Coastal geomorphology and tsunami hazard scenario along the Kachchh coast, western India

549-556Geomorphology and coastal configuration plays a vital role during tsunami events as different coastal geomorphic units respond differently to a tsunami hazard. The study of ability of different coastal landforms to respond tsunami surge is very much important for vulnerability mapping of coast. The Kachchh coast that runs for about more than 450 km has conspicuous presence of both, wave as well as tide influenced landforms. Following the classification suggested by Ramasamy et al.1, the geomorphic features for possible response of tsunami event can be classified as facilitators, conveyors, accommodators, absorbers and barriers. Depending upon its action as facilitator, conveyor or accommodator, the geomorphic units like estuary, creek, mudflats and backwater increase the possibility of tsunami run ups and inundation. The beach ridges and wide sandy beaches on the other hand absorb tsunami energy and act as barriers. In view of these six distinct segments have been identified along the Kachchh coast and are described for their possible response to tsunami event. Accordingly, the segment between Jakhau and Suthari has barrier kind of geomorphic set up with presence of backswamps that has higher preservation potential of tsunami deposits. The segment from Suthari to Kanthada has steep beaches and dune ridges that can reduce the intensity of tsunami hazard. The Kanthada - Rawal Pir segment has Rukmavati River mouth that can convey the effect of tsunami to a considerable landward area whereas, the Rawal Pir - Mundra and Mundra – Tuna segments have dominant accommodator type of geomorphic assemblage that also has a higher preservation potential for tsunami sediments. The segment between Tuna and Kandla has relatively much wider mudflats and mangrove swamps which accommodates as well as reduces tsunami energy. However, the configuration suggests much intensified tsunami surge that can devastate the large scale developments in this part. Response mechanism of the coastal geomorphic assemblages will not only help in the disaster risk reduction activities but will also be useful in better understanding of palaeo and historical tsunamis

Evidence for Seawater Retreat With Advent of Meghalayan Era (∼4200 a BP) in a Coastal Harappan Settlement

Abstract The transformation of mature (urbanized) phase of the ancient Indus civilisation between ∼4200 and 3800 years Before Present (yr BP) overlaps with the beginning of the Meghalayan Age (∼4200 ± 100 yr BP). Though exact cause(s) for decline of urbanized Indus phase are not yet clear, researchers continue to debate whether monsoonal dryness was the sole cause or several other regional factors manifested in a compounding manner. Here, we show a regional relative sea level fall in the downstream area of Indus habitation (south‐western Gujarat region) which initiated at 4150 ± 230 and continued up to 3625 ± 200 yr BP. We provide a multi‐proxy (chronological, sedimentological, mineralogical, isotopic and elemental abundance) data set from a well‐dated vertical sediment trench from Lothal (ancient dockyard area of Indus era) to support this inference. Chief proxies used for inferring the relative sea level fall were bulk sediment carbon and sulfur contents along with their stable isotopes (δ13C and δ34S) and foraminiferal assemblage. The conspicuous shifts in majority of proxies hint at a lowering of sea stand at the regional level that likely dried this ancient Harappan dockyard (used for sea trade). Findings of our study possess implications for Holocene climate changes and their plausible impact(s) on Harappan trade and culture. Additionally, it invites evidences for large scale geological changes at ∼4200 yr BP distinct to the Meghalayan era