Erosion Test

Mass wasting

movement of rock and soil down slope due to gravity and poor slope stability

Mass wasting triggers

Excess water (most common), vibrations, increased weight, undercutting, human activities

USGS identifies unstable areas by

Existing landslides, on or at base of slopes, in or at base of drainage areas, on developed hillsides with septic systems

Regolith

Loose rocks and soil over bedrock

Creep

movement of regolith by freeze-thaw patterns; indicated by curved tree trunks, bent fences, retaining walls, small soil ripples/ridges

Solifluction

slow movement of saturated soil down slope above frozen ground; need permafrost underground and a large amount of water; sub-Arctic, Arctic, Antarctic locations

Slump

rock and soil layers move downslope along a concave plane; near rivers

Earthflow

water saturated soil (small particles) under sod moves downhill w/o tearing overlaying sod

Debris flow

rapid transport of sand and larger sized particles that have become partially or fully liquified; associated w/ recent fires

Landslide

movement of material down a straight, non-vertical plane

Debris slide

rock, wood, brush

Rock slide

Mostly rocks, especially bedrock

Rock and debris fall

Rock or debris fall through the air at near vertical angle

Talus

regolith at the base of a slope

Angle of repose

maximum steepness of particles before gravity pulls them down; caused by ice or root wedging

Lahar

volcanic mudflow that forms from rapidly melting snow or glaciers; triggered by volcanic eruption

Submarine landslide

transport sediment across the continental shelf (near shore) and into the deep ocean; can create a tsunami

Mudflow

mud or debris flow of pyroclastic material, rocky debris and water; often from melted glacier

Avalanche

snow slides downslope pulled by gravity

Human behaviors that cause mass wasting

Building roads and settlements in unstable places, carving out rock to build (steepens rock = more susceptible), mining (landslides), deforestation, septic systems or pools (adds water to soil), vibrations

Weathering

Disintegration or chemical alteration of rock at or near Earth’s surface (chem, biochem, mech)

Erosion

Grinding away and transportation of material by moving water, air, ice

Ice erosion

occurs from particles being picked up or incorporated by moving ice to transport downhill; freeze/thaw cycle

Air erosion

Picks up small particles temporarily and transports them to new locations

Deflation

transport of particles through the air

Abrasion

Wind transported particles sculpt features in the landscape

Water erosion

transports weathered materials from source to location where they are deposited

Rain splash erosion

particles are knocked into the air by a raindrop

Sheet erosion

loosened particles transported by runoff water down the slope of a surface

Rill erosion

Water concentrates during sheet erosion, causing rilled that can be tilled to remove

Badlands

areas where rills expand into permanent gullies

Alluvium

sediment move by water erosion

Alluvial fan

deposited, eroded material at an angle of repose

Groundwater

water contained underground within pores and crevices of soil, sediment, bedrock

Infiltration

Water entering groundwater soaks in and moves downward

Zone of moisture

top layer of soil the water soaks through; plants located here

Zone of aeration (unsaturated zone)

pore space includes water and air

Zone of saturation (groundwater zone)

pore space includes only water

Water table

boundary between the zone of saturation and the zone of aeration; level varies based on landscape, not a consistent level everywhere

Porosity

Percent of rock volume that is open space; ability to store water

Permeability

Ability of a rock to transmit fluids through connected spaces; ability to transport water

Aquifer

body of rock that stores and transmits water

Unconfined aquifer

has direct vertical connection between water table and atmosphere

Confined aquifer

Has no direct vertical connection between water table and atmosphere; sandwiched between confining beds

Aquitard

Either low porosity or permeability; doesn’t allow water to flow through

Spring

groundwater reentering the surface water system; natural outflow where water table intersects Earth’s surface

Subsidence

ground sinks down because water is no longer filling space

Cone of depression

rapid removal results in lowered area water table (groundwater normally moves slowly)

Stream

surface water flowing downhill between banks

Headwaters/source

small streams near water source; sediment is usually sand and gravel

Closer to source =

larger sediments

Delta/mouth

outlet of stream into ocean, lake, wetland; sediment deposits around the mouth can form a delta; very fine sediments

Channel

path a stream follows

Bank

boundary of a stream (steep valley sides)

Cut bank

outside edge of a bend where the bank is eroded

Point bar

inside edge of a bend with sand deposited

Thalweg

deepest part of a stream, usually has strongest current in a channel; high enough energy to cause erosion; closer to cut bank

Headwaters

steep sided, v shaped valley; waterfalls, rapids, limited floodplain

Transfer zone

merging streams create small rivers that have a floodplain and the river meanders

Depositional zone

large river with wide floodplain and many meanders, but not that deep

Sorting

particles separated based on density

Abrasion

rounding due to transport

As transport distance increases..

grain size decreases

Sedimentary basins

dissolved compounds transported from weathering sites to here

Meandering

a stream with many bends and sometimes oxbows

Oxbow

U-shaped bend in a river

Oxbow lake

U-shaped bend cut off from river; happens when a cut bank erodes enough to cut through and cut off extra bend; lots of tadpoles here b/c no predator fish

Levee

earthen wall parallel to waterway in the floodplain; keeps river within banks by slowing it down

Mill dam

use hydropower to spin a wheel on a mill

Hydroelectric dam

generate electricity by storing water in a reservoir, release it through turbines, and use resulting motion to spin a generator

Flood control dam

designed to hold and store water for flood control or irrigation

Glacier

snow that has accumulated, compacted, and recrystallized into glacial ice

Where glaciers can exist

At cold temperatures at any elevation, at warm temperatures only at a higher elevation

Continental glaciers

continuous mass of ice that covers large areas of land

Mountain glaciers

confined by surrounding mountain terrain, slowly moves downhill due to gravity

Ablation zone

where there is a net loss of ice from evaporation, melting, and breaking off

Accumulation zone

where snow accumulates into glacial ice

Internal flow

occurs because glacial ice is clastic and flows downslope

Basal sliding

occurs because gravity pulls the mass downslope (only in mountain glaciers)

Zone of fracture

top 46m of a glacier remain brittle and fracture

Crevasse

stress from plastic glacier moving below fractures the top

Glacial budget

advancing and retreating glaciers, keep track of snow coming in and snow leaving the glacier

Meander scar

scar-like depression in the floodplain where an oxbow lake was or will be

Yazoo stream

stream that runs parallel to the floodplain of a large river