Glacier Movement and Flow: A Comprehensive Guide, Summaries of Environmental Science

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Changing Landscapes:^ Glaciated Landscapes

How do glaciers move?

What you need to know

Differences between cold- and warm-based glaciers, their locationsand rates of movementGlacier ice movement including internal deformation, basal sliding,sub-glacial bed deformation, surge conditions, compressional/extensional flow

Glacier ice temperatures

Is usually close to the area’s mean annual air temperaturePolar ice is much colder than ice at lower latitudes – in Antarctica it canbe -40°CReasons why ice temperatures vary within the glacier:^ •^

Geothermal heat can warm basal ice • Moving ice warms basal ice through friction • As meltwater refreezes it releases latent heat • Pressure melting, e.g. at 2000m the melting point is -1.6°C…

Warm- and cold-based glaciers 1. Describe how the temperature

2. varies over the year and with^ depth through the iceWhat is meant by the pressure
3. melting point of the ice? How^ does this change with depth?What do you notice about the ice temperature and the pressure melting point at the base of the glacier?
4. Why is this significant?

Glacial flow

Large glaciers and ice sheets can be cold-based in their upper regionsand warm-based near their margins –

how?

Ice thickness also affects the temperature at the base –

how?

Normal flow rate for glaciers varies between 3-300m/yrThe world’s fastest moving ice masses = outlet glaciers of W Greenlandice sheet: velocities > 12 km/yr. Pressure of ice sheet pushes glaciersthrough mountain valleys.Build-up of meltwater at glacier’s base can cause surges: speeds 10-100x normal rates. Surging glaciers tend to be found in Svalbard, Iceland, theCanadian Arctic and Alaska

Glacier movement

In a typical glacier, two zones of movement may be seen: ^ an upper zone of fracturing (up to 60m deep) where the ice is very cold andbrittle – it shears under sudden changes of tension to form crevasses: ^ a lower zone of flow, wheremore steady pressure andlubricating meltwater allow itto deforms plastically andmove as a viscous body

Chikamin Glacier, Washington state

Glacier movement

Glacier movement

Basal sliding:^ •^

Meltwater acts as a lubricant at the ice/rock interface…so this doesn’thappen in cold-based glaciers • A few mm of meltwater can significantly reduce friction • Flow rates can be 1-2 m/day • Contribution to total movement of ice can vary from 20-80% • Most effective on steep slopes in summer • Two components:^ •^ Enhanced basal creep

• where basal ice deforms around irregularities on the bedrock surface • Regelation slip - localised increase in pressure in front of an irregularity causes pressure melting – the ice refreezes after the irregularity hasbeen passed and pressure drops again

Glacier movement

Extending and compressional flow:^ •^

Former occurs where bed gradient increases – causing the ice to accelerate,making it thinner and forming crevasses at the surface through shearing • Latter happens where bed gradient decreases – causing the ice to slow,thicken and shear upwards. Can also happen at glacier’s snout as movingice rides up over stagnant ice

Glacier flow

^ is mostly slow and regular (average is < 1m/day, but can be 50m/day) ^ Is usually fastest around the equilibrium line as ice is usually thickest here ^ decreases from the

surface to the base

^ is fastest in the

middle

^ varies with the weather and seasons The speed of a glacier’s flow is controlled by: ^ the gradient of the rock floor ^ ice thickness and its impact on the temperature of the ice ^ the internal temperatures of the ice

Glacier flow

Why ice displacement is fastest at the surface of the glacier:^ Base