Transcript File

World Geography 3200
Chapter 2 Wearing Down
Landforms: River and Ice
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1. Terms

A. Weathering - is the breakdown but not
the removal , of rocks.
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b. Erosion – is the breaking down and
removal of part of the land surface from
one location to another by wind, water,
gravity or ice.
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2. Two types of Weathering

A. Physical weathering- occurs when
natural forces and physical processes
break down rocks into smaller pieces.
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
B. Chemical weathering- involves the
action of chemical elements or
compounds to change the chemical
composition of a rock or mineral.
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3. Four (4) Processes of Physical
Weathering

A. Frost fracture- is the cracking of rocks
when ice forms in fractures , and then
expands, widening the cracks in the
rocks.
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
B. Temperature change- is the
fracturing of rocks when sudden changes
in temperature cause rocks to expand or
contract.
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
C. Exfoliation- is the sheeting action
along curved surfaces in coarse –
grained rocks when these rocks expand
and fracture. ( rocks break apart in
rounded sheets like the layers of an
onion)
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Exfoliation
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D. Plant Growth and Burrowing
animals- plants can cause sidewalks
and foundations to crack by the roots of
trees and plants.
 - burrowing animals can expand existing
cracks and fractures in rocks as they
tunnel through them.

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Plant Growth
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Burrowing animals
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4. Chemical weathering

The breakdown of rock minerals by
chemical reaction is usually related to
the action of rainwater.
solution
oxidation
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3 Main processes occur when rainwater
comes in contact with rock:

A. Solution- is the process whereby a
fluid , usually water or carbonic acid,
picks up and dissolves particles of a
solid. (limestone is a good example
when broken down caverns and
sinkholes appear in the limestone mass.
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Solution
Solution pits caused by
chemicals
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B. Hydrolysis

- Is the chemical reaction of a compound
with water . Carbonic acid reacts with a
kind of mineral called a silicate and
forms a new, soft clay material. The
minerals are dissolved and carried away
in solution.
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Hydrolysis
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C. Oxidation

- This process involves the reaction of
metallic minerals in rocks to oxygen in
water. The result is a new mineral called
an oxide . Oxidation often creates a
softer mineral thus weakening the rock.
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Oxidation
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5. Rivers as Agents of Erosion

A. Drain Basin- is the area in which all
surface run-off water flows into a river. (
Literally , it’s the area drained by a river
and it’s tributaries.)
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
B. Divide- is a line of separation
between waters flowing to different
rivers, basins, or seas.
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
Animation:http://images.google.ca/im
gres?imgurl=http://www.nationalgeog
raphic.com/geographyaction/rivers/im
ages/riversys_illus.gif&imgrefurl=http
://www.nationalgeographic.com/geogr
aphyaction/rivers/&h=189&w=296&sz
=13&tbnid=wEwEZ5UV7APDM:&tbnh=70&tbnw=111&hl=e
n&star
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6. River Life Cycle

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A. Youthful
- found in highland or mountainous areas
- characterized by steep slopes , relatively
small volume of water and rapid flow
- they cause rapid erosion which causes vshaped valleys that are relatively straight
- rapids and waterfalls are a common feature
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Youthful River
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B. Maturity or Mature River
 - gentler slope and flatter land surface
 - well developed branches or tributaries
 - characterized by a broad , flat river
valley with a well developed flood plain
 - gentle meanders
 - moving a maximum amount of water in
a fairly efficient manner

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Mature River
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C. Old Age
 - relief around the river is extremely flat
 - no slope thus very little speed
 - characterized by elaborate and intricate
meanders
 - often swampy areas develop
 - rivers are usually muddy
 - are prone to flooding

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Old Age
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
Note: See page 28 for pictures for
Stages in the River Life Cycle
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Terms

A. Vertical Erosion- is when a river erodes
the bottom of it’s channel (especially during
youth.)
 Animation:http://images.google.ca/imgres?img
url=http://library.thinkquest.org/28022/erosion/
erosion.gif&imgrefurl=http://library.thinkquest.o
rg/28022/erosion/&h=300&w=550&sz=13&tbni
d=UUC8nDGt4oX8M:&tbnh=70&tbnw=130&hl=en&s
tart=6&prev=/images%3Fq%3Derosional%2B
proce
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
B. Lateral Erosion- occurs when rivers
erode their banks rather than the river
bed.
Remnants of the previous river terrace bank,
indicating a high rate of lateral erosion.
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C. Meanders- are sweeping curves in a
river channel.
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D. Delta’s- are low-lying areas found at
the mouth of a river and formed of
deposits such as silt laid down by rivers.
(deposition occurs)
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E. Deposition- is the dropping of
materials which has been picked up and
transported by wind, water and ice.
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9. Glaciers as Agents of Erosion
Glacier – is a mass of ice which may be
moving or has moved , overland by the
influence of gravity.
 Two Types
 A. Alpine Glaciers- form in high
mountain valleys above the snowline
(the altitude above which snow is
permanently maintained on a mountain
top.)

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Alpine Glaciers
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B. Continental Glaciers- are large ice
sheets covering major portions of the
entire continental land area. ( found in
and covering large portions of Greenland
and Antarctica)
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Continental Glacier
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10. Features of Continental Glaciers
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A. Outwash Plain- is a plain formed by
sediments washed out by glacial
meltwater and deposited beyond the ice
sheets or glacier supplying the water and
debris.
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B. Terminal Moraine- is a landform
(rock’s gravel or sand ) deposited by a
glacier or ice sheet which marks the end
of a glacier.
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Terminal Moraine
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C. Erratic – is a large boulder or rock
differing in character ( composition,
structure, texture and hardness ) from
the pre-existing rock on which it rests.
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Erratics
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D. Drumlins- are long hummocks or
hills, egg- shaped and deposited and
shaped under an ice sheet while the ice
was still moving.
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The yellow areas highlight drumlins ,the
elongated hills of glacial sediment.
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E. Esker- is a ridge of sand or gravel
formed by a glacial river under a glacier
as it retreats.
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Esker
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Continental Glacier Features
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11. Features of Alpine Glaciation

A. Cirque- is a circular hollow cut into
the bedrock during glaciation. The side
and back walls are steep but the front
opens out downslope.
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Formation of a Cirque
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B. Arete- is a steep knife-edged ridge
between cirques in a mountainous
range.
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Arete, Mt. Logan, Yukon Teritory
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C. Hanging Valley- is a high – level
tributary valley from which the ground
falls sharply to the level of the lower ,
main valley.
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Alpine Glacier
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Two types of Moraines found in
most Mountain ranges:
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D. Lateral Moraines- are ridges of eroded
materials that are dragged and pulled along
the sides of an alpine glacier.
 E. Terminal Moraines- forms when glacial
debris ( rocks, sand , gravel) is pushed ahead
of an advancing glacier. When the glacier
melts back or retreats , this debris is left
behind. The terminal moraine marks the
lowest advance of the alpine glacier.
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Lateral Moraines
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12. Glacial Crevasses
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Glacial Erosion and Striations
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Crevasse Development
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Striated Bedrock
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13. Fiord

Is a long narrow arm of the sea which is
the result of the “drowning” of a glaciated
valley.
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