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Sculpting the Earth’s Surface

Explore how glaciers sculpt land with layers of ice and learn about the desert's arid conditions, types, and erosive effects. Uncover the movement, formation, and impacts of these natural forces on Earth's surface.

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Sculpting the Earth’s Surface

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  1. Sculpting the Earth’s Surface Glaciers, Deserts, and Wind

  2. Glaciers • Glaciers are a part of both the hydrologic cycle and rock cycle • A thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow

  3. Glaciers • Location • Occupy 10% of Earth’s surface • Primarily located in polar regions (Antarctica & Greenland) • But found on every continent • Form above the snow line

  4. Glaciers • Formation • New layers form each year • Weigh of overlying layers compresses buried layers • Snow recrystallizes – looks like sugar • Snow begins to grow, air pockets decrease • compacts & becomes very dense • After 2 winters => FIRN

  5. Glaciers • Formation (continued) • Firn • Generally 16x the size of a snow crystal • ½ as dense as water • Increase in size as the overburden increases • Over time, grows to form even larger crystals • Forms glacial ice

  6. Glaciers • Movement • When ice sheet thickness > 18 meters, the ice sheet: • Deforms • Flows • Movement slower at base than at top • Advance and retreat • Surge

  7. Glaciers • Types of glacial movements • Plastic flow • Basal slip

  8. Glaciers • Rates of movement • Average velocities vary considerably • Rates of up to several meters per day • Some glaciers exhibit extremely rapid movements called surges

  9. Glaciers • Movement (continued) • Budget of a glacier • Accumulation + loss = glacial budget

  10. If accumulation exceeds loss (called ablation), the glacial front advances

  11. If ablation increases and/or accumulation decreases, the ice front will retreat

  12. Crevasses Moraines Glaciers • Features Barnard Glacier http://nsidc.org/glaciers/questions/components.html

  13. Ice Ice Sheets, Ice Shelves, Ice Caps, Ice Streams, and Ice fields Glaciers Mountain Glaciers, Valley Glaciers, Piedmont Glaciers, Cirque Glaciers, Hanging Glaciers, Tidewater Glaciers. Glaciers • Types

  14. Types of Glaciers

  15. Glaciers • Glaciers erode by • Plucking – lifting of rock blocks • Abrasion • Rock flour (pulverized rock) • Striations (grooves in the bedrock)

  16. Glaciers • Glacial deposits • Glacial drift • All sediments of glacial origin • Types of glacial drift • Till – material that is deposited directly by ice • Stratified drift - sediment deposited by meltwater

  17. Glaciers • Glacial deposits • Depositional features • Moraines – layers or ridges of till • Types of moraines • Lateral • Medial • End • Ground

  18. Glaciers • Glacial deposits • Depositional features • Outwash plain, or valley train • Kettles • Drumlins • Eskers • Kames

  19. Glacial depositional features

  20. Glaciers • Ice Ages • Have occurred throughout Earth’s history

  21. Glaciers • Ice Age • Began 2 to 3 million years ago • Division of geological time is called the Pleistocene epoch • Ice covered 30% of Earth's land area

  22. Glaciers • Indirect effects of Ice Age glaciers • Migration of animals and plants • Rebounding upward of the crust • Worldwide change in sea level • Climatic changes

  23. Glaciers • Causes of glaciation • Successful theory must account for • Cooling of Earth, as well as • Short-term climatic changes

  24. Glaciers • Causes of glaciation • Proposed possible causes • Plate tectonics • Continents were arranged differently • Changes in oceanic circulation (Thermohaline Current)

  25. Glaciers • Causes of glaciation • Proposed possible causes • Variations in Earth's orbit • The Milankovitch hypothesis • Shape (eccentricity) of Earth’s orbit varies • Angle of Earth’s axis (obliquity) changes • Earth’s axis wobbles (precession)

  26. Desert • Definition : • A region so arid that it contains no permanent streams except for those that bring water in from elsewhere, and has very sparse vegetation cover. • NOT related to temperature! • Deserts can be • Hot (>35 °C) • Cold (< 20 °C)

  27. Desert • Location • Dry regions cover 30% of Earth’s land surface

  28. Desert • Types of deserts • Two climatic types are commonly recognized • Desert or arid • Steppe or semiarid

  29. Deserts • Types of deserts • Classified by environment in which they are formed • subtropical: in the hot dry latitudes between 20 and 30°, both north and south • rain shadow: on the landward side of coastal mountain ranges • coastal: along coasts bordering cold ocean currents • continental interior: deep within continents, far from major water sources • polar: in the cold dry polar regions, both north and south

  30. Location of Deserts

  31. Earth’s dry regions coincide with the subtropical high pressure belts & solar heating

  32. Deserts • Weathering and Erosion • Not as effective as in humid regions • Mechanical weathering forms unaltered rock and mineral fragments • Some chemical weathering does occur • Clay forms • Thin soil forms

  33. Deserts • Weathering and Erosion • Water Erosion • Desert rainfall • Rain often occurs as heavy showers • Causes flash floods • Poorly integrated drainage • Most erosional work in a desert is done by running water

  34. Deserts • Weathering and Erosion • Water Erosion • Streams are dry most of the time • Desert streams are said to be ephemeral • Flow only during periods of rainfall • Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah

  35. A dry stream channel in the desert

  36. The same stream channel following heavy rainfall

  37. Deserts • Weathering & Erosion • Wind erosion • Differs from that of running water in two ways • Wind is less capable of picking up and transporting coarse materials • Wind is not confined to channels and can spread sediment over large areas

  38. Deserts • Weathering & Erosion • Wind erosion • Mechanisms of transport • Bedload • Saltation – skipping and bouncing along the surface • Suspended load • In the air as duststorms

  39. Deserts • Weathering & Erosion • Wind erosion • Mechanisms of wind erosion • Deflation • Lifting of loose material • Produces Blowouts & Desert pavement

  40. Deserts • Weathering & Erosion • Wind erosion • Mechanisms of wind erosion • Abrasion • Produces ventifacts (stones with flat faces) and yardangs (wind sculpted ridges) • Limited in vertical extent

  41. Deserts • Depositional Environments • Water Deposits • Talus Aprons • Alluvial Fans • Bajada • Playas and Salt Lakes

  42. Deserts • Depositional Environments • Wind deposits • Dunes • Mounds or ridges of sand • Often asymmetrically shaped • Characteristic features • Slip face • Cross beds

  43. Types of Sand Dunes

  44. Deserts • Depositional Environments • Wind deposits • Loess • Deposits of windblown silt • Extensive blanket deposits • Primary sources are deserts and glacial stratified drift

  45. Deserts • Basin and Range: the evolution of a desert landscape • Uplifted crustal blocks • Interior drainage into basins produces • Alluvial fans and bajadas • Playas and playa lakes

  46. Deserts • Basin and Range: the evolution of a desert landscape • Erosion of mountain mass causes local relief to continually diminish • Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment filled basin

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