"Have We not made the earth a resting place? And the mountains as stakes?"
[78:6-7]
SubhanaAllah, verily, Allah is the All-Knowing. Geomorphic studies found that there is a crustal root beneath a mountain building. The root, however, could be 5 times deeper than the height of the mountain itself. Isostasy, density difference in crust and mantle and other factors could explain this in great details.