I would guess that the word Delicate isn't really the case, more "fine tuned". They say the volcanos are about a mile deep, so based on this calculator - http://www.calctool.org/CALC/other/games/depth_press , thats about 2360PSI. I am not a physicist, but it seems that if that pressure were to decrease because of a greater pull on the water from the Sun, then it would be less able to "contain" the magma underneath. unfortunately, I don't know what the actual deviation in pressure down there might be with the fluctuations of the earth's tides.

This also reminds me of this - http://blogs.discovermagazine.com/d-brief/2014/10/01/antarct...

If the icecaps melt, and the water migrates into the oceans, then the pressure on the seafloor increases by some amount, which might further decrease seafloor volcanism?