A Geology Group Visit to Stump Cross Caverns
Dr John Helm is a UWFS member of long standing and a Geologist who now works part time at the above caverns, he was kind enough to lead a group of members round these caves.
His initial illustrated lecture helped us to understand their formation and history adding to our interest in the visit. The site became an early Tourist attraction helping its preservation. Over the years much has been learnt from cave systems about past climates, fauna and flora, and beliefs.
Water landing on the land surface percolates down through the underlying slate of the Yoredale series, north of the North Craven Fault, drains through the cracks and along the beds of limestone until it reaches the impermeable rocks below. The dissolving of the limestone is accelerated by mildly acidic water formed from the carbon dioxide in the air and the acidic vegetation. The water eventually drains out through a resurgence, at Stump Cross Caverns this is at Black Hill Resurgence to the south of the main Hebden Greenhow road. It has taken millions of years for this system to have formed. Though a space cannot be dated, the features formed in the cave can be using radioactive decay of Uranium and Thorium.
When the water table is high and water fills the growing gaps a rounded tunnel or Phreatic cave system is formed, the acidic water wearing away all the sides. When the water table falls and the water runs only in the base of the gap a Vadose system ensues. The former becoming the latter can make a Keyhole system.
Stalagmites growing upwards, Stalactites growing downwards
As calcite containing water slowly drips from the roof of a cave a calcite Stalactite forms and hangs in increasing length from the ceiling. When the drop falls more quickly and lands on the base a Stalagmite grows upwards. The combination of time and imagination can make all sorts of shapes of these features.
The Organ, flow stone and imagination.
Where water flows very slowly over a slope and forms a small pool, here the calcite is deposited at the edge or rim forming a small dam, now known as Rimstone or a Gour.
Rimstone, Gour, forming pools
The use of a UV light torch can highlight the different minerals in the rocks and cause fascinating scenes.
Minerals in the rock fluorescing under UV light
It was good to see many children in the caves each age group following a different “version” be it Fairy Doorways, Dinosaurs Eggs or just the straight knowledge base but all learning something while having fun.
Lunch afterwards gave us all a chance to discuss what we had seen and reflect on how lucky we are in the Yorkshire Dales.
Many thanks to Dr John and all at Stump Cross Caverns, do check out their website for more excellent information.
Josephine Drake
Photos
Ann Shaw and Stella Hughes.
