Transcript Wind erosion - Ms. Banjavcic`s Science

Chapter 8
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Erosional Forces
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Flatten the soil in your plate.
Find 3 ways to move the soil from one side of the
plate to the other.
You may not touch the soil with your hands! But,
you can touch the plate.
Do not spill!
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Erosion: process that wears away surface material and moves
them from one place to another
•
major causes: gravity, glaciers, wind, water
•
they all need energy for motion!
Deposition: the dropping of sediments that occur when an
agent of erosion looses its energy of motion and is no longer
able to carry the load
•
drop when energy of motion decreases!
What causes erosion and deposition?
- Gravity! What is gravity? The force of attraction that
exists between all objects
- Since Earth is so large, all objects are attracted to it.
- The Earth is the source of all our gravity.
- Any loose material will be pulled down a slope (hill), due to
gravity.
- When gravity alone causes material to slide down a slope this is
called mass movement.
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Examples of mass movement:
1)
Slump: mass movement that happens
when loose rock layers slip down a
slope.
•
When a slope becomes too steep,
the base material no longer can
support the rock and sediment
above it.
•
The soil and rock slip downslope as
one large mass or break into several
sections.
2) Creep: sediments slowly inch their way
down a hill…most common in freezing
areas.
•
Ex: Leaning trees and fence posts
that lean downhill.
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3)
Rockfalls and Rock Slides: when large
rocks break loose and tumble down a
hill…can be very destructive!
•
Rockfalls - As rocks fall and
tumble through the air, they crash
into other rocks and knock them
loose. More and more rocks
break loose and tumble to the
bottom.
•
Rock Slides – occur when layers
of rocks – usually steep layers –
slip down a slope suddenly.
Happen most after heavy rain or
earthquakes.
4) Mudflows: a thick mixture of
sediment and water flowing down a
slope…dry areas with thick layers of
sediment that suddenly get really wet
from rain…
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All mass movements…
•
•
•
Occur on slopes…
Occur more often after a rain…
Increase if vegetation has been removed…
How can you prevent these problems?
•
Strengthen slopes with vegetation…roots hold
soil together
•
Walls made of concrete…
We can try all we want to avoid erosion and deposition
problems, but in the long run…gravity will still be too
powerful!
IE – video of mudslide…
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Review:
1. Define erosion. What force causes it?
2. Explain how deposition changes the surface of the Earth.
3. Describe the characteristics that all types of mass movements have
in common.
4. Describe ways to help slow erosion on steep slopes.
5. What are the similarities and differences between rock falls and
rock slides?
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Erosion by Glaciers!
•
Glacier – a large mass of ice and snow moving on land under its own weight.
•
As glaciers pass over land, they erode it, changing features on the
surface.
•
They then carry eroded material along and deposit it somewhere else.
•
Change large areas of the earth’s surface.
Plucking – process that adds gravel, sand and boulders to a glacier’s bottom and
sides as water freezes and thaws, breaking off pieces of surrounding rock.
•
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Transporting and Scouring – as glaciers
move forward over land, they can
transport huge volumes of sediment and
rock.
• Plucked rock fragments and sand at its
base scour and scrape the soil and
bedrock like sandpaper against wood,
eroding the ground below even more.
•
When bedrock is gouged deeply
by rock fragments being dragged
along, marks are left behind.
•
Deep, long parallel scars
are called grooves.
•
Shallow marks are called
striations.
•
These indicate the
direction in which the
glacier moved.
•
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Ice Depositing Sediment…
When glaciers begin to melt, they are unable to carry much
sediment and that sediment drops, or is deposited, on the land.
• When a glacier melts and begins to shrink back, it is said to
retreat.
• As it retreats, a jumble of boulders, sand, clay and silt is left
behind.
• The mixture of different sized sediments is called till.
•
Till deposits can cover huge areas of land.
•
Thousands of years ago, huge ice sheets in the northern US
left enough till behind to fill valleys completely and make
these areas appear flat.
•
Ex: areas of Montana, Iowa, Ohio, Illinois, Indiana and
New England.
•
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Moraine Deposits –
large ridges of rocks and
soil deposited by a
glacier when it stops
moving forward.
• Outwash Deposits –
material deposited by
meltwater from a
glacier.
• Eskers – a winding
ridge of sand and gravel
left behind when a
glacier melts.
• Pg. 217
•
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Continental Glaciers – huge masses of ice and snow that cover
10% of Earth…mostly near the poles of Antarctica and Greenland.
•
Thicker than some mountain ranges and make it
impossible to see most of the land features of those
regions.
• Valley Glaciers – occur in high mountains where the average
temperature is low enough to prevent snow from melting during
the summer…these grow and creep along.
•
Importance of Glaciers…
•
Shaped mountain tops and transformed valleys.
•
Left behind sediments that are economically important
•
Ex: sand and gravel deposits are excellent starting
materials for the construction of roads and buildings.
•
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Wind!
Wind erosion: air moves and picks up particles and deposits them in
other places
•
Air differs from other erosional forces because it can’t normally
pick up heavy objects, but it can deposit sediment over a large
area
•
Wind erodes Earth’s surface by deflation and abrasion…
•
Deflation: wind blows across loose sediment and removes small
particles and leaves behind heavy material…big rocks…
•
Abrasion: windblown sediment hit rocks and surface gets worn away –
occurs everywhere…but mostly in deserts, beaches & plowed fields
•
WHY? – fewer plants to hold sediment
•
Sandstorms - sand is normally too heavy for wind…wind blows
forcefully & sand bounces & hits other grains causing them to rise
into air (low cloud just above ground…)
•
Dust storms - dry soil picked up by wind and blown high into
atmosphere because they weigh less than sand…carries particles
far distances…
•
•
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•
IE – 1930…dust picked up in Kansas was found in New England…
important part of soil erosion…
Reduce wind Erosion:
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Erosion is most common in areas with no plants…
•
Stop erosion?…PLANTS!
•
Vegetation will reduce erosion…
•
Roots hold soil in place
•
Windbreaks with trees – slow down wind…
•
Stop energy of motion…
•
IE – row of cottonwood trees reduced wind to 66% of normal
speed
But…strong wind with dry soil…nothing will stop erosion by wind!
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Deposition by wind: sediments are eventually
deposited in new areas…
Creates a variety of land forms…
Loess: wind deposits of fine- grained
sediment…packed together creates a thick
unlayered yellowed- brown colored deposit
What happens when wind blows sediment
against an obstacle? = dune!
Dunes: created when sediment settles behind
an obstacle
Dunes can be moved as sand is lifted and
deposited downwind…(picture )
Overall…Erosion and Deposition constantly
shape and reshape the land!
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Create a Study Guide!
Using key terms and main ideas from
chapters 7 and 8, create a study guide AND
answer key (on separate sheets of paper).

10 fill in the blank questions
 5 multiple choice questions
 5 true or false questions


Ex: ______ is a mixture of weathered rock,
organic matter, mineral fragments, water and
air.
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