... and yes, it appears it has begun.
Especially when we consider that this is all in the Ring of Fire area, so close to the Alaskan peninsula and bay. Keep in mind that issue about Ice IX expanding within the planet's crust. Keep in mind the issue about methane geysers in the tundra areas. It isn't simply one effect that causes this collapse, but a complexity of chain events, that need, also, to include the Chandler Wobble.
Like a coffee carafe with a cup of water, when swished rapidly around in an eccentric path, rises toward, if not over, the top of the container. Some even believe these so-called Vimana flying machines use this action to generate vertical, linear thrust and that may, in fact, be quite possible.
These are all factors that add up to the probability of the water levels rising, while the land masses collapse. Can it happen suddenly, forcefully, massively and globally? I hope it's gradual, but I wouldn't count on it. I certainly wouldn't be bringing any more babies into the world just now...