Sernageomin reports Nevados de Chillán continues to be in yellow alert status for phreatic eruptions from its newly formed crater.
Eric Klemetti has a couple posts up about the new activity. You can find the newest at his Eruptions blog. http://www.wired.com/2016/02/restless-chilean-volcano-nevados-de-chillan-unleashes-a-series-of-explosions/
He pointed to a superb post by Dave McGarvie on Jan 30. Well worth your read. https://davemcgarvie.wordpress.com/2016/01/30/nevados-de-chillan-volcano-chile-is-it-about-to-erupt/
The activity centers on the new Arrau crater and dome complex. Appears that new magma is finding its way up into the complex and starting to interact with snow and ice on the volcano. So far, there have been explosions coming out of a newly formed crater some 30 m in diameter. Some new fumaroles have been spotted in the vicinity. IR temperature scans of the newly active area suggest that new magma is not yet particularly near the surface.
Dave McGarvie is making a prediction that this eruptive sequence may be similar to the 2003 eruptions in the dome complex. He suggests the current activity represents a vent-clearing phase as new magma works its way up into the system. This is essentially a new eruption from the newest active cone on the complex. He also notes that in previous times, such a small eruption would not have been noticed at all due to the relative remoteness of the volcano.
You can find Sernageomin’s page on Nevados here: http://www.sernageomin.cl/volcan.php?iId=32
Active webcam on Nevados can be found here: http://www.sernageomin.cl/rnvv/v-chillan.php
Nevados is located some 500 km south of Santiago, Chile. It is located near the continental divide of the Andes with a broad, populated valley to the west and drier portions of Argentina to the east. The Pacific Ocean is some 160 km to the west.
There is a ski resort and thermal spa on its flanks. http://www.powderquest.com/ski-resorts/chile/nevados-de-chillan/
Visitors recorded videos of the January eruptions from the resort. A video can be found on Erik Klemetti’s Eruptions site. http://www.wired.com/2016/01/nevados-de-chillan-in-chile-rumbles-to-life-forming-a-new-crater/
Nevados de Chillán is a line of several volcanic centers in the Southern Volcanic Zone (SVZ) of the Andean cordillera in central Chile. It is a large stratovolcano with two primary eruptive centers separated by 6 km in generally a N – S axis.
The primary eruptive centers are Cerro Blanco and Las Termas, with Cerro Blanco at the northern end of the complex. Eruptive products vary across the complex with Las Termas being primarily dacitic while Cerro Blanco is primarily andesitic to basalt. Eruptive products are sub-aerial, subglacial and snow-contact lavas, pyroclastic flows, scoria cones, tephras and lahar deposits.
The largest portion of the Las Termas complex is also called Volcán Viejo (Volcán Chillán). It was the main active vent during the 17th – 19th centuries. A new lava dome complex called Volcán Nuevo was constructed between the two ends of the stratovolcano between 1906 – 1945 and is about the same height above sea level as the other two peaks. A second lava dome complex called Volcán Arrau was constructed between Nuevo and Viejo between 1973 – 1986. It is similar in height as the other three volcanic centers. Primary eruptive products from Arrau are dacite and rhyolite, extremely viscous and evolved magma.
The new activity is taking place in the Arrau dome complex. The eruptive cycle for this volcano appears to be a series of eruptions producing explosions, lava and tephra followed by some number of years of relative quiet.
The entire complex occupies three nested calderas. Ignimbrite sheets extend more than 100 km from the complex to the south and west but have not yet been studied in detail or characterized.
Last known eruption was 2003. The complex tops out at just over 3,200 m above sea level.
The area is sparsely populated. Over a half million reside within 100 km from the complex, mostly to the west.
The complex has gone through at least three phases of volcanic activity. The initial period was a constructive pre-caldera collapse activity, a period of caldera collapse, and a constructive period of dome formation and growth thought to be a precursor to a second caldera formation period which has not yet arrived. This style of stratovolcano growth, caldera formation and subsequent stratovolcano and dome growth is common for Andean volcanoes.
The age of the volcano is at least 640 KA years BP via dating of subglacial Los Pincheira lavas. These are thought to be deposited before the caldera formation events, as they tend to flow radially from a long gone central cone. Ages of these lavas range between 640 – 90 KA years BP.
There was at least two and perhaps as many as three caldera forming events following the emplacement of these lavas. Following the caldera events, volcanism switched to the Los Termas and Cerro Blanco complexes. The oldest lavas dated from Cerro Blanco are some 24 KA years BP.
Deposits from caldera formation have been identified south and west of the complex, but have not been studied or mapped in detail. While they are probably related to the caldera forming events some 90,000 years ago, volcanologists have not made that formal connection yet. There is some suggestion of a post-caldera shield cone, which was overlain by a steep sided andesitic stratovolcano cone. There appears to be a period of relative quiet between 80 – 24 KA years ago at Cierro Blanco while there was vigorous activity elsewhere in the complex.
Cierro Blanco has two categories of volcanic units. The first are previously described voluminous lava flows that radiate from a volcanic center. These are lavas over 10 km3 in volume. The second unit was erupted from the caldera wall faults and are far less voluminous at less than 1 km3. Age constraints for the older unit is the previously mentioned 640 – 90 KA BP.
These dates are constrained by at least three caldera formation events between 90 – 80 KA BP.
Note that all eruptions from the complex took place in conjunction with massive ice and snow coverage of the complex, so there is significant interaction between magma, ice and snow.
Tectonics of the Southern Volcano Zone (SVZ) are driven by the subduction of the Nazca Plate under the South American Plate. The Chile Trench is offshore. It is filled with some 1,500 – 2,000 m of debris and erosive products from South America. Total depth of the trench is 7,000 – 9,000m. Rate of subduction is 7-9 cm.yr. Direction is generally WNW.
The SVZ has at least 60 historically active and potentially active volcanic centers in Chile and Argentina. In addition to Nevados de Chillán it contains at least three additional caldera systems formed in the last 1.1 Ma.
Subduction of the Nazca Plate steepens from around 20 degrees in the north to over 25 degrees in the south. This decreases the distance of the trench from the volcanic front by some 20 km. Average distance from the line of volcanic activity is around 280 km. Depth of the subducted slab decreases from 120 – 90 km from north to south along the length of the zone. Crustal thickness decreases from over 50 km in the north to 30 – 35 km along the length of the zone.
There is a 1,000 km long north – south fault system along the line of volcanoes called the Liqune – Ofqui Fault zone. This fault system seems to control the location of some of the larger stratovolcanoes and hundreds of smaller monogenetic eruptive centers in the central and southern portions of the SVZ. Nevados de Chillán is located in the central part of the zone. http://www.scielo.cl/scielo.php?pid=s0716-02082004000200001&script=sci_arttext
Nevados de Chillan is a large Andean volcanic complex. It went caldera some 90 ka years ago. New activity appears at this time to be an extension of recent dome building and related activity from the Los Arrau dome complex. I have not yet found any reporting of significant inflation taking place in the complex. While nothing particularly large is expected this time around, it is always possible. In preparation, Sernageomin created a 2 km diameter exclusion zone around the new activity.