Bengali deep sea fan

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Bay of Bengal
The Bengal fan forms the seabed in the Bay of Bengal, which slopes from the Ganges Delta to the Indian Ocean, in the north the submarine canyon "Swatch of No Ground" can be seen.

The Bengali deep-sea fan is the largest connected and now active deep-sea fan on earth . It builds up east and south-east of India in the Bay of Bengal due to the inflow of sediments from the Ganges and Brahmaputra .

Origin and morphology

Emergence

The Bengal fan stretches from the Ganges Delta in the north to about seven degrees south latitude and thus reaches a length of almost 3000 kilometers with an area of ​​more than three million square kilometers. The thickness of the sediments reaches more than ten kilometers in the northern area and up to fifteen kilometers near the estuaries. The formation of the fan began about 55 million years ago when India collided with the Eurasian plate while migrating north . With the beginning of the uplift of the Himalayas and the highlands of Tibet about forty million years ago and the associated erosion of the young mountains, the sediment load increased rapidly, with about seventy percent of the material being transported from the Ganges and the Brahmaputra into the Bay of Bengal. Every year around two billion tons of sediment are deposited in the form of turbidites in this way , so that in the meantime many times the current mass of the Himalayan mountains lie on the bottom of the ocean. The deposits from the Quaternary , where glacial erosion rapidly accelerated the erosion of the mountains, are particularly thick .

Submarine canyons

The entire area of ​​the fan is criss-crossed by an extensive and constantly changing network of submarine gorges through which turbid currents carry their cargo far to the south. This mechanism also explains how the Turbidites were able to cover such enormous distances despite the slope of the fan decreasing to almost zero degrees to the south. Most of the sediments are now transported south-southwest to the south coasts of India and Sri Lanka .

A distinctive submarine canyon , the Swatch of No Ground , runs through the northern Bengal Fan in a south-south-west direction. Since the late Quaternary it has been an important channel for the transport of sediments from the Ganges river system far into the Bay of Bengal.

Nicobar fan

The Nicobar fan to the east was once part of the Bengal fan. In the early Quaternary, the ninety-degree east ridge , which had approached the Eurasian plate as a result of the subduction of the sea floor in the Sunda Trench , closed the narrow gap to the Nicobar Islands and thus cut off the fan behind from the sediment supply, so that the thickness of the deposits there is only about one kilometer.

swell

Individual evidence

  1. ↑ created with GeoMappApp , based on GMRT data: WBF Ryan, SM Carbotte, J. Coplan, S. O'Hara, A. Melkonian, R. Arko, RA Weissel, V. Ferrini, A. Goodwillie, F. Nitsche , J. Bonczkowski, and R. Zemsky: Global Multi-Resolution Topography (GMRT) synthesis data set . In: Geochem. Geophys. Geosyst. tape 10 , Q03014, 2009, doi : 10.1029 / 2008GC002332 (data doi: 10.1594 / IEDA.0001000 ).
  2. ↑ Bay of Bengal. In: Banglapedia - National Encyclopedia of Bangladesh. Retrieved March 29, 2020 .
  3. ^ V. Subrahmanyam, KS Krishna, MV Ramana, KSR Murthy: Marine geophysical investigations across the submarine canyon (Swatch-of-No-Ground), northern Bay of Bengal . In: Current Science . tape 94 , no. February 4 , 2008, JSTOR : 24101997 .
  4. ^ SA Kuehl, MA Allison, SL Goodbred, H. Kudrass: The Ganges-Brahmaputra Delta . In: Liviu Giosan, Janok P. Bhattacharya (Ed.): River Deltas-Concepts, Models, and Examples . January 2005, doi : 10.2110 / pec.05.83.0413 .