The only volcano on Earth that spews black lava

Africa's Ol Doinyo Lengai volcano spews unusual carbonate-rich lava that is not red hot but black and viscous like motor oil.

Ol Doinyo Lengai is one of the strangest volcanoes on Earth, and indeed in the solar system. From a distance, the mountain looks unremarkable, but when you look into its northern vent, you will see that it is spewing a unique form of black lava, relatively cool and flowing like motor oil.

Located in the East African Rift, north of Tanzania, Ol Doinyo Lengai is the only active volcano known to erupt carbon-based lava, or natrocarbonatite lava. There is some evidence that volcanoes on Venus may also erupt natrocarbonatite lava, but on Earth, Ol Doinyo Lengai is the only active volcano.

Most volcanoes erupt lava rich in silicate minerals, which causes the lava to melt at temperatures exceeding 900°C. Ol Doinyo Lengai’s lava is relatively low in silicate but contains a lot of carbonate minerals, allowing it to remain liquid at just 540°C. The lack of silicate makes the lava extremely viscous. When an eruption occurs, instead of spewing red-hot lava, the mountain looks like it’s spewing black motor oil.

Given the viscosity of the lava, scientists were surprised that Ol Doinyo Lengai could erupt so violently. Explosive eruptions are common in other volcanoes because gas bubbles can get trapped in thick, viscous lava. Ol Doinyo Lengai can still erupt violently, with the liquid lava likely filled with dissolved CO2 and other gases, causing it to fizz like carbonated water.

Standing at 2,962 m tall, the volcano has two vents, but only the northern one is erupting. The most recent eruption began in April 2017 and is still ongoing as of March 2024.

In 2009, a team of volcanologists collected gas samples from Ol Doinyo Lengai to study the unique carbonaceous lava flows. They found that the composition of the gases was very similar to that of the gases emitted from mid-ocean ridges, despite Ol Doinyo Lengai being quite inland.

This led the team to conclude that the carbon-rich lava was produced by minerals melting in the upper mantle—the thick layer of rock just below the Earth's crust. "The chemistry and isotopic composition of the gases suggest that the CO2 originated directly from the upper mantle, beneath the East African Rift," said David Hilton, a professor of geochemistry at the Scripps Institution of Oceanography at the University of California San Diego and co-author of the 2009 study.

The East African Rift has been tectonically active for about 25 million years and remains one of the world’s most interesting geological hotspots. It is a giant crack in the African Plate that is pulling apart at a rate of a few millimeters per year. Over time, it could eventually tear Africa in two, creating a new ocean between East Africa and the rest of the African Plate. In addition to Ol Doinyo Lengai, the East African Rift is also responsible for many of the region’s towering mountains, including Mount Kilimanjaro and Mount Kenya.

Thu Thao (According to IFL Science )

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