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 Plate Tectonic Stories

Ganges Delta, Bangladesh and West Bengal

Ganges Delta

The Ganges Delta: ©  NASA

As with the gritstone escarpments found at Stanage Edge, the sediments found at the mouth of the Ganges and Brahmaputra rivers form vast river deltas of material washed off the nearby mountains. Except here, the sediments are washing off the modern-day Himalayas as opposed to the uplifted regions of Scandinavia that supplied the Namurian (326 to 313 million years ago) rivers that created the sandstone deposits of Stanage Edge. The Ganges-Brahmaputra delta is the world’s largest delta, covering most of Bangladesh and the state of West Bengal (India). The size of the delta is a reflection of the enormous input of sediment being washed off the still-growing Himalayan mountains into the Ganges river basin. This material is transported by the two largest (Ganges and Brahmaputra) of eight rivers that drain the mountain belt.

  Himalayan river
  A river in the Himalayas carrying sediment eroded off the
mountain down to the flood plain and delta: © Steve Hicks

Since the collision of India and Asia formed the Himalayan mountain chain, the sediment output alone has pushed the coastline 400 km out into the Indian Ocean, with deposits 16 km thick along the 310 km-wide bay. The material enters directly through the Meghna Estuary, a 100 km-wide migratory river channel, before opening into the bay, creating a v-shaped delta.

This delta provides a good (if over-sized) analogue for the delta system that covered Britain in the Carboniferous Period. The silt, sand and grit that the Ganges brings into the Bay of Bengal will lithify into rocks similar to the delta deposits found today in Stanage Edge. The meandering channels of braided river systems are similar to those that would have been found in Carboniferous Britain.

Further reading:

Akter, J., Sarker, M, H., Popescu, Roelvink. Evolution of the Bengal Delta and Its Prevailing Processes. Journal of Coastal Research, Vol. 32, No. 5, 2016