Thursday, December 26, 2013

Nyiragongo


Africa's most active stratovolcano culminates at 3,470 metres over lake Kivu and the city of Goma on the Albertine branch of the great East African rift, where a new ocean may be in its early birth throes. Located in the Virunga volcanic field and national park (seehttp://tinyurl.com/ntwhof8) in the Democratic Republic of Congo, it is one of 8 active smokers in the field. The mountain sits at the intersection of several major faults, which allow the magma to rise from the mantle below. The extensional tectonics of the rift part the plate allowing the magma through.

The summit has a 2 kilometre wide caldera, that has had periods (including the present) of containing a long lived seething lava lake. Since the mountain's product is very fluid alkaline basalt, the convection patterns and overturns in the lake make for an ever shifting pattern of cooling black rocky crust and molten red lava. The lake existed continuously between 1894 and 1977, when it emptied in less than an hour as the crater walls fractured, engulfing several villages downstream. The lava is so fluid due to its low silica content that it can race down the steep conical sides of the mountain at up to 100kph. The flanks are littered with cinder cones. It was famously explored and studied by Belgian/French vulcanologist Haroun Tazieff in the early 70's (seehttp://tinyurl.com/m3b9oob)

It presents a serious hazard to Goma, and the 2002 eruption lava flows carved through parts of the city, including the airport runway, whose population was swollen with refugees from the endemic war that has raged in the Kivus since the 1990's. This led to serious disruption, as aid could not arrive by air until the runway was cleared. Lava flows also reached lake Kivu, prompting fears that it might cause its higly stratified waters to overturn, potentially releasing the CO2 in the saturated deeper layer and axphyxiating people and livestock, as happened at Lake Nyos (Cameroon) in 1982 (see http://tinyurl.com/qxnsx34)

It has erupted at least 34 times since 1882, sometimes continuously for years. The dense population in the area and the exceptional lava flow risk led to it being nominated a Decade volcano, and extensively studied and mapped from a hazards perspective. Ongoing conflict has made the required amount of study difficult.


Image credit: Matin Rietze
http://www.volcanolive.com/nyiragongo.html
http://www.atlasobscura.com/places/lava-lake-nyiragongo-volcano
http://www.photovolcanica.com/VolcanoInfo/Nyiragongo/Nyiragongo.html
http://www.volcanodiscovery.com/nyiragongo.html
http://ngm.nationalgeographic.com/2011/04/nyiragongo-volcano/finkel-text

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