volcanic eruptions on io nine eruption plumes were observed over a period of 6 1 2 days during the voyager 1 encounter with io during the voyager 2 encounter 4 months later eight of these eruptions were still active the largest plume viewed by voyager 1 became inactive sometime between the two encounters however a major eruption occurred at surt sometime between the two encounters and deposited an ejecta blanket comparable in size to those associated with the largest plumes the plumes range in height from about 60 to over 300 km with corresponding ejection velocities of about 0 5 to 1 0 km s where topographic information exists plumes 1 and 8 the plume source is located on level plains rather than topographic highs and consists of either fissures or calderas with the exception of plume 1 pele the brightness distribution monotonically decreases from the core to the top of the plume the shape and brightness distribution together with the pattern of the surface deposit of at least plume 3 prometheus can be simulated by a ballistic model in which the ejection velocity is constant 0 5 km s and ejection angles vary from vertical 0 to 55 the brightness distribution of plume 1 is probably better explained by a shock front near the top of the plume numerous surface deposits similar to those associated with active plumes probably mark the sites of recent eruptions the distribution of active and recent eruptions appears to be concentrated in the equatorial regions and indicates the volcanic activity is more frequent and intense in the equatorial regions than the polar regions this suggests that the depositional rate is greater and the surface age younger in the equatorial regions which may account for the darker polar regions the geologic setting of certain plume sources and the very large reservoirs of volatiles required for the active eruptions suggests that sulphur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes

charting thermal emission variability at amirani with the galileo nims io thermal emission database nited abstract we have examined the variability of thermal emission from lava flows at amirani on io using measurements of radiant flux from detections by the galileo near infrared mapping spectrometer nims between 1996 and 2001 amirani is the longest currently active lava flow field in the solar system and a persistent thermal source in every galileo nims observation that covers its location we have quantified the thermal emission from hot spots correlated with discrete areas of new lava flow emplacement at points along the length of the amirani flow field in high spatial resolution nims observations in 2000 and 2001 where discernible the position of some effusive activity changes from orbit to orbit we find the implied style of emplacement of lava at amirani is consistent with pahoehoe like flows there is an estimated 50 decrease in discharge rate between 1997 and late 2001 perhaps linked to an outburst eruption in the amirani vicinity in february 2001 the variability of thermal emission from amirani is less than that seen at a number of other persistently active ionian volcanoes such as prometheus culann and loki patera all of these volcanoes exhibit large increases and decreases in the absolute magnitude of thermal emission see matson et al 2006 loki patera davies a g et al 2006 icarus 184 460 477 prometheus and davies a g ennis m e 2011 icarus 215 401 416 culann at amirani as at these volcanoes the thermal emission measured between 1996 and 2001 indicates a persistent although variable supply of magma to the surface in high spatial resolution nims observations of hot spots obtained in 2000 and 2001 we estimate the emitted power from active lava flows associated with amirani to be 170 30 gw which corresponds to total effusion rates assuming a basaltic composition from multiple points along the amirani flow of 34 56 m 3 s

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

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

large scale topography of io implications for internal structure and heat transfer new stereographic techniques were applied to voyager 1 images to determine the shape and large scale topography of io the best fit triaxial figure has semiaxes of 1830 0 1818 7 and 1815 3 kilometers with random errors of about 200 meters systematic navigation and optical system errors are comparable the resulting figure is consistent with a differentiated satellite in hydrostatic equilibrium the deviation from homogeneity could be explained by the presence of an iron core with a radius of about 800 km most elevations over areas larger than 500 km diameter deviate from the triaxial figure by no more than 1 km we suggest that many of these broad topographic swells and basins may be due to isostatic responses to thermal changes in the lithosphere asthenosphere system in the simplest picture increasing the heat flow converts the basal lithosphere into lower density asthenosphere resulting in isostatic uplift lithospheric thicknesses ranging from 5 to 100 km may result in elevation variations of up to 1 km if the large scale topography is positively correlated with heat flow then the global pattern of basins and swells suggests tidal dissipation in a molten or partially molten asthenosphere rather than in the mantle areas higher than 1 km may consist of low density crustal materials media regio the largest such region is centered near the equator at longitude 70

a history of high temperature io volcanism february 1995 to may 1997 ground based observations of io s infrared thermal emission between february 1995 and may 1997 show several discrete brightenings for which we can constrain locations fluxes and durations several of these were brief high temperature events with temperatures up to at least 1500 k similar to but often smaller than the rare outbursts seen previously loki io s most powerful volcano was relatively active before and probably during galileo s december 1995 io flyby was faint during most of 1996 and began a major long lived brightening between february 20 and march 12 1997 thermal emission was not seen from ra patera site of an active plume in galileo images major outbursts were seen on march 2nd and september 27 1995

a survey of io s volcanism by adaptive optics observations in the 3 8 μm thermal band 1996 1999 in this study we analyze a series of images of io obtained with the european southern observatory adaptive optics system adaptive optics near infrared system adonis at 3 8 m from 1996 to 1999 with particular emphasis on the observations carried out in late 1999 in support of the galileo flybys of io use of a new myopic deconvolution method myopic iterative step preserving algorithm mistral especially designed for planetary objects significantly improves the quality and the reliability of the reconstructed images using a simulation of artificial images of io we estimate the extent to which this algorithm is able to prevent noise amplification to better restore sharp edges and to preserve the initial photometry once this algorithm has been applied to our data and the solar reflected background has been subtracted we have 89 images of io available for search and temporal survey of the hot spots over 4 years in most cases the data acquired during two consecutive nights provide an almost global view of the surface of io we identify 20 hot spots for which we determine the coordinates and the brightness at 3 8 m as a function of time more than half of the hot spots were detected on all the images and were considered as persistent particular emphasis has been put on the brightest two hot spots loki and pele for which we obtain a center to limb variation curve a cosine curve for loki and a curve decreasing slightly faster than a cosine law for pele with possible physical interpretations the temporal variations of their activity have been derived over these 4 years and for loki compared with the results of other ground based surveys the variability of the other fainter sources has also been derived but with less accuracy we have also identified a few new hot spots some of which are transient such as a diffuse emission seen in september and november 1999 at the location of the upcoming tvashtar outburst the data are based on observations 58 f 1003 63 s 0260 and 64 s 0661 collected at the european southern observatory in la silla chile

io evidence for silicate volcanism in 1986 infrared observations of io during the 1986 apparition of jupiter indicate that a large eruptive event occurred on the leading side of io on 7 august 1986 universal time measurements made at 4 8 8 7 and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of 900 kelvin together with previously reported events these measurements indicate that high temperature volcanic activity on the leading side of io may be more frequent than previously thought the inferred temperature is significantly above the boiling point of sulfur in a vacuum 715 kelvin and thus constitutes strong evidence for active silicate volcanism on the surface of io

advanced techniques in site characterization and mining hazard detection for the underground coal industry abstract today s highly productive coal mining systems represent large capital investments careful geotechnical planning and design are essential to protect these systems and to help ensure their overall success too often however the ability of the mine operator to adequately characterize the geotechnical environment and keep up with changing geologic conditions lags the advance rate of the mining equipment seismic tomographic imaging based on the same principles as medical computer aided tomography cat scans offers the ability to identify changing geologic conditions loading patterns and the location of nearby abandoned mine workings although seismic tomography has been used for many years in the oil industry until recently its practicality in the mining industry has been limited because the processes involved interfered with mining productivity and were labor intensive in terms of data collection and interpretation new advancements in signal processing have greatly enhanced the speed resolution and range of applications of tomographic imaging in underground coal mine settings many tomography applications in the mining industry use seismic velocity and or attenuation tomography within a volume enclosed by the seismic source and receiver array although results obtained using this geometry work well in many situations recent developments in reflection tomography show promise in eliminating the requirement that the target volume be surrounded by sources receivers for example in seam seismic reflection tomography may now be used to image structures and or old workings from one general location in the mine e g face areas of mains and panel developments well ahead of planned developments largely eliminating the need to probe hole drill on regular intervals these new developments have greatly expanded the ability of the mine operator to cost effectively characterize previously inaccessible areas of the property this paper gives an overview of the theories and processes involved in seismic tomography applicable to coal mine settings recent examples are presented of tomographic imaging applied to a variety of coal mine ground control problems and old works detection in the united states and europe the applicability of both seismic refraction and seismic reflection tomography is discussed

volcanic eruptions on io heat flow resurfacing and lava composition abstract we model an infrared outburst on io as being due to a large erupting lava flow which increased its area at a rate of 1 5 10 5 m 2 sec 1 and cooled from 1225 to 555 k over the 2 583 hr period of observation the inferred effusion rate of 3 10 5 m 3 sec 1 for this eruption is very high but is not unprecedented on the earth and is similar to the high eruption rates suggested for early lunar volcanism eruptions occur 6 of the time on io these eruptions provide ample resurfacing to explain io s lack of impact craters we suggest that the large total radiometric heat flow 10 14 w and the size and temperature distribution of the thermal anomalies mcewen et al 1992 bull am astron soc 24 935 veeder et al 1994 j geophys res 99 17 095 17 162 can be accounted for by a series of silicate lava flows in various stages of cooling we propose that the whole suite of io s currently observed thermal anomalies was produced by multiple high eruptive rate silicate flows within the past century

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

the variability of volcanic activity at zamama culann and tupan patera on io as seen by the galileo near infrared mapping spectrometer abstract zamama culann and tupan patera are three large persistent volcanic centers on the jovian moon io as part of an ongoing project to quantify contributions from individual volcanic centers to io s thermal budget we have quantified the radiant flux from all suitable observations made by the galileo near infrared mapping spectrometer nims of these volcanoes in some cases filling omissions in previous analyses at zamama after a long period of cooling we see a peak in thermal emission that corresponds with new plume activity subsequently toward the end of the galileo epoch thermal emission from zamama drops off in a manner consistent with a greatly reduced eruption rate and the cooling of emplaced flows culann exhibits possible episodic activity we present the full tupan patera nims dataset and derive new estimates of thermal output and temporal behavior eruption rates at these three volcanoes are on the order of 30 m 3 s 1 consistent with a previous analysis of nims observations of prometheus and nearly an order of magnitude greater than kilauea volcano hawai i earth s most active volcano we propose that future missions to the jovian system could better constrain activity at these volcanoes and others where similar styles of activity are taking place by obtaining data on a time scale of ideally at least one observation per day observations at similar or even shorter timescales are desirable during initial waxing phases of eruption episodes these eruptions are identifiable from their characteristic spectral signatures and temporal behavior

geochronological constraint on the cambrian chengjiang biota south china the cambrian chengjiang biota of south china provides compelling fossil evidence for the rapid appearance of metazoan phyla in earth history the cambrian explosion however the timing of the chengjiang biota is poorly constrained owing to lack of datable rock materials within the maotianshan shale that yields the fossils here we integrate secondary ion mass spectrometry sims and chemical ablation isotope dilution thermal ionization mass spectrometry ca id tims u pb analyses of detrital zircons from the maotianshan shale to provide high precision geochronological constraint on the chengjiang biota the youngest group of sims u pb detrital zircon dates yields an age peak at 520 ma six zircons from this group are further dated by the ca id tims u pb technique but suggesting that they were not formed from a single zircon growth event thereby neither the age peak nor the weighted mean age defined by the youngest sims u pb dates could represent the maximum depositional age of the maotianshan shale instead the youngest ca id tims u pb date 518 03 0 69 0 71 ma 2 analytical uncertainty incorporates u pb tracer calibration uncertainty provides the first robust maximum age of the chengjiang biota this new geochronological constraint on the chengjiang biota indicates that the cambrian explosion reached its major phase around 518 03 0 69 0 71 ma demonstrating a protracted process 22 myr for the cambrian explosion supplementary material sims and ca id tims zircon u pb data are available at https doi org 10 6084 m9 figshare c 4024849

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

near infrared monitoring of io and detection of a violent outburst on 29 august 2013 abstract we present initial data from our campaign to monitor io in the near infrared beginning in august 2013 using 3 8 m adaptive optics imaging at gemini n and 2 5 m disk integrated spectroscopy at nasa s irtf conducted during 2013 2014 these observations are coincident with the isas jaxa exceed mission s continuous monitoring of the io plasma torus and will enable the speculated effects of volcanic outgassing on the torus to be observed directly in addition to enabling an assessment of the frequency and properties of large scale outbursts on 29 august 2013 we detected a powerful eruption designated 201308c on io at 223 5 2 6 w 29 1 1 8 n emitting between 15 and 25 tw this event is one of the most powerful eruptions ever seen on io and falls into the rare outburst class this was the third eruption of this type seen on io in august 2013 an unprecedented occurrence also unprecedented was the charting of the decay in thermal emission over the subsequent days and weeks modeling of the outburst spectrum places a lower bound of 1200 1300 k on the eruption temperature and is suggestive of temperatures 1900 k or higher typically associated with ultramafic lava composition the eruption is likely a highly energetic high volume lava fountain event

galileo s first images of jupiter and the galilean satellites the first images of jupiter io europa and ganymede from the galileo spacecraft reveal new information about jupiter s great red spot grs and the surfaces of the galilean satellites features similar to clusters of thunderstorms were found in the grs nearby wave structures suggest that the grs may be a shallow atmospheric feature changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on io patchy emissions were seen while io was in eclipse by jupiter the outer margins of prominent linear markings triple bands on europa are diffuse suggesting that material has been vented from fractures numerous small circular craters indicate localized areas of relatively old surface pervasive brittle deformation of an ice layer appears to have formed grooves on ganymede dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution

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

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

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

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

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

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

geologic mapping of the zal region of io abstract we produced a regional geologic map of the zal region of io s antijovian hemisphere using galileo mission data we discuss the geologic features summarize the map units and structures that are present discuss the nature of volcanic activity and present an analysis of the volcanic tectonic and gradational processes that affect the region the zal region consists of five primary types of geologic materials plains mountains paterae floors flows and diffuse deposits the flows and patera floors are similar but are subdivided based on uncertainties regarding emplacement environments and mechanisms the zal region includes two hotspots detected by galileo one along the western scarp of the zal patera volcano and one at the rustam patera volcano name submitted to iau a third hotspot at the nearby at am patera volcano name submitted to iau is the source of diffuse and pyroclastic materials that blanket north zal mons the western bounding scarp of zal patera is the location of a fissure vent that is the source of multiple silicate lava flows the floor of zal patera has been partially resurfaced by dark lava flows although portions of the patera floor appear bright and unchanged during the galileo mission this suggests that the floor did not undergo complete resurfacing as a flooding lava lake but does contain a compound flow field mountain materials exhibit stages of degradation lineated material degrades into mottled material we have explored the possibility that north and south zal mons were originally one structure we propose that strike slip faulting and subsequent rifting separated the mountain units opened a fissure which serves as a vent for lava flow and created a depression which by further extension during the rifting event became zal patera with comparison to other regional maps of io this work provides insight into the general geologic evolution of io

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

the summer 1997 eruption at pillan patera on io implications for ultrabasic lava flow emplacement galileo data and numerical modeling were used to investigate the summer 1997 eruption at pillan patera on io this event now defined as pillanian eruption style keszthelyi et al this issue included a high temperature 1600 c possibly ultrabasic 140 km high plume eruption that deposited dark orthopyroxene rich pyroclastic material over 125 000 km2 followed by emplacement of dark flow like material over 3100 km2 to the north of the caldera we estimate that the high temperature energetic episode of this eruption had a duration of 52 167 days between may and september 1997 with peak eruption temperatures around june 28 1997 galileo 20 m pixel 1 images of part of the pillan flow field show a widespread rough pitted surface that is unlike any flow surface we have seen before we suggest that this surface may have resulted from 1 a fractured lava crust formed during rapid low viscosity lava surging perhaps including turbulent flow emplacement 2 disruption of the lava flow by explosive interaction with a volatile rich substrate or 3 a combination of 1 and 2 with or without accumulation of pyroclastic materials on the surface well developed flow lobes are observed suggesting that this is a relatively distal part of the flow field shadow measurements at flow margins indicate a thickness of 8 10 m we have modeled the emplacement of putative ultrabasic flows from the summer 1997 pillan eruption using constraints from new galileo data results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50 150 km on a flat unobstructed surface which is consistent with the estimated length of the pillan flow field 60 km our modeling suggests low thermal erosion rates 20 m erosion channels was unlikely especially distal to the source we calculate a volumetric flow rate of 2 7 103 m3 s 1 which is greater than those for typical mauna loa kilauea flows but comparable to those for the 1783 laki eruption and the inferred flow rates of the roza flows in the columbia river flood basalts the differences in ultrabasic eruption styles on earth and io appear to be controlled by the different eruption environments plumes at sites of ultrabasic eruptions on io suggest strong magma volatile interactions on a low gravity body lacking an atmosphere whereas the geology at sites of komatiite eruptions on earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity