What causes sea foam?
Overnight the surf world learnt of the death of five Dutch surfers. They were amongst a group of nine who paddled out at Scheveningen during a large storm and were overcome by beds of sea foam.
Early reports said the foam was toxic and alluded to death by poisoning, however at least two of the surfers showed signs of asphyxiation. A tragic result caused by what's usually harmless matter.
Sea foam naturally occurs whenever saltwater is agitated. You may have seen it on rocky coasts, where waves break abruptly onto rocks and a line of spume then drifts downcurrent, or down the line on big days where wave action alone creates the foam.
Turbulence makes the impurities in saltwater - some of them naturally-occuring such as salts, proteins, fats, and algae, but also additives such as detergents and other pollutants - to bubble and froth. It can happen on a very small scale, but is more noticecable when either the waves are big, or the surface is agitated by strong winds.
Most sea foam is only a few inches thick and begins to break up and settle shortly after it's created. However, given a mixture of a fresh water source, particularly from a river that contains organic materials, and a surface blend of storm waves and strong wind, sea foam can grow two to three metres high. It then begins to create it's own environment, the bubbles bonding stronger and lasting longer.
In Australia, this often happens during storm conditions in SE Queensland and northern NSW, where many large, freshwater rivers empty out into the sea. Associated rainfall swells the rivers, and the floodwaters mix with the churning sea to make banks of sea foam. Depending on the direction of the wind it can also blow inland smothering all features.
In 2013, the wind and waves from Tropical Cyclone Oswald mixed with freashwater from the Maroochy River to create large beds of sea foam:
While it looks fun, there are some hidden dangers. In 2015, Ben Redman, then-director of Far North Coast Lifesaving, told The Northern Star that, "foam usually results in a large number of snake sightings."
"People shouldn't swim in it," said Redman. "You'll usually find a lot of sea snakes in the foam, they seem to be attracted to it."
In 2008, claimed Redman, they counted 21 snakes during a sea foam event at Ballina's Lighthouse Beach.
Most sea foam is harmless to humans, however as it can be caused by many ingredients, most of them invisible, it's impossible to say with certainty that it's safe. Agricultural runoff or urban pollutants may be causing the foam, and hence making it harmful to humans.
If you've ever swallowed sea foam, you'll know it's highly irritable, but death by asphxiation is rare. While it may seem implausible, there's very little air in the bubbles, mostly organic aerosols and toxic aerosols. The foam displaces the air from above the water surface like a gentle avalanche. If this happens amongst breaking waves...breaking waves that you can't see, then the danger is obvious.
Consider that during the Scheveningen tragedy, the authorities had to use a hovering helicopter to move the sea foam and continue their search.