Thematic Mapper Studies of Central Andean volcanoes 

--- 

Progress report, 

January 1987 

Ne 7- 189 10 

Unclas , 

(IiASA-CR- 180252) T6EEATIC BA€E-EEB STUDIES Of 

CElTBAL AhDEAbl VCICAWCES Ercgr~ss Beport 

(Lunar and Planetery Inst,) 17 F CSCL 08K 

G3/43 43791 

P.W. Francis 

Lunar and Planetary Institute. 

3303 NASA Road 1 

Houston 

Texas 77058 Phone: (713) 486 2174 

1. STATUS OF DATA AQUISITION 

A total of 51 quads of day time TM data were included in the original 

proposal. Three full night scenes were also requested on an experimental basis, 

with others to be acquired if the experimental scenes were successful. 36 of 

the day time scenes requested have been received to date, mostly covering the 

sou hern part of the area under investigation. Two night time scenes over path 

row 233/ 75 have been acquired in photographic form for examination, but the 

dig tal data have not yet been delivered. In addition, because of the interest 

in current volcanic activity at Lascar volcano, north Chile, two further 
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Fiqure 1. Locations of TM scenes already obtained, and those 

awaiting acquisition. 90% of the Central Andean volcanic 

Yrovince will ultimately be covered. 
acquisitions have been made of path row 233/76, and further digital data are 

expected. (Figure 1). 

--- 

2. QUALITY OF THE DATA 

As described in the previous report, the quality of the data has been 

uniformly extremely high, and has not been a problem in the research. Care has 

been taken to examine photographic products first before obtaining digital 

data. 

3. RESULTS TO DATE 

-- 3.1. Preparation of hard CODY data base. 

In order to provide a comprehensive and consistent data base for 

volcanogical studies, a series nf false color composite images covering the 

volcanic cordillera has been written to film on the Institute’s Optronics film 

writer. Each image is 45 km square (1536 x1536 pixels) and is constructed 

using bands 7, 4 and 2 of the TM data. This provides a working data base on 

which individual volcanoes of interest can be identified. Approximately 100 

images have been prepared to date. 

- 3.L Compilation of volcano data base. 

A set of Landsat MSS images was used in conjunction with the TM 

hardcopy images to compile a computer data base of all volcanic structures in 

the Central Andean province. Over 500 individual volcanic structures were 
identified, ranging in age from -20 my to Recent not including numerous small, 

monogenetic scoria cones and lava flows. About 75 major volcanoes were 

identified as 'Iactive", or potentially active. Many of these are extremely 

large composite cones reaching over 6,000 m in altitude. Only fourteen of these 

were previously known and listed in the 'Cataloque of Active Volcanoes of 

World', (Casertano, 1963) but the remainder (about 80%) were not. In principle, 

an "active" volcano is usually taken as one that may erupt in the future. In 

practice, the criterion we have is evidence of eruptive activity in 

post-glacial times, roughly the last 10,000 yr. Glacial moraines are well 

developed on Central Andean volcanoes down to altitudes of - 4,300~1 

(Hollingworth and Guest 1967). Fortunately, the resolution of the TM data is 

sufficiently good that moraines are clearly identifiable where present. Thus, 

moraines an excellent and consistent stratigraphic marker for most of 

the study area. The southernmost part of the region (lats. 26- 29's) is 

exceptionally arid at the present day, and appears to have been so during 

glacial times also. Moraines are difficult to identify in this area, and thus 

in this area the best criterion of activity we have used is simply morphologic 

youthfulness. 

provide 

times, perhaps in excess of 1 million years. Given the 

that exist, criteria for recognising those that are 

urgently required. k'e hope that the Andean study wi 

guidelines in dealing with this problem. 

A serious problem arises in dealing with the very largest volcanic 

systems, especially resurgent silicic calderas. These may have very long repose 

of large calderas 

ally active are 

de some important 

number 

potent 

1 prov 

- 3.3 Identification of larqe volcanic debris avalanche deposits. 
The eruption of Mount St. Helens on May 18, 1980 focussed the 

attention of volcanologists on this distinctive mode of eruption, in which 

catastrophic gravitational failure of a large segment of the volcanic edifice 

produces a huge avalanche, while the concomitant sudden depressurisation of the 

volcano’s interior triggers a violent explosive blast (Lipman and Mull ineaux, 

1982). Many other examples of this phenomenon have been identified around the 

world since 1980. This work has been reviewed by Siebert (1984) and by Siebert 

et al. (in press). One of the most outstanding examples was identified in Chile 

at the western foot of the Socompa volcano (Francis et al, 1985, Rothery and 

Francis., Self and Francis 1986). Debris from this avalanche covers some 500 

km2 of the Atacama desert. TM images have been invaluable in field studies of 

Socompa because of their high resolution and spectral discrimination. In 

particular, the TM allows distinction between debris streams with subtly 

different contents of iron oxide minerals (mostly goethite), such that the 

trajectories of individual components of the original volcanic edifice can be 

traced in the debris avalanche deposit. 

--- 

Since work on Socompa began, we have identified many other major 

debris avalanche deposits on TM imagery. Their properties are summarised in 

Tab 

Par 

by 

Oal 

e 1. Of these, only Socompa has so far been studied closely in the field. 

nacota has been visited on a reconnaisance basis, and studied in the field 

a collaborating group (R.S. Harmon et al., Southern Methodist University, 

as). The others have been studied only on TM images, and require field 

investigations to provide ‘ground truth’, but some conclusions can already be 

drawn (e.g. Francis and Ramirez, 1985). Because of the generally exceptionally 

arid environment, the Central Andes provides a unique opportunity to study this 
CHARACTERISTICS OF PREVIOUSLY UNDESCRIBED ANDEAN VOLCANIC DEBRIS AVALANCHES 

Vol can0 Lat. Summit Max. Vert. Horiz. H/L Area Azimuth 

Long. Height summit descent run 

Parinacota 18:10’S, 6348 35 1900 23 0.08 156 253 

Tata Sabaya 19:08’S, 5430 35 1730 25 0.07 331 166 

Titivilla 19:43’S, 5050 30 1350 20 0.07 189 68 

69 8’W 

68 31’W 

68 ll’W 

San Pedro 19:53’S, 6145 45 2845 1 €id 

68 23’W 

0.18 118 275 

Napa 20:31’S, 5170 21 1450 16 0.09 139 109 

68 40’W 

Aucanqui 1 cha 21:13’S 6176 25 2100 17 0.12 59 311 

68 28’W 

01 1 ague 21:18’S, 5863 35 

68 ll’W 

2171 16 0.14 113 286 

- 0.17 5 216 

Socompa 24z25’S 6051 35 3020 37 0.08 606 324 

Lull ai 11 aco 24:43’S 6723 -36 2500 25 0.1 197 114 

22:37’S 4986 e -500 3 

68 Ol’W 

68 15’W 

68 33’W 

Ro s ado 24:46’S7-5100 e -960 6 0.16 10 96 

Lastarri a 25:10’S, 5700 e 1200 9 0.13 18 105 

68 24’W 

68 31’W 

a Summit altitudes given are those of the present volcanoes; the 

height of the volcanoes at time of collapse 

b Maximum slopes for the uppermost 500m were measured from 

topograqphic maps. 

at the time of collapse. 

c Vertical height descended assumes present summit height. 

d Distal margin has been eroded. 

was probably different. 

They may not be representative of volcano slopes 

e Detailed topographic information not available. 
important phenomenon. Deposits which are rapidly obliterated in temperate 

environments such as those of Indonesia or Mexico are perfectly preserved. 4c 

dates on Socompa, for example, show that the deposit is -7,000 yr old, yet the 

morphology of the distal parts is such that it appears pristine. 

--- 

3.4. Inteqration of TM with other remotely sensed data sets 

The availability in recent years of several new remote sensing 

techniques have made it worthwhile to explore means whereby the best features 

of each technique can be extracted and combined with others to maximise the 

geological knowledge of an area. This seems to be inevitably the direction of 

future remote sens ng research, especially in the ‘Space Station Era’, when 

many different kinds of data will be available. Data sets that we have used in 

a preliminary way nclude Hasselblad and Large Format Camera photography fron 

the Space Shuttle; Shuttle Imaging Radar and MOMS -01 (Modular Optoelectronic 

Mu1 ti spectral Scanner) images. Shuttle photography was obtained over the 

Socompa test site on several occasions. With the 250 mm lens, the resolution 

obtained comparable to that of TM, but its chief advantages for geological 

interpretation lie in the flexibility of illumination and viewpoint: the 

Shuttle is not locked in to a sun-synchronous orbit, and photographs obtained 

in late afternoon or early evening revealed some very important textural 

features in the secondary deposits of the Socompa avalanche. A further very 

important asset of the Shuttle photography is the stereo cover; in this regard 

it forms a valuable complement to the TM images, on which it can often be 

difficult to interpret slopes. 

is 

We have also begun pilot studies combining SIR data with TM for a test 
Page (1) 

area in north Chile and Boliviz (Cerro Quemado volcano). Although interesting, 

these data are difficult to interpret at present, because of uncertainties of 

what the radar signal is responding to. Field work to obtain ground truth is 

required, but even this may not resolve all the uncertainties - in the test 

area, som areas covered by young ash deposits appear bright in the radar image; 

others appear dark. The moisture content of the ash is suspected to be 

responsible for variations in the returned signal, and this is a factor that is 

difficult to quantify. 

The MOMS-01 was the first high resolution pushbroom dev ce to be used 

for remote sensing from Earth orbit (Bodechtel at al, 1984, 1985) It was flown 

experimentally on STS 7 and STS 11 in June 1983 and February 1984. The system 

has two spectral bands (600 and 900 urn) and a pixel size of 20m. Coverage of 

the Socornpa test site was obtained on STS 11. Initially, it was anticipated 

that the higher resolution of the MOMS would offer additional opportunities for 

textural and strlrctlrral interpretations of the debris deposit, and that the 

spectral capabilities would not offer any advantage over the TM. 

the optics of the MOMS system turned out be poorly focussed, and 

resolution no better than TM. MOMS data proved to be useful 

however: the Socompa orbital pass took place in late afternoon, 

elevation of only 25'. The low, westerly illumination ernphasised 

number of subtle topographic features. By combining the spect 

contained in the TM with textural information from the MOMS, we 

Unfortunately, 

the effective 

n one respect, 

with a solar 

and revealed a 

a1 i nforrnat i on 

were able to 

create images with a potential for interpretation significantly enhanced over 

either system alone (Rothery and Francis, in press). 

The Socompa test area was also been selected as one of the sites for 
the preliminary series of PEPS experiments for the French SPOT satellite, in a 

collaborative project with D. Rothery, Open University, United Kingdom. Our 

data arrived in the same week that this report was prepared, so no definitive 

conclusions are possible. However, from preliminary studies it appears that the 

spectral capabilities of the SPOT system offer no advantage over the TM. The 

enhanced reso ution will certainly prove valuable for some applications, but 

much the most mportant advantage will be the stereo facility offered. This has 

already led to some revised interpretations of the Socompa morphotectonic 

setting. 

. 

-- 3.5. Applications of TM data to studies of volcanic thermal anomalies 

From the outset of our TM project, it was planned to attempt to use 

the therixal band to 'ibent i fy and characteri se thermal anomal i es associ ated with 

volcanic phenomena. Given the ambiguities that can arise from the effects of 

djfferential solar heating on day time TM data, a special request was made for 

night scenes to be acquired to minimise these complications, a1 though 

unfortunately the timing of the night overpass is too early to be ideal 

(Watson, 1971). The night time scenes have not yet been acquired, but are 

expected soon. In the meanwhile, a careful search was made with the day time 

thermal data for evidence of thermal anomalies associated with sites of 

fumarolic activity on known active volcanoes. Several of the 1 isted "active' 

volcanoes have continuously active fumaroles, and a few have steam plumes 

sufficiently large to be observable at large distances on the ground (-100km), 

and to be identifiable on the TM imagery (e.g. Guallatiri, north Chile). With 

one exception, none of these volcanoes exhibits a significant thermal anomaly, 

and therefore can be regarded as quiescent. 
The single exception is Lascar volcano, north Chile, a 5,145 m high 

volcano located east of the Salar de Atacama. This volcano has a complex summit 

area of six nested craters, the largest about 1 km in diameter and 200 m deep. 

-.- - 

Located in a deep pit crater at the centre of the complex is a small (~200m) 

but intense thermal anomaly, suffiently intense that it radiates not only in 

the thermal infrared (band 6) but also in mid-infrared bands 7 and 5. This 

anomaly has been observed on scenes acquired on two separate March 

and July 1985. Temperature calculations in bands 7 and 5 give values of 

300-400°, but these may not accurately reflect the actual temperature of the 

occasions, 

hot body, because of the likelihood that it is observed through a drifting veil 

of steam or vapor. (Francis and Rothery, submitted). The following volcanic 

phenomena may account for the observed thermal anomaly: 

1. A lava lake in a deep pit crater, with a solid or semi-solid crust 

(cf Erebus, Antarctica; Giggenbach, et a1 1973; Kyle, 1986). 

2. An extrusive dacite lava dome, with a relatively cool, fractured 

surface and a hotter interior (cf Mt St Helens; Lipman and Mullineaux, 1982). 

3. An area of strong fumarolic activity, heated by superheated steam 

or gas escaping at the surface, indicating the presence of hot magma at shallow 

depths (cf Poas, Costa Rica; Barquero 1985). 

This exceptionally interesting observation is important in two 

regards. First, it reveals Lascar to be in an unusually ‘active’ condition, 

with the possibility that it may erupt at some point in the short term future. 

Lascar therefore is certainly worthy of further study and monitoring. Second, 

and of more general importance, it demonstrates that the TM provides a means 
whereby even rather smal 1 (<loom) and rather cool (<400°C) volcanic 

manifestations can be confidently identified. The TM thus represents a powerful 

new tool for the monitoring of active or potentially active volcanoes, 

especially in remote or inacessible regions. 
Landsat Thematic Mapper (Band 5) image of Lascar volcano, north Chile. 

Image is 15 km across. Thermal anomaly iswhite spot at centgr of Summit 

crater complex. Measured temperatures are approximately 360 C. Image 

acquired March 1985 
-.,.. .... _... * . . .- . . _. . i 

203 

244 

>268 

265 

234 

MARCH 16,1985 

246 240 

>270>270 241 

>268 >268 247 

>267>267 234 

257 260 214 

198 

JULY 21,1985 

226 

221 

c 

Band 5 

Band 7 

21 1 

251 

263 

235 

- 

- 

Band 5 

148 

194 

21 4 

Band 7 

+ 210 188 243 274 

234 I276 

248 >27S I 

226 I240 

Temperatures derived from Landsat Thematic Mapper for Lascar 

volcano, north Chile, thermal anomaly, bands 5 and 7, March 

and July 1985 

275 

276 

221 

21 1 + 
Publications arising from this work in the last six months: 

Francis, P.W. and Rothery, D.A.; Using the Landsat Thematic Mapper to detect 

and monitor active volcanoes: an example from Lascar volcano, north 

Chile. Geoloqy; submitted 

Rothery, D.A. and Francis, P.W. Synergistic use of MOMS 01 and Landsat TM 

data; Remote Sensinq Letters,. in press 

Allmendinger, R.W.; Eremchuk, J.E. Sosa Gomez, J; Ojeda, J. and Francis P.W. 

The Pasto Ventura pull-apart and the southward collapse of the 

southern Puna pl ateau, Geol oqy , submitted. 
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Baker, M.C.W. and Francis, P.W., Upper Cenozoic volcanism in the Central Andes - ages and volumes. Earth Planet. Sci. Lett. 41, 175-87, 1978. 

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Chile. Geoloqy, 13, 600-603, 1985. 

--- 

Francis, P.W. and Ramirez, C. Nuee ardente deposits at Tata Sabaya volcano ... by Deruelle and Brousse: A reinterpretation. Rev. Geol. de Chile; 22, 

3-15, 1985. 

Francis, P.W. and McAllister, R. Volcanology from Space: Using the Landsat 

Thematic Mapper in the Central Andes. Eos, 67, 170-171, 1986. 

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Erebus, Ross Island, Antarctica. Geoloqy, 1, 135-136, 1973. 

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in silicic magma chambers. Geol. SOC. Amer. Spec. Pap. 180; 43-75, 

1979. 

Hildreth, W. 1981. Gradients in si1 icic magma chambers: imp1 ications for 

lithospheric magmatism. J. Geophys. Res. 86, 10153-10192, 1981 

Hollingworth, S.E. and Guest, J.E. Pleistocene glaciation in the Atacma desert, 

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Rose, W.I. Santiaguito dome, Guatemala. J. Volcanol. Geotherm. Res., in press. 

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Remote Sensinq Letters, in press 

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caldera. J. Volcanol. Geotherm. Res. 24, 205-248, 1985. 

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