Jack Anderson, a Science and Solutions for a Changing Planet DTP research postgraduate based at London’s Natural History Museum, describes his fieldwork on the highly-active Volcán de Colima in Mexico, and explains the significance of his research.
As my Aeroméxico flight begins its descent into Colima, I eagerly position my phone in preparation to capture a first glimpse of its formidable volcano. I am greeted instead by a thin line of haze, which covers it in a shroud and denies me the excellent photo opportunity. Still, I can make out its outline, and after a long journey, it is only now that the realisation of what I am embarking on really starts to sink in: seven weeks of fieldwork collecting samples from the flanks of an active volcano.
Centuries of eruptive behaviour
Firstly, a bit of background… Volcán de Colima or Volcán de Fuego (Fire Volcano), as it is sometimes poetically referred to, is located in the west of Mexico, 80 kilometres from the Pacific coast. It falls within the western part of the Trans-Mexican Volcanic Belt (TMVB), an active continental volcanic arc that stretches across central Mexico for about 1000 kilometres. The ongoing subduction of the Cocos and Rivera plates beneath the North American plate means that there is a significant amount of volcanic and seismic activity in this region.
As I step off the plane into the unexpectedly intense sunshine, I immediately appreciate how Volcán de Colima looms over the city of Colima and the smaller villages that dot its lower flanks. It poses a significant threat to the 300,000 people who live within 40 kilometres, which is why it is so important for scientists to understand more about the volcano’s eruptive behaviour.
Volcán de Colima’s recent activity has been ‘effusive’, which in the case of this volcano, means that sticky molten rock (called lava) solidifies as a dome within the crater, acting to plug the vent. The plug is eventually destroyed by moderately-sized vulcanian explosions, which generate columns of ash and send pyroclastic flows – mixtures of ash and superheated gases – cascading down the side of the volcano through deep and narrow gorges (called barrancas) at high speeds – not something to get in the way of! Endless cycles of dome growth and destruction have characterised Volcán de Colima over the past couple of decades.
During my stay, volcanic activity is especially calm, marked only by the gentle, almost soothing, wisps of water vapour and sulphur dioxide from degassing fumaroles (openings at the vent of the volcano where gases emerge). Yet, this serves as a constant reminder that the volcano is still stirring – and conceals a far more dangerous and threating side to its character.
Volcán de Colima also produces intensely violent ‘plinian‘ eruptions (named after the Roman nobleman Pliny the Elder, who perished during the AD79 eruption of Mount Vesuvius) roughly every one hundred years. The last two of these were in 1818 and 1913, so we are potentially overdue another of these large eruptions.
Needless to say, an event on this scale would undoubtedly have very serious consequences for the local population. What drives this cycle of eruptions is not well known, but I aim to address this through my research.
What’s stirring beneath the volcano?
Evidence of past eruptions at Volcán de Colima are well-preserved. Pumice and ash are scattered across the Nevado de Colima mountain to the north and north-east of the active Volcán de Colima crater, and my trip provides me with a great opportunity to survey the sequences of erupted material. These display an incredible array of colours, from brick orange, to pale green. To expose the pumice requires a lot of scraping – luckily we have strong shovels and enthusiastic volunteers. The freshly excavated material is scooped out and bagged up ready to be sent back to the Natural History Museum in London.
I also visit the south-west of the crater – the alien landscape of Montegrande – to collect lava samples from several other eruptions, including a lava flow from 1998-99. Walking through the crumbling barrancas from the south, the views of the volcano are awe-inspiring. Here, I collect samples, which involves hammering with considerable at the solidified lava flows to break off suitably large-sized pieces, which are broken up for chemical analysis, and for the museum’s collection. A rucksack of these blocks – each weighing 8-10 kilogrammes – quickly adds up when you have to haul it back to the truck!
Over seven weeks in Mexico, my team and I collect almost 200 kilogrammes of solidified lava and pumice, which is currently en route to the UK. The samples, as with other rocks, contain crystals with zones (like growth rings in trees) that are a record of the conditions in the magma chamber where they were formed. It is these zoned crystals that I will study, using high-precision analytical techniques, back at the Natural History Museum in London.
Once the samples make it safely back to London, I will prepare them for chemical and mineralogical analysis. By studying the crystals within them, we can determine the temperature, pressure and composition of the molten rock stored in the volcano’s magma chamber. This will give us a much greater understanding of what is going on beneath the volcano. When combined with other evidence, including seismic activity, gas and thermal measurements, this can provide indications about when the next big eruption could take place. This vital information can then be passed on to local authorities to provide early warnings for the residents, and in doing so, help limit the damage another eruption could cause.