With Prof. Chris Clark having visited the department on Monday for the Gregory Lecture, I thought a post on drumlins would be appropriate as its a landform he’s done a fair bit of work on. The drumlin is another stalwart of GCSE geography/glaciology so I’m sure lots of people will be familiar with them, but if not I’ve added a nice diagram from BBC Bitesize.
‘Drumlins are elongated hills of glacial deposits. They can be 1 km long and 500 metres wide, often occurring in groups. A group of drumlins is called a drumlin swarm or a basket of eggs, eg Vale of Eden. These would have been part of the debris that was carried along and then accumulated under the ancient glacier. The long axis of the drumlin indicates the direction in which the glacier was moving. The drumlin would have been deposited when the glacier became overloaded with sediment. However glaciologists still disagree as to exactly how they were formed.’
They’re pretty enigmatic landforms, and have precipitated a massive amount of literature. A quick search on Web of Knowledge for journal articles with ‘drumlin’ in the title produces 1801 results…BBC Bitesize is spot on with its last sentence in that quote, there isn’t a huge amount of agreement about how drumlins form, and that has produced this massive amount of debate. Sedimentary evidence seems to suggest that they’re either pre-existing sediments that are eroded into a drumlin, new sediments that are deposited forming a drumlin, or sediments that are deformed into a drumlin shape. For an accessible review check out this article by Chris. Personally I really like his theory that we should be more interested in why the ice tended to a drumlin like shape at its base rather than what’s inside drumlins. However, that’s still a tad controversial, especially with my supervisor, so I better leave the issue alone…
Moving swiftly to safer territory, what about that classic asymmetric drumlin shape? Its extremely distinctive with its stoss and lee sides, nice and easy to draw, and another classic GCSE question like the cirques I’ve covered previously. But do drumlins really look like this? Well, sometimes, but generally no. One of Chris’s PhD students, Anna Hughes, spent her PhD mapping every single drumlin (and other bedforms) she could find in on an elevation model of the UK, and another student, Sarah Greenwood, did a similar study for Ireland. I don’t envy the task at all, hence why I’m doing a process based glaciology PhD instead, buts its a really useful bit of data and easily the most consummate quantitative mapping study of drumlins that exists. Analysis of this data shows that rather than having distinct stoss and lee ends, drumlins actually tend to have a symmetrical long axis on average, and the same number have the stoss end down ice as up ice. So if you’re doing your GCSE this summer, maybe consider just drawing any broadly streamlined feature and labelling it as a drumlin. It’ll be pretty much correct.
So perhaps the interesting question is why do we teach teenagers (and sometimes undergrads) to draw drumlins this way? If you go out into the field and look at drumlins, the Vale of Eden is a nice place for it, you’ll quickly notice that not many drumlins look like they do in the text book. This is well represented in papers from the early part of the last century and before with lots of references to variation in the drumlin shape. So at what point did we start banging on about these stoss-lee drumlins? Well most of it can be put down to a seminal paper by Chorley in 1959. In it he compared the shape of a drumlin to that of half a lemniscate loop, and related the streamlined shape to its formation by the fluid ice. Its a good theory, but it caught on particularly well because it arrived in the midst of the quantitative revolution in geography. The neat mathematically based theory fitted the times well, and influenced drumlin literature and textbooks for a few decades afterwards.
Really this was to the detriment of drumlin studies as it was so influential I’m sure lots of people went out into the field with a biased opinion of what they were looking for and so didn’t map properly. In his talk earlier this week Chris mentioned how quaternary glaciology started well with people undertaking intensive mapping exercises collecting lots of evidence to interpret, but then strayed off course a bit. Whilst the Chorley 1959 paper presented lots of great ideas, at the time it just didn’t really have the data from which to make those type of conclusions, something that happened quite a lot in that period, and perhaps still happens today in some fields (or so asks the BSG anyway). That’s why Chris’s BRITICE GIS project, and generally the revolution remote sensing has brought to data collection, is so important.
So in summary, if you’re teaching or learning about drumlins, consider branching out from that Chorley lemniscate loop. And I’ll leave you with what I think is an incredibly cool bit of landscape architecture from Minneapolis…