weathering: -the breakdown of rock due to physical or chemical changes *two main types of...
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Weathering:-The Breakdown of rock due to physical or chemical changes
*TWO MAIN TYPES OF WEATHERING*
1) Physical Weathering:
-Changes the size or shape of a rock- for example, by breaking it into smaller pieces- without changing its chemical composition
Examples:
1)Frost Action:
- important agent of weathering in climates that experience above and below 0oC-water seeps into pores of rocks, freezes and therefore expands, causing cracks in the rocks.
- over an extended period of freezing and melting, the rock will crumble
Plant Roots:-Grow in the crack of rocks
Animals:-animals that burrow beneath the ground
-roots expand in the crevices of rocks and gradually push the rock apart
- constantly expose new rock surfaces to weathering
Abrasion:-rocks carried by a stream , bump and rub against one another. These collisions cause the rock to break down.
-wind, moving ice and gravity are also agents of abrasion.
CHEMICAL WEATHERING:- requires heat energy and often water
- changes the chemical composition of the rock, forming new substances.Ex:-Feldspars uplifted to the earth’s surface come in contact with water and chemically weather to clay.
-takes place more rapidly in warm and moist climates
-rusting of a nail: iron rusts in the presence of moisture. O2
combines with the iron atoms and forms rust
SOIL-the mixture of weathered rock and organic remains that cover bedrock.
- under natural conditions, both physical and chemical weathering play a part in soil development.Physical weathering; breaks solid rock into small particles
Chemical weathering: changes hard minerals into softer forms
- the decay of organic remains produce organic acids that accelerate chemical weathering
SOIL HORIZONS:
-created by the weathering of bedrock* the top layer is the best for growing crops. Rich in dark colored organic remains called humus
*ground water filtration does transport some minerals to the lower layers* the lowest layer of soil is generally composed of broken up bedrock.
ORGANIC MATERIAL
BROKEN BEDROCK-SOME ORGANIC MATERIAL
COMPLETELY BEDROCK
Important things to know about soil
* It takes 100 to 400 years for one centimeter of topsoil to form
* Destruction of plant cover and poor farming and mining practices leave soil exposed and unprotected. It is then quickly carried away by water and wind
Sediments:-rocks that have been broken into various sized fragments.
Erosion:Involves the transporting of sediments away from their place of origin and depositing them elsewhere
- running water transports sediments in several ways
1) Erosion by water :
- the smallest particles remain suspended in solution because they cannot be filtered out
- largest most dense particles are rolled or bounced along the streambed- low density material such as organic remains are carried along the surface of the water by flotation
- water velocity indicates transported particle size
Larger= greater velocity
smaller= lower velocity
The Velocity Of Streams
-as stream gradient and or water quantity increases,, velocity of water increases.* most erosion takes place when streams are in flood
- slowest moving water sticks to the inside of the bends, causing deposition on the inner banks
- fastest flowing water swings at the outside of river beds causing erosion along the outer banks.
Erosion By Wind
- wind can carry away sand silt and clay
-occurs mainly in dry areas such as deserts, because there is not much plant life to hold soil in place
-wind erodes by abrasion
Erosion by Ice:Glacier: large mass of ice that
moves due to its weight under gravity.
-as it moves, it picks up and carries loose rock material
-acts like a huge abrasion system
- when ice melts, unsorted deposits are left behind
- rocks are left angular and often scratched
WHAT IS DEPOSITION?
- occurs when agents of erosion, deposit or lay down particles and fragments of sediments
- Factors That Affect Deposition
Particle Size:
Smaller particles such as clay and silt, settle more slowly than cobbles and boulders
Particle Shape:Flat angular pieces of sediment settle more slowly because of their increased surface area and friction with the water.-smooth, rounded particles settle more quickly
Particle Density:Among particles of the same average size and shape, more dense particles settle faster.
Settling Rate and Settling Time:- as the rate of settling increases,
settling time decreases
Sorting of Sediments:Horizontal Sorting:
-largest, roundest and densest particles are deposited first near the oceans coastline, while the smallest, flattest and least dense are carried further form the shorelineVertical Sorting:
Where particles sort out from bottom to top in a layer
Deposition in Streams
- sediment can cause sand bars in slower sections of the stream
Deposition By Wind:
-Like running water, wind deposits sediments in layers
Ex. Sand dunes
SORTED DEPOSIT:
EX:
When streams slow down, largest particles settle out first , then smaller particles.
Deposition by Gravity:- does not create sorted
sediments. (many different sediment sizes mixed together.Deposition by
Glaciers:- occurs when glaciers melt and sediments are released.
- unsorted unless glacial sediments are deposited as a result of melt-water
NEW YORK AND THE ICE AGES-as recently as 20,000 years ago, most of New York was covered by a continental ice sheet.
Alpine Glaciers:-occur in mountain regions-will flow downhill under its own weight due mainly to slope.-Flow at a rate of a few centimeters to several meters per day-ice rubbing against surrounding
rock carves out valleys
Continental Glaciers- known as ice sheets- responsible for most glacial features in NYS- rock carried within the glacier that causes erosion of the land
Striations:Parallel grooves and scratches in bedrock