Volcanoes: Ready, stead, blow

Some of the world's most destructive volcanoes are long overdue for major eruptions. But which will be first? And how can we avert disaster? Mary Morgan reports

On 3 January 1983, Mount Kilauea came to life – and it hasn't stopped erupting yet. Now officially the world's most active volcano, it has been oozing lava and coughing up hot ash for 24 years. It has destroyed towns and its molten rock has added more than 200 hectares to the volcano's southern shore. So when Donna O'Meara, a world-leading volcanologist, pinpoints the location of her Hawaiian home, it comes as something of a surprise. "I live right on top of Kilauea," she says with a smile.

Since O'Meara moved there in 1993, she has not been blasted by the volcanic cauldron which bubbles away just three miles behind her home. In fact, O'Meara is convinced she's a lot safer than millions across the globe who live their lives oblivious to the very real threat posed by some of the world's most menacing volcanoes.

O'Meara recently returned from a trip to the American Midwest, where people were fascinated to hear of her volcano-top home. "They all asked me, 'Don't you think it's scary that you live on Kilauea?' and I said, 'No, I think that it's really scary that you live on Yellowstone. At least at Kilauea I see it erupting and I know what it's doing."

For there is a rule with volcano-monitors: always watch the quiet ones. While Kilauea's activity is plain to see, other volcanoes follow different eruption patterns, lying dormant for thousands – or even hundreds of thousands – of years before blowing their tops, freeing in one almighty blast the slowly accumulated pressure.

Yellowstone, in Wyoming, is the world's most powerful supervolcano. It is 40,000 years late in its hitherto regular 600,000-year cycle. Yellowstone is due to wake up with a cataclysmic eruptive yawn. Millions live in the firing line. Films such as the BBC's 2005 Supervolcano have attempted to show what the impact of such a blast could be – with ash, rock and debris devastating vast swathes of North America, an ash cloud triggering catastrophic climatic-cooling, which in turn leads to crop failure and starvation around the world – but for many people, volcanoes have remained in the realm of the fantastical. O'Meara says: "A volcano to most human beings anywhere on the planet is something we see in a movie. It's not something we're living next door to."

Much research is done on the subject. The International Association of Volcanology and Chemistry of the Earth's Interior publishes a list of "Decade Volcanoes" which are due to erupt within the next 10 years, for example. But the list does not always pick out those in areas of dense population, where an explosion might have a real and significant impact on human life and activity. Another major problem is the political inexpedience of planning for a deathly eruption. Politicians in Naples have been accused of shying away from the question of how to evacuate the three million people who live in the shadow of Vesuvius, says O'Meara, and the situation is similar worldwide. "Everywhere I've been, it comes down to politics, and usually those politics endanger people." She remembers the 1985 eruption of Nevado del Ruiz in Colombia, in which a local official, up for re-election, ignored warning signs for fear an evacuation would damage his campaign – 21,000 people died.

Volcano monitoring does allow for warning systems, although the unpredictability of volcanoes and relative newness of the science means hours, not days, of notice might be given, to evacuate potentially millions of people. O'Meara is researching the correlation between lunar activity and volcanoes, in the hope of developing more advanced prediction systems.

O'Meara has been involved with volcanic research and education for over 25 years. At the age of 30, disillusioned with her work as a painter and photographer, she went to Harvard University to study sciences. She first set foot on Kilauea inon Christmas Eve 1986, on her first expedition as a research assistant for her former professor Steve O'Meara, a planetary geologist. Six months later, Donna and Steve were married.

Between them, the couple have now climbed, studied, photographed and videoed over 100 active volcanoes. In the past 10 years, Donna O'Meara has been mostly concerned with educating people about the threat, this year publishing two books: Into the Volcano for children, and most recently Volcano: Portrait of a World on Fire.

Volcano-climbing started out as a thing of "excitement" for O'Meara, but two decades of intense study have convinced her of the immense threat volcanoes pose to our planet – and our terrifying lack of preparation in facing that challenge.

Donna O'Meara's six to watch

Vesuvius, Italy

Danger rating: 5/5

What damage could it do? The AD79 flattening of Pompeii was tame compared to the cataclysmic potential of this monster volcano. In a full-size blast, everything within a 12-mile radius would be pulverised – including the city of Naples, population three million. The air-fall deposit would travel 800 miles, covering much of Europe and causing roofs to collapse, crops to fail and animals to die. Ash would mix with water to form mud as thick as cement, enough to bury whole towns.

Will it really erupt soon? Vesuvius has a known 2,000-year cycle for massive eruptions and another big one is due – with increasing signs of life, including earthquakes and gas emissions. Evacuation plans, which allow for the escape of 600,000 people in 72 hours, have been criticised as insufficient.

Tambora, Sumbawa, Indonesia

Danger rating: 4/5

What damage could it do? Potentially the most deadly of them all, when Tambora last erupted in 1815 it led to the "year without a summer" around the world. So much sulphur and ash was blasted into the troposphere that it circled the planet and lowered temperatures by 2C, killing crops and causing famine as far away as North America. In total, 92,000 people died. If Tambora blew today, the ash cloud could wreak global havoc.

Will it really erupt soon? Tambora has an irregular eruptive cycle, with three known eruptions before 1815: around 3910BC, 3050BC and AD790. The last blow was in 1967. Seismic activity is monitored, but the warning could be just a few hours.

Yellowstone, Wyoming, USA

Danger rating: 5/5

What damage could it do? Yellowstone volcano is so destructive that it's in a class of its own. Scientists rate volcanoes on a scale from one to eight; Yellowstone is the only known eight, and is a so-called "supervolcano". A super-blast like its last one would be equivalent to 8,000 eruptions on the scale of Mount St Helens in 1980 (pictured). The resultant ash could destroy most of North America and create a volcanic winter across the globe.

Will it really erupt soon? Carbon dating shows a 600,000-year cycle for the Yellowstone supervolcano, but the last eruption was 640,000 years ago. Predicting the date of the next eruption cannot be done with any certainty, but experts do know that the cavernous vats beneath the surface are refilling with magma.

Mt Unzen, Japan

Danger rating: 3/5

What damage could it do? Unzen sits close to Nagasaki, population 457,000. Its last big eruption in 1792 killed 15,000 people, and an eruption today could devastate Japan and send shock waves around the Pacific Rim, causing tsunamis as far away as Hawaii, 6,000 miles to the east.

Will it really erupt soon? Mount Unzen has had a steady cycle of massive eruptions about every 200 years. Recent warning signs that a cataclysmic blow is on its way include a series of eruptions between 1990 and 1995. In 1991, two close friends of the O'Mearas, along with 39 other scientists and journalists, were killed by an avalanche of volcanic rock following a blast. The area was evacuated and 2,000 houses were destroyed.

Casade range, USA

Danger rating: 3/5

What damage could it do? There are about a dozen active volcanoes spread across northern California, Oregon and Washington, where population growth is high and millions live in grave danger every day. The 1980 explosion of Mount St Helens was just a small warning of what could be to come. That "medium-sized" eruption killed 57 people and thousands of animals, causing $1bn worth of damage ($2.7bn, or £1.3bn, in today's money).

Will it really blow soon? There have been more than 100 eruptions in the Cascade Range in the past few thousand years. Scientists believe another is imminent, with O'Meara putting her money on Mount Rainier in Washington State. The highest peak in the Cascade Range, Rainier last erupted in 1894. Evacuation plans have been formulated, with the help of the US Geological Survey.

Popocatepetl, Mexico

Danger rating: 3/5

What damage could it do? More than 30 million people live within view of Popocatepetl, 60km south-east of Mexico City. The immediate danger zone is the 12km surrounding the volcano, but recent rumblings have seen volcanic lava fired some 10km into the air.

Will it really blow soon? It is blowing at the moment. Since December 2000, there have been a series of earthquakes and blasts – several times resulting in the evacuation of tens of thousands of people. Now there is another danger; as people grow tired of false alarms, how will they respond to the real thing?