the temperature and width of an active fissure on enceladus measured with cassini vims during the 14 april 2012 south pole flyover abstract the width and temperature of the active fissures on saturn s satellite enceladus provide key observable constraints on physical models of these geyser like eruptions we analyze a sequence of high spatial resolution near infrared spectra acquired with vims at 0 025 s intervals during a 74 km altitude flyover of the south pole of enceladus by the cassini spacecraft on 14 april 2012 utc a thermal emission spectrum covering 3 to 5 m wavelengths was detected as the field of view crossed one of the four major fissures baghdad sulcus within 1 km of 82 36s latitude and 28 24w longitude we interpret this spectrum as thermal emission from a linear fissure with temperature 197 20 k and width 9 m at the above wavelengths the spectrum is dominated by the warmest temperature component looking downward into the fissure at only 13 from the vertical we conclude that our results measure the temperature of the interior fissure walls and the h 2 o vapor at depths within 40 m of the surface

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

fluid volcanism on miranda and ariel flow morphology and composition several types of volcanic units have been recognized on the icy uranian satellites miranda and ariel on miranda ridges characterized by crest grooves are up to 10 km wide and 500 m high a continuous flat topped flow band also 10 km wide and 500 m high forms the outer southern margin of elsinore corona elsinore coronae at least appears to comprise coalesced flow bands and ridges on ariel in addition to at least one ridge unit similar to these on miranda flood plains material has covered the floors of deep chasmata grabens and an irregular depression flows on both satellites are characterized by linear vent geometries and distinct topographic margins which indicate extrusion of a relatively viscous material the topography of the flows can be used to estimate flow viscosity or yield strength using a bingham plastic model extrusion viscosity estimates incorporating plausible volcanologically based emplacement time scales and a rigid crust correction range from 107 to 109 p 1013 p in the unlikely absence of a chilled crust viscosity estimates are dependent on the assumed emplacement time scale however and could be as high as 1016 p if a solid stale based time scale is assumed bingham models indicate that it is yield strength that controls the final flow width and thickness that we see yield strength estimates are probably more reliable because of uncertainties in the viscous flow time scale yield strength estimates range from 10 1 to 10 2 bars consistent with yield strengths of partially crystallized silicate melts on other planets nevertheless both the viscosities and yield strengths are well within the range of and in some cases lower than silicate flows silicate compositions are not possible for these flows because of the ice rich composition of these satellites measured properties of ammonia water liquid crystal mixtures are consistent with the observed and estimated flow rheologic properties however and extrusion of such material s is a viable alternative to solid state extrusion for the origin of these flow features

metasomatic clathrate xenoliths as a possible source for the south polar plumes of enceladus abstract the composition and abundance of volatile gases observed in the jets emanating from fissures near the south pole of saturn s moon enceladus are strongly indicative of outgassing from clathrate hydrates which formed as a result of hydrothermal activity rather than nebula condensation i suggest that fluids must be able to permeate the ice shell extensively metasomatising the mantle by emplacement of clathrates along fractures and grain boundaries which subsequently are entrained in rising cryomagmas as xenoliths these are carried upwards to the point where they dissociate releasing their gas load into the magma and promoting the vigorous ice fountaining observed a direct analogue of terrestrial basaltic fire fountains caused by volatile exsolution this clathrate xenolith model can explain the measured volatile abundances eruption velocities the ice to vapour ratio in the plumes and the vent temperatures

prerequisites for explosive cryovolcanism on dwarf planet class kuiper belt objects explosive extrusion of cold material from the interior of icy bodies or cryovolcanism has been observed on enceladus and perhaps europa triton and ceres it may explain the observed evidence for a young surface on charon pluto s surface is masked by frosts here we evaluate prerequisites for cryovolcanism on dwarf planet class kuiper belt objects kbos we first review the likely spatial and temporal extent of subsurface liquid proposed mechanisms to overcome the negative buoyancy of liquid water in ice and the volatile inventory of kbos we then present a new geochemical equilibrium model for volatile exsolution and its ability to drive upward crack propagation this novel approach bridges geophysics and geochemistry and extends geochemical modeling to the seldom explored realm of liquid water at subzero temperatures we show that carbon monoxide co is a key volatile for gas driven fluid ascent whereas co 2 and sulfur gases only play a minor role n 2 ch 4 and h 2 exsolution may also drive explosive cryovolcanism if hydrothermal activity produces these species in large amounts a few percent with respect to water another important control on crack propagation is the internal structure a hydrated core makes explosive cryovolcanism easier but an undifferentiated crust does not we briefly discuss other controls on ascent such as fluid freezing on crack walls and outline theoretical advances necessary to better understand cryovolcanic processes finally we make testable predictions for the 2015 new horizons flyby of the pluto charon system

thermal diffusivity of upper mantle rocks influence of temperature pressure and the deformation fabric 1 thermal diffusivity measurements of seven naturally deformed upper mantle rocks were made as a function of pressure up to 1 gpa temperature up to 1250 k and the deformation fabric of the samples for each sample the strain induced crystal preferred orientations of olivine and pyroxenes were measured and petrophysical models based on the thermal diffusivity tensors of the olivine and enstatite crystals were used to evaluate the three dimensional distribution of the thermal diffusivity both model predictions and measurements show that the anisotropy of thermal diffusivity remains large at the rock scale 15 28 depending on the strength of the olivine crystallographic fabric the direction of maximum thermal diffusivity is parallel to the lineation flow direction and the minimum of thermal diffusivity is normal to the foliation plane flow plane this anisotropy is preserved at high temperature and pressure however measured thermal diffusivities are 20 30 lower than model predictions this discrepancy between measurements and model predictions cannot be explained by the presence of cracks in the samples because the closure of these void spaces evaluated through the high pressure experiments is found to have a negligible effect on measured thermal diffusivities thermal diffusivity for all samples displays a weak linear dependence on pressure of 10 gpa 1 thermal diffusivities observed in the high temperature experiments 1000 1250 k are compatible with a weak radiative contribution to the total heat diffusion

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

solid state ice volcanism on the satellites of uranus voyager images of the uranian satellites ariel and miranda show flow features with morphologies indicating that ice has been extruded to the satellites9 surfaces in the solid state these images provide the first observational evidence for solid state ice volcanism in the solar system topographic profiles have been measured across a number of flow features on ariel with a simple model of extrusion spreading and cooling of a viscous flow the initial viscosity of the flow material is found to have been no more than about 10 16 poise far lower than expected for h 2 o ice at the ambient surface temperatures in the uranian system sharply reduced viscosities may have resulted from incorporation of ices like nh 3 or ch 4 in the uranian satellites

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

intrusive and extrusive growth of the mount st helens lava dome lava domes grow by a combination of endogenous intrusive and exogenous extrusive addition of magma either as single continuous events1 2 or through a series of relatively small pulses which together build a larger construct3 evaluating the hazards that attend growth of a dome requires an assessment of the processes controlling whether lava is added to its interior or surface because many of these dangers depend on how volatiles are admitted to or released from hot magma if the volatile pressure inside an inflating dome becomes high enough sudden exposure provided by flow front slumping can lead to explosive decompression and the generation of pyroclastic flows4 5 on the other hand lava erupted on the oversteepened surface of a dome may collapse fragment and mix with snow or ice to form pyroclastic flows surges and mudflows6 7 here we provide a quantitative assessment of the partitioning of magma into endogenous intrusions and exogenous lobes using high resolution digital topographic maps of the mount st helens dome derived from aerial photographs taken periodically between 1980 and 1986 endogenous exogenous and total volume production rates follow distinct trends which provide important clues about the nature of eruption mechanisms calculating endogenous and exogenous components for active domes like those recently formed at redoubt volcano may help quantify magma chamber processes and provide another tool for understanding the re equilibration of shallow magmatic systems

constraining the thickness of europa s water ice shell insights from tidal dissipation and conductive cooling abstract the time of crystallization of a 100 km thick ocean on europa is estimated using a stefan style solidification solution this solution is then extended to estimate the present thickness of the ice shell it is assumed that the shell is initially in a steady state conductive regime and the ocean is taken to be an infinite liquid half space cooling from above we find that in the absence of tidal heating and without the presence of low eutectic impurities to serve as anti freezes a 100 km thick ocean solidifies in about 64 myr conversely when considering the present thickness of europa s ice shell if tidal heating is included at a global dissipation rate of 1 tw the shell is found to be on average approximately 28 km thick however if this dissipative heating is solely restricted to the shell the local rate of heating may vary significantly due to crustal compositional heterogeneities and it is shown that this process may in turn produce thermal maxima in the crust which could lead to local melting and structural instabilities perhaps associated with the formation of chaos regions our approach is also extended to ganymede and callisto in order to estimate the time of solidification of their putative subsurface oceans and the current thicknesses of their ice i shells

seismic reflection study of upheaval dome canyonlands national park utah the origin of upheaval dome in canyonlands national park of southeastern utah has been a topic of controversy among geologists and planetary scientists the structure has long been thought to have been created by salt diapirism from the underlying paradox formation recent studies have suggested that impact could have formed the dome to test the various hypotheses we acquired processed and interpreted seismic reflection data within and adjacent to the structure both conventionally stacked and prestack migrated images show 100 m relief in the paradox formation contrary to salt diapirism hypotheses further we have identified features within the images typical of impact structures such as listric normal faults having displacements toward the center of the dome deformation occurs in two depth ranges with the faulting that created the central uplift appearing only above the hermosa formation in the upper 800 m of the structure the images also suggest limited fracturing of the hermosa and salt flow in the paradox formation perhaps due to gravitational relaxation of the crater form our image of a nearly flat top of the paradox salt strongly favors an impact origin for upheaval dome

a clathrate reservoir hypothesis for enceladus south polar plume we hypothesize that active tectonic processes in the south polar terrain of enceladus the 500 kilometer diameter moon of saturn are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the cassini spacecraft advection of gas and ice transports energy supplied at depth as latent heat of clathrate decomposition to shallower levels where it reappears as latent heat of condensation of ice the plume itself which has a discharge rate comparable to old faithful geyser in yellowstone national park probably represents small leaks from this massive advective system

a possible brine reservoir beneath occator crater thermal and compositional evolution and formation of the cerealia dome and vinalia faculae abstract the dawn spacecraft has imaged several putative cryovolcanic features on ceres and several lines of evidence point to past cryovolcanic activity at occator crater it is therefore possible that cryovolcanism played a key role in delivering sodium carbonate and chloride enriched brines to ceres surface in recent geological times the detection of a 200 km 200 km negative bouguer anomaly beneath occator suggests the presence of a low density region beneath the crater if this region is a residual partially crystallized cryomagma chamber excess pressures caused by its gradual freezing or stresses produced by the occator forming impact could have facilitated the delivery of cryolavas to the surface in the geologically recent past here the progressive solidification of a cryomagma chamber beneath occator and implications for the delivery of cryolavas to the surface has been explored models for the behavior of cryolavas at ceres surface and for the formation of the cerealia dome and vinalia faculae are also presented minimal crystallization of a subsurface fluid reservoir located at the crust mantle boundary could have driven cryolavas enriched in chloride salts and nh3 to ceres surface however cryolavas enriched in sodium carbonates would have had to have existed at shallower levels in the crust in order to be delivered to the surface via pressure driven ascent depending on the size of the reservoir cryolavas could have been driven to ceres surface for tens to hundreds of millions of years after cooling of the cryomagma chamber commenced the mineralogy at occator is suggestive of subsurface cryomagma reservoirs enriched in sodium carbonate and chloride salts aqueous solutions enriched in chloride salts and or ammonia would have arrived at the surface at warm enough temperatures to erupt if transported in propagating fractures that traveled at least 10 5 m s additionally if the cerealia dome was formed from viscous cryolava extrusions bulk kinematic lava viscosities may have been between 106 108 m2 s at the onset of relaxation plausible relaxation times to form the dome which are linked to bulk cryolava rheology are found to have ranged from 2 5 to 273 days moreover the low volatile content necessary to drive explosive eruptions on ceres supports the possibility that cerealia and vinalia faculae were emplaced as a consequence of ballistic eruptions the enigmatic geology of occator crater is consistent with a diversity of exchange processes operating on ceres in the geologically recent past further the processes that have occurred at occator could shed light on the changing geology associated with a relic ocean world future studies of occator and ceres should be undertaken with these results in mind

ice covered water volcanism on ganymede eruption of liquid h2o magmas along extensional fractures and graben bounding normal faults may have played a critical role in the development of ganymede s grooved terrain the resurfacing potential of a water magma is dependent on a variety of factors including the areal extent of the source region the rate of discharge the thickness of the flow and the time that it takes the flow to completely freeze to its base in this paper the thermal evolution of such a flow is considered in detail the minimum unfrozen lifetime of a 5 m flow is approximately 12 5 days while a 10 m flow would survive for at least 50 days heating resulting from factional head loss could reasonably extend these lifetimes by 50 or more with a discharge rate of the order of 1 10 km3 d 1 an individual volcanic water flow could flood an area of 104 km2 before freezing as the flow solidifies its volume will increase thus lifting and arching its protective ice cover extensional fractures may then develop in the ice subparallel to the graben walls these fractures could result in grooves directly given a sufficiently thick 1 km flow or they may simply act to concentrate various tectonic forces that could initiate groove producing faults

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

compositional diapirism as the origin of the low albedo terrain and vaporization at midlatitude on ceres recent observations of ceres made using the heterodyne instrument for the far infrared on board the european space agency s herschel space observatory have shown that water vapor is emanated from the low albedo midlatitude regions based on the supposition that some dark spots on europa may be caused by diapirism we explored whether ceres environment also can induce compositional diapirism and whether an upwelling diapir could explain the origin and distribution of the dark spots and vaporization of ceres if the density of the rock that constitutes ceres is around 2700 kg m 3 the undifferentiated crust is stable over geological time periods at less than 180 k at a surface temperature of 170 k a diapir can reach the surface if the crust is a few tens of kilometers thick alternatively if the surface temperature is 150 k a large contrast in viscosity would prevent diapirs from reaching the surface the relatively moderate surface temperature in the midlatitude regions of ceres may be the reason for the formation of dark terrains occurring only in such areas our finite difference calculations do not show that diapirism melts the surface ice because the temperature gradient changes very little however if the observed vapor emission is caused by the sublimation of fresh ice compositional diapirism could be the mechanism that transports the fresh ice to the surface in addition to other mechanisms such as cryovolcanism diapirism is a valid hypothesis for explaining the dark terrain and vapor emissions of ceres

investigating pressure magnitudes at depth for oblique impacts into layered targets applications to terrestrial impacts in sedimentary targets the positive identification of the rock elm impact structure wisconsin usa and the upheaval dome utah usa as impact craters was complicated by a lack of distinctive shock features in the record low impedance surface layers over high impedance bedrock affect energy coupling and shock effects in the substrate in both cases removal of surface sediments erased most of the original impact structures thereby making identification of the impact origin difficult in this study a combination of laboratory and 3 d numerical experiments reveals the underlying processes controlling subsurface deformation and demonstrates that a low impedance layer can reduce expression of peak shock pressures left in the rock record as at the rock elm and the upheaval dome impact sites 3 d cth models of the rock elm impact structure predict that peak shock pressures should fall below the hugoniot elastic limit of quartz in the basement rocks yet still induce permanent deformation the model predicts peak pressures around 5 10 gpa levels consistent with field observations of shocked quartz from both rock elm and the upheaval dome consequently other impact sites exhibiting minimal shock features might be explained

origin of silicic magmas along the central american volcanic front genetic relationship to mafic melts abstract silicic pyroclastic flows and related deposits are abundant along the central american volcanic front these silicic magmas erupted through both the non continental chorotega block to the southeast and the paleozoic continental chortis block to the northwest the along arc variations of the silicic deposits with respect to diagnostic trace element ratios ba la u th ce pb oxygen isotopes nd and sr isotope ratios mimic the along arc variation in the basaltic and andesitic lavas this variation in the lavas has been interpreted to indicate relative contributions from the slab and asthenosphere to the basaltic magmas carr m j feigenson m d bennett e a 1990 incompatible element and isotopic evidence for tectonic control of source mixing and melt extraction along the central american arc contributions to mineralogy and petrology 105 369 380 patino l c carr m j and feigenson m d 2000 local and regional variations in central american arc lavas controlled by variations in subducted sediment input contributions to mineralogy and petrology 138 3 265 283 with respect to along arc trends in basaltic lavas the largest contribution of slab fluids is in nicaragua and the smallest input from the slab is in central costa rica similar trends are observed in the silicic pyroclastic deposits data from melting experiments of primitive basalts and basaltic andesites demonstrate that it is difficult to produce high k 2 o na 2 o silicic magmas by fractional crystallization or partial melting of low k 2 o na 2 o sources however fractional crystallization or partial melting of medium to high k basalts can produce these silicic magmas we interpret that the high silica magmas associated central america volcanic front are partial melts of penecontemporaneous mantle derived evolved magmas that have ponded and crystallized in the mid crust or are melts extracted from these nearly completely crystallized magmas

a hybrid model for leveed lava flows implications for eruption styles on mars 1 many channelized lava flows on the plains of mars have substantial embanking margins and levees inferred to have been stationary while the central channel was active levee formation can be attributed to two end member processes during emplacement construction during passage of the flow front and growth along the entire length of the flow while it is active it is shown here that the amount of lava that can be deposited by the flow front alone is limited estimates of the levee volume for many mars plains flows exceed this limit and must have formed by processes that continued after the passage of the front experimental studies of analogous laboratory flows also indicate a combination of both modes of emplacement a model that combines both modes of levee formation is presented including a method for estimating volumetric flow rate eruption duration and viscosity six lava flows on the plains of the tharsis volcanic province are used as illustrative examples crustal thicknesses for the six flows examined range from 9 to 23 m estimated emplacement times required to cool crusts of these thicknesses range from 1 year to 10 years corresponding viscosities are on the order of 105 106 pa s effusion rates range from 25 to 840 m3 s 1 and are all within the range of terrestrial observations therefore the large leveed plains flows on mars are not dramatically different in eruption rate or lava viscosity from large terrestrial analogs

structure and evolution of upheaval dome a pinched off salt diapir upheaval dome canyonlands national park utah is an enigmatic structure previously attributed to underlying salt doming cryptovolcanic explosion fluid escape or meteoritic impact we propose that an overhanging diapir of partly extrusive salt was pinched off from its stem and subsequently eroded many features support this inference especially synsedimentary structures that indicate jurassic growth of the dome over at least 20 m y conversely evidence favoring other hypotheses seems sparse and equivocal in the rim syncline strata were thinned by circumferentially striking low angle extensional faults verging both inward toward the center of the dome and outward near the dome s core radial shortening produced constrictional bulk strain forming an inward verging thrust duplex and tight to isoclinal circumferentially trending folds farther inward circumferential shortening predominated radially trending growth folds and imbricate thrusts pass inward into steep clastic dikes in the dome s core we infer that abortive salt glaciers spread from a passive salt stock during late triassic and early jurassic time during middle jurassic time the allochthonous salt spread into a pancake shaped glacier inferred to be 3 km in diameter diapiric pinch off may have involved inward gravitational collapse of the country rocks which intensely constricted the center of the dome sediments in the axial shear zone beneath the glacier steepened to near vertical the central uplift is inferred to be the toe of the convergent gravity spreading system

ceres predictions for near surface water ice stability and implications for plume generating processes this paper will constrain the possible sources and processes for the formation of recently observed h2o vapor plumes above the surface of the dwarf planet ceres two hypotheses have been proposed 1 cryovolcanism where the water source is the mantle and the heating source is still unknown or 2 comet like sublimation where near surface water ice is vaporized by seasonally increasing solar insolation we test hypothesis 2 comet like near surface sublimation by using a thermal model to examine the stability of water ice in the near surface for a reasonable range of physical parameters thermal inertia surface roughness and slopes we find that water ice is only stable at latitudes higher than 40 60 these results indicate that either a the physical properties of ceres are unlike our expectations or b an alternative to comet like sublimation such as the cryovolcanism hypothesis must be invoked

localized sources of water vapour on the dwarf planet 1 ceres the largest asteroid of the solar system 1 ceres has been thought to have an icy surface here it is observed to be emitting water vapour the presence of hydrated minerals on the surface of ceres the largest body in the solar system s main asteroid belt suggested that there may be water there too now infrared spectra obtained by esa s herschel space observatory provide unambiguous evidence that there is water ice at or near the surface of ceres water vapour is issuing at a rate of at least 1026 molecules per second from sources on ceres localized to mid latitude regions the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks this finding supports models that propose that the icy bodies such as comets may have migrated into the asteroid belt from beyond the notional snowline dividing the early solar system into a dry inner and icy outer regions the snowline conventionally divides solar system objects into dry bodies ranging out to the main asteroid belt and icy bodies beyond the belt models suggest that some of the icy bodies may have migrated into the asteroid belt1 recent observations indicate the presence of water ice on the surface of some asteroids2 3 4 with sublimation5 a potential reason for the dust activity observed on others hydrated minerals have been found6 7 8 on the surface of the largest object in the asteroid belt the dwarf planet 1 ceres which is thought to be differentiated into a silicate core with an icy mantle9 10 11 the presence of water vapour around ceres was suggested by a marginal detection of the photodissociation product of water hydroxyl ref 12 but could not be confirmed by later more sensitive observations13 here we report the detection of water vapour around ceres with at least 1026 molecules being produced per second originating from localized sources that seem to be linked to mid latitude regions on the surface14 15 the water evaporation could be due to comet like sublimation or to cryo volcanism in which volcanoes erupt volatiles such as water instead of molten rocks

mechanics of tidally driven fractures in europa s ice shell abstract a fracture mechanics model is developed for the initiation and propagation of a crack through a porous ice layer of finite thickness under gravitational overburden it is found that surface cracks generated in response to a tidally induced stress field may penetrate through the entire outer brittle layer if a subsurface ocean is present on europa such penetration is found to be very unlikely in the absence of an ocean a cycloidal crack would then form as a sequence of near instantaneous discrete failures each extending roughly the brittle layer thickness in range linked with a much lower apparent propagation speed set by the moving tidal stress field the implications of this porous ice fracture model for ice penetrating radar scattering loss and seismic activity are quantified

the transition from endogenous to exogenous growth of lava domes with the development of shear bands the transition from an endogenous to an exogenous regime of lava dome growth must be achieved by the formation of discontinuities within the dome such transitions and vice versa are an important characteristic of most long lived lava domes and often coincide with significant changes in the dynamics of magma supply and lava dome collapse events for the purpose of this paper following recent experimental and observational evidence we assume that such a transition occurs when shear bands are generated a model for the formation of shear bands and therefore the growth transition within a dome and coupled conduit domain is presented shear bands are most likely to initiate at the junction of the conduit and base of the dome where the shear stress experienced between new lava entering the dome and existing lava is greatest stress accumulation within the shear bands is likely to lead to brittle shear resulting in the formation of fractures finite element modelling of lava flow shows that such shear bands only develop for certain extrusion rates and lava viscosities similarly the growth regime of the lava dome will depend upon the extrusion rate and viscosity within the conduit which is largely controlled by volatile loss and the growth of crystals in the upper part of the conduit we consider a simplified rheology during lava dome growth considering isothermal conditions with crystal growth the development of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for soufriere hills volcano montserrat during october to december 1996 this lava dome forming eruption experienced a transition from endogenous to exogenous growth as it grew in height by about 90 m modelling indicates that the observed fall in magma extrusion rate from about 2 0 m3s 1 to 0 5 m3s 1 as a result of the increased pressure head from the dome and the evolution in viscosity could have subsequently changed the dome growth regime due to the development of shear bands our models provide insight into the shear stress fields possible within the conduit and the shear stresses required for shear band development

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

eruption of lava flows on europa theory and application to thrace macula europa on the basis of its spectral characteristics and its apparently young surface age is likely to be at least partially resurfaced by liquid water volcanic processes however convincing evidence for lava flow morphology in voyager data has not previously been found and the lower density of liquid water relative to an overlying solid water ice crust suggests that extrusive volcanism could be uncommon we examine a candidate lava flow like feature thrace macula and compare its characteristics with theoretical predictions for the ascent and eruption of water magma on europa outlining a range of conditions under which water ice magma could plausibly be erupted to the surface thrace macula 45 s 171 w is a dark lobate feature extending nnw to sse its northern part is centered in a 140 km diameter arcuate to circular lineament and within this zone are radial and concentric lineaments and three dark lobes similar in appearance to flow lobes extending away from a central region for distances of 40 50 and 160 km the 160 km lobe appears to follow local topographic features producing lobate margins at subdued structures broadening locally parallel to structural trends and terminating against a gray band models for the present structure and state of the predominantly h2o exterior of europa range from solid water ice to a thin ice layer overlying a liquid water layer and these conditions may even vary as a function of space and time ascent and eruption of h2o magma through a less dense water ice crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water or salt water layer exists e g crawford and stevenson 1988 kargel 1991 for flows as extensive as the thrace macula feature we thus require magma source regions sufficiently localized that excess pressure can be built up in the source region given the elastic properties of ice at these source depths the most likely scenario is intrusion of silicate magma into the base of an ice crust and melting and mobilization of water magma with this range of magma source settings we model plausible surface vent geometries for a water lava flow interpretation of thrace macula modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on europa involving discharge rates of 2 105 m3 s through dikes with widths in the range 5 10 m these discharge rates about 3 times larger than those of terrestrial flood basalts should not be unusual for water eruptions on europa under these conditions and suggest that water volcanic resurfacing could be common on the satellite if source regions meeting these criteria were readily available the lack of abundant similar dark flows could be due to brightening with time or might imply that conditions for their formation grounded or nearly solid ice crust only evolved in the latter part of europan history

pressurized oceans and the eruption of liquid water on europa and enceladus 1 it is difficult for liquid water to erupt onto the surface of icy satellites such as europa and enceladus because liquid water is more dense than ice if the ice shell thickens the volume expansion of ice upon freezing increases pressure in the subsurface ocean the excess pressure is determined by a balance between compression of ocean water and elastic expansion of the ice shell we show that on europa the freezing of 1 10 km of ice generates tangential stresses that exceed the tensile strength of ice excess pressure however is insufficient for liquid water to erupt to the surface within smaller icy satellites such as enceladus ocean pressure can become large enough to cause an eruption of large amounts of liquid water

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

modelling of possible mud volcanism on titan possible sedimentary basins on titan are potential sites for the formation of mud volcanoes in order to constrain the appearance of such features in remotely sensed imagery being acquired by the cassini spacecraft we have modelled the formation of mud volcanoes on titan for a series of plausible mud compositions climatic conditions and geological settings as well as addressing the full range of eruption variables mud viscosity conduit diameter and eruption duration we find that for an acetylene mud source containing 20 wt liquid methane in pore spaces overlain by a sheet of water ice 500 m thick a mud volcano can grow as high as 140 m assuming reasonable eruption parameters such an edifice may develop into a pancake like dome several kilometres in diameter if observed and properly characterised mud volcanoes would provide an important window on the subsurface distribution and dynamics of solids and liquids in sedimentary basins on titan

considerations for effusive cryovolcanism on europa the post galileo perspective 1 cryovolcanic resurfacing is a popular mechanism to explain relatively young surface units on icy satellites of jupiter saturn uranus and neptune prior to the galileo data acquired between 1996 and 2001 europa was thought to have undergone significant cryovolcanic resurfacing facilitated by a global ocean beneath the icy surface however close examination of galileo data at resolutions much better than those of voyager images show that many of the features previously thought to be cryovolcanic are commonly best explained by other formative mechanisms including tectonism and diapirism in this study i present an examination of the characteristics of a variety of europan surface features for which effusive cryovolcanism is a possible origin including apparently lobate flows certain elliptical to circular lenticulae and low lying smooth low albedo surfaces a review of cryovolcanic eruption theory together with galileo data analysis of europan surface geology and composition indicates that cryovolcanism is a viable though not unequivocal explanation for some of these features some constraints on cryomagma properties and lithospheric structure are offered for these cases the presence of small volume low viscosity effusions is supported by observations and modeling some positive relief lenticulae could represent more viscous effusions although diapirism may be a preferable explanation however strong evidence is lacking for cryovolcanic resurfacing on a large scale on the basis of our experience with galileo images of europa and ganymede voyager era inferences for widespread cryovolcanism on icy satellites may be overstated and will need to be carefully reexamined in the light of new data from upcoming spacecraft missions

magma degassing and intermittent lava dome growth 1 after its 1980 explosive eruption mount st helens developed a lava dome that grew intermittently for several years each growth episode was followed by a long repose suggesting that the magma column above the reservoir was in hydrostatic equilibrium a mechanism allowing an increasingly thicker dome is proposed loading of the crater floor by the dome acts to prevent gas leakage from magma by closing fractures around the volcanic conduit fractures get closed down to a depth that increases as the dome grows calculations of dome thickness as a function of dome radius are in good agreement with observations renewed growth is triggered by the spreading of the dome gas retention over a larger depth extent allows smaller magma densities and a taller magma column above the reservoir according to this model small domes can in fact promote explosive volcanic conditions and be unstable

putative ice flows on europa geometric patterns and relation to topography collectively constrain material properties and effusion rates europa s surface exhibits numerous small dome like and lobate features some of which have been attributed to fluid emplacement of ice or slush on the surface we perform numerical simulations of non newtonian flows to assess the physical conditions required for these features to result from viscous flows our simulations indicate that the morphology of an ice flow on europa will be at least partially influenced by pre existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude three classes of features can be identified on europa first some possibly most putative flow like features exhibit no influence from the pre existing topography such as ridges although their thicknesses are generally on the same order as those of ridges therefore flow processes probably cannot explain the formation of these features second some observed features show modest influence from the underlying topography these might be explained by ice flows with wide ranges of parameters ice temperatures 230 k effusion rates 10 7 m 3 year 1 and a wide range of grain sizes although surface uplift e g by diapirism and in situ disaggregation provide an equally compelling explanation third several observed features are completely confined by pre existing topographic structures on at least one side these are the best known candidates for flow features on europa if these features resulted from solid ice flows then temperatures 260 k and grain sizes 2 m are required such small grain sizes seem unlikely low viscosity flows such as ice slurries or brines provide a better explanation for these features our results provide theoretical support for the view that many of europa s lobate features have not resulted from solid ice flows