Glacier and Ice Sheet Modelling

Glaciers and ice sheets play a complex role in controlling, and responding to, the Earth's climate. Mathematical and computational models help to understand this role and to explore their future behaviour.

The diagram above shows some of the processes that control the growth and shrinkage of ice sheets. Many of them are poorly understood and their representation in the current models is not complete.

ImPISM

I am currently running a project called 'Improving the Physics in Ice Sheet Models'. This will develop improved methods to account for poorly represented components of the current models. Key processes being studied are the influence of water moving under the ice and the sliding of the ice over its bed.

Glacial hydrology

Meltwater on a glacier's surface usually runs into crevasses or other vertical shafts known as 'moulins'. Combined with the meltwater produced within the ice and at its base (due to frictional and geothermal heating) the water flows along the glacier 'bed', driven by pressure gradients due to the weight of the overlying ice. Sometimes it flows through discrete 'tunnels', sometimes in a wide-spread network of 'cavities', and sometimes in shallow 'canals' eroded into the subglacial sediments. Understanding how much water escapes from under the ice, how quickly, and how effectively it lubricates the ice flow, are all important questions.

Sliding

The presence of water at much of an ice sheet's base allows the ice to slide over the rock or sediments on which it rests. Water-saturated sediments can themselves deform easily, allowing for very fast ice flow above (tens of metres per day). Particularly in Greenland and on smaller mountain glaciers, ice speeds are observed to fluctuate on daily and seasonal time scales. This is thought to be largely due to changing water pressures at their base. The figure on the left shows a calculation of the seasonal evolution of basal water flow (white/blue) and ice surface speed (yellow/red), shown in plan view with ice flow from left to right [Hewitt (2013)]