Unit 4: Gradational Processes Ms. Thind Running Water Unit 4: Gradational Processes Ms. Thind

Running Water Today we will: Identify the processes associated with running water AND Identify the erosional and depositional features associated with running water

Drainage Patterns As rivers erode the landscape a certain drainage pattern begins to take shape. A definite determining factor in the formation of a drainage pattern is the hardness of rock layers in a region.

Drainage Patterns There are four main types of drainage patterns: 1. Dendritic 2. Trellis 3. Radial

Dendritic Most common Resembles the veins of a leaf Pattern found in areas where rock layers are of uniform hardness

Trellis In areas where folding and tilting of rock layers confine rivers to parallel valleys that meet a larger stream at right angles.

Radial Occurs on cone-shaped mountains (volcanoes) Water will flow away from the high point of equally in all directions

Typical Drainage Patterns Note: Have a look at the landscape in which these drainage patterns occur and the direction of running water.

Name that drainage pattern:

Four stages of river development: Youth Stage: cuts a deep V-shaped valley as fast moving water transports material downstream. Rivers are dominated by erosion as turbulent water allows little deposition to occur. Features: rapids, waterfalls, various boulders along river bed.

Four stages of river development 2. Mature Stage: Definite drainage pattern evident in watershed. Vertical erosion continues but downstream lateral erosion of banks is evident as meanders and flood plain start to take shape. Velocity of flow slows and deposition of river sediment is common.

Four stages of development 3. Old age stage: Flood plain that developed in mature stage continues to widen and meanders widen. River can cut across meanders to create oxbow lakes. Natural levees develop along river banks as materials get deposited by flooding. River delta is well developed and can continue to grow each year as sediment is flushed down from the highland regions.

Four stages of development 4. Rejuvenated stage: Land has undergone a slow uplifting and the river has returned to a period of vertical erosion like the youthful stage and a deep v shaped valley takes shape. River continues to cut through flood plain that was created in old age stage and continues vertical erosion until elevation is close to sea level again. Once elevation has been reduced lateral and vertical erosion take place = new flood plain.

Erosion action by rivers Hydraulic action: Force of water has great power. Material is worked loose from banks and river bed then carried downstream and deposited in lower regions where water flow diminishes. Greater the velocity the greater the erosion

Erosion action by rivers Abrasion: Debris and sand have an abrasive effect on river banks and river beds. Rocks look polished by the abrasive power of the river’s load. Attrition: When water moves fast, rocks of varying sizes are moved along by the river and they repeatedly strike other rocks  breakup of rock into smaller pieces.

Erosion action by rivers Corrosion: Rivers are mildly acidic and some rocks are dissolved in water and transported.

Transporting Sediment: Solution: Suspension: Saltation: Traction:

Unit 4: Gradational Processes Ms. Thind Running Water Part II Unit 4: Gradational Processes Ms. Thind

Let’s Review… 1) Identify the form of erosion where rocks repeatedly strike other rocks. 2) This form of erosion dissolves rock and is transported by the river. 3) This feature includes the building of alluvium deposits. 4) _______________ is when very heavy rocks drag along the river bottom. 5) Identify the process of rocks bouncing and rolling off other rocks along river bottom.

River Landforms Waterfalls Rapids Flood plains Levees Meanders Oxbow Lakes Undercut/point bar

Today we look at… Potholes Gorges/Canyons River Terraces Braided Rivers Sand bars Deltas

Pothole A deep abraded hole in a riverbed created by pebbles caught in a circulating hole.

How potholes are formed Regions with volcanic origin have many waterfalls that cascade over igneous rock of varying hardness. As water moves along, a pothole may form along a river bed where pebbles can become trapped in a small depression. Power of water spins these pebbles around and abrasive action deepens the hole.

Gorges/Canyons When vertical erosion is rapidly occurring, a river may form a deep, narrow slot through the landscape known as a gorge or canyon.

River Terraces Uplifting of land occurs a river must again begin vertical erosion and a gorge is cut through the original flood plain. The old uplifted flood plain is known as a terrace.

Braided Rivers Some rivers take on a braided appearance with many sand and gravel islands splitting up the water flow  braided rivers. They transport large volumes of debris and deposit it along the river channel to create sand bars and islands.

River Deltas A river carries sediment from its drainage basin toward the sea and much of it is deposited on the flood plain when the stream slows down. The deposits form river deltas. There are 3 main types of deltas: arcuate, bird’s foot, and estuarine.

Arcuate delta Has many distributaries that carry water and sediment across a symmetrical delta Shape of an inverted cone

Bird’s food delta Has many distributary channels that branch out from the main river channel Bird’s foot appearance

Estuarine delta Forms when river sediment is deposited in a submerged river mouth. Grows in shape of estuary.

Erosional or Depositional Landform? V Shaped Valley Waterfall Levees Delta Gorge Sandbars