Unveiling the Pasqale Avalanche: A Perilous Prehistoric Landslide Proximity to Tehran's Metropolis in Darband Valley, Iran

This research introduces the Pasqale rock/debris avalanche, an occurrence of a prehistoric landslide in the upstream region of Darband Valley in northern Tehran metropolitan that is exemplified as an instance of a high-risk geohazard encountered in the proximity of a metropolitan area. Its initiation as a slide from a steep scarp, with an elevation of approximately 3000 m, nestled within Eocene volcanic rocks and tuff, is noted. The local geology and geomorphology of the Pasqale landslide are described in this paper, relying on topographical data, satellite imagery, and field observations. Through various considerations and the utilization of high-resolution satellite data, the total volume of the landslide is estimated to be in the range of 800,000 m3. Remarkably, the occurrence of this landslide is found to be influenced by intense fracturing and hydrothermal alterations of the Eocene pyroclastic rocks. Moreover, the seismic aspect of the region is emphasized, with particular attention given to the likelihood of a large earthquake being the most probable triggering factor for the Pasqale avalanche, originating from the Mosha or North Tehran faults. The significance of the cascading hazards that may be brought about following a major earthquake event in the northern Tehran metropolitan area is featured in this paper.