estimating eruption temperature from thermal emission spectra of lava fountain activity in the erta ale ethiopia volcano lava lake implications for observing io s volcanoes 1 we have analysed high spatial resolution and high temporal resolution temperature measurements of the active lava lake at erta ale volcano ethiopia to derive requirements for measuring eruption temperatures at io s volcanoes lava lakes are particularly attractive targets because they are persistent in activity and large often with ongoing lava fountain activity that exposes lava at near eruption temperature using infrared thermography we find that extracting useful temperature estimates from remote sensing data requires a high spatial resolution to isolate lava fountains from adjacent cooler lava and b rapid acquisition of multi color data because existing spacecraft data of io s volcanoes do not meet these criteria it is particularly important to design future instruments so that they will be able to collect such data near simultaneous data at more than two relatively short wavelengths shorter than 1 m are needed to constrain eruption temperatures resolving parts of the lava lake or fountains that are near the eruption temperature is also essential and we provide a rough estimate of the required image scale

numerical modeling of endogenic thermal anomalies on europa abstract a variety of recent resurfacing features have been observed on europa which may produce thermal anomalies detectable by a future mission however the likelihood of such a detection depends on their size and lifetimes the results of this numerical study suggest that the lifetime of a thermal anomaly associated with the emplacement of 100 m of water onto the surface of europa is several hundred years and 10 years for 10 m of water if warm ice is emplaced on the surface instead of liquid water these lifetimes decrease by up to a factor of two exploration of model parameters indicates that a thin insulating surface layer can double thermal anomaly lifetimes anomalies emplaced at a latitude of 80 can remain detectable nearly a factor of two longer than those at equatorial latitudes and anomalies on the night side can remain detectable for up to 20 longer than those on the day side high temperatures are very short lived as the surface ice cools very rapidly to below 200 k due to sublimation cooling assuming steady state resurfacing the number of detectable thermal anomalies associated with the emplacement of 100 m of water would be on the order of 10 if the typical resurfacing area is 15 km 2 if recent resurfacing is dominated by chaos regions with typical areas of 100 to 1000 km 2 and lifetimes of 1000 to 4000 years the number of detectable thermal anomalies would be on the order of 1 to 10

experimental insights into pyroclast ice heat transfer in water drained low pressure cavities during subglacial explosive eruptions subglacial explosive volcanism generates hazards that result from magma ice interaction including large flow rate meltwater flooding and fine grained volcanic ash we consider eruptions where subglacial cavities produced by ice melt during eruption establish a connection to the atmosphere along the base of the ice sheet that allows accumulated meltwater to drain the resulting reduction of pressure initiates or enhances explosive phreatomagmatic volcanism within a steam filled cavity with pyroclast impingement on the cavity roof heat transfer rates to melt ice in such a system have not to our knowledge been assessed previously to study this system we take an experimental approach to gain insight into the heat transfer processes and to quantify ice melt rates we present the results of a series of analogue laboratory experiments in which a jet of steam air and sand at approximately 300 c impinged on the underside of an ice block a key finding was that as the steam to sand ratio was increased behavior ranged from predominantly horizontal ice melting to predominantly vertical melting by a mobile slurry of sand and water for the steam to sand ratio that matches typical steam to pyroclast ratios during subglacial phreatomagmatic eruptions at 300 c we observed predominantly vertical melting with upward ice melt rates of 1 5 mm s 1 which we argue is similar to that within the volcanic system this makes pyroclast ice heat transfer an important contributing ice melt mechanism under drained low pressure conditions that may precede subaerial explosive volcanism on sloping flanks of glaciated volcanoes

evaluating sub pixel offset techniques as an alternative to d insar for monitoring episodic landslide movements in vegetated terrain article spaceborne synthetic aperture radar sar sensors obtain regular and frequent radar images from which ground motion can be precisely detected using a variety of different techniques the ability to measure slope displacements remotely over large regions can have many uses although the limitations of the most common place technique differential insar d insar must be considered prior to interpreting the final results one such limitation is the assumption that different rates of movement over a given distance cannot exceed a thresh old value dependent upon the pixel spacing of the sar images and the radar wavelength characteristic features of landslides i e the sharp boundary between stable active ground and the range of temporally variable veloc ities can exhibit high spatial displacement gradients breaking a fundamental assumption for reliable d insar analysis areas of low coherence are also known to hinder the exploitation of insar data this study assesses the capability of terrasar x spotlight terrasar x stripmap and envisat stripmap images for monitoring the slow moving shuping landslide in the densely vegetated three gorges region china in this case study the epi sodic nature of movement is shown to exceed the measurable limit for regular d insar analysis even for the highest resolution 11 day tsx spotlight interferograms a sub pixel offset time series technique applied to cor ner reflectors spot cr using only the sar amplitude information is applied as a robust method of resolving time varying displacements with verifiable offset measurements presented from tsx spotlight and tsx

shallow magma transport for the 2002 3 mt etna eruption inferred from thermal infrared surveys abstract the 26 october 2002 28 january 2003 eruption of mt etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km long eruptive fissure on the southern upper flank of the volcano the intense activity promoted rapid growth of cinder cones and several effusive vents analysis of thermal images recorded throughout the eruption allowed investigation of the distribution of vents along the eruptive fissure and of the nature of explosive activity the spatial and temporal distribution of active vents revealed phases of dike intrusion expansion geometric stabilization and drainage these phases were characterised by different styles of explosive activity with a gradual transition from fire fountaining through transitional phases to mild strombolian activity and ending with non explosive lava effusion here we interpret the mechanisms of the dike emplacement and the eruptive dynamics according to changes in the eruptive style vent morphology and apparent temperature variations at vents detected through thermal imaging this is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event

applicability of insar to tropical volcanoes insights from central america measuring volcano deformation is key to understanding the behaviour of erupting vol canoes and detecting those in periods of unrest satellite techniques provide the opportunity to do so on a global scale but with some notable exceptions the deformation of volcanoes in the tropics has been understudied relative to those at higher latitudes largely due to technical difficulties in applying interferometric synthetic aperture radar insar we perform a systematic survey of the central american volcanic arc to investigate the appli cability of interferometric synthetic aperture radar insar to volcanoes in the tropics volcano characteristics that may prevent insar measurement include 1 dense vegetation cover 2 per sistent activity and 3 steep slopes measurements of deformation are further inhibited by atmos pheric artefacts associated with 4 large changes in topographical relief we present a systematic method for distinguishing between water vapour artefacts and true deformation our data show a linear relationship c 2 cm km between the magnitudes of water vapour artefacts and volcano edifice height for high relief volcanoes e g fuego guatemala 3763 m a s l above sea level errors are of the order of 4 5 cm across the volcano s edifice but are less than 2 cm for lower relief e g masaya nicaragua 635 m a s l examples such as arenal atitlan and fuego illustrate that satellite acquisition strategies incorporating ascending and descending tracks are particularly important for studying steep sided volcanoes poor coherence is primarily associated with temporal decorrelation which is typically more rapid in southern central america where evergreen broadleaf vegetation dominates land use classification is a better predictorof decorrelation rate thanvegetationindex comparisonof coher ence for different radar wavelengths match expectations high resolution x band radar is best suited to local studies where high resolution digital elevation models dems exist while l bandwavelengths are necessary for regional surveys however this is the first time that relation ships between phase coherence and time perpendicular baseline radar wavelength and land use have been quantified on the scale of a whole volcanic arc

experimental studies of heat transfer at the dynamic magma ice water interface application to subglacially emplaced lava experiments simulating processes operating in volcano ice interactions were carried out to explain and quantify lava thermal properties and processes of heat transfer from pure lava melt to water and ice and from hot crystalline lava to water the samples used 70 200 g were obtained from an intermediate lava flow benmoreite trachyte that was emplaced under and within the outlet glacier gigjokull in the 2010 eruption of eyjafjallajokull experiments involved settings with direct contact between ice and lava and settings where melt and ice were separated by a few centimeters direct contact involved melt being emplaced on ice and ice placed on melt the direct contact experiments provided initial heat flux of up to 900 kw m 2 at an initially lava melt surface temperature of 1100 c declining to 100 kw m 2 at 200 300 c within 1 2 min while the experiments without melt ice contact yielded an initial maximum of 100 180 kw m 2 dropping to 50 80 kw m 2 in 2 3 min in other experiments where cubes of hot crystalline lava were subjected to forced convection of water at initial temperature of 20 30 c initial heat fluxes of 400 770 kw m 2 were followed by fast decline to 100 kw m 2 in 15 35 s the rate depending on cube size the hot rock experiments provided thermal conductivity values of 1 2 1 7 w m 1k 1 and diffusivity of about 9 10 7 m2s 1 values for heat flux obtained in these experiments are in the same range as those obtained from field observations of the lava emplacement in the eyjafjallajokull 2010 eruption

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

the potential of alos palsar backscatter and insar coherence for forest growing stock volume estimation in central siberia abstract the full potential of alos palsar l band interferometric insar coherence data for the estimation of forest growing stock volume gsv in the boreal forest has rarely been investigated moreover alos palsar backscatter and insar coherence have yet to be used together to delineate gsv due to the observation strategy and the high acquisition success rate over eurasia a large amount of high quality alos palsar l band data is available over siberia consequently this paper investigates the capability of alos palsar backscatter and insar coherence for the estimation of gsv in central siberia russia the potential of backscatter and coherence are directly compared using the same inventory data altogether 87 palsar images are used and eleven forest inventory sites are investigated based on this large dataset it was observed that insar coherence acquired in frozen conditions offers the highest potential for gsv estimation the saturation level for single coherence images was on average 230 m 3 ha with an average r 2 between coherence and gsv of 0 58 palsar backscatter acquired in unfrozen conditions could also estimate gsv however the saturation levels 75 100 m 3 ha and the average r 2 0 42 0 48 were lower hv backscatter offered only a slightly greater potential than hh backscatter a simple inversion approach aiming at the delineation of forest gsv maps based on the multitemporal sar data was developed and applied to five forest inventory sites this approach combines hv backscatter data acquired in unfrozen conditions and insar coherence data acquired in frozen conditions in general the produced maps feature a corrected relative rmse corr of 2 between inventory data and sar data based maps varied between 0 54 and 0 83

a persistent scatterer interpolation for retrieving accurate ground deformation over insar decorrelated agricultural fields interferometric synthetic aperture radar insar is a radar remote sensing technique for measuring surface deformation to millimeter level accuracy at meter scale resolution obtaining accurate deformation measurements in agricultural regions is difficult because the signal is often decorrelated due to vegetation growth we present here a new algorithm for retrieving insar deformation measurements over areas with severe vegetation decorrelation using adaptive phase interpolation between persistent scatterer ps pixels those points at which surface scattering properties do not change much over time and thus decorrelation artifacts are minimal we apply this algorithm to l band alos interferograms acquired over the san luis valley colorado and the tulare basin california in both areas the pumping of groundwater for irrigation results in deformation of the land that can be detected using insar we show that the ps based algorithm can significantly reduce the artifacts due to vegetation decorrelation while preserving the deformation signature

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

quantification of l band insar coherence over volcanic areas using lidar and in situ measurements abstract interferometric synthetic aperture radar insar is a powerful tool to monitor large scale ground deformation at active volcanoes however vegetation and pyroclastic deposits degrade the radar coherence and therefore the measurement of 3 d surface displacements in this article we explore the complementarity between alos palsar coherence images airborne lidar data and in situ measurements acquired over the piton de la fournaise volcano reunion island france to determine the sources of errors that may affect repeat pass insar measurements we investigate three types of surfaces terrains covered with vegetation lava flows a a pahoehoe or slabby pahoehoe lava flows and pyroclastic deposits lapilli to explain the loss of coherence observed over the dolomieu crater between 2008 and 2009 we first use laser altimetry data to map topographic variations the lidar intensity which depends on surface reflectance also provides ancillary information about the potential sources of coherence loss in addition surface roughness and rock dielectric properties of each terrain have been determined in situ to better understand how electromagnetic waves interact with such media rough and porous surfaces such as the a a lava flows produce a higher coherence loss than smoother surfaces such as the pahoehoe lava flows variations in dielectric properties suggest a higher penetration depth in pyroclasts than in lava flows at l band frequency decorrelation over the lapilli is hence mainly caused by volumetric effects finally a map of lai leaf area index produced using spot 5 imagery allows us to quantify the effect of vegetation density radar coherence is negatively correlated with lai and is unreliable for values higher than 7 5

ice melt rates by steam condensation during explosive subglacial eruptions subglacial volcanism melts cavities in the overlying ice these cavities may be flooded with meltwater or they may be fully or partially drained we quantify for the first time heat transfer rates by condensation of steam on the walls and roof of a fully or partially drained subglacial eruption cavity our calculations indicate that heat fluxes of up to 1 mw m 2 may be obtained when the bulk vapor in the cavity is in free convection this is considerably smaller than heat fluxes inferred from ice penetration rates in recent subglacial eruptions forcing of the convection by momentum transfer from an eruption jet may allow heat fluxes of up to 2 mw m 2 consistent with values inferred for the gjalp 1996 subglacial eruption vapor dominated cavities in which vapor liquid equilibrium is maintained have thermal dynamic responses that are an order of magnitude faster than the equivalent flooded cavities

active formation of chaos terrain over shallow subsurface water on europa the galileo spacecraft revealed a number of chaos regions on jupiter s moon europa where the surface terrain appears to have been disrupted from below in many places the surface contains sharp edged blocks or rafts of ice that have at some point been flipped or rotated some characteristics of these regions have been hard to explain such as the fact that the archetypal conamara chaos stands above its surroundings and contains matrix domes schmidt et al apply lessons learned from analogous processes within earth s subglacial volcanoes and ice shelves to an analysis of archival data that suggests chaos terrain forms above liquid water lenses that are perched only 3 kilometres deep within the ice shell the data suggest that ice water interactions and freeze out give rise to the varied morphology of chaos terrains implying that more water is involved than has been previously appreciated for instance the sunken topography of thera macula a large chaos area may indicate that europa is actively resurfacing over a lens comparable in volume to north america s great lakes europa the innermost icy satellite of jupiter has a tortured young surface1 2 3 4 and sustains a liquid water ocean1 2 3 4 5 6 below an ice shell of highly debated thickness1 2 3 4 5 7 8 9 10 quasi circular areas of ice disruption called chaos terrains are unique to europa and both their formation and the ice shell thickness depend on europa s thermal state1 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 no model so far has been able to explain why features such as conamara chaos stand above surrounding terrain and contain matrix domes10 18 melt through of a thin few kilometre shell3 7 8 is thermodynamically improbable and cannot raise the ice10 18 the buoyancy of material rising as either plumes of warm pure ice called diapirs1 9 10 11 12 13 14 15 or convective cells16 17 in a thick 10 kilometres shell is insufficient to produce the observed chaos heights and no single plume can create matrix domes10 18 here we report an analysis of archival data from europa guided by processes observed within earth s subglacial volcanoes and ice shelves the data suggest that chaos terrains form above liquid water lenses perched within the ice shell as shallow as 3 kilometres our results suggest that ice water interactions and freeze out give rise to the diverse morphologies and topography of chaos terrains the sunken topography of thera macula indicates that europa is actively resurfacing over a lens comparable in volume to the great lakes in north america

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

particle water heat transfer during explosive volcanic eruptions 1 thermal interaction between volcanic particles and water during explosive eruptions has been quantified using a numerical heat transfer model for spherical particles the model couples intraparticle conduction with heat transfer from the particle surface by boiling water in order to explore heat loss with time for a range of particle diameters the results are combined with estimates of particle settling times to provide insight into heat removal during eruption from samples of volcanic particles produced by explosive eruption heat removal is restricted by resistance to heat transfer from the volcanic particles with intraparticle thermal conduction important for large particles and surface cooling by boiling dominating for small particles in most cases volcanic particles approach thermal equilibrium with the surrounding fluid during an explosive eruption application of the results to a sample from the gjalp 1996 iceland eruption indicates that relative to 0 c 70 80 of the heat is transferred from the particles to boiling water during the settling time before burial in the stratigraphic succession the implication is that for subglacial explosive eruptions much of the heat content of the magma is coupled into melting ice extremely rapidly if all particles of the gjalp 1996 deposit were cooled to the local boiling point by the end of the eruption then approximately 78 of the initial heat content was removed from the erupting magma during the eruption this is consistent with calorimetric calculations based on volumes of ice melted during and after the eruption

dynamics stratigraphy and proximal dispersal of supraglacial tephra during the ice confined 2004 eruption at grimsvotn volcano iceland the basaltic phreatomagmatic eruption of grimsvotn volcano iceland in november 2004 g2004 lasted for 5 days during which time two separate vents were active significant deposition of tephra occurred in the first 45 h only we have subdivided the deposit into seven units a g on the basis of differences in texture grain size and componentry and the presence of sharp contacts between the layers the distribution of tephra lobes was used to infer the vent of origin for each unit the g2004 deposit is poorly sorted overall and consists of non vesicular to highly vesicular juvenile components units a and b comprise almost exclusively non to poorly vesicular glass fragments whereas units c g contain at least 30 vol highly vesicular pumice the proportion of non juvenile fragments increases significantly in the final unit unit f of the main phase non juvenile fragments are restricted to the coarse 0 fraction of the deposit main phase units c and e account for 80 of the total deposit volume including the entire distal portion and are interpreted to represent a mixture of 1 a widely dispersed component that fell from the upper margins of a strongly inclined 45 6 10 km high plume and 2 a locally dispersed 3 km from source component originating from pyroclastic density currents and minor tephra jets

galileo ppr observations of europa hotspot detection limits and surface thermal properties abstract the galileo photopolarimeter radiometer ppr made over 100 observations of europa s surface temperature we have used these data to constrain a diurnal thermal model and thus map the thermal inertia and bolometric albedo over 20 of the surface we find an increased thermal inertia at mid latitudes that is widespread in longitude and does not appear to correlate with geology albedo or other observables our derived thermophysical properties can be used to predict volatile stability across the surface over the course of a day and in planning of infrared instruments on future missions furthermore while observations in the thermal infrared can and have been used to find endogenic activity no such activity was detected at europa we have calculated the detection limits of these ppr observations and find that 100 km2 hotspots with temperatures of 116 1200 k could exist undetected on the surface depending on the location

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

maps of tethys thermophysical properties on 11th april 2015 cassini s composite infrared spectrometer cirs made a series of observations of tethys daytime anti saturn hemisphere over a nine hour time period during this time the sub spacecraft position was remarkably stable 0 3 s to 3 9 s 153 2 w to 221 8 w and so these observations provide unprecedented coverage of diurnal temperature variations on tethys anti saturn hemisphere in 2012 a thermal anomaly was discovered at low latitudes on tethys leading hemisphere it appears cooler during the day and warmer at night than its surroundings howett et al 2012 and is spatially correlated with a decrease in the ir3 uv3 visible color ratio schenk et al 2011 the cause of this anomaly is believed to be surface alteration by high energy electrons which preferentially bombard low latitudes of tethys leading hemisphere schenk et al 2011 howett et al 2012 paranicas et al 2014 schaible et al 2017 the thermal anomaly was quickly dubbed pac man due to its resemblance to the 1980s video game icon we use these daytime 2015 cirs data along with two sets of nighttime cirs observations of tethys from 27 june 2007 and 17 august 2015 to make maps of bolometric bond albedo and thermal inertia variations across the anti saturn hemisphere of tethys including the edge of its pac man region these maps confirm the presence of the pac man thermal anomaly and show that while tethys bolometric bond albedo varies negligibly outside and inside the anomaly 0 69 0 02 inside compared to 0 71 0 04 outside the thermal inertia varies dramatically 29 10 j m 2 k 1 s 1 2 inside compared to 9 4 j m 2 k 1 s 1 2 outside these thermal inertias are in keeping with previously published values 25 3 j m 2 k 1 s 1 2 inside and 5 1 j m 2 k 1 s 1 2 outside the anomaly howett et al 2012 a detailed analysis shows that on smaller spatial scales the bolometric bond albedo does vary increasing to a peak value at 180 w for longitudes between 100 w and 160 w the thermal inertia increases from northern to southern latitudes while the reverse is true for bolometric bond albedo the thermal inertia on tethys generally increases towards the center of its leading hemisphere but also displays other notable small scale variations these thermal inertia and bolometric bond albedo variations are perhaps due to differences in competing surface modification by e ring grains and high energy electrons which both bombard tethys leading hemisphere but in different ways a comparison between the observed temperatures and our best thermal model fits shows notable discrepancies in the morning warming curve which may provide evidence of regional variations in surface roughness effects perhaps again due to variations in surface alteration mechanisms

basalt unveiling fluid filled fractures inducing sediment intra void transport ephemerally examples from katla 1918 abstract this article documents textures within basaltic katla 1918 pyroclasts where particle filled fractures and bubbles have been observed these features are analogous to tuffisite veins particle filled fractures which represent the preserved remains of transient degassing pathways in shallow conduits such fractures have long been considered restricted to high viscosity silicic melts however through bse images and compositional maps we have identified similar tuffisite like features in crystal poor basalt pyroclasts from the 1918 ce subglacial eruption of katla iceland k1918 clast textures record transient mobility of juvenile lithic particles melt droplets and gas through magmatic fractures and connected vesicles key evidence includes 1 the presence of variably sintered fine ash particles within variably healed fractures and vesicles present in 80 of clasts analysed 2 compositional maps that reveal the presence of foreign particles within preserved and healed permeable pathways and 3 lower vesicularities immediately surrounding fracture walls suggestive of diffusive volatile loss into a permeable network the 1918 ce eruption of katla occurred under a thick glacier however the ice was quickly breached owing partly to the explosive nature of the eruption we propose that the formation and preservation of these transient permeable networks have been facilitated by rapid decompression of a relatively volatile rich magma in a confined subglacial environment with combined magmatic and phreatomagmatic fragmentation followed by rapid quenching by meltwater tuffisite veins in rhyolite demonstrate repeated fracture healing cycles which drive incremental release of overpressured gas and help to defuse explosive eruptions interestingly the permeable network at katla failed to defuse the 1918 ce eruption which involved a particularly violent subglacial eruptive phase it is unclear whether this demonstrates an inability of mafic tuffisite like features to efficiently degas magma perhaps owing to the especially transient nature of permeable pathways in low viscosity magmas or an ability to enhance fragmentation by providing infiltration pathways for external water the latter scenario may explain the rapid melting of the overlying glacier as the large surface area to volume ratio of fractured magma would allow rapid heat transfer nevertheless we document a previously unrecognised texture in basaltic magmas it is intriguing why it has not to the best of our knowledge been documented elsewhere have these permeable pathways been overlooked in the past e g mistaken for bad sample preparation or not noticed without high magnification bse images and are in fact a widespread phenomenon in subglacial and other basalts or do our samples in fact represent a rarely preserved texture either way they offer a new insight into the degassing and fragmentation of subglacial basalt

detectability of thermal signatures associated with active formation of chaos terrain on europa abstract a recent study by schmidt et al 2011 suggests that thera macula one of the chaos regions on europa may be actively forming over a large liquid water lens such a process could conceivably produce a thermal anomaly detectable by a future europa orbiter or flyby mission allowing for a direct verification of this finding here we present a set of models that quantitatively assess the surface and subsurface temperatures associated with an actively resurfacing chaos region using constraints from thera macula the results of this numerical study suggest that the surface temperature over an active chaos region can be as high as 200 k however low resolution galileo photo polarimeter radiometer ppr observations indicate temperatures below 120 k over thera macula this suggests that thera macula is not currently active unless an insulating layer of at least a few centimeters in thickness is present or activity is confined to small regions reducing the overall intensity of the thermal signature alternatively thera may have been cooling for at least 10 100 yr and still contain a subsurface lake which can take 300 000 yr to crystallize according to the present study a more sensitive instrument capable of detecting anomalies 5 k above ambient could detect activity at thera macula even if an insulating layer of 50 cm is present

the structure of oriented vegetation from polarimetric interferometry polarimetric radar interferometry is much more sensitive to the distribution of oriented objects in a vegetated land surface than either polarimetry or interferometry alone this paper shows that single baseline polarimetric interferometry can be used to estimate the heights of oriented vegetation volumes and underlying topography while at least two baselines are needed for randomly oriented volumes single baseline calculated vegetation height accuracies are in the range of 2 8 m for reasonable levels of vegetation orientation in forest canopies

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

thermodynamics and fluid dynamics of effusive subglacial eruptions we consider the thermodynamic and fluid dynamic processes that occur during subglacial effusive eruptions subglacial eruptions typically generate catastrophic floods jokulhlaups due to melting of ice by lava and generation of a large water cavity we consider the heat transfer from basaltic and rhyolitic lava eruptions to the ice for typical ranges of magma discharge and geometry of subglacial lavas in iceland our analysis shows that the heat flux out of cooling lava is large enough to sustain vigorous natural convection in the surrounding meltwater in subglacial eruptions the temperature difference driving convection is in the range 10 100 c average temperature of the meltwater must exceed 4 c and is usually substantially greater we calculate melting rates of the walls of the ice cavity in the range 1 40 m day indicating that large subglacial lakes can form rapidly as observed in the 1918 eruption of katla and the 1996 eruption of gjalp fissure in vatnajokull the volume changes associated with subglacial eruptions can cause large pressure changes in the developing ice cavity these pressure changes can be much larger than those associated with variation of bedrock and glacier surface topography previous models of water cavity stability based on hydrostatic and equilibrium conditions may not be applicable to water cavities produced rapidly in volcanic eruptions energy released by cooling of basaltic lava at the temperature of 1200 c results in a volume deficiency due to volume difference between ice and water provided that heat exchange efficiency is greater than approximately 80 a negative pressure change inhibits escape of water allowing large cavities to build up rhyolitic eruptions and basaltic eruptions with less than approximately 80 heat exchange efficiency cause positive pressure changes promoting continual escape of meltwater the pressure changes in the water cavity can cause surface deformation of the ice laboratory experiments were carried out to investigate the development of a water cavity by melting ice from a finite source area at its base the results confirm that the water cavity develops by convective heat transfer

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

surface temperature measurements of active lava flows on kilauea volcano hawai i systematic hand held radiometer measurements of lava surface temperatures in active flows and tubes on kilauea volcano hawai i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites using portable infrared minolta land cyclops radiometers we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components core 1050 c visco elastic skin 750 900 c rigid solid crust 750 c and flow margins 175 c for the a a flows investigated a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels this affects the heat loss and morphology of lava in active channels our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150 c above active tubes and tumuli

ice melt rates during volcanic eruptions within water drained low pressure subglacial cavities subglacial volcanism generates proximal and distal hazards including large scale flooding and increased levels of explosivity direct observation of subglacial volcanic processes is infeasible therefore we model heat transfer mechanisms during subglacial eruptions under conditions where cavities have become depressurized by connection to the atmosphere we consider basaltic eruptions in a water drained low pressure subglacial cavity including the case when an eruption jet develops such drained cavities may develop on sloping terrain where ice may be relatively shallow and where gravity drainage of meltwater will be promoted we quantify for the first time the heat fluxes to the ice cavity surface that result from steam condensation during free convection at atmospheric pressure and from direct and indirect radiative heat transfer from an eruption jet our calculations indicate that the direct radiative heat flux from a lava fountain a dry end member eruption jet to ice is c 25 kw m 2 and is a minor component the dominant heat transfer mechanism involves free convection of steam within the cavity we estimate the resulting condensation heat flux to be c 250 kw m 2 absorption of radiation from a lava fountain by steam enhances convection but the increase in condensing heat flux is modest at c 25 kw m 2 overall heat fluxes to the ice cavity surface are likely to be no greater than c 300 kw m 2 these are comparable with heat fluxes obtained by single phase convection of water in a subglacial cavity but much less than those obtained by two phase convection

a survey of temporal decorrelation from spaceborne l band repeat pass insar abstract in this paper we quantify the effects of temporal decorrelation in repeat pass synthetic aperture radar interferometry insar temporal decorrelation causes significant uncertainties in vegetation parameter estimates obtained using various insar techniques which are desired on a global scale because of its stochastic nature temporal decorrelation is hard to model and isolate in this paper we analyze temporal decorrelation statistically as observed in a large swath of sir c l band insar data collected over the eastern united states with a repeat pass duration of one day in october 1994 and a near zero perpendicular baseline the very small baseline for this particular pair makes the effect of volumetric scattering on correlation magnitude statistics nearly imperceptible allowing for a quantitative analysis of temporal effects alone the swath analyzed in this paper spans more than a million hectares of terrain comprised primarily of deciduous and evergreen forests agricultural land water and urban areas the relationships of these different land cover types phenology and weather conditions i e precipitation and wind on the measures of interferometric correlation is analyzed in what amounts to be the most geographically extensive analysis of this phenomenon to date

c band repeat pass interferometric sar observations of the forest properties of ers 1 c band repeat pass interferometric sar information for a forested area are studied the intensity information is rather limited but including coherence and effective interferometric sar insar height more information about the forest parameters can be obtained via satellite such information is also important for correction of insar derived topographic maps coherence properties have been used to identify forested nonforested areas and the interferometric effective height of the forest determined by comparison to a dem of the area the authors have developed a model to relate basic forest properties to insar observations these show that the coherence and interferometric effective height of a forested area change between image pairs the model demonstrates how these properties are related to the temporal decorrelation and the scattering from the vegetation canopy and the ground surface gaps in the vegetation are found to be important in the characterization of boreal forests

convective instability in europa s floating ice shell models of the tidally heated floating ice shell proposed for the jovian satellite europa generally find shell thicknesses less than 30 km past parameterized convection models indicated that such shells are stable against convective overturn which otherwise ostensibly leads to freezing of the ocean underneath here i apply the temperature dependent viscosity convection scaling developed by solomatov and coworkers to the europan ice shell the temperature dependent properties of ice are linearized about 260 k as any convective interior should be close to this temperature with the colder ice forming an essentially passive stagnant lid ice shells 10 km thick are found to be unstable to convection at their base for melting point viscosities of 1013 pa s as linearized by tidal stresses if the ice deforms by superplastic creep but such low viscosities require small grain sizes 1 mm this requirement may be met if grain sizes observed in terrestrial polar glaciers can be strain rate scaled to europa regardless convection at the base of the ice shell if initiated may not freeze the ocean because of tidal heating a stagnant lid regime ice shell is much more dissipative than a conductive shell of the same thickness such a shell should thin not thicken and the potential exists for further thermal instabilities and runaways

single baseline polarimetric sar interferometry examines the application of single baseline polarimetric sar interferometry to the remote sensing and measurement of structure over forested terrain for this a polarimetric coherent scattering model for vegetation cover suitable for the estimation of forest parameters from interferometric observables is introduced discussed and validated based on this model an inversion algorithm which allows the estimation of forest parameters such as tree height average extinction and underlying topography from single baseline fully polarimetric interferometric data is addressed the performance of the inversion algorithm is demonstrated using fully polarimetric single baseline experimental data acquired by dlr s e sar system at l band

repeat pass sar interferometry over forested terrain repeat pass synthetic aperture radar sar interferometry provides the possibility of producing topographic maps and geocoded as well as radiometrically calibrated radar images however the usefulness of such maps and images depends on our understanding of how different types of terrain affect the radar measurements it is essential that the scene coherence between passes is sdcient in this paper we derive a general system model including both radar system and scene scattering properties the model is used to interpret measurements over a forested area where the scene coherence varies between 0 2 and 0 5 the coherence is found to be sensitive to temperature changes around 0 c but surprisingly insensitive to wind speed the interferometric height discontinuity at the forest to openfield boundary shows good agreement with in situ tree height measurements for a dense boreal forest but is observed to decrease for a less dense forest this suggests the possibility of estimating bole volume from the interferometric tree height and a ground dem the decrease of scene coherence over a dense forest with increasing baseline is also used to estimate the effective scattering layer thickness

habitability of europa s crust the role of tidal tectonic processes jupiter s satellite europa has been identified as one of the most likely sites for life in the solar system the tidal tectonic processes that appear to have governed europa s geology seem to require interaction with an ocean under only a very thin crust providing a variety of evolving environmental niches the mutually dependent relationship between orbital evolution and tidal processes in turn controls europa s rotation heating and stress surface lineaments are correlated with global stress patterns demonstrating that they form by crustal cracking but only if a substantial ocean is present to give adequate tidal amplitude tidal driving of strike slip faulting indicates that cracks penetrate to a fluid layer which is possible only with a very thin ice crust the characteristic ridge sets that cover tectonic terrain are likely built by tidal pumping of fluid and slush to the surface on a daily basis widespread tectonic dilation creates new surface as material rises from below chaotic terrain has morphology and other characteristics indicative of melt through from below surface colorants correlate with locations such as along large scale ridge systems and around chaotic terrain where ocean water reached the surface this model implies that as a result of tides liquid water regularly bathed crustal cracks and surfaces with heat and whatever nutrients are included in the oceanic chemistry creating a variety of habitable environments the processes were recent and thus most likely continue today longer term evolution of environmental conditions provided the need for adaptation and opportunity for evolution

the origin of domes on europa the role of thermally induced compositional diapirism 1 the surface of jupiter s moon europa is peppered by topographic domes interpreted as sites of intrusion and extrusion diapirism is consistent with dome morphology but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations instead diapirs may initiate by thermal convection that induces compositional segregation exclusion of impurities from warm upwellings allows sufficient buoyancy for icy plumes to create the observed surface topography provided the ice shell has a small effective elastic thickness 0 2 to 0 5 km and contains low eutectic point impurities at the few percent level this model suggests that the ice shell may be depleted in impurities over time

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

the 1969 subglacial eruption on deception island antarctica events and processes during an eruption beneath a thin glacier and implications for volcanic hazards a short lived eruption of basaltic andesite to andesite on deception island in 1969 occurred from a series of fissures underneath a glacier the glacier was thin c 100 m and the eruption created a large and sudden discharge of meltwater that overflowed the glacier severely damaging buildings on the island the eruption was unusually well documented and it illustrates several features of subglacial eruptions that are only poorly known and not well understood in particular overflowing meltwater is contrary to predictions based on existing simple hydrological models for eruptions beneath thin glaciers the eruption is analysed in this paper and used as a model for the fluid dynamics and thermodynamics of eruptions beneath a thin glacier mainly composed of impermeable ice it is suggested that in eruptions of relatively fluid magmas with a low magma rise rate volatiles and magma are able to decouple and subglacial melting is strongly influenced by the superheated magmatic and hydrothermal gases mainly steam thus melting is much faster than that due solely to coupled conductive magma and convective meltwater heat transfer the influence of gasdriven melting also has an important effect on the shape of the meltwater cavity and may be at least partly responsible for the cylindrical ice chimneys developed above vents on deception island the results of the study are important for reconstructing the shapes of englacial cavities melted above a vent they also highlight the importance of glacier structure and densification rather than simply glacier thickness in determining the hydraulic evolution of an eruption even eruptions beneath thin glaciers can generate significant meltwater floods

tectonic processes on europa tidal stresses mechanical response and visible features abstract europa s orbital eccentricity driven by the resonance with io and ganymede results in diurnal tides 3 5 day period and possibly in nonsynchronous rotation both diurnal variation and nonsynchronous rotation can create significant stress fields on europa s surface and both effects may produce cracking patterns and time sequences of apparent tectonic features on europa include lineaments that correlate with both sources of stress if we take into account nonsynchronous rotation after initial crack formation by amounts ranging up to several tens of degrees for example the crosscutting time sequence of features in the cadmus and minos linea region is consistent with a combined diurnal and nonsynchronous tensile stress field as it evolves during tens of degrees of nonsynchronous rotation constraints on the rotation rate from comparing voyager and galileo images show that significant rotation requires 104yr but could be fast enough to have allowed significant rotation since the last global resurfacing even if such resurfacing was as recent as a few million years ago once cracking is initiated diurnal tides work cracks so that they open and close daily although the daily effect is small over 105yr double ridges could plausibly be built along the cracks with sizes and morphologies consistent with observed structures according to a model in which underlying liquid water fills the open cracks partially freezes and is extruded during the daily closing of the cracks thus several lines of observational and theoretical evidence can be integrated if we assume nonsynchronous rotation and the existence of a liquid water layer

interpretation of recent alpine landscape system evolution using geomorphic mapping and l band insar analyses abstract alpine landscapes are typically characterized by inherited features of past glaciations and for the more recent past by the interplay of a multitude of types of geomorphic processes including permafrost creep rockfalls debris flows and landslides these different processes usually exhibit large spatial and temporal variations in activity and velocity the understanding of these processes in a wide alpine area is often hindered by difficulties in their surveying in this study we attempt to disentangle recent changes in an alpine landscape system using geomorphic mapping and l band dinsar analyses alos palsar in the zermatt valley swiss alps geomorphic mapping points to a preferential distribution of rock glaciers on north facing slopes whereas talus slopes are concentrated on south facing slopes field based interpretation of ground deformation in rock glaciers and movements in talus slopes correlates well with the ratio of insar images showing potential ground deformation moraines formed during the little ice age rock glaciers and talus slopes on north facing slopes are more active than landforms on south facing slopes implying that the presence of permafrost facilitates the deformation of these geomorphic units such deformations of geomorphic units prevail also at the elevation of glacier termini for rock cliffs the ratio of images indicating retreat is affected by slope orientation and elevation linkages between sediment supply from rock cliffs and sediment transport in torrents are different among tributaries affected by relative locations between sediment supply areas and the channel network we conclude that the combined use of field surveys and l band dinsar analyses can substantially improve process understanding in steep high mountain terrain

models of ice melting and edifice growth at the onset of subglacial basaltic eruptions 1 models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities the cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage eruptions of basaltic magma from fissures and point sources are considered which form either hemicylindrical or hemispherical cavities the rate of roof closure can therefore be estimated using nye s law the cavity size edifice size and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms explosive and intrusive when the cavity is considerably larger than the edifice hydroclastic fragmentation is possible via explosive eruptions with deposition of tephra by eruptionfed aqueous density currents when the edifice completely fills the cavity rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner the models were run for a range of magma discharge rates ice thicknesses and cavity pressures relevant to subglacial volcanism in iceland explosive eruptions occur at high magma discharge rates when there is insufficient time for significant roof closure the models correctly predict the style of historic and pleistocene subglacial fissure eruptions in iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas the models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions

geothermal activity in the subglacial katla caldera iceland 1999 2005 studied with radar altimetry the katla caldera is located under the myrdalsjokull ice cap and is one of the most hazardous volcanoes in iceland due to major jokulhlaups that accompany eruptions subglacial geothermal activity is manifested in several 10 50 m deep depressions ice cauldrons within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts a short lived but powerful pulse in geothermal heat output took place in 1999 probably including a minor subglacial eruption when new ice cauldrons formed in three places and an unexpected jokulhlaup occurred following these events a comprehensive monitoring program was set up for katla including ice surface elevation profiling from aircraft to monitor variations in geothermal heat and detect signs of subglacial water accumulation a radar altimeter coupled with a kinematic gps is used achieving an absolute elevation accuracy of 3 m and internal consistency of 1 2 m profiles across the caldera are flown twice a year an annual accumulation ablation cycle in surface elevation with amplitude of 5 10 m is observed by removing this cycle from the data changes due to subglacial geothermal activity are obtained after the events in 1999 a decline in geothermal activity was observed in 2001 03 some ice cauldrons expanded and deepened by 10 15 m indicating renewed increase in geothermal activity this trend is also apparent for 2003 05 the increase in geothermal power amounts to a few tens of megawatts it is likely that the increased thermal output is related to increased seismicity and caused by magma inflow

baseline characteristics of a debris covered snow covered gorge in a typical japanese mountainous terrain abstract debris covered snow covered gorges dsgs are common in the mountainous environment of the japanese alps in the western pacific region but are almost absent in subdued landscapes where snow melting rates are higher our study demonstrates that the effect of debris coverage on the shrinkage of snow covered gorges of the japanese alps results in differences in how the gorges respond to climate change which has been neglected in predictions of future water availability snow covered gorges and glacial meltwater make important contributions to drinking water irrigation water and hydropower supply in the japanese alps region global warming is expected to increase mountainous river discharge and snowmelt in the short term but long term predictions are uncertain therefore detailed and reliable baseline data about the mountainous environment of the japanese alps and its effects on the cryosphere are essential for predicting the future hydrosphere of japan however field investigations in this region are difficult and to date studies have not collected enough data to fully understand the processes involved supraglacial debris influences the terminus dynamics and can thereby modify the migration of a snow covered gorge under climate change recent studies have found several dsgs that are stagnant i e almost non flowing in the mountainous environments of southwest saskatchewan canada two surface samples were taken on 24 june 2014 and 27 june 2014 to determine the mean grain size of sediment at the site it was found that dsgs extended for several kilometres through valleys in this region our results indicated that the maximum temperature within 10 cm of the ground surface varied from 10 c to 15 c which may be the crucial baseline factor for the existence of dsgs although the increasing rates of meltwater discharge and surface lowering indicate that these snow covered gorges are currently shrinking their fronts remain remarkably stable a phenomenon that has also been observed in other regions the significance of debris cover and its impact on regional differences in the mountainous environment of the japanese alps has not been established in the mountainous valley belt of the region in this study we report the baseline characteristics of dsg during the beginning of the snowmelt period in the extreme mountainous environment region of the japanese alps

the 1996 eruption at gjalp vatnajokull ice cap iceland efficiency of heat transfer ice deformation and subglacial water pressure the 13 day long gjlp eruption within the vatnajkull ice cap in october 1996 provided important data on ice volcano interaction in a thick temperate glacier the eruption produced 0 8 km 3 of mainly volcanic glass with a basaltic icelandite composition equivalent to 0 45 km 3 of magma ice thickness above the 6 km long volcanic fissure was initially 550 750 m the eruption was mainly subglacial forming a 150 500 m high ridge only 2 4 of the volcanic material was erupted subaerially monitoring of the formation of ice cauldrons above the vents provided data on ice melting heat flux and indirectly on eruption rate the heat flux was 5 6 10 5 wm 2 in the first 4 days this high heat flux can only be explained by fragmentation of magma into volcanic glass the pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50 60 if this is characteristic for magma frag mentation in subglacial eruptions volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers deforma tion and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure it is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice since the load is partly compensated for by shear forces in the rapidly deforming ice in addition to intensive crevassing due to subsidence at gjlp a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption it is suggested that the feeder dyke may have overshot the bedrock ice interface caused high deformation rates and fractured the ice up to the surface the crevasse later modified the flow of meltwater explaining surface flow of water past the highest part of the edifice the dominance of magma fragmentation in the gjlp eruption suggests that initial ice thickness greater than 600 700 m is required if effusive eruption of pillow lava is to be the main style of activity at least in similar eruptions of high initial magma discharge

studies of multibaseline spaceborne interferometric synthetic aperture radars the authors have utilized a set of seasat synthetic aperture radar sar data that were obtained in nearly repeat ground track orbits to demonstrate the performance of spaceborne interferometric sar insar systems an assessment of the topography measurement capability is presented a phase measurement error model is described and compared with the data obtained at various baseline separations and signal to noise ratios finally the implications of these results on future spaceborne insar design are discussed

thermal orbital evolution of io and europa coupled thermal orbital evolution models of europa and io are presented it is assumed that io europa and ganymede evolve in the laplace resonance and that tidal dissipation of orbital energy is an internal heat source for both io and europa while dissipation in io occurs in the mantle as in the mantle dissipation model of segatz et al 1988 icarus 75 187 two models for europa are considered in the first model dissipation occurs in the silicate mantle while in the second model dissipation occurs in the ice shell in the latter model ice shell melting and variations of the shell thickness above an ocean are explicitly included the rheology of both the ice and the rock is cast in terms of a viscoelastic maxwell rheology with viscosity and shear modulus depending on the average temperature of the dissipating layer heat transfer by convection is calculated using a parameterization for strongly temperature dependent viscosity convection both models are consistent with the present orbital elements of io europa and ganymede it is shown that there may be phases of quasi steady evolution with large or small dissipation rates in comparison with radiogenic heating phases with runaway heating or cooling and oscillatory phases during which the eccentricity and the tidal heating rate will oscillate europa s ice thickness varies between roughly 3 and 70 km dissipation in the silicate layer or 10 and 60 km dissipation in the ice layer suggesting that europa s ocean existed for geological timescales the variation in ice thickness including both convective and purely conductive phases may be reflected in the formation of different geological surface features on europa both models suggest that at present europa s ice thickness is several tens of km thick and is increasing while the eccentricity decreases implying that the satellites evolve out of resonance including lithospheric growth in the models makes it impossible to match the high heat flux constraint for io other heat transfer processes than conduction through the lithosphere must be important for the present io

brine mobilization during lithospheric heating on europa implications for formation of chaos terrain lenticula texture and color variations the background lineated plains on europa are locally highly modified and destroyed in regions known as chaos and lenticulae produced there are 1 isolated fragments and polygons of background material which rotate and translate 2 matrix which fills in the areas between the fragments and polygons and 3 surface discolorations using observations and constraints from high resolution galileo images we find that a model for the formation of these terrains which involves mobilization and migration of brines and a possible percolation phase transition as the europan lithosphere is warmed can readily explain the vast majority of their characteristics in addition the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates the characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer

ice volcano interactions during the 2010 eyjafjallajokull eruption as revealed by airborne imaging radar 1 during the eruption of the ice covered eyjafjallajokull volcano a series of images from an airborne synthetic aperture radar sar were obtained by the icelandic coast guard cloud obscured the summit from view during the first three days of the eruption making the weather independent sar a valuable monitoring resource radar images revealed the development of ice cauldrons in a 200 m thick ice cover within the summit caldera as well as the formation of cauldrons to the immediate south of the caldera additionally radar images were used to document the subglacial and supraglacial passage of floodwater to the north and south of the eruption site the eruption breached the ice surface about four hours after its onset at about 01 30 utc on 14 april 2010 the first sar images obtained between 08 55 and 10 42 utc show signs of limited supraglacial drainage from the eruption site floodwater began to drain from the ice cap almost 5 5 h after the beginning of the eruption implying storage of meltwater at the eruption site due to initially constricted subglacial drainage from the caldera heat transfer rates from magma to ice during early stages of cauldron formation were about 1 mw m 2 in the radial direction and about 4 mw m 2 vertically meltwater release was characterized by accumulation and drainage with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods after the third day of the eruption meltwater generation at the eruption site diminished due to an insulating lag of tephra

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

ice melt rates in liquid filled cavities during explosive subglacial eruptions subglacial eruptions are often associated with rapid penetration of overlying ice and release of large flow rates of water as jokulhlaups observations of recent subglacial eruptions indicate rapid syn eruptive ice melting within liquid filled subglacial cavities but quantitative descriptions of possible heat transfer processes need to be developed calculations of heat flux from the ice cavity fluid to the melting ice surface indicate that up to 0 6 mw m 2 may be obtained for fluids undergoing single phase free convection similar to minimum estimates of heat flux inferred from observations of recent eruptions our model of boiling two phase free convection in subglacial cavities indicates that much greater heat fluxes in the range 3 5 mw m 2 can be obtained in the vent region of the cavity and may be increased further by momentum transfer from the eruption jet rapid magma water heat transfer from fragmented magma is needed to sustain these heat fluxes similar heat fluxes are anticipated for forced convection of subcooled cavity water induced by momentum transfer from an eruption jet these heat fluxes approach those required to explain jokulhlaup flow rates and rapid ice penetration rates by melting in some but not all recent eruptions

does europa have a subsurface ocean evaluation of the geological evidence it has been proposed that jupiter s satellite europa currently possesses a global subsurface ocean of liquid water galileo gravity data verify that the satellite is differentiated into an outer h2o layer about 100 km thick but cannot determine the current physical state of this layer liquid or solid here we summarize the geological evidence regarding an extant subsurface ocean concentrating on galileo imaging data we describe and assess nine pertinent lines of geological evidence impact morphologies lenticulae cryovolcanic features pull apart bands chaos ridges surface frosts topography and global tectonics an internal ocean would be a simple and comprehensive explanation for a broad range of observations however we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm soft ice with only localized or partial melting two different models of impact flux imply very different surface ages for europa the model favored here indicates an average age of 50 myr searches for evidence of current geological activity on europa such as plumes or surface changes have yielded negative results to date the current existence of a global subsurface ocean while attractive in explaining the observations remains inconclusive future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within europa today

galileo magnetometer measurements a stronger case for a subsurface ocean at europa on 3 january 2000 the galileo spacecraft passed close to europa when it was located far south of jupiter s magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward jupiter this pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of europa s internal field the galileo magnetometer measured changes in the magnetic field predicted if a current carrying outer shell such as a planet scale liquid ocean is present beneath the icy surface the evidence that europa s field varies temporally strengthens the argument that a liquid ocean exists beneath the present day surface

formation of cycloidal features on europa cycloidal patterns are widely distributed on the surface of jupiter s moon europa tensile cracks may have developed such a pattern in response to diurnal variations in tidal stress in europa s outer ice shell when the tensile strength of the ice is reached a crack may occur propagating cracks would move across an ever changing stress field following a curving path to a place and time where the tensile stress was insufficient to continue the propagation a few hours later when the stress at the end of the crack again exceeded the strength propagation would continue in a new direction thus one arcuate segment of the cycloidal chain would be produced during each day on europa for this model to work the tensile strength of europa s ice crust must be less than 40 kilopascals and there must be a thick fluid layer below the ice to allow sufficient tidal amplitude

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

effects of plasticity on convection in an ice shell implications for europa abstract europa s surface exhibits numerous pits uplifts and disrupted chaos terrains that have been suggested to result from convection in the ice shell to test this hypothesis we present numerical simulations of convection in an ice shell including the effects of plasticity which provides a simple continuum representation for brittle or semibrittle deformation along discrete fractures plastic deformation occurs when stresses reach a specified yield stress at lower stresses the fluid flow follows a newtonian temperature dependent viscosity four distinct modes of behavior can occur for yield stresses exceeding 1 bar plastic effects are negligible and stagnant lid convection with no surface motion and minimal topography results at intermediate yield stresses a stagnant lid forms but deforms plastically leading to surface velocities up to several millimeters per year slightly smaller yield stresses allow episodic catastrophic overturns of the upper conductive lid with transient stagnant lids forming in between overturn events the smallest yield stresses allow continual recycling of the upper lid with simultaneous gradual ascent of warm ice to the surface and descent of cold near surface ice into the interior the exact yield stresses over which each regime occurs depend on the ice shell thickness melting temperature viscosity and activation energy for viscous creep to form hummocky matrix and translate chaos plates by several kilometers substantial surface strain must accompany chaos formation and the three plasticity dominated convection modes described here can provide such deformation our simulations suggest that if yield stresses of 0 2 1 bar are relevant to europa then convection in europa s ice shell can produce chaos like structures at the surface however our simulations have difficulty explaining europa s numerous pits and uplifts when plasticity forces the upper lid to participate in the convection dynamic topography of 50 100 m amplitude results but the topographic structures generally have diameters of 30 100 km an order of magnitude wider than typical pits and uplifts none of our simulations produced isolated pits or uplifts of any diameter

temperatures on europa from galileo photopolarimeter radiometer nighttime thermal anomalies galileo observations of europa s thermal emission show low latitude diurnal brightness temperatures in the range of 86 to 132 kelvin nighttime temperatures form an unexpected pattern with high temperatures on the bright ejecta blanket of the crater pwyll and an equatorial minimum in temperatures after sunset uncorrelated with surface albedo or geology the nighttime anomalies may be due to regional thermal inertia variations of an unknown origin which are equivalent to a two to threefold variation in thermal conductivity or to endogenic heat fluxes locally reaching 1 watt per square meter endogenic heat flow at this high level although consistent with some geological evidence is theoretically unlikely