Ol Doinyo Lengai

Ol Doinyo Lengai

Basic FactsLocated north of Tanzania and part of the East African Rift volcanic system.It is classified as a stratovolcano.Has a summit elevation of 2890m.Known as the home of God locally.Only active volcano known to erupt carbonatite lava.

TanzaniaA country inEast Africabordered byKenyaandUgandato the north,Rwanda,Burundi, and theDemocratic Republic of the Congoto the west, andZambia,Malawi, andMozambiqueto the south. The country's eastern border lies on theIndian Ocean

Geological Background The cone-building stage of the volcano ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra eruptions and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Nature of EruptionUnlike other volcanoes, which spew silica-rich basalts, Ol Doinyo Lengai is the only active volcano on Earth that erupts with a carbonatite, a type of igneous rock rich in carbonates such as calcite and dolomite. Usually carbonatites are intruded into other formations and rarely reach Earth's surface as eruptions.

Carbonatite LavaCarbonatite is literally the coolest lava on earth, erupting at 500-600 degrees Centigrade.Freshly cooled flows in the crater of Ol Doinyo Lengai are black but soon turn white because of chemical reactions that occur as the lava absorbs water. In rainy weather, this color change can occur before the flows are cold. Within a few months of erupting, lava flows turn into a brown powder due to water absorption.Contains very little silica as compared to the more common basaltic magma.

Videoshttp://www.youtube.com/watch?v=3Ck4q1d2-XEhttp://www.youtube.com/watch?feature=endscreen&NR=1&v=JjLDfesA0N0

Pyroclastic flowsAlso known as nuees ardentes, these are responsible for most of the dangers caused.Pyroclastic bursts surge downhill with a heavy load of lava fragments, crystals, ash, pumice and glass.As the surrounding areas of Oldinoyo Lengai are sparsely populated, pyroclastic flows are more dangerous to livestocks and properties as compared to humans.Water contamination

Air-fall Tephra

Lava FlowsOn 30 March 2006 some quite powerful activity began in the summit crater, which led to the movement of people from nearby villages, and to news headings and stories such as Villagers flee as volcano erupts (IPP Media 1 April 2006) The only active volcano in Tanzania burst into flames at least six villages occupied mostly by nomadic Maasai herdsmen were rocked by red-hot landslide, spewing scalding fumes and lava covering a big area on the mountain slopes (AfricaNews 26 April 2006)

TremorsVolcanic activity in the mountain caused dailyearth tremorsin Kenya and Tanzania beginning on July 12, 2007. The latest to hit parts ofNairobicity was recorded on July 18, 2007 at 8.30pm (Kenyan Time). The strongest tremor measured 6.0 on theRichter scale. Geologists suspected that the sudden increase of tremors was indicative of the movement of magma through the Ol Doinyo Lengai.

Volcanic GasesReleased by explosive eruption, carbon dioxide (CO2) is the second-most abundant gas that issues from Oldoinyo LengaiOdorless, invisible, and heavier than air, CO2 accumulates in low-lying areas, where it may reach toxic concentrations. Asphyxiation occurs without warning. Fortunately, winds disperse the gas safely across most of the summits active crater.

Problems Eruptions life pretty difficultwhen the ash and rocksrained downon nearby Masai villages like Naiyobi, seen in this image. The villages were evacuated for a while. When people returned they found their water fouled and many grazing lands unusable -- a hard blow for people who depend on their cattle for their living.

ProblemsCurrently, the volcano has no monitoring of earthquakes, deformation or gases.And the rainy season which is coming up for May through October, rains will cause and trigger mudflows and flash floods.

Hazard ManagementForeign Technical AssistanceDisaster Management LevelsVillage level evacuationLack of monitoringSparse population to controlThe government of Tanzania requested technical assistance from the United States on Dec. 24, 2008, to help conduct a preliminary hazard and risk assessment of the volcano. Three scientists travelled to Tanzania Jan. 10 - Jan. 28, 2009, as part of the Volcano Disaster Assistance Program (VDAP), a 22-year collaborative partnership between the U.S. Geological Survey and the U.S. Agency for International Development's (USAID) Office of Foreign Disaster Assistance (OFDA).

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EffectivenessBibliographyhttp://my.opera.com/nielsol/blog/crater-highlands-tanzaniahttp://en.wikipedia.org/wiki/Ol_Doinyo_Lengaihttp://www.volcanodiscovery.com/lengai.htmlhttp://dsc.discovery.com/earth/slideshows/tanzania-volcano/ol-doinyo-lengai-07.htmlhttp://www.usgs.gov/newsroom/article.asp?ID=2159http://www.tanzania.go.tz/government/disaster.htm#villhttp://blogs.stlawu.edu/lengai/activity-2008/http://ngm.nationalgeographic.com/ngm/0301/feature2/http://en.wikipedia.org/wiki/Tanzania