Diatremes

(volcanic pipes), volcanic vents in the shape of vertical pipes widening toward the top to form a funnel. Diatremes result from major gas eruptions. They are common in the vicinity of Kimberley (South Africa), where they have been filled with a volcanic breccia-like rock (kimberlite) containing diamonds. In the last decade diamond-bearing kimberlite volcanic pipes have been discovered in the Yakut ASSR.