Geological evidence for AD 1008 tsunami along the Kachchh coast, Western India: Implications for hazard along the Makran Subduction Zone

Abstract

The 2004 Sumatra-Andaman tsunami emphasized the catastrophic nature of such disasters and exposed our knowledge gap of the historical and palaeo events. In the aftermath of this deadly event, the thrust in palaeotsunami studies was restricted to areas in the Indian Ocean, affected by this tsunami. The northern Arabian Sea, which hosts a similar tsunamigenic source i.e. the Makran Subduction Zone (MSZ), has so far remained ‘Terra-Incognita’. Here, for the first time, we report geological evidence of the 1008 AD tsunami, also mentioned as ‘an enigma’ in the historical reports, by identifying a >250 km long sand sheet with a landward extent of more than 250 m from the Indian coastline. Detailed sedimentology and geochemistry reveals an offshore origin of this sand sheet, from where it was eroded by a high energy wave and deposited in a supratidal environment. Optical and AMS 14C chronology constrains its age of deposition around 1000 AD. The shear size of the sand sheet, laterally and across the coast, along with grain size, a characteristically different provenance, are some of the major indicators, which can be useful in palaeotsunami/palaeostorm deposit distinction. Our report of the AD 1008 event from the Indian coastline, also supports the claim that the Western MSZ, albeit at longer intervals, has experienced major thrust earthquakes (Mw > 8) in the historical past. The proximity of this sand sheet to the shoreline does not discount the role of extremely unlikely, large storms as its causal mechanism.

Paleoseismological Studies in India (2016-2020): Status and Prospects

“…Geological evidence for a paleo-tsunami has been reported from the Saurashtra Coast, Gujarat ( Fig. 7; inset) This tsunami event deduced from the preserved sand sheet is dated at 1008 CE (Prizomwala et al, 2018).The sedimentological and geochemical analyses of the sand sheet point to an offshore origin, potentially transported by a high energy wave and deposited in a supratidal environment. The authors suggest its source being a tsunami wave originated from the Makran region in the north Arabian Sea although they do not discount the role of a very large storm as its depositional agent.…”

New Geological Evidence of the 1755 Lisbon Tsunami from the Rock of Gibraltar (Southern Iberian Peninsula)

“…Research on tsunami deposits has grown exponentially since the 2004 Indian Ocean Tsunami [1,2], the 2010 Maule Tsunami [3,4], and the 2011 Tohoku-oki Tsunami [5,6], with numerous papers dedicated to the associated tsunamiites. Special attention has been paid to their textural and stratigraphic features [7,8], macrofauna and microfauna m, geochemistry [11,12], and the associated coastal changes [13,14].…”

A 1000-yr-old tsunami in the Indian Ocean points to greater risk for East Africa: REPLY

“…Inferred tsunami deposits ~1000 years old have also been identified along the coastlines of western India (Prizomwala et al, 2018), Iran (Shah-Hosseini et al, 2011), and Oman (Hoffmann et al, 2020). We were conservative in our assessment and did not include these results in our published study, as the origin of the tsunami responsible for these deposits has been attributed to a megathrust earthquake from the Makran subduction zone, a submarine landslide in the Arabian Sea, or a combination of both, and not to an earthquake from the Sumatra-Andaman plate boundary.…”