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1
Chapter 1
Landform Patterns and Processes
Topography
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the natural and human features of the Earth’s surface. ie. Surface
features
·
need to understand difference between relief and elevation
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elevation - the height of a particular point of land above sea level
·
relief - the change in elevation over a given distance
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hill
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areas of high relief with elevations no higher than 300 - 600 m
·
isolated features
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mountain
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areas of high relief with elevations higher than 300 - 600 m
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most occur in long linear chains called ranges (usually along
margins of continents)
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plain
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a level tract of land
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frequently found along coastal areas or at lower elevations
·
very gentle slope and no local a relief for thirty metres or more
·
plateau
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an extensive, relatively flat upland area
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have been raised upward into higher elevations by movements
of the Earth’s crust
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often found in interiors of continents
·
because they are often deeply eroded by stream valleys, they
have more rugged appearances than plains
Draw conclusions about patterns in major landforms on the earth’s surface.
·
figures on page 8 & 9 of text
·
reproducible worksheets 1.3 & 1.4
2
Mountain building
Fold mountains
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an upland area formed by the buckling of earth’s crust. Many fold
mountains are associated with destructive or collision margins of
plates.
·
amount and extent of force and pressure, can create simple or
complex forms.
·
anticline
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an arch-like upfold in buckled,
bent, or contorted rock.
·
looks like the letter ‘A’
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syncline
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a downfold of rock layers.
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looks like a ‘S’mile
Mountains formed by faulting
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normal fault
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a fault in which rocks have moved down the slope of the fault
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two normal faults occur parallel to each other, with plate inbetween dropping down as plates
move away from each other - forms
rift valley
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land between two parallel faults rises
- forms block mountain
·
reverse fault
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a fault, perhaps caused by a compressional force, where
3
movement is up, rather then down, the face over which
movement occurs
4
The structure of the earth
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have fill in details from page 5 of text on reproducible worksheet 1.1
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core
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inner core
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deepest part of the earth (1512 miles deep)
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solid that contains both iron and nickel
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is a magnet, a compass
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outer core
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(1419 miles deep)
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similar to the inner core but it is a liquid (contains sulphur and oxygen which
lowers the melting point)
·
mantle
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Occupying 1789 miles
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magma (iron and magnesium) that makes up the mantle
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mostly solid except the outer 200-300 Km which is extremely hot and goopy; very
plastic-like
·
outermost liquid layer of the mantle is referred to as the asthenosphere
·
Mohorovicic Discontinuity
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boundary between the mantle (asthenosphere) and the lithosphere.
·
lithosphere
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the crust and that upper layer of the mantle which lies above the asthenosphere
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basically hardened mantle (magma)
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contains two segments, the oceanic and continental crusts
Compressional force
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a force pushing into a part of the earth’s crust, causing it to buckle
·
plates move towards one another, squeezing together
·
subduction zones sometimes form along these areas
Tensional force
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a stretching force in the earth’s surface which may cause faulting
·
plates break apart, moving away from or past each other, which may
form a trench as one plate drops downward
·
ridge zones sometimes occur where two plates move apart. Magma
may rise between the plates and form a ridge
See figure 1.9 page 11 and figure 1.10 page 12 - discuss
Discuss formation of volcanoes along ridges, etc. by looking at figures
World Geography 3202/3200
Landform Patterns and Processes
Normal Fault - a fault in which rocks have moved down the slope of the
fault
Reverse Fault - a fault, perhaps caused by a compressional force, where
movement is up, rather then down, the face over which movement occurs
Three types of volcano
·
·
·
ash and cinder
shield cone
composite cone
6
Mountains Formed by Volcanoes
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Along plate boundaries, heat is generated because of friction,
pressure, and decay of radioactive materials.
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Intense heat melts rock beneath the crust producing magma
·
If it reaches surface - through fractures or vents, extrusive volcanic
activity takes place.
·
Terms
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Lava - liquid rock
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Ash (cinder) - small molten rock fragments
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Vent - Single opening through which the volcanic products
erupt
Mild volcanic eruptions
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thin, liquid lava flows
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small amounts of gas
Explosive volcanic eruptions
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thick lava flows
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large quantities of gas, ash and cinders
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why? - thick lava hardens quicker - plugs up - and then must be
exploded out
Three types of Volcanic Cones:
Ash and Cinder Cone
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eruptions consist mainly of ash and cinders
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thick, slow flowing, rapidly solidifying lava
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shape is symmetrical
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steep sides
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large crater
Shield Cone
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usually milder eruption
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little or no ash and cinders
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very thin, liquid lavas
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broad, flat cones
7
Composite Cone
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undergoes periods of both explosive and quiet activity
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layers of ash and cinders intermixed with layers of lava
·
weak spots may develop on sides with smaller lava flows forming
smaller craters
Reproducible Worksheet 1.6 - Enlarge map part to full page
Mark subduction zones and mid-oceanic ridges
Page 16 question 16a and page 17 question 17a
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Chapter 2
Wearing Down Landforms: Rivers and Ice
Physical Weathering
Weathering vs. Erosion
·
Weathering is the breakdown of rock and minerals.
·
Erosion is a two fold process that starts with 1) breakdown of land
(weathering) and also includes the movement (transportation) of these
weathered materials 2) Deposition of the eroded material occurs when
it is dropped in a new location.
·
Denudation is a term that refers to the wearing down or smoothing
off of land features. The processes of weathering and erosion are
denudational. They are also gradational because they grade the earth’s
surface.
Physical Weathering vs. Chemical Weathering
·
·
Physical weathering is the breakdown of rock and minerals by
mechanical stress
Chemical weathering breaks down rock with chemical reactions
often including water.
Types of Physical Weathering
·
·
·
·
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Frost fracture – the expansion of freezing water that causes rocks to
crack.
Heat expansion – rocks can expand and subsequently fracture.
Plant growth – expansion due to root growth as shown in the picture
below.
Burrowing animals- tunneling animals can increase the size of
existing cracks
Exfoliation – as internal pressure is released from certain rocks, it can
cause layers to split and fall off.
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Environment’s Affect on Physical Weathering
Fast temperature, changes like those that occur in the desert, increases the
amount of physical weathering due to heat expansion. Conversely, in
regions like the tropics where there is little temperature change, the amount
of physical wreathing due to heat expansion is minimal.
Abundant precipitation combined with alternating freezing/thawing
temperatures increases the amount of frost fracture. Conversely, the
absence of those climatic conditions reduces the amount of frost fracture.
Running water increases physical erosion as friction occurs between water
and rock.
Ocean waves cause hydraulic pressure and abrasion on the shore leading to
physical weathering.
Chemical Weathering
Types of Chemical Weathering
Chemical weathering is the breakdown of rocks and minerals by chemical
reactions and usually involves the action of rainwater.
There are three different types of chemical weathering described below:
·
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The formation of solutions as rainwater absorbs CO2 , SO2, and
other chemicals from the atmosphere along with organic acids from
the soil, which then reacts with rock and minerals causing some to
dissolve and move away.
Hydrolysis, like the first process, involves the minerals in solution. In
this case, carbonic acid reacts with silicates in some rocks leaving a
soft clay from which potassium, sodium and magnesium are
subsequently leached.
10
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Oxidation is the reaction of metallic minerals to oxygen (mainly in
water). This results in the formation of oxides, which tend to be softer
than the original mineral. For example, rust on iron.
·
How Environmental Conditions Affect Chemical Weathering
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Heavy rain, running water, and abundance of water increases the
amount of dissolving that occurs. Conversely less abundance of water
leads to less dissolving.
·
High temperatures will increase the rate of chemical reactions. It is a
fact of chemistry that heat increases the speed of many reactions like
oxidation.
·
Ocean water contains salt which can increase the rate of many
reactions like oxidation
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Life Cycle of a River
Rivers change over time and seem to go through three stages:
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Youth
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Maturity/Late Maturity
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Old Age
Youth (figure 2.7 p.28)
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Are usually found in highland or mountain regions.
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They tend to have a steep slope (high gradient)
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Usually have a small volume of water
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They have a rapid flow of water
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There is usually very rapid erosion especially vertically
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A narrow ““V”” shaped valley is characteristic
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Water falls and rapids are common
Maturity (figure 2.7 p.28)
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Most high relief is eroded
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Gentler slope
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Many well developed tributaries
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Broad flat river valley
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Well developed flood plain
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More lateral erosion than vertical
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Meandering results
Late Maturity (figure 2.7 p.28)
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Remember the stages are not distinct.
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These changes occur over long periods of time.
Old Age (figure 2.7 p.28)
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Almost no slope
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Very little relief
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Elaborate meandering
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Oxbow lakes develop
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·
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Often swampy areas around river
Very muddy due to slow speed
Most susceptible to flooding because of large flood plain.
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Evaluating Evidence to Determine the Age of Rivers
There are six common pieces of evidence you can look for to determine the
stage of a river:
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·
·
·
·
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Slope of the river (steeper = younger)
Relief of the banks (steeper = younger)
Width of the valley (wider = older)
Meandering (more = older)
Size of flood plain (wider = older)
Rapids or water falls (more = younger)
Two Directions of River Erosion:
Vertical erosion makes rivers deeper as is the case in young rivers
Lateral erosion makes rivers wider leading to the meandering of mature
rivers.
Drainage Basin is the area of land drained by a river and its tributaries.
Red River Case Study
pages 29-30
Question 7
14
River Deltas
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A delta is a low lying area at the mouth of a river formed by
deposition of silt. Deposition occurs because a river slows as it enters
an ocean or lake.
There are three types:
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arcuate
·
digitate
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estuarine.
Arcuate Delta:
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named from Latin word for curved in the shape of a bow.
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Fan shaped
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ex. Nile Delta ( p. 32)
Digitate Delta:
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From Latin for finger
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Delta with long fingers of sediment reaching into the sea
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ex. Mississippi Delta ( p. 32)
Estuarine Delta:
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Formed when river runs into a bay or estuary
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Tidal mud flats form which can be seen at low tide
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Sediment deposited from river outflow and from Tidal inflow
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The Seine River Delta (figure 2.12 on p. 32)
15
Continental Glaciers vs. Alpine Glaciers
Continental Glaciers
There are two types of glaciers, Alpine Glaciers and Continental Glaciers.
Continental Glaciers cover parts of continental land masses like
Greenland
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a mass of ice, situated over most of a continent, which may be
moving, or has moved, overland.
Alpine Glaciers are found high in mountain valleys, above the snow-line
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a mass of ice, situated on an upland, which may be moving, or has
moved, overland.
Differences:
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Location; Alpine glaciers are only found on mountain tops whereas
continental glaciers are only found at the earth's poles regardless of
elevation.
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Size; Alpine glaciers are smaller compared to Continental glaciers.
Similarities:
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Both move and cause erosion
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Both change the landscape
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Both developed in constantly cold temperatures below freezing.
Land Forms Created by Continental Glaciers
Figure 2.13 on page 34 of your text shows a continental glacier and the
land forms it creates through weathering and deposition.
Give Handout on Glacier Features
Features of Continental Glaciation
Outwash plain:
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Like a river Delta
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Melt water flowing from glacier deposits silt like river deltas
16
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·
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Silt is deposited in layers
Small particles are carried further away
Larger particles drop closer to the glacier
Terminal Moraine:
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Heap or ridge of bulldozed gravel that marks the end of the forward
motion of a glacier.
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As a glacier retreats it deposits debris/gravel
Erratics:
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Large boulders that were transported long distances and dropped.
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They now sit in a region and look very much out-of-place.
Drumlins:
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Egg shaped hill
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Formed under glaciers
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Sloped or Pointy end points in direction of ice flow
Formation:
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Ice melts under glacier
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Deposits of gravel are made
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Glacier moves forward
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Deposits are bull-dozed along and catches up in rough
areas forming piles or drumlins.
Eskers:
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Long deposits of eroded glacial material
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Formed by sub-glacial streams that deposit material like all rivers.
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They are sometimes known as Highways of the North because they
are good for traveling on with ATV's.
17
Evidence for Direction of Glacier Movement
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·
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The gently sloped end of drumlins point in the direction of glacier
movement.
The terminal moraine marks the furthest extent of the glacier.
The layers of silt in an outwash plain can indicate direction of glacier
movement. fine particles would be at the leading edge while larger
particles would have been closer to the glacier.
Question #12, page 33
Alpine Glaciers
Alpine glaciers are like very slow moving rivers of ice flowing down high
mountain valleys.
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create land forms by weathering and deposition
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typically erode the mountain beneath them into a U-shaped valley
with steep sides
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Some alpine or valley glaciers are 1000m thick and up to 160 km
long, though most are only a few km in length
Features of Alpine Glaciation
Cirque
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a circular hollow cut into bedrock during glaciation
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Side and back walls are steep but front wall opens downward
Cirque Formation
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Alpine glacier freezes onto mountain valley and as is proceeds it
plucks/gouges rock from the mountain top leaving the cirque shape.
Arête
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Steep knife edged ridge between two cirques in a mountainous region.
18
Hanging Valley
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A high level tributary valley from which the ground falls sharply to
the level of the lower, main valley. The depth of the lower valley is
due to more severe glaciation.
Lateral Moraines
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a landform deposited by a glacier or ice sheet at the side of the
glacier.
Terminal Moraines
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deposits that mark the farthest extent of the alpine glacier the same as
with continental glaciers.
Fjords
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Alpine Glaciers erode troughs and valleys in the mountain
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Glacier valley reaches the coast.
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Glacier melts and sea water floods the valley
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Fjords are very common in Norway and a quick search on web can
find you some amazing pictures.
Question #14, page 36
19
Wind Erosion
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not usually very strong
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tends to just pick up and transport sand and fine sediment, wearing
down
Deflation
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the action of the wind in removing material from a surface and
lowering that surface.
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most effective where extensive areas of non-cohesive deposits are
exposed (ie. Loess or dry lake beds)
Abrasion
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the grinding away of bedrock by fragments of rock incorporated in
ice, water, or wind
Wind Deposition - if wind takes away sand and particles - must deposit
them somewhere.
5 Formations of Wind Deposition/Erosion:
1. Hamada
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level, rocky desert that has been smoothed by abrasion
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northern Africa
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an example of deflated landscape - landscape in which the wind has
blown away all fine, loose material - appears as deserts of jagged
rocks or pebbles
2. Erg
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arid, sandy desert
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consists of extensive dunes, mounds and ridges of sand
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Great Erg - Sahara Desert - area of Atlantic Provinces - mounds of
sand 1200 m thick
20
3. Sand Dunes
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a hill or ridge of sand sorted and accumulated by wind action
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crescent or triangle shaped piles of sand deposited when the wind
slows down or stops blowing
·
shape depends on amount of sand available, the speed and duration of
the wind, the wind’s direction, and the amount of vegetation in the
area
4. Barchan
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a sand dune formed with the horns pointing downwind
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crescent shaped – migrate
5. Loess
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any unconsolidated, non-stratified soil composed primarily of siltsized particles
·
moved by winds can be carried thousands of miles - across continents,
oceans etc.
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sometimes very fertile soil.
Terms Related to Water/ Wave Erosion
Three processes by which wave action erodes coastal areas:
1. Hydraulic pressure = The pounding force of water/waves
2. Corrosion = Minerals such as calcium carbonate and limestone
dissolve in the water
3. Abrasion = rock and sand particles suspended in the water bump,
grind, scrape and gouge surfaces the water hits.
Refer to diagrams in handout.
Longshore drift terms
Headlands = the protrusions of land that extend the farthest out into wave
21
action.
Longshore drift = refers to the fact that dominant waves have enough
energy to carry silt/sand from headlands along the shore where it is later
deposited.
Wave Refraction = waves bending around headlands as they hit the shallow
water by shore
Spit = A ridge of sand running away from the coast, usually with a curved
seaward end. Spit grows in the prevailing direction of longshore drift. Ends
are curved by the action of waves in different directions.
Bay Bar = A ridge of mud sand or silt extending across a bay. Formed
when spits stretch across the mouth of the bay.
Bay Beach = An accumulation of sediment deposited by waves and
longshore drift along the shore of a bay.
Straightening of an Irregular Submerging Coastline
·
·
·
·
·
Irregular submerging coastlines have headlands that protrude out from
the shore line.
The erosion of the headland can deposit silt in the bay which forms a
bay beach as it tends to reduce the irregularity of the coastline. The
headland is reduced due to erosion and the bay is being filled by
deposition.
Longshore drift results in some sand being deposited parallel to the
shore but connected to the headland. These silt deposits are known as
spits.
Longshore drift and deposition can continue to the point that the spit
closes off the mouth of the bay. This extensive deposit is known as a
bay bar. As you can see it tremendously reduces the irregularity in the
coastline.
Continued erosion and deposition can straighten a coastline over a
22
long period of time.
Erosion of Emerging Coastlines
The Evolution of Sea Stacks
·
·
·
·
·
·
Sea stacks are columns of land standing in the ocean just off shore.
They are created over a long period of time after a series of other land
structures have eroded away. First sea caves are formed in a headland.
Continued erosion turns sea caves in to the second land feature, sea
arches.
Sea stacks are common in eastern Canada.
Many have plant growth on top.
sea arches are an interesting sight too and have drawn many tourists
to the northern Peninsula of Newfoundland.
Erosion and eventual collapse of the arch top leaves a sea stack
standing in the ocean. Figure 3.11 on pages 48-49 shows this
evolution from three different points of reference.
You must look at this figure it will help cement the concepts in your
mind.
Sea Cave Formation: "a" in figure 3.11 on page 48
Waves strike the headland first
Waves refract around the headland and put hydraulic pressure on both sides
of the headland.
Erosion of the weak portions create caves and blow holes in the sides of the
headland.
Sea Arch Formation : "b" in figure 3.11 on page 48
Eventually sea caves, on alternate sides of the headland get deeper until
they connect inside the headland forming a complete passage way or tunnel
or “arch” through the head land.
Sea Stack Formation: "c" in figure 3.11 on page 48
Continuous erosion, of sea arches, causes the collapse of the ground over
the arch.
23
This leaves a pillar or column or “STACK” of land standing alone where
the headland was.
24
Straightening of Emerging Coastlines
-Emerging coastlines straighten in much the same fashion as submerging
coastlines.
-Erosion of headlands creates sea caves, sea arches and sea stacks instead
of bay beaches, spits and bay bars.
-However the result is similar in that headlands are reduced in size which
straightens the coastline. Compare the headland length in figure 3.11 before
and after erosion.