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Chile: big quake = more volcanic activity? 2 March 2010

Posted by admin in Chile.
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The M8.8 earthquake that hit Chile at the weekend has raised the question of whether such large quakes have any effect on activity in nearby volcanoes. In Chile itself, geologists from Chile’s Observatorio Volcanológico Andes del Sur (OVDAS) have publicly ruled out any such connection; New Scientist, by contrast, has a headline excitedly claiming ‘Volcanic explosions expected in Chile quake’s wake’.

The New Scientist article refers to a research paper by Sebastian Watt, David Pyle and Tamsin Mather of the University of Oxford which appeared in Earth and Planetary Science Letters in 2008 (‘The influence of great earthquakes on volcanic eruption rate along the Chilean subduction zone’, Earth and Planetary Science Letters, vol. 277, nos. 3-4, 30 January 2009, Pages 399-407 [doi:10.1016/j.epsl.2008.11.005]). This paper looked into a potential connection between earthquakes and increased local volcanic activity in Chile over the past two centuries, and concluded that there was some evidence of such a connection:

We show a significant increase in eruption rate following earthquakes of MW > 8, notably in 1906 and 1960, with similar occurrences further back in the record. Eruption rates are enhanced above background levels for ~ 12 months following the 1906 and 1960 earthquakes, with the onset of 3–4 eruptions estimated to have been seismically influenced in each instance.

Given the claim that the ‘enhanced’ eruption rates may manifest over around 12 months after the earthquake, OVDAS’s denial that the 27 February quake will produce an increase in volcanic activity is premature. However, the 2008 paper raises many questions about the nature of the mechanisms at work, the time lag involved, and the real significance of the phenomenon (an estimated 3-4 additional eruptions is not very many). As Erik Klemetti has just observed,

Complex systems have many inputs – maybe the volcano that erupts next week would have erupted with a magnitude 4 earthquake, maybe it would have erupted without an earthquake at all. To connect the two merely because they are temporally juxtaposed is not scientifically sound. There is evidence that there could be an effect on nearby volcanism after large earthquakes in some settings, however, it is far from proven.

A further point is that, whatever New Scientist‘s headline writer may think, not all volcanic activity is explosive, or even dangerous in any way. Increased volcanic activity does not necessarily equate to increased hazard – as David Pyle points out in the New Scientist article: ‘At volcanoes that are already active we might see an increase in steam explosions, but we don’t expect it to present a significantly increased danger’. So even if there is a volcano-earthquake connection, and the question very much remains open, it is not necessarily something people living in active subduction zones should consider an additional significant threat.

N.B. ‘Llaima, one of the largest and most active volcanoes in Chile, is back on the watch list’, says the caption to a dramatic picture of Llaima accompanying the New Scientist story. In fact Llaima has been ‘on the watch list’ (if that means ‘at higher alert’) since mid-February, but of course it increases the drama to imply that the raised alert level is the result of the earthquake, and if that misleads your readers, so what?

Descartan que volcanes Llaima y Villarrica estén con actividad irregular luego de terremotoLa Tercera, 28 February 2010
Descartan que el terremoto un aumento de la actividad volcánica – Europa Press, 1 March 2010
Completa normalidad se observa en volcanes de la zonaEl Austral, 1 March 2010
Volcanic explosions expected in Chile quake’s wakeNew Scientist, 1 March 2010

The Volcanism Blog