ZEITSCHRIFT FUR GEOMORPHOLOGIE, cilt.47, sa.2, ss.235-250, 2003 (SCI İndekslerine Giren Dergi)
Linear cluster distribution of adjacent volcanoes and their elongate shape can be used to define the tension fractures that are preferential pathways for the magma upwelling. In this paper, we apply to Digital Elevation Model (DEM) automated geomorphometric analysis procedures in order to obtain objective criteria. Our examples are main Plio-Quaternary volcanoes of Eastern Anatolia (Turkey). The Voxel Wall procedure, which computes intersections in a 3D space of the wall with the normal to the DEM surface at each point, permits to separate several elementary peaks in composite volcanoes. If adjacent, their alignment is the trend of the underlying tension fracture. The geomorphic character which is generally taken into account for defining the elongation of a volcano is the baseline of the edifice. Using the parameters provided by the tomomorphometric method, the baseline can be defined taking into account the convexity index, the width/length ratio and the coordinates of the center of mass. It is then possible to compute the main baseline direction that is supposed to be correlated with the trend of the corresponding tension fracture. Computing the direction of all the elevation contour lines that are above the baseline has shown that this trend does not change with time in our examples. Significant geologic results demonstrate the validity of our methodology. in Eastern Anatolia, the main Plio-Quaternary volcanoes are generally N-S elongated. This is also the case for the Bilican and Nemrut volcanoes, as a consequence of N-S shortening and E-W lengthening. Other directions are original but compatible with particularities of the regional tectonics. The NW-SE trend of Ararat is related with the formation of a pull-apart basin which has modified the regional stress field. The E-W trend of Suphan and Tendurek volcanoes, belonging to the Lake Van basin, is at right angle to the N-S compression in the Bitlis belt and must be taken into account in any attempts to explain this problem.