RELATION BETWEEN BEDROCK GEOLOGY, TOPOGRAPHY AND LAVAKA DISTRIBUTION IN MADAGASCAR
2012; Geological Society of South Africa; Volume: 115; Issue: 2 Linguagem: Inglês
10.2113/gssajg.115.225
ISSN1996-8590
AutoresNy Riavo G. Voarintsoa, Rónadh Cox, M. O. M. Razanatseheno, Amos Fety Michel Rakotondrazafy,
Tópico(s)Geology and Paleoclimatology Research
ResumoResearch Article| June 01, 2012 RELATION BETWEEN BEDROCK GEOLOGY, TOPOGRAPHY AND LAVAKA DISTRIBUTION IN MADAGASCAR N.R.G. VOARINTSOA; N.R.G. VOARINTSOA Départment des Sciences de la Terre, Université d'Antananarivo, Madagascar, Department of Geosciences, Williams College, Williamstown, Massachusetts 01267, USA, Present address: Department of Geology, University of Georgia, Athens GA 30602, USA. e-mail: nyriavony@gmail.com Search for other works by this author on: GSW Google Scholar R. COX; R. COX Corresponding author: Department of Geosciences, Williams College, Williamstown, Massachusetts 01267, USA, e-mail: rcox@williams.edu Search for other works by this author on: GSW Google Scholar M.O.M. RAZANATSEHENO; M.O.M. RAZANATSEHENO Départment des Sciences de la Terre, Université d'Antananarivo, Madagascar, e-mail: cariongranite@yahoo.com Search for other works by this author on: GSW Google Scholar A.F.M. RAKOTONDRAZAFY A.F.M. RAKOTONDRAZAFY Départment des Sciences de la Terre, Université d'Antananarivo, Madagascar, e-mail: rakotondrazafyafmichel@gmail.com Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2012) 115 (2): 225–250. https://doi.org/10.2113/gssajg.115.225 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation N.R.G. VOARINTSOA, R. COX, M.O.M. RAZANATSEHENO, A.F.M. RAKOTONDRAZAFY; RELATION BETWEEN BEDROCK GEOLOGY, TOPOGRAPHY AND LAVAKA DISTRIBUTION IN MADAGASCAR. South African Journal of Geology 2012;; 115 (2): 225–250. doi: https://doi.org/10.2113/gssajg.115.225 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The characteristic gullies of central Madagascar–lavakas–vary greatly in abundance over short distances, but existing understanding does not explain why some hillsides should have high concentrations of lavakas when nearby slopes have fewer. We present a GIS analysis of lavaka abundance in relation to bedrock geology and topography, covering two areas in the central highlands: the region near Ambatondrazaka and that around Tsaratanana. Both regions have similar average lavaka density (6 lavakas/km2 in Ambatondrazaka, and 5 lavakas/km2 in Tsaratanana, but local lavaka concentrations vary widely. Individual one-km2 squares can host up to 50 lavakas/km2 in Tsaratanana and up to 150 lavakas/km2 in Ambatondrazaka. We find no predictive relationship between bedrock type and lavaka abundance. There is, however, a relationship between lavakas and slope such that lavakas increase in abundance as slopes get steeper, up to an optimum steepness, beyond which they become less numerous. The optimum steepness for lavaka development is about 10 to 15° in Tsaratanana and 25 to 30° in Ambatondrazaka. Lavakas also seem to favour slopes where the gradient changes locally, with an optimum change in grade somewhere in the range 2 to 5°. Our results provide quantitative constraints on lavaka distribution that can be tested in other areas. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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