Archive for November 2015

Recent volcanism at Volcán Quetrupillán, Chile   Leave a comment

This short blog entry is rich on images and short on text. Its purpose is two-fold. First – to provide a brief introduction to the recent (Holocene) volcanism of this poorly-understood volcano, and second – to provide a bit more information for candidates interested in applying for the currently-advertised PhD project at the University of Edinburgh on this very topic, on which I am a supervisor.

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The ‘beheaded’ Quetrupillan stratocone from the SW, with Laguna Azul in the foreground. The sheets and lobes on the ridge in front of the main stratocone are formed from a subglacial (Pleistocene) dacite eruption of unknown age.

So why is so little known about Quetrupillán? One key reason is that with one of Chile’s most active volcanoes (Villarrica) being such a close neighbour and with Villarrica’s past reputation for causing death and disruption, a nearby volcano that hasn’t erupted within living memory and has no obvious signs of current/recent unrest, won’t be given much if any attention. And that’s fair enough, because when you have finite resources to monitor potentially dangerous volcanoes, you need to focus those resources wisely. Even knowing what I now know about Quetrupillán, with limited resources I’d still put my monitoring equipment onto volcanoes such as Villarrica, Llaima, Calbuco, Puyehue-Cordon Caulle, and so on.

Quick big-picture context. Running through this part of Chile is a c.1200 km long approximately N-S fault zone called the Liquiñe-Ofqui fault zone LOFZ, along which many of the volcanic centres of Chile are associated. Quetrupillán lies in the middle of a NW-SE chain of three volcanoes that cuts obliquely across this fault zone, with Villarrica at the NW end and Lanín at the SE end.

I’m only mentioning this because one of the key features that distinguishes Quetrupillán from its two neighbours in the chain is that it sits astride part of the LOFZ, and on closer examination it is clear that many volcanic vents to the south and around the east and west flanks are aligned along roughly N-S fissures. This has given Quetrupillán a rather mixed morphology, with focused vent activity producing a ‘beheaded’ stratocone developed to the north, and more dispersed fissure-controlled activity producing a fascinating volcanic field to the south with abundant evidence of (Pleistocene) volcano-ice interactions as well as recent (i.e. Holocene) explosive and effusive eruptions.

I’m currently writing a paper on the volcano-ice interactions that have taken place during the Pleistocene, and I’ll write another blog entry when this is close to publication with more images than a journal will allow. Previous blog enties contain some information: Blog 1 and Blog 2

There’s also evidence of lateral transport of pyroclastic material in surrounding valleys (i.e. pyroclastic flows – or pyroclastic density currents for the pedants), as well as pyroclastic deposits formed via sedimentation from volcanic plumes. What we call ‘fall’ deposits which are important as they represent the remnants of sizeable eruption plumes in the past.

So enough of the text and onto the images.

Slide1

Western side of Quetrupillan (north to top) showing the beheaded stratocone to the north with ice-filled summit crater, along with two key geographic features – Laguna Azul and Laguna Blanca.

 

 

Picture3

Eruption 1 is a dog-leg fissure eruption (probably dacite), which in the south has been highly productive in producing lavas. In the north it has mainly resulted in initial vent clearing with the formation of craters that have cut into pre-existing Pleistocene deposits. Eruption 2 comprises part-eroded lavas that are more likely to be early than late Holocene. Eruption 3 is a thin lava flow (basaltic andesite?) that is partly covered by aeolian deposits and the rising waters of Laguna Blanca. Eruption 4 is a small lava flow than has not travelled far from its vent (hidden) to the SE.

Read the rest of this entry »

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Posted November 23, 2015 by davemcgarvie in Chile, Eruptions, Lava, Volcanism