Report on Lascar (Chile) — July 2013
Bulletin of the Global Volcanism Network, vol. 38, no. 7 (July 2013)
Managing Editor: Richard Wunderman.
Lascar (Chile) Seismicity, glow, gray plumes, and other anomalies suggest April 2013 eruption
Please cite this report as:
Global Volcanism Program, 2013. Report on Lascar (Chile) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 38:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN201307-355100.
23.37°S, 67.73°W; summit elev. 5592 m
All times are local (unless otherwise noted)
Our previous Láscar Bulletin report (BGVN 32:09) discussed behavior through July 2007. Observatory volcanologists reported plume and seismic activity during February-March 2012, and again during March-April 2013. Emissions during early April 2013 were interpreted by authorities as a weak eruption.
The Servicio Nacional de Geología y Minería (SERNAGEOMIN) furnishes on line reports on Láscar. The Observatorio Volcanológico de los Andes del Sur (OVDAS) in Temuco monitors the volcano. OVDAS observations in the form of monthly and special reports were found on the SERGEOMIN website starting on January 2012. Those reports, unless otherwise noted, formed the basis of this report.
OVDAS monitors Láscar with several webcams, with GPS, and with airborne and remote sensing surveillance (eg. Landast). Their tool kit also includes findings from images gathered by OMI (The Ozone Monitoring Instrument on the NASA Aura satellite).
Location. Láscar volcano lies within the Andes mountains, which run N to S, as seen on figure 41. The Andes contain the highest volcanoes in the world. Nearby Holocene volcanoes include Camachi at 6,046 m elevation and Colachi at 5,631 m elevation (figure 42).
|Figure 42. A N-looking oblique view of Láscar and vicinity made with Google Earth. Note Camarachi, and Colachi, two Holociene volcanoes, both less than 18 km away. Courtesy of Google Earth.|
Láscar seismic activity in 2012. In 2012, the volcano monitoring network recorded 1,679 seismic events; about 1,300 of these were hybrid earthquakes (HB) (table 4). Seismic activity increased sharply between 29 and 31 January 2012. A swarm with a total of 59 that were volcano-tectonic (VT); 491 that were long period (LP); and one that was hybrid (HB).
During 1-15 February, a total of ~350 seismic events detected, averaging ~21 per day. This included 233 LP signals. Visible activity consisted of pulsating columns of gasses reaching 50-250 m height.
|LP events, #||507||233||77||88||64||76||70||78||52||--||--||45|
Láscar reports for 2013. In 2013, the volcano monitoring network recorded 506 seismic events. About 70% of these occurred during July (table 5). There were episodes of gas emissions, increased temperatures and seismic events starting in March and continuing through 10 April. This behavior prompted OVDAS to examine the likelyhood of an eruption. In March 2013, cameras detected mainly white gas columns reaching heights to 600 m above the crater.
|2013||01-28 Feb||01 Mar-04 Apr||05-15 Apr||01-14 May||15-31 May||01-15 Jul||16-30 Jul||16-31 Aug||01-15 Sep|
|HB||--||--||--||--||--||8 out of 24||11 out of 19||--||--|
|main plume color||--||--||white/gray||na||--||brown||brown||white||--|
During the nights of 2 to 4 April incandescence appeared in the active crater. Also on 3 April gases emitted from the inside of the volcano fluctuated between white and gray, the latter taken as indicative of ash emissions. The resulting plume rose 320 m and drifted SE. No anomalous SO2 was seen in OMI (The Ozone Monitoring Instrument) satellite data.
The OVDAS/SERNAGEOMIN geologists issued a special report on 10 April 2013 discussing a 9 April flyby at 1115 in a helicopter. The observers saw intense fumarolic activity along the inner walls of the crater. The emitted plume was steady, white to brown, and smelled of sulfur.
A thermal imager that day detected temperatures of ~600°C at the bottom of the crater. Although gases often thwarted observations of the crater floor, some deformation seemingly took place there suggestive of a rise of magma. Figures 43 and 44 show two images of the active crater on 9 April.
|Figure 43. Visible light photo of the active crater at Láscar taken during an overflight on 9 April 2013 and included in the OVDAS 10 April 2013 report. Courtesy of OVDAS/SERNAGEOMIN.|
|Figure 44. Thermal image of the active crater at Láscar showing computed temperatures at ~600°C (the scale maximum). Taken during the 9 April 2013 overflight and included in the OVDAS 10 April 2013 report. Courtesy of OVDAS/SERNAGEOMIN.|
During 1-17 July 2013, Láscar's cameras observed mainly brown-colored outgassing. The plumes reached a maximum heights of 500 and 1,000 m on 1 and 13 May, respectively. Incandescence occurred on the nights of 1 and 2 July. After mid-July, the seismic activity tapered off to 10 or fewer events during the months of August and September. Láscar emitted white plumes on 4 November 2013 (figure 45).
|Figure 45. Láscar volcano, as seen amid calm conditions on 4 November 2013, capped by a faint white plume. Image taken from the OVDAS/SERNAGEOMIN webcam. Courtesy of OVDAS/SERNAGEOMIN.|
Compaction of 1993 pyroclastic flows. Welley and others (2011) examined changes to the unconsolidated pyroclastic flow deposits from the date of the 1993 eruptions to 2010. The changes were examined using a combination of shallow surface geophysical imaging tools, remote sensing observations, and field measurements. Over time these deposits become increasingly dissected by a network of deeply penetrating fractures. Based on ground penetrating radar images, the fractures propagated to depths of up to 10 m.
Welley and others (2011) associated the fractures with post-eruptive settling and compaction processes inherent in thick pyroclastic sequences. In addition, orbiting radar interferometry found subsidence over the deposit's surface of up to 1 cm/year during 1993 and 1996 with continued subsidence occurring at a slower rate thereafter.
In situ measurements 18 years after emplacement showed that 1 m below the surface, the 1993 deposits still remained 5°C to 15°C hotter than adjacent deposits. Figure 46b shows a view of the N flank. Figure 46c illustrates N flank pyroclastic sequences annotated by age in an aerial view.
2012 hazard report. SERNAGEOMIN's January 2012 hazard summary notes the danger from Láscar volcanic processes. Two of the many processes are pyroclastic flows and ash fall. Pyroclastic flows could affect the town of Tumbes, ~20 km SSE of the volcano and Talabre village, located ~10 km NNE of the volcano. The dispersion and pyroclastic ash fall could affect distant regions located to the E, where in the past there have been deposits with thicknesses of a few ten's of centimeters.
|Figure 47. Láscar hazard map showing simulated ash fall hazard areas. Modified from Argentinan report image. Courtesy of Instituto Inenco-Geonorte, Universidad National De Salta-CONICET. Image by Jose G. Viramonte.|
The Instituto Inenco-Geonorte, Universidad National De Salta-CONICET prepared a mathematical model to simulate ash fall. The Láscar eruptions served as a case study to compare to the model simulation. The fall zones from 18 April 1993, 18 Oct 1996, and 20 July 2000 are shown on figure 47.
Láscar residing in the highest and driest desert in the world. Láscar sits in the center of the Atacama High Desert (figure 48). The greater Atacama occupies 105,000 square kilometers, with a surface composed mostly of salt lakes, sand, and towards the Andes, felsic lava flows. Besides the high elevation, Vesilind (2003), reports this portion of the Atacama surrounding Láscar undergoes extremes in temperature, −25 C to 45 C, and is exceedingly arid. Thus, Láscar may reside in among the highest and driest volcanic settings in the world.
|Figure 48. The dashed square represents the Upper Atacama Desert Region [Atacama High Desert]. The city of Calama (open blue circle), and the town of San Pedro de Atacama (filled blue circle) are indicated. Courtesy of CIA world factbook.|
The climate, environment, and similar factors have been postulated to be among the factors that impact the behavior and evolution of volcanoes. For example, QU Wei-Zheng and others (2011) discuss the relevance of geology and location with regard to volcanic behavior, including earthquakes. Láscar and neighboring volcanoes may offer a means to help test these postulates.
References. Qu Wei-Zheng, Huang Fei, DU Ling, Zhao Jin-Ping, Deng Sheng-Gui, Cao Yong, 2011,The Periodicity of Volcano Activity and Its Reflection in Some Climate Factors, Chinese Journal of Geophysics, Vol. 54, No. 2, pp: 135-149.
Vesilind, Priit J. (August 2003). "The Driest Place on Earth". National Geographic Magazine. Retrieved 2 April 2013. (Excerpt)
Whelley P., Jay, J., Calder, E., Pritchard, M., Cassidy, N., Alcaraz, S., Pavez, A., (2011) Post-depositional fracturing and subsidence of pumice flow deposits: Lascar Volcano, Chile, Bulletin of Volcanology, pp. 1-21.
Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.
Information Contacts: Oficina Nacional de Emergencia Ministerio del Interior (ONEMI) (URL: http://www.onemi.cl/); Servicio Nacional de Geología y Minería (SERNAGEOMIN) (URL: http://www.sernageomin.cl/volcanes.php); Observatorio Volcanológico de los Andes del Sur (OVDAS), Temuco (URL: http://www.sernageomin.cl/volcan-observatorio.php); Jose G. Viramonte, Instituto Inenco-Geonorte, Universidad National De Salta-CONICET; Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina; and Buenos Aires Volcanic Ash Advisory Center (VAAC) (URL: http://www.smn.gov.ar/vaac/buenosaires/productos.php).