Birker Fell, also known as ''Birker Moor'', is an upland wilderness area in the western portion of the

Lake District National Park The Lake District, also known as ''the Lakes'' or ''Lakeland'', is a mountainous region and National parks of the United Kingdom, national park in Cumbria, North West England. It is famous for its landscape, including its lakes, coast, and mou ...

, in

Cumbria Cumbria ( ) is a ceremonial county in North West England. It borders the Scottish council areas of Dumfries and Galloway and Scottish Borders to the north, Northumberland and County Durham to the east, North Yorkshire to the south-east, Lancash ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. Rather than being formed of one single high peak, the

fell A fell (from Old Norse ''fell'', ''fjall'', "mountain"Falk and Torp (2006:161).) is a high and barren landscape feature, such as a mountain or Moorland, moor-covered hill. The term is most often employed in Fennoscandia, Iceland, the Isle of M ...

is a broad, undulating area, approximately 6 km square, with numerous

crag Crag may refer to: * Crag (climbing), a cliff or group of cliffs, in any location, which is or may be suitable for climbing * Crag (dice game), a dice game played with three dice * Crag, Arizona, US * Crag, West Virginia, US * Crag and tail, a ...

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 The Duddon Valley is a valley in the southern 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 ...

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 ''The Tragedy of Hamlet, Prince of Denmark'', often shortened to ''Hamlet'' (), is a Shakespearean tragedy, tragedy written by William Shakespeare sometime between 1599 and 1601. It is Shakespeare's longest play. Set in Denmark, the play (the ...

, 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 Eskdale Green is a village in Cumbria, England, 10 miles west of Coniston. Historically in Cumberland, it lies off the A595 road and is one of the few settlements in Eskdale. Main sights The village is centred on the small St. Bega's Church ...

and

Ulpha Ulpha is a small village and civil parish in the Duddon Valley in the Lake District National Park in Cumbria, England. Historic counties of England, Historically in Cumberland, it forms part of the Cumberland unitary authority area. At Ulpha a ...

, in the

Landscape

Apart from ''Green Crag'', other notable high points on the fell include: ''Crook Crag'' (469m, ); ''White How'' (444m, ); ''Great Worm Crag'' (427m, ); ''Iron Crag'' (408m, ); ''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 knolls, 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 A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...

s in the Lake District.

Geology

Geologically, Birker Fell is of importance as the type locality of the Birker Fell Formation (BFF) of the

Borrowdale Volcanic Group The Borrowdale Volcanic Group is a group of igneous rock formations named after the Borrowdale area of the Lake District, in England. They are Caradocian (late Ordovician) in age (roughly 450 million years old). It is thought that they represen ...

(BVG). The BFF forms the lowest, and hence oldest, portion of this famous sequence of

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 predomina ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

rocks. The ''Birker Fell Andesite'' occurs throughout much of the western Lake District. The BVG are thought to have formed in the early

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

island arc Island arcs are long archipelago, chains of active volcanoes with intense earthquake, seismic activity found along convergent boundary, convergent plate tectonics, tectonic plate boundaries. Most island arcs originate on oceanic crust and have re ...

volcanic activity, due to

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

during the closing of the

Iapetus Ocean The Iapetus Ocean (; ) existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). It was in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalon ...

. The central and northern areas of Birker Fell are dominated by composite andesite

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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

flows. Within the andesitic lava flows, the ''Great Whinscale Dacite'' lava flow and the associated, underlying ''Little Stand

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 co ...

'' 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 (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic material occurs approximately 1 km north of Birkerthwaite, composed of

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

- and

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

- phyric andesite-basalt lavas (the ''Birkby Fell Member''), and tuff and

lapilli Lapilli (: lapillus) is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' is Latin for "little stones". By definition lapilli range from in dia ...

-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 ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

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 In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

has juxtaposed the BVG rocks against

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

s of the late Ordovician Eskdale Intrusion.

References

* Akhurst, M.C.; Chadwick, R.A.; Holliday, D.W.; McCormac, M.; McMillan, A.A.; Millward, D.; & Young, B. (1997). ''Geology of the west Cumbria district''. Memoirs of the British Geological Survey, sheets 28, 37, 47 (England and Wales). British Geological Survey. Keyworth, Nottingham. pp. 138 * British Geological Survey (1996). ''Ambleside''. England and Wales Sheet 38. Solid Geology. 1:50 000. British Geological Survey. Keyworth, Nottingham. * Moseley, F. (Ed.) (1990). ''The Lake District'' (2nd ed.). Geologists' Association Guide No. 2. The Geologists' Association. pp. 213 {{ISBN, 0-900717-73-4. Fells of the Lake District Cumberland (unitary authority)