17 December 2009
There were two highlights of day 3 for me, which to be honest did not have much of interest on landslides. The first was the Geobloggers lunch, which was attended by about 30 bloggers. It was interesting to put names to faces and also to learn about some new blogs. I was struck by two things: 1. the range of ages of bloggers – far less oriented towards the young than I had expected; and 2. the diversity of reasons for blogging. All were pretty sure that they got a lot out of it and were enthusiastic about the role that they play. I sense that organisations like AGU have a sense that blogs and bloggers need to be a part of their future, but don’t know what that role would be. I am not sure that this session will have helped though!
The second was a session on coastal processes, mostly focused on erosion. In most cases erosion is a mass movement (landslides or rockfalls) process of course, so this was of direct relevance. I presented the work of my PhD student Emma Norman, and a post-doc in my team, Mike Lim, presented his work too. There was one other hard rock talk, a presentation from Limber and colleagues on the development of a model for coastal erosion, with an emphasis on how bays and headlands form. The headline message was interesting – that headlands can only be preserved if erosion is enhanced in bays by small pocket beaches, which provide sediment that increases the rate of abrasion on the cliffs. This is all very well, but the model appeared to over-simplify to the point of irrelevance. I sensed that the audience was pretty frustrated too, with a quite pointed question about the assumption that the geology is homogeneous.
After that attention turned to erosion in the Arctic. This session was started with a quite surreal presentation. Jesse Walker is one of the gods of Arctic geomorphology, so the convenors asked him to attend to give a presentation on this theme as background. Unfortunately he was unwell – I hope he recovers quickly – so one of the session chairs gave it on his behalf. A presentation of over 50 slides in 15 minutes by someone who did not put together the talk was not a great experience, although the presenter did the very best he could in the circumstances.
Afterwards there were four rather mixed presentations on the processes and rate of coastal erosion in Alaska. The underlying message is startling – erosion rates of 10-15 m per year are common at these latitudes. Given that most of the erosion occurs in a very short summer season, this gives retreat rates of 10 to 15 cm per day!!! One of the speakers, Cameron Wobus, presented some fabulous time-lapse photography over a full summer season to show this erosion. Just to give you an idea of how fast this erosion occurs, the image below is from his website, showing just a few years of retreat:
The real concern must be the response of this system to the rapid and massive changes in temperature and summer ice cover at these high latitudes. The eroding bluffs primarily consist of ice (dirty icebergs was one description of them). The warming is causing increases in erosion because:
1. The temperatures are warmer so the bluffs are thawing;
2. Under normal conditions at the start and end of the warm season the shore is protected by ice berms – basically marine ice that has blown onshore. These berms are smaller and are melting faster;
3. The loss of sea ice in the summer means that the waves have a larger fetch, so that they are larger and more powerful;
4. The melting season has become longer;
5. Sea level is rising;
6. The time period of ice free marine conditions each year is longer, so the sea erodes for more time;
7. The sea is warmer so can erode more quickly (much of the erosion is caused by the warm sea melting a notch in the bluff).
Overall the picture painted was alarming. As Tom Ravens said, most coastal erosion in the US is undertaken in the south where rates are generally small. The reality is that the serious problems are in the high latitudes, so there is a desperate need to reorient coastal research.
Tomorrow is the main landslide day. This appears to have a mass of stuff of interest. I can’t wait. Tonight I have to work on a research grant proposal – what joy!