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GEOL 1301: Final Review
Barchan dune
|
- uni-directional wind
- concave slip face
- crescent shaped |
Blowout dune
|
- reverse of barchans
- convex downwind |
Linear dunes
|
- orientation parallel to wind direction
|
Transverse dunes
|
- orientation 90 degrees to wind direction
- formed in places with abundant sand and no vegetation |
Loess |
- 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 |
Where deserts are formed
|
- 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) |
Desert weathering
|
rusty colors made from ferric iron oxide (hematite and limonite) produced by weathering of iron silicate minerals (pyroxene) |
Desert varnish
|
- a dark brown, shiny material that forms from dew and from clay with iron oxides and manganese
|
Snow line
|
- altitude above which snow doesn't melt entirely in the summer
|
How glaciers form
|
- 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 |
Glacial budget
|
- 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 |
Glacier front
|
- accumulation > ablation = glacier advances
- accumulation = ablation = glacier stays the same size
- accumulation < ablation = glacier retreats |
How glaciers move
|
- 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 |
Plastic flow
|
- dozens of tiny particles start moving short distances all at once, triggering movement
|
Basal slip
|
- when a glacier slides along the boundary between the ice and the ground
|
Surge
|
- 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 |
Movement
|
- A glacier drags rocks and scratches, or grooves, the pavement
- this is called striation
- this is evidence that a glacier moves |
Moraines
|
- bodies of rock created by ice or deposited as sill
- most prominent is the end moraine
- all moraines consist of till |
End moraine
|
- at ice front
- after the glacier melts, seen as ridge parallel to former ice front |
Terminal moraine
|
- see end moraine
- marks the maximum advance of a glacier |
Lateral moraine
|
- one that scrapes against the valley walls
- seen parallel |
Medial moraine
|
- joining of two lateral moraines
- a lateral moraine sandwiched between two glaciers |
Ground moraine
|
- beneath the ice as a layer of glacial debris
- ranges from thin and patchy to thick blanket of till |
Kettles
|
- depressions that are filled with water to create ponds or lakes
- originate as isolated blocks of ice or outwash plains |
Glaciers
|
- 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 |
Varves |
- a series of alternating coarse and fine layers
|
Water-laid deposits
|
- 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 |
Eskers
|
- 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 |
Wisconsin glaciation
|
- 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 |
Things responsible for ablation
|
- 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) |