Grade 9 Academic Geography
Glacial Processes
Glacial Erosion
Two major erosional processes occur at the base of a glacier.
 At the base of a glacier, large amounts of loose rock and sediment are incorporated into the moving
glacial ice by partial melting and refreezing. These incorporated materials held in the ice on the surface
underneath the glacier provide an abrasive process, known as scouring, that creates a variety of features
(e.g., Striations that appear as scratches of various sizes on rock surfaces). In some cases, abrasion can
polish the surface of some rock types smooth, called glacial polish. The abrasive scouring action also
produces a fine clay-sized sediment that is often transported away from the glacier by meltwater. As a
result of this process, glacial meltwater can have a light, cloudy appearance, and is called glacial milk.
 Plucking is the process of particle detachment by moving glacial ice. In this process, ice freezes in cracks
in rock. As the main body of the glacial ice moves material, the ice in the cracks is pulled and plucked out.
The intensity of the plucking process is greatest on the lee-side of rock mounds. When combined with
glacial abrasion, the action of plucking on rock mounds produces a unique asymmetrical feature known
as roche moutonnee, smooth on the side of ice advancement and steep and jagged on the opposite side.
Glaciers generally flow over the land surface along a path of least resistance. The flow of an alpine glacier into a
valley, causes the glacier to rapidly advance producing a swollen tongue of ice at the glacier's snout, known as a
lobe. As the lobe moves down the valley, it often encounters the lobes of other glaciers from connecting valleys.
The glacier grows in size with addition of the flow of connected sub-valleys. The following image illustrates one of
these networks of connected alpine glaciers
A number of distinct glacial erosional features can be observed in mountainous regions.
 Much of the erosional force is exerted on the bottoms and sides of alpine valleys that guide the flow of
glaciers. This erosion causes the bottom and the sides of any glaciated valley to become both wider and
deeper over time.
 Glacial erosion also results in a change in the valley's cross-sectional shape. Glacial valleys tend to have a
pronounced U-shape that contrasts sharply with V-shape valleys created by stream erosion.
 Small adjoining feeder valleys entering a large valley in a glaciated mountainous region tend to have their
floors elevated some distance above the level of the main valley's floor, called a hanging valley. Hanging
valleys develop because of two reasons: (1) larger glaciers create greater erosion and subsequently a
deeper valley, and (2) some valleys have seen more glacier ice pass through them which also results in
more erosion and a deeper valley. Many hanging valleys are also the sites of sensational waterfalls.
Some of the other features associated with glacier erosion in alpine regions are cirques, horns, and arêtes.
 Cirques are the bowl shaped depressions
found at the head of glacial valleys. For
most alpine glaciers, cirques are the
areas in the alpine valleys where snow
first accumulated and was modified into
glacial ice. The glaciers that occupy
cirques are called cirque glaciers.
 Horns are pyramidal peaks that form
when several cirques chisel a mountain
from three or more sides. The most
famous horn is the Matterhorn found in
the Swiss Alps.
 Arêtes are the narrow serrated ridges
found in glaciated alpine areas. Arêtes
form when two opposing cirques back erode a mountain ridge.
Glacial Deposition
A large part of the surface of a glacier is covered with a coating of sediment and rock debris. This is especially
prevalent near the snout of the glacier, where most of the ice has been lost to ablation and sediment is left behind.
Sediment is added to glacial ice in two ways.
 Large quantities of sediment are picked up by abrasion and plucking at the base of the ice. In alpine
areas, sediment is added to the surface of the glacier from the valley walls through various types of mass
movement. Much of the debris that is added to the ice of the glacier is eventually delivered to the snout
because of the continual forward flow of glacial ice. From the snout, this material can be placed directly
from the ice or it can be deposited through the action of flowing meltwater, the latter deposits are called
glaciofluvial deposits. The technical term used to describe material deposited by the ice is called till. All
glacial deposits are known as glacial drift.
 Till is a heterogeneous combination of unstratified sediments ranging in size from large boulders
to minute particles of clay. When till is deposited along the edge of a glacier it tends to form
irregular hills and mounds known as moraines. A terminal moraine is a deposit that mark, the
farthest advance of a glacier.
 A till plain is a large, relatively flat plain of till that forms
when a sheet of ice becomes detached from the main
body of the glacier and melts in place.
 Sometimes the sediments in a till plain can contain large
boulders. If these boulders are transported a great
distance from their place of origin, they are called erratics
 Glaciers can also contain sinuous flows of meltwater that occur in
ice tunnels at the base of the ice. The beds of these sub-surface glacial streams are composed of layers of
sand and gravel. When the ice melts from around the meltwater tunnels, the beds of sand and gravel are
deposited on the Earth's surface as long twisting ridges known as eskers
 Drumlins resemble an extended teaspoon laying bowl down. The gently sloping tapered end of the
drumlin points in the general direction the glacier traveled. Drumlins also come in a variety of dimensions.
Lengths can range from 100 to 5000 meters and heights can exceed 200 meters. A couple theories exist
to explain their formation. The most accepted theory suggests they form when saturated ground
sediments oozes up into hollows at the base of an advancing glacier.
The sediment is then stretched out and molded into a streamline
form as the ice moves forward.
 When glaciers are rapidly retreating, numerous blocks of ice can
become detached from the main body of the glacier. If glacial drift is
then placed around the ice, a depression on the surface called a hole
can be created when the ice melts. These create kettle lakes.