Saturday, November 26, 2011

Columbia's Galeras Volcano Alert Level Raised to Orange

BOGOTA, Columbia
11/26/2011

INGEOMINAS, the Columbian volcano monitoring institute, has raised the alert level at Galeras volcano to Orange, after a spate of "tornillos", or rapidly increasing, slowly decreasing harmonic tremor was recorded over the past couple of weeks. These harmonic signals are characteristic of Galeras, which, in 1992 were detected by seismologists and identified as magma intrusion. Unfortunately for the seismologists who were curious about these tremors, they decided to hike to the summit, and were caught in an eruption.

The signals have been said to successfully predict eruptions within a few days at Galeras, and have been used as models for other active volcanoes. Harmonic tremor signals are generally thought to indicate magma intrusion for most volcano types, especially stratovolcanoes, and this research mostly comes from Galeras.

From Wikipedia:
"Galeras is considered the most active volcano in Colombia, followed by Nevado del Ruiz. Its earliest activity during the Holocene has been dated at 7050 BC ± 1000 years through radiocarbon dating. Other eruptions similar to this event include those in 3150 BC ± 200 years, 2580 BC ± 500 years, 1160 BC ± 300 years, 490 BC ± 100 years, and in 890 AD ± 200 years. Typically these eruptions consist of a central vent explosion, conducive to an explosive eruption causing pyroclastic flows and/or lahars. Eruptions in more recent times, which have been recorded consist of those in 1535, December 1580, July 1616, 1641, 1670, 1754, November 1796, June 1823, October 1828, 1834, October 1865, July 1889, 1891, December 1923, October 1924, October 1932, February 1936, July 1947, January 1950, 1974, February 1989, January 1990, January 1993, March 2000, June 2002, July 2004, November 2005, and October 2007. Reported incidents with no official proof occurred in 1836, 1930, 1933, and 1973."

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