Glaciation Terminology
Unit 4: Gradational Processes
Geography 12
Name:
Period:
Surface features resulting from alpine glaciation:
Cirque: constant thawing and freezing of the head of glacier plucks out the side of a
mountain. Circular shape is cut in peak, arm-like depression.
Horn: cirque cut into the mountain from all sides and single pinnacle or rock is left.
Tarn: lake formed in a cirque after glacier has melted.
Col: two cirques erode the wall of rock between them and a mountain pass is created.
Arête: formed when two glaciers erode parallel U shaped valleys and sharp knife like
ridges are created between cirques.
U shaped valley: V shaped valley eroded into a U shape as glacier advances.
Hanging Valleys: formed by tributary glaciers that flow into the main glacier eroding
steep vertical cliffs.
Truncated Spurs: ridge of land where the end has been cut off by the erosion of ice as
the glacier forms its U shaped valley. Triangular shape.
Lateral Moraines: debris carried along and deposited at the side of the glacier as it
melts.
Medial Moraines: as valley glaciers come together, lateral moraines join to become medial
moraines. Strands of debris appear as dark lines in the middle of the main glacier.
Terminal Moraines: when ice begins to melt it begins to drop its load of rock. Over time,
large quantities of eroded material are brought to its terminus and are deposited across
the U shaped valley. Marks the maximum extent of ice.
Finger Lake: Finger shaped lake. Formed when glacier erodes a depression in an area of
soft rock and terminal moraine blocks drainage of melt water and water begins to pool.
Fiord: formed when glaciated valleys flood with sea water to form steep walled, deep
inlets.
As ice continues to move south, the ice went through periods of retreat and advances. The
term retreat refers to the ice melting and the mass of ice begins to look like it is moving
backwards. The term advance refers to the forward movement of ice. When ice sheets
moved slowly over existing landforms, they scraped and scoured everything like giant
earth moving machines. The constant plucking of material by large masses of ice and the
abrasive power of the eroded material picked up and has left very distinct landforms.
Surface features resulting from continental glaciation:
Striations: glacial “scratches” left in bedrock by debris frozen in glacial ice.
Glacial Till: as ice continued in southward movement it began to melt. The ice was carrying
its maximum load, and it passed over these areas, dropped the eroded material called till.
Composed of fragments and chips that have been chewed and ground up by ice. Unsorted.
Outwash Plain: as ice sheet melted the running water carried glacial debris deposited at
the end of the ice as an outwash plain.
Ground Moraine: the layer of till that covers the underlying bedrock.
Recessional Moraine: as a glacier recedes, ridges of debris are deposited. This occurs
when ablation equals accumulation and the glacier remains stationary, depositing debris at
its snout.
Erratics: isolated boulders carried by glaciers and deposited far from their source of
origin.
Kettle Lake: as glaciers moved over the landscape, sometimes a block of glacial ice broke
loose and was left behind in a depression gouged out by a glacier. When the ice melted, the
lake was created.
Drumlin: small hill-like deposits of debris. The long axis of the drumlin always points in the
direction of ice movement, and the steep end usually faces in the direction from which the
ice came.
Spillway: A valley created by the erosion of a large river of glacial meltwater.
Esker: long, snake-like deposits that run across a glaciated countryside left behind by
glacial melt water.