> I'd like to ask a question of the geology braintrust. A while ago there
> was a very informative post, perhaps by Mr. Morton, on why mountains on
> Earth cannot be higher than some height (perhaps 6 miles?). But these
> conditions can't apply to Mars, which has Olympus Mons at 8 miles high or
> thereabouts. How come Mars can have higher mountains? Does it have
> something to do with the red planet having a solid core?
I believe it has to do with the mass of the planet, which affects the value
for the gravitational acceleration on the planet's surface (little g). On
Mars, we would weigh less on the surface than we do on earth. Similarly, a
given volume of rock will weight less as well and you can pile up a higher
pile before it collapses of its own weight. On earth, there's evidence of
the Himalaya mountain chain spreading E-W laterally through normal faulting
as they're being pushed up by the northward-directed collision of India with
Also, on Mars, there appears to be no plate tectonic activity (except
maybe very early in its history). That means that a section of the crust
sitting over a mantle plume would stay there allowing a volcano like Olympus
Mons to grow quite high. On earth, crustal plates move and you get chains
of volcanoes like the Hawaiian Islands.
> Also, is there any limit to how deep an ocean trench might be?
That I'm not sure about. I would also guess that it's gravitationally
controlled. Any geophysicists out there to correct me?
-- Steven H. Schimmrich KB9LCG firstname.lastname@example.org Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, Urbana, IL 61801 (217) 244-1246 http://www.uiuc.edu/ph/www/s-schim Fides quaerens intellectum