i've also read somewhere that strong underwater currents - several hundred feet below ocean surface - can cause coastal surges when these underwater currents hit the coast line or encounter currents of a different temperature .
we have noticed that in lake ontario during the fall - when air temperatures are falling - water may "erupt" or have a "crown" even in the absence of any wind . those water disturbances just roll along the the lake surface for no visible reason .
similarly the lake water starts "to boil" in the fall when air temperatures are falling ; it's like looking into a pot of boiling water . of course , the overall water temperature is low , but the different temperature levels within the lake make the water look like it's "boiling" when the different masses of water are mixing (the differences in water temperatures between various water levels may be minute , but the mixing makes it look like some strange event is taking place .
after living along lake ontario for some years , we've gotten used to it - nothing unusual any more .