slopes and streams

what are landforms controlled by

interactions of tectonics and climate

the role of rivers in erosion

rainwater falling on upland slopes provides potential energy that turns into kinetic energy that can detach rock/soil to carry it through a stream

base level

the level below which a river/stream cannot cut (ultimate base level is sea level)

erosive potential

depends on velocity and resistance to erosion

hydraulic action

work of water itself as it dislodges + drags bed material

abrasion

mechanical erosion by transport particles

corrosion

dissolution of minerals by water (limestone)

bedload

large particles that move along the bottom of a stream or river

suspended load

muddy water; sediment that stays floating within the water column because the water is moving so fast

dissolved load

minerals dissolved in water

transport capacity

max load of sediment that a stream can carry at a given discharge

competence

largest particle size that a stream can set in motion

what controls sediment yield?

• glaciers (southern alaska and Andes)

• volcanic belts (Sumatra/cascades)

• monsoon regions (Southeast Asia lots of rain lots of runoff)

• arid regions (low vegetation density→ erosion)

anthropogenic

human activities affect erosion rates and sediment yields (forest clearing, cultivation, dams, city construction)

rainsplash erosion

soil particles displaced/loosened because of rain impact

radial drainage pattern

develops mostly on volcanic cones

annular drainage pattern

develops on dorres

trellis drainage pattern

develops on parallel folding/dipping sedimentary rocks of different hardness

rectangular drainage pattern

forms where joints and faults dominate

dendritic drainage pattern

forms on extensive batholiths / flat lying sedimentary rocks

fluvial landforms

created directly by running water (meanders, cut banks and point bars)

alluvial landforms

formed by sediment deoposited in rivers (alluvial fans and deltas)

graded rivers

those which maintain balance between erosion and deposition

aggradation

occurs when sediment supply is greater than stream transport capacity : the stream is building up its bed

incision

occurs when transport capacity is greater than the sediment load : sediment is cutting into its bed

meandering river

single winding channel formed by low slope and fine sediment

entrenched meander

deeply carved meander canyon formed by incision and tectonic uplift

braided channel

many shallow formed by sediment and variable flow

floodplain

flat area next to river formed by overbank deposition

river terrace

abandoned floodplain above current river formed by incision

strath terrace

bedrock terrace formed by lateral erosion and incision

fill terrace

terrace made of sediment formed by aggradation