Weathering and Erosion Unit 9

Weathering Sediments- rock particles that are carried by wind and water. Weathering- chemical and physical breakdown of rocks. Occurs when rocks are exposed to the environment.

Types of Weathering Chemical- results in a change in mineral or chemical composition. EX. Iron exposed to oxygen produces rust. Water can also dissolve most rocks, acids enhance this process. Physical- breakdown of rocks into smaller rocks, no change in composition. Abrasion- rock grinding on rock.

Factors Effecting the Rate and Type of Weathering Exposure- rate and type of weathering depends on exposure, generally the closer to the surface the greater the exposure. Particle Size- smaller particles weather faster. Mineral Composition- diff. minerals have diff. chemical properties. EX. Calcite in limestone and marble dissolve in acidic water, quartz does not.

More Factors Climate- chemical weathering is most pronounced in warm, moist climates. the more warm and moist the more weathering. In cold climates frost action is most common form of weathering.

Soil Formation Soil is a mixture of rock particles and organic matter on the Earth’s surface. Living things play a significant role in soil formation. EX. Ants burrowing exposes rock to environment, plant roots widen cracks in rocks, plants drop leaves that decay which produces acid that dissolves rocks.

Soil Formation Can form in place from parent material Can also be transported from another area. Usually by wind, water, or glaciers. Most soils in NY were transported by glaciers.

Erosion Weathering of rock, producing particles that are transported.

Transporting Systems Agent of erosion- stream, glacier, wave, current, wind, or human activity Sediments need to be moved by a driving force. gravity is the most common driving force. Everything is being pulled towards Earth. Sun. Drives water cycle.

Gravity Erosion Mass movement- the pull of gravity on rocks and sediments downhill. 2 major opposing forces- gravity and friction. EX. The ground is saturated and friction can no longer “hold on to” the soil or ground. Movements can be slow or fast.

Running Water Erosion Most common Begins with rain drops- rain storms create a thin sheet of water that runs on top of the ground, eventually forms a temporary stream or gully. Stream- water flowing through a channel. Tributary- water that flows into a larger stream or river.

Running Water Erosion… Streams carry sediments in different ways, depends on _____. Dissolved minerals are carried in solution Solid sediments (small) suspended in the water Solid sediments (large) bounce, roll, slide along the bottom All of these cause abrasion. This rounds the sediments. Speed of stream determines what particles do.

Running Water Erosion Over time, streams carve deeper channels. V-shaped valley forms. Watershed- area of land drained by the river.

Stream Velocity 3 factors: Gradient Discharge Stream Channel Shape - large flat = slower - semicircular = fastest

Stream Velocity… H2O does NOT flow at equal velocities throughout the stream When the stream changes direction the area with the greatest speed changes: straight, fastest in middle Curved, outside of curve is fastest

Stream Evolution Early stages - most energy is used to downcut a narrow V-shaped valley, usually a steep slope. Downstream tributaries flow into the stream making it larger. As it gets larger it starts to bend or meander. This movement side to side widens the valley. When there are floods the river deposits sediment and the area is known as a flood plain.

Evolution… At the mouth discharge is often great with little slope. Here, the valley is the flood plain. Frequent flooding causes mounds of deposits to form on the banks of the river, called levees.

Wind Erosion Arid regions, and lake or ocean coasts are common places for wind erosion. Two main types: deflation and abrasion (sandblasting) Deflation - small, loose sediments are blown by the wind until there is no more loose sand. This results in desert pavement. Sandblasting- sand is blown against rocks or other hard surfaces.

Glacial Erosion Naturally formed mass of ice and snow that moves downhill. Form in high mountain valleys. If more snow accumulates than evaporates than a glacier can form and advance.

Movement Plastic flow. Acts like a fluid, moves a lot like a stream. Middle of a valley glacier is moving fastest. Also move fastest at top and slowest at bottom.

Types of Erosion When a glacier moves, loose rocks and other materials are swept up and frozen into the ice. These sediments act like sandpaper. Produce- glacial grooves, glacial parallel scratches. Most sediments are carried on top.

Glacial Erosion Often fragments can be the size of a small house. Sediments can be carried hundreds of miles and differ from the local bedrock. These are called erratics. Create U-shaped valleys. Horns, Bowl-shaped basins, waterfalls, and fan-shaped deposits are formed by glaciers.

Wave and Current Erosion When waves reach shallow water they start to drag along the bottom. This forms a breaking wave. Wave action can erode a beach into a cliff. Waves usually hit the shore at an angle, causing a longshore current. Can carry sediment parallel to shore. As water from the shore flows back to the sea it flows down hill, creating a zig-zag path.

Sediment Features Tell Us Where They Come From Each agent of erosion produces distinctive characteristics of the sediments it carries. Wind, beach, and stream erosion- sediments become rounded,smooth, and smaller. Glacial- partly rounded, scratches of various sizes and directions Gravity or physical weathering- very angular.