Accueil > Documentations scientifiques > Revues récentes > Madagascar : revue de géographie > Archives > Volume 8, janvier-juillet 1966 > La Morphologie de l’escarpement de l’Isalo et de son revers dans la région de (...)

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  La Morphologie de l’escarpement de l’Isalo et de son revers dans la région de Ranohira (Sud-Ouest de Madagascar)
  Madagascar : revue de géographie, Volume 8, janvier-juillet 1966 pp:67 - 92

  Auteur(s) : Andrianaivo L.

  Auteur correspondant :

  Mots-clés : GEOMORPHOLOGIE/RELIEF (GEOGRAPHIE)/MADAGASCAR/ATSIMO ANDREFANA/TOLIARA/RANOHIRA/ISALO
  
  

  Résumé de l’article

  [FR]

  [MG]

  [EN] Made of somewhat loose and straggling sandstone, the Isalo chain, in S.W. Madagascar, produces a powerful jagged relief in the Northern and Southern massives of the Isalo. The resistance of the sandstone may be accounted for by a general process of crusting which protects it against the onslaughts of erosion. Both massives seem to have been more or less completely levelled at various moments of the Tertiary era. This complex cyclic evolution gave birth to several generations of broken eminences of various heights, according as they drive from a dissection of the higher surface (mid-tertiary) or of the lower one (late tertiary). The broken eminences on the reverse side offer a conventional sandstone morphology, with their jagged clumps of binnacle-shaped rocks, and a rich variety of shapes, some corbelled out by the differential erosion of re-cristallized fissures on planes of stratification, others linked with the evolution and sealing of the crust, others again, such as the \"taffonis\" sculpted by the wind. The escarpment of the sandstone Isalo massive overlooking, Eastwards, in the Ranohira region, the peripheric depression of the Sakamena is not a cuesta, contrarily to what has often been stated, but the inverted escarpment of a fault-line ; and the rectilinear cliff roughly corresponds to the open fault-line of the Sakamena. Southwards, on the other hand, the escarpment, less marked and more irregular, has appreciably dwindled. The composite order of the fault-scarp in the sectors where it is still more or less clogged by the Sakamena, supports the hypothesis of a damper paleo-climate than the present one, beneath which was moulded the great concave basal versant, cluterred with half dissolved fragments of the Isalo. The fossilized appearance of certain layers of crust covering the residual eminences of the opposite side, also, supports the hypothesis of climatic variation in the quaternary era.