Major Submarine Fans the North Indian Ocean Has Two Major Submarine Fans

The ocean floor

The ocean floor can be divided into continental margin anddeep-sea floor. • The continental margin consists of l e

the continental shelf, the continental s v e t a

slope, and the continental rise i r r o G s

s h r • The continental shelves have a flat , c a l p i e d i l g s l c n

topography (0.1° gradient), the o l

o a a a t l a e h r s r

average depth being ~130 m. They S e P d u t e P e u l f s t l u m s d t

are sites for the deposition of a r i a y u e f s l b l C n s n s u o

abundant land-derived sediments o u r a e l P s C c and biogenic carbonates. The g u n d

continental shelf is separated from a o l l l M n a a a the continental slope by the shelf- t t t t n n n n l l

edge or shelf-break at u e e e a a o s n n n s s i i i approximately 200 m depth. The y e f t t t m s s l n e

i l p n n n t y a y e l e l gradient of the slope (4° on an f l a o i o o o b e b s i l a l h i

average) is much higher than that of R v A h S A p C r C s C s the continental rise (1°). Mid oceanic Ocean C ontinental ridge basin margin • Abyssal plains are sea floors with a slope of only 0.001o for hundreds Physiographic features of the ocean floor and associated mineral deposits. of kilometres. About 42% of the deep-sea floor area shows relatively gentle relief. • Hydrothermal vents: the mantle material upwells, and as a result of • Seamounts are elevations on the seafloor spreading and plate movement, seawater comes in deep-sea floor exceeding 1 km in contact with fresh magmatic material. The seawater circulates height. Both flat-topped (guyot) and within the newly formed hot rocks, and this forms 'hot springs' peaked seamounts are known to similar to those on land. Hot water, whose temperature can reach occur. Fossil corals, phosphorites, 400°C (in contrast to the ambient seawater temperature of 1-3°C), and cobalt-rich manganese crusts gushes out of the cracks. These are called hydrothermal vents. may be found at their summits. • Trenches are deep, V-shaped valleys on the ocean floor (below the • Mid-ocean ridges are elevated continental slope). They generally occur at the subduction zones physiographic features of the ocean where oceanic crustal plates collide with continents or island arcs. basins and are the sites of Water depth in the famous Mariana Trench (~11 km) located in the formation of new oceanic Pacific Ocean exceeds the height of Mt. Everest. lithosphere. The global system of mid-ocean ridges is about 74000 km in length. Major submarine fans The North Indian Ocean has two major submarine fans. These fans are the Bengal fan and the Indus fan. The basins are filled with sediments that are mostly derived from the continents through river systems. The Bengal fan in the Bay of Bengal is the largest deep-sea fan in the world (total area is ~3.0 x 106 sq. km, ~3000 km in length, 1430 km at its maximum width, and 20 km at its maximum Indus fan thickness). The sediments of the fan are largely eroded from the Himalayas and transported by the Bengal fan Ganga-Brahmaputra River system. The sediments making up this deep-sea fan at times were deposited at a rate of 35 cm /1000 yr, a rate comparable to that of deposition in shallow shelves (20-30 cm /1000 yr). By investigating the sediments of the Bengal fan it is possible to identify different phases of the Himalayan uplift history.

Bengal fan and Indus fan The Indus fan (1.1 x 106 sq. km area, 1500 km length, 960 km maximum width, >10 km maximum thickness) in the Arabian Sea not only receives sediments from the Himalayas, but also from the alluvial soils of Pakistan and the arid soils of Arabia.