Geology Exam 3

Start Studying!

Terms

undefined, object

copy deck

Groundwater: water found in sediment & fractures in bedrock

-largest freshwater resource available to humans (makes up majority of non-frozen freshwater) (second after glaciers when including all freshwater)

-sustains streams during dry periods
[stores rainwater]

-makes sinkholes and caves (removal of limestone)

-moves only a few CM / day

-powered by energy from gravity
--->allows water to move from where h2o table is high to where it is low
rate of exchange for groundwater v rivers: rate of groundwater exchange:
280 YEARS

rate of exchange for rivers:
11 DAYS
[w/o rain river would run dry in 11 days]
distribution of groundwater: *more steep = less groundH2O

ZONE OF AERATION:
1)belt of soil moisture
2)capillary fringe
{can't be pumped into wells bc clings to rock}

ZONE OF SATURATION:
1)WATER TABLE
(upper limit of saturation zone & ground water)
belt of soil moisture term: the water in the near surface zone

-doesn't travel far due to molecular attraction at surface --->film on soil particles
*where roots and organic matter are
zone of saturation term: where all pore spaces are completely filled w/H2O

-water within zone of saturation = GROUNDWATER!

-the upper limit = water table
capillary fringe term: where "groundwater" is held by surface tension in passages between grains of soil/sediment
zone of aeration term: the area above water table including ccapillary fringe and belt of soil moisture

-water here can't be pumped by wells b/c it clings to rock/soil
water table variations: -depth is highly variable
-varies seasonally & from yr to yr due to changes in rainfall

-not flat
-->resembles surface topography
-moves slowly & "piles up" beneath high areas
(if rain ceased, H2O"hills" would decrease and reach valley level)
"gaining streams": streams gain water from groundwater

-water table must be at higher elevation than surface of stream

*most common*
"losing stream": stream loses water to groundwater

-water table elevation must be lower than surface of stream
porosity influencing groundwater: porosity = % of total volume that consists of pore spaces
permeability: the ability to transmit a fluid

-smaller the pore spaces slower water moves

groundwater divided into:
1)specific yield
2)specific retention
specific yield: the portion of groundwater that will drain under influence of gravity

*indicates how much water is actually available for use

[ex. clay's porosity = high; spaces small = h2o can't move thru it = LOW specific yield]
specific retention: groundwater that's retained as film on surfaces and in tiny openings

*indicates how much water is bound in material
aquitards: impermeable layers hindering or preventing h2o movement

*CLAY*
aquifers: permeable rock that transmits groundwater freely

*SANDS & GRAVELS*
Spring: natural outflow of groundwater resulting from when water table intersects earth's surface

also result when aquitard blocks downward movement and forces it laterally ->spring results where bed is outcropped

also a small aquitard can prevent a portion of water intercepted creating localized zone of saturation & a PERCHED water table
perched water table: localized zone of saturation above the main water table
-->created by impermeable layer [aquitard]
hot springs: result from grounwater circulated and heated at great depths

*water = 6-9*C warmer than avg air temp

-source of heat for most = cooling igneous rock
---->most in WEST!
Geysers: intermittent hot springs
-water ejected then steam
-occur where extensive underground chambers exist w/i hot igneous rock

PROCESS:
-cool groundwater enters chamber
-heated by surrounding rock
-great pressure prevents it from boiling
-heating of water causes expansion
-some forced out at surface
-loss of water reduces pressure on remaining water
-->lowering the boiling point
-portion of h2o deep w/i chamber turns to steam and geyser erupts

(groundwater heats, expands, turns to steam, erupts)
aquifer: underground bed / strata that yields water
Well: hole penetrating into the zone of saturation

-to ensure continuous water supply hole must penetrate below the water table
drawdown: the effect of the water table lowering around a well when water is withdrawn from it

-decreases w/ distance from well

-results in a depression in the water table (a cone of depression)
cone of depression: a depression in the water table resulting from the drawdown effect from a well

-->increases hydraulic gradient near well --> water flows more rapidly toward opening

-->causes nearby shallow wells to become dry
problems associated w. groundwater withdrawal: 1)treating groundH2O as nonrenewable
-h2o available to recharge aquifer often less than amt being withdrawn

2)subsidence {to sink lower than normal levl}
-ground sinks when h2o pumped out faster than its recharged

3)saltwater contamination
-saltwater is drawn into wells, contaminating supply
-major problem in coastal areas

-freshwater less dense than saltwater...floats on top
-water table 40x greater below sea level than above sea level
-excessive pumping lowers water table ==> the bottom of freshwater zone rises by 40x that amount

*also as more surface is covered by parking lots/buildings/etc
--->reduction in h2o infiltration
groundwater contamination: sewage = common source
-increasing # of septic tanks
-can become purified after passing thru few dozen meters of sand or permeable sandstone
-gravel and other really permeable aquifers have large pores thus groundH2O can travel LONG distances w/o being cleansed

-a sinking well -->cone of depression-->steeper slope-->faster movement of water--->
*Original Slope Can Be Reversed!*
*faster movement of water can also allow for less time for water to be purified*

-fertilizers
-pesticides
caverns: created when slightly acidic groundwater dissolves limestone in zone of saturation
groundwater dissolves rock when...: groundwater contains carbonic acid (when rainwater dissolves carbon dioxide)
-carbonic acid reacts w/calcite in limestone
dripstone: (travertine) - found w/i caverns

-calcite deposited as carbon dioxide evaporates from water

-collectively called speleothems
speleothems: -the various dripstone features found in caverns
-no two exactly alike

types:
1)stalactites
2)stalagmites
stalactites: type of speleothem

-hang from ceiling
-carbon dioxide escapes from drop and calcite precipitates
-hollow limestone tube created [SODA STRAW]
stalagmites: type of speleothem

-form on floor of cavern and reach toward celing
-don't have central tube
-more massive

*given enough time stalactite and stalagmite can form a column
karst topography: landscapes that have been shaped by dissolving forces of groundwater

-areas typically have irregular terrain punctuated with sinkholes
-lack surface drainage (streams)
--->after rain water funneled below ground thru sinks -- flowing through caverns until reaching the water table
sinkholes (sinks): depressions
formed by:
1)gradually without physical disturbance ->limestone just below soil dissolved by freshly charged rainwater
-shallow w/gentle slopes

2)abruptly when roof of cavern collapses under its own weight
-steepsided & deep
Glaciers: thick mass of ice originating on land from accumlation, compaction, & recrystallization of snow
-cover ~10% of earth's land surface
-h2o stored as glacial ice for tens, hundreds, thousands of years
-powerful erosional force
--->accumulates, transports, deposits sediments
(they FLOW)
Valley / Alpine Glaciers: -exist in mountainous areas
-flows down valley from accumulation center at head

-advange a few CM / day
-stream of ice bounded by rock walls
-widths usually small compared to length
Formation of glaciers: -form in areas where more snow falls in winter than melts in summer

STEPS:
-air infiltrates pores in snow crystals
-water vapor condenses
-->snowflakes become smaller, thicker, spherical
(& large pores disappear)
-air has been forced out and snow has recrystallized into a denser mass of small grains [FIRN]
-more snow = pressure increases
-->when thickness exceeds 50 M weight fuses firn into solid mass of interlocking ice crystals
-> GLACIAL ICE

*snowflakes smaller, thicker, spherical; air forced out; recrystallized into grains -FIRN; thickness exceeds 50 M -becomes glacial ice
Firn: granular recrystallized snow

-denser mass of coarse grains
w. consistency of sand
transformation of snow to ice: snowflake

granular snow

firn

glacial ice
2 types of glacial "flow" (movement): 1) plastic flow

2) basal slip
plastic flow: -movement WITHIN the ice
-ice behaves as brittle solid until pressure exceeds 50 M then behaves as plastic (silly putty)

-glacial ice = molecules stacked on eachother
-bonds between layers weaker than bonds w/i layers
-->LAYERS SLIDE OVER ONE ANOTHER
basal slip: -entire ice mass slips on ground
-most glaciers flow by this process
-occurs in discrete "JUMPS"

-meltwater acts as hydraulic jack / lubricant helping ice over rock

-temperatures can be increased by friction from plastic flow --> glacier moves by both plastic flow & basal slip
zone of fracture: uppermost zone
-top 50 M (can't move by plastic flow)
-brittle
-carried along "piggyback" style by ice below
-when glacier goes over irregular terrain the zone is subjected to tension, creating fractures
-->cracks/ crevasses
crevasses: cracks that form in zone of fracture when subjected to tension from moving over irregular terrain
-can extend to 50 M
(below 50 M plastic flow seals them off)
rate of glacial movement: -several meters / day
-valley glaciers experience friciton on sides --> rate of flow greatest in center
-can experience surges
surges: periods of extremely rapid movements then returning to normal rate
-as much as 100x normal rate

-could be caused by increase water pressure reducing friction & increasing basal slip
zone of accumulation: where snow accumulation and ice formation occur

-->outer limits = snowline
zone of wastage: beyond the snowline
--where there is a net loss to the glacier
(snow from previous winter melts, as does some of glacial ice)

wastage due to
1)MELTING
2)CALVING
calving: occurs in zone of wastage

-large pieces of ice break off the front of the glacier

-responsible for icebergs (when near ocean/lake)
-->icebergs SLIGHTLY less dense than water = 80% mass underwater
ablation: the loss at the lower end of the glacier
(in zone of wastage)
glacial erosion: capable of great erosion & transport, more than any other erosional force
(& much faster)

-ice doesn't allow debris to settle out like streams & such

Erode in 2 ways:
1)PLUCKING
2)ABRASION
Plucking: -the lifting of rocks

-loosens and lifts rock incorporating them into ice
-happens when meltwater penetrates cracks in bedrock beneath glacier and freezes
Abrasion: rocks w/i ice act as sandpaper to smooth/polish rock below

-pulverized (powdered) rock produced = rock flour
rock flour: when rocks in bottom of glacier produce pulverized rock / rock powder

-->can cause glacier to appear gray / milky

{PRODUCED BY GLACIAL ABRASION - friction}
landforms created by glacial erosion LIST: glacial trough
truncated spurs
hanging valleys
pater noster lakes
cirques
tarns
fiords
aretes
horns
GLACIAL TROUGH (landform by glacial erosion): the U shaped broader/deeper valley

-changes the V-shaped valley created by streams into U-shaped trough
-straightens the valley
TRUNCATED SPURS (landform by glacial erosion): triangular shaped cliffs

-created by the removal of spurs of land extending into glacial valley
HANGING VALLEYS (landform by glacial erosion): valleys left standing above the main glacial trough

-due to the fact that deepness of glacial erosion depends on thickness of ice
-valleys feeding into main trough not as deep
PATER NOSTER LAKES (landform by glacial erosion): bedrock depressions created by plucking *when they're filled with water!*
TARN (landform by glacial erosion): -small lake
-often occupies cirques
ARETES (landform by glacial erosion): -sharp edged ridges
-carved by valley glaciers
-cirques exist on opp sides of a divide
-->as cirques grow the divide reduced to a narrow knifelike structure
HORNS (landform by glacial erosion): -pyramid like peaks
-carved by valley glaciers
-produced by groups of cirques enlarging and converging, producing an isolated horn
Glacial Drift: term for all sediments of glacial origin
-glacial deposits consist primarily of mechanically weathered rock (with little / no mechanical weathering)

2 types:
1)TILL
2)STRATIFIED DRIFT
TILL (glacial drift): material deposited directly by ice

-typically unstratified & unsorted!

*landforms made by till::
-moraines
-drumlins
STRATIFIED DRIFT (glacial drift): sidiments laid down by glaical meltwater
Glacial erratics: boulders found in till

-know they've been transported bc different from bedrock below
Moraine: layers or ridges made by glacial till

TYPES:
[made by alpine glaciers]
-lateral moraine
-medial moraine
[other types]
-end moraine (terminal or recessional)
-ground moraine
lateral moraine: ridges of till paralleling sides of the valley
-made by alpine glaciers

-ice erodes sides of valley & debris is collected on edges of moving glacier
-ice melts & debris is dropped next to valley walls
medial moraines: dark stipes of till within ice stream
-created by alpine glaciers

-when two alpine glaciers coalesce to form single ice stream
--till once on sides of each glacier joins to form single dark stripe of debris within newly enlarged glacier

*proof that glacial ice moves
End Moraine: ridge of till that formed at terminal end of glacier

-deposited when there is equilibrium between ablation & accumulation
-->ice is melting at end but ice flow continually deposits more sediments

TYPES:
1)terminal moraine
2) recessional moraine
terminal moraine: -type of end moraine

-marks the limit of glacial advance
recessional moraine: -type of end moraine

-end moraines that were created as the ice front OCCAIONALLY stabilized during retreat
(ablation & accumulation were balanced in different places along retreat)

*difference between terminal moraine & recessional morain = relative positions*
DRUMLINS: smooth elongated parallel hills
-COMPOSED OF TILL

-steep side faces direction ice advanced FROM
-gentler slope points in direction ICE MOVED

-occur in clusters (drumlin fields)
4 major stages in ice age: 1) Nebraskan

2) Kansan

3) Illinoian

4) Wisconsinan
ICE AGE: ice covered ~30% of earth's land area

-had 20 glacial/interglacial cycles (occuring every 100,000 yrs)

-most major glacial stages occured during
PLEISTOCENE EPOCH

-began 2-3 ma ago
how much of world's H2o is in glaciers?: ~ 2 %
the antartic ice sheet (#'s): 80% world's ice
65% of earth's freshwater

if melted, sea level rise 60 - 70 M
indirect effects of ice age: -as ice advances & retreats animals/plants forced to migrate
-change courses of rivers
-upward rebound of crust
(raising after the downwarping {curstal subsidence} from heavy ice)
-->up and in now rather than down & out

-during ice age sea level ~ 100 M lower than today
-climatic changes (ice age = response to significant climate changes)
-during pleistocene epoch = "wetter climate" creating pluvial lakes
any successful theory of glaciation has to account for: -cause for onset of glacial conditions
-cause of glacial/interglacial periods during pleistocene epoch
tillite: deposits indicating earlier glaciations (prior to ice age)
PLATE TECTONICS as a cause for glaciation: -supercontinent was located at latitudes far south of present positions
-(OR, earlier) ice ages occured when continents in tropical latitudes were carried toward poles

-most commonly accepted

-changes in ocean circulation altered heat/moisture (& in turn CLIMATE)

*ALL OCCUR OVER VAST SPANS OF TIME - SCALE OF MILLIONS OF YEARS*

->*DOES NOT EXPLAIN ALTERNATING GLACIAL/INTERGLACIAL PERIODS*
MILANKOVITCH HYPOTHESIS as a cause for glatiation: -variations of incoming solar radiation due to variations in earth's orbit

1)ECCENTRICITY
-variations in shape of orbit around sun
2)OBLIQUITY
-changes in angle of axis
3)PRECESSION
-wobbling of earth's axis

-->can lead to milder winters & cooler summers

*Explains glacial/interglacial periods (on scale of thousands of yrs not millions)*

***accounts for changes in climate over past 300,000 yrs

--called milankovitch cycles
eccentricity: the shape of earth's orbit around sun
obliquity: change in angle of earth's axis
precession: wobbling of earth's axis
structural geology: studies architecture of crust & processes responsible for deforming it
rock structures contain: oil fields

ore deposits
deformation: all changes in size shape orientation and position of a rock mass

-most deformities occur along plate margins

-occurs from tectonic forces

-includes:
1)STRESS
2)STRAIN
Stress: force / area

(measure of how concentrated the force is)
differential stress: stress applied unequally in different directions

INCLUDES:
1)compressional stress
2)tensional stress
3)shear stress
compressional stress: differential stress that shortens a rock body
-plate collisions
-shortens & thickens crust by folding / flowing / faulting
Tensional stress: differential stress elongates or pulls apart rock unit
-plates are rifted - divergent plate boundaries
-lenthens rock bodies
shear stress: -often occurs on closely spaced parallel surfaces of weakness (bedding planes)

-similar to slipage between playing cards
strain: changes in shape or size of rock body from stress
how rocks deform: rocks subjected to stresses greater than their own strength

deform BY:
1)fracturing
2)folding
3)flowing
steps of rock deformation: 1)first deform elastically
-elastic deformation
(recoverable)
2)after elastic limit surpassed it either FLOWS (ductle deformation) or FRACTURES (brittle deformation)
elastic deformation: rock will return to original size / shape when stress is removed

*earthquakes release elastic energy*
ductile deformation: rock flows after elastic limit surpassed
brittle deformation: rock fractures after elastic limit surpassed
factors influencing how rock strength & thus deformation: 1)temperature

2)confining pressure

3) rock type [rheology]

4)availability of fluids

5)time [strain rate]
temperature and confining pressure affecting rock deformation: low temp & low pressure:
Brittle Deformation
[fractures]

high temp & high pressure:
Ductile Deformation
[flows]
clays
rock type affecting rock deformation: crystalline rocks composed of minerals = brittle fracture

weakly cemented sedimentary rocks & meta rocks w. zones of weakness = ductile flow
"rock structures" term: deformations from mountains to fractures

(the largest folds to the smallest fractures)
when studying a region geologists:: identify & describe the dominant rock structure

-aided by aerial photography, satellite imagery, digital topography, global positioning systems (GPS)
used to decribe orientation of rock layer: 1)STRIKE (trend)

2)DIP (inclination)

by knowing strike & dip geologists can predict nature, structure & faults of the rock unit
strike: compass direction of the line of intersection of inclined rock layer or fault with horizontal plane

-expressed as angle relative to N (N10*E ->strike is 10* E of N)
dip: angle of inclination of the rock compared to horizontal plane

includes angle of inclination and direction rock is inclined toward
folds: rocks bent into series of wavelike undulations
(during mtn building especially)

-microscopic to hundreds of meters

-result from COMPRESSIONAL stresses
-->the shortening and thickening of crust

PARTS:
limbs
axis
axial plane
limbs (part of fold): refers to the two sides of a fold
AXIS (book calls hinge) (part of fold): where fold is divided along max curvature pt
--just a line

(like dividing into symmetrical sides)
Axial Plane (part of fold): imaginary surface dividing fold in half
--PLANE dividing into "symmetrical sides" of fold
ANTICLINE type of fold: upward / arched rock layers

(the limb of an anticline can also be the limb of a syncline)
SYNCLINE type of fold: downfolds / troughs of rock layers
basic folds can be :: -symmetrical
-asymmetrical
-overturned (type of asymmetrical)
symmetrical folds: limbs are mirror images of eachother
asymmetrical folds & overturned folds: asymmetrical folds:
limbs are NOT mirror images

overturned folds:
in asymmetrical folds when one limb is tilted beyond the vertical
(can go so far as to lay on its side ->axis would be horizontal)
Plunging of folds (and how anticline & sincline plunge): folds plunge when their axis penetrates the ground

anticlines point IN the direction they're plunging

sinclines point the OPPOSITE direction they're plunging

*plunging = from hitting surface down*
Monocline (type of fold): large, step like folds in otherwise horizontal strata

-ONLY ONE INCLINED LIMB (the other horizontal)

-result from movement along buried faults
DOME (type of fold): upward displacement of rocks
-circular, elongated structure
**LOOKS LIKE A BALD HEAD**

-OLDEST rocks in CENTER, youngest rocks at edge

-can be formed by magma intrusion
BASIN (type of fold): downward displacement of rock
-circular, elongated structure
**LOOKS LIKE A BOWL**

-YOUNGEST rocks in CENTER,
oldest at edges
faults: fractures in rock allowing displacement to occur

-sudden movements along faults cause most earthquakes
dip-slip fault: faults in which movement is parallel to dip (inclination) of fault surface
-can produce fault scarps
-parts = hanging wall & footwall
fault scarp: long low cliffs produced by vertical displacement along dip slip fault
hanging wall v footwall: HANGING WALL:
rock surface above fault
(where miners hung their lamps)

FOOTWALL:
rock surface below fault
(miners foot was)
2 Types of Dip-Slip faults: 1) Normal Fault

2)Reverse Faults
Normal Fault [type of dipslip fault]: when hanging wall moves DOWN relative to foot wall
-accomodates extension of crust
-large scale normal faults = associated w/ "fault-block mtns"
Fault Block Moutains: large scale normal faults

-extend for tens of KMs
Horsts: alternating uplifted fault blocks
from movement along fault

-create elevated ranges
Grabens: down dropped blocks from movement along fault

-FORM BASINS

[half grabens = tilted fault blocks]
Reverse & Thrust Faults: hanging wall moves up relative to footwall
-accomodate shortening of crust
-result from COMPRESSIONAL forces

*reverse faults = dips greater than 45*
thrust faults = dips less than 45*
STRIKE SLIP FAULTS {as opposed to dip slip}: displacement is horizontal and parallel to strike of fault

2 types:
1)RIGHT LATERAL:
as you face the fault the block on the opposite side moves right

2)LEFT LATERAL:
as you face the fault the block on the opposite side moves left
Transform Fault: Types of strike slip fault

-cuts through the lithosphere and accommodates motion between 2 large crustal plates

-many cut thru oceanic lithosphere & link spreading ocean ridges

*EX. SAN ANDRES
SAN ANDRES example of: major transform fault

(a large strike slip fault cutting thru lithosphere)
hydrologic cycle: -endless cycle
-constantly movement
-powered by energy from the sun (provides link between oceans & continents)
-winds transport moisture filled air
-water falls in ocean = completed cycle
-water falls on land = must make its way back to ocean

*BALANCED*
(ie total water vapor in atmosphere remains the same)
infiltration: the portion of water that soaks into the ground

move downward then laterally (into streams oceans etc)
runoff: the water that flows over the surface into bodies of h2o ... when rate of rainfall greater than land's ability to absorb it
evapotranspiration: combined effect of transpiration & evaporation

[transpiration = water released by plants into atmosphere]
earth's allocation of h2o: oceans: 97 %

glaciers: 2 %

groundwater: .6 %

lakes/rivers, atmosphere: ~.02 %
most important erosional agent?: RUNNING H2O
sheet flow: broad thin sheets of h2o across ground

*depends on infiltration capacity of soil*

runoff begins as sheet flow
infiltration rate: CONTROLLED BY:

1)intensity / duration of rainfall
2)prior wetted condition of soil
3)soil texture
4)slope of land
5)vegetation cover
rills: tiny channels of current developed from sheet flow

*happens after sheet flow*

-carries water to streams
stream's erosional power: depends on velocity!
velocity of stream: depends on :
1)gradient
2)shape / size / roughness of channel
3)discharge
gradiant: slope of the stream

measured by vertical drop of stream over fixed distance

**the steeper the gradiant the more energy available for streamflow**

**higher gradiant = higher velocity**
cross-sectional shape of stream affecting velocity: determines amount of water in contact w/channel & thus the amt of frictional drag

*most efficient stream = least perimeter for its cross section

*less water in contact = less frictional drag = higher velocity
size & roughness of channel affecting velocty of stream: bigger size = lower perimeter:cross section ratio = increases velocity

smooth channel = more uniform flow

irregular channel filled w/ boulders = slows flow
discharge: amt of water flowing past a certain point at a given time

(cross sectional area)x(velocity)

*normally not constant due to rain & snowmelt

*if discharge increases the stream either increases depth & stays at same rate OR must flow faster*
changes from upstream to downstream: 1)profile
2)velocity increases
3)discharge increases
4)channel size increases
5)gradiant DECREASES
6)channel roughness DECREASES

(width depth and velocity increase due to more water added to stream from groundwater & other sources)
profile (aka longitudinal profile): cross sectional view of a stream from source area (head) to mouth (where river's emptied)
base level: the lowest elevation to which a stream can erode

*where mout enters body of h2o*

--accounts for fact that streams have low gradients near mouths

2 types:
1)ultimate base level
2)local / temporary base level

*raised base level = deposition
*lower base level = erosion
--->lower base level -->excess energy --> downcuts channel to balance
ultimate base level: sea level
temporary / local base level: lakes, resistent layers of rock

limits stream

*when stream enters lake velocity approaches 0 & erosional power is gone

*upstream from resevoir = gradiant reduced, lower velocity, lower transporting ability

*change in local base level = waterfall

*changes river profile
graded stream: correct slope & characteristics to maintain velocity to transport material supplied

[not eroding or depositing, just transporting]

->becomes a self regulating system -->EQUILIBRIUM
load: transported material by stream

1)dissolved load
2)suspended load
3)bed load
dissolved load: supplied by goundwater

*groundwater dissolves minerals and such from soil
bed load: sediment too large to be carried in suspension
-move along bottom of stream

moves by saltation (jump / skip along bed

-in motion intermittantly
capacity: maximum load of solid particles that a stream can transport

-1/2 controlling load stream can carry
competance: max particle size a stream transports
-determined by stream velocity

-2/2 controlling load stream can carry

*competence increases as velocity squared (v increases 2 times, competence increases 4 times)
deposition: caused by decrease in velocity
-competence reduced
-sediment begins to drop out

1)channel deposits
2)floodplain deposits
3)alluvial fans
4)deltas
channel deposits: 1)BARS:
-coarser components (sand gravel)
-temporary

2)BRAIDED STREAMS
-stream deposits material on floor
-accumulate thick enough to choke channel
-force stream to split in multiple paths
--converging & diverging channels threading along bars
*often when load supplied exceepds competency / capacity
*also form when abrupt decrease in gradient or decrease in discharge

3)DELTAS
-forms when stream enters body of h2o
-dying current deposits load of sediments
-delta grows outward -> streams gradient lessens
--channel becomes choked w.sediment & river seeks higher gradient, shorter route
--main channel divides into several smaller ones (distributaries)
floodplain deposits: [part of valley that gets flooded]

1)NATURAL LEVEES
-form parallel to stream channel by successive floods over many yrs
-when stream overflows it flows over land as broad sheet---decreasing velocity & allowing for load to be deposited
Alluvial Fans: develop where high gradiant stream leaves a narrow valley
-drop in v causes dumpage of load quickly in cone / fan shaped accumulation

-slopes outward in broad arc

**deposited on land
[deltas deposited in water]
3 types of delta beds: 1)FORESET BEDS
-coarser particles drop out immediately form layers sloping down

2)TOPSET BEDS
-usually covers foreset bed
-deposited during flood stage

3)BOTTOMSET BEDS
-finer silts and clays settling out at a distance from mouth
-horizontal layers
stream valleys: most common landform on earth

2 types:
1)NARROW VALLEYS
-v shaped
-downcutting toward base level
-can include rapids & waterfalls

2)WIDE VALLEYS
-often include floodplains & meanders
floodplains in wide valleys: 1)erosional floodplains

2)depositional floodplains
meanders in wide valleys: streams that move in sweeping bends

-can produce CUT BANKS
(the zone of erosion outside of a meander)

-when the neck of a meander is narrowed close enough the river can erode thru the narrow neck to the next loop
-->creates new shorter segment [CUTOFF]
---abondoned bend of river = OXBOW LAKE

-can create a point bar
point bar (resulting from a meander): crescent shaped accumulation of sediment deposited inside of meander
oxbow lake (resulting from a meander): the abandoned bend when river assumes the shorter route, cutting off the neck and creating a "cutoff" (the new shorter segment)
incised meander: meanders in steep, narrow valleys

-caused by drop in base level or uplift of a region

(probably originally developed on floodplain that was near base level -- a change in base level cause downcutting
terraces: -remnants of former floodplain
-after a river has adjusted to drop in base level by downcutting
floods: most common & most destructive geologic hazard

caused by natural and anthropogenic factors
flood control: -artificial levees
-flood control dams
-channelization
rivers meander more in:: SOFT SEDIMENT
How long does it take to remove groundwater resources:: TENS of years

(turnover of groundwater is not in our lifetime)
are glaciers shrinking?: YES bc of global warming

which appears anthropogenic
rivers change on what time scale? river turnover time scale?: rivers change in time scale of our lifetime

river turnover takes place in a few weeks
problems with flood control?: by trying to control floods the frequency is lowered but intensity is increased when one finally does occur
what % of earth's freshwater is groundwater?: 0.6 %
measure of amt of water that can be stored by rock / sediment: porosity
currently glaciers cover __% of earth's land area: 10 %
during last major ice age advance sea level:: was 100 m lower
broad deposit of stratified drift thats deposited beyond the end moraine of an ice sheet is:: Outwash Plane
what fault displaces older strata over younger strata?: THRUST FAULTS
gentle rainfall favors (infiltration or runoff?): infiltration
surface lacking vegetation favors? (infiltration or runoff??): runoff
what caused the formation of yosemite and the great lakes?: GLACIERS

Start Studying!

Deck Info

Number of cards 187