Monday, February 11, 2013

Colombian Volcano Cerro Machin Showing Unrest

While this has been going on for nearly a year now, a Colombian volcano with no recent records of historical eruption is beginning to show signs that it could be preparing for a bang soon. IGNEOMINAS has raised the volcanic alert level to "Amarillo" (or Yellow) and is beginning to issue warnings. Cerro Machin in Western Colombia is experiencing up to 200+ volcanic quakes a day, and the trend is showing that this is increasing. Cerro Machin, much like Chaiten in Chile, is a small lava dome occupying a small caldera. It's last eruption is thought to be about 800 years BP (however Chaiten's last eruption before its most recent was thought to be about ten times longer ago, 8,000 years at least), and it has not shown signs of unrest since.


Cerro Machin in Colombia. Picture from Smithsonian GVP.


The unrest began about a year ago, and seismicity has steadily risen during that time. The volcanic quakes being recorded are thought to indicate shallow rock fracturing, which is indicative of rising magma within the chamber. An eruption today would most likely be a large initial explosive event, which would be accompanies by pyroclastic flows and heavy ash fall, similar to the Chaiten event. As a lava dome 'plugs' the vent, rising magma would likely destroy it and 'uncork' the system like a bottle of Coca Cola. Simply, if this volcano erupts, it will make life pretty miserable for people in the near vicinity, and undoubtedly cause loss of life for anyone or anything that does not evacuate when told. Warnings from IGNEOMINAS should be quickly heeded by the population.

Colombia is no stranger to volcanic disaster, being one of the big reasons there have been such advances in volcanology and eruption 'prediction' have been made at all. In 1993, Galeras began to show signs of unrest that we now know means that a volcano is inflating with magma. So called 'long period events' and 'low frequency tremor' were detected at the volcano. A scientist with a theory that this meant magma was rising and an eruption was imminent decided to mount an expedition to the summit to see if gases and temperatures had increased with the tremor was tragically killed along with his science team as the volcano erupted when  they were at the summit. Their deaths did, however, result in scientists taking his theory of harmonic tremor and long-period events seriously, and since then volcanologists routinely rely on these types of quakes as good indicators of impending activity.

At this time, it appears that volcanologists are watching this volcano quite closely to see what it will do. As it has no recent eruptive history, it could be quite a large eruption as the pressure it takes for magma to break through to the surface through cooled, solid rock would be immense. It is looking likely, given that quakes are getting much shallower that the magma intrusion is getting closer to the surface, which makes an eruption even more likely. Most magma dike intrusions never result in an eruption, however most intrusions are short lived, and this has been going on for over a year now.