I remember seeing a program several years ago that tried to explain why
mountains on Mars(Olympus Mons)are higher than anything on Earth.The
main reason is gravity.The height and mass of a mountain or volcano can
only be so great without caving in on itself.Olympus Mons is an
extinct volcano with a very broad base allowing it to to reach its
height gradually.I found a good site showing Olympus Mons and giving a
better description.Bill.
http://sprite.phys.ncku.edu.tw/~astr.../ap970915.html