I was taking a plane trip home recently. To kill the time I got talking with the person sitting next to me and naturally one of their first questions was to ask me what I did for a living. To avoid a complicated discussion about the nuances of my research I summarised – ‘I am a volcanic meteorologist’. They were interested and wanted to know all about how volcanoes affect the weather, my opinion on ‘that Icelandic eruption’ and told me some slightly left-field opinions on climate change. It was an interesting chat and it got me thinking, volcanoes seem to have several well known impacts on weather but can weather have an impact on volcanoes?
At first it appears quite strange that something seemingly so solid can be altered by atmospheric processes. But in the case of mudflows this is exactly what can happen – rain mixing with soil causing soft wet mud to slide down a hill. In the case of volcanoes, a lahar can form, a mudflow consisting of volcanic debris with the consistency of wet concrete which cascades down the slopes of a volcano.
Water has also been known to trigger rockfalls by getting into the cracks between rocks and weakening them. This same erosion process can erode scree from the summit of a volcano.
Lava domes (a roughly circular shaped mound created from the slow extrusion of lava from a volcano) are known to grow in the absence of rainfall. When it rains water seeps into the cracks between rocks in the lava dome. The lava dome is very hot so rain instantly vapourises. Hence a large rain rate is needed to get further inside cracks in the rocks. Once deep inside, the rainwater vapourises into high pressure steam as it encounters temperatures in excess of 300 C. This destabilises the lava dome and sometimes leads to a collapse.
A collapsing lava dome creates a pyroclastic flow, a high-density mix of volcanic rocks and gas travelling down the slopes of a volcano at high speed and destroying almost everything it its path. A 2001 lava dome collapse is thought to have been triggered by rainfall.
Excessive rainfall can and does impact volcanoes. Having said this hurricanes and other large storms, having a rainfall rate needed to cause water to seep into the lava dome of a volcano are mostly found in the tropics.
Do you know of any other cases of weather affecting volcanoes? The author would be interested to know – please post your suggestions in the comments.