The Volcano at Middle Hope

On Thursday 19th April 2018 we went on a field trip to Middle Hope to investigate the volcano there.

We did this in two parts:

The first part was to look at the volcanics on the beach at Swallow Cliff Bay.
The second part was to investigate the volcanics at the Middle Hope Bay further to the East.

The first part has been very well written up by Charley Stamper who, at the time was a student at Bristol so there seems little point in rewriting it so the link to her article on ‘Outcrop’, is here:

http://avonrigsoutcrop.blogspot.co.uk/2013/03/rigs-of-month-march-middle-hope.html

A report on the second part follows on here:
For this part we relied on the directions given in the book, “Geological excursions in the Bristol District” Edited by R.J.G. Savage.
We followed the directions in the book to site 1.3 ‘The Eastern Exposure at ST 3390 6655 at the eastern end of a small bay. There are no pillow lavas here, which indicates that the vent was probably to the West. There is an excellent exposure of the Tuffs as a fault has offset them to the North by a fault that can clearly be seen in South-West corner of the bay.This fault separates the tuffs from the Black Rock Limestones to the West.
I won’t copy out the text from the book, it can be seen on pages 52/3.

Care is required clambering down into the bay to examine the exposures.

This is a very interesting site and, apart from the missing pillow lavas, demonstrates the  volcanic activity very well.

References:

– Faulkner TJ (1989) The early Carboniferous (Courceyan) Middle Hope volcanics of Weston-super-Mare: development and demise of an offshore volcanic high. Proc. Geol. Ass., 100(1), 93-106.

– Volcanic rocks of the Bristol region, Speedyman DL. in Geological excursions in the Bristol District. Savage RJG (1977). University of Bristol.

– OS Sheet 153 Weston-super-Mare and Bleadon Hill © Crown Copyright 2011

– Sedimentary Petrology. Maurice E Tucker © Blackwell science Ltd 1981

– The Coast of the Bristol Region. Quaternary Geology and Geomorphology. David J. Case
Geologists’ Association Guide No. 71. © The Geologists’ Association 2013

– All photos © Charlotte Stamper. 2013

Richard Kefford 2020 Eorðdraca

My books are for sale here:  Richard

The Clapton Klippen

Photo credit  Mark Howson

Upper left  –  Sigillaria
Right           –  Calamites
Lower left  –  Lepidodendron

It was a mizzly sort of day but, as daft geologists, we decided to go anyway. We met at the agreed time under the motorway bridge. It was dry there, except for the rivulets running down the gutters on each side of the road. It was also dark so ferreting out our gear from the car boot was mostly feeling for the oh so familiar objects.

We dressed up for cold, wet weather and muddy ground, secured the cars and then set off up the familiar road which quickly morphed into a track. At the branch, we headed left through a kissing gate onto a rocky path that hugged the higher side of the field, up against the barbed wire that kept us out of the wood that was groaning in the erratic wind. The path was muddy with many rocks intruding through the red mud, their curiosity driving them up into the damp air above . We had a look at these rocks and speculated about their provenance. We identified them as Pennant Sandstone from the Carboniferous but why were they so separate instead of just being a massive exposure? Was there a quarry nearby ? Perhaps this was the discarded waste from the quarry that was graded as poor quality?

We came to another gate that led us uphill into the wood. It was a public path through private woodland that permission is required to visit, so we had asked for ,and were given, permission to divert from the path as we thought fit, to investigate any quarries or interesting whatevers that we spotted. The path curved to the left and we could see an outcrop over to the right. This was a valley curving away to the North about 5 metres deep and 10 metres wide at its crest. On the Southern side it was steep with several near vertical cliffs that looked like old quarry faces. Close inspection showed that the rock was Pennant Sandstone. We were now higher than the footpath along the edge of the wood so this tended to confirm our hypothesis that the questing stones we had seen on the footpath were indeed from a quarry – this one? Perhaps as surface treatment for a muddy path?

We started looking along the opposite side from the face as stone that was discarded was usually dumped away from the active face. We knew that the Pennant was usually  quarried for building and was prized for its prized ‘flats’. Any fossils were regarded with suspicion as “the devil’s work” or because they broke up the smooth style of the rock and reduced its quality as building stone. This was something we had learned – when looking for fossils in a disused quarry, always look for the rejected stone pile – unless, of course, the quarry is for road-stone, which is destined to be crushed and screened anyway so any fossils will have been destroyed in the process.

We found a ring of charred wood and rocks which had been clearly gathered for a fire – perhaps a barbecue? We started sorting through the stones and found an interesting rock with two fossils in it. We were delighted as my companion – a geologist – had found a Sigillaria specimen here a few weeks before. Just after we found this, a couple turned up from the local Court. We had invited them to join us on the fossil hunt. They told us that their house, near the top of the hill was built from Pennant Sandstone – most likely from this quarry. They had brought the previously found Sigillaria fossil as they wanted to bring it back and leave it at its birthplace.

We spent another half an hour or so looking for more fossils but it was not to be so, after many photos we carefully hid the fossils in a cleft in the old quarry face for others to find. There wasn’t much else to see as it is a small quarry. I would like to stress again that it is on private land and permission should be sought from the owner before entering it.

We then looked around the area because we were looking for the variously named Clevedon or Naish House fault as we knew it ran from Clevedon beach West along and through this area. We found clues – a change from woodland to a field used for grazing sheep above the quarry. As we walked up to the wire fence between the two, we found an increasing density of limestone rocks. These rocks had crinoid fossils in so were probably either from the Avon Group, Lower Limestone Shales or from the Black Rock Limestone. This demonstrated that the fault was in this area. The vegetation change from woodland to grazing fields followed the underlying geology change from acid to alkaline soil

It was now time to retrace our steps to the motorway bridge and  then walk along the side of the motorway towards Nicholas Wood which is a wood perched on a large, almost circular, mound. This one of the Clapton Klippen. Klippen is a plural German word that translated to the English, Cliffs. A Klippe is a peculiar feature where older rocks have been moved by faulting and erosion. The Oxford Dictionary of Earth Sciences defines it thus: A tectonic outlier produced by the erosion or gravity-gliding of one or more nappes. The front portions of the nappes become detached to produce the klippe structure. A nappe is defined as: from the French nappe, meaning ‘cover’ a thrusted mass or folded body in which the fold limbs and axes are approximately horizontal.

So this means that, as you approach Nicholas Wood and transition from a grazing meadow to wood land, you walk up a hill from a muddy red field into a dry ground wood. Rock clasts are randomly scattered on the surface and can clearly be seen to be Black Rock Limestone complete with Crinoid fossil ossicles.

Nicholas Wood covers just one of the Clapton Klippen. There are four others in the area – one of which has been quarried for its limestone. We debouched on to St Michael’s church path and walked back through the village then up Wood Lane to the cars.

The other Klippen will be investigated another day.

© Richard Kefford    2020                               Eorðdraca

My books are for sale here:      Richard