Stromboli is a volcanic island in the Mediterranean that erupts continually and has for at least 2,000 years, probably more. Mostly molten rocks explode inside the craters causing a light show that has earned it the nickname of Lighthouse of the Mediterranean. In doing so it produces clouds up to 1/2 mile in height, that can become detached when the wind is strong enough. In this case the cloud was just off to the side of the volcano itself, with the warm air currents producing a visual effect of it floating on water.