GEO 303 Exam 3 Shanahan

erosion

the grinding away and removal of the Earth's surface

deposition

the accumulation of transported sediment

mass movements

downslope motion of rock, regolith (soil, sediment, and debris), snow, and ice

creep

slow, gradual downslope movement of regolith on a slope

solifluction

the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations

landslide

a slide of a large mass of dirt and rock down a mountain or cliff

rock glacier

a slow-moving mixture of rock fragments and ice

slump

a type of mass movement that occurs when a mass of material moves down a curved slope

failure surface

a weak surface that forms the base of a landslide

head scrap

the distinct step along the upslope edge of a slump where the regolith detached

mudflow

a downslope movement of mud at slow to moderate speed

debris flow

a mudflow with many large rocks

lahars

a thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano

rockslide/debris slide

a sudden downslope movement of rock (or of regolith)

snow avalanche

rapid downslope movement of snow, ice, and rock, typically transforms snow into a turbulent cloud

rock falls and debris falls

a mass of rock that separates from a cliff and free falls downslope

talus

a sloping apron of fallen rock along the base of a cliff

submarine slumps

the underwater downslope movement of a semicoherent block of sediment along a weak mud detachment

turbidity current

a submarine avalanche of sediment and water that speeds down a submarine slope

liquefication

the process by which an earthquake's violent movement suddenly turns loose soil into liquid mud

identifying regions at risk

head scarp, swampy low area, dead trees, sinking foundations, tight power lines, tilted poles, cracked roads, etc.

slope stability

gravity - driving force for movement

steeper slopes create a larger force imbalance

angle of repose

slope strength - weathing, vegetation cover, water content

preventing mass movements

trees - roots stabilize potential failure plane

terrace steps - remove load and catch debris

drainage - potential failure plan dries and becomes stronger

reducing undercutting

engineering structures - traps debris

hydrologic cycle

the cycle through which water in the hydrosphere moves; includes such processes as evaporation, precipitation, and surface and groundwater runoff

sheet wash

a film of water less than a few mm thick that covers the ground surface during heavy rains

runoff

water that flows over the ground surface rather than soaking into the ground

downcutting

the process in which water flowing through a channel cuts into the substrate and deepens the channel relative to its surroundings

headward erosion

the process by which a stream channel lengthens up its slope as the flow of water increases

tributaries

smaller streams and rivers that flow into a main river (trunk stream)

drainage network

an array of interconnecting streams that together drain an area

drainage basin/watershed

the region that collects water that feeds into a given drainage network

drainage divide

a highland or ridge that separates one drainage basin from another

gaining stream

the volume of water increases in the downstream direction

losing stream

the volume of water decreases in the downstream direction

permanent vs ephemeral stream

flow all year or only part of the year

all ephemeral streams are losing streams

hyporheic zone

region of saturated sediment next to a stream and immediately beneath it

stream discharge

the volume of water that passes through an imaginary cross section across a stream, generally increases downstream, controls amount of material a river can carry

stream velocity

the rate of flow (not the amount of water)

discharge and velocity are not equivalent

thawleg

the deepest part of the channel (usually highest current velocity)

turbulence

the chaotic twisting and swirling motion in flowing fluid

sediment transport

the material moved by streams is the sediment load

erosion in streams

streamflow does work - material carried by stream abrades channel

maximized during floods - high discharge and velocity

longitudinal profile of a stream

graph of the change in the stream's elevation beginning in its headwaters and ending in its base level

toward the mouth of the stream the gradient flattens, discharge increases, sediment grain sizes are smaller and channels develop broad meander belts

bars

a sheet or elongate lens or mound of alluvium

point bars

a wedge-shaped deposit of sediment on the inside bank of a meander

cut bank

the steep bank feature that forms on the outside of a river bank due to erosion

floodplain

flat land along a river that is prone to flooding

headwaters

high velocity = erosive = high competence

stream mouth

low velocity = depositional = low competence

base level

the lowest point to which a stream can erode

meandering streams

channels form intricately looping meanders along the lower gradient portion of the longitudinal profile

oxbow lake

a meander that has been cut off from the river

alluvial fan

a gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions

deltas

the triangle-shaped deposit of sand and sediment that occurs where a river flows into an ocean

delta classification

1. rivers - sediment delivery

2. waves - sediment redistribution

3. tides - sediment removal/erosion

bathymetry

variation in depth

passive continental margin

a continental margin that does not occur along a plate boundary, does not display seismicity

older, higher sediment supply

active continental margin

a continental margin that coincides with a plate boundary

younger, less sediment supply

abyssal plains

broad, relatively flat regions of the ocean that lie at a depth of about 4 to 5 km below sea level

Coriolis effect

the deflection of an objects, winds, and currents path due to the rotation of Earth

Ekman

the overall movement of a mass of water resulting from the Ekman spiral, in a direction 90 degrees to the wind direction

downwelling

places where near-surface water sinks

upwelling

places where deeper water rises

thermohaline circulation

an oceanic circulation pattern that drives the mixing of surface water and deep water

tides

the regular rise and fall of the ocean's surface influenced by the moon's gravity pulling on earth

water waves

driven by wind shear across the surface

wave refraction

bends the waves parallel to the beach due to the increases in velocity as water shallows

headland erosion

wave energy erodes protrusions into the open water, erosion works to straighten out an irregular shoreline

wave-cut notches and bences

gradually undercut cliff face

barrier island

a long ridge of sand or narrow island that lies parallel to the shore

examples of different kinds of coasts

estuaries, uplifted terraces, swampy delta, coast plains and offshore sandbars, glacial fjords, coastal sand dunes, coral reefs off a mangrove swamp

coastal stabilization techniques

groins - concrete walls protruding perpendicular to the shore

jetties - protect entrance to a harbor

breakwater - parallel to the beach to prevent full force waves reaching the harbor

groundwater

water in the Earth's subsurface filling the porous spaces in soils, sediments, and rocks

groundwater table

the depth at which all the pores in an interconnected geological unit are filled

primary vs secondary porosity

primary: consist of vesicles, relicts of air bubbles that were trapped during cooling

secondary: new pore space produced in rocks some time after the rock first formed

permeability

the degree to which a material allows fluids to pass through it via an interconnected network of pores and cracks

aquifers vs aquitards

sediments or rocks that have both high porosity and high permeability VS.

sediments or rocks that have low permeability

recharge area

a location where water enters the ground and infiltrates down to the water table

discharge area

a location where groundwater flows back up to the surface and may emerge at springs

hydraulic head

the potential energy available to drive the flow of a given volume of groundwater at a location

Darcy's Law

a mathematical equation stating that a volume of water, passing through a specified area of material at a given time, depends on the material's permeability and hydraulic gradient

springs

occur when the aquifer intersects the surface

land subsidence

the sinking or settling of land to a lower level in response to various natural and human-caused factors, wells

groundwater contamination

addition of chemicals or microbes to the groundwater supply

karst landscapes

a region underlain by caves in limestone bedrock; the collapse of the caves creates a landscape of sinkholes separated by higher topography, or of limestone spires separated by low areas

sink holes

a cavity in the ground in limestone bedrock, caused by water erosion and providing a route for surface water to disappear underground

hydrocarbons

a chain-like or ring-like molecule made of hydrogen and carbon atoms; petroleum and natural gas are hydrocarbons

crude oil

petroleum that has not been processed

diversity of hydrocarbon products

as the length of the molecule increases the viscosity increases

source of oil

plankton (microscopic plants and animals that live in the ocean)

mid-Mesozoic times

migration

liquid oil and gas will buoyantly migrate upwards

primary migration: movement out of the source rock to a more porous rock

secondary migration: movement through the carrier rock to a trap

reservoir rocks

ock with high porosity and permeability, so it can contain an abundant amount of easily accessible oil

hydrocarbon traps

a subsurface configuration of seal rocks and structures that keep oil or gas underground so it doesn't seep out of the surface

directional drilling

the process of controlling the trajectory of a drill bit to make sure that the drill hole goes exactly where desired

fracking

a process by which drillers generate new fractures or open preexisting ones underground

time scales of climate variation

climate varies on all timescales ranging from annual to tectonic

Snowball Earth

the hypothesis that glaciers covered the planet's land masses from pole to pole 750 to 570 million years ago

Earth's energy budget

the balance between the amount of energy coming in from the Sun and going back out into space

feedback loops (positive and negative)

positive feedback: a change causes a process to continue (amplify)

negative feedback: a change causes a process to stop (supress)

rock CO2 cycle

on tectonic timescales geology controls climate through changes in atmospheric CO2

weathering increases CO2 - supplies nutrients to oceans to stimulate productivity