The volcano’s activity level is: Level YELLOW: changes in the behavior of volcanic activity -Time For a probable eruption: weeks / months.
Based on the analysis of information obtained by monitoring equipment and the observation of volcanoes, the Volcano Observatory of the Southern Andes (OVDAS) of the National Service of Geology and Mining (SERNAGEOMIN), communicates the following :
In the first half of the month of April, a total of 1878 earthquakes were recorded:
1687 of them have been classified as long-period earthquakes (LP) related to fluid dynamics inside the volcano, with reduced displacement values (RDC) less than 20 cm2.
Note that on April 10 and 11, the LP activity recorded have decreased significantly and the 12, they become visible again, exceeding in size the level of tremor.
It was further classified, one hundred ninety-one (191) volcano-tectonic type events (VT) associated with fracturing of a rigid material. The event of highest magnitude presented a local energy (ML) equal to M 2.7 and was 4.6 km to the east (E) of the active crater with a depth of 3.8 km.
The appearance of “seismic shooting” VT type of earthquakes (recording of multiple events in a short time), although there had in the past, were more common from April 11.
Most events are concentrated as before, in an area of ??approximately 10 km of length elongated in the direction Northwest-Southeast, within the caldera.
The energy of the volcanic tremor signal (TR), also associated with the fluid dynamics inside the volcano showed a stable trend with reduced displacement values (DRC) averaged on 3cm2, values ??considered low, while the dominant frequencies persisted between 1.0 and 2.1 Hz mainly.
After minor crisis occurred on 03 April last, the energy measures and the reduced size of the tremor with an oscillating behavior in number, indicate a downward trend, a feature that persists until the publication of this report.
The microphone installed 4 km from the crater of the volcano recorded minor pulses associated with surface activity, which were down by day, reaching maximum pressure equal to 0,3Pa.
Images recorded with IP cameras installed near the volcano, the days without cloud cover showed a predominantly white degassing with maximum heights of the column about 600 meters and a continuous filament, without noting exceptional activity in the crater.
According to data obtained from 5 GNSS stations that control the deformation of the volcano, small variations in its two components, horizontal and vertical, have been observed.
The highest horizontal displacement rates were observed at the station located in the southeast area of the volcano, with rates of 0.3 cm / months. It was also noted that the length of the control line that crosses the volcano is stable. In addition the data of the two (2) inclinometers show variations of low amplitude that are not directly related to other parameters.
The data obtained by the equipment DOAS (Differential Absorption Spectrometer Optics) Station Los Nevados and Tralco, installed 10 km to the east-northeast (ENE) and 6 km to the east-southeast (ESE) of the active crater, respectively, recorded a monthly average value of sulfur dioxide emissions (SO2) of 865 ± 22 t / day and a maximum value of 1707 ± 59 / day associated with minor strombolian activity, which took place on April 3. It was then noticed an increase in SO2 emissions, perhaps associated with a new magmatic material contribution in the shallow layers of the volcano.
The satellite images of the OMI (Ozone Monitoring Instrument – Http://so2.gsfc.nasa.gov/) and NESDIS (National Environmental Satellite, Data and Information -http: //satepsanone.nesdis.noaa. gov), alerts of sulfur dioxide (SO2) into the atmosphere, have reported no abnormalities in the volcanic complex.
Thermal radiation released by Mirova (Middle Infra Red Observation) on its website (http://www.mirovaweb.it/), indicating significant changes in surface temperature, reported alerts (considered to be medium) in the area associated with the volcano throughout the month, with most thermal anomaly on April 3, with a value of volcanic radiative power (RVP) of 172MW.
The behavior of volcanic activity generally show a gradual reduction of its energy after minor crisis which took place on April 3.
However the appearance of “seismic shooting” concentrated preferably in the South-East of the main crater, suggest a possible movement magma at depth that could destabilize the system.
In this scenario, and considering the characteristic of the volcanic conduit of Villarrica, this opens the possibility of occurrence of explosions and strombolian activity, from low to high, with the dangers associated with the fallout of pyroclastic material in the adjacent area of the crater, higher than in recent months. Therefore, it is recommended as a preventive measure to apply restrictions on access to the proximal zone within a radius of 1.0 km from the crater center.
The volcanic alert level remains at Yellow with special attention.
April 19 , 2016.Villarica , Chile :
Source : Sernageomin
Photos : Miguel Angel Albornoz ,María José Escobar.