Ol Doinyo Lengai is an extraordinary stratovolcano in northern Tanzania (2.751°S, 35.902°E, 2890m, map) producing natro-carbonatitic lava, very rich in sodium and carbonates. It is highly fluid and emerges at 500 to 590°C only. It glows dull red in the dark and is the «coolest» lava of any known volcano. Major ash eruptions were observed in 1917, 1926, 1940 and 1966-67 (image). Since April 1983 lava has been extruded and gradually has been filling up the summit crater: (photos by Bell, Keller and Haefeli).