SO2 degassing at Tungurahua volcano (Ecuador) between 2007 and 2013: Transition from continuous to episodic activity

Abstract

International audienceWe present continuous SO2 measurements performed at Tungurahua volcano with a permanent network of 4 scanning DOAS instruments between 2007 and 2013. The volcano has been erupting since September 1999, but on the contrary to the first years of eruption when the activity was quasi-continuous, the activity transitioned in late 2008 towards the occurrence of distinct eruptive phases separated by periods of quiescence. During our study period we distinguish 11 phases lasting from 17 to 527 days separated by quiescence periods of 26 to 184 days. We propose a new routine to quantify the SO2 emissions when data from a dense DOAS monitoring network are available. This routine consists in summing all the highest validated SO2 measurements among all stations during the 10 h of daily working-time to obtain a daily observed SO2 mass. Since measurement time is constant at Tungurahua the “observed” amounts can be expressed in tons per 10 h and can easily be converted to a daily average flux or mass per day. Our results provide time series having an improved correlation on a long time scale with the eruptive phases and with quiescence periods. A total of 1.25 Mt (1.25 × 109 kg) of SO2 has been released by Tungurahua during the study period, with 95% of these emissions occurring during phases of activity and only 5% during quiescence. This shows a contrast with previous volcanic behaviour when passive degassing dominated the total SO2 emissions. SO2 average daily mass emission rates are of 73 ± 56 t/d during quiescent periods, 735 ± 969 t/d during long-lasting phases and 1424 ± 1224 t/d during short-lasting phases. Degassing during the different eruptive phases displays variable patterns. However, two contrasting behaviours can be distinguished for the onset of eruptive phases with both sudden and progressive onsets being observed. The first is characterised by violent opening of the conduit by high energy Vulcanian explosions; and the second by a progressive, in crescendo, development of the activity. The first case is becoming more frequent at Tungurahua making the volcano more dangerous and less predictable

Rapid hazard assessment of volcanic ballistic projectiles using long-exposure photographs: insights from the 2010 eruptions at Tungurahua volcano, Ecuador

“…Eruptive styles at Tungurahua are often characterized as Strombolian, Vulcanian and Sub-Plinian [Eychenne et al 2013;Hidalgo et al 2015;Hall et al 2015]. Comparing with other studies, metric-size ballistic projectiles are not typical of Strombolian and Sub-Plinian activity and are more common during Vulcanian explosions [Maeno et al 2013;Bombrun et al 2015;Taddeucci et al 2017].…”

“…These velocities are significantly lower compared to Sub-Plinian eruptions [Robertson et al 1998]. In Hidalgo et al [2015], the January, May-June and November eruptions are named phases IV, V and VI and our photographs fall in the high-explosive activity (HEA) field that is interpreted as Vulcanian activity, supporting the seismo-acoustic analysis from Kim et al [2014]. Although the Vulcanian classification fit closely the May activity that exhibits discontinuous explosive activity, the January and November activities are characterized by continuous ash venting and pyroclastic fountaining.…”

Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

“…A map of the different NOVAC stations at Tungurahua can be found in Galle et al (2010) and additional information on the gas emissions from Tungurahua is available in Hidalgo et al (2015). We used data recorded between January 2009 and December 2011 from the three stations that are located in the main wind direction: Pillate, 8000 m W, Huayarapata, 9100 m NW, and Bayushig, 11900 m SW of the volcano.…”

“…All spectra were evaluated for SO 2 using the DOASIS software package (Kraus, 2006) with two different settings.…”

Exploring the Utility of IASI for Monitoring Volcanic SO2 Emissions

“…A change in the gradient of the regression line describing the relationship between the two is also noted, with a fall from 1.08 to 0.8 in the first period, and an increase from 0.61 to 0.75 in the second. Nevertheless, it is clear that both instruments are capable of detecting relative changes in volcanic activity and that these match the periods of activity as noted in Hidalgo et al ().…”