ESS 230 Midterm

Mechanical Weathering Processes (PEWTS)

Pressure release (Exfoliation); Water freeze/thaw cycles; Thermal Expansion; Salt crystallization

Chemical Weathering Processes (HHOOS)

Hydration, Hydrolysis, Oxidation, Organic activity, Solution

Mechanical Weathering

No change in chemical composition; material breaks down into smaller pieces

Rates of Weathering Influenced by

Moisture, Surface Area, Temperature

Factors in Eroding Landscape Rates (CVLLT)

Climate-precipitation, Topography, Vegetation, Lithology, Land Use

Soil Creep

Gradual downslope movement of weathered material by gravity

Overland Flow

When enough flow accumulates to overcome erosion resistance of ground surface- Precipitation rate>infiltration rate

Landslides

downslope movement of soil/rock due to gravity; can be slow or rapid

Debris Flows

Type of landslide, high water content, rapid

Glacier Erosion

scours bedrock, picks up sediment and moves it; rapid, depends on glacier size, precipitation rate

~10mm/yr

River Incision

Carve into bedrock, slow erosion process

<.01 mm - 1 mm yr

Bank Erosion

recycles materials stored on valley bottom, typically in floodplain, delivered by other erosion processes

Joint

Crack in rock

Fault

Crack in earth

Soil

solid earth material weathered by physical, chemical, and organic processes, so it can support plant life

Mainstem

Main, thickest river

Hillslope

Unchannelized land surface

Discharge

All water moving thru cross section of river in given amount of time: width x av depth x velocity, m3/s

Factors of Soil Formation (COPTT)

Climate, Organisms, Parent Material, Topography, Time

Humic acids

Produced by plants and animals; effective chemical weathering agent

Elluviation

leaching by infiltrating water

Illuviation

deposition and accumulation of materials from higher levels of soil

O layer

humus

A layer

zone of leaching soluble salts

Weathering

The disintegration or breakdown of rock materials

Chemical Weathering

Breakdown as a result of chemical reactions

Bicarbonate Ion

dominant ion in surface runoff

Biological Weathering

Weathering by plant/animals, can be mechanical or chemical

B layer

zone of accumulation of salts

C layer

Weathered parent material

Aridisols

arid zone soil; physically weathered rock- not much plant life

Mollisols

grassland soils; decomposed organic material and soil material

Oxisols

tropical soils; oxidized

Continental Crust

thick, granite, not so dense

Oceanic Crust

thin, basalt, dense

Continental plate collison

high mountain ranges form

Oceanic plate collision

island arc and submarine trench form

Oceanic-continental plate collision

mountains and trench form

Subduction

when ocean crust is carried down into mantle following collision; sediment and basalt heated to form magma

Mid Ocean Ridges

underwater mountain ranges, 2k-4k m deep

Abyssal Basins

4k-6k m deep, include abyssal hills and plains

Continental Margin

created by sediment from land that builds into ocean basins when rifting occurs, 10% of land

Continental Shelf

gently dipping, land surface when tide is out, glacial ice melted and flooded this portion of land

Continental Slope

steep, edge of continental crust, eroded by sediment, has underwater canyons

Continental Rise

gentle gradient, sediment from land piled onto ocean crust. 10% of ocean floor. between slope & plain

Submarine Fan

formed thru sediment accumulating at base of submarine canyon

Trailing Edge (passive) Margin

same direction of both plates, coastal plane, broad shelf, slope, and rise

Collision (active) Margin

oceanic-continental plates collide, coastal mountain range/volcanoes, earthquakes, steep shelf, slope, and submarine trench

Lithogenic Sediment

from disintegration of rock on land, dominant near continental shelf slope & rise

Biogenic Sediment

Dissolved materials become solid, causing biogenic oozes; made up of microscopic single celled plants and animals; include calcium carbonate (limestone) and silicon dioxide (opal)

Authigenic Sediment

dissolved inorganic materials become sediment, sea water supersaturated with some chemicals (magnese nodules, red clay)

Cosmogenic Sediment

From outside earth (meteorites)

Milankovitch cycles- earth orbits

main reason for sea level changes over thousands of years

Glacial Rebound

inc in sea level resulting from continental crust rising after weight of glacier disappears after melting

Delta Subsidence

changes in sea level; when delta falls below sea level due to lack of sediment

Turbidity Currents

occur during low sea level; underwater landslide, earthquake triggers, moving sediment down continental slope and creating underwater canyons thru erosion

Transgressive sand layer

relic deposits of old sand beach

Sedimentation during high sea level

estuaries/fjords filled and deltas formed, sediment can only escape to shelf, or to slope if on collision margin

World water in rivers

.0001%, 3% of water on land

Runoff

Precipitation - (evaporation +infiltration)

Watershed/drainage basin

portion of landmass where runoff goes into a specific stream, separated by drainage divides, usually mountain ridges

Drainage Divide

separates watersheds

Tributaries

Any smaller stream that feed larger streams w/in watershed

Base Level

physical lower limit to river incision (gradient of 0)

If base level goes up, caused by deposition

down, caused by erosion/incision

River

flows downslope along a clearly defined passageway, transporting a load of sediment

Channel

Passageway that river runs down

Gradient units

m/km

Cross Sectional Area

wxd, m2- all increase with downstream evolution as opposed to the slope

Load units

kg/m3

Downstream evolution

Inc in: discharge, velocity, width, depth; Dec in: slope

Flood

Discharge so great that it exceeds capacity of channel and overflows banks

Dissolved load

dissolved ions, finest clay particles & depends on rocks being weathered into river

Suspended load

sediment fine enough to remain in suspension: silt and clay; size depends on velocity + turbulence

Occurs when turbulent upward currents exceed the “settling” velocity of silt and clay particles

Bed Load

Sediment rolling and bouncing along riverbed, 5-20% of sediment; sand, gravel, and boulders

Saltation

Series of short, intermittent jumps by bedload

Estuary

semi-enclosed coastal environment where saltwater and freshwater mix

Delta

sedimentary deposit at mouth of a river causes coastline to protrude into ocean

evolve from estuaries

more sediment supply than removal

Little Sediment supply

estuaries and fjord filling, trapping mechanisms important

Moderate Supply

some estuaries fill, sediment leaks into shelf

Large Sediment supply

Deltas built seaward (Mississippi)

Coastal plain estuary

drowned river valley

Fjord

estuary w/ glacial origin, deep w/ shallow sill near mouth

Bar-built Estuary

sand spit or barrier island encloses embayment

Tectonic Estuary

dropped down basin, near ocean, seawater floods basin (Sao Fran)

Consolidation

How much water has been removed from between particles

Salt Wedge

landward bottom current of salt water in esturine circulation

saltwater moving inward to replace saltwater being expelled

Halocline

freshwater-saltwater boundary (denser saltwater is underneath)

Fjord Circulation

Sill causes little circulation: little oxygen present and marine life dies

Flocculation

formation of aggregates from individual silt and clay particles

Turbidity

sediment in suspension

Turbidity Maximum

when fluvial and esturine suspended particles meet at halocline, where most particles are deposited into bed

To Form a Delta, Sediment Supply must overcome (STECH)

Slow sea level rise, tectonic subsidence, erosion, consolidation, human removal of ground water

Most common location for Delta

Where sediment enters protected body of water

Topset

Freshwater swamps, brackish water marshes

Sediment accumulation is controlled by rise of sea level

Land surface sinks from consolidation of mud underlying

Lobe of Maximum Sedimentation

depression filled w/ sediment, river switches to another location

Sill

shallow area separating basins of two bodies of water

Central basin

largest volume

Southern basin

largest shoreline

Whidbey Basin

largest tidelands

River Salinity

0 ppt