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GEOG 203: EXAM 2
Fluvial processes |
refers to erosion by water. Most important erosion agent on Earth |
base flow |
all the water below the surface, feeds rivers through seepage |
surface (overland) flow |
combination of storm water, melt water, and precipitation at the surface |
drainage basin |
'catchall area' - area of land where surface water converges to a single point. Topography is most important constraint on size of drainage basins. IT IS POSSIBLE FOR RIVERS TO FLOW NORTH
|
drainage patterns |
1. dendritic
2. parallel
3. rectangular
4. trellis
5. radial
6. centripetal |
dendritic pattern |
occurs when there is homogenous topography |
parallel pattern |
occurs on steep landscapes |
rectangular pattern |
occurs where there's faults or a hard Earth material blocking flow |
trellis pattern |
occurs where there's valleys and hills |
radial pattern |
occurs when there is a mountain in the middle |
centripetal drainage pattern |
occurs when there is a depression in the middle that water flows to |
drainage networks |
how streams are ordered. Main channel is a tributary. 2+2=3, DONT SUM THE NUMBERS. The higher the number, the more important it is |
ephemeral stream |
comes and goes. When a storm hits it fills up. There is only water when it rains. |
Intermittent |
seasonal stream. Wet during wet seasons and dry during dry season. |
Perrennial streams |
always filled with some amount of water year-round |
flow velocity |
how fast water is moving in m/s. Surface water at the center flows faster because there's less friction (true for straight moving streams). Water flows faster at steeper slopes. If the river bends, water will flow fastest on the outside bend. Factors include slope, channel roughness (friction) |
discharge |
meters cubed/second = widthXdepthXvelocity. Volume of water per unit of time |
turbulence |
how water moves into channel |
turbulent flow |
speed and direction of water will change constantly. This results in erosion
|
material transport and alluvium (3 types of loads and 2 ways they move) |
1. dissolved load
2. suspended load
3. bedload
1. saltatation
2. traction |
dissolved load |
everything completely dissolved in water (minerals, etc), invisible |
suspended load |
all the material suspended in the water - not touching the bottom, small particles like clays and sands |
bed load |
bigger particles that sink to the bottom of the stream but still move through saltation and traction |
saltation |
skipping of the particles, pushed by water above |
traction |
pushed slowly by current |
alluvium |
name given to material that's transported and deposited by the river |
stream grade evolution |
stream always wants to create a smooth concave slope
1. Upper course
2. Middle course
3. Lower course |
upper course |
very steep, in headwaters, form v-shape valleys in the mountains, river cuts down |
middle course |
no more waterfalls, knickpoints, water flow is smoother and less gradient |
lower course |
gradient close to 0, really flat, almost at sea level, floodplains |
floodplains |
large valley where you find a river, flat surface, and it meanders |
fluvial cycle |
youth: mountain just born, a lot of mountains
maturity: fewer mountains, more like hills
old age: flat plains
|
oxbow lake |
abandoned arm of a meander |
meandering stream pattern |
one main channel found on flat plains, not stable over time |
braided stream |
not in flat lands, multiple channels disconnecting and reconnecting constantly over the landscape
seasonal, ex: glacial outwash |
terrace |
elevated portion of the floodplain where the stream has not cut down, tells where the older elevation used to be. One on each side of the river, two terraces |
delta |
water of the channel meets the larger body of water, a lot of sediment carried by the water and accumulated at the end makes a half circle or a fan |
alluvial fan |
alluvium gets deposited at the end of the channel, can't carry it anymore so it drops it down because fast moving water meets slower moving water |
barrier island |
in order to form- need a shallow and flat continental shelf, a source of sediments, and mid-range waves to form
they are narrow and parallel to the coast, but are completely separated from coast
unstable, can migrate and will protect land from strong storms |
bays |
indentations in coastline usually u-shaped, mostly easily eroded soft rock
usually don't exist without capes |
capes |
non-indented part of landscape, rocks are harder to erode
usually don't exist without bays |
beach |
created by wave action. Seasonal cycle: winter - high energy waves hit shore and erode sand away from the beach depositing it to the continental shelf. Summer - low energy waves carry the sand back to the beach
Unstable
most important landform of coastal processes |
Beach terms |
wave refraction
swash
backwash
longshore drift
formation
boundaries |
wave refraction |
happens close to shore, when wave hits shallow zone |
swash |
wind deposits sediments on the beach |
backwash |
erodes beach away and brings sediment back into the water |
longshore drift |
current that forms parallel to the beach and very close to the coast line |
formation |
need sediments eroded from somewhere, sand picked up by long drift currents |
boundaries |
marked between high tide and low tide |
lagoon |
areas of shallow water that are dammed by a barrier island, spit, or tombolo. Fragile ecosystems. Some lagoons 100% fresh water, others have some salt water |
spit |
long narrow ridge of sand and sediments, extends out to the sea. Exists because of longshore drift. Need a shallow continental shelf |
tombolo |
narrow ridge of sand that connects the mainland with an island |
aeolian processes |
wind is important agent. Wind processes erode, transport, and deposit. Found mostly in places with little vegetation and there are 2 main ways wind can erode landforms; deflation and abrasion |
deflation |
wind picks up sediments, includes suspension and saltation |
abrasion |
sandblasting by wind, can erode structures away |
dunes |
most important form of aeolian processes. Need sand, wind, and an obstacle (rock, dead tree, etc). Sand is deposited and built up on top of the obstacle creating a dome, sand keeps rolling up the hill and eventually gets too steep at the angle of repose (34 degrees). Then it collapses
unstable
migrates over time
2 types of dunes: barchan and parabolic |
barchan dune q |
wind hits the big face side of the dune, u-shaped |
parabolic dune |
center part of the dune migrates and creates a concave dune rather than convex |
desert pavement |
most important desert landform next to sand dunes. Result of erosion. It is what's left behind that the wind cannot pick up through deflation, etc. |
loess |
deposit by wind, mostly made of silt |
how does current climate change compare to previous 2000 years? |
rapid increase in atmospheric CO2 concentration
increasing trend i global temperature
past 2000 years temperatures have been decreasing
rapid increase in temperature
rapid decrease in arctic sea ice
rapid increase in greenhouse gases over the past 200 years |
Holocene epoch |
last 12,000 years
when humans started populating every continent, Bronze Age, Iron Age. Warm and stable climate, interglacial |
Sangamonian |
last interglacial, warmer than today. CO2 almost 300 ppm. Potentially warmer than Holocene |
Wisconsinian |
last glacial ice sheets from north pole to wisconsin. Lasted nearly 100,000 years. CO2 declining
|
quarternary period |
current period we're in now
last 2.6 million years
Holocene is part of it
climate is cooling and becoming more variable |
three main factors impacting the pacing of the glacial-interglacial cycles
|
atmospheric CO2
amount of ice
solar radiation
|
hoodoo |
soft rocks erode faster than the harder ones above
caprock on top
Bryce Canyon in Utah |
yardang |
shaped by wind abrasion in the form of low ridges lying parallel to the wind direction
soft bedrock underneath
common in dry sandy areas
aeolian landform |
how does the current climate change compare to previous 400,000 years? |
temperature and CO2 concentration has cycles (higher temperature, higher CO2 and vice versa)
we are currently at a peak - each peak is a warm period of an ice house
4 big cycles in the last 400,000 years, so one every 100,000 years |
glacial to interglacial |
happens rapidly because ice melts faster than it builds |
interglacial to glacial |
happens slower because ice builds slower than it melts |
relationship between glacial cycles and Milankovitch cycles |
more ice = less CO2
glacial to interglacial = eccentricity
lag between Milankovitch cycle and ice age |
Last Glacial Maximum
|
30% covered in ice
ice sheets on land: more than 1 mile thick, ocean levels a lot lower
sea level change: 25 m rise since LGM. As ice melted the ice went back into the ocean. Ice is bending the coast down so when it melts, the crust rises - thermoexpansion
land bridges: how humans went from Europe to North America between Siberia and Alaska
Biotic change: large animals, vegetation different at the base of glaciers, permafrost, Know this bc pollen reconstruction |
ice sheets |
as ice sheets grow, they change the albedo every year creating cold conditions
creating a cold mountain, promotes ice build up
earth's crust sinks down to adjust for the weight
ice melts and leaves water which creates proglacial lakes
bedrock forms back to where it was |
how we know the size and volume of previous ice sheets |
glaciers leave moraines
volume: use oxygen isotopes O16 and O18.
O16 gets evaporated easier |
aphelion |
coolest summers, ice not melting, farthest from the sun |
perihelion |
warmest summers in Northern Hemisphere, closer to the sun, more radiation, ice melting |
how do we know that atmospheric CO2 concentration goes down by about 30% during glacials? |
CO2 goes down into the ocean: transfer from biosphere to ocean. Ice sheet is growing and grinding away everything that contained CO2 on land (lose 25%)
CO2 is more soluble in cold water: when ocean gets cooler, lose about 10 ppm of CO2
biologic activity increases because iron in the sands acts as a fertilizer for the phytoplankton, generating photosynthesis, and carbon gets sequestered into the ocean |
an example showing how important CO2 is in controlling Earth's temperature during glacial |
ice sheet growth: because of less CO2 in the atmosphere, Earth's temperature decreases everywhere
Example: Andes, ice caps are growing |
what is abnormal with post-industrial atmospheric CO2 concentration? |
long term trend. Normal interglacial would be 280 ppm, we are now at 400. |
what evidence do we have that this CO2 is caused by human activity? |
timing: burning coal = more CO2 in the air
isotopes: can trace where CO2 comes from |
glacial processes |
mechanical actions performed by glaciers that result in landforms
|
periglacial processes |
mechanical actions performed by freeze-thaw cycles |
glacier |
geographically/geometrically constrained within mountain ranges and valleys. Smaller in size. Ex: Sierra Nevadas, Glacier National Park, Alaska, Himalayas |
ice sheet (continental glacier) |
not constrained, huge and cover large areas of land. Ex: Greenland, Antarctica |