Geological evidences of extreme waves along the Gujarat coast of western India

Indian Ocean Tsunami 2004 informed on the amplitude of marine inundations that can occur in the eastern coasts of India. Geological signatures of such high-energy marine wave events are inferred from the older sedimentary records using chaotic deposits and/or boulder deposits with a word of caution to link them with tsunami, as similar records could be seen linked with super typhoon like Haiyan occurred in Pacific Ocean on 7 November 2013 (Kennedy et al. in Coast Eng J 58(1):1640004, 2016). We present here the geological evidences of high-energy marine wave events from the coastline of Gujarat in western India and suggest that these are tsunamigenic because the Arabian Sea has not experienced super cyclones (known as typhoon in Pacific region) at least since 100 years (Dube et al. in Appl Math Model 9:289–294, 1985), and local bathymetric conditions are not favourable to cause strong coupling of infragravity waves and sea swells that happened at eastern Samar island, the Philippines (Roeber and Bricker in Nat Commun 6:1–18, 2015. doi: 10.1038/ncomms8854 ; Shimozono et al. in J Geophys Res Oceans 120(6):4463–4486, 2015). In the region between Mundra and Bhadreshwar of the Kachchh coast, a tsunami event inferred by the presence of sand layer sandwiched between mud layers occurred around 1.3 ± 0.3 ka, based on optically simulated luminescence (OSL) dating method. Further, in the coastline between Madhavpur and Chorwad, large boulders as imbricates, scattered and embedded blocks in a sandy matrix are seen. OSL date for this event was 6.6 ± 0.7 ka. Occurrence of a tsunamite at Ratiya, north of Madhavpur yielded an OSL date of 35.4 ± 4.3 ka. Geological evidences further suggested that the possible energy source of sand layers was a tsunami event in the Strait of Hormoz. And, the boulders of Ratiya–Madhavpur–Chorwad segment were most possibly driven by waves from the submarine earthquake and/or landslides in the southern Owen Ridge.