RIVERS!!!!!!!! (and valleys)
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Transcript of RIVERS!!!!!!!! (and valleys)
RIVERS!!!!!!!!(and valleys)
Chapter 12 (page 39)
http://www.youtube.com/watch?v=Xtk_bqkfeyE
Because Bill Nye always makes things better…
A drainage basin (watershed, catchment) is a piece of land where water (rain and melting ice) drains into a larger body of water. Includes the streams, rivers and channels OPEN SYSTEM separated by divides
When water accumulates upland, and flows along a definite course, they are called streams
Small streams tributary streams
Tributary streams flow down and join together to connect to a river
Drainage Basins, Streams, Rivers
Drainage Basin
The hardness of the rock layers in the region determines the formation of certain drainage pattern that results
There are three types of drainage patterns
Types of drainage patterns
Most common pattern
Resembles vein or tree branch pattern
Forms on flat surfaces where the rock layers are of uniform hardness
Form in v-shaped valleys where many small tributaries join together and then join onto a main river, giving it the appearance of a tree
Drainage pattern #1: Dendritic
As a river flows down a valley, smaller tributaries flow into it from steep mountain slopes
Tributaries enter the main river at approximately 90 degree angles, causing a trellis-like appearance of the drainage system
Trellis drainage is characteristic of areas with alternating parallel valleys and ridges, and folded mountains
Drainage pattern #2: Trellis
The streams radiate equally outwards from a central high point
Volcanoes (as well as domes and laccoliths Cone-shaped mountains) usually display excellent radial drainage
Drainage pattern #3: Radial
Dry (arid) regions steep slope forms canyons
(vertical erosion) Wet regions gentle slope heavy sediments in
water
(vertical erosion)
River Valley shapes
Youth stage
Mature stage
Old age stage
Rejuvenated stage
http://www.youtube.com/watch?v=AjZLAw_lgZ4&feature=related
Four stages of a River development
River cuts a deep V-shaped valley (steep gradient)
Flows in highlands of mountainous areas with very little shifting of its channel
Usually small in size
Dominated by erosion fast, violent water little deposition
Little floodplain, but rapids, waterfalls, and boulders may be found
Stage #1: Youth Stage
Receives the waters of many tributaries River increases in size and slows in velocity more
deposition Eroded the bed downward and gotten closer to the base level Though it is still eroding downwards, it mainly erodes
laterally to form meanders and eventually flood plains
Stage #2: Mature Stage
Extensive meandering forms oxbow lakes
Its gradient and speed are very slow,
Because of this it has lost the power to erode downwards and carry as much sediment load deposits rich alluvium on the floodplain
http://www.igeography.ie/mature-stage.html
Stage #3: Old Age stage
River returns to the youthful stage
Vertical erosion creates v-shaped valley and process starts again
Stage #4: Rejuvenated stage
http://www.slideshare.net/Dannyoc/stages-of-a-river
The four stages
THIS SHOULD BE FAMILIAR!!!
Hydraulic action
Abrasion
Attrition
Corrosion
Erosional action of rivers (4 types)
THIS SHOULD BE FAMILIAR!!!
Solution Suspension Saltation Traction
http://library.thinkquest.org/28022/transport/index.html
Ways that rivers transport sediments
Rivers PART TWO!!
Steep gradient (steep slope)
Water flows swiftly with vertical erosion
Waterfalls occur where rocks have eroded quickly
Igneous rock wears out much slower than others (e.g. sedimentary rock)
Landforms associated with upland rivers
Potholes develop along river beds
Pebbles get trapped Water spins and
abrasion deepens the hole
Eventually a gorge or even a canyon may result (narrow slot in landscape)
Potholes, Gorges and Canyons
When the river has reached an elevation close to the sea level, a flood plain may result
Lateral erosion and energy
River can flow overflow and deposit rich alluvium (ideal for farming)
Landforms associated with lowland rivers
Erosion is greatest and fastest along the outer edge of a meander (bend)
Undercut bank (outer edge)
Point bar/ slip-off slope (inner bank)
Meanders, undercut banks and slip-off slopes
Levees: mounds of sediment that slowly build up along the river bank
Hold in flood waterNatural dikesCommon in valleys where
river cannot carry all of its load
• Dikes: artificial levees created to minimize flooding
Levees and dikes
Mississippi River floods of 1993
Lowland regions sometimes uplift and the meandering river begins vertical erosion again
Once uplifting stops and a flood plain is formed, lateral erosion is once again dominant
The old, uplift flood plain sits high above river banksThese ledges are called river terraces
Let’s draw it out!!!
River terraces
Sand and gravel “islands” may break up the water flow, so rivers take on a braided appearance
Transport large volumes of debris when deposited, creates sand bars and islands
Braided river channels
A river carries sediment from its drainage basin into the ocean
Current carries them into the ocean before they are deposited
Sand (heavy) silt clay (light)
Large rivers have broad deltas with shallow water extending far into the sea
Very gentle slopeWaves cannot erode as effectively
River deltas
Arcuate delta
Bird’s foot delta
Estuarine delta
LOOK ON PAGE 190 OF BLUE GEOGRAPHY BOOK FOR AWESOME ILLUSTRATIONS FO DELTAS AROUND THE WORLD!!!
3 main types of delta
Carries water and sediment across a symmetrical delta in distributaries
Inverted cone shape
EX. Nile River Delta
Arcuate delta
Many distributary channels branch out from main river channel
Bird’s foot shape
EX. Mississippi River Delta
Bird’s foot delta
Forms when river sediment is deposited in a submerged river mouth
Estuary shape
Estuarine delta