Chapter 17: Glacial and Periglacial Processes and Landforms
Glacier – A large mass of ice, resting on land or
floating as an ice shelf in the sea adjacent to land. They form by the continual accumulation of snow that
recrystallizes under its own weight into an ice mass. Glaciers move slowly under pressure and by the pull of gravity.
Today 11% of the
earth’s land mass is dominated by glaciers but in the past during ice ages up
to 30% of continental land was covered.
Alpine Glaciers – A glacier that forms in a mountain range.
Continental Glacier – Vast ice sheets that are connected to
continental land masses. Antarctica
alone contains 91% of all glacial ice on the planet. Some of these ice sheets are 3000m thick so that only the highest
peaks stick out above them.
Glacial Processes – Glaciers are dynamics, moving downslope
and excavating the landscape through which they flow. A glacier is made up of dense ice, which accumulates through snow
and water that compact, recrystallize, and grow. A glacier’s mass budget determines whether the glaciers will
buildup and expand or melt and retreat.
Ablation – Toward a glacier’s lower end it is reduced
by melting on the surface, internally, and at the base. It is also removed through deflation,
calving, and sublimation.
Glacial Movement – Glaciers flow downslope with the greatest
amount of movement at their centers where the pressure is fairly high but there
is no friction with the valley walls and bottom.
Glacial Erosion – The glacier plucks rocks from the valley
floor and incorporates them into the ice.
This ice then abrades the valley floor eroding more sediment. The debris in the ice also works to polish
the rocks over which it flows and also leaves striations.
Glacial Landforms
U-shaped valleys – Glaciers carve out the bottom of the
valley leaving behind a distinctive U-shape.
Cirques – A scooped out bowl-shaped recess at the
head of a valley. These are source
areas for mountain glaciers and leave behind an open mountain valley.
Arêtes – From French meaning “knife-edge”. A saw-toothed, serrated ridge in glaciated
mountains.
Horn – A mountain peak created by several cirques
surrounding a mountaintop.
Hanging Valleys – Valleys that are left high above the
current main valley floor.
Fjords – Glacial valleys that intersect the ocean
and subsequently fill with seawater after the glacier retreats.
Glacial Drift – A general term for glacial deposits both
sorted and unsorted.
Till – Glacial deposits of unstratified and
unsorted debris.
Erratics – Large rocks that are of foreign composition
that are left behind by retreating glaciers.
Lateral Moraine – Unsorted
glacial debris that is deposited along the side of a glacier.
Medial Moraine – Unsorted
glacial debris that is deposited down the middle of a glacier where two
separate glaciers have joined.
Terminal Moraine – Unsorted
glacial debris that is deposited at the farthest extent of the glacial advance.
Erosional and Depositional Landforms of Continental
Glaciers
Till Plain – A broad plain of unsorted coarse debris
deposited behind an end moraine
and left after glacial retreat.
Outwash Plain – A broad plain of stratified drift
that forms beyond a terminal moraine by out-flowing stream channels that form
braided streams.
Esker – A sinuous curving, narrow ridge of coarse
sand and gravel that formed along the meltwater stream underneath a glacier.
Kettle – A steep sided depression that is left by a
large melted chunk of ice.
Kame – A small hill, knob, or mound of poorly
sorted sand and gravel that is deposited directly by water or ice.
Roche Moutonee – An asymmetrical hill of exposed bedrock
whose upstream side is polished smooth by glacial action and its downstream
side is steep due to the plucking action of the glacier.
Drumlin – Deposited till that has been streamlined
by the retreating glacier so that they align with the flow direction and have a
blunt end upstream and a tapered end downstream.
Periglacial
Landscapes – Cold-climate
processes, landforms, and topographic features that exist along the margins of
glaciers.
Permafrost – Permanently frozen ground.