The physics of the internal processes are well known.
Vertical uplifts at plate rates would quickly produce extreme
elevations in the absence of erosion or gravitational resistive
forces. However, uplift by a height H above its surroundings exerts
a vertical force per area of 
where g is the acceleration
of gravity and 
is the density of the uplifted crust.
This force significantly resists further uplift once a
mountain has formed. For example, heat flow measurements near the
San Andreas fault indicate that the shear traction on the fault is
less than 20 megapascals
( Lachenbruch and Sass, 1980; Hickman, 1991).
Uplift of a hill 800 m high with a density of 2500 kg m
would provide more resistance per area to vertical motion than
the fault does to horizontal motion.
For broad uplifts, the lithosphere may be considered to the first order to be a very viscous, isostatically compensated fluid. The change of height per change in crustal thickness is (on land)
where 
is mantle density. For a mantle density of
3300 kg m
, and a crustal density range of 2500 kg m
to 3000 kg m
, the derivative ranges from 0.25 to 0.09 or the
crust needs to be thickened from 4 to 11 times the amount of uplift.
The ``spreading force'' per length of isostatically compensated
orogen that must be exceeded to further thicken the crust is dimensionally
where 
is the depth of compensation.