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
Image from

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. Glaciers Features Crevasses Moraines Barnard Glacier

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

15. Types of Glaciers

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

18. Glaciers Landforms created by glacial erosion Glacial Valleys Fjords
Pater noster lakes
Cirques
Tarns
Arêtes
Horns

19. 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

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

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

22. Glacial depositional features

23. Glaciers
Ice Ages
Have occurred throughout Earth’s history

24. 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

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

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

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

29. 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)

30. 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)

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

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

33. 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

34. Location of Deserts

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

36. 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

37. 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

39. 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

40. A dry stream channel in the desert

41. The same stream channel following heavy rainfall

42. 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

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

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

45. 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

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

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

48. Types of Sand Dunes

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

50. 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

51. 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

52. Landscape evolution in a mountainous desert – early stage

53. Landscape evolution in a mountainous desert – middle stage

54. Landscape evolution in a mountainous desert – late stage

55. Inselbergs in Southern California

56. ~ End ~