Mechanism of landslide damming in Morzarrin Valley and its consequences, Lorestan Province, western Iran

Abstract

Landslide dams are common geomorphic phenomena, especially in high relief mountains characterized by steep slopes and narrow valleys, where even small landslides can easily block the valleys and give rise to the formation of dam lakes. Mass movements and landslide dams are among active geohazards along river valleys of the Zagros Mountains of southwestern Iran, which pose serious risks to the local inhabitants and infrastructures. This paper explores the mechanism and consequences of a typical landslide dam in 2019 in the Morzarrin Valley in Lorestan Province, Iran. Meteorological data, satellite images and Google Earth images, geology and topography maps, as well as field observations were used to evaluate the morphometric characteristics of the landslide dam. Our investigations indicate that a heavy precipitation (rain and snowfall) triggered the occurrence of the landslide in marl and limestone formations. Moreover, high steepness of the slopes and river undercutting are other controlling factors on the occurrence of landslides in this basin, as indicated by the evidence of multiple landslides along the Morzarrin Valley. The studied landslide blocked the valley and formed a dam lake with an area of 3.3 km2. The landslide also destroyed and blocked the nearby road and caused damages in power lines and water transportation infrastructures and inundated fish farms. Digging a canal in the landslide dam and gradual discharge of the lake water reduced the landslide dam-break risks which particularly threatened the areas downstream.