methodology for dense spatial sampling of multicomponent recording of converted waves in shallow marine environments a widespread use of converted waves for shallow marine applications is hampered by spatial aliasing and field efficiency their short wavelengths require dense spatial sampling which often needs to be achieved by receivers deployed on the seabed we adopted a new methodology where the dense spatial sampling is achieved in the common receiver domain by reducing the shot spacing this is done by shooting one track multiple times and merging the shot lines in an effective manner in a separate processing step this processing step is essential because positioning errors introduced during the field measurement can become significant in the combined line particularly when they exceed the distance between two adjacent shot positions for this processing step a particular shot line is used as a reference line and relative variations in source and receiver positions in the other shot lines are corrected for using crosscorrelation the combined shot line can subsequently be regularized for further processing the methodology is adopted in a field experiment conducted in the danube river in hungary the aim of the seismic experiment was to acquire properly sampled converted wave data using a multicomponent receiver array the dense spatial sampling was achieved by sailing one track 14 times after correcting for the underwater receiver positions using the direct arrival the crosscorrelation step was applied to merge the different shot lines the successfully combined result is regularized into a densely sampled data set free of visible spatial aliasing and suitable for converted wave processing

the non geometric p s wave in high resolution seismic data observations and modelling summary in data from a high resolution seismic survey conducted over a near surface environment consisting of homogeneous soft clay we consistently observe a distinct seismic phase arriving between the direct compressional wave and the rayleigh wave this phase is characterized by high amplitudes at near offsets and a phase velocity corresponding to about twice the shear wave velocity based on analytical and numerical analyses this signal could be unambiguously identified as a non geometric wave which is excited if the source is located near the earth s surface and the poisson s ratio in the vicinity of the source is unusually high to date there are only a few speculative observations of this particular non geometric seismic wave phenomenon however given the commonly very high poisson s ratio of surficial materials we expect this phase to be present albeit unidentified in many near surface seismic surveys the presence of this non geometric wave increases the complexity of the seismic record and failure to identify it may result in misinterpretations particularly of high resolution seismic reflection data as well as of shear wave and surface wave data potential applications of this seismic phase may arise from its high sensitivity to the shear wave velocity in the immediate source region

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

morphometry of glaciovolcanic edifices from iceland types and evolution abstract the morphology of many glaciovolcanoes is considered one of the distinctive characteristics of their ice confining eruption environment however a thorough morphometric analysis of a large number of glaciovolcanic edifices has never been performed based on a semi automatic geomorphometric mapping of glaciovolcanic edifices of the icelandic neovolcanic zones we present a morphometric database of 155 glaciovolcanic edifices formed during the last 0 78 ma this database enables a comprehensive analysis of the morphometric diversity of a large suite of glaciovolcanic edifices sheet like formations however are not considered due to lack of data using three planimetric measurements basal length average basal width and average summit plateau width and their ratios three main morphometric groups can be distinguished in a ternary diagram 1 conical edifices with no or small summit plateaus 2 linear ridges and 3 flat topped edifices subdivided into equidimensional and elongated all three groups contain edifices with and without lava caps these morphometric groups can be fitted to the commonly accepted terminology for cone mound tindar and tuya however since lava caps occur in all morphometric groups a grouping based on its existence is not practical this suggests that by adding the descriptor lava capped to any of the three classes may be a useful way to refine the classification based on the ternary diagram ridges are the most morphometrically distinct glaciovolcanic edifice because of their very extreme elongation followed by flat topped edifices and finally conical edifices however morphometric parameters cannot be used singlehanded to identify glaciovolcanic edifices from other types of volcanic edifices such as composite volcanoes shields or submarine volcanoes and should always be complemented with other observations the glaciovolcanic edifice volumes range from 0 15 10 2km3 to 32 km3 conical edifices are the smallest 1 km3 overall with growth three morphological evolutions can be considered a an initial eruptive fissure concentrates into one vent generating an equidimensional edifice that either can be a conical or a flat topped edifice b the edifice maintains its elongation suggesting that a fissure is the dominating vent structure and during continued eruption develops significant summit plateaus generating elongated flat topped edifices and c the edifice increases in elongation because the fissure lengthens during the eruption and a plateau building stage does not occur producing increasingly elongated ridges

possible sub glacial eruptions in the galaxias quadrangle mars we have identified several landforms in the galaxias quadrangle of mars mtm 35217 33 0 35 5 n 216 0 218 0 w which are consistent with this area having been covered by an ancient ice sheet concurrent with volcanic eruptions volcanic activity was initiated by the intrusion of several large dikes measuring 50 100 m wide and protruding up to 35 m above the present day surface these dikes appear to have originated from elysium planitia 600 km to the se in one instance a dike at an elevation of 3750 m appears to have produced a subglacial mound referred to here as galaxias mons 2 that evolved into an extrusive eruption and produced copious volumes of melt water that carved an outflow channel that extends almost 300 km to the north at a lower elevation 3980 m a second putative dike may have failed to break the surface of the ice sheet and formed galaxias mons as a laccolithic intrusion we numerically model the formation of galaxias mons and find that at least 200 m of ice may once have existed at this latitude at the time of the dike intrusions such a conclusion supports the idea that enigmatic small domes in the area may be pingoes collectively these observations suggest that the previous interpretations for the origin of near by hrad vallis as a sub aerial eruption may need to be revised

petrology and chemistry of mil 03346 and its significance in understanding the petrogenesis of nakhlites on mars antarctic meteorite miller range mil 03346 is a nakhlite composed of 79 clinopyroxene 1 olivine and 20 vitrophyric intercumulus material we have performed a petrological and geochemical study of mil 03346 demonstrating a petrogenetic history similar to previously discovered nakhlites quantitative textural study of mil 03346 indicates long 1 x 101 yr residence times for the cumulus augite whereas the skeletal fe ti oxide fayalite and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling probably as a lava flow from the relatively high forsterite contents of olivine up to fo43 compared with other nakhlites and compositions of augite cores wo38 42en35 40fs22 28 and their hedenbergite rims we suggest that mil 03346 is part of the same or a similar martian cumulate rich lava flow as other nakhlites however mil 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date calculated trace element concentrations based upon modal abundances of mil 03346 and its constituent minerals are identical to whole rock trace element abundances parental melts for augite have ree patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients this parallelism reflects closed system crystallization for mil 03346 where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization a model for the petrogenesis of mil 03346 and the nakhlites nakhla governador valadares lafayette yamato 000593 northwest africa nwa 817 nwa 998 would include 1 partial melting and ascent of melt generated from a long term lree depleted mantle source 2 crystallization of cumulus augite olivine magnetite in a shallow level martian magma chamber 3 eruption of the crystal laden nakhlite magma onto the surface of mars 4 cooling crystal settling overgrowth and partial equilibration to different extents within the flow 5 secondary alteration through hydrothermal processes possibly immediately succeeding or during emplacement of the flow this model might apply to single or multiple flow models for the nakhlites ultimately mil 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on mars with analogous petrogenetic histories to pyroxene rich terrestrial lava flows and to komatiites

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

candidate volcanic and impact induced ice depressions on mars abstract we present an analysis of two concentrically fractured depressions on mars one in northern hellas and the second in galaxias fossae volumetric measurements indicate that 2 4 km3 and 0 2 km3 of material was removed in order to form the north hellas and galaxias depressions the removed material is inferred to be predominantly water ice calorimetric estimates suggest that up to 103 105 m3 of magma would have been required to melt sublimate such a volume of ice under an ice magma interaction scenario this process would lead to subsidence and cracking of the surface which could produce the observed concentric fracture crevasse like morphology while the galaxias fossae landform morphology is consistent with an impact origin the large volume of removed material in north hellas is less consistent with an impact origin and is interpreted to have resulted from volcanic melting of ice the possibility of liquid water formation during or subsequent to volcanism or an impact could generate locally enhanced habitable conditions making these features tantalizing geological and astrobiological exploration targets

thermal and mechanical aspects of magma emplacement in giant dike swarms we consider the thermal history and dynamics of magma emplacement in giant feeder dikes associated with continental flood basalts for driving pressure gradients inferred for giant dike swarms thicknesses of 10 m would enable dikes to transport magma laterally over the distances observed in the field up to thousands of kilometers without suffering thermal lock up using time dependent numerical solutions for the thermal evolution of a dike channel under laminar and turbulent flow conditions in the presence of phase transitions we investigate the possibility that the observed dike thicknesses of the order of 100 m result from thermal erosion of the country rocks during dike emplacement this implies that the observed range of dike widths in giant dike swarms may reflect variations in the source volume and not the excess magma pressure it is found that the total volume of intruded magma required to produce an order of magnitude increase in dike width via wall rock melting broadly agrees with the estimated volumes of individual flows in continental flood basalts the presence of chilled margins and apparently low crustal contamination characteristics of some giant dikes may be consistent with turbulent magma flow and extensive melt back during dike emplacement in this case measurements of the anisotropy of magnetic susceptibility most likely indicate magma flow directions during the final stages of dike intrusion shear stresses generated at the dike wall when the dike starts to freeze strongly decrease with increasing dike width which implies that thicker dikes may have less tendency to produce consistent fabric alignment our results suggest that if the dike was propagating downslope off a plume related topographic swell the mechanism responsible for flow termination could possibly have been related to underpressurization and collapse implosion of the shallow magma plumbing system feeding the intrusion radial dikes that erupted at the periphery of the topographic uplift might have increased rather than decreased extensional stresses in the crust within the topographic uplift upon their solidification

thermally distinct craters near hrad vallis elysium planitia mars abstract evidence of volcano ground ice interactions on mars can provide important constraints on the timing and distribution of martian volcanic processes and climate characteristics northwest of the elysium rise is hrad vallis a 370 m deep 800 km long sinuous valley that begins in a source region at 34 n 218 w flanking both sides of the source region is a lobate deposit that extends 50 km perpendicular from the source and is an average of 40 m thick previous studies have suggested the formation of the hrad vallis source region was the result of explosive magma ice interaction and that the lobate deposit is a mudflow here we use newly available mola moc and themis data to investigate the evidence supporting this hypothesis within the lobate deposit we have identified 12 craters with thermal infrared signatures and morphologies that are distinct from any other craters or depressions in the region the thermally distinct craters are distinguished by their cool interiors surrounded by warm ejecta in the nighttime themis ir data and warm interiors surrounded by cool ejecta in the daytime themis ir data the craters are typically 1100 1800 m in diameter one crater is 2300 m across and 30 40 m deep but may be up to 70 m the craters are typically circular and have central depressions several with interior dune fill surrounded by 1 to 6 concentric fracture sets the distribution of the craters and their morphology suggests that they are likely the result of the interaction between a hot mudflow and ground ice

episodes of aqueous flooding and effusive volcanism associated with hrad vallis mars nasa planetary geology and geophysics program nasa planetary science division nnx13ar14g 80nssc17k0307 nasa earth and space sciences fellowship nessf program nnx16ap09h

dynamics of a confined lava flow on kilauea volcano hawaii this paper presents a new method of analysing lava flow deposits which allows the velocity discharge rate and rheological properties of channelled moving lavas to be calculated the theory is applied to a lava flow which was erupted on kilauea in july 1974 this flow came from a line of fissures on the edge of the caldera and was confined to a pre existing gully within 50 m of leaving the vent the lava drained onto the floor of the caldera when the activity stopped but left wall and floor deposits which showed that the lava banked up as it flowed around each of the bends field surveys established the radius of curvature of each bend and the associated lava levels and these data together with related field and laboratory measurements are used to study the rheology of the lava the results show the flow to have been fast moving but still laminar with a mean velocity of just over 8 m s 1 the lava had a low or negligible yield strength and viscosities in the range 85 140 pa s an extension of the basic method is considered and the possibility of supercritical flow discussed

evidence age and thickness of a frozen paleolake in utopia planitia mars abstract recent mapping studies west of elysium mons mars have pinpointed subice features that suggest the existence of a frozen paleolake in utopia planitia as recently as 1 8 billion years ago the subice features are interpreted to be hyaloclastic ridges and hills table mountains associated jokulhlaup deposits and fluvial channels photoclinometric studies of these features and of a basal scarp around the northwest flank of elysium mons interpreted to have been an ice sheet boundary indicate that the maximum thickness of ice within the basin may have been about 180 m this thickness of ice during a relatively late stage of martian geologic history would have important implications concerning the atmospheric the climatic and possibly the exobiologic history of the planet

nongeometrically converted shear waves in marine streamer data under certain circumstances marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging these shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom they are called nongeometrical because the evanescent part in the water does not satisfy snell s law for real angles but only for complex angles the propagating shear waves then undergo reflection and refraction in the subsurface and arrive at the receivers via an evanescent compressional wave the required circumstances are that sources and receivers are near the water bottom irrespective of the total water depth and that the shear wave velocity of the water bottom is smaller than the p wave velocity in the water most often the normal situation this claim has been tested during a seismic experiment in the river danube south of budapest hungary to show that the shear related arrivals are body rather than surface waves a borehole was drilled and used for multicomponent recordings the streamer data indeed show evidence of shear waves propagating as body waves and the borehole data confirm that these arrivals are refracted shear waves to illustrate the effect finite difference modeling has been performed and it confirmed the presence of such shear waves the streamer data were subsequently processed to obtain a shear wave refraction section this was obtained by removing the scholte wave arrival separating the wavefield into different refracted arrivals stacking and depth converting each refracted arrival before adding the different depth sections together the obtained section can be compared directly with the standard p wave reflection section the comparison shows that this approach can deliver refracted shear wave sections from streamer data in an efficient manner because neither the source nor receivers need to be situated on the water bottom

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

possible ancient oceans on mars evidence from mars orbiter laser altimeter data high resolution altimetric data define the detailed topography of the northern lowlands of mars and a range of data is consistent with the hypothesis that a lowland encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle mars history the contact altitude is close to an equipotential line the topography is smoother at all scales below the contact than above it the volume enclosed by this contact is within the range of estimates of available water on mars and a series of extensive terraces parallel the contact in many places

volcanism induced local wet based glacial conditions recorded in the late amazonian arsia mons tropical mountain glacier deposits abstract the tropical mountain glacial fan shaped deposit fsd to the northwest of the arsia mons volcano on mars contains numerous glacial and volcanic landforms while most of the glacial landforms are interpreted to have formed by cold based glacial processes several glacial landforms near glaciovolcanic edifices are more consistent with localized wet based glacial processes these landforms include ribbed moraines which suggest local thermal transitions between wet and cold based ice thrust block moraines whose formation is typically assisted by the presence of subglacial water streamlined knobs that we interpret to have been sculpted by ice sliding along its base and a braided outflow channel the presence and association of these features together with evidence of both subglacial volcanic eruptions and local ice marginal advances favor polythermal glaciers with localized wet based conditions we propose that lava to ice heat transfer during the eruption of the glaciovolcanic edifices caused the arsia mons paleoglacier to melt at its base in some areas resulting in these locally wet based glacial conditions a polythermal glacier provides more potential microbial habitats and more connectivity between habitats than does a cold based glacier and we review glacial and glaciovolcanic habitats on earth that may provide insight into the likelihood of potential microbial habitats within the arsia mons fsd on mars

the dynamic relationship between ground water and the columbia river using deuterium and oxygen 18 as tracers abstract deuterium and oxygen 18 were used as natural tracers to investigate the hydraulic relationship between the columbia river and the blue lake gravel aquifer near portland oregon a time series of stable isotope data collected from surface and ground waters during a march 1990 aquifer test confirms that the river and aquifer are hydraulically connected calculations based on simple mixing show that the river contributed 40 50 of the yield of three wells after 5 6 days of pumping data collected during august 1990 show that the river contributed 65 80 of the yield of one well after 22 days of pumping and indicate that the contribution of the river was still increasing

phreatomagmatic explosive origin of hrad vallis mars 1 hrad vallis is a 370 m deep 800 km long depression located at 34 n 218 w in elysium planitia mars a distinctive deposit present on both sides of the source area of hrad vallis has a maximum width of 70 km along the strike of the depression a lower unit extends for nearly 100 km away from the depression on either side and an upper unit extends for 50 km viking and mars orbiter camera moc images show lobate deposit boundaries rheomorphic deformation and numerous craters 270 580 m in diameter within the deposit the deposit coincides with a broad topographic rise 30 km wide and 100 150 m high extending along the sides of the valley for at least 100 km along strike we propose that these features formed when a dike underlying the axis of the valley generated a shallow sill which in turn is partly responsible for the rise topography the remainder of the rise consists of a mud like deposit of ejecta from a large scale phreatomagmatic explosion due to violent mechanical and thermal mixing between the central part of the sill and ice rich rock layers in the upper few hundred meters of the crust in a fuel coolant type interaction the observed range and thickness of ejecta and the depth of the hrad depression imply explosion steam pressures up to 360 mpa ejecta speeds of 400 m s 1 and a sill at least 150 m thick intruded at a depth of 350 400 m below the original surface

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

sedimentary deposits in the northern lowland plains mars the lowland plains on mars have surfaces marked by large polygonal fracture patterns it was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels we support this hypothesis because of the following observations 1 polygonal fracture patterns tend to occur in low areas on mars that apparently received influx of sediments the area of northern plains in which the fractures occur also forms a regional low 2 the fracture patterns are concentrated near reentrants of the plains projecting into the southern highlands not only are these reentrants associated with outflow channels but channels and polygonally fractured deposits have similar ages 3 sinuous ridges at the mouths of martian outflow channels resemble ridges in antarctic ice streams and ice shelves the similarity suggests that the martian material was transported from the southern highlands toward the northern plains as the antarctic material is transported from the continent toward the adjacent ocean overall it appears that a massive transfer of material took place midway in martian history either through the outflow channels or elsewhere along the northern highland scarp and that this material probably formed the deposits now characterized by polygonal fracture patterns

converted waves in a shallow marine environment experimental and modeling studies seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear wave velocity information but also for improved processing of deeper reflection data these waves generated at deep seas have been used successfully in hydrocarbon exploration however acquisition of good quality converted wave data in shallow marine environments remains challenging we have looked into this problem through field experiments and synthetic modeling a high resolution seismic survey was conducted in a shallow water canal using different types of seismic sources data were recorded with a four component water bottom cable observed events in the field data were validated through modeling studies compressional waves converted to shear waves at the water bot tom and at shallow reflectors were identified the shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments modeling results indicated the presence of a nongeometric shear wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water sediment interface as observed in air gun data this type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source thus these shear waves excited by the source water bottom coupled system kinematically behave as if they were generated by an s wave source placed at the water bottom in a shallow water environment the condition appears to be favorable for exciting such shear waves with nongeometric arrivals these waves can provide useful information of shear wave velocity in the sediments

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy 2 application to martian surface spectra from the mars global surveyor thermal emission spectrometer atmospherically corrected thermal infrared spectra of large regions of the martian surface from the mars global surveyor thermal emission spectrometer mgs tes previously have been interpreted to represent two general spectral classes one class represents a basalt to basaltic andesite composition and the other class represents a basaltic andesite to andesite composition we have performed new linear deconvolutions of the two martian surface type spectra with an end member set tailored to represent volcanic rock types our preparatory study of laboratory spectra of terrestrial volcanic rocks acquired at 2 cm 21 sampling convolved to tes spectral sampling 10 cm 21 shows little degradation in deconvolution results when compared to results acquired using the higher spectral resolution data indicating that the deconvolution technique is valid for analyzing data at tes resolution our spectral fits to the martian data agree well with previous models and do not exhibit any notable deviations from the martian spectra that would indicate the absence of any significant end members in our model modal mineralogies obtained with these new spectral fits also compare favorably within the previously stated uncertainties to prior results the newly derived modal mineralogies are used with new and traditional classification schemes for volcanic igneous rocks introduced in a companion paper wyatt et al this issue to classify the martian compositions our results substantiate the previously proposed hypothesis that these two spectral classes on the martian surface represent volcanic compositions with distinguishable differences in silica content ranging from basalt to andesite

the mid hungarian line a zone of repeated tectonic inversions abstract the mid hungarian line is a major tectonic feature of the intra carpathian area separating two terranes of different origin and tectonic structure although this tectonic line was known from borehole records it has not been described in seismic sections the study presents interpreted seismic lines crossing the supposed trace of the mid hungarian line these seismic sections show north dipping normal faults and thrust faults as well as cross cutting young strike slip faults a complex tectonic history is deduced including intra oligocene early miocene thrusting middle miocene extension local late miocene inversion and late miocene pliocene normal faulting and left lateral wrenching in the light of our seismic study we think that the best candidate for the mid hungarian line is a north dipping detachment fault beneath large masses of neogene volcanics the auxiliary structures to the north seen on seismic sections suggest that it moved as a south vergent thrust fault during the palaeogene early miocene which later was reactivated as a set of normal faults the northern alcapa unit overrode the southern tisza dacia unit along this fault zone the same relative positions are observed in the northern termination of the line other structures along the supposed trace of the line are north dipping normal or strike slip faults which frequently were reactivated as smaller thrust faults during the late neogene palaeogene early miocene thrusting along the line might be the result of the opposite tertiary rotations of the two major units as suggested by palaeomagnetic measurements and earlier models

mineralogic evidence for subglacial volcanism in the sisyphi montes region of mars abstract here we examine the mineral assemblages detected on possible glaciovolcanic edifices in the sisyphi planum region of mars a high latitude region in the southern highlands nestled between the argyre and hellas impact basins minerals were identified utilizing visible near infrared spectra from the compact reconnaissance imaging spectrometer for mars crism analysis of eleven crism images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be gypsum dominated smectite zeolite iron oxide dominated possibly palagonite and polyhydrated sulfate dominated material while sulfates can form under a variety of alteration conditions palagonite like mineral assemblages require low temperature and high water to rock hydrothermal conditions typically found in subglacial or subaqueous volcanic eruptions the possible palagonite detections on the volcanic edifices the geomorphology of the region and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems this implies that thick water ice sheets were present in this region in the late noachian or early hesperian and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential

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

geostatistical inference using crosshole ground penetrating radar high resolution tomographic images obtained from crosshole geophysical measurements have the potential to provide valu able information about the geostatistical properties of unsaturat ed zonehydrologic statevariablessuchasmoisturecontent un der drained or quasi steady state conditions the moisture con tentwillreflectthevariationofthephysicalpropertiesofthesub surface which determine the flow patterns in the unsaturated zone deterministicleast squaresinversionofcrossholeground penetrating radargprtraveltimesresultinsmooth minimum variance estimates of the subsurface radar wave velocity struc ture whichmaydiminishtheutilityoftheseimagesforgeostatis tical inference we have used a linearized stochastic inversion technique to infer the geostatistical properties of the subsurface radar wave velocity distribution using crosshole gpr travel times directly expanding on a previous study we have deter minedthatitispossibletoobtainestimatesofglobalvarianceand mean velocity values of the subsurface as well as the correlation lengths describing the subsurface velocity structures accurate estimation of the global variance is crucial if stochastic realiza tions of the subsurface are used to evaluate the uncertainty of the inversion estimate we have explored the full potential of the geostatisticalinferencemethodusingseveralsyntheticmodelsof varying correlation structures and have tested the influence of different assumptions concerning the choice of covariance func tionanddatanoiselevel inaddition wehavetestedthemethod ology on traveltime data collected at a field site in denmark there inferred correlation structures indicate that structural dif ferences exist between two areas located approximately 10 m apart anobservationconfirmedbyagprreflectionprofile fur thermore the inferred values of the subsurface global variance and the mean velocity have been corroborated with moisture content measurements obtained gravimetrically from samples collectedatthefieldsite

formation and degradation of chaotic terrain in the galaxias regions of mars implications for near surface storage of ice galaxias chaos is a region of low plateaus separated by narrow fractures a chaotic terrain galaxias mensae and galaxias colles are characterised by mesa and knobby terrains of individual landforms or small assemblages separated by plains galaxias chaos has been attributed to ground disturbance due to sublimation in shallow subsurface ice rich deposits galaxias mensae and galaxias colles to sublimation and degradation of icy surface materials without production of chaotic terrain liquid water has not been regarded as a product of the degradation of these icy terrains this paper asks two research questions 1 what was the total extent of the different modes of landscape degradation especially chaotic terrain involved in producing the present landscapes of galaxias chaos and galaxias mensae colles 2 can the generation of liquid water as a product of landscape degradation be ruled out using a morphological statistical approach including power spectrum analysis of relief our observations and analyses show that present mesa knobby terrains of galaxias mensae colles evolved from a landscape that had the same directional pattern and relief as presently found in galaxias chaos this terrain extended across 440 000 km2 but 22 000 km3 average thickness 77 m have been lost across 285 000 km2 this represents a significant loss of ice bearing deposits moreover this surface degradation was spatially partitioned by landforms associated with elevated ground heating and the transmission of a fluid in the shallow subsurface towards a distal channel in answer to research question 2 it cannot be determined definitively if the fluid involved was groundwater generated by the thermal destabilisation of the icy deposits or low viscosity lava however it is likely that the degradation of galaxias mensae colles was not a consequence of sublimation alone these findings underscore the significance of cryo volcanic interactions in the cycling of water between the martian surface and the atmosphere

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

fissure eruptions in tharsis mars implications for eruption conditions and magma sources the tharsis region has been the focus of many studies of volcanism on mars not only are the largest volcanoes on the planet located here but also many of the youngest volcanic features are found within tharsis comparatively little attention has been given to understanding the origin of the smaller volcanoes within tharsis and these smaller structures may provide important information on both the regional tectonics of the area and the availability of magma from the shallow or deep crust we have identified six separate but physically close vent systems in eastern tharsis just to the east of the volcano jovis tholus these vents are typically linear fissures a few to 20 km in length that have built small shields rising to 50 85 m above the level of the surrounding topography the maximum length of individual lava flows from these fissures is 30 km but more typical lengths are 15 20 km mapping of the vent complexes reveals that smooth material interpreted to be spatter from fire fountaining is located on the rims of some of the fissures this spatter then formed either short 5 km flows or merged close to the fissure to form the longer flows there appears to have been some temporal evolution of the flow field as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows we find evidence of frozen lava ponds and channelized flows from central vents photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute originally identified by mouginis mark and christensen mouginis mark p j christensen p r 2005 new observations of volcanic features on mars from the themis instrument j geophys res 110 e8 doi 10 1029 2005je002421 of the flows from the central vent complex they are all 5 m thick which is a factor of 8 15 thinner than flows elsewhere on mars to investigate the unusual eruption conditions limited total volume of the construct and of individual flows we model the lava rheology the duration of emplacement the subsurface conditions that may have led to these eruptions and the volatile content of the magma we find lava viscosities and yield strengths to be 100 pa s and 100 pa respectively eruption rates to be 5000 m3 s 1 flow speeds to be 1 2 m s 1 durations of emplacement of individual flow units to be 5 h and the equivalent magma water content to be 0 1 0 2 mass these eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions small vents such as the ones studied here have also been identified in other parts of eastern tharsis so that the eruptions described here may characterize a common style of volcanism on mars that can only be identified now that image spatial resolution in the range 1 20 m pixel is available it is therefore possible that additional searches of other volcanic areas syrtis planum elysium planitia and hesperia planum may also show greater diversity of activity than is currently accepted