Volcanoes
Volcanoes rarely erupt without warning.
Around 5% of all active volcanoes can be found on continental margins and island chains. Most volcanic activity occurs on the deep ocean floor and so goes unnoticed.
The avalanche of rocks and debris following some volcanic eruptions can cause devastating tsunamis.
Scientists monitor only a few hundred of the 1500 or more, active or potentially active volcanoes.
Constant monitoring greatly reduces the death toll when a volcano erupts as exclusion zones are usually very accurate.
In 1988 scientists suggested there would be an increase in volcanic activity on the Caribbean island of Montserrat sometime in the mid-1990s. The volcano erupted in 1995, but good monitoring procedures meant fatalities were few, though damage to the surrounding area was extensive.
Volcanic eruptions have far reaching effects. All eruptions throw huge clouds of sulphur dioxide gas into the atmosphere. When Pinatubo in the Philippines erupted in 1991 a plume of gas spiralled into the atmosphere and enveloped the planet, lowering temperatures by about 0·25°C for a few weeks.
Probably the largest eruption in the last 1000 years was in Tambora, Indonesia, in 1815. The massive explosion ejected volcanic gases high into the atmosphere causing a global cooling of 0·7°C. Global weather was chaotic and unpredictable the following year with crop failures and frosts in July in Europe - 'the year without summer'.
Volcanic activity is not entirely random. It is often seasonal, suggesting environmental factors such as weather, climate and sea level exert an influence on volcanoes. The volcano on Montserrat seems to have a tendency for large eruptions in summer, which may be due to increased rainfall at that time of year.
Volcanic plumes cause ozone depletion in the upper atmosphere. The fine ash in these plumes can stop a jet engine, so air traffic controllers must divert aircraft away from large eruptions.
Clouds often blanket active volcanoes, meaning impending eruptions could go undetected. NERC's Environmental Systems Science Centre (ESSC) has developed an all-weather volcano sensor that can map volcanoes from up to 4km away, even through dense cloud.
Super-eruptions, large enough to cause a global disaster, occur on average every 100,000 years. The last super-eruption was 74,000 years ago in Toba, Indonesia. Super-eruptions are most commonly found where the Earth's tectonic plates collide or where hot material wells up from deep within the Earth's interior. Yellowstone volcano in the USA , the Phlegrean Fields volcano near Naples, Italy, and Lake Taupo in New Zealand are three examples of active volcanoes capable of producing super-eruptions. But there are many other regions where such volcanoes are found or suspected, including Indonesia, the Philippines, Central America, the Andes, Japan and Eastern Russia. Some of these sites are close to densely populated cities.
Some scientists believe an area the size of North America or Europe could be devastated in the event of a super-eruption, global climate could change dramatically ruining world agriculture, disrupting food supplies and causing mass starvation.