[GRASS-user] Volumes of intersections

[Adam Dershowitz]

Is it possible to use grass to calculate the volume of a part of a 3-D  
vector object?
What I mean is if I have a mountain, for example, that is defines in  
one vector map.  Then, in another map, I define an area (a plane for  
example).  This represents a slice through the mountain.
Is it possible to calculate the volume of the mountain that lies above  
the second plane?  (how much rock is above the slice through it?) It  
seems like it should be doable, but I am not really sure how to get  
going.
Any suggestions?

Thanks,

--Adam