Volcanic pipe

As the body of magma rises toward the surface, the volatile compounds transform to gaseous phase as pressure is reduced with decreasing depth.

This sudden expansion propels the magma upward at rapid speeds, resulting in a supersonic Plinian eruption.

Over time, the tuff ring may erode back into the bowl, leveling out the depression by filling it with washed-back ejecta.

Kimberlite pipes are the source of most of the world's commercial diamond production, and also contain other precious gemstones and semi-precious stones, such as garnets, spinels, and peridot.

The result is a funnel shaped deposit of volcanic material (both solidified magma, and ejecta) which appears mostly flat from the surface.