Unit 9 Glaciers (H) Rugg 24-25

Alpine Glacier

A glacier forming in high elevations and confined to a valley

Arete

rocky, narrow ridge created by Alpine glaciers when two cirques erode in valleys next to each other

Calving

process of glacial ice breaking off into a body of water, releasing icebergs

Cirque

A glacial erosion feature shaped like a half-bowl that forms in a valley at the head of an alpine glacier

Col

A saddle shaped arete created by back to back alpine glaciers eroding the arete between them

Crevasse

A crack in the top section of a glacier created by uneven movement of ice beneath such as when the glacier goes over a steeper section of valley floor

Drumlin

a ramp shaped hill of glacially deposited till with the steep side facing where the glacier came from

Erratic

a large boulder transported by and deposited by a glacier

Esker

long, meandering ridge of drift deposited by a glacial meltwater stream flowing beneath a glacier so it will be aligned roughly parallel to glacial advance direction

Fjord

narrow, deep salt water inlet formed as sea-level rose and flooded a glacial valley

Hanging Valley

A valley left by a melted tributary glacier that enters a larger glacial valley above its base, high up on the valley wall. With less mass and sediment a tributary glacier doesn't carve as deep as the main glacier in an alpine glacial setting

Horn

a pyramid shaped mountain peak created by three or more cirques that eroded the mountain sides leaving behind aretes and a horn

Ice Cap

a glacier that is the same shape and flow pattern as a continental glacier but smaller, it covers less than 50,000 square miles

Ice Shelf

A thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface but hasn't calved off yet.

Kettle Pond

a kettle that intersects the water table and therefor filled with water

Lateral Moraine

a ridge of till that forms from the sediment concentrated along the sides of an alpine glacier where it meets the valley walls

Medial Moraine

a ridge of till that forms from the deposition of sediment concentrated in middle of alpine glaciers when two tributary valley glaciers come together to form a single ice stream and their lateral moraines join together.

Moulins

A cylindrical, vertical shaft that extends through a glacier and is carved by meltwater from the glacier's surface.

Outwash Plains

A ramp of sorted glacial sediment, drift, that forms beyond the end of a glacier where the meltwater streams converge and deposit their sediment

Snow line

The elevation above which snow remains all year long

Striations

Scratches left on bedrock by sediment carried along the base of a glacier. They will be parallel to glacial flow direction.

Glacial Trough

U-shaped valley formed by the erosion of the glacier that followed a river valley and widened and flattened the V's base.

end moraine

a ridge of till that forms from the sediment concentrated along the terminus/front edge of a glacier from bulldozing as well as the internal conveyor belt depositing where it melts

Kettle

A depression in the outwash plain formed when the glacial ice melts unevenly leaving a chunk of ice to get buried in meltwater stream sediment. Once the ice melts this can form a valley or if it intersects the water table, a lake.

Till

Unsorted sediment deposited by a glacier

continental glacier

Dome shaped glacier of at least 50,000 square miles

Firn

partially compacted granular snow that is the intermediate stage between snow and glacial ice.

glacier

A large, dense body of ice that is flowing on land

Ice Age

A period of time lasting tens of thousands of years, where Earth's temperature drops low enough that continental glaciers grow toward the equator.

Louis Agassiz

A Swiss glaciologist and Harvard professor who proposed the theory of Ice ages to support the "mystery of the boulders" in New England

Milankovitch cycles

changes in the earth-Sun orientation in terms of 1)Earth's tilt amount 2)the eccentricity of Earth's orbit 3) direction of earth's axis tilt that together can align to cause conditions for glacial and interglacial cycles within an ice age

Moraine

a ridge of till that forms from the sediment concentrated along the sides (lateral), middle (medial), or end (end, terminal) of a glacier

recessional moraine

a type of end moraine in which the ridge of till forms at the end of a glacier from bulldozing and conveyer-belt sediment delivery when a glacial retreat stagnates, neither advancing nor retreating for a time.

terminal moraine

a type of end moraine in which the ridge of till forms at the end of a glacier from bulldozing and conveyer-belt sediment delivery when a glacial advance stagnates, neither advancing nor retreating for a time. This will mark the furthest advance the glacier made in the landscape.

rigid zone

the upper brittle zone (top 130 ft) of a glacier where the ice cracks into crevasses

zone of plastic flow

the lower section (deeper than 50 m) of a glacier that behaves like a plastic solid due to the confining pressure of ice above allowing for slow plastic flow in response to gravity and stress

zone of accumulation

the part of a glacier that receives more mass by accumulation than loses by melting (above the snow line)

zone of wastage

The area on a glacier where there is a net loss of snow and ice (below the snow line)

ground moraine

glacial till deposited by melting glaciers that were in retreat spread in a layer across the ground

Nunatak

an un-eroded mountain peak that sticks up taller than the continental glacier

roches moutonnee

a ramp shaped mountain carved by continental glacial erosion with the gentle sloping side being ground down by abrasion during the ice advance and the steep side being plucked steeper as the ice rides over the mountain.

tarn

a lake that forms in a cirque that collects rain and melt water in its depression