glacial unit 3

drumlin

drumlin

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?

1. Boulton model

2. Hindmarsh instability model

3. Hooke/Mickelson frozen margin model

4. 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

1. Holocene Alluvium

2. Wisconsinan age drift

3. Sangamon soil

4. Illinoian drift (only in extreme SE Iowa)

5. Yarmouth soil

6. Pre Illinoian drift

7. 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

1. Missouri river alluvial plain

2. Paleozoic plateau

3. Southern Iowa drift plain

4. Iowan surface

5. Northwest Iowa plains

6. Loess hills

7. 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?

1. solifluction

2. wind transport

3. 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

1. loveland loess - late Illinoian

2. Pisgah - 25-35 ka (late Wisconsinan)

3. 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

1. Mtn uplift

2. Continents move poleward

3. Isolation of Antartica and Greenland

4. AIS starts to grow

what factors allowed an increase in ice volume

1. isolation of land masses

2. uplift (increases mean elevation)

3. poleward movement of continents

4. global cooling

benthic

bottom dwelling organisms

What are 4 reasons the Cenozoic got colder over time?

1. Uplift (locally cooled uplifted land mass)

2. Isolation of landmasses thru plate tectonics

3. Poleward movement of land masses

4. 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?

1. Weathering hypothesis

2. 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