Presentation on theme: "Weathering, Erosion, and Soil What type of rock is this, how can you tell?"— Presentation transcript:
Weathering, Erosion, and Soil What type of rock is this, how can you tell?
Yosemite Valley, California Mountains Carved by Glaciers
Grand Canyon, Arizona Carved out by the Colorado River
Bryce Canyon, Utah Acidic Rainfall has worn away these rocks. The harder rocks remain standing… but for how long?
Weathering Process by which rocks are broken down due to exposure to processes occurring at the Earth’s surface Caused by –Water –Waves –Wind –Gravity –Glaciers The 2 G’s and the 3 W’s
2 Types of Weathering A. Mechanical Weathering also called Physical weathering –Rock is broken down into smaller pieces of the same material –( no change in composition) B. Chemical Weathering –The breakdown or decomposition of rock that occurs when minerals are changed into different substances –( change in composition)
Mechanical/Physical Weathering 1.Frost (Ice) Wedging –Process in which water freezes in the cracks of rock and wedges (pushes) it apart because water expands when it freezes. –Occurs where there are frequent freezes and thaws.
Chemical Weathering –The breakdown or decomposition of rock that occurs when minerals are changed into different substances –( change in composition) Involves Water,water vapor, Acids, and/or Oxygen O2O2O2O2
Chemical Weathering 1.Hydrolysis Carbonic Acid in water dissolves Calcite. This chemical weathering can hollow out underground Caverns Carbonic Acid in water dissolves Calcite. This chemical weathering can hollow out underground Caverns Limestone and Dolomite both dissolve because they contain Calcite
Acid rain (carbonic acid) weathering the details of statues and tombstones Ex: Marble and Limestone
Chemical Weathering 2.Oxidation Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide. Oxidation of minerals with iron (magnetite, pyrite) results in the formation of rust or iron oxide. This is why Mars is the red planet This is why Mars is the red planet Copper turns rocks green Copper turns rocks green
Rate of Weathering How fast a rock weathers depends on 3 factors : –Surface area –Rock composition –Climate
Rate of Weathering Surface area –The greater the surface area, the faster the weathering rate –There are more surfaces to be weathered
Rate of Weathering Rock composition –Some minerals are more resistant than others –For example, quartz is more resistant (harder) than calcite QuartzCalcite
Rate of Weathering Climate (long term pattern of moisture and temperature) –Weathering rates are faster in warm, wet climates Desert vs. Rainforest
Erosion –The removal and transport of weathered materials by natural agents such as –Caused by 1.Glaciers 2.Running water 3.Gravity 4.Wind 5.Waves
Glaciers Mass of compacted ice and snow that moves under its own weight
Glaciers reducedFriction at the base of the glacier is reduced by a thin film of melt water. fresh water on EarthGlaciers account for about 75% of the fresh water on Earth
Glaciers can leave behind large boulders that are known as an erratic
Glaciers Glaciers can move lots of sediment that can carve striations (grooves) into rocks These Striations show how glaciers moved
Glacial Deposits Drift or Till - all sediment that is deposited by glacial activity –Loess: fine powder, pulverized rock, that blankets much of the northern mid-west –Moraine: ridge or pile of boulders, gravel, sand, and silt left at the end of a glacier Esker: type of outwash that accumulates in the channels and tunnels of a glacier
Glacial Landforms Cirque –Steep-walled bowl- shaped depression Horne : a pyramid shaped peak where 3 or more cirques meet
Glacial Landforms Trough –U -shaped valley, Glaciers carve U shaped valleys
Glacial Landforms Hanging valley –Straight drop-off at the end of a trough Arete –Narrow flat-topped ridge that forms between two parallel troughs or cirques
Glacial Landforms Moraine : Pile of mixed sediments that have been carried and dropped by the glacier
Glacial Landforms Eskers -Mounds of rock from melt tunnels
Streams and Rivers Velocity - How fast the water moves Gradient - The steepness, the slope that a river or stream travels Discharge - The amount of water that moves past a certain point in a river in a given amount of time If there is a steep gradient, high velocity, and a large discharge, then Erosion will be severe! Rivers have energy to move lots of sediment, and even large boulders.
River stages affect: Velocity, Gradient, & discharge which cause Erosion
Seven Bends of the Shenandoah Is the Shenandoah and old river or a young river? River meanders Bends in the river, shows how mature a river is.
Erosion-Mass Movement The downward transportation of weathered materials by gravity Massive Landslide
Erosion-Mass Movement Creep Slump Mudflow/Earthflow Landslide/Rockslide
Erosion-Mass Movement: A large mass of sediment drops down!
Erosion-Mass Movement Creep –Very slow movement of earth material. –Caused by repeated freezing and thawing. Sediments are loosened by expanding frost and contracting thaw. Leaning fence posts and telephone poles are a sign of Creep.
Erosion-Mass Movement Mudflow/Earthflow –Thick pastes of sediments that travel downhill at great speeds Usually occur in dry areas that get a large quantity of rain all at once Leaves a cone shaped deposit
Mudflow in the Blue Ridge Mooreman’s Gap near Charlottesville
Erosion-Mass Movement Landslide/Rockslide –Fast movement of large blocks of rock Occurs in very steep vertical cliffs Accelerated by ice wedging
At the bottom of an old rock slide in N.C. 2011
Wave Erosion The crashing of waves on a shoreline combined with storms continually shape the beach. This is a shoreline with erosion.
Where soil forms Residual soil –The parent rock is the bedrock beneath the soil (the soil has not moved ) Transported soil –Soil forms from parent material left by winds, rivers, glaciers, or soil that was moved from its original location. This soil has been transported by erosion and deposition
Factors that affect Soil Composition Parent material: What bedrock is it from? Time: How long has it had to decompose? Plants and animals: How have roots and animals helped break up the rocks? Were there acid producing mosses that help break down the rocks (chemical weathering)? Topography: What is the shape of the landscape? Climate: Is it warm & wet? Were there glaciers present? Was there acid rain?
Soil Profile Cross section of soil layers revealing all soil horizons
Soil Horizon differentA soil layer with physical and chemical properties that are different from adjacent layers O Horizon= organic material (humus) A Horizon = topsoil B Horizon = subsoil C Horizon = partially weathered parent material
Idealized Soil Profile Humus: Dark organic matter in soil that is rich in nutrients.
Leaching: The removal of nutrients or toxins in soil as water passes through the layers.
Particle size ranges for sand, silt and clay Type of Mineral Particle Size Range Sand 2.0 - 0.06 millimeters Silt 0.06 - 0.002 millimeters Clay less than 0.002 millimeters Large/ Coarse Medium Small/ Fine