# Borrowdale Volcanic Group > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Borrowdale_Volcanic_Group > Markdown URL: https://mediated.wiki/source/Borrowdale_Volcanic_Group.md > Source: https://en.wikipedia.org/wiki/Borrowdale_Volcanic_Group > Source revision: 1302725992 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Borrowdale Volcanic Group Stratigraphic range: Caradocian (late Ordovician) Lapilli tuff of the Helvellyn Tuff Formation on High Crag Type Group Sub-units Birker Fell Andesite Formation, Whorneyside Tuff Formation, Airy's Bridge Tuff Formation, Lingwell Tuff Formation, Seathwaite Fell Sandstone Formation, Lincomb Tarns Tuff Formation, Esk Pike Formation, Tarn Hows Tuff Formation Underlies Windermere Supergroup Overlies Skiddaw Group Thickness probably up to 6000m Lithology Primary volcanic rocks Other siltstone, sandstone Location Region Cumbria Country England Extent Central Lake District & Cross Fell Type section Named for Borrowdale Fells formed of the volcanics around [Borrowdale](/source/Borrowdale) The **Borrowdale Volcanic Group** is a [group](/source/Group_(stratigraphy)) of [igneous](/source/Igneous) rock formations named after the [Borrowdale](/source/Borrowdale) area of the [Lake District](/source/Lake_District), in [England](/source/England). They are Caradocian (late [Ordovician](/source/Ordovician)) in age (roughly 450 million years old).[1] It is thought that they represent the remains of a volcanic [island arc](/source/Island_arc), approximately similar to the island arcs of the west [Pacific](/source/Pacific) today. This developed as [oceanic crust](/source/Oceanic_crust) to the (present) north-west and was forced by crustal movement under a continental land-mass to the present south-east. Such forcing under, as two [plates](/source/Tectonic_plates) meet, is termed [subduction](/source/Subduction). This land-mass has been named [Avalonia](/source/Avalonia) by geologists. It is now incorporated into England and [Wales](/source/Wales) and a sliver of [North America](/source/North_America). ## Geology At that time the rocks that now comprise most of [Scotland](/source/Scotland) (and part of the northern [Irish](/source/Ireland) landmass) were not attached to Avalonia. They were separated by an ocean, called the [Iapetus Ocean](/source/Iapetus_Ocean) by geologists. The line of joining, or suture, is approximately under the [Solway Firth](/source/Solway_Firth) and [Cheviot Hills](/source/Cheviot_Hills). In the Lake District, the junction between the early Ordovician series, [Skiddaw Slate](/source/Skiddaw_Slate), and the Borrowdale Volcanic that was forced under it, can be seen on the slopes of [Fleetwith Pike](/source/Fleetwith_Pike). In the English Lake District, the Borrowdale Volcanic Group is composed of [lavas](/source/Lava) (mainly [andesites](/source/Andesite)), [tuffs](/source/Tuff) and [agglomerates](/source/Agglomerate), along with some major [igneous](/source/Igneous_rock) [intrusions](/source/Intrusion). These rocks of the Borrowdale Volcanic Group give rise to dramatic scenery. The mountainous nature of the area, its high rainfall and the relative impermeability of the rock give rise to a high risk of storm flooding as demonstrated by the 2009 flooding of [Cockermouth](/source/Cockermouth). Volcanic activity lasted in the region until, at earliest, the Burrellian period (± 455 MYA).[2] ## Boundaries The upper boundary of the group is an unconformity with the overlying [Windermere Supergroup](/source/Windermere_Supergroup). The lower boundary is an unconformity with the underlying [Skiddaw Group](/source/Skiddaw_Group).[1] ## Significance The outcrop of this sequence on [Crinkle Crags](/source/Crinkle_Crags) (and other surrounding peaks in the [Lake District](/source/Lake_District)), was chosen as one of the top 100 geosites in the [United Kingdom](/source/United_Kingdom) by the [Geological Society of London](/source/Geological_Society_of_London).[3] ## See also - [Eycott Volcanic Group](/source/Eycott_Volcanic_Group) ## References 1. ^ [***a***](#cite_ref-BGS_Lexicon_1-0) [***b***](#cite_ref-BGS_Lexicon_1-1) ["Borrowdale Volcanic Group"](http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BVG). *The BGS Lexicon of Named Rock Units*. British Geological Survey. Retrieved 14 October 2014. 1. **[^](#cite_ref-GeoEngWal_2-0)** [Geology of England and Wales, pp118ff](https://books.google.com/books?id=-6gqvAbdS-MC&pg=PA118&lpg=PA118) 1. **[^](#cite_ref-GeolSoc_3-0)** ["The Geological Society's 100 Great Geosites"](https://web.archive.org/web/20141016064151/http://apps.esriuk.com/app/GreatGeosites/3/wmt/view/5e0d44970b3a4b4dafb7da0404b2d8ed/index.html). The Geological Society. 2014. Archived from [the original](http://apps.esriuk.com/app/GreatGeosites/3/wmt/view/5e0d44970b3a4b4dafb7da0404b2d8ed/index.html) on 16 October 2014. Retrieved 14 October 2014. --- Adapted from the Wikipedia article [Borrowdale Volcanic Group](https://en.wikipedia.org/wiki/Borrowdale_Volcanic_Group) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Borrowdale_Volcanic_Group?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.