A Level Geogrpahy

1. Periglacial landforms

2. Nivation Hollows
• Description: Ground depression found in periglacial areas that is
created by nivation.
• Nivation takes place beneath patches of snow in hollows, particularly
on north and east facing slopes. Freeze-thaw action and maybe
chemical weathering, operating under the snow, can cause the
underlying rock to disintegrate. As some of the snow gets ablated in
spring, the weathered particles are moved downhill by solifluction and
by the meltwater. Over time, nivation hollows can form, which can
later be enlarged and can be the beginnings of cirques.
This is an example of
nivation hollows in Prince
Patrick Island, Canada.

3. Blockfields
• Freeze-thaw action provides a great deal of
erosive material in glaciers. In periglacial
areas, scree develop at the foot of slopes as a
result of this. On relatively flat areas,
extensive spreads of angular boulders are left,
which are known as blockfields.
This is a blockfield on the
summit of the Scafell Pike in
the English Lake District.
You can see the angular
boulders .

4. Stone Polygons
• Description: The surface of periglacial areas is often characterized by
the presence of ground materials arranged in a variety of symmetrical,
geometric shapes.
• Patterned groung is a general term to describe the stone-circles,
polygons and stripes found in soils subjected to intense frost action. An
example is the Grimes Graves in Norfolk. On steeper slopes, stone
stripes replace stone polygons. Their exact formation is unclear
although ice sorting, differential frost heave and the effect of
vegetation are widely held to be responsible.
This is at the summit of the
highest hill on Blomstrandoya
in northwestern Spitsbergen.
Here you can see the polygon
shaped ground materials.

5. Coombe rock
• Coombe rock or head is a periglacial deposit
comprising of chalk, mud and clay, compacted
with angular fragments of frost-shattered
rock, e.g. at Scratchey Bottom in Dorset.
This is an example of Coombe
rock at Scratchey Bottom in
Dorset.
You can see angular fragments of
rock formed by frost shattering

6. Ice-wedge polygons
• Refreezing of the active layer during winter causes the soil
to contract and cracks open up on the surface. During
melting the following summer, the cracks open again and
fill with meltwater and fine sediment, which helps to
partially fill the crack. Over time, repetition widens and
deepens the crack to form an ice wedge.
This is an ice wedge polygon
in Hudson Bay Lowlands,
Manitoba
They are 1 m wide and 3 m
deep.

7. Pingos
• Description: A large conical mound that contains an ice core. This feature can be
up to 60 to 70 meters in height. Common in the Mackenzie Delta region of Canada.
• Freezing of water in the upper layer of soil where permafrost is thin or
discontinuous leads to the expansion of ice within the soil. This causes the
overlying sediments to heave upwards into a dome-shaped feature known as a
pingo.
• Closed system- progressive inward and downward freezing if a talikunder a drained
lake.
• Open system- Development above a talik in permafrost where water escapes from
a confined aquifer.
This is a pingo in the
Mackenzie Delta region in
Canada.
You can see the sheer size in
height of the pingo. This
particular pingo is 65 metres in
height.

8. Scree
• Description: An accumulation of weathered rock fragments at
the base of a steep rock slope or cliff.
• Scree slopes are slopes composed of large quantities of
angular fragments of rock e.g. the slopes at Wastwater in the
Lake District. They typically have an angle of rest of about 350.
Extensive upland surfaces of angular rocks are called
blockfields.
This is a “sea” of scree
at Wastwater in the
Lake District
Angular fragments of
rock at an angle of 350

9. Solifluction lobe
• Description: Rounded, tongue-like features often forming
terraces on the sides of valleys. They are composed of
angular debris from fines to boulders. A location of a
solifluction lobe is at Maiden Castle, Dorset.
• When the active layer thaws in summer, excessive lubrication
reduces the friction between soil particles. Even on slopes as
shallow as 20, parts of the active layer then begin to move
downslope. This leads to solifluction lobes forming terraces
on the sides of valleys.
This is a solifluction lobe near
Chicken Creek, Alaska.
Tongue-like features found on
the sides of valleys. About
20m long.