Bull Volcanol (1991) 53:572-574 Volc ii ology �9 Springer-Verlag 1991

Short communication

Monitoring Colima Volcano, Mexico, using satellite data Michael Abrams x, Lori Glaze x, and Michael Sheridan 2

Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA 2 Geology Department, SUNY Buffalo, Buffalo, NY, USA

Received April 10, 1991/Accepted May 3, 1991

Abstract. The Colima Volcanic Complex at the western end of the Mexican Volcanic Belt is the most active an- desitic volcano in Mexico. Short-wavelength infrared data from the Landsat Thematic Mapper satellite were used to determine the temperature and fractional area of radiant picture elements for two January data acqui- sitions in 1985 and 1986. The 1986 data showed four 28.5 m by 28.5 m pixels (picture elements) whose hot subpixel components had temperatures ranging from 511-774~ and areas of 1.8-13 m 2. The 1985 data had no radiating areas above background temperatures. Ground observations and measurements in November 1985 and February 1986 reported the presence of hot fumaroles at the summit with temperatures of 135- 895 ~ C. This study demonstrates the utility of satellite data for monitoring volcanic activity.

Introduction

Volcanoes are among the few geological features that change rapidly enough to warrant frequent surveil- lance. Monitoring is important to understand their be- havior and thus more effectively predict eruptions and related hazards. Remote sensing by satellite measure- ments can provide an improved technique for volcano monitoring. Previous researchers have shown that short-wavelength infrared data from the Landsat satel- lites, with spatial resolutions less than 100 m, can pro- vide information on surface conditions and magmatic events (Francis and Rothery 1987; Rothery et al. 1988; Glaze et al. 1989a, b; Pieri et al. 1990). Here we de- scribe the use of Landsat Thematic Mapper data at Colima Volcano, Mexico. We obtained two images of Volcan Colima, 7 January 1986 and 4 January 1985, and used data from the two reflected infrared channels to determine the temperatures of eruption activities.

Offprint requests to: M Abrams

Colima Volcanic Complex

The Colima Volcanic Complex, Mexico's most histori- cally active andesitic composite volcano (Luhr and Car- michael 1980), is located at the western end of the Mex- ican Volcanic Belt (Fig. 1). The complex consists of a northern, inactive summit cone (Nevado de Colima) and a southern, active cone (Fuego de Colima) (Fig. 1) (Robin et al. 1987). Since 1576, Fuego has gone through three cycles of activity, each cycle ending in a major ash flow eruption, followed by 50 or more years of

COLIMA VOLCANIC COMPLEX

~ LAVA FLOWS N

DEBRIS FLOWS | 1=,

Fig. 1. Simplified geologic map of Colima Volcanic Complex (modified from Robin et al. 1987; Stoopes and Sheridan 1990). Areas covered by Fig. 2 A and B delineated for location

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quiescence. Lava eruptions starting in 1961 marked the inception of activity in a fourth cycle (Luhr and Carmi- chael 1980).

Activity of Fuego in the last decade has consisted of fumarolic phenomena, fracturing, minor ash-cloud eruptions, and rockfalls. In 1983, visitors to the summit reported no activity (SEAN 1985). Dartmouth volcano- logists visited the summit in November 1985 and re- ported (SEAN 1985) fumaroles on the NE flank of the summit, with several measured temperatures greater than 600 ~ C. In early January 1986, residents of San Marcos reported (SEAN 1986) seeing a red glow at the summit at night and a dark ash plume during the day. A visit to the summit in February 1986 found summit fu- maroles with temperatures of 135-895~ and continu- ing fumarolic activity along the NE flank fractures (SEAN 1986). In May 1988, a group from the Univer- sity of Colima measured average temperatures of 118~ adjacent to the main fumaroles (SEAN 1988). Explosions at the summit dome in 1989 and 1990 scat- tered bombs about the summit area and modified the topography, indicating that hot juvenile magma may be near the summit zone. In February 1991, the local au- thorities declared the volcano dangerous and restricted access to the summit area. In April 1991, Colima began its next phase of eruptive behavior.

Methodology

To extract the subpixel thermal structure of features, we used the method of Dozier (1981) and Matson and Dozier (1981), modified for the Landsat Thematic Mapper (TM) bands by Rothery et al. (1988) and Glaze et al. (1989b), using band 5 (1.55-1.75 txm) and band 7 (2.08-2.35 ktm) in the short-wavelength infrared region of the spectrum. With this technique, if a radiant pic- ture element (pixel) is composed of two distinct temper- ature components (one very hot and one much cooler), the signal received by the sensor (the pixel-integrated temperature) is a weighted average of the radiance from each component. By assuming a background tempera- ture (cooler component) for two radiance channels at two wavelengths, we have two equations with two un- knowns (the hot temperature and the fraction of the pixel it occupies) that can be solved simultaneously. The characteristics of the Thematic Mapper bands al- low sensing pixel-integrated temperatures in the range of 160-420~ for bands 5 and 7, and 700 ~ to over 1200~ in theshorter wavelength bands 1-4 (Rothery et al. 1988). With its pixel size of 28.5 m by 28.5 m, the TM is capable of detecting and monitoring phenomena with temperatures typical of magmatic and fumarolic activity.

Results of temperature determinations

Color composites of the two TM data sets covering the Colima Volcanic Complex are shown in Fig. 2. These were produced by displaying bands 4, 5 and 7 in blue,

green, and red, respectively, resulting in vegetation ap- pearing blue. No activity was observed in the 1985 data (Fig. 2A). In the 1986 data (Fig. 2B), a smoke plume was seen in the visible channels, emanating from Fuego and blowing toward the east.

Using the method described above, temperatures were calculated for the area at the summit of Fuego from both the data sets. A background reflectance was identified in the caldera, away from the hot spots, to use to subtract the solar reflectance component of the radiance signal. A background temperature of 125~ was assumed, which is the detection limit for thermally emitting pixels. An emissivity of 0.8 was also assumed. (For a discussion of the sensitivity of derived tempera- tures as a function of assumptions about the atmos- phere, assumed emissivity values, and other sources of error, see Rothery et al. 1988.) Using the above model, temperatures calculated for the hot portion of four ra- diating pixels in the 1986 data were 511 ~ 529 ~ 728 ~ and 774~ These are shown in the inset labelled "TEMP" Fig. 2B; the 2 x 3 box represents the six pixel area of the summit shown in the white box in the mid- dle inset of Fig. 2B. The same pixels in the 1985 data were at background temperatures; no additional radiat- ing pixels were found. Our model also provides the area fraction of the pixel occupied by the hot compo- nents: these values ranged from 0.0018 to 0.016 of each pixel. Since a pixel covers an area of 812 m 2, these val- ues correspond to hot areas of 1.5 to 13 m 2.

The temperatures and areas of the hot fraction of the radiant pixels correspond quite well with the reported occurrences of fumarolic activity on Fuego: 600-800 ~ C fumaroles seen in November, 1985 and 135-895~ fu- maroles measured in February 1986 (SEAN 1985, 1986). Other reports of temperatures and areas of hot fumaroles from different volcanoes (LeGuern and Ber- nard 1982) are also in excellent agreement with these values. The temperature values determined in this study were less than those found by similar satellite-derived investigations of magmatic sources such as basaltic lava lakes and lava flows, with reported hot area tempera- tures of 1050-1150~ (Rothery et al. 1988; Glaze et al. 1989b; Pieri et al. 1990).

Conclusions

The two-band method of determining the temperature and fractional area of the hot component of radiant pixels on Fuego, using Landsat Thematic Mapper data, shows the potential value of satellite data for volcano monitoring. This example illustrated the correspond- ence between ground-based observations and measure- ments with satellite-derived temperature measurements of hot fumaroles on an active volcano.

The main limitation to the use of current data for routine world-wide monitoring of potential volcanic ac- tivity is the cost. A second limitation is the 16-day re- peat cycle of Landsat; volcanic phenomena can and do change over much shorter time periods. Future satellite systems planned for the next decade should allow more

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Fig. 2A, B. Landsat Thematic Mapper color composites of Colima Volcanic Complex. The large images cover an area of 30 • 45 km. In- sets show enlargements of Fuego, enlarge- ments of Fuego summit area with radiant pixel area marked with white box, and de- rived temperatures of hot fraction for radiant pixels within the box. A January 1985 image; B January 1986 image

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f requent observa t ions of vo lcan ic activity and ma y ev- en tua l ly lead to a systematic, wor ld-wide p rog ram of vo lcano moni to r ing .

Acknowledgements. Work at the Jet Propulsion Laboratory, Cali- fornia Institute of Technology, was performed under contract to the National Aeronautics and Space Administration.

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Editorial responsibility: G. A. Mahood