Birker Fell
Encyclopedia
Birker Fell, also known as Birker Moor, is an upland wilderness area in the western portion of the Lake District National Park
, in Cumbria
, England
. Rather than being formed of one single high peak, the fell
is a broad, undulating area, approximately 6 km square, with numerous crag
s and prominences scattered across its area. The highest point of the fell is at Green Crag
(489m). The fell is bordered by the Duddon Valley
to the south-east, Ulpha Fell to the south-west, Harter Fell
to the north-east, and Eskdale
to the north-west.
One small hamlet
, Birkerthwaite
, lies in a shallow valley near the centre of the fell, but other than this the only human habitations are scattered hill farms. A road crosses the fell between Eskdale Green
and Ulpha
, in the Duddon Valley
.
, separated by shallow valleys and bogs, giving the high fell an uneven and chaotic appearance.
Water plays an important role in defining the character of Birker Fell. Between the crags flow many small streams, known as becks or gills
in the local terminology. Many of the becks rise in one of the numerous bogs which occur in the area, the largest of which are White Moss, Sike Moss, Tewitt Moss and Foxbield Moss. At the western edge of the fell lies Devoke Water
, which claims the title of largest tarn
in the Lake District. It lies at an altitude of 235 m (770 ft) and is approximately 1 km long (east-west) and 0.4 km wide. The southern border between Birker Fell and Ulpha Fell traces a line between Devoke Water and the valley of Crosby Gill, a large stream that drops down the southern flanks of the fell to the village of Ulpha in the Duddon Valley. The northern edge of the fell is marked by a steep range of crags which drop sharply to the floor of Eskdale. These crags are cut by the cascades of Stanley Force and Birker Force, two of the most spectacular waterfall
s in the Lake District.
of the Birker Fell Formation (BFF) of the Borrowdale Volcanic Group (BVG). The BFF forms the lowest, and hence oldest, portion of this famous sequence of andesite
and dacite
volcanic rocks. The Birker Fell Andesite occurs throughout much of the western Lake District. The BVG are thought to have formed in the early Ordovician
by island arc
volcanic activity, due to subduction
during the closing of the Iapetus Ocean
.
The central and northern areas of Birker Fell are dominated by composite andesite lava
flows. Within the andesitic lava flows, the Great Whinscale Dacite lava flow and the associated, underlying Little Stand Tuff
form a marker band that runs northeast-southwest across the fell, but are best seen at Silver How and Great Whinscale . A small area of basalt
ic material occurs approximately 1 km north of Birkerthwaite, composed of plagioclase
- and pyroxene
-phyric
andesite-basalt lavas (the Birkby Fell Member), and tuff and lapilli
-tuffs (the Devoke Water Member). The main outcrop of the Devoke Water Member occurs to the south-west of Devoke Water itself, on Ulpha Fell. The south and south-eastern portion of the fell is composed of a sequence of tuff beds with highly variable composition: from rhyolitic
through to basaltic. These overlie the BFF and form the next section of the BVG sequence.
In the north-western corner of Birker Fell, extensive faulting has juxtaposed the BVG rocks against granite
s of the late Ordovician Eskdale Intrusion.
Lake District National Park
The Lake District National Park is located in the north-west of England and is the largest of the English National Parks and the second largest in the United Kingdom. It is in the central and most-visited part of the Lake District....
, in Cumbria
Cumbria
Cumbria , is a non-metropolitan county in North West England. The county and Cumbria County Council, its local authority, came into existence in 1974 after the passage of the Local Government Act 1972. Cumbria's largest settlement and county town is Carlisle. It consists of six districts, and in...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. Rather than being formed of one single high peak, the fell
Fell
“Fell” is a word used to refer to mountains, or certain types of mountainous landscape, in Scandinavia, the Isle of Man, and parts of northern England.- Etymology :...
is a broad, undulating area, approximately 6 km square, with numerous crag
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s and prominences scattered across its area. The highest point of the fell is at Green Crag
Green Crag
Green Crag is a fell in the English Lake District. It stands between Eskdale and the Duddon valley in the Southern Fells.-Topography:The headwaters of Eskdale and the Duddon are separated by a ridge falling south west from the summit of Crinkle Crags. This line of high ground continues over many...
(489m). The fell is bordered by the Duddon Valley
Duddon Valley
The Duddon Valley is a valley in the Lake District National Park in Cumbria, England. The River Duddon flows through the valley, rising in the mountains between Eskdale and Langdale, before flowing into the Irish Sea near Broughton in Furness...
to the south-east, Ulpha Fell to the south-west, Harter Fell
Harter Fell (Eskdale)
Harter Fell is a mountain in the western part of the English Lake District located between the Eskdale and Duddon valleys. Its height is 649 m . There are several walking routes to the summit.-Topography:...
to the north-east, and Eskdale
Eskdale, Cumbria
Eskdale is a glacial valley and civil parish in the western Lake District National Park in Cumbria, England. It forms part of the Borough of Copeland, and has a population of 264....
to the north-west.
One small hamlet
Hamlet (place)
A hamlet is usually a rural settlement which is too small to be considered a village, though sometimes the word is used for a different sort of community. Historically, when a hamlet became large enough to justify building a church, it was then classified as a village...
, Birkerthwaite
Birkerthwaite
Birkerthwaite is a village on Birker Fell, Eskdale, Cumbria, England, UK.-External links:...
, lies in a shallow valley near the centre of the fell, but other than this the only human habitations are scattered hill farms. A road crosses the fell between Eskdale Green
Eskdale Green
Eskdale Green is a village in Cumbria, England, 10 miles west of Coniston. It lies off the A595 road and is one of the few settlements in Eskdale.The village is centred around the small St. Bega's Church and hall...
and Ulpha
Ulpha
Ulpha is a small village and civil parish in the Duddon Valley in the Lake District National Park in Cumbria, England. It forms part of the Borough of Copeland. At Ulpha a road leaves the Duddon Valley to cross Birker Fell to the valley of Eskdale...
, in the Duddon Valley
Duddon Valley
The Duddon Valley is a valley in the Lake District National Park in Cumbria, England. The River Duddon flows through the valley, rising in the mountains between Eskdale and Langdale, before flowing into the Irish Sea near Broughton in Furness...
.
Landscape
Apart from Green Crag, other notable high points on the fell include: Cook Crag (469m); White How (444m); Great Worm Crag (427m); Kepple Crag (328m,); Great Crag (323m); Rough Crag (319m); Water Crag (305m); and Brantrake Crags (259m). Between these points are a plethora of smaller crags and knollsHillock
A hillock or knoll is a small hill, usually separated from a larger group of hills such as a range. Hillocks are similar in their distribution and size to small mesas or buttes. The term is largely a British one...
, separated by shallow valleys and bogs, giving the high fell an uneven and chaotic appearance.
Water plays an important role in defining the character of Birker Fell. Between the crags flow many small streams, known as becks or gills
Gill (stream)
Ghyll or Gill is used for a stream or narrow valley in the North of England and other parts of the United Kingdom. The word originates from the Old Norse Gil...
in the local terminology. Many of the becks rise in one of the numerous bogs which occur in the area, the largest of which are White Moss, Sike Moss, Tewitt Moss and Foxbield Moss. At the western edge of the fell lies Devoke Water
Devoke Water
Devoke Water is a small lake in the mid-west region of the English Lake District, in the county of Cumbria. It is the largest tarn in the Lake District....
, which claims the title of largest tarn
Tarn (lake)
A tarn is a mountain lake or pool, formed in a cirque excavated by a glacier. A moraine may form a natural dam below a tarn. A corrie may be called a cirque.The word is derived from the Old Norse word tjörn meaning pond...
in the Lake District. It lies at an altitude of 235 m (770 ft) and is approximately 1 km long (east-west) and 0.4 km wide. The southern border between Birker Fell and Ulpha Fell traces a line between Devoke Water and the valley of Crosby Gill, a large stream that drops down the southern flanks of the fell to the village of Ulpha in the Duddon Valley. The northern edge of the fell is marked by a steep range of crags which drop sharply to the floor of Eskdale. These crags are cut by the cascades of Stanley Force and Birker Force, two of the most spectacular waterfall
Waterfall
A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...
s in the Lake District.
Geology
Geologically, Birker Fell is of importance as the type localityType locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
of the Birker Fell Formation (BFF) of the Borrowdale Volcanic Group (BVG). The BFF forms the lowest, and hence oldest, portion of this famous sequence of andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
and dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
volcanic rocks. The Birker Fell Andesite occurs throughout much of the western Lake District. The BVG are thought to have formed in the early Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
by island arc
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
volcanic activity, due to subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
during the closing of the Iapetus Ocean
Iapetus Ocean
The Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
.
The central and northern areas of Birker Fell are dominated by composite andesite lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
flows. Within the andesitic lava flows, the Great Whinscale Dacite lava flow and the associated, underlying Little Stand Tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
form a marker band that runs northeast-southwest across the fell, but are best seen at Silver How and Great Whinscale . A small area of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic material occurs approximately 1 km north of Birkerthwaite, composed of plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
- and pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
-phyric
Phenocryst
thumb|right|300px|[[Granite]]s often have large [[feldspar|feldspatic]] phenocrysts. This granite, from the [[Switzerland|Swiss]] side of the [[Mont Blanc]] massif, has large white [[plagioclase]] phenocrysts, [[triclinic]] [[mineral]]s that give [[trapezium|trapezoid]] shapes when cut through)...
andesite-basalt lavas (the Birkby Fell Member), and tuff and lapilli
Lapilli
Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli means "little stones" in Latin. They are in some senses similar to ooids or pisoids in calcareous sediments.By definition lapilli range...
-tuffs (the Devoke Water Member). The main outcrop of the Devoke Water Member occurs to the south-west of Devoke Water itself, on Ulpha Fell. The south and south-eastern portion of the fell is composed of a sequence of tuff beds with highly variable composition: from rhyolitic
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
through to basaltic. These overlie the BFF and form the next section of the BVG sequence.
In the north-western corner of Birker Fell, extensive faulting has juxtaposed the BVG rocks against granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
s of the late Ordovician Eskdale Intrusion.