Pillows...
Posted: Thursday, 30 August 2007 |
Every now and again the opportunity arises to get out and about with a professional geologist. I had this occasion today, Thursday, well the morning anyway. Dr John Faithfull works at the Hunterian Museum in Glasgow, but was up on one of his many visits here. We had agreed to meet up and try to locate the "pillow lavas" above Loch Sguaban in Glen More.
What's a pillow lava? Well, to put it simply, if lava gets erupted under water, either in the sea or into a crater lake, it cools quickly and forms distinctive round pillow shapes. These are found in central Mull in various places and have been used to deduce the presence of a large crater lake way back in Tertiary times.
Today's project was to track down these locations
It was wet to begin with but gradually got better - we had a great day. And we found the pillows after much searching. Pics are better than me rabbitting on, so here we go:
This is the start of the walk, at Loch Sguaban. Note the crannog in the loch. Its quite boggy and tussocky here, so we were keen to get as far uphill as possible.
However, there were stepping stones to cross. Fun that was let me tell you....
This is more like it. Rock. Hard Rock. Lots of it. Here we have an intrusion breccia. Good word that. The basalt that lies at a higher level has been intruded and generally chopped up by other igneous material. Very common in this area.
Heres this sort of thing again.That's John's GPS in the middle there for scale. Actually it looks better in a larger pic - these small pic sizes dont do the subject justice.
The view over to Glen Forsa was a bit misty as you can see above
Like most of Mull there are lots of dykes crossing the rocks. This one shows very clearly what is called a chilled margin - where the hot rock comes in contact with cooler rock, it cools much faster and can develop a different appearance and a much finer grain size. Geologists get all excited about this sort of thing.
Here's another example of chilling. Actually, there was a lot of stuff that I saw today that would be great as a teaching resource. Any students of mine reading this, be warned, you'll see these pics again. Bigger. Better.
Time to find those pillow lavas. Not easy let me tell you. We had consulted a recent publication which gave a grid reference. The grid ref was hopelessly wrong...
No this isnt it either - this was an odd looking rock - it appears a bit like the stuff that makes up the Loch Ba Ring Dyke (qv) - one type of rock with bits of the other kind in amongst it - strange, and I dont think its mentioned in the Memoir or other books on the subject. The pillow lavas had to be close:
This is more like it. Lots of rounded lumpy looking bits. Fascinating to think that when that lot went hard, it was molten rock pouring into a crater lake. Now on a wet miserable day above a tussock defended Loch Sguaban, it looks like this. Well we got all excited about it. So there.
Back down the hill again after taking some more pics and measurements, GPS stuff and notes. This isnt just for fun you know, this is to help further the public understanding of science. And my students will be the first victims when the nw classes start up! Hah!
One last view of Loch Sguaban and the crannog from a heathery knoll.
What a great morning that was - the pics at this resolution probably dont do it justice, and the weather and lighting was about as flat as you could get, but we saw what we came to see and a whole lot more..
More mountainman madness soon!
MM
What's a pillow lava? Well, to put it simply, if lava gets erupted under water, either in the sea or into a crater lake, it cools quickly and forms distinctive round pillow shapes. These are found in central Mull in various places and have been used to deduce the presence of a large crater lake way back in Tertiary times.
Today's project was to track down these locations
It was wet to begin with but gradually got better - we had a great day. And we found the pillows after much searching. Pics are better than me rabbitting on, so here we go:
This is the start of the walk, at Loch Sguaban. Note the crannog in the loch. Its quite boggy and tussocky here, so we were keen to get as far uphill as possible.
However, there were stepping stones to cross. Fun that was let me tell you....
This is more like it. Rock. Hard Rock. Lots of it. Here we have an intrusion breccia. Good word that. The basalt that lies at a higher level has been intruded and generally chopped up by other igneous material. Very common in this area.
Heres this sort of thing again.That's John's GPS in the middle there for scale. Actually it looks better in a larger pic - these small pic sizes dont do the subject justice.
The view over to Glen Forsa was a bit misty as you can see above
Like most of Mull there are lots of dykes crossing the rocks. This one shows very clearly what is called a chilled margin - where the hot rock comes in contact with cooler rock, it cools much faster and can develop a different appearance and a much finer grain size. Geologists get all excited about this sort of thing.
Here's another example of chilling. Actually, there was a lot of stuff that I saw today that would be great as a teaching resource. Any students of mine reading this, be warned, you'll see these pics again. Bigger. Better.
Time to find those pillow lavas. Not easy let me tell you. We had consulted a recent publication which gave a grid reference. The grid ref was hopelessly wrong...
No this isnt it either - this was an odd looking rock - it appears a bit like the stuff that makes up the Loch Ba Ring Dyke (qv) - one type of rock with bits of the other kind in amongst it - strange, and I dont think its mentioned in the Memoir or other books on the subject. The pillow lavas had to be close:
This is more like it. Lots of rounded lumpy looking bits. Fascinating to think that when that lot went hard, it was molten rock pouring into a crater lake. Now on a wet miserable day above a tussock defended Loch Sguaban, it looks like this. Well we got all excited about it. So there.
Back down the hill again after taking some more pics and measurements, GPS stuff and notes. This isnt just for fun you know, this is to help further the public understanding of science. And my students will be the first victims when the nw classes start up! Hah!
One last view of Loch Sguaban and the crannog from a heathery knoll.
What a great morning that was - the pics at this resolution probably dont do it justice, and the weather and lighting was about as flat as you could get, but we saw what we came to see and a whole lot more..
More mountainman madness soon!
MM
Comments
Hi MM - great photos as usual - note to Santa - please can I have a decent camera! I have been good, honest!
Wild Freckle from Mull
No`
Hermit from Sanday
ahem..no` a pillow I would like tae lay me heid on, but it does look interesting MM. :-)
Hermit` from continuing the comment afore I hit the button agai
Great pics again - and I'm really getting interested in geology again. I won't be back on the island until New Year, but I'll be looking at the place differently this time.
Mrs Trellis from N E Wales
Well. As pillows go these look just a bit too like mortification of the flesh, sort of Opus Dei-ish on a big scale. So I think I'll just admire the photos if that's alright and try and learn stuff and leave the pain to others...
Flying Cat from in knox
Now I will print this blog and take it with me next time my son and I go poking around the beaches of Tiree...great stuff..
Off Shore View from Currently Libya.
Thanks MM, great photos and illuminating ones, too. Do you pinpoint whatever feature you're looking for on GPS and then record this so that other people can find it?
Jill from EK
Hah! I like the mortification comment - wasnt Columba supposed to have slept on a stone pillow? And the stone of destiny - did that not get called Jacobs pillow? Re Jills question - the GPS in the picture actauly belonged to John who I was out walking with. I dont use GPS myself, havent bought one yet - maybe get one some day - I actually prefer the traditional method of map compass and taking bearings. Actually, a lot of the stuff that you read about in geology books and reports is very vague - the pillow lavas were mentioned in a report from the Geological Conservation Review web site (a great place for stuff) www.thegcr.org.uk but the grid refs were woefully wrong! Mind you , if you read any of the writings of the great mineralogist, Matthew Heddle, he used to describe things and locations in the most vague ways imaginable "gem quality tourmaline, near Braemar" or "6 inch garnets, Loch Ness side" Unbelievably frustrating so it is! However, maybe part of the fun is only getting a vague reference and then having to go and really seek it out - youu know "no pain, no gain" Matthew Heddles book, the Mineralogy of Scotland, is a gold mine of info. It is very rare and very valuable. Someone is selling a copy on Abebooks.com for wait for it 1500 dollars! But know what, dig around my own website, and I 'll tell you where you can perfectly legally download a pdf file of it! Its out of copyright and a scanned copy is held on a server of archived books. Heddle was prof of Chemistry at St Andrews (shameless plug for the alma mater) famous for his huge hammers, and use of dynamite.... I could go on. I wont! Cheers MM
mountainman from mull
would back you on compasses and bearings but have to say, given magnetic anomalies on mull this gets a bit dodgey at times. mind you, gps has its issues, Jill, trying running out of fuel 36 miles down a gps shortcut that ended in a locked gate on a private road! The person I was following in good faith is still cringing coz it cost me getting to a wedding the next day! So when's next geology course MM and what's happening with getting more on geology upfront with the visitors?
Seonag from Mull
Seonag, good point about magnetic anomalies - top of Ben More is the famous one, Others as well - last year on a field trip we came across a dyke at Carsaig which was seriously magnetic. There is actually a video on youtube of the effect on the compass at the top of Ben More - dont know who posted it but it shows it quite well. Go to: http://www.youtube.com/watch?v=gJ1_AADAr1U and you'll see it . Regarding more geology for visitors, watch this space, I am working on it! MM
MM from Mull
Exploring the hills and coasts of Mull and Iona and occasionally elsewhere, with a close eye on the geology
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