WATER AND ICE - Physical Geography - page 110

where there are hundreds of roche mountonées spread over large
areas. Crag and tail features form where resistant rock leaves
small mounds protruding above the surrounding surface but on the
downslope side the feature is formed from deposited sediment
behind the obstruction. The setting for Edinburgh Castle, in Scot-
land, is a crag and tail feature.
The deposition of eroded material from glaciation has also pro-
duced important landforms. The glacier itself can produce the land-
form, or the landform may be left when the ice in the glacier melts.
Finally, the meltwater can produce depositional features quite some
distance from the glacier itself. Depositional landforms associated
with glaciers are not as dramatic as those produced by erosion.
Nevertheless, glacial deposits cover around 75 per cent of the mid-
latitude land mass and 8 per cent of the Earth's surface. Features
may be formed by the direct action of ice such as moraines which
are linear mounds of sediment. Push moraines form when a glacier
forces itself into sediment at the front of the glacier raising it into a
ridge. These moraines can mark the maximum extent of glaciers in
the past, helping us to map the extent of former ice masses. Dump
moraines are formed at the front of a glacier where material being
transported through the glacier is eventually deposited at its front
end as the ice melts. There can be many of these left as a glacier
retreats. Lateral moraines are those that have formed on the glacier
surface collecting rockfall from the cliffs above. As the glacier
moves, the intermittent rockfall debris appears as a linear feature on
the glacier surface. Sometimes there can be massive boulders that
are transported this way and once they are deposited a long dis-
tance from their original source they are often known as erratics .
Hummocky moraines occur where there is a deposit of material
from inside the glacier or on top of the glacier as the glacier melts.
Moraines are formed by the action of ice whereas eskers are
features of water. Eskers are snaking ridges of sand and gravel that
are thought to form mainly in R-channels at the glacier bed. They
can be 20 to 30 metres high and up to 500 kilometres in length.
Eskers may flow uphill as well as down, simply representing the
fingerprint of an internal channel system within the ice mass.
Drumlins are streamlined mounds of sediment, sometimes with a
rock core, aligned in the direction of ice flow typically with a blunt
end upstream and a more pointed end downstream. They often