Ice Ages glacials The common term for the periods when there were major cold phases known as glacials, and ice sheets covered large areas of the world. The last ice age lasted from about 2 million years ago to about 10,000 BP (Before Present). It was also known as the Quaternary glaciation

Glaciation timeline showing the glacials and interglacial episodes A chronology of ice ages [in bold]

interglacials glaciations

Ice Age Environments 18,000 years ago

Use an atlas to help you name the source regions of the valley glaciers. How much of the British Isles was covered in ice? During this time temperatures fluctuated and ice advanced and retreated four times. The northern and eastern parts of the British Isles were covered in ice. The Ice Age in Britain began about 1,000,000 years ago and lasted until about 20,000 years ago.

Cold Environments today Glacial environments – areas covered by ice sheets and glaciers Glacial environments – areas covered by ice sheets and glaciers Periglacial (& tundra) regions – exist in dry high-latitude areas not permanently covered by snow and ice Periglacial (& tundra) regions – exist in dry high-latitude areas not permanently covered by snow and ice Alpine Regions – such areas may contain small ice caps, mountain glaciers and tundra environments Alpine Regions – such areas may contain small ice caps, mountain glaciers and tundra environments

Ice formation & movement

For glaciers to form, there must be a year-round thick mass of snow which becomes compacted to form ice. Abundant snowfall and cool summers help this process.

From snow to glacier ice SNOW FIRN ICE From snow to glacier ice SNOW FIRN ICE

The snow that eventually makes up ice-sheets and glaciers undergoes a sequence of conversion stages: Settling of snow – loose granular consistency Settling of snow – loose granular consistency Nivation – annual and diurnal temperature changes lead to thaw- freeze alternation, and the conversion of snow to ice crystals Nivation – annual and diurnal temperature changes lead to thaw- freeze alternation, and the conversion of snow to ice crystals

Firn or neve – increased pressure between individual grains causes pressure melting to eventually change the loose snow into a dull, white, structureless mass, with far less pore space which is therefore more impermeable. Firn or neve – increased pressure between individual grains causes pressure melting to eventually change the loose snow into a dull, white, structureless mass, with far less pore space which is therefore more impermeable. Sintering – continued fusion and squeezing out of air as a result of further compression by the continuing accumulation of snow and ice. Sintering – continued fusion and squeezing out of air as a result of further compression by the continuing accumulation of snow and ice.

Prominent layering in the firn is visible in the wall of a large crevasse on Weissmiesgletscher, Switzerland.

Glacier ice – bluish in colour and containing little air Glacier ice – bluish in colour and containing little air

Once formed ice moves in 5 basic ways Internal deformation Internal deformation Rotational Rotational Compressional Compressional Extensional Extensional Basal sliding Basal sliding

Internal deformation occurs under pressure – individual particles of ice melt around their edges allowing air to escape; one by one the particles slip forward on the thin film of water and immediately refreeze, and the influence of gravity - layers of granules in the ice slide across each other. Layered structures and folding resulting from internal deformation Axel Heiberg Island, Canadian Arctic

rotational flow of ice Here's a graphic showing rotational flow of ice through a mountain glacier. This is a downhill flow of ice which, like a landslide, pivots around a point producing a rotational movement.

Basal sliding The sliding of a glacier over bedrock, a process usually facilitated by the lubricating effect of meltwater Basal sliding of a small mountain glacier in the Cordillera Blanca, Peru, has deformed icicles, which originally grew downwards vertically.

Can you account for a.the location of the areas of extending and compressing flow; b.the formation of crevasses and seracs?

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.

Crevasse A deep V-shaped cleft formed in the upper brittle part of a glacier as a result of the fracture of ice undergoing extension Aerial view of crevasses in the accumulation area of Fox Glacier, South Island, New Zealand.

Longitudinal crevasse A crevasse oriented more or less parallel to the long axis of a glacier. Longitudinal crevasses typically open when the glacier becomes wider. Longitudinal crevasses on Persgletscher, Grisons, Switzerland

Icefall A steep, heavily crevassed, section of a glacier where it flows over a step in the bedrock. Icefall below Ewigschneefeld, part of Grosser Aletschgletscher, Bernese Alps Switzerland.

Sérac (from the French) A tower of unstable ice that forms between crevasses, commonly in icefalls or other regions of accelerated glacier flow. Séracs in an icefall on Oberer Grindelwaldgletscher, Bernese Alps, Switzerland

Surge A short-lived phase of accelerated flow during which the glacier surface becomes broken up into a maze of crevasses. Variegated Glacier, southern Alaska, during a surge.

Surge front The zone of intense compression between surging ice and non-surging ice. This is commonly marked by a bulge and a transition from heavily crevassed to crevasse-free ice. The surge front rapidly moves through the glacier, and if it reaches the snout, the glacier advances. Heavily fractured surge front of the glacier Fridtjofbreen, Bellsund, Spitsbergen, Svalbard. The glacier advanced approximately a kilometre during the surge, overriding a marine embayment and the adjacent land area.