Hazards

Volcanic Hazards

Location

Constructive plate margins

• Basaltic lava - hot and low viscosity so runny. Easily flows. Not violent but frequent and go for long time
• If underwater = magma rise to fill space from plates moving apart to form ocean ridge
• If on land = form rift valley so thin crust and magma able to break through
• Shield volcano

Destructive plate margins

• Andesitic and rhyolitic lava = cooler and more viscous (less runny). Erupt less but explosive
• Subduction zone - subducting plate melts and magma rises to surface. Forms blockages as viscous so increase in pressure then violent eruption
• Composite / stratovolcano

Hotspot volcano

• Away from plate margins
• 5% of all volcanoes are hotspot
• Shield volcano - gentle slopes

Primary hazards

Pyroclastic flow

• Hot gas, ash, tephra,
• High speed for a long distance
• Little warning due to speed - death, destruction

Lava flow

• Flow from a volcanic vent down side of volcano
• Speed and distance depends on steepness of slope and plate margin
• Most flows are slow so have time to evacuate

Gasses

• Carbon and Sulphur Dioxide
• Can cause acid rain

Pyroclastic and ash fallout

• Pyroclastic fallout = material ejected from volcano then falls back to ground. Mainly ash falls
• From pieces of ash to boulders (tephra)
• Can travel 1000s of km but heavier rocks deposited first

Secondary hazards

Lahar

• Mudflow - volcanic material foxes with water
• Quick flow and can travel for 10s of km

Acid rain

• Volcanic gasses react with water vapour in atmosphere
• Sulphur dioxide forms weak sulphuric acid

Magnitude and frequency

• Magnitude - measured on Volcanic Explosivity Index - graded 0-8
• Frequency - 100,000s of years vs months. Less frequent = larger magnitude = more damage
• Random vs regular - regular or dormant
• Predictability - regularity helps to predict eruptions. Monitor earthquakes, gas samples, etc

Prevention, preparedness, adaption

• Prevention…