Running Water Flashcards
Talus
Eroded rock fragments that accumulate in a fan or cone shape at the bottom of a cliff
Landslide
Large mass of rock, soil, and water than moves down a hill all at once
Chief method of erosion
Running water: streams, rivers, creeks, rainwater, melting ice, etc.
Water both mechanically chemically wears down the rock or land and then carries particles way
How are lakes and ponds formed?
By intersection of the groundwater table and the surface. This can be a true water table or a perched water table sitting on an impermeable rock layer
How is a river system created? 5 stages
- rain flows downhill and forms gullies
- gullies deepen until they reach source of groundwater
- permanent stream is formed in the gully if the groundwater supplies water constantly
- networks of small streams combine to form a larger mainstream
- mainstreams combine to form a river system (like Mississippi River and its tributaries)
tributary
one of the branching streams that supply the mainstream of a river system
mouth of a river
the place into which a river empties; usually a large body of water (ocean or lake)
ex: the Hudson river’s mouth is at Manhattan and empties into NY Bay and then into Atlantic Ocean
watershed
entire land area drained by a river system
Abrasion
Mechanical erosion of bedrock by a stream or river. Pieces of rock are carried by the running water and rub against the bedrock, wearing it down bit by bit
River may erode rock by abrasion or by….
Chemical action
Compounds dissolved in streams may wear down rock by dissolving the minerals in the rock
4 factors that affect how fast a stream erodes its bed
- volume of water that flows past a point per unit time
- type of rock of which the bed is made
- substances being carried in stream
- speed of water
Why does a quickly moving river erode its bed fast?
It can carry large particles at a high speed, resulting in more power to wear down the river bed
Will a stream carrying small fragments of rock erode its bed slower or faster than one carrying large rocks?
Slower. smaller rock has less cutting power because force of collisions with the stream bed is less. Larger rocks with sharper edges erode faster.
Whick will erode more easily, a river bed made of shale or slate?
Shale is softer than slate and will erode more easily
4 occassions when a stream loses speed
- ground becomes less steep
- changes direction (rounds a bend)
- overflows the bank
- enters a lake that doesn’t have same forward flow
stream deposition
quantity of rock material left behind when a stream loses speed and is no longer able to carry as much rock
delta
Rock particles (sediment) collect and create a mass when a river slows down. A delta is formed at the mouth of a river as it flows into a larger body of water (lake, bay, ocean); has the shape of a triangle. Generally good area to grow cops, ie the Mississippi, Nile, and Niger deltas
Alluvial fan
Deposit of rock formed when a river flows from high in the mountains into flatter land. It has a triange shape, like a delta. Usually forms in arid areas where there is erratic rainfall and no rivers exist to carry away the sediment.
Levee
low wall formed on the banks of a river; created by deposits of material collected every time the river overflows its bank and the flow decreases
sandbar
deposit of material along inside bank of a river at a point where river curves. Caused by a slower water velocity at the inside part of curve
Qualities of a young river
- starts at high altitude
- flows quickly
- carries many loose rocks
- erodes a deep and narrow channel
- waterfalls and rapids are present
Ex: Colorado River
Qualities of a mature river
- eroded channel with few waterfalls in wide valley
- channel is wide
- slower speed of water
- carries fine grained sediment
- developing flood plain
Ex: Ohio River
Qualities of an old river
- flows slowly
- broad flood plain (flat river valley)
- high levees
Ex: lower part of Mississippi River
Meander
s-shaped curve found in a mature river
How is a meander formed?
Formed when the river flows around an obstruction, rather than eroding it
Flood plain
Materials carried by river are deposited in valley after flood. Eventually a large, flat area is formed. Flood plain can become a swamp if there is nowhere for flood water to drain
2 ways to form a waterfall
- Unequal erosion: rocks of different hardness make up the river bed; over time the soft rock erodes more quickly, leaving a drop (Yellowstone falls, Niagara Falls)
- Glacier cuts off a valley, leaving it hanging; the stream flowing in the hanging valley falls to the glaciated valley floor
