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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.

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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?

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