Large earthquakes may trigger volcanic eruptions

10 December 2008

Large earthquakes can trigger volcanic eruptions up to a year later and up to 500 kilometres away from their epicentres, according to new research.

Chilean volcano

Parinacota volcano, Chile

The findings suggest that volcanoes in regions of high earthquake activity should be more closely monitored after a large earthquake has struck.

Sebastian Watt and colleagues Professor David Pyle and Dr Tamsin Mather from the University of Oxford analysed continuous records of earthquakes and volcanic eruptions from southern Chile going back to 1850. Records since then include 206 eruptions from 25 different volcanoes.

Two major earthquakes in 1906 and 1960 led to a large rise in the number of volcanic eruptions in the year following each earthquake. Before the end of 1907, seven volcanoes erupted and by the end of 1961 after the 1960 earthquake, there were six eruptions. On average, the researchers say, there are 1·32 eruptions every year in this region.

Watt and his colleagues also studied data from records that weren't continuous, and linked two large earthquakes in 1751 and 1835 to an increase in volcanic activity in the area. The work is due to be published in the journal Earth and Planetary Science Letters.

"We had access to data going back to 1550, but decided not to include large chunks of it because it wasn't continuous and therefore wasn't completely reliable," says Watt.

This could also be happening in other areas with high earthquake and volcanic activity, like Indonesia and Alaska.

- Sebastian Watt, University of Oxford

Charles Darwin also noticed that volcanoes to the north of the 1835 earthquake in Concepción, Chile were 'in great activity' a few days after the earthquake and the whole of the volcanic chain was active for the rest of the year.

Despite Darwin's observations, linking large earthquakes with volcanic eruptions is a fairly young science and many scientists have been sceptical.

"Previous studies looked at global datasets, where it's very difficult to elucidate a link on a timescale longer than a few days," says Watt.

Looking at the detail

Watt and his team took a different approach. They are the first to look at a longer timescale and focus on a specific area. Along the continental margin - where the oceanic crust meets the continental crust - Chile has some of the largest earthquakes in the world with magnitudes over eight on the Richter scale.

Next to the continental margin, following the Andes, the country also has numerous active volcanoes in a so-called 'arc' - where one tectonic plate moves beneath another.

"At the moment the precise process causing eruption is unclear. Given the distance at which this eruption-triggering happens, we suggest that seismic waves radiating from the earthquake zone disrupt bodies of molten rock beneath volcanoes eventually leading to eruption.

"The same process could also happen in other areas with high earthquake and volcanic activity, like Indonesia and Alaska.

"The next step is to investigate the mechanisms causing this by studying specific eruptions and looking at the rocks spewed out," Watt adds.

'The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone' - SFL Watt, et al., Earth and Planetary Science Letters (2008) in press.