Surface Water Stream landscapes, erosion and deposition

The Water Cycle Water constantly moves among the oceans, the atmosphere and on land. This unending circulation of Earth’s water supply is the water cycle. Evaporation- liquid water to water vapor Precipitation- water vapor to liquid water Infiltration- water absorbed by land (soil, cracks in rocks) Runoff- water flowing over land

Erosion Erosion is the transport of weathered material Caused by water, wind or glaciers.

Gravity The root cause of all erosion Materials falling downhill are called Mass Movements Examples Landslides Avalanches mud flow rock fall

RUNNING WATER The most common agent of erosion on Earth’s surface Streams or water flowing over the ground pick up and move material. These particles weather rocks from abrasion

Stream Formation Run-off is the flow of water over the ground Run-off results in the formation of streams Streams that flow into other streams are called tributaries

Stream velocity Velocity is fastest at the top center Slowest near the stream bed Velocity is fastest at the outside of a turn Results in rapid erosion and carves out the deepest part of stream

Meanders As a stream flows across the flood plain, it meanders, or curves back and forth This is caused by erosion over time.

Point bar- deposition occurs on the inside of the curve where flow slows down Cut bank- erosion occurs on the outside of the curve where flow is fastest

Oxbow lakes When a meander gets extreme it will erode back on itself and form an oxbow lake

Carrying Capacity Particle size How much material a stream can carry relates to the velocity (speed) of water. Particle size Higher velocity = larger sediment can be carried down stream As the stream slows, it deposits larger particles.

Page 6 ESRT

Stream Velocity…(see page 6 of ESRT) As stream velocity increases, the volume and size of sediments being carried increases. Volume and particle size Velocity of stream

Conversely, as stream velocity decreases, the settling rate increases. Incoming stream with sediments Coarse gravel Finer sand Finer silt Finest clay

STOP!

River Deposition Deposition is the laying down of weathered and eroded sediments (bits and pieces of larger rock masses). Occurs when velocity of the erosional agent (water, wind, glaciers) decreases Most deposition occurs in bodies of water.

River deposits Deltas - triangular fan shaped deposits that develop as a stream or river flows into a larger body of water Alluvial fans – same kind of deposits but on land

GLACIAL EROSION As a large mass of ice (at least 100 ft thick) moves downhill, from gravity, it picks up rock material. The material grinds against and scratches the underlying rock. This is called abrasion. There are two types of glaciers, valley glaciers and ice sheets

This is a valley glacier, which flows like a stream, down hill.

V U Streams cut V-shaped valleys due to downward erosion Glaciers cut U-shaped valleys due to sideways erosion

http://www.youtube.com/watch?v=FIn0UoeDyVg

YOSEMITE VALLEY, California

Deposition by Glaciers As a glacier retreats (ice melts), it drops all the material in and on it. Note: the glacier never moves backwards, the front just melts back. A variety of deposits are left behind, some are sorted and some are unsorted.

GLACIER animation