TheBorrowdale Volcanic Group is agroup ofigneous rock formations named after theBorrowdale area of theLake District, inEngland. They are Caradocian (lateOrdovician) in age (roughly 450 million years old).^[1] It is thought that they represent the remains of a volcanicisland arc, approximately similar to the island arcs of the westPacific today. This developed asoceanic 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 twoplates meet, is termedsubduction. This land-mass has been namedAvalonia by geologists. It is now incorporated into England andWales and a sliver ofNorth America.

Borrowdale Volcanic Group
Stratigraphic range: Caradocian (lateOrdovician)
Lapilli tuff of the Helvellyn Tuff Formation onHigh 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	CentralLake District &Cross Fell
Type section
Named for	Borrowdale

At that time the rocks that now comprise most ofScotland (and part of the northernIrish landmass) were not attached to Avalonia. They were separated by an ocean, called theIapetus Ocean by geologists. The line of joining, or suture, is approximately under theSolway Firth andCheviot Hills. In the Lake District, the junction between the early Ordovician series,Skiddaw Slate, and the Borrowdale Volcanic that was forced under it, can be seen on the slopes ofFleetwith Pike.

In the English Lake District, the Borrowdale Volcanic Group is composed oflavas (mainlyandesites),tuffs andagglomerates, along with some majorigneousintrusions. 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 ofCockermouth.

Volcanic activity lasted in the region until, at earliest, the Burrellian period (± 455 MYA).^[2]

The upper boundary of the group is an unconformity with the overlyingWindermere Supergroup. The lower boundary is an unconformity with the underlyingSkiddaw Group.^[1]

The outcrop of this sequence onCrinkle Crags (and other surrounding peaks in theLake District), was chosen as one of the top 100 geosites in theUnited Kingdom by theGeological Society of London.^[3]

• Eycott Volcanic Group