All good books on volcanoes describe well-known eruptions, including Vesuvius 79 AD, Tambora 1815, Krakatau 1883, Mount Peleé 1902, Katla 1918, Mount St. Helens 1980, Pinatubo 1991. Who are we to be any different?
There is a good reason for this. Most famous eruptions are large and explosive, causing loss of life and considerable property damage – in other words, headline-grabbing. Later eruptions have impacted aviation – volcanic ash and jet engines are not a good mix; airports near erupting volcanoes are closed and flights re-routed to avoid the ash clouds.
Catastrophic events are the reason volcanology is such an important subject. Understanding these and other eruptions is important to find out how to minimise the risk; i.e. reduce loss of life.
Researchers have shown that volcanoes usually very kindly give us some warning in the lead up to an eruption. Magma is viscous, rarely moves fast and, when moving, causes earthquakes, usually small, but some are felt without equipment. As magma ascends, degassing starts to occur, some of which is detectable at the surface. Rising magma also causes ground deformation, e.g. it causes the volcano to inflate, measurable by tilt-meters and GPS, and some of which may even be visible to the naked eye (Mount St Helens).
I read somewhere that the first piece of equipment required to monitor a volcano is a seismometer, the second is another seismometer, as is the third; earthquakes are often the first sign of impending trouble (if I can remember / find the source, I will accredit it properly). Scientists observing volcanoes will have a raft of equipment in place: seismometers, GPS stations, tilt-meters and gas monitoring; satellite monitoring may also detect ground deformation. Drones may be used to inspect craters which are not readily accessible or where it would be unsafe to visit. Our maps of Iceland include some GPS stations as markers to indicate where the earthquakes are occurring but still evidence that Iceland has several in place at its active volcanoes.
Given that volcanoes give some warning, why are people killed? Unfortunately, magma ascent and the build up to an eruption is a slow process with many stops and starts. A major eruption may be preceded by a few small throat clearing events before the volcano unleashes the main eruption. An evacuation may take place, but if it is quiet between the precursors and the main event, people may think that the volcano has finished and return home to be at ground zero at the wrong time, irrespective of whether or not any alert is in place. People living close to volcanoes tend to be farmers with strong bonds to both their land and livestock. On the other hand, the volcano may not behave as expected – e.g. a phreatic eruption or edifice failure. Volcano hazard assessment is an interesting topic for future posts.
We will also look at some of the more famous eruptions over the coming weeks.
We’ve already touched a bit on Katla (The Katla Volcanic System, Myrdaksjökull – the not so cuddly Katla) and Mount St Helens (Mount St Helens – 18 May 1980 Eruption) so we’ll carry on by looking at Tambora’s 1815 eruption (Tambora 1815).
The Armchair Volcanologist
7 July 2020