A bornhardt (/ˈbɔːrnˈhɑːrt/) is a dome-shaped, steep-sided, bald rock outcropping at least 30 metres (100 ft) in height and several hundred metres in width.[1] They are named after Wilhelm Bornhardt (1864–1946), a German geologist and explorer of German East Africa, who first described the feature.[2][3]
While bornhardt was originally used to sometimes denote a type of inselberg (literally island mountain—an isolated dome in an otherwise flat landscape), the term bornhardt is used in modern literature to refer to domed hills and mountains regardless of isolation; thus, not all bornhardts are inselbergs and not all inselbergs are bornhardts.[4] Bornhardts are commonly composed of igneous rocks,[4] often granites,[4][5] but examples of gneiss, quartzite and arkose bornhardts exists.[5]
The Sugarloaf Mountain of Rio de Janeiro is a typical example of this landform and is the origin of the common bornhardt nickname "sugar loaf".[6]
Bornhardts are most easily seen in arid and semi-arid regions, but occur over a wide range of climates. Found in diverse topographic settings, they mainly occur in multicyclic landscapes. Over geological time, bornhardts may degrade to form other landforms such as nubbins (or knolls) and castle koppies.[7] Bornhardts were previously thought of as characteristically tropical landforms, but have been shown to be more related to lithology and rock structure than climate.[8]
Depending on their shape, they are also referred to as sugar loaves, whalebacks, turtlebacks or domes. In certain locales they may be known as dwalas, half-oranges, matopos, etc. Often, the underlying geological fracture pattern is shown by the surface arrangement of bornhardts, as can be seen in the Kamiesberge of Namaqualand and the Everard Ranges of Central Australia.[9]
Bornhardts commonly show extensive sheet jointing (fracture systems in the rock parallel to its surface). There are two main theories on the origins of bornhardts, each relating to jointing. The exogenetic theory asserts that sheet jointing is formed in response to the emerging topography, while the endogenetic theory suggests that the topography in bornhardts reflects already existing sheet jointing.[10]
^Thomas, Michael F. (2004). "Tropical Geomorphology". In Goudie, Andrew S. (ed.). Encyclopedia of Geomorphology. Vol. 2. London: Routledge. pp. 1063-1069. ISBN0-415-32738-5.
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December 14, 2023
bornhardt, bornhardt, ɔːr, ɑːr, dome, shaped, steep, sided, bald, rock, outcropping, least, metres, height, several, hundred, metres, width, they, named, after, wilhelm, 1864, 1946, german, geologist, explorer, german, east, africa, first, described, feature, . A bornhardt ˈ b ɔːr n ˈ h ɑːr t is a dome shaped steep sided bald rock outcropping at least 30 metres 100 ft in height and several hundred metres in width 1 They are named after Wilhelm Bornhardt 1864 1946 a German geologist and explorer of German East Africa who first described the feature 2 3 Sugarloaf Mountain a non inselberg bornhardt in Rio de Janeiro BrazilKata Tjuṯa in Northern Territory AustraliaWhile bornhardt was originally used to sometimes denote a type of inselberg literally island mountain an isolated dome in an otherwise flat landscape the term bornhardt is used in modern literature to refer to domed hills and mountains regardless of isolation thus not all bornhardts are inselbergs and not all inselbergs are bornhardts 4 Bornhardts are commonly composed of igneous rocks 4 often granites 4 5 but examples of gneiss quartzite and arkose bornhardts exists 5 The Sugarloaf Mountain of Rio de Janeiro is a typical example of this landform and is the origin of the common bornhardt nickname sugar loaf 6 Bornhardts are most easily seen in arid and semi arid regions but occur over a wide range of climates Found in diverse topographic settings they mainly occur in multicyclic landscapes Over geological time bornhardts may degrade to form other landforms such as nubbins or knolls and castle koppies 7 Bornhardts were previously thought of as characteristically tropical landforms but have been shown to be more related to lithology and rock structure than climate 8 Depending on their shape they are also referred to as sugar loaves whalebacks turtlebacks or domes In certain locales they may be known as dwalas half oranges matopos etc Often the underlying geological fracture pattern is shown by the surface arrangement of bornhardts as can be seen in the Kamiesberge of Namaqualand and the Everard Ranges of Central Australia 9 Bornhardts commonly show extensive sheet jointing fracture systems in the rock parallel to its surface There are two main theories on the origins of bornhardts each relating to jointing The exogenetic theory asserts that sheet jointing is formed in response to the emerging topography while the endogenetic theory suggests that the topography in bornhardts reflects already existing sheet jointing 10 Contents 1 See also 2 References 2 1 Citations 2 2 Sources 3 External linksSee also editGranite dome Rounded hills of bare granite formed by exfoliation Inselberg Isolated steep rock hill on relatively flat terrain Monolith Stone block made of one single piece object made of one single rock piece References editCitations edit Mayhew Susan 2015 A Dictionary of Geography 5th ed Oxford University Press p 56 ISBN 978 0 19 968085 6 Glossery of Terms Bornhardt InfoCenter for Environmental Geology Archived from the original on 25 April 2012 Twidale amp Vidal Romani 2005 pp 109 116 a b c Migon Piotr 2004 Bornhardt In Goudie Andrew S ed Encyclopedia of Geomorphology Vol 1 London Routledge pp 92 93 ISBN 0 415 32737 7 a b King Lester 1975 Bornhardt landforms and what do they teach Zeitschrift fur Geomorphologie 19 3 299 318 Allaby Michael 2010 A Dictionary of Ecology 4th ed Oxford University Press p 53 ISBN 978 0 19 956766 9 Twidale C R 2007 Bornhardts and associated fracture patterns Revista de la Asociacion Geologica Argentina 62 1 139 153 hdl 2440 43513 ISSN 0004 4822 Thomas Michael F 2004 Tropical Geomorphology In Goudie Andrew S ed Encyclopedia of Geomorphology Vol 2 London Routledge pp 1063 1069 ISBN 0 415 32738 5 Twidale C R 1981 Granitic Inselbergs Domed Block Strewn and Castellated The Geographical Journal 147 1 54 71 doi 10 2307 633409 JSTOR 633409 Twidale amp Vidal Romani 2005 pp 32 48 Sources edit Twidale Charles Rowland Vidal Romani Juan Ramon 2005 Landforms and Geology of Granite Terrains A A Balkema ISBN 0 415 36435 3 External links edit nbsp Wikimedia Commons has media related to Bornhardts Granite Inselbergs of the Central Namib Deserts Boulders Tors Inselbergs Retrieved from https en wikipedia org w index php title Bornhardt amp oldid 1111844785, wikipedia, wiki, book, books, library,
