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.

P1010267

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.

Holocene dacite lavas

Lavas from Eruption 1. The prominent crater with the pale interior is one of the Eruption 1 vents, but the pale interior is pyroclastic material from an older Pleistocene eruption.

 

Picture6

Eruptions on the eastern and south-eastern flanks of the stratocone. Lavas from Eruptions 6 and 7 may have travelled for 10-12 kilometres to the north. Eruption 8 is an older lava that is much eroded and/or covered by aeolian material, and in many respects is similar to most of the lavas draping the current stratocone. The prominent fault scarp is considered to be linked to the LOFZ.

14 chile pan 27 b

Eruption 3 is the lava flow on the right partly covered by Laguna Blanca. The cones of Eruption 6 are on the left-hand skyline. The pominent peak in the distance is the eroded volcano of Colmillo del Diablo, and the prominent ridge of the right is a Pleistocene fissure eruption.

Holocene tephra ring

Eruption 5 crater. Below is a bomb on the rim of the crater, and a lava lobe.

So the images above provide some insight into Holocene (recent) volcanism at Quetrupillán.

The images that follow firstly describe some of the explosive products found in the valley to the north west (Palguin), and then go on to describe some of the more enigmatic aspects of recent Quetrupillán volcanism that await further detailed study and discovery.

 

palguin alto tephra 4.JPG

Good sections through pyroclastic deposits are revealed in road cuttings. Here, OU PhD student Jonathan Moles is more interested in taking a picture of a fine speciment of a Darwin’s Frog.

palguin alto tephra 2.JPG

In this section, different pyroclastic layers can be distinguished.  Well-sorted layers usually indicate airfall (i.e. sedimentation from a plume), whereas poorly-sorted layers usually indicate lateral transport as a pyroclastic flow (PDC) or lahar.

near laguna blanca

Near Laguna Blanca, there are beds of pyroclastic material and lake sediments. These have never been studied.

Holocene lava on SE side of laguna blanca

The lava of Eruption 3 forms the uneven terrain in front of the ridge. The ridge itself is a subglacial fissure eruption. On the left of the pass are the remnants of an eroded tuff cone. There are several tuff cones in the area, but their age and origins are unknown. Below are two other tuff cone images, on the left a slump feature, and on the right a ‘dyke’ which is in fact a lava that has flowed down into a fracture in consolidated tuff, and which erosion has exposed.

 

So I hope you’ve enjoyed this little insight into this little-known Chilean volcano.  I’ll leave you with a shot of me working on one of the (Pleistocene) subglacial dacite lava domes.Dave working in Chile.jpg

Advertisements

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

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: