Post M-9 event changes on bathymetry and sediment characteristics of innershelf zone off Kayamkulam, southern Kerala, India

Abstract

Significant changes in the bathymetry and variation in the sediment distribution is recorded in the innershelf region off Kayamkulam in southern Kerala India. A relative deepening of the innershelf, particularly shallower portions of depths less than 15 m is noticed based on bathymetric records. Generally the innershelf is dominated by sand-silt-clay (mud), except in the region where the inlet is seen, the silty sand dominates. Sand percentage has increased even upto 75% near the northern shelf where the run up levels goes to as high as 5 m. The sediment distribution along the southern shelf is unimodal whereas along the northern shelf the sediments are mixed nature with poorly sorted distribution. Organic matter in the sediment varies from 0.6 to 6.1%. Predominance of kaolinite (av. 70%) and montmorilllonite (av. 22%) with illite (av. 6%) and gibbsite (av. 3%) is recorded from these sediments. Fine clayey type sediments are enriched towards the offshore, which could be related to the tsunami backwash.