort Richardson,

Alaska

Charles M. Collins and Darryl J. Calkins January 1995

Prepared for

DIRECTORATE OF PUBLIC WORKS

FT. RICHARDSON, ALASKA

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Charles M. Collins, Research Physical Scientist, and Darryl

J. Calkins, Chief, Geological Sciences Branch, Research Division, U.S. Army Cold Regions

Research and Engineering Laboratory.

Funding for this effort was provided by the Directorate of Public Works, Sixth Infantry

Division (Light), Ft. Richardson, Alaska.

The authors acknowledge William Gossweiler, Directorate of Public Works, Ft. Richardson, for his support in helping to arrange the test firing. The authors thank Bruce Brockett, Geological Sciences Branch, for his assistance in the field measurements of craters. The

authors also thank Edward Chacho and Paul Sellmann for technically reviewing the manuscript. Finally, they thank the members of the 176th Explosive Ordnance Disposal Detachment for escorting them into the Eagle River Flats impact area and assisting them in the

field measurements of craters.

The contents of this report are not to be used for advertising or promotional purposes.

Citation of brand names does not constitute an official endorsement or approval of the use

of such commercial products.

ii
CONTENTS

Page

Preface ................................................................................................................................. ii

Introduction........................................................................................................................ 1

Background ........................................................................................................................ 1

Historical perspective .................................................................................................. 1

Evironmental setting .................................................................................................... 1

Impact area description ............................................................................................... 3

Previous research on cratering ................................................................................... 3

Artillery tests ...................................................................................................................... 4

Results ................................................................................................................................. 5

105-mm howitzer test firing........................................................................................ 5

81-mm mortar test firing ............................................................................................. 8

60-mm mortar test firing ............................................................................................. 10

Explosive residue .......................................................................................................... 10

January 1992 105-mm howitzer firing ....................................................................... 10

Analysis and discussion ................................................................................................... 11

105-mm howitzer test results ...................................................................................... 11

81-mm mortar test results ........................................................................................... 12

60-mm mortar test results ........................................................................................... 12

January 1992 105-mm howitzer firing results .......................................................... 12

Conclusions ........................................................................................................................ 13

Literature cited ................................................................................................................... 14

Abstract ............................................................................................................................... 15

ILLUSTRATIONS

Figure

1. Eagle River Flats, showing the firing points and impact areas ......................... 2

2. Explosion of a 105-mm HE projectile in the test area ......................................... 5

3. Crater formed by a 105-mm HE projectile ........................................................... 5

4. Ice lifted out of the bottom of crater no. 2, exposing frozen ground ............... 6

5. Ricocheting projectile exploding near the ice surface ........................................ 7

6. Shallow elongated crater produced by a ricocheting delay-fused projectile . 7

7. Ricocheting delay-fused projectile exploding high in the air ........................... 8

8. Crater formed by a point-detonating 81-mm mortar projectile on

grounded ice ................................................................................................... 8

9. Crater formed by a point-detonating 81-mm mortar projectile on a floating

ice sheet ............................................................................................................ 8

10. Camouflet formed by a delay-fused 81-mm mortar projectile ........................ 9

11. Nearly vertical hole in the camouflet ................................................................... 9

12. Crater formed by a 60-mm mortar projectile ...................................................... 10

13. Dud 60-mm projectile ............................................................................................. 10

14. Typical crater cross sections ................................................................................... 13

TABLES

Table

1. Predicted apparent scaled radius and depth of craters...................................... 4

2. Firing information for weapons used in the tests ............................................... 4

3. Measurement data from craters ............................................................................. 6

4. Measurement data from craters on pond ice ....................................................... 11

iii
INTRODUCTION

The objective for the winter tests of artillery firing into the Eagle River Flats (ERF) impact area

was to determine the physical effects of exploding

rounds on winter terrain. The winter ground conditions of interest include snow cover, ice cover, frozen and unfrozen sediments and to some extent

water beneath the ice covers in the pond areas.

Observations were based on the disturbance of the

snow, ice and sediment layers caused by exploding

105-, 81- and 60-mm high-explosive (HE) projectiles with both point detonation and delay fuses.

To determine the effects of these projectiles, test

firings using 105-mm howitzers and 60- and 81-

mm mortars were conducted in a small portion of

ERF during March 1991.

The purpose of these tests was to assess if seasonal firing of HE projectiles into ERF could be

resumed without significantly disturbing contaminated sediments. Firing only during the winter,

when the salt marsh is covered by a seasonal cover

of snow, frozen ground and ice, might significantly

reduce the disturbance of the sediments, compared

to the previous practice of year-round firing.

BACKGROUND

Historical perspective

In 1990 white phosphorus (WP) was identified

as the cause of waterfowl mortality in Eagle River

Flats, a U.S. Army artillery impact range at Ft.

Richardson, Alaska (Racine et al. 1992, 1993). Waterfowl use ERF as a resting, feeding and staging

area during the spring and fall migration periods.

In the past ten years, thousands of waterfowl have

died annually in ERF. The WP particles found in the

sediments of the shallow ponds were derived from

WP smoke projectiles fired into the impact area

over the years. The sediments are anoxic, allowing

the particles of white phosphorus to persist for

many years, posing a continual risk to waterfowl

feeding in the ponds.

Firing into the impact area was suspended in

February 1990. However, there is a continuing need

to conduct artillery training at Ft. Richardson, and

Eagle River Flats is the only feasible impact range

available. Renewed artillery firing would only use

high-explosive (HE) projectiles; the use of white

phosphorus would be discontinued. Continued firing into ERF during the summer would cause redistribution and mixing of the bottom sediments

in the shallow ponds and make buried WP particles accessible to feeding waterfowl. Winter firing into ERF has been proposed as a solution. The

purpose of this study was to determine if the snow

cover, ice cover and frozen ground that exist over

extensive areas of ERF during the winter would

isolate the sediments containing white phosphorus particles and prevent them from being disturbed or brought nearer to the surface by the explosion of artillery projectiles.

Environmental setting

Eagle River Flats, at the mouth of the Eagle

River, is an 860-ha estuarine salt marsh on the south

side of Knik Arm in upper Cook Inlet (Fig. 1). It is

approximately triangular in shape, 2.75 km wide

near the coast and 4 km long in an inland direction. It is bounded inland by a sharp topographic

and vegetation boundary of spruce- and birchcovered uplands. The salt marsh is composed of a

complex of landforms and vegetation zones. Natural levees occur along the banks of the river, with

large expanses of sparsely vegetated mudflats

along either side of the river and near the shore of

Knik Arm. The backwater areas away from the river

consist of zones of low sedge meadow, tall coarse

sedge marsh and shallow open-water ponds (Racine

Winter Tests of Artillery Firing into

Eagle River Flats, Fort Richardson, Alaska

CHARLES M. COLLINS AND DARRYL J. CALKINS
as deep as 40 cm in the tall coarse sedge

marsh area adjacent to the EOD pad.

Ice cover conditions

The duration, extent and properties

of the ice cover that forms over much

of ERF during each winter are governed by meteorological conditions,

snow cover, tidal effects, vegetation and

local hydrology. The number and peak

heights of high tides during the winter

determine the extent of periodic inundations and the rate of ice buildup. Observations and measurements of the ice

cover on a portion of ERF during the

1990-91 winter indicate a very complex

situation (Taylor et al. 1994).

The extent and thickness of the ice

cover are initially governed by the water surface elevations in the pond areas. The open ponds are normally the

first areas to freeze over, forming congelation ice. Standing-water areas with

heavy sedge and bulrush vegetation

normally freeze later due to the insulating effect of the vegetation. Without

tidal influences the growth of the ice

sheet in the ponds will be a function of

the heat loss (primarily radiation cooling and sensible heat conduction, both of which are

affected by the snow cover thickness). A thin or

nonexistent snow cover will promote rapid freezing; a thicker snow cover will reduce both radiative

cooling and sensible heat conduction, thus reducing

the rate of freezing. The weight of an even thicker

snow cover, however, will exceed the buoyancy of

the ice sheet, causing flooding of the sheet, saturation of the overlying snow cover and rapid ice thickening.

The role of the tides is important to both the

continued growth of the existing ice sheets and

extension of the area of ice cover. During a flooding high tide, water will back up in the channel of

the Eagle River and then back up into the series of

distributary channels and gullies that drain ERF

into the Eagle River. The tide water floods out of

the channels onto the mudflats and onto the icecovered ponds; the water depth of the tide depends

on the tidal elevation and the terrain features.

When the water flows over an existing snow-free

ice sheet or bare frozen ground when the air temperature is below freezing, a thin layer of ice is

formed on the surface. This superimposed ice can

Figure 1. Eagle River Flats, showing the firing points and impact

areas.

et al. 1993). The ponds, used by feeding waterfowl, are mainly located along the eastern and

western perimeters of ERF. A 10-ha gravel pad (the

EOD pad) is located along the eastern edge of ERF

(Fig. 1). The EOD pad is a former open-burn, opendetonation disposal site.

Seasonally frozen ground

In areas of ERF without standing water, such as

the mudflats, the natural levees and the tall coarse

sedge marsh area adjacent to the EOD pad on the

east side, the ground freezes each winter. The soils

are generally saturated, and their properties generally do not vary appreciably. The soils consist of

a mixture of silt and clay with a very small sandsize fraction (Racine et al. 1992). The depth of seasonal freezing primarily depends on the depth of

the overlying snow cover, the frequency of tidal

flooding and the seasonal air temperatures. Sediments underlying the shallow ponds along either

side of the flats may or may not freeze, depending

on the depth of the overlying water and whether

the ice freezes completely to the bottom during

the winter. In March 1991 the ground was frozen

FP

Fox

FP Upper Cole

FP 1

EOD

Pad

Test

Impact

Area

60

mm

81

mm

105

mm

FP

Fagan

2
be built up in multiple layers by succeeding flooding tides.

The extent and thickness of the existing snow

cover also play a role in the rate of ice buildup due

to tidal flooding. When snow is present, the tidal

water moves laterally through the snow cover and

wicks upward several centimeters into the overlying snow pack, either partially or totally saturating the snow, depending on its thickness. Water

under the snow that has only partially saturated the

snow cover can remain unfrozen for a considerable length of time due to the insulating properties of the overlying snow. The saturated snow,

when it freezes, produces a characteristic bubbly

or white “snow ice” that is less dense than the

clear congelation ice. This frozen saturated snow

produces a thicker ice layer than would be produced if no snow cover had been present. Most

high tides do not flood the entire flats. Rather, tidal

flood water spreads out from the heads of tidal

distributary channels as lobes or splays of water that

saturate the snow cover, freeze and build up a layer

of ice several centimeters thick over a limited area.

These lobes of superimposed ice are then slightly

higher than the surrounding non-flooded areas.

Flooding water from the next high tide will then

be displaced slightly, building up a lobe of ice adjacent to the previous ice lobes. Over time, much

of the area of ERF can be covered by an ice sheet

built up from successive multiple lobes of ice. An

occasional extreme tide may flood the entire area,

adding an additional ice layer.

During the 1990-91 winter, sparsely vegetated

mudflat areas that are normally subaerially exposed in the summer had 30–60 cm of superimposed ice by March. The ice thickness in the ponds

ranged from 40 to 70 cm, with the ice surface of

the ponds as much as 20 cm above the normal summer water surface elevation due to the superimposed ice. In the mudflat areas where a superimposed ice sheet had formed, frozen sediments were

found under the ice sheet, and in some cases the

sediments were frozen greater than 40 cm. The

brackish water from the tidal flooding did not appear to significantly alter the ice growth rate relative to freshwater behavior. The salinity gradient

in ice samples ranged from brackish (20 ppt) near

the river channel to fresh (<2 ppt) in the pond near

the east edge of ERF. Petrographic and chemical

analysis of the ice and sediment cores taken during the 1990-91 field season indicate a complex

buildup of ice from tidal flooding and some freshwater runoff (Taylor et al. 1994).

The ice cover in the Eagle River within ERF continually moves up and down because of the tidal

fluctuations. The surface of the ice sheet along the

banks and extending into the channel was very

smooth because of the constant flux of water from

successive flooding. Ridges of broken ice, 2–4 m

wide, in the centerline of the channel extend over

a major portion of the river reach. Wide hinge

cracks were evident along both shorelines at low

tide. Ice chunks and flows up to several meters in

diameter were scattered along either riverbank and

extended a short distance from the channel. During the high tides, parts of the ice cover detached

from the bank support, broke into small floes and

floated onto the Flats for a short distance, depending on the terrain topography and water depth.

Impact area description

The impact area for the test was located on the

east side of the Eagle River, about 500 m west of

the EOD gravel pad, and covered an area of approximately 700 × 700 m (Fig. 1). Prior to the artillery tests, we characterized the site by measuring

ice thicknesses and snow depths. Six ice cores were

obtained using a hand-held 7.62-cm-diameter SIPRE

core barrel. Ice thicknesses varied from 30 to 60

cm, with a minimum of 25 cm and a maximum of

40 cm of frozen sediment below the ice. The snow

depth ranged from 15 to 20 cm within the test impact area, with an estimated snow density of 0.3

g cm–3.

Previous research on cratering

Little information is available in the literature

on the cratering and demolition effects of artillery

fire on ice. A few 105- and 155-mm projectiles were

fired onto the Imjin River in 1977 to determine their

effectiveness in breaking floating ice covers; they

were not effective. Several authors have looked at

the effects of explosions in ice and snow (Livingston 1960, Mellor 1965), in frozen ground (Livingston 1956, 1959, Mellor and Sellmann 1970) and in

and under floating ice sheets (Mellor 1982, 1986a,

1986b). Mellor (1986a) summarized the guidelines

for blasting on ice sheets and gave estimates for

the sizes of craters that will form, depending on

the weight of the explosive charge and its position

in the ice sheet.

The traditional analysis for determining the apparent scaled radius Ra and the scaled depth Da of

craters formed by explosions uses cube-root scaling

(Mellor 1986a) to remove the effect of charge size

(all linear dimensions are divided by the cube root

3
sisted of firing a series of 105-mm howitzer HE

projectiles with point-detonating fuses, the type

of fuse and projectile normally fired into the ERF

impact area for training. A series of HE projectiles

with time-delay fuses was also fired to determine

if the slight delay before detonation would allow

the projectile to penetrate the ice cover before exploding. The HE projectiles were fired from M101A1

105-mm howitzers of the 4th Battalion, 11th Field

Artillery. The howitzers were set up at Firing Point

One (FP1), 4 km east of the impact area (Fig. 1).

The second phase of tests used 81-mm mortar projectiles, using both point-detonating and delay

fuses, into an area just north of the 105-mm impact area. The 81-mm mortars were set up at FP

Fox, 1500 m southeast of the impact area. The

third phase of tests consisted of 60-mm mortar

projectiles with point-detonating fuses fired into

an area west of the 105-mm impact area. The 60-

mm mortars were set up at FP Upper Cole, 1000 m

south of the impact area. The tests were observed

and photgraphed from Observation Point Fagan,

1000 m east of the impact area. Firing information

for the weapons used is presented in Table 2.

After the firing we photographed and measured

the apparent diameters and apparent depths of the

craters. Samples of snow were collected from around

the craters to analyze for explosive residues.

All the dimensions given in this report are apparent crater diameters and depths. Because of the

safety constraints and time limitations, none of the

craters were excavated to measure true crater dimensions. However, except for the broken ice observed in the bottom of some 105-mm-howitzer

craters, most craters appeared to have little loose

material in them.

The analyses of our crater measurements assume that all explosions were contact bursts. A

contact burst is one in which the center of mass of

the exploding charge is at the surface, giving a

depth ratio of zero. In actuality, the projectile with

a point-detonating fuse may penetrate the surface by some unknown amount before exploding,

Table 2. Firing information for weapons used in the tests.

Weapon Round Barrel angle HE weight

105-mm howitzer 105–mm HE M1 350–354 mils = 2.3 kg

M101A1 19.7−19.9° (5.0 lb)

81-mm mortar M374-A-3-81 mm 1217–1289 mils = 0.95 kg

M252 68.5–72.5° (2.1 lb)

60-mm mortar M49-A-4-60 mm 1166 mils = 65.6° 0.19 kg

M224 (0.42 lb)

Table 1. Predicted apparent scaled radius and

depth of craters.

Snow* Ice† Frozen silt**

Ra 0.87 Mc

1/3 0.71 Mc1/3 0.56 Mc1/3

Da 0.3–0.5 Mc

1/3 0.24 Mc1/3 0.28 Mc1/3

Mc is the mass of the explosive charge in kilograms.

Radius and depth of craters are in meters.

*Mellor (1965)

†Mellor (1986a)

**Mellor and Sellmann (1970)

of charge mass), allowing comparisons of craters

formed by explosive charges of various sizes. For

surface explosions, that is, explosions with a depth

ratio of zero, the predictions in Table 1 can be made

for the size of craters formed in snow, ice and frozen silt using the equations presented in Mellor

(1965, 1986a) and Mellor and Sellmann (1970).

For example, a 105-mm howitzer M1 projectile,

containing 2.3 kg of HE, has predicted apparent

radii of the craters resulting from a contact burst

for snow, ice and frozen silt of 1.15, 0.94 and 0.74

m, respectively. The predicted apparent depths

would be 0.40–0.66, 0.32 and 0.37 m, respectively.

The differences between the apparent crater formed

by an explosion vs. the true crater may be substantial; they depend on whether the charge depth is

zero (i.e. at the surface) or at some depth below

the surface. The apparent crater is the excavation

as it appears to an observer immediately after a

blast (Livingston 1960). It often contains fall-back

material, defined as the loose material thrown up

by the explosion that has fallen back into the crater. Excavation of the fall-back material in the crater reveals the true crater.

ARTILLERY TESTS

The test firing onto the ice of Eagle River Flats

took place on 20 March 1991. The test firing was

conducted in three phases. The first phase con4
because of the small time delay between the impact 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 impacted 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 completed we were able to measure several of the

craters formed in the ice of the shallow ponds.

We wanted to compare the effects of exploding

105-mm howitzer projectiles on a floating ice

sheet with our previous observations on the effects on grounded ice and frozen ground. We also

compared the measured crater parameters with the

predicted parameters for explosives on floating ice.

RESULTS

105-mm howitzer test firing

Eight high-explosive 105-mm projectiles with

point-detonating fuses were fired into the impact

area. Seven of the eight projectiles detonated on

contact with the ice (Fig. 2). The impact area had a

20-cm snow cover on the ice sheet, and the ice

thickness varied from 0.30 to 0.60 m. The measurements of seven craters are included in Table 3 (craFigure 3. Crater formed by a 105-mm HE projectile.

Figure 2. Explosion of a 105-mm HE projectile in the test

area.

ters no. 1–6 and 9); all values are for the apparent

craters. All seven measured craters were oblong

in shape, probably due to a low impact angle caused

by the low firing angle (19.7–19.9°). 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

mean lengths for maximum and minimum axes

were 3.17 and 2.45 m, respectively. This gives a

mean apparent diameter of 2.81 m, or a mean apparent radius Ra of 1.41 m. The seven measured

craters were shallow, between 0.2 and 0.44 m, with 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-

m-diameter area of broken ice in the center of the

crater (Fig. 3).

5
Figure 4. Ice lifted out of the bottom of crater no. 2, exposing frozen

ground.

Table 3. Measurement data from craters.

Maximum Minimum Center Snow

Crater no. Description axis (m) axis (m) depth (m) depth (m) Notes

105-mm howitzer

1 PD 2.26 1.89 0.30 0.20

2 PD 2.90 2.10 0.44 0.20 1.2- × 0.6-m area of ground exposed

at bottom of crater.

3 PD 3.29 2.50 0.37 0.20

4 PD 3.38 2.32 0.39 0.20

5 PD 3.20 2.77 0.30 0.20

6 PD 3.63 2.50 0.27 0.20 0.6-m area in center where ice shattered.

7 D 1.07 0.61 — Point where projectile ricocheted.

9 PD 3.54 3.05 0.20 0.20 0.6-m area of shattered ice in center.

8 D 7.62 2.44 0.20 0.20 Shallow, elongated crater. Ricocheted

projectile blew up near surface.

10 D 3.00 2.40 0.35 0.20

81-mm mortar

1 PD 2.59 2.29 0.15 0.15 Bottom of crater is on top of ice sheet.

2 PD 2.49 2.29 0.16 0.15

3 PD 2.26 1.86 0.16 0.15

4 D 1.83 1.83 0.17 0.15

5 D Camouflet Not measured.

6 D Camouflet 0.6- × 2-m mound of ice rubble. 0.6-m-diam ×

approx. 1.8-m-deep crater hidden under

rubble.

60-mm mortar

1 PD 1.83 1.83 0.21 0.21 Depth of crater is equal to depth of snow

on ice sheet, i.e. bottom of crater is top of

ice sheet.

2 PD 1.83 1.52 0.15 0.15

3 PD 1.80 1.89 0.18 0.18 0.10-m-diam × 0.08-m-deep hole in ice in

exact center. Fuse parts in hole.

4 PD 1.83 1.52 0.22 0.20

5 PD 1.83 1.83 0.17 0.17

* PD = point-detonating fuse

D = delay fuse.

6
Figure 6. Shallow elongated crater produced by a ricocheting delay-fused

projectile.

In one crater (no. 2 in Table 3), a 1.2- × 0.6-m

area of the 0.25-m ice sheet was completely lifted

and blown out of the crater, exposing the frozen

ground underneath. The exposed frozen ground

was not visibly disturbed or removed by the explosion (Fig. 4). There was no cratering of the frozen ground beneath the ice. One of the eight pointdetonating projectiles was a dud, creating only a

white plume of snow and ice when it hit the ice

surface. The dud projectile produced a small crater

estimated to be less than 1 m in diameter and of

unknown depth; we did not measure this crater for

safety reasons.

Four 105-mm projectiles with delay fuses were

fired into the test area; three ricocheted off the ice

before exploding, and one detonated in the snow

and ice cover similar to the point-detonating projectiles. Figure 5 shows one ricocheting projectile

exploding near the ice surface. This explosion

produced a shallow elongated crater (no. 8) in

the snow (Fig. 6), approximately 2.4 m wide at the

near end, narrowing down to 0.6 m wide at the far

end and 7.6 m long. Two ricocheting projectiles

exploded in the air. Figure 7 shows the white plume

of snow and ice where the projectile first hit and

the dark explosion cloud high in the air (50 m?),

near the skyline. The ricocheting projectile produced a small crater (no. 7), 1.07 × 0.60 m. The one

delay-fused projectile that appeared to detonate

normally produced a crater (no. 10) similar to those

of the point-detonating fused projectiles, measuring 3.0 × 2.4 × 0.35 m.

All of these test firings of point-detonating and

delay-fused 105-mm projectiles were done at a low

angle of fire (19.7–19.9°). This is the standard procedure for firing into the impact range for training, with the projectiles reaching the target in the

shortest time. A target can also be engaged from

the same firing point with a high angle of fire, producing a high parabolic flight path, a longer flight

time and a more vertical impact angle. Delay-fused

105-mm projectiles fired at a high angle would not

Figure 5. Ricocheting projectile exploding near the ice

surface. The white plume of snow and ice shows where the

projectile initially hit, and the explosion was just beyond it.

7
be expected to ricochet but would penetrate the

ice sheet before exploding, similar to the 81-mm

delay-fused mortar projectiles discussed below.

81-mm mortar test firing

Both point-detonating and delay-fused 81-mm

projectiles were fired during the test. Several of the

mortar projectiles fell in the river and were inaccessible to us. We measured three craters formed by

point-detonating projectiles. These craters averaged

2.45 × 2.15 m in diameter (Table 3), and they were

more nearly circular than the howitzer craters,

probably because of the higher trajectory of the

mortar projectile. The mean apparent radius of the

craters was 1.15 m.

The mean depth of the craters was 0.16 m, with

most of the depth caused by removal of the 0.15-mthick snow cover. A shallow depression was blown in

the underlying ice cover in the center of the craters,

Figure 9. Crater formed by a pointdetonating 81-mm mortar projectile

on a floating ice sheet.

Figure 7. Ricocheting delay-fused projectile exploding high in the air.

Figure 8. Crater formed by a pointdetonating 81-mm mortar projectile

on grounded ice.

8
similar to the 81-mm point-detonating projectiles

but smaller and slightly deeper.

The second and third delay-fused projectiles

each produced a camouflet, or a hidden crater. The

projectiles penetrated the ice cover and the underlying frozen and unfrozen sediments before exploding. The confining strengths of the ice, the upper

seasonally frozen sediment and the underlying saturated unfrozen sediment allowed the explosion to

be confined and prevented it from ejecting material and producing a surface crater. The only evidence of the two camouflets was conical mounds of

broken ice rubble, one of which measured 0.6 m

high and 2 m in diameter (Fig. 10). Closer inspection and judicial digging into the mound by the

EOD escort revealed a nearly vertical hole 30 cm

in diameter and 1.5 m deep (Fig. 11).

but the ice was not broken or penetrated by the

explosions (Fig. 8).

One of the point-detonating projectiles landed

on the ice of a shallow pond north of the main

impact area. The ice cover on the pond was 40 cm

thick over about 30 cm of water. The crater (no. 1)

produced by this projectile (Fig. 9) looked no different from the craters (no. 2 and 3) produced by

projectiles landing on areas of grounded ice over

frozen ground (Fig. 8).

Three delay-fused 81-mm projectiles (no. 4–6)

landed in an area of grounded ice over frozen

ground in the center of the test impact area. The

cloud produced by the explosion of the 81-mm

mortar projectiles was noticeably smaller than that

produced by the 105-mm howitzer projectiles. The

crater (no. 4) produced by the first projectile was

Figure 11. Nearly vertical hole in the camouflet.

Figure 10. Camouflet formed by a delay-fused

81-mm mortar projectile.

9
60-mm mortar test firing

Only point-detonating 60-mm mortar projectiles were fired for the test. Craters produced by

the 60-mm projectiles (Table 3, no. 1–5) were smaller

than those produced by either the 105-mm howitzer or 81-mm mortar projectiles, averaging 1.83 ×

1.70 m in diameter. This gives a mean apparent

radius of 0.88 m.

The craters were very shallow, averaging 19 cm,

essentially the depth of the snow cover in this part

of the impact area. The snow was blown out by the

explosion, and the underlying ice sheet remained

intact (Fig. 12). There was usually a small dimple in

the ice at the center of the crater where parts of the

fuse of the projectile were sometimes found. One

60-mm projectile was a dud. The projectile appeared

to penetrate into the ice (Fig. 13), with only the tail

fins visible (again after careful digging of the snow

around the projectile by the EOD escort).

* Personal communication with Marianne Walsh, CRREL,

1991.

Figure 13. Dud 60-mm projectile.

Explosive residue

Snow around craters formed by 105-mm howitzer and 81-mm mortar projectiles was sampled

and tested for the high-explosive components TNT

and RDX. Darkened, ash-covered snow surrounding the crater was collected in a 500-mL I-Chem

glass sample jar. The samples were returned to the

laboratory and analyzed for HE components by

high-performance liquid chromatography. No explosive components were detected, indicating that

they were completely consumed in the explosions

of the projectiles.*

January 1992 105-mm howitzer firing

Six craters formed in the ice sheet covering the

shallow ponds along the eastern edge of the imFigure 12. Crater formed by a 60-mm

mortar projectile.

10
pact area were measured. The ponds in the area of

impact are very shallow. The ice sheet covering

the ponds was either partially grounded on the

pond bottom or barely afloat. Because of the unevenness of the pond bottom sediment and the

very soft nature of the sediment, it was difficult to

determine the exact water depth beneath the ice

cover. In part, the determination that an ice sheet

was floating or not was based on the water surface

level in the center crater. The water surface levels in

four craters were obviously below the ice buoyancy point, indicating the ice sheet was grounded

on the bottom at that location. The ice sheet at the

other two crater locations was floating, although

the water depths below the bottom of the ice sheet

were only a few centimeters. The measured variables for these six craters are summarized in Table 4.

All the craters had a large, shallow outer crater

formed in the overlying snow cover. All had a

smaller inner crater consisting of a hole blasted

through the underlying ice sheet. The longest axis of

the outer craters ranged from 3.95 to 4.90 m, and

the shortest axis ranged from 2.30 to 3.15 m. The

mean lengths for maximum and minimum axes

were 4.04 and 2.84 m, respectively. This gives a

mean apparent diameter of 3.44 m, or a mean

apparent radius Ra of 1.72 m. The depths of the

outer crater averaged 0.17 m, which is the same as

the average snow depth.

The longest axis of the inner crater or hole in

the ice sheet ranged from 1.15 to 1.68 m, and the

shortest axis ranged from 1.15 to 1.46 m. This gives a

mean apparent diameter of 1.36 m, or a mean

apparent radius Ra of 0.68 m. In the pond bottom

sediments directly beneath the hole in the ice was

a crater-shaped depression. However, at none of

the craters was there any sediment displaced out

of the hole and scattered on the surface. The shock

wave of the explosion on the ice surface appeared

to have compressed the soft pond bottom sediments into a crater-shaped depression without lifting or throwing sediment out of the hole. The

center depth of the craters given in Table 4 is the

total depth from the top of the original snow surface to the bottom of the depression in the pond

bottom sediments. This averaged 0.68 m for the

six craters.

ANALYSIS AND DISCUSSION

The analysis of the craters formed by the 105-m

howitzers and 60- and 81-mm mortars and comparison of these crater data with published data

on crater formation is complicated because these

were formed by impacting projectiles, while much

of the published data are for stationary explosive

charges. Also, the published data are for a uniform medium, while these craters were formed in

a three-layer medium with quite different densities and structural properties. The upper layer was

snow, 0.15–0.19 m thick. The middle layer consisted of a 0.30- to 0.60-m-thick ice cover, and the

bottom layer was a seasonally frozen, saturated

fine-grained soil. The explosion of point-detonating mortar projectiles, both 60 and 81 mm, only

removed the snow and rarely penetrated the surface of the ice cover. The explosion of point-detonating 105-mm howitzer projectiles removed the

snow cover and at least part of the ice cover. In at

least one case the entire ice cover was removed, but

the crater did not penetrate into the underlying frozen soil layer.

105-mm howitzer test results

The mean apparent radius of the seven craters

resulting from the point-detonating projectiles was

1.41 m. The mean scaled apparent radius of the

Table 4. Measurement data from craters on pond ice (105-mm howitzer).

Water Water

Max. Min. Max. Min. Center Snow Ice depth in below

axis axis axis in axis in depth depth thick. crater ice sheet*

Crater no. (m) (m) ice (m) ice (m) (m) (m) (m) (m) (m) Notes

1 3.95 2.75 1.58 1.40 0.92 0.20 0.27 0.60 <0.01 ice partially grounded

2 4.90 3.05 1.20 1.20 0.50 0.14 0.25 0.29 <0.01 ice partially grounded

3 3.40 2.75 1.15 1.15 0.60 0.19 0.29 0.39 0.02 ice floating

4 3.95 3.05 1.43 1.37 0.63 0.16 0.22 0.40 <0.01 ice partially grounded

5 3.95 2.30 1.68 1.46 0.76 0.18 0.25 0.53 <0.01 ice partially grounded

6 4.10 3.15 1.43 1.22 0.66 0.16 0.25 0.48 0.03 ice floating

Ave. 4.04 2.84 1.41 1.30 0.68 0.17 0.26 0.45

* The water depth below the bottom of the ice sheet is very difficult to measure because of the very soft pond bottom

sediments.

11
seven craters was 1.07 m/kg1/3. This is considerably larger than the predicted Ra of 0.71 m/kg1/3

for ice and is out of the range of the scaled crater

radius data for ice (Mellor 1986a). If we use the

estimates for the scaled apparent radius of a crater

in snow (Mellor 1965) instead of ice, we get closer

agreement between the predicted and measured

crater radii. The predicted value would be 0.87

m/kg1/3 vs. the measured 1.07 m/kg1/3.

The size of a crater created by an explosion increases as the depth of the explosive charge below

the surface increases up to a certain depth, known

as the critical depth. If we assume that the projectile did not explode at the surface but penetrated

through the snow and a short distance into the ice

(<0.05 m) before exploding, then the data would

be within the maximum range of experimental data

for ice presented by Mellor (1986a). However, there

is no field evidence that the projectiles did penetrate into the ice before exploding.

The seven measured craters had a mean apparent depth of 0.32 m. This gives a scaled apparent

depth of 0.25 m/kg1/3, much shallower than the

predicted depth for snow but almost the same as

the predicted value given by Mellor (1986a) for

ice. Obviously these comparisons are complicated

by several factors. The experimental data used by

Mellor in developing the scaled radius relationships were produced by static spherical explosive

charges placed on the snow or ice surface. The artillery tests used a cylindrical projectile traveling

at high velocity. The experimental data were for a

single, uniform, semi-infinite-depth medium; we

had a relatively thin, multiple-layered medium with

quite different densities and structural properties.

The interaction of the snow and ice layer may

explain the differences in crater size. As the 105-

mm HE projectile penetrates the snow cover and

the point-detonating fuse contacts the ice surface,

the projectile explodes, producing a shock wave.

The shock wave collapses the snow cover as it

propagates downward and outward. Snow is a

very good absorber of shock wave energy (Johnson et al. 1991, 1992), so the snow cushions part of

the explosion. Part of the shock wave propagating

downward will be reflected back off the snow–ice

interface; this may increase the radius of the crater

formed in the snow layer. Part of the shock wave

will continue downward through the ice layer,

hitting the ice–frozen soil interface. Part of the

wave will then be reflected back up. This reflected

wave, traveling back upward through the ice, can

pop portions of the ice layer out of the crater without damaging the underlying frozen ground, as

seen in one of the craters (Fig. 4). These reflected

waves, traveling upward through the ice, may reduce or cancel later shock waves penetrating downward, thus reducing the total effect of the explosion.

81-mm mortar test results

The mean apparent radius of the three craters

formed by point-detonating fused projectiles was

1.15 m, resulting in a scaled radius of 1.17 m/kg1/3.

The craters were almost entirely confined to the

snow layer on top of the ice. The measured scaled

radius is higher than the predicted scaled radius

of a crater in snow from a surface-placed explosive.

The mean depth of the craters was 0.16 m, giving a scaled depth of 0.16 m/kg1/3. Because the

snow layer was shallow (0.15 m) and the crater

was almost entirely confined to this layer, the scaled

depth may be low because of the reflection of

the shock wave off the ice layer, inhibiting the crater depth development.

60-mm mortar test results

Craters formed by the 60-mm mortar projectiles had a mean apparent radius of 0.88 m, or a

scaled apparent radius of 1.53 m/kg1/3. The craters were entirely confined to the snow layer. The

measured scaled apparent radius was much higher

than the predicted scaled radius of 0.87 m/kg1/3.

The measured scaled depth was 0.33 m/kg1/3; this

is very close to the predicted scaled depth for snow.

January 1992

105-mm howitzer firing results

The mean apparent radius of the outer craters

formed in the snow on the ice sheet of shallow

ponds was 1.72 m. The mean scaled apparent radius of the six craters was 1.30 m/kg1/3. This is

considerably larger than the predicted Ra of 0.87

m/kg1/3 for snow, even larger than the differences

noted in the March 1991 test firing. The mean apparent radius of the six inner craters or holes

formed in the ice sheet of shallow ponds was 0.68

m. The mean scaled apparent radius of these inner

craters is 0.90 m/kg1/3, very close to the predicted

scaled apparent radius of 0.94 m/kg1/3 for ice.

The mean depth of the inner craters was 0.68

m, or a scaled depth of 0.52 m/kg1/3. It is difficult

to compare this to a predicted depth, since the inner crater completely pierced the ice sheet and extended into the soft pond bottom sediments below the ice.

12
radius of 1.53 m/kg1/3, fully 76% larger than the

predicted scaled radius in snow. The equations developed by Mellor (1986a) for predicting the scaled

radius from experimental data greatly underestimate the radius of craters in layered snow and ice

produced by artillery projectiles. On the other hand,

the scaled depths of the artillery craters were similar

to or less than the predicted depths; 0.25 vs. 0.4

and 0.24 m/kg1/3 in snow and ice for the 105-mm

projectiles, 0.16 vs. 0.4 and 0.24 m/kg1/3 in snow

and ice for the 81-mm mortars, and 0.33 vs. 0.40

m/kg1/3 in snow for the 60-mm mortars.

The shapes of the craters formed were influenced

by the multiple-layered medium of snow, ice and

frozen ground into which the firing took place (Fig.

14). The greater-than-predicted radii of the craters

CONCLUSIONS

The sizes of craters we measured during these

tests were all larger than predicted from previous

data for static spherical explosive charges set on the

snow or ice surface. The mean scaled apparent radius of the craters formed by 105-mm point-detonating projectiles was 23% greater than predicted for a

crater in snow and 50% greater than predicted for

ice, 1.07 vs. 0.87 and 0.71 m/kg1/3. The mean scaled

apparent radius of the 81-mm point-detonating projectile craters was 1.17 m/kg1/3, 34% larger than the

predicted scaled apparent radius in snow and 65%

larger than the predicted radius in ice. The 60-mm

mortar projectiles produced craters confined to the

shallow snow layer, with a mean scaled apparent

13

a. Typical 60-mm mortar crater.

b. Typical 81-mm mortar crater.

c. Typical 105-mm howitzer crater in shallow ice.

d. Typical 105-mm howitzer crater in thick ice.

e. Typical 105-mm howitzer crater in a floating ice sheet.

Figure 14. Typical crater cross sections.
can be attributed to the multiple-layered medium.

The reflections of the shock waves off the multiple

interfaces tended to decrease the depths of the

craters, especially in the ice layer, and increase the

radii of the craters in the snow layer.

In all cases the underlying frozen sediments

were not disturbed when point-detonating projectiles were fired into Eagle River Flats with the

ground frozen and covered with a 0.30- to 0.60-m

ice sheet and 0.15- to 0.20-m of snow. The craters

formed by point-detonating projectiles of both

mortars and 105-mm howitzers were confined to

the overlying snow and ice sheet. With the exceptions of one 105-mm and one 60-mm dud, all of

the point-detonating projectiles performed satisfactorily. Delay-fused projectiles operated very erratically in areas with frozen ground and an ice

cover.

The mean scaled apparent radius of craters we

measured in January 1992 formed by 105-mm

point-detonating projectiles in the ice sheet of

shallow ponds were very close to those predicted

from previous data for static spherical explosive

charges set on the ice surface, 0.90 vs. 0.94 m/kg1/3.

However, the measured vs. scaled apparent radius

of the outer crater in the shallow snow cover was

50% greater than predicted, again indicating the

difficulty in predicting crater size in a shallow,

multi-layered medium such as a thin snow layer

over ice (Fig. 14).

In summary, based on the results of the test firing and observations of subsequent firing, winter

firing into Eagle River Flats under conditions similar to those during the tests will not disturb the

underlying sediments containing white phosphorus particles. For 105-mm howitzers, a minimum

of 25 cm of ice over frozen sediment or a minimum of 30 cm of floating ice over shallow water is

required. For 60- and 81-mm mortars, minimums

are much less, on the order of 10 cm of ice. Winter

firing with point-detonating projectiles when a

sufficiently thick snow and ice cover is present

appears to be the best approach to training in Eagle

River Flats to prevent disturbance and mixing of

the WP-contaminated sediments.

LITERATURE CITED

Johnson, J.B., J.A. Brown, E.S. Gaffney, G.L. Blaisdell and M. Sturm (1991) Shock wave studies of

snow. In Proceedings, Seventh Topical Conference on

Shock Compression in Condensed Matter, Williamsburg, Virginia, 17–20 June 1991. American Physical

Society.

Johnson, J.B., J.A. Brown, E.S. Gaffney, G.L. Blaisdell and D.J. Solie (1992) Shock response of snow:

Analysis of experimental method and constitutive

model development. USA Cold Regions Research

and Engineering Laboratory, CRREL Report 92-

12.

Livingston, C.W. (1956) Excavations in frozen

ground. Part I: Explosion tests in Keweenaw silt.

USA Snow, Ice and Permafrost Research Establishment, Technical Report 30.

Livingston, C.W. (1959) Excavations in frozen

ground. Part II: Explosion tests in frozen glacial

till, Fort Churchill. USA Snow, Ice and Permafrost

Research Establishment, Technical Report 30.

Livingston, C.W. (1960) Explosions in ice. USA

Snow, Ice and Permafrost Research Establishment,

Technical Report 75.

Mellor, M. (1965) Explosions and snow. USA Cold

Regions Research and Engineering Laboratory,

Monograph III A3a.

Mellor, M. (1982) Breaking ice with explosives. USA

Cold Regions Research and Engineering Laboratory, CRREL Report 82-40.

Mellor, M. (1986a) Revised guidelines for blasting floating ice. USA Cold Regions Research and

Engineering Laboratory, Special Report 86-10.

Mellor, M. (1986b) Blasting and blast effects in cold

regions. Part II: Underwater explosions. USA Cold

Regions Research and Engineering Laboratory,

Special Report 86-16.

Mellor, M. and P.V. Sellmann (1970) Experimental blasting in frozen ground. USA Cold Regions

Research and Engineering Laboratory, Special Report 153.

Racine, C.H., M.E. Walsh, C.M. Collins, D.J. Calkins and W.D. Roebuck (1992) Waterfowl mortality in Eagle River Flats, Alaska: The role of munition residues. USA Cold Regions Research and

Engineering Laboratory, CRREL Report 92-5.

Racine, C.H., M.E. Walsh, C.M. Collins, S. Taylor, W.D. Roebuck, L. Reitsma and B. Steele (1993)

White phosphorus contamination of salt marsh

pond sediments at Eagle River Flats, Alaska. USA

Cold Regions Research and Engineering Laboratory, CRREL Report 93-17.

Taylor, S., C.H. Racine, C.M. Collins and E. Gordon (1994) Ice formation in an estuarian salt marsh,

Alaska. USA Cold Regions Research and Engineering Laboratory, Special Report 94-17.

14
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January 1995

Analysis of Artillery Winter Test Firing into Eagle River Flats, Fort

Richardson, Alaska

Charles M. Collins and Darryl J. Calkins

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-2

Hanover, New Hampshire 03755-1290

Directorate of Public Works

Sixth Infantry Division (Light)

Fort Richardson, Alaska

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

21

Artillery High-explosive projectiles

Eagle River Flats Ice-covered terrain

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Winter tests of artillery firing were conducted in the Eagle River Flats impact range to determine the physical

effects of exploding high-explosive (HE) projectiles on the ice-covered terrain. Eagle River Flats is an estuary at the

mouth of the Eagle River used as the artillery impact range for Ft. Richardson. The Army suspended use of the

impact range following the discovery that white phosphorus (WP) deposited in the salt marsh was responsible for

large numbers of waterfowl deaths each summer. The purpose of these tests was to assess if seasonal firing of HE

projectiles from 60- and 81-mm mortars and 105-mm howitzers into Eagle River Flats could be resumed without

significantly disturbing the sediments contaminated with WP. The results of the test firings indicated that a

minimum of 25 cm of ice over frozen sediment or a minimum of 30 cm of floating ice over shallow water was

required to prevent disturbance of the WP-contaminated sediment by exploding 105-mm howitzer projectiles.

Only 10 cm of ice was required to prevent disturbance by exploding 60- and 81-mm mortar projectiles.