Waves in the Ocean - redone

A photo of waves taken from the safety of the shore

Some time back, I wrote about how, once you are out of sight of the shore, waves in the ocean look the same at different heights (original post is here). I reworked the post, removing the helicopter scariness for the UVic Ocean Student Society's blog - find the post here.

Down on the beach

Breaking waves on a sandy beach

I took a group of students down to a local beach last week – it turned out to be the only day that week that poured rain (I often have that kind of luck). As the students were doing their work, I walked up and down the beach to check on them. Since I was dressed for the rain I didn't mind the weather, in fact I found it pleasant to be away from my computer for a few hours. In addition to my rain jacket, I wore my rubber boots so I could walk through the shallowest waves and feel their strength tugging at my ankles. Okay, the real reason I wore my rubber boots was because they were dirty and I hoped the wave action would clean them.

Most of the beach was cobble, that is, composed of golfball to baseball sized smooth stones. With each step shifting rocks allowed my foot to sink in a bit, it almost felt like I was wading. Off shore, breaking waves (less than 1 metre) formed perfect curls along their tops before crashing down. Beneath the crashing waves, rocks tumbled with the moving water adding their own sound to that of the waves. Constant wave action was moving the rocky beach, in fact, all beaches exist in a constant state of change. At different time of year a beach may look completely different. In summer, gentle waves bring more sand on shore while in the winter, larger waves can remove the sand entirely.

Beaches are made from loose sediments like rock and sand or even ground up hardened lava (Hawaii has beaches like this) that are deposited. A sheltered place in between headlands is ideal as the headlands will take the brunt of wave energy. Beach sediments can originate from a far off river or from right close by. The cliffs overlooking the beach I was on provided all the sediments needed for the beach to form.

As a tangent – my rubber boots are now nice and clean.

Waves in the ocean - or why I don't like helicopters

It is a confused pattern that the waves make in the open sea – a mixture of countless different wave trains, intermingling, overtaking, passing, or sometimes engulfing one another; each group differing from the others in the place and manor of its origin, in its speed, its direction of movement; some doomed never to reach any shore, others destined to roll across half an ocean before they dissolve in thunder on a distant beach.

– Rachel Carson, "The Sea Around Us"

Years ago I took a ride in a helicopter that took off from a ship's deck. I was able (with a tether) to sit with my feet dangling out the door and nothing obstructing my view to the ocean surface. I watched the undulating waves below. At the ocean surface there was little wind that day, so the waves weren't breaking. I thought we were a short distance from the surface, maybe less than 50 m, until a seagull flew beneath us. The bird was a tiny white speck, so we had to be several hundred metres up. The fact that I couldn't tell how high we were is interesting and many other observers have noticed the same thing.

The surface of the open ocean is complex, like the quote above describes. Waves of all sizes occur at the same time. Ocean surface waves are mostly created by the wind; once they are created they can travel a great distance and interact with waves created else-where. The size and speed, thus energy, of a wave is related to the length of sea the wind blows over, called fetch, and the strength of the wind. A large storm lasting several days can create energetic waves. Once these energetic waves move out of the storm area they are called swell. Now the more energetic waves move faster than less-energetic ones resulting in a sorting of waves. Water is great at transmitting waves, meaning these energetic waves can reach the opposite side of an ocean basin where they potentially create great fun for surfers.

Without a point of reference, like a shoreline or a seabird, there is no way to tell what size of motions you are looking at once you reach a certain distance above the water. Obviously, you could tell how far away you were if you were getting sprayed by the water – but by then you are very close. A skydiver over the open ocean wouldn't be able to tell how high they were without an altimeter. If the altimeter failed it could be a potentially dangerous situation.

On the next flight of that helicopter there was an in flight emergency that resulted in a near water landing. Passengers on helicopter that land (or crash) on the water, typically don't make it out. Helicopters usually flip when they hit the water and dealing with getting out can be very disorientating without training. Since there was a passenger on board, the pilots attempted a deck landing (they didn't want to be responsible for a dead passenger). Those of us on the ship were all in our firefighting gear just waiting for a crash – so it was a very serious situation. Although everyone was okay, at that point I decided never to ride in a helicopter just for fun again (even though I am up in them quite often for work).