Evening star., 1954-04-21
Antarctic Ice Sheet
Believed 5 Miles Thick.
Tips Of Mountains Protrlde
Through Level PIuteuus

By Thomas R. Henry
The earth's greatest ice sheet, cover
ing more than IS per cent of a dead
land as large as the United States and
Europe combined-is believed to have
an average thickness Of thousands Of
feet.
It may be as much as five miles thick
over the greater part of the area. 1t is
difficult to believe that it is less than
1000 feet thick except where it covers
deep interior mountain valleys.
This is about the best estimate that
can be made. according to the report
OF geological Investigations made on the
1948-49 Antarctic expedition led by
Comdr. Finn Rome, which has just
been issued by the ONCE of Naval Re-
search. until extensive geophysical in
veStigations can be conducted on the
inland ice which is very difficult TO
reach.
On the basis of magnetic data OBJ
tanned by British explorers, DR.. Francis
Birch Of Harvard University maintains.
according to the report, that there is
no Justification for assuming that the
ice cap is less than miles thick over
AAASAA Va AID ChOCA4bs i IlC odlklG UUScIVa@
tions have been used, however. to
maintain that the cap may not be
more than a thousand feet thick.
6,3OO-FOot Average.
DR.. Robert L. Nichols. geologist of
the Rome expedition, who prepared
the report. estimates that an average
depth of $500 feet would account for
the present contour of the continental
slopes which are determined in part by
weight of ice necessary to depress the
surface of the continent. A measured
depth of about 5000 feet has been
shown just south of the great Ross
Shelf.
Rome expedition members studied
the highland ice" at the Palmer penin-
sula, the f1ngerlike northern projection
Of the Antarctic continent which is
trimmed with mountains and the interior
OF which is presumably quite mountain
GUS. Once in the interior the explorers
seemed to be on fiat plateau. 1t was
hardly to be assumed, however, that
this actually represented the contour Of
the underlying land. Even on the
plateau occasional mountainous pro-
trude through the ice.
This Is not true, however, of the vast
interior of the continent, so far as
can be determined by air photographs.
Expeditions which have penetrated
towards the pole have travelled over
great glaciers for large parts of the
distance and have had no opportunity
to make geophysical measurements on
the interior ice cap. 1t hardly can be
assumed, however, that there can be a
level surface below. any more than on
the Palmer Land plateau. Whatever
mountain ranges may exist ARE cer-
tainly completely buried in ice.
Geological Curiosities.
Several geological curiosities of the
Far South. noted by members of the
Rome expedition, are described by DR..
Nichols in the Navy report. Among
these are little islands of sky-blue ice
set in seas of white ice.
Says DR.. Nichols: "TheSe blue ice
masses are without exception round or
sub-round. and vary in size from a few
inches up to three feet in diameter.
The contacts between them and the
white ice are sharp and hundreds of
them cover the surface of the glacier.
In one case it was found that the blue
ice was several inches thick, that be-
meath it there was a pit filled with
water, that a good-sized rock was at
the bottom of the pit, and that the
blue ice was composed of vertical crys-
tails, some of which were four inches
long.
These blue areas apparently were
formed as follows: Fragments which
broke of from the bedrock cliffs fell
on the glacier. Round pits were formed
as these fragments. heated by insula-
ton. slowly sank into the ice. Later
melt water ran down the slopes and
filled the pits. With the beginning Of
cold weather the water in the pits froze.
forming the blue roundish areas. The
blue ice is water ice and the white ice
is snow ice."
Radiation M0ats."
Another curious phenomenon was
that of radiation moats," bitches full
Of water foot or more deep in front
of castle-like rock structures, similar
on small scale to the moats around
castles in Normandy. A glacier surface
was found crossed by radiation gull
lies" formed wherever there were rock
outcrops close to snow or ice. The larg-
est of these bitches was 10 to Is feet
deep and is to Is feet wide. Another
phenomenon difficult to explain is that
of "cryoconite wells" holes in the ice
about two feet deep and two to five
inches wide. AT the bottom Of each pit
there always is small rock fragment.