Undertow (wave action)
Encyclopedia
Undertow is a subsurface flow of water returning seaward from shore as result of wave
action. This type of shore current can play a role in material deposition such as creating sand bars.
Undertows are below-surface rushes of water returning to sea after the water comes ashore as breaking wave
s. If there is an area under the waves where water can flow back out to sea more easily (such as a break in a sand bar) then a narrow rip current
can form. (A rip current is much more powerful and thus more hazardous to inexperienced people than ordinary undertow.) If however there is no weak point in the surf line, then the water that has run up onto the beach simply flows back out to sea under the waves, forming a simple undertow.
There is a popular misconception that the undertow is responsible for many drowning
s by somehow pulling people vertically down, so that they are then held under the water surface. While people can drown in any body of water, even a puddle, undertow itself is relatively harmless; the great majority of drownings near the beach happen because people get caught in a rip current
which draws them out to sea, and they are either poor swimmers or do not understand how to get free from a rip current.
Wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
action. This type of shore current can play a role in material deposition such as creating sand bars.
Undertows are below-surface rushes of water returning to sea after the water comes ashore as breaking wave
Breaking wave
In fluid dynamics, a breaking wave is a wave whose amplitude reaches a critical level at which some process can suddenly start to occur that causes large amounts of wave energy to be transformed into turbulent kinetic energy...
s. If there is an area under the waves where water can flow back out to sea more easily (such as a break in a sand bar) then a narrow rip current
Rip current
A rip current, commonly referred to by the misnomer rip tide, is a strong channel of water flowing seaward from near the shore, typically through the surf line. Typical flow is at 0.5 metres per second , and can be as fast as 2.5 metres per second...
can form. (A rip current is much more powerful and thus more hazardous to inexperienced people than ordinary undertow.) If however there is no weak point in the surf line, then the water that has run up onto the beach simply flows back out to sea under the waves, forming a simple undertow.
There is a popular misconception that the undertow is responsible for many drowning
Drowning
Drowning is death from asphyxia due to suffocation caused by water entering the lungs and preventing the absorption of oxygen leading to cerebral hypoxia....
s by somehow pulling people vertically down, so that they are then held under the water surface. While people can drown in any body of water, even a puddle, undertow itself is relatively harmless; the great majority of drownings near the beach happen because people get caught in a rip current
Rip current
A rip current, commonly referred to by the misnomer rip tide, is a strong channel of water flowing seaward from near the shore, typically through the surf line. Typical flow is at 0.5 metres per second , and can be as fast as 2.5 metres per second...
which draws them out to sea, and they are either poor swimmers or do not understand how to get free from a rip current.