Week 9 Lecture: Glaciers Flashcards
What is a glacier?
A permanent body of ice and recrystallized snow that shows evidence of downslop or outward movement due to the pull of gravity.
What are the two categories of Glaciers?
- Ice Sheets and Shelves
- Alpine Glaciers
What is the difference between an ice shelf and an ice sheet?
An ice shelf is a sheet of ice extending overtop of the water, whereas an ice sheet is overtop of land
List the types of Alpine glaciers:
- Ice Cap
- Cirque Glacier
- Fijord Glacier
- Valley Glacier
- Piedmont Glacier
What are Ice Caps?
Tim Hortons beverages that have become drastically overpriced
:P
A glacier that covers a mountain highland or low-lying land at high altitudes and spreads out laterally
What are Cirque Glaciers?
Glaciers that occupy a protected bowl-shaped depression in a mountainside
What are Fijord Glaciers?
A large valley glacier that extends down to the mouth of a fijord at sea level
What is a Valley Glacier?
An enlarged cirque glacier that spreads out down a valley
What is a Piedmont Glacier?
Occurs when steep valley glaciers flow onto flat areas and spread out into fan shapes
What two elements are required for the formation of glaciers?
- Low temperatures
- Abundant snowfall
What two components can a glacier be divided into?
- A zone of growth (accumulation)
- A zone of shrinkage (ablation)
What are the two main mechanisms of Glacier Movement?
- Internal Plastic Flow
- Basal Sliding
What is Internal Plastic Flow?
Where glaciers flow and deform in a manner similar to ductilely deforming rocks. This involves slip and deformation of the ice crystal structure at the microscopic scale (millions of tiny displacements).
What is Basal Sliding?
Where glaciers have abundant melt water at the base which lubricates the base of the glacier, allowing it to slide over the underlying rocks and gravel.
What is the Firn Line?
The elevation to which the snow recedes in the summer (below which you don’t see last year’s snow)
Useful since:
- if firn limit moves downslope, glacier has (+) budget
- if it recedes, budge is (-)
- if unchanged, glacier is balanced
What is rock flour?
Where glaciers grind rock to clay sized material
What are striations?
A series of scratches and grooves parallel to the movement direction of the glacier and caused by the grinding action of rock fragments against the underlying bedrock.
What are Cirques?
An amphitheater-like hollow high up in the mountains
What are Aretes?
Sharp ridge tops with cirques on either side of the ridge
What is a Horn?
A high, sharp-pointed peak formed when three or more cirques have sculpted a mountain mass
What is a U-Shaped Valley?
Characteristic U-shaped valley that is produced by a valley glacier
What is a Hanging Valley?
A valley that lies above the main U-shaped valley floor - created when a tributary glacier joins a larger valley glacier
What is a Fijord?
Large U-shaped valley that is filled with sea water and extends a large distance inland from the coast
What is Glacial Drift?
A poorly sorted, heterogenous mix of boulders, pebbles, sand and clay that is left behind when a glacier melts.
Drift is used to describe all types of glacial deposits
What are the two main types of drift?
- ice-laid deposits
- water-laid deposits
What are Ice laid deposits?
drift formed by deposition of material directly out of the glacier as it melts
Name and describe the most common type of ice-laid deposit
Moraines
This is a deposit of rocky, sandy, or clayey material carried and deposited by the glacier
What are Terminal Moraines?
They mark the farthest advance of the ice sheet
What are Lateral moraines?
Form along edges of glaciers
What are Medial moraines?
They form where two joining glaciers merge their lateral moraines below the junction. Commonly visible as line of dirt in middle of glacier.
What are Ground Moraines?
Piles of debris formed at base of the ice
What are Erratics?
Large boulders that are left lying in isolation after the glacier melts. Can be recognized by different composition than local bedrock
What are water-laid deposits?
Formed by transportation of material that has melted out of the glacier by rivers and streams. These rivers and streams may flow within or underneath glaciers.
What are Eskers?
Long, narrow, winding ridges of sand and gravel that are formed from the deposition of material out of streams that run along the base of the glacier (parallel to direction of ice movement).
What are Kettles?
Hollows or undrained depressions that are often occupied by ponds and lakes. Formed by large blocks of ice taht are left behind as the glacier melts.
What are Kames?
Small hills of sand and gravel dumped near the edge of the ice
When did the most recent glacial episode end?
~10,000 years ago
What causes land bridges and thereby the migration of animals and plants between continents?
The lowering of the sea level by water being tied up in continental ice sheets during a glacial period.
What is Isostacy?
The enormous weight of continental ice sheets on teh land causing the crust to subside beneath them.
What is Isostatic Rebound?
Once the ice melts, the crust gradually rebounds
Why are glacier responsible for the Viking invasion of Britain?
Because Viking in Finland and Norway lived down fijords on small areas of land that was flat enough. But since there was little flat land due to the rugged terrain of the fijord and the steep sides, the Vikings who grew in population needed to find more land. Therefore they set out on expeditions from which they eventually found Britain and invaded it.
Oh, and glaciers created the fijords - that’s why :P
