Tracing the evolution of 2010 Merapi volcanic deposits (Indonesia) based on object-oriented classification and analysis of multi-temporal, very high resolution images

About 40% of the devastated upper catchment was recolonized by vegetation between 2010 and 2012. The recovery also took place in the forested valley margins affected by ash-cloud surges. The morphometric analysis of the initial drainage network, digitized from the 2011-2012 images, demonstrated (1) the resurfacing of pristine 2010 PDC deposits by runoff and (2) incision or remobilization by lahars. It took two years following the eruption in the rugged upper catchment devastated by high-energy surges to fully develop the hydrographic network. It is, however, still rudimentary on gently sloping fans created by overbank PDC deposits in the middle valley, thus suggesting the importance of slope gradient, grain size, permeability and thickness of deposits. As much as 35% of the 2010 PDC deposits, emplaced in the vicinity of the river channels, were remobilized by lahars over the two post-eruption rainy seasons and also by constant mining activities. Studies on the erosion of the pyroclastic deposits after 2012 need to concentrate on the upper reach of the catchment on the south flank.