L

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 96, NO. BI, PAGES 475-484, JANUARY 10, 1991

Combined Use of Visible, Reflected Infrared, and ThermalInfrared Images for Mapping Hawaiian Lava Flows

MICHAEL ABRAMS, ELSA ABBOTT, AND ANNE KAHLE

Jet Propulsion Laboratory, California Institute of Technology,Pasadena, California

The weathering of Hawaiian basalts is accompanied by chemical and physical changesof the surfaces. These changes have been mapped using remote sensing data from the visible and reflectedinfrared and thermal infrared wavelength regions. They are related to the physical breakdown of surfacechill coats, the development and erosion of silica coatings, the oxidation of mafic minerals, and thedevelopment of vegetation cover. These effects show systematic behavior with age and can be mappedusing the image data and related to relative ages of pahoehoe and aa flows. The thermal data are sensitiveto silica rind development and fine structure of the scene; the reflectance data show the degree ofoxidation and differentiate vegetation from aa and cinders. Together, data from the two wavelengthregions show more than either separately. The combined data potentially provide a powerful tool formapping basalt flows in arid to semiarid volcanic environments.

Il'<'TRODUCTION

The weathering of Hawaiian basalts in arid to semiaridenvironments is accompanied by distinctive chemical andmechanical changes, beginning after initial eruption andcontinuing over a period of thousands of years. Thesechanges can be used to estimate relative ages ofindividual basalt flows. We have used remote sensingtechniques, combining visible/near-infrared/short-waveinfrared (VNIR) images from the NS-001 scanner andthermal infrared images from the Thermal InfraredMultispectral Scanner (TIMS) to map these changesquantitatively. This approach is particularly effectiveboth for young flows ( <1.5 ka) that are just beginning toweather and whose ages are difficult to assess by eye, andfor older more oxidized flows.

Lava flows in arid regions on the island of Hawaii arenearly unvegetated and may be exposed for manythousands of years. During this time the change mostobvious to the eye is the alteration of the surface colorfrom black or dark brown to reddish or tan due to theoxidation of iron [Lockwood and Lipman, 1987]. Otherless obvious changes also occur. Among these are theaccretion of silica-rich veneers or coatings (- 80 wt %SiOz) probably derived from windblown soil [Curtis et al.,1985] or tephra [FaiT and Adams, 1984], and thedevitrification of the thin (- 50 ~m) glassy crusts or chillcoats common on fresh pahoehoe flows. These chill coats

Copyright 1991 by the American Geophysical Union.

Paper number l)(U BO 1392.o14lHl227N0/90] B-O 13lJ2$05.00

475

may also spall to reveal a more vesicular and crystallinesubstrate.

The effect of silica rinds and glassy chill coats on thethermalIR emittance spectra of the lavas is quite strong,as predicted by Farr and Adams [1984], although not asstriking to the eye as the reddening due to the oxidationof iron. We have measured these effects using NASA'sTIMS and NS-001 scanners, together with laboratory andfield spectrometers. We find that TIMS data, displayedas images, can be used as a basis for quantitativerelative-age assessment and mapping of the youngerflows [Kahle et al., 1988]. Older flows can be mappedusing NS-001 VNIR data, relying on the progressivedevelopment of iron oxides and brightening of the flowsby weathering. In addition, the VNIR data differentiate!'Teen vewationfrom cinders and aa._ The combineddtSp>ayol lloth data sers allows wapp11lg of the relativeages of all the flows in the study area and show morethan either data set separately.

DESCRIPTION OF STUDY SITE

The study area shown in Figure 1 is at an altitude of2000- 2300 m, on the northern flank of Mauna Loavolcano, on the island of Hawaii; it covers an area of 7 x10 km. Average annual precipitation grades from 50 cmon the northwestern side to 125 cm on the northeasternside of the study area [Annstrong, 1973].

Basalt flows exposed in the study area vary in age, butthey are all similar in composition [Wright, 1971]. Theyhave phenocrysts of plagioclase, pyroxene, and/or olivine.The groundmass includes glass, magnetite, and ilmenite,in addition to plagioclase and pyroxene. Flows are bothpahoehoe (ropey) and aa (blocky) in form. Within the

476 ABRAMS ET AL.: REMOTE MAPPING OF HAWAIIAN LAVA FLOWS

; t

o 20~

km

Fig. I. Index map of the island of Hawaii showing thelocation of the Mauna Loa study area.

study area about 20 individual flows have been reported(J. Lockwood, unpublished data, 1988); these includethree flows of historic age (1935, 1899, and 1843) andprehistoric flows ranging in age from 200 to >8000 years.The prehistoric flows were separated into five agegroups (J. Lockwood, unpublished data, 1988): group I(0.2-0.5 ka), group II (0.5-1.5 ka), group III (1.5-4 ka),group IV (4-8 ka), and group V (>8 ka) (Plate 1).

Vegetation cover measured in the study area varies asa function of age of the surface (J.B. Adams, personalcommunication, 1985). Historic flows are essentiallyunvegetated owing to the aridity of the area; group I andII flows have only a few percent cover of shrubs andgrasses; group III flows have 5-15% cover; flows ofgroup IV are heavily vegetated and extensivelyweathered, especially in the eastern part of the studyarea; group V flows are also heavily weathered andvegetated, and are often covered wi h h eru ted from

~~n~ Kea to the north Lichen cover, which has been

shown to be an important factor in contributing toage-related VNIR spectral response changes [Rotheryand Lefebvre1, 1985], is minimal.

~ ---~----

REMOTE SENSING DATA

TIMS and the NS-001 scanner (a Thematic MapperSimulator), were flown aboard a NASA C-130 aircraftover the island of Hawaii during November, 1985.TIMS acquires digital radiance data in image format.There are six spectral channels of data between 8 and12 ~m (Table 1) [Palluconi and Meeks, 1985]. The

sensitivity is - 0.1 K Images are acquired using a mirrorthat scans an arc of +38° to -38° about nadir, with anangular resolution of 2.5 mrad. The NS-001 acquireseight channels of data in the visible, reflected infrared,and thermal infrared parts of the spectrum (Table 1).Images are acquired with a scan angle of 100°, and anangular resolution of 2.5 mrad. The C-130 operates ataltitudes up to 7.7 km above sea level; thus the scannersacquire data with a nadir ground resolution of 25 m orless. For this data flight, the aircraft operated at analtitude of 3.5 km above terrain, producing 8-m pixels.

TIMS data were processed using a decorrelation stret~h_

algorithm [Gillespie et al., 1986]. This procedureexaggerates subtle color differences in image data byincreasing the saturation and intensity and generally?reserving the hue information. 'Thus the resulting

.Images canbe relatc:9:back to the spectral informationof t~co~-'p_onentsE_s~4.~() c~~~~_th~__c<?_l.<?~- ttiE!t:_timage~~~NS-001 data were processed using Karhunen-Loeve- orprincipal components transformations. This is adimension reduction procedure that forms linearcombinations of the original data based on thevariance-covariance matrix [Gillespie, 1980]. Thecombined TIMSINS-OOl data set was processed in asimilar fashion.

IMAGE ANALYSES

The NS-OOl data were digitally registered to the TIMSdata by selection of tie-points and rubber sheetstretching. The NS-001 data were processed by principalcomponents transformations, based on statistics acquiredover the entire image (but ignoring the thermalchannel); components 2, 3, and 4 were displayed in red,green, and blue, respectively. The weightings of theeigenvectors indicate that component 2 is the differencebetween the near (reflected) infrared and visiblechannels. Component 3 is mainly the difference of bands3 and 1, and component 4 mainly the difference betweenbands 4 and 7. The resulting image (Plate 2) depictsthe flows in various colors; the interpretation mapdelineates flow boundaries recognized from the image.Unit designations are taken from Plate 1. (Thetrapezoidal shape of the map compared to therectangular shape of the images is due to residualgeometric distortion from aircraft motion; the areascovered are identical.) The difference in detail betweenthe image interpretation and the map is due to the use ofhigher resolution field and air photo observations used toproduce the map. On the image, the young pahoehoeflows (1935, 1843,200-500 years old, and 500-1500 yearsold) are all displayed as indistinguishable blue coloredunits, in contrast with the TIMS image which allowedeasy separation of these units. They are labeled "p" and"Op" to indicate that they were not differentiable. Theseflows are still very dark and fresh-looking in the field,and they have not as yet developed significant oxidationof mafic minerals. Spectrally, they are all dark and show

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Plate I. Geologic map of the Mauna Loa test site. Spectral sample sites are indicated by numbers 1-12;p=pahoehoe; a=aa; l=unit I (0.2-0.5 ka); 2=unit II (0.5-1.5 ka); 3=unit III (1.5-4 ka); 4=unit IV (4-8 ka);

5=unit V (>8 ka). Modified from J. Lockwood (unpublished data, 1988).

~-.I-.I

ABRAMS ET AL.: REMOTE MAPPING OF HAWAIIAN LAVA FLOWS

TABLE 1. Band Passes of Scanners

1·

478

CHANNEL12345678

NS-OOIWAVELENGTH. Urn

0.45-0.520.52·0.600.63-0.690.76-0.901.00-l.3O1.55-1.752.08-2.3610 4-12.5

CHANNEL123456

TIMSWAVELENGTH. Urn

8.2·8.68.6-9.09.0-9.59.6-10.2

10.2-11.211.2·11.7

no distinguishing features. Older pahoehoe flowsbecome greener on the image, and the oldest, withvegetation cover, are magenta. The aa flows progressfrom reddish-brown (1935) to brown (1899) to lightbrown (1843) to blue-brown (200-500 years old) to lightblue-green (500-1500 years old) to green-yellow(1500-4000 years old) to dark green (> 4000 years old).On the TIMS image, these aa flows become uniformlybrown and are indistinguishable from each other.

Laboratory spectral reflectance measurements (Figure2) of samples obtained from a wide range of the MaunaLoa aa flows (Plate 1) were made. They show very flatspectra for the young flows. Increasingly older flowsdevelop higher reflectance at 0.8 IJ.m and correspondingstronger absorptions toward shorter wavelengths (seenas a reddening of the rocks to the eye). We attribute thedistinct absorption bands seen as shoulders near 0.55 and0.65 IJ.m in the oldest rocks, and the general falloff inreflectance shortward of 0.8 IJ.m, to electronic, crystalfield, and charge transfer effects in ferric iron [Hunt,1977]. The decrease in reflectance longward of 0.8 IJ.m isattributed to ferrous iron electronic effects. The slightabsorption features seen at 1.4 and 1.9 IJ.m are due tothe presence of water. The small absorption band near2.2 IJ.m in the oldest rocks is probably due to the pre­sence of a minor clay phase. A plot of the spectral slopefrom 0.8 to 0.4 J.Lm (Figure 3) shows a systematicincrease of this slope with age, indicating an increase inthe amount of ferric iron versus ferrous iron minerals[Elom et ai., 1980].

Wet chemical analyses of these samples were done tomeasure ferric iron content. The 1935 flow had a valueof 3.3%; the 1899 had 3.7%; the 200- to 500- year-oldflows had an average ferric content of 4.2%; the 500- to1500-year-old flows had 4.1%; and the 1500- to 4000­year-old flows had 4.6% ferric iron. These values show asystematic increase with age, which correlates with theirobserved spectral characteristics. The relatively limitedrange of values can be explained by the difficulty ofextracting only surface material for analyses. Thesamples analyzed were a mixture of surface material

with some interior (less oxidized) material. Since theflows are similar mineralogically [Lockwood andLipman, 1987], the interior material should only add aconstant ferric component to each of the analyses, andnot bias them.

The relations between the image colors and theincrease in iron oxidation and change in reflectancespectra are consistent. Examination of the aa imagecolors as a function of age is shown in Table 2. Therelative contributions of each of the three components(component 2 as red, component 3 as green, andcomponent 4 as blue) toward producing the image colorsare tabulated as high, medium, or low. Magenta, thecolor of vegetation, is produced by high values of red andblue, and medium to low values for green. Spectrally,vegetation has higher reflectance in band 3 compared to1 (red component), higher band 4 reflectance comparedto band 7 (blue component), and moderately higherinfrared reflectance compared to visible reflectance(green component) [Gates et ai., 1965]. The older aalflows have higher reflectances in the infrared relative tothe visible, manifest by an increase in the red component II

in the image. Similarly, their reflectance in band 3increases relative to band 1 as the units become older,resulting in an increasing green component. Both factorsare due to the increase in ferric iron, producing the drop­off in reflectance at wavelengths short of 0.8 IJ.m and alow reflectance in band 1. Reflectance in band 7 relativeto band 4 decreases with age owing to increased 0.8-1.1 mreflectance and development of clays (decrease ofreflectance towards wavelengths longward of 2.0 IJ.m);these effects increase the blue component with age offlows. The systematic progression of image colors istherefore a good indicator of the relative age of aa flows,based on spectral reflectances variations due toincreasing oxidation.

Colors of pahoehoe flows on the NS-OOI image given inTable 3. The youngest, historic flows are blue, group Iflows are blue and blue-green, group II flows are alsoblue-green; group III flows are green-blue; group IVflows are dark green; group V flows are very dark green.

Plate 2. NS-()(JI principal components image. The overlay shows interpreted flow contacts, with age labelsa~ in Plate I; p = pahoehoe; a = aa; Op = undifferentiable prehistoric pahoehoe; 43a= 1X43aa; 35a = 1935aa.

j

480 ABRAMS ET AL.: REMOTE MAPPING OF HAWAIIAN LAVA FLOWS

6NS-OOl CHANNELS

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RELATIVE AGE

Fig. 2. Laboratory reflectance spectra of Mauna Loa aa flowsdating from IY3S, IINY, ZOO-SOO years B.P. (I), 500-1500 yearsB.P. (II), and 1500-4000 years B.P. (III). Reflectance valuesat O.H m are indicated above each curve. Spectra havebeen offset vertically for clarity. Sample locations areindicated on Plate 1.

The relative contributions of the three components whichmake up the colors are indicated in Table 3. The redcomponent stays relatively constant. The greencomponent increases with age, indicating a decrease inreflectance in band 1 relative to band 3 with age. Thiscan be attributed to the development of ferric iron as aweathering product, similar to what was observed forthe aa flows. The decrease in the blue component withage of pahoehoe flows, reflecting a decrease of band 4reflectance relative to band 7, indicates a progressivedecrease in ferrous iron with age; the young flows showa broad absorption feature longward of 1 IJ.m, whichdisappears as ferrous iron is oxidized to ferric iron. The

Fig. 3. Spectral slope versus relative age for Mauna Loa aaflows. The spectral slope is the difference in reflectancebetween O.H and 0.4 11m. Sample numbers refer tolocations on Plate 1. Percent number below the curve isthe average ferric iron content for each age group.

relative separation of pahoehoe flows, particularly youngflows, is not as good using NS-OOl data as with theTIMS data, described below.

A summary of our previously published TIMS analysis[Kahle et al., 1988] follows. The radiance from a surfaceis a function of both its temperature and spectralemittance. The emittance is the parameter related tothe composition of the surface. The spectral emittancevariation in most natural terrestrial surfaces is subtle,and temperature dominates TIMS images. In order toenhance the subtle emittance differences, we processedthe calibrated TIMS data using a decorrelation stretchmethod [Gillespie et al., 1986].

,, ~

TABLE 2. NS-OOI Image Colors of AA Flows

COMPONET·COLOR

EIGENVECTOR LOAPINGS

~ ~ ±l2!Y.£IR·VIS 3-1 4-7

UNIT IMAGE COLOR1935 red-brown L VL VL1899 brown L L VL1843 It. brown M L L

I blue-brown M M Mn blue-green M M-H M-Hill green-yellow M H ~[

IV <irk. green L M LVeg magenta H L HH, high; M, medium; L, loW; VL, very low.

ABRAMS ET AL.: REMOTE MAPPING OF HAWAIIAN LAVA FLOWS

TABLE 3. NS-OOl Image Colors of Pahoehoe Flows

COMPONEI-COLOREIGENVECTOR LOADINGS

.l:.wl ~ ~IR-VJS 3-1 4-7

UNIT IMAGE COLOR1935 blue L L H1843 dk.blue L L M

I blue L L Mblue-green L M M

IT blue-green L M Mm green-blue L M-H MIV die. green L M LV dk. green VL L "'L

Veg mngenta H L HH, high; M, medium; L, low; VL, very low.

481

After stretching, the data from three of the sixchannels were displayed in "false color" by assigning theprimary colors blue, green, and red to channels 1, 3, and5, respectively. Relative spectral emittance informationwas displayed as the chromaticness (color hue andsaturation), whereas temperature information wasdisplayed as the intensity or lightness (hot equals light,cold equals dark).

Field checking of a TIMS image over the north flankof Mauna Loa (Plate 3), and comparison with geologicmaps revealed systematic relationships between the TIMScolors and the type of basalt and its degree ofweathering, and hence its age. Pahoehoe and aa flowswere consistently separable in the images where therewas little or no vegetation. Single flows of basalt ofeither type may show some image color differences evenimmediately after eruption; however, the greatest colordifferences appear related to age.

There was a striking systematic color change withincreasing age of pahoehoe. The initial colors for freshpahoehoe were dominantly blue, but included magenta.Increasingly, older flows showed colors not observed foryoung flows: magenta (1843) and orange (0.2-1.5 ka),mixed orange and green (1.5-4.0 ka) and ultimately, lightgreen (4-8 ka). The oldest lavas (>8 ka) are forestedand appeared dark green.

Field comparison of the Mauna Loa TIMS image (Plate3) with a field-derived geologic map of the same area(Plate 1) showed that the contacts of some flows weremore accurately portrayed in the images. In a few cases,geologic relations that were difficult to map in the fieldcould be seen easily on the images, for example, thecontact between the 1935 and 1843 pahoehoe flows.

Image colors for Mauna Loa aa flows were more tightlyclustered and less variable than for pahoehoe flows.Nevertheless, if the data were viewed as a function ofage, some structure was evident. The youngest aa flows(1935) were dark blue-green. Older historic flows areprogressively redder; this trend culminated with theyoungest prehistoric flows (0.2-0.5 ka), which werereddish brown. Older prehistoric flows proceed toward

yellow-brown, and became indistinguishable from eachother.

The orderly behavior of the colors is best explained asa consequence of systematic changes to flow surfacescaused by weathering. For aa, young rough flows ar~~ -)associated with dark blue-green TIMS colors and very / ,~eak s ectral features attnbutedto multi Ie scattering '--;,_in the rough surfa~e (cavity or blackbody radia~n). T e _ (dark colors in the radiance images are <h!e to low. \~mperatures in the shadowed portions of the roug!: )surface, not yet warme~cfl5y the morning sun at the time0rdaiaacquisition. The shift to brown image color withincreasing age of aa is directly caused by the silica-richrinds.

The young pahoehoe colors are controlled by theoriginal state of the glassy chill coat and its degree ofdevitrification, chemical alteration, and spalling. Theshift to orange reflects the addition of the silica-richrinds. The pervasively weathered palagonitic pahoehoeflows are spectrally flat. The pahoehoe, at least in ourstudy area, progresses to green (spectrally flat in thethermal infrared) as it ages.

The raw NS-001 and TIMS data (13 channels total)were combined by a principal components analysis, anda color composite (Plate 4) was produced from three ofthe components (components 1, 5, and 6). While othermethods could have been used to combine the data (forexample, creating an "oxidation index" and "silica index"first, then combining them), peA was tried first, andexamination of the eigenvectors and eigenvalues indicatedthat the two data sets were not independent andorthogonal. Several of the eigenvectors were weightedon both thermal channels and reflectance channels,indicating that emittance and reflectance spectralproperties of the rocks were correlated to some degree.The three components chosen for display had just suchmixtures of thermal and reflectance bands. The firstcomponent contained 48% of the variance, the flfthcontained 4%, and the sixth 1.5%. In this picture theseparation of young pahoehoe flows from the TIMS dataand the separation of old aa flows from the NS-001 data

TIMS

Plate 3. TIMS decorrelation stretched image of the Mauna Loa test area. Bands 1, 3, and 5 are displayedin blue, green, and red, respectively. The overlay shows interpreted flow contacts, with age labels as in Plate1; p=pahoehoe; a=aa; units labeled "a" alone=undifferentiable aa; 35p=1935p; 43p= IH43p.

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484 ABRAMS ET AL.: REMOTE MAPPING OF HAWAIIAN LAVA FLOWS

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are preserved, in addition to separations of old pahoehoeflows and young aa flows seen on both data sets. Theinterpretive overlay delineates units that are separablebased on image color differences; unit designations aretaken from the geologic map of Plate 1. All units mappedby Lockwood are separable and show systematic colorchanges, relatable to relative ages.

In addition to the above analyses, we have studied theMauna Loa flows in the field to establish acorrespondence between image color and visual estimatesof weathering; we have made laboratory infraredspectral reflectance measurements of samples of thedifferent flow units; we have acquired in situ fieldemittance spectra; we have analyzed samples usingscanning electron microscopy; and we have calculatedemittance spectra from the TIMS data for the same areaswe sampled in the field [Kahle et al., 1988].

All of these measurements confirm our interpretationsof image colors in terms of silica-rich rinds in differentstates of formation and degradation, depending on theages of the flows. Field observations verified the changein physical state of the flows: aa flows, originally vuggyand replete with gas vesicles, tended to become moremassive as the cavities were filled in; pahoehoe flowslost their glassy chill coats, either by chemical or physicalprocesses; the color of the flows became progressivelymore rusty or redder with increasing age. The field andimage emittance spectra matched laboratory spectra ofsamples, providing the intermediate scale measurementsto bridge the 8-m scanner pixel size and the 1-cmlaboratory spectrometer sample size.

CONCLUSIONS

Our results show the utility of remote sensing in therelative dating of similar basalts in an arid environment,using combined data from the reflectance and emittanceparts of the spectrum. The existence of weat~systematics implies that itma~ible toes~

.£lmy age from rem~l~ sensed data, provided that"'progression of colors bas already beenc~

-roven re~Qn... Important influences n the thermal__~ caVity radiation, physical and

~ chemical degradation 0 g s, accretion ofsilica-rich coats, iron oxidation, and vegetation. Importantinfluences on the reflectance spectra appear to bedevelopment of iron oxide minerals from weathering, andvegetation. At least for the north flank of Mauna Loa,these effects occur in characteristic sequences and atdifferent rates, so that color pictures created from visibleto thermal infrared data depict flows at different stagesoftheir development in different colors. We have shownthat combined use of data in the two wavelength regionsprovides more information than the use of eitherseparately. Although we have not yet tried to extrapolatethese relationships to other arid or semiarid volcanicterranes, the possibility exists that similar ones will befound. These will prove useful in reconnaissancegeologic mapping in volcanic fields.

ACKNOWLEDGMENTS. This work was performed atthe Jet Propulsion Laboratory, California Institute ofTechnology, under contract to the National Aeronauticsand Space Administration. Thanks to Alan Gillespie andDave Rothery for suggestions which improved thismanuscript.

REFERENCES

Armstrong, R, (Ed.), Atlas ofHawaii, p. 221, Universityof Hawaii Press, Honolulu, 1973.

Blom, R., M. Abrams, and H. Adams, Spectralreflectance and discrimination of plutonic rocks in the0.45 to 2.45 ~m region, I. Geophys. Res., 85,2638-2648, 1980.

Curtis, J., J. Adams, and M. Ghiorso, Origin,development and chemistry of silica-alumina rockcoatings from the semi-arid regions of the island ofHawaii, Geochim. Cosmochim. Acta, 49, 49-56, 1985.

Farr, T., and J. Adams, Rock coatings in Hawaii, Geol.Soc. Am. Bull., 95, 1077-1083, 1984.

Gates, D., H. Keegan, J. Schleter, and V. Weidner,Spectral properties of plants, Appl. Opt., 4,11-20,1965.

Gillespie, A, Digital Techniques of ImageEnhancement, in Remote Sensing in Geology, editedby B. Siegal and A Gillespie, John Wiley, New York,pp. 139-226, 1980.

Gillespie, A, A Kahle, and R Walker, Colorenhancement of highly correlated images: 1.Decorrelation and HSI contrast stretches, Remote Seils.Environ., 20, 209-235, 1986.

Hunt, G., Spectral signatures of particulate minerals inthe visible and near infrared, Geophysics, 42, 501-513,1977.

Kahle, A, A Gillespie, E. Abbott, M. Abrams, RWalker, G. Hoover, and J. Lockwood, Relative datingof Hawaiian lava flows using multispectral thermalinfrared images: A new tool for geologic mapping ofyoung volcanic terranes, I. Geophys Res., 93, 15,239-15,251, 1988.

Lockwood, J. and P. Lipman, Holocene eruptive historyof Mauna Loa volcano, Volcanism in Hawaii, vol. 1,U.S. Geol. Surv. Prof. Pap., 1350, 1987.

Palluconi, F. and G. Meeks, Thermal InfraredMultispectral Scanner (TIMS): An investigator's guideto TIMS data,IPL Publ., 85-32, 1985.

Rothery, D., and R. Lefebvre, The cause of agedependent changes in the spectral response of lava,Craters of the Moon, Idaho, V.SA., Int. I. RemoteSens., 6, 1483-1489, 1985.

Wright, T., Chemistry of Kilauea and Mauna Loa lavain space and time. U.S. Geol. Surv. Prof. Pap., 735,1971.

E. Abbott. M. Abrams, and A. Kahle. Jet PropulsionLaboratory. California Institute of Technology, Pasadena, CA91109.

(Received March 12, ]99();revised June 13, 199();

accepted June 19, 1990.)