how do weathering & erosion work together to change the shape of earth’s surface?
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How do weathering & erosion work together to change the shape of Earth’s
surface?
Erosion
• The movement of rock particles by wind, water, ice, or gravity
Weathering
• The process that breaks down rock & other substances on Earth’s surface
2 types of weathering:
• Mechanical
• Chemical
Mechanical Weathering
• Rock is physically broken into smaller pieces
• By the process of:– Freezing & thawing– Release of pressure– Growth of plants– Actions of animals– Abrasion
Mechanical weathering can wear away more than whole rock…
New mechanical weathering terms:
• Abrasion: grinding away of rock by rock particles carried by water, ice, wind, or gravity
• Ice wedging: wedges of ice in rocks widen & deepen cracks
Chemical Weathering
• Breaks rocks down through chemical changes
• By the process of:– Water– Oxygen– CO2– Living organisms– Acid Rain
Water…
• The most important chemical agent
• Water weathers rock by dissolving it
How does water assist in weathering & erosion?
• Runoff: all the remaining water that moves over Earth’s surface– It picks up soil particles as it moves across
the land
Rills
• Tiny grooves in the soil caused from runoff
Gullies
• Large grooves, or channel, in the soil the carries runoff after a storm
• They flow only after it rains
Stream
• Channel in which water flows in constantly
Tributary
• A stream that flows into a larger stream
River
• A large stream
• Rivers erosion creates:– valleys– waterfalls – flood plain– meanders– oxbow lakes
Valley
Waterfalls
Flood Plain
• Flat, wide area of land that runs along side a river
Meander
• Looplike bend in the course of a river
Oxbow Lake
• A meander that has been cut off from the river
River Deposits
• Water moves sediments & rocks with it depositing them elsewhere
• River deposits create landforms like:– Alluvial fans– Deltas– Soil on a flood plains
Alluvial Fan
• Wide, sloping deposit of sediment formed where a stream leaves a mountain range
Delta
• Sediment deposited where a river flows into an ocean
• Can be shaped like an arc, triangular, bird’s foot
How do sediments enter rivers & streams?
• Most washes or falls into the river as a result of mass movement or runoff
• Other sediments erode from the bottom or sides of the river
Abrasion
• Wearing away of rock by a grinding action
• Boulders become smaller and smaller as they move down a streambed
How much sediment can a river carry?
• A load!
• Load: the amount of sediment that a river carries
Groundwater can create erosion too!
• Groundwater: underground water
• Stalactite: a calcite deposit that hangs like an icicle from the roof of a cave
• Stalagmite: cone shaped calcite deposit growing up from the cave floor
What does the amount of runoff depend on?
• 5 factors determine the amount of runoff an area receives:– Amount of rainfall– Vegetation– Type of soil– Shape of land– How people use land
How does ice change the shape of the land?
• Glaciers: large mass of ice that moves slowly over land
• 2 kinds:– Valley– continental
Valley Glacier
• Long, narrow glacier that forms when snow & ice build up high in a mountain valley
Continental Glaciers
• Glacier that covers much of a continent or island
• Much larger than valley glaciers
• They cover @ 10% of Earth
How do glaciers form?
• They form in areas where more snow falls than melts
• Snow builds up over time
• The pressure compacts the snow into ice
How do glaciers move?
• Gravity!
• Valley glaciers flow a few cm-a few meters each day
• Continental glaciers flow in all directions
How do glaciers change the land?
• Glaciers erode the land through 2 processes called plucking & abrasion
Plucking
• When a glacier flows over land, it picks up rocks in the process
• Rock fragments freeze to the bottom of the glacier
Abrasion
• As the glacier drags the rocks across the land it gouges & scratches the bedrock
What is glacial deposition?
• When the glacier melts, it deposits the sediment it eroded from the land creating various landforms– Moraine– Prairie pothole– Kettle Lake
Moraine
• A ridge formed by the till deposited at the edge of a glacier
Kettle
• A small depression that forms when a chunk of ice is left in glacial till
Wave Erosion
Wind Erosion
How does gravity assist in weathering & erosion?
• Gravity: a force that moves rocks & other materials downhill
• Gravity causes mass movement
• Mass Movement: any type of process that moves sediment downhill– Ex: landslides, slump, mudflows, creep
Landslides
• Most destructive kind
• Occurs when rock & soil slide quickly down a steep slope
• Caused by earthquakes, roadwork
Slump
• A mass of rock& soil that suddenly slips down a slope
Mudflows
• Rapid, downhill movement of a mixture of water, rock, & soil
• Amount of water can be as much as 60%
• Can occur during heavy rains or earthquakes
Creep
• Very slow downhill movement of rock & soil
• It’s barely noticeable
• It can tilt telephone poles, fenceposts, or gravestones in weird ways
At what rate does rock weather?
• Depends on type of rock & climate
Type of rock
• Permeable: material is full of tiny, connected air space that allow water to seep through it
Climate
• Average weather conditions in an area
• Chemical & Mechanical weathering occurs faster in wet climates
• Chemical reactions occur faster in higher temperatures
What is soil?
• Soil is loose, weathered material on Earth’s surface
How does soil form?
• It forms when rock that is broken down by weathering mixes with other materials on the surface
• Soil is constantly formed where bedrock (layer of rock beneath the dirt) is exposed
What’s in the soil?
• Soil is a mixture of rock particles, minerals, dead stuff, air, & water
• Type of rock depends on bedrock & weathering
• Humus: dark substance that forms as plant & animal remains decay
How does the soil feel?
• Sand is gritty while clay is smooth
• Texture depends on size of individual soil particles
• Texture is important for plant growth
• Largest to smallest:– Gravel– Sand– Silt– Clay
Loam
• Soil made of equal parts of clay, sand, & silt
• Holds both water & air
• Best for growing most types of plants
What is a soil horizon?
• Layer of soil that differs in color & texture from the layers above or below it
• Soil is divided into 4 horizons:– Horizon A-Topsoil: dark brown, crumbly layer– Horizon B-Subsoil: clay, little humus, particles– Horizon C-Parent Material: partly weathered
rock– Horizon D-Bedrock: large pieces of rock`
What lives in the soil?
• Organisms make space in the soil for air & water – Ex: mice, ants, snails, beetles, worms, lots of
plants
What do these organisms do to the soil?
• Plants shed leaves which is called litter• Litter & dead plants become part of the
soil• The organisms living there turn the dead
organic stuff into humus• This process is called decomposition
– Decomposers: organisms that break down the remains of dead organisms
– Ex: fungi, bacteria, worms
Is the soil in Montana the same as in Georgia?
• NO!
• Soil is classified into groups according the climate, plants, composition
• 7 groups: tundra, n. forest, prairie, mountain, s. forest, desert, tropical
How do people use soil?
• Agriculture, development, mining, recreation
Is soil important to me & you?
• YES!
• Everything needs soil
• It’s a renewable resource
• However it can take a long time for new soil to form
How is our soil being damaged?
• Overused• Polluted• Eroded away• Desertification: the advance of desertlike conditions in an area due
– Caused by climate change, overgrazing, cutting down trees
What was the Dust Bowl?
• 1930’s
• Most of the Great Plains had been turned into farm or ranch land
• This caused the topsoil to dry out and dust to form
• Lots of people moved away abandoning their farms
What does it mean to conserve soil?
• Soil conservation: the management of soil to prevent its destruction
What are some ways to conserve soil?
• Crop rotation
• Contour plowing
• Conservation plowing
• Windbreaks
• Terracing
Is it possible to restore destroyed land?
• Yes!
• Land reclamation: restoring an area of land to a more natural, productive state
Where does our trash go?
• In the soil!
Municipal Solid Waste
• Waste materials produced in homes, businesses, and other places in a community
• 3 ways of handling solid waste: – Bury it– Burn it– Recycle it
Staten Island LandfillNew York City
Burying Trash
• PROS– Can be used for parks
• CONS– Pollute groundwater– Pollute soil– They eventually fill to
capacity
Landfill: holds solid waste
Burning Trash
• PROS
-Doesn’t take up as much space as a landfill
-Doesn’t pollute groundwater
-Heat produced can be changed into electricity
• CONS– Pollute the air– Some waste still
remains– More expensive than
landfills
Incineration: burning of solid waste
Recycling TrashRecycling: process of reclaiming of reusing raw materials
• PROS– Conserves
nonrenewable resources
– Inexpensive– Saves trees– Can be used to make
other products
• CONS– You can’t recycle
everything
What can you do to help?
• Reduce, Reuse, & Recycle– Reduce: create less waste in the 1st place– Reuse: reuse items in your house– Recycle: take your recycling to a local center
where they can break it down & make new things from it
The Decomposition Times we used were:
•Glass Bottles/Jars 1,000,000 years •Aluminum Cans 80-100 years •Plastic Bags 10-20 years •Plastic Coated Paper 5 years •Orange and Banana Peels 2-5 weeks •Newspaper 2-4 weeks
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