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 National Park is a national park in North West England that includes all of the central Lake District, though the town of Kendal, some coastal areas, and the Lakeland Peninsulas are outside the park boundary. The area was desi ...

, in

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. Cumb ...

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 b ...

. 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 o ...

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

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 tragedy written by William Shakespeare sometime between 1599 and 1601. It is Shakespeare's longest play, with 29,551 words. Set in Denmark, the play depicts ...

, 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. Historically in Cumberland, it forms part of the borough of Copeland. At Ulpha a road leaves the Duddon Valley to cross Bir ...

, 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 a 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 several wa ...

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 represent t ...

(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 predomi ...

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 a rupture 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 found where tectonic plates a ...

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. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

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 ...

volcanic activity, due to

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, the ...

during the closing of 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 paleoco ...

. 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 moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

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 cont ...

'' 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 tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...

- and

pyroxene The pyroxenes (commonly abbreviated to ''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 calcium (Ca), sodium (Na), iron (Fe II) ...

phyric 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

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

lapilli Lapilli 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'' (singular: ''lapillus'') is Latin for "little stones". By definition lapilli range f ...

-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 mineral ...

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 (phaneritic) 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 cools and solidifies undergro ...

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 Borough of Copeland