Chapter 10 Flashcards
(9 cards)
Define glaciers and the process of their formation.
Glaciers are moving ice.
The key to building them is to have sufficient moisture in the air to produce the necessary precipitation, and low temperatures in summer time so that the snow that falls the previous winter doesn’t completely melt. Glacial ice forms by the persistence of snow over a cool summer and snow accumulation from winter to winter.
What are the stages of formation of Glacial Ice?
Accumulation of snow
In lower levels, snow turns into firn by thawing and refreezing
Further compaction of the accumulated snow due to the weight of the partially thawed and refrozen snow above into firn.
The pressure caused by this compaction leads to freezing of the firn into crystalline glacial ice.
When ice accumulates to a mass sufficient for gravity to act on it => Glaciers are born
This process might take 10 to 20 years
How do glaciers move and where do they form?
Glacial ice forms only on continents, not in the ocean. Pieces of glaciers that break off & float in the ocean until they melt are known as Icebergs (~ 90% of its volume is below water surface).
Ice under pressure is not brittle–it is plastic. It will begin to deform at the base under weight of the overlying ice; this is called plastic flow, and this causes the glacier to move.
- Valley glaciers move by basal slip, the actual movement of glacial ice over the ground lubricated by a layer of meltwater
- Continental glaciers, however, are solidly frozen to the ground and move only by plastic flow.
Where are glaciers mainly formed?
a. High Altitudes: in highly elevated alpine mountains, valley glaciers (alpine glaciers); the ice can be several hundred meters thick and the glaciers more than 100 km long; the glaciers move downhill along valley slopes until they melt or calve into the sea (i.e. break off in the form of icebergs).
Examples: glaciers of the Alps, of the Andes Mountains in Colombia & Mt. Kilimanjaro in Africa.
b. High Latitudes – from the equator towards the poles, there is enough precipitation in the form of snow to form continental glaciers (ice sheets, ice caps); these are both extremely large and the ice is more than 3 km thick; the ice moves laterally over essentially flat land for hundreds of miles until they calve into the sea.
Example: only two of these on the Earth today, one on Antarctica (south pole) and the other on Greenland (near north pole)
Where are glaciers mainly formed?
a. High Altitudes: in highly elevated alpine mountains, valley glaciers (alpine glaciers); the ice can be several hundred meters thick and the glaciers more than 100 km long; the glaciers move downhill along valley slopes until they melt or calve into the sea (i.e. break off in the form of icebergs).
Examples: glaciers of the Alps, of the Andes Mountains in Colombia & Mt. Kilimanjaro in Africa.
b. High Latitudes – from the equator towards the poles, there is enough precipitation in the form of snow to form continental glaciers (ice sheets, ice caps); these are both extremely large and the ice is more than 3 km thick; the ice moves laterally over essentially flat land for hundreds of miles until they calve into the sea.
Example: only two of these on the Earth today, one on Antarctica (south pole) and the other on Greenland (near north pole)
What is the glacial budget?
The upper part of valley glaciers in which snow accumulates is a zone of accumulation; this is in a bowl-shaped depression high in the mountains called a cirque. As the glacier moves down the valley, it begins to melt and evaporate: this is the zone of wastage (down the valley), called zone of ablation.
The two zones are separated by the snowline (firn limit). At the foot or toe of the glacier (the terminus), melting is complete and the ice disappears. Crevasses: as the valley glacier moves over high areas, it forms an icefall with cracks in the ice called crevasses.
What are the processes that glaciers carry out while moving?
Glacial surging: Movement of the glacier.
Glacial plucking: Erosion/Weathering of sediments by Glaciers.
Glacial abrasion: Grinding & polishing of underlying bedrock
Describe and draw the glacial erosional (topographic) features.
Glacial erratics: huge glacial boulders left on the ground after the ice sheet melts. The spectacular mountain scenery is created by glacial erosion. Most distinctive are:
Fjords: U-shaped valleys carved by glaciers moving in former V-shaped stream valleys. Near the coast, deep glacially eroded valleys later were drowned by rising sea level to form fjords (fiords).
Horns: Sharp peaks eroded on all sides by glaciers
Arête: A steep knife-like ridge separating two glacial valleys
Hanging valleys: Tributary glaciers leave behind hanging valleys, which often have lovely waterfalls into the main valley.
Cirque Lake or Tarn: the bowl-shaped cirques, now abandoned by alpine glaciers, often have water in them, forming cirque lakes, or tarns.
Types of glacial deposits and description
Picture 9
1. Non stratified Drift: occurs as un-stratified & unsorted sediment deposited directly by glacial ice forming a till. Till is deposited in landforms (ridges) called moraines and drumlins.
Types of moraines:
a) Ground moraine: is deposited beneath the ice
b) End moraines: is deposited at terminus of the glacier.
There are two types of end moraines: a
(i)Terminal moraine present at the greatest extent of the glacier
(ii) Recessional moraine is formed as the glacier front recedes.
Drumlins: teardrop-shaped hills composed of till molded by the glacial ice; the pointed end points in the direction of ice flow, while the rounded end faces the direction the ice came from
2. Stratified Drift: stratified & sorted glacial meltwater sediments creating outwash deposits which are glacial drift that was picked up and distributed by meltwater stream.
Kames are small conical hills composed of sediment dropped from depressions in the glacier after it melts.
Eskers are long sinuous ridges of gravel deposited as meltwater streambeds underneath the glacial ice.
Kettles are depressions in outwash plains left by isolated glacial ice remnants that had outwash deposited around them. Usually the kettles fill with water to create kettle lakes.
Varves are bi-layers consisting of a coarser-g
rained, light-colored layer (deposited in spring & summer of a glacial lake) & a fine-grained, dark layer (deposited during winter when lake is frozen); a single varve, therefore, represents one year of glacial lake deposition. The varves can be counted to determine the age of the lake.
