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Facts About Sandbars

When people think about Caribbean landscapes, many people envision sun, water and sandbars. The truth is that sandbars exist all over the world. A sandbar, or shoal, is essentially a sand dune that is partially or completely submerged under water. Because of the current of the water, sediment, sand and soil builds up into the mounds that form sandbars.

How They Are Formed
- Sandbars can form in rivers, lakes and seas. Sometimes the sandbar is created because of a strong current, like the Minnesota Point Sandbar. It is the longest freshwater sandbar in the world, and it formed from the silt and sand deposits from the St. Louis River. Sandbars are also formed because of breaking waves. A wave hits shallow water and breaks. The break creates a current moving in the opposite direction to the wave's current. Sand caught up in that current gets held up when the two currents collide. Eventually that sand builds up into a sandbar.
Shoal Waves
- When a wave comes up suddenly on a sandbar, it slows down. This change in momentum causes the waves to suddenly get closer together and therefore rise up and crash. Shoal crashes are more intense than regular wave crashes because of the increased height of the waves.
Fluidity
- Smaller sandbars that are submerged underwater are often temporary and can shift on a daily basis. Sediment can begin to form a pile, but an increase in the strength of a current can move the entire sandbar.
Hazards
- Sandbars can be dangerous to swimmers and boaters. Because some sandbars are completely submerged, boats have to be careful to not run into one. Even experienced boaters must use caution when they suspect a strong current has caused a shift in the location of the dunes. Swimmers, surfers and divers can be knocked unconscious if they are not aware of the location of a sandbar.

Nature