Weathering and Erosion

Objective: 2.1.3 I can explain how natural actions such as weathering, erosion (wind, water and gravity), and soil formation affect Earth’s surface.

What is Weathering? Is the breaking down and changing of rocks near Earth’s surface Two Types Mechanical Chemical

What is Mechanical Weathering? When physical forces break rock into smaller pieces Does not change the rock’s composition Three Ways Frost Wedging Unloading Biological Activity

Mechanical Weathering: Frost Wedging Water enters cracks and crevices in rocks Water freezes expanding the cracks Eventually breaking rocks into pieces

Mechanical Weathering: Unloading The uplift and weathering of rocks overlying igneous rocks Why? Pressure on igneous rocks is reduced causing uplift Exfoliation: slabs of outer rock separate and break loose

Mechanical Weathering: Biological Activity Activities of living organisms Example: Plant roots wedge into rocks, breaking them apart

What is Chemical Weathering? Is the transfer of rock into one or more new compounds

Agents of Chemical Weathering Water Most important agent Picks up gases from the atmosphere Oxygen Causes oxidation of metal minerals Ex: rusting Carbon Dioxide Combines with water in the atmosphere Causes acids to form like in acid rain

Chemical Weathering in Action Granite Minerals turns into clay Washed away with water Spheroidal Weathering Causes the corners and edges of rock to be rounded

Rate of Weathering What affects it? Rock Characteristics Mineral composition Mineral solubility Climate Temperature and moisture Favors high temperatures and abundant moisture

What is Soil? Part of the regolith that supports the growth of plants Layer of rock and mineral fragments that cover most of Earth’s land surface

How is Soil Formed? Weathering of rocks that is carried away Factors Parent Material Time Climate Organisms Slope

Soil Formation Factors Parent Material Source of the mineral matter in the soil Time Important in all geologic processes The longer a soil has been forming, the thicker it becomes

Organisms Climate Slope Furnish organic matter in soil Steep slopes often have poorly developed soils Climate Greatest effect on soil formation Influences of temperature and precipitation affect rate, depth and type of weathering

Characteristic of Soil: Soil Composition 45% mineral matter 25% air 25% water 5% humus Decayed remains of organisms

Characteristic of Soil: Soil Texture Refers to the proportions of different particle sizes Sand (large size) Silt (feels like flour) Clay (small size) Loam (mix of all three; best for plants)

Soil Texture Triangle 60 20 40 10 70 Percent Clay Percent Silt Percent Sand Texture Type 60 20 40 10 70

Characteristic of Soil: Soil Structure Clumping together of the particles

Soil Types Pedalfer Pedocal Laterite Forest areas Drier grasslands Hot, wet, tropical climates

What is Erosion? Removal and transport of weathered material from one location to another

Agents of Erosion Running Water Wind Glaciers Ocean currents and Waves Biological Organisms

What happens to the Material? Deposition Materials are dropped in another location Final stage of erosion

How does Water Erode Soil? Rain uses gravity as a force to move soil down a slope

Process of Water Erosion Sheet Erosion Thin surface of water moving soil particles Rills Tiny streams Gullies Trenches Each move the soil a small distance

What is a Glacier? Large, moving mass of ice that forms near Earth’s poles and in mountainous regions at high elevations

How do Glaciers Erode Soil? Scrape and gouge out large sections of landscape Can carry huge rocks and piles of debris over great distance

Landforms Created by Glaciers Glaciated Valley U-shaped valley Cirques Bowl-shaped depression at the head of a glaciated valley, that is surrounded on three sided by steep rock walls Arêtes Snaking ridge Horns Pyramid-like peaks

How does Wind Erode Soil? Strong in areas of little vegetation cover Picks up and carry sediment These particle batter other structures

Landscapes Shaped by Wind Sand Dunes Mounds or ridges of sand Wind also can cause them to move Loess Windblown silt that blankets the landscape

How can humans control erosion? Planting rows of trees called windbreakers Terracing hillsides Plowing along the contours of hills Rotating crops

Objective: 2.1.4 I can explain the probability of and preparation for geohazards such as landslides, earthquakes, tsunamis, sinkholes, groundwater pollution, and flooding.

What is Mass Movement? The transfer of rock and soil down-slope due to gravity

Triggers of Mass Movement Water Heavy rain and rapid snow melting saturate the surface Particles slid past one another easier Over-steepened Slopes The steeper the slope, the greater the chance for movement

Removal of Vegetation Earthquakes Roots keep soil intact Removing plants increase chances of movement and erosion Earthquakes Dislodge rocks and minerals

How to Classify Mass Movement? Classified by Kind of material the move How it Moves Speed of movement

Types of Mass Movement Rock falls Slides Slumps Flows Avalanches Creep Rockslides Landslides Slumps Flows Mudflow Earthflow Avalanches Creep

Rock falls When rock or rock fragments fall freely through the air

Slides A block of material moves suddenly along a flat, inclined surface Rockslides Include segments of bedrock Landslides Movement of relatively thin block of loose soil, rock and debris

Slumps Downward movement of block of material along a curve surface

Flows Containing a large amount of water which move downslope as a thick fluid Mudflow Swiftly moving mixture of mud and water Earthflow Moves relatively slow Carry clay-rich sediment

Extremely rapid movement of Earth material or snow Avalanches Extremely rapid movement of Earth material or snow

Creep Slow, downhill movement of soil Only noticeable over long period time Slowest type of mass movement

Preventive Actions Dig series of tranches to divert running water Constructing protective fences on highways Retaining walls for weak slopes Don’t build on steep slopes