Evening star., 1951-11-12
Ice Wedges Yielding
Clues on Permufrost
Gruve-Iike Arctic Mounds
Are Dissected in Studies
BY Thomas R. Henry

7bS ~ISSCStCu
By Thomas R. Henry
Notable features of Arctic landscapes
are lice wedges"
Old proSpectors used to call them
cemetery hummocks' because they
looked so much like the grass-covered
mounds over graves.
That, in sense, is what they are-but
the corpses buried in them are corpses
OF ice and they are apt to show signs
OF life at times.
They are-many of them-little vege-
tation-covered hillocks with hearts of
ice. They are literally "wedges"-masses
of ice sometimes tens of feet in diameter,
and ranging in shape from six-sided to
nearly round
Sometimes they extend to depths of
many feet They are scattered over
much of the Arctic coast of Alaska and
Canada and through the Arctic archi-
pelago. The larger ones are easily
diScernible in air photos.
Years Study Completed.
Geological Survey scientists have COM
pleted an intensive years study of these
curious formations in an effort to get
further light on the phenomenon of
permafrost, the constantly frozen area
few feet down. knowledge of which
is essential for water supplies, agri-
culture and building operations in the
Far North. Permafrost constituted a
bad handicap during the war.
Up to 1850 practically all scientific
work on this phenomenon had been
Russian. The Soviet government has
wrestled for years with the problems Of
human settlement in the Far North and
the rest of the world had depended on
its findings.
In the Geological Survey study, how
ever, several hundred of these wedges
were studied in their natural setting and
35 of them from four different geologic
environments were studied intensively in
an "icebox laboratory" set up on the
field. Microscopic examinations showed
much the same structure as that Of
rocks twisted and contorted by earth
movements. With the ice wedges.
though, the distortions were caused by
forces set up in the ground through
changes in temperature.
Put Under Microscope.
A great many of the specimens were
gathered in the neighborhood of Point
Barrow, northernmost point of American
territory, through the facilities of the
Arctic Research Laboratory Of the ONCE
of Naval Research. Preparing thin sec
tions of ice meant working continuously
in intense cold, most of the time inside
the "icebox' The specimens were sawed
into small rectangular blocks about a
half-inch thick and then sandpapered
down to paper thinness for use under the
microscope. Structures within the ice
were disclosed as multicolored bands or
veins, sometimes containing bubbles and
bits of soil.
The report likens the ice wedges to
similar patterns in dried-up mud lakes
where cracks, formed on the surface.
gradually are filed with other materials.
Soil contracts as temperature drops.
Obviously" the report says. "this
results in intense stresses. These are
relieved generally by formation Of open
cracks, horizontally and vertically.
Seeding ice crystals grow in these
openings by sublimation from overlying
snow. BY spring about fourth to a
half the void is filled with ice and
new ice wedge has started or an older
one has grown.
THE conflguration assumed by these
cracks bears no direct relationship to
the climate or latitude but is dependent
on the nature of the material and the
amount and direction Of the stresses.
The cracks usually have the same con-
figuration in marine. continental or
Alpine climates. One notes tendency
for the theoretically simplest form-a
hexagon-to predominate. Stress is
relieved most easily by three radial
cracks, 100 degrees from each other.
Such a group of points results in
hexagons, like those formed in cooling
lava"
Found in Bedrock.
The initial ice wedge polygons, it
was determined, bear no direct rela-
tionship to climate but are determined
by ground temperatures. The largest
and most irregular cracks form in areas
of lowest moisture content in the
ground.
These ice wedges occur in silt, sand.
gravel or even bedrock. Often layers
of soil form over them. resulting in
little hills which may or may not be
covered with vegetation. Such vegeta-
ton includes many species of lichens.
moses, sedges, grasses, shrubs and
trees and is conspicuous from place to
place.
"a particular ice wedge" the report
explains, may crack each year for
several years, lie dormant, or crack
at irregular intervals. Construction
and destruction of ice wedge polygons
was found to be continuously f1uc-
tuating process with construction taking
place by addition of ice within wedges,
preferential accumulation of ice, vege-
tation and wind-blown silt within
polygon ponds or tops of ridges and
accumulation of droppings of birds
and rats on tops of high centered
polygons. These elevate the surface Of
the tundra"