GEOL 1301: Final Review
30 Cards in this Set
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Barchan dune
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- uni-directional wind
- concave slip face
- crescent shaped
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Blowout dune
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- reverse of barchans
- convex downwind
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Linear dunes
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- orientation parallel to wind direction
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Transverse dunes
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- orientation 90 degrees to wind direction
- formed in places with abundant sand and no vegetation
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Loess
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- a blanket of sediment
- lacks internal stratification
- covers 10% of Earth's land
- major deposits in China, North America
- 1,000,000 sq km of loess deposits in China, 2 million years old, formed after increase in elevation of the Himalayas
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Where deserts are formed
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- rainfall is an important factor
- Sahara, Kalahari, Great Australian desert all have low rainfall and are under high pressure
- mainly between 30 degrees North and South
- all sun and no humidity
- formed also between 30-50 degrees North and South (Great Basin, Mohave)
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Desert weathering
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rusty colors made from ferric iron oxide (hematite and limonite) produced by weathering of iron silicate minerals (pyroxene)
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Desert varnish
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- a dark brown, shiny material that forms from dew and from clay with iron oxides and manganese
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Snow line
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- altitude above which snow doesn't melt entirely in the summer
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How glaciers form
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- burial and aging produce ice as grains recrystallize
- 10-20 year process
- glaciers grow in the winter
- accumulation means that glaciers grow due to added snow
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Glacial budget
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- the difference of accumulation and ablation
- if accumulation - ablation = 0, then the glacier stays the same size
- accumulation in the upper parts of the glacier
- ablation in the lower parts
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Glacier front
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- accumulation > ablation = glacier advances
- accumulation = ablation = glacier stays the same size
- accumulation < ablation = glacier retreats
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How glaciers move
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- when gravity wins, it pulls the glacier down so it starts moving
- it moves downhill with the same laminar flow of a stream
- plastic flow and basal slip
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Plastic flow
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- dozens of tiny particles start moving short distances all at once, triggering movement
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Basal slip
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- when a glacier slides along the boundary between the ice and the ground
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Surge
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- a sudden fast movement of a glacier after little or no movement
- can move 6 km/year, 1000x faster than normal
- follows the build up of meltwater in tunnels or at base near glacier
- enhances basal slip
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Movement
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- A glacier drags rocks and scratches, or grooves, the pavement
- this is called striation
- this is evidence that a glacier moves
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Moraines
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- bodies of rock created by ice or deposited as sill
- most prominent is the end moraine
- all moraines consist of till
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End moraine
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- at ice front
- after the glacier melts, seen as ridge parallel to former ice front
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Terminal moraine
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- see end moraine
- marks the maximum advance of a glacier
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Lateral moraine
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- one that scrapes against the valley walls
- seen parallel
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Medial moraine
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- joining of two lateral moraines
- a lateral moraine sandwiched between two glaciers
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Ground moraine
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- beneath the ice as a layer of glacial debris
- ranges from thin and patchy to thick blanket of till
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Kettles
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- depressions that are filled with water to create ponds or lakes
- originate as isolated blocks of ice or outwash plains
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Glaciers
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- blocks of ice 1 km in diameter can take 30+ years to melt
- by the time it melts completely, the margin of the glacier has retreated so far from the region that little outwash reaches the area
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Varves
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- a series of alternating coarse and fine layers
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Water-laid deposits
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- in summer when the lake is free of ice, coarse silt is laid down by abundant meltwater streams flowing from the glacier to the lake
- in the winter, fine clays settle, depositing a thin layer on top of the coarse summer layer
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Eskers
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- thin, long, narrow ridges of sand and gravel found in the middle of ground moraines
- run for kms in a direction parallel to the direction of ice movement
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Wisconsin glaciation
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- glacial period along the east coast, named after Wisconsin
- continents were larger back then
- 18,000-21,000 years ago
- continental shelves grow, sea level drops
- continental shelves shrink, sea level increases
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Things responsible for ablation
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- melting (losing material from iceberg)
- iceberg calving (parts breaking off)
- sublimation (from solid to gas without passing through liquid)
- wind erosion (wind can erode ice by blowing it enough and through sublimation or melting)
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GEOL 1301: Final Review