Geology Final Test
Chapter 12
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75% of all freshwater on earth is cryosphere
Glacier: a mass of flowing ice
 Formed on land
 Snow survives from year to year
 Creeps down slope or out ward due to stress of its own weight
Glacier ice flow: laminar flow mostly gravity causes down slope flow or outward spreading
Plastic deformation: within the ice basal sliding along the base
moves a few inches to a few miles per year
GLACIAL EQUILIBRIUM
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Winter – accumulation throughout the glacier
Summer – complete melt off on lower glacier ablation
Equilibrium line: areas of net gain and net loss
Movement of Equilibrium Line: indicates a change of regime,
growth or shrinkage
Glacial advance
Glacial retreat
GLACIER DISTRIBUTION AROUND THE WORLD
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Latitude and altitude: control alpine glacier distribution
Requirements: Sufficient moisture to provide precipitation (snow)
Cold Season – accumulation matches warm season ablation loss
ALPINE GLACIER
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Four sources of sediments into glaciers
1. Dust
2. Rockfalls
3. Abrasion
4. Plucking
HIMILAYA MOUNTAINS
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Orographic effect: monsoon precipitation increases towards mountains
ELA – equilibrium line altitude. Elevation of equilibrium lines for each glacier, increases towards
equator
RECRYSTALLIZATION OF SNOW TO GLACIAL ICE
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Results from – temperature changes and compaction. Crushing of flakes, sublimation, crystal
growth
Compression – causes recrystallization of snow to ice, and the loss of air-filled spaces
Sublimation – allows movement of water vapor from high pressure to low pressure points
GLACIAL TYPES
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Alpine glacier
 Occupies a valley in a mountainous area
 Most numerous, but smaller than continental glaciers
 Start in a cirque near mountain top
 Flow down slope within valleys
Continental glacier
 Large areas of land surface
 Unconfined by topography
 Start in high latitudes and flow outwards
 May be several km thick
 Antarctica = ice sheet / Iceland = ice cap
Calving Glaciers
 Icebergs are created
 Glaciers flow into the sea, which creates calving glaciers
GLACIERS – EROSION AND TRANSPORT
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Glaciers are very effective at ERODING and TRANSPORTING geological materials
2 main EROSIONAL “methods”
1. Plucking – melt and refreeze around loose rocks
2. Abrasion/milling – ice + rock = geo sandpaper
3. Rockfalls + dust – on top of ice
Glaciers transport sedimentary materials of all sizes together = no sorting by particle size
Glacier erosion examples = great lakes and finger lake of New York State
ABRASION FEATURES
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Glacial grooves and striations – created when rocks held in a glacier’s base grind against bedrock
as the glacier moves
Orientation of abrasion features – indicates the direction of glacier movement
Striations, glacial polish, plucked fractures
ALPINE GLACIATION: EROSIONAL FEATURES
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Cirque – deep, steep walled concave mountain. Depression scooped out of the bedrock at the
head of a glacier
Arete – sharp ridge between 2 or more cirques
Horn: spire separating multiple cirques
Glacial valley – deep, steep-sided U-shaped valley.
Hanging valley – tributary valley intersecting the main valley
V- shaped valleys are created by streams
HANGING VALLEYS
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Common product of alpine glaciers where tributaries join the main stem ice flow
Valleys “HANG” because ice is more viscous than water
Glacier energy grade line is the top surface of ice
GLACIAL DEPOSITS
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Till
 Unsorted, unlayered sediment deposited directly by glacial ice
 Under the ice or at the terminus
 Dominated by fine-grained (clay size) materials
 Also contains sediment up to boulder size
Outwash
 Glacially-derived alluvial sediment that is MOVED and REDEPOSITED by MELTWATER.
 Layered and well sorted due to their transport by streams (stratified drift)
WATER LAID SEDIMENT
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Outwash – glacially derived sediment that has been sorted and deposited by meltwater
Outwash sediments – sediment overloaded glacial melt water river
GLACIAL LAKE SEDIMENTS
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Fine grained silt and clay, eroding after lake drained
GLACIAL MORAINE
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Moraine – landform made of till
Lateral moraine -linear strip of rock and smaller debris formed along the edge of a valley glacier
by plucking and rockfalls
Medial moraine – joining of two lateral moraines when two valley glaciers merge
End moraine – curved elongated ridge that accumulated at downstream end of glacier
Terminal – end moraine marking a glacier’s farthest advance
Recessional – lateral or end moraine formed during a pause in a glaciers retreat
Ground – till that is deposited along the base of a glacier
World’s two ice sheets are:
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At low elevations
Cover Antarctica and Greenland
Contain three-fourths of the worlds fresh water
A glacier’s boundary between permanent and seasonal snow is the snow line.
Which of the following is not an erosional landform caused by an alpine glacier? A v-shaped valley
Which of the following is not an erosional landform caused by an alpine glacier? Kettles
Carbon dioxide levels in the atmosphere have increased about 50% in the past century. Recent increases
appear to corelate with a INCREASE in average temperate and a DECREASE in glacial ice.
GLACIAL ICE FEATURES
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Ice flows in direction of the energy grade line (surface slope)
Slope – ice flows, like water, down slope
Energy grade line – slope of surface of a fluid
Wind – dunes, zstrugi
Melt – sun cups, granular ice, ponds, streams
Crevasses – bergschrund indicates brittle deformation on the surface, plastic deformation at
depth
Moulons – englacial rivers, sinks, lakes and springs
GLACIAL ICE
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Snow starts out as hexagonal flakes
Ice grains metamorphose into bigger crystals but still angular
During flow granules become rounded, equant, and interlock
EROSIONAL FEATURES
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Roches moutonees – streamlined bedrock nobs
Drumlines – streamlined unconsolidated till hills, water saturated till
Underfit streams – streams that are much too small for the flood plain they are located in
EROSIONAL FJORDS
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U-shaped valleys
Below Sea Level
Morainal sills under water
DEPOSITIONAL FEATURES
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Glacial erratic – large rocks randomly left behind by a glacier
Kettle ponds – small ponds left by melting blocks of ice
Kame mounds – un-streamlined hills of glacial till
Eskers – linear hills made of well sorted river gravels
Outwash – braided rivers dump tons of river alluvium
Loess – wind blown silt derived primarily by scraping of glacier held rocks against bedrock
DEPOSTITIONAL LANDFORMS
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Glacial re-entrant – an embayment of the ice front, sometimes associated with a hill
Glacial salient/ice lobe – low elevation
STRATIFIED DRIFT
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Outwash (stratified drift) deposits:
 Outwash plain – broad gently sloping sheet of stratified sand and gravel sediment
deposited by meltwater streaming out of the front of a glacier
 Esker – long winding ridge of roughly stratified sand and gravel formed a stream flowing
along glacial tunnel
 Kettle – depression in ground moraine or an outwash plain formed when a block of ice
was buried and melted after the glacier retreated
PLIESTOCENE ICE SHEETS
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North America – covered by a huge glacier during the Pleistocene epoch
3 spreading centers – Laurentia mountains, Greenland, Canadian rockies
Major outflow rivers – Missouri/Mississippi, Ohio, Columbia
GLACIAL ADVANCES
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Wisconsin, Illinois, Kansas, Nebraska
DESERTS
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Desert – area so dry it cant support considerable plant or animal population
Four types of deserts:
1. Polar – snow cover and little moisture due to cold temps, polar high pressure
2. Horse latitude – cold, dry air sinks to the surface
3. Middle latitude – little rainfall and high summer temps. Separated from
moisture by mountain ranges rain shadow. Separated from moisture source by
great distances.
4. Coastal – cold ocean current with associated cold, dry air impinges on a western
coastline of a continent. Air warms over land but carries little moisture
3 classes of arid lands – semi arid, arid, extremely arid
DESERTIFICATION
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A patchy conversion of dry but habitable land to uninhabitable desert as a consequence of
human land use practices
2 main causes – replacement of natural vegetation with non adapted crops and overgrazing by
domestic animals
Other mechanisms – clearing of vegetation, soil erosion, temp increase due to loss of
vegetation, global warming, off-road vehicles
GULLY EROSION – lowers water table, drying a whole area
EROSION PREVENTION – Contour plowing, tree shelter belts, stream bed and gully protection, reduced
or late plowing, riparian forests, soil amendments
WIND EROSION
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In arid regions – water actually causes most landscape modification
Wind – carries sediment particles as bed load by saltation, and by suspension
Deflation – loss of finer-grained materials as a result of wind transport
Erosion – abrasion performed by sediment particles moved by wind
Vegetation – tends to reduce wind erosion rates
Desert pavement – left behind after deflation occurs, keeps dust down, gather water for plants
ABRADED FEATURES
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Ventifacts and pedestals are created by wind erosion
DEPOSTION OF WIND BORNE SEDIMENTS
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Dune – mound, ridge, or hill of windblown sand, either bare, or vegetated
Dune formation – formed downwind of an obstacle. Compression of overhead wind stream lines
Dune features – back slopes, crest – highest point
Cross beds indicate ripples and dunes
TYPES OF DUNES
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Barchan dunes – form where sand is relatively scarce, fairly constant wind direction
Transverse dunes – form where sand is abundant and wind direction is fairly constant
DESERTS: MAIN POINTS
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Location of deserts – are controlled by global air circulation. The locations of high mountain
ranges and upwelling ocean currents
Wind erosion and deposition create characteristic landforms
Infrequent, intense rainstorms modify arid landscapes to a greater degree than wind
Mismanagement of marginal areas can result in human-induces desertification
COASTAL ENVIRONMENTS chapter 14
NATURE OF COASTLINES
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Active margin – coast near an active plate boundary, rugged, mountainous, faulting, western
USA
Passive margin – not near active plate boundary. Flat, few faults, coastal plain
BEACH CROSS SECTION
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Winter berm – bigger waves make steep high beach
Summer berm – mellow waves carve wide, flat beach
Beach face – foreshore, between highest and lowest tide
Wave base – depths little affected by waves
HOW ARE WAVES GENERATED? Waves of oscillation (deep water) translational waves (shallow water)
WAVE FORMATION
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Wind – velocity, length of windy time, fetch (distance across open water)
Waves
 Fully developed sea – largest waves possible for the wind conditions
 Chop – short steep waves
 Swell – longer, storm driven waves, most powerful
Wave refraction – waves slow down in shallow water, bend around headlands
Beach cusps – form when wave crests come at an angle in from ocean
TSUNAMI
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Caused by – earthquake, meteorite impact, underwater landslide, volcano
Travel – fast, broad, 1-2 meters high
Shoaling – condensation of energy
Causes of Emergence – tectonic uplift, isostatic rebound. Lowered seas – glaciation
OCEAN CURRENTS
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Shallow currents – driven by Coriolis force, clockwise in northern hemisphere
Deep currents – driven by density/salinity thermohaline circulation