geology exam 3

isotasy

the state of gravitational equilibrium between earth’s crust and mantle where the crust floats.

pratt theory

same mass of different densities

airy theory

blocks of same density with different masses

asthenosphere

allows for motion of lithosphere

flexural istoasy

mantle material subsides and uplifts occur with high viscosity

accretion

when continental crust is nonsubductable and enters a subduction zone at edge of continent

cratons

low elevation regions of continents with long term stability

soil

nonrenewable product holding groundwater and providing the foundation of construction

bedrock

large, continuous occurrences of solid rock

regolith

all unconsolidated rocks and organic material on top of bedrock

soil horizons

o,a,e,b,c

O horizon

decomposing organic matter and plant growth

A horizon

organic matter mixed with minerals and rock fragments

E horizon

organic matter depleted in oxides, clay and weathered material

B horizon

horizon of accumulation with a wide range of textures, oxides and hydroxides.

C horizon

least weathered material mainly regolith that resembles parent rock

formation of soil

chemical weathering, subtraction and addition of minerals and organic matter

landscape relief

use of soil maturity to determine landscape stability

sediment disposition

contains thick and immature soils

forest soil

thick A and O horizons

rainforest soil

most intense weathering oxidizing and low fertility

wetland soil

O and A horizons only with saturated water and low oxidation

desert soil

dry climate with calcite common in the B horizon

agriculture activities

disturb soil by plowing and reshaping the land

shallow gullies

response to heavy rainfall before planting crops

terracing

decreasing spread of overland waterflow on steep slopes which in turn decreases erosion

mass movement

downslope movements of rock, regolith and soil due to gravity

free fall

material detaches from slope and falls

talus slope

loose material that piles at base of steep slope

planar slope

moves downslope in contact with surface of rupture

slump

rupture surface caves un, slide mass rotates as it moves downslope causing rock layers and surface to tilt

foliation

describes planes of minerals formed in response to stress of metamorphism

flows

continuous movement of rock, regolith or both that behave like high viscosity liquid

creep

slow and detected by dissociation or bending of features at surface

debris avalanches

very rapid flows of rock, regolith, vegetation or ice

increasing slope

favors motion and slope instability

for motion to occur gravity must be greater than resisting strength

smoother surface

favors motion and slope instability

friction and cohesion are resisting forces of gravity

presence of water

favors motion and slope instability

water creates weight and breaks particles due to it being soluble

angle of repose

maximum angle of a stable slope as determined by friction cohesion and particle shape

hazard maps

indicate areas susceptible to future mass movements

GIS

computer software capable of connecting, storing, retrieving and manipulating data

drainage basin

area that drains into a stream

discharge

amount of water that flows through a channel

rock erosion

particles loosened by weathering that is picked up in surface runoff and transported into a stream

sediment load

delivery of sediment to a stream from drainage basin and climate

dissolved load

ions from chemical weathering carried by water to streams

bedload

large grains that cannot be picked up but still move like roll, slide or bounce

suspended load

small sediment grains mixed with flowing water are transported above waterbed making water cloudy

stream power

ability of stream to do work

multiply the sheer stress and average velocity

without water there is no such thing as sheer stress and velocity

alluvial fans

deposition in deep water decreases and stream power drops off

often forms when stream goes from confined to unconfined

delta

forms where stream enters lake or ocean

meandering

single main channel interwoven into a whole

braided

series of small channels interwoven into larger whole

oxbow lake

cut banks of meandering stream erode toward each other and upon meeting meander gets cut off

point bar

accumulation inside meander

fastest flow velocity

at the outside bank of meander and center stream

porosity

percent of total volume of regolith or rock with pores

permeability

ability for water to flow through material

water table

top surface of groundwater that mimics topography of ground surface

saturated zone (phreatic zone)

below water table and filled with water

unsaturated zone (vadose zone)

above water table with air in pores

artesian aquifer

underground layer holding water under pressure causing water to rise

cones of depression

forms because a pumping well withdraws water faster than recharge causing resistance to flow

water mineral reactions

slow moving water, long travel paths, and increased temperature at depth increase reaction potential in saturated zones

cementation

occurs where mineral precipitation takes place and slows down water creating more reaction potential

composition of groundwater

economic minerals associated with groundwater

coastal groundwater

freshwater that is less dense and floats over salt water

scenic canyons

wide floor, unchanging valley, main and side canyons terminate in vertical alcoves and contain pockets of dense vegetation

marine formaminifera (forams)

secrete mini calicite shells to which atoms record oxygen and compare isotopes

milanrovitch cycles

variation in earths orbital characteristics causing ice age initiation

orbital eccentricity

cycle length of 413,000 years

axial tilt obliquity

cycle length of 41,000 years

wobble precession of axial tilt and orbit

cycle length of 23,000 years

tidewater glacier

glacier descends into sea but does not float

ice berg

fragments breaking off of glacier because of erosion from waves

sea ice

frozen sea water

ice shelf

segment of tidewater glacier that is submerged but buoy to float

glacier

84% of earths freshwater and cover 10% of earths surface

valley glacier

long narrow glaciers confined to bedrock valleys that flow from high elevation to low elevation

ice sheets

unconfined glaciers larger than 50,000 km2

ice caps

unconfined glaciers smaller than ice sheets with radial flow

snow line

elevation above which snow persists year round

snow metamorphism

rounded ice grains that recrystallize close to earth

creavasses

result of brittle fracture

zone of accumulation

high elevation when winter accumulation exceeds summer melting

zone of wastage

low elevation where summer melting exceeds accumulation of winter

erosion by plucking

glacial force acting on preexisting faults and fractures

erosion by abrasion

rock picked up by glacial ice contacts bedrock below gouging it as it presses down

glacial transportation

transports sediment along base within ice and atop glacier due to mass wasting along valleys, walls and sediment

till

sediment directly deported by glaciers often have cobbles with edges and striations

outwash (kame)

sediment carried out by meltwater from glaciers and often have rounded cobble

glacial erratics

long traveled and out of place rock

moraines

bumpy, ridgelike structures of sediment deported by glaciers

end moraines

glacier retracts and deposits sediment at base

glacial landscape features

moraines, v shaped valleys, knife edge ridge, pointed peaks, cirques, hanging valleys

erosion is greatest when flowing against bedrock

cirques

scooped out landform common near head of glacier where erosion is highest often filling in afterward to make bowl shaped lake

hanging valley

rapid erosion in main glacier channel causing large vertical differences

aretes

ridges between glacial valleys becoming narrow and forming knife like features

horn

where several aretes meet

landscape features

large areas of scoured, plucked and abraded rock, large regions covered by till and streamlined ridges parallel to movement