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Look into the Volcano

GAZE INTO THE DEPTHS OF GHYLL SCAUR QUARRY and you’re looking back 450 million years into the heart of a vast caldera volcano that once covered most of the Lake District. Over several million years, the lavas and tuffs ejected by the volcano formed rocks up to eight kilometres thick.

Most of the rocks in this quarry were formed in explosive - or pyroclastic - eruptions. The volcano discharged huge volumes of foaming magma and rock, with an ash cloud towering up to 50 kilometres into the sky. The volcanic ash cooled and hardened to form rock called tuff. Other tuffs in the quarry formed when hot magma mixed explosively with cold groundwater. Later, magma that was trapped and cooled in cracks in the tuff formed other rocks called intrusions.

The diagram shows the relationship between the volcano and the different types of rock found in the quarry. You can examine the different tuffs and intrusions in the nearby Rock Street.

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Photographs: Ben Barden www.benbarden.co.uk; Aggregate Industries www.aggregateindustries.com
Geologist: Eric Johnson BSc, PhD, FGS, CGeol. Formerly British Geological Survey
Copyright © Millom Geodiversity Project 2009
Millom Geodiversity Project is a not for profit, unincorporated association
Email: info@millomrockpark.org.uk
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