Studied by 19 peopledrumlin
elongate hill streamlined in direction of glacier movement that forms subglacially
drumlin characteristics
elongate hill
100-2000m long
5-40 m high
do drumlins occur under valley glaciers?
NO
drumlins can be composed of ____
till
sand and gravel
combo
rock cored
are drumlins up against the glacier margin?
NO, they are near it
drumlins almost always have _________ at the top
unconformities
what are the 4 models for drumlin formation?
Boulton model
Hindmarsh instability model
Hooke/Mickelson frozen margin model
Iverson model
which drumlin model does not involve bed deformation?
the Iverson model
how does the Boulton model work
meltwater streams emerge from margin (creates sand and gravel bars)
bars become nucleus for drumlins
ice elongates the bars into drumlins
What is the equation for strength
S = c + σe tanΦ
how does the Hindmarsh instability model work
how does the Mickelson frozen margin model work
partially frozen lumps of sed under glacier (due to PMT and isotherms)
frozen lumps are stronger than thawed
thawed sed leaves
frozen cores become drumlins
how does the Iverson model work
instead of bed deformation, regelation infiltration occurs
NEED MORE INFO FROM NOTES
which is the only model for drumlins based on field observations
Iverson model
Mulajokull, Iceland
only place in the world with modern drumlin field
(more/less) elongate drumlins have been under the ice longer
more elongate because they’ve had more time for “sculpting”
are drumlins more elongate upglacier or downglacier?
upglacier
flutes
small, very elongate ridges of till that are parallel to glacier flow and headed upglacier by a boulder
herring-bone pattern is evidence for…
till flow into a flute behind a boulder
what are the steps for flutes forming
cavity forms on downglacier side of boulder
till fills in cavity
cavity moves downglacier (because Pw fluctuations at bed extend cacity downstream)
process repeats
mega-scale lineations
shaped like flutes but 10-100 km long
not many theories on how they form
rogen moraine
ribbed moraine that forms subglacially from extension of thin frozen till sheet just upglacier from a transition from cold to warm ice, and is perpendicular to the flow
5-5000 m long
5-25 m high
rogen moraine characteristics
5-25m high
5-5000m long
which side are end moraines steeper on?
the upglacier side
list IA strat from youngest to oldest
Holocene Alluvium
Wisconsinan age drift
Sangamon soil
Illinoian drift (only in extreme SE Iowa)
Yarmouth soil
Pre Illinoian drift
Late tertiary drift
what do soils represent
interglacial periods
any sediment deposited by the DML is part of the _____
Dows Formation
Wisconsinan years
11ka - 30ka
Illinoian years
130ka - 300ka
Pre Illinoian years
335ka - 2500 ka
how are paleosols dated?
radiocarbon dating using wood found in the soils
Robert V Ruhe
guy that described Iowa landforms
List the Iowa landforms
Missouri river alluvial plain
Paleozoic plateau
Southern Iowa drift plain
Iowan surface
Northwest Iowa plains
Loess hills
Des Moines lobe
Missouri river alluvial plain characteristics
up against loess hills
used to be braided stream
topographic break from plain to loess hills
Paleozoic plateau characteristics
thin loess cover
isolated patches of pre-Illinois drift
almost 400 ma bedrock
karst topography with carbonate bedrock near surface
sinkholes near surface
deeply entrenched valleys
Southern Iowa drift plain
big, broad open valleys
older landscape than DML
rolling landscape with integrated rivers
soil layer on top of loess
no kettles, kames, hummocky topo…
Iowan surface characteristics
lower elevation than southern IA drift plain
no paleosols
lots of erratics
thin, discontinuous loess cover
pre-Illinois drift at surface
periglacial erosion processes
what are the three periglacial erosion processes?
solifluction
wind transport
slope wash
what is thought to be the cause for no paleosols being present?
the periglacial erosion processes
solifluction
permafrost partially thaws and mass wastes
slope wash
hard rain transports sediment downhill
colluvium
material that moves by mass wasting down hill slopes and is then redeposited
paha
oblong hills
30 - 100 ft
aligned with glacial winds
Northwest Iowa plains characteristics
Sheldon Creek formation
gently rolling, broad hills and valleys
no paleosols
faster loess accumulation than Iowan surface
Sioux quartzite characteristics
oldest rocks in IA (1.2 Ga)
NW Iowa and SW Minnesota
Loess hills characteristics
thick loess (60 - 200 ft thick)
steep, narrow crested hills
valleys filled with loess alluvium
gullys at base of valleys
loess is mostly made of ______
silt
what are the 3 periods of loess deposition in IA
loveland loess - late Illinoian
Pisgah - 25-35 ka (late Wisconsinan)
Peoria - 17-25 ka
Des Moines lobe characteristics
NO loess on top
no deeply incised river valleys
youngest part of IA
poorly integrated river network
Bemis moraine dates
deposited 17 ka
Altamont moraine dates
deposited 16.5 ka
Algona moraine dates
deposited 14 ka
Noah creek formation
any wisconsinan age sediment that emminates from a valley train
DML stratigraphy
Lake mills member
Pilot Knob member
Morgan member
Alden member
Peoria loess
Pre-Illinoian drift
Bedrock
Quaternary period dates
1.81 ma - present
T/F: the Quaternary has had repeated glaciations
t
When did the current AIS start forming?
15 ma
what are the events of the cenozoic
Mtn uplift
Continents move poleward
Isolation of Antartica and Greenland
AIS starts to grow
what factors allowed an increase in ice volume
isolation of land masses
uplift (increases mean elevation)
poleward movement of continents
global cooling
benthic
bottom dwelling organisms
What are 4 reasons the Cenozoic got colder over time?
Uplift (locally cooled uplifted land mass)
Isolation of landmasses thru plate tectonics
Poleward movement of land masses
Earth got colder globally
What GHG is more potent that CO2?
methane
Co2 levels were _____ times greater than today during the PETM
2.5
What are 2 theories for CO2 increase during the cenozoic?
Weathering hypothesis
Decreasing volcanism caused by closure of Tethys Sea
where is the best record of glaciation?
the deep ocean
what in the ocean is used to reflect δ18O in water?
shells
there is more δ——O in glaciers and more δ——O in water
16, 18
how long have the recent glaciations been
100,000 years
older glaciations were ______ years long
40,000
what event changed glaciation length?
Mid-Pleistocene Transition
What are the 3 Milankovich cycles?
Eccentricity
Change in tilt magnitude
Precession
Eccentricity period
100,000 years
Change in tilt magnitude period
41,000 years
Precession period
21,000 years
___________ controls glaciations during the quaternary
orbital variations
the colder the atmosphere, the ______(more/less) δ18O accumulates
less
what part of Earth responds to feedback the fastest
atmosphere
how do we get past temp info?
δ18O in ice cores
AMOC meaning
Atlantic Meridional Overturning Convection
how long does the AMOC take to circulate
500-1000 years
T/F: upwelling of cold water near Antartica released CO2
t
does eccentricity cause glaciations?
NO, it is negligible
it takes ________ years for ice sheets to grow large enough to become sensitive to small changes in climate
100,000
what does isostatic depression drive glaciers to do
become unstable
Pleistocene
epoch before current (Holocene)
What epochs make up the Quaternary
Holocene and Pleistocene
Mid Pleistocene Transition
change from 41,000 yr to 100,000 yr ice age frequency
NADW
north Atlantic deep water
what are the AMOC modes
warm mode
cool mode
cold mode
AMOC warm mode
current day
AMOC cool mode
flow in N cut off, some flow near equator
AMOC cold mode
circulation shutdown
what causes a change in AMOC modes
freshwater addition
does glacier and climate interaction work two ways?
YES
foram
lives near ocean surface
records ocean surface temps
N Pachyderma
foram
likes cold water
study abundance in sed cores for water temp indicator
what Heinrich event is the Younger Dryas
H0
What happens during a Heinrich event
ice shelves break off into the ocean (Ice rafted debris)
occurs at Laurentide, Iceland, and Scandinavian ice sheets
correlate to cold ocean
happens at coldest times
causes AMOC to go into cold mode 200 years later
AMOC currents are driven by ______
change in salinity and temp
When was the younger dryas
11.8 - 13 ka
Note
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