high resolution keck adaptive optics imaging of violent volcanic activity on io io the innermost galilean satellite of jupiter is a fascinating world data taken by voyager and galileo instruments have established that it is by far the most volcanic body in the solar system and suggest that the nature of this volcanism could radically differ from volcanism on earth we report on near ir observations taken in february 2001 from the earth based 10 m w m keck ii telescope using its adaptive optics system after application of an appropriate deconvolution technique mistral the resolution 100 km on io s disk compares well with the best galileo nims resolution for global imaging and allows us for the first time to investigate the very nature of individual eruptions on 19 february we detected two volcanoes amirani and tvashtar with temperatures differing from the galileo observations on 20 february we noticed a slight brightening near the surt volcano two days later it had turned into an extremely bright volcanic outburst the hot spot temperatures 1400 k are consistent with a basaltic eruption and being lower limits do not exclude an ultramafic eruption these outburst data have been fitted with a silicate cooling model which indicates that this is a highly vigorous eruption with a highly dynamic emplacement mechanism akin to fire fountaining its integrated thermal output was close to the total estimated output of io making this the largest ionian thermal outburst yet witnessed

global near ir maps from gemini n and keck in 2010 with a special focus on janus patera and kanehekili fluctus abstract we have imaged io in the near infrared 1 5 m with adaptive optics on the 10 m w m keck ii and the gemini north telescopes we have constructed global maps from the data taken in 2010 although numerous hot spots are visible the maps are dominated by two volcanic centers loki patera and kanehekili fluctus we have examined in detail the thermal emission from janus patera and kanehekili fluctus using images obtained between 2003 and 2010 and have created a timeline of volcanic activity at these locations utilizing data from a wide variety of sources based on our data and this timeline we find that the thermal emission from janus patera is relatively steady indicative of an active lava lake the thermal emission from kanehekili fluctus however is quite variable and is indicative of the emplacement of extensive lava flows in 2010 the thermal emission from this location was 10 times higher than ever seen before indicative of a particularly voluminous eruption of lava

calderas a planetary perspective caldera bearing volcanoes are the largest volcanic edifices on a planet and are expressions of long lived near surface magma chambers on earth only three morphological classes of calderas are common shield calderas e g mauna loa hawaii stratocone calderas e g crater lake oregon and ash flow calderas e g valles caldera new mexico each of these classes has a characteristic caldera size magma type and tectonic location no calderas have been recognized on the moon or mercury but mars has large shield calderas as well as the unique highland patera calderas the latter may represent an explosive ultramafic style of volcanism unlike any volcanic activity in modern earth history radar images suggest that venus has at least one large caldera bearing shield volcano and possible calderas of other types jupiter s satellite io has abundant large shieldlike calderas but no shield massifs the number and variety of calderas on a planet may be proportional to planet mass consistent with a previous suggestion that volcanic complexity increases with planet size io is an exception but heating in io is generated tidally rather than by the decay of radioactive elements so that its calderas are not related to its size the occurrence of shield volcanoes on four solar system bodies suggests that thermal and tectonic mechanisms i e hot spots giving rise to construction of shield mountains and associated collapsed summits are basic processes in planetary geology hot spot volcanism is expected to be most important on planets lacking plate tectonics on earth large shields have lifetimes of only a few million years but on mars large shields may have been active for 1 5 109 years shield calderas on earth are smaller than 20 km in diameter but known or suspected shield calderas on mars venus and io have considerably larger diameters assuming that caldera diameters are related to magma chamber diameters and depths magma chambers on other planets are significantly larger and or deeper than their counterparts on earth terrestrial magma chambers are small because terrestrial shield volcanoes are small in comparison to shields on mars and venus and terrestrial shields are small because the earth s mobile plates move growing shields away from their deep sources thus distributing magma along a narrow chain rather than piling it up around a central vent finally the long lava flows of mars are also explained if the volume of erupted magma has any simple relation to magma chamber volume

the computation of body wave synthetic seismograms in laterally homogeneous media synthetic seismograms computed for realistic horizontally stratified media are now routinely used as an aid to seismic interpretation this paper reviews the theoretical background to these methods and presents comparisons of the two popular algorithms reflectivity and wkbj seismograms for a variety of earth models the transformed wave equations are developed from the equations for a spherical gravitating medium in a symmetric form suitable for body wave calculations four methods of solving these equations in general inhomogeneous layers are described the wkbj and langer asymptotic expansions and the wkbj and langer iterative solutions together with the earth flattening transformation and the ray expansion transformed solutions for body waves can then be obtained for realistic layered media four methods of inverting the frequency and wave number transformations are also described the real and complex spectral and slowness methods although realistic seismic models are normally sufficiently complicated that numerical calculations are essential before proceeding with numerical comparisons we have included a review of the canonical signals included in body wave seismograms these analytic results for direct rays partial and total reflections turning rays on forward and reversed branches head waves interface waves airy caustics and fresnel and interface shadows are useful to anticipate and understand numerical problems and results finally a comparison of green s functions for crustal mantle and whole earth models calculated using the wkbj and reflectivity algorithms is included

introduction to the special section geology and geophysics of io io is about the size and density of earth s moon but it has a dramatically different thermal state and geologic history tidal heating leads to intense volcanic and tectonic activity so io is an accelerated experiment in planetary geology and geophysics here we can witness volcanic activity on very large scales and at very high temperatures perhaps providing insights into the early histories of the terrestrial planets io has always been a high priority objective of galileo but her proximity to jupiter s intense radiation belt has meant saving the best for last an io flyby occurred during jupiter orbit insertion in december 1995 but a tape recorder anomaly led to cancellation of remote sensing observations no further close flybys of io were planned until the final two orbits i24 and i25 of the galileo europa mission gem late in 1999 in order to minimize radiation damage to spacecraft and instrument electronics i24 was an exciting encounter with a spacecraft safing event and recovery just hours before io closest approach most of the io data were acquired but not without problems the majority of images from the solid state imager ssi were acquired in a mode that failed due to the cumulative radiation damage producing garbled images although reconstruction has produced some useful pictures keszthelyi et al this issue also the grating of the near infrared mapping spectrometer nims became stuck leading to loss of spectral sampling lopes et al this issue these instrument problems were mitigated by the use of different observation modes or strategies in subsequent orbits the 125 polar pass included another safing event this time eliminating the recording of the highest resolution observations however the medium resolution observations were of excellent quality and provided a surprise look at a new fissure eruption at tvashtar catena gem was followed by the galileo millennium mission gmm including another close io flyby in orbit i27 a fully successful encounter three additional io flybys are anticipated in august 2001 i31 october 2001 i32 and january 2002 i33 the groundtracks for all six io encounters are shown in plate 1

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

io s thermal anomalies clues to their origins from comparison of ground based observations between 1 and 20 µm io s thermal emission for 1995 from eclipse photometry at 2 2 m broad band radiometry at 4 8 m 8 7 m and 20 m and in eclipse imaging between 1 7 and 5 m are compared the variability of thermal emission from io at wavelengths between 1 5 m silverstone et al 1995 spencer et al 1997 is in agreement with the expected variability based on the 13 year record presented in veeder et al 1994 and goguen et al 1996 we conclude that 1995 was typical for io in terms of overall observed variability in the volcanic sources detailed comparison of data from goguen et al on aug 24 and spencer et al on aug 26 provides evidence of a high temperature eruption that produced a larger cooler region over the course of two days the observed frequency of occurrence of high temperature events the linking of high and lower temperature thermal anomalies and the observed stability of volcanic regions since voyager suggests that high temperature silicate eruptions could support the entire observed population of cooler temperature anomalies it may be more productive to consider sulfur flows on io in the context of remobilization of existing sulfur deposits

magma ascent pathways associated with large mountains on io abstract while jupiter s moon io is the most volcanically active body in the solar system the largest mountains seen on io are created by tectonic forces rather than volcanic construction pervasive compression primarily brought about by subsidence induced by sustained volcanic resurfacing creates the mountains but at the same time inhibits magma ascent in vertical conduits dikes we superpose stress solutions for subsidence along with thermal stress both from the crustal conveyor belt process of resurfacing in io s lithosphere with stresses from io mountain sized loads in a shallow spherical shell solution in order to evaluate magma ascent pathways we use stress orientation least compressive stress horizontal and stress gradient compression decreasing upwards criteria to identify ascent pathways through the lithosphere there are several configurations for which viable ascent paths transit nearly the entire lithosphere arriving at the base of the mountain where magma can be transported through thrust faults or perhaps thermally eroded flank sections the latter is consistent with observations of some io paterae in close contact with mountains

ground based observations of volcanism on io in 1999 and early 2000 ground based observations of volcanism on io during the period of the 1999 and early 2000 galileo close flybys have detected several types of activity providing information which complements the spacecraft observations at loki a brightening began between august 25 and september 9 and continued through february on august 2 a major outburst was observed near 14 n 74 w whose brightness corresponds to an area of approximately 350 km 2 at a temperature of 1100 k observations of eruptions in late june 9906a and in late november 9911a at tvashtar provide temporal and photometric constraints on activity also seen by galileo high resolution adaptive optics images provide further information on the fainter sources distributed across the surface

a post galileo view of io s interior abstract we present a self consistent model for the interior of io taking the recent galileo data into account in this model io has a completely molten core substantially molten mantle and a very cold lithosphere heat from magmatic activity can mobilize volatile compounds such as so 2 in the lithosphere and the movement of such cryogenic fluids may be important in the formation of surface features including sapping scarps and paterae

predation scar frequencies in chemosymbiotic bivalves at an oligocene seep deposit and their potential relation to inferred sulfide tolerances abstract three species of chemosymbiotic bivalves with different inferred sulfide tolerances and life habits from a lower oligocene seep deposit in eastern hokkaido japan were investigated for drill holes and scars of durophagous predation the thyasirid conchocele bisecta had the lowest inferred sulfide tolerance and showed the highest frequencies of repair 0 4 and drilling predation 0 1 and specimens with drill holes were on average smaller than non drilled specimens indicating that large size is a refuge from drilling predation in this species the bathymodiolin bathymodiolus inouei and the vesicomyid hubertschenckia ezoensis are inferred to have lived at higher sulfide concentrations than c bisecta based on comparisons to their living relatives and show lower repair frequencies 0 24 in b inouei and 0 17 in h ezoensis based on the assumption that increased sulfide concentrations are increasingly toxic to predators we conclude that the frequency of shell injuries in the three investigated species is inversely related to the sulfide concentrations that these species are able to tolerate thus when applied carefully the frequency of shell injuries among shelled invertebrates at fossil seeps may be used to infer their relative tolerances toward sulfide and may thus represent a tool to assess the life habits of extinct invertebrates that inhabited methane seeps in the geologic past

sulphur flows at lastarria volcano in the north chilean andes although several authors have suggested that sulphur plays an important role in the volcanism on the jovian moon io1 8 some deny the participation of elemental sulphur there at least in the form of cooled flows9 studies of volcanism on io have focused attention on the role of sulphur in terrestrial volcanism on earth fumarolic sulphur is very common in almost all active volcanoes but sulphur flows are rare having been reported only on siretoko iosan volcano in japan10 on sierra negra and azufre volcanoes in the galapagos islands11 12 and on mauna loa in hawaii13 14 of these the siretoko iosan example is the only natural molten sulphur flow to have been observed in the process of formation the others being rather poorly exposed i describe here a singularly well exposed example of sulphur lava flows on lastarria volcano in chile where the liquid sulphur appears to have been formed by melting of fumarolic sulphur deposits caused by a rise in the thermal gradient owing to the renewed activity of the magmatic source

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

imaging of volcanic activity on jupiter s moon io by galileo during the galileo europa mission and the galileo millennium mission the solid state imaging ssi instrument provided the first high and medium resolution views of io as the galileo spacecraft closed in on the volcanic body in late 1999 and early 2000 while each volcanic center has many unique features the majority can be placed into one of two broad categories the promethean eruptions typified by the volcanic center prometheus are characterized by long lived steady eruptions producing a compound flow field emplaced in an insulating manner over a period of years of decades in contrast pillanian eruptions are characterized by large pyroclastic deposits and short lived but high effusion rate eruptions from fissures feeding open channel or open sheet flows both types of eruptions commonly have 100 km tall bright so2 rich plumes forming near the flow fronts and smaller deposits of red material that mark the vent for the silicate lavas

temperature and area constraints of the south volund volcano on io from the nims and ssi instruments during the galileo g1 orbit analysis of data from darkside and eclipse observations of io by the nims and ssi instruments show that the south volund hot spot is a manifestation of high temperature active silicate volcanism the nims data are fitted with a two temperature model developed from modelling terrestrial lavas which yields a better fit to the data than a single temperature fit the multispectral color temperatures obtained from nims are compared with the brightness temperatures obtained from the ssi instrument and show excellent agreement for the hotter of the two components fitted to the nims data the two components might correspond to a cooled crust which has formed on the surface of an active flow or lava lake at a temperature of approximately 450 k and covering an area of about 50 km and a hotter and much smaller component at a temperature of approximately 1100 k and an area of less than 0 1 km the hot component implies the existence of cracks in the surface crust of a flow or lake through which the hot interior radiates a hot vent area or breakouts of lava forming new flow lobes the ratio of these areas is consistent with the crack to crust ratio of some lava flows and lava lakes on earth

the thermal signature of volcanic eruptions on io and earth abstract we investigate a spectrum based technique to identify the style of active volcanic eruptions on jupiter s moon io thermal remote sensing of io has had to rely primarily on low spatial resolution data similar to low spatial resolution satellite data applied to detecting and charting the temporal evolution of terrestrial hot spots these terrestrial analyses use data from sensors designed to monitor the weather and sea surface temperature on io such low spatial resolution data are used to classify eruption styles modes of emplacement by means of several criteria related to the temporal evolution of the infrared spectrum associated with the eruptive activity at each hot spot which we term thermal signature we find that the ratio of the emission at 2 and 5 m and how this ratio changes with time is often diagnostic of eruption style even in low spatial resolution data tests using thermal data for terrestrial ground truth cases show that our classification system is valid on earth the results of our analysis can be used to aid in the design of future space based instruments that can be used for volcano monitoring on io as well as earth

orogenic tectonism on io 1 we catalog 143 ionian mountains montes and mountain like features mensae tholi plana and small peaks in order to investigate orogenic tectonism on io from this comprehensive list we select 96 mountains for which there are sufficient coverage and resolution to discern spatial relationships with surrounding geologic features three of the 96 mountains are probably volcanoes 92 appear to be tectonic massifs and 1 is ambiguous of the 92 tectonic mountains 38 abut paterae volcanic or volcano tectonic craters with irregular or scalloped margins this juxtaposition is unlikely to be a coincidence as the probability of it occurring by chance is 0 1 we propose instead that orogenic faults may act as conduits for magma ascent thus fueling patera formation near mountains as resurfacing buries a shell of material from io s surface to the base of the lithosphere its effective radius is reduced and it heats up we calculate the lithospheric volume change due to subsidence and thermal expansion as a function of lithospheric thickness conservation of volume dictates that this material must be uplifted at io s surface by estimating the total volume of the mountains we are able to place a lower limit of 12 km on io s lithospheric thickness we hypothesize that in some cases mountain formation may be facilitated by asthenospheric diapirs impinging on the base of the lithosphere the resulting lithospheric swell could focus the compressive stresses that drive orogenic tectonism this model is one of several possible mechanisms for uplifting isolated mountains such as are observed on io

a novel technology for measuring the eruption temperature of silicate lavas with remote sensing application to io and other planets abstract the highly variable and unpredictable magnitude of thermal emission from evolving volcanic eruptions creates saturation problems for remote sensing instruments observing eruptions on earth and on io the highly volcanic moon of jupiter for io it is desirable to determine the temperature of the erupting lavas as this measurement constrains lava composition one method of determining lava eruption temperature is by measuring radiant flux at two or more wavelengths and fitting a blackbody thermal emission function only certain styles of volcanic activity are suitable those where detectable thermal emission is from a restricted range of surface temperatures close to the eruption temperature volcanic processes where this occurs include large lava fountains smaller lava fountains common in active lava lakes and lava tube skylights problems that must be overcome to obtain usable data are 1 the rapid cooling of the lava between data acquisitions at different wavelengths 2 the unknown magnitude of thermal emission which has often led to detector saturation and 3 thermal emission changing on a shorter timescale than the observation integration time we can overcome these problems by using the hot bird detector and a novel advanced digital readout circuit d roic to achieve a wide dynamic range sufficient to image lava on io without saturating we have created an instrument model that allows various instrument parameters including mirror diameter number of signal splits exposure duration filter band pass and optics transmissivity to be tested to determine the detectability of thermal sources on io s surface we find that a short wavelength infrared instrument on an io flyby mission can achieve simultaneity of observations by splitting the incoming signal for all relevant eruption processes and still obtain data fast enough to remove uncertainties in accurate determination of the highest lava surface temperatures observations at 1 and 1 5 m are sufficient for this purpose even with a ten way beam split instrument throughput generates acceptable signal to noise values accurate constraints on lava eruption temperature are also possible with a visible wavelength detector so long as data at different wavelengths are obtained simultaneously and integration time is very short fast integration times are important for examining the thermal emission from lava tube skylights due to rapidly changing viewing geometry during close flybys the technology described here is applicable to instruments observing terrestrial volcanism and for investigating proposed volcanic activity on venus where lava composition is not known

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

volcanic hot spots on io correlation with low albedo calderas comparison of voyager imaging data with voyager 1 infrared observations iris and with ground based telescopic infrared data demonstrates a strong correlation between hot spots and low albedo features reflectivity 0 3 in all visual wavelengths on io most of these low albedo areas occur on the floors of volcanic calderas and many are associated with active or recent volcanism we use this correlation to identify additional hot spots in regions not observed by iris and to model their temperatures the major features discovered by this method are in a ringlike structure in the south polar region centered at 140 w 75 s and amaterasu patera 307 w 38 n our model temperature for the south polar feature is 280 50 k taking account of the high latitudes of these features the estimated global average heat flow from the hot spots becomes 1 8 0 5 w m 2 most of this heat emanates from just a few very large hot spots the global distribution of hot spots is further evidence that io is a dimorphous body the hemisphere centered on 310 w 30 s is much more volcanically active than the opposite hemisphere the styles of heat transfer in io conductive versus convective may be related to the global distribution of hot spots large eruptive plumes and large scale topographic relief the correlation between hot spots and dark areas is due to 1 the absence of the bright materials such as so2 frost which cover most of the surface and 2 the presence of a low albedo substance spectral properties of the low albedo features extracted from the voyager multispectral data are consistent with a number of candidate materials liquid sulfur boiled sulfur silicate sulfur mixtures zinc sulfide fe sulfate and fe chloride quenched sulfur allotropes on the other hand are redder than the low albedo features on io and are incompatible with the elevated temperatures of the hot spots some of the dark caldera floor materials may be liquid sulfur and or thermally altered boiled sulfur liquid sulfur would tend to collect in the topographic depressions and fractured bedrock of the calderas and this would explain the concentration of low albedo material in the calderas the presence of liquid sulfur is also suggested by the hot spot temperature distribution typically 200 400 k and by morphologies suggestive of lava lakes however the liquid boiled sulfur model does not seem to work for babbar and amaterasu paterae and the evidence for liquid sulfur is not conclusive

factors influencing the morphology of volcanic landforms an earth moon comparison abstract the products of volcanism on the earth and moon differ widely in terms of morphology distribution composition and age these differences result partly from the different thermal histories of the two bodies and partly through the different controls on volcanic eruption conditions the controls of volcanism are here separated into three groups 1 controls which remain constant on any one body but which differ from planet to planet 2 parameters that are controlled by the rheology of the magma and 3 controls which are intrinsic properties of individual eruptions and are themselves dependent upon the planetary and rheological variables in terms of planetary variables it can be predicted that lunar volcanic morphologies are influenced by greater tephra range hemispherical eruption clouds lesser lithostatic pressures at corresponding depths slower cooling slower erosion lesser horizontal stress differences and no features typical of hydrosphere magma interaction in terms of rheology the lunar eruptions had different rock and gas compositions low yield strengths and viscosities and high densities many lunar basalts appear to have been produced at high eruption rates to have been derived from monogenetic volcanoes and to have flowed in a turbulent manner the weight of available data points to the vast majority of lunar craters being of impact origin though some dark halo craters sinuous rille source craters rimless pits and craters atop domes and cones are undoubtedly of volcanic origin other impact craters appear to have been modified by volcanic events included within this latter group are the floor fractured craters and the mare basins studies of volcanic morphologies on bodies other than the earth may help isolate the effectiveness of those controls of volcanism which remain constant on any one body although volcanology has advanced substantially within the last few decades much more detailed integrated scientific research is required before we are able to predict confidently the environmental hazards that result from volcanism and to understand the role of volcanism in planetary evolution

layered convection in io implications for short wavelength surface topography and heat flow abstract io one of the four galilean moons of jupiter is remarkable for its extensive volcanism and extreme interior tidal heating the tidal heating likely yields a very low viscosity asthenosphere and consequently a very high rayleigh number of o 10 12 for convection in the interior in a state of quasi steady balance the internally generated heat must be transported from the interior to the base of the io lithosphere and exhausted to space the mechanisms whereby the convective radial heat transfer is evacuated involve both conduction and volcanism despite io s ubiquitous volcanism only 4 of its mountains montes appear to have a volcanic origin and most of the mountainous regions seem to be related to tectonic processes by employing an original control volume based numerical model we investigate the style of convection in the interior of io and the correlation of the scale of convection with the ionian surface heat flux and topography our control volume results support the existence of significant asthenospheric heating and demonstrate that short wavelength features of the surface heat flux are well correlated in scale to an expected layered intra lithospheric style small scale convection these numerical analyses suggest that the amplitude of the short wavelength topography of io is expected to be on the order of a few hundreds of meters the model results also demonstrate that the ionian highs cannot be produced by a lithospheric flexure process above the hot upwellings and therefore other tectonic events such as have previously been suggested must be responsible for the formation of the high ionian mountains that reach in excess of 17 km in elevation

comment on the surface of lo a new model by bruce hapke abstract hapke 1989 icarus 79 56 74 proposed that the surface of io is dominantly basaltic with thin coatings of polysulfur oxide s 2 o ad so 2 however observations and models of the active volcanism indicate that volatiles such as sulfur and so 2 must be more abundant than envisioned by hapke

silicate cooling model fits to galileo nims data of volcanism on io abstract the near infrared mapping spectrometer nims has obtained spectra of volcanoes on the surface of the jovian satellite io fits to data using a silicate cooling model allow us to constrain lava eruption rates and eruption age the thermal signatures of the hot spots are indicative of active and cooling silicate lava flows for large active hot spots maximum ages of flow surfaces detected by nims typically range from days to months although in one case it is nearly 30 years mass eruption rates for the main hot spots are in the range 7 m3 s 1 to 79 m3 s 1 using an average flow thickness of 1 m these mass eruption rates are orders of magnitude less than those implied for large thermal outbursts on io the eruptions observed during june 1996 are most likely of a different eruption style on a much smaller scale the observation analyzed here may be representative of the current background level of volcanic activity on the anti jove hemisphere of io the global mass eruption rate from these non outburst hot spots is calculated to be 43 km3 year equivalent to a global resurfacing rate of about 1 mm year about 10 of the minimum required global resurfacing volume the total observed energy output from the 14 hot spots analyzed is 3 6 1012 w normalized globally these hot spots contribute approximately 10 of io s radiometric heat flux

topographic mapping of paterae and layered plains on io using photoclinometry we have generated regional scale photoclinometry digital elevation models dems from voyager and galileo imagery of io that resolve small scale topographic features including paterae and layered plains given the difficulty of applying this technique to io due to its anomalous surface albedo properties we have experimented extensively with the relevant procedures in order to generate what we consider to be the most reliable dems the dems have been used to gauge the depths of 23 paterae and the heights of 12 layered plains outcrops and we find the very similar relief and frequent close association of the two landforms to support the existence of a mixed silicate volatile layer covering much of the surface of io

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

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

subsidence of topography on io topographic features on io tend to subside because their underlying roots are softened and eroded by contact with hot mantle this can be offset by crustal thickening due primarily to ongoing volcanism but observations suggest that this is 1 cm year 1 at current topographic highs since crustal thinning occurs at 50 cm year 1 if the underlying material is a pure magma ocean we conclude that io has no global magma ocean viscosities in excess of 10 10 p are implied for io s interior

loki io new ground based observations and a model describing the change from periodic overturn 1 loki patera is the most powerful volcano in the solar system we have obtained measurements of loki s 3 5 micron brightness from nasa s infrared telescope facility irtf and have witnessed a major change in eruptive behavior while loki brightened by a factor of several every 540 days prior to 2001 from 2001 through 2004 loki remained at a constant intermediate brightness we have constructed a quantitative model of loki as a basaltic lava lake whose solidified crust overturns when it becomes buoyantly unstable by altering the speed at which the overturn propagates across the patera we can match our ground based brightness data in addition we can match other data taken at other times and wavelengths by slowing the propagation speed dramatically we can match the observations from 2001 2004 such slowing could be due to a small change in volatile content in the lava

seismic stratigraphy of the flexural moat flanking the hawaiian islands the elastic thickness of oceanic lithosphere based on flexure studies in the region of surface loads is two to three times smaller than its seismic thickness1 thus as a load ages the thickness of the mechanically supportive part of the lithosphere must decrease from its short term seismic thickness to its long term mechanical thickness extrapolation of data from experimental rock mechanics suggests that thinning occurs by brittle failure in the uppermost part of the lithosphere and thermally activated creep in its lower part2 modelling shows that for load ages less than about 1 myr flexural moats change shape and the peripheral bulges migrate in towards the load3 these transient changes in flexure are best manifest we believe in the stratigraphical sequences that infill flexural moats the largest thicknesses of sediments occur in moats flanking orogenic belts4 5 however the stratigraphical record in these basins is complicated by the effects of compaction sub aerial erosion and sea level changes and by the fact that the loading history extends over very long periods of time here we describe a multichannel seismic reflection profile across a flexural moat flanking the volcanic load of oahu in the hawaiian islands the advantages of oahu are that it is located in the interior of a plate the load is 2 7 myr old and formed within 1 myr6 and the flexural moat was not significantly affected by sea level changes and erosion we show that the observed stratigraphical patterns cannot be explained by changes in material influx load distribution and rapid relaxation of the lithosphere to its long term mechanical thickness rather the observed patterns suggest a prolonged relaxation 1 myr due to either local or regional re heating of the lithosphere this re heating has important implications for the relationship between elastic thickness and age of the lithosphere at the time of loadings

variations in oceanic layer 2 elastic velocities near hawaii and their correlation to lithospheric flexure analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant systematic and symmetric dependence of average layer 2 velocities on their distance to the north and south of the hawaiian ridge beyond the flexural arch surrounding the ridge the velocity depth solutions indicate a normal layer 2 within the arch approximately 155 km from the ridge the average elastic velocities in layer 2 are lowered by 0 8 0 9 0 2 km s within 75 km of the ridge the average velocities are again normal elastic and elastic plastic flexural models for the regional compensation of the hawaiian islands predict tensional stress drops of 0 8 kbar in the upper lithosphere for the region having lowered velocities in layer 2 which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0 5 km s a significant inverse relationship correlation coefficient of 0 818 exists between the average elastic velocities in the upper 1 0 km of the igneous crust and the strain in the upper crust calculated from these flexural models the correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure these observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones

internal structure of io and the global distribution of its topography abstract the distribution of equatorial long wavelength topography on io consists of alternating basins and swells similar to the pattern expected if tidal heating in a thin asthenosphere controls the elevation of the surface through a conductive lithosphere in isostatic equilibrium the equatorial basin swell pattern is shifted in longitude with respect to theoretical tidal heating patterns however making the correlation between theoretical heat flow and elevation unclear we calculate global topography for multilayer io models with dissipation occurring in a viscous asthenosphere and a solid mantle two models are considered a thermal swell model in which topography and heat flow are positively correlated and a differentiated lithosphere model in which topography and heat flow are negatively correlated both models match the observed pattern of alternating basins and swells along the equator and moderate polar topography if about two thirds of the tidal heating occurs in the asthenosphere and about one third occurs in the underlying solid mantle the mean thicknesses of the model lithospheres are 35 km in the differentiated model and 150 km in the thermal swell model polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model match the observations better than the thermal swell model in a differentiated lithosphere model consistent with the topography the asthenosphere is at least 50 km thick with viscosity about 100 mpa sec and is about 7 more dense than the lithosphere the mantle density exceeds the asthenosphere density by at least 10 the shift of the equatorial basin swell pattern suggests that io s lithosphere has recently undergone a zonal rotation of about 25

io loki patera as a magma sea 1 we develop a physical model for loki patera as a magma sea we calculate the total volume of magma moving through the loki patera volcanic system every resurfacing cycle 540 days and the resulting variation in thermal emission the rate of magma solidification at times reaches 3 106 kg s 1 with a total solidified volume averaging 100 km3 yr 1 a simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations the loki patera surface temperature distribution shows that different areas are at different life cycle stages on a regional scale however there can be coordinated activity indicated by the wave of thermal change which progresses from loki patera s sw quadrant toward the ne at a rate of 1 km d 1 using the observed surface temperature distribution we test several mechanisms for resurfacing loki patera finding that resurfacing with lava flows is not realistic only the crustal foundering process is consistent with observations these tests also discovered that sinking crust has a heat deficit which promotes the solidification of additional magma onto the sinking plate bulking up in the limiting case the mass of sinking material can increase to a mass of 3 times that of the foundering plate with all this solid matter sinking there is a compensating upward motion in the liquid magma this can be in excess of 2 m yr 1 in this manner solid liquid convection is occurring in the sea

structure and variability of oceanic crust on the flanks of the east pacific rise between 11 and 13 n we use over 500 seismograms collected by five ocean bottom seismometers to examine the structure and variability of 0 5 m y old crust in the rivera ocean seismic experiment rose area of the east pacific rise between 11 and 13 n there are no significant differences among the first arrival travel times for 10 independent refraction line segments along the isochron amplitude patterns recorded on the individual lines however suggest that structural boundaries within the upper crust vary by hundreds of meters in depth over lateral distances of tens of kilometers within this 200 km segment of lithosphere on the basis of the modeling of amplitude patterns at ranges of 5 10 km and of comparisons with the upper crust sampled at deep sea drilling project hole 504b and in ophiolite complexes layer 2 can be divided into three units 2a corresponds to extrusive volcanics with a steep velocity gradient 2b to extrusives with a near zero velocity gradient and 2c to a complex region of transition from extrusives to sheeted dikes the total thickness of layer 2 varies by about 0 7 km over the length of the line another amplitude peak which varies in range between 14 and 21 km may be related to the downward transition from sheeted dikes to isotropic gabbros within layer 3 the variability of these two amplitude patterns provides direct evidence that the along strike structure of oceanic crust in the rose area is definably heterogeneous and that the process of crustal accretion is likewise variable on the scale resolved by amplitude and travel time information

dsdp hole 504b the first reference section over 1 km through layer 2 of the oceanic crust hole 504b provides a reference section for correlation of in situ petrological and geophysical studies with regional crustal models based on dredged samples and remote surveys and at least for the medium spreading rate costa rica rift hole 504b confirms that the main features of the upper part of an idealized ophiolite sequence occurs in the oceanic crust

spatial variations in lava flow field thermal structure and effusion rate derived from very high spatial resolution hyperspectral mivis data 1 high spatial resolution hyperspectral measurements of volcanic thermal anomalies allow for an unconstrained solution of a two component thermal model this can be used for identification of lava flow emplacement style and the calculation of lava flow heat and volume flux the multispectral infrared and visible imaging spectrometer mivis is an airborne sensor equipped with 72 bands in the short infrared range and 10 bands in the thermal infrared region of the spectrum we used mivis acquired for mount etna italy during the july august 2001 eruption to solve the dual band equations in an unconstrained fashion using three bands of unsaturated data our results suggest a complex thermal structure for etnean lava flows this is characterized by a downflow transition from a lightly crusted active channel to a more heavily crusted distal section both surrounded by zones of stagnant cooling flow where exposed molten material is absent and maximum temperatures are thus lower the total flow field effusion rate obtained for 29 july 2001 0700 local time of 8 16 m3 s is in excellent agreement with that obtained from ground based measurements and advanced very high resolution radiometer data flow by flow effusion rates obtained from the mivis data vary depending on whether the vent is linked to the central conduit or the dyke that was injected from greater depth as well as vent elevation with lower elevation vents experiencing higher effusion rates

ground based observations of io ground based observations are providing new information about the volcanic phenomena at io s surface thermal emission from lava can be seen routinely at infrared wavelengths one result of recent work is the reinvigoration of a familiar theme silicate volcanism in the following paragraphs we will focus on such advances which have resulted from a better understanding of io s thermal emission this emission tells us about ongoing volcanic processes and heat flow io s total heat flow is especially important because of the tidal interactions among the bodies in the jovian system the value of this heat flow not only constrains models for io s interior but also those for jupiter and for the long term orbital evolution of the whole system

the relationship between the height of a volcano and the depth to its magma source zone a critical reexamination it is commonly assumed that hydrostatic pressure balance arguments can be used to establish a relationship between the maximum height to which a volcanic edifice is able to grow and the depth at which the partial melts providing its magma supply are formed such a relationship has been used to infer various aspects of the thermal and stress state of the lithosphere beneath volcanic constructs on earth mars io and venus we examine the assumptions behind this relationship which are that 1 a continuous pressure connection exists between source and summit 2 the pressure around the magma source is the local hydrostatic pressure dictated by the depth below the geoid and 3 the melt erupting at the summit has a net positive buoyancy and show that many of them require geologically unreasonable conditions we then critically assess the evidence cited in the literature for the relationship and find that there are other factors that may explain the observations we conclude that volcano heights on the terrestrial planets cannot be related in any simple way to lithospheric thickness or depth to the magma source zone and we review the range of other factors controlling volcano height

mountains and calderas on io possible implications for lithosphere structure and magma generation abstract the combination of voyager images and newly acquired galileo images with low illumination and resolutions ranging from 2 to 6 km pixel now allows determination of the global distribution of mountains and volcanic centers on io the mountains generally do not have characteristics typical of terrestrial volcanic landforms they are evenly distributed across the surface and show no obvious correlation with known hot spots or plumes relative elevations determined by shadow measurements and stereoscopy indicate that mountains in the newly imaged area range in elevation up to at least 7 6 km the origin of the mountains remains uncertain some appear to be multitiered volcanic constructs others enclosing the partial remains of large circular depressions appear to be remnants of old volcanoes yet others show extensive tectonic disruption volcanic centers also appear to be distributed evenly across the surface except for an apparently somewhat lower density at high latitudes the low latitudes have one volcanic center per 7 10 4 km 2 and on average the centers are spaced roughly 250 km apart the global distribution of high mountains suggests that the lithosphere over most of io is thick although the thickness cannot be calculated the previously suggested 30 km appears reasonable as a lower limit the high rates of resurfacing combined with the likely dissipation of most of the tidal energy in the asthenosphere and underlying mantle implies a very low temperature gradient in the upper part of the lithosphere and steep gradients in the lower lithosphere the slow rate of separation of melt from host rock in the magma source regions as a consequence of the low gravity on io coupled with the high rate of magma production will likely result in larger melt fractions than is typical for source regions on earth the variety of volcanic landforms suggests that volcanic products with a range of compositions are deposited on the surface this mixture will be carried downward through the lithosphere as a consequence of the 0 5 1 5 cm yr resurfacing rates during descent the more volatile components will tend to be driven off early but complete or near complete melting at the base of the lithosphere may result in rehomogenization of the silicate mixture that remains

active volcanism on io io one of jupiter9s moons has hundreds of active volcanoes many of which are erupting high temperature silicate lavas in his perspective mcewen reviews how data returned by the galileo spacecraft have helped to resolve some questions regarding io9s volcanism but have raised others especially regarding the moon9s internal structure

a komatiite analog to potential ultramafic materials on io ultramafic volcanism is one model which fits currently available data for some eruptions on jupiter s moon io assuming that such activity does occur it is possible to apply komatiitic analogs and terrestrial ultramafic flow models to io we have used such analogs and models along with galileo data to investigate the nature of ultramafic materials that are assumed to occur at high temperature hotspots on io the unusual komatiites of the commondale greenstone belt south africa are consistent with available galileo data on the temperatures and composition of potential ionian ultramafic materials these komatiites had high sio2 50 wt and mgo 31 wt contents which are inferred to result in high liquidus temperatures 1610 c low dynamic viscosities 0 2 pa s and low densities 2680 kg m and in the crystallization of orthopyroxene phenocrysts not found in other komatiites we used the commondale composition and the model of williams et al 1998 to investigate potential ultramafic flow behavior on io compared to their terrestrial counterparts ionian ultramafic lava flows would have less potential for turbulent flow lower maximum emplacement distances and lower thermal erosion rates because of the lower ionian gravity and their more silicic composition shallow 10 m thermal erosion channels seem less likely on io unless 1 lavas are superheated 2 lavas are more ultramafic 31 mgo 3 eruption rates eruption durations or flow volumes are high or 4 substrates are unconsolidated partly consolidated or volatile rich and thus more erodable if volatiles are present in the lava as vesicles then increasing lava vesicularity results in decreasing maximum emplacement distances decreasing thermal erosion rates and decreasing erosion channel depths for given eruption durations

periodic hot spot distribution on io the jovian satellite io has active volcanic hot spots the point to point correlation of the hot spot distribution indicates that the hot spots preferentially make chains the arrangement of the chains is periodic with a typical spacing of 120 kilometers the chains exhibit concordant trends with stresses imposed by the tidal deflection of the lithosphere suggesting that the hot spots are formed along fissures in the lithosphere the typical spacing may be controlled by lithosphere thickness

high temperature hot spots on io as seen by the galileo solid state imaging ssi experiment high temperature hot spots on io have been imaged at 50 km spatial resolution by galileo s ccd imaging system ssi images were acquired during eclipses io in jupiter s shadow via the ssi clear filter 0 4 1 0 m detecting emissions from both small intense hot spots and diffuse extended glows associated with io s atmosphere and plumes a total of 13 hot spots have been detected over 70 of io s surface each hot spot falls precisely on a low albedo feature corresponding to a caldera floor and or lava flow the hot spot temperatures must exceed 700 k for detection by ssi observations at wavelengths longer than those available to ssi require that most of these hot spots actually have significantly higher temperatures 1000 k or higher and cover small areas the high temperature hot spots probably mark the locations of active silicate volcanism supporting suggestions that the eruption and near surface movement of silicate magma drives the heat flow and volcanic activity of io

the heartbeat of the volcano the discovery of episodic activity at prometheus on io the temporal signature of thermal emission from a volcano is a valuable clue to the processes taking place both at and beneath the surface the galileo near infrared mapping spectrometer nims observed the volcano prometheus on the jovian moon io on multiple occasions between 1996 and 2002 the 5 micron m brightness of this volcano shows considerable variation from orbit to orbit prometheus exhibits increases in thermal emission that indicate episodic though non periodic effusive activity in a manner akin to the current pu u o o kupaianaha afterwards referred to as the pu u o o eruption of kilauea hawai i the volume of material erupted during one prometheus eruption episode defined as the interval from minimum thermal emission to peak and back to minimum from 6 november 1996 to 7 may 1997 is estimated to be 0 8 km3 with a peak instantaneous volumetric flux effusion rate of 140 m3 s 1 and an averaged volumetric flux eruption rate of 49 m3 s 1 these quantities are used to model subsurface structure magma storage and magma supply mechanisms and likely magma chamber depth prometheus appears to be supplied by magma from a relatively shallow magma chamber with a roof at a minimum depth of 2 3 km and a maximum depth of 14 km this is a much shallower depth range than sources of supply proposed for explosive possibly ultramafic eruptions at pillan and tvashtar as prometheus type effusive activity is widespread on io shallow magma chambers containing magma of basaltic or near basaltic composition and density may be common this analysis strengthens the analogy between prometheus and pu u o o at least in terms of eruption style even though the style of eruption appears to be similar effusive emplacement of thin insulated compound pahoehoe flows the scale of activity at prometheus greatly exceeds current activity at pu u o o in terms of volume erupted area covered and magma flux whereas the estimated magma chamber at prometheus dwarfs the pu u o o magma chamber it fits within expectations if the pu u o o chamber were scaled for the greater volumetric flux and lower gravity of io recent volumetric eruption rates derived from galileo data for prometheus were considerably smaller than the rate that produced the extensive flows formed in the 17 years between the voyager and galileo missions these smaller eruption rates coupled with the fact that flows are not expanding laterally may mean that the immediate heat source that generates the prometheus plume is simultaneously running out of available volatiles and the thermal energy that drives mobilization of volatiles this raises the question of whether the current prometheus eruption is in its last throes

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

structure porosity and stress regime of the upper oceanic crust sonic and ultrasonic logging of dsdp hole 504b abstract the layered structure of the oceanic crust is characterized by changes in geophysical gradients rather than by abrupt layer boundaries correlation of geophysical logs and cores recovered from dsdp hole 504b provides some insight into the physical properties which control these gradient changes borehole televiewer logging in hole 504b provides a continuous image of wellbore reflectivity into the oceanic crust revealing detailed structures not apparent otherwise due to the low percentage of core recovery physical characteristics of the crustal layers 2a 2b and 2c such as the detailed sonic velocity and lithostratigraphic structure are obtained through analysis of the sonic borehole televiewer and electrical resistivity logs a prediction of bulk hydrated mineral content consistent with comparison to the recovered material suggests a change in the nature of the alteration with depth data from the sonic borehole televiewer electrical resistivity and other porosity sensitive logs are used to calculate the variation of porosity in the crustal layers 2a 2b and 2c several of the well logs which are sensitive to the presence of fractures and open porosity in the formation indicate many zones of intense fracturing interpretation of these observations suggests that there may be a fundamental pattern of cooling induced structure in the oceanic crust

composition and location of volatiles at loki patera io abstract volatiles play a critical role in determining the nature of volcanic activity on earth but their role in the volcanism on io is less clear to help determine that role we analyze voyager and galileo images of loki patera loki is the largest caldera in the solar system and io s most powerful volcano however its eruptive behavior is still not understood it appears to be relatively volatile poor in comparison to other sites like pele where volatiles drive a 350 km high plume a resurfacing wave either from spreading flows or from foundering of a lava lake crust periodically sweeps around loki patera photometry from voyager i and ii violet and blue images shows that most of the features in and around loki have colors well matched by macroscopic mixing of sulfur and basalt the dark western portion of the patera has the color of bare basalt assuming such a macroscopic sulfur basalt mix in the voyager i images most of the rest of the patera appears to be covered with a background of 13 38 sulfur we infer this background sulfur was deposited from the nearby plume observed by voyager i and ii the surface of the patera is also dotted by numerous small bright areas which have colloquially been called bergs we find that they are also composed of sulfur with coverage ranging up to 100 darker regions adjacent to the patera such as the southwest overflow are a mixture of intermediate amounts of sulfur and basalt the bathtub ring at the edge of the overflow is again roughly 100 sulfur perhaps with significant amounts of so 2 included colors seen during the voyager ii flyby are also consistent with this general pattern but most of the patera has a sulfur abundance higher than that seen in voyager i while the then dark southern portion is again close to the reflectance of bare basalt we have also analyzed the spatial distribution of the bergs they clearly avoid the inner and outer margins of the patera and they also avoid each other while a simple explanation of the above patterns could be that the bergs are fumarolic sulfur deposited on a periodically resurfaced lava lake crust other observations seem inconsistent with that simple model careful comparison of voyager i and galileo data shows that the largest bergs in the southern patera have survived the intervening 22 years this requires that at least those larger bergs represent some more permanent feature perhaps higher standing kipuka which avoid inundation by the lava resurfacing wave

cooling and deformation of sulfur flows abstract an investigation is made to determine whether discrimination of sulfur from silicate lava flows on io might be possible on the basis of surface morphology resulting from the unusual rheology of liquid sulfur the cooling of a sulfur flow by upward radiation and downward conduction is modeled in order to determine how the rheological profile evolves with time and what surface deformation results in contrast to silicate lavas which become increasingly viscous on cooling liquid sulfur has a viscosity minimum at a temperature of about 160 c flows extruded below 160 c develop crusts at their upper and lower surfaces like silicate lavas whereas flows with higher eruption temperatures develop a series of alternating fluid and viscous interior zones in both cases a surface folding instability results which can produce ridges with spacings on the order of centimeters the density of sulfur increases upon cooling so that gravity instabilities can develop at the upper flow surface leading to crustal overturning and resurfacing tensile stresses due to cooling may cause fracturing of the surface which can also promote upwelling of hot sulfur local turbulence destroys the vertical zonation of viscosity formed in slower moving areas these processes may cause a sulfur flow to have surface ridges interrupted by cracks zones of diapiric upwelling and turbulence none of these surface structures are large enough to be identified on voyager images but they will affect surface coloration which has been the principal criterion used to distinguish sulfur from silicate flows on io by several previous investigators

violent silicate volcanism on io in 1996 we monitored io s volcanic thermal emission from 1 7 to 4 8 m in 1995 96 the data reveal a number of brightenings when io s thermal emission increased several fold we use a model of emission from lava flows to understand observations of two brightenings in 1996 the brightenings were caused by eruptions 3km in extent with eruptive rates of 104 106 m s 1 and with maximum lava temperatures 1400 k these events were probably lava lakes and or fire fountains

magmatic differentiation of io abstract if io has been volcanically active through much of its history it must be highly differentiated we present an initial attempt to quantify the differentiation of the silicate portion of io we suggest that on average each part of io has undergone about 400 episodes of partial melting we employ a widely used thermodynamic model of silicate melts to examine the effect of such repeated differentiation despite many caveats including a grossly oversimplistic model of the differentiation process uncertainties in the initial composition of the mantle and the failure to model more than four episodes of partial melting we are able to make some robust conclusions io should have a roughly 50 km thick low density 2600 2900 kg m 3 alkali rich siliceous crust composed primarily of feldspars and nepheline the crustal magmas should have relatively low melting temperatures

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

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

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

sulfur flows of ra patera io abstract voyager 1 imaging data have been used to investigate the color and morphology of several radial flow like features at ra patera a broad volcanic structure at approximately 8 latitude and 325 longitude on the galilean satellite io j1 it was found that downstream progressions of flow color and morphology are consistent with lava of a predominately sulfur composition cooling radiatively and erupting in the range of 470 to 520 k at effusion rates at 1010 to 1011 cm3 sec this implies global resurfacing rates by volcanic flows on io of the order of 1 cm year calculated energy content and effusion rates for flows at ra patera using the physical parameters of sulfur are of the order of the largest known terrestial basaltic eruptions and are consistent with calculations of globally available energy

formation of mountains on io variable volcanism and thermal stresses abstract thermal stresses are potentially important drivers of io s tectonics and mountain building it has been hypothesized that sustained local or regional shut down of heat pipe volcanism on io could lead to deep crustal heating and large compressive stresses mckinnon w b schenk p m dombard a j 2001 geology 29 103 106 such large stresses would then be relieved by thrust faulting and uplifting of crustal blocks producing mountains like those observed on io here we analyze the tectonic consequences of the heat pipe model in detail considering both the initial thermal stress state of a basalt or peridotite crust created by heat pipe volcanism and relative roles of subsidence stresses due to burial of preexisting layers and thermal stresses arising from variable volcanism and changes in crustal lithosphere thickness we limit the magnitude of the potential subsidence stresses in our study because the magnitude of subsidence stresses can be quite large if not dominant results indicate that for a fixed crustal thickness the region of failure and faulting moves closer to the surface as eruption rate decreases and time increases when the crust melts at its base as volcanism decreases as might occur under steady state tidal heating resulting in crustal thinning the region of failure is brought even closer to the surface naturally when compressive subsidence stresses are included the vertical extent of crust in brittle failure thickens to include most of the lithosphere in contrast increases in eruption rate cause the extent of the region in compressional failure to decrease and be driven very deep in the crust in the absence of sufficient subsidence stress therefore regions of declining volcanism are more likely to produce mountains whereas regions of extensive or increasing volcanism are less likely to do so this is consistent with the observation of a global anticorrelation between mountains and volcanic centers on io finally we find that the choice of crustal composition rheology dry basalt vs dry peridotite has little effect on our results implying that basalt peridotite and komatiite are all similarly stiff in the io environment

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

inverting multispectral thermal time series images of volcanic eruptions for lava emplacement models we present a novel method for interpreting time series of multispectral observations of volcanic eruptions we show how existing models relating to radiance and area emplacement can be generalized into an integration convolution of a net area emplacement nae function and a coolingfunction assumingallsurfacesfollowthesamecoolingcurve thenaedescribesthevari ation in the rate of emplacement of hot material with time and temperature while the cooling func tion describes the cooling of a hot surface with time discretizing the integration convolution equation yields an underdetermined matrix equation that we solve using second order tikhonov regularization to stabilize the solution we test the inversion by modelling plausible nae surfaces calculating the radiances adding noise and inverting for the original surface three or more spec tralbands are requiredtocapture theoverallshapeofthenae andrecovering specificquantitiesis difficult single wavebands that yield flat kernels recover the total area emplacement curve rate of increase of hot area the integral of the nae with respect to temperature surprisingly well due to their property of conserving nae suggesting novel methods for calculating area emplacement rates and effusion rates from time series of satellite images and radiometer measurements gold open access this article is published under the terms of the cc by 3 0 license

io s loki patera modeling of three brightening events in 2013 2016 abstract loki patera is one of the most dramatically time variable volcanic features on io exhibiting episodic brightening events every 1 3 years that may produce over 15 of io s global heat flow we observed three such brightening events with adaptive optics imaging at the keck and gemini n telescopes over the course of 70 nights of observation in 2013 2016 the high cadence and multi wavelength nature of the observations provides constraints on models for activity at loki patera the matson et al 2006 model for loki patera as an overturning basaltic magma sea is adapted to fit the observations of all three events in particular we adjust the details of the overturn progression and modify the lava thermal properties to include dependencies on temperature and porosity to improve the fit to the data the preferred models find overturn front propagation velocities of 1 2 1 7 km day corresponding to resurfacing rates of 1500 2200 m2 s the time intervals of 440 540 days between successive events are roughly consistent with the 540 day period calculated by rathbun et al 2002 for events prior to 2001 the best coverage was obtained for the 2016 brightening model fits to this event require a lava bulk thermal conductivity of 0 55 0 75 w m k with the best fit obtained for a value of 0 7 w m k and an average porosity that decreases during cooling for all three events the overturn front appears to propagate around the patera in the clockwise direction opposite to what has been inferred for past brightening events there is evidence that the overturn may be more complex than a single propagating wave perhaps involving multiple simultaneous resurfacing waves as well as portions of the patera that are active even after the nominal bright phase has ended the measured intensities are anomalously low when loki patera is viewed at high emission angles suggestive of topographic shadowing due to a raised area or the edge of the depression in which the magma sea resides

lava fountains from the 1999 tvashtar catena fissure eruption on io implications for dike emplacement mechanisms eruption rates and crustal structure the first direct evidence that patterns of basaltic eruptive activity may be very similar on io and earth was seen on november 26 1999 when the solid state imaging system on board the galileo spacecraft obtained high resolution images of a fissure eruption taking place in one of the calderas of the tvashtar catena complex we analyzed the dynamics of the fissure eruption from the morphology of the lava fountains and pyroclastic deposits and derived an estimate of the eruption rate our best estimate of the volume eruption rate per unit length of fissure lies in the range 0 7 to 7 m3 s 1 m 1 and multiplying this rate by the fissure length of 25 km yields a total volume eruption rate of magma of 2 104 to 2 105 m3 s 1 the upper end of the inferred eruption rate is very close to the upper end of the range of eruption rates observed or inferred for fissure eruptions on earth theoretical models of the possible dike systems feeding the fissure show that for eruptions of positively buoyant magma the elastic properties of rocks are such that a magma flux of 6 to 7 m3 s 1 m 1 is the largest value that can ever be realized in such eruptions this limiting value being independent of planetary gravity and thus the same on all silicate bodies the eruption rate inferred for tvashtar can also be achieved by a negatively buoyant magma but in that case the source depth cannot be much greater than a few tens of kilometers we find that some eruptive events are consistent with the effusion of magmas which are buoyant relative to the crust whereas others appear to involve magmas which are not this implies that the distribution of crustal volatiles is laterally very inhomogeneous our analyses suggest that the depths from which magmas make their final ascent to the surface of io are generally of order tens rather than hundreds of kilometers

charting thermal emission variability at pele janus patera and kanehekili fluctus with the galileo nims io thermal emission database nited abstract using the nims io thermal emission database nited a collection of over 1000 measurements of radiant flux from io s volcanoes davies a g et al 2012 geophys res lett 39 l01201 doi 10 1029 2011gl049999 we have examined the variability of thermal emission from three of io s volcanoes pele janus patera and kanehekili fluctus at pele the 5 m thermal emission as derived from 28 night time observations is remarkably steady at 37 10 gw m 1 re affirming previous analyses that suggested that pele an active rapidly overturning silicate lava lake janus patera also exhibits relatively steady 5 m thermal emission 20 3 gw m 1 in the four observations where janus is resolved from nearby kanehekili fluctus janus patera might contain a pele like lava lake with an effusion rate qf of 40 70 m3 s 1 it should be a prime target for a future mission to io in order to obtain data to determine lava eruption temperature kanehekili fluctus has a thermal emission spectrum that is indicative of the emplacement of lava flows with insulated crusts effusion rate at kanehekili fluctus dropped by an order of magnitude from 95 m3 s 1 in mid 1997 to 4 m3 s 1 in late 2001

the zamama thor region of io insights from a synthesis of mapping topography and galileo spacecraft data abstract we have studied data from the galileo spacecraft s three remote sensing instruments solid state imager ssi near infrared mapping spectrometer nims and photopolarimeter radiometer ppr covering the zamama thor region of io s antijovian hemisphere and produced a geomorphological map of this region this is the third of three regional maps we are producing from the galileo spacecraft data our goal is to assess the variety of volcanic and tectonic materials and their interrelationships on io using planetary mapping techniques supplemented with all available galileo remote sensing data based on the galileo data analysis and our mapping we have determined that the most recent geologic activity in the zamama thor region has been dominated by two sites of large scale volcanic surface changes the zamama eruptive center is a site of both explosive and effusive eruptions which emanate from two relatively steep edifices zamama tholi a and b that appear to be built by both silicate and sulfur volcanism a 100 km long flow field formed sometime after the 1979 voyager flybys which appears to be a site of promethean style compound flows flow front so2 plumes and adjacent sulfur flows larger possibly stealthy plumes have on at least one occasion during the galileo mission tapped a source that probably includes s and or cl to produce a red pyroclastic deposit from the same vent from which silicate lavas were erupted the thor eruptive center which may have been active prior to voyager became active again during the galileo mission between may and august 2001 a pillanian style eruption at thor included the tallest plume observed to date on io at least 500 km high and new dark lava flows the plume produced a central dark pyroclastic deposit probably silicate rich and an outlying white diffuse ring that is so2 rich mapping shows that several of the new dark lava flows around the plume vent have reoccupied sites of earlier flows unlike most of the other pillanian eruptions observed during the galileo mission the 2001 thor eruption did not produce a large red ring deposit indicating a relative lack of s and or cl gases interacting with the magma during that eruption between these two eruptive centers are two paterae thomagata and reshef thomagata patera is located on a large shield like mesa and shows no signs of activity in contrast reshef patera is located on a large irregular mesa that is apparently undergoing degradation through erosion perhaps from so2 sapping or chemical decomposition of sulfur rich material from multiple secondary volcanic centers

geologic mapping of the amirani gish bar region of io implications for the global geologic mapping of io abstract we produced the first geologic map of the amirani gish bar region of io the last of four regional maps generated from galileo mission data the amirani gish bar region has five primary types of geologic materials plains mountains patera floors flows and diffuse deposits the flows and patera floors are thought to be compositionally similar but are subdivided based on interpretations regarding their emplacement environments and mechanisms our mapping shows that volcanic activity in the amirani gish bar region is dominated by the amirani eruptive center aec now recognized to be part of an extensive combined amirani maui flow field a mappable flow connects amirani and maui suggesting that maui is fed from amirani such that the post voyager designation maui eruptive center should be revised amirani contains at least four hot spots detected by galileo and is the source of widespread bright sulfur flows and active dark silicate flows being emplaced in the promethean style slowly emplaced compound flow fields the floor of gish bar patera has been partially resurfaced by dark lava flows although other parts of its floor are bright and appeared unchanged during the galileo mission this suggests that the floor did not undergo complete resurfacing as a lava lake as proposed for other ionian paterae there are several other hot spots in the region that are the sources of both active dark flows confined within paterae and so2 and s2 rich diffuse deposits mapped diffuse deposits around fractures on mountains and in the plains appear to serve as the source for gas venting without the release of magma an association previously unrecognized in this region the six mountains mapped in this region exhibit various states of degradation in addition to gaining insight into this region of io all four maps are studied to assess the best methodology to use to produce a new global geologic map of io based on the newly released combined galileo voyager global mosaics to convey the complexity of ionian surface geology we find that a new global geologic map of io should include a map sheet displaying the global abundances and types of surface features as well as a complementary gis database as a means to catalog the record of surface changes observed since the voyager flybys and during the galileo mission

tvashtar awakening detected in april 2006 with osiris at the w m keck observatory abstract we detected a volcanic outburst in io s northern hemisphere on 17 april 2006 with the osiris imaging spectrometer at keck and confirmed it was still erupting on 2 june 2006 the eruption which we name 060417a was located in tvashtar paterae 100 km southeast of the february 2000 eruption the observed temperature was 1240 4 k over a surface area of 60 5 km 2 providing a total thermal output of 7 7 0 9 10 12 w

post solidification cooling and the age of io s lava flows abstract the modeling of thermal emission from active lava flows must account for the cooling of the lava after solidification models of lava cooling applied to data collected by the galileo spacecraft have until now not taken this into consideration this is a flaw as lava flows on io are thought to be relatively thin with a range in thickness from 1 to 13 m once a flow is completely solidified a rapid process on a geological time scale the surface cools faster than the surface of a partially molten flow cooling via the base of the lava flow is also important and accelerates the solidification of the flow compared to the rate for the semi infinite approximation which is only valid for very deep lava bodies we introduce a new model which incorporates the solidification and basal cooling features this model gives a superior reproduction of the cooling of the 1997 pillan lava flows on io observed by the galileo spacecraft we also use the new model to determine what observations are necessary to constrain lava emplacement style at loki patera flows exhibit different cooling profiles from that expected from a lava lake we model cooling with a finite element code and make quantitative predictions for the behavior of lava flows and other lava bodies that can be tested against observations both on io and earth for example a 10 m thick ultramafic flow like those emplaced at pillan patera in 1997 solidifies in 450 days at which point the surface temperature has cooled to 280 k and takes another 390 days to cool to 249 k observations over a sufficient period of time reveal divergent cooling trends for different lava bodies examples lava flows and lava lakes have different cooling trends after the flow has solidified flows cool faster thin flows solidify and cool faster than flows of greater thickness the model can therefore be used as a diagnostic tool for constraining possible emplacement mechanisms and compositions of bodies of lava in remote sensing data

tidally induced lateral variations of io s interior abstract satellite and recent earth based observations of io s surface reveal a specific spatial pattern of persisting hotspots and sudden high intensity events io s major heat producing mechanism is tidal dissipation which is thought to be non uniformly distributed within io s mantle and asthenosphere the question arises to what extent io s non homogeneous heat production can cause long wavelength variations in the interior and volcanic activity at the surface we investigate dissipation patterns resulting from two different initially spherical symmetric visco elastic rheological structures which are consistent with geodetic observations the spatial distributions of the time averaged tidal heat production are computed by a finite element model whereas for the first rheological structure heat is produced only in the upper viscous layer asthenosphere heating model the second rheological structure results in a more evenly distributed dissipation pattern mixed heating model with tidal heating occurring in the deep mantle and the asthenosphere to relate the heat production to the interior temperature and melt distribution we use steady state scaling laws of mantle convection and a simple melt migration model the resulting long wavelength thermal heterogeneities strongly depend on the initial tidal dissipation pattern the thickness of the convective layer the mantle viscosity and the ratio between magmatic and convective heat transport while for the asthenosphere heating model a strong lateral temperature signal with up to 190 k peak to peak difference can remain convection within a thick convective layer as for the mixed heating model can reduce the lateral temperature variation to

regional stress field of the indian plate we have calculated the regional stress field in the indian plate implementing dependence of slab pull and ridge push on the age of the oceanic lithosphere in the finite element procedure the high level of the calculated stress field order of a few kbar and the dominance of compression in the plate are consequences of the unique dynamic situation of the present day indian plate the calculated stress field explains the concentration of intraplate deformation in the region of the ninetyeast ridge and yields insight into the variations in stress directions in the australian continent

high temperature silicate volcanism on jupiter s moon io infrared wavelength observations of io by the galileo spacecraft show that at least 12 different vents are erupting lavas that are probably hotter than the highest temperature basaltic eruptions on earth today in at least one case the eruption near pillan patera two independent instruments on galileo show that the lava temperature must have exceeded 1700 kelvin and may have reached 2000 kelvin the most likely explanation is that these lavas are ultramafic magnesium rich silicates and this idea is supported by the tentative identification of magnesium rich orthopyroxene in lava flows associated with these high temperature hot spots

volcanic hotspots on io stability and longitudinal distribution we report the first results of a program to determine the longitudinal distribution of volcanic activity on jupiter s satellite io infrared measurements at 8 7 10 and 20 micrometers have been taken at a variety of orbital longitudes strong variation in the 8 7 and 10 micrometer flux with longitude demonstrates that infrared emission arising from volcanic hotspots on io is strongly concentrated in a few locations analysis of these data suggests that the active volcanic regions observed by the voyager experimenters are still active particularly the region around the feature known as loki another source of flux although of somewhat smaller magnitude is indicated on the opposite hemisphere if these sources are the only major volcanic centers on io then current global heat flow estimates must be revised downward however heat flow from as yet unobserved longitudes hotspots at high latitudes and conducted heat flow must still be measured

the galilean satellites nasa s galileo mission to jupiter and improved earth based observing capabilities have allowed major advances in our understanding of jupiter s moons io europa ganymede and callisto over the past few years particularly exciting findings include the evidence for internal liquid water oceans in callisto and europa detection of a strong intrinsic magnetic field within ganymede discovery of high temperature silicate volcanism on io discovery of tenuous oxygen atmospheres at europa and ganymede and a tenuous carbon dioxide atmosphere at callisto and detection of condensed oxygen on ganymede modeling of landforms seen at resolutions up to 100 times as high as those of voyager supports the suggestion that tidal heating has played an important role for io and europa

background heatflow on hotspot planets io and venus on planets where most of the heat is transported to the surface by igneous activity extrusive volcanism or near surface intrusions the surface heatflow at localities well away from regions of current igneous activity need not be even approximately the conductive heatflow through the entire lithosphere but may instead be dominated by the residual heat leaking out from the last igneous event in that locality on io it is likely that 1 2 lithosphere thickness thermal diffusivity typical time between resurfacing events and the background heatflow may be very large comparable or even larger than the current observational heatflow which is associated with the hotspots alone this upward revision of io s heatflow is compatible with observations and with recent indications of a non steady tidal and thermal evolution on venus 1 2 is probably comparable to the lithosphere thickness and the resulting upward revision of heatflow may be only marginally significant unless magmatic activity is enormously greater than on earth

volcanism on io estimation of eruption parameters from galileo nims data 1 galileo near infrared mapping spectrometer nims data of volcanic thermal emission are analyzed to determine the power output of a number of ionian volcanoes from which are calculated volumetric eruption rates a two temperature model is used to determine surface temperatures and power output portions of prometheus and six other volcanoes are found to be in excess of 1100 k areas of prometheus are at temperatures close to 1500 k these are minimum eruption temperatures and are consistent with basaltic silicate volcanism for the 14 volcanoes in g1innspec01 volumetric eruption rates e are constrained between 3 and 300 m3 s for basaltic and ultramafic compositions actual e values lie between these limits the small crack fractions hot area to warm area ratio implied from these fits are indicative of a relatively quiescent eruption style such as the emplacement of a pahoehoe or a a flow field the volumetric eruption rates derived from the nims data are greater than those observed in similar styles of volcanism on earth it is apparent that for similar eruption styles the areal extent of activity is greater on io than on earth derived flow thicknesses range from 0 1 to 13 m

color and morphology of lava flows on io abstract analyses of color and morphologic changes in voyager images of lava flows on io were conducted to extend previous flow studies to additional volcanoes in preparation for comparison to galileo data blue and orange filter images of atar daedalus and ra paterae were examined to identify systematic downflow decreases in blue orange reflectivity suggested in earlier studies as diagnostic of color changes in cooled sulfur flows analyses of the color and morphology of 21 lava flows were conducted at these volcanoes with additional morphologic analysis of lava flows at agni masaaw mbali shoshu and talos paterae a total of 66 lava flows of up to 245 km in length were mapped to identify morphologic changes consistent with the rheologic changes expected to occur in sulfur flows although downflow color changes are observed the trends are not consistent even at the same edifice individual flows exhibit a statistically significant increase in blue orange ratio decrease in blue orange ratio or a lack of progressive downflow color variation color changes have similar magnitudes downflow and across flow and the color ranges observed are similar from volcano to volcano suggesting that similar processes are controlling color ratios at these edifices in addition using flow widening and branching as an indicator of the low viscosity exhibited by sulfur cooling from high temperatures these flows do not exhibit morphologic changes consistent with the systematic behavior expected from the simple progressive cooling of sulfur

evaluation of sulfur flow emplacement on io from galileo data and numerical modeling galileo images of bright lava flows surrounding emakong patera have been analyzed and numerical modeling has been performed to assess whether these flows could have resulted from the emplacement of sulfur lavas on io images from the solid state imaging ssi camera show that these bright white to yellow emakong flows are up to 370 km long and contain dark sinuous features that are interpreted to be lava conduits 300 500 m wide and 100 km long near infrared mapping spectrometer nims thermal emission data yield a color temperature estimate of 344 k 60 k 131 c within the emakong caldera we suggest that these bright flows likely resulted from either sulfur lavas or silicate lavas that have undergone extensive cooling pyroclastic mantling and or alteration with bright sulfurous materials the emakong bright flows have estimated volumes of 250 350 km3 similar to some of the smaller columbia river basalt flows if the emakong flows did result from effusive sulfur eruptions then they are orders of magnitude greater in volume than any terrestrial sulfur flows our numerical modeling results show that sulfur lavas on io could have been emplaced as turbulent flows which were capable of traveling tens to hundreds of kilometers consistent with the predictions of sagan 1979 and fink et al 1983 our modeled flow distances are also consistent with the measured lengths of the emakong channels and bright flows modeled thermal erosion rates are 1 4 m d 1 for flows erupted at 140 180 c which are consistent with the melting rates of kieffer et al 2000 the emakong channels could be thermal erosional in nature however the morphologic signatures of thermal erosion channels cannot be discerned from available images there are planned galileo flybys of io in 2001 which provide excellent opportunities to obtain high resolution morphologic and color data of emakong patera such observations could along with further modeling provide additional information to better constrain whether sulfur lavas produced the emakong flows