A booklet for Students and the Community
Chapter 11
Volcano Hazards and Disasters
THE FIERY PACIFIC REGION
The Earth, in geological terms, is relatively young and still changing. There are over 1,500 potentially-active volcanoes world-wide and eight to ten erupting at any time. There are at least as many more under the oceans. Pacific region countries contain about 80% of these volcanoes, which encircle the Pacific Ocean in a belt known as the ‘Ring of Fire’. Although there are no active volcanoes in Australia, vulcanologists believe that at least minor future activity is still possible from dormant volcanoes in eastern SA and western Victoria, which last erupted relatively recently (eg Mt Gambier, SA - 4,600 years ago and Mt Napier, Vic - 7,200 years ago). There are also two active volcanoes in the Australian Antarctic Territories of Heard and McDonald Islands, the larger of which is named Big Ben (2,750 m).
Range of Destruction
Danger from Below - Volcanoes form when a break in the Earth’s crust allows magma (molten rock) and hot gas to reach the surface under pressure, resulting in dangerous eruptions.
Major Threats - In the immediate area, main threats are: high-speed, super-heated toxic gases and debris (pyroclastic flows); blast effects; lava flows; volcanic earthquakes; landslides; collapses; and lahars (mudflows), while ash clouds or deposits and tsunamis can be hazards much further away.
Variables - Over 100,000 deaths have been caused by volcanoes world-wide. However, compared to some hazards this figure is relatively low, varying with size, location and numbers of settlements using nearby rich agricultural land. Volcanoes can cause immense destruction to whole towns, crops, forests, roads, etc creating many evacuees who must be sheltered, fed and resettled. Lava flows may also block streams, causing floods, mud flows and landslides.
Research - Volcano research and monitoring is increasing in most countries with the common goal of providing greater warning time of likely eruptions.
The Australian Region
Indonesia and Philippines - Eruptions of the Galunggung volcano in West Java, one of many in Indonesia, caught our attention in 1982 when volcanic ash temporarily stopped engines of passenger planes en route to Australia. (It also destroyed many hundreds of homes and crops.) Australian scientists have since developed the ‘Airborne Volcanic Ash Detection System (AVADS)’ which enables pilots to detect ash clouds due to heat radiation produced. The 1991 eruption of Mt Pinatubo in the Philippines was the most significant in recent history (see Case Study 2).
PNG and New Zealand - In September 1994, two volcanoes, Vulcan and Tavurvur erupted and literally buried the town of Rabaul, PNG under millions of tonnes of ash and made 80,000 people homeless. As recently as late-1995 and June 1996 Mt Ruapehu in New Zealand erupted, closing ski fields, causing floods from its crater lake, and interrupting air traffic in the North Island.
United
States of America
Mt St Helens in Washington (state) erupted violently in 1980 (see Case Study 1). Hawaii’s Kilauea Volcano is the world’s most active volcano. It erupted many times during 1982-85 (48 times in 1983 alone) and again in 1990 with no loss of life, but huge lava flows destroyed a building, several main roads and vehicles, and threatened homes and properties in the area.
VOLCANIC ERUPTION - CASE STUDIES
1.
Mt St Helens, Washington, USA, 1980
Build-Up -
During 1980 scientists had warned that a large bulge which was developing on the
snow-covered, upper-northern slopes of Mt St Helens might trigger a great avalanche or
eruption. They
were correct. The disaster
began early on 18 May with an earthquake (magnitude 5) which loosened the whole northern
slope of the mountain. A gigantic avalanche
followed.
Eruption - Then, in an enormous blast, hot gases, earth and rocks rocketed out of the volcano’s side, flattening forests over 25km away! At the same time, furious blasts sent lava, steam, ash and rock skyward. The initial blasts ejected about 400 million tonnes of debris.
Death Toll and Damage - 62 people died in thick ash and choking smoke
and many more were injured. Damage caused by
the eruption and subsequent ash-fall has never been fully calculated. Rivers were flooded and silted for up to 24
kilometres, 400 square kilometres of forests were flattened and disappeared, and roads and
bridges were demolished. Total economic
losses were estimated at US $1.2 billion (in 1980 values).
2. Mt Pinatubo, Philippines, 1991
The Re-awakening -
On 9 July 1991, the 1,463 metre, dormant volcano near Subic Bay, came back to life after
six centuries. It began a series of eruptions
which were to last for months.
Massive Eruptions - By mid-July the eruption reached an initial, mighty climax as it belched billions of cubic metres of red-hot magma, gases and ash (tephra) from a three kilometre-long fissure (crater) near the mountain’s summit. Such was the explosive force of the main eruption, that it ejected enormous clouds of ash and gas vertically to an altitude of about 40 km!
Physical Effects - Ash fallout from the volcano settled deep on
the ground over huge areas, up to hundreds of kilometres away. By mid-afternoon on 17 July, the sky was as black
as night as far south as Manila (85 km away). A
relentless ‘rain’ of golfball-size pumice pebbles and ash poured down, while
thunder and lightning from a tropical storm alternated with brilliant orange flashes from
the volcano. There were also numerous
earthquakes, all resulting from Pinatubo’s continual violent eruptions. Fortunately, because the bulk of its eruptive
energy was directed vertically upwards (unlike Mt St Helens), it did not produce large
pyroclastic and molten lava flows that could have devastated towns on the mountain’s
flanks.
Secondary Effects - A week later, heavy rains from Typhoon Brenden sent thousands of tonnes of ash, silt and volcanic debris surging down the mountain. Enormous mud flows and slides (taller than houses) wrecked many foothill villages, killed many people and forced thousands to flee from their homes.
Human and Property Toll - These secondary events
caused the greatest loss of life and human suffering.
Over the period of eruptions, about 700 died.
One million others were forced from their homes (42,000 were destroyed) and 40,000
ha of cropland were buried under ash.
Atmospheric Effects - Mt Pinatubo’s massive eruption was the largest on record in the Philippines, and in the world for a century, producing the largest cloud of climate-modifying gases since mighty Krakatoa erupted in Indonesia in 1883. Scientists estimated that Pinatubo’s eruption added more aerosols (light gases and particles) than all human-caused ‘greenhouse gases’ since the industrial revolution. A reduction of up to 1°C in the Earth’s average temperature was recorded by NASA satellites within a year of the main eruption. This cooling effect persisted for about two years, temporarily more than offsetting any global warming effect.
STUDENTS - FIND FURTHER INFORMATION
As a project on volcanoes, find out more about:
the difference between active, dormant and extinct volcanoes;
extinct and dormant volcanoes in Australia and active ones in New Zealand;
the eruption of Mt Vesuvius, Italy, AD 79, or Krakatoa, Indonesia, 1883; and
the possible effect of volcanic gases etc on global warming.
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| This page was last updated May 31, 2001 |
