My research project is a fascinating topic, and I am very lucky to be part of the team that I work in here. I work as part of the Sedimentology and Marine Geohazards research group, specifically on the Arctic Landslide Tsunami Project which is seeking to address the risks posed to the UK by tsunamis.
Fortunately these events are very rare, the last major event was the Storegga Slide (8170 years ago), which generated a wave over 25m high in the Shetland Islands, and over 5m high around the northern coastlines. A similar event today is probably the most serious geohazard we could experience in the UK. The movie below is a simulation of the event showing where the wave would impact. (For further details see previous posts)
At the moment, I am working on dating some older landslide events from across the Nordic Seas. Many of these have not yet been dated, and the way in which I am hoping to obtain dates is through the use of tephrochronology. This involves searching the mud within sediment cores for tephra grains. You will probably recall the issues associated with tephra during the 2009 Eyjafjallajokull eruption, during which ash spread across Europe, forcing our planes out of the sky, and prompting significant transport problems.
The reason as to why these subglacial eruptions cause problems like this, is due to the unique location of Iceland, and the fact that the lava erupts at the base of the ice sheets. This forces lava to cool rapidly, and turns the ice to steam, which rises taking with it the tiny particles of volcanic glass that form from this process. This process is particularly useful to geologists, especially if you are working within the last 125 000 years. The reason being, that ash travels widely, but it eventually falls to ground and settles in lakes, peat bogs, ice caps and marine sediments, thus forming a unique layer that can be traced across continents.
This simple diagram shows how some eruptions leave a trace across the the Northern Hemisphere. These particles are so important, because the ice cores from Greenland contain layers that can be counted back to 128 000 years ago. Each eruption centre on Iceland has a unique geochemistry or composition. Therefore, if you can match the tephra you find in marine sediments, to the tephras from a known and dated ice core deposits, you can find the exact age of your marine muds.
This is what I am currently working on, it is quite a slow process, but I have selected key parts of my marine cores where I want to apply a date, and I am scanning them for tephras. This will allow me to accurately date older landslide deposits, and contribute to a chapter of my PhD. So at the moment I have been sampling my cores:
Washing the muds through increasingly fin sieves (6 different mesh sizes…):
Separating the tephra using heavy density liquids in a centrifuge, then mounting them onto glass slides:
Drying the water off the samples and mounting them in Canada Balsalm:
I am now searching all of them for tephra grains and counting each slide (72/400 done…)
Sadly the fieldwork for my PhD was last year, we gathered 88 new sediment cores from across the Nordic Seas during a month long project cruise. Once the tephras have been isolated, they will be mounted in blocks and analysed at a dedicated tephra lab at Edinburgh University, but this is some way off.
Why is this important? Because until we know when landslides like Storegga happened, we won’t be able to understand why, and one the concerns is that they seem to happen during periods of significant change. This data will be used to assess whether this statement is true, and what the timing of the event will tell us about the cause.