Week 7 PowerPoint Week 7 PowerPoint Lecture Lecture Objectives: Objectives: 4.01 Evaluate erosion and depositional 4.01 Evaluate erosion and depositional processes: processes: Formation of stream channels with respect to Formation of stream channels with respect to the work being done by the stream (i.e. down- the work being done by the stream (i.e. down- cutting, lateral erosion, and cutting, lateral erosion, and transportation). transportation). Nature and characteristics of sediments. Nature and characteristics of sediments. Effects on water quality Effects on water quality Effect of human choices on the rate of Effect of human choices on the rate of erosion. erosion.
Objectives:Objectives:4.01 Evaluate erosion and depositional 4.01 Evaluate erosion and depositional processes:processes:
Formation of stream channels with respect to Formation of stream channels with respect to the work being done by the stream (i.e. down-the work being done by the stream (i.e. down-cutting, lateral erosion, and transportation).cutting, lateral erosion, and transportation).
Nature and characteristics of sediments.Nature and characteristics of sediments. Effects on water qualityEffects on water quality Effect of human choices on the rate of erosion.Effect of human choices on the rate of erosion.
Groundwater and Groundwater and Chemical WeatheringChemical Weathering
As groundwater passes through permeable rock, As groundwater passes through permeable rock, minerals in the rock dissolve. The warmer the minerals in the rock dissolve. The warmer the rock is and the longer it is in contact with water, rock is and the longer it is in contact with water, the greater the amount of dissolved minerals in the greater the amount of dissolved minerals in the water.the water. Water that contains relatively high Water that contains relatively high
concentrations of dissolved minerals, concentrations of dissolved minerals, especially minerals rich in calcium, especially minerals rich in calcium, magnesium, and iron, is called magnesium, and iron, is called hard waterhard water..
Water that contains relatively low Water that contains relatively low concentrations of dissolved minerals is called concentrations of dissolved minerals is called soft watersoft water..
Results of Weathering Results of Weathering by Groundwaterby Groundwater
Watch this video to view Watch this video to view how caves form. Click on how caves form. Click on “How Caves Form” on the “How Caves Form” on the left side of your screen left side of your screen once you go to the website. once you go to the website. Use the information to Use the information to help with your worksheet. help with your worksheet. http://www.pbs.org/wgbh/nova/caves/form.html
Caverns - Caverns - a natural cavity a natural cavity that forms in rocks as a that forms in rocks as a result of the dissolution of result of the dissolution of minerals; also a large cave minerals; also a large cave that commonly contains that commonly contains many smaller, connecting many smaller, connecting chamberschambers
Results of Results of Weathering by Weathering by Groundwater, Groundwater,
continuedcontinuedStalactites and StalagmitesStalactites and Stalagmites
When water containing When water containing dissolved calcite drips from the dissolved calcite drips from the ceiling of a limestone cavern, ceiling of a limestone cavern, some of the calcite is deposited some of the calcite is deposited on the ceiling.on the ceiling.
As this calcite builds up, it As this calcite builds up, it forms a suspended, cone-forms a suspended, cone-shaped deposit called a shaped deposit called a stalactitestalactite. .
When drops of water fall on When drops of water fall on the cavern floor, calcite the cavern floor, calcite builds up to form an upward-builds up to form an upward-pointing cone called a pointing cone called a stalagmitestalagmite..
Results of Results of Weathering by Weathering by Groundwater, Groundwater,
continuedcontinuedSinkholes - Sinkholes - a a circular circular depression that depression that forms when rock forms when rock dissolves, when dissolves, when overlying sediment overlying sediment fills an existing fills an existing cavity, or when the cavity, or when the roof of an roof of an underground underground cavern or mine cavern or mine collapsescollapses
Results of Results of Weathering by Weathering by Groundwater, Groundwater,
continuedcontinuedNatural BridgesNatural Bridges
When the roof of a cavern collapses in several When the roof of a cavern collapses in several places, a relatively straight line of sinkholes places, a relatively straight line of sinkholes forms.forms.
The uncollapsed rock between each pair of The uncollapsed rock between each pair of sinkholes forms an arch of rock called a sinkholes forms an arch of rock called a natural natural bridge.bridge.
When a natural bridge first forms, it is thick, but When a natural bridge first forms, it is thick, but erosion causes the bridge to become thinner. erosion causes the bridge to become thinner.
Karst topography -Karst topography -a type of a type of irregular topography that is irregular topography that is characterized by caverns, characterized by caverns, sinkholes, and underground sinkholes, and underground drainage and that forms on drainage and that forms on limestone or other soluble rocklimestone or other soluble rock
Common features of karst Common features of karst topography include many closely topography include many closely spaced sinkholes and caverns.spaced sinkholes and caverns.
Generally, karst topography forms Generally, karst topography forms in regions where the climate is in regions where the climate is humid and where limestone humid and where limestone formations exist at or near the formations exist at or near the surface. surface.
Results of Weathering Results of Weathering by Groundwater, by Groundwater,
continuedcontinued
Parts of a River SystemParts of a River System
A river system is made up of a A river system is made up of a main stream and tributaries.main stream and tributaries. Tributary - Tributary - a stream that a stream that
flows into a lake or into a flows into a lake or into a larger streamlarger stream
Watershed - Watershed - the area of land that the area of land that is drained by a river systemis drained by a river system
The ridges or elevated regions The ridges or elevated regions that separate watersheds are that separate watersheds are calledcalled divides. divides.
Can you find the tributaries that Can you find the tributaries that are part of this watershed?are part of this watershed?
Can you identify the divide in Can you identify the divide in the diagram?the diagram?
Parts of a River System, Parts of a River System, continuedcontinued
The relatively narrow depression that a stream follows as The relatively narrow depression that a stream follows as it flows downhill is called its it flows downhill is called its channelchannel.. A stream channel gradually becomes wider and deeper as it A stream channel gradually becomes wider and deeper as it
erodes its banks and bed.erodes its banks and bed. River systems change continuously because of erosion.River systems change continuously because of erosion.
The edges of a stream channel that are above water level The edges of a stream channel that are above water level are called the stream’s are called the stream’s banksbanks..
The part of the stream channel that is below the water The part of the stream channel that is below the water level is called the stream’s level is called the stream’s bedbed..
Stages of a River SystemStages of a River System YouthfulYouthful
V-shaped valley with steep sidesV-shaped valley with steep sides Erodes beds faster than banksErodes beds faster than banks Most rapid water flowMost rapid water flow
MatureMature Less steep gradientLess steep gradient Erodes banks more than bedsErodes banks more than beds Meanders often formMeanders often form
OldOld Deposits sediment, does not eroseDeposits sediment, does not erose Broad, flat plain forms in river valleyBroad, flat plain forms in river valley Slowest water flowSlowest water flow
Click to view formation Click to view formation and evolution of a river:and evolution of a river: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/10_22_10_23.swf::Figs.%2010.22,%2010.23%20-%20Meander%20Cut-Offs%20and%20Oxbow%20Lakes
Channel ErosionChannel ErosionStream Load - Stream Load - materials other than the water materials other than the water
that are carried by a streamthat are carried by a stream1.1. The The suspended loadsuspended load consists of particles of consists of particles of
fine sand and silt. The velocity, or rate of fine sand and silt. The velocity, or rate of downstream travel, of the water keeps downstream travel, of the water keeps these particles suspended, so they do not these particles suspended, so they do not sink to the stream bed.sink to the stream bed.
2.2. The The bed loadbed load is made up of larger, coarser is made up of larger, coarser materials, such as coarse sand, gravel, materials, such as coarse sand, gravel, and pebbles. This material moves by and pebbles. This material moves by sliding and jumping along the bed.sliding and jumping along the bed.
3.3. The The dissolved loaddissolved load is mineral matter is mineral matter transported in liquid solution.transported in liquid solution.
Stream Discharge -Stream Discharge - volume of water volume of water that flows within a given timethat flows within a given time
The faster a stream flows, the higher The faster a stream flows, the higher its discharge and the greater the its discharge and the greater the load that the stream can carryload that the stream can carry..
Stream Gradient - Stream Gradient - the change the change in elevation over a given in elevation over a given distancedistance
Near the Near the headwatersheadwaters, or the , or the beginning of a stream, the beginning of a stream, the gradient generally is steep. gradient generally is steep. This area of the stream has a This area of the stream has a high velocity, which causes high velocity, which causes rapid channel erosion.rapid channel erosion.
As the stream nears its As the stream nears its mouthmouth, , where the stream enters a where the stream enters a larger body of water, its larger body of water, its gradient often becomes flatter. gradient often becomes flatter.
Evolution of River Evolution of River ChannelsChannels
Meandering Channel - Meandering Channel - one of the one of the bends, twists, or curves in a low-bends, twists, or curves in a low-gradient stream or rivergradient stream or river
When a river rounds a bend, the When a river rounds a bend, the velocity of the water on the outside of velocity of the water on the outside of the curve increase. However, on the the curve increase. However, on the inside of the curve, the velocity of the inside of the curve, the velocity of the water decreases.water decreases.
This decrease in velocity leads to the This decrease in velocity leads to the formation of a formation of a barbar of deposited of deposited sediment, such as sand or gravel.sediment, such as sand or gravel.
Evolution of River Evolution of River Channels, Channels, continuedcontinued
Meanders can become so Meanders can become so curved that they almost curved that they almost form a loop, separated by form a loop, separated by only a narrow neck of only a narrow neck of land.land.
When the river cuts across When the river cuts across this neck, the meander this neck, the meander can become isolated from can become isolated from the river, and an the river, and an oxbow oxbow lake lake forms. (See Sims forms. (See Sims Lake, Wedgeworth Lake to Lake, Wedgeworth Lake to right)right)
Evolution of River Evolution of River Channels, Channels, continuedcontinued
Braided stream - Braided stream - a stream a stream or river that is composed or river that is composed of multiple channels that of multiple channels that divide and rejoin around divide and rejoin around sediment barssediment bars
direct result of large direct result of large sediment load, sediment load, particularly when a particularly when a high percentage of the high percentage of the load is composed of load is composed of coarse sand and coarse sand and gravel.gravel.
can cause much can cause much erosion, affecting erosion, affecting water quality.water quality.
Deltas and Alluvial Fans Deltas and Alluvial Fans
Delta Delta a fan-shaped mass of rock material a fan-shaped mass of rock material deposited at the mouth of a streamdeposited at the mouth of a stream
Deltas form where streams flow into Deltas form where streams flow into the ocean at the edge of a continentthe ocean at the edge of a continent
A stream may deposit sediment on A stream may deposit sediment on land or in water.land or in water.
Alluvial fan Alluvial fan a fan-shaped mass of rock a fan-shaped mass of rock material deposited by a stream when material deposited by a stream when the slope of the land decreases the slope of the land decreases sharplysharply
Alluvial fans form when streams flow Alluvial fans form when streams flow from mountains to flat landfrom mountains to flat land
When a stream descends a steep slope When a stream descends a steep slope and reaches a flat plain, the speed of and reaches a flat plain, the speed of the stream suddenly decreases. As a the stream suddenly decreases. As a result, the stream deposits some of its result, the stream deposits some of its load on the level plain at the base of load on the level plain at the base of the slope.the slope.
Alluvial fans differ from deltas in that alluvial fans form on Alluvial fans differ from deltas in that alluvial fans form on land instead of being deposited in water.land instead of being deposited in water.
A floodplain A floodplain an area along a river that forms from sediments an area along a river that forms from sediments deposited when the river overflows its banksdeposited when the river overflows its banks The volume of water in nearly all streams varies depending The volume of water in nearly all streams varies depending
on the amount of rainfall and snowmelt in the watershed.on the amount of rainfall and snowmelt in the watershed.
When a stream overflows its banks and spreads out over the When a stream overflows its banks and spreads out over the floodplain, the stream loses velocity and deposits its coarser floodplain, the stream loses velocity and deposits its coarser sediment load along the banks of the channel.sediment load along the banks of the channel.
The accumulation of these deposits along the banks eventually The accumulation of these deposits along the banks eventually produces raised banks, called produces raised banks, called natural leveesnatural levees..
Finer sediments are carried farther out into the floodplains by Finer sediments are carried farther out into the floodplains by the flood waters and are deposited there.the flood waters and are deposited there.
A series of floods produces a thick layer of fine sediments, A series of floods produces a thick layer of fine sediments, which becomes a source of rich floodplain soils.which becomes a source of rich floodplain soils.
Floodplains
Human Impacts on Human Impacts on FloodingFlooding
Human Impacts on FloodingHuman Impacts on Flooding Vegetation, such as trees and grass, protects the Vegetation, such as trees and grass, protects the
ground surface from erosion by taking in much of ground surface from erosion by taking in much of the water that would otherwise run off. the water that would otherwise run off.
Logging and the clearing of land for agriculture or Logging and the clearing of land for agriculture or housing development can increase the volume and housing development can increase the volume and speed of runoff, which leads to more frequent speed of runoff, which leads to more frequent flooding.flooding.
Flood ControlFlood Control Indirect methods of flood control include forest and Indirect methods of flood control include forest and
soil conservation measures that prevent excess soil conservation measures that prevent excess runoff during periods of heavy rainfall.runoff during periods of heavy rainfall.
More-direct methods include the building of More-direct methods include the building of artificial structures that redirect the flow of water, artificial structures that redirect the flow of water, such as such as damsdams or or artificial leveesartificial levees..
Do you remember a recent natural disaster that Do you remember a recent natural disaster that resulted from failed levees? Hint: New Orleans, resulted from failed levees? Hint: New Orleans, LALA
BibliographyBibliographyPictures and information gathered from:
