Page 279 - Fundamentals of Geomorphology

262 PROCESS AND FORM

Plate 10.9 Chattermarks on Cambrian quartzite, An Teallach, north-west Highlands, Scotland.
(Photograph by Mike Hambrey)

different sides, a pyramidal peak or horn may eventu- Supraglacial landforms
ally form. The classic example is the Matterhorn on the
Swiss–Italian border. Debris on a glacier surface lasts only as long as the glacier,
but it produces eye-catching features in current glacial
environments. Lateral moraines and medial moraines
Nunataks lie parallel to the glacier. Shear or thrust moraines,
produced by longitudinal compression forcing debris to
Nunataks are rock outcrops, ranging from less than a the surface, and rockfalls, which spread debris across a
kilometre to hundreds of kilometres in size, surrounded glacier, lie transversely on the glacier surface. Dirt cones,
by ice. They include parts of mountains where erratics (Plate 3.3), and crevasse fills have no particular
ice has not formed, or entire mountain ranges, orientation with respect to the ice movement.
including the Transantarctic Mountains on Antarctica Many features of supraglacial origin survive in the
(see Figure 10.2), that have escaped ice formation landscape once the ice has gone. The chief such forms
everywhere but their flanks.
are lateral moraines and moraine dumps, both of which
lie parallel to the ice flow, and hummocky moraines
and erratics, which have no particular orientation. Lat-
DEPOSITIONAL GLACIAL LANDFORMS eral moraines are impressive landforms. They form from
frost-shattered debris falling from cliffs above the glacier
Debris carried by ice is eventually dumped to produce and from debris trapped between the glacier and the
an array of landforms (Table 10.3). It is expedient to valley sides (Figure 10.6c). Once the ice has gone,
group these landforms primarily according to their posi- lateral moraines collapse. But even in Britain, where
tion in relation to the ice (supraglacial, subglacial, and glaciers disappeared 10,000 years ago, traces of lateral
marginal) and secondarily according to their orienta- moraines are still visible as small steps on mountain-
tion with respect to the direction of ice flow (parallel, sides (Plate 10.10). Moraine dumps rarely survive glacial
transverse, and non-orientated). recession.