Landforms Geography

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Landforms Geography
Glaciers
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Development of a Glacier

• Glacier slowly moving mass of dense ice formed
  by gradual thickening, compaction, and refreezing
  of snow water over time
• After summer melt, some snow left over
• With weight and partial melting, snow turns to
  Firn, crunchy transition from snow to ice
• Further compaction, ice crystals align, become
  dense glacial ice which flows slowly downslope
• At least 40-m thick to become glacier

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Glacial Mass Budget

• Glacial input Snow
• Glacial output ice, meltwater or water vapor
• Zone of Accumulation top of glacier where temps
  are cooler - input gt output
• Zone of Ablation lower part of glacier where
  temps are higher output gt input
• Equilibrium line point on glacier where input
  output

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Glacial Formation
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Glacial Mass Budget
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Glacial Mass Budget
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Glacial Movement

• Glaciers move through internal deformation
• Interior of glacier like malleable plastic

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Glacial Movement
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Glacier Types

• Mountain Glaciers
• Ice Cap Continuous sheet of ice covering entire
  landscape
• Ice Field Buries all but tallest mountains
  can be very thick
• Alpine Glacier Flows down valleys away from
  high country
• Cirque - Bowl-shaped depression on mountain flank
  due to glacial erosion snow source

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Alaskan Glaciers
Hubbard Glacier
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Continental Glaciers

• Huge ice masses covering a large part of a
  continent or large island also called ice
  sheets
• More than 3000 m deep in places
• Covers most of Antarctica and Greenland
• Weight of ice presses lithosphere down into
  asthenosphere, called isostatic depression

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Continental Glaciers
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Glacial Landforms

• Rock debris picked up by glaciers, transported
  in direction of movement deposited
• Glacial erosion
• Glacial Abrasion scratch and gouge bedrock
• Glacial Striations caused by glacial abrasion
• Glacial Grooves deep striations
• Glacial Plucking boulders ripped from ground by
  glacier deposited by retreating glacier, called
  Glacial Erratics

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Glacial Erosional Landforms

• Roche Moutonnée rounded hill, gradual on side
  toward direction from which glacier comes

Glacial Erratic
Glacial Striations
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Alpine Erosional Landforms

• Glacial Erosion
• Cirque bowl-like feature on mountain flanks
• Tarn small lake in bottom of cirque
• Arête narrow, steep ridges between cirques
• Horn mountain with 3 or more arêtes at summit
• Glacial Trough u-shape valley eroded by glacier
• Hanging Valley side trough above main trough
  possible waterfall

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Alpine Erosional Landforms
Cirque
Horn Matterhorn
Glacial Trough
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Glacial Depositional Landforms (Till)

• Glacial Till sediment directly deposited by
  glacier many particle sizes
• Moraine winding ridge formed by till at the
  front or side of glacier Moraine types
• Lateral along former edges of glacier
• Terminal along front of former glacier
• Recessional formed as glacier recedes
• Medial between 2 glaciers
• Ground irregular deposition as glacier recedes

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Glacial Depositional Landforms (Till)
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Glacial Depositional Landforms (outwash)

• Glacial Outwash sediments deposited by water
  out under a glacier as it melts forms Outwash
  Plain, flat feature in front of former glacier
• Kame large mound deposited near glacier front
• Esker winding ridge from water flowing in
  tunnel through ice under glacier
• Kettle Lake big ice block fallen off glacier
  front is buried by outwash, melts later forming
  lake

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Glacial Depositional Landforms
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Glacial Depositional Landforms
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Physical Geography
Arid Landscapes and Eolian Processes
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Arid Landscapes Eolian Processes

• Arid Landscapes
• Eolian Erosion Transportation
• Eolian Deposition Landforms
• Human Interactions with Eolian Processes

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Arid Landscapes

• 3 factors influence arid climates
• Subtropical high pressure
• Rainshadow
• Distance from large bodies of water

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Desert Geomorphology

• Water important to landforms in arid regions
  little vegetation to slow intermittent erosion
• Arroyo steep-sided gully cut into alluvium
• In undisturbed, horiz. rock layers more resistant
  sandstone or limestone forms flat caprock above
  easily eroded shale
• Result is landforms flat on top w/steep sides
• Plateau -Canyon -Butte -Mesa
• Pinnacle -Playa

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Arroyo
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Desert Landforms
Note Tops of most landforms once part of same
surface, since partially eroded away
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Playa
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Eolian Erosion and Transport

• Wind-based processes important in deserts b/c
• Strong winds common in desert
• Large supply of sand silt to be blown
• Vegetation minimal wind free to erode

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Fluid Behavior of Wind

• Wind acts like a fluid, like water, but less
  dense
• Faster wind can move larger particles

Threshold Velocity for wind to carry different
sized particles
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Particle Transport

• Silts and Clays carried in suspension
• Sand bounces along saltation, or
• Sand rolls slowly along creep

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Eolian Erosional Landforms

• 2 types of wind erosion
• Deflation wind blows loose soil away
• leaves coarser pebbles cobbles, called Desert
  Pavement
• when deflation causes basin to form, called
  Deflation Hollow

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Eolian Erosional Landforms

• Abrasion wind blows sand along a surface to
  polish abrade it
• Ventifacts rocks shaped by abrasion pitted,
  grooved, polished
• Yardangs elongated, wind-sculpted ridges caused
  by abrasion

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Eolian Erosional Landforms
Deflation/Desert Pavement
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Eolian Erosional Landforms
Abrasion
Ventifacts
Yardangs
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Loess

• Fine-grained, wind-blown silt high in calcium
  usually from alluvial deposits or glacial till
• Can be transported farther than sand

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Loess Deposits around the World
Arid Landscapes and Eolian Processes
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Loess Terraces
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Human Impact/Desertification

• Desertification transforming a vegetated
  landscape to one that is barren susceptible to
  wind erosion
• Population pressure has forced more people to
  clear marginal, semi-arid-to-arid land for
  agriculture firewood
• In wind, cleared land loses topsoil and nutrients
• Vegetation unlikely to reestablish

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Regions Prone to Desertification
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Desertification in African Sahel

• Semi-arid region in transition region from Sahara
  Desert in north to rainforest in south
• Traditionally nomadic herders small, sedentary
  farmers north-south migrations to follow rain
• Into 20th century, European borders resource
  exploitation made people more sedentary
  over-cultivation of soil, overgrazing, and tree
  removal
• Add in extended drought since late 1960s, you
  have desertification

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The Sahel
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Desertification in Great Plains

• Great Plains lie east of Rocky Mts in semi-arid
  climate with short grass as dominant natural
  vegetation

Dust Bowl Region
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Desertification in Great Plains

• Early 1900s Americans moved to region to farm,
  plowing and clearing native grasses unusually
  wet period
• 1930s terrible drought hits topsoil blows
  into dust storms called Dust Bowl
• Many migrated to California elsewhere
• Those who stayed have employed irrigation soil
  conservation, including windbreaks, and
  conservation tillage