资源环境科技发展态势分析平台

The Colombian volcano Galeras is one of the most active volcanoes in the world, and it has an andesitic composition and high explosive potential. We consider the period of 1989-2015, in which the volcano manifested frequent eruptions and high seismic activity. To study the temporal variations in the seismic structure beneath Galeras, we implemented an algorithm of repeated tomography using selected data sets with similar geometries. We obtained the variations in the seismic velocity structures beneath Galeras during the three time episodes of 1989-2000, 2001-2007, and 2008-2015. In the second episode, we observe a columnar anomaly with a high V-p/V-s ratio that possibly represents a conduit transporting a new portion of magma material from below. This result may indicate that in this period, which culminated with dome emplacement and collapse, the volcano was directly fed from deeper magma sources. In other episodes, the conduit is less visible in the tomography models, and we propose that the volcanic activity was merely controlled by shallow magma reservoirs at 2-4 km below the surface.

Plain Language Summary The Galeras volcano is one of the most active and hazardous volcanoes in the world; it is located in the Colombian Andes near Pasto City, which has approximately 450,000 inhabitants. In this study, we implement the repeated tomography algorithm to reveal the temporal changes beneath the Galeras volcano from 1989 to 2015 and associate them with features of the eruptive activity of the volcano in the same period. During 2001-2007, we observed a columnar anomaly with a high V-p/V-s ratio located beneath the active cone of the Galeras volcano. For the preceding period of 1989-2000, this anomaly did not exist, and in the following period of 2008-2015, it appeared less clearly. It may testify that in the period of 2001-2007, the activity of the Galeras volcano was fed directly from a deep reservoir, whereas in other periods, it was mostly connected with shallow reservoirs at 2-4 km below the surface. Comparison of results of the similar studies in other volcanoes shows that the periodic inflation and deflation of shallow reservoirs by the transport of magmas through a temporarily opened conduit might be a common mechanism that determines the regimes of the eruption activities of different volcanoes throughout the world.