Hazards Of Volcanic Activity

• Some volcanoes erupt wihtout significant violence but some can be enormous.
• When Krakatoa erupted in Indonesia in 1883, it was heard 4,000km away in Australia. The blast destroyed the island itself and 36,000 people drowned in the 40m tsunami that swept the coasts of the neighbouring islands.
• Tsunamis are huge waves generated by either volcanic eruptions or earthquakes which can travel across oceans at great speed resulting in devastation of coastal regions.
• The 2004 Boxing Day Tsunami was the result of a submarine earthquake off Sumatra, rather tha a volcanic eruption.

• LAVA rarely threatens life as its flow is predictable but it does destroy propertyby swamping buildings or starting fires.
• The frequent lava that flow down the slopes of Mount Etna has destroyed cable car stations and overwhelmed houses, hotels and restaurants. The same events buried rich farmland burning vines and orchards.
• A lava flow in 1990 from Kilauea, Hawaii gradually burned houses and buried the village of Kalapana. Over a three year period the flow gradually covered 181 houses, much local arable farmland and crossed the main coast road.

PRYOCLASTIC FLOWis the term used to describe a variety of solid materials ejected from volcanic activity other than lava.

• Nuee ardentes are spectacular and potentially lethal mixtures of superheated gases, hot ash and rock fragments that flow at enormous speed down the side of some volcanoes.
• EXAMPLE: volcanic ash from the Mount St. Helens eruption of 1980 created spectacular sunsets for months,

• VOLCANIC GASES are often hot and toxic.
• EXAMPLE: When the town of Pompeii was uncovered centuries after it had been buried by an eruption of Mount Vesuvius in Southern Italy, the buried inhabitants were found with their hands at their mouths or throats suggesting mass suffocation.
• EXAMPLE: One August night in 1986 at Lake Nyos, a crater lake in cameroon, over 1,700 people died of carbon dioxide poisoning. A heavier than air cloud, rich in carbon dioxide, was expelled from the volcanic lake and swept down adjacent valleys. Up to 23km away people died in their sleep as the cloud replaced the air. 

• Volcanoes often bulge as magmatic pressure builds up beneath them.
• This deformation of steep slopes may cause landslides.
• The devastating eruption of Mount St Helens in 1980 followed the collapse of the north side of the mountain, in the largest landslide ever recorded on film.
• It is currently feared that volcanic activity in the Canary Islands might cause a hiugh landslide to generate an enormous tsunami, with devastating consequences especially on the densely populated eastern seaboard of the USA.

• These are volcanic mud flows.
• When hot ash mixes with river water or with heavy rain, which can be triggered by eruptions, it can flow as thick hot mixture at great speed, flooding valleys, burying the environment and drowning people.
• EXAMPLE: In1985- eruption of Nevado del Ruiz- resulted in a lahar flowing at 100km per hour through the town of Armero, some 50km from the volcano. In one night over 20,000 of the town's 23,000 inhabitants perished, buried by hot mud.

• These are floods causes by volcanic eruptions beneath ice sheets or glaciers.
• EXAMPLE: in 1996, the Grimsvotn volcano in Iceland erupted beneath the Vatnajokull icefield. Just hours after emerging from the ice sheet, the jokulhlaup had a discharge of 5,000 cumecs , which increased to 15,000 within 90 minutes. Two large bridges were destroyed, aong with a section of the main coastal highway. On the glacier itself, the collapse and subsidence associated wiht the eventleft an ice canyon 6km long with an average depth of 100m.