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32 Cards in this Set
- Front
- Back
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Glacier
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A mass of ice that MOVES over land (or water) under its own weight through the action of gravity
-if it doesn't move it's not a glacier |
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Continental Glacier
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(Ice sheets) - vast layers of ice occupying thousands of square kilometers
-Greenland, Antartica |
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Alpine Glaciers
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Flow in and from mountain valleys
-small, limited in extent |
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Firn
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Little pellets of snow with small crystals, that have been compacted from overlying weight, which causes pressure melting; contains air, but maybe only 25%
-is in the intermediate stage between snow and glacier |
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Snow Line
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The elevation at which snow/ice remains frozen year round
-determines presence and absence of glaciers -a certain elevation is needed for a snowline to have a glacier - need enough room for accumulation??? |
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Frozen-base glaciers & how they move
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Glaciers that stay frozen/dry; move by internal deformation
-when they move, crystal shear takes place & the crystals change shape...sliding happens on crystal boundaries and the glacier skews; new crystals grow as movement takes place -does NOT erode material |
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Wet-based (temperate) Glaciers & how they move
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Glaciers that have periods of freeze & thaw; move from basal sliding
-the bottom of the glacier gets melt water & saturates the sediment; a water film forms, and the whole glacier physically slides downslope -erodes LOTS of material |
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Glacier Equilibrium
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Controls the glacier movement
-if accumulation = ablation, then the ice front does not move -if accumulation > ablation, then the glacier advances -if accumulation < ablation, the glacier retreats **Ice is always moving forward even if the glacier is still retreating -retreat means ice is melting faster than can be replaced by flow*** |
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Accumulation
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The process of building up a glacier, often from snow pack & melt water
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Ablation
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The removal of ice at the toe of a glacier by melting, sublimination (vaporizing), and/or breaking pieces off
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Glacial Erosion (The ways it erodes)
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Plucking - Ice breaks off and removes bedrock fragments; ex: the steep side of Mt. Kineo
Abrasion - Rocks in ice polish and smooth or gouge substrates; like sandpaper Causes: polish, striae, grooves, & glacial pavement -like the flatter side of Mt. Kineo |
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Glacial Transportation (3 ways)
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1. At the base of the ice:
-till -range of transport distances -roughly mirrors bedrock composition, but can include erattics 2. In the ice: -collects things like a conveyor belt 3. Water in ice: through -moulins: "potholes" in the ice where surface melt drains - can sometimes go to the bottom -ice tunnel mouth: where the water from a moulin can come out, with rocks & other debris |
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Glacial Deposition
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Roche Mountonee
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A glacial eroded hill that becomes elongate in the direction of flow and asymmetric; glacial rasping smooths the upstream part of the hill into a gentle slope while glacial plucking erodes the downstream edge into a steep slope
-encounters a bedrock obstruction, pressure melts (abrades the first side), then refreezes and plucks the other side |
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Till
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Heterogenous mixture of glacially eroded & transported material
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Erratic
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A boulder that has a composition different than the underlying bedrock, that has been carried by glacial transport
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Cirque
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A bowl-shaped depression carved by an ALPINE glacier on the side of a mountain
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Arete
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A residual knife-edge ridge of a rock that separates two adjacent cirques
ex: Knife's edge on Katahdin -from ALPINE glaciers |
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Tarn
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A lake that forms at the base of a cirque on a glacially eroded mountain
-ALPINE glacial feature -ex: Chimney pond |
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U-shaped Valley
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A steep-walled valley shaped by glacial erosion into the form of a U
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Hanging Valley
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A glacially carved tributary valley whose floor lies at a higher elevation than the floor of the trunk valley
-waterfalls can occur here |
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Moraine
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A sediment pile composed of till deposited by a glacier
-depositional feature -poorly sorted -Long Island is a moraine |
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Outwash Plain
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A broad area of gravel and sandbars deposited by a braided stream network, fed by the meltwater of a glacier
-depositional feature -carried out by water, *well sorted* |
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Kettle Lake
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A circular depression in the ground made when a block of ice breaks off the toe of a glacier, becomes buried by till, and later melts
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Esker
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A ridge of sorted sand and gravel that snakes across a ground moraine; the sediment of an esker was deposited in subglacial meltwater tunnels
-long, linear accumulations of sand & water -high, dry, sandy |
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Glaciomarine Delta
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A delta that was originally fed by a stream from a glacier, which carried material from the glacier as well
-well sorted -topset beds, foreset beds |
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Isostatic Depression (Weight of ice)
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Occurs when a very heavy glacier occurs on land, and from the load, a depression forms and the land subsides under the glacier, whilon the sides it bulges
-it makes the asthenosphere flow away -caused on a regional scale |
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Discuss the advance and retreat of glaciers in terms of snowline, accumulation, and ablation.
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When a glacier is entirely above the snowline, there is usually only accumulation, and the glacier builds.
Once part or all of the glacier is below the snowline, any part below the snowline starts to ablate, or melt. If the ablation amount is equal to the amount of accumulation, then the glacier will stay the same size. If the ablation is greater than the accumulation, then the glacier will retreat. If the accumulation is greater than the ablation, then the glacier will advance |
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How do glaciers move?
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Glaciers move through either:
1. Internal Deformation 2. Basal sliding |
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How do glaciers affect landscapes?
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Glaciers affect landscape in:
Erosion Transportation Deposition |
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Compare and contrast the effects of alpine glaciation & continental glaciation
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Alpine glaciers sharpens the surface, while continental glaciers smooth out the surface. The continental glaciers scours away the high points, and fills in the low ones with that material.
They both erode material & transport it, & they both move. |
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How do geologists use glacial deposits to understand the glacial history of a region?
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Geologists can use glacial deposits to understand the glacial history of a region by being able to identify glacial depositional features, and knowing how they are formed. For example, if there is a terminal moraine, geologists know that that's where the point of a particular glacier stopped advancing and started retreating. If they find an outwash plain, they know that there was a glacier once just upland from the plain, and meltwater from the glacier had carried the finer sediment away from the moraine and deposited it across a wide area. If they find a kettle lake, they know that a glacier was once at this location, and when it retreated a huge chunk of ice broke off & got buried by till. This chunk of ice eventually melted, forming a kettle lake.
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