FROM GLACIAL GEOLOGY TO PALAEOGLACIOLOGY

After the demonstration by Louis Agassiz in the 1840s of the reality of the glacial theory, scientists have systematically attempted to establish the extent of former ice sheets, and to create a narrative history of Quaternary glaciations and the environmental and climatic changes associated with them.

However, although intensive studies of the sediments produced by former ice sheets have created criteria by which past glacial events can be identified in the stratigraphic record, there has been very limited success in using the attributes of sediments to infer the properties of the glaciers that produced them. Meanwhile, the last 50 years has seen the development of a rigorous, quantitative science of glaciology that has made it possible to simulate and predict the climate driven behaviour of glaciers, and which, in the last decade, has been applied to glacial erosional and sediment transport processes.

It therefore timely to attempt to create a science of palaeoglaciology, where understanding of the physics of glaciers and their interactions with the surface over which they flow are combined with understanding of glacial sediments, quantitatively to reconstruct the nature of former ice sheets and their role in the Earth system.

Theories of glacial erosion and transport have been embedded in large scale, high resolution, computer simulation models of Quaternary ice sheets in such a way as to predict properties of the geological record such as the thickness, distribution and age of tills, the distribution of indicator erratics, the distribution of eskers and tunnel valleys, the evidence of relative sea level change, the glacial sedimentary and isotopic flux to the oceans etc. These are then compared with actual geological evidence in a way that severely constrains ice sheet simulations, and permits us to infer glaciological characteristics of the ice sheet such as its time dependent form and flow, the locations of ice streams, the rate of basal melting, ice velocities and shear stresses, and such large scale properties of the continents as the glacial component of the long term denudation rate and associated crustal movements.

Although these are early days, this programme for research must be part of the perspective of Quaternary Science if it is to continue to make a major contribution to understanding the Earth system.