La Grille is a basaltic shield volcano at the N end of Grand Comore Island (also known as Ngazidja). Unlike the larger and better-known Karthala volcano to the S, it lacks a summit caldera but has an abundance of pyroclastic cones. The cones were erupted along fissures paralleling the summit ridge, which has an irregular profile and is elongated in a N-S direction, and from radial fissures that reach as far as the coast. Recent lava flows, some perhaps as young as a few hundred years, have reached the sea from fissures on the lower W, N, and E flanks.