I had a delightful month in Chile earlier this year (February-March 2015) with the main focus being a two week expedition to Volcán Quetrupillán to continue my project on volcano-ice interactions.
Whilst at Quetrupillán our nearest volcanic neighbour (Villarrica) erupted and showered the tent and landscape in ash. And for the final few days of my trip I helped US colleagues do a recce of Volcán Llaima as they wanted my help to look for examples of lava-ice and lava-water interactions (two of my research specialisms).
So let’s deal with the excitement of Villarrica’s big eruption first! Prior to the big eruption there had been a number of small eruptions – a bit of throat clearing as well as small amounts of new magma exploding. I saw a few of these – see below.
Villarrica had its big eruption early in the morning of 3 March 2015, in clear and cloudless weather. http://www.bbc.co.uk/news/in-pictures-31726286 This meant that many people took great images and videos. Not us unfortunately. At our campsite c.25 km away we were in thick cloud and heavy rain, with a c.300 m high ridge between us and Villarrica. We awoke to a bright and sunny morning, and immediately noted something was odd: there was ash on the soap, in the cooking pots, and on the tent, and when we brushed against the trees we had the rare experience of ‘ash showers’.
On examining the ash shards it was clear that it wasn’t just a big throat clearing event – this was an eruption of fresh and gas-rich magma. It had to be Villarrica! After a hasty breakfast we ascended the c.300 m high ridge to see what had happened. What a transformation – the summit cone was coated in thick black pyroclastic deposits, with clear evidence of material being mobilised and flowing down towards the base of the summit cone. The day on the ridge (4 March) as we travelled north the ash layer became thicker and the shards became bigger, so we were clearly walking towards the main axis of dispersal (i.e. the direction-line along which wind had blown the ash cloud).
We saw the unusual sight of pumice floating in the lake below us (Laguna Azul), and saw that the summit ice cap of Quetrupillán was dusted in ash. A dusting of ash is known to increase ice melting rates, so the Quetrupillán ice cap may melt at a higher rate until the next big snowfall covers the new ash.
We still had no idea how big the eruption was, and we only found out how serious it had been when we got back to civilisation and hearing that over 3,000 people had been evacuated from the town of Pucón. So we were there, but we missed the big one.
Although Quetrupillán has the potential to produce decent eruptions that could affect nearby towns and communities – and there is evidence of such eruptions in the past few thousand years – what most interests me is that Quetrupillán has an unusual number of well-preserved examples of volcano-ice interactions. In 2014 I had a couple of weeks discovering and working on some, and the aim of 2015 trip was to discover new examples and do some detailed sampling and work on selected examples. So the images below and their captions describe some of the examples of volcano-ice interactions that exist at Quetrupillán.
One of the chief aims of this work is to provide insight into the longer timescale over which a volcano has been growing and erupting.
Basically, for volcanic systems that have been active for hundreds of thousands of years, the past 9-12 thousand years is a mere snapshot and is unlikely to be representative. Having a longer timescale to play with allows insight into cycles of behaviour and activity (e.g. surges of fresh material rising into the volcano over centuries to millennia) and this can improve predictions of future eruptive activity and the associated hazards.
We only have good knowledge of the eruptive history of volcanoes spanning the last 9-12 thousand years – basically since the end of the last glacial period when the ice sheets melted and left the land ice-free. So the carpets of explosive pyroclastic deposits, and the lava flows, have not been destroyed and are therefore available for study. And we have techniques such as carbon dating to tell us when eruptions happened. Some example of recent eruptions at Quetrupillán are below.
A US colleague from Boise (Brittany Brand http://earth.boisestate.edu/people/brittany-brand/) asked me to help out on a recce of Llaima volcano with the aim of looking for lava-ice and/or lava-water interactions, as she was running a field trip afterwards. It’s tough finding such evidence in terrain covered with abundant young lava flows, especially as Llaima is one of Chile’s most frequently erupting volcanoes. But I found a few (subtle) examples where lavas had flowed into an old river valley. One is below.
A particularly spectacular eruptive unit we also looked at is the Curacautín Ignimbrite, which erupted c.13,200 years ago with a volume estimated at 24 km3. What’s unusual is that this ignimbrite is basaltic to andesitic in composition (50-59% SiO2 for those who are interested). It’s unusual because basaltic-andesitic ignimbrites are very rare – usually it’s the more evolved rocks (dacites and rhyolites) that produce large ignimbrite-forming eruptions. However there are few in this part of Chile, and good old Villarrica has also produced ignimbrites of basalt-andesite composition. It’s fair to say that why these volcanoes have produced ignimbrites of this composition is not fully understood.
Other beauties of being around Llaima are the lava-dammed lakes, and the ethereal Araucaria woods and forests (commonly known as Monkey Puzzle trees). These trees are highland trees and only feel comfortable growing naturally at elevations above c.1000 metres. There are some beautiful examples growing on the slopes of Llaima, and there’s also areas where the Araucaria forests have been invaded by lava flows.
To push back the timeline of Quetrupillán’s geological history I’ll be working with colleagues to obtain dates of selected volcano-ice eruptives. When I have some reliable dates and have worked what it all means, I’ll do another blog entry. More about my research and publications can be found at http://www.open.ac.uk/people/dwm4
The fieldwork was partly funded by a Santander mobility fund, which is gratefully acknowledged http://www.santander.co.uk/uk/business. As usual, the ever-reliable Rancho de Caballos provided the horses and expert guides to take us up to the volcano with our food and equipment, and came to collect us at the end with our many kilograms of rock samples. http://www.rancho-de-caballos.com/