Most waves are formed by wind on the water. Sea waves usually result from storms, often hundreds of miles from shore. Waves are not all equal in size. Sometimes a group of larger waves comes ashore one after another. This is known as a "set" of waves.
When waves break, water is pushed up the slope of the shore. Gravity pulls this water back toward the sea. If it converges in a narrow, river-like current moving away from shore, it forms what is known as a Rip Current.
Rip currents can be 50 feet to 50 yards or more wide. They can flow to a point just past the breaking surf (the surfline) or hundreds of yards offshore. Some 80% of rescues by lifeguards at America's surf beaches are due to persons being caught in rip currents.
Rip currents may pull continuously, but they can suddenly appear or intensify after a set of waves, or when there is a breach in an offshore sandbar. Longshore currents,inshore holes, and other bottom conditions contribute to the formation of rip currents. Inshore holes and sandbars can also greatly increase the danger of spinal injury
Rip Current Survival
The sea is a wonderful playground, but you must respect its power. Learn to swim and consider participating in a junior lifeguard program. When swimming, choose an area protected by lifeguards. If you are not a strong swimmer, go no further than knee deep. If you decide to swim, check the conditions first to identify any dangerous currents. Ask a lifeguard for assistance.
You can sometimes identify a rip current by its foamy and choppy surface. The water in a rip current may be dirty (from the sand being turned up by the current). The water may be colder than the surrounding water. Waves usually do not break as readily in a rip current as in adjacent water.
If caught in a rip current, try to relax. A rip current is not an "undertow" -- it will not pull you under. Do not try to swim against the current as this is very difficult, even for an experienced swimmer. If you can do so, tread water and float. Call or wave for assistance. You can also try to swim parallel to shore until you are out of the current, then swim directly toward shore.
The same forces which cause rip currents also cause longshore currents. These currents are most evident when waves hit the shore at an angle. This tends to cause the water to be pushed along the beach away from the direction of the oncoming waves. Usually, longshore currents are less hazardous than rip currents because they move along the shore, not away from the shore, but they can knock children and weaker adults off their feet. More importantly, longshore currents can feed and increase the power of rip currents. In other words, the longshore current may move along the shore, then turn offshore to become a rip current.
Variable wave conditions, particularly seasonal changes in wave patterns, can create unevenness in the ocean bottom. This includes sandbars and sudden deep spots, called inshore holes. They can surprise waders, who suddenly find themselves over their heads. They can also create channels in the bottom, which concentrate and greatly intensify the power of rip currents. At any beach with uneven bottom conditions or obvious sandbars, a higher level of caution should be used.
Why Rip Currents Form
As waves travel from deep to shallow water, they will break near the shoreline. When waves break strongly in some locations and weakly in others, this can cause circulation cells which are seen as rip currents: narrow, fast-moving belts of water traveling offshore.
Why Rip Currents are Dangerous
Rip currents are the leading surf hazard for all beachgoers. They are particularly dangerous for weak or non-swimmers. Rip current speeds are typically 1-2 feet per second. However, speeds as high as 8 feet per second have been measured--this is faster than an Olympic swimmer can sprint! Thus, rip currents can sweep even the strongest swimmer out to sea.
Over 100 drownings due to rip currents occur every year in the United States.More than 80% of water rescues on surf beaches are due to rip currents.
Rip currents can occur at any surf beach with breaking waves, including the Great Lakes.
When Rip Currents Form
Rip currents can be found on many surf beaches every day. Under most tide and sea conditions the speeds are relatively slow. However, under certain wave, tide, and beach profile conditions the speeds can quickly increase to become dangerous to anyone entering the surf. The strength and speed of a rip current will likely increase as wave height and wave period increase.They are most likely to be dangerous during high surf conditions as the wave height and wave period increase.
Where Rip Currents Form
Rip currents most typically form at low spots or breaks in sandbars, and also near structures such as groins, jetties and piers. Rip currents can be very narrow or extend in widths to hundreds of yards. The seaward pull of rip currents varies: sometimes the rip current ends just beyond the line of breaking waves, but sometimes rip currents continue to push hundreds of yards offshore.
How to Identify Rip Currents
Look for any of these clues:
- a channel of churning, choppy water
- an area having a notable difference in water color
- a line of foam, seaweed, or debris moving steadily seaward
- a break in the incoming wave pattern
None, one, or more of the above clues may indicate the presence of rip currents. Rip currents are often not readily or easily identifiable to the average beachgoer. For your safety, be aware of this major surf zone hazard. Polarized sunglasses make it easier to see the rip current clues provided above.
Rip Current Myth
A rip current is a horizontal current. Rip currents do not pull people under the water–-they pull people away from shore. Drowning deaths occur when people pulled offshore are unable to keep themselves afloat and swim to shore. This may be due to any combination of fear, panic, exhaustion, or lack of swimming skills.