WEATHERING & EROSION



Erosion:

When the rock disintegrates into the water. Transportation of sediments.
Weathering is the breaking down of rocks at or near the surface of the earth.
Physically or chemically- The breakdown of rock into smaller pieces without chemical change.


Random Example:
If your lighting a piece of paper with a match or ripping a piece of paper - ripping the piece of paper would be a physical change.


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Ice Wedging (frost action)

- Water held in the crack 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 expansions leads to curved breaks which may peel off in layers.
exfoliation_dome_in_yosemite.jpg


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 most easily attacked resulting in rust. (Iron Oxides)

Carbonic Acid
- When carbon dioxide dissolves into water. It dissolves many common minerals.
CAVE:
cave.jpg



Minerals Resistance To Weathering
- Different minerals and rocks ave different physical and chemical properties which allow them to weather at different rates.
Quartz
- Almost unchanged by chemical weathering. It is hard and does not have cleavage so it also resists mechanical weathering.




FELDSPAR, MICA, CALCITE, AND GYPSUM
- Affected by both types of weathering and will break down into clay with calcite and gypsum dissolving and being carried of in solution.

SEDIMENTARY ROCKS
shale- Is the 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
calcite- Low resistance
silica- High resistance.


Rocks which contain the mineral calcite, such as LIMESTONE or MINERAL calcite, are somewhat resistant to mechanical weathering but is the least resistant to chemical weathering.

FACTORS AFFECTING RATE OF WEATHERING
EXPOSURE

- The closer to the surface of the earth, the faster it will weather.

- Rate and type of weathering depends on exposure of rocks to air, water and the action of living things


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. If one sample is a large piece of marble with a mass of 50g, and the other is 50g of many small pieces of marble. The smaller size pieces will have the greater surface area.

surface_area.gif
^ increase surface area by breaking it down into more pieces ^

Climate Effect On Weathering
Chemical Weathering Is usually greater in warm, moist climates.
Physical weathering Is usually greater in moist areas with temperature variations (cold and warm)



SoiLS

Soil is 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 is 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.

Random; Most of the transported soil are in New York.
SOIL LAYERS: V
soil_layers.png

A-HORIZON TOPSOIL
Darkest color due to organic material.

B-HORIZON SUBSOIL
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 form above and wash down.


C-HORIZON
- Made of slightly weathered parent material (Rock Fragments)

UNWEATHERED BEDROCK:
bedrock.jpg


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 trees about 1 meter thick and fertile.


Forest soils form in humid regions with cool seasons. soil frofile is less then 1 meter thick with well developed A, B, AND C horizons.

desert soils form in very dry climates. soil profiles is a few centimeters thick and be very fertile when they are watered:

dry_soils.gif


Arctic soils form at high elevations and high latitudes. poorly drained surfaces and the bottom layers are constantly frozen.



Mass Movements:
- Movements of loose earth material down a slope.
A)
Gravity is an aid in weathering and erosion. Steep slopes weather to gentile slopes.

Creep- Slow, imperceptible down slope movement of the soil. Causes objects that are fixed in the soil to lean downhill water in the soil is what adds the weight.
Mudflow- the rapid movement of a water saturated mass of soil.

CREEP: EXAMPLE-
creep.jpg creep2.jpg



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 bedrock 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.

Wind Erosion
-wind transports materials causing their particles to move in different ways
Suspension- a method of transport by which strong winds cause small particles to stay airborne for long distance.
Saltation- causes a bouncing of motion of larger particles. saltation accounts for most sand transport by wind.

Wind Erosion is greatest in arid climates with little vegetation.
wind_erosion.jpg

Abrasion- 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- rocks shaped by windblown sediments.

Wind deposition occurs in areas where wind velocity decreases.
Dunes- piles of windblown sand that have a gentle side and a steep side.

The gentler slope occurs when the side on which the wind is blowing. the steeper slope occurs on the side protected from the wind.

Loess- thick deposits of fine lightweight particles 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.
louis_agassiz.jpg


Glaciers- accumulations of ice larfe enough to survive summer melt0 forms from snow under pressure which turns to ice.
Snow Lines- the lowest level that permanent snows reach in summer.

Firn- granular ice material formed in snow fields from freshly fallen snow becoming compressed and re crystallizing.
-the lower layers become ice and begin flowing down or outward because of overlying pressure.

Alpine Glaciers
- occur in mountain regions above the snow line
- flow downhill and carve out U-shaped valleys.


Continental Glaciers
- 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.
- 20,000 years ago, new york state was covered by huge ice sheet that originated in canada.


Glacier Movement
- the overlying weight of snow and ice causes grains of ice to partially melt and refreeze. as the happens ice grains slip past each other and move downhill.
- glacier movement 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.


glacier_movement_1.jpg


Crevasses- cracks across the width of the glacier that form when glaciers move over steep slopes.

Ice front is the end of a glaciers
-the ice front is stationary as long as the rate of movement and melting are equal
-A glacier recedes when it melts faster than normal
-a glacier advances when the rate of movement is greater then the rate at which it melts.


Pieces of rock are picked up as glaciers move and then dragged along the bedrock and/or valley wall.
-fine sand acts as sandpaper and polish the bedrock
-larger sediments leave long parallel scratches called striations



Calving- when blocks of ice break off into the sea
CALVING.jpg



-The finger lakes of NY were formed as advancing ice deeply scoured out valleys.
-Glacial trough are formed when a glacier carve out a valley forming a u-shape valley.
- valley glaciers leave sharp mountain tops while continental glaciers leave rounded tops.



HERE ARE A FEW DEPOSITIONAL FEATURES OF GLACIERS.

-Moraine is a glacial deposit of unsorted rock material.
Ground moraine- carried along the bottom
lateral moraine- lonh lines of rock pieces along the valley sides
Medical moraine- when two glaciers come together and there lateral moraines join together.



Cirque- geology a half-open steep-sided hollow at the head of a valley or on a mountainside, formed by glacial erosion

arete- a sharp mountain ridge

horn- a hard permanent outgrowth, often curved and pointed, found in pairs on the heads of cattle, sheep, goats, giraffes, etc., and consisting of a core of bone encased in keratinized skin.

truncated spur-

tarn- small lake at the base of a cirque

hanging valley- a valley that is cut across by a deeper valley or a cliff.

crevasse- deep open crack.

roches moutonees- outcrop of bedrock which has become elongated. sculpted by a glacier one side smooth and the other is left rough.

striations- marked with straie

drift- be carried slowly by a current of air or water :

Till- an unstratified sediment consisting of particles of various sizes and deposited by melting glaciers or ice sheets.

Moraine
a- forms along the side of a glacier
b- media merging lateral moraines of two glaciers form a moraine in the middle of the glacier.
c- ground- a melting glacier deposits till in a thin layer over a broad area.

d- recessional- deposits of till that form at the end of a glacier as it retreats.
e- terminal- the end found at the farthest advance of a glacier
.

outwash plain- material carried away from a glacier by meltwater and deposited beyond the moraine.

kame- a steep-sided mound of sand and gravel deposited by a melting ice sheet.

kettle- a vessel, usually made of metal and with a handle, used for boiling liquids or cooking foods; a pot.

drumlin- a low oval mound or small hill, typically one of a group, consisting of compacted boulder clay molded by past glacial action.

rock flour- finely powdered rock formed by glacial or other erosion.

erratics- not even or regular in pattern or movement; unpredictable : her breathing was erratic.

Esker- a long ridge of gravel and other sediment, typically having a winding course, deposited by meltwater from a retreating glacier or ice sheet.


Erosion and Deposition

Erosion- the process by which earth materials are moved by natural agents like water, wind, and ice.
Running Water
Running water is the most effective agent of erosion.
The sun is where running water gets its' energy.

Rocks are both weathered both Chemically and Physically by running water.
Physical
Abrasion - the rerm given to the use of sand, pebbles, and even boulders as cutting tools to grind away at the steam bed. during this process the "tools" themselves wear down.
Chemical - water dissolves soluble minerals.


Rivers carry rock material in three ways.
Solution-
this is material that is dissolved from the bedrock. most commonly found in solution are compounds of calcium and magnesium.
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.


Carrying Power
Carrying power is indicated by both the total amount sediment in a stream and by the size of the particles being moved.
The stream discharge and speed will determine the carrying power of the stream.*
Discharge- volume of water flowing past a given point at a given time
Speed- generally determined by the steepness, or gradient, of its bed.
- a stream moving at high speed with a high discharge can carry much larger sediments then a slow moving stream. Example: spring time snow melting and excessive rain.

The Rover Valley
Rivers tend to have a v-shaped valley because they tend to flow at high speeds and dig into the stream bed.
Base Level is the lowest level a river can cut into its bed.
-To form a permanent stream rain water must flow down a slope and dig deep to cut into the water table. this wearing away of the land to form a stream valley is called headward erosion.

V-SHAPED VALLEY ! VVVV
V-shapedvalley.jpg


visualizing -

v-shapedvalleys.gif



-A Divide is an area of high land that separates one river valley from another.
-On either side of a divide a river system may form.

Watershed is all of the land that drains into the river either directly or through its tributaries.

Waterfalls
Water flowing over a steep cliff will result in a waterfall. waterfalls are not permanent structures.
Undermining is the erosional 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 overhand. over time this overhand will collapse and the stream will move back towards its source.
waterfalls.jpg
diagram:
waterfall.jpg



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 with low precipitation.
-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 widened.
- a
Flood Plain is the widened valley floor area which will accumulate water during times of excess rain when the river floods.
river_dep.jpg

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 the fastest.
(cut bank)
- deposition is greater on the inside of the meander where the water flows slower.
(fill bank)

this is called an oxbow lake:
oxbow_lake.gif
Oxbow Lake- Meanders can only become so before they break through into another meander. the river then deposits mud and silt along the end of the abandoned meander. The now separated meander becomes a lake.

Running Water Deposits Well- Sorted particles
Vertical Sorting - when sediments are suddenly deposited into water. the particles separate by size with the largest on the bottom and smallest on the top.
Vertical_sorting.gif vertical.gif
the larger and rounder usually settle in to the bottom.


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.

horizontal.jpg the first particle to be deposited is going to be the largest one.

Delta: a fan-shaped deposit of sediment at the mouth of a river.


River Vocabulary

River Deposition- rivers deposit their bed load when they slow down. This can occur in these ways.
-slope of land decreases
-stream channel widens
-stream empties into a lake or ocean.
  1. A stream that flows year-round because its bed lies below the water table, or because more water is supplied from upstream than can infiltrate the
  2. A stream is a flowing body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics
  3. source - the fouintain head of a stream where water begines to folw
  4. mouth- the opening of a stream where it empties into another water body
  5. tribuatry- any stream that flows water to another stream
  6. watershed-an area or region drained by a river
  7. channel- the area of a valley occupied by running water
  8. valley- any low writing land bounded by higher ground
  9. meanders- a winding curve or bend of a river
  10. valley- any low writing land bounded by higher ground
  11. meanders- a winding curve or bend of a river