Monday, 5 August 2013

A journey through time – geological boundaries in Arran

Corrie is a small village on the east coast of Arran, not far north of Brodick. The rocks here range from the Devonian (north of the village) to the Permian (to the south). There are also some basaltic lavas dating from the Carboniferous, but on this shore these are not visible, being overlain by weathered boulders and stones.

When looking at changes in rocks through time, it is often best to start with the oldest rocks and walk up through the succession, but for reasons that will become apparent later, this story starts in the Permian and journeys back through time.

In the Permian, the bit of land that is now Arran was north of the equator, at a similar latitude to today's Sahara desert, and had a generally arid climate with only occasional rainfall.

The rocks on the foreshore are red, with large scale cross bedding in places, and with frosted and rounded grains – all clues to generally aeolian deposition. There are some sections showing only planar bedding, which may represent sheet floods in a temporary fluvial setting.
Permian rocks just south of Corrie, Arran.
Changes in bedding

Thursday, 1 August 2013

RHS Wisley

In July I spent three days visiting gardens. The most impressive was the RHS garden at Wisley, tucked in the corner between the A3 and the M25. I've visited the RHS gardens at Harlow Carr and at Rosemoor, but Wisley is much bigger and with more to see. Not really surprising, as this is also the RHS's main research base, with a large field given over to plant trials, and a whole orchard to fruit tree trials.

Tuesday, 16 July 2013

Hutton's Unconformity - revisited

My first visit to Hutton's Unconformity on Arran was many years ago, prompted only by a geology map on the wall of a Youth Hostel, and a rough idea of what to look for. A recent visit on a geology holiday, and hence with a knowledgeable tutor, suggests that I didn’t quite locate the actual unconformity correctly on my first visit!

Hutton spotted two other similar unconformities, at Jedburgh, and Siccar Point on the east coast of Scotland, but the one on Arran was his first. 

Wednesday, 29 May 2013

The New Fancy Map

We are here...
We were at the New Fancy viewpoint in the Forest of Dean today (the site of an old coal mine). While there we had a look at the map with a difference. There is a standard display board with a geological map on one side and a list of the old mines and quarries in the Forest on the other. But there is also a large stone map on the ground, with the appropriate stones being used to show the various rocks outcropping in the area.

Monday, 27 May 2013

No Apparent Danger

by Victoria Bruce

I bought this book because I read about it while writing my review for Surviving Galeras. Surviving Galeras is Stanley Williams' account of his career as a vulcanologist, culminating in the story of being caught out by an unexpected small eruption of Galeras, in Columbia.

I say 'unexpected', but after reading No Apparent Danger I'm not so sure this is true.

The eruption of Galeras in 1993 was small, and was not the first small eruption in recent years. It was a fatal eruption because a vulcanology conference was being held in a nearby town, and on the day it erupted there were field trips on the volcano. The scientists working inside the caldera, on a field trip led by Williams, got caught in the eruption. Six people died, including three tourists visiting the summit.

Friday, 29 March 2013

Scoria cones

Scoria cones are also known as ash cones or cinder cones. They are formed when ejecta collect around the vent. If erupted over a short period, the cone will be higher on the downwind side.

Bayuyo is a scoria cone at the north end of Fuerteventura, formed in a single Strombolian eruption. These eruptions are explosive, but in a fairly mild way (in volcano terms!). The ejecta can contain lots of vesicles. 

View Larger Map

Sunday, 24 March 2013

Lava tubes

A lava tube can form when the surface of a stream of lava solidifies, leaving hotter, still-liquid lava beneath. When the lava stops flowing, it leaves a hollow tube. If you know where to look on Fuerteventua and Lanzarote, you can see small holes in fields, where the roof of a tube has collapsed, and in some places it is possible to trace the lava tube over several miles by looking for these holes and linking them.

However there are two much larger examples of lava tubes to be visited, and the tour of the Timafaya National Park actually drives you through part of a lava tube that has lost its roof!