Olympus Mons stands nearly three times the height of Everest, yet standing at its base you would not see a mountain at all, because its slopes rise so gently across roughly 600 kilometres that the summit sits well beyond the Martian horizon and the ground at your feet looks almost flat

Olympus Mons stands nearly three times the height of Everest, yet standing at its base you would not see a mountain at all, because its slopes rise so gently across roughly 600 kilometres that the summit sits well beyond the Martian horizon and the ground at your feet looks almost flat

If you approached Olympus Mons from the Martian plains, the first thing you met might not be a gentle incline. It could be a wall. Much of the volcano ends in a basal escarpment several kilometres high. Along some sections, published measurements put that cliff close to nine kilometres from bottom to top. It is a vertical interruption taller than Mount Everest is high above sea level, attached to a volcano whose upper flanks are routinely descri…