Depositional landforms usually are located at the bottom of lakes and oceans. They are generally flat, because they are formed by material washed away by gravity which then settles in flat areas. Soil is the natural growth medium for land plants. So, since plants grow in volcanic ash, it can be considered a soil. As far as 'balancing it out'.
Mountains have little or no effect on the rotation of the Earth.
Compared to the diameter of the Earth, mountains are no more than a roughness on the surface. If you look at a textured globe, you can see and feel that the mountains are no more than small bumps compared to the Earth. I read from a magazine that mountains can prevent earthquakes. As far as I know, mountains cannot prevent earthquakes because earthquakes are generated deep within the Earth. The bottom line is that earthquakes facilite heat escaping from the Earth, so there i s no way that mountains can prevent that process from happening.