I didn't know that Io, the highly volcanically active moon of Jupiter, had really high blocky mountains. But it does -- even higher than Olympus Mons on Mars, which is an absolutely gigantic volcano.
The mountains on Io aren't volcanoes. They are just big blocks of sulfurous rock. A new study indicates that the reason for them is the volcanic activity on the moon, which are spewing out huge amounts of what's inside Io. So much, in fact, that the crust of the moon is actually shrinking because there isn't enough stuff inside the moon to hold it up.
This causes faulting in the crust, which forces ridges to form, which turn into the blocky high mountains.
I was thinking that if the crust on a pizza had the same problem (i.e., shrinkage), then there would be ridges of mozzarella and tomato sauce on a standard deep dish pizza. But they wouldn't be ten miles high, hopefully.