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
Millie
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