Report on Colima (Mexico) — July 1995
Bulletin of the Global Volcanism Network, vol. 20, no. 7 (July 1995)
Managing Editor: Richard Wunderman.
Colima (Mexico) Measurements of SO2 flux, fumarole temperatures, and a lahar channel
Please cite this report as:
Global Volcanism Program, 1995. Report on Colima (Mexico) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 20:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199507-341040.
19.514°N, 103.62°W; summit elev. 3850 m
All times are local (unless otherwise noted)
The following report concerns Colima's SO2 flux between 1 April and 31 July 1995, its summit fumarole geochemistry, and a topographic profile of a barranca (steep-walled canyon).
SO2 measurements. Using a Cessna Skyhawk aircraft chartered by the Colima Civil Protection Authorities, a COSPEC survey was made on 30 March 1995. The wind speed and direction were computed for each of the six traverses by a global positioning system (GPS). At an altitude of 3,200 m, the average wind speed was 8.6 ± 1.1 m/s. The corresponding average SO2 flux estimate was 491 ± 104 metric tons/day (t/d).
On 5 July five vehicle-based terrestrial COSPEC transects were made along the Colima-Guadalajara highway, ~19.4 km NE of the summit. The average elevation of the transects was 1,300 m; the transects were oriented perpendicular to the direction of the plume axis. The average SO2 flux was 214 ± 91 t/d. The wind speed, measured at the Guadalajara City International Airport, averaged 7.62 m/s.
A third aerial COSPEC measurement was done on 11 July at an altitude of 3,050 m, ~3.5 km SW of the summit. GPS calculated wind speed averaged 9.26 m/s. The average SO2 flux for the six transects was 159 ± 78.5 t/d.
Field observations. On 28 July, the Colima Volcano Observatory group and J-C. Komorowski measured summit fumarole temperatures for the same three areas reported earlier; in summary the new temperatures had maximum values that were 14 and 43°C lower and 68°C higher than those reported in previous months (Areas I, II, and III, respectively).
Specifically on 28 July, in Area I, E of the summit, the six hottest fumaroles averaged 409°C and had a maximum value of 490°C. Area II, NE of the summit, contained two fumaroles with temperatures of 415 and 447°C. Area III, N of the summit, contained four fumaroles with an average 485°C; the maximum value reached 556°C.
An experimental gas analysis was conducted on an isolated 60°C fumarole (the same one reported in BGVN 20:02). The sampled gases and their concentrations were as follows: SO2, 20 ppm (1 minute sample time); HCl, 3 ppm (1 minute), HF, none detected (5 minutes); and CO2, 1,100 ppm (15 minutes).
An increase in the number of low-temperature fumaroles was seen in the 1987 explosion crater (E part of the summit). Some members of the group noted possible offset in the NE sector of the summit, a displacement identified by ~10-cm-long striations on the base of some big bread-crust blocks.
A topographic profile was measured perpendicular to the Cordoban barranca at the 1,620-m elevation and ~6.5 km SW of the summit, in order to study lahar deposits. Major lahars have been funneled down this barranca since 1991. During the rainy season, lahars have threatened the village of Becerrera (6.1 km downstream). This profile furnished evidence of 5-12 cm of deposition in the barranca during 4-18 July 1995.
Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.
Information Contacts: Juan J. Ramirez Ruiz, Carlos Navarro Ochoa, Abel Cortes Cortes, Juan Carlos Gavilanes Ruiz, and Ricardo Saucedo Giron, Colima Volcano Observatory, Univerisidad de Colima.