Mass Wasting

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Landscapes Fashioned by Water
Running Water
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Running Water

• Most important agent in modifying the Earths
  land surface
• 97 of Earths water in oceans, but constantly
  recycled by the hydrologic cycle of evaporation,
  transpiration, condensation, and precipitation
• 20 of all precipitation falls on land, with
  precipitation returning annually to the ocean via
  runoff, surface flow in rivers and streams

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Water Flow

• Water flows from slopes as laminar or turbulent
  flow
• Laminar flow lines of flow parallel one another,
  no mixing of layers, flow primarily in one
  direction, rare

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Water Flow

• Turbulent flow complex mixing occurs as water
  molecules move in all directions, most water flow
  is turbulent

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Runoff

• Runoff controlled by infiltration capacity, the
  ability of the surface to absorb water

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Downhill Flow

• Downhill flow causes erosion as water moves by
  sheet or channel flow-
• Sheet flow continuous sheet of shallow water
  moving over the surface

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Downhill Flow

• Channel flow flow confined to long, trough-like
  depressions described according to size rill,
  brook, creek, stream, river (fluvial channels)

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• Some water is supplied to streams and rivers via
  runoff, but most by groundwater, which is
  evidenced by continually running rivers in arid
  regions

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Measuring Running Water

• Gradient the downhill flow of a stream or river
  over a given distance defines its gradient, or
  vertical drop over horizontal distance (rise over
  run)

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Measuring Running Water

• Velocity the measurement of downstream water
  travel distance in a given time, expressed in
  m/sec or ft/sec

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Measuring Running Water

• Discharge a measurement of the amount of water
  passing a given point in a given period of time,
  expressed in cubic meters or feet per second

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Erosion

• Water modifies the surface via erosion and
  transport of sediments
• Erosion occurs as sediments are put into motion
  by hydraulic action, but also includes the
  abrasion of carried particles against the exposed
  rock
• Eroded particles are transported by running water
  and eventually deposited

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Particle Transport

• Transported particles are known as the load may
  include these types
• Dissolved load materials taken into solution by
  chemical weathering
• Solid load solid particles, includes
• Suspended load-small particles (clay and silt)
  suspended above the channel bed by turbulence
• Bed load-larger particles (sand and gravel to
  boulders) that cannot be kept in suspension by
  turbulence

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• Bed load is transported by saltation, the
  intermittent
• bouncing or skipping of particles along the
  stream
• channel, or traction, particles dragged or rolled
  
• along the bottom of the channel

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• Sediments deposited by running water are
  collectively known as alluvium, or alluvial
  deposits

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Types of Stream/River Channels

• Stream and river channels are characterized as
  meandering or braided
• Meandering stream consists of a single sinuous
  channel with looping curves known as meanders

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Meandering Stream

• The outside of a stream meander has greater
  velocity and produces a cut bank, while the
  inside of which has a point bar, where sediments
  are dropped by slower moving waters
• Oxbow lakes are produced as meanders are cut-off
  by the main channel

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Braided Stream

• Braided stream possess an intricate network of
  dividing and rejoining channels separated from
  one another by sand and gravel bars develop when
  sediment supply exceeds transport capacity

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Depositional Structures

• Floodplains form in flat-lying areas of the
  stream gradient as heavy rains cause the stream
  to overflow its banks these consist primarily of
  fine-grained sediments deposited from the
  suspended load (overbank deposits)
• Natural levees are produced along the edges of
  stream channels by overbank deposits

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Floodplain
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Natural Levees
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Depositional Structures

• Deltas fan shaped sedimentary structures
  produced as moving water flows into a standing
  body of water and drops sediments
• Alluvial fans produced when running water from
  highlands deposits alluvium on the plains below

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Drainage Basins

• A drainage basin is an area drained by a river or
  stream and all its tributaries
• Topographical highs separating drainage basins
  are know as divides (Continental Divide)

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Continental Divide
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Drainage Basins

• Drainage basins develop distinctive patterns
  based upon the composition, relief, and geologic
  structure of underlying rocks include
• Dendritic
• Parallel
• Trellis
• Radial

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Base Level

• Streams and rivers flow to base level, the lowest
  point to which they can erode ultimate base
  level is sea level, which can change and affect
  continental erosion rates

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Fluvial channels

• Valleys are created as runoff creates erosion and
  channels are incised within drainage basins
  valleys include gullies, canyons, and gorges
• Valleys also grow through headward erosion,
  lengthening at the upstream end of a channel
• Continued headward erosion may connect two
  channels and result in stream piracy, the
  diversion of part of a drainage basin into
  another stream

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Fluvial Channels

• Stream terraces are sometimes found along the
  margins of floodplains, and represent remnants of
  floodplain deposition during periods of higher
  flow or continued downcutting due to eustatic
  fluctuations
• Incised meanders form as channels cut into solid
  bedrock as underlying rocks are uplifted

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Stream Terraces