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Report on Galeras (Colombia) — March 1990

Bulletin of the Global Volcanism Network, vol. 15, no. 3 (March 1990)
Managing Editor: Lindsay McClelland.

Galeras (Colombia) Small phreatic ash emissions with spasmodic tremor and long-period seismicity

Please cite this report as:

Global Volcanism Program, 1990. Report on Galeras (Colombia). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 15:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199003-351080.

Volcano Profile |  Complete Bulletin


Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Small phreatic ash emissions continued in March, accompanied by spasmodic tremor and long-period seismicity (table 2). Incandescence was mainly observed in the W part of the crater. The number of low-frequency earthquakes increased 47% relative to February values, with an 86% increase in seismic energy release. However, the number of high-frequency events decreased 38% from February and energy release declined 28% (figures 17 and 18). Most earthquakes were centered in two zones under, W of, and S of the summit (figure 19). SO2 emissions measured on 15 and 22 March by COSPEC were at low-moderate levels, ranging from 630 to 1,380 t/d.

Table 2. Phreatic ash emissions and associated seismicity at Galeras, March 1990. Courtesy of INGEOMINAS.

Date Time Seismic Signal
09 Mar 1990 0233 Spasmodic tremor
11 Mar 1990 1448 Spasmodic tremor
11 Mar 1990 1618 Spasmodic tremor
11 Mar 1990 1652 Long-period
11 Mar 1990 2036 Spasmodic tremor
17 Mar 1990 1817 Long-period
17 Mar 1990 1921 Spasmodic tremor
18 Mar 1990 0631 Spasmodic tremor
27 Mar 1990 0609 Long-period
27 Mar 1990 1552 Spasmodic tremor
28 Mar 1990 1359 Spasmodic tremor
29 Mar 1990 0948 Spasmodic tremor
Figure (see Caption) Figure 17. Number of seismic events at Galeras, February 1989-March 1990. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 18. Daily energy release of high-frequency (dashed line) and low-frequency (solid line) seismicity at Galeras, March 1990. Courtesy of INGEOMINAS.
Figure (see Caption) Figure 19. Epicenters of 67 seismic events at Galeras, March 1990. Courtesy of INGEOMINAS.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS-OVP.