GlacialLandscapes Bowen

Glacial LandformsGlacial Landforms

By Colin Bowencolin.bowen@colorado.eduBy Colin Bowencolin.bowen@colorado.edu

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Erosional Landforms Createdby Alpine Glaciation

• Cirque• Arête• Col• Horn• Bergschrund• Tarn• Paternoster Lake• Hanging Valley• V & U shaped Valleys• Fjord• Erratics• Truncated Spurs

Cirque

• Cirque: A scooped-out,amphitheater shapedbasin at the head of analpine glacier.

• Arêtes: (knife-edge in French) Asharp sawtooth or serrated ridgethat divides two cirque basins.

Arêtes

• Col: A saddle-like narrow depression formed by twoheadward eroding cirques that reduce an arête.

• Horn: A pyramidal, sharp-pointed peak that results whenseveral cirques glaciers gorge an individual mountainsummit from all sides.

Bergschrund

• Bergschrund: These form when a crevasse or wide crack opens along theheadwall of a glacier; most visible in the summer when covering snow isgone.

• Tarns: A small mountain lake especiallyone that collects in a cirque basin behindrisers of rock material or in an ice gougeddepression.

• Paternoster Lake: One of a series of small,circular stair-stepped lake formed inindividual rock basins aligned down thecourse of a glaciated valley.

Paternoster Lakes

Hanging Valleys

• Hanging Valley:Valleys carved bytributary glaciers thatare left standing highabove the primaryvalley floor.

V & U shaped Valleys

• V-Shaped valleys aretypically formedfrom streams orrivers slowly cuttingthrough the earth.

• U-Shaped valleys occur in postglaciation conditions where thecontinual freeze and thaw hasweathered away the rock walls.

• Fjord: A drowned glaciated valley or glacial troughalong a seacoast.

Erratics

• Erratics: An unique rock carried by a glacial formation that deviates insize and or type relative to the native area.

Truncated Spurs: Occur where a glaciercarves its way though rock, cutting off

the edges of interlocking spurs.

Depositional Landforms Createdby Alpine Glaciation

• Glacial Drift: A general term for all glacial deposits both sorted andunsorted.

• Stratified Drift: Sediments deposited by glacial meltwater that aresorted by size.

• Tills: Unstratified and unsorted debris from ice deposits.• Moraines:• Valley Train Deposit:

Moraines

• Lateral Moraines: A deposition of sediments along bothsides of a glacier.

• Medial Moraine: A deposition of sediments betweentwo lateral moraines.

• Terminal Moraine: Eroded debris that is dropped atthe glacier’s farthest extent.

Valley Train Deposit

• Valley Train Deposits: Material deposited down-valley of a glacier via melt-water.

Erosional and Depositional Landforms Createdby Continental Glaciation

• Till Plain:• Outwash Plain:• Esker:• Kettle:• Kame:• Roche Mountonnée:• Drumlin:

Till Plain

• Till Plain: Forms behind a end moraine; it features unstratified coarsetill, has low and rolling relief, and has a deranged drainage pattern.

Outwash Plain

• Outwash Plains: Are Glacial stream deposits of stratified driftfrom melt-water, braided, and overloaded. They occurbeyond a glacial morainal deposit.

• Esker: A sinuously curving, narrow deposit of coarse gravel that formsalong a melt-water stream channel, developing in a tunnel beneath aglacier.

Kettle

• Forms when an isolated block ofice persists in a ground moraine,an outwash plain or valley floorafter a glacier retreats; as theblock finally melts, it leavesbehind a steep sided hole thatfrequently fills with water.

• Kame: A depositional feature of glaciation; asmall hill of poorly sorted sand and gravel thataccumulates in crevasses or in ice causedindentations in the surface.

Roche Mountonnée:• Roche Mountonnée: An asymmetrical hill of exposed bedrock;

displays a gently sloping upstream side that has been smoothed andpolished by a glacier and an abrupt, steep downstream side.

Drumlin

Drumlin: composed of till (unstratified, unsorted) and isstreamline in the direction of continental ice movement-blunt end

upstream and tapered end downstream with a rounded summit.

Periglacial Landscapes

• Periglacial: Cold climate processes, landforms, and topographicfeatures along the margins of glaciers, past and present; periglacialcharacteristics exist on more than 20% of the earth’s land surface;includes– Permafrost– Frost action

– Ground ice

Geography of Permafrost

• Permafrost: Forms when soil or rock temperature remains below 0degrees Celsius for at least two years in areas consider periglacial.Based on temperature rather than the presence of water.

Continuous and Discontinuous Permafrost• Continuous Area: Regions poleward of the -7 degree Celsius mean

annual temperature isotherm.– Affects all surfaces except those under deep lakes or rivers

• Discontinuous Area: Disappears near the -1 degree Celsius meanannual temperature isotherm.– Cryotic (frozen)– Noncryotic (unfrozen)– Alpine Permafrost: Microclimatic factors such as slope orientation and

snow cover are important in sustaining these lower latitude regions• The Colorado Rockies experience continuous permafrost down to an

elevation of 11,150ft and discontinuous permafrost to 5600ft.

Active Layer: Seasonallyfrozen ground between thesubsurface permafrost andthe ground layer.

Ground Ice• Ground Ice: Subsurface water that is frozen in regions of permafrost.

– Pore Ice: Subsurface water frozen in the soil’s pore spaces.– Lenses/Veins: channels extending in any direction– Segregated Ice: Layer of buried ice that increases in mass by accreting

water as the ground freezes– Intrusive Ice: The freezing of water injected under pressure, as in pingo– Wedge Ice: Surface water entering a crack and freezing.

Frost Action• The 9% expansion of water as it freezes creates a strong mechanical

force.– Frost Heaving: (vertical movement)– Frost Thrusting: (horizontal movement)– Cryoturbation: Soil horizons may be disturbed by frost action and

appear churned.

Frost Action Landforms• Pingo: Large area of frozen ground can develop a heaved up, circular,

ice cored mound.• Palsa: Round or elliptical mound of peat containing a thin perennial ice

lense, rather than a core.• Patterned Ground: An area with a system of ground ice and frost action

develops sorted and unsorted accumulations of rock at the surface thattake the shape of polygons.

Gelifluction and Solifuction

• Solifuction: The flow of soil during a thaw cycle from high to lowerelevation.

• Gelifluction: The flow of soil during a thaw cycle from high to lowerelevation during the presence of ground ice or permafrost.– Resulting in the flattening of the landscape with noticeable sag

marks.

Human Impact

GlacialLandscapes Bowen

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