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