Identification of sinkhole origin using surface geophysical methods, Dead Sea, Israel Michael G. Ezersky a, ⁎, Amos Frumkin b a Geotec Engineering & Environmental Geophysics Ltd., PO Box 25031, Rishon Lezion 7502501, Israel b Institute of Earth Sciences, The Hebrew University of Jerusalem, 9190400, Israel abstract article info Article history: Received 4 March 2020 Received in revised form 21 April 2020 Accepted 21 April 2020 Available online 27 April 2020 The western and eastern Dead Sea (DS) shores are hit by intensive sinkhole collapse during the last 30 years. The first researchers have considered a piping model of sinkhole formation, based on washing out fines by under- ground flows. Then, it was proved by numerous boreholes and seismic refraction surveys that sinkholes along western shore are caused by dissolution of buried salt layers and collapse of the surface into dissolution caverns. However, signs of piping and subsurface flows were observed in some sinkhole sites. In this paper, we show that robust identification of sinkhole origin can be achieved when proper geophysical methodologies and their appli- cation are used. We consider Newe Zohar site located in the southern part of the Dead Sea in order to analyse dif- ferent signs of sinkhole formation models using various geophysical methods. The Seismic refraction method (SRFR), enables us to discover the salt layer based on longitudinal wave velocity Vp; the Multichannel Analysis of Surface Waves (MASW) method allows to determine the salt layer properties (rigidity) based on shear wave velocity Vs; finally, the Time Electromagnetic (TEM) method allows us to evaluate the degree of aggressive- ness of groundwater with respect to salt, based on bulk resistivity values. Here we analyse competitive models of sinkhole formation and suggest geophysical methods to determine the subsurface geomorphology. We show that various geophysical methods should be applied in concert to explore the subsurface for the occurrence of salt, as well as understanding sinkhole formation processes. The underlying voids along the Dead Sea are shown to form primarily by salt dissolution, with some cases of additional piping. Applying the right geophysical parameters for groundwater and salt sediments classification proves to be crucial for understanding the subsurface geomorphology. © 2020 Elsevier B.V. All rights reserved. Keywords: Dead Sea Dissolution Salt Seismic methods Sinkholes Piping 1. Introduction Intensive sinkhole development along the Dead Sea shores both in Israel and Jordan (Fig. 1) has attracted great attention of the scientific community (Arkin and Gilat, 2000; Yechieli et al., 2006; Legchenko et al., 2008b, 2008c; Closson and Abou Karaki, 2009; Frumkin et al., 2011; Abelson et al., 2017; Al-Halbouni et al., 2017; Polom et al., 2018; Arav et al., 2019). There are two competitive geological models that may explain the Dead Sea sinkhole formation: (a) piping and (b) salt dissolution. The first model in unconsolidated sediments is associated with high gradi- ents of flow, such as the frontal areas of young alluvial fans or high benches of the Lisan Formation (Arkin and Gilat, 2000). These sinkholes are typically funnel-shaped with a surface diameter ranging from 1 to 30 m. The sinkhole depth is commonly not more than 15 m, and down- stream from its bottom it may extend tens to hundreds of meters sub- horizontally. Existing flow lines may form the focus for developing sink- holes. Fine particles are washed out along the flow path, followed by the formation of a hollow pipe, or subsurface channel. The process may con- tinue in an upward direction by consecutive breakdown. As the collaps- ing void approaches the surface, sudden collapse may occur, forming a funnel-shaped sinkhole. Another type of sinkhole formation model (salt dissolution) requires the presence of (a) a salt layer (lithological factor), (b) under-saturated groundwater flowing in contact with the salt layer (hydrological factor), and (28a) fractures or faults allowing the unsaturated water to flow in con- tact with the salt layer (tectonic factor) (Yechieli et al., 2006). Frumkin and Raz (2001) discussed two types of salt dissolution underlying the sink- holes. The first is associated with vadose dissolution, as occurs in Mount Sedom salt diapir (Frumkin, 2013). The second is associated with salt dis- solution under the watertable along the retreating Dead Sea shore. The un- derwater dissolution model is accepted presently as the main mechanism of sinkhole formation along the Dead Sea. None of the models, however, fully explains the sinkhole formation mechanism. Pollution of the DS by suspended silt arriving with underground flows has rarely been confirmed Geomorphology 364 (2020) 107225 ⁎ Corresponding author. E-mail addresses: mikhail@geotec.co.il (M.G. Ezersky), amos.frumkin@mail.huji.ac.il (A. Frumkin). https://doi.org/10.1016/j.geomorph.2020.107225 0169-555X/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph