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What is Weathering? Weathering is
the breaking down of rocks and other materials on the earth’s surface
Two Types of weathering
1. Mechanical/Physical – Breaks rocks into different shapes and smaller pieces.
o There is no change in the rocks chemical composition.
Agents of mechanical weathering
Temperature : Changes in temp. cause repeated expansion and contraction.
Agents of mechanical weathering
Ice Wedging: when liquid water goes into cracks and then freezes causing the cracks to get wider.
A rock in Iceland that has been weathered by the freeze-thaw process.
Agents of mechanical weathering
Abrasion: Wearing away by solid particles. Happens when 2
rocks rub together
Wind Blown Sand
Agents of mechanical weathering
Unloading: The expanding of high pressure rock when exposed to a lower pressure rock
Sheeted Granite in Yosemite National Park. The granite is broken into gently plates by unloading joints. This happens as the rock is exposed by erosion. These joints provide pathways for water to enter the rock.
Chemical weathering
The altering of the composition of minerals within a rock that results in a reduction in size.
Agents of chemical weathering
Water: Dissolves minerals in rocks, making them weaker.
Agents of chemical weathering
Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid)
Limestone and marble are the most affected types of rocks.
Acidic Water has dissolved the limestone on the statue.
This marble tombstone in New Orleans has been weathering by acid rain.
Lichens, a moss like plant that grows on rocks, can produce weak acids that react with the rock, causing weathering.
Agents of chemical weathering
Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock
Oxidation turned these rocks in Nevada's Valley of Fire red.
Factors that determine the rate of weathering
Composition: What the rock is made of
Physical condition of rock: Cracks, holes, crevices – easier weathering
Solid, unbroken – more weather resistant
Factors that determine the rate of weathering
Climate: Cold Climates: mechanical weathering
breaks down rocks rapidly Warm, wet Climates: chemical weathering
breaks down rocks rapidly Topography:
The position of the rock. Air Pollution:
Amount of time rock was exposed. Surface area that was exposed.
Erosion
The movement of weathered particles from one location to another, where it is deposited.
The 4 main agents of erosion are: Water, Wind, Gravity, and Ice.
Ice erosion
Moving ice, in the form of glaciers, changes the surface of the Earth.
Glaciers are the most powerful form of erosion, but the least common.
Deposition
The process by which material is laid down or dropped.
Water, wind, ice and gravity all move the sediments (erosion).
Eventually, the energy is lost and this movement slows down. When the sediments no longer move, they are deposited.
Objects with more mass will settle faster than objects with less mass.
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