# Large scale topography Tectonics and Structure www.montana.edu/kmw/

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Large scale topography Tectonics and Structure www.montana.edu/kmw/

Response of the mantle and crust to loading: Lake Bonneville http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm http://geology.utah.gov/utahgeo/gsl/flash/lb_flash.htm

Say an icesheet is 4000 m thick, (the Antarctican icesheet is roughly this thick at its maximum thickness.) How far does the lithosphere deflect beneath the icesheet? Step 1. Calculate pressure due to ice + crust Step 2. Calculate pressure due to mantle + crust Step 3. Pressures are equal due to hydrostatic equilibrium Given, ice has a density of 917 kg/m3 crust has a density of 2700 kg/m3 upper mantle (that gooshes out of the way to allow this deflection of the surface) has a density of 3300 kg/m3 thickness of the crust beneath the center of the icesheet and the region outside of it is the same.

Brook manual, p. 2-4 Q 2-3 Q 2-3 –Magnetic declination: the difference between geographic north and magnetic north –Magnetic declination of Philipp quad= 7.5 deg E 7.5 deg E –Verbal scale in in/mi Philipp: 1” = 62,500” =.98mi Philipp: 1” = 62,500” =.98mi Kingston: 1” = 24,000” =.38mi Kingston: 1” = 24,000” =.38mi –Verbal scale in cm/km Philipp: 1 cm =.625km Philipp: 1 cm =.625km Kingston: 1cm =.24 km Kingston: 1cm =.24 km

Brook manual, p. 2-10 Q 2.6 Q 2.6 –Horiz scale is 1:25,000 or 1” on map = 25,000” on ground 1:25,000 or 1” on map = 25,000” on ground –Vert scale is 1” = 100’ or 1”=1200” 1” = 100’ or 1”=1200” –VE=Horiz scale/Vert scale = 25,000/1200=20.8 25,000/1200=20.8 Q 2.7 Q 2.7 –Average gradient (or slope) = rise/run, in words –500 ft/(520 yds x 3 ft/yd)=500 ft/1560 ft = 1 ft/3.12 –for every vert. ft of elev gain, the dist moved in 3.12ft

Rock Cycle Repeated creation and destruction of crustal material (rocks and minerals) Repeated creation and destruction of crustal material (rocks and minerals) Volcanoes, folding faulting, uplift Volcanoes, folding faulting, uplift –bring rock, water, gas to the Earth surface Rocks disintegrates Rocks disintegrates –weathers by exposure to water and air Transport by gravity, water, wind Transport by gravity, water, wind –weathering products go back to the ocean Deposition and burial Deposition and burial –formation of sedimentary rocks Deep burial Deep burial –metamorphic rocks Uplift, intrusion, or extrusion Uplift, intrusion, or extrusion –rocks exposed, process begins again Weathering, transport, deposition

Landform creation by: Weathering, transport, deposition Weathering agents move into soil and rock along a weathering front Weathering agents move into soil and rock along a weathering front –brings fresh rock up Weathered material (regolith; soil) on surface + material brought in by wind, water, ice, animals = weathered mantle Weathered material (regolith; soil) on surface + material brought in by wind, water, ice, animals = weathered mantle Mantle remains in place or moves downslope by gravity Mantle remains in place or moves downslope by gravity –water can also carry it downslope –wind can remove it

processes in the core and mantle => processes and structure in the lithosphere large scale features of the Earth are the product of tectonic process tekton, Gr. for mason or builder http://www.geosociety.org/gsatoday/archive/15/7/pdf/i1052-5173-15-7-4.pdf

Plate Tectonics: the quick and dirty

Oceanic plate tectonics Mid-ocean ridges: Mid-ocean ridges: –the seams of a baseball Volcanic eruptions produce new oceanic lithosphere Volcanic eruptions produce new oceanic lithosphere Cools, thickens, sinks Cools, thickens, sinks http://www.pmel.noaa.gov/vents/nemo/education/images/plates_sm.jpg

Ocean landforms: Continental Shelf The edges of the continents slope down from the shore into the ocean. The edges of the continents slope down from the shore into the ocean. The part of the continent located under the water is known as the continental shelf. The part of the continent located under the water is known as the continental shelf. In some places the continental shelf is fairly shallow and in other place it becomes very deep, but it is not the deepest part of the ocean. In some places the continental shelf is fairly shallow and in other place it becomes very deep, but it is not the deepest part of the ocean.

Ocean Landforms: Continental Slope The steep slope where the continental shelf drops to the bottom of the ocean floor is called the continental slope. The steep slope where the continental shelf drops to the bottom of the ocean floor is called the continental slope. The depth of the ocean water increases greatly here. The depth of the ocean water increases greatly here.

Ocean Landforms: Mid-ocean ridge and Abyssal plain On the bottom of the ocean, there is a central ridge, or mountain range, that divides the ocean floor into two parts. On the bottom of the ocean, there is a central ridge, or mountain range, that divides the ocean floor into two parts. These underwater volcanic mountains are known as the mid-ocean ridge. These underwater volcanic mountains are known as the mid-ocean ridge.

Ocean Landforms: Trenches There are many steep-sided canyons and deep, narrow valleys in the bottom of the ocean. There are many steep-sided canyons and deep, narrow valleys in the bottom of the ocean. Ocean trenches are the deepest part of the ocean basin and are deeper than any valley found on land. Ocean trenches are the deepest part of the ocean basin and are deeper than any valley found on land.

Ocean landforms: Guyots and Seamounts http://www.utdallas.edu/~pujana/oceans/guyot.html seamount

http://www.sanctuarysimon.org/monterey/sections/seamounts/project_info.php?projectID=100114&sec=sm

Brook, p 4-4 and 4-5 Q 4.1(b) Q 4.1(b) –Cones are associated with major river systems carrying high sediment loads –often formed at low stand (glacial times) –cones were then river deltas Q 4.1 (c) Q 4.1 (c) –St Helena Island (15S, 5W); Easter Island (27S, 109W); Amsterdam Island (37S, 77E) –Islands, guyots, and seamounts were all formed at ocean ridges –The further it is from the ridge, the older it is Q 4.2 (a) Q 4.2 (a) –Red Sea is the result of divergent plates under the continent –Arabian plate moving away from African plate –divergent plate boundary