This section covers everything you need to know about waves and rip currents
Skills & Environment — Topics
What Causes Waves
The primary cause of waves is wind. When you see waves on the ocean, wind is almost certainly the cause. Waves can also be generated by seismic activity — tsunamis caused by underwater earthquakes or landslides — but these are rare. For exam purposes, and in everyday diving, waves mean wind.
Why Waves Break
Water particles inside a wave move in a circular path. Roughly one third of that circle extends below the waterline. As a wave approaches shore and the water gets shallower, the bottom of that circle starts dragging along the seabed. The wave loses stability and breaks.
Rip Currents
Rip currents are narrow, fast-moving currents that flow away from shore through the surf zone. They are sometimes called undertow or rip tides — but the correct term is rip current.
| Property | Typical values |
|---|---|
| Width | 50–100 feet |
| Extent offshore | 100 yards or more |
| Speed | Can exceed 5 mph — faster than an Olympic swimmer |
How a rip current forms
Waves continuously push water toward the beach. That water has to go somewhere — it cannot keep piling up on the shore. It runs sideways along the beach (the feeder current), finds the path of least resistance — a channel, a gap in a sandbar, or a break in a fringing reef — and flows seaward through it. As it goes, it erodes sand and deepens the channel, which strengthens the rip further.
When rip currents form
- Waves only need to be 2–3 feet to generate a rip — they do not need to be large
- They often occur on calm days following a storm, not only during bad weather
- They are usually strongest near low tide but can form at any tidal state
- Common where sandbars are present — rips form at breaks or channels in the bar
How to recognise a rip current
- A line of turbid (discoloured) or foamy water moving seaward
- An area where waves are not breaking, while waves break on either side
- Foam, seaweed, or debris being carried offshore
- Much easier to spot from an elevated position — a dune, lifeguard tower, or dive boat
Skills & Environment — Topics