landforms geography

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