Sunday, November 7, 2010

Ol Doinyo Lengai: An Active Tanzanian Volcano with a Twist

The native Maasai people regard this mountain as the "Mountain of God" which is what Ol Doinyo Lengai translates to in the Maa language.  Ol Doinyo Lengai is a stratovolcano that is part of the Great Rift Valley located in Eastern Africa where the Nubian Plate and the Somali Plate are diverging (moving away) from each other.  The geology of this system is pretty spectacular but I am focussing on Ol Doinyo Lengai because it is currently the only known ACTIVE natrocarbonatite volcano in the world.

Satellite image of Ol Doinyo Lengai aquired July 16, 2004 while the landscape still showed effects of effusive eruptions.  Recent lava flows (white/beige areas) are days to weeks old.  
Most lavas are rich in silicate minerals (minerals containing silicon and oxygen), hence most of the earth's crust is made up of silicate minerals.  However the natrocarbonatite lava that erupts from Ol Doinyo Lengai are rich in rare sodium and potassium carbonate minerals.  The lava is erupted at low temperatures (500-600 degrees Celcius), due to these low temperatures (the lowest temperature lava on Earth) the erupting lava appears black in the sunlight unlike other lavas which have that characteristic red glow.  Natrocarbonatite lavas are much more fluid that silicate lavas and flow almost as fast as water.  When the minerals in the lava react with moisture in the atmosphere they undergo rapid weathering causing the erupted black lava to quickly turn a grey white color within a few hours.  The resulting volcanic landscape is unique from any other volcanic landscape in the world.  The last known eruptions were in 2007/2008.

Ol Doinyo Lengai 1966 eruption
Carbonatites contain niobium, a metallic element used in the production of steel alloys, superalloys, and superconducting alloys.  The unique properties of niobium make it ideal for construction of jet engines, rocket systems and airframes.  Carbonatites may also contain tantalum (used as a capacitor in electronic equipment and as a substitute for platinum), uranium, thorium, copper, iron, titanium, vanadium, barium, fluorine, zorconium, anomalous concentration of RRE (rare earth elements) and other rare elements.  Some of these elements are of economic importance for obvious reasons and therefore carbonatites are valuable resources.

Industrially important minerals associated with some carbonatites are apatite, barite and vermiculite.

Lave appears black and very fluid when it erupts

Some sources:
Ol Doinyo Lengai (Wikipedia)
Carbonatite (Wikipedia)
Under the Volcano: Roger Mitchell's Geological Research has Economic Implications for Canada and Beyond (AGORA Online)