Jackson, Ian. Cumbria Rocks — 60 extraordinary rocky places that tell the story of the Cumbrian landscape. Newcastle upon Tyne : Northern Heritage, 2022. The richly illustrated and accessible book series of Cumbria, Northumberland and Durham Rocks are available to purchase from Northern Heritage.
19 High Rigg
Theme: Volcanoes and molten rock
Location
19 High Rigg — BVG Andesite phase 1. St John’s Church has a small car park and the summit of High Rigg is a 1 kilometre walk south from there
Description
In Cumbria between 450 and 460 million years ago volcanoes spewed ash and lava over a vast area and red-hot clouds of molten debris flowed down slopes at hurricane speeds.
Most of the central Lake District is made of these ancient volcanic rocks but it always disappoints to have to explain that, despite their triangular shape, mountains like Bow Fell and Catstye Cam are not themselves volcanoes but are huge chunks of volcanic terrain that have been broken apart, re-arranged and then eroded. So the eastern face of High Rigg is a geology teacher’s dream; in clear view as you drive through St John’s in the Vale, is one of the very few places where that primeval volcanic terrain is obvious at landscape scale. The sloping crags and benches are alternate layers of harder lava and more easily eroded volcanic breccias (a rock made of angular fragments). The lavas, an igneous rock called andesite, are from some of the earliest eruptions in the Lake District. They are part of a unit called the Birker Fell Formation which spreads over 315 square kilometres. The landscape then was more like Hawaii than Krakatoa; these are shield volcanoes, vast sheets of molten magma bursting from fissures and flowing down low-angled slopes.
High Rigg’s wildlife is almost a microcosm of the wider Lake District fells. Its slopes are covered by coarse bent and mat grasses with just a few heathery shrubs and flowering herbs such as the white heath bedstraw or the yellow tormentil. Bracken is common and may reveal where the broadleaved ‘rainforest’ woodland once grew. High Rigg is one of the ‘Wainwright’ fells and an easy one to climb from St John’s church; the views south are worth it.