Final (Chapter 13-20) Flashcards
why do continents rise above oceans?
isostasy
what is isostasy?
buoyant continental lithosphere floats on dense asthenosphere
what is orogenesis?
mountain-building processes
what are the 3 plate boundaries?
divergent, passive, convergent
what are divergent continental margins?
mantle plume rises, uplifts and splits continental lithosphere to form rift valley with blocks dropped along normal faults, and volcanoes along valley sides
what are passive continental margins?
rift widens, seawater invades, and a new ocean basin forms whose sides experience no seismic activity but gradually subside under weight of sediment load
what are convergent continental margins? (2 types)
as mountains grow, undergo isostatic adjustments to balance weight
what are andean-type convergent margins?
oceanic crust subducts beneath continental, developing accretionary wedge, continental volcanic arc, and plutons in core of deformed mountain belt
what are aleutian-type convergent margins?
oceanic crust subducts under oceanic, to form volcanic island arc
what is continental collision? (convergent margins)
ocean basin closes, subduction stops, highest mountains form (continental crust cannot subduct under more continental crust therefore creates very high mountain *push eachother up*)
what are accreted terranes? (convergent margins)
foreign pieces of crust forefully attached to continental margin
what is the Wilson cycle?
oceans opened and closed, mountains built and rebuilt repeatedly; rarely pieces of oceanic crust got stuck onto continental margin during obduction
what is uplift? (broad vertical movements in continents)
by mantle upwelling pushing up continental lithosphere in continent interiors
what is subsidence?
how is it caused?
gradual sinking in or land
mainly due to weight of sediment deposited along passive continental margins as mountain belt erodes; also downward mantle flow pulling on lithosphere
what is the origin and evolution of continental crust?
formed by the combining of volcanic arcs above subduction zones
where is the earliest continental crust found today?
in shield areas of continental interiors
what is the main trigger of mass wasting? and what intensifies this trigger?
gravity: always pulling rock, regolith and soil down slopes….more effective if water saturates materials on slopes, reduces cohesion friction and adds weight
what causes oversteepened slopes?
due to undercutting by waves, streams, and human excavation, resulting in loss of support for materials higher up in the slope
how does removing vegetation trigger mass wasting?
vegetation anchors soil and regolith with plant roots; removing plants make the slope unstable and susceptible to failure
how do earthquakes trigger mass wasting?
can dislodge rock and unconsolidated material, resulting in landslides
how is mass wasting classified?
based on types of materials, types of motion (freefall, sliding and flowing) and how fast they move
what is slump mass wasting?
rotation of a block of slope material along a sliding surface (usually lubricated by water) gravity pulls the block in a rotational motion away from a scarp with the block’s surface tilting back - happens when they slop is undercut by a stream, by waves or by human excavation
what is rockslide mass wasting?
common where rock structures parrallel slopes (mountainous areas) provide sliding surface, or where stronger rock rests on weaker rock especially if the slope is undercut, sliding surface is lubricated after heavy rain or snowmelt, or shaken by an earthquake
what is debris flow?
fast flow of saturated soil and regolith down valleys following heavy rain OR during and after volcanic eruptions where ash gets mixed with melted snow and ice rushing down valleys (lahars)
what is earthflow?
slower movement of (mainly) mud down hillsides in humid areas following heavy rain or snowmelt; forms a tongue-shaped mass that may continue to move slowly for years; commonly starts as a slump
what is a creep?
gradual down-slope movement of soil and regolith under gravity; caused by repeated freezing and thawing, wetting and drying, or water saturation following heavy rain or snowmelt - results in tilted trees, fences and utility poles
what is solifluction?
flow in saturated ground resting on impermeable rock, clay or permafrost in polar areas; water cannot percolate downward below the impermeable surface and so material flows slowly downhill as lobes
what is the hydrologic cycle?
97% of earths water is stored in the oceans, evaporated then precipitated on land - some soaks in (infiltration) some flows over the land as streams (runoff), some evaporates back into the atmosphere and is transpired by plants, and some is stored in glaciers, but most returns to the oceans by streams
what is streamflow?
stream erodes, transports according to its veolcity and channel shape
what is gradient? (in relation streamflow)
slope of stream channel over its length; cross-sectional shape determines how much of the channel contacts water, slowing it down; rougher, more friction
what is discharge? (in relation to streamflow)
volume of water flowing through the stream’s cross-section per second; if discharge increases, stream usually gets wider, deeper, and faster downstream
streams _____, _____ and _____ simultaneously over their lengths
erode, transport and deposit
how do streams cause erosion?
by wearing down from particles in transport acting as cutting tools to scour channel walls (like sandblasting) and in circular eddies (circular movements of water) to cut potholes into the channel floor
what are the 3 types of sediment loads transported by streams?
dissolved : ions in solution from chemical weathering and groundwater
suspended : sediment that remains above the bed;
bed load : is particles sliding and rolling along the channel floor
saltation : involves jumping and skipping of particles that alternate between bed and suspended loads
what is deposition?
occurs when stream can no longer cary its load and particles fall to the bed; can form a channel deposit of sand and gravel in bars, or floodplain deposit of mud beyond the channel
what are stream valleys?
a stream cuts vertically but its bandks cave in by mass wasting to develop narrow V-shaped valleys with waterfalls and rapids in rough channels
where do wide valleys form?
on gentle gradients and cut mainly sideways forming flooplains as the stream shifts back and forth across the valely leaving a thick fill of sediment
what are drainage patterns determined by?
network of tributaries (river or stream flowing into a larger river of lake) feeding the stream
what does the pattern of a basin (large low-lying area) depend on?
rock types and structures
where do dendritic patterns of drainage occur?
uniform bedrock where channels follow local slopes
where do radial patterns of drainage occur?
from a volcano or rock dome
where do rectangular drainage patterns occur?
where stream flows over joints or a fault system with right angle bends
what are artificial levees? and why are they built? (in relation to flood control)
man-made wall built to keep water from going into certain areas and prevent flooding
built along stream banks to increase the volume the stream can hold
why are flood control dams built?
to store water then let it out slowly - resulting reservoirs are used for irrigatio, power generation
what are some of the downfalls of flood control dams?
flood river valleys, displace wildlife, drown forests, and fill with sediment that reduces their holding capacity and effectiveness
what is the most effective way of getting water underground?
steady rainfall soaking into the ground because heavy rain produces mostly runoff and little infiltration once plant requirements are met
what is the zone of saturation?
pores of sediment or rock are completely filled with water
what is the zone of aeration?
pores contain mainly air and minor water held as soil moisture
what is the water table? and what does it mimic?
the surface between the zone of saturation and the zone of aeration
mimics the land surface eg. the water table is highest under hills and lowest under valleys
what does the movement of ground water depend on?
nature of materials
what is porosity?
volume of open space in rocks or sediment, including fractures and openings
how is porosity reduced?
by pores getting filled with cement and fine particles
what is permeability?
connection of pore spaces and ability of material to transmit
what is impermeable material called?
aquitard
what is permeable material called?
aquifer
how does groundwater flow?
under gravity in a pattern of long curving paths towards streams
what are springs?
where water table meets the ground surface; springs may occur where an aquitard causes the local water table to be “perched” above the main water table
what are hot springs?
where groundwater is heated at depth then rises to the surface
what are geysers?
water boils under pressure, vaporizes and blasts water into the air, then water refills the pipe and cycle starts over again (old faithful erupts ever hour)
what are wells?
holes drilled into the zone of saturation; must be drilled deep enough below the water table to retrieve water during the dry season
what do wells cause?
cones of depression in the water table where it is drawn down toward the base of the well
what are artesian wells?
tap water under pressure in an aquifer that is sandwiched between aquitards; water naturally rises to the ground surfce with minimal pumping
what is subsidence?
pumping water for irrigation faster than it can be replenished causes underlying sediment to compact, resulting in gradual sinking of the ground surface
how does groundwater contamination happen?
from septic tanks, fertilizers, toxic spills, buried chemical tanks, and leaking sanitary landfills; polution can make its way into aquifers
where should cities dispose their waste and why?
in impermeably sites because it takes many years to flush out (cleanse) an aquifer
what is the geologic work of groundwater?
by solution of soluble rocks to form
what are caverns?
by groundwater solution enlarging cracks and bedding planes in soluble rocks just below the water table
how do needle-like stalactites (icicle-shaped formation that hangs from the ceiling of a cave) form?
by water dripping from cave ceilings
what are stalagmites?
upward-growing mound of mineral deposits (looks like a post)
what do stalactites and stalagmites eventually form?
columns (conjoin because of upward and downward growing)
what are ice-sheets?
type of glacier: radial-spreading large ice masses on continents (eg. Anartica)
what are valley mountains?
type of glacier: commonly flow down old stream valleys
if accumulation > ablation what happens?
the glacier’s terminus (end point) commonly advances
if accumulation < ablation what happens?
terminus (end point) usually retreats
what are glaciated valleys?
U-shaped valleys
what are cirques?
rock bowls at heads of valley glaciers, gnaw into a mountain divide from the sides
what are fjords?
U-shaped valleys along coasts
what are drumlins?
mounds streamlined under the glacier (blunt ends point-up glacier)
what is stratified drift?
comprises sand and gravel deposited by glacial melt-water
what are wave-cut cliffs?
wave-cut platform caused by collapse and retreat of cliff from cutting action of surf against the base of cliffs sweeping debris out to sea
what are arches?
where waves cut caves into the sides of headlands until the caves join; eventually arch collapses and leave a stack sitting along on the wave-cut platform
what are spits?
elongated sand ridges that form where beach drift, longshore currents move sand into the mouths of bays
what is a bay-mouth bar?
where a ridge crosses the bay
what is a tombolo?
a sand ridge that connects an island to the mainland or another island
what are jetties used for?
to keep sand out of river mouths
what are groins used for?
lie perpendicular to the shore to trap sand and widen beaches
what are breakwaters used for?
built parallel to the shore to protect marinas and beaches from storm waves
