Plate Tectonics and the movement of the Indian plate

The governing concept is the tectonic setting of volcanism. At a divergent plate boundary, mantle material rises as plates separate, producing magma and new oceanic crust along a mid-ocean ridge. Intraplate volcanism occurs away from a plate boundary, commonly above a relatively persistent mantle hotspot; as the plate moves, a chain of volcanic islands or seamounts may form. Option A is correct because it contrasts the boundary location of ridges with the within-plate setting of hotspots. The other choices confuse geological volcanism with river, atmospheric or non-volcanic processes and therefore do not explain the distinction.