2/23/2009. Visualizing Earth Science. Chapter Overview. Deserts and Drylands. Glaciers and Ice Sheets

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Glaciers and Ice Sheets Deserts Geography Categorization of deserts by geography Due to

1 Visualizing Earth Science By Z. Merali and B. F. Skinner Chapter 6 Deserts, Glaciers and Ice Sheets Chapter Overview Deserts and Drylands Glaciers and Ice Sheets Deserts Geography Categorization of deserts by geography Due to global air circulation Subtropical deserts Sahara, Kalahari, Namib Polar Due to local climate conditions Continental interior Rain shadow Coastal 1

2 Wind Erosion Little flowing water Main erosion mechanism: wind blown sand Processes moving wind blown sediments Largest grains: surface creep Medium sized grains: saltation Fine grains: Suspension Cause dust storms Hot Deserts Mechanisms of Wind Erosion Abrasion Air borne particles chip-off rock fragments Mechanisms of Wind Erosion Deflation Removal of loose particles by wind Desert pavement forms 2

Wind Deposits and Desert Landforms Dunes Wind deposited Hill or ridge of sand Typically asymmetrical in shape Gently sloping long windward face Steep

Desert Landforms Dune Formation and Types Factors influencing dune formation and behavior Wind Barchan dunes unidirectional wind Star dunes No wind

3 Wind Deposits and Desert Landforms Dunes Wind deposited Hill or ridge of sand Typically asymmetrical in shape Gently sloping long windward face Steep leeward face: slip face Interior cross-beds are - Dune strata - Buried former slip faces Angle of repose Maximum steepness of slip-face Wind Deposits and Desert Landforms Dune Formation and Types Factors influencing dune formation and behavior Wind Barchan dunes unidirectional wind Star dunes No wind direction preferred Vegetation Parabolic dunes presence of vegetation Sand supply Transverse dunes large sand supply Longitudinal dunes low sand supply or bidirectional wind 3

4 Dune Formation and Types The Work of Desert Streams Flash floods Creates fast moving short lived streams Erode steep sided canyons Deposit alluvial fans in flat areas Many alluvial fans coalesce into a bajada Creation of desert conditions in non-desert areas Can be natural or produced by human activity Signs Lowering water tables Higher salt content in soil and water High rates of soil erosion Destruction of vegetation Desertification 4

Areas most vulnerable Semi-arid areas near deserts Poor soil management

the Cryosphere Cryosphere is the frozen part of the hydro sphere

Increasing weight forces ice formation Ice sheet flows under gravity

5 Areas most vulnerable Semi-arid areas near deserts Poor soil management in intensely farmed areas Desertification Desertification Glaciers and the Cryosphere Cryosphere is the frozen part of the hydro sphere Glaciers are moving layers of ice Snow accumulations in cold climates Increasing weight forces ice formation Ice sheet flows under gravity Movement regulated by internal temperature of ice temperate vs. polar glaciers 5

6 Glaciers and the Cryosphere Glaciers and the Cryosphere Continent sized glacial surface ice cover Antarctica and Greenland Expand and contract with changing global climate Contain ice shelves Thick floating sheets of ice land-based Adjacent to land based ice sheet glaciers Sea ice Formed by freezing sea water Antarctic ocean and Arctic ocean Ice Sheets 6

Glacier Formation Compaction and recrystallization of snow Gradual

crystalline structured of ice Glacier ice impermeable to air Mass

ablation Motion Glacial Budget Glacial Motion Occurs due to gravity

7 Glacier Formation Compaction and recrystallization of snow Gradual accumulation of snow Increase in pressure Reconfiguration of crystalline structured of ice Glacier ice impermeable to air Mass balance Net gain or loss or ice Gain called accumulation Loss called ablation Motion Glacial Budget Glacial Motion Occurs due to gravity Usually slow Two important processes Internal flow Basal sliding Glacial surge 7

Glacial Motion Glaciers erode efficiently Filing

Transporting sediments Filing and plowing action

base, rock fragment scrape the ground The action of

Glacial grooves Glacial Landscaping Mountain

at the glacier s head Ridge between two adjacent

cut out on all sides of a mountain U-shaped valleys

8 Glacial Motion Glaciers erode efficiently Filing rock surfaces smooth Plowing rocks from the ground Transporting sediments Filing and plowing action Rock fragments carried within the glacier Near the base, rock fragment scrape the ground The action of large rock fragments makes Glacial striations Glacial grooves Glacial Landscaping Mountain glaciers produce distinctive land marks Cirques form at the glacier s head Ridge between two adjacent cirques called arête Horns develop when cirques are cut out on all sides of a mountain U-shaped valleys Depth of valley related to volume of ice in eroding glacier Glacial Landscaping 8

Glacial Deposition Glaciers carry large loads Varying rock sizes Deposition usually unsorted

Lateral moraines form along the sides of glacier A terminal moraine forms at the end of a

Glacial Deposition and Periglacial Landforms Melt water streams in a glaciers body Leave

behind in the deposited till makes Kettle lakes and ponds Periglacial regions near glacial

9 Glacial Deposition Glaciers carry large loads Varying rock sizes Deposition usually unsorted Rocks form glacial deposition called till Glaciers can deposit in ridges called moraines Lateral moraines form along the sides of glacier A terminal moraine forms at the end of a glacier Converging glaciers leave a ridge of till called a medial moraine Glacial Deposition Glacial Deposition and Periglacial Landforms Melt water streams in a glaciers body Leave behind sediment in a raised bed called an esker When glaciers retreat Trapped ice left behind in the deposited till makes Kettle lakes and ponds Periglacial regions near glacial ice Have certain distinguishing land marks Tundra regions Have permafrost covered by a thin active layer 9

classifications D tifi ti Desertification Glaciers and Icesheets Glaciers and the

10 Glacial Deposition and Periglacial Landforms Glacial Deposition and Periglacial Landforms Chapter Summary Deserts and Drylands Deserts: Geography Desert Landforms Dunes, and their classifications D tifi ti Desertification Glaciers and Icesheets Glaciers and the Cryosphere Ice Sheets Glacier Formation and Budget Glacial Motion, Landscaping and Deposition 10

Chapter 5: Glaciers and Deserts

I. Glaciers and Glaciation Chapter 5: Glaciers and Deserts A. A thick mass of ice that forms over land from the compaction and recrystallization of snow and shows evidence of past or present flow B. Types