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

mechanical modeling of thrust faults in the thaumasia region mars and implications for the noachian heat flux abstract insight into the state of the early martian lithosphere is gained by modeling the topography above surface breaking thrust faults in the southern thaumasia region crater counts of key surface units associated with the faulting indicate a scarp emplacement in the late noachian early hesperian periods between 4 0 and 3 7 gyr the seismogenic layer thickness at the time of faulting is constrained to 27 35 km and 21 28 km for the two scarps investigated implying paleo geothermal gradients of 12 18 and 15 23 k km 1 corresponding to heat flows of 24 36 and 30 46 mw m 2 the heat flow values obtained in this study are considerably lower than those derived from rift flank uplift at the close by coracis fossae for a similar time period indicating that surface heat flow is a strong function of regional setting if viewed as representative for magmatically active and inactive regions the thermal gradients at rifts and scarps span the range of admissible global mean values this implies d t d z 17 32 k km 1 with the true value probably being closer to the lower bound

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

post voyager brightness variations on io imaging of io with the faint object and planetary cameras of the hubble space telescope in 1992 and 1993 at wavelengths of 3450 3700 and 4100 a shows two surface areas that have undergone significant large scale change in reflectivity since the 1979 voyager encounters the first is located in colchis regio and covers 106 km2 between longitudes 150 180 and latitudes 25 to 30 the second is centered at longitude 130 latitude 30 and extends for 105 km2 both areas have darkened by 45 since 1979 in light of the active volcanism discovered on io by the voyager 1 encounter it seems reasonable to infer that these large scale changes in surface morphology are due to some type of volcanic activity in the intervening 14 years we hypothesize two possible causes for these darkenings either large scale eruptions of the pele type have covered areas of existing so2 surface frost with new much darker deposits or previously active eruptions of the prometheus type or smaller scale venting which apparently produce so2 gas that is bright in the visible when it condenses as surface frost have become inactive

the jackass mountain group of south central british columbia depositional setting and evolution of an early cretaceous deltaic complex121this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2earth science sector ess contribution 20100280 the lower cretaceous jackass mountain group of southwestern british columbia records a complex history of deltaic and proximal marine sedimentation in a tectonically active area of the canadian cor

crustal velocity structure of the southern nechako basin british columbia from wide angle seismic traveltime inversion1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia in the batholithsonland seismic project a refraction wide angle reflection survey was shot in 2009 across the coast mountains and interior plateau of central british columbia part of the seismic profile crossed the nechako basin a jurassic cretaceous basin with potential for hydrocarbons within sedimentary strata that underlies widespread volcanic rocks along this 205 km long line segment eight large explosive shots were fired into 980 seismometers forward and inverse modelling of the traveltime data were conducted with two independent methods ray tracing based modelling of first and secondary arrivals and a higher resolution wavefront based first arrival seismic tomography material with velocities less than 5 0 km s is interpreted as sedimentary rocks of the nechako basin while velocities from 5 0 6 0 km s may correspond to interlayered sedimentary and volcanic rocks the greatest thickness of sedimentary rocks in the basin is found in the central 110 km of the profile two sub basins were id

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

martian impact crater ejecta morphologies as indicators of the distribution of subsurface volatiles 1 fresh martian impact craters display a variety of ejecta blanket morphologies the fluidized appearance of most fresh ejecta types is commonly ascribed to heating and vaporization of subsurface volatiles during crater formation we have conducted a study of the distribution of the three dominant fluidized ejecta morphologies single layer ejecta sle double layer ejecta dle and multiple layer ejecta mle within the 60 latitude zone on mars we have subdivided this region into 5 5 latitude longitude boxes and have computed the following for each box 1 percentage of craters showing any ejecta morphology as a function of total number of craters 2 percentage of sle craters as a function of craters with an ejecta morphology 3 percentage of dle craters as a function of craters with an ejecta morphology and 4 percentage of mle craters as a function of craters with an ejecta morphology we confirm previous reports that the sle morphology is the most common ejecta type within the study area constituting 70 of all ejecta morphologies over most of the study area the dle and mle morphologies are much less common but these morphologies are concentrated in localized regions of the planet using these results we discuss how subsurface volatile reservoirs may be distributed across the planet the regional variations found in this study generally correlate with the proposed locations of near surface h2o reservoirs detected by mars odyssey

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

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

io s volcanic and sublimation atmospheres abstract computer simulations of so 2 and h 2 s frost sublimation and so 2 day and nightside volcanic atmospheres on io are presented the models include a surface temperature which is a function of distance from the volcanic vent or subsolar point sublimation and condensation with a sticking coefficient of unity and a crude radiative transfer approximation the full three dimensional axisymmetric gas dynamic equations are solved numerically using a time explicit finite volume formulation neither a so 2 frost sublimation atmosphere nor a so 2 pele type eruption centered on the dayside extends into the nightside however if the volcanic emissions contain a gas with a lower condensation rate than so 2 for example h 2 s then a pele type volcanic eruption centered on the dayside can reach the terminator with the pressure required by the pioneer 10 radio occultation measurements also the atmosphere generated by a so 2 pele type volcano located at a distance of 400 km from the terminator can extend to the terminator with the required pioneer 10 radio occultation pressure an extended nightside atmosphere could be formed by horizontal flow from multiple volcanoes located on the nightside both sublimation and volcanic atmospheres produce horizontal supersonic winds away from the subsolar point or the volcanic vent the sublimation atmosphere is driven mainly by horizontal pressure gradients determined by surface temperatures the volcanic atmosphere is driven by pressure gradients determined by the source rate the near surface momentum flux for a dayside pele type volcanic atmosphere is consistent with observations of winds blowing vent emissions at 700 km from the main vent the volcanic atmosphere features a shock that forms as the gas falls supersonically toward io s surface the volcanic nightside shock comes closer to io s surface than the dayside shock no shock develops in the sublimation atmosphere sublimation and condensation produce patterns of surface deposits which are characteristic of the two types of atmospheres a sublimation atmosphere develops a resurfacing band pattern sublimation removes mass from an equatorial band of 27 of iographic latitude while condensation deposits mass poleward of 27 latitude the maximum condensation rate per io rotation period occurs at 50 iographic latitude and the rate decays to zero at 80 latitude volcanic atmospheres have condensation deposits in the form of rings that fall within the particulate plume and are caused by plume shock conditions the volcanic model is quantitatively consistent with voyager observations of ring deposits volcanic eruptions expose so 2 and other possible gaseous constituents of the plume such as sodium to sputtering by corotating torus ions in times very short 1 hr compared to diffusion and dissociation times thus the source of neutrals to the jovian magnetosphere reflects the volcanic source composition and meets the constraints imposed by multiple torus observations particularly the ratio of oxygen to sulfur furthermore the elevation of the exobase above the surface in the vicinity of volcanic vents may locally increase the neutral sputtering rate if the diversion of magnetospheric plasma flow around io is considered

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

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

bolometric albedos and diurnal temperatures of the brightest regions on io abstract using voyager imaging data we have constructed simple cylindrical maps giving the locations and estimated bolometric or bond albedos of the brightest regions on the surface of io straightforward calculations that have previously indicated a bond albedo for io as a whole of 0 50 d p simonelli and j veverka 1984 icarus 59 406 425 lead to the following highest computed albedos ab 0 5 0 6 using the mean macroscopic surface roughness of io as a whole represented by 25 and ab 0 6 0 7 if one assumes a smoother surface 5 albedos are then rescaled to correct for 1 radiometric calibration uncertainties and 2 indications from infrared observations that ab for io as a whole is closer to 0 56 the highest surface albedos then become ab 0 6 0 7 25 or a b 0 7 0 8 for 5 in any case the highest albedos are only moderately larger than the bond albedo of io as a whole so that temperatures computed for the brightest parts of the satellite are not that much colder than typical ionian surface temperatures this may limit the efficiency of regional cold trapping of so2 frost the brightest regions on io include 1 two bright patches southeast of the active vents maui and amirani which contain the brightest point on the satellite latitude 22 longitude 110 a b 0 68 for 25 2 the largest field of high albedo material on io on the equator to the north northwest and west of emakong patera longitudes 115 135 and 3 a lone bright patch at high northern latitudes latitude 65 longitude 200 likely to be one of the coldest points on the satellite the latter region which also has a strong albedo contrast with surrounding dark material may perturb locally the global flow of so2 gas modeled by ingersoll et al 1985 icarus 64 375 390 our albedo map emphasizes that throughout longitudes 0 270 the distribution of albedos on io is strongly latitude dependent bolometric albedos averaged over these longitudes show a well defined falloff from equator to pole with polar albedos on the order of 60 as large as those near the equator

global color and albedo variations on io abstract three multispectral mosaics of io have been produced from voyager imaging data a global mosaic from each of the voyager 1 and voyager 2 data sets and a high resolution mosaic of the region surrounding the volcano ra patera the mosaics are maps of normal albedo and color in accurate geometric map formats io s photometric behavior mapped with a two image technique is spatially variable especially in the bright white areas the disk integrated color and albedo of the satellite have been remarkably constant over recent decades despite the volcanic activity and the many differences between voyager 1 and 2 images acquired just 4 months apart this constancy is most likely due to the consistent occurrence of large pele type plumes with relatively dark red deposits in the region from long 240 to 360 a transient brightening southeast of pele during the voyager 1 encounter was probably due to real changes in surface and or atmospheric materials rather than to photometric behavior the intrinsic spectral variability of io as seen in a series of two dimensional histograms of the multispectral mosaics consists of continuous variation among three major spectral end members the data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur and it is closely associated with the peletype plume deposits unit 2 is strongly confined to the polar caps above about latitude 50 but its composition is unknown unit 5 is probably so 2 with relatively minor contamination it is concentrated in the equatorial region and near the long lived prometheus type plumes units 3 and 4 are gradational between units 1 and 5 in addition to so 2 and elemental sulfur other plausible components of the surface are polysulfur oxides fecl 2 na 2 s and nahs

the relation of catastrophic flooding of mangala valles mars to faulting of memnonia fossae and tharsis volcanism detailed stratigraphic relations indicate two coeval periods of catastrophic flooding and tharsis centered faulting producing memnonia fossae in the mangala valles region of mars major sequences of lava flows of the tharsis montes formation and local lobate plains flows were erupted during and between these channeling and faulting episodes first late hesperian channel development overlapped in time the tharsis centered faulting that trends north 75 to 90 e next late hesperian early amazonian flooding was coeval with faulting that trends north 55 to 70 e in some reaches resistant lava flows filled the early channels resulting in inverted channel topography after the later flooding swept through both floods likely originated from the same graben which probably was activated during each episode of faulting faulting broke through groundwater barriers and tapped confined aquifers in higher regions west and east of the point of discharge the minimum volume of water required to erode mangala valles about 5 1012 m3 may have been released through two floods that drained a few percent pore volume from a relatively permeable aquifer the peak discharges of the floods may have lasted from days to weeks the perched water discharged from the aquifer may have been produced by hydrothermal groundwater circulation induced by tharsis magmatism tectonic uplift centered at tharsis montes and compaction of saturated crater ejecta due to loading by lava flows

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

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

landform hierarchy and evolution in gorgonum and atlantis basins mars abstract this paper describes the evolution of landforms in atlantis and gorgonum basins using a geomorphologic approach which interprets landform distribution and hierarchy rather than looking at the distribution of large area 10 6 km 2 geologic sequences this study focuses on interpreting the local scale 3 km 2 cratered terrains tectono structural basins and local manifestation of exogenic processes specifically the evolution of fluvio lacustrine landforms is interpreted as being functionally subordinated to the evolution of the cratered terrains and to the tectono structural modifications of the landscape results show that three major phases of landscape evolution in atlantis and gorgonum basins can be identified a major impact cratering during the heavy bombardment period b tectonic displacements in response to volcano emplacement in the tharsis region and simultaneous landform creation by fluvial and lacustrine processes and c exogenic modification of the older landforms through weathering and eolian processes our results show that the smaller morphological features which form on the older geological units are not necessarily old themselves and can in fact be relatively recent e g amazonian the main implication of these results is that martian morphology did not form only during a period immediately following the heavy bombardment as commonly postulated but rather that landform evolution continued throughout the entire martian history

volcanic eruptions on mid ocean ridges new evidence from the superfast spreading east pacific rise 17 19 s uniform sediment cover were recovered from lava that buries older faulted terrain the boundary in lava composition coincides with a change in depth to the top of an axial magma lens seismic reflector consistent with magmas from two separate reservoirs being erupted in the same event chemical compositions from throughout the area indicate that lavas with identical compositions can be emplaced in separate volcanic eruptions within individual segments a comparison of our results to global data on submarine mid ocean ridge eruptions suggests consistent dependencies of erupted volume activated fissure lengths and chemical heterogeneity with spreading rate consistent with expected eruptive characteristics from ridges with contrasting thermal properties and magma reservoir depths index terms 3035 marine geology and geophysics midocean ridge processes 8414 volcanology eruption mechanisms 8439 volcanology physics and chemistry of magma bodies 3655 mineralogy and petrology major element composition keywords lava flow chemical heterogeneity erupted volume lava morphology side scan sonar

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

evidence of gully formation by regional groundwater flow in the gorgonum newton region mars abstract the discovery of gullies on mars suggests liquid water activity near the surface of the planet in recent times since liquid water is unstable under the present day p t martian conditions the formation mechanisms of the gullies and the source of the putative water have been a matter of debate for the last years to provide new insights into these matters we have approached the problem studying the gullies in relation to their regional setting a major point in our study relates to the geographic orientation of gullies an aspect that has been previously regarded as a crucial matter in different models and has profound implications regarding their origin we present a comprehensive and detailed survey of the gorgonum newton region and a study of the dao and nirgal vallis regions the survey was carried out with the aid of 965 high resolution moc images 752 for gorgonum newton 102 for nirgal vallis and 111 for dao vallis regions and mola derived dems we found that gullies display a clear regional pattern geographically and topographically consistent with a decreasing regional slope we interpret the results in terms of the existence of several groundwater flow systems operating at different scales which ultimately may have led to gully formation by seepage at the slopes of craters and canyons we suggest that aquifers discharging at gully systems may have recharged from the surface in response to the melting of young partially eroded ice rich deposits

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

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

dynamics of triton s atmosphere the recent voyager encounter established certain facts about triton s atmosphere the surface pressure is in the range 1 5 1 9 pa 15 19 bar the surface temperature is 38 3k ref 2 molecular nitrogen is the dominant atmospheric constituent hazes and clouds are visible not only on the limb but also against the surface the wind in the southern hemisphere is to the northeast at low altitudes as shown by streaks on the surface and to the west at high altitudes as shown by geyser like plume tails triton rotates with a period of 5 877 days in a right hand sense about the south pole where the season now is late spring4 here we argue that these features can be explained if triton like mars has a global well structured atmosphere in equilibrium with surface frosts the subliming frost cap produces a polar anticyclone at low altitudes with northeastward winds of 5 m s 1 within the ekman boundary layer the temperature contrast between the cold frost covered pole and the warm unfrosted equator produces westward winds at high altitudes

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

geology and activity around volcanoes on io from the analysis of nims spectral images abstract the last two successful flybys of io by galileo in 2001 orbits i31 i32 allowed the near infrared mapping spectrometer to enrich its collection of ir spectral image cubes of the satellite these data cover hemispheric portions of io several volcanic centers as well as their surroundings with a spatial resolution ranging from 2 to 93 km pixel 1 they map thermal emission from the hot spots and the distribution of solid so 2 in the 1 0 4 7 m spectral range we obtain maps of so 2 abundance and granularity from the nims data using the method of doute et al 2002 icarus 158 460 482 the maps are correlated to distinguish four different physical units that indicate zones of so 2 condensation metamorphism and sublimation we relate these information with visible images from galileo s solid state imaging system and with detailed mapping of the thermal emission produced by io s surface our principal goal is to understand the mechanisms controlling how lava pyroclastics and gas are emitted by different types of volcanoes and how these products evolve the 800 km diameter white ring of fallout created by a violent pillanian eruption during summer of 2001 is at least partly composed of solid so 2 and has enriched preexisting regional deposits orange materials have been recently or are currently emplaced 240 km south from the main eruption site possibly as sulfur flows a similar event may have taken place in the past at ababinili patera 12 5 n 142 w carefull study of so 2 maps covering the emakong region also suggests that sulfur forms the bright channel fed flow emerging from the south eastern side of the caldera within the main caldera of tvashtar catena completely cooled patches of crust exist elsewhere the caldera is still cooling from previous episodes of flooding we confirm that amirani emits constantly large amount of so 2 gas by interaction of fresh lava with the volatiles of the underlying plains nevertheless so 2 frost is not the major component of the bright white ring seen in the ssi images over the whole gish bar region so 2 frost seems barely stable and is constantly regenerated the stability increases along gray filamentary structures which could be faults filled with materials having peculiar thermal properties northwest of gish bar patera a localized bright deposit shows an unusual spectral signature potentially indicative of h 2 o molecules forming ice crystals or being trapped in a nonidentified matrix the chaac region may present a thickened old crust reducing the geothermal flux to levels lower than 0 5 w m 2 and thus creating a cold trap for so 2 looking at the abundance and degree of metamorphose of so 2 we establish the relative age of different flows and ejecta for the sobo fluctus finally the assumption that the white patches in visible images indicate so 2 rich deposits is once again challenged in the camaxtli region we identify a topographically controlled compact white deposit showing only moderate so 2 abundance in contrast we detect two spots of quite pure so 2 ice on the gray flanks of emakong furthermore the close association of fumarolic so 2 and red s 2 already noted for several volcanic centers is observed at tupan

lithostratigraphic and tectonic framework of jurassic and cretaceous intermontane sedimentary basins of south central british columbia1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia the south central intermontane belt of british columbia has a complex architecture comprising late paleozoic to mesozoic volcanic and plutonic arc magmatic suites marine and nonmarine clastic basins high grade metamorphic complexes and accretionary rocks jurassic and cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential the geology is complicated by cretaceous to eocene deformation dismemberment and dislocation the eocene to neogene history of the southern intermontane belt is dominated by non arc volcanism followed by pleistocene to recent glaciation the volcanic and glacial cover makes this a difficult region to explore for resources much recent work has involved re evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis this paper summarizes the lithological and stratigraphic fra

strike slip faults on mars observations and implications for global tectonics and geodynamics 1 the tectonic evolution of mars has been driven primarily by the interaction of tharsis induced loading stresses with a uniform contractional stress field leading to global assemblages of graben and wrinkle ridges until recently strike slip faults have appeared to be largely absent from the tectonic record we here present evidence for a new set of noachian to early hesperian strike slip faults southwest of tharsis the best preserved fault in the newly mapped set has a length of 200 km and measured lateral offset of 5 9 km we use the locations of both previously mapped and newly identified strike slip faults to investigate the tectonic and geodynamic evolution of mars we model the tectonic evolution of the planet in response to the evolving balance between the loading and contractional stresses finding widespread regions in which strike slip faulting was favored the observed tectonic history is consistent with a scenario in which loading induced stresses peaked early in mars history followed by the growth of contractional stresses leading to a shift in the preferred locus of strike slip faulting from regions southwest of tharsis in the noachian to early hesperian to northwest of tharsis in the early amazonian the contractional strain history inferred from the ages and locations of the strike slip faults is consistent with the strains calculated from models of the thermal evolution of mars in which the gradual secular cooling of the planet over time was augmented by plume induced contraction during tharsis formation in the noachian

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

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

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

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

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

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

compositional investigation of the proposed chloride bearing materials on mars using near infrared orbital data from omega mex 1 several hundred occurrences of chloride bearing salt deposits have been proposed in terrains within the southern highlands of mars on the basis ofthermal emission imaging system and thermal emission spectrometerinfrared observations the spectral identification of chloride salts by remote sensing is challenging because they are transparent over much of the thermal infrared portion of the spectrum further ambiguity arises from the diverse geologic settings in which the putative chloride bearing materials are found in order to better constrain the composition of these unique compositional units we perform a global survey of these materials in the near infrared nir domain with theobservatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer the spectral signatures of the deposits are consistent with although not specific of chlorides we do not observe olivine to be associated with the deposits which confirms that sulfides are an unlikely alternative candidate our systematic search reveals the global lack of association with hydrated minerals phyllosilicates sulfates hydrated silica except for a few deposits noteworthy in northwestern terra sirenum where a small fraction of chloride material overlaps fe mg rich clay bearing terrains even in these locations the morphology and crosscutting relationships of the deposits suggest two separate episodes of mineralization first phyllosilicates then chlorides followed by subsequent formation of sulfates our study shows that local groundwater upwelling seems to be the most frequent source for the water involved in the formation of chloride rather than surface runoff

competition between na2so4 and na sulfide in the upper crust of io the na atmosphere of io requires a na s o phase in the outer surface layers considering the various mechanisms for extraction of na to the surface the possible primary phases are na 2o na 2s x and na 2so 4 however regardless of the primary phases brought to the surface the shallow crustal recycling of material implied by the ongoing volcanism will tend to produce thermochemical equilibrium and cause all na to end up as na 2so 4 or na 2s x this hypothesis is investigated by relatively model independent thermodynamic calculations the major assumption is that material is statistically circulated to sufficiently high temperatures by burial that thermochemical equilibrium can be attained for a wide range of assumed crustal pt conditions na 2o will be converted to na 2so 4 during residence in the shallowest crustal regions dominated by liquid so 2 e g so 2 geysers or fumaroles or for any crustal regimes where so 2 and s are in comparable abundances na sulfides will be converted to na 2so 4 however in high temperature low pressure regimes with a low relative abundance of so 2 relative to s e g due to outgasing of so 2 na 2so 4 is converted to na sulfides such regimes could be relatively common on io e g associated with flows lava lakes or shallow intrusions consequently because of thermochemical equilibration in different crustal environments both na 2so 4 and na sulfides will coexist on the io surface

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

source rock potential of lower to middle jurassic black clastic sequences of the intermontane belt1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia lower to middle jurassic clastic sequences are widespread within the interior of the canadian cordillera these successions cap waning jurassic volcanism in many cordilleran arc terranes and are succeeded by clastic sequences of the intermontane basins fine grained carbonaceous lithologies which locally contain elevated levels of organic carbon characterize these clastic successions these include sections of the spatsizi formation abou member and smithers formation in northern and western bowser basin respectively ashcroft formation and equivalent strata in central quesnellia and last creek formation and junction creek rocks below the tyaughton methow basin these rocks locally contain metre thick sections with total organic carbon toc levels 5 wt and others have thicknesses approaching 100 m with toc between 3 and 5 wt thermal maturation levels are high in many sections suggesting original organic contents were greater and that these rocks may have been excellent source beds associate

galileo search for so2 frost condensation on io s nightside abstract new high quality galileo images of io s dayside and jupiterlit nightside examined for diurnal changes in violet albedo patterns and diurnal changes in hemispheric color do not provide any evidence for significant nighttime condensation of the satellite s thin so 2 atmosphere in particular the galileo images do not show the major change in io s average hemispheric color between day and night that was reported by buratti et al 1995 icarus 118 418 422 in a study of voyager data the lack of detectable nighttime frost deposition in the galileo images is not surprising given the tenuous patchy nature of io s so 2 atmosphere and the associated difficulty in producing optically thick nighttime frost layers

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

volcanic resurfacing of io post repair hst imaging abstract in march 1994 we used the newly refurbished hubble space telescope hst to obtain global imaging of io at five wavelengths between 0 34 and 1 02 m with a spatial resolution of 160 km the images provided the clearest view of io since voyager and the first systematic observations in the wavelength range 0 7 1 0 m we have produced absolutely calibrated global mosaics of io s reflectance in all our five wavelengths the near infrared images reveal that the 0 55 to 0 7 m absorption edge seen in io s disk integrated spectrum has a very different spatial distribution from the better known 0 40 to 0 50 m absorption edge studied by voyager and must be generated by a different chemical species the 0 55 to 0 7 m absorption edge is strongly concentrated in the pyroclastic ejecta blanket of the volcano pele at a few much smaller discrete spots and probably also in the polar regions the pele ejecta spectrum is consistent with the idea that s 2 o partially decomposed to s 4 and probably s 3 may be the species responsible for the 0 55 to 0 7 m absorption edge at pele and elsewhere on io though s 4 generated by other processes may also be a possibility s 2 o can be produced by high temperature decomposition of so 2 gas and the high temperature of the pele volcano may account for its concentration there spectral anomalies of comparable size and prominence are not seen around the other pele type volcanos surt and aten a s mcewen and l a soderblom 1983 icarus 55 191 217 suggesting that these volcanos if chemically similar to pele are much less active the spectrum of high latitude regions is similar to that of quenched red sulfur glass and if this similarity is not coincidental the glass may be preserved here by the low polar surface temperatures alternatively the low polar temperatures may preserve sulfur that has been reddened by radiation there are many changes in albedo patterns in the 15 years between voyager and these hst observations but these are generally subtle at hst resolution and are not strongly concentrated in longitude however there was a major brightening of a 400 km diameter region centered on ra patera between march 1994 and repeat hst observations in july 1995 which was a larger albedo change than any seen in the previous 15 years this was presumably due to a large eruption at ra patera as confirmed by galileo images long exposure eclipse images of io at 1 02 m on march 6 1994 place strong limits on the area of exposed silicate magma on io at the time of the observations

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

interpretation of structures in the southeastern nechako basin british columbia from seismic reflection well log and potential field data1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2geological survey of canada contribution 20100002 the structure and stratigraphy of the southeast nechako basin which are poorly understood primarily because of substantial volcanic cover are investigated in an analysis of seismic reflection well and potential field data formation and development of the se nechako basin resulted in sub basins containing cretaceous and eocene rocks interpretation reveals that dextral transtension in the early to middle eocene created nnw trending en echelon strike slip faults linked by pull apart basins which locally contain a thickness of eocene volcaniclastic rocks of 3 km this structural pattern is consistent with regional observations that suggest the transfer of slip from the yalakom fault to the north via a series of en echelon strike slip faults in the middle to late eocene faults associated with a change in the direction of stress echoed by the north trending right lateral fraser fault reactivated and cut earlier structures a simple model agrees with local observations that northeast directed comp

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

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

characterizing deposits emplaced by cryovolcanic plumes on europa abstract in the absence of direct observations of europa s particle plumes deposits left behind during eruptive events would provide the best evidence for recent geological activity and would serve as indicators of the best places to search for ongoing activity on the icy moon here we model the morphological and spectral signatures of europan plume deposits utilizing constraints from recent hubble space telescope observations as model inputs we consider deposits emplaced by plumes that are 1 km to 300 km tall and find that in the time between the galileo mission and the arrival of the europa clipper spacecraft plumes that are

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

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

eocene and neogene volcanic rocks in the southeastern nechako basin british columbia interpretation of the canadian hunter seismic reflection surveys using first arrival tomography geological investigation of the near surface in the southeastern nechako basin is difficult shallow seismic reflection imaging is poor due in part to an extensive cover of eocene and neogene volcanic rocks outcrops of these volcanic rocks and the primarily cretaceous bedrock are commonly obscured by quaternary deposits and vegetation estimates of near surface p wave velocity are derived from the tomographic inversion of seismic first arrivals an effective tool when seismic imaging is poor tomographic model velocities are in agreement with sonic logs and laboratory samples except for those from the neogene chilcotin group cretaceous sedimentary rocks have velocities of 2800 4200 ms 1 the eocene endako and ootsa lake groups which have velocities of 3000 4200 ms 1 are not distinguishable based on velocity the velocity the character density focus and penetration depth of rays and ties with well and surface geology constrain the subsurface extent of the endako group adjacent to well b 82 c

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

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

scarp bounded benches in gorgonum chaos mars formed beneath an ice covered lake 1 level bench like platforms edged with scarps facing the interior of the martian gorgonum chaos basin may have formed in conjunction with an ancient ice covered lake these benches however lack the typical features of shorelines associated with wave and current transport and erosion such as crescentic embayments spits barrier islands and wave cut cliffs rather the basin facing platform edges are commonly rounded and cumulate in planform often evenly encircling buttes protruding above the level of the benches the benches are postulated to have been formed by outward growth in a quiescent environment possibly by deformative lateral flow of sediment below the ice water interface in a perennially frozen lake due to the weight of the ice overburden

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

mapping so2 frost on io by the modeling of nims hyperspectral images abstract we analyze a collection of hyperspectral images of io acquired by the near infrared mapping spectrometer nims of galileo during the g2 to e16 orbits of jupiter this analysis leads to the geographical distribution and physical characterization of so 2 frost deposits over about three fourths of io s surface these deposits are excellent tracers of various phenomena including volcanic production and emission atmospheric transportation condensation metamorphism irradiation and sublimation that occur throughout the so 2 cycle we assume that the deposits of solid so 2 are optically thick and are geographically mixed with other sulfur bearing compounds we first assess the mean moderate backscattering behavior of the so 2 frost henyey greenstein phase function parameter g 0 27 0 05 using a sequence of spectra at two different locations over a large range of phase angles this behavior may indicate a granular texture with many defects or a fluffy texture second a more systematic inversion of the hyperspectral images is achieved based on a linear spectral model of pure so 2 with variable grain size mixed with a spectrally neutral unit as a result we produce two global mosaics that map so 2 frost coverage and mean grain size so 2 deposits are omnipresent on io s surface at the spatial scale of this study 200 km but the so 2 frost is concentrated within several large areas centered at medium latitudes these so 2 rich regions surface coverage higher than 60 show a longitudinal correlation with plumes located lower in latitude suggesting that these plumes are the principal sources of so 2 gas after a possible dynamic condensation around the plumes or at the equator the gas is remobilized by the solar or thermal fluxes and flows mostly latitudinally toward the coldest and nearest regions devoid of hot spots third the correlation of the distribution and grain size mosaics distinguishes four different so 2 physical units that indicate relative regional variations of condensation metamorphism and sublimation finally comparisons with voyager ultraviolet a s mcewen t v johnson d l matson and l a soderblom 1988 icarus vol 75 pp 450 478 and galileo visible p geissler a s mcewen l keszthelyi r m c lopes gautier j granahan and d p simonelli 1999 icarus vol 140 pp 256 282 observations demonstrate molecular contamination of so 2 at medium and high latitudes and that these contaminated so 2 deposits may be optically thin

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

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

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

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

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

knob fields in the terra cimmeria terra sirenum region of mars stratigraphy mineralogy and morphology abstract we investigate the stratigraphy morphology and mineralogy of five major knob fields in the region between terra cimmeria and terra sirenum on mars based on hrsc ctx moc and hirise imagery together with hyperspectral data from crism the knob fields comprise ariadnes colles atlantis chaos and gorgonum chaos and further unnamed fields of mounds they have been mapped in previous studies as hesperian or amazonian units and are located within the shoreline of the proposed eridania lake the putative source of ma adim vallis the mounds contain mg fe bearing phyllosilicates and locally al rich phyllosilicates our geological mapping shows that the knob fields have a late noachian age which indicates later phyllosilicate formation than typically observed on mars the knob fields formed by alteration of the electris deposit an airfall deposit possibly rich in basaltic glass grant j a schultz p h 1990 icarus 84 166 195 in local depressions possibly in the eridania lake the spectroscopic detection of phyllosilicates here may indicate that liquid water persisted longer in this region than elsewhere on mars the knob fields are embayed by the hesperian ridged plains numerous valleys carve into the ridged plains and document that the aqueous history of this region continued into the hesperian and amazonian the study area is traversed by the sirenum fossae these graben appear to post date the aqueous activity in the study area except in the gorgonum basin where a lake developed after their formation

stealth plumes on io we suggest that io s eruptive activity may include a class of previously undetected so2 geysers the thermodynamic models for the eruptive plumes discovered by voyager involve low to moderate entropy so2 eruptions the resulting plumes are a mixture of solid and gas which emerge from the vent and follow essentially ballistic trajectories we show that intrusion of silicate magma into buried so2 deposits can create the required conditions for high entropy eruptions which proceed entirely in the vapor phase these purely gaseous plumes would have been invisible to voyager s instruments hence we call them stealth plumes such eruptions could explain the patchy so2 atmosphere inferred from recent uv and microwave spectral observations the magma intrusion rate required to support the required gas production for these plumes is a negligible fraction of estimated global magma intrusion rates

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

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

viscous relaxation of craters within the martian south polar layered deposits abstract the south polar layered deposits pld are of fundamental importance to martian climatology as they may comprise the largest reservoir of near surface water on mars the south pld exhibit relatively young crater retention surface ages which are widely attributed to recent resurfacing however we show that both constructional and destructional resurfacing mechanisms such as dust deposition and water ice sublimation respectively are inconsistent with the size depth and spatial distributions of south pld craters we demonstrate that another process viscous creep relaxation of dusty water ice is more compatible with the observed cratering of south pld surfaces the results of our finite element relaxation simulations suggest that despite their apparent youthfulness the pld have been stable for at least several hundred million and perhaps even over a billion years consequently our modeling implies that the time scales for the formation and preservation of the layers characteristic of the south and possibly north pld are much longer than generally assumed

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

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

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

dynamics and evolution of so2 gas condensation around prometheus like volcanic plumes on io as seen by the near infrared mapping spectrometer abstract we analyze a series of spectral image cubes acquired by the galileo near infrared mapping spectrometer nims over the prometheus region of io we use so2 frost a volatile compound ubiquitous on the surface as a tracer to understand various thermodynamic and volcanic processes acting in this equatorial region here we develop a new method to derive from the 12 wavelength nims products the distribution and physical properties of solid so2 this method is based on the inversion of a bidirectional reflectance model on two observed spectral ratios sensitive to 1 the areal abundance of so2 and 2 its mean grain size as a result reliable and consistent maps of so2 abundance and granularity are obtained which can be correlated to distinguish four different physical units the distribution of these so2 units indicates zones of condensation metamorphism and sublimation linked with the thermodynamic and volcanic processes of interest our maps depict equatorial plains undisturbed by any kind of vigorous volcanic activity over 35 40 of their surface elsewhere 10 20 of the equatorial plains display abnormally low frost coverage which may imply the recent presence of positive thermal anomalies with temperatures in the range 110 200 k hot spots such as prometheus culann surya and tupan to mention the most persistent emit a great variety of gases some of which will condense at io s surface near their source regions associated fields of freshly condensed so2 are easily observed and deposits of more refractory compounds with higher e g s8 or lower e g nacl molecular weight must also be present although their exact nature is unknown three different mechanisms of emission are proposed for the volatile compounds and supported by the distribution maps these are a the interaction between flowing lava and preexisting volatile deposits on the surface b direct degassing from the lava an d c the eruption of a liquid aquifer from underground the geometric elongation of the prometheus so2 deposition ring being related to the development of a 95 km long lava field is the best illustration of mechanism a details of the progressive emplacement of the so2 ring by the associated plume are examined by the development of a semiempirical model of material deposition based on a ballistic transfer from the sources to the surface this model shows that lava emission may have been occuring at prometheus at a fairly constant rate since voyager mechanism b may operate at the hot spot surya which presents a noticeable field of fresh so2 frost but no extended lava flow finally we have noted on the northwestern flank of the volcanic edifice emakong the existence of an extremely deep 1 3 so2 absorption which is indicative of abundant pure and perhaps icy so2 deposits these could be the result of the eruption of an so2 liquid aquifer mechanism c

new geoscientific constraints on the hydrocarbon potential of the nechako chilcotin plateau of central british columbia infestation by the mountain pine beetle dendroctonus ponderosae decimated the forests of central british columbia from 1999 to 2012 severely impacting the forest industry of the nechako chilcotin plateau in response all levels of government recognized the value in developing other areas of economic activity such as hydrocarbon and mineral exploitation to support local economies exploration for resources beneath the nechako chilcotin plateau has historically been constrained by tertiary volcanic sequences and quaternary glacial deposits that obscure the underlying geology and limit geophysical imaging thus a coordinated program comprising additional geological mapping borehole data analysis and modern geophysical surveys of the area was initiated in 2006 with the objective of better defining the subsurface geology solving problems of imaging through the complex near surface and developing improved regional geological and tectonic models an initial set of papers arising from this fieldwork

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve