Erosion – the carrying away of weathered rock by gravity, water, wind, and ice Running Water Wind Ice

Gravity Erosion: mass movements of materials down hill Soil creep (slow, 1 cm/year) Debris flow (slow to fast, mm/day – km/hr) Mud flow (fast, 1-5 km/hr) Rock fall (very fast, >4 km/hr)

SOIL CREEP

Rock Fall

Rock fall

Most erosion is caused by water moving across the Earth’s surface (runoff) Random runoff – this is rain water that runs down any exposed slope and often produces gullying

RECALL: What factors favor runoff? 1. slope 2. lack of vegetation 3. low permeability 4. saturated ground

Classic gullying in the Badlands Badlands National Park (South Dakota) Notice the many gullies

Similar gullying in Bryce Canyon in Utah

Organized runoff – this is water that moves through a series of developed channels until it eventually reaches the ocean. Also referred to as a drainage pattern. Random runoff –produces gullying The area drained by a river and its tributaries is called a WATERSHED or DRAINAGE BASIN

Organized runoff This is the Mississippi River drainage basin or WATERSHED Every location in green, drains into the Mississippi River ^ ^ ^ ^ ^ ^ ^ ^ Continental Divide The small rivers are tributaries of the Mississippi River

Which way is the river flowing? Which are the tributaries?

Grand Canyon from space

Rivers and streams can be grouped into 3 stages of development Young Mature Old

Summary of Young Stream 1.Mostly erode down 2. High velocity, steep gradient 3. Characterized by rapids and waterfalls 4. Narrow and carve a “V” shaped valley 5. Straight unless forced to curve by topography 6. canyons may form

Streams start out high in the mountains as young streams

These young mountain steams have a high velocity and can move even large boulders

Their velocity and eroding power grows as smaller streams join the main stream

Young rivers often carve “V” shaped valleys

The young stage usually produces a “V” shaped valley

Waterfalls and rapids are common In this stage

When a young river cuts through a plateau, a canyon is created Grand Canyon

Velocity of any stream is determined by: 1. Gradient or slope of land 2. Volume of water in stream Glacier Nat. Park Streams usually flow fastest In spring, why?

Rivers and streams transport rock and sediment in 3 ways suspension Rolling and tumbling solution Abrasion causes rocks in a stream to become rounded