T1 Shetland Day 2: da sampling of Foula

Transect leader Tom

Transect leader Tom

By Tom Bradwell

As Scottish islands go Foula is off the beaten track. 180 km N of mainland Scotland, 30 km W of the Shetland mainland and 280 km SE of the Faeroe Islands. One of only a handful of places west of Orkney and Shetland where the topography of the UK continental shelf protrudes above the surface of the ocean. The others being the uninhabited island of North Rona, and the rocks of Sula Sgeir and Sule Skerry. Home to just 38 inhabitants and Scotland’s 2nd highest sea cliffs (after those on St Kilda), Foula is a stunning island mountain, devoid of trees but teeming with seabirds. But was it glaciated by the last ice sheet? And if so when? Britice Chrono members Tom Bradwell, Derek Fabel and David Small went there to find out.

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After a short flight from Tingwall Airport in an 8-seater islander operated by (Directflights) we landed at Foula Airstrip bang on time at 9.30am. We had chosen to visit Foula today (a Wednesday) as it is only one of 2 days a week when you can visit the island and return the same day. Well… only if the weather plays ball. Something which we were keenly aware of as thick sea fog had shrouded the island for the previous 4 days, restricting all access by plane. To make things more challenging we had been informed by the aircrew as we boarded that there were no guarantees that the return flight would go ahead today and that we should be prepared for an extended stay on the island, perhaps until Friday or perhaps even longer. I was naturally hoping to get back tonight to catch a bit of Cash in the Attic at 5.30, and after David thought in light of this news he may have to start rationing his caramel bars: 1 bite per meal. But we had made it to the island, with only 6 hours to hunt for and sample glacially transported rocks, and that was the most important thing.

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Given the size of the island and the task in hand we decided to split up: Derek taking the low ground in the south where granite erratics transported from the Shetland mainland had been previously reported; whilst David and I took the ground in the east and north. The cloud base was down at 200 m and we knew that searching the high ground on Foula would probably not yield the type of material we needed for cosmogenic dating. But we were confident that by splitting up we could tackle the two best sites and secure the maximum number of samples (hopefully 10 or more).

After walking the length of the island by the only road, passing Da Toon o the Ham, and Da Loch we arrived at Da Heights, with great views across Da Sheepie and Gaada Stack. Sampling the 3 largest glacially transported sandstone boulders on this ridge took us up to lunch satisfied that we had at least bagged some good rocks. On the other end of the island Derek was working his way across Da Daal to Da Noup. He had seen one or 2 different looking rounded grey boulders on a hillside of more angular rounded grey boulders. The rounded grey boulders were granites sourced from the Shetland Mainland; the less rounded grey boulders were sandstones from the old red sandstone. By covering the ground in a slow and systematic way Derek was able to find 5 granite boulders and sample a few hundred grams of each – the old fashioned way with hammer, chisel and brute force. Meanwhile David and I had climbed up to Da Loch o Ouvrafandal searching for more boulders laid down by the last ice sheet, only to be disappointed by their absence. Two bedrock samples were taken before we walked back to the airstrip in glorious sunshine… backpacks considerably heavier than when we set out.

With 15 minutes to spare before the plane arrived we had time to chat to Jane the island’s primary school teacher, who was keen to tell her class the next day what we had been up to. The boulders we sampled contain a signal that has grown in them since they were last eroded and transported their current location, this signal is like a clock that we can use to work out when Foula was last covered by ice probably more then 20,000 years ago. I hope this blog helps!

All in all a great day: 11 rock samples, 50 field observations, 200 photographs and experiencing a stunning landscape and place. Our work should help to constrain the timing of the last ice sheet to cross Foula, the most westerly and glaciologically most important of the Shetlands islands. Tomorrow North Maven, Friday Skerries, hopefully. Saturday, Cash in the Attic on ‘Catch Up TV’. We will keep you posted on our progress over the next eight days…..

Taxi for Bradwell (et al.)

Taxi for Bradwell (et al.)

4 thoughts on “T1 Shetland Day 2: da sampling of Foula

  1. Foula Primary School

    We have loved reading your blog today but now we have lots of questions we hope you can help us with!
    We can’t wait to find out when Foula was last covered with ice, but we also want to know when it was first covered. Will you be able to find out with the rocks you found? We hope you can!
    Why was Foula covered in ice? We know that you like rocks, but do you know why caterpillars came to Foula?
    How many rocks did you see while you were in Foula? How are rocks made? We have a little poly-crub at home and we have lots of tiny bits of quartz in it.
    Will we be able to see where you have used the hammer on the big rocks? We are going to go and look for big rocks and see if we can! What will you being doing with our rocks now?

    Reply
    1. briticechrono Post author

      Thank you for reading the blog and you were the first to ask questions: hopefully here are some answers 🙂
      We can’t wait to find out when Foula was last covered with ice, but we also want to know when it was first covered? When Foula was covered by ice is a much more difficult question to answer! The Earth has been glaciated numerous times in the last 2.6 million years, and these cold periods allowed large scale expansion of ice mostly in the last 800,000 years. Today, we were excited to find scratches on bedrock, called striations, in north Maven recently uncovered by coastal erosion that probably date to around 440,000 years ago.

      Will you be able to find out with the rocks you found? We hope you can! Sadly almost certainly not, our focus is on when ice last covered the Island and how quickly it vanished. The speed of ice leaving the Shetlands is an aspect that we are most interested in. Why? Well because there are concerns about rapid collapse of ice sheets today and understanding how quickly old former ice sheets declined can help us predict future changes in Antarctica or Greenland.

      Why was Foula covered in ice? Around 30,000 years ago the climate on Earth became much cooler, so cold ice sheets covered most of northern Britain and all of Ireland. At this time the sea levels were much lower and so the land area of Shetland much larger, and ice probably grew here, with snow lasting year around compacting gradually to ice and with time expanding and flowing west to cover Foula and out 100km west of the Shetlands.
      We know that you like rocks, but do you know why caterpillars came to Foula? No we have not got a clue! Do you know why they came?

      How many rocks did you see while you were in Foula? Derek saw 10 important and big rocks, and these came from the mainland carried by ice onto Foula around 20,000 years ago. David on the other hand saw 100’s and liked them all but he only sampled 6. And Tom saw 191 rocks and did not sample any, but did lose his blue water bottle on the island!

      How are rocks made? That is a tough question, on Foula you mostly have Old Red Sandstone which are very old and were made by rivers in warm desert environments, think Australia, but they are 375-390 million years old and all this time has made them very very hard.

      We have a little poly-crub at home and we have lots of tiny bits of quartz in it? We do not know what poly-crub is? Help!

      Will we be able to see where you have used the hammer on the big rocks? We are going to go and look for big rocks and see if we can! Yes we have posted clickable links in the blog that open Googlemaps webpages with the view centered on the boulders we hit with a hammer and sampled. See if you can find the really really big one……

      What will you being doing with our rocks now? For the next 8 days they are driving around the rest of the Shetlands, but when we move them back to the laboratories at Glasgow University they will be crushed, sieved, we will extract and clean the quartz, dissolve it in acid, and then extract the Beryllium isotope, we need Beryllium-10. From the Beryllium-10 we can work out when the ice sheet retreated and dropped the boulders that lie around Foula.

      Reply
      1. Foula Primary School

        Wow! What a lot of information, you are very good at answering questions!
        We are going to go and have a look for the big boulder! We love the quartz that we found. The poly-crub is a Shetland name for a poly tunnel, like a big greenhouse. We have a peerie (little) one at home which we have put our collection of quartz in.
        We think the caterpillars came to Foula to eat all the cabbage we had planted! Slugs came here to eat the cabbage too!!!
        We hope you enjoy visiting the Skerries today 🙂

      2. briticechrono Post author

        Hello again
        Cruise two of Britice-Chrono will pass your island probably over the weekend, we currently are in the Minch between the Hebrides and mainland Scotland for a couple of days on our ship the RRS James Cook, but will be sampling around west Shetland Saturday – Sunday, going passed Foula into St Magnus Bay, you may be able to see us! Updates are posted on @briticechrono twitter feed, we are still chasing that icesheet and the time it left Shetland! http://noc.ac.uk/research-at-sea/research-expeditions
        best wishes
        Britice-Chrono Team

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