Tanzania: The Volcano "Ol Doinyo Lengaï" Erupts Mysterious Black Lava by Day, White Lava by Night

All volcanologists will agree that no two volcanoes are alike. However, Ol Doinyo Lengaï in Tanzania is truly unique. When it erupts, it spews out white lava resembling chalk, unlike the typical black lava from other volcanoes. This unusual color is due to the specific composition of its lava, known as carbonatites. While most magma contains silica in varying amounts, the magma from Lengaï is primarily composed of sodium carbonate. Although other volcanoes have emitted this type of lava in the past, Lengaï is currently the only active stratovolcano with this characteristic.

A Volcano Under Close Watch

Indeed, its carbonated lava is light-colored, highly fluid, and erupts at a relatively low temperature of around 500 °C. The potentially explosive nature of this volcano makes it hazardous for nearby populations, which is why it is currently under close surveillance. This monitoring is facilitated by a network of seismometers and GNSS stations that measure ground movements and uplift.

Data analysis from GNSS over the past seven years has shown that between March and December 2022, the volcano’s flanks rose rapidly. By August 2023, this uplift remained stable. These findings were published in the journal Geophysical Research Letters.

A Precursor Signal Indicating an Eruption is Coming

It's important to remember that the uplift of a volcano's flanks is considered a precursor signal of an impending eruption. This indicates that pressure is building up inside the magma reservoirs feeding the volcano, similar to a pressure cooker without a safety valve. When the pressure exceeds a certain threshold—which varies from one volcano to another—the conduits open, allowing magma to rise to the surface, resulting in an eruption. Thus, while flank uplift is a sign that something is brewing, this data alone cannot determine if an eruption is imminent. That is why GNSS sensors are paired with seismometers, which can detect when the conduits open; the injection of magma that forces this opening generates small earthquakes.

For now, there is no indication that an eruption is imminent at Lengaï. However, the ground uplift should prompt authorities to remain vigilant.