Volcanic Hazards

Volcanic hazards By Anne - Sophie

Pyroclastic flows •Pyroclastic flows are liquid masses of rock fragments that can move quickly. •They can form in several different ways. They can form when there is a volcanic eruption, a lava flow or can be a result of a gravitational collapse. •These flows contain water and gas from the eruption, water vapor from melted snow or ice, air and rock fragments.

T h is im a g e sh o w s th e fo rm a tio n of p yro cla stic flo w s d u rin g 1980 e ru p tio n o f M o n t S tH e le n s.

Lava flows Hawaiian The lava flows are the least volcano lava dangerous of all the flows processes in a volcanic eruption. • How far a lava flow will go depends on the temperature of it and of the silica content or the slope of the land. A cold lava flow or a lava flow that has a high silica content will not travel far. • Lava flows don’t move very fast so people rarely get killed by them but they can cause In theserious 1980’s, injuries the town as of they Kalapana are in Hawaii was destroyed by lava flows very as they cars, 550 burt homes, buildings and vegetation. hotburied (between degrees C and 1400 degrees C).

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LAHARS • Lahars are similar to pyroclastic flows but they contain more water. • Lahars can form in many different ways. They can form from debris avalanches, from pyroclastic flows and surges, from natural barrage failure (a lava flow barrage or crater lake) and from rainfall on loose material such as ash. • They have a wide range of speeds changing from 1 m/s to 40 m/s and they can travel very far. • Lahars are extremely dangerous because they can undercut banks and the houses on those banks will be destroyed. They can bury and destroy roads and bridges. At Nevado del Ruiz in Colombia lahars destroyed the entire city. •

Volcanic gases An erupting volcano will release gases into the atmosphere.

• • 90% of all gases made by volcanoes is water vapor. • Some volcanic gases are toxic, which means they cause death if they’re breathed in. • Volcanic gases can be produced when water is heated by magma. They can escape from other volcanic hazards such as pyroclastic flows, lahars and lava flows. • Acid rain can be formed when high concentration of these gases are leached out of the atmosphere. • Harmful concentrations of volcanic gases usually do not extend further than 10km away from the volcano.

• B u t w h e n a vo lca n o in V a n co u ve r in C a n a d a e ru p te d in 1 9 1 2 , a cid ra in d a m a g e d clo th e s th a t w e re d ryin g o u tsid e o n a lin e 2 0 0 0 km a w a y fro m th e vo lca n o .

Ash clouds •The cloud that is often seen above an erupting volano is made of ash and steam. •Ash clouds are created when solid rock and magma separates onto particles during an eruption. •The particles can be carried many miles away settling a thick cloud across the landscape. •Volcanic ash by itself is not very dangerous. But with pyroclastic flows or other volcanic hazards, it can be very dangerous as it can destroy buildings and vegetation.

Volcanic bombs •A volcanic bomb is a mass of molten rock formed when a volcano ejects fragments of lava during an eruption. They cool into a solid before they reach the ground. •Volcanic bombs can be ejected many kilometres away from the erupting volcano. •They can be very small (65mm of diameter) or very large (up to 5-6m of diameter). •They can cause serious injuries and death to people in a zone of an erupting volcano. •At Galeras volcano in Colombia in 1993, six people near the erupting volcano were killed by lava bombs.