<P> The character of the shelf changes dramatically at the shelf break, where the continental slope begins . With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 140 m (460 ft); this is likely a hallmark of past ice ages, when sea level was lower than it is now . </P> <P> The continental slope is much steeper than the shelf; the average angle is 3 °, but it can be as low as 1 ° or as high as 10 ° . The slope is often cut with submarine canyons . The physical mechanisms involved in forming these canyons were not well understood until the 1960s . </P> <P> The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents . However, little of the sediment is from current rivers; some 60--70% of the sediment on the world's shelves is relict sediment, deposited during the last ice age, when sea level was 100--120 m lower than it is now . </P> <P> Sediments usually become increasingly fine with distance from the coast; sand is limited to shallow, wave - agitated waters, while silt and clays are deposited in quieter, deep water far offshore . These accumulate 15--40 cm every millennium, much faster than deep - sea pelagic sediments . </P>

The continental shelf surrounding the indian coast is widest of the