Earth Science, 12e

1
Earth Science, 12e

• Glaciers, Deserts,
• and WindChapter 6

2
Glaciers a part of two basic cycles in the Earth
system

• Glaciers are a part of both the hydrologic cycle
  and rock cycle
• Glacier a thick mass of ice that forms over
  land from the compaction and recrystallization of
  snow and shows evidence of past or present flow

3
Glaciers a part of two basic cycles in the Earth
system

• Types of glaciers
• Valley, or alpine glaciers form in mountainous
  areas
• Ice sheets, or continental glaciers
• Large scale
• e.g., Over Greenland and Antarctica
• Other types
• Ice caps and piedmont glaciers

4
Currently ice sheets cover Greenland and
Antarctica
Figure 6.2
5
Glaciers a part of two basic cycles in the Earth
system

• Movement of glacial ice
• Types of glacial movements
• Plastic flow
• Slipping along the ground
• Zone of fracture
• Uppermost 50 meters
• Crevasses form in brittle ice

6
Glaciers a part of two basic cycles in the Earth
system

• Movement of glacial ice
• Zone of accumulation the area where a glacier
  forms
• Zone of wastage the area where there is a net
  loss due to melting

7
The glacial budget
Figure 6.7
8
Glaciers a part of two basic cycles in the Earth
system

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

9
Glaciers a part of two basic cycles in the Earth
system

• Landforms created by glacial erosion
• Glacial trough
• Hanging valley
• Cirque
• Arête
• Horn
• Fiord

10
Erosional landforms created by alpine glaciers
Figure 6.10 C
11
The Matterhorn in the Swiss Alps
Figure 6.12
12
Glaciers a part of two basic cycles in the Earth
system

• 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

13
Glacial till is typically unstratified and
unsorted
Figure 6.13
14
Close-up view of the boulder in the previous slide
15
Glaciers a part of two basic cycles in the Earth
system

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

16
Glaciers a part of two basic cycles in the Earth
system

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

17
Glacial depositional features
Figure 6.18
18
Kettle lakes
Figure 6.18
19
Glaciers a part of two basic cycles in the Earth
system

• Glaciers of the past
• Ice Age
• Began 2 to 3 million years ago
• Division of geological time is called the
  Pleistocene epoch
• Ice covered 30 of Earths land area

20
Maximum extent of ice during the Ice Age
Figure 6.22
21
Glaciers a part of two basic cycles in the Earth
system

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

22
Glaciers a part of two basic cycles in the Earth
system

• Causes of glaciation
• Successful theory must account for
• Cooling of Earth, as well as
• Short-term climatic changes
• Proposed possible causes
• Plate tectonics
• Continents were arranged differently
• Changes in oceanic circulation

23
Glaciers a part of two basic cycles in the Earth
system

• Causes of glaciation
• Proposed possible causes
• Variations in Earths orbit
• Milankovitch hypothesis
• Shape (eccentricity) of Earths orbit varies
• Angle of Earths axis (obliquity) changes
• Axis wobbles (precession)
• Changes in climate over the past several hundred
  thousand years are closely associated with
  variations in Earths orbit

24
Deserts

• Geologic processes in arid climates
• Weathering
• 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

25
Deserts

• Geologic processes in arid climates
• Role of water in arid climates
• 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

26
Deserts

• Geologic processes in arid climates
• Role of water in arid climates
• 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

27
A dry stream channel in the desert
Figure 6.28 A
28
The same stream channel following heavy rainfall
Figure 6.28 B
29
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

30
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

31
Landscape evolution in a mountainous desert
early
Figure 6.29 A
32
Landscape evolution in a mountainous desert
middle
Figure 6.29 B
33
Landscape evolution in a mountainous desert late
Figure 6.29 C
34
Deserts

• Wind erosion
• Deflation
• Lifting of loose material
• Produces
• Blowouts
• Desert pavement
• Abrasion

35
Formation of desert pavement
Figure 6.34
36
Deserts

• Types of wind deposits
• Loess
• Deposits of windblown silt
• Extensive blanket deposits
• Primary sources are deserts and glacial
  stratified drift

37
Deserts

• Types of wind deposits
• Sand dunes
• Mounds and ridges of sand formed from the winds
  bed load
• Characteristic features
• Slip face the leeward slope of the dune
• Cross beds sloping layers of sand in the dune

38
Formation of sand dunes
Figure 6.37
39
Deserts

• Types of wind deposits
• Sand dunes
• Types of sand dunes
• Barchan dunes
• Transverse dunes
• Longitudinal dunes
• Parabolic dunes
• Star dunes

40
Sand dune types
Figure 6.38
41
Sand dunes in the western United States