Volcanoes

Shield

Wide, gently sloping sides, basic lava, central vent, acidic lava, form at hotspots

Cinder Cone

Built of ejected lava fragments(tephra), small, steep slopes, form near larger volcanoes

Acid Dome

Highly acidic, convex steep sides, plug or spine forms, e.g. Mont Pelee

Caldera

Hollow caused by the collapse of a composite cone

Composite/Strato Volcano

Alternating eruptions of lava and ash, usually acidic, e.g. Mount Etna, Fujyama, St Helens

Eruption Type

Icelandic, Hawai’ian, Strombolian, Vulcanian, Plinian, Pelean

Fissure

Divergent boundary, basic lava, very fluid

Intrusive vs Extrusive

Intrusive → doesn’t reach the surface

Extrusive → fumaroles, mud volcanoes, geysers

Explosive vs Effusive

Explosive → acid lava, destructive, severe environmental and climatic effects

Effusive → basic lava, constant outpouring of lava onto the ground

Magnitude

VEI, Volcano Explosivity Index, measured by ejecta volume, logarithmic

Lava Type

Basic

• Relatively safe

• Low viscosity, 1200°, runny

• Lower silica content

• Shield/Fissure

• Hotspots/divergent boundaries

• Straight from mantle

Acid

• Much more dangerous

• Viscous, 800°

• Higher silica content

• Composite cones/Acid domes

• Destructive/subduction boundaries

Signs of Volcanic Processes

• Eruption history

• Volcanic gases

• Heat and hydrothermal activity

• Earthquakes

• Ground deformation

Volcano Alert System Levels

0. Background level, no activity

1. Slight unrest, 4km exclusion zone

2. Elevated unrest

3. High unrest, exclusion zone 6km

4. Eruption imminent

5. Life-threatening eruption

Lava Flows

Heimay, Iceland, 1973 → water slows flows

Kilauea 1940s → bombed

Barriers, feeder tube blocking, diversion

Gas Monitoring

Samples collected from fumaroles and active vents, remote sensing techniques, can indicate volcanic activity

Hazard Mapping

Volcanoes give so much warning, maps can be drawn up of predicted impacts

Why do people live in volcanic areas?

fertile soil, ancestral ties, geothermal power, tourism industries

Who is most vulnerable?

• poor

• elderly

• proximal regions

• previous impacts

• no living memory

• isolated areas

Lake Nyos, Cameroon

21st August 1986, CO2 build up at the bottom of a caldera was pushed out by an earthquake-triggered landslide, 1,700 people died

Surface Tilting

Change in land surface angle due to pressure changes, tiltmeter

Earthquake Monitoring

Harmonic tremor indicates volcanic activity