Shoal

In oceanography, geomorphology, and geoscience, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water close to the surface or above it, which poses a danger to navigation.

Sometimes, the term refers to either any relatively shallow place in a stream, lake, sea, or other body of water; a rocky area on the seafloor within an area mapped for navigation purposes; or a growth of vegetation on the bottom of a deep lake, that occurs at any depth, or is used as a verb for the process of proceeding from a greater to a lesser depth of water.

They can develop where a stream, river, or ocean current promotes deposition of sediment and granular material, resulting in localized shallowing (shoaling) of the water.

Marine shoals also develop either by the in-place drowning of barrier islands as the result of episodic sea level rise or by the erosion and submergence of inactive delta lobes.

A shoal–sandbar may seasonally separate a smaller body of water from the sea, such as: The term bar can apply to landform features spanning a considerable range in size, from a length of a few meters in a small stream to marine depositions stretching for hundreds of kilometers along a coastline, often called barrier islands.

They are typically composed of sand, although they could be of any granular matter that the moving water has access to and is capable of shifting around (for example, soil, silt, gravel, cobble, shingle, or even boulders).

In Russian tradition of geomorphology, a peresyp is a sandbar that rises above the water level (like a spit) and separates a liman or a lagoon from the sea.

A bar can form a dangerous obstacle to shipping, preventing access to the river or harbor in poor weather conditions or at some states of the tide.