New Insights on the Emplacement Kinematics of the Seymareh Landslide (Zagros Mts., Iran) Through a Novel Spatial Statistical Approach

Abstract

The giant prehistoric Seymareh landslide in the Zagros Mountains (Iran) is one of the largest known landslides on the Earth’s surface. The debris with an estimated volume of 44 km3 dammed two rivers, generating three lakes, that persisted for about 3 ka after the event. The post-overflow morphodynamics, characterized by an accelerated and intense stream network erosion, obliterated most of the primary landforms, such as ridges and blocks on the debris surface, making it difficult for scientists to interpret the emplacement kinematics of the landslide. In this regard, a novel spatial statistical approach is proposed here to zone the landslide debris in primary (original) and secondary (modified) regions which are, respectively, attributed to the original shape of the landslide debris and the one reshaped by fluvial erosion. The zonal computation combines the density classes of the mapped primary (ridge and blocks) and secondary (gullies) landforms, according to assumed conditions for representativeness of primary and secondary zones. For validating the model, 62 soil samples taken from the debris surface were classified according to the Unified Soil Classification System standard, and the field density measurements were performed in 28 sites. Based on the classification results, six types of soils were detected, among which 68% of them were ML. The ML samples were aggregated into five subgroups based on their relative proximity, and for each subgroup, four permeability tests were performed. The permeability results demonstrate that the high permeability values are associated with secondary zones, while low values with primary ones, thus confirming the zonation proposed by the statistical approach. The study of the spatial arrangement of the kinematic evidence on the primary landforms allowed to deduce that the landslide was a double-step single event, which infilled a paleo-valley enclosed by two anticline folds. During the emplacement, a part of the debris dissipated its energy over passing the anticlines with divergent directions, NW and NE, while the rest swept back into the Seymareh paleo-valley into the SE direction. The proposed approach represents a promising tool for the detection of primary landforms to assess the emplacement kinematics of landslides.

Using Public Landslide Inventories for Landslide Susceptibility Assessment at the Basin Scale: Application to the Torto River Basin (Central-Northern Sicily, Italy)

“…In fact, the proposed procedure simply requires, together with a first susceptibility model, a status slope unit check for a small percentage of the study area and systematic mapping in one or more smaller subareas. The study was focused on slide and flow landslide typologies, but the strategies of analysis can also be helpful for increasing landslide archives and related resolution of landslide susceptibility maps for any other type of landslide (such as falls, topples, and deep-seated typologies) with the aim of identifying areas to be analyzed at a larger scale through the application of empirical or analytical models for rockfalls (e.g., [57][58][59]) or to assess the magnitude and deformations rate for other slower and more complex landslides (e.g., [60,61]).…”

Morphoevolution of the Seymareh landslide-dam lake system (Zagros Mountains, Iran): Implications for Holocene climate and environmental changes

“…Recently, Rouhi et al (2022) proposed a zonation of the landslide debris based on a spatial statistical approach where primary (original) and secondary (modified) regions, respectively, attributed to the original shape of the landslide debris and the one reshaped by fluvial erosion, are distinguished. Permeability tests performed on soil samples taken from the debris surface allowed the authors to validate the model obtaining a permeability zonation consistent with the statistical model.…”

“…In this paper, we focused on Seymareh Lake, which was generated at ~10 ka by the largest rock slope failure (44 Gm 3 ) ever recorded on the exposed Earth surface, known as the giant Seymareh landslide (Watson and Wright, 1969;Roberts and Evans, 2013;Shoaei, 2014;Delchiaro et al, 2019Delchiaro et al, , 2020Rouhi et al, 2019Rouhi et al, , 2022. The Seymareh landslide (33 • 03 ′ 33.13 ′′ N, 47 • 39 ′ 52.87 ′′ E) detached from the northeastern limb of the Kabir-Kuh anticline (Zagros Mountains, Iran) creating the natural dam responsible for the formation of a three-lake system consisting of Seymareh, Jaidar, and Balmak lakes, with areas of 259, 46, and 5 km 2 , respectively.…”

“…Sampling location from this study (green circle) and from available literature (white and red circles) used for the chronological model of lake infill and overflow are reported (see Table1for details). The permeability zonation of the landslide debris proposed byRouhi et al (2022) is reported. The grey-scale map indicates elevation, which is derived from the 30-m SRTM(Farr et al, 2007).…”

Geology, Geomorphology and Geochronology of the Coseismic? Emad Deh Rock Avalanche Associated with a Growing Anticline and a Rising Salt Diapir, Zagros Mountains, Iran

“…7000 fatalities, Plafker and Ericksen, 1978;Evans et al, 2009), or recent avalanches occurred in Pakistan (2005, M7.6 Kashmir earthquake) and the Philippines, each killing >1000 people (Harp and Crone, 2006;Lagmay et al, 2006). The most remarkable example in the Zagros Mountains is the gigantic Seymareh rock avalanche (44 Gm 3 ; 220 km 2 ), considered the largest subaerial rock slope failure worldwide (Roberts, 2008;Roberts and Evans, 2013;Shoaei, 2014;Delchiaro et al, 2019Delchiaro et al, , 2022Rouhi et al, 2022). This landslide was initiated by the detachment along multiple bedding planes of a rock slab comprising a weak unit of marls with limestone interbeds capped by thick and resistant limestone.…”