magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

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

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

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

three dimensional simulation of gas and dust in io s pele plume abstract io s giant pele plume rises high above the moon s surface and produces a complex deposition pattern we use the direct simulation monte carlo dsmc method to model the flow of so2 gas and silicate ash from the surface of the lava lake into the umbrella shaped canopy of the plume and eventually onto the surface where the flow leaves black butterfly wings surrounded by a large red ring we show how the geometry of the lava lake from which the gas is emitted is responsible for significant asymmetry in the plume and for the shape of the red deposition ring by way of complicated gas dynamic interactions between parts of the gas flow arising from different areas in the lava lake we develop a model for gas flow in the immediate vicinity of the lava lake and use it to show that the behavior of ash particles of less than about 2 m in diameter in the plume is insensitive to the details of how they are introduced into the flow because they are coupled to the gas at low altitudes we simulate dust particles in the plume to show how particle size determines the distance from the lava lake at which particles deposit on the surface and we use this dependence to find a size distribution of black dust particles in the plume that provides the best explanation for the observed black fans to the east and west of the lava lake this best fit particle size distribution suggests that there may be two distinct mechanisms of black dust creation at pele and when two log normal distributions are fit to our results we obtain a mean particle diameter of 88 nm we also propose a mechanism by which the condensible plume gas might overlay black dust in areas where black coloration is not observed and compare this to the observed overlaying of pillanian dust by pele s red ring

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

volcanic activity at tvashtar catena io abstract galileo s solid state imager ssi observed tvashtar catena four times between november 1999 and october 2001 providing a unique look at a distinctive high latitude volcanic complex on io the first observation orbit i25 november 1999 resolved for the first time an active extraterrestrial fissure eruption the brightness temperature was at least 1300 k the second observation orbit i27 february 2000 showed a large 500 km 2 region with many small hot regions of active lava the third observation was taken in conjunction with cassini imaging in december 2000 and showed a pele like annular plume deposit the cassini images revealed an 400 km high pele type plume above tvashtar catena the final galileo ssi observation of tvashtar orbit i32 october 2001 revealed that obvious to ssi activity had ceased although data from galileo s near infrared mapping spectrometer nims indicated that there was still significant thermal emission from the tvashtar region in this paper we primarily analyze the style of eruption during orbit i27 february 2000 comparison with a lava flow cooling model indicates that the behavior of the tvashtar eruption during i27 does not match that of simple advancing lava flows instead it may be an active lava lake or a complex set of lava flows with episodic overlapping eruptions the highest reliable color temperature is 1300 k although higher temperatures cannot be ruled out they do not need to be invoked to fit the observed data the total power output from the active lavas in february 2000 was at least 10 11 w

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

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

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

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

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

spatial color variations in the volcanic plume at loki on io multicolor voyager 1 photographs of the loki volcanic plume on io have been analyzed to determine the nature and quantity of the scattering material within the plume this work indicates that there are two particle populations the first population consists of particles with radius of 0 001 0 01 microns while the second population which is concentrated near the source comprises particles with radius greater than 1 micron the population of smaller particles includes most of the particulate mass in the plume this work increases the previously estimated particulate mass johnson et al 1979 and suggests that the so2 gas spectroscopically identified by pearl et al 1979 may represent transient flow from the volcano instead of an atmosphere in stable equilibrium with the local surface

cassini imaging of jupiter s atmosphere satellites and rings the cassini imaging science subsystem acquired about 26 000 images of the jupiter system as the spacecraft encountered the giant planet en route to saturn we report findings on jupiter s zonal winds convective storms low latitude upper troposphere polar stratosphere and northern aurora we also describe previously unseen emissions arising from io and europa in eclipse a giant volcanic plume over io s north pole disk resolved images of the satellite himalia circumstantial evidence for a causal relation between the satellites metis and adrastea and the main jovian ring and information on the nature of the ring particles

explosive volcanism and the graphite oxygen fugacity buffer on the parent asteroid s of the ureilite meteorites the 39 ureilite meteorites are in many respects primitive objects they are highly carbonaceous averaging 3 0 wt c mostly as graphite yet their consistently coarse grained textures and plagioclase depleted compositions imply that they are igneous despite diverse mafic silicate mg mg fe and pyroxene olivine ratios plagioclase is totally absent among 35 monomict unbrecciated ureilites even among 4 polymict brecciated ureilites the average al concentration is only 0 28 0 04 wt we suggest that the ureilites are residues from partial melting of graphite rich source materials which formed sufficiently deep in a relatively large low f o2 asteroid or more likely asteroids for graphite to be stable even at magmatic t the al rich basaltic magmas that ascended from the residues were nearly quantitatively lost from the asteroid during pyroclastic eruptions graphite entrained in the ascending magmas was oxidized by an extremely pressure sensitive reaction into cox the expansion of which into the vacuous environment of the asteroid engendered pyroclastic exit velocities greatly in excess of the asteroid s escape velocity carbon would oxidize long before the attainment of magmatic temperatures in small asteroids but we infer that basalt dissipative explosive volcanism was common on all c rich asteroids that were roughly 100 200 km in radius and heated to widespread deep melting and most unmetamorphosed chondritic meteorites are c rich based on the ureilites consistently modest depletions of light rare earth elements siderophile elements and feni metal we infer that the melt fraction was removed mostly by equilibrium batch partial melting late stage ureilite evolution involved an abrupt increase in the cooling rate implying a drop in environmental temperature and a slight amount of graphite oxidation implying a drop in pressure the simplest model to account for this non sequitur and for the conversion of some of the graphite into diamonds is catastrophic impact disruption of the primary asteroid the remarkably efficient removal of the final traces of melt from the ureilites is difficult to explain by any model but possibly was caused by thermal migration along steep thermal gradients engendered after the catastrophic disruption

long term growth of the himalaya inferred from interseismic insar measurement the rise and support of the 5000 m topographic scarp at the front of indian eurasian collision in the himalaya involves long term uplift above a mid crustal ramp within the main himalayan thrust mht system locking of the shallower portion of the flat ramp flat during the interseismic period also produces transient uplift above the transition zone however spatial and temporal relationships between permanent and transient vertical deformation in the himalaya are poorly constrained leading to an unresolved causal relationship between the two here we use interferometric synthetic aperture radar insar to measure interseismic uplift on a transect crossing the whole himalaya in central nepal the uplift velocity of 7 mm yr at the front of the annapurna mountain range is explained by an 18 21 mm yr slip rate on the deep shallow dipping portion of the mht with full locking of the mid crustal ramp underlying the high himalaya the transient uplift peak observed by insar matches spatially with the long term uplift peak deduced from the study of trans himalayan river incision although models of the seismic cycle involving thrusting over a ramp of fixed geometry predict an 20 km separation between the two peaks we argue that this coincidence indicates that today s mid crustal ramp in central nepal is located southward with respect to its average long term location suggesting that mountain growth proceeds by frontward migration of the ramp driven by underplating of material from the indian plate under the himalaya

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

volcanic plume heights on mars limits of validity for convective models 1 previous studies have overestimated volcanic plume heights on mars in this work we demonstrate that volcanic plume rise models as currently formulated have only limited validity in any environment these limits are easily violated in the current mars environment and may also be violated for terrestrial and early mars conditions we indicate some of the shortcomings of the model with emphasis on the limited applicability to current mars conditions specifically basic model assumptions are violated when 1 vertical velocities exceed the speed of sound 2 radial expansion rates exceed the speed of sound 3 radial expansion rates approach or exceed the vertical velocity or 4 plume radius grossly exceeds plume height all of these criteria are violated for the typical mars example given here solutions imply that the convective rise model is only valid to a height of 10 km the reason for the model breakdown is that the current mars atmosphere is not of sufficient density to satisfy the conservation equations it is likely that diffusion and other effects governed by higher order differential equations are important within the first few kilometers of rise when the same criteria are applied to eruptions into a higher density early mars atmosphere we find that eruption rates higher than 1 4 109 kg s also violate model assumptions this implies a maximum extent of 65 km for convective plumes on early mars the estimated plume heights for both current and early mars are significantly lower than those previously predicted in the literature therefore global scale distribution of ash seems implausible

volcanic activity on io during the galileo era abstract galileo s explorations have revealed a remarkable variety of eruptive styles among io s diverse volcanoes activity at hundreds of volcanic centers ranges from dormant through sporadic to continuous over the 20 year period of spacecraft observation high temperature volcanism is common on io suggesting that the lavas are made up of mafic to ultramafic silicates rather than sulfur compounds io s largest plumes are driven by so2 and sulfur rich gasses vented from the silicate interior that produce prominent red pyroclastic deposits red deposits flag the source regions of many other ongoing or very recent eruptions smaller plumes are produced near the margins of active lava flows by explosive volatilization of the underlying or surrounding so2 these plumes produce so2 snowflakes that mantle existing topography io s volcanism drives significant variations in the atmosphere and plasma torus yet most of the heat loss occurs through lava flows and by the quiet overturning of lava lakes without

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

the mountains of io global and geological perspectives from voyager and galileo to search for local and global scale geologic associations that may be related to the internal dynamics of lo we have completed a global catalog of all mountains and volcanic centers we have identified 115 mountain structures covering 3 of the surface and 541 volcanic centers including paterae calderas and dark spots and shield volcanoes the average length of an ionian mountain is 157 km with the longest being 570 km the mean height of ionian mountains is 6 3 km and the highest known mountain is boosaule montes 17 5 3 km five basic morphologic types of mountains have been identified mesa plateau peak ridge and massif very few mountains bear any physical similarity to classic volcanic landforms but many resemble flatiron mountains on earth and are interpreted as tilted crustal blocks this would be consistent with the hypothesis that most mountains are thrust blocks formed as a result of compressive stresses built up in the lower crust due to the global subsidence of volcanic layers as they are buried over time schenk and bulmer 1998 more than one mechanism may be responsible for all ionian mountains however the proximity of some mountains to paterae may indicate a direct link between some mountains and volcanism although it is not always clear which came first in contrast to earlier studies a pronounced bimodal pattern is observed in the global distribution of both mountains and volcanic centers the regions of highest areal densities of volcanic centers are near the sub and anti jovian regions but are offset roughly 90 in longitude from the two regions of greatest concentration of mountains this anticorrelation may indicate the overprinting of a second stress field on the global compressive stresses due to subsidence the bimodal distribution of volcanic centers and mountains is consistent with models of asthenospheric tidal heating and internal convection developed by tackley et al 2001 over regions of mantle upwelling compressive stresses in the lower crust induced by global subsidence might be reduced encouraging volcanism and discouraging mountain building in regions of mantle downwelling these compressive stresses in the lower crust might be increased discouraging volcanism and encouraging mountain building alternatively the global pattern may be related to possible but undocumented nonsynchronous rotation of lo which would produce two regions each of compression and extension in the crust evidence of layering and of mass wasting including landslides block sliding debris aprons and downslope creep on ionian mountains suggests that the crust of lo is essentially a layered stack of partially consolidated volcanic lavas and plume deposits becoming more consolidated with depth the lower crust especially may also be ductily deformed punctuated by volcanic intrusions and faulting at paterae and broken into blocks some of which have been uplifted to form mountains

geologic mapping of the hi iaka and shamshu regions of io abstract we produced regional geologic maps of the hi iaka and shamshu regions of io s antijovian hemisphere using galileo mission data to assess the geologic processes that are involved in the formation of io s mountains and volcanic centers observations reveal that these regions are characterized by several types of volcanic activity and features whose orientation and texture indicate tectonic activity among the volcanic features are multiple hotspots and volcanic vents detected by galileo one at each of the major paterae hi iaka shamshu and tawhaki we mapped four primary types of geologic units flows paterae floors plains and mountains the flows and patera floors are similar but are subdivided based upon emplacement environments and mechanisms the floors of hi iaka and shamshu paterae have been partially resurfaced by dark lava flows although portions of the paterae floors appear bright and unchanged during the galileo mission this suggests that the floors did not undergo complete resurfacing as flooding lava lakes however the paterae do contain compound lava flow fields and show the greatest activity near the paterae walls a characteristic of pele type lava lakes mountain materials are tilted crustal blocks that exhibit varied degrees of degradation lineated mountains have characteristic en echelon grooves that likely formed as a result of gravitational sliding undivided mountains are partially grooved but exhibit evidence of slumping and are generally lower elevation than the lineated units debris lobes and aprons are representative of mottled mountain materials we have explored the possibility that north and south hi iaka mons were originally one structure we propose that strike slip faulting and subsequent rifting separated the mountain units and created a depression which by further extension during the rifting event became hi iaka patera this type of rifting and depression formation is similar to the mechanism of formation of terrestrial pull apart basins with comparison to other regional maps of io and global studies of paterae and mountains this work provides insight into the general geologic evolution of io

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

fracture energies at the rupture nucleation points of large strike slip earthquakes on the xianshuihe fault southwestern china abstract earthquake cycles along a pure strike slip fault were numerically simulated using a rate and state dependent friction law to obtain the fracture energies at the rupture nucleation points in the model deep aseismic slip is imposed on the fault which generates recurrent earthquakes in the shallower velocity weakening friction region the fracture energy at the rupture nucleation point for each simulated earthquake was calculated using the relation between shear stress and slip which indicates slip weakening behavior the simulation results show that the relation between the fracture energy at the nucleation point and other source parameters is consistent with a theoretical approach based on fracture mechanics in that an earthquake occurs when the energy release rate at the tip of the aseismic slip zone first exceeds the fracture energy because the energy release rate is proportional to the square of the amount of deep aseismic slip during the interseismic period which can be estimated from the recurrence interval of earthquakes and the deep aseismic slip rate the fracture energies for strike slip earthquakes can be calculated using this result we estimated the fracture energies at the nucleation points of large earthquakes on selected segments of the xianshuihe fault southwestern china we find that the estimated fracture energies at the rupture nucleation points are generally smaller than the values of average fracture energy for developed ruptures as estimated in previous studies suggesting that the fracture energy tends to increase with the rupture propagation distance

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