Aerial surveillance.

Surface activity:
During the overflight, it was observed that the surface activity of the volcano was characterized by the generation of small explosions and pyroclastic flows. The explosions produced small columns of gas with a high ash content, which did not exceed 500 meters above the summit and were dispersed to the west (Fig. 1 and Fig. 3 on the left). The displacement and deposition of pyroclastic flows were limited to the internal part of the ravine on the south-eastern flank, while its ashes were quickly displaced in the form of columns which reached about 200 meters above the surface of the ravine and, due to the action of the winds were dispersed from the southern flank to the west, surrounding the volcano (Fig. 3 Der.). Together, the emissions and columns derived from pyroclastic flows contribute to a large amount of ash in the environment. Transported by the winds, these ashes reached populations located in its path.

Thermal anomalies:
According to the acquisition and analysis of thermal or infrared images, it was possible to observe the presence of different anomalies (areas with a temperature higher than the environment) on the southeast flank of the volcano ( Fig. 4). Thanks to the construction of thermal image mosaics, these anomalies are represented from different angles in Figure 4 (below). In its relief, it is obvious that in the upper part of the ravine there are two very marked thermal anomalies; while the third is scattered and heterogeneous towards the base of the ravine, the edge of which is represented by the solid black line (Fig. 4, above). Analysis showed that Anomaly 1 had a temperature of 125 ° C, which was associated with explosive activity, during the overflight. Anomaly 2 could be linked to effusive activity, with the potential presence of a small lava flow whose maximum temperature reached 147 ° C. Finally, the third anomaly corresponds to the accumulation of hot deposits of pyroclastic flows in the lower part of the Southeast ravine with temperature values ​​of 165 ° C.

It should be mentioned that the amount of ash and gas covering these deposits at the time of image capture considerably reduces the measured temperature values, which can indeed be higher for each anomaly.

Figure 4. Above: thermal image of the southeast flank of the Sangay volcano, the highest temperature zones: yellow-red-white and the lowest temperature zone: dark blue. The escarpment of the ravine formed in this eruptive phase (black line) is shown, which shelters thermal anomalies linked to explosive activity, effusion and deposits of pyroclastic flows. Bottom: thermal image mosaics of the gorge on the Southeast flank with three views, from left to right: Southwest, Southeast and East-Southeast. Thermal image and mosaics: S Vallejo Vargas, IG EPN.

Morphology:
The morphology of the volcano has changed dramatically and continuously in this last eruptive phase which started in May 2019. These changes have shown that the summit of the volcano now has at least two maximum elevations, separated by a relatively small saddle of about 181 meters wide, possibly formed by the erosion of the northwest wall of the crater. Figure 5 shows the estimate of the width of the Southeast gorge in its upper part, with about 397 m.

Figure 5. Left: processed amplitude image, which was used to contrast certain measurement estimates in the most relevant morphological characteristics (amplitude image http://www.mounts-project.com/volcano/352090, Track Ascending June 30, 2020). Right: approach to the summit of the Sangay volcano, accompanied by an illustration which highlights its new morphological characteristics. Photo: M Almeida, IG EPN.

In the photographic sequence of Figure 6, we can synthetically observe the change that the volcano has undergone since May 2019. This sequence includes two photographs and a thermal image, which were captured in the same direction (N100 °) and altitude (5644 m / 18517 ft), May 17, 2019 and June 24, 2020, respectively. The area of ​​fumaroles aligned in the vicinity of the summit of the volcano was used as a clear reference for the superimposition of said images (see Ref. Fumerole aligned in Fig. 5 and Fig. 6). Thanks to this, it was possible to confirm that the top of the volcano was eroded, showing a complete change, compared to the configuration of May 2019, when the current eruptive phase had just started. Apparently, the height of the volcano could have changed, however, to confirm, this will require the development of digital terrain models, with the appropriate conditions in terms of climate and absence of ash in the environment.

Figure 7. The MultiGAS equipment consists of a complex system of sensors, data processors and special pipes, which are installed on the plane before takeoff, so that they are not contaminated by the system. engine exhaust. (Photo: E. Camacho Chamba, CBOP of 2op A.E.).

Unfortunately, the presence of ashes in the work area did not allow the maneuvers necessary to obtain said data. In FIG. 8, it is possible to observe the maneuvers carried out, which are limited to the eastern flank. The gases that this equipment can measure are: sulfur dioxide (SO2), hydrogen sulfide (H2S), carbon dioxide (CO2) and water (H2O). Figure 8 shows the set of data collected and analyzed, where the gas concentrations of the volcano were not observed (Figure 8). The yellow arrow indicates the start of the measurements.