Cotopaxi, Ecuador : a decrease in the number of events is observed.

Cotopaxi, Ecuador : a decrease in the number of events is observed.

Seismicity.
In recent weeks a decrease in the number of events is observed, recording daily least 20 earthquakes , volcano-tectonic types (VT), between 1 and 6 earthquakes hybrid type (HB), and 1 to 3 internal explosions. However, the size of these events remained similar to that recorded in January and February, with magnitudes between 2.8 and 1 Mlv. These events are between 2 and 9 km below the crater.

Deformation.
GPS stations on the western flank (CAME, NAS1) and the eastern flank (TAMB) show a movement from West to East (O-E) that are not observed in other stations. This movement could be associated with a small disturbance inside the volcano that can be associated with a rearrangement of magma. However, the evolution of the movement in the vertical component can not be a clear indication of the rise of magma (inflation).

SO2 emissions.
There has been a steady decline of the daily flow of SO2 from December 2015). At the end of March, there was a slight increase, however, these values are in background levels observed since 2011
The number of valid measurements recorded on the station showing the greatest flow value of SO2 shows a downward trend from December 2015 .These last month, it was not detected by satellite observations SO2 emission due to the decrease in the amount of emitted gas. Even the gas measurement by the mobile stations DOAS failed to detect the presence of SO2.

visual observations.
In recent weeks, visual observation conditions were mostly unfavorable weather with high clouds. The surface activity was mainly characterized by a low energy gas emission sometimes reaching up to 900 m above the crater.

So far, observations show the continuation of glacial melt process initiated during the explosions that started in August 2015. The presence of water and humidity is maintained at the base of the glacier fronts generated by the merger. These thin fillets are flowing water on the sides to the main drain. In the last flyby of January 26, 2016, it was obvious that the glaciers continue to suffer from displacement in the downward slope with cracks and formation of fractures.

Ashfall.
Since November 23, 2015, no significant ash fall s associated with volcanic activity has been recorded. Small emissions of January probably did not cause measurable ash fall in the vicinity of the volcano.

Thermal monitoring.

Regarding the temperatures of different parts of the cone where routine monitoring is carried out, in general, it may be noted that the values of TMA (high apparent temperature) measured on 26 January 2016 are slightly lower than those measured previously especially compared those months of September and October 2015, when they reached their highest values. On the upper flanks, the most important impact on the cone were accelerated loss of glaciers, almost continuously observed on the glacier between Yanasacha and south summit. In addition this phenomenon apparently weakening of the upper walls on the lateral flanks, in which the lack of ice cover causes the phenomenon of detachment and fall of the material of the sidewalls.

Because varying intensity of rains occurred around the Cotopaxi volcano, it was recorded 58 secondary lahars since August 2015. Most of them are descended from the West and Northwest sides, mainly by Cutzualo ravine located west of the volcano, which joined the Agualongo near the bridge that is on the road in the National park of Cotopaxi.
Most of the time these lahars are very small and have a lower throughput than 5 m³ / s. Limited to areas in the national park in general, they do not pose a threat to populated areas and infrastructure. Sometimes the most powerful events (> 30 m³ / s) were observed and lahars have invaded the road.

The largest number of lahars took place in November 2015 and February 2016, with 13 events.
After the lahar which occurred on January 13, 2016, which was the most powerful recorded event and invaded the runway (reported in the Special Report # 2), it has not been re-recorded events of this kind because the rain does not have very high intensity. Lahar flows that took place during the months of February and March 2016 were in average (5 m³ / s), except the last recorded stream which had a rate of 20-25 m³ / s and had place on March 19.

Interpretation

The monitoring data obtained until 28 March 2016 confirmed that some monitoring parameters (SO2, LPs, tremor, ash) returned to the level of pre-eruptive base. All these parameters are related in some way to the gas outlet. The deformation of the volcano marks a break from November 2015, but has not returned to pre-eruption level and ultimately a new small anomaly possibly associated with the reorganization of deep magma is observed. This suggests that part of the magmatic intrusion responsible for eruptive activity between August and November 2015 remains in depth. The number of VT type of earthquakes has decreased compared to previous months, but not their sizes. In addition, small internal explosion continue to be recorded, indicating that persists a pressure source inside the volcano.

03/04/2016. Cotopaxi, Ecuador :

 

Source : IGEPN

Photos : IGEPN , José Luis Espinosa-Naranjo .

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