Weathering and Erosion Notes Weathering is the breaking down of rocks and other materials on the earth’s surface Types of Weathering: 1. Physical or Mechanical Weathering– Breaks rocks into different shapes and smaller pieces. There is no change in the rocks chemical composition. o Agents of Physical Weathering: Temperature : Changes in temp. cause repeated expansion and contraction. Ice Wedging: when liquid water goes into cracks and then freezes causing the cracks to get wider. Biological activity (root-pry, burrowing animals, human activities) Unloading: The expanding of high pressure rock when exposed to a lower pressure rock 2. 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. Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid) Limestone and marble are the most affected types of rocks. Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock 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 --------------------------------------------------------------------------------------------------- Erosion is 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. Water Erosion: Liquid water is the most common type of erosion. Why? Streams, raindrops, waves Wind Erosion: Happens mainly in dry, windy climates. Ex: Deserts, the beach (sand dunes) 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. Gravity Erosion: Movement of particles on steep slopes because of the influence of gravity.