Volcanic eruption
Mechanism of destruction
Gradual or explosive eruption, ejecting hot ashes, pyroclastic
flows, gases and dust. Blast pressures may destroy structures, forests and
infrastructure close to the volcano and noxious gases may kill. Hot ash falls
for many kilometers around the volcano, burning and burying settlements. Dust
may carry for long distances, and fall as a pollutant on other settlements
further away. Molten lava is released from the volcanic crater and may flow for
many kilometers before solidifying. The heat of lava will burn most things in
its path. Snow-capped volcanoes suffer ice-melt causing debris flows and
landslides that can bury buildings. A volcanic eruption may alter the regional
weather patterns, and destroy local ecology. Volcanoes may also cause ground
upheaval during their formation.
Parameters of severity
Volume of material ejected. Explosiveness and duration of
eruption, radius of fall-out, depth of ash deposit.
Causes
Ejection of magma from deep in the earth, associated with mantle
convection currents. Tectonic processes of continental drift and plate
formation.
Hazard assessment and mapping techniques
Identification of active volcanoes. Volcanoes readily
identifiable by their topographical and geological characteristics. Activity
rates from historical records and geological analysis. Seismic observation can
determine whether a volcano is active.
Potential for reducing hazard
Lava flows and debris flows may be channelled, dammed and
diverted away from settlements to some extent, by engineering works.
Onset and warning
Eruption may be gradual or explosive. Seismic and geochemical
monitoring, tiltmeters, and mudflow detectors may be able to detect build up of
pressure over the hours and days preceding eruption. Mud flow detection,
geotechnical monitors and tiltmeters are some of the monitoring strategies
available. Evacuation of population away from volcano environs is often
possible.
Elements most at risk
Anything close to the volcano. Combustible roofs or buildings.
Water supplies vulnerable to dust fall-out. Weak buildings may collapse under
ash loads. Crops and livestock are at risk.
Main mitigation strategies
Location planning to avoid areas close to volcano slopes being
used for important activities. Avoidance of likely lava-flow channels. Promotion
of fire-resistant structures. Engineering of structures to withstand additional
weight of ash deposit.
Community participation
Awareness of volcano risk. Identification of danger zones.
Preparedness for evacuation. Fire-fighting skills. Taking shelter in strong,
tire-resistant
buildings.
