Hi, I PMd a couple of other people about the true height/deposit thickess issue, but was doing it from a vague memory rather than anything concrete. Do you have a reference for your 56,000ft figure? Thanks.
The figures giving the true height of the island have been copied and recopied so many times I don't know what is closest to "original" research and what isn't. What I have gathered from the many sources I've read is that the figure refers to the actual thickness of the material ejected over the years. This includes the ~13,800' above sea level; the height of the mountain under water from the mean depth (~18,000') in that part of the ocean; and the amount that the shear weight of the mass of material has depressed the crust of the earth (~24,000') which equals approx. 56,000'.
The height above sea level is the only figure we can really trust, of course. You have to go a long way off into the ocean to find a depth of 18,000 feet - more like 15 to 16 thousand within couple hundred miles of the island. The depth that the seafloor has been crushed is a guess, too, so who knows what the "real" figure is. - It's a stretch, but I suppose one could argue that Aconcagua is 56,000'+ high too if you add the depth of the ocean trench (>24,000') to the height of the mountain.
If you could come up with some more info and sources, I'd sure appreciate it and would add it to the page.