lava lake surface characterization by thermal imaging erta ale volcano ethiopia the project sviluppo di sistemi di monitoraggio dipartimento di protezione civile di regione sicilia ingv catania section italy the leverhulme trust the bbc and the ethiopian air force

two classes of volcanic plumes on io abstract comparison of voyager 1 and voyager 2 images of the south polar region of io has revealed that a major volcanic eruption occured there during the period between the two spacecraft encounters an annular deposit 1400 km in diameter formed around the aten patera caldera 311 w 48 s the floor of which changed from orange to red black the characteristics of this eruption are remarkably similar to those described earlier for an eruption centered on surt caldera 338 w 45 n that occured during the same period also at high latitude but in the north both volcanic centers were evidently inactive during the voyager 1 and 2 encounters but were active sometime between the two the geometric and colorimetric characteristics as well as scale of the two annular deposits are virtually identical both resemble the surface features formed by the eruption of pele 255 w 18 s these three very large plume eruptions suggest a class of eruption distinct from that of six smaller plumes observed to be continously active by both voyagers 1 and 2 the smaller plumes of which prometheus is the type example are longer lived deposit bright whitish material erupt at velocities of 0 5 km sec 1 and are concentrated at low latitudes in an equatorial belt around the satellite the very large pele type plumes on the other hand are relatively short lived deposit darker red materials erupt at 1 0 km sec 1 and rather than restricted to a latitudinal band are restricted in longitude from 240 to 360 w both direct thermal infrared temperature measurements and the implied color temperatures for quenched liquid sulfur suggest that hot spot temperatures of 650 k are associated with the large plumes and temperatures 2 in their annuli whereas the large plumes apparently do not two other plumes that occur at either end of the linear feature loki may be intermediate or hybrid between the two classes exhibiting attributes of both additionally loki occurs in the area of overlap in the regional distributions of the two plume classes two distinct volcanic systems involving different volatiles may be responsible for the two classes we propose that the discrete temperatures associated with the two classes are a direct reflection of sulfur s peculiar variation in viscosity with temperature over two temperature ranges 400 to 430 k and 650 k sulfur is a low viscosity fluid orange and black respectively at other temperatures it is either solid or has a high viscosity as a result there will be two zones in io s crust in which liquid sulfur will flow freely a shallow zone of orange sulfur and a deeper zone of black sulfur a low temperature system driven by so 2 heated to 400 to 400 k by the orange sulfur zone seems the best model for the small plumes a system driven by sulfur heated to 650 k by hot or even molten silicates in the black sulfur zone seems the best explanation for the large plume class the large pele type plumes are apparently concentrated in a region of the satellite in which a thinner sulfur rich crust overlies the tidally heated silicate lithosphere so the black sulfur zone may be fairly shallow in this region the prometheus type plumes are possibly confined to the equatorial belt by some process that concentrates so 2 fluid in the equatorial crust

new estimates for io eruption temperatures implications for the interior abstract the initial interpretation of galileo data from jupiter s moon io suggested eruption temperatures 1600 c tidal heating models have difficulties explaining io s prodigious heat flow if the mantle is 1300 c although we suggest that temperatures up to 1450 c may be possible in general io eruption temperatures have been overestimated because the incorrect thermal model has been applied much of the thermal emission from high temperature hot spots comes from lava fountains but lava flow models were utilized we apply a new lava fountain model to the highest reported eruption temperature the ssi observation of the 1997 eruption at pillan this resets the lower temperature limit for the eruption from 1600 to 1340 c additionally viscous heating of the magma may have increased eruption temperature by 50 100 c as a result of the strong compressive stresses in the ionian lithosphere while further work is needed it appears that the discrepancy between observations and interior models is largely resolved

lava lakes on io observations of io s volcanic activity from galileo nims during the 2001 fly bys abstract galileo s near infrared mapping spectrometer nims obtained its final observations of io during the spacecraft s fly bys in august i31 and october 2001 i32 we present a summary of the observations and results from these last two fly bys focusing on the distribution of thermal emission from io s many volcanic regions that give insights into the eruption styles of individual hot spots we include a compilation of hot spot data obtained from galileo voyager and ground based observations at least 152 active volcanic centers are now known on io 104 of which were discovered or confirmed by galileo observations including 23 from the i31 and i32 io fly by observations presented here we modify the classification scheme of keszthelyi et al 2001 j geophys res 106 e12 33 025 33 052 of io eruption styles to include three primary types promethean lava flow fields emplaced as compound pahoehoe flows with small plumes 200 km high plumes and rapidly emplaced flow fields and a new style we call lokian that includes all eruptions confined within paterae with or without associated plume eruptions thermal maps of active paterae from nims data reveal hot edges that are characteristic of lava lakes comparisons with terrestrial analogs show that io s lava lakes have thermal properties consistent with relatively inactive lava lakes the majority of activity on io based on locations and longevity of hot spots appears to be of this third type this finding has implications for how io is being resurfaced as our results imply that eruptions of lava are predominantly confined within paterae thus making it unlikely that resurfacing is done primarily by extensive lava flows our conclusion is consistent with the findings of geissler et al 2004 icarus this issue that plume eruptions and deposits rather than the eruption of copious amounts of effusive lavas are responsible for io s high resurfacing rates the origin and longevity of islands within ionian lava lakes remains enigmatic

io s volcanism thermo physical models of silicate lava compared with observations of thermal emission abstract analyses of thermal infrared outbursts from the jovian satellite io indicate that at least some of these volcanic events are due to silicate lava analysis of the january 9 1990 outburst indicates that this was an active eruption consisting of a large lava flow with mass eruption rate of order 10 5 m 3 sec 1 and a sustained area at silicate liquidus temperatures this is interpreted as a series of fire fountains along a rift zone a possible alternative scenario is that of an overflowing lava lake with extensive fire fountaining the january 9 1990 event is unique as multispectral observations with respect to time were obtained in this paper a model is presented for the thermal energy lost by active and cooling silicate lava flows and lakes on io the model thermal emission is compared with earth based observations and voyager iris data the model a provides an explanation of the thermal anomalies on io s surface b provides constraints on flow behavior and extent and infers some flow parameters and c determines flow geometry and change in flow size with time and the temperature of each part of the flow or lava lake surface as a function of its age models of heat output from active lava flows or inactive but recently emplaced lava flows or overturning lava lakes alone are unable to reproduce the observations if the january 9 1990 event is the emplacement of a lava flow the equivalent of 27 such events per year would yield a volume of material sufficient if uniformly distributed to resurface all of io at a rate of 1 cm year

io volcanism seen by new horizons a major eruption of the tvashtar volcano jupiter s moon io is known to host active volcanoes in february and march 2007 the new horizons spacecraft obtained a global snapshot of io s volcanism a 350 kilometer high volcanic plume was seen to emanate from the tvashtar volcano 62 n 122 w and its motion was observed the plume s morphology and dynamics support nonballistic models of large io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source in images taken in jupiter eclipse nonthermal visible wavelength emission was seen from individual volcanoes near io s sub jupiter and anti jupiter points near infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150 to 1335 kelvin range consistent with basaltic composition

galileo observations of volcanic plumes on io abstract io s volcanic plumes erupt in a dazzling variety of sizes shapes colors and opacities in general the plumes fall into two classes representing distinct source gas temperatures most of the galileo imaging observations were of the smaller more numerous prometheus type plumes that are produced when hot flows of silicate lava impinge on volatile surface ices of so2 few detections were made of the giant pele type plumes that vent high temperature sulfur rich gases from the interior of io this was partly because of the insensitivity of galileo s camera to ultraviolet wavelengths both gas and dust spout from plumes of each class favorably located gas plumes were detected during eclipse when io was in jupiter s shadow dense dust columns were imaged in daylight above several prometheus type eruptions reaching heights typically less than 100 km comparisons between eclipse observations sunlit images and the record of surface changes show that these optically thick dust columns are much smaller in stature than the corresponding gas plumes but are adequate to produce the observed surface deposits mie scattering calculations suggest that these conspicuous dust plumes are made up of coarse grained ash particles with radii on the order of 100 nm and total masses on the order of 106 kg per plume long exposure images of thor in sunlight show a faint outer envelope apparently populated by particles small enough to be carried along with the gas flow perhaps formed by condensation of sulfurous snowflakes as suggested by the plasma instrumentation aboard galileo as it flew through thor s plume frank l a paterson w r 2002 j geophys res space phys 107 doi 10 1029 2002ja009240 31 1 if so the total mass of these fine nearly invisible particles may be comparable to the mass of the gas and could account for much of io s rapid resurfacing

multi instrument remote and in situ observations of the erebus volcano antarctica lava lake in 2005 a comparison with the pele lava lake on the jovian moon io abstract the stable persistent active lava lake at erebus volcano ross island antarctica provides an excellent thermal target for analysis of spacecraft observations and for testing new technology in the austral summer of 2005 visible and infrared observations of the erebus lava lake were obtained with sensors on three space vehicles terra aster modis aqua modis and eo 1 hyperion ali contemporaneous ground based observations were obtained with hand held infrared cameras this allowed a quantitative comparison of the thermal data obtained from different instruments and of the analytical techniques used to analyze the data both with and without the constraints imposed by ground truth from the thermal camera data in december 2005 the main erebus lava lake ray lake had an area of 820 m2 surface colour temperatures ranged from 575 k to 1090 k with a broad peak in the distribution from 730 k to 850 k total heat loss was estimated at 23 5 mw the flux density was 29 kw m 2 mass flux was estimated at 64 to 93 kg s 1 the best correlation between thermal emission and emitting area was obtained with aster which has the best combination of spatial resolution and wavelength coverage especially in the thermal infrared the high surface temperature of the lava lake means that hyperion data are for the most part saturated uncertainties introduced by the need to remove incident sunlight cause the thermal emission from the hyperion data to be a factor of about two greater than that measured by hand held thermal camera modis also over estimated thermal output from the lava lake by the same factor of two because it was detecting reflected sunlight from the rest of the pixel area the measurement of the detailed temperature distribution on the surface of an active terrestrial lava lake will allow testing of thermal emission models used to interpret remote sensing data of volcanism on io where no such ground truth exists although the erebus lava lake is four orders of magnitude smaller than the lava lake at pele on io the shape of the integrated thermal emission spectra are similar thermal emission from this style of effusive volcanism appears to be invariant excess thermal emission in most pele spectra compared to erebus at short wavelengths

surface changes on io during the galileo mission abstract a careful survey of galileo ssi global monitoring images revealed more than 80 apparent surface changes that took place on io during the 5 year period of observation ranging from giant plume deposits to subtle changes in the color or albedo of patera surfaces explosive volcanic activity was discovered at four previously unrecognized centers an unnamed patera to the south of karei that produced a pele sized red ring a patera to the west of zal that produced a small circular bright deposit a large orange ring detected near the north pole of io and a small bright ring near io s south pole only a handful of io s many active volcanoes produced large scale explosive eruptions and several of these erupted repeatedly leaving at least 83 of io s surface unaltered throughout the galileo mission most of the hot spots detected from ssi nims and ground based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period surface changes were found at every location where active plumes were identified including acala which was never seen in sunlight and was only detected through auroral emissions during eclipse two types of plumes are distinguished on the basis of the size and color of their deposits confirming post voyager suggestions by mcewen and soderblom icarus 55 1983 191 smaller plumes produce near circular rings typically 150 200 km in radius that are white or yellow in color unless contaminated with silicates and frequently coat their surroundings with frosts of fine grained so2 the larger plumes are much less numerous limited to a half dozen examples and produce oval orange or red sulfur rich rings with maximum radii in the north south direction that are typically in the range from 500 to 550 km both types of plumes can be either episodic or quasi continuous over a five year period repeated eruptions of the smaller so2 rich plumes likely contribute significantly to io s resurfacing rate whereas dust ejection is likely dominated by the tenuous giant plumes both types of plume deposits fade on time scales of months to years through burial and alteration episodic seepages of so2 at haemus montes zal montes dorian montes and the plateau to the north of pillan patera may have been triggered by activity at nearby volcanic centers

io meteorology how atmospheric pressure is controlled locally by volcanos and surface frosts the hydrodynamic model of a p ingersoll m e summers s g schilpf 1985 icarus 64 375 390 is modified to include the effects of nonuniform surface properties as revealed in recent observational studies the observations indicate that so 2 frost is concentrated in a band within 30 latitude of the equator covering 270 of longitude and that the darker surface at midlatitude is warmer than the frost at times of maximum insolation the approach to the hydrodynamics has been to make the model simpler and more versatile solutions are now obtained in closed analytic form we calculate atmospheric pressures horizontal winds sublimation rates and condensation rates for a wide variety of surface conditions patchy and continuous frost cover volcanic venting treated as a source of mass distributed over the plume area discontinuities of surface temperature subsurface cold trapping and insolation propagation into the frost the principal new concept is the horizontal averaging length l which is equal to 2 h where h is the atmospheric scale height and is the sticking coefficient if frost is present either on the surface or just below it then each area of dimension l of order 100 km determines its own atmospheric pressure away from the volcanic plumes the pressure follows the local vapor pressure inside the plumes the pressure is higher e g a volcanic source of 10 6 kg sec spread over an area 300 km in radius raises the local pressure by an amount equal to the vapor pressure of a frost at 124 k the key unknowns for io are the strength of the volcanic sources and the temperature of frost near the subsolar point if the frost is cold below 110 k then the only substantial atmospheres are beneath the plumes if the frost is warm e g 125 k then there is also a substantial atmosphere near the subsolar point the equatorial frost deposits are then losing net mass at a substantial rate e g 0 1 cm year for a subsolar frost temperature of 125 k

identification of variable convective regimes at erta ale lava lake abstract during february 17 19 2002 we collected a combined thermal and seismic data set for persistent lava lake activity at erta ale volcano ethiopia these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 surface velocities typically lasting tens to hundreds of minutes these periods of high and low velocity motion define periods of vigorous and sluggish convection respectively spectral analysis revealed that vigorous convection periods were characterized by high frequencies and energies in the thermal data and an increased presence of high frequency energy in the seismic data the data show that vigorous periods were characterized by formation of hot short lived plastic crusts and sluggish periods by cooler longer lived brittle crusts here the higher transit velocity across the lake surface from upwelling zones of crust formation to downwelling zones of crust destruction during the vigorous periods decreases the crust lifetime this in turn decreases the total cooling and thickening experienced by a plate of crust moving across the lake surface two scenarios can be envisaged to explain such convection cycles the first relates variable convection rates to changes in the volume flux and rheology of magma entering the lake in the second cyclic convection is set up by the generation of convective instabilities within the lake in this case cooling of a surface layer generates a slow moving viscous increasingly dense convection layer at the lake surface which is consumed and replaced during overturn

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

a model for large scale volcanic plumes on io implications for eruption rates and interactions between magmas and near surface volatiles 1 volcanic plumes deposit magmatic pyroclasts and so2 frost on the surface of io we model the plume activity detected by galileo at the pillan and pele sites from 1996 to 1997 assuming that magmatic eruptions incorporate liquid so2 from near surface aquifers intersecting the conduit system and that the so2 eventually forms a solid condensate on the ground the temperature and pressure at which deposition of solid so2 commences in the ionian environment and the radial distance from the volcanic vent at which this process appears to occur on the surface are used together with observed vertical heights of plumes to constrain eruption conditions the temperature pressure and density of the gas magma mixtures are related to distance from the vent using continuity and conservation of energy similar eruption mass fluxes of order 5 107 kg s 1 are found for both the pillan and the pele plumes the pele plume requires a larger amount of incorporated so2 29 34 mass than the pillan plume up to 6 mass implied vent diameters range from 90 m at pillan to 500 m at pele the radial extents of the optically dense isothermal incandescent parts of the eruption plumes immediately above the vents are 100 m at pillan and 1300 m at pele gas pressures in the vents are 20 kpa at pillan and 2 kpa at pele and the eruption conditions appear to be supersonic in both cases though only just so at pele

the nature of the volcanic activity at loki insights from galileo nims and ppr data abstract loki is the largest patera and the most energetic hotspot on jupiter s moon io in turn the most volcanically active body in the solar system but the nature of the activity remains enigmatic we present detailed analysis of galileo near infrared mapping spectrometer nims and photopolarimeter radiometer ppr observations covering the 1 5 100 m wavelength range during the i24 i27 and i32 flybys the general pattern of activity during these flybys is consistent with previously proposed models of a resurfacing wave periodically crossing a silicate lava lake in particular our analysis of the i32 nims observations shows over much of the observed patera surface temperatures and implied ages closely matching those expected for a wave advancing counterclockwise at 0 94 1 38 km day the age pattern is different than other published analyses which do not show as clearly this azimuthal pattern our analysis also shows two additional distinctly different patera surfaces the first is located along the inner and outer margins where components with a 3 00 4 70 m color temperature of 425 k exist the second is located at the southwestern margin where components with a 550 k color temperature exist although the high temperatures could be caused by disruption of a lava lake crust some additional mechanism is required to explain why the southwest margin is different from the inner or outer ones finally analysis of the temperature profiles across the patera reveal a smoothness that is difficult to explain by simple lava cooling models paradoxically at a subpixel level wide temperature distributions exist which may be difficult to explain by just the presence of hot cracks in the lava crust the resurfacing wave and lava cooling models explain well the overall characteristics of the observations however additional physical processes perhaps involving heat transport by volatiles are needed to explain the more subtle features

active volcanism on io as seen by galileo ssi abstract active volcanism on io has been monitored during the nominal galileo satellite tour from mid 1996 through late 1997 the solid state imaging ssi experiment was able to observe many manifestations of this active volcanism including 1 changes in the color and albedo of the surface 2 active airborne plumes and 3 glowing vents seen in eclipse about 30 large scale tens of kilometers surface changes are obvious from comparison of the ssi images to those acquired by voyager in 1979 these include new pyroclastic deposits of several colors bright and dark flows and caldera floor materials there have also been significant surface changes on io during the galileo mission itself such as a new 400 km diameter dark pyroclastic deposit around pillan patera while these surface changes are impressive the number of large scale changes observed in the four months between the voyager 1 and voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive there are two reasons why this was not actually the case first it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years second it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of io s surface the plume monitoring has revealed 10 active plumes comparable to the 9 plumes observed by voyager one of these plumes was visible only in the first orbit and three became active in the later orbits only the prometheus plume has been consistently active and easy to detect observations of the pele plume have been particularly intriguing since it was detected only once by ssi despite repeated attempts but has been detected several times by the hubble space telescope at 255 nm pele s plume is much taller 460 km than during voyager 1 300 km and much fainter at visible wavelengths prometheus type plumes 50 150 km high long lived associated with high temperature hot spots may result from silicate lava flows or shallow intrusions interacting with near surface so2 a major and surprising result is that 30 of io s volcanic vents glow in the dark at the short wavelengths of ssi these are probably due to thermal emission from surfaces hotter than 700 k with most hotter than 1000 k well above the temperature of pure sulfur volcanism active silicate volcanism appears ubiquitous there are also widespread diffuse glows seen in eclipse related to the interaction of energetic particles with the atmosphere these diffuse glows are closely associated with the most active volcanic vents supporting suggestions that io s atmopshere is dominated by volcanic outgassing globally volcanic centers are rather evenly distributed however 14 of the 15 active plumes seen by voyager and or galileo are within 30 of the equator and there are concentrations of glows seen in eclipse at both the sub and antijovian points these patterns might be related to asthenospheric tidal heating or tidal stresses io will continue to be observed during the galileo europa mission which will climax with two close flybys of io in late 1999

silicate volcanism on io io is currently emitting 1 1 5 w m 2 of tidal energy as a result of its volcanic activity if the lithosphere is more than 20 km thick as appears probable from the surface relief only a fraction of the tidal energy can be dissipated within the lithosphere otherwise it will become thinner the rest of the tidal energy must be dissipated below the lithosphere io is likely to be highly differentiated as a result of the volcanic activity with a low melting temperature fraction such as basalt near the surface and a high melting temperature fraction such as peridotite at depth if solidus temperatures are reached at depths shallower than the thickness of the basalt layer a partial melt zone will separate an all basalt lithosphere above from a peridotite mantle below and part of the tidal energy will be dissipated by viscous deformation within the melt zone most of the energy dissipated below the lithosphere will be transported upward through the lithosphere as silicate magma which is generated in quantities sufficient to resurface the satellite at a rate of a few tenths of a centimeter a year depending on the lithosphere thickness many of the characteristics of the ionian surface have been explained in terms of sulfur volcanism however most of the features observed can be as readily explained by silicate volcanism and silicates are more consistent with the apparent strength of the surface as implied by the relief simulations of basaltic eruptions indicate that the surface temperatures that would result from basaltic eruptions are similar to those measured by the voyager infrared interferometer spectrometer experiment the high rates of emission by the ionian hot spots imply eruption rates that are high compared with typical terrestrial eruptions an eruption rate of 4000 m3 s 1 may be required to explain loki which is currently emitting 1013 w although the near surface materials are mainly silicate they may contain several percent of volatile components rich in s na and k remobilization of these components by the ongoing silicate eruptions causes the plumes provides material to the torus and gives the satellite its characteristic reflectivity

observations and temperatures of io s pele patera from cassini and galileo spacecraft images abstract pele has been the most intense high temperature hotspot on io to be continuously active during the galileo monitoring from 1996 2001 a suite of characteristics suggests that pele is an active lava lake inside a volcanic depression in 2000 2001 pele was observed by two spacecraft cassini and galileo the cassini observations revealed that pele is variable in activity over timescales of minutes typical of active lava lakes in hawaii and ethiopia these observations also revealed that the short wavelength thermal emission from pele decreases with rotation of io by a factor significantly greater than the cosine of the emission angle and that the color temperature becomes more variable and hotter at high emission angles this behavior suggests that a significant portion of the visible thermal emission from pele comes from lava fountains within a topographically confined lava body high spatial resolution nightside images from a galileo flyby in october 2001 revealed a large relatively cool

sulfur volcanism on io abstract in february 2003 march 2003 and january 2004 pele plume transmission spectra were obtained during jupiter transit with hubble s space telescope imaging spectrograph stis using the 0 1 wide slit and the g230lb grating the stis spectra covered the 2100 3100 a wavelength regions and extended spatially along io s limb encompassing the region directly above and northward of the vent of the pele volcano the s2 and so2 absorption signatures evident in these data indicate that the gas signature at pele was temporally variable and that an s2 absorption signature was present 12 from the pele vent near 6 5 s and 264 15 w suggesting the presence of another s2 bearing plume on io contemporaneous with the spectral data uv and visible wavelength images of the plume were obtained in reflected sunlight with the advanced camera for surveys acs prior to jupiter transit the dust scattering recorded in these data provide an additional qualitative measure of plume activity on io indicating that the degree of dust scattering over pele varied as a function of the date of observation and that there were several other dust bearing plumes active during the observations we present constraints on the composition and variability of the gas abundances of the pele plume as well as the plumes detected by acs and recorded within the stis data as a function of time

reply to comment by y park and j h ree on chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt summary in their comment park ree have raised several points against the interpretation by park et al and argued that the remagnetization in the jeongseon area was caused by the thermal effects of a late cretaceous pluton and or associated short range hydrothermal fluids rather than by long range fluids advocated by us we disagree with most points raised by park ree and we make a case that these are invalid because of what we believe is incorrect geologic evidence hence our model that the fluids causing the chemical remagnetization might migrate through the fault system within the ogcheon fold belt is the most plausible scenario we recognize that our model needs to be tested in a future study and we welcome new interpretations for or against our model based on reliable geologic or geophysical data

io in the near infrared near infrared mapping spectrometer nims results from the galileo flybys in 1999 and 2000 galileo s near infrared mapping spectrometer nims observed io during the spacecraft s three flybys in october 1999 november 1999 and february 2000 the observations which are summarized here were used to map the detailed thermal structure of active volcanic regions and the surface distribution of so2 and to investigate the origin of a yet unidentified compound showing an absorption feature at 1 m we present a summary of the observations and results focusing on the distribution of thermal emission and of so2 deposits we find high eruption temperatures consistent with ultramafic volcanism at pele such temperatures may be present at other hot spots but the hottest areas may be too small for those temperatures to be detected at the spatial resolution of our observations loki is the site of frequent eruptions and the low thermal emission may represent lavas cooling on the caldera s surface or the cooling crust of a lava lake high resolution spectral observations of emakong caldera show thermal emission and so2 within the same pixels implying that patches of so2 frost and patches of cooling lavas or sulfur flows are present within a few kilometers from one another thermal maps of prometheus and amirani show that these two hot spots are characterized by long lava flows the thermal profiles of flows at both locations are consistent with insulated flows with the amirani flow field having more breakouts of fresh lava along its length prometheus and amirani each show a white ring at visible wavelengths while so2 distribution maps show that the highest concentration of so2 in both ring deposits lies outside the white portion visible measurements at high phase angles show that the white deposit around prometheus extends into the so2 ring this suggests that the deposits are thin and that compositional or grain size variations may occur in the radial direction so2 mapping of the chaac region shows that the interior of a caldera adjacent to chaac has almost pure so2 the deposit appears to be topographically controlled suggesting a possible origin by liquid flow

origins and implications of zigzag rift patterns on lava lakes abstract the distinctive rift patterns observed on newly formed lava lakes are very likely a product of interaction between heat transfer cooling of lava and deformation of the solid crust in response to applied stresses one common pattern consists of symmetric zigzag rifts separating spreading plates zigzags can be characterized by two measurable parameters an amplitude a and an angle between segments that make up the zigzags similar patterns are observed in analog wax experiments in which molten wax acts as cooling and solidifying lava we perform a series of these wax experiments to find the relationship between a and the cooling rate we develop a model to explain the observed relationships is determined by a balance of spreading and solidification speeds the amplitude a is limited by the thickness of the solid wax crust theoretical predictions agree well with experimental data this enables us to scale the model to basaltic lava lakes if zigzag rifts are observed on the surface of lava lakes and if physical properties of the lava crust can be measured or inferred by other means measurements of and a make it possible to calculate crust spreading velocity and crust thickness

morphology temperature and eruption dynamics at pele abstract the pele region of io has been the site of vigorous volcanic activity from the time of the first voyager i observations in 1979 up through the final galileo ones in 2001 there is high temperature thermal emission from a visibly dark area that is thought to be a rapidly overturning lava lake and is also the source of a large sulfur rich plume we present a new analysis of voyager i visible wavelength images and galileo solid state imager ssi and near infrared mapping spectrometer nims thermal emission observations which better define the morphology of the region and the intensity of the emission the observations show remarkable correlations between the locations of the emission and the features seen in the voyager images which provide insight into eruption mechanisms and constrain the longevity of the activity we also analyze an additional wavelength channel of nims data 1 87 m which paradoxically because of reduced sensitivity allows us to estimate temperatures at the peak locations of emission measurements of eruption temperatures on io are crucial because they provide our best clues to the composition of the magma high color temperatures indicative of ultramafic composition have been reported for the pillan hot spot and possibly for pele although recent work has called into question the requirement for magma temperatures above those expected for ordinary basalts our new analysis of the pele emission near the peak of the hot spot shows color temperatures near the upper end of the basalt range during the i27 and i32 encounters in order to analyze the observed color temperatures we also present an analytical model for the thermal emission from fire fountains which should prove generally useful for analyzing similar data this is a modification of the lava flow emission model presented in howell howell r r 1997 icarus 127 394 407 adapted to the fire fountain cooling curves first discussed in keszthelyi et al keszthelyi l jaeger w milazzo m radebaugh j davies a g mitchell k l 2007 icarus 192 491 502 when applied to the i32 observations we obtain a fire fountain mass eruption rate of 5 1 10 5 kg s 1 for the main vent area and 1 4 10 4 kg s 1 for each of two smaller vent regions to the west these fire fountain rates suggest a solution to the puzzling lack of extensive lava flows in the pele region much of the erupted lava may be ejected at high speed into the fire fountains and plumes creating dispersed pyroclastic deposits rather than flows we compare gas and silicate mass eruption rates and discuss briefly the dynamics of this ejection model and the observational evidence

thermal signature eruption style and eruption evolution at pele and pillan on io the galileo spacecraft has been periodically monitoring volcanic activity on io since june 1996 making it possible to chart the evolution of individual eruptions we present results of coanalysis of near infrared mapping spectrometer nims and solid state imaging ssi data of eruptions at pele and pillan especially from a particularly illuminating data set consisting of mutually constraining near simultaneous nims and ssi observations obtained during orbit c9 in june 1997 the observed thermal signature from each hot spot and the way in which the thermal signature changes with time tightly constrains the possible styles of eruption pele and pillan have very different eruption styles from september 1996 through may 1999 pele demonstrates an almost constant total thermal output with thermal emission spectra indicative of a long lived active lava lake the nims pillan data exhibit the thermal signature of a pillanian eruption style a large vigorous eruption with associated open channel or sheet flows producing an extensive flow field by orbit c10 in september 1997 the high mass eruption rate high liquidus temperature at least 1870 k eruption at pillan is the best candidate so far for an active ultramafic magnesium rich komatiitic flow on io a style of eruption never before witnessed the thermal output per unit area from pillan is however consistent with the emplacement of large open channel flows magma temperature at pele is 1600 k if the magma temperature is 1600 k it suggests a komatiitic basalt composition the power output from pele is indicative of a magma volumetric eruption rate of 250 to 340 m3 s 1 although the pele lava lake is considerably larger than its terrestrial counterparts the power and mass fluxes per unit area are similar to active terrestrial lava lakes