Deformation associated with the extrusion of a dome at Galeras volcano, Colombia, 1990–1991

During 1989–1992, two electronic tilt meters named Cráter and Peladitos, and a short level line named Las Piedras, were used for monitoring Galeras volcano. The two tilt meters detected considerable changes of uplift mainly from June to November 1991. The Cráter station showed cumulative values of more than 600 microradians, while the Peladitos station exhibited values of more than 100 microradians. The short level line showed inflationary tilt of more than 20 microradians in 1989. This behavior was related to increases in the daily occurrence of long-period seismic events during July–November 1991 caused by the rise and extrusion of a lava dome, which was subsequently destroyed in July 1992. At the end of 1990, the deformation source was located at a depth of 2–3 km. By December 1991, the source had migrated to less than 500 m in depth. The magma ascent rate was 1–4 m/day during this period. The dome emplaced in the crater had a volume between 300,000 to 400,000 m3. Using a hydrodynamic model and the tilt changes registered by the Peladitos station, the volume of the magma body is estimated at approximately 2.8 × 106 m3.