application of synthetic aperture radar sar imagery to volcano mapping in the humid tropics a case study in east java indonesia volcanoes in humid tropical environments are frequently cloud covered typically densely vegetated and rapidly eroded these factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes numerous previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions here cloud and vegetation penetrating lhh band 24 cm synthetic aperture radar sar data from the japanese earth resources satellite jers 1 are used to investigate persistently active volcanoes and prehistoric calderas in east java indonesia the lhh band jers 1 sar produces high spatial resolution 18 m imagery with relatively high incidence angle that highlights structures and topographic variations at or greater than the wavelength scale while minimising geometrical distortions such as layover and foreshortening these images along with internet browse data derived from the canadian radarsat mission provide new evidence relating regional tectonics to volcanism throughout east java volcanic events such as caldera collapse at the tengger caldera appear to have been partly controlled by northwest aligned faults related to intra arc sedimentary basins similar regional controls appear important at historically active lamongan volcano which is encircled by numerous flank maars and cinder cones a previously undocumented pyroclastic sheet and debris avalanche deposit from the jambangan caldera complex is also manifested in the synoptic radar images at the currently active semeru volcano these data permit identification of recent pyroclastic flow and lahar deposits radar data therefore offer a valuable tool for mapping and hazard assessment at late quaternary volcanoes the criteria developed in the analysis here could be applied to other regions in the humid tropics

modvolc near real time thermal monitoring of global volcanism modvolc is a non interactive algorithm developed at the hawaii institute of geophysics and planetology higp that uses low spatial resolution 1 km pixel size infrared satellite data acquired by the moderate resolution imaging spectroradiometer modis to map the global distribution of volcanic thermal anomalies in near real time modvolc scans the level 1b modis data stream on a pixel by pixel basis for evidence of pixel and sub pixel sized high temperature radiators once a hot spot has been identified its details location emitted spectral radiance time satellite observation geometry are written to ascii text files and transferred via ftp to higp from where the results are disseminated via the internet http modis higp hawaii edu in this paper we review the underlying principles upon which the algorithm is based before presenting some of the results and data that have been obtained since its inception we show how modvolc reliably detects thermal anomalies at a large number of persistently and sporadically active volcanoes that encompass the full range of common eruptive styles including erebus antarctica colima mexico karymsky kamchatka popocatepetl mexico etna italy and nyiragongo democratic republic of congo amongst others we also present a few cautionary notes regarding the limitations of the algorithm and interpretation of the data it provides

the sensitivity of a volcanic flow model to digital elevation model accuracy experiments with digitised map contours and interferometric sar at ruapehu and taranaki volcanoes new zealand abstract a growing trend in the field of volcanic hazard assessment is the use of computer models of a variety of flows to predict potential areas of devastation these can be compared against historic and geologic evidence of past events for model calibration or used to construct hazard zone maps for mitigation and planning purposes the accuracy of these computer models depends on two factors the nature and veracity of the flow model itself and the accuracy of the topographic data set over which it is run all digital elevation models dems contain innate errors the nature of these depends on the accuracy of the original measurements of the terrain and on the method used to build the dem in this paper we investigate the effect that these errors have on the performance of a volcanic flow model designed to delineate areas at risk from lahar inundation the model was run over two dems of southern ruapehu volcano derived from 1 digitised 1 50 000 topographic maps and 2 airborne c band synthetic aperture radar sar interferometry obtained using the nasa airsar system on steep slopes of 4 or more drainage channels are more likely to be incised deeply and flow paths predicted by the model are generally in agreement for both dems despite the differing nature of the source data over shallow slopes

the 1997 eruption of okmok volcano alaska a synthesis of remotely sensed imagery abstract okmok volcano in the eastern aleutian islands erupted in february and march of 1997 producing a 6 km long lava flow and low level ash plumes this caldera is one of the most active in the aleutian arc and is now the focus of international multidisciplinary studies a synthesis of remotely sensed data airsar derived dems landsat mss and etm data avhrr ers jers radarsat has given a sequence of events for the virtually unobserved 1997 eruption elevation data from the airsar sensor acquired in october 2000 over okmok were used to create a 5 m resolution dem mosaic of okmok volcano avhrr nighttime imagery has been analyzed between february 13 and april 11 1997 landsat imagery and sar data recorded prior to and after the eruption allowed us to accurately determine the extent of the new flow the flow was first observed on february 13 without precursory thermal anomalies at this time the flow was a large single lobe flowing north according to avhrr band 3 and 4 radiance data and ground observations the first lobe continued growing until mid to late march while a second smaller lobe began to form sometime between march 11 and 12 this is based on a jump in the thermal and volumetric flux determined from the imagery and the physical size of the thermal anomalies total radiance values waned after march 26 indicating lava effusion had ended and a cooling crust was growing the total area 8 9 km 2 thickness up to 50 m and volume 1 54 10 8 m 3 of the new lava flow were determined by combining observations from sar landsat etm and airsar dem data while the first lobe of the flow ponded in a pre eruption depression our data suggest the second lobe was volume limited remote sensing has become an integral part of the alaska volcano observatory s monitoring and hazard mitigation efforts studies like this allow access to remote volcanoes and provide methods to monitor potentially dangerous ones

topographic analyses of k lauea volcano hawai i from interferometric airborne radar we analyze digital topographic data collected in september 1993 over a 500 km2 portion of k lauea volcano hawai i by the c band 5 6 cm wavelength topographic synthetic aperture radar topsar airborne interferometric radar field surveys covering an 1 km2 area of the summit caldera and the distal end of an 8 m thick a flow indicate that the 10 m spatial resolution topsar data have a vertical accuracy of 1 2 m over a variety of volcanic surfaces after conversion to a common datum topsar data agree favorably with a digital elevation model dem produced by the u s geological survey usgs with the important exception of the region of the ongoing eruption which postdates the usgs dem this dem comparison gives us confidence that subtracting the usgs data from topsar data will produce a reasonable estimate of the erupted volume as of september 1993 this subtraction produces dense rock equivalent dre volumes of 392 439 and 90 106 m3 for the pu u k pa ianah and episode 50 53 stages of the eruption respectively these are 124 89 and 94 of the volumes calculated by staff of the hawaiian volcano observatory hvo but do not include lava of k pa ianah and episodes 50 53 that flowed into the ocean and are thus invisible to topsar accounting for this lava increases the topsar volumes to 124 159 and 129 of the hvo volumes including the 2 m uncertainty derived from the field surveys produces topsar derived volumes for the eruption as a whole that range between 81 and 125 of the usgs derived values the vesicularity and ocean corrected topsar volumes yield volumetric eruption rates of 4 5 4 5 and 2 7 m3 s for the three stages of the eruption which compare with hvo derived values of 3 6 2 8 and 2 1 m3 s respectively our analysis shows that care must be taken when vertically registering the topsar and usgs dems to a common datum because c band topsar penetrates only partially into thick forest and therefore produces a dem within the tree canopy whereas the usgs dem is adjusted for vegetation

relative dating of hawaiian lava flows using multispectral thermal infrared images a new tool for geologic mapping of young volcanic terranes the weathering of hawaiian basalts in arid and semiarid environments is accompanied by change in their thermal infrared emittance spectra the spectral differences can be measured and mapped with multispectral imaging systems the differences appear to be related to the degree of development preservation and alteration of glassy crusts the oxidation of iron and the accretion of silica rich surface veneers because the measurements are quantitative and in image format they are useful for estimating relative ages in geologic mapping of lava flows in hawaii this technique is most diagnostic for distinguishing among sparsely vegetated flows less than 1 5 ka in age

estimating silicic lava vesicularity with thermal remote sensing a new technique for volcanic mapping and monitoring remote monitoring of active lava domes pro vides insights into the duration of continued lava extru sion and detection of potentially associated explosive activity on inactive flows variations in surface texture ranging from dense glass to highly vesicular pumice can be related to emplacement time volatile content and internal structure pumiceous surface textures also pro duce changes in thermal emission spectra that are clear ly distinguishable using remote sensing spectrally the textures describe a continuum consisting of two pure end members obsidian and vesicles the distinct spec tral features of obsidian are commonly muted in pu mice due to overprinting by the vesicles which mimic spectrally neutral blackbody emitters assuming that this energy combines linearly in direct proportion to the percentage of vesicles the surface vesicularity can be estimated by modeling the pumice spectrum as a lin ear combination of the glass and blackbody spectra based on this discovery a linear retrieval model using a least squares fitting approach was applied to airborne thermal infrared data of the little glass mountain and crater glass rhyolite flows at medicine lake volcano california as a case study the model produced a ve sicularity image of the flow with values from 0 to f70 which can be grouped into three broad textural classes dense obsidian finely vesicular pumice and coarsely vesicular pumice values extracted from the image compare well with those derived from sem anal ysis of collected samples as well as with previously re ported results this technique provides the means to accurately map the areal distributions of these textures resulting in significantly different values from those de rived using aerial photographs if applied to actively deforming domes this technique will provide volcano logists with an opportunity to monitor dome wide de gassing and eruptive potential in near real time in july 1999 such an effort will be possible for the first time when repetitive global multispectral thermal infrared data become available with the launch of the advanced spaceborne thermal emission and reflectance ra diometer aster instrument aboard the earth ob serving system satellite

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

the evolution of an active silicic lava flow field an etm perspective an active dacitic lava flow began advancing down the south flank of the caliente dome unit santiaguito volcano guatemala during july 1999 by january 2002 continued activity had built a 1 km2 66 106 m3 flow field using a time series of landsat 7 etm images and field observations the evolution and characteristics of this flow field are described throughout the period of emplacement flow front advance rates have been extremely slow 2 13 m day 1 consistent with a viscosity of 109 1010 pa s however extremely efficient thermal insulation has allowed flow fronts to extend up to 3 75 km from the vent in spite of extrusion rates of just 0 5 1 6 m3 s 1 surface temperatures along most of the flow are less than 75 c and typically 40 c such surface temperatures result in extremely low rates of heat loss and thus core cooling of just 0 03 0 09 c h 1 or 0 01 0 12 c m 1 the flow field itself clearly displays the same systematic spatial variations in structure and morphology as described by lipman and banks prof pap geol surv u s 1350 1987 1527 for a basaltic a a flow where a stable and then transitional channel zone feeds a distal area of dispersed flow the stable channel dominates the proximal and medial sections of the flow field and comprises a 90 375 m wide channel flanked by levees that are up to 117 m high a marked increase in the flow area and thickness occurred between january 2001 and january 2002 and was coincident with an increase in the extrusion rate from 0 5 0 7 to 1 2 1 6 m3 s 1 however this increase in extrusion rate did not bring an increase in flow lengths indicating that the flow may have reached its cooling limited length around january 2001

accuracy of topographic maps derived from ers 1 interferometric radar an interferometric radar technique for topographic mapping of surfaces promises a high resolution approach to the generation of digital elevation models the authors present analyses of data collected by the synthetic aperture radar instrument on board the ers 1 satellite on successive orbits use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity also it permits inference of changes in the surface from the correlation properties of the radar echoes the data have been reduced to correlation maps and digital elevation models the correlation maps show that temporal correlation decreases significantly with time but not necessarily at a constant well defined rate likely depending on environmental factors when correlation among passes remains high however it is possible to form digital elevation models analyses of noise expected in ers 1 interferometric data collected over alaska and the southwestern united states indicate that maps with relative errors less than 5 m rms are possible in some regions however orbit uncertainties imply that tie points are required in order to reduce absolute height errors to a similar magnitude the authors find that about 6 tie points per 40 spl times 40 km scene with 5 m rms or better height accuracy are needed to keep systematic map height errors below 5 m rms the performance of the ers 1 radar system for topographic applications though useful for a variety of regional and local discipline studies may be improved with respect to temporal decorrelation errors and absolute height acuity by modifying the orbit repeat period and incorporating precise orbit determination techniques the resulting implementation will meet many but not all objectives of a global mapping mission

the evaluation of eccentricity related amplitude modulation and bundling in paleoclimate data an inverse approach for astrochronologic testing and time scale optimization cyclostratigraphic analysis has produced fundamental advancements in our understanding of climate change paleoceanography celestial mechanics geochronology and chronostratigraphy of central importance to this success has been the development of astrochronologic testing methods for the evaluation of astronomical climate influence on sedimentation most pre pleistocene astrochronologic testing methods fall into one of two categories 1 those that test for expected amplitude or frequency modulation imposed by an astronomical signal or 2 those that test for bedding hierarchies frequency ratios or bundling that are predicted by the dominant astronomical periods in this study a statistical methodology for combining these complementary approaches is developed which identifies the time scale that simultaneously optimizes eccentricity amplitude modulation of the precession band and the concentration of power at precession carrier and eccentricity modulator frequencies the technique is demonstrated to have high statistical power it is capable of identifying astronomical cycles when present under a wide range of conditions and its application to synthetic models illuminates a range of potential pitfalls that are encountered when more conventional nonoptimization approaches are used the method is also independent from the interpretation of power spectrum peak significance resolving previous concerns regarding appropriate confidence level assessment and multiple testing as two case studies the algorithm is applied to miocene strata of ocean drilling program odp site 926b and the paleocene eocene thermal maximum eocene thermal maximum 2 interval at odp site 1262 the results verify published cyclostratigraphic interpretations and support the theoretical astronomical solutions this new astrochronologic testing approach can be used to evaluate cyclostratigraphic records spanning the phanerozoic and potentially beyond

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

discrimination of geophysical phenomena in satellite radar interferograms various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar sar images the fringes generated by the topographic relief can be removed using a digital elevation model dem the remaining fringes map the change in satellite to ground range which occurred between the acquisition times of the two images by comparing different pairs of images spanning different intervals of time it is possible to discriminate between geophysical signal and interferometric artifact here we apply this pair wise logic to the area around the 1992 landers california earthquake using sar images acquired by the ers 1 satellite the range varies with time as a constant step impulsive or sloping function examples of each type include a dem error an aftershock two atmospheric perturbations and postseismic afterslip respectively their signatures are identified and separated using the pair wise logic

preliminary ers 1 observations of alaskan and aleutian volcanoes abstract we used ers 1 radar images collected between october 1991 and february 1993 to study volcanic landforms of the alaska peninsula and aleutian islands these data were used to map a little eroded even textured unit that is a thick low mobility pyroclastic deposit around aniakchak caldera also we have identified possible caldera remnants at black peak and located volcanically related collapse pits and depressions in the summit glacier of veniaminof observations of westdahl and mt spurr both of which erupted during our observation period demonstrate that new lava flows and debris flows can be mapped by virtue of their high radar backscatter and contrast with the surrounding terrain these data demonstrate the utility of frequent orbital radar observations in this area regional mapping can be carried out for volcanoes that are difficult to study in the field due to adverse working conditions e g frequent cloud cover bad weather long periods of darkness during winter and remote locations timely acquisition of images soon after or during an eruption can assist in the monitoring of active volcanoes the 23 incidence angle causes strong foreshortening and there is sometimes up to 35 days between repeat observations of certain locations however we conclude that the routine collection of sar data from ers 1 can provide valuable rapid information for assessing volcanic hazards in this region whatever the weather or time of year the situation will be improved with the additional use of jers 1 data and the launch of the radarsat spacecraft in 1995

aster watches the world s volcanoes a new paradigm for volcanological observations from orbit onboard nasa terra spacecraft is one of the most sophisticated earth observing instruments ever flown the advanced spaceborne thermal emission and reflection radiometer aster created as part of a joint project between the japanese ministry of economy trade and industry and nasa this instrument consists of three independent bore sighted telescopes with 14 channels in the visible near infrared and thermal infrared regions capable of being pointed up to 22 5 off nadir in addition there is an additional backward looking visible channel telescope for stereo photogrammetric observations the spatial resolutions are 15 m pixel in the visible 30 m pixel in the near ir and 90 m pixel at thermal wavelengths and the swath width is 60 km aster instrument offers unprecedented opportunities for observing volcanoes and their activity from low earth orbit it is the purpose of this short paper to introduce aster to the volcanological community highlight its capabilities advantages and limitations and to show some examples of aster data and related analyses we will also explain how users can readily access aster data

volumetric characteristics of lava flows from interferometric radar and multispectral satellite data the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos we have used a suite of remotely sensed data numerical lava flow modeling and field observations to determine quantitative characteristics of the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos islands flank lava flow areas volumes instantaneous effusion rates and average effusion rates were all determined for these two eruptions for which only limited syn eruptive field observations are available using data from spot topsar ers 1 and ers 2 we determined that the 1995 fernandina flow covers a subaerial area of 6 5 106 m2 and has a subaerial dense rock equivalent dre volume of 42 106 m3 field observations atsr satellite data and the flowgo numerical model allow us to determine that the effusion rate declined exponentially from a high of 60 200 m3 s 1 during the first few hours to 5 m3 s 1 prior to ceasing after 73 days with a mean effusion rate of 4 16 m3 s 1 integrating the atsr derived exponentially declining effusion rate over the eruption duration produces a total subaerial submarine dre volume of between 27 and 100 106 m3 the range in values being due to differing assumptions about heat loss characteristics only values in the higher part of this range are consistent with the independently derived subaerial volume using spot topsar ers 1 and ers 2 data we determine that the 1998 cerro azul flow is 16 km long covers 16 km2 and has a dre volume of 54 106 m3 flowgo produces at vent velocity and effusion rate values of 11 m s 1 and 600 m3 s 1 respectively the velocity value agrees well with the 12 m s 1 estimated in the field the mean effusion rate total dre volume duration was 7 47 m3 s 1 dike dimensions fissure lengths and pressure gradients along the conduit based on magma chamber depth estimates of 3 5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude the range being due to uncertainty in the magma viscosity dike dimensions and pressure gradient between magma chamber and vent although somewhat consistent with mean effusion rates from other techniques their wide range makes them less useful the exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption as well as time constants of exponential decay during the eruption the results and theoretical relationships combine to indicate that at both volcanoes probably 25 30 of the volumetric increase in the magma chamber erupted as lava onto the surface in both eruptions the lava flow volumes are less than 1 of the magma chamber volume

experimental exsolution textures in the system bornite chalcopyrite genetic implications concerning natural ores textural interpretation of ore mineral assemblages such as bornite chalcopyrite bn cpy intergrowths should be based on definite experimentation appropriate exsolution and coarsening experiments were performed using sealed evacuated silicaglass tubes synthetic bn cpy solid solutions were annealed between 100 and 350 c for times of 20 min to 10 weeks early formed textures develop through nucleation and growth and depend on the initial degree of supersaturation and the metal diffusivities final textures due to additional growth and coarsening are very sensitive to temperature and may serve as geothermometers mutual boundary textures which form above 250 c can originate by 1 simultaneous precipitation 2 exsolution during slow cooling from above the solvus and 3 metamorphism to temperatures above about 250 c widmanstatten textures are not compatible with slow cooling but indicate 1 low temperature replacement of bn or 2 exsolution of cpy lamellae from anomalous bn heated to around 200 250 c during mild metamorphism

nasa eos terra aster volcanic topographic mapping and capability up to date accurate topographic data are a crucial resource for volcanic research and risk mitigation efforts in particular for modeling volcanic flow processes at a detailed spatial resolution in this paper we examine the utility of the advanced spaceborne thermal emission and reflection radiometer aster instrument currently operating on the nasa terra satellite which provides near infrared vnir stereo imaging from which topography can be derived we wrote software to generate digital elevation models dems from the aster level 1a product which employs an automated stereo matching technique to calculate the parallax offsets between the images acquired by the nadir and aft looking sensors comparison of aster dems with dems derived from other sources digitized 1 50 k topographic maps and aerial interferometric radar at ruapehu volcano reveal an rms error of about 10 m for the aster dem in the absence of significant atmospheric water vapor a qualitative assessment of surface features showed that the aster dem is superior to the interpolated 1 50 k map product but falls short of the detail provided by aerial interferometric radar especially in terms of stream channel preservation a second aster dem was generated for taranaki volcano where previously only 1 50 k topographic map data were available although the 2000 space shuttle radar topography mission srtm will largely remedy the previous global paucity of adequate topographic data at volcanoes such as taranaki we anticipate the problem that at active volcanoes the topography may change significantly following activity rendering the srtm data inaccurate with the high temporal coverage of the dataset aster not only provides a means to update significant 10 m topographic measurements at active volcanoes via a time series of dems but also provides a simultaneous means to map surface cover and localized land use via the near infrared sensors thus we demonstrate the potential for up to date volcanic economic risk assessment using geographic information systems gis analysis

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

application of the landsat thematic mapper to the identification of potentially active volcanoes in the central andes abstract landsat thematic mapper tm images have been used to make the first comprehensive study of the central andean volcanic province 14 s 28 s one of the world s largest zones of active volcanism more than 60 major volcanoes have been identified as potentially active whereas only 16 had been previously cataloged most of these are large composite cones up to 6000 m in height some of which threaten nearby settlements apart from its consistent coverage the chief merit of the landsat tm in making this study has been spatial resolution provided by the 30 m pixel size this has been particularly important for the recognition of subtle glacial morphological features such as valley and terminal moraines which can be used to determine relative ages of the volcanoes on the tm images we have classified a volcano as potentially active if it has i a well preserved summit crater ii pristine lava flow texture and morphology iii flank lava flows with low albedo and iv evidence of post glacial

the effect of varying acquisition parameters on the interpretation of sir c radar data the virunga volcanic chain abstract in 1994 the spaceborne imaging radar experiment c sir c acquired five data takes with different acquisition parameters over the virunga volcanic chain zaire changes in incidence angle 20 0 48 1 look direction west and east looking and pulse bandwidth 10 mhz 20 mhz and 40 mhz affect the geologic interpretations drawn from these data we examine differences in spatial distortion of features near the summit of nyiragongo volcano finding that opposite look direction data are helpful in interpreting volcanic features such as the shape of small craters in areas of high relief the relative brightness of lava flows and vegetation change and actually reverse for different wavelengths and polarizations although l band data are best for mapping the outline of the flows c and x band cross polarization data show differences in backscatter intensity between and within flows in addition our ability to discriminate lava flows and vents from surrounding vegetation is strongly influenced by pulse bandwidth resolution and angle of incidence pulse bandwidth is the most important parameter in mapping small topographic features such as volcanic cones and a set of particularly thick flows on the flanks of karisimbi volcano these examples illustrate important considerations of the tradeoffs and priorities in acquisition parameters for future missions such as envisat as well as potential pitfalls for interpretation of existing data

the socompa collapse and avalanche event failure of the northwestern flank of the socompa volcano north chile about 7000 years ago created a 40 km long debris avalanche deposit the deposit is remarkably well exposed we have combined spectral reflectance data field observations and analysis of digital topographic surfaces to reconstruct the sequence of collapse events and to constrain the volumes and sources of materials comprising the avalanche collapse involved three principle components the debris avalanche deposit itself volume 26 km3 after 30 expansion large slide blocks 11 km3 and detached blocks 23 km3 which remained in the upper part of the amphitheatre the debris avalanche deposit comprised two main units and seven subunits landsat thematic mapper data enabled estimation of the proportions of spectrally distinct lithological components within these heterogeneous units about 35 of the deposit area is composed of ignimbrites and gravels derived from a 100 200 m thick slice of basement rock underlying the northwestern flank of the volcano dacite domes and lavas originally situated in the southern and western parts of the amphitheatre constitute much of the remainder of the deposit blocks composed largely of sequences of lavas and pyroclastic deposits originally located in the northern and eastern parts of the amphitheatre slid coherently 7 km northwestwards and accumulated near the mouth of the amphitheatre modelling of locations of centroids in the original cone and of displaced components shows that potential energy loss during collapse was 3 8 1017 j cf 0 7 1017 j for mount st helens 1980 significantly components of the avalanche with least potential energy travelled the furthest laterally perhaps demonstrating efficient transfer of momentum from rear to front of the avalanche retrogressive flank failures of the original cone contributed successive components to the avalanche most of these combined to form a single moving mass but some appear to have been emplaced separately