Volcanic hazards Flashcards
(24 cards)
Where do volcanoes usually occur?
destructive and constructive plate boundaries however some can form over hot spots above magma plumes
what is the nature of volcanoes formed at constructive margines?
basaltic lava (hot, low viscosity). eruptions of basaltic lava are frequet ad long lasting but not very violent.
if plate margin is underwater, magma rises to fill space left by parting plates forming ocean ridges, on land, ridge valleys form and as they are pulled apart they are thinned, and magma is able to break through the surface.
what is the nature of volcanoes formed at destructive margines?
andesitic and rhyolitic lava are formed here, they are cooler and more viscous than basaltic lava. eruptions with this lava are intermitent and short.
formed at subduction zones where the plate pulled beneath the other andthe melting plates forms magma which rises to the surface forming a volcano. as the lava is viscous, blockages are are made which builds up pressure causing eruptions.
what type of volcanos and what lava form over hot spots?
basaltic lava, shield volcano
pyroclastic flow/nuee ardente
mixture of super heated gas ash and volcanic rock often travels over 80km/h nd may travel tens of km. due to their speed they provide little warning
lava flow
low viscosity lava can travel up to 10mph
Volcanic gases
e.g. co2 and sulfur dioxide. often undetectable e.g. Carbon dioxide was blamed for the deaths of around 1700 people in Cameroon, west Africa, in 1986 when a massive release of gas occurred from Lake Nyos, a volcanic crater lake.
ash and pyroclastic fallout
pyroclastic and ash fallout is tephra that has been ejected during eruption that falls back down.
consists of material of a range and can travel thousands of km e.g. ash cloud
lahars (mudflows)
occur when volcanic material mixes with water e.g. mountain snow melt or rainfall, can bury or destroy inhabited areas
acid rain
volcanic gas can react with water vapour in atmosphere and fall as acid rain e.g. sulfur dioxide reacts with water to form weak sulfuric acid. Can corrode shit
tephra
rock fragments and particles ejected by a volcanic eruption.
explain the magnitude and frequency of earth quakes
magnitude can be measuredon scaale of 0-8 on the volcanic explosivity index. huge range
frequency: some every 100,000 years and some every few months, generally the less frequent has greater magnitude.
some erupt in regular intervals and some are random. Kowing the regularity of the erutions helps to predict.
describe shield volcanos
no steep relief, basaltic lava, low in silica, gas bubbles. freely expand as magma rises resulting in free flowing eruption.
temps between 1100and 1250
example: mauna loa, hawaii
describe stratovolcano/composite
steep relief, triangular
viscous, adesitic and rhyolitic lava are rich in silica so gas bubbles struggle to expand, leading to build up in pressure and a violent eruption. temps between 600 and 1000 and tend to be more of a hazard to property than life.
example: mount pinatubo, the philippines
how is explosivity of an eruption event measured?
volcanic explosivity index = logarithmic scale 0-8
basaltic lava silica content, temp, viscosity and gas content, products, eruption interval, tectonic setting, processes, hazardous?
silica = 45-50%
temp = 1000
visc and gas = low gas, runny
interval = continuos like hawaii
tectonic setting = oceanic hotspots and constructive margins
processes = dry partial melting of upper mantle/lower lithosphere.
andesitic lava silica content, temp, viscosity and gas content, products, eruption interval, tectonic setting, processes, hazardous?
silica = 55-60%
temp = 800
visc and gas content = sticky, intermediate gas
products = tephhra,ash, gas, sticky lava
eruption interval = decades or centuries
setting = destructive including ocean/ocean
processes = wet partial melting of subducting oceanic crustcontaaminated by water and other material as it rises.
hazardous? very
rhyolitic lava silica content, temp, viscosity and gas content, products, eruption interval, tectonic setting, processes, hazardous?
silica = 65%
temp = 700 degrees
visc and gas = sticky, high gas
products =. pyroclastic flows, gas and volcanic ash
interval = millenia
tectonic = continental hotspots and continental/continental margins
processses = in situ melting of lower continental crust, most magma cools before it reaches the surface
hazardous? yes but rare
Mount Nyiragongo (Jan 2002) primary impacts
-The lava flow and earthquakes triggered by volcanic activity destroyed 12,500 homes. (social)
-At least 15% of Goma was covered by lava, with one-third of the city being destroyed. (social, economic, political)
-80 per cent of the airstrips at Goma International Airport were covered in lava. (social, economic)
The majority of the 147 deaths were caused by carbon monoxide poisoning from the eruption (this continues to be a threat today). (social, environmental)
The lava flows destroyed crops, and many livestock were killed.
There were drinking water shortages due to the disruption caused to main water supplies.
350,000 people were evacuated from their homes to avoid the lava, many to neighbouring country of Rwanda
Mount Nyiragongo (Jan 2002) secondary impacts
Acid rain fell due to the reaction of volcanic gases in the atmosphere, damaging farmland.
Refugee camps were overcrowded as many of the 120,000 homeless could not afford to rebuild their homes.
Overcrowding and poor hygiene conditions led to the spread of cholera in refugee camps.
The economic impact of the eruption was felt across the region as businesses and shops were destroyed.
After people evacuated Goma, looting broke out.
Short term response
Approximately 350,000 people were evacuated from the vicinity of the volcano. The pace of evacuation was slow until plumes of smoke from the volcano were visible.
The evacuation plans were very limited, many residents had not experienced a volcanic eruption. This led to people heading to the volcano to see the eruption, slowing the evacuation process. As a result, around 50,000 inhabitants of Goma became trapped between two lava flows.
The damage to Goma’s airport disrupted the arrival of international aid.
The United Nations sent 260 tonnes of food to the affected area within a week of the eruption. Families received 26kg of rations each.
UK Oxfam sent 33 tonnes of water-cleansing equipment for 50,000 people in refugee camps. The £150,000 package mainly contained water purification kits to provide clean water for drinking and sanitation. This stopped people from drinking contaminated water from Lake Kivu and helped to reduce the spread of cholera in some refugee camps.
The World Health Organisation and Médecins Sans Frontières (MSF) conducted emergency measles vaccinations to 28,000 children to stop the spread in refugee camps.
Refugee camps, made from scrap metal, were set up to house the displaced populations.
Communication was poor between agencies and refugees. Many people began to travel back to the affected area within a few days to collect belongings and supplies from their homes, even though it was not yet safe. Some walked across hot lava that was not yet solidified and cooled to get home.
Governments around the world gave $35 million in aid to support refugees.
long term response
Preparation
Thirty new signs that detail the early warning signs of a volcanic eruption have been put up in high-risk areas. Evacuation routes have also been mapped.
Communities and schools now have evacuation drills to prepare people for future eruptions.
Leaflets have been distributed to vulnerable people containing information on evacuation routes, shelters and advice on what to do in an emergency.
The International Federation of Red Cross and Red Crescent Societies has expressed a need for more funding to release further educational materials to communities in need.
Planning
Officials have been retrained and provided with evacuation plans; each has a designated community to support.
Community officers have been trained to relay information to vulnerable communities if an eruption occurs.
Prediction
Knowledge from similar volcanoes has encouraged vulcanologists to measure carbon dioxide emissions from the volcano and within Lake Kivu to predict if levels will become lethal (as people can die from carbon dioxide poisoning).
An observatory for the volcano, The Observatoire Volcanologique de Goma, constantly monitors the volcano.
The large lava lake in Mount Nyiragongo is visible from above, so its levels can be carefully monitored to see if an eruption is impending.
Search
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Mt Nyiragono background info
Located in the DRC
located on a divergent plate boundary where the African plate is being pulled apart into the Nubian plate (east) and Somali plate (west), causing lava to rise between. Eruptions are non-explosive as the lava is basaltic, with a low viscosity, which means it is runny and fast flowing (up to 37 mph).
