Physical Geology Notes
Chapter Seven
Weathering: Chemical alteration and mechanical breakdown of rock and sediment.
* depth of air/water penetration
* as distance of formation from surface rises, so does susceptibility to weathering
* physical weathering: The physical breakup of rocks.
* chemical weathering: The decomposition of rocks and minerals caused by stability-increasing chemical reactions.
-rate of weathering positively linked to presence or absence of high mountains, and thus to plate tectonics
Physical Weathering-Mechanical Processes (water, fire, roots)
* development of joints- rock moved upward after erosion, causes fractures
-columnar joints in igneous rock
* crystal growth- salts precipitated from seeping groundwater
* frost wedging- frozen seeping water
* effects of heat- rocks don’t conduct, spall (outer shell) breaks away
* plant roots- seeds germinate in cracks
Chemical Weathering-Chemical Reactions (stabilize to surface temp)
* carbonic acid- rain + CO2 makes carbonic acid, frees H+ (comp. chg.)
* hydrolysis- water ions replace mineral ions
-decomposed potassium feldspar, kaolinite replaced
* leaching- water removes soluble materials from bedrock/regolith
-seeps into water, bad taste
* oxidation- post-weathering iron release, goethite prod w/ hydration (O)
-hematite produced w/ dehydration
-intensity of color tells time/severity of weathering
* dissolution- carbonic acid dissolves calcite (previously unsoluble)
Results of Weathering
* common rocks- granite’s high silica hydrolysis=* clays & soluble min.
-basalt oxidizes, limestone dissolves
* conc of stable minerals- resistant to attack, @ streambeds/beaches b/c spec. grav. (cw)
* weathering rinds- light colored rind surrounding a darker core of rock
-composed of solid byproduct of chemical weathering
* exfoliation- spalling off of outer rock shells caused by stress during weathering
* spheroidal weathering- rock tendency to be rounded by weathering
-weathering most effective w/ *surface area, & subdivision
Factors of Weathering
* rock type/structure- minerals: quarts & granite resistant
-differential weathering based on composition & structure
* slope- steep =* rapid, gradual =* slow
* climate- moisture and heat promote reactions (chem. react. prev. @ =* eq.)
-carbonate rocks (calcite diss.) in different regions
* time- hundreds/thousands years for a few mm
Soils: The part of the regolith that can support rooted plants. Formed by the weathering of bedrock: mineral component mixed with organic material.
* soil horizons: identifiable succession of subhorizontal weathered zones
* distinct physical, chemical, and biological characteristics
* collectively known as soil profile (parent material =* surface)
* O- surface organic debris
* A- humus, chemical leaching
* E- gray/white, present in evergreen forests (acidic soil)
* B- enriched in clay produced by weathering within the horizon
* K- only in arid zones (rich in calcium carbonate)
* C- deepest, slight weathered parent material, lacks distinct properties, yel/brn oxidation
* soil forming factors:
* time
* climate- rain & temperature
* composition of parent material
* vegetation cover
* soil organisms
* topography
Soil Types (influence the process, classified by chem/phys properties)
* polar soils- well drained, lack well-developed horizons, weak oxidation
-wetter env’ts: tundra causes water-logged, organic rich soil, A not B
* temperature-latitude soils- well-developed horizons, unique to env’t
-deciduous Affisols, evergreen Spodosols, mountainous Entisols and Inceptisols, prairie Mollisols
* desert soils- no leaching produces solid, impervious layer of caliche
* tropical soils- heavy weathering, leaching produces iron-rich laterite
Environmental Aspects of Soils
* rate of soil production: dependent on climate (in regolith, not bedrock (cw)
* mod. T. & high R.- rapid, within 100s years
* mod. T. & avg. R.- 100,000 years
* low. T. & low. R.- millions of years
* paleosols are ancient soils recorded in rock as unconformities
Soil Erosion
* indirect effects- lake infilling behind dams
* rate of soil loss- 7% of soil lost each decade
* control of erosion- soil conserving farming practices, terracing, tree planting
* the world economy- soil is nonrenewable resource
Chapter Eight
Mass Wasting: The movement of regolith and masses of rock down slope under the pull of gravity.
-No Carrier: Gravity is the primary force for mass movement. Requires slope.
* role of gravity
* shear stress (as slope +, tc +)
-perpendicular component of gravity (perpendicular to inclined surface)
holds in place
-tangential component of gravity (parallel to inclined surface)
causes to move
* shear strength: internal resistance to movement
-particle cohesion and plant roots govern
* role of water
-capillary attraction is cohesive until saturated (failure)
Mass Wasting Processes
-landslides = down slope movement of rock and/or regolith.
* types of mast wasting
* slope failure- sudden down slope movement of coherent masses (rocks) (dry)
* sediment flows- down slope flow of mixtures (sediment, water, and air)
Slope Failure
* slump- down/out rotational movement on tilted concave up surface
-can be annual event, associated w/ heavy rains or shock (earthquakes)
* falls
-rockfall- sudden free falling of detached bedrock from a steep slope
-debris fall- accompanying regolith and vegetation
* slides
-rockslide- sudden movement of detached masses across bedding plane
-debris slide- accompanying movement across plane of reg. and veg.
* talus-body of debris beneath a cliff; settle @ angle of repose
Sediment Flows (controlled by)
-relative proportion of solids, water, and air
-physical and chemical properties of the sediment
-steepness of slope
-can start and stop
* slurry flows- water saturated moving mass (soil & regolith ) (20-40% water)
-solifluction- very slow (cm/yr)
-debris flow- coarse * sand, poorly sorted, moves along alluvial fan (m/hr)
-mudflow- highly fluid, moves along valley floor (km/hr)
* granular flows- not water saturated (20%-0% water)
-creep- loose deposits that move = colluvium, very slow (cm/yr)
-earthflow- narrow shape, bulging front (m/hr)
-abrupt shock to porous, wet sediment leads to liquefaction
-grainflow- sand grains, etc: angle of repose is exceeded (km/hr)
-debris avalanche- rare, spectacular event (100km/hr)
-huge masses, pulverize and continue moving (stratovolcanoes)
* *40% water constitutes a stream
Mass Wasting in Cold Climates (especially active)
* frost heaving- lifting of regolith by the freezing of ground-contained water
* gelifluction- thin surface layer thaws in summer and refreezes in winter (unstable)
-cm/yr
* rock glaciers- ice cemented debris which move similar to glaciers
-m/yr (Alps, Andes, Rockies)
Subaqueous Mass Wasting
-submarine slope failures cause turbidity currents
* deltas- region of slumping, central channel to transport sediment, zone where sediment is deposited
* continental slope- disturbed and contorted layering caused by earthquakes, slumping, and glacial cycles (ice ages) has built a thick wedge of sediment along base
* oceanic island submarine flanks- lava flows and unstable rubble placed by massive volcanic landslides
Triggering of Mass Wasting Events
* shocks- earthquakes
* slope modification- human construction
* undercutting- stream or surf action
* exceptional precipitation- ground becomes saturated and unstable
* volcanic eruptions- slope failure and large volumes of released water
* submarine slope failures- high internal pressure of water trapped under sediment bed, methane gas of organic matter, angle of repose issues
Mass Wasting Hazards
* assessment of hazards
-maps of geology surrounding the site
* mitigation of hazards
-drain/pump soil to de-saturate
-empty dams
-minimize activity in danger zones
Chapter Nine
Streams: A body of water that flows down slope along a clearly defined natural passageway. Part of the hydrologic cycle.
* streams as geologic agents:
-carry water to the ocean
-carry soluable salts to the ocean
-shape the surface of the Earth
-transport sediment to the ocean
Factors in Streamflow
Stream Channels
* the passageway is called a channel
* the load is the sediment and dissolved matter the stream transports (kg/m3)
* the discharge is the volume of water passing a given point at a given time (m3/s)
* gradient- the vertical distance a stream cannel falls between two points (m/km)
* long profile- long curve of gradient from stream’s mouth to delta (m2)
Dynamics of Streamflow
* runoff- the portion of precipitation that flows on land surface
* overland flow- broad sheets of runoff moving down slope
* streamflow- the runoff and overland flow that flows in defined channels
Changes Downstream
* discharge increases
* channel cross-sectional area increases
* velocity increases slightly
* gradient decreases
* grain size decreases
* mineralogy may change
Floods (when the stream’s discharge exceeds the capacity of the channel)
* First, discharge increases (shown by hydrograph)
-channel is scoured
-cross-sectional area increases
-velocity increases
* Then, discharge decreases
-sediment is deposited
-cross-sectional area decreases
-velocity decreases
* Floods are predicted using frequency curves.
* Catastrophic floods are rare (Columbia River)
Base Level (level below which a stream cannot erode the land)
* types of base levels:
-sea level (base level for most streams)
-lakes
-natural dams (landslides & lava)
-artificial dams
Channel Patterns
factors
* stream gradient
* discharge
* sediment load
Types of Channel Patterns
* straight channels- rare, sinuous max. depth, sandbar on opposite side
* meandering channels- switchback bends in stream, gentle gradients
-max velocity @ outer curve, pointbars on inner curve
-oxbow lakes result from two meanders intersecting
* braided stream- water divides and reunites through interconnected channels
-separated by bars or islands
-occurs most in streams w/ highly variable discharge and erodible banks
-only 10% active at a given time
Erosion by Running Water
before streams form
* sheet erosion- due to rain drops and overland flow
-vegetation reduces runoff and roots percolate water
after streams form
* laminar flow- particles travel in parallel layers, slow and smooth velocity
* turbulent flow- swirls and eddies, high and complex velocity
-bed and channel walls maintain laminar flow (frictional drag)
Transport by Running Water
Types of Stream Load
* bed load- coarse particles that move along stream bed (up to 50% load) via
-rolling or sliding
-saltation-short intermittent jumps
* suspended load- fine particles that move along surface
-silt and clay
* dissolved load- dissolved substances (underground seepage) (product of chemical weathering)
* sediment size correllated to velocity of stream (greatest w/ steep slopes or basins)
* alluvium- name for solid particles wherever they are dropped
downstream changes:
* grain size decreases (opposite than expected)
* composition/mineralogy of sediments (new rocks)
* placer deposit- concentration of heavy minerals
* sediment yield- amount of sediment eroded and transported
Deposits by Streams (alluvium)
* point bars (see: meandering channel pattern)
* floodplains (part of natural valley) and natural levees (low ridge of alluvium along side of channel) (see: frictional drag and turbulent flow)
* terraces- remnant of abandoned floodplain
* alluvial fans- fan-shaped alluvium deposits where a channel leaves a valley
* deltas- stream flows into standing water (sharp velocity drop)
-fan vs. braid deltas (shape determined by sedimentation/erosion balance)
-foreset layer =* topset layers of deposition
-topset layers between channels (distributaries)
Drainage Systems
terminology
* drainage basin- total area that contributes water
* divide- line that separates adjacent basins
* continental divide- basins drain to different oceans (follow techtonic allignment)
-velocity- steep Andes, gradual Atlantic
* stream order- system of numbering streams (first-? order)
drainage pattern development
* rock type
* rock structure
* stream history (stream capture)
Types of Drainage Patterns
* dendritic
* parallel
* radial (center =* out)
* rectangular (90 degrees)
* trellised (criss-crossed)
* annular (concentric radial)
* centripetal (out =* center)
* deranged (sand bars, topset layers)
Stream Histories produce Drainage Patterns
* consequent stream pattern- formed by uniform rock units and general slope of region (dendritic or parallel)
* subsequent stream pattern- follow folds or rock units, formed in folded or faulted regions (trellissed)
* antecedent stream- cuts across folds due to incision during uplift
* superposed- cut across different rock units due to stream cutting and angular unconformity
Chapter Ten
Groundwater: All the water contained in spaces within bedrock and regolith.
-less than 1% of all water, up to 750m deep
-rainfall is source
Zones Near the Surface
* zone of aeration- water is present, but ground is not saturated
* saturated zone- all openings are filled with water
* water table- top of saturated zone
Porosity- % of total volume of bedrock/regolith with pores
-determins quantity of water a sediment or rock can contain
-affected by sorting, arrangement, and cementation
Permeability- how easily fluids pass through
-molecular attraction affects flow
-sediment larger than sand is very permeable
Recharge Area- area of water input
Discharge Area- area of water output
water table shape
* humid regions
-river is discharge
-river is low on water table
* dry regions
-river is recharge
-river is high on water table
movement of groundwater
1. rain goes in (recharge area)
* moves downhill thru zone of aeration (percolation-chief movement)
1. soil is less permeable than underground
2. some water held by molecular attraction
* movement in zone of saturation
* direction is generally downhill (hydraulic gradient)
-Darcy’s Law- discharge=flow, permeability, and gradient
* velocity relates to water table slope
* moves from high points to low points
* moves from high pressure to low pressure
* subsurface water comes out (discharge area)
Springs (groundwater emerging at the surface)
* caused by intersection of water table with the surface (edge of 2 layers)
* most major springs emerge from lava, limestone, or gravel
* appear via
-aquicludes- impermeable unit
-aquifers- permeable unit in saturated zone
permeable sediments and rocks
* sand and course sediments
* sandstone
* limestone
* jointed lava flow
* jointed granite
impermeable rocks
* clay
* mudstone
* unjointed granite
* bedrock
Wells (drilled to intersect water table) (zone of saturation)
* cone of depression- conical depression of water table surrounding well
* perched water body- different confined aquifers at different depths
Aquifers (body of highly permeable rock or regolith w/in the zone of saturation)
types of aquifers
* unconfined aquifer- its upper surface coincides with the water table
-30% of water from high plains aquifer
* confined aquifer- aquifer bounded by aquicludes
-Dakota aquifer
* artesian aquifer- confined aquifer under hydrostatic pressure
-water can rise in artesian well to height of recharge area
* complex regional aquifer- system of unconfined/confined aquifers connected by atrtesian aaquifers
-Floridian aquifer
Environmental Stuff
Mining Groundwater (major source of freshwater, non-renewable resource)
lowering of the water table
* due to excessive consumption
* causes land subsidence (artesian pressure supports rock weight above)
* artificial recharge (spraying of biodegradable liquid waste)
Water Quality
chemistry of groundwater (dissolved components)
* chlorites
* sulfates
* bicarbonates of Ca, Mg, Na, K, Fe
-soft water vs. hard water: Ca, Mg
* hydrogen sulfide
* salts (NaCl)
Groundwater Contamination
* sewage
* seawater
* toxic wastes
* agricultural poisons
* underground storage of hazardous wastes
Geologic Activity of Groundwater
* dissolution- chemical weathering in soil (carbonate rocks) (carbonic acid)
-limestone (completely away), dolostone, and marble
-exceeds avg. erosion of mass wasting, sheet erosion, and streams
-10mm/1000yr
* chemical cementation- converts sediment into sedimentary rock
-calcite, quartz, and iron are chief cementing substances
* chemical replacement- dissolves one substance and replaces it with another
-mineral and organic substances can be replaced (petrified wood)
* carbonate caves and cave formation (cavern =* system of caves)
-rate of formation = rate of dissolution (acidic water +)
1. shallow saturated zone
* initial dissolution along joints by percolating groundwater
-carbonic acid ; sulfuric acid
* deposition of carbonate formations on cave walls while a stream occupies the cave floor
* continued deposition after the stream has stopped flowing
* cave deposits
-insoluable clay and silt
-deposits chemically precipitated from dripping water: dripstone, stalactites
-deposits chemically precipitated from flowing water: flowstone, stalagmites
-columns- stalactites and stalagmites grown together
-dripstone and flowstone can only be deposited if cave is partially filled with air (lie at or above water table)
-crystals and cave form when in zone of saturation, mites/tites when in zone of aeration
Karst Topography
Factors of Karst Topography
* warm temperature promotes dissolution
* adequate rain =* groundwater, soil ; plants -CO2
Features
* sinkhole- dissolution cavity open to the sky (caused by falling water table)
* solution valleys- channels of sinkholes
* cones and towers- steep topography
Karst Topography (small, closed basins, disrupted drainage (springs))
-steep hydraulic gradient
-limestone or dolomite
-usually in tropical areas
* sinkhole karst- landscape dotted with sinkholes
* cone karst/tower karst- thick, well-jointed limestone that separates into isolated blocks as it weathers
-cone karst- closely spaced conical hills separated by deep sinkholes
-tower karst- isolated limestone hills separated by expanses of alluvium
* pavement karst- broad areas of bare limestone in which joints and bedding planes have been etched and widened by dissolution (glaciation areas)
Chapter Eleven
Glaciers: -A permanent body of ice that shows evidence of down slope or outward movement due to the pull of gravity.
-recrystallized permanent snow
types of glaciers
* classified according to form and size
* mountain glaciers and ice caps
-cirque- occupies enclosed by headwall
-a growing cirque glacier (spreading down and out) becomes a valley glacier
-valley glaciers that extend to the sea are called fjord glaciers
-when it spreads beyond the mountain front it becomes a piedmont glacier
-an ice cap covers top of mountain, spreads outward
* ice sheets and ice shelves
-ice sheets are the largest glaciers on earth (Greenland and Antarctica=95%)
-Antarctica’s Transantarctic Mountains, East sheet larger, + altitude, – T
-ice shelves are thick, nearly flat sheets of floating ice
-fed by glaciers, terminate w/ steep ice cliffs
-Antarctic, Canadian Arctic Islands
* classified according to internal temperature
* temperate glacier- ice at pressure melting point (spec. pres =* melt)
-low altitudes, meltwater and ice exist together
* polar glacier- ice below pressure melting point
-where temperatures remain below freezing
Where do Glaciers Occur?
-glaciers can form at or above the snowline
-snowline- lower limit of perennial snow, dependent on local climate
-climate-temperature and precipitation
-sea level in polar altitudes, mountaintops in the tropics
Glacier Ice
-a metamorphic rock that consists of interlocking crystals of the mineral ice
conversion of snow to glacier ice:
1. melting
2. evaporation
3. freezing
4. deformation under the weight of overlying snow and ice
-under pressure grains develop
-smaller, rounder, denser
Glaciers Change in Size
factors:
* accumulation- snow that is added to a glacier by precipitation
* ablation- snow and ice that is lost from a glacier by melting and evaporation
* mass balance- difference between accumulation and ablation
* equilibrium line- boundary line between the accumulation area and the ablation area (last year’s snow gone)
fluctuations of the glacier terminus (front):
* terminus retreat- accumulation is greater than ablation
* terminus advance- ablation greater than accumulation
* other terms
-response lags- time it takes for the effects of an increase or a decrease in accumulation above the equilibriujm line to change the terminus location (longer for large or polar glaciers)
-calving- breaking off of icebergs from the front of a glacier that terminates in deep water; produces icebergs (fjord glaciers)
How Glaciers Move
types of movement:
* internal flow/creep- movement within ice crystals due to high stress from weight of overlying snow and ice
-crystal axes alligned
-crevasse- deep gaping fissure in glacier surface caused by uneven ground
* basal sliding- movement of a body of glacier ice, by sliding across the underlying rocks or sediments (not polar glaciers)
other considerations:
* velocity- faster in uppermost center (same as rivers)
* directions of flow- snow/ice initially flows downward, then downglacier, and finally upward toward the surface @ the terminus
* glacier surges- rapid movement and dramatic changes in size and form
-due to hydrostatic pressure and hydroplaning
Glaciation (the modification of the land surface by glaciers)
-mass wasting and erosion haven’t had time to cover up
* erosion
* transport
* deposition
Glacial Erosion and Sculpture
a glacier acts as a plow, file, and sled:
* plow- scrapes up weathered rock and soil, and plucks pieces of bedrock
* file- rasps and polishes away firm rock
* sled- carries away the load of sediment
landforms of glaciated mountains (erosional):
* cirques- bowl shaped depression open on one side, located on the side of a mountain (small lakes)
* arete- shart crested ridge formed by the intersection of cirques
* horn- sharp three-sided peak formed by the intersection of cirques
* glacial valleys- U shaped cross section and main floor that lies below that of eroded tributary valleys
* fjords- glacial valley on a coastline so that the sea fills the lower end
landforms produced by ice caps and ice sheets:
* abrasional features
-glacial striations/grooves- parallel scratches and grooves in bedrock, aligned in the direction of flow
-glacial polish- sand and silt polish bedrock
* streamlined features
-drumlin- streamlined hill of glacial sediments
-rock drumlin- streamlined hill made of bedrock
Glacial Deposits (glacial drift-from glaciers and streams they produce)
-sediments deposited by a glacier or by streams produced by melting glacier ice
-carried sediments are neither sorted nor stratified
-load concentrated at base and sides, sand and silt (rock flour) (pluck/abrade)
ice-laid deposits
* till- nonsorted drift deposited directly from ice
* erratic- glacially deposited rock that is different from the underlying bedrock
* glacialmarine drift- sediment deposited on the sea floor from ice shelves or bergs (till in water) (dropstones)
* moraines- accumulation of drift unrelated to underlying bedrock
-ground moraine- widespread gentle undulating knolls
-lateral morraine- ridge along side of valley
-medial moraine- ridge along glacier center
-terminal (end) moraine- ridge along terminus
stratified drift
* outwash- stratified sediment deposited by glacial streams
-outwash plain- if streams freely swing back and forth
-valley train- meltwater streams confined by valley walls
-outwash terraces- during retreat, sediment load reduced, stream cuts into outwash deposits
* ice-contact stratified drift- sediment deposites into drifts which slump following recession
-kame- small hill
-kettle- small basin
-esker- long, sinuous ridge of sand and gravel
The Glacial Ages
-periods of geologic time when glaciers coered extensive regions of the earth
climate change over time
* climate is cooling over tens of millions of years
-now at point of maximum warmth
* last 3 million years- glacial-interglacial cycles (*20)
glacial age changes
1. number of glaciers increase
2. volume of glaciers increase
* during the last glacial age (Pleistocene Epoch) (30,000 years ago)
-glaciers covered 29% of present land (vs. 10% today)
-central Canada to Scandinavia
3. drainage diversions and glacial lakes
* disruption of major stream systems
-Missouri, Ohio rivers displaced courses
* ice-damned lakes
-formed when ice blocked preglacial drainage paths
4. lowering of sea level
* sea level is lowered in proportion to the volume of increased ice on land
* during last glacial age, sea level fell *100m
* causes continental shelves to emerge as dry land (English Channel)
5. deformation of the crust
* weight of ice sheets causes the crust to subside
-Ohio still rising
-3km sheet lowers crust 1km
Evidence for Earlier Glaciations
major glacial ages in terrestrial sediments
* layers of glacial till
* soil horizons and wild-blown dust between layers
sea floor evidence-marine sediment cores (uniform vs. earth)
* biologic evidence
-shift from warm to cold environment indicated by animal/plant habitat
* ratio of oxygen isotopes
-high O18/O16- more ice, glacier age
-low O18/O16- less ice, interglacier age
What Causes Glacial Ages
* shifting continents from plate techtonics
-glaciation is enhanced by high latitudes
-large-scale uplift of continents =* high altitudes
* variations in solar radiation (astronomical theory)
-variations in earth’s orbit (eccentricity)
-variations in earth’s tilt
-variations in earth’s wobble (equinoxes, etc) (precession)
* atmospheric factors
-greenhouse gases (magnitude of changes)
-Co2 and methane
-dust in the atmosphere
* other factors
-oceanic circulation
-salinity controls deep circulation
-permafrost in europe and operational currents (during interglacial)
-reflectivity of earth’s surface
-snow and ice have high reflectivity- lowers temp
-solar output
Chapter Twelve
* convection- unequal amount of sun @ equatorial latitudes
* coriolis effect- wind deflection (r-n & l-s) caused by the Earth’s rotation
* air moves from high to low atmospheric pressure
-trade winds =* westerlies =* polar front
latitude belts of circulation:
* equatorial low- region of ascending, warm, moist air
* trade winds- 0-20 degrees latitude
* subtropical high pressure- 20-30 degrees latitude
* westerlies- 30-50 degrees latitude (mid)
* easterlies- 50 degree latitude (high)
* polar high- region of descending cold, dry air
factors controlling climate: (average weather and its variability)
* variables: temperature, rain, clouds, wind
* global air circulation (latitude belts of circulation)
* distribution of land and sea (oceans, currents, continents)
* topography of the land (mountains, plateaus
Geologic Processes of Wind
transport of sediment:
* wind-blown sand (low altitude)
* surface creep- rolling motion of sand
* saltation- moving sand grains by hopping (3/4 moves this way)
* sand ripples- linear ridges of sand perpendicular to wind direction (sorting)
* wind-blown dust (faster and larger)
* mobilization of dust
-dust in the laminar air flow is NOT mobilized
-dust is mobilized by turbulence
* transport of dust (wind’s suspended load)
-gravity pulls dust down
-wind turbulence carries dust forward
* dust storms- large scale dust transport (drought) (low visibility)
-thin-windward, thick-lee
erosion:
* deflation- pick-up and removal of loose material
* deflation hollows and basins (little vegetation) (Quattara Depression) (1m/yr)
* desert pavement- continuous cover of oversized alluvium cobble
* abrasion- shaping and polishing of rock surfaces
* ventrifacts- any abraded bedrock surface (1 smooth upwind surface)
* yardangs- streamlined, wind-eroded ridge (groups)
-differential deflation
eolian deposits-sand:
* dunes- hill or ridge of sand formed by deposition of sand on the leeward side (slip face) (avalanche)
* form- asymmetrical in cross-section; with a gentle windward slope and steep slip face
* size- determined by maximum wind velocity; typically 30-100m, rarely 500m
* types-
-barchan dune- limited sand, crescent shaped, will travel
-transverse dune- abundant sand, perpendicular to wind
-linear dune- limited sand, parallel to variable wind direction
-star dune- wind blows from all directions
-parabolic dune- stabilized by vegetation, U/V shaped
* dune migration- movement or migration of whole dune slowly downwind due to the transfer of sand from the windward to the lee side of an active dune
* sand seas- deserts of vast tracks of shifting sand (4/5 dune types)
-Africa, Arabian Peninsula, W. China
eolian deposits-dust:
* loess- thick and uniform deposit of wind-laid dust
* characteristics that identify loess from water deposits
-uniform blanket, mantling hills and valleys (disregards Prin. of Horizontality)
-fossils of land plants and mammals
-homogenous: lacks stratification
-forms vertical cliffs (molecular attraction)
* origin of loess particles
-deserts (China)
-floodplains of glacial meltwater streams (Mississippi River valley)
* dust in ocean sediments
* dust in glacier ice
eolian deposits-volcanic ash:
* tephra ejected into the atmosphere during explosive volcanic eruptions is a significant source of wind-transported sediment
* ash-tuff- layers of tephra similar to loess except particles are volcanic minerals and glass
* course and dense particles fall out quickly
* small particles may be carried great distances
* fine ash that reaches stratosphere may circle the earth
Deserts: Region of annual rainfall less than 250mm; evaporation rate exceeds precipitation rate.
desert types:
* subtropical- global circulation, dry descending air
* continental- far from moisture sources
* rainshadow- lee of mountain barriers
* coastal- cold ocean cools air flowing onshore (fog)
* polar- global circulation, cold dry descending air (ice and moisture) (mars)
desert climates:
* arid climate of hot desert
* high T, low rain, high evaporation, windy
* arid climate of polar desert
* low T (all ice), low precipitation, extremely dry air
Surface Processes in Deserts: None restricted to deserts.
weathering:
* mechanical weathering dominates
mass-wasting:
* regolith is thin and noncontinuous
* regolith is course, angular fragments
* slopes are steep, with rugged cliffs
* desert varnish- older sediment is darker
desert streams:
* flash floods- sudden swift flood caused by a rainstorm
* surface runoff is abundant due to lack of vegetation
* transports large quantities of sediment
* deposits sediments into distinctive desert landforms
Landforms in Deserts
* butte- isolated, steep-sided hill or pillar
* mesa- flat topped wide butte
* fans- made of alluvium and debris-flow deposits
* bajadas- broad alluvium apron, coalescing adjacent fans
* pediments- broad relatively flat surface made of eroded bedrock (running water)
* desert lakes- rarely permanent, only water after rains
* playas- dry lake bed
* inselbergs- steep-sided mountains, ridges, or isolated hills
* homogenous, found in grasslands, resistant: shed vs. absorb
* steepen with time
Desertification: Desert enters into non-desert areas.
* groundwater, erosion, vegetation, saltiness
Chapter Thirteen
Earth’s Ocean
Physical Characteristics
-71% of earth’s surface
-97% of earth’s water
* depth of the oceans:
* 3.8km avg. depth (11km Marinana Trench deepest)
-.75km avg. land height (9km Mt. Everest tallest)
* ocean salinity: 3.5% dissolved salts
* mostly sodium and chlorine (NaCl, salt)
-small amounts of sulfate, magnesium, calcium, potassium, bicarbonate, and bromine
* factors: evaporation, precipitation, fresh water, ice
* temperature:
* related to latitude- 30 deg. C @ equator, -2 deg. C @ polar regions
* heat capacity of the ocean:
* high heat capacity: ability to absorb and release large amounts of heat without changing temperature very much (isotherms-map of sea)
* ocean water moderates coastal climates by cooling in the summer and warming in the winter
* vertical stratification: 2 layers, surface and deep water
* variations of density of sea water relate to salinity and temperature
-cold water sinks
-salty water sinks
Ocean Circulation
* factors that cause seawater movement:
* prevailing winds- caused by planetary wind system (belts)
* coriolis effect creates gyres: large circular current
-CW in NH, CCW in SH
* seawater density- salinity and temperature
* major water masses:
* surface water layers- mostly warm (cold @ poles)
* 0-35 deg. latitude surface water- central water mass: warm, avg. salinity, flows northward
* polar surface water mass- cold, less saline, flows in the Antarctic Circumpolar Current (ACC)
* deep water layers- cold
* Intermediate water mass (AAIW)- originates from the ACC, flows northward under the central surface water mass
* North Atlantic Deep Water (NADW)- originates in N. Atlantic, dence (cold and saline), flows to deep regions near Greenland and then southward
* Antarctic Bottom Water (AABW)- originates at Antarctica, densest (coldest and most saline), flows down near Antarctica and into the deepest ocean region then northward under the NADW into the N. Atlantic, then returns southward still under the NADW
* global ocean conveyor system:
* thermohaline circulation system- global circulation of seawater through interconnected currents in all oceans
-1000 years to replace all deep water (20-30mil. m3/sec.)
Ocean Tides: Twice-daily rise and fall of ocean waters.
* forces that cause ocean tides:
* gravitational pull that the Moon exerts on the Earth
* intertial force created by the Earth’s rotation about the center of mass
* tidal bulges: due to the sum of forces
* towards the moon- gravitational force is greater
* towards opposite- intertial force is greater
Sea-Floor Landforms
* mid-ocean ridge: most pronounced feature on earth
* broad fractured mountain system
* continuous ridge around globe
* 1500km wide and 3km high
* 23% of earth’s surface
* rift valley along crest marks axial spreading zone
* transform faults and fracture zones form numerous fault blocks
* composed entirely of basalt
* abyssal floor: flat sea-floor
* abyssal hills
* abyssal plains- pelagic sediments
* deep-sea fans- gravity-drivin turbidity currents
* trenches:
* deepest part of the ocean
* narrow asymmetrical valleys
* subduction zone topographic features
* islands and seamounts:
* hot spot chains, mantle plume
* guyots and atolls
* submerge with age
* continental margins: adjacent to collision/subduction zone
* continental shelf- submerged portion of continent
* continental slope- slope beyond shelf margin
-submarine canyons
-turbidity currents
-deep-sea fans
* continental rise- gentle slope where basin meets continent
Coasts: Coastal Erosion
* ocean waves and wave motion:
* wave base- depth (L/2), lower limit of wave motion
* breaking waves- distortion due to decrease in depth
* height increases
* wavelength decreases (successive crests)
* front of the wave steppes and breaks as the rear part continues to move forward
* surf: wave activity between the breakers and the shore, turbulent motion of water
* wave refraction: bending of waves due to a change in direction of travel caused by approach at an angle to the shoreline
* smooth, irregular coasts reduced
* erosion by waves:
* erosion below sea-level- due to surf, limited to 1.5x wave height
* abrasion in the surf zone- wearing down of rock by rock particles
* erosion above sea-level- mainly during storms
Coasts: Sediment Transport
* sediment transport by waves and currents:
* longshore currents- current in surf zone, parallel to shore
* beach drift- transport of sediment along the shore, zigzag
* beach placers- concentration of heavy minerals
* offshore transport and sorting: seaward of the surf zone
* sediments moved by currents and storm waves
* energy of wave motion decreases with depth
* sorting of particles due to increase in depth
* normally grade seaward from sand into mud
* shore profile: vertical section through shore
* on beach coasts:
* beaches- wave-washed sediment on a coast including surf zone
* foreshore- zone from lowest tide to average high-tide
* berm- bench formed of sediment deposited by waves
* backshore- zone extending inland from berm to high-tide
* rocky/cliffed coasts:
* wave-cut cliff- coastal cliff cut by waves
* wave-cut bench- platform cut across bedrock by surf
* sea caves, arches, and stacks- differential erosional features
* factors affecting the shore profile:
* constructive forces- deposition of sediment
* deconstructive forces- erosion, creation, transport of sediment
Coasts: Deposits and Landforms
* marine deltas- prograded coastline due to river sediment
* spits- elongated ridge of sediment that extends from land
-tombolos if connecting
* beach ridges- old berms
* barrier islands- islandlying offshore and parallel to coast
* lagoon- bay inshore from a barrier island
* organic reefs and atolls: stages of reef development on submerging volcanic is.
* fringing reef- reef built along the coast
* barrier reef- reef separated from the coast by a lagoon
* atoll- circular reef enclosing a shallow lagoon
Types of Coasts
* rugged, mountainous- due to deformation at plate margins (Pacific)
* low relief- due to techtonically passive, interplate reggion (Atlantic)
* embayed rocky- due to glaciation and changing sea level (Europe)
* complex- due to differential erosion of various rock types
* change in sea level:
* submergence- rise in water level relative to the land (interglacial per)
* estuaries- submerged former river valleys
* emergence- lowering of water relative to the land (glacial per)
* coastal terraces
Coastal Hazards
* storms- increased wave energy and erosion
* tsunamis- sea wave caused by earthquake, landslide, or volcanic eruption
* landslides- along cliffed shorelines
Protection Against Shoreline Erosion
* protection of sea cliffs- addition of armor (rocks or walls)
* protection of beaches
* breakwater- offshore barrier
* groin- low wall built out into the water at a right angle to the shoreline
* artificial nourishment- additional sand brought in
* effects of human interference- loss of beaches and coastal environment due to depletion of sediment blocked by dams and flood controls
Environmental Issues
