Report on Chaiten (Chile) — August 2013

Bulletin of the Global Volcanism Network, vol. 38, no. 8 (August 2013)
Managing Editor: Richard Wunderman

Chaiten (Chile) Declining seismicity, thermal emissions, and plumes during 2013

Please cite this report as:

Global Volcanism Program, 2013. Report on Chaiten (Chile). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 38:8. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN201308-358041.

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Chaiten

Chile

42.833°S, 72.646°W; summit elev. 1122 m

All times are local (unless otherwise noted)


In this report, we cover declining activity observed at Chaitén during 2012-2013. The Servicio Nacional de Geología y Minería (SERNAGEOMIN) had reduced the Alert Level to Green on 2 May 2011 (BGVN 36:11) and continued to monitor activity and release online bulletins. These activity bulletins were available during February 2012-October 2013. We also note the thermal alerts from MODVOLC during January 2010-April 2013.

The recent rhyolitic eruption of Chaitén began in May 2008 (BGVN 33:04) and, according to Pallister and others (2013), comprised five major phases: (1) an explosive sequence (1-11 May 2008), (2) a transitional time that included ash plumes and lava extrusion (11-31 May 2008), (3) lava flows and dome growth (June-September 2008), (4) spine extrusion and dome growth (October 2008-February 2009), and (5) endogenous lava dome growth (February 2009-early 2010). Following those phases of activity, ash plumes and thermal emissions declined during 2010-2011 (figure 30); intermittent thermal anomalies and vapor emissions dominated activity during 2011-April 2013. Since April 2013, thermal alerts were no longer reported by the MODVOLC system.

Figure (see Caption) Figure 30. On 25 October 2011, this Landsat 5 image captured a small plume rising from Chaitén's active lava dome. A) This wideview includes the caldera and surrounding region of Chaitén. Meandering river systems link the volcanic highlands with the Pacific coast. A) and B) The town of Chaitén is located at the red circle, on the delta formed by runoff from the highlands that include Chaitén ~11 km NE. Note that the scale bars are approximate. Courtesy of USGS/NASA.

SERNAGEOMIN reported decreasing seismicity during 2012-2013 (table 3). Volcano-tectonic (VT) events dominated these datasets while hybrid events were very rare. Local magnitudes (ML) and magnitudes calculated from signal duration (MD) were reported as well as the reduced displacement (calculated for long-period earthquakes).

Table 3. Seismicity during February 2012-September 2013 is reported for total earthquake counts (#EQ), volcano-tectonic earthquakes (#VT), long-period earthquakes (#LP), and hybrid (#HYB). Note that "**" indicates reporting of ML values where MD values were not reported. Reduced displacement (RD) is reported for LP events. Courtesy of SERNAGEOMIN.

  Date # EQ # VT Max ML # LP MD RD cm2 # HYB MD
2012 Feb 226 170 1.9 54 1.8 4.0 2 1.3
Mar 303 216 3.0 86 0.6 9.3 0 0
Apr 179 106 1.8 73 2 2.3 0 0
May 109 47 2.3 62 1.6 58.2 0 0
Jun 47 22 1.6 25 1 5.4 0 0
Jul 93 63 2.8 30 1.7 0.5 0 0
Aug 96 72 2.5 23 2.3 9.6 0 0
Sept 56 41 2.5 15 0.5 0.1 0 0
Oct 49 39 1.9 10 2.3 3 0 0
Nov 61 49 1.9 12 1.9 7.4 0 0
Dec 45 42 2.7 3 1.7 1.1 0 0
2013 Jan 76 55 2.9 16 2.3 11.4 5 na
Feb 43 28 1.7 15 na 0.8 0 0
Mar 5 4 1.0 1 na 1.7 0 0
Apr na na na na na na na na
May 53 44 1.9 11 1.6** 3.8 na na
Jun na na na na na na na na
Jul 67 50 0.8 17 1.3** 5.6 na na
Aug 38 29 1.4 8 1.3** 6.4 1 2.0**
Sept 5 5 1.3 na na na na na
Oct 30 21 2.4 9 1.7** na na na

When clear viewing conditions permitted, nighttime incandescence and vapor plumes were captured by the SERNAGEOMIN webcamera during February 2012-September 2013. Observations included plume heights ranging 300-600 m above the crater.

Thermal alerts. Elevated temperatures were detected from Chaitén during much of the eruption that began in May 2008. Thermal anomalies were detected by MODIS sensors on the Terra and Aqua satellites every month until September 2010 (table 4). As the eruption waned, elevated temperatures were observed less often and were absent during the months of July 2011, May 2012, August-October 2012, December 2012, March 2013, and after 2 April 2013. The MODVOLC alerts chiefly occurred in the immediate area of the crater (figure 30).

Table 4. The MODVOLC system generated alerts during January 2010-April 2013. The number of thermal alerts detected per year decreased from 2010 through early 2013. Months are highlighted blue where alerts were absent. Courtesy of HIGP.

Year Month # Days/Month # Pixels/Month
2010 Jan. 5 5
Feb. 7 9
Mar. 7 9
Apr. 6 6
May 4 4
Jun. 1 1
Jul. 2 2
Aug. 3 3
Sept. 0 0
Oct. 3 3
Nov. 1 1
Dec. 4 4
2011 Jan. 6 6
Feb. 7 7
Mar. 1 1
Apr. 4 4
May 3 3
Jun. 3 3
Jul. 1 1
Aug. 1 1
Sept. 2 2
Oct. 4 4
Nov. 1 1
Dec. 9 9
2012 Jan. 7 7
Feb. 2 2
Mar. 3 4
Apr. 2 2
May 0 0
Jun. 3 3
Jul. 2 3
Aug. 0 0
Sept. 0 0
Oct. 0 0
Nov. 2 2
Dec. 0 0
2013 Jan. 3 3
Feb. 2 2
Mar. 0 0
Apr. 1 1
May 0 0
Figure (see Caption) Figure 31. As seen here, from April 2012 to April 2013, MODVOLC generated alerts (red and orange point) on 15 days for Chaitén. Those alerts indicated elevated temperatures within 2 km of the summit area. Courtesy of HIGP.

References. NASA Landsat Program, 2011, Landsat ETM scene LT52320902011298COA00, SLC-Off, USGS, Sioux Falls, October 25, 2011.

Pallister, J.S., Diefenbach, A.K., Burton, W.C., Muñoz, J., Griswold, J.P., Lara, L.E., Lowenstern, J.B., and Valenzuela, C., 2013, The Chaitén rhyolite lava dome: Eruption sequence, lava dome volumes, rapid effusion rates and source of the rhyolite magma, Andean Geology, 40, (2): 277-294.

Geologic Background. Chaitén is a small, glacier-free caldera with a compound Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. Early work had identified only a single explosive eruption during the early Holocene prior to the major 2008 eruption, but later work has identified multiple explosive eruptions throughout the Holocene. A rhyolitic obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km from the volcano to the N and S. The caldera is breached on the SW side by a river that drains to the bay of Chaitén. The first historical eruption, beginning in 2008, produced major rhyolitic explosive activity and growth of a lava dome that filled much of the caldera.

Information Contacts: Observatorio Volcanológico de los Andes del Sur-Servicio Nacional de Geologia y Mineria (OVDAS-SERNAGEOMIN), Avda Sta María No. 0104, Santiago, Chile (URL: http://www2.sernageomin.cl/ovdas/ ); and Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).