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66 Cards in this Set
- Front
- Back
3 major points about glaciation
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Ice flow
Glacial landforms Periods of glaciation |
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Ice flow: ice in glaciers is like what type of rock?
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Metamorphic rock, recrystallized by pressure and temperatures close to melting, deformed by intra-crystalline creep
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Glaciers flow in directions based on their...not based on their...
What do temperate glaciers slide on? |
Surface slopes, not their basal slopes
Their bases |
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Glacier definition
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A mass of ice large enough to flow under the influence of gravity
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Glacial cover and mass balance process
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On cirque accumulation of snow, cold
On toe less snowfall, warmer |
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What is mature ice like? (effect of recrystallization)
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Dense with little air
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Burial by later deposits causes shear stress, proportional to... (2)
Stress+heat+time=? |
Surface slope and depth
Plastic flow |
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When does plastic flow occur?
Plastic flow makes ice viscous, so it flows... |
Greater than 60% of the melting temp in K (for ice=-164 deg and all glaciers are warmer on Earth)
downhill by deforming internally |
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Ice deforms tremendously during flow, first stretching in zone of accumulation then shortening in zone of ablation
What does the zone of ablation look like |
Dirty, melting ice reveals rock debris that was distributed through the ice
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Describe visual process
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Snow accumulation on the cirque, flows downhill to the toe/zone of ablation where summer melting exceeds winter snowfall (after equilibrium line attitude)
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Despite flowing faster, toe position can retreat if..
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Supply of ice is reduced
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Erosional landforms-how do all glaciers and temperate glaciers erode
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Glaciers erode by plucking blocks of jointed bedrock
Temperate glaciers also erode by abrasion using included rocks as tools |
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Temperate glacier erosion rates are proportional to...forcing valley floors to become...
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Ice velocity times ice thickness
Semicircular (U-shaped) |
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Depositional forms
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Glaciers also build constructive depositional landforms, such as end moraines
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Glacial striations
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scratches or gouges cut into bedrock by glacial abrasion
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Before glaciation
During glaciation After glaciation |
Mountain river cuts a V-shaped valley
Cirques and toes form, U-shaped valley Tributary valley as left as a hanging valley |
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What are fjords?
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U-shaped glacial valleys whose bottoms are hidden by the sea
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Glaciers can cut below current sea levels down to a depth of about?
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80% of ice thickness
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What is a small glacier? When melted there is a...
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Cirque glacier
Lake or tarn |
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Nunatak
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isolated bedrock outcrop protruding from a continental icecap
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Depositional landform - moraine, outwash
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Sediment transported by ice
Fluvial deposits typically braided rivers |
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Till
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Ice deposited, many grain sizes mixed together
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Recessional moraines
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Formed by temporary stand-still of receding terminus
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Lateral and medial moraines location
Material dropped onto glacier by...(3) |
To side, in middle
Rockfall, landslides, avalanches |
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Ground moraine
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Semi-continuous cover of till
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Dead ice
Drumlins |
Forms kettle holes
Streamlined mounds of till |
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Esker
Varve |
Deposit from river within or beneath ice
Annual band in lake deposit |
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Kame Terraces
When the glacier melts... |
Stratified deposits laid down ON the glacier by melt streams or beside the ice
They are dumped roughly |
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Lake deposits record history in annual...
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Varves (fine-course sediment bands)
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Past glaciation evidence-erratics
Lakes bounded by... |
Rocks different from the bedrock on which they now rest
Striking end moraines and lateral moraines composed of till |
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Variations of (hebrew L)18O of marine forminifera show...
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Size of land-based glaciers back through time
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Cold periods are...
When was the last glacial maximum? Gradual cooling under... |
Glaciation
20,000 years ago Shorter fluctuations |
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Variations in (hebrew l)18O gives...
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Precipitation temperature
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Relative dating until 1940
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Placed rocks into named eras, periods and epochs in a universal time scale, based on superposition, inclusion, etc.
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Absolute or radiometric dating
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Uses radioactive decay of an unstable isotope as a clock, read by measuring conc. or parent and daughter isotopes
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Stratigraphic and radiometric dating methods combined provide
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A quantitative history of the evolution of life
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In a stack of undeformed sedimentary beds...
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age increases downward
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First early attempts to name the periods referred to...
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lithology/rock-type of sediments
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Better system was devised that put emphasis on...
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fossils
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William smith
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Observed association of fossils with formations
Created the first statigraphic column Made the first geologic map |
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Smith's advance in geology and how it relates to Darwin
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Groups of fossils occur in the same order everywhere in the world, could be determined for sedimentary rocks that did not touch one another
Branches can diverge, converge, or end BUT they never recombine |
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Mass extinctions form
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A convenient boundary
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Geologic groups applied to fossil groups and then transformed into the names of...
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Geologic periods
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Unconformity
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limestone/sandstone that is younger than the bedding surfaces in the sandstone
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Unconformities are not the only cross cutting surfaces, others include...
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Intrusions, faults, folds, soil horizons, erosion surfaces
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Most easily interpreted dates from...
Can be reasonably sure the age of the mineral is close to the age of... |
Fine-grained igneous rocks
The volcanic event |
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Boundary most studied is...
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the Cambrian radiation or "explosion"
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Hard body parts expanded...
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The fossil record from the Cambrian
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Animals with no hard parts from the...
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Precambrian
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Metamorphic rocks record what kind of history?
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Down-then-up history
Bobs down then up and pulls up stuff with it (subduction of buoyant continent down then isostatic rebound) |
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Continent subducts beneath oceanic crust, the oceanic crust will be uplifted as..
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An ophiolite suite
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If a continent subducts beneath a continent then...
Former site of the ocean is marked by a suture |
Double-thick crust is form, which supports 5km topography
Suture |
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Deformation (orogeny) spreads across both continents until...
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The plates finally stop
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Subduction can recycle old seafloor indefinitely but cannot swallow...and struggles to consume...
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A whole continent
A young seafloor |
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Metamorphic rocks that leave rocks on the surface are caused by...
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Subduction of a buoyant cont, an end to subduction, then isostatic rebound linked with erosion
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If a buoyant cont is pulled into a subduction zone by a dense slab of seafloor lithosphere, subduction will stop after...
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Consuming only one edge of the continent
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Dense slab of seafloor lithoshere tears off, continent released and will...
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Spring upward, lifting the crust of the overriding plate into the air
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If a cont subducts beneath oceanic crust, oceanic crust will be uplifted as...
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An ophiolite comprising bedded chert, pillow basalts, sheeted dikes, gabbro, peridotite
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Ophiolites include scattered Cu/Mn ore deposits, now recognized as...
Cyprus=cuprous=? |
Black smoker hydrothermal vents
Copper |
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Inactive thrust fault with scraps of ophiolite (former seafloor) and turbidites (trench deposits) are...
This is formed when |
Sutures
2 smaller continents drifted together |
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Youngest continental collision, From Pliocene-now; Arabia/Eurasia
What does seismicity show? |
Zagros
Subduction has stopped |
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Next youngest continental collision, from Eocene-now, in India/Eurasia
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Himalayas/Tibet
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Next youngest continental collision, From Cretaceous to now in Europe/Africa, also the longest running active continental collision
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Alps of Europe
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Next youngest, from Pensylvanian-Permian, Europe/Asia
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Urals, inactive "dead"
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Erosion has removed the mountains many times, but isostasy causes them to rise...
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less each time since the crust is thinner than before
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Next youngest, from Pennsylvanian-Permian in Laurentia/Gondwana
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Carbon copy of the urals
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