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Why Does This Volcano Erupt Black Lava That Turns White?

Ol Doinyo Lengai, in northern Tanzania, erupts the coldest and runniest lava on Earth. It comes out black, and within hours or days it turns white as snow.

Ol Doinyo Lengai, a symmetrical grey volcano with a white summit, seen across a shallow stream near Lake Natron in Tanzania
Ol Doinyo Lengai from the shore of Lake Natron. The white streaks on its summit are not snow; they are lava that changed colour after it cooled.Photo: Clem23, CC BY-SA 3.0

The short answer

It is not made of the same thing as other lava.

Almost every volcano erupts molten silicate rock. Ol Doinyo Lengai erupts a carbonate melt called natrocarbonatite, and no other volcano is known to have done so in historical times.

  • 540–593 °CThe temperature of its lava, about half that of a typical basalt eruption.
  • Hours to daysHow long fresh black lava takes to turn white once it meets moisture in the air.
  • One volcanoThe only one on Earth known to have erupted this kind of lava in recorded history.

Black, then white

The colour change happens after the eruption.

The crater floor of Ol Doinyo Lengai, white and crusted, with tall grey and white hornitos and a dark band of recent lava crossing it
Inside the crater in 2007. The dark band in front of the spires is a recent flow; everything around it was once just as black.Photo: Pedro Gonnet, CC BY 2.5

  1. During the eruption

    Black or dark brown

    The lava pours out dark and glistening. It glows only faintly, dull orange or red, and only at night.

  2. Hours to days later

    White

    Its minerals absorb water from the air and react, turning the surface white. In rain, this can happen before the flow has even cooled.

  3. Within a few months

    Brown powder

    The white crust keeps weathering and breaks down into a soft brownish powder.

The coldest lava on Earth

Hot enough to burn. Too cool to glow.

Ordinary lava is so hot it shines yellow and orange in daylight. Lengai's lava is roughly 600 °C cooler, so it looks like flowing mud. It is also the least viscous lava known, and can run at 1 to 5 metres per second.

Eruption temperatures, from the U.S. Geological Survey.

A grey and cream piece of natrocarbonatite rock, about 4 centimetres across, from a 1963 lava flow of Ol Doinyo Lengai
Natrocarbonatite from a 1963 flow, about 4 cm across.Photo: James St. John, CC BY 2.0

What it is made of

Natrocarbonatite, a lava made of salts.

Natrocarbonatite is a carbonate lava rich in sodium and potassium. Those carbonates melt at far lower temperatures than silicate rock, which is why the lava is so cool and so runny, and why it reacts so quickly with water.

Most volcanoes

Molten silicate rock, around 1,000 °C or more. Cools into dark basalt or andesite that stays dark.

Ol Doinyo Lengai

Molten sodium and potassium carbonates, around 550 °C. Erupts black and weathers to white.

Aerial view of the summit of Ol Doinyo Lengai, with a white crater floor and white streaks of altered lava running down its dark flanks
The summit from a light aircraft in February 2006, before the 2007 eruption.Photo: Wcalvin, CC BY-SA 4.0

From the air

Snow on the Equator? Not quite.

The volcano sits less than 3° south of the Equator, where it never snows at this height. The white crater floor and the streaks running down its slopes are old lava flows that have changed colour.

Where on Earth

On the floor of the East African Rift.

Ol Doinyo Lengai rises from the Gregory Rift, the eastern branch of the great crack where Africa is slowly pulling apart. Lake Natron lies 16 km to the north.

The globe turned to East Africa, with the eastern and western branches of the East African Rift drawn as dashed lines and Ol Doinyo Lengai marked Eastern branch Western branch Lake Victoria Ol Doinyo Lengai
The two branches of the rift, drawn by hand on the SeekGlobe globe.
Satellite image of Ol Doinyo Lengai seen from above, a ribbed cone with a small summit crater, beside the parallel ridges of the rift
From orbit in 2009, after the explosive eruption. The ridges on the left are the faulted wall of the rift.Image: NASA Earth Observatory, Robert Simmon, public domain
  • 2,962 mSummit height, more than 1,800 m above the rift floor
  • 2.76° SLess than 310 km south of the Equator
  • 16 kmTo the southern shore of Lake Natron
  • Mountain of GodIts name in the Maasai language
Ol Doinyo Lengai as a distant cone above the forested rim of Empakaai Crater and its lake, in the Tanzanian highlands
Lengai, the pale cone on the left, seen across Empakaai Crater in the Ngorongoro highlands.Photo: Daniel Msirikale, CC BY-SA 4.0

Its neighbour

At its foot lies a lake that turns red.

Lake Natron is shallow, hot and so alkaline that few animals can live in it. Salt-loving microorganisms colour its water red, and its salt flats are the nursery of East Africa's flamingos.

  • pH above 12, from sodium carbonate washed in from the surrounding rocks
  • Often above 40 °C, and up to 60 °C in the shallows
  • 75% of the world's lesser flamingos are born here

An active volcano

It is still erupting.

  1. 1880s

    The first recorded eruptions. Activity is noted many times through the twentieth century.

  2. 1983

    A long phase of activity begins, with lava flows filling the summit crater on and off for decades.

  3. 2006

    A lava flow spills onto the western flank.

  4. 4 September 2007

    A large explosive eruption begins. Its ash column rises about 3 km, a new crater forms and three villages are evacuated.

  5. 2008

    Lava begins to flow again in the new crater.

  6. Since 2016

    Seismometers and GPS stations monitor the volcano.

Quick answers

Questions people ask about Ol Doinyo Lengai.

Why does Ol Doinyo Lengai have black lava that turns white?

Its lava is natrocarbonatite, made of sodium and potassium carbonates. It erupts black or dark brown, then absorbs water from the air and reacts chemically, turning white within hours to days.

What is the coldest lava in the world?

The natrocarbonatite of Ol Doinyo Lengai in Tanzania, which erupts at about 540–593 °C. Typical basalt lava, like Kīlauea's, erupts at around 1,160 °C.

Is the white on Ol Doinyo Lengai snow?

No. The volcano lies less than 3° south of the Equator. The white on its summit and slopes is weathered lava.

Where is Ol Doinyo Lengai?

In the Arusha Region of northern Tanzania, in the East African Rift, about 16 km south of Lake Natron and 120 km northwest of Arusha.

The short version

Ol Doinyo Lengai erupts black lava that turns white, because it is made of carbonate salts instead of molten rock.

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