Monitoring surface activity of Nevado del Ruiz volcano, Colombia

Nevado del Ruiz volcano had a phreato-magmatic eruption in 1985, which caused one of the largest volcanic disasters in the history. The eruption partially melted the volcano's ice cap leading to floods and lahars flowing down to nearby towns. It killed at least 25,000 lives. This event has raised particular importance of monitoring ice-capped high-altitude volcanoes including small eruptions. However, the high altitude makes it difficult to maintain monitoring stations near the summit crater. Moreover, visibility of the summit area is frequently prevented by clouds. Here we report the feasibility study of detecting small eruptions and thermal anomalies of Nevado del Ruiz volcano using infrasound data from newly installed stations and thermal data from satellite remote sensors.

At the end of 2016, pairs of infrasound sensors were installed at three stations from 4.2 to 6.1 km away from the summit. Infrasound signals were generally smaller than 1 Pa in amplitude and covered by wind noise. We distinguished signals from noise by cross-correlation analysis between the pair of collocated sensors.

'REALVOLC' is a real-time monitoring system of active volcanoes using multiple satellite images. We used infrared images with moderate spatial resolution (1km per pixel) in 3.9 and 11-micrometer bands from MODIS boarded on the Terra and Aqua satellites.

The most recent activity-stage of Nevado del Ruiz began in October 2010. Two episodes of lava-dome formation have been reported in October 2015 and September 2016. However, the associated thermal anomaly was not obvious. Apparent annual change was observed, which was due to the effect of clouds over the volcano. Infrasound data was available after the second dome-forming episode. Comparing the results of infrasound and thermal analyses from December 2016 to February 2018, it is concluded that the surface activity of the volcano was high from December 2016 to April 2017 and continued with decreasing level.