WATER AND ICE - Physical Geography - page 109

tributary glaciers feeding into the main glacier. The landscape of
Yosemite in California is a good example where there are plentiful
hanging valleys often with large waterfalls tumbling over them for
several hundred metres down vertical cliffs into the main valley.
Small glaciers often form dome shaped depressions, known as
corries or cirques , near the top of mountains. Once the ice has
retreated the depression can form a small lake often called a tarn .
The cirques are essentially small forms of hanging valleys. Glacial
valleys and cirques may extend backwards particularly as freeze-
thaw activity is intense, resulting in rock shattering. Two cirques
that cut backwards into each other may leave a narrow ridge
between them known as an arête . If three or more cirques cut
back together they may leave a pyramidal peak or horn such as
Mont Blanc in eastern France. Sometimes weathering or erosion of
part of an arête can produce a dip in it known as a col . These often
form low points in mountain ridges that humans have turned into
routes to get across the mountains, as is the case for many Alpine
passes.
On a smaller scale there are smoothed whaleback forms ,
which range from ten metres to hundreds of metres in length,
which are the product of abrasion across the surface of an obstruc-
tion. The rock may be particularly resistant and so the glacier was
unable to abrade it fully thereby leaving a smoothed mound orien-
tated in the direction of glacier flow. However, many of these
small mounds that are the product of erosion are not smooth all
over. Stoss-and-lee forms are streamlined features that have a
gently sloped, glacially smoothed upstream side and a steeper,
plucked, downstream side. They are much more common than
whaleback forms and occur when the glacier flows over the obs-
tacle smoothing the upslope side. The stoss side is often scratched
with grooves ( striations ) from sediment that has abraded the rock
as it passed over it. On the downslope side of these forms, bedrock
fracturing, loosening and displacement can occur and the fragments
can be incorporated into the ice. Therefore, the downslope side of
stoss-and-lee forms tends to be rough. Small stoss-and-lee forms are
often called roche mountonées . These landforms tell us that
there was warm ice in the glacier that once existed at that location.
Roche mountonées are typically a few metres in height and tens of
metres in length. There are many remarkable undulating landscapes