El Reventador is currently the most active volcano in Ecuador. When this volcano (whose name translates as the Exploder) erupts, it sends incandescent rock projectiles into the air, along with ash columns approximately 3 kilometers high. The volcano also releases significant amounts of lava flows, volcanic bombs, and ash from flow and fall deposits onto the surrounding ground. This relatively small stratovolcano has destroyed and rebuilt its edifice on a large scale throughout its evolution. Its eruptive behavior changes rapidly, and its complex behavior is significantly different from that of all other volcanoes in the Ecuadorian Andes.
Aerial view of El Reventador volcano, showing the emission column after an explosion on 27 August 2017. Credit: P. Ramon, IG/EPN
During the past 3 years, El Reventador has repeatedly destroyed and rebuilt itself on a smaller scale, and inherent instabilities in its edifice pose an ongoing hazard. This hazard is particularly severe on the active cone, where complex effusive and explosive events occur on a daily basis. Our research group, which monitors this remote jungle volcano, has found evidence of multiple small collapses in the border flanks of the crater, complex multivent behavior, and the opening and closing of new vents on a relatively short timescale—weeks to months. Our studies are providing new insights into the inner workings of this volcanic system.
Monitoring El ReventadorEl Reventador (Figure 1a) is part of the back-arc volcanism on the eastern side of the Cordillera Real of Ecuador, located approximately 90 kilometers (km) east of the capital city of Quito. The Instituto Geofísico (IG) of the Escuela Politécnica Nacional (EPN) in Quito monitors the activity of this remote volcano. A very large explosive eruption in 2002 initiated the current period of activity, prompting the IG to install a permanent, telemetered seismic monitoring station in 2003.
Over the past 16 years, the IG’s monitoring capabilities at El Reventador have expanded into a comprehensive network of seismometers, infrasound stations, thermal and visual cameras, a digital optical absorption spectroscopy (DOAS) gas monitoring station, and acoustic flowmeter lahar monitoring stations within the caldera itself (Figure 1b). Since 2016, 10 ash meters installed on the volcano have collected high-quality volcanic ash samples for ongoing petrological monitoring of the eruption [Bernard, 2013].
We conduct monthly field campaigns on foot and by air to complement data recorded by the permanent monitoring network. During these field campaigns, we collect targeted thermal image sequences, gas measurements (e.g., multiGAS, mobile DOAS), and visual photography. In conjunction with the U.S. Geological Survey’s Volcano Disaster Assistance Program, the IG conducts photogrammetric surveys to create 3-D models of the lava flows and edifice. Samples of ash, ballistics, and lava flows are also regularly collected and used for petrological analyses, which provide insights into eruption dynamics, magma storage, and the geometry of the plumbing system.
Fig. 1. (a) El Reventador volcano. Note the small stratovolcano inside the Paleo Reventador amphitheater. (b) El Reventador monitoring network stations. BB: broadband; DOAS: differential optical absorption spectroscopy; IR: infrared; SO2: sulfur dioxide; SP: short period; PSAD: Provisional South American Datum 1956; UTM: universal transverse Mercator. Credit: M. Almeida, IG/EPN Past and Present Activity
During El Reventador’s history, at least two catastrophic events almost completely destroyed the edifice, although the timing of these events is not known [Instituto Ecuatoriano de Electrificación, 1988]. The current active cone of El Reventador sits within the collapse caldera of Paleo Reventador on the western side (Figure 2). Since 1541, the volcano has experienced about 20 different eruptive periods [Naranjo et al., 2016].
Fig. 2. El Reventador volcano, showing the ridges of Basal Reventador, Paleo Reventador, and the new stratocone. Credit: M. Almeida, IG/EPN
El Reventador’s 3 November 2002 eruption, after 26 years of quiescence, is considered to be the largest Ecuadorian eruption in the last century. It was categorized as a subplinian eruption, and it spewed out 0.37 cubic kilometer of material [Hall et al., 2004]. During the eruption, a large part of the summit was destroyed, reducing its height by almost 100 meters and creating a large crater approximately 480 meters in diameter.
One of the most interesting aspects of recent activity at El Reventador is the configuration of the active eruptive vents. During a field campaign in January 2016, we observed two different active summit vents for the first time. Subsequent overflights confirmed the presence of these two separate vents, now called the north vent (NV) and the south vent (SV; Figure 3). Following overflights and continued visual monitoring of the activity through the permanent cameras revealed that the mode of activity in the SV was predominantly explosive, whereas the NV was mostly effusive.
Fig. 3. (a) Explosion in the southern vent on 7 June 2017 and a small lava flow associated with the north vent. (b) A trace of the activity of the north and south vents highlighting the explosion (exp.) and lava flow. (c) Superposition of visible and thermal images showing the separate north and south vents and the lava flow being extruded from the north vent on 28 January 2016. Credit: (a), (b) P. Ramón; (c) M. Almeida, IG/EPN
Activity in the two vents often appears to be independent, where explosions occur out of either one vent or the other. Occasionally, however, the explosions originate from both vents simultaneously. These observations suggest that at some level in the conduit, the feeding system to the two vents is connected but that the vents are also able to behave independently.
We observed intermittent, but less frequent, explosions from the NV. During November 2016, activity in the NV seemed to shift to a more explosive regime, and this shift in activity persisted until January 2017. Moreover, during May 2017, while the two summit vents continued their hourly explosive activity, a new third vent producing lava flows was identified on the northeast flank about 70 meters below the summit (Figure 4a).
Fig. 4. (a) Superposition of visible and thermal images showing the two summit vents, the lateral vent, and lava flow on 2 June 2017. (b) Superposition of visible and thermal images of the large lava flow extruded between 22 June and 1 July 2017. This was the largest lava flow emitted since 2008. Credit: M. Almeida, IG/EPN
This multivent behavior, coupled with continued high levels of activity, has filled the crater left by the 2002 eruption, reconstructing the active cone to its pre-2002 height. Frequent moderate-scale collapses of the edifice and high levels of ongoing eruptive activity result in regular, significant changes to the shape of the summit area of the active cone.
El Reventador Starts Another MakeoverIn June 2017, El Reventador experienced its highest level of activity in more than 10 years, beginning with the explosive opening of a new vent on the northeast flank.In June 2017, El Reventador experienced its highest level of activity in more than 10 years, beginning with the explosive opening of a new vent on the northeast flank. This vent released large, fast-moving currents of hot gases and volcanic matter called pyroclastic density currents (PDCs) that reached more than 5 km from the summit. This PDC activity was followed by the rapid effusion of the largest lava flow since 2008, which reached nearly 3 km from the summit (Figure 4b).
The edifice collapsed again in April 2018, destroying a large section of the summit and forming a new large crater, open to the north-northwest (Figure 5). We identified three new vents within the collapse scar, highlighting how quickly the morphology of this volcano can change. These rapid changes and frequent collapse and rebuilding events have resulted in an inherently unstable cone. Collapse events, big and small, are commonplace, with small collapses occurring on a weekly basis. Moderate to large collapses also occur yearly, such as before the June 2017 lava flow and in April 2018.
Fig. 5. (a) After an explosive event in 2002, part of the summit of El Reventador volcano was destroyed, as shown in this aerial photo. (b) Since then, the crater has been almost completely filled in, as shown in this photo of the active cone in June 2017. (c) This aerial photo shows the most recent collapse event, which occurred in April 2018. Credit: (a) P. Ramón, IG/EPN; (b) M. Almeida; (c) S. Vallejo, IG/EPN.
Particularly unstable areas include the edge of the current crater, where loose material builds up during explosive and effusive events and intermittently collapses, leaving easily identifiable collapse scars around the summit area. Explosions and sector collapses of the edges of the crater regularly produce primary and secondary PDCs. These sector collapses are not always necessarily associated with explosive behavior, so they are inherently unpredictable.
Preparing for Future Hazards
A view of El Reventador from a helicopter overflight around the southeastern flank of the volcano over the jungle. Note the deposits of previous pyroclastic flows and the hot rock derivatives from the fronts of active blocky lava flows (black color close to the summit of the volcano) rolling from the top of the volcano and raising light-colored ash along the way. Credit: M. Almeida, IG/EPN
Eruptive activity at volcanoes can change rapidly from relatively benign activity to potentially life threatening with very little warning. The history of El Reventador demonstrates that it is capable of not only its hourly explosive behavior but also catastrophic activity.
Recent events have demonstrated that rapid changes can occur and that inherent instabilities exist within the volcanic edifice. New eruptive vents can open up anywhere on the active cone, and the daily high levels of eruptive activity create the potential for new edifice collapses and the generation of large PDCs, which could affect local infrastructure.
At present, El Reventador’s activity levels remain high, and the volcano shows no signs of slowing down. Continuous monitoring by the IG and the constant work to improve the monitoring network will enable us to provide better early warnings of impending volcanic activity in the future.
AcknowledgmentsWe acknowledge the whole team at the IG EPN, and specifically, we thank all those involved in the monitoring of El Reventador volcano.
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