9/2/2019 1313

Tohlum geosite

Mass movement is a geomorphic process by which soil and rocks move downslope, largely caused by earthquake that it in turn results from plate movements and continental collision in the plate boundaries. This unique landscape is a complex consequence of many other factors including joint and fracture systems, and lithological composition variations. As a result of the historical earthquake, a large landslide has happened in Tohlum area, west of Jolfa City. Occurrence of many rock fall and rock avalanche near this landslide, confirm the potential seismicity of Jolfa. A myriad of factors such as composition, dip direction and position of layers as well as the abundance of fractures involve in landslide hazard happening and its pattern.  In Tohlum, thick red layers of Eocene conglomerates and sandstones along with the interlayers of marl are outcropped in the eastern slope of Alli-Bashi Mountain.  Layers have eastward dip and those near the end of the precipice are prone to slip downslope. In addition, conjugate fracture systems are seen in the conglomerate and sandstone layers in this region. Because of the above-mentioned reasons, an earthquake can suddenly move the heavy blocks of rocks on unconsolidated layers of marl and cause landslide in downslope direction.  In Tohlum area, some of the adjacent layers to the Alli-Bashi precipice have displaced about 200m downslope toward the east and have creating massive piles of rock fragments.