Subject: internal activity level of the Nevado del Ruiz volcano.
Yellow activity level or (III): changes in the behavior of volcanic activity.
Regarding the monitoring of the activity of the Nevado del Ruiz volcano, the SERVICIO Geologico COLOMBIANO through the OBSERVATORIO VULCANOLÓGICO Y SISMOLÓGICO OF MANIZALES, reports that:
During the last week, the volcanic system continued to show unstable behavior. The recorded seismic activity was mainly due to the fracturing of the rock in the volcanic structure. This type of seismicity was located in the North-East areas and South-east of the volcano, in the Arenas crater, and to a lesser extent in the Northwest sectors and southwest of the volcanic structure at depths between 0.5 km and 7.8 km. The maximum magnitude recorded during the week was 2.6 ML (local magnitude), corresponding to an earthquake on November 20 at 09:58 (local time), located in the eastern sector of the Arenas crater at depth of 2.8 kilometers.
Seismic activity associated with fluid dynamics in volcanic conduits, was characterized by record of LP type earthquakes (long period) and episodes of volcanic tremor of short duration, not associated with emissions of ash in the atmosphere. The volcanic deformation measured from electronic inclinometers, global navigation satellite stations (GNSS) and satellite images, which record changes in tilt, position and shape of the volcano (respectively) during the last period evaluated, showed no major change.
The volcano continues to emit into the atmosphere an significant amounts of water vapor and gases, including sulfur dioxide (SO2). The gas and steam column reached a height of 2000 meters above the volcano’s summit on November 17. The direction of the dispersion of the column was in harmony with the wind regime, which during the week showed a predominant direction toward the northwest.
In recent months, very quietly, there have been several shorts episodes of fracture seismic events characterized by low energy, that occur at regular time intervals with waveforms and similar energy. Technically these signals are known as « drum » or « drum roll » for their meaning in Spanish. The most important of these signals episodes was reported by extraordinary bulletin on August 20, 2015. They correspond more recently to 13 events recorded in November, characterized by a much lower energy level. The presence of these seismic events has been associated on other volcanoes, when the magma rise to the surface and his implementation in the form of lava domes. To verify the existence of morphological changes in the Arenas crater of the volcano Nevado del Ruiz, associated with these « drums« signals during the last week, two overflights were carried out with the support of the Colombian Air Force (FAC) and USAID / OFDA. However the weather in the volcano area and in particular high density and volume of the gas and vapor column has prevented the observation of the crater. Overflights of the Colombian Geological Service continued to manage the increased monitoring of surface activity and to verify the changes.
While so far the seismic events mentioned above are considered as very low energy and associated with the rise of small volumes of magmatic material, the volcano remains at yellow activity. It is important to note that the system continues to evolve and no new events can indicate an acceleration of the process, involving greater system instability. The changes, therefore, of the level of activity is rejected. It is essential to pay attention to official information to be published by the Colombian Geological Service.
November 26, 2015. Nevado Del Ruiz, Colombia :
Source : SGC.