Weathering & Erosion

Earth’s Changing Surface Earth is a constantly changing body affected by natural forces: On the Inside: Plate Tectonics = moving of Earth’s Plates driven by convection currents Earthquakes & Volcanoes On the Outside: Weathering & Erosion

Weathering & Erosion Weathering is the process of breaking down or dissolving the earth’s rocks. Mechanical Weathering Chemical Weathering Erosion is the process of moving particles of rock from one locations to another. Water Glaciers Wind No rock is heard enough to resist the forces of weathering and erosion. Together they shape Earth’s topography.

Weathering The interaction of the lithosphere (rock) with the atmosphere (air) and hydrosphere (water) results in weathering. Driven by climate, combination of temperature and precipitation. Hot & humid = greater amount of weathering Cool & Dry = reduced amounts of weathering

Physical Weathering The type of weathering in which rock is slowly, mechanically broken down into smaller pieces. Changes the size and shape of the rock but not is composition. Factors: Freezing and Thawing Plant & Animal Actions Abrasions

Freezing and Thawing In colder climates, water seeps into cracks and freezes. The freezing water expands, making the crack bigger – frost action.

Growth of Plants As plants grow, their roots move into the cracks of rocks. As roots grow, cracks become larger. Roots grow into cracks and make them bigger.

Animal Actions As animals dig burrows in the ground they loosen and break apart rocks in the soil.

Abrasion Wind, water and ice carry smaller sand and rock particles that act like sandpaper on other rock surfaces. Glacial Abrasion Wind Abrasion

Chemical Weathering The process of weathering that changes the rock’s size, shape AND composition. Produces rock particles that have a different mineral makeup from the rock that it came from. Agents: Water Oxygen Carbon dioxide Acid rain

Water The universal solvent that dissolves substances, solutes, into solution. As a rock is covered by water, minerals leave the rock by dissolving out. Creates spaces in the rock that can weaken it and cause it to break apart.

Oxygen Oxygen reacts easily with other substances changing their properties. Oxygen (O) + Iron (Fe) = Iron oxide (Fe2O3), rust

Carbon Dioxide Does not contribute to chemical weathering until dissolved in water. Water (H2O) + Carbon Dioxide (CO2) = (H2CO3) carbonic acid Carbonic acid dissolves calcite, found in limestone. Causes caves and caverns; Howe Caverns

Acid Rain Acid rain comes mostly from the burning of coal by power plants in the Midwest. Sulfur oxides rise into the air combining with water to form sulfuric acid. Lowers the pH of water and bedrock killing off living organisms. pH of lemon juice

Soil Formation The formation of soil is a slow and complex process through the processes of weathering mixing with organic matter. Can be hundreds to thousands of years, 200-1200 years, in hard rock areas. Can takes less time, 20 years, in softer bedrock areas of shale and sandstone.

Soil Formation Partially weathered Rock Unweathered Rock Immature Soil Top Soil Top Soil Partially weathered Rock Subsoil Unweathered Rock Partially weathered Rock Unweathered Rock Unweathered Rock Immature Soil Mature Soil

Soil Horizons Horizons: O Horizon – organic material Decayed plants and animals, humus A Horizon – topsoil Humus, clay and minerals B Horizon – subsoil Clay but little humus C Horizon – bedrock Partly weathered rock

Soil Composition Soil – a mixture of rock particles (sand, silt and clay), minerals, decayed organic material (humus), air and water formed from weathered rock.

Soil Texture Soil texture depends on the size of individual soil particles that make it up. Gravel – 2mm and larger Sand – less than 2mm Silt – less than 1/16mm Clay - less than 1/256mm

Erosion The movement of rock particles from one location to another, Erosion, in a downhill motion toward their lowest possible location; sea level. Agents of Erosion: Water Glaciers Wind

Erosion by Water Water is always moving downhill due to the force of gravity. The greatest force of erosion. Wears down mountains to hills Carves out valleys Changes the direction of river flow.

Erosion by Glaciers Glaciers are formed from accumulated snow, compacted into ice and being pulled downhill by the force of gravity. Begin to form when snow reaches approximately 150ft in depth. Act as bulldozer, moving large amounts of rock and soil over time, till. Material deposited after a glacier stops moving, moraine.

Erosion by Wind A major force of physical weathering, wind is also a contributor to erosion. Creates and transports rock particles.