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The Mam Tor landslide, geology & mining legacy around Castleton, Peak District National Park, Derbyshire, UK

The Mam Tor landslide, geology & mining legacy around Castleton, Peak District National Park, Derbyshire, UK,LAURANCE DONNELLY

The Mam Tor landslide, geology & mining legacy around Castleton, Peak District National Park, Derbyshire, UK  
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This guide provides information to support a one-day field trip to the Mam Tor landslide and Castleton which is situated in the Peak District National Park, North Derbyshire. The village is surrounded by dramatic, often spectacular and rare sites of geological significance and geological interest. Mam Tor forms the highest point in the area and contains the ramparts of a prehistoric hillfort, on a ridge of sandstone, running almost east to west, separating the Hope Valley (to the south) from the Edale Valley (to the north) This site provides an excellent opportunity to inspect Carbonifeorus stratigraphy showing the relationships between the Mam Tor Beds, Edale Shales (both of Namurian, or 'Millstone Grit' age) which unconformably overlie Limestone (Dinantian, or Lower Carboniferous age). Between about 3000 and 4000 years ago a huge section of the Mam Tor Beds and Edale Shales began to fail. This generated an 80m high scarp on the western face of Mam Tor and a landslide over 750m long and 300m wide. The slipped mass has been in a state of continual, gradual, creep type motion since its generation. The rate of slippage has varied and is thought to be controlled principally by fluctuation in ground water levels following prolonged heavy rain. For almost 200 years this slump earth-flow type landslide has caused extensive, dramatic and spectacular damage to the road which was built across it in 1810, culminating in its abandonment and closure in 1979. The limestone around Mam Tor and Castleton has a long mining legacy which dates back to at least Saxon and Roman times. The primary minerals which have been mined include lead (galena), fluorite (fluorspar or 'Blue John'), calcite and baryte. Other minerals found in the area include silver, sphalerite and hydrocarbons. These exist in epigenetic mineral veins, faults, fissures and caves which occur naturally in the limestone (formed by the slow, gradual dissolution of the soluble limestone by slightly acidic rainwater and groundwater). This has left a dramatic impact on the landscape including steep, narrow, open gullies (where mineral were mined where they outcrop), abandoned mine shafts, mineral tips, soughs (drainage adits) mine entries and evidence for medieval mineral processing techniques (including a crushing circle). The limestone represents part of a coral, apron-reef complex (similar to atolls found today in the Pacific Ocean) and in many places contains abundant fossils including corals, algae, brachiopods, bivalves, crinoids and goniatites. Volcanic activity during the Carboniferous resulted in the deposition of basaltic lava flows and vent agglomerate, which has have been exposed by weathering and erosion.
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