2010 Paper 1 Question 2: Lithosphere
(a)
Describe and explain the conditions and processes which encourage
the formation of scree slopes
(7)
Scree slopes are found below steep and bare rock faces (1) with lines
of weakness or many joints, such as carboniferous limestone (1). They
are formed in cold climates where temperatures fall below freezing at
night (1).
These conditions allow physical weathering to take place in the form
of freeze-thaw action (or frost shattering) (1). This occurs where
water enters cracks in the rock, freezes at night and expands (1). If
this happens repeatedly huge pressure is exerted on the rock and it
will split (1). Fragments of rock are moved downhill by gravity (1),
accumulating at the base of the slope as large heaps of rock debris (1).
Credit will be given for appropriate diagrams e.g. one which shows how
freeze thaw happens.
(b)
With the aid of annotated diagrams, explain the processes involved in
the formation of a corrie.
(9)
Snow accumulates in a hollow on a mountain side from year to year if
there is a lack of summer warmth to melt it (1). More will accumulate
on a north facing slope due to a lack of insolation (1). The compressed
layers of snow will form firn (or névé) and eventually ice (1). The ice,
or glacier, will now start to flow downhill under the force of gravity
(1). Plucking will occur, where ice freezes onto the bedrock and pulls it
away from the mountain (1) and incorporates the rock into the ice (1),
steepening the back wall. Abrasion will overdeepen the hollow by
scraping or grinding it with the rock debris carried by the ice (1). The
rotational movement of the ice will also overdeepen the hollow (1).
Frost shattering around the hollow will provide rock debris which will
become incorporated into the ice and cause more erosion (1). Frost
shattered rock may fall into crevasses, or bergschrund (1). A rock lip
is formed at the corrie edge because the rotational movement is so
strong (1). This traps water as the ice melts, leaving a tarn or corrie
lochan (1).
Named examples of corries will get a maximum of 1 mark.
A maximum of 7 marks only if there is no diagram.
A series of fully annotated diagrams could score full marks but only if
the annotations include enough explanation of the processes.