16 
Sa 
Fig. 4. Contrast between depth hoar crystals 
and overlying fine-grained snow. 
Road 
9b 
P2 
. 
Fig. 5. Sketch map of test area near pingo and 
PZ 
the entire snowpack including any ice lenses that 
may be in it, as referred to below. 
3. Snow probing: In addition to the above 
measurements, which yield information on 
physical characteristics of the snow, a snow 
probing method was used extensively to deter- 
mine snow depth along nine selected traverses 
(Fig. 1). The probing was done with a steel rod, 
graduated in centimeters, which was poked 
through the snow at 2 m intervals several times 
during May and early June. This technique 
provides a rapid means of measuring snowdrift 
distributions. 
Physical Characteristics of the Snow 
General features 
The snow cover formed at Prudhoe Bay 
before the first of September in 1971. An 
example of its appearance, exposed in a shallow 
pit on 6 September, is shown in Fig. 2. In this 
place the snow was only 13 cm deep, coarse and 
wet at the bottom, with an icy crust 2-3 cm 
above the base. Some complexity already was 
apparent, especially in contact with clumps of 
vegetation. 
In some places the snow depth did not 
increase much during the entire winter, as shown 
in the photograph (Fig. 3) taken near Barrow on 
13 April 1972. In this example the snow depth 
varied from 10 to 17 cm, the bottom tempera- 
ture was -13°C, and the coarse crystalline depth 
hoar layer at the base of the snow varied in 
thickness from 1 to 5 cm. In places where the 
snow is more than 40 cm deep, the basal depth 
hoar layer may be 20 cm thick. (In interior 
Alaska the entire snowpack may be predomi- 
nantly depth hoar.) The contrast between depth 
hoar crystals from the base of the snowpack and 
the finer grained material from the top is illus- 
trated in Fig. 4. Depth hoar crystals with dimen- 
sions of 1cm are common, but grains in the 
fine-grained snow are generally less than 1 mm 
diameter. Between these extremes is a medium- 
grained (1-2 mm) snow which is generally inter- 
mediate in grain size, hardness and density. The 
fine-grained snow is often wind packed and 
hard—frequently called a wind slab. Another 
extreme case, the most unstable of all, is fresh 
new snow which is usually transformed rather 
quickly into one of the other types. 
