(13) + (14) Glaciation Flashcards
(30 cards)
1
Q
Ice is a
A
Mineral
2
Q
Glaciation
A
- Glacier = mass of ice, formed on land, and moving because of its own weight and/or gravity
- Pleistocene Epoch – period of geological time about 1.6 Ma to 10Ka
o What we consider the last ice age
o We are likely in an interglacial period – warm periods between major ice sheet formation and movement
o Landforms shaped by glaciation are an important part of our present landscapes
3
Q
Formation of glaciers
A
- Snowflakes -> granular snow (firn) ~7weeks
- Firn -> glacial ice ~8 weeks
- Due to pressure of overlaying material
4
Q
Accumulation and Melting Zones
A
- Zone of accumulation: snowfall > melting
- Zone of ablation/wastage: melting > snowfall
5
Q
Types of glaciers
A
1. Valley or alpine type o Length >> width o Longest ~100km long, thickness ~700m long o Flows downhill 2. Continental (ice sheets) o Broad, thick (Greenland = ~3km thick) o Flows outward in all directions
6
Q
Movement
A
- Velocity: ~30 cm/day up to ~50m/day
- May increase with increased slope, thickness, temperatures
- Velocity greatest at top
7
Q
Types of Movement
A
- Basal sliding – on film of water
- Plastic flow – higher molecules flow faster
- Zone of fracture – upper rigid zone (molecules move together)
8
Q
More on movement
A
- Valley glaciers move down-valley fed by snow accumulation on top
- Ice sheets move outward from thicker regions of accumulation
- THE ICE IS ALWAYS MOVING FORWARD, EVEN DURING PERIODS OF RETREAT
9
Q
Erosion of glaciers
A
- Mainly at the base, but valley glaciers also erode material along the sides
- Basal sliding leads to scouring, grinding, crushed, etc. resulting in flattened surfaces, polished and scoured surfaces (striation), as well as plucking of bedrock material
10
Q
Erosional landscapes
A
- U-shaped valleys
- Hanging valleys
- Cirques
- Horns
- Aretes
- Rock-basin lakes (tarns)
- Rock steps
- Fiords
11
Q
Glacial depositional landforms
A
- Some forms of glacial deposits may be formed by both types of glaciers, however, extensive area dominated by glacial deposits (most of North America) were mainly produces by large ice sheets
12
Q
Types of Deposits
A
- Drift
- Till
- Moraine
- Outwash
- Drumlin
- Erratics
- Kame
- Esker
- Kettle
- Knob
13
Q
Drift
A
- A general term for any deposit of glacial origin
14
Q
Till
A
- Similar to drift
- General term usually unsorted and unstratified
15
Q
Moraine (tyoes of Moraine)
A
- A layer or ridge of till
o Lateral moraine – along the side
o Medial moraine – marks where two glaciers marge
o End moraine – marks furthest advance – may be terminal or recessional
o Ground moraine – from under the glacier
16
Q
Outwash
A
- Outwash debris carried away from the gacier by meltwater – usually sorted and stratified
17
Q
Drumlin
A
- Shallow/steep-sided hills, point direction of ice travel
- Formed in crevasses or over-run moraines
18
Q
Erratics
A
- Large deposits such as boulders (rock not the same as the bedrock)
19
Q
Kame
A
– Steep-sided hill of sorted sediments
– Collected in crevasses, surface streams, or deltas into proglacial lakes
20
Q
Esker
A
– Long, sinuous ridge of sorted sediments formed by meltwater streams
21
Q
Kettle
A
– Depression formed where ice-block was buried, then melted
22
Q
Knob and kettle topography
A
Characteristic kettle and kames in SW Manitoba, Sask, and Alb
23
Q
Effects of continental glaciation
A
- In the recent past, at least 4 major stages of glaciation have affected North America
- Most of Canada was glaciated – ie moraines in Manitoba, drumlins in Ontario, knob and kettle terrain in Sask and Alb
24
Q
Other features of glaciers
A
- Ice-margin glacial lakes – Lake Agassi, Manitoba – remnants = Lakes Winnipeg, MB, Winnipegosis
- Pluvial Lakes – different climatic conditions in the past Salt Lake
- Delta – Carberry Sand Hills/ Spirit Sands
- Beaches – east of Wpg = Milner Ridge
- Iceberg scours
- Meltwater channels – flood bursts = Pembina River trench
- Varved lake clays – 2 layer packages of different coloured clays
25
Large scale effects
- Climatic shifts – lower temperature, change precipitation patterns, change vegetation patterns
- Lowering of sea level – water tied up as ice = eustatic changes; 100 – 300m drop = continental margin actually edge of continental shelf; Bering Land Bridge
- Crustal rebound – isostatic rebound after 1-2 km ice melts; Hudson’s Bay shoreline = ~200m rise in 10Ka
26
Sea-level changes in response to major episodes of glaciation
- Sea level drops during major glaciation
- When ice melts, the sea level rises
- We know from submerged beach deposits and artifacts
27
Evidence of Isostatic Rebound
- Areas covered by ice sheets are now nearly 300m above sea level, before they were at sea level when the level was even shallower before
28
Possible causes of glaciation
- Confusing evidence, we don’t actually know how
- Variations in amount of radiation from sun
- Change in position of continents – when gathered near poles?
- Variation in e’s orbit and inclination (can’t explain absence of glaciation)
- Changes in atmosphere conditions = volcanic eruptions/dust, increase/decrease CO2?
- How to explain cyclic/non-cyclic nature?
- Changes in ocean circulation patterns = can’t explain warming between episodes
29
Milankovitch Theory
- Glacial advance/retreat due to cyclic changes to Earth’s orbit, tilt, wobble, changing amount of solar radiation received
30
Temperature of the Earth
- Climate variations between “Ice House” and “Hot House” Earth
- Most of Earth’s history: temp’s 8-15deg warmer than now (global avg)
- 4-5 major ice ages in earths history
