Volcanoes 4

Hazard vs risk

• Hazard: the shark

• Risk: probability of getting bitten

6 volcanic hazards

• lava flow

• ash fallout

• pyroclastic flows

• lahars

• sector collapse

• toxic gases

Lava flows

• slow

• not that dangerous

• can predict path

• mafic, low viscosity

• but very hard to stop

• dangerous to buildings, infrastructure, etc.

Fire fountaining

• happens if basaltic lava is gas rich

• when liquid falls on ground, may coalesce into lava flow

• causes Volcanic bombs

Ash fallout

• hot ash + gas ejected

• breathing in ash can be deadly

• total darkness

• roof collapse- causes most death

• hazard to aircraft

Pyroclastic flows

• avalanche of pyroclastic material, air, gas

• driven by gravity

• velocity 40-400kmh

what are pyroclastic flows caused by?

• usually the collapse of a volcanic column

• sometimes explosive collapse of lava domes

lava domes

• silica rich magma

• highly viscous

• steep-sided domes

• glow at night

• mt. unzen & montserrat

Dome collapse

• can cause pyroclastic flow to race down slop

• ex. unzen

Pyroclastic flows hazards

• usually stay in valleys

• can flow over ridges

• very fast moving

• can move even over water

Lahars hazards

• indonesian word for “volcanic debris flow”

• flow of water + loose volcanic debris

• prevalent at snow-clad and ice-clad volcanoes

• very hazardous esp. in valleys

• can travel far

Sector collapse hazard

• volcanic landslide

• debris avalanche ex. mt. st helens

• landslide triggered explosive eruption —> lateral blast

Volcanic Gases hazard

• highly acidic (pH1)

• toxic

• mostly H20, Co2, HCI, SO2, and HF

fumarole

openings or vents on volcano where volcanic gasses are released