Six collapsed craters nested at the roof of a giant.
At the very top of Olympus Mons sits its caldera — a vast volcanic crater complex about 80 km wide and up to 3 km deep. It is not one pit but six overlapping craters, each marking a moment when an emptied magma chamber collapsed beneath the summit.
Claim your plot here →A caldera forms when a volcano erupts, empties its underground magma chamber, and the unsupported roof drops. Olympus Mons did this at least six separate times, each collapse cutting into the last, so the summit today is a stack of overlapping bowls at different depths — a record of the volcano's eruptive lifetime.
The whole complex spans roughly 80 km, wide enough to swallow a large city, with cliff walls up to 3 km tall ringing the floors. Crater counts suggest some of these floors solidified only a few hundred million years ago — geologically recent, hinting the giant may not be entirely dead.
At ~80 km across, the caldera could contain a metropolis the size of greater Los Angeles.
Yellowstone's caldera is huge at ~55-70 km — Olympus's summit complex rivals or exceeds it, atop a mountain 2.5× Everest.