Jökull - 01.12.1972, Page 64

The Map of Falljökull
E. A. ESCRITT,
HARROW SCHOOL, HARROW ON THE HILL, MIDDLESEX, ENGLAND
Although Falljökull is divided into two ton-
gues by the ridge Raudikambur it is all one
glacier with a surface area of about 10 square
miles whose catchment lies immediately below
and to the south of the Hvannadalshnúkur. As
the ice slips westward out of the crater of
the Öraefajökull giant crevasses form step-
faults facing the basin that lies above the ice-
fall that is shown on the map. The floor of
this basin contains huge blocks of faulted ice
creating a most dramatic landscape. As the ice
approaches the edge of the plateau at about
3,500 feet it begins to break up into smaller
and smaller blocks prior to sliding in chaotic
fashion over the edge. When the sun is on
them in the late afternoon the seracs frequent-
ly collapse with a thunderous roar. In cloudy
weather however such ice falls were occasional,
giving evidence that they were due to melting
rather than to glacier movement. The ridges
either side of the glacier and Raudikambur it-
self are formed of easily eroded ashes, lavas
and tuffs of Pleistocene age. It is not surpris-
ing therefore to lind ice-cored moraine quite
high on the glacier on the southern fall at ap-
proximately 3,000 feet. The icefall of the north-
ern tongue divides at about 2,000 feet, forming
a small lobe of ice which might be described
as the ‘shoulderblade’ of the glacier.
The whole glacier is called Falljökull but
the name Virkisjökull is applied to the south-
ern arm. The two arms join up below Raudi-
kambur but are effectively divided to their
snouts by the medial ice-cored moraine. This
moraine is a complicated mass of ridges and
cones upon which movement is extremely diffi-
cult. In all areas this moraine stands higher
than the glacier surface. There is an interest-
ing deposit of moraine, still ice-cored, liigh on
the valley side opposite the ‘shoulderblade’.
Ablation is so rapid that even on the dullest
of days lieat may be seen rising from the ice
62 JÖKULL 22. ÁR
and ice-cored moraine. The surface of the
glacier gives every impression of stagnation.
To the south of spot height 1745' pools of
water may be seen among the seracs at the foot
of tlie icefall. Crevasses and seracs have mark-
edly rounded edges and the ice supports numer-
ous rivulets that have carved miniature valleys
for themselves. Few actually drain off the
glacier; in general they disappear into potholes
or drain into ice-cored moraine to reappear
beyoncl the snout as impressive vauclusian
springs. The power of these spouts and of the
streams in flood is readily appreciated when
one hears the boulders grinding along the bed.
Several non-glacial streams also feed these
systems, notably the stream from Hvannadalur
which disappears under the ice into a cave.
After heavy rainfall a large lake ponds up at
this point. Similar lakes occur at the foot of
Raudikambur where the two glaciers coalesce
ancl below the northern snout datum pole