Managing Editor: Richard Wunderman
Ongoing emissions leading to a larger, late-2014 eruption with ashfall
Strombolian eruptions, ash emissions, and new effusive vents through February 2015
Fournaise, Piton de la (France)
June 2014 and February 2015 eruptions
During November 2012-December 2014, ongoing exhalations and explosions
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
Ongoing emissions leading to a larger, late-2014 eruption with ashfall
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This report summarizes behavior at Naka-dake (Nakadake) crater at Asosan (Aso, Aso-san) caldera chiefly during January 2014-February 2015. During this reporting interval Naka-dake continued to emit gas, steam, and small ash plumes. A larger eruption took place starting 25 November 2014, causing ashfall and glowing emissions. This closed a local airport, and triggered hundreds of reports on ash plumes for the aviation community by the Tokyo Volcanic Ash Advisory Center (VAAC). That eruption continued through 2014. The eruption went on into 2015 but was generally described as intermittent during late December 2014 through at least the end of February 2015. The Alert Level remained at 2 (on a scale increasing from 1 to 5) for the duration of the reporting interval. Our last report, BGVN 37:08, described the emission of ash plumes and other behavior during May-June 2011. Some remarks in this report also refer to earlier behavior, for example, a short subsection includes what JMA recorded as important in a terse summary of 2011.
Eruption details were extracted and synthesized mainly from Japan Meteorological Agency (JMA) sources. JMA frequently communicated with the Tokyo VAAC about Asosan’s eruptive status. This report also discusses Volcano Ash Advisories (VAAs) issued by the JMA’s Tokyo VAAC. For many of the VAAs, evidence of ash-bearing plumes reported by JMA could not be reliably detected in the satellite images. For example, the images were sometimes obscured by overlying weather-cloud cover. The plumes were also generally only rising to a few kilometers in altitude. In at least some cases, the low plumes appeared bent by high winds.
Naka-daka Crater Number 1 remained the active vent for the most part during the past eight decades. That same pattern held true during this reporting interval when myriad small eruptions, often to or below 1 km above the crater rim were documented. Visibility was sometimes impaired but monitoring instrumentation confirmed a pattern of ongoing eruption. In some cases, the eruption was not clearly seen but fresh ash was recorded. Webcameras regularly documented incandescence both in the crater and onto the crater rim. Smaller ash plumes were too numerous to mention except in occasional cases. High winds were often mentioned, which may have bearing on restricting plume heights.
Location and brief background. Asosan is located on the S of the main island of Japan (Honshu) on the island of Kyushu (figure 32).
|| Figure 32. Location maps showing (circular ‘global’ inset) Japan, and (larger map) the location of Asosan (Aso) on Kyushu island. Taken from The Daily Mail news article issued on 28 November 2014 (Malm, 2014).
The rim of Nake-dake is unusually developed for such an active volcano. Both a road and cable car carry tourists there. Shelter dugouts are provided around the crater. The Aso Volcano Museum is located nearby.
Figure 33, made from radar imagery, shows Asosan’s morphology.
|| Figure 33. Morphology of the Asosan caldera seen in shaded relief (color scale for elevations absent). N is towards the top; the N-S cross-caldera distance is ~25 km. Note the central highlands, a series of ~17 post-caldera cones that includes the active Nake-dake and its Crater Number 1. The caldera’s topographic boundary is distinct on all sides but a drainage has breached the W side. This caldera vented four sets of massive eruptive deposits (pyroclastic-flows and associated ash-falls; Miyabuchi, 2013; Fujii, 2001). Source: Wikipedia (from a Nasa Shuttle Radar Topography Mission).
JMA (2013) includes a map showing the location of 12 calderas in Japan. Asosan, the largest and most active, has had many small eruptions in the past few thousand years, including many witnessed eruptions in the interval of recorded history. Spica (2013) discusses Aso in the context of other calderas in the Kyushu region.
Figure 34 shows a shaded-relief map focusing on the post-caldera cones in the central highland area.
|| Figure 34. A shaded relief map of the elevated central area (post-caldera cones and their craters) of the Aso caldera, adding naming labels in English of some of the main features. As seen in the previous figure, the caldera floor (moat) is outside and encircling this central topographic high. Both conventional topographic and a digital elevation map (50 m grid) were used to make this map, which was published by the Geospatial Information Authority of Japan. Source: JMA (2013).
JMA’s website features this summary on Asosan.
“Asosan (Aso Volcano) comprises the Aso caldera and post-caldera central cones. The Aso caldera, 25 km north-south and 18 km east-west in diameter, was formed by four gigantic pyroclastic-flow eruptions from approximately 270,000 to 90,000 years ago. Post-caldera central cones were initiated soon after the last caldera-forming eruption, producing not only local lava flows but also voluminous tephra layers which fell far beyond the caldera. Nakadake Volcano, which is the only active central cone of basaltic andesite to basalt [composition], is one of the most active volcanoes in Japan. The active crater of Nakadake Volcano is a composite of seven craterlets aligned N-S [elongate zone of depressions to the left of the label “Nakadake” and above the letter ‘t’ in the label “Nakadake-Crater” on figure 34; see also SEAN 04:07 for a sketch map focused on this area)]. Only the northernmost [Nakadake] crater (No. 1 crater) has been active in the past 80 years, although some others were active before the 1933 eruption. The Nakadake No. 1 crater is occupied by a hyperacidic crater lake during its calm periods. During active periods, its volcanic activity is characterized by ash and strombolian eruptions and phreatic or phreatomagmatic explosions.”
According to Fujii and others (2001), “Aso caldera in central Kyushu, Japan, is one of the largest calderas in the world and covers an area of 380 km2. In late Pleistocene time, eruptions of voluminous pyroclastic flows occurred intermittently, resulting in formation of the caldera. The Aso pyroclastic-flow deposits are divided into four major units, i.e. Aso-1, Aso-2, Aso-3, and Aso-4 . . . [and] welded tuffs of these units are widely distributed in central Kyushu, and are generally well suited for paleomagnetic research . . .. K-Ar ages for Aso-1, Aso-2, Aso-3, and Aso-4 have been determined to be 266 ± 14 ka, 141 ± 5 ka, 123 ± 6 ka, and 89 ± 7 ka, respectively (Matsumoto and others, 1991).”
JMA summary for 2011 activity. JMA (2013) tabulated a summary of witnessed events (eruptions, possible eruptions, damage, significant behavior, etc.) at Asosan going back to the year 553. In the most recent behavior discussed, the authors briefly note that during 2011 (an interval they term Heisei 23) the following behavior occurred.
First, after the Mw ~9 Tohoku earthquake ~70 km off the Pacific coast on 11 March 2011, earthquakes temporarily increased roughly 10 km to the NW of the active crater. Second, very small emissions of gray-white volcanic ash occurred during 15 May to 9 June 2011. On 15 May a very small amount of tephra fall was confirmed at Sensuikyo, ~2 km to the NE of the Nakadake Number 1 crater.
2014 Activity. JMA reporting for 13 January 2014 noted the emission of a very small eruption. This came in the wake of increased tremor in late December 2013 and an increase in hazard status to Alert Level 2. (As previously mentioned, the Level remained at 2 for the duration of the reporting interval.) Further escalation in tremor took place on 2 January. On 10 January emissions reached 1,200 metric tons/day (t/d) of sulfur-dioxide (SO2). The 13 January 2014 eruption took place at Naka-dake, which emitted a grayish-white plume that rose to 600 m that traveled S and deposited traces of ash. The resulting report from the Tokyo VAAC (a Volcanic Ash Advisory (VAA)) stating they failed to detect identifiable ash in the plume data captured on satellite images.
The small 13 January 2014 eruption triggered the first Asosan VAA in over a year. The other VAAs during January 2014 were issued on the 27th, 29th, 30th, and 31st. On one of those days, two VAAs were issued, and thus, for January there were 6 VAAs.
Bulletin editors note that the VAAs are not a linear measure of the number of eruptions. Small eruptions may not trigger a VAA at all. Several consecutive VAAs may occur associated with a single potentially larger eruption, which are issued in an effort to track an ash plume. Again, this may be an example where the number of VAAs is not reflective of the number of eruptions. Despite this, the number of VAAs are easily counted owing to new online archives. The Tokyo VAACs online presentation system is tablular in nature and is thus well suited to enable a count of reports per month.
The tally for VAAs on Asosan during 2013 was zero. The tally for 2014 involved 171 VAAs. Monthly totals for 2014 are as follows: January, 6; February, 3; March-July, 0; August, 3; September, 2; October, 0; November, 25; and December, 132. For further comparison, the tally for January and February 2015 involved 250 VAAs, with January, 132, and February, 118.
JMA reported that seismicity increased from 21 to 23 January 2014, and then decreased on 24 January. On 23 January a volcanologist observed ash plumes rising from the central vent on the crater floor. On 29 January an ash plume reported by a pilot rose to 2.7 km altitude and drifted NW. Later that day a plume rose to an altitude of 1.5 km and drifted N. JMA reported that a very small Asosan explosion occurred on 31 January. An off-white plume rose 100 m above the crater rim and drifted S.
On 5 February 2014 scientists measured decreased SO2 emissions and fewer volcanic earthquakes.
According to the Tokyo VAAC during 30 August-1 September 2014 eruptions continuously emitted ash plumes that rose to heights of 1.2-2.1 km drifting N and NE. For example, on 1 and 6 September eruptions emitting trace amounts of ash sent plumes 600 m above the rim. (Tokyo VAAC issued VAAs stating this plume lacked identifiable ash in available satellite images.) JMA instrument surveys established SO2 flux rates on 21 August of 1,000 t/d, and in early September of 1,200 tons/day. Counts tallying daily volcano-tectonic earthquakes (and cases of tremor) were made during 1-4 September occurring in the range 48-92 (429-500); during 5-7 September occurring the in the range 55-129 (401-463); during 8-15 September occurring in the range 394-564 (80-174).
JMA reported that during 8-16 September a persistent white plume was observed 1 km above the crater.
Preliminary counts for volcanic earthquakes (394-564 per day) and tremor (80-174 per day) were reported during 8-15 September. Field surveys conducted on 9 and 12 September yielded elevated temperatures from fumaroles and the surface of the S crater wall.
Tremor accompanied a very small eruption recorded on 22-24 October. Ashfall observed on the 24th indicated another such eruption.
During 7 September and 24 November 2014, VAAs were absent for Aso. In contrast, during 25 November 2014-31 December 2014 there were 171 VAAs issued. Multiple VAAs were issued on several different days in this later interval, for example, on 26 November, 7 VAAs were issued.
Asosan continued to erupt during the 7 September-24 November 2014 interval. Some monitored parameters such as earthquakes, tremor, and SO2 emissions were elevated. A small eruption took place on 6 September, for example, sending a plume to 600 m above the crater. During 8-16 September JMA noted a persistent white plume 1 km above the crater. During the week 12-18 November, a steam plume rose 400 m above the crater rim.
With the start of the surge in VAAs beginning on 25 November 2014 (noted above), a stronger and comparatively sustained eruption began. During the eruption on the 25th an ash plume rose to 1.8 km above the crater rim. Ash soon fell to the E in Hanoi Aso (Kumamoto Region), Taketa (30 km NE, Oita Region), Gokase (25 km WSW, Miyazaki Region), and in Minamiaso (10 km SW, Kumamoto Region). Incandescence at night was seen with webcams.
On 26 November tephra ascended 100 m above the crater rim and an ash plume rose 1 km. Tremor began a few hours before the eruption and on the 26th, continued to be elevated. The eruption continued on 27 November; ash plumes rose 1.5 km. Volcanologists observed a strombolian eruption and found 7 cm of fresh ash that contained fist-sized scoria. Ash fell to the W, affecting the city of Kumamoto (38 km WSW). According to a news article, flights in and out of Kumamoto airport were either cancelled or diverted. On 28 November ash plumes rose 1.5 km. The eruption continued through at least 30 November; ash plumes rose at most 1.5 km and incandescent material was ejected onto the crater rim.
Although inclement weather restricted views of the crater, monitored parameters and available views indicated that the 25 November eruption continued through to at least 22 December, when it became intermittent. Ash plumes to about 1 km above the crater rim and incandescent material on the crater rim were common through the end of the year (and beyond, through this reporting interval ending in February 2015, and described as the ongoing eruption.
A news report in the 28 November 2014 issue of the Daily Mail by Sara Malm (Malm, 2014) indicated dozens of cancelled flights at Kumamoto’s airport. That report included the Associated Press photo seen in figure 35. The date of the photo in that article was ambiguous, but a different article with the same photo (see caption) gave 26 November 2014 as the photo’s date. The angled, bent-over character of the ash plume and location of Crater Number 1 (the active crater, at the N end of the row of craters) indicate the view was from the NW and implies strong winds roughly from the N.
|| Figure 35. A photo taken on 26 November 2014 of Asosan in eruption. The gray ash plume is escaping at Nake-dake Crater Number 1 blowing roughly S. The plume does not rise vertically. The plume ascends near the vent but for some distance beyond the vent the plume descends. At distance the plume appears to spread over considerable vertical extent, from near the ground surface to above the field of view. Source: Phys.Org news (crediting AP/Kyodo News).
An undated video in Malm (2014) also showed the plume. The video also showed an aerial view of the visitor area on the crater rim, which was blanketed in gray ash. Other scenes included children walking to school wearing dust masks and carrying folded umbrellas, and close up shots of what appeared to be dark colored, highly vesicular spatter.
In a 29 November 2014 MODIS image of the region, Asosan was under weather clouds but a clear view revealed a prominent ~30-km-long, beige-colored, funnel-shaped area trending SE. This was interpreted by Nasa Earth Observatory authors Jeff Schmaltz and Adam Voiland as airborne ash. Webcamera images around this time showed a glowing pit crater with extensive areas containing incandescent tephra around it. A copious plume also discharged nearby.
During a field survey on 10 December volcanologists observed 20-cm-wide blocks near the crater and 5- to 10-cm-wide blocks within 1.2 km SW of the crater. During 12-15 December the plume rose 1 km above the crater rim and ash fell to the E in Hanoi Aso (Kumamoto Region).
JMA reports for 15-30 December described the usual eruptive ash plumes that again rose 600-1,000 m above the crater and some cases of still glowing material on the crater rim. SO2 fluxes were 2,000-3,100 t/d during 15 and 18 December.
2015 activity. As noted above, the VAAs for 2014 totaled 171, and the VAAs for the months of January and February 2015 totaled 250. This is consistent with ongoing eruption at Asosan, which was also the basic conclusion in JMA reports from monitoring and direct observations during January-February 2015, although they often described the eruption during both these months as intermittent.
JMA reported cases during January where plumes rose up to 1 km above the crater, and in some cases glowing material reached the crater rim. JMA reported SO2 fluxes of 500-2600 tons of SO2. Both tilt and GPS instrumentation recorded slight growth across the active crater. A pilot report on 29 January indicated an ash plume to 2.7 km altitude (~1.1 km above the rim) and drifting NW.
An image acquired on 13 January 2015 was discussed by Jesse Allen and Adam Voiland of Nasa Earth Observatory. They reported that the image was from the Operational Land Imager (OLI) on Landsat 8. They indicated that it showed ash drifting ten’s of kilometers S from Aso.
For February 2015, JMA reported episodes of volcanic earthquakes, high-amplitude tremor, and infrasound data that continued to indicate ongoing intermittent eruptions. Webcamera views again documented cases of glowing material reaching the rim during the first half of the month. Plumes again rose up to 1 km above the crater rim. JMA reported intermittently detected eruptions, including during 2-6, 9-13, and 16-20 February.
Fujii, J., Nakajima, T., & Kamata, H., 2001, Paleomagnetic directions of the Aso pyroclastic-flow and the Aso-4 co-ignimbrite ash-fall deposits in Japan. Earth, planets and space, 53(12), 1137-1150. (URL: http://download.springer.com/static/pdf/873/art%3A10.1186%2FBF03352409.pdf?originUrl=http://link.springer.com/article/10.1186/BF03352409&token2=exp=1434307643~acl=/static/pdf/873/art%253A10.1186%252FBF03352409.pdf?originUrl=http%3A%2F%2Flink.springer.com%2Farticle%2F10.1186%2FBF03352409*~hmac=b718e24427a5900c5057d59ebb12b501c1ae870b932122de89cc3a01a5f5318f ).
JMA (Japan Meteorological Agency), 2013, National Catalog of the Active Volcanoes of Japan (4th edition; online English version), (URL: http://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/souran_eng/menu.htm ) (accessed in June 2015)
Khin, K, 2013, Field trip to Aso volcano, Kyushu, Japan, Slideshare.net (13 annotated slides) (URL: http://www.slideshare.net/kyikyaw2/field-trip-to-aso-volcano-kyushu-japan )
Malm, S, 2014, Flights cancelled across Japanese region after Mount Aso volcano erupts for the first time in 22 years, spewing lava, smoke and a kilometre-high ash cloud, The Daily Mail 28 November 2014 (7 graphics files and a 58-second video) (accessed online June 2015) ((URL: http://www.dailymail.co.uk/news/article-2852674/Volcano-south-Japan-erupts-disrupting-flights.html#ixzz3d5POqZhu )
Matsumoto, A., K. Uto, K. Ono, and K. Watanabe, 1991, K-Ar age determinations for Aso volcanic rocks—concordance with volcano stratigraphy and application to pyroclastic flows, Abstracts to Fall Meeting in 1991, Volcanol. Soc. Japan , 73 (in Japanese).
Miyabuchi, Y, 2013, A 90,000-year tephrostratigraphic framework of Aso Volcano, Japan, Sedimentary Geology, Volume 220, Issues 3–4, 15 October 2009, Pages 169-189, ISSN 0037-0738, (URL: http://dx.doi.org/10.1016/j.sedgeo.2009.04.018 ; http://www.sciencedirect.com/science/article/pii/S0037073809001006 )
Spica, 2013, Southern Japan Calderas, Volcano Café (Volcano discussions in your living room), Wordpress.com (22 July 2013)(accessed June 2015) (URL: https://volcanocafe.wordpress.com/2013/07/22/southern-japan-calderas/ )
Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 cu km of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 AD. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Aso Volcano Museum (URL: http://www.asomuse.jp; and Jeff Schmaltz and Adam Voiland, NASA Earth Observatory (URL: http://earthobservatory.nasa.gov).
37.734°N, 15.004°E; summit elev. 3330 m
All times are local (unless otherwise noted)
Strombolian eruptions, ash emissions, and new effusive vents through February 2015
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Our last report (BGVN 39:11) covered activity at Etna through 13 June 2014, which consisted primarily of ongoing emissions of E-directed lavas from a vent area on the lower E flank of the New South East Crater (NSEC). This report, summarizing first-hand accounts by the Istituto Nazionale di Geofisica e Vulcanologia (INGV-Catania), covers the subsequent interval from 14 June 2014 through 2 February 2015. INGV described several eruptive episodes, including strombolian eruptions, ash emissions, and the appearance of new effusive vents at the E base of the North East Cone (NEC) and on the high E flank of the NSEC cone.
2014. On 14 June a new eruptive episode began within the NSEC, with near-continuous strombolian explosions and lava fountaining. Fine ash emissions were concurrent with lava that began to overflow the edge of the South East Crater (SEC), forming a flow that continued downhill on the W wall of Valle del Bove. During the morning of 15 June the overflowing lava followed the fissure that had been formed on 28 November 2013. Explosive activity occurred from three vents inside the crater. A spatter cone also formed in the NSEC’s E sector, partially filling the fissure formed on the high NE flank during eruptions of late December 2013, and January–March 2014. During 14-15 June tremor increased sharply and remained moderately high until 18 June, when it returned to normal levels.
INGV noted that this lively strombolian activity over the course of four days was similar to the episode of effusive lava emissions observed during 14-16 and 19-31 December 2013 in terms of duration and intensity.
After images of a thermal anomaly in webcam images from Monte Cagliato, located on the E flank of Etna, a new, small fissure (tens of meters long) at the E base of the North East Crater (NEC) was observed by INGV Etna observatory personnel during 5-6 July. The vent was located between 3,015 and 3,025 m elevation. Weak spattering from this vent fed a lava flow that extended ~100 m within the saddle of the NSEC and SEC cones. Weak and sporadic strombolian explosions and small ash emissions were observed during 6-7 July from NSEC, but by 11 July this activity had ceased. Activity from the new fissure continued through 11 July with frequent strombolian explosions that were audible in nearby towns. The lava flow diverged; the longer of the two branches extended ~1.5 km, reaching the bottom of Valle del Leone.
On the morning of 25 July about 1114 local time, a new eruptive vent opened near the same eruptive fissure. This new vent (“25 July vent”), located at a distance of about 150-200 m to the N of the one from 5 July, was a source of strombolian explosions, accompanied at times by modest quantities of ash. This activity continued through 31 July. The strombolian explosions occurred at intervals of about 2-5 seconds and were often accompanied by visible compression waves (“flashing arcs”) and audible rumblings up to a few tens of meters away, mostly in the E and NE sectors of the volcano. As previously observed, for example during the paroxysmal episode at the NSEC during 14-16 December 2013, the rumblings were interpreted as the result of explosions of gas bubbles inside the eruptive vent. Emissions of bombs and scoria occasionally rose 200 m high and fell within a few hundred meter radius around the vent. In a few instances, the explosions were accompanied by small quantities of ash. The lava flows, which had reached ~1.8 km during the preceding week, (halting on the saddle between the Valle del Leone and the Valle del Bove), had in the recent days overlapped the earlier ones, with active fronts at least 1 km from the effusive vent.
On 9 August INGV reported a strong decrease in volcanic tremor. From the 25 July vent, there began a gradual increase in the ash emissions that formed an ash plume, which rose to 1 km above the vent area and renewed strong strombolian activity in the evening. Strombolian activity increased at NSEC and was accompanied by small emissions of black ash that remained within the crater.
With the intensification of activity at the NSEC, the eruptive activity at the E flank of the NEC diminished. At 0645 on 9 August an effusive vent opened on the high E flank of the NSEC cone, which caused a small landslide and emitted a lava flow that after an hour had reached the E base of the cone. During the first 24 hours of activity, a small pyroclastic cone in the W portion of the NSEC summit appeared, increasing the height of the NSEC structure that began to grow in 2011. On 13 August INGV reported continued strombolian explosions, accompanied by modest emissions of ash and lava from a single vent on the high E flank of the NSEC. The lava flows emitted from the effusive vent to the E had almost ceased to advance the evening before, but two new branches were overlapping the earlier flow. The longest flow changed direction to later descend about 3 km NE toward Monte Simone. INGV reported that the eruption at NSEC had ended on 15 August and that the lava flow activity had ceased by 16 August. See figure 151.
|| Figure 151. This photo was taken on the morning of 16 August 2014 from the town of Tremestieri Etneo (from 20 km S of Etna). It shows Etna’s NSEC (at right) with its new peak formed during the eruptive episode of 9-15 August. The old SEC cone (which appears lower) resides at left. Courtesy of Istituto Nazionale di Geofisica e Vulcanologia (INGV-Catania).
Beginning in the afternoon of 7 October through 16 October the NSEC produced weak and intermittent explosive activity; small ash puffs were rapidly dispersed by the wind. During some nights small strombolian explosions ejected incandescent material a few tens of meters above the crater rim.
Starting at 1850 on 28 December the NSEC produced a short but intense eruption characterized by lava fountains, lava flows, and an ash plume that drifted E, and caused ash and lapilli fall in the nearby towns of Milo, Fornazzo, Sant’Alfio, and Giarre. It was the first typically “paroxysmal” event at the NSEC since 2 December 2013. Inclement weather prevented observations of the summit area, so the erupting crater was not identifiable. Two lava flows traveled E and NE, towards the Valle del Bove. Tremor began to decrease at 2030, and indicated that the eruption was over at 2200 (figure 152).
|| Figure 152. Lava flows deposited associated with Etna’s large 28 December 2014 eruption (red). N is towards the top. The NSEC vented on a fissure developed a few hundred meters to the SE of the SEC (NNW-trending dashed blue line). Courtesy of INGV.
On 29 December, cameras viewing Etna recorded small ash emissions from the NSEC and persistent glow from the saddle between the SEC and NSEC cones at dusk. INGV indicated that this paroxysmal episode occurred at a series of eruptive vents along a NE-SW fissure that cut across the NSEC and the southern flank of the old SEC. From the two extremities of this fissure lava flows emerged, traveling SW toward the area of Milia-Galvarina and NW toward the northern part of the Valle del Bove near Monte Simone, reaching lengths of about 4.5 and 3.3 km, respectively (figure 152).
2015. During the night on 1 and 2 January, cameras recorded intermittent flashes from Voragine Crater (one of four summit craters), indicating strombolian activity there for the first time in nearly two years. At 0730 on 2 January explosions at NSEC generated ash plumes that drifted SW. Emissions ejected pyroclastic materials up to ~150 m above the crater rim, which intensified during the evening of 3 January.
At night during 6-7 January the frequency of strombolian explosions at the Voragine Crater decreased; however, some of the explosions ejected incandescent pyroclastic material outside of the crater and onto the W and SW flanks. On 7 January many of the small explosions generated brown ash plumes that rose a few hundred meters above Etna's summit and quickly dissipated. Strombolian activity increased on 8 January, possibly from two vents within the crater. Pyroclastic material continued to be ejected out of the crater. Early on 9 January strombolian activity again decreased and gave way to ash emissions that rose several hundred meters. During the evening on the same day some ash emissions were accompanied by incandescent pyroclastic material that at times fell on the external flanks of the central summit. Ash emissions continued the next morning, decreased, and had almost completely ceased by late morning. Ash emissions rapidly resumed in the afternoon and were sometimes accompanied by strombolian explosions. During the morning of 13 January, new ash emissions began at the Voragine. For some hours, these emissions were continuous, but successively diminished in the afternoon to every 5-10 minutes. Marco Neri, of the INGV- Osservatorio Etneo, during a helicopter overflight on 14 January, captured a clear view of these emissions and of the summit crater area (figure 153).
|| Figure 153. Summit craters of Etna seen from helicopter on the morning of 14 January 2015, looking NW. In the foreground is the cone of the New South East Crater (NSEC), its summit vent being much enlarged after the 28 December 2014 paroxysm, and the old South East Crater (SEC), with an extensive fumarolic area on the saddle between the two cones. Note the two conspicuous eruptive fissures (labeled), one on the NE flank of the NSEC (in the lower right portion of the image), and the other on the S flank of the old SEC (which opened on 28 December 2014). In the background are the Bocca Nuova (at left), the Voragine (center, emitting a dense white vapor plume), and the North East Crater (NEC) (at right). The town visible in the distance at upper right is Randazzo, on the N-NW flank of Etna. Photo and caption courtesy of Marco Neri, INGV-Osservatorio Etneo.
In the evening on 14 January weak strombolian activity was recorded at the Voragine Crater and NEC. The next day, occasionally pulsating ash emissions rose from the NEC and drifted SE. Ash emissions continued through 17 January; cloud cover prevented observations of the summit area on 18 January.
A new eruptive episode began on 31 January and continued through the morning of 2 February. Poor meteorological conditions prevented views of the summit area during the first 36 hours of the eruption. During improved viewing conditions on the evening of 1 February, volcanologists observed lively strombolian activity from a single vent in the saddle between the SEC and NSEC cones. Explosions occurred every few seconds and ejected incandescent bombs 200 m high, which fell on the S flank of the SEC. At the same time, from a vent at the southern base SEC cone corresponding to the lowest part of the SE eruptive fissure from 28 December, a lava flow issued that traveled 2 km S, dividing into two branches. At dawn on 2 February the strombolian activity produced a dense ash cloud that drifted E. At about 0750 emissions stopped, and volcanic tremor suddenly decreased.
Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater (the latter formed in 1978). Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.
Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/).
Piton de la Fournaise
21.244°S, 55.708°E; summit elev. 2632 m
All times are local (unless otherwise noted)
June 2014 and February 2015 eruptions
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Piton de la Fournaise is located on Réunion island, which lies to the E of Madagascar in the Indian Ocean (figure 84). In this Bulletin report, we discuss eruptions in June 2014 and February 2015. The June 2014 eruption took place on 21 June, from 0135 to 2109 local time. The February 2015 eruption occurred from 1100 local time on 4 February to 2230 local time on 15 February. In this report, all times are local unless otherwise stated (local time= UTC + 04 hours). This report represents a synthesis of available information published by Observatoire Volcanologique du Piton de la Fournaise (OVPDLF).
Our last Bulletin report on Piton de la Fournaise (BGVN 37:03) documented increased seismicity and eruptive activity from August to December 2010. Piton de la Fournaise’s last eruption took place from 14 October 2010 through 10 December 2010 (BGVN 37:03).
||Figure 84. Map of Reunion Island, highlighting the location of Piton de la Fournaise, a basaltic shield volcano. As shown in the inset map (top right corner), Reunion is located to the E of Madagascar. Source: Observatório Vulcanológico Geotérmico Açores.
June 2014. Piton de la Fournaise erupted on 21 June 2014, ending a three and a half year period of quiescence that began on 11 December 2010.
Preceding the eruption, Piton de la Fournaise experienced a period of high activity from 7 to 20 June 2014. Table 4 details the number of volcano-tectonic (VT) earthquakes and rock-fall events recorded during this interval. The greatest number of daily VT earthquakes was recorded on 20 June, and highest number of rock-fall events occurred on 17 June. Through email correspondence, OVPDLF personnel reported that over this period (7-20 June), no deformation or significant gas emissions were detected. They also reported that observed seismicity occurred between 500 and 1,200 m above sea level (a.s.l.).
Table 4. The number of volcano-tectonic (VT) earthquakes and rock-fall events recorded at Piton de la Fournaise from 7 to 20 June 2014, which was considered a period of high activity. Source: email correspondence with OVPDLF personnel.
|Date (June 2014)
||Volcano-tectonic (VT) earthquakes
On 21 June 2014, at 0006, a seismic crisis began and continued for 74 minutes (email correspondence). Then at 0020, deformation began and persisted for ~3 hours (email correspondence). At 0120, tremor was detected and, at 0135, an eruption began as verified by OVPDLF cameras, which captured incandescence given off by the eruption (email correspondence). The venting took place within Enclos Fouqué on the ESE side of the central cone (figure 85) (email correspondence). OVPDLF reported that the eruptive fissures on the cone’s ESE side sat between the Maillard crater and a small plateau at ~2300 m altitude (figure 85) (OVPDLF, 2014a).
During the morning of 21 June, a helicopter flyby noted (a) the presence of two eruptive fissures. From the more active fissure, small lava fountains emanated and built a spatter rampart; (b) two lava flows developed and travelled more than 1.5 km from the more active fissure. One of the flows, continued moving ~250 m E after passing the Langlois crater and the other flow continued ~500 m E-S after passing the Langlois crater (the Langlois crater is located ~2 km SE of the Dolomieu crater, figure 85); and (c) a very dilute SO2 plume extended N (OVPDLF, 2014a).
|| Figure 85. Topographic map of Piton de la Fournaise, which includes the names of features associated with the volcano (the labelling on the map is in French; cratère translates to crater in English). Source: Gaba (2007).
During 21 June 2014, OVPDLF raised the Alert Level to 1 (“probable or imminent eruption”), and public access to the volcano was restricted. According to email correspondence with OVPDLF personnel, the eruption ended at 2109 on 21 June. OVPDLF further reported that the intensity of the detected tremor decreased during the day and disappeared at 2109 (OVPDLF, 2014a).
November and December 2014. On 2 December 2014, OVPDLF published an activity report (OVPDLF, 2014b), which indicated the following, (a) 113 VT earthquakes were recorded between 1 November and 1 December, with the highest number of earthquakes being recorded on 1 November (figure 86); (b) the majority of the earthquakes were located between 500 and 1,000 m a.s.l. at the base of Piton de la Fournaise’s summit; (c) deformation registered by OVPDLF’s geodetic network remained the same since September 2014; and (d) since 1 September 2014, the geochemical station at the summit detected low emissions of SO2 that were often coupled with CO2, H2O and H2S. That report also stated that on 1 November 2014, the hazard status “Vigilance Volcanic phase” was initiated due to increased geophysical activity. OVPDLF (2014b) stated that this status was lifted on 1 December 2014.
|| Figure 86. Histogram of the number of volcano-tectonic earthquakes recorded from 1 November 2014 to 1 December 2014. A total of 113 VT earthquakes were recorded over this interval and the highest number of earthquakes was recorded on 1 November 2014. Source: OVPDLF, 2014b.
February 2015. The next eruption at Piton de la Fournaise began on 4 February 2015. The information in this section was found in the reference, OVPDLF (2015), unless otherwise stated. Between 0400 and 0900 on 4 February, 180 earthquakes were recorded, five of which had magnitudes greater than 2. At 0910, a seismic crisis started and at 1050, a volcanic tremor began. Ten minutes later, at 1100, an eruption began at an eruptive fissure on the S flank of Piton de la Fournaise’s cone within Enclos Fouqué. Due to the eruption, Alert Level 2-2 (“ongoing eruption”) was declared.
On 5 February 2015, the eruption continued even though the intensity of the tremor had decreased since its initiation on 4 February. OVPDLF reported that the eruptive fissure formed 100 m W of Bory crater (figures 85 and 87). The fissure had a length of ~500 m and activity was reported to be concentrated at its southernmost end. The fissure emitted a lava flow that travelled S-SW, and after passing Rivals crater, it divided into several branches as it continued to spread farther S and SW (figure 87). The southernmost branch of the flow travelled passed Cornu crater (figure 85). That evening, at 1800 local time, the tremor had significantly decreased in intensity. The intensity of the tremor was about six times lower than it was at the beginning of the eruption. The eruptive fissure remained active and projected lava ~10 m high.
The eruption continued on 6 February 2015. The tremor intensity was still very low and the lava flow and its branches were still active. OVPDLF reported that during field observations, there was low levels of outgassing and material projected from eruptive vents had built small cones. On 8 February, the eruption continued and low magnitude earthquakes located in the upper part of Piton de la Fournaise reappeared. Despite poor weather, OVPDLF observed that lava continued flowing from the vents and one flow travelled farther W. By 9 February, no significant changes were noted and by late morning, the eruptive fissure was weakly active and only small splashes of lava were observed.
|| Figure 87. Map highlighting the margins of the lava flow and its branches in red as of 8 February 2015. For scale, the Dolomieu crater is ~1.0 km in E-W diameter. The lava that fed this flow was emitted from an eruptive fissure 100 m W of Bory crater. On the map, Bory crater is the small indent to the left of the larger Dolomieu crater. The flow length is ~2.4 km. Although the eruption continued until 15 February, there was little change to the basic pattern of the lava flow and its branches according to OVPDLF. Source: OVPDLF.
The eruption continued in a similar manner until 15 February 2015. Between 10 and 15 February, OVPDLF reported that the tremor remained low and there were no significant changes in other recorded geophysical parameters. During this interval, poor weather conditions sometimes hindered observations. On the morning of 14 February, due to the absence of clouds, OVPDLF observed a clear plume rising between 2.8 and 3 km in altitude, and concluded it was probably rich in water vapor.
In the morning of 15 February, the tremor was low and stable, and equivalent to what was recorded in previous days. According to OVPDLF, at 1700 on 15 February, the tremor began to decrease in intensity. The tremor then underwent a few hours of rapid fluctuations in its intensity, before disappearing at 2230. With the disappearance of the tremor, the eruption ended. The following day, Volcano Discovery reported that the Alert Level had been lowered.
References. Gaba, E. (Wikimedia Commons user, Sting), 2007, Topographic map of the Piton de la Fournaise shield volcano on the Réunion island, Wikipedia (initial image from the NASA Shuttle Radar Topography Mission), URL: http://commons.wikimedia.org/wiki/File:Piton_Fournaise_topo_map-fr.svg#/media/File:Piton_Fournaise_topo_map-fr.svg, accessed on 27 May 2015
OVPDLF, 2014a, Actualités (News), URL: http://www.ipgp.fr/fr/ovpf/actualites-ovpf, accessed in June 2014
OVPDLF, 2014b, Bilan d’activité à la levée de la vigilance volcanique (Activity report to the lifting of the volcanic alert), URL: http://www.ipgp.fr/fr/OVPDLF/communique-de-lOVPDLF-2-decembre-2014, accessed on 10 June 2015
OVPDLF, 2015, Archive actualités (News Archive), URL: http://www.ipgp.fr/fr/OVPDLF/archive-actualites, accessed on 27 May 2015
Observatório Vulcanológico Geotérmico Açores, 2015, Notícia nº 1682 - Vulcão Piton de la Fournaise, Ilha da Reunião: nova erupção registada este domingo (News No. 1682 - Piton de la Fournaise volcano, Reunion Island: new recorded eruption on Sunday), URL: http://ovga.centrosciencia.azores.gov.pt/sites/default/files/Map_ide-reunion-piton-de-la-fournaise.jpg, accessed on 10 June 2015
Volcano Discovery, 2014, Piton de la Fournaise volcano (La Réunion): eruption ends, URL:
http://www.volcanodiscovery.com/piton_fournaise/news/45631/Piton-de-la-Fournaise-volcano-La-Runion-eruption-ends.html, accessed on 27 May 2015
Volcano Discovery, 2014, Piton de la Fournaise volcano (La Réunion): alert level raised, eruption warning, URL: http://www.volcanodiscovery.com/piton_fournaise/news/49537/Piton-de-la-Fournaise-volcano-La-Runion-alert-level-raised-eruption-warning.html, accessed on 27 May 2015
Volcano Discovery, 2015, Piton de la Fournaise volcano (La Réunion): eruption seems to have ended, URL: http://www.volcanodiscovery.com/piton_fournaise/news/51262/Piton-de-la-Fournaise-volcano-La-Runion-eruption-seems-to-have-ended.html, accessed on 27 May 2015.
Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.
Information Contacts: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr/OVPDLF/observatoire-volcanologique-piton-de-fournaise); Nicolas Villeneuve, OVPDLF.
19.023°N, 98.622°W; summit elev. 5426 m
All times are local (unless otherwise noted)
During November 2012-December 2014, ongoing exhalations and explosions
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Introduction. This report summarizes events at Popocatépetl during November 2012-December 2014. Almost all of the data discussed came from (~800) online daily reports by the Centro Nacional de Prevención de Desastres (CENAPRED). Many of those reports are issued covering a 24 hour interval (from 1000 on the stated day back to 1000 on the previous day), with occasional cases of later supplemental reports the same day. A link to those reports is provided in the “Information Contacts” section. Our previous report on Popocatépetl discussed the ongoing eruption during July-October 2012 (BGVN 37:09).
Behavior during the reporting interval included persistent emissions (often containing ash). When visibility permitted, web cameras documented nighttime emissions containing incandescent fragments, in many cases, rising hundreds of meters above the crater rim and spreading across the upper flanks. These eruptions typically deposited tephra up to ~1.5 km from the crater where it was conspicuous on the snow and ice that crowns the summit. Occasional air photos also depicted ballistics or their impacts and tracks in the summit area. Ashfall was not uncommon in villages on the volcano and it occasionally fell in parts of Mexico City and the city of Puebla. Many plumes rose on the order of 1 km, reported by CENAPRED in many cases several times a week if not more frequently. Periods of tremor occurred, some of which lasted for more than one hour. At least one volcanic-tectonic earthquake occurred on many days (maximum coda magnitudes, Mc, generally 2.0 to 2.5). Earthquakes are in general thus dismissed from detailed discussion below; however, for one sample month, November 2013, we include a larger emphasis on the record of larger earthquakes reported daily by CENAPRED. Many of the commonplace processes such as those in the above list were sufficiently common that, in order to save space, they are often omitted from this narrative.
One way CENAPRED quantifies Popocatépetl’s behavior is to use daily ‘exhalations’ (substantive plumes inferred to contain ash) which have long been a means of monitoring and characterizing this large and tall andesitic stratovolcano. The term ‘exhalation’ was used extensively in Bulletin reports starting with BGVN 22:03 in 1997. Exhalations are still currently tabulated by CENAPRED. Those appear in histograms in each daily report (assessing a 24 hour interval ending at 1000 on the stated reporting date).
Wright and others (2002) explain ‘exhalations’ further and clarify the distinction to the larger events that they classify as ‘explosions.’ The authors included photos and infrared imagery to illustrate the term (omitted here).
“Exhalations are short duration (3–90 min) ash-rich gas plumes . . .. CENAPRED provide daily Web-based activity updates in which exhalations are classified as small, moderate, or large on the basis of their duration and resultant plume height. Plumes can rise as much as 5000 m above the crater rim but are generally smaller. Exhalations are common and as many as several tens can occur each day. The ash they transport may be non-juvenile in nature (possibly with a juvenile component since March 1996 when lava extrusion began), and exhalations are thought to be the result of intermittent high-pressure gas streams that scour rock fragments from the conduit walls. Thermal video images, which measure the amount of radiation emitted in the 8–14 μm region of the electromagnetic spectrum . . ., indicate that by the time the plumes have reached the altitude of the crater rim, the ash-gas mixture is generally of a very low temperature (9–12°C at the plume exterior) due to the rapid entrainment of air at ambient temperatures.
“Explosions are less frequent than exhalations. They result in larger, darker ash plumes, with bombs often thrown clear of the crater to form a high-temperature ejecta blanket on the upper slopes of the volcano . . .. The plumes most commonly reach heights of between 3000 and 5000 m above the crater rim, although several larger explosions have occurred during the recent activity. The explosion of 30 June 1997, for example, was the largest recorded since 1922 and generated a plume 13,000 m high. Although explosions during the recent activity have been most common during periods of dome growth, they have also been observed during periods when no magmatic activity has been observed on the crater floor.”
Wright and others (2002) also make this comment: “Clearly, periods of prolonged and total cloud cover will prevent any useable data being acquired.” They were addressing satellite observations but this also applies to visual- and webcamera-based observations. This means that during some intervals adverse meteorological factors (clouds, rain, snow, etc.) could reduce the number of reported exhalations.
From this it is reasonably clear that the vast majority (if not all) of the eruptions during the reporting interval (November 2012-December 2014) were in the category of exhalations. During this reporting interval, several plumes did reach 3-4 km above the crater rim, as is noted below (e.g., during May-July 2013) and but we know of none reported that rose to over 5 km over the crater rim (~10.4 km altitude).
The maximum number of daily exhalations in the recent past stood, since July 2012, at 211. On 23 May 2013 that record was broken when 314 daily exhalations occurred. A second increase in that maximum value occurred twice more when the daily values reached 480 exhalations on both 4 and 6 June 2014.
As discussed in other Bulletin reporting since the onset of the eruption in March 1996 (BGVN 21:01), dramatic events involved dome dynamics in the steep-walled, cylindrical, ~0.5-km-diameter summit crater. There, emissions of lava and tephra constructed the dome. Occasional energetic discharges from the vent beneath this growing dome blew out the dome’s central area, leaving the dome with a ring-shaped morphology. This process has taken place many times in the intervening years since 1996 and continued in this reporting interval too.
Further discussion and references on the topic of exhalations and explosions with particular reference to Popocatépetl also appear in other studies (e.g., de la Cruz-Reyna and others, 2008; González-Mellado and de la Cruz-Reyna, 2008; and Tárraga and others, 2012).
November 2012-December 2013 activity. During the remainder of 2012, the Alert Level remained at Yellow, Phase Two (where it had been since lowered on 1 September 2012).
The usual plumes, occasionally bearing ash, rose up to ~1 km above the crater on many days during November-December 2012. For example, during 3-4 November 2012, CENAPRED daily reports noted 9 more significant eruptions and associated plumes registered at these respective times: 1100, 1450, 1548, 2346, 0157, 0240, 0532, 0835, and 0931.
On the basis of 15-day averages shown on histograms in CENAPRED daily reports, the overall November monthly average was 43. During December 2012 the overall average was 31. Lower monthly averages than December’s 31 appeared during January 2013 through the first half of March 2013. During the second half of March 2013 the average daily exhalations again rose to similar levels (31). The averages dropped again after that the averages remained low well into May and early June 2013 although during these later months some daily values increased significantly. The average value for the second half of June 2013 was 33.
During the first two weeks of May 2013 there were increases in earthquakes, tremor, and emissions. During 7-8 May, CENAPRED called attention to an episode of high amplitude spasmodic tremor. It was accompanied by an explosion on 8 May that ejected an ash plume that rose 3 km above the crater and drifted SE. Ashfall was reported from the villages of San Pedro Benito Juarez (10-12 km SE), San Juan Tianguismanalco (22 km SE), and Atlixco (23 km SE), and in some areas of the City of Puebla (~50 km to the E). The main tremor episode was accompanied by incandescent fragments that reached up to 500 m distance from Popocatépetl (chiefly NE). As reported on the 8th, during the last 24 hours CENAPRED detected 40 low intensity exhalations; 2 additional stronger ones sent a small amounts of ash towards the SE. Tremor during early May generally remained below daily intervals of up to a few hours.
On 10 May 2013 CENAPRED noted that during the last 24 hours there occurred 46 generally small exhalations. In addition, two explosions occurred, of moderate magnitude, sending ash ~1 km above the crater. Tremor duration for that interval lasted ~3 hours, including some time periods with high-amplitude signals. Three small volcano-tectonic earthquakes also occurred. A second report later on 10 May indicated that during 1142-1443 a series of ash emissions and periods of spasmodic and harmonic tremor occurred with ash plumes rising as much as 1 km above the crater, again producing ashfall. Similar plume heights were seen on 11 May, and the daily report noted there were in the last 24 hours a total of 53 (chiefly small-to-moderate) exhalations.
According to CENAPRED, seismicity had intensified on the afternoon and night prior to 12 May (when the Alert Level rose to Yellow, Phase Three, stipulating a 12 km radius exclusionary zone). Additionally, the report for 12 May 2013 said that in the last 24 h, 43 exhalations of low and moderate intensity were recorded. In general, steam-and-gas plumes with small amounts of ash rose from the crater. Although foggy conditions sometimes limited visibility, sporadic ejections of incandescent tephra fell back into the crater and onto the NNE flank, 300 m from the crater rim. Tremor registered in 1-2 hour intervals, continuously or in segments. Each such interval began with an eruptive burst of moderate intensity. The most important burst took place at 1700 on the 12th and was perceived by many residents in the E and SE sectors.
On 13 May 2013 steam-and-gas plumes were observed rising from the crater during periods of good visibility. On 14 May an explosive event generated an ash plume that rose to 3 km altitude. Incandescent tephra landed up to 600 m away on the NE flank. Cloud cover again obscured summit views. Seismicity, including tremor, remained elevated. The histogram in the daily report listed 25 exhalations during the past 24 hours.
On 14 May 2013, volcanologists aboard an overflight observed a lava dome 350 m in diameter and 50 m thick, found the dome slightly deflated after an explosion. Similar dome- related events seemingly took place again during the next few days. The histogram in the daily report listed 41 exhalations during the past 24 hours.
CENAPRED noted a vigorous eruption at 0146 on 15 May that discharged an ash plume to over 3 km above the crater rim, blown NE sending tephra up to 1.5 km downslope. At 1804 that day a second blast sent a column to somewhat below 3.5 km above the crater, blown N. Both these events correlated with spasmodic tremor. The histogram in the daily report listed 56 exhalations during the past 24 hours.
On 16 May 2013, some intervals of tremor again corresponded with discharge of glowing fragments, the majority of which fell back into the crater (a process frequently mentioned throughout the reporting interval). Ash plumes rose 2 km and drifted NE. Minor ashfall was reported in Paso de Cortés, 7 km N. Incandescent tephra reached 400 m from the crater rim to the N and NE. Seismometers registered an Mc 2.2 earthquake. The histogram in the daily report listed 55 exhalations during the past 24 hours.
Two punctuated eruptions were described for the 24-hour interval ending at 1000 on the 17th (one reaching 4 km above the rim) The first took place at 2214, when the crater issued a strong explosion; the resulting incandescent fragmental material covered the flanks to 1.5 km distance and the associated gas-and-ash column rose to under 3 km above the crater, drifting NE. The second took place at 0028, generating an eruption column to 4 km above the crater and casting glowing fragments up to 1.5 km from the crater. The report for the 17th said that moderate-to-small exhalations during the past 24 hours totaled 31. On 17, 18, 19, and 20 May 2013 histograms in the respective CENAPRED reports noted that in the past 24 hours they each registered 31, 18, 24, and 54 exhalations.
During an overflight on 18 May, volcanologists observed the active crater, 200 m wide and 40 m deep, located in the dome’s surface. The rest of the dome was covered with rock fragments. Tephra had landed as far as 0.5 km down the NE flank. CENAPRED inferred that the missing material forming this crater was likely excavated by explosions associated with hours of tremor that took place during 14-17 May.
On 23-27 May 2013, tremor decreased. A flight on 28 May captured several photos, one of which appears in figure 67. Note the steep crater within the ring-shaped dome and the abundance of fragmental character of some material on the dome’s surface. The CENAPRED caption also drew attention to marks made by ballistic material that burrowed into the snow and ice in the summit area.
|| Figure 67. Aerial photo taken looking downward at the summit area of Popocatépetl on 28 May 2013. The summit hosts a deep, steep sided circular crater, within which grows a dome. The dome is frequently reamed out by powerful explosive bursts leaving the dome with a crater as seen here. Courtesy of CENAPRED (from their 1 June 2013 daily report).
During 1-7 June exhalations on the daily histograms ranged between 32 and 93. They were often described as of low intensity (steam rich and ash poor), but in some cases they were described as reaching moderate intensity. Cloud cover often prevented visual observations. Volcano-tectonic earthquakes up to Mc 2.7 took place. On 7 June 2013 the Alert Level was lowered to Yellow, Phase Two.
During the rest of June 2013, significant emissions continued. For example, during 12-17 June 2013, plumes containing ash rose as high as 4 km above the crater, and ashfall was reported in many nearby villages (figure 68). For the eruption on the 17th, perceptible ash fell as far as the SE portion of Mexico City. The eruption on the 17th was accompanied by tremor with a duration of over 2 hours and other seismicity also remained at times high.
|| Figure 68. Webcam image of an explosion at Popocatépetl on 17 June 2013 (at 13:26:55 local time, which corresponds to 18:26:55 UTC). The explosion generated an ash plume that reached greater than 4 km above the crater and threw incandescent fragments up to 2 km out of the crater, causing small grassland fires. Courtesy of CENAPRED.
An overflight on 25 June led to the insight that eruptions in the past few days had further altered the dome. It then had the dimensions of 250 m in diameter and 60 m deep.
According to CENAPRED’s daily report on 3 July 2013, seismic activity increased again during the past 24 hours when the seismic network detected tremor for 36 minutes and two larger earthquakes (at 0407 and 0918 on the 3rd) with respective coda magnitudes, Mc 2.9 and 2.6. The daily report noted 84 exhalations on the part of the histogram for the last 24 hour interval ending at 1000 on 3 July. This was accompanied by persistent gas and ash emissions and diffuse ash plumes that rose 2-3.5 km above the crater and produced ashfall in areas as far as México City. Incandescent tephra was ejected short distances onto the N and E flanks.
This increased activity continued on 4 July 2013. According to news articles, multiple airlines canceled flights to and from the México City and Toluca (105 km WNW) airports on 4 July. The number of cancelled flights, according to the news, was 47. Flights resumed later that day.
On 5 July 2013, almost continuous tremor was recorded. Ash plumes drifted NW. Scientists employed both infrared webcamera imaging and an overflight to observe continuously ejected incandescent tephra that landed as far away as 1.5 km from the crater on almost all flanks, and an ash plume that rose 2 km. Cloud cover often obscured visual observations. A news article stated that four airlines canceled a total of 17 flights.
On 6 July 2013, low frequency, high amplitude tremor was accompanied by gas, steam, and ash emissions that rose 3 km. Three explosions were detected, but cloud cover prevented visual confirmation. News articles noted ashfall again in parts of México City. Government officials raised the Alert Level to Yellow, Phase Three, excluding the public within a 12 km radius of the crater. Later that day, the low frequency tremor amplitude decreased, followed by diminishing emissions of gas and ash.
During 7-9 July 2013, tremor was accompanied by persistent emissions of steam, gas, and small amounts of ash that drifted WSW and NW; cloud cover continued to hinder visual observations. Three explosions produced gas containing ash. Incandescence and ejected incandescent tephra were sometimes observed. During overflights on 7 and 10 July, scientists observed that a new lava dome, 250 m in diameter and 20 m thick, had recently formed in the crater.
During an overflight on 15 July 2013, scientists observed a 200-m wide and 20 to 30 m deep crater in the lava dome. The attributed the new morphology last seen on 10 July to dome destruction owing to explosions in the past few days. They also reported on M 2.3, 1.8 and 1.7 earthquakes, as well as 82 minutes of high-frequency tremor on 15 July 2013.
Emissions and occasional explosions that generated plumes with some ash continued during 10-16 July 2013 (figure 68). According to a news article, on 12 July 2013 an Alaska Airlines flight to México City’s international airport was canceled and operations at a small airport in Puebla were suspended.
On 23 July 2013, the Alert Level was lowered to Yellow, Phase Two, a status that prevailed through December 2014 (the end of this reporting interval).
On 31 July 2013 a clear decrease in the size of the water vapor and gas plumes was observed; plumes blew down the NW flank and rose only 100 m above the crater rim. An explosion was detected at 2312 on 1 August, but cloud cover prevented confirmation of any ejecta. On 2 August minor amounts of ash fell in the Tepetlixpa, Atlautla, Ecatzingo, and Ozumba municipalities of Mexico State. On 4 August emissions of gas, steam, and ash drifted NW. During 5-6 August a few observed plumes rose 1-2 km and drifted WNW, W, and WSW.
On 14 August 2013 a period of tremor was accompanied by an ash emission that drifted W and fell on towns as far as ~20 km away. Gas-and-steam plumes were observed during 15-16 August. A period of tremor on 17 August was accompanied by an ash plume that rose 1.5 km and drifted WSW. Ash fell in in towns as far as 65 km SW (Cuernavaca). On 18 August tremor was accompanied by an ash emission that rose 1.2 km and drifted SW. On 19 August minor steam-and-gas emissions drifted W. During 19-20 August emissions likely contained small amounts of ash but cloud cover prevented confirmation. On 28 August ash plumes rose 200-800 m and drifted SW. Gas-and-steam plumes were observed the next day and on the 30th an ash plume rose 1 km above the crater and drifted W.
During much of September and October 2013 clouds sometimes blocked clear views of the volcano. The volcano continued to undergo seismic unrest and to emit steam and gas plumes often containing minor amounts of ash. Early September ash blew WSW to fall on settlements as far as 24 km away (including, on the 1st, at Tetela del Volcán, 20 km SW, and Ocuituco, 24 km SW, and on the 2nd, at Ecatzingo, 15 km SW. On 4 September the number of daily exhalation during the previous 15 days averaged at 5, but on that day it stood at 44 exhalations. Average values for 15 day intervals remained under ~25 during September through December 2013.
Other observational details from this interval are similar to those noted above. For example, on 24 October an explosion at 2111 produced an ash plume that rose 1 km and drifted SW. Eight low-intensity explosions on 26 October increased gas and steam emissions and produced slight amounts of ash.
Despite the low number of exhalations near year’s end, during 30 October 5 November 2013, exhalations were frequently detected, varying from 30 to 97 times per day. Between 31 October and 5 November, four volcano tectonic earthquakes were recorded (Mc 2.1-2.5). Tremor was frequently detected; on 1 November, 3 hours and 21 minutes of high-frequency tremor was recorded.
During November 2013 tremor durations reached highs on the 5th, 6th, and 17th, respectively, at 55, 60, and 67 minutes. November’s larger local earthquakes reported by CENAPRED included the following: on the 5th, Mc 2.1-2.5; 6th, Mc 2.7; 9th, Mc 2.3; 10th, two cases with Mc 2.1; 11th, Mc 2.3, 18th, three cases with Mc approaching 2; 20th, 6 cases with some Mc approaching 2.5; 21st; Mc 2.0; 22nd, five cases, Mc 2-3.5; 23rd, Mc 2.0; 24th, two cases with Mc 2.1; 25th, Mc 2.0; 28th, Mc 1.8; and 29th, Mc 1.2.
The Washington Volcanic Ash Advisory Center (VAAC) issued advisories for Popocatépetl every month during 2013, except for November and December 2013. The advisories were most numerous during April through July 2013. According to CENAPRED, a daily average of about 6,000 metric tons of sulfur dioxide was emitted during both 2013 and 2014.
2014 activity. During 2014, the Washington VAAC issued advisories for Popocatépetl every month, except for March. The number of advisories issued was considerably lower than that for 2013. At year’s end, the Alert Level remained at Yellow, Phase Two.
Activity in 2014 was broadly similar to that in 2013, with above-mentioned frequent gas-and-steam emissions, often with minor ash content. Issues with limited visibility at times due to cloud cover also remained.
The 15-day average of the daily exhalations often stood at less than 4 during January and through 19 February 2014. Activity increased during 19-25 February 2014. At least eight explosions generated plumes (mostly ash) that rose 1-2 km above the crater. An explosion at 1233 on 21 February sent an ash plume to 4 km above the crater rim. On 26 February, scientists aboard an overflight observed that another lava dome (dome number 48) had been destroyed, leaving a funnel shaped cavity about 80 m deep. A new dome 20 30 m wide was at the bottom of the cavity. On 27 February, activity decreased considerably.
CENAPRED’s 15-day average of the daily exhalations stood at 7 or below during March 2014 but it rose to 34 by 18 April 2014 and dropping to 22 by the end of that month. It rose again in late May 2014 (to 45 on 31 May). On 16 June it stood at 57; and for the last half of June it declined to below 10.
The daily value reached 480 exhalations on 4 and 6 June 2014, a new record.
Monitored and eruptive activity briefly increased in early July 2014. For example, CENAPRED reported tremor on 2 July (maximum of 80 minutes in 24 hours) and 12 July (minimum of 8 minutes). Up to 216 exhalations of low and moderate intensity were detected on 9 July. The 15-day average of the daily exhalations also rose during early July 2014, reaching over 50 during the first half of the month but dropping towards the end to 15 (on the 31st).
The first half of August had a 15-day average of 33 daily exhalations and the second half, 46 daily exhalations. Those averages (first half of the month and second half of the month) were as follows for the rest of the year: September (14 and 31); October (40 and 39); November (55 and 13); and December (41 and 72).
During 27 August and 2 September 2014, plumes reached as high as 3 km above the crater. Tremor and volcanic-tectonic earthquakes were recorded in early September.
On 17 September 2014, a day with 126 exhalations recorded by CENAPRED’s monitoring system, an ash emission at 1813 resulted from a moderate explosion. The emission reached 3 km above the crater rim. It blew SE and light ash fell at villages in that direction. During the same day five other exhalations reached ~1.5 km above the crater rim. During 7-8 October 2014 ashfall was reported in Cuautla (43 km SW), Tetela del Volcán (20 km SW), Huaquechula (30 km SSW), and Morelos (60 km SW). On 12 October ash plumes rose 2 km and drifted NE. Ashfall was reported in Paso de Cortés (8 km NNW) and Tlalmanalco (30 km NW).
CENAPRED reported that during a 14 October 2014 overflight, volcanologists observed that the diameter of the inner crater (formed in July 2013) had increased to 350 m. The bottom of the inner crater floor was 100 m below the floor of the main crater, cup shaped, and covered with tephra. No sign of the lava dome (number 52) emplaced in early August 2014 was visible. Steam emissions originated from a crack in the N wall of the inner crater and ash emission came from the bottom of the crater.
Although for brevity we have generally excluded examples of explosions and ashfall for September and October 2014, which were broadly similar to previous months, a small explosion at 0317 on 25 October ejected tephra 100 m outboard onto the S flank. A steam-and-gas plume containing a small amount of ash rose 1.5 km above the crater and drifted SW. Ashfall was reported in Tetela del Volcán (20 km SW). A small explosion at 0111 on 26 October ejected a plume that rose 1.1 km above the crater rim and sent tephra 200 m onto the N flank.
Histograms in daily reports issued during 3-5 November 2014 described exhalations totaling 267, 190, and 147, respectively. These were broadly described as a continuous gas-and-steam plume, mainly with minor amounts of ash. Some more vigorous and ash rich emissions occurred and, for example, on 5 November the plume rose as high as 1 km and caused light ashfall in Paso de Cortés. That daily report also showed videos that showed incandescent fragments spreading ~800 m over the upper flanks. The 5 November report also showed a seismic record captured in the interval 2000 on the 4th to 0130 on the 5th illustrating ~190 seismic events. About an hour after those events, the same record indicated an Mc 2.1 earthquake. On 6 November, a small rockslide on the SW flank was recorded by a webcam and the seismic network. Scientists aboard an overflight observed a new dome (number 53), emplaced during 4 5 November; it was an estimated 250 m in diameter and 30 m thick.
During 7 11 November 2014, seismicity indicated continuing gas-and-steam emissions, with small amounts of ash. Incandescence from the crater was observed most nights. Explosions during 10-11 November ejected incandescent tephra and generated ash plumes that rose 1.2 km above the crater. Gas-and-steam emissions continued through the rest of November.
During December 2014, occasional explosions continued, generating ash plumes that rose as high as 3-3.5 km, resulting in minor ashfall on nearby villages. One or more rockslides were noted in addition to the usual small ash plumes, the occasional incandescence at the crater and associated with tephra. One plume on 8 December rose to 3 km above the crater. CENAPRED reported that the international airport in Puebla was temporarily closed on 17 December 2014 due to ashfall from an explosion that generated a 2 km high ash plume. The explosion also ejected incandescent tephra that landed 700 m down the N flank. During an overflight during the last half of December, volcanologists observed a lava dome at the bottom of the crater. The Alert Level remained at Yellow, Phase Two.
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González-Mellado, AO, and de la Cruz-Reyna, S, 2008, A simplified equation of state for the density of silicate hydrous magmas: an application to the Popocatépetl buoyancy-driven dome growth process. Journal of Volcanology and Geothermal Research, 171(3), 287-300.
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Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, towers to 5426 m 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major plinian eruptions, the most recent of which took place about 800 CE, have occurred from Popocatépetl since the mid Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since precolumbian time.
Information Contacts: Centro Nacional de Prevencion de Desastres (CENAPRED), (URL: http://www.cenapred.unam.mx/es; Daily reports, http://www.cenapred.gob.mx/reportesVolcan/BuscarReportesVolcan?optBusqueda=1 ); Washington Volcanic Ash Advisory Center (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/index.html); Agence France Presse (AFP)(URL: http://www.afp.com/en/); Associated Press (URL: http://www.ap.org); Stuff (URL: http://www.stuff.co.nz).