McKnight's Physical Geography Chapter 15 Preliminaries to Erosion: Weathering and Mass Wasting Modified by AJ Allred for Geography 1000 Salt Lake Community College Original by Andrew Mercer Mississippi State University © 2014 Pearson Education, Inc.

Learning Goals of Chapter 15 Define denudation, weathering, mass wasting, and erosion. Differentiate between mechanical, chemical, and biotic weathering. Explain frost wedging, salt wedging, temperature changes, exfoliation, angle of repose, and oxidation. Identify mass wasting, glaciation, landslide, slump, earthflow, mudflow, creep and solifluction.

The sun uses water & gravity to wear down landforms Weathering Mass wasting Erosion

Weathering and Rock Openings Notice how water gradually opens joints by gravity flow, freeze/expansion and chemically dissolving rocks.

More examples of weathering into joints

Weathering Agents Oxygen, carbon dioxide, and water Temperature changes – freeze/thaw, expand/contract Water penetration in bedrock openings Biotic agents Burrowing and/or plant roots Chemical alteration Three principal categories Mechanical Chemical Biotic

Weathering Agents Mechanical Weathering Frost wedging Physical disintegration of rock without changes to its chemical composition Frost wedging Freeze–thaw action of water Ice wedges downward in openings Ice melts and water falls farther into larger opening Process repeats Frost shattering

Weathering Agents Salt wedging Temperature changes Salt left behind from evaporated water collects and pries apart rock openings Temperature changes Diurnal and seasonal temperature fluctuations modify volumes slightly Fracturing of rock over long time scales

Weathering Agents Exfoliation Other mechanical weathering processes Curved layers peel off of bedrock Exfoliation dome Unloading through erosion Hydration Other mechanical weathering processes Chemical and biotic impacts on mechanical weathering

Biological Weathering Agents Plant roots break apart rocks, and may also hold soils together. Burrowing animals promote water entry and chemical change to soil and rock Lichens slowly consumes rock, turning it into soil and dust.

Mass Wasting

Mass Wasting Fall Rockfall Talus/Scree Uniform accumulation of rockfall material – talus apron Material tends to collect in cone shaped heaps – talus cones Talus cones grow up the mountain Slow talus flow in glaciers – rock glaciers

Slumping – semi-wet material

Very wet soil can flow

Slow Creep Walls, poles, head stones and other structures slowly move downhill over many years.