Electrical resistivity tomography and forward modelling in hyper-arid environments – A case study from Erg Chebbi, Southeast Morocco

Abstract

Electrical Resistivity Tomography (ERT), a non-destructive geophysical method, which aims at detecting sediment conductivity and its distribution including e.g. stratification, has been used in manifold research topics, for example in sedimentology, hydrology, and geoarchaeology. However, ERT is mostly used in humid to semi-arid environments, where at least some underground moisture guarantees reliable conductivity. In this paper, for the first time, the results of ERT measurements are presented in combination with geomorphological and sedimentological investigations in a dune-interdune system in a hyper-arid environment. Erg Chebbi in South-East Morocco and its environment is characterized by very scarce precipitation and high evaporation rates, which presents significant methodological challenges. Reliable results were generated, displaying a distinct border between a dune body and underlying playa sediments. In the latter, a thin calcareous crust, found by drillings, was not displayed by ERT data due to their spacial depth resolution. To account for this, robust resistivity forward modelling was used to explain contradicting ERT data and corresponding sedimentological results. Major advantages and drawbacks concerning measurement set ups, modelling and interpretation arc finally discussed. In conclusion, the use of ERT in a hyper-arid environment proved to be a successful and reliable tool if mentioned precautions (in field validation, suitable array layout) are taken into account.