Hundreds of seismic tremors: Colombian volcanoes are stirring

September 12, 2011 – BOGATA – Ruiz and Machin are both on elevated alert status, but Machín is the more interesting of the two as it has likely been almost 900 years since it last erupted. The volcano is a dome complex that has produced pyroclastic flows and mudflows sourced from explosive eruptions, some of which traveled over 40 km from the domes in the ancestral caldera. There has been an increase in seismic activity – 139 earthquakes in August alone – under Machín for the past year or so thus necessitating the increased alert status, but little else has changed. These earthquakes have been at two depths, from 1-5 km and 5-14 km below and to the southeast of the main domes. This potential activity has real ramifications in the region around Machín, such as decisions on where to build schools. Over at the more famous Nevado del Ruiz (see above), seismicity has increased dramatically over the course of 2011 (the 20 year anniversary since its last eruption). During the month of August alone, almost 400 likely volcanically-related earthquakes occurred at Ruiz. Sulfur dioxide measurements are listed as “moderate” but no signs of deformation have occurred at the volcano. All that shaking means that Ruiz is also on yellow alert status, suggesting that an eruption might be in the cards. These two volcanoes are located close to populated areas – Manizalez and Pereira (my mother’s hometown) for Ruiz and Ibague for Machín, so they will be closely watched by INGEOMINAS for the slightest change in their activity. –Big Think