Terrain modeling of the complex volcanic terrain of Ischia Island (Italy).

Abstract

A high resolution 2 meters spacing DEM is used in an attempt to model the volcanic terrain of Ischia Island (~150 ka≥age≥1302 AD). Ischia consists of (a) a high relief, resurgent central-western sector, (b) a western sector affected by landslides related to the resurgence and (c) an eastern, lowland sector in which a volcanic field emplaced. The elevation, slope and aspect images evidence two volcanic cones near the NE coastline and a huge semi-circular ridge in central portion of the island corresponding to the Mt. Epomeo resurgent block. Mt. Epomeo area shows extensive drainage network developed on the southern flank, which represents the scar of a huge, prehistoric debris avalanche. The elevation and slope statistics and hypsometric curve allowed terrain classification according to well known standards (present mean earth elevation, hypsometric integral ranking). Peaks and critical points were discovered in elevation and slope frequency distribution while asymmetries in the directional development of island relief in relation to area extent, slope and elevation were revealed from aspect rose-diagrams. Results allow us to the discriminate among zones with different volcanic structures and deposits, e.g., zones affected in the past by resurgence phenomena (Mt. Epomeo relief, central sector of the island), by the emplacement of a volcanic field with lava flows and domes (eastern sector), landslides (western sector), or controlled by tectonic processes (western flank of Mt. Epomeo). The segmentation of terrain to aspect regions, followed by objects parametric representation on the basis of elevation and slope allowed the terrain classification to 8 classes by the centroid method of cluster analysis. The interpretation of cluster centroids and the spatial distribution of the 8 clusters revealed a terrain organization controlled by both endogenic (volcanic and tectonic) and exogenic (erosion) processes. In particular, clusters allow us to evidence topographic features related to gravity flows (lava flows, domes, landslides, debris flows), tectonics (faulting), and volcanic structures (resurgent blocks, volcanic fields).