Geog 1111: Volcanism, Tectonic Plates, and Landforms - Prof. Parker K., Study notes of Geography

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Volcanism and Volcanic landforms

Landform: surface configuration of the land
Balance between:
Internal forces that push the crust upward
Denudation processes that weather and erode mineral matter

Volcanism:
Formation of new igneous rock at the earth’s surface
Magma surface and cools forms rock
Creates landform immediately
Eruptions involve:
Lava
Gas (CO2, H20

Sites of current volcanoes:
Plate boundaries
Plate tectonics

Types of magma
Basaltic magma:
silica content=low, viscosity content=low, forms lava=yes, forms pyroclastics=no, melting temperature=high, type eruption=non violent
Andesitic/granitic magma:
silica content=high, viscosity content= high, forms lava=no, forms pyroclastics=yes, melting temperature=low, type eruption=explosive

Shield volcanoes and flood basalts
do involve basaltic magma
magma surface through vents, flows long distance
largest volcanic landform
built up over thousands to millions of years
occur at spreading centers, island arcs and hot spots

Cinder cones
basaltic or andesitic
magma surface under great pressure
pyroclastics/lava ejected into air, solidify fast as ash and cinders
falls back around vent to build cone
smallest of volcanoes
takes least time to form

composite volcanoes
more andesitic magma than shield volcanoes or flood basalt
form from series of eruptions involving different types of magma Geog 1111 04/19/2011
short-term hydrographs and drainage basins
high base flow, high through flow
low overland flow, low runoff
low flood peaks
more consistent Q

sediment load and stream capacity
source of sediment: surrounding hillsides

types of stream loss
1. dissolved load: lots of chemicals carried
2. suspended load: sediment particles settle slowly enough to be carried into flowing water (w/o touching the bed)
3. bedload big rocks, way to heavy to be suspended up usually
floods pick up boulders and move them

stream capacity: total amount of sediment a stream can carry
influenced by:
gradient: elevation change with horizontal distance

stream in equilibrium: sediment load=capacity
capacity<load stream cant carry its load--> deposition, aggradations
deposition: sediment will settle out

streams and fluvial landforms
1. longitudinal profiles
headwaters
steeper gradient
bedload
small channel
valley deepening
mouth
flatter gradient
suspended load
large channel
valley widening
2. streams as agents of work
headwaters
mouth
3. changes in drainage basins over time
4. aggradational and degradational landforms
Geog 1111 04/19/2011
Streams and Fluvial Landforms
Streams as agents of work:
Work done by:
1. Water itself
2. Sediment- mechanically abrading channel

work done by streams:
Headwaters: erosion and down cutting
Valley deepening
Wearing down waterfalls
Cutting into the head of the drainage basin
Mouth: lateral shifting of streams across floodplain
Gradients are a lot gentler
Not a straight channel (slithers back and forth): meandering
1. Creation of cut banks and point bars
maximum velocity is in the middle of the channel, or where the water is deepest will send you down river fastest
where velocity is fastest is where capacity to carry sediment is greatest
2. Overbank flooding deposition on the floodplain
normal Q- confined to channel
changes in drainage basins over time
irregularities in longitudinal profile are worn down
lakes fill in
valleys become deeper and wider
hillsides become flatter and smoother
aggradational landforms
capacity< load stream cant carry its load deposition, aggradation
infilling of channel bed at head of lake
degradational landforms
capacity> load stream has excess energy erosion, degradation
climate change > rainfall > Q
damming a stream (below dam)
uplift of land > gradient

Pleistocene: (ice age) 30% of land area ice covered, 2 mil years ago to 10 thousand years ago. Temperatures fluctuated 3-5 degrees from glacials to interglacials. Many advances and meltbacks (“retreats”) of the ice. Best understood last 15- 20k years, accompanied by many environmental changes away from the ice.
Landforms: Continental Glaciation:
Zone of ice accumulation: Canadian shield results in erosion, abraided rock, thin veneer (light layer of soil) of weathered rock debris over exposed bedrock- infertile soil, irregular depressions and lakes, mainly Canada think about it. Not much deposition, ice retreaded quickly over the region.
Zone of ice ablation: American Midwest, prairie provinces, deposition, thick deposits of glacial till and backwash, bulldozing of preglacials landscape
Kettle lake: when a chunk of glacier breaks off and forms a kettle like hole
Moraines: linear landscape
Geog 1111 04/19/2011
Landforms: continental glaciation
Zone of ice ablalation: Midwest and prairies deposition
Thick deposits of glacial till and outwash
Moraines- linear hills of glacial till
Bulldozing of preglacial landscape
Kettle lakes: lakes formed by melting ice blocks

Types of glaciation
Continental:
Ice overrides all terrain features—obliterates preglacial relief, topography
Valley or mountain
Ice restricted to preglacial stream valleys—leaves drainage divides above the ice

Landforms: mountain glaciation
Ice only modifies pre-glacial landscape, doesn’t completely override it, doesn’t create hills or valleys.
Ice has tendency to oversteepen slopes, and broadens valleys out so that they are much much wider than before.
V-shaped valley, if glacier moves down it, it turns into a u shaped valley
Moraines are deposited—damming lakes
Occur in mountain glaciers as well.
Often times dam up rivers and you get lakes forming that are made from moraine dams
Longitudinal profiles of streams more irregular
After time as ice melts back, it will become smoother

Actively glaciers: Alaska. Because of the precipitation in Alaska. As long as rate of snowfall exceeds rate of melting, there will be glaciers
Ablating glaciers- Colorado. (30-40 yrs ago) glacier is melting

Glacial recession
Most of the glaciers in Alaska

Indirect effects of the ice
1. Sea level changes
takes all water from ocean/continental glaciers to drop sea level
sea level changes to ice, then decreases
2. Deserts-wetter pluvial lakes
lakes that exist in areas that are too dry today Nevada, Utah
3. vegetation change worldwide
areas of mountains would have vegetation and places where glaciers were there was no vegetation
4. stream adjustment to glacial meltwater
as glaciers are melting, there is more sediment
sediment load is spread out across the Midwestern united states
Long/short currents occur because wind almost invariably comes into the coastline not perpendicular to the coast. If wind is coming in at angle to the coast, along the beach when the wave crashes its gunna break in line with direction of wind and waves, but when water falls back into the ocean, it goes back down the beach. Sand gets transported down the beach long/short drift

Differential erosion is when you have rock layers that erode differentially. You can apply the same stresses the same temperature and chem actions to them and they will not erode equally. Rocks are dense and strong. Some rocks like shale which is like mud cemented together, something like sandstone is super strong, chemically cemented together. Shale is going to weather and erode much more quickly than sandstone and so it will be removed and weathered away.

Plate boundaries different from continental to oceanic
Oceanic plate is denser, sub ducted beneath continental plate. It melts and causes molten to weld up, and as it does so it melts part of continental plate. Formation of composite volcanoescascadesSeries of eruptions and forms layer cake feature when done. Oceanic oceanic boundaries coming together you tend to get deep sea trenches, both things coming together are dense material. Continental continental plates come together, seen today where indo-Australian plate is crashing into Asia to give Himalayas, now you have both low density plates coming together, everything buckles up on top of the surface.

Marine terrace: tectonic activity and erosion of wave action. Along the beach you get wave action attacking base of the rocks and erodes away here and any time you undercut the base support, it makes it unstable (overhanging rock). If cut into, the stuff above it will fail. Over time you get a pretty flat area and a cliff and it continues on above that. Then these occur where there are changes in sea level relative to the land, because sea level drops of land is lifted up. Then eventually the sea is breaking in a new area instead and you have a flat area that is elevated.  Involves formation of cliff and change in sea level…

What is a moraine: movement of ice, like a conveyor belt, any sediment in ice brought forward, dumped in mouth…