Weathering+and+Erosion

__**//Weathering and Erosion//**


 * Weathering**__

-th__e__ breakdown of rocks at or near the surface of the Earth -**__physical weathering__-**the breakdown of rock into smaller pieces without chemical change -**ice wedging (frost action)-**water held in the cracks of rocks wedges the rock apart when it freezes. -**root wedging (plant action)-**tiny roots grow into cracks in the rock and then as the root grows the rock splits.

-**exfoliation-**when large masses of rock, mainly igneous, are lifted up to the surface the relief of overlying pressure causes the rock to expand. Upward expansion leads to curved breaks which may peel off the layers

-**__chemical weathering-__**the breakdown of rock through a change in mineral or chemical composition. -**oxidation-**the chemical reaction of oxygen with other substances. Iron is the most easily attacked resulting in rust (iron oxides) -**carbonic acid-**when carbon dioxide dissolves into water. it dissolves many common minerals -different minerals and rocks have different physical and chemical properties which allow them to weather at different rates -ex.**quartz-**almost unchanged by chemical weathering. it is hard and does not have cleavage so it also resists mechanical (physical) weathering.

-feldspar, mica, calcite, and gypsum are affected by both types of weathering and will break down into clay with calcite and gypsum dissolving and being carried off in solution -sedimentary rocks ex. **shale-** least resistant to mechanical weathering -**sandstone**- is the most resistant to mechanical weathering -the type of cement which holds the sandstone together determines how resistant the rock is -silica-high resistance
 * -calcite-low resistance

Rocks that contain the mineral calcite, such as limestone or marble, are somewhat resistant to mechanical weathering but is the least resistant to chemical weathering

**__**Factors affecting the Rate of Weathering**__ -rate and type of weathering depends on exposure of rocks to air, water and the action of living things
 * Exposure- the closer to the surface of the Earth, the faster it will weather

**-Surface Area-**the greater the surface area exposed to weathering the faster the rate of weathering -two samples of the same material having the same mass can have different surface areas**

- physical weathering is usually greater in moist areas with temperature variations (cold and warm) - soils- made of loose, weathered rock and organic material in which plants with roots can grow. the rock material is composed of sand, silt, and clay - parent material -the material from which a soil is formed - residual soil- soil that has the bedrock beneath the soil as a parent material - transported soil- soils formed from deposits left by winds, rivers, and glaciers. - topsoil (a-horizon)- darkest cloro due to organic material - subsoli (b-horizon)-1**) clay is washed to the subsoil **2)**may contain soluble minerals, such as calcium and magnesium carbonates **3)** color is usually red-brown from iron oxides that dorm above and wash down -**c-horizon-** made from slightly weathered parent material (rock fragments)
 * __Climate Efecting Weathering__**
 * -Chemical weathering is usually greater in warm, moist climates
 * unweathered rock

__Climate__ -tropical soils form in areas with high temperatures and heavy rainfall. A thick infertile soil profile are results of heavy rain. -grassland soils form in areas with enough rainfall for heavy grass, but not tees. About 1 meter thick and fertile -forest soils form in humid regions with cool seasons. Soil profile is less then 1 meter thick with well developed A, B, and C -desert soils form in very dry climates. soil profile is a few centimeters thick and be very fertile when they are watered -artic soils form at high elevations and high altitudes. Poor drained surfaces and the bottom layers are constantly frozen

**__Erosion__ a) gravity is an aid in weathering and erosion. Steep slopes weather to gentle slopes -creep- slow, imperceptible down slope movement of the soil. Causes objects that are fized in the soil to lean downhill. Water in the soil is what adds weight - mudflow- the rapid movement of a water saturated mass of soil - slump- occurs when a section of land moves downhill as a whole because of a plane of weakness in the underlying soil. - landslide -sudden movement of a mass of bed rock or loose rock down the slope of a hill or mountain. (Avalanche-snow, ice, rock, and soil) **-talus**-is a pile of rock fragments at the base of a cliff.
 * - **mass movement** of loose earth material down a slope

__//Wind Erosion//__ //-//wind transports materials by causing their particle to move in different ways. -suspension- a method of transport by which strong winds cause small particles to stay airborne for long distances. - saltation- causes a bouncing of motion of larger particles. Saltation accounts for most sand transport by wind -wind erosion is greatest in arid climates (low precipitation) with little vegetation. (deserts and sea shores) - abrasion-**a process of erosion found in wind, water, and ice. It occurs when particles such as sand rub up against the surface of rocks or other materials -**ventifacts**-are rocks shaped by windblown sediments -wind deposition occurs i areas where wind velocity decreases. -**dunes-**piles of windblown sand that have a gentle side and a steep side. the gentler the slope occurs when the side on which the wind is blowing (windward side). the steeper slope occurs on the side protected from the wind (leeward side).
 * -loess**-thick deposits of fine lightweight particles (silt, clay) that are carried by the wind in great quantities of long distances. They are some of the most fertile soils

//**-Louis Agassiz**// **is known for the idea that glaciers once covered many parts of the world

__Formation of a Glacier__ -glaciers are acumulations of ice large enough to survive sumer melt-forms from snow under pressure which turns to ice - snow line -the lowest level that permanent snows reach in summer -highest near the equator - firn- granular ice material formed in snow fields from freshly fallen snow becoming compressed and recrystallizing -the lower layers become ice and begin flowing downward or outward because of overlying pressure - alpine glaciers (valley glaciers)- occur in mountain regions above the snow line. flow downhill and carve out u-shaped valleys - continental glaciers (ice sheets)- a glacier that spreads over a wide geographic area. Form in polar areas where the snow line is close to sea level and wide areas are above the snow line.

//__Glacial Movement__ -overlying weight of now and ice causes grains of ice to partially melt and refreeze. As this happens ice grains slip past each p\other and move downhill -glaciers move more rapidly at the surface than at the base and faster at the center than at the sides. Friction with the valley walls slow the flow - // **//crevasses-**cracks across the width of the glacier -ice front- the end of a glacier -stationary as long as the rate of the movement and melting are equal - a glacier recedes when it melts than normal -a glacier advances when the rate of movement is greater than the rate at which it melts -pieces of rock are picked up as glaciers move and then are dragged along the bedrock and or valley wall -fine sand acts as sandpaper and polish the bedrock - larger sediments leave long scratches called ****striations** -**striations show the direction of movements** - finger lakes of NY were formed as advancing ice deeply scoured out valleys -g lacial trough are formed when a glacier carve out a valley forming a u-shaped valley -valley glaciers leave sharp mountain tops while continental glaciers leave rounded tops - **moraine-**a glacial deposit of unsorted rock material -**ground moraine-**carried along the bottom -**lateral moraine-long lines of rock pieces along the valley sides -**medial moraines-**when two glaciers come toether joining together
 * - calving- when blocks or ice break off into the sea

__**Vocabulary**__
 * 1. Cirque**-deep depression scooped out by a valley glacier
 * 2.Arete-**alpine structures carved by glacial ice
 * 3.Horn-**?
 * 4.Col-**break in an arete (mountain pass)
 * 5.****Truncated Spur -**occurs when spurs, formed in mountainous area by river action, are traveled by actions of ice
 * 6.Tarn-**a small lake at the base of a cirque
 * 7.Hanging Valley-**valley that is cut across by a deeper valley or a cliff
 * 8.Crevasse-**deep open crack in a glacier
 * 9.Roches Moutonees (resting sheep)-**an outcrop of bedrock which has become elongated. Sculpted by a glacier one sideis smooth and the other is left rough
 * 10,Striations-**cuts made by glaciers in underlying bedrock
 * 11.Drift-**to be carried slowl by a current of air or water

-erosion-__** process by which earth materials are moved by natural agents like water, wind, and ice -the sun is where running water gets it's energy from -rocks are weathered both physically and chemically by running water -**abrasion (physical)-**term given to the use of sand, pebbles and even boulders as cutting tools to grind away at the stream bed. During this process the "tools" themselves wear down -**chemical-**water dissolves soluble materials
 * __Erosion and Deposition
 * __-__****__Running Water__** **__-__**most effective agent of erosion

r**ivers carry rock material in three ways solution-**this is the material that is dissolved from the bedrock. Most commonly found in solution are compounds of calcium and magnesium. -**carrying power-**indicated by both the total amount of sediment in a stream and by size of the particles being moved. -the stream discharge and speed will determine the carrying power of the stream -speed-**generally determined by the steepness. or gradients, of its bed -a stream moving at a high speed with a high discharge can carry much larger sediments then a slow moving stream. ex. spring time melting and excessive rain. Rivers tend to have a V-Shaped valley because they tend to flow at high speeds and dig into the stream bed. -**base level-**the lowest level a river can cut into its bed. -to form a permanent stream rain water flow down a slope and dig deep into the water table. This wearing away of the land to form a stream alley is called headward erosion -**divide-**an area of high land that separates one river valley from another. -on either side of a divide a river system may form -**watershed-**all of the land that drains into the river either directly or through tributaries -**waterfalls-**water flowing over a steep cliff. Waterfalls are not permeant structures. -**undermining-e**rosional process occurring at the base of a waterfall. Here water carrying sediment plunges down and back into the stream bed and cliff below. This causes the rocks at the top of the falls to overhang. Overtime this overhang will collapse and the stream will move back toward the source.
 * suspension-**when small rock particles, such as clay, silt, and fine sand are kept from sinking by the turbulence of the stream. This gives the water a muddy-look
 * bed load-**sand, pebbles, and some boulders which move along the stream bed
 * -discharge-t he volume of water flowing past a given point at any given time.

-as rivers begin to decrease their slope they move slower and will begin to move side to side -as the valley wall on either side is eroded the valley floor is widen -a Flood Plain is the widened valley floor area which will accumulate water during times of excess rain when the river floods
 * __-river deposition-__**deposition occurs when a stream either decreases in speed or discharge. Generally the speed decreases when its slope decreases or its bed widens. The greatest loss of speed occurs when a river empties into a quiet body of water. A decrease in discharge would occur if a river traveled through an area of low precipitation.

//Erosion and Deposition in a River -**Meanders** are broad curves in the river (each bend or turn) -erosion is greatest on the outside of a meander where water is flowing fastest (cut bank) -deposition is greater on the inside of the meander where the water flows slower(fill bank) -**Oxbpw Lake-**meanders can only become so large before they break through into another meander. The river then deposits mud and silt along the end of an abandoned meander. The now separated meander becomes a lake.

-vertical sorting-**when sediments are suddenly deposited into water. The particles separate by size with the largest on the bottom and smallest on top**. -****horizontal sorting-**when rivers empty their sediments into quiet bodies of water. Particles are sorted by size with larger particles being found closer to the shore and smaller particles being carried out into the body of water to be deposited -**Delta-**a fan shaped deposit of sediment at the mouth of a river
 * -*Running Water Deposits well sorted particles**