Salt and Sinkhole: Corrosion as a Principal Factor Governing Topography and Mass Movement in Northeast Thailand

Abstract

This paper presents a hypothesis that corrosion of salt beds of the Mahasarakham formation has been the principal factor on the topography development in Northeast Thailand. Chapter 1 presents observation on salt-making which seems to have its origin in ancient periods some time in B.C. In Chapter 2 discussions are presented on the possible source of salt, and we agree to the hypothesis by Takaya et al. and Sompob, who sought the source to the clastic members of the Mahasarakham formation. Chapter 3 presents observations to indicate that, contrary to conventional view to presume thick clastic deposits covering the Mahasarakham formation, this formation is exposed directly on the ground surface. Because of this situation, salt crust is so common at valley floor where "short-distance interflow" seepages out. Chapter 4 presents a sinkhole hypothesis on the topography of Northeast Thailand. Salt dome development and its collapse due to the salt corrosion are presumed to be the cause of sinkhole topography. Each salt dome development causes an anticlinal dome which can be identified as an assemblage of turtle-back shaped polygons in the aerial photographs. In the course of corrosion, anticlinal dome collapses. This leads to the initiation of sinkhole topography. At advanced stages of corrosion, large-scale sinkholes are developed. This paper presents a first approximation for demarcating anticlinal salt domes and sinkholes based on LANDSAT imageries. Chapter 5 presents mass movement phenomena caused by sinkholes. Laterite pan and gravel beds retards this mass movement process. The conclusion of this paper is that Khorat Plateau is a corrosion basin. Location map of the sites mentioned in the text is given at the end of this paper (Fig. 29).