Glaciers and ice ages

Question 1

What evidence was found for glaciation?

Answer 1

erratics: fine sediment of large boulders found 100s of km in local bedrock
unsorted sediments

Question 2

what are glaciers?

Answer 2

thick masses of recrystallized ice. last all year long. flow via gravity. cover about 10% of the earth.

Question 3

when did the most recent ice age end?

Answer 3

11000 years ago. ice sheets were hundreds to thousands of metres thick.

Question 4

is ice a mineral?

Answer 4

yes

Question 5

how is snow transformed into ice?

Answer 5

can form slowly (thousands of years) or quickly (tens of years)
Snow is buried by later falls. Compression reduces volume. Burial pressure causes melting
and recrystallization. Snow turns into granular firn.
Over time, firn becomes
interlocking crystals of ice.

Question 6

what conditions are necessary for glacier formation?

Answer 6

cold local climate (polar latitudes or high elevations)
lots of snow in winter and can’t all melt in summer

Question 7

what are the two types of glaciers?

Answer 7

mountain and continental

Question 8

describe mountain glaciers

Answer 8

flow from high to low elev in mountain settings

Question 9

name and describe 4 types of mountain glaciers

Answer 9

cirque: fill mountain top bowls
valley: flow like rivers down valleys
mountain ice caps cover peaks
piedmont: spread out at end of valley

Question 10

descrive continental glaciers

Answer 10

Greenland and Antartica
Vast ice sheets covering large land areas. Ice flows outward from thickest part of sheet.

Question 11

what is basal sliding?

Answer 11

meltwater forms at base of glacier, it decreases friction and ice slides along substrate
movement of glacier

Question 12

what is plastic deformation?

Answer 12

movement of glacier
occurs below, about 60m depth. grains of ice change shape slowly. new grains form while old grain disappear. crevasses form at surface, upper zone too brittle to flow

Question 13

why do glaciers move?

Answer 13

gravity is strong makes ice flow.
glacier moves in the direction of its surface slope.
ice base can flow up a local incline.
In continental glaciers, ice spreads away from center of
accumulation. because
ice sheet always thicker in the middle, so it spreads
toward the edges.

Question 14

what control’s a glacier’s rate of flow?

Answer 14

The severity of slope angle: steeper = faster
Basal water: wet-bottom = faster
Location within glacier:
faster in ice center, slower due to Friction at margins.

Question 15

what is zone of accumulation vs of ablation?

Answer 15

accumulation: net snow addition
colder temps prevent melting, snow remains in summer
ablation: net ice loss
zones meet at equilibrium line

Question 16

what is toe?

Answer 16

leading edge of a glacier

Question 17

what are toe positions based on accumulation and ablation?

Answer 17

accumulation = ablation: stays in the same place
accumulation > ablation: advances
accumulation < ablation: retreat upslope

Question 18

what are tidewater glaciers?

Answer 18

valley glaciers entering the sea

Question 19

what are ice shelves?

Answer 19

continental glaciers entering the sea

Question 20

what is glacial abrasion?

Answer 20

a “sandpaper” effect on substrate
Substrate is pulverized to fine “rock flour” which abrades and polishes bedrock. Large rocks are dragged across bedrock gouge striations causing striations parallel to ice motion direction

Question 21

what are cirques?

Answer 21

bowl-shaped basins high on a mountain. form at uppermost portion of glacial valley. after ice melt, will become a tarn (lake)

Question 22

what is an arete?

Answer 22

a knife-edge ridge formed by 2 cirques that have eroded toward one another

Question 23

what is horn?

Answer 23

a pointed mountain peak. formed by 3+ cirques that surround the peak

Question 24

what are u-shaped valleys?

Answer 24

glacial erosion creates a distinctive trough. likeV-shaped fluvial valleys

Question 25

what are hanging valleys?

Answer 25

look at slide lol idk what this is

Question 26

what is glacial plucking?

Answer 26

Ice freezes around bedrock fragments and plucks chunks as glacier advances.
Forms asymmetric hill called a roche moutonée

Question 27

what is a fjord?

Answer 27

U-shaped glacial troughs flooded by the sea

Question 28

what can glaciers be compared with in terms of deposition?

Answer 28

large-scale conveyor belt. pick up, transport, deposit sediment. sediment transport always downhill

Question 29

what is moraine?

Answer 29

unsorted debris deposited at toe of a glacier

Question 30

what is glacial till?

Answer 30

sediment dropped by glacial ice. consists of all grain sizes. unmodified by water there4 unsorted, unstratified
accumulates beneath glacial ice, at toe of glacier, along glacial flanks

Question 31

what are erratics?

Answer 31

boulders dropped by glacial ice. rocks are different from underlying bedrock. been carried long distances in ice.

Question 32

what is glacial marine?

Answer 32

sediments from an oceanic glacier. melting icebergs drop stones into bottom mud

Question 33

what is glacial outwash?

Answer 33

sediment transported by meltwater. muds are removed, sizes graded and stratified, grains abraded and rounded. outwash dominated by sand and gravel

Question 34

what type of muds are formed in winter vs summer months?

Answer 34

winter: finest silt and clay
summer: coarser silt and sand

Question 35

what is loess?

Answer 35

“luss”
wind-transported silt.
fine sediments produced abundantly by glaciers. Strong winds over ice blow
the rock flour away, it settles out near glaciated areas as
loess deposits.
Deposits are unstratified and distinct in color.

Question 36

where are different types of moraines formed?

Answer 36

end: stable toe of a glacier
terminal: farthest edge of flow
recessional: retreating ice stalls

Question 37

what is ground moraine?

Answer 37

till left behind by rapid ice retreat. hummocky mostly flat land surface. kettle lakes form from stranded ice blocks

Question 38

what are drumlins?

Answer 38

long, aligned hills of molded lodgement till
steep up-ice; tapered down-ice
parallel to ice-flow direction

Question 39

what are eskers?

Answer 39

long, sinuous ridges of sand and gravel
form as meltwater channels within or below ice. channel sediment released when the ice melts

Question 40

what are consequences of continental glaciation?

Answer 40

ice loading and glacial rebound (ice sheets depress, rebounds after melting)
sea level rise and fall (fall when water stored on land, rise when water returns to oceans)

Question 41

lakes and glacial consequences

Answer 41

Gigantic proglacial lakes formed near the ice margin.
Pluvial features—large lakes formed during ice age. lakes where today’s deserts are

Question 42

what is unique about periglacial environments?

Answer 42

“near-ice”
year-round frozen ground (permafrost).
Freeze-thaw cycles generate unusual patterned ground

Question 43

approximately how many glaciations throughout earth history?

Answer 43

20 or more. 4 largest. indicated by fossil tills and striated bedrock

Question 44

what are causes of glaciation?

Answer 44

plate tectonics
atmospheric chemistry (changes in GHG concentrations)

Question 45

how do plate tectonics cause glaciation?

Answer 45

tectonics move higher latitudinally. uplift leads to absorbance of CO2 from atmosphere (and CO2 keeps Earth warm), blocking warm water flow.

Question 46

what is milankovitch hypothesis?

Answer 46

Earth climate variation predicted by orbital movements.
1. temp drops, glaciers form
2. glaciers grow, albedo cools more
3. temp warms, interglacial begins

Question 47

we have forestalled the next glaciation

Answer 47

human-induced warming
last 150 years, temperatures have risen and most mountain glaciers have dramatically retreated.
“super-interglacial”
period