geol assignment
hahhah
Chapter 9
Rivers and Flooding
Dr. Joao Santos
Chapter 9
Rivers and Flooding
Dr. Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Stream Flow � Streams – Ribbons of water that flow down channels.
� Runoff – Water in motion over the land surface.
� Stream runoff is crucial for humans.
� Drinking water.
� Transportation.
� Waste disposal.
� Recreation.
� Commerce.
� Irrigation.
� Energy.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Stream Flow � Stream runoff also causes many problems.
� Flooding destroys lives and property.
� Stream runoff also causes many problems.
� Flooding destroys lives and property.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Stream Flow � Stream runoff is an important geologic agent.
� Flowing water…
�Erodes, transports, and deposits sediments.
�Sculpts landscapes.
�Transfers mass from continents to ocean basins.
� Earth: Only planet in the solar system with flowing water.
� Without flowing water, Earth might resemble Mars.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
The Hydrologic Cycle � Stream runoff is a component of the hydrologic cycle.
� Hydrologic cycle processes.
� Evaporation.
� Transpiration.
� Precipitation.
� Infiltration.
� Runoff.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Forming Streams � Streamflow begins as water is added to the surface.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Forming Streams � Streamflow begins as moving sheetwash.
� Thin surface layer of water.
� Moves down the steepest slope.
� Erodes substrate.
� Sheetwash erosion
creates tiny rill channels.
� Rills coalesce, deepen,
and downcut into channels.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Forming Streams � Intense scouring marks entry into the channel.
� Rapid erosion lengthens the channel upslope.
� This process is called headward erosion.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Forming Streams � Over time, nearby channels merge.
� Smaller tributaries join a larger trunk stream.
� The array of linked channels is a drainage network.
� Drainage networks change over time.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Networks � Drainage networks often form geometric patterns.
� These patterns reflect underlying geology.
� Common drainage patterns.
� Dendritic – Branching, “treelike” due to uniform material.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Networks � Common drainage patterns.
� Radial – From a point uplift (mesa, volcano, etc.)
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Networks � Common drainage patterns.
� Rectangular – Controlled by jointed rocks.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Networks � Common drainage patterns.
� Trellis – Alternating resistant and weak rocks.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Networks � Common drainage patterns.
� Parallel – Streams developed on a uniform slope.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Basins � Land areas that drain into a specific trunk stream.
� Also known as catchments or watersheds.
� Divides are uplands that separate drainage basins.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Divides
� Watersheds exist in a variety of scales.
� Tiny tributaries.
� Continental rivers.
� Large watersheds…
� Feed large rivers.
� Section continents.
� Continental divides separate flow to different oceans.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Permanent vs. Ephemeral
� Permanent streams
� Water flows all year.
� At or below water table.
� Humid or temperate.
�Sufficient rainfall.
�Lower evaporation.
� Seasonal discharge
variation.
� Ephemeral Streams
� Do not flow all year.
� Above the water table.
� Dry climates.
�Low rainfall.
�High evaporation.
� Flow mostly during rare
flash floods.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
� The amount water flowing in a channel.
� Volume of water passing a point per unit time.
�Cubic feet per second (ft3/s or cfs).
�Cubic meters per second (m3/s).
� Given by cross-sectional area times flow velocity.
� Varies seasonally due to precipitation and runoff.
Discharge
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Discharge � Velocity is not uniform in all areas of a channel.
� Friction slows water along channel edges. Friction is…
�Greater in wider, shallower streams.
�Lesser in narrower, deeper streams.
� In straight channels, highest velocity is in the center.
� Few natural channels are straight.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Discharge � Velocity is not uniform in all areas of a channel.
� In curved channels, max. velocity traces the outside curve.
�The outside curve is preferentially scoured and deepened.
�The deepest part of the channel is called the thalweg.
�Flow around curved channels follows a spiral path.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Discharge � Velocity is not uniform in all areas of a channel.
� Stream flow is characteristically turbulent.
�Chaotic and erratic.
�Abundant mixing.
�Swirling eddies.
�High velocity.
� Turbulence caused by…
� Flow obstructions.
� Shear in water.
� Turbulent eddies scour
the channel bed.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Erosional Processes � Erosional processes – Streamflow does work.
� The energy imparted to streamflow is derived from gravity.
� Streams do work by converting potential to kinetic energy.
� Erosion is maximized during floods.
� Large water volumes.
� High water velocities.
� Abundant sediment.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Erosional Processes � Streams scour, break, abrade, and dissolve material.
� Scouring – Running water picks up sediment and moves it.
� Breaking and lifting – The force of moving water can…
�Break chunks of rock off of the channel.
�Lift rocks off of the channel bottom.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Erosional Processes � Abrasion – Sediment grains in flow “sandblast” rocks.
�Bedrock exposed in channels is often polished smooth.
�Gravel swirled by turbulent eddies drills holes in bedrock.
�These bowl-shaped depressions are called potholes.
�Potholes are often intricately sculpted.
� Dissolution – Mineral matter dissolves in water.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Sediment Transport � The material moved by streams is the sediment load.
� There are 3 types of load.
� Dissolved load – Ions from mineral weathering.
� Suspended load – Fine particles (silt and clay) in the flow.
� Bed load – Larger particles roll, slide and bounce along.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Sediment Transport � Sediment transport changes with discharge.
� High discharge – Large cobbles and boulders may move.
� Low discharge – Large clasts are stranded.
� Competence – The maximum size transported.
� Capacity – The maximum load transported.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Sediment Deposition � When velocity decreases so does competence.
� Sediment grains drop out; water sorts them by size.
�Gravel settles in channels.
�Sands are removed from the gravels; muds from both.
�Sands drop out in near channel environments.
�Silts and clays are suspended only to settle in slack water.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Sediment Deposition � Fluvial sediments are called alluvium.
� Channels may be decorated with mid-channel bars.
� Sands build up the point bars inside meander bends.
� Muds are deposited away from the channel during floods.
� A stream builds a sediment delta upon entering a lake.
Point Bar
Meander
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Longitudinal Changes � The character of a stream changes with flow distance.
� In profile, the gradient describes a concave-up curve.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Longitudinal Changes � The character of a stream changes with flow distance.
� Near the headwater source of the stream…
�Gradient is steep.
�Discharge is low.
�Sediments are coarse.
�Channels are straight and rocky.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Longitudinal Changes � The character of a stream changes with flow distance.
� Toward the mouth…
�Gradient flattens.
�Discharge increases.
�Grain-sizes are smaller.
�Channels describe broad meander belts.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Base Level � The lowest point to which a stream can erode.
� Ultimate base level is defined by the position of sea level.
�Streams cannot erode below sea level.
� A lake serves as a local (or temporary) base level.
� Base level changes cause stream re-adjustments.
�Raising base level results in an increase in deposition.
�Lowering base level accelerates erosion.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Base Level � The lowest point to which a stream can erode.
� A ledge of resistant rock may define the local base level.
� Erosive forces act to slowly remove the resistant layer.
�This acts to restore the longitudinal profile.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Fluvial Landforms: Valleys and Canyons
� Land far above base level is subject to downcutting.
� Rapid downcutting creates an eroded trough.
� Canyon – Steep trough sidewalls form cliffs.
� Valley – Gently sloping trough sidewalls define a V-shape.
� Determined by rate of erosion vs. strength of rocks.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Valleys and Canyons � Stratigraphic variation often yields a stair step profile.
� Strong rocks yield vertical cliffs.
� Weak rocks produce sloped walls.
� Geologic processes stack strong and weak rocks.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Valleys and Canyons � Active downcutting flushes sediment out of channels.
� Valleys store sediment when base level is raised.
� Renewed incision creates stream terraces.
� Terraces mark former floodplains.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Rapids � Rapids are turbulent water with a rough surface.
� Rapids reflect geologic control.
� Flow over resistant bedrock steps.
� Flow over large clasts.
� Abrupt narrowing of a channel.
� Sudden increase in gradient.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Waterfalls � Streams that cascade or free-fall.
� Waterfall energy scours a plunge pool at the base.
� Basal erosion initiates collapse of overlying rocks.
� Waterfalls are temporary base levels.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Waterfalls � Niagara Falls – Lake Erie drops 55 m to Lake Ontario.
� Dolostone caprock is resistant; underlying shale erodes.
� Blocks of unsupported dolostone collapse and fall.
� Niagara Falls continuously erodes south toward Lake Erie.
� Erosion since deglaciation has formed Niagara Gorge.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Waterfalls � Niagara Falls.
� Diversion of American Falls revealed huge blocks of rock.
� The rate of waterfall retreat is presently 0.5 m/yr.
� Lake Erie will drain when the Falls reach it.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Alluvial Fans � Alluvial fans build at the base of a mountain front.
� Sediments rapidly dropped near the stream source.
� Coarsest material found near the stream source.
� Sediments are fine and thin away from canyon stream.
� Sediments create a conical, fan-shaped structure.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Braided Streams � Form where channels are choked by sediment.
� Flow is forced around sediment obstructions.
� Diverging – converging flow creates sand and gravel bars.
� Bars are unstable, rapidly forming, and being eroded away.
� Flow occupies multiple channels across a valley.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Channels can form intricately looping curves…
� Along the lower portion of the profile with a low gradient.
� Where streams travel over a broad floodplain.
� When substrates are soft and easily eroded.
� Meanders increase the volume of water in the stream.
� Meanders evolve.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Meanders change from variation in thalweg position.
� Maximum velocity swings back and forth across flow.
� Fast water erodes one stream bank.
� The opposite bank collects sediment.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Erosion accentuates the cut bank.
� High-velocity flow scours the outside of the meander bend.
� Collapsed cut-bank material is transported away.
� Deposition builds the point bar.
� Sediment accumulates inside the meander bend.
� Continued addition expands the point bar laterally.
Cut-Bank Point Bar
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Meanders become more sinuous with time.
� The cut bank erodes; the point bar accretes.
� Meander curves become more pronounced.
� Meanders elongate.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Meander sinuosity increases until the meander is cut off.
� Cut banks converge and a meander neck thins.
� During flooding, high-velocity flow saws through the neck.
� The meander cut-off forms an oxbow lake.
� The oxbow fills with sediment, leaving an arcuate scar.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Meandering Streams � Occupy only a small part of the floodplain.
� Floodplains are typically bounded by eroded bluffs.
� During floods, the floodplain may be immersed.
� Natural levees form ridges parallel to the channel.
� Made of sand dropped as floodwaters jump from channel.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Deltas � Deltas form when a stream enters standing water.
� Current slows and loses competence; sediments drop out.
� Stream divides into a fan of small distributaries.
� Shape due to the interplay of flow, waves, and tides.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Deltas � Distinct lobes preserve past Mississippi Delta history.
� The river periodically switches course via avulsion.
� River breaks through a levee upstream.
� Establishes a shorter, steeper path to the Gulf of Mexico.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Deltas � Abandoned delta lobes are sediment-starved.
� Sediments deposited before avulsion slowly subside.
� Compaction, dewatering, and decay of organic matter.
� Lack of sediment nourishment.
� Abandoned delta lobes are eventually submerged.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Deltas � Subsidence is a problem for cities built on deltas.
� Lack of regular flooding leads to sediment starvation.
� Subsidence below sea level magnifies flood risks.
�New Orleans is an example.
�Other cities also face this threat.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Evolution
� Landscapes evolve over time.
� Streamflow is the cause of most landscape changes.
� Example:
� Uplift sets a new base level.
� Stream cuts into former surface.
� Valleys widen; hills erode.
� Landscape eroded to base level.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Evolution � Stream rejuvenation is initiated by base level drop.
� Meanders initially develop on a gentle gradient.
� Uplift raises the landscape or base level falls.
� The river chainsaws downward
creating incised meanders.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Evolution
� Stream Piracy.
� A stream captures another’s flow.
� One stream, with more vigorous
headward erosion (a steeper
gradient), intercepts a neighbor.
� The captured stream flows into the
new stream.
� Below the point of capture, the old
stream dries up.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Evolution � Superposed streams.
� Incises deformed terrain, yet ignores underlying structure.
�Streams initially develop in younger, flat-lying strata.
�The stream then chainsaws into the older underlying rocks.
�Stream maintains the geometry developed at an earlier time.
Edited by Joao Santos
Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 14: The Geology of Streams and FloodsChapter 14: The Geology of Streams and Floods
Drainage Evolution
� Antecedent streams.
� Tectonic uplift may raise ground
beneath established streams.
� If erosion keeps pace with uplift, the
stream will cut through the uplift.
� If the rate of uplift exceeds erosion, the
stream is diverted by the range.
Edited by Joao Santos
© 2012 Pearson Education, Inc.
End of Chapter 9