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Glossary of Glacier Terminology


Small tarns in ice-free cirques in the Coast Mountains, north-east of Juneau, Alaska.

Tarn

A lake that develops in the basin of a cirque, generally after the melting of the glacier.


The retreating tide water terminus of South Sawyer glacier, Coast Mountains, Alaska.

Terminus

The lower-most margin, end, or extremity of a glacier. Also called Toe, End or Snout.


Vertical face of the tidewater calving terminus of Lamplugh Glacier, Glacier Bay National Park, AK. The height of the face is more than 100 feet, or ~30 meters.

Tidell Glacier's iceberg-calving terminus in front of Mt. St. Elias, Icy Bay, Wrangell-St. Elias National Park, Alaska. The elevation difference between the glacier and the mountain is 18,008 ft.

The retreating terminus of Mendenhall Glacier, Juneau Ice Field, Tongass National Forest, Alaska. The grey sediment ridge in the right center of the photo is a recessional moraine.

The massive sediment in the background is a poorly-sorted till, deposited at the base of the now-thinning and retreating casement glacier. The boulders in the foreground are a lag deposit resulting from the removal of the finer grain-sizes in the till by the ice-marginal stream. Glacier Bay National Park, Alaska.

Till

An unsorted and unstratified accumulation of glacial sediment, deposited directly by glacier ice. Till is a heterogeneous mixture of different sized material deposited by moving ice (lodgement till) or by the melting in-place of stagnant ice (ablation till). After deposition, some tills are reworked by water.


The surface of the ground in this area adjacent to Sherman glacier is covered with a coarse glacial till. Chugach Mountains, Chugach National Forest, Alaska.

The top of the uniform band of grey-brown sediment on the wall of the valley is the trim line, marking the past thickness of Tana Glacier, Wrangell-St. Elias National Park, Alaska.

Trimline

A clear boundary line on the wall of a glacier valley that delineates the maximum recent thickness of a glacier. It may be a change in the color of the bedrock, indicating the separation of weathered from unweathered bedrock; the limit of a former lateral moraine or other sediment deposit; or the boundary between vegetated and bare bedrock.


The top of the eroding sediment of the south wall of Reed Inlet is the trim line, indicating a recent maximum thickness of Reed Glacier in Glacier Bay National Park, Alaska.

Northeast-looking photograph of a symmetrical, unnamed U-shaped valley cut into the crystalline rocks of the Coast Mountains, Tracy Arn, Tracy Arm-Ford's Terror Wilderness, Tongass National Forest, AK. The valley walls are >2,000 ft. high and the valley is ~1/4 mile wide.

U-Shaped Valley

A valley with a parabolic or "U" shaped cross-section, steep walls and generally a broad and flat floor. Formed by glacier erosion, a U-shaped valley results when a glacier widens and over-steepens a V-shaped stream valley.


A large ice-free u-shaped valley on the north end of the Juneau Ice Field, near Juneau Alaksa

The u-shaped valley to the right side of the photo is the ice-free valley of Talkeetna Glacier, Talkeetna Mountains, Alaska. Note the rock glaciers in the foreground.

Photograph of an outcrop containing a thick section of Pleistocene age varves, Scarboro Cliffs, Toronto, Ontario, Canada. The largest of the varve couplets are more than .5 inches thick.

Varve

A varve is a pair of sedimentary layers, a couplet, that form in an annual cycle as the result of seasonal weather changes. Typically formed in glacial lakes a varve couplet consists of a coarser grained summer layer formed during open-water conditions, and a finer grained winter layer formed from deposition from suspension during a period of winter ice cover. Many varve deposits contain hundreds of couplets.


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