Glaciers are some of the best indicators of climate change. Their existence depends on a fine balance between mass accumulation (usually through snowfall) and mass loss (mainly by ablation or melting). Any small increases in mean annual temperature elicit an amplified response in glaciers and can drastically reduce their mass balance – more ice lost than gained. This is why glaciers are responding so rapidly to rising temperatures.
However, it isn’t as simple as that; there are a number of complicating factors that alter how fast or slow glaciers respond, some occurring on a case-by-case basis. For scientists to use glaciers as a robust and reliable indicator of climate change, both past and future, then we need to learn as much about their behaviour as possible.
For example, in the early 1980s a “paradigm shift” occurred in glaciology when scientists discovered that many glaciers do not simply slide over rigid rock. A large proportion of ice masses are underlain by layers of soft sediment which deforms and can increase the speed of ice flow by much more than sliding (over hard, rigid rock) or deformation of the glacier ice itself. This sparked a lot of interest in studying the subglacial environment underneath the glacier. These layers of sediment are called subglacial till, but unfortunately this area is very dangerous to work in and natural exposures of the sediment in safe environments are quite rare.
Luckily, when a team of young scientists from QMUL travelled to Iceland this past summer that’s exactly what they found. As part of a month long expedition, 2 PhD researchers and 3 undergraduates studied the subglacial environment of Falljökull, a small glacier in Skaftafell national park. By studying these sediments, particularly their composition and evidence of deformation, it was possible to understand past glacier motion and variations in stress penetrating down from the ice.
In order to do this, the team took several undisturbed samples of this subglacial till back to the UK for analysis using a cutting-edge method called X-ray computed microtomography (X-ray µCT). This method, akin to CAT scanning, provides very high-resolution 3D reconstructions of sediment samples and allows scientists to assess their internal structure and ultimately provide more information about the land system in general.
The logistics required to get these samples from beneath a glacier in Iceland back to the geography department at QMUL can be quite complicated. Extraction requires a great deal of care as any small disturbances will be amplified in the µCT scanner; some samples took over 3 hours to remove from beneath the glacier and these were often taken in some very bad weather conditions by very wet, cold and hungry glaciologists. Due to the highly fragile nature of the samples, transport by air was not an option. This meant that the team was required to ship them back with another expedition around one month after departure – thanks go to Durham University & Prof. Dave Evans for this. When back in the UK, the samples were kept in cold storage and prepared for scanning. After scanning a huge amount of work must be done on the X-ray images in order to process them into meaningful data; only at this point can the team start to make sense of the data they extracted.
Video: A 3D reconstruction of subglacial sediment sample taken from beneath Falljökull, Iceland.
This video shows some of the preliminary data extracted from a sample; when all samples are scanned and processed then this data will be combined with other data collected in the field: geomorphological mapping, sediment analysis, photography and other lab analysis, in order to produce an overall assessment of the subglacial system at Falljökull. In the video, blue represents discrete particles, grey is matrix and orange areas are voids.
Understanding how these glaciers such as Falljökull are behaving currently, and the role of deforming sediment in their motion and dynamics, is of vital importance for reconstructing glaciers which have long since vanished, and ultimately for improving our understanding of cryospheric response to climate change.