Saturday, December 17, 2005

Coolest lava in the world

Ol Doinyo Lengai, which translates to “Mountain of God”, is in northern Tanzania, fifty kilometres south of the Kenyan border. It is a volcano along the African Rift Valley that has small eruptions multiple times per year, but has not had a major eruption since 1967.

The top of the mountain is crowned with a ring of spires in the crater, 2000 metres above the surrounding grass plains, and there is a white stain down the south western side where lava has overflowed the crater in recent years.

The lava is chocolate brown when it is molten, at around 400 degrees Celsius. This is just hot enough to glow a dull red in the dark, and is the coolest type of lava of all the worlds’ volcanoes. The lava which issues forth from Ol Doinyo Lengai is a natrocarbonatite lava which, unlike common basalt lavas, is made up almost exclusively of sodium carbonate, giving it the lowest viscosity of any lava, like that of hot melted chocolate. Ol Doinyo Lengai is the world’s only active carbonite volcano.

Once the lava has been hurled out of the ground it flows in waves and rivulets towards the crater rim, and slowly cools. As it cools it starts to skin over, and with the hotter lava below the surface still flowing the top cracks up and slowly moves in crumpled file. The cooled edges set to a chalky white plaster in intricate patterns, and the entire lava flow crackles like a cooling engine after a hot drive for days.

When I was on the mountain a week ago, it had recently erupted and the lava flows were still cooling, but set enough to walk on the crust without breaking through. Near the centre of the crater was a hole emitting heat waves and cavernous wave sounds. A peek into the hole revealed a churning mass of molten rock sloshing around as if in a large cauldron, ready to spew at any moment, which inspiring a quick retreat on my part.

A knowledgeable guide who takes people up the mountain is Bura Ammy, based in Ngarasero village near Lake Natron. He charges $50 per trip. The standard route up the mountain is a four hour hike on a path up the eastern face.

My group ascended the mountain up the rarely climbed and steeper west face, taking a day and a half up grass slopes and a beautiful final curving ascent to the crater on a lava capped knife-edge ridge. We parked at the base of the mountain, GPS co-ordinates S 02 45 421, E 35 57 303, in a large river bed and climbed the grass embankment dead ahead up to the curving ridge, with a camp halfway up at S 02 45 663, E 35 55 938.

To get to the mountain, drive the Ngorongoro Crater road until Mto Wa Mbu, then head north for 60 km past Engaruka before taking the left fork towards Lake Natron and Ngarasero. The road requires a 4WD or high clearance vehicle.

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