Volcanoes, their eruption and management of risk
Erupting volcano with lightning bolts

Volcanoes, their eruption and management of risk

Professor Sir Stephen Sparks, University of Bristol

We were privileged to have as our speaker a scientist internationally recognised for his research on volcanoes. His presentation, illustrated with informative slides and videos, gave comprehensive coverage of his topic.

Earth is a hot planet and underneath its solid crust lies a mantle of solid rock at very high temperatures: the centre of the earth is at 5,200°C, whereas 100km below the surface the temperature is 1,200°C. The surface of the Earth moves slowly around the globe as a system of tectonic plates, and most volcanoes occur at plate boundaries where two of these plates are moving apart or coming together. The friction generated by movement between two plates can melt solid rock and turn it into magma. This hot molten rock is then forced up to the surface through fissures in the Earth’s crust, to create a volcano. As the magma cools on reaching the surface it forms lava. Underwater volcanoes also occur, creating subsurface mountains as the lava cools.

Globally, there are 551 historically active volcanoes and about 50 eruptions a year. They are spectacular natural phenomena, releasing clouds of ash and gas to the atmosphere and spilling acres of lava over land. These emissions can travel vast distances from the original site, particularly in the case of super eruptions, which occur about once every hundred years. Such large eruptions can affect the global climate as dust particles in the emissions reflect heat back into the stratosphere causing the earth to cool. For example, a giant eruption occurred in 1815 on Tombora in Indonesia, releasing ash that had a significant effect, lowering the global temperature by 0.4 to 0.7 degrees Celsius. In 1816, known as the year without summer, this caused a world-wide failure of crops and a consequent famine. However, one positive outcome of living near a volcano is the increased fertility of the soil due to beneficial minerals in the volcanic ash.

Explosive eruptions occur when the gases dissolved in the magma build up sufficient pressure to exceed the magma strength. This is accompanied by a dense, fast moving flow of solidified lava pieces, volcanic ash and hot gases moving along the ground away from the volcano at speeds up to 700km/h, known as pyroclastic flow. This is the most dangerous of all volcanic hazards and accounts for 40% of all volcanic fatalities.

A good example was seen in the Mount St Helens eruption of 1980 in the US, when a series of volcanic explosions and pyroclastic flows caused large scale death and destruction. The eruption column rose 24 km into the atmosphere and deposited ash over 11 US states.  However, the deadliest eruption of the 20th century took place on Mount Pelee in Martinique in 1902 when 29,000 people died in the pyroclastic flow.

To minimise these hazards, a system of monitoring volcanoes to forecast likely eruptions has been adopted. Earth quakes usually occur near to eruption so seismometers are used to detect activity. Ground deformation often occurs prior to an eruption, so an increase in the upward movement can alert geologists that the magmas is moving towards the surface, and the amount of sulphur dioxide in the volcanic gas can be another indicator.

In 1985 Colombia suffered its greatest natural disaster when 23,000 people lost their lives in the town of Armero. The volcano’s eruption, after 69 years of dormancy, caught nearby towns unaware, even though geologists had warned the government to evacuate the area after they detected activity two months earlier. As pyroclastic flows erupted from the volcano’s crater, they melted the mountain’s glaciers, sending four enormous lahars (volcanically induced mudflows, landslides, and debris flows) down its slopes at 50 km/h. This tragedy could have been avoided if due regard had been paid to the prediction of geologists, but with an election looming, political priorities took precedence over public concerns.

To conclude, Sparks described a case study of his involvement in the monitoring of the Soufriere Hills Volcano in Montserrat. The above-mentioned techniques, combined with a probabilistic approach used to assess the of risk of an eruption, predicted the likely danger zone and so happily, when the eruption occurred, there were no fatalities.

                                                                                                                                                      Valerie Conniff



Tue 11 Jul 2023


2:30pm - 4:00pm
Bridges Centre, Drybridge Park, Monmouth NP25 5AS
Cherry Lewis

Accessibility at Bridges Centre

Members’ monthly meetings are held at Bridges Community Centre, Drybridge Park. Some group meetings and activities also take place at Bridges. Off street parking is available here outside the building, and disabled parking is adjacent to the building entrance. There are no external steps or slopes, and the entrance doors are automatic. The ground floor is fully accessible and level throughout, and there is space for wheelchairs. There is a lift to the first floor, and accessible toilets on both floors. There is a hearing induction system in the Agincourt room where the monthly meetings are held.

Accessibility at Ty Price

Some group activities and meetings are held at Ty Price, St Thomas Community Hall, St Thomas’s Square. There is no off street parking here. The approach on foot is a gentle slope to double entrance doors. The ground floor of the building is fully accessible and there is a disabled toilet. The stairs to the first floor are wide and well-lit with a handrail on both sides, but there is no lift. There is a hearing induction system on the ground floor.