.. ssure 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.