What causes unusual wave activity?

Sunday evening we were walking along a beach when waves suddenly began rolling in and breaking, from a previously calm surface, first near the inside of a point and then moving farther down. This went on for many minutes. I checked time and it was precisely the moment of predicted maximum ebb flow. However, the actual flow speed that evening was not especially high. Upon looking out to the water, we saw exactly one ship that had passed by earlier, in the shipping channel; no other boats were in sight. There was no wind to speak of, nor had there been swell that day or the previous day.

Curious, Monday evening we set off again to see if the event would repeat itself. My reasoning was that Monday’s max ebb was slightly faster and coming off a higher high tide also. There was a light wind but other than that, weather was similar. No ships present. Nothing unusual happened this time. So there must’ve been some other variable creating the sudden wave activity on Sunday night.

I’ve seen many, many ships pass by in the same location before, yet I never saw any of them generate that kind of wake/wave. While I still wouldn’t rule that out, what other kinds of things would cause unusual wave activity? Would a submarine do it?

The barometric pressure in the area was dropping all day both days. Someone told me a few small earthquakes had occurred not far away, but I don’t know the timing of them in relation to what we saw.

if not ship may very long period swell
With swell around 22 seconds or more I’ve seen lulls last twenty minutes or more then a set of several big waves before another long lull. So not sure if later after your waves it happened again but one possibility. The ebb tide could further jack up whatever was coming in.

I’m always very careful in longer period swells because of those lulls. It’s easy to think it’s safe to be inside near the rocks only to see a big set roll in.<br />

Location Location Location
Its always frustrating when someone posts a highly detailed report of an unusual occurance but neglects to include WHERE THEY ARE AT!

Nessie ???
Was this in the ocean ?

I have seen some big wakes from porpoises

Jack L

variation in ships
I’ve seen wide variations in ship wakes in my years of paddling SF Bay. The vast majority I have seen put out just about no wake. But I guess if they are loaded just right (or maybe just wrong is a better way to say it), they kick up huge wakes.

A few months back, I was waiting at the South Tower of the GG bridge to cross to the north side. Had to wait for a container ship to pass. All the times I have been there and waited for a ship to pass in the past, there was basically no wake. But for some reason, this one was kicking up a huge wake. I watched it come along and figured it would make a good surf ride, so turned away from it and got ready. Then watched some more as it approached and decided it was too big for me to comfortably surf, so started back paddling to hit it tail on with some speed (not enough time for me to turn back forward). Was definitely the biggest wake I had ever seen, and from a situation where ships I’ve seen before had no wake.

Don’t know if yours was a wake, but it is worth keeping in mind that not all ships make the same wake.

east coast tsunami reported


Yes and no
It was in the ocean (or sea, if you get picky…).

The only porpoises I’ve seen in the area are harbor porpoises, and they never generated much movement. Too small. Ditto for the various seals and sea lions.

There could’ve been an orca, though unlikely.

Between Point Wilson and Hudson Point, with the movement starting at PW and progressing down the beach. We’ve seen submarines nearby before, but always with a tender (I think that’s what they call them).

Didn’t think east coast got them
The article stated that weather, not seismic activity, might have caused it. Interesting stuff.

It was an isolated event
We watched to see if it would happen again but it didn’t. Good advice, though–22 sec is a long stretch, much longer than I’d expect. Something to keep in mind when paddling. Thanks for the heads-up.

Maybe it was perfect timing
The one ship that had passed might have gone by some “triggering” location at precisely the right time to create big wakes.

I’ve seen wakes near both Point Wilson and Point Hudson before, just not as long-lasting or loud as Sunday night’s.

only will see that period in open ocean
These long lulls start to be a minor issue closer to around 18 seconds and a big issue by 22. But you only see that in places like the open Pacific coast where you have many miles for the far storms to organize into fewer but larger waves. I’m guessing the ship – maybe loaded but moving fast or it made a sudden slow down.

Seas vs. swell
There are seas and there are swells - essentially, local events and conditions which were created distantly, but which arrive at your location.

Seas and swells caused by the same conditions, but because swells are generated distantly, they tend to settle and calm and become much more “regular” in behavior. Swells become waves when the depth of the water is 1/2 the size of the swell (example: 6 foot swell will break in 3 feet of water).

Seas are local conditions influenced by the wind, wakes, currents, wakes, or other disturbances of water near your location.

When swells meet local conditions, a variety of complex interactions take place. Add this to irregular winds, gusts, shoreline which creates rebound waves (aka. clapotis), currents, wakes, angle of arriving swell vs. angle of shore, and you can have very odd and unpredictable local conditions.

Because of this complexity, it is difficult to determine why the conditions varied so greatly. Most likely, there was incoming swell which caused somewhat confused conditions on one day vs. other.


When we were in Johnstone Straight, BC
Long after a Cruise ship went by, (it was almost out of sight) we got the swells from it, but we fully expected it.

Jack L

As above …
My first guess would be a shipwake; a ship can pass a long way off shore and waves can be fairly large, the shape of the ship determines what kind of waves you will get, some smaller boats can actually throw very impressive wakes. But as mentioned forerunners of a long period swell, start to show up as rogue sets that may be spaced quite a bit a part like 20 minutes or so. There have been several nice south swells in the last few weeks of long period coming up from New Zealand area … also this week there was a little bit of a Freak North west swell that was long period (unusual this time of year). The long period swells of course come from huge storms that blow for days with very high winds.

unusual waves
Wakes from shipping seems logical. People often forget about wind driven waves from a long distance away doing some strange things. A shoreline with lots of irregularities can deflect waves and surf. Sometimes harmonics are involved. Opposing wind and tides do unusual things. The ocean is more dynamic than many realize.