What Does a Delta Mean?
A delta is land that forms at the mouth of a river, where it empties into an ocean, sea, another river or a lake. The river deposits vast amounts of sediment into the other body of water, which gradually builds up into a land mass. The simplest way to explain how one forms is the amount of material that the river deposits is more than what the tides and waves can carry away. The largest delta in the world is the Ganges Delta on the Indian sub-continent, home to some of the most fertile land on Earth.
Time Frame
Most deltas are very young geological features, with some only a few hundreds years old. Older deltas will be built one on top of another, with the river forming new deltas once the old ones build up to the point that the river can no longer flow through them. A new channel will form and the river will begin to deposit material to form another delta. The Mississippi River's current delta, for example, is about 600 years old.
Types
There are different types of deltas, with the most common being the triangular-shaped delta that most major rivers form when they reach the ocean. The Nile River in Egypt is the most famous of this kind of delta. A Gilbert delta is one that can occur only in fresh water, where a mountain river, for instance, flows into a freshwater lake. Some rivers do not form deltas. They flow into what is called an estuary, where freshwater meets saltwater but no land forms. When a river delta occurs inside a valley the delta is called an inverted delta.
Size
The Ganges Delta in South Asia is in the Bay of Bengal and is formed by the Ganges River and its many tributaries. It is 220 miles across and the land is so fertile that it is called the "Green Delta." It is able to support a population of almost 140 million people, who depend on it for agricultural purposes to feed their families. The delta has many different ecosystems within its boundaries, from mangrove swamps to coastal marshes to farmable land.
Geography
Because of their proximity to the water and being only a few feet above sea level, deltas are vulnerable to storms, especially hurricanes and tropical cyclones. The Mississippi Delta region was blitzed by Hurricane Katrina in 2005, with the storm surge from the monster storm easily able to destroy coastal areas along the delta. The Ganges Delta is home to constant flooding during the rainy season, with massive loss of life being documented during direct hits by powerful cyclones.
Expert Insight
The actual term delta was first used to describe the sediment deposit at the mouths of rivers until around 450 B.C. A Greek historian, Herodotus, saw that the Nile where it dumped into the ocean, resembled the greek letter delta, a triangular shape and coined the term.
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