Geology

Geology

Co-ordinator:  Mark Barley

Tel:  0161 929 9438

Email: info@knutsfordu3a.co.uk

Regular meetings are currently taking place using Zoom. The first of these was on 20th April and included the showing of a Youtube video of the 2018 eruption of Anak Krakatoa, a talk on a free online course on geochemistry from Kyoto University and a presentation on the geology of part of the Northumberland coast.

Prior to the lockdown the group met in members’ homes on the third Monday of the month at 7.30.  Please contact Mark Barley if you wish to join the group.

A Geological Field Trip to Malham

A group of 6 of us set out for Malham on Friday 23rd November. From the main car park we followed the Pennine Way to the south and then took a side path towards Janet’s Foss and Cautley Spout. The route took us across a flat area of pasture land which my iGeology app showed was sandstone/siltstone. However we were clearly approaching some small hills with many outcrops of white rock. The transition from the flat pasture land of the sandstone/siltstone to the rocky hills of limestone was very marked and we were soon following a stream through woods in a steep sided rocky valley. The limestone had been laid down more than 300 million years ago when the piece of land that was eventually to become Britain was close to the equator and was submerged under a tropical warm shallow limey sea.

The scenic waterfall (Janet’s Foss- see photo) suggests that a layer of harder rock sits on weaker rock but here all the rock is limestone. However different limestones may have different degrees of consolidation:- a pure limestone is a strong rock (often used in buildings) but if the lime has some mud mixed in when it is deposited then a weak knobbly type of limestone is formed. Janet’s Foss may result from a layer of strong limestone overlaying a much weaker (possibly muddier) limestone which is readily eroded by the water in the plunge pool.

Further on we took the trail towards Cautley Spout. The dramatic limestone cliffs narrowing to a gorge with a couple of waterfalls (see photo below) is thought to be due to the collapse of a massive limestone cave during the last ice age.

There are several springs close to the main stream suggesting that an impervious rock layer (possibly the sandstone/siltstone seen on the way to Janet’s Foss) is just below the level of the main stream.

From Cautley Spout we headed back to Malham for some lunch in the local pub. After lunch we walked to the base of Malham Cove. The dramatic limestone cliff of Malham Cove (see photograph below) is believed to have been made by a

massive waterfall during the last ice age. It is believed that as the glaciers melted towards the end of the ice-age, a large lake of melt water built up somewhere to the north of where Malham Tarn is today. This eventually broke through to the south and a huge volume of water poured down into what is now Malham cove cutting out the massive cliff we see today. From the base of the Cove we climbed the steps to view the limestone pavement above the cliff and then took the footpath towards Cautley Spout until we reached the road to Malham where we had tea/coffee before heading back home.

Mark Barley 2018

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