GLACIERS, DESERTS, AND WIND (chapter 7)
I.
Glaciers
A. A glacier is a thick ice mass that moves slowly over the land surface.
1. They form above the snowline over hundreds or thousands of years.
II.
2. The Ice Age was a period of time when much of the Earth was covered in glaciers.
Types of glaciers
A. Valley glaciers
1. Ice masses that move slowly down mountain valleys that originally had streams.
2. A stream of ice that flows between mountains, from a place near the top of the valley.
B. Ice sheets
1. Ice sheets are enormous ice masses that flow in all directions and cover everything but the
highest land.
2. They are sometimes called continental ice sheets because they cover large regions where
the climate is extremely cold.
3. They are huge compared to valley glaciers.
4. They currently cover Greenland and Antarctica.
III.
How glaciers move
A. Flow = The movement of glaciers. Two ways it happens:
1. Plastic flow = movement within the ice
2. Basal slip = slipping and sliding downward due to gravity
IV.
Glacial erosion
A. Many landscapes were changed by the glaciers of the recent Ice Age.
B. How Glaciers Erode
1. Plucking: The ice loosens and lifts blocks of rock
V.
2. Abrasion: Rocks in the ice scrape and smooth the land underneath, like sandpaper
Glacial deposits
A. Types of glacial drift
1. Glacial drift = sediments that are moved and deposited by glaciers
a. Two types of glacial drift:
i.
Till = sediment deposited directly by the glacier.
ii. Stratified drift = sediment laid down by glacial meltwater (water from melting
glacier)
VI.
Landforms created by glacial erosion
A. Glaciers are responsible for a variety of erosional landscape features
B. Glaciated valleys
1. A glacial trough is a U-shaped valley that was once V-shaped but was deepened by a glacier
Sketch of glacial trough:
C. Glaciers are responsible for a variety of land features created by deposition, including:
1. Moraines = layers or ridges of till
Sketch of moraine:
2. Outwash plains = sloping plains consisting of deposits from meltwater streams in front of the
margin of an ice sheet
3. Kettles = depressions created when a block of ice becomes stuck in glacial deposits and
subsequently melts
Sketch of kettle lake:
D. Glaciers are responsible for a variety of land features created by deposition, including:
1. drumlins = streamlined, asymmetrical hills composed of glacial dirt
Sketch of drumlin:
2. eskers = ridges composed largely of sand and gravel deposited by a stream flowing beneath a
glacier
Sketch of esker:
VII.
Geologic processes in arid climates
A. Weathering
1. Much of the weathered debris in deserts results from mechanical weathering.
2. Chemical weathering is not completely absent in deserts. Over long time spans, clay and thin
soils do form.
B. The role of water
1. In the desert, most streams are ephemeral—they only have water after it rains.
2. Most desert streams dry up before they reach the ocean. The water evaporates or infiltrates into
the soil.
3. Interior drainage into basins produces:
a. alluvial fan—a fan-shaped deposit of sediment formed when a stream’s slope is abruptly
reduced
b. playa lake—a flat area on the floor of an undrained desert basin (playa) that fills and
becomes a lake after heavy rain
4. Most desert erosion results from running water.
C. Wind erosion
1. Wind erosion happens in the desert in two ways:
a. Deflation is the lifting and removal of loose particles such as clay and silt.
i.
It produces desert pavement—a layer of coarse pebbles and gravel created when
wind removed the finer material
b. Abrasion = the act or process of damaging or wearing away something by rubbing,
grinding, or scraping
2. Wind deposits
a. The wind can create landforms when it deposits its sediments, especially in deserts and
along coasts.
b. Loess and sand dunes are landscape features deposited by the wind.
c. Loess
i. Deposits of windblown silt
ii. Primary sources are deserts and glacial stratified drift.
iii. Loess have a different shape than dunes – they are blanket-like layers that cover
broad areas
d. Sand dunes
i.
Dunes = Mounds or ridges of sand that is deposited by wind.
e. Types of sand dunes
i.
The form (shape) of a sand dune depends on:
i. wind direction and speed
ii. how much sand is available
iii. the amount of vegetation
Honors: sketch and label the six different types of sand dunes below: