{{noref, date=July 2008 Mali

An inverted river delta is special category of

river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...

in which the narrow end of the delta emerges on the seafront and the wide end is located further inland, so that with respect to the seafront, the locations of both ends of the delta are inverted.

Explanation

River deltas typically form on flat, coastal floodplains: the narrow end located at the point where a river fans out and deposits sediment in a region extending outward into the body of water which the river empties. In the case of an inverted delta, the delta is located at the waterway's exit from a large, flat valley, yet still inside the valley. The sediment is dropped within the valley and the clear water then exits into a bay or the ocean, so the apex of the delta is at this exit, a configuration said to be inverted from that usually seen. Inverted deltas typically do not last long in geological terms, since they tend to fill up with sediments rather quickly and eventually become normal deltas.

Examples

The Sacramento-San Joaquin River Delta

A classic example of an inverted river delta is the Sacramento-San Joaquin River Delta, which lies at the confluence of the

Sacramento ) , image_map = Sacramento County California Incorporated and Unincorporated areas Sacramento Highlighted.svg , mapsize = 250x200px , map_caption = Location within Sacramento ...

and San Joaquin rivers in

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

. The water from the rivers that drain the entire, large

California Central Valley The Central Valley is a broad, elongated, flat valley that dominates the interior of California. It is wide and runs approximately from north-northwest to south-southeast, inland from and parallel to the Pacific coast of the state. It covers ...

exit through the

Carquinez Strait The Carquinez Strait (; Spanish: ''Estrecho de Carquinez'') is a narrow tidal strait in Northern California. It is part of the tidal estuary of the Sacramento and the San Joaquin rivers as they drain into the San Francisco Bay. The strait is ...

, a narrow gap in the Coast Range. An inverted river delta exists behind this strait.

The Tagus River

Another example is the delta of the

Tagus The Tagus ( ; es, Tajo ; pt, Tejo ; see below) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales near Teruel, in mid-eastern Spain, flows , generally west with two main south-westward sections, to ...

river in Portugal, although due to sedimentation this delta is now only very partially inverted, with the valley now mostly filled with sediment. It is still about 15 km wide and 25 km long, compared with the 2 km wide exit into the sea, and forms a large lagoon with large and very shallow sand banks which go uncovered during low tides. The delta used to be even bigger thousands of years ago. Landforms Inverted river delta