Seabed features of undersea volcanic ridge in the Andaman Sea - Signatures of pyroclastic flow
Presented by Dr. Bijan Kumar SAHA on 25 Sep 2013 from 14:30 to 14:45
Type: Oral presentation, full-paper
Session: 11: Indian Ocean and Asian Pacific
Track: Oral presentations
The Barren and the Western ridge, in a subduction related setting, forms a part of inner volcanic arc in the Andaman Sea. Barren Island is the sub-aerial expression of the Barren volcanic ridge. Bathymetric survey has delineated the submarine extension of Barren ridge as well as another 55 km long Para longitudinal submarine volcanic ridge, 16 to 18 km west of Barren Island. Both the ridges might have been formed during late to post Pleistocene volcanism. But the recent cycles of volcanic eruptions are restricted to Barren Island only. There are no signatures of recent eruptions on the Western ridge. The basaltic fragments, recovered from the Western ridge are having biogenic growth on the surface. The Western ridge has come out from about 1500m water depths with peaks at 600 and 437m water depths. The eastern slope is steeper and may be due to large scale lateral collapses, followed by modern sedimentation. Western flank is gentle. The top part of the ridge is mostly veneered by sand/ silty sands. Silty sediments cover its flank. There are four to five down depth layers of sand size pyroclastic materials, ranging from 40 to 80 wt %, consisting of volcanic glass, plagioclase feldspars, hypersthenes along the western slope. These sub seabed layers vary in number and thickness (3 to 11cm) and spread over in different domains at varying water depths with higher concentrations in the central sector mostly down to 80-110 cm sediment columns. Presence of smectite and absence of other clay minerals in the sediments in the core are significant. On the contrary, these types of layers are absent in the outer flank of Barren ridge. Flow of pyroclastic materials during different periods might have resulted in depositions of these buried multiple layers combined with other sediments along the slope of the ridge.