Transcript Weathering Erosion and Deposition notes.ppt

1.Weathering,
2.Erosion
&
3. Deposition
What is weathering?
Weathering - the process that
breaks down rock at or near the
earth's
surfachttp://www.brainpop.com/science/weather/weathering/e to form sediment
There are 2 types of weathering
• Mechanical
• Chemical
Mechanical weathering:
physically breaks rocks down into smaller
pieces.
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Types of mechanical weathering include:
Plant growth (root pry)
Animal Actions (burrow, dig)
Freezing and Thawing (ice wedging)
Abrasion (rock scraping)
Release of Pressure (rock surfacing)
Plant Growth or Root Pry: roots
are wedges (simple machines) that slowly move
rock and soil out of their way as they grow
Animal Actions: Animals move soil
&rocks and change the flow of water.
Freezing and Thawing:
When water
in cracks of rock freezes, it expands, widening
cracks and weakening rock
Abrasion: when rock is scraped away by other
rocks, sand, wind, water, or ice
Release of Pressure: When erosion
occurs above large rocks (plutons), they surface due to
lack of pressure. As they surface they crack and weather,
as well as weather the area above them.
Enchanted Rock:
a surfaced pluton near
Fredricksburg TX in the
Edwars Plateau Ecoregion
Mechanical
Weathering
Rocks do not
Change their
mineral
Composition
Abrasion & Pressure
Chemical
Weathering
Rock is
broken
down
into
sediment
Mineral
composition
of rock is
Altered
Organisms
& water
Acids &
chemical reactions
Chemical weathering breaks rocks down by chemically
adding or removing chemical elements, and changes
them into other materials.
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Chemical weathering can be caused by:
Water (dissolves minerals)
Oxygen (creates rust)
Carbon dioxide (SINKHOLE)
Living organisms (create wastes)
Acid Rain (pollution)
Water —Dissolves minerals out of
washes them away
rocks and
Carbon Dioxide: CO mixes with water to form
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carbonic acid. This easily chemically weathers limestone. When the
sediments are washed away, caverns, and sinkholes can form.
Oxygen- can react with iron in rock and
form rust
Organisms: can excrete wastes that break
down rock
• Lichen that grow on rocks release acidic
wastes. The acids break the rock down to
form soil.
Acid Rain/Pollution: can easily break down
rock. Limestone is especially susceptible to weathering and
erosion by acid rain.
Chemical weathering happens
quickly in warm, moist
environments because water is
needed for the chemical
reactions.
The warm, wet weather speeds up
the reactions.
What’s the difference between
weathering and erosion??
If a particle is loosened, chemically or mechanically, but
stays put, we call it weathering.
Once the particle starts moving, we call it erosion.
EROSION:
the removal and movement of earth materials by natural
agents (When the products of weathering are moved
away)
http://www.brainpop.com/science/earthsystem/erosion/
What causes erosion?
WATER
is the main agent of erosion.
Other agents include
1. glaciers
2. wind
3. Earthquakes
4. volcanoes
5. Tornadoes & hurricanes
6. Mass wasting (avalanche, rock slide, mudflow)
Water is the most important erosional agent and erodes most
often as running water in streams or rivers. Water in all its forms is
erosional. Raindrops create splash erosion that moves tiny particles
of soil. Water collecting on the surface of the soil collects as it moves
towards tiny streams and creates sheet erosion.
Click the link to see how river erosion
forms waterfalls:
http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es1305/es
1305page01.cfm?chapter_no=visualization
Waves in oceans and other large bodies of water cause coastal
erosion.
The power of ocean waves is awesome; large storm waves can
produce 2000 pounds of pressure per square foot. The pure
energy of waves along with the chemical content of the water is
what erodes the rock of the coastline.
Click the link below for a short demo of
wave erosion:
http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es1606/es
1606page01.cfm?chapter_no=visualization
Wind
Erosion by
usually occurs in deserts. Wind
erosion of sand in the desert is partially responsible for the
formation of sand dunes
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Glaciers cause erosion two ways - they pluck and abrade.
1. Plucking takes place by water entering cracks under the glacier,
freezing, and breaking off pieces of rock that are then moved by the
glacier.
2. Abrasion cuts into the rock under the glacier, scooping rock up like a
bulldozer and smoothing and polishing the rock surface
.
Click & observe
landscapes formed by
erosion
There are 5 ways that man can
cause erosion:
1. Forestry – all vegetation of removed, and
without roots, the soil will erode away.
2. Strip Mining – removing rock cover to get
to the resources below, which causes the
loose sediments to erode away.
3. Construction – the clearing of land to build
buildings/houses also causes all loose soil
to erode away.
4. Improper Farming – not plowing the land
at right angles to slopes causes soil to
erode away.
5. Salting Highways – the salt is washed off
the road to the sides, where it prevents
vegetative growth along the sides.
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Deposition – the process where sediments are
released/dropped by their agent of erosion. Most deposition happens in
standing/still bodies of water (oceans/lakes). Deposition is caused by
the slowing down (loss of kinetic energy) of the agent of erosion.
There are 3 factors that influence the rate of sediment deposition:
Sediment size, Sediment shape ,Sediment density -
This brainpop talks briefly about river delta
deposition and introduces some of the
concepts for watershed
http://www.brainpop.com/science/earthsyst
em/rivers/
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Delta – a fan shaped deposit that forms at the mouth of a
river/stream when it enters a larger body of water. This is seen
under the water. The particles are horizontally sorted.
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Alluvial Fan - a fan shaped deposit of sediments that forms
when a stream/river flows out of a mountain on to flat, dry plains.
These are not under water and are very visible. This only
happens on the land. You can call it a “land delta”.
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Cross-Bedding – a situation where
layers of sediments are deposited
at angles to one another as a result
of a change of direction of the
erosional agent.
These are usually found in sand
dunes, deltas, and alluvial fans.
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Texas Ecoregions
Effects of Weathering, Erosion
and Deposition
What is an Ecoregion?
• an area defined by its environmental
conditions, esp. climate, landforms, and
soil characteristics.
Factors Affecting Our
Ecoregions
Weathering – chemical and physical break
down of rocks into sediment
Erosion – the movement of sediment from
one place to another
Deposition – the placement of sediment
after being carried from place of origin
Piney Woods
• It is the wettest region of the state.
• This allows for a high rate of decomposition to
occur resulting in healthy, nutrient-rich soils.
• The topography is gently rolling to near flat
through out the region.
• Pine trees, woody vines, and hardwood trees
dominate the vegetation.
• Unless an area has been clear-cut of
vegetation for construction, the amount of
trees and plants can prevent erosion.
• Very little erosion takes place in these areas.
http://www.youtube.com/watch?v=9o8lKGh
J5KI&list=PL6353227E5419A80D
Oak Wood Prairies
•
These areas have
nutrient-rich soils and
receive good amounts of
rainfall through the year.
•
If the land is clear-cut of
natural vegetation for
construction nutrients can
easily be eroded by wind
and water.
Blackland Prairies
• Large herds of bison grazed on the
grasses at one time.
• Blackland prairies in Texas, which are
mostly composed of clays, are eroded
primarily by water. Secondary causes
include wind, and the action of
burrowing animals (bio erosion).
http://www.youtube.com/watch?v=lBlFruPos0&list=PL6353227E5419A80D
Llano Uplift
• A basin; in some places, it is 1000 feet
below the level of the surrounding
limestone escarpment.
• It gets its name from the granitic mass
that is exposed in the basin, granite
that has been dated at one billion years
old.
• Upland soils are shallow, reddish
brown, stony, sandy loams over
granite, gneiss, and schist with deeper
sandy loams in the valleys.
South Texas
Brush Country
•
The area is known as “Brush
Country” due to the shorter trees
and many shrubs.
•
Overgrazing of the land has
allowed nutrient-rich topsoil to
erode way by wind and water.
•
Rocky, dry soil cannot support
grasses, trees can thrive
because of their deeper root
system.
http://www.youtube.com/watch?v=XyluCiA
Odso&list=PL6353227E5419A80D
Edwards Plateau
•
This region is located between dry
western plains and moist prairies
and woods.
•
Unfortunately, water erosion has
left most of the region with very
shallow soils (less than 10 inches)
lined with limestone rock layers.
•
High amounts of rain in a short
amount of time can. cause flash
flooding
http://www.youtube.com/watch?v=DY7ueu
kM1QQ&list=PL6353227E5419A80D
Trans-Pecos
• “Desert portion” of Texas.
• The weathered bedrock in this area has
high amounts of calcium.
• The Guadalupe Mountains and the Davis
Mountains are located in this ecoregion,
making it the most mountainous area of
Texas.
• * In general, soil in this region is eroded
due to the decline of grasslands.
• Flash-flooding and rapid runoff are causes
of erosion in the park.
• Erosion of the limestone cliffs takes place
because of acid rain.
• http://www.youtube.com/watch?v=b1FErNr
xVZo&list=PL6353227E5419A80D
Rolling Plains
•
This region is part of the Great
Plains of the central United
States.
•
Soils in this area are most
fertile and sought after for crop
production.
•
Periods of drought and then
sudden increase in rainfall
causes large amounts of
erosion and deplete the soil of
nutrients.
http://www.youtube.com/watch?v=0UlDeYfJ
1XU&list=PL6353227E5419A80D
Coastal Sand Plains
•
Soil in the region is primarily
sand-based.
•
If there isn’t enough
vegetation to keep the soil in
place, rainfall received can
cause severe erosion.
•
Catastrophic events such as
hurricanes can increase
wave erosion.
High Plains
•
•
“Texas Panhandle”
Largest and most completely flat
areas of it size in the world!
• The High Plains ecoregion is one of
the windiest regions in the United
States.
• The climate is generally dry, and areas
without vegetation experience wind
erosion.
• The Palo Duro Canyon was formed by
water erosion by a fork of the Red
River. The canyon continues to
become deeper as the water moves
sediment downstream. Wind and water
erosion gradually widen the canyon.
Gulf Coast Prairies and
Marshes
• A narrow band about 60 miles wide along the Texas coast
from the Louisiana border to Brownsville roughly outlines
the Gulf Coast Prairies and Marshes
• Near the gulf waters you can see marshes, barrier islands,
estuaries (where salty sea water and fresh river water
meet), and bays.
• Catastrophic events such as hurricanes can increase wave
erosion.
http://www.youtube.com/watch?v=mZdsy
KaIAYE&list=PL6353227E5419A80D
Marine
Environment
• This ecoregion has seagrasses,
oyster reefs, barrier islands,
muddy estaurine bottoms, reefs
and open water.
• These areas provide plants and
animals with their basic needs
and support hundreds of species.
• Global warming has one of the
most negative impacts in marine
ecosystems.