An ice mass that covers less than 50 000 km² of land area
Ice caps are not constrained by topographical features
their dome is usually centered on the highest point of a massif .
Ice flows away from this high point (the ice divide ) towards the ice cap's periphery.
Ross Ice Shelf (Sheet)
Masses of ice covering more than 50 000 km² are termed an ice sheet.
Thick plates of ice, fed by glaciers, that float atop an ocean.
The presence of the shelves acts as "brakes" for the glaciers.
They also moderate the amount of melting that occurs on the glaciers' surfaces and act as a breaking force for glaciers.
It’s about the size of France (area of roughly 487 000 km², and about 800 km across)
Not confined by topography
Cover the entire surface beneath them.
Flow outward in all directions.
Not visibly affected by the landscape underneath.
Antarctica and Greenland are the only places where continental ice sheets currently exist.
Contain vast quantities of fresh water.
Part of the Greenland Ice Sheet; Covers about 1.8 million Km2
Form where snow and ice accumulation exceed snow and ice melt
Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser and denser firn
Firn is partially-compacted neve.
Neve is a young, granular type of snow which has been partially melted, refrozen and compacted.
Firn from South Cascade Glacier, 80x magnified.
Growth of Glaciers
Glaciers grow or recede as a function of the balance between accumulation and ablation of snow and ice.
The accumulation zone is a region where snowpack or superimposed ice accumulation persists.
The ablation zone is the region where all of the snow has melted away and bare glacier ice is exposed.
Crevasses in Glaciers
Crevasses are common in the upper parts of glaciers when the ice is subjected to tension.
Crevasses in a continental glacier near the Ross Sea .
Study of glaciers and ice sheets using radar.
It employs a geophysical method similar to ground-penetrating radar.
Uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum.
Detects the reflected signals from subsurface structures.
GPR can be used in a variety of media, including rock, soil, ice, fresh water, pavements and structures.
It can detect objects, changes in material, and voids and cracks.
National Snow and Ice Data Center http://www.nsidc.org/
center in support of polar and cryospheric research
maintains information about snow cover, avalanches, glaciers, ice sheets, freshwater ice, sea ice, ground ice, permafrost, atmospheric ice, paleoglaciology , and ice cores
Anatomy of a Glacier
A cirque is an amphitheatre-like valley, or valley head, formed at the head of a glacier by erosion.
A medial moraine is a ridge of moraine that runs down the centre of a valley floor. It is formed when two glaciers meet and the debris on the edges of the adjacent valley sides join and is carried on top of the enlarged glacier.
The Glacial Budget
The glacial budget is the total of accumulation and ablation for a glacier.
In winter the budget is equal or can exceed melt causing the glacier to grow, but in summer snow and ice melt exceed deposition.
A glacial surge is a short-lived episode of accelerated flow in which the surfaces breaks into a maze of crevasses and its terminus advance noticeably.
The fastest glacial surge ever recorded was in 1953 in the Kutiah Glacier in Pakistan, the glacier advanced 12 km in 3 months.
Glacial Movement Variables
Temperature of the area
The slope of the glacier
The bed's sediment size
The amount of meltwater from the glacier
The glacier's size
Basal Sliding is the act of a glacier sliding over the bed before it due to meltwater under the ice acting as a lubricant.
Anatomy of a Receding Glacier I
Lateral moraines are parallel ridges of debris deposited along the sides of a glacier.
A terminal moraine forms at the end of the glacier called the snout and marks the maximum advance of the glacier.
Ground moraines are till covered areas with irregular topography and no ridges often forming gently rolling hills or plains.
Sediment Transport by Valley Glaciers The dark material on the glacier is sediment.
A sandur is a glacial outwash plain formed of sediments deposited by meltwater at the terminus of a glacier.
An outwash plain might contain surface meandering streams that rework the original deposits.
The flow pattern of glacial rivers across sandar is typically diffuse and unchannelized.
The western edge of Skeiðarársandur in Iceland shows the diffuse drainage channels typical of sandur.
A varve is an annual layer of sediment or sedimentary rock.
The light layer usually comprises a coarser laminaset of silt and fine sand deposited under higher energy conditions when meltwater introduces sediment load into the lake water.
Varve deposits from a glacial lake.
Anatomy of a Receding Glacier II
A kettles are fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming buried partially to wholly by glacial outwash.
A kame is a geological feature, an irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier.
An esker is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions.
A glacial erratic is a piece of rock that deviates from the size and type of rock native to the area in which it rests.
These rocks were carried to their current locations by glacial ice, often over hundreds of kilometres.
Erratics can range in size from pebbles to large boulders.
The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles.
Existed during the Pleistocene between c. 95,000 and c. 20,000 years before the present day.
Some parts were up to 2 miles think, depressing the crust up to 300 meters.
Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate.
The Earth's axis completes one full cycle of precession approximately every 26,000 years.
The elliptical orbit rotates leads to a 21,000-year cycle between the seasons.
Earth's rotational axis moves between 22.1 degrees to 24.5 degrees creating a 41,000-year cycle.
Formed during the recession of the Pleistocene ice shelf.
Rebound began in the southern region and proceeded north.
Lakes were formed because of crustal depression and melting of receding ice sheet.
A satellite image of the Great Lakes.
State of Glaciers Today
Most are melting because of climate change.
Many scientist believe that humans have greatly contributed to a natural melting cycle by adding carbon dioxide to the atmosphere causing global warming .