Volcanic Hazards 🌋
What are the different eruptions?
Strombolian eruption
low level - small to medium eruptions
Strombolian eruptions are relatively mildly explosive, with a volcanic explosivity index of about 2 to 3.
They are named for the Italian volcano Stromboli
Strombolian eruptions consist of ejection of incandescent cinder, lapilli, and lava bombs, to altitudes of tens to a few hundreds of metres.
Plinian eruption
Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, the second layer of Earth's atmosphere. :
rhyolitic lava
The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions
According to the Volcanic Explosivity Index, Plinian eruptions have a VEI of 4, 5 or 6, sub-Plinian 3 or 4, and ultra-Plinian 6, 7 or 8.
Lava
basaltic lava
hottest and most common
Basaltic lava flows erupt primarily from shield volcanoes, fissure systems
Pahoehoe - As the smooth lava surface cools to turns to a dark gray color and becomes less fluid and more viscous, behaving more like a plastic substance than a truly liquid substance
rhyolitic lava
thick and slow
crystallising rocks such as granite
What are the hazards associated?
pyroclastic flow
ash cloud
falling rocks and volcanic bombs (tephra)
Vulcanicity
shield volcano - basic, fluid lava, gentle sides eg Mauna Loa
Dome volcano - acid, viscous lava, rhyolitic eg Puy, France
ash and cinder - formed from ash, cinder, steep sided, produce volcanic bombs
composite cones - pyramid shaped, layers of ash and lava - adesitic eg Mt Fuji, Japan
Calderas - build-up,removes core, opening is km in width and the caldera may be flooded into a lake
Nuee ardente
burning cloud
part of pyroclastic flow
Lava flows
slower and lower temp - viscous
faster and higher temp - fluid
Mudflows/Lahars
melt water
mud and ash follow river paths
fallout
settlements from ash clouds
Composite Volcanoes
converging, destructive boundary
subducting plate is molten due to friction
increased pressure causes lava to exert through
Hotspot Volcanoes
super heated radioactive magma swelling in the asthenosphere, which remains in situ
Types of volcano
Fissure volcano - gentle slope, diverging boundary
Shield volcano
gentle sloping slides
infrequent eruptions
frequent, runny lava eruptions
layers of solidified lava
layers of lava and ash
CASE STUDIES
Montserrat
causes - soufriere hills lies on a volcano which has been dorment for 300 years, lies on a subduction zone destructive boundary, north american subducts beneath carribean - both oceanic, subducting plate becomes molten increasing the pressure.
effects - pyroclastic flow, evidence of hot ash, 19 people died, only hospital destroyed , ash and tephra fallout, series of eruptions, 6000 evacuatuions
responses - british government referred £2,400 to each adult to help with relocation away from montserrat, british navy evacuated to barbados and UK, forced evacuation in the exlcusion zone, MVO montserrat volcano observatory, £20mil in aid
Iceland - Eyjafjallajokull
causes - sits on mid atlantic ridge, divergent boundary, Eurasian and North American plate, under a glacier, march 10 lava, april 14th pyroclastic flow and ash.
all planes were grounded, gas cloud and ash plume, magma broke through, local water supplies were contaminated with flouride, homes and roads were damaged, primary impacts - ash fallout destroying crops - no sales
responses - evacuations, face mask, deliberate breaching of embankments to allow floodwater to pass through, 800 people evacuated, flights were grounded