landforms geography glaciers. development of a glacier glacier – slowly moving mass of dense ice...
TRANSCRIPT
Landforms Geography
Glaciers
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
Glacial Mass Budget
• Glacial input : Snow
• Glacial output : ice, meltwater or water vapor
• Zone of Accumulation – top of glacier where temps are cooler - input > output
• Zone of Ablation – lower part of glacier where temps are higher – output > input
• Equilibrium line – point on glacier where input = output
Glacial Formation
Glacial Mass Budget
Glacial Mass Budget
Glacial Movement
• Glaciers move through internal deformation
• Interior of glacier like malleable plastic
Glacial Movement
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
Alaskan Glaciers
Hubbard Glacier
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
Continental Glaciers
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
Glacial Erosional Landforms• Roche Moutonnée – rounded hill, gradual on
side toward direction from which glacier comes
Glacial Striations Glacial Erratic
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
Alpine Erosional Landforms
Cirque
Horn
“Matterhorn”
Glacial Trough
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
Glacial Depositional Landforms (Till)
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
Glacial Depositional Landforms
Glacial Depositional Landforms
Physical Geography
Arid Landscapes and Eolian Processes
Arid Landscapes & Eolian Processes
• Arid Landscapes
• Eolian Erosion & Transportation
• Eolian Deposition & Landforms
• Human Interactions with Eolian Processes
Arid Landscapes• 3 factors influence arid climates:
– Subtropical high pressure– Rainshadow– Distance from large bodies of water
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
Arroyo
Desert Landforms
Note: Tops of most landforms once part of same surface, since partially eroded away
Playa
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
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
Particle Transport• Silts and Clays carried in suspension
• Sand bounces along – saltation, or
• Sand rolls slowly along – creep
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
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
Eolian Erosional LandformsDeflation/Desert Pavement
Eolian Erosional LandformsAbrasion
Ventifacts Yardangs
Loess
• Fine-grained, wind-blown silt – high in calcium – usually from alluvial deposits or glacial till
• Can be transported farther than sand
Loess Deposits around the World
Loess Deposits
Arid Landscapes and Eolian Processes
Loess Terraces
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
Regions Prone to Desertification
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
The Sahel
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
• 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
Desertification in Great Plains