Galeras volcano (Colombia): seismic swarm triggers eruption warning
The Colombian volcano monitoring institute INGEOMINAS has raised the alarm level for Galeras volcano, after a number of so-called tornillos, a characteristic seismic signal often preceding eruptions at Galeras, were detected in recent days. Tornillos consist of a screw-driver shaped signal of rapdily increasing and then slowly decreasing harmonic tremor and preceded most eruptions of Galeras between 1992 and 2010.
The Galeras volcano in Colombia‘s western department of Nariño could erupt within weeks or days, according to authorities.
The level of volcanic activity was increased to orange alert Thursday 9PM by the Colombian Geological Service and the Volcanology and Seismology Observatory of Pasto, which are monitoring the activity of Galeras.
The institutions stated that in the last 24 hours, tremors have been registered that have similar characteristics to those in the period prior to the majority of eruptions, which occurred between 1992 and 2010.
There has been a reduction in the emission of gases, reflected in the low values of sulphur dioxide measured, both coming from craters and fields of volcanic fissures.
Some 8,000 people live in the area surrounding the volcano that reawakened in 1988.
The Colombian Geological Service will continue to monitor the situation of the Galeras volcano.
Galeras, a stratovolcano in the southwestern part of Colombia, is one of the South American country’s most active volcanoes. Historic records of eruptions at Galeras date back to the 16th century, and the active cone is part of a volcanic complex that has been erupting for more than one million years. Galeras is only a few kilometers from the city of Pasto, and poses an immediate threat to the more than 300,000 people who live there.
Simplified plate tectonics cross-section showing the subducting Nazca Plate providing magma that feeds the eruption of Galeras Volcano.
The Galeras volcanic complex is located in the Colombian segment of the South American Andes mountains. The Andes in Colombia are the result of a collision between the Panamanian tectonic block with South America, which detached part of the South American plate from the continent. This segment was pushed northward and upward, and this thrusting (in addition to the subduction of part of the Nazca plate under the Colombian block) created the Northern Andes. Galeras is located near a northwest-dipping thrust fault zone that resulted from this collision.
Seismic activity at Galeras has displayed characteristic signals known as “”. “Tornillo” is Spanish for ‘screw’, and these seismic signals are so named because their shape on a seismograph resembles a screw with a wide head and tapered tail. At Galeras, these signals are generally regarded as short-term precursors to explosive eruptions. 
. In 1993, Galeras erupted with no warning (seismic precursors) while a group of volcanologists and visitors were visiting the crater of the active cone. Nine people were killed and six were injured in the explosion; because of the lack of seismic activity, many of the victims were not wearing adequate safety equipment. The disaster served as a cautionary example to other volcanologists, and now many are much more wary of venturing into an active volcanic crater.
http://geology.com/volcanoes/galeras/
Some content on this page was disabled on July 30, 2018 as a result of a DMCA takedown notice from Geology.com. You can learn more about the DMCA here:
abraveheart1 
