Lake Lapworth

Lake Lapworth was a postulated glacial lake in Great Britain, believed to have formed during the last ice age when glaciers blocked the northern outlet of the River Severn through the River Dee near present-day Chester. As the Severn backed up, it formed Lake Lapworth until it overflowed southwards cutting the Ironbridge Gorge. This permanently diverted this part of the Severn drainage basin to the south.

Etymology

The lake was named by Leonard Johnston Wills for Charles Lapworth, who first suggested its existence in 1898.[1] Frederic William Harmer (1835-1923) also proposed a similar theory in 1907 based on observations of glacial lake sediments found on the Shropshire Plain.[2][3]

Geography and geology

Lake Lapworth is one of several glacial lakes that are thought to have existed during the Ice Age in the late Pleistocene.[4] This was the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations.[5] Aqualate Mere is a remnant of Lake Lapworth.

The flood that carved Ironbridge gorge exposed deposits of coal, iron, fireclay and limestone. The existence of these minerals and ore in close proximity contributed to the development of the ironworks that started the Industrial Revolution in the 18th century.

The market town of Newport, Shropshire, sits atop a sandstone ridge, which in the last Ice Age was an island or peninsula in Lake Lapworth. Long after the supposed lake had vanished, early man fished here, and two log boats were uncovered a mile from Newport. One has been preserved and is now at Harper Adams University at Edgmond in Shropshire.

Re-evaluation

Wills' theory was widely accepted until the 1980's but research starting in the 1970's had shown the existence of a bedrock trench, up to 120m in depth, beneath the course of the Severn running east from the Melverley area beneath Shrewsbury to the head of the Ironbridge Gorge. It is but one of several such buried trenches known beneath the surface of Shropshire and Cheshire whose form indicates erosion by sub-glacial meltwater under considerable pressure, the long profile of this and others being undulating, i.e. with water flowing uphill in certain sections. It is postulated that this sub-glacial version of the Severn rose to the surface at the ice front and cut the gorge; no lake is required in this scenario. The process may have been initiated during the Anglian glaciation of 450,000 years ago and continued during the Devensian. Other work on features interpreted as the shoreline of Lake Lapworth has revealed that the levels do not match from one area to another leaving open the possibility of multiple smaller lakes having existed at different times, rather than one large one.[6]

References
  1. Wills, L.J. (1924). "The Development of the Severn Valley in the Neighbourhood of Iron-Bridge and Bridgnorth". J. Geol. Soc. 80 (1–4): 274–308. doi:10.1144/GSL.JGS.1924.080.01-04.15. Retrieved 27 August 2011.
  2. "The Monthly Record". Geogr. J. 31 (2): 215–224. February 1908. JSTOR 1776890.
  3. Harmer, F.W. (November 1907). "The Origin of Certain Cañon-like Valleys". J. Geol. Soc. 63: 470–513. doi:10.1144/GSL.JGS.1907.063.01-04.33.
  4. Hamblin, R.J.O. (1986). "The Pleistocene sequence of the Telford district". Proceedings of the Geologists' Association. 97 (4): 365–377. doi:10.1016/S0016-7878(86)80028-1.
  5. Jones, Daniel (2003) [1917], Peter Roach; James Hartman; Jane Setter (eds.), English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN 3-12-539683-2
  6. Toghill, Peter (2006). Geology of Shropshire (second ed.). Marlborough: The Crowood Press. pp. 239–243. ISBN 1861268033.
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