Thursday, May 18, 2006

Facts about volcano eruptions

Lava streamed down the slopes of Indonesia's Mount Merapi on Tuesday and vulcanologists say the nearly 3,000 metre (10,000 feet) volcano is in its final eruption phase.

Here are some of the major hazards to people and the environment from a volcanic eruption:

VOLCANIC GASES - The most dangerous gases released during an eruption are sulphur dioxide, carbon dioxide and hydrogen fluoride. High concentrations of sulphur dioxide injected into the atmosphere by large explosions can result in lung ailments, acid rain, lower surface temperatures and depletion of the earth's protective ozone layer. When carbon dioxide, which is heavier than air, settles in low-lying areas or collects in the soil, it can be lethal to people and animals.

ERUPTION COLUMNS - Billowing clouds of gas and debris can reach more than 12 miles (20 km) above a volcano, posing a serious threat to aviation. Some commercial jets have nearly crashed after flying into clouds of ash. Large rock fragments falling to the ground can kill people and destroy property.

ASH FALL - Large volumes of ash can settle on buildings, resulting in their collapse. High levels of ash particles can cause increased coughing and irritate the eyes and skin and sometimes result in serious lung conditions. When the acid coating on ash is removed by rain, it can pollute local water supplies and damage vegetation. On the other hand, ash deposits can be beneficial by improving the fertility of soil.

PYROCLASTIC FLOWS - An avalanche of hot ash, rock fragments and gas can flow down the side of a volcano at speeds of up to 150 miles an hour (240 km) during explosive eruptions, burning everything in its path. People on the margins of the flows can suffer serious injury or even death from burns and inhalation of hot ash and gases.

LAHAR - Lahar is an Indonesian term describing a mixture of mud, water and rock fragments that flows down the slopes of a volcano. One of the deadliest volcano hazards, they can bury buildings and farmland, destroy roads and bridges.

LAVA FLOWS - Lava flows are streams of molten rock that ooze from an erupting vent and destroy everything in their path. While lava flows usually don't travel far from the vent and are easy to avoid, deaths can result from asphyxiation caused by inhaling accompanying toxic gases.

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