Sunday, 6 July 2014

A-Level Science and Geography Post

As part of some outreach in June, the cruise team took part in a visit day from a Somerset sixth form college, Richard Huish, who came to the National Oceanography Centre for a series of talks about our on-going research. As part of their visit day, they had a lecture from Dr. James Hunt on the history of landslides from the Canaries, and a visit to the core store (BOSCORF) to see several cores and get an overview of how we interpret landslide deposits. This post is aimed specifically at students during their A-Levels, and hopes to explain the science we are working on within the context of the A-Level syllabus. If you are taking your A-Levels at the moment, please take part in our Q and A on the “Chat to the Team” post; we would love to hear from you!

Part of the A-Level geography syllabus covers tsunamis as a hazard in addition to climatic hazards that affect the UK. Though most case studies focus on the recent earthquake induced events in Indonesia and Japan, though it is worth remembering, that over the Holocene (the most recent geological time period spanning 12000 years ago to present), several landslides have occurred on European continental margins that had the potential to generate tsunamis that would affect the UK. The Arctic Landslide Tsunami Project is playing a key role in working out how much of a hazard submarine landslides pose, and when or if they are likely to occur.  

Shot of dawn from the Pelagia while winching back the CTD (Conductivity, Temperature Depth: measures the characteristics of the water column)

One of the biggest research questions of the Arctic Landslide Tsunami Project, is to assess the link between when these landslides occur, and the climate at the time. This is largely driven by one of the biggest coincidences in timing between two events that occurred approximately 8200 years ago: the Storegga Landslide, and the 8.2 ka BP cooling event.

The 8.2 event was the last of the major climatic shifts to occur, though there have been several others (the Younger Dryas event is a case study within the Climate module, during which time half of the deglacial warming occurred in year (almost 10-12°), at 8.2 ka, a 5.4-11.7° C drop in temperature over Northern Europe occurred in less than 10 years). The 8.2 event is interesting to climatologists as it occurred during a period of relative warmth and stability. During glacial periods, there are numerous records of rapid and large climate shifts known as Dansgaard-Oeschger cycles, which follow a pattern of slow cooling and rapid warming, but few rapid climate shifts are known from the warmer interglacial periods.

Why this matters, is that we are currently in a warm period, not too different to the conditions just before the 8.2 event, and we need to understand not only what triggered the event, but also, the other hazards that were potentially generated by it. The widely accepted theory for the cause of the 8.2 is that an ice dam that had been holding back a large volume of very cold fresh water, generated by the melting of Laurentide Ice sheet (covering North America during the last glacial) suddenly broke, and released this water into the North Atlantic. The North Atlantic is one of the most important components of the global climate system, as the formation of deep water in the Nordic Seas and to the south of Greenland helps drive the northward flow of warm water held within the Gulf Stream that keeps the UK nice and warm.

The second event, the Storegga Landslide, is the largest known and dated submarine landslide in the North Atlantic, and has been placed at 8.15 ka BP. Though this is a hard date to refine, it falls exactly within the coldest period of time recorded in the Greenland Ice records (8.16 ka BP). The landslide generated a tsunami that was 10 m high when it reached Scotland and the Shetland Islands (comparable in height to the two recent tsunamis), and tsunami deposits have been found along the Norwegian coast and as far afield as Greenland. The landslide itself moved enough sediment to cover all of Scotland in a 100 m thick layer, and an event of this size today would cause significant damage to UK industry and infrastructure, and represent a significant risk to the large oil and gas operations in the North Sea (The headwall of the Storegga Slide is very close to one of the largest complexes: the Ormen Lange field, which was subject to a comprehensive assessment of stability and landslide frequency in 2005 before operations began).

Landslide events are recorded as turbidites, distinctly different layers of silt or fine sand in an otherwise muddy (hemipelagite) background, by looking at the nature of the material in the turbidites, its size, chemical composition, how well sorted it is and the structures it shows, we can tell where the landslide came from, how old it is and whether or not it happened in one big slide (likely to generate a tsunami) or in several smaller slides from the same region (less tsunamigenic potential, but still likely to cause a hazard).

The key question for my PhD, is looking at the timings of these two events, in order to determine if there is a relationship between them. Did the cooling cause the landslide, or did the landslide contribute to the cooling? Are landslides caused by rapid changes in the oceans? If so, are we more likely to see one happen with contemporary global warming?

These questions can only be answered by heading to the deepest parts of the Nordic Seas, the Lofoten basin, and to the parts of the ocean floor that sit directly beneath the deep water currents. This current is generated by the sinking of water in the Nordic Seas, where it splits and part heads north along the Voring Plateau margin towards the Barents sea, and part heads south over the Iceland Scotland Ridge, a shallow sill of 800 m water depth where we are hoping to collect a core that records the strength of this current, and any landslide events that occurred over the Holocene.

If you have a question, A-Level student or not, please feel free to join in the live chat next week, and keep an eye on our other social media streams:

Twitter: #ArcticSlides


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