[badcppdev]

I think you could watch some of the youtube videos the Professor Shawn Willsey has posted about the Icelandic volcanic activity over the last 6 months. As well as lots of cool stuff about the actual volcanoes and lava floes there is a lot of information about the magma chamber underneath the peninsula that is filling up and raising the land in a very measurable way. That's over a time scale of months. I think you'll see it's very plausible that over decades and centuries the level of land can change dramatically with respect to a the local 'base' level.

[prometheus76]

I understand that land can change levels over time due to magma. What is harder for me to understand is land doing so in a uniform way that maintains a flat floor and leaving intricate mosaic patterns intact. Especially when you take into account the earthquakes that would also be a part of a magma shift like that.

It's obviously possible, but hard to understand how the tensions would be spread evenly as the level raised up and down.

[mbreese]

I know nothing about this specifically. To me, it makes sense if you think about just how big these fields are and how slow of a process it is. Changes that take place slowly over a large area are more likely to cause shifts that seem relatively flat at the scale of a house. Another way to say it: at the geologic scale, a tile mosaic may as well be a point on a plane. Unless there is a fault line at that exact position, I can see how the area would move up and down relatively uniformly.

What I’d like to know is how long of a process was it really to lose a city into the bay. It would have happened while people were around, so is there some kind of historical record?