BANDED TUFF - EVIDENCE OF LAKE DISTRICT VOLCANISM - Cumbria
« back450 million years old (Ordovician period)
Patterdale, Cumbria
The dramatic scenery at the heart of the Lake District is the result of cataclysmic volcanic eruptions in the late Ordovician period. Glacier-sculpted peaks such as Helvellyn may not look like volcanoes but they are entirely composed of lavas and other rocks that are the products of these eruptions and known as the Borrowdale Volcanic Group.
At that time what is now Cumbria is thought to have been an island arc, similar to those in the west Pacific today, formed of a chain of volcanoes close to the boundary of two converging tectonic plates. The lavas were gaseous and rich in silica which led to violent eruptions and explosive flows of red hot ash and molten rock known as pyroclastic flows.
When this ash was deposited and compacted it formed a rock called tuff, which is often finely bedded or banded, sometimes as a result of deposition in lakes.
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Size: approx. 12 x 8 x 4 centimetres
Weight: 360 grams