Bengal Delta
Climate Change Daily Earth Science Geosphere Repost

The Bengal Delta

The heart of Bangladesh

Understanding Bangladesh requires you to first know that its life springs from the Ganges-Brahmaputra delta. This delta system, also known as the Bengal Delta, dominates the country’s geography and makes it one of the most fertile regions on the planet Earth.

The Bengal Delta also has the distinction of being a geological triple point. The delta marks a location on Earth’s surface where three tectonic plates meet: the Indian Plate, The Eurasian Plate, and the Burma Plate. Fortunately, or unfortunately, depending on your point of view, this triple point creates the Bengal Basin. Geologists use the term ‘Basin’ to designate an area of sinking land. Water naturally flows to the lowest point, and thus the Ganges and Brahmaputra rivers flow from the mountains and converge on the basin above the triple junction.

The delta

The point where the rivers meet the open ocean marks the seaward edge of Bengal Delta. Three things can happen over time from this point. The delta can grow, changing the ocean into the land. The delta can recede, turning land into open sea, or lastly, the delta can reach a temporary stasis where neither ocean nor land is growing or shrinking. But the planet is dynamic, and the stasis is always temporary.

The two major rivers feeding the Bengal delta originate in the Himalaya mountains, where they have their start as meltwater from snow and ice in the high mountain glaciers. During the monsoon season, the runoff from the rains also drains into these rivers, sometimes turning them into raging torrents.

However, the vast volumes of water draining from the continent into the Bay of Bengal do not directly give rise to the delta. It is the sediments carried in the water that matter. These flowing waters transport massive volumes of minute soil and rock fragments. About one billion tons of sediment were delivered annually to the delta in the early 2000s.

A dynamic system

Moving water carries sediment with it, and the higher the velocity of the water flow, the larger the soil and rock particles it can move. A delta typically owes its geographical position to changes in water velocity. As the fast-moving waters of the rivers encountered the still waters of the ocean, they slow down. Then, as velocity slows, sediments drop out of suspension and start building new land.

Put all of this together, and you have a dynamic system in constant tension. The basin is sinking, causing the land surface to drop, and allowing ocean waters to encroach inland from the coast. The rivers seek to counteract this invading ocean by depositing sediment in the space created by the dropping land surface. Year after year and century after century, the battle continues between the river and the sinking basin. If the river is winning, then the delta builds into the ocean. If the basin is sinking fast enough, the ocean creeps inland, taking away land from coastal communities.

Today, as ice fields in the mountains disappear and sea levels rise from climate change, the Sundarbans, on the leading, seaward edge of the delta, are disappearing. But with the Sundarbans also goes the heat of Bangladesh.

Also See:

Climate change at the margins (Source: ArcheanWeb) –

Tasfin’s Documentary of the Sundarbans (By William House; Medium) –


Feature Image: Credit: By Addicted04 – Own work, CC BY-SA 3.0,

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.