Borrowdale and Glaramara from Grange Fell

The Borrowdale Volcanic Group is a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

rock formations named after the

Borrowdale Borrowdale is a valley and civil parish in the English Lake District in the Borough of Allerdale in Cumbria, England. It lies within the historic county boundaries of Cumberland. It is sometimes referred to as ''Cumberland Borrowdale'' ...

area of the

Lake District The Lake District, also known as the Lakes or Lakeland, is a mountainous region in North West England. A popular holiday destination, it is famous for its lakes, forests, and mountains (or '' fells''), and its associations with William Wordswor ...

, in

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. They are Caradocian (late

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

) in age (roughly 450 million years old). It is thought that they represent the remains of a volcanic

island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

, approximately similar to the island arcs of the west

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

today. This developed as

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic ...

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 meet, is termed

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

. This land-mass has been named

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of West ...

by geologists. It is now incorporated into England and

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

and a sliver of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

Geology

At that time the rocks that now comprise most of

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...

(and part of the northern

Irish Irish may refer to: Common meanings * Someone or something of, from, or related to: ** Ireland, an island situated off the north-western coast of continental Europe ***Éire, Irish language name for the isle ** Northern Ireland, a constituent unit ...

landmass) were not attached to Avalonia. They were separated by an ocean, called the

Iapetus Ocean The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleo ...

by geologists. The line of joining, or suture, is approximately under the

Solway Firth The Solway Firth ( gd, Tràchd Romhra) is a firth that forms part of the border between England and Scotland, between Cumbria (including the Solway Plain) and Dumfries and Galloway. It stretches from St Bees Head, just south of Whitehaven ...

and

Cheviot Hills The Cheviot Hills (), or sometimes The Cheviots, are a range of uplands straddling the Anglo-Scottish border between Northumberland and the Scottish Borders. The English section is within the Northumberland National Park. The range includes T ...

. In the Lake District, the junction between the early Ordovician series,

Skiddaw Slate Skiddaw slate is an early Ordovician metamorphosed sedimentary rock, as first identified on the slopes of Skiddaw in the English Lake District. The base of this series is unknown. The thickness could, therefore, amount to several thousand feet of ...

, and the Borrowdale Volcanic that was forced under it, can be seen on the slopes of

Fleetwith Pike Fleetwith Pike is a fell in the English Lake District in the county of Cumbria which reaches a height of 648 metres (2,126 feet). The fell is a well-known feature of the area as it casts an imposing presence over Buttermere and the ...

. In the English Lake District, the Borrowdale Volcanic Group is composed of

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

s (mainly

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

s),

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s and

agglomerate Agglomerate (from the Latin ''agglomerare'' meaning "to form into a ball") is a coarse accumulation of large blocks of volcanic material that contains at least 75% bombs. Volcanic bombs differ from volcanic blocks in that their shape records flu ...

s, along with some major

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s. 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 Cockermouth is a market town and civil parish in the Borough of Allerdale in Cumbria, England, so named because it is at the confluence of the River Cocker as it flows into the River Derwent. The mid-2010 census estimates state that Cocke ...

. Volcanic activity lasted in the region until, at earliest, the Burrellian period (± 455 MYA).Geology of England and Wales, pp118ff
/ref>

Boundaries

The upper boundary of the group is an unconformity with the overlying Windermere Supergroup. The lower boundary is an unconformity with the underlying Skiddaw Group.

Significance

The outcrop of this sequence on

Crinkle Crags Crinkle Crags is a fell in the English Lake District in the county of Cumbria. It forms part of two major rings of mountains, surrounding the valleys of Great Langdale and Upper Eskdale. The name reflects the fell's physical appearance ...

(and other surrounding peaks in the

), was chosen as one of the top 100 geosites in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...

by the

Geological Society of London The Geological Society of London, known commonly as the Geological Society, is a learned society based in the United Kingdom. It is the oldest national geological society in the world and the largest in Europe with more than 12,000 Fellows. Fe ...

References

{{Reflist Geological groups of the United Kingdom Geology of Cumbria Volcanic groups Volcanism of England Ordovician volcanism

Geology

Boundaries

Significance

See also

References