Erosion and Deposition Changing Earth’s Surface Chapter 7.1 Erosion and Deposition Changing Earth’s Surface

Erosion The process by which natural forces move weathered rock and soil from one place to another.

Sediment This is the material moved by erosion. Sediment may consist of pieces of rock or soil or the remains of plants and animals. Both weathering and erosion produce sediment.

Deposition Deposition occurs where the agents of erosion deposit (or lay down) the sediment. Deposition changes the shape of the land.

Weathering, erosion, and deposition act together in a cycle to wear down and build up Earth’s surface. Erosion and deposition are at work everywhere on Earth.

Gravity Gravity is the force that moves rocks and other materials downhill. Gravity causes Mass Movement. Types of mass movement include: Landslides Mudflows Slumps Creep

Landslides This is the most destructive of mass movement. Landslides occur when rock and soil slide quickly down a steep slope.

Mudflows This is the rapid downhill movement of a mixture of water, rock, and soil. The amount of water in a mudflow can be as high as 60%. Mudflows often occur after heavy rains in a normally dry area. They can be very dangerous.

Slump In a slump, a mass of rock and soil suddenly slips down a slope. The material in a slump moves down in one large mass. It often occurs when water soaks the bottom of soil that is rich in clay.

Creep Creep is the very slow movement downhill of rock and soil. Creep is so slow that you can barely notice it.

Section 7.2 Water Erosion

Moving water is the major agent of the erosion that has shaped Earth’s land surface.

Runoff As water moves over the land, it carries particles with it. The moving water is called runoff. Runoff is the water that moves over Earth’s surface.

Rills and Gullies As runoff travels, it forms tiny grooves in the soil called rills. As a rill moves into another, they grow larger, forming gullies. As water flows through gullies, it moves rocks and soil with it. This enlarges the gullies through erosion. Gullies contain water only after it rains.

Streams and Rivers Gullies join together to form a larger channel called a stream. A stream is a channel along which water is continually flowing down a slope. Small streams are also called creeks or brooks. As streams flow together, they form larger and larger bodies of flowing water. A large stream is often called a river.

Erosion by Rivers As a river flows from the mountains to the sea it can form a variety of features: Valleys Waterfalls Flood plains Meanders Oxbow lakes

Waterfalls As a river moves over harder rock, the softer rock moves away. The hard rock erodes slowly. The area where the softer rock has moved away creates a waterfall. Areas of rough water called rapids occurs where a river tumbles over hard rock.

Flood Plain Lower down on its course, a river usually flows over more gently sloping land. The river spreads out and erodes the land, forming a wide river valley. A flat, wide area along a river is called a flood plain. It can often overflow its banks during a flood.

Meanders A river often develops meanders where it flows through easily eroded rock or sediment. A meander is a loop-like bend in the course of a river.

Oxbow Lake Sometimes a meandering river sometimes forms a feature called an oxbow lake. An oxbow lake is a meander that has been cut off from the river…often due to floods.

Deposits by Rivers As water moves it carries sediment with it. It will then drop (or deposit) some of the sediment. As the water slows down, fine particles fall to the river bed. Larger stones quit rolling and sliding. This can create: Alluvial fans Deltas

Alluvial Fans An alluvial fan is a wide, sloping deposit of sediment formed where a stream leaves a mountain range. This deposit of sediment is shaped like a fan.

Deltas Sediment that deposits where a river flows into an ocean or lake builds up a landform called a Delta

Groundwater Erosion Sometimes water will soak through the ground. It fills the openings in the soil and trickles into cracks and spaces in layers of rock. Groundwater is the term that geologists use for this underground water.

Cave Formations Inside limestone caves, deposits called stalactites and stalagmites often form. A deposit that hangs like and icicle from the roof of a cave is know as a stalactite. Slow dripping builds up a cone-shaped stalagmite from the cave floor.

Karst Topography If the roof of a cave collapses because of the erosion of underlying limestone, the result is a depression called a sinkhole. This type of landscape is called karst topography after a region in Eastern Europe.