environmentalresearchweb blog

« Renewable breeders | Main | Delhi congestion delimited »

Glaciological classics

I was asked recently to make suggestions for a list of classic papers in the Journal of Glaciology and Annals of Glaciology, the two main publications of the International Glaciological Society (IGS). If you are keen, you can expect to see a feature on glaciological classics in the Journal’s 200th issue later this year. It will be interesting to see what the community of glaciologists comes up with as its selection of the papers about which it is proudest.

My own little list begins with Anonymous 1969. We have got into the habit of calling it that, although it baffles people from neighbouring disciplines (and in fact most of us know who wrote it). It codified the thinking on which we have relied over the past 40 years for describing the components of glacier mass balance, enshrining for example b_n as the symbol for net mass balance, and c and a for accumulation and ablation respectively. Even its author would not, I imagine, describe it as exciting, but that hundreds of glaciologists take it for granted every day shouldn’t disqualify it from classic status to my mind.

Then I added Jay Zwally’s 1977 paper about the emission of microwaves by cold snow. This work opened up a new part of the electromagnetic spectrum to glaciological investigation. We know what glaciers look like in the visible part of the spectrum, in which our eyes make pretty good sensors. But microwaves, with wavelengths of millimetres rather than nanometres, show us a new world. Not the least of their advantages is that they pay no attention to clouds and don’t need sunlight. If you have a microwave radiometer, or better still a radar with which to make your own microwaves and bounce them off your target, you can look at your glaciers whenever you want. (Oh, you also have to have an orbiting satellite on which to mount your instrument.)

Zwally’s particular contribution was to show that the strength of microwave emission from cold snow is proportional to temperature and grain size and therefore, by an ingenious and very productive analysis, to the rate of accumulation of the snow. This has become a leading way of estimating accumulation rates above the dry-snow line. (Things become a lot more complicated if the snow starts to melt).

My all-time most significant IGS paper is probably Geoff Boulton’s 1979 work on the deformation of the glacier bed by the flowing ice. He showed that, by comparing the along-glacier stress due to the glacier’s flow to the downward pressure due to its thickness (possibly offset by pressurized basal water), you can fashion any of a variety of intriguing and familiar shapes. For example you can make drumlins (by lodgement of the glacier’s sediment load; steep end up-glacier) or roches moutonnées (by abrasion of the bed; steep end down-glacier) algebraically, both from the same equation.

The crucial insight for this study came from a “Why didn’t I think of that?” measurement at the bed of Breiðamerkurjökull, a large outlet glacier in southern Iceland. Drill a hole in the sediment of the bed, and drop into it a metal rod with many metal rings fitted around it, one on top of another. Withdraw the central rod. Return ten days later, dig an access pit, and make the observations summarized in the diagram and its caption: “90% of the forward motion of the glacier sole is accounted for by deformation of the till”.

Deformable glacier beds are now universally understood to be fundamental pieces of many glaciological puzzles, on scales ranging from the 50-metre tunnel dug by Boulton (or, if he had any sense, by his student assistants) to reach the bed of Breiðamerkurjökull up to the behaviour of whole ice sheets.

Boulton has gone on to a distinguished career as a glacial geologist, elaborating his early ideas about the interaction of glaciers with their beds and about the intellectual importance of coupling observation with thought. At about the time you read this you will be hearing from him as a member of the team commissioned by the University of East Anglia to look into the doings of its Climate Research Unit. I notice that there is a surprising quantity of nonsense about Boulton on climate-denialist web sites. You can safely ignore it. Reading his classic paper would be a far more profitable investment of your time.

Come to think of it, reading classic papers is a profitable investment of time, period.

Posted by Graham Cogley on May 10, 2010 3:00 PM | Permalink