Today in Geological History; 17th January – Northridge and Nyiragongo

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The Northridge Earthquake 1994

At 4.30 am local time, the residents of the San Fernando Valley region of L.A were awoken by a shallow magnitude 6.7 earthquake. It is estimated to be one of the most costly natural disasters the state has faced causing up to 40 billon US dollars and killed over 60 people.

The earthquake struck along a fault line which was previously unknown off, the Northridge blind thrust fault. It produced the highest ever recorded ground motions at the time and literally threw many buildings off their foundations. It sparked greater mapping of the L.A fault systems so places could be better prepared for further destructive quakes in the future.

Some of the most dramatic pictures of the destruction came from the many freeways and interstates which suffered structural failure and/or collapse.

One of the most unusual outcomes of this earthquake was the outbreak of coccidioimycosis, or more commonly known as Valley fever. There were over 200 cases reported in the weeks after the quake and 3 fatalitites. Valley fever is a respiratory disease brought on by airborne spores of fungus. It is thought that landslides caused by the earthquake sent a cloud of the spores in the the air which the wind carried to surrounding areas.

 

Nyiragongo 2002

After months of increased activity at the stratovolcano in the DRC, a 13 km fissure opened along the southern flank of Nyiragongo in a matter of hours. The fissure reached all the way down to the town of Goma and Lake Kivu.

Over 400,000 people were evacuated from Goma and the surrounding area, many across the border to Rwanda. Despite these efforts 147 were killed, mainly from asphyxiation and some from collapsing buildings from volcanic tremors. About 4,500 buildings were destroyed in Goma and two-thirds of its airport left unusable as lava devoured the run ways.

When the flows reached Lake Kivu, due to the high gas emissions, a new fear was put in place. Similar to events at Lake Nyos 1986, there was a chance that the high emissions of carbon dioxide and methane could be stored in the lake waters and released lethal limnic eruption. Although this was not the case there have been numerous cases in the area around Nyrigongo of particularly children dying from asphyxiation due to random degassing of the volcano. An experimental syphon was put in place in 2001 to try to limit the amount of gas in the bottom waters, but it was not untill 2004 when an energy company wanted to harness the gas as a resource, did any really system come in to place to limit the risk of limnic eruption.

Nyrigongo is one of the 17 decade volcanoes, ones believed to pose greatest risk to human life. Caused by a mixture of rifting and hot spot activity, unlike many volcanoes of its kind, its lavas have an extreamly low silica content. Predominately melilite nephelinite, instead if more common more common basalts, it is extreamly fluid and can reach speed on average of 100 km/ph. It has also had a near constantlty active lava lake giving us the gentle reminder that it can fatally burst to life at any time.

 

1. Http://dart2.arc.nasa.gov

2. http://m.utsandiego.com/news/2014/jan/15/northridge-earthquake-anniversary-20/

3. http://www.unisdr.org/2006/ppew/info-resources/ewc2/UK/galerie/pg000057.htm

4. http://www.geo.arizona.edu/geo5xx/geos577/projects/kayzar/html/nyiragongo_volcano.html

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