wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

seismic velocities in the uppermost oceanic crust age dependence and the fate of layer 2a it has been widely accepted that upper crustal seismic velocities gradually increase from low values in the youngest crust to typical crustal velocities 5 2 km s 1 over a period of 30 40 million years with a corresponding decrease in the observed heat flow deficiency caused by hydrothermal circulation some recent seismic studies however suggest that the seismic velocities actually rise rapidly nearly doubling in 5 km s 1 and velocities 3 km s 1 are not observed in crust older than 5 ma there is no detectable systematic change in the seismic properties of the uppermost oceanic crust after 10 million years median and average velocities increase from 2 3 to 4 4 km s 1 by 7 5 ma and remain unchanged thereafter if layer 2a is an interval capping the oceanic crust in which velocities are significantly lower than velocities that are typical of the underlying rocks layer 2b 5 2 km s 1 it follows that layer 2a does not disappear but is a persistent feature of the oceanic crust these results are consistent with geochemical evidence that most hydrothermal alteration occurs within 3 million years after the formation of the oceanic crust and suggest that there is little correlation between seismic velocities and ongoing hydrothermal circulation

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

the first direct measurements of upper oceanic crustal compressional wave attenuation the first direct measurement of compressional wave attenuation of the uppermost 650 m of oceanic crust was performed using data recorded by seafloor hydrophones and large 56 116 kg deep explosive sources the site was 13 km east of the southernmost juan de fuca ridge on crust 0 4 m y old spectral ratios were performed between bottom refracting waves and direct water waves adjusted for spreading losses and transmission coefficient losses several tests of the data were performed demonstrating that attenuation is linearly related to frequency between 15 and 140 hz but frequency independent components of attenuation are also evident values of compressional wave q cluster between 20 and 50 and do not show any systematic variation with depth over 650 m the attenuation results also indicate the presence of heterogeneities within the crust as the solutions for each receiver s data set are significantly different no evidence for azimuthal variations of attenuation are supported by the data although the data do not optimally sample a wide variation of azimuths our attenuation values are judged to be normal to higher than expected for the whole oceanic crust based upon comparisons to results from synthetic seismogram modeling by others and by modeling signal to noise ratios of typical seismic refraction profiles the results are consistent with recent laboratory measurements at ultrasonic frequencies for dry and saturated basalts at seafloor pressures and temperatures

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

shear wave velocity in marine sediments on young oceanic crust constraints from dispersion analysis of scholte waves summary an experiment with a newly developed implosive source located about 1 m above the sea oor at 3665 m depth revealed a slow interface wave this wave is attributed to s waves in a soft sediment layer covering the hard rock sub bottom dispersion analysis by means of the multiple lter technique yields the group velocity as a function of frequency model calculations showed that the observed dispersion curve can be reproduced by considering a steep gradient of s velocity within the sediment layer nearly perfect agreement of experimental and model data could be achieved with a sediment layer thickness of 21 5 m an s speed of 225 m s 1 at the water sediment interface and an increase by 23 s 1 within the layer these values are relatively high compared to data from the literature however previous estimates of in situ s wave velocity have been obtained on old oceanic crust in the vicinity of continents or islands while our experiment was carried out on young paci c crust therefore we suggest two mechanisms which could support a relatively high s speed in sediments 1 the input of hydrothermally generated metalliferous sediments from the adjacent spreading axis and 2 post depositional diagenesis which has accelerated the induration of sediments

surge of bering glacier and bagley ice field alaska an update to august 1995 and an interpretation of brittle deformation patterns in the summers of 1993 1994 and 1995 video and global positioning system location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the bering glacier and bagley ice field system alaska in an effort to characterize surge crevasse patterns and surge propagation during survey flights in late august 1995 we observed that the 1993 94 bering glacier surge was continuing and still expanding affecting new areas farther up in bagley ice field new crevasse fields similar in pattern to the first surge crevasses we had observed in june 1993 below khitrov hills and in other isolated areas of central bering glacier and in july 1994 near the head of bering glacier near the junction of bering glacier and bagley ice field in both upper bering glacier and bagley ice field were opening in eastern bagley ice field and in the steller side of bagley ice field the type of crevasses seen in the new fields suggested that the surge was propagating into these areas by analysis and interpretation of the brittle deformation patterns apparent in the crevasse patterns some aspects of the past kinematic framework of the surge can be deduced this approach may lead to a more general classification of ice surface structures and to their linkage to ongoing processes

constraints on the shallow seismic structure at ocean drilling program site 1107 ninetyeast ridge from implosive bottom sources and airgun shots on ninetyeast ridge the seismological community drilled ocean drilling program odp site 1107 coincident with odp site 757 for the future host of a long term seismological observatory in the central indian ocean to study the shallow seismic structure at the drill site we developed a unusual on bottom seismic tool five implosive sources were placed along a 2 km line four ocean bottom sensors recorded seismic waves over epicentral distances of 400 m to 2200 m revealing seismic velocities of the immediately subjacent sediments velocities within this portion of crust are generally not detectable by traditional marine seismic techniques airgun shots however can be used to determine velocities of basement rocks one dimensional travel time inversion of both bottom sources and water path corrected surface shots yields a velocity structure which is in excellent agreement with odp drilling results three lithological units are imaged a 150 m thick sediment section with velocities of 1600 1720 m s underneath a layer of 230 m thickness with velocities ranging from 2080 to 2250 m s corresponding to volcanic ashes and tuffs the volcanic basement occured at 380 m below seafloor velocities rapidly increase from 3500 m s to values of more than 4500 m s within a few hundred metres

crustal architecture and deep structure of the ninetyeast ridge hotspot trail from active source ocean bottom seismology a 550 km long transect across the ninetyeast ridge a major indian ocean hotspot trail provided seismic refraction and wide angle reflection data recorded on 60 ocean bottom instruments about 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track two approaches have been chosen i a first arrival tomographic inversion yielding crustal properties and ii forward modelling of mantle phases revealing the structure at the crust mantle boundary region and of the uppermost mantle away from the volcanic edifice seismic recordings show the typical phases from oceanic crust that is two crustal refraction branches pg a wide angle reflection from the crust mantle boundary pmp and a wave group turning within the upper mantle pn approaching the edifice three additional phases have been detected we interpret these arrivals as a wide angle reflection from the base of material trapped under the pre hotspot crust pm2p and as a wide angle reflection pnp and its associated refraction branch pn from a layered upper mantle the resulting models indicate normal oceanic crust to the west and east of the edifice crustal thickness averages 6 5 7 km wide angle reflections from both the pre hotspot and the post hotspot crust mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere and hotspot volcanism has underplated the pre existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks 7 5 7 6 km s 1 in total the crust is up to 24 km thick the ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0 7 an important observation is that underplating continued to the east under the wharton basin during the shield building phase however ninetyeast ridge was located adjacent to the broken ridge and was subsequently pulled apart along a transform fault boundary therefore underplating eastwards of the fracture zone separating the edifice from the wharton basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield building stage this fact however requires mantle flow along the fossil hotspot trail the occurrence of pnp and pn arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere

seismic velocities of the uppermost igneous crust versus age summary seismic refraction velocity data from the acoustic basement called layer 2a have been compiled for different mid ocean ridges the data from post 1970 studies show a strong correlation between velocity and basement age importantly velocities double in less than 10 myr for all ridges but for older crust up to 160 myr in age velocities do not increase significantly

structural glaciology of the fast moving jakobshavn isbrae greenland compared to the surging bering glacier alaska u s a

flow thermal structure and subglacial conditions of a surge type glacier temperature measurements in a subpolar surge type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas in the receiving area the glacier is cold based but bottom temperature has increased as much as 0 5 c between 1981 and 1982 and the basal heat flux is roughly 10 times the expected geothermal flux water percolation through permeable subglacial material is the probable energy source deformation of the substrate could destroy this drainage system and trigger a surge

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

experimental and theoretical fracture mechanics applied to antarctic ice fracture and surface crevassing recent disintegration of ice shelves on the antarctic peninsula has highlighted the need for a better understanding of ice shelf fracture processes generally in this paper we present a fracture criterion incorporating new experimental fracture data coupled with an ice shelf flow model to predict the spatial distribution of surface crevassing on the filchner ronne ice shelf we have developed experiments that have enabled us to quantify for the first time quasi stable crack growth in antarctic ice core specimens using a fracture initiation toughness kinit for which crack growth commences the tests cover a full range of near surface densities 560 871 kg m 3 10 9 75 7 m depth results indicate an apparently linear dependence of fracture toughness on porosity such that kinit 0 257 80 7 predicting a zero porosity toughness of ko 155 kpa m1 2 we have used this data to test the applicability to crevassing of a two dimensional fracture mechanics criterion for the propagation of a small sharp crack in a biaxial stress field the growth of an initial flaw into a larger crevasse which involves a purely tensile crack opening depends on the size of the flaw the magnitude of kinit and the nature of the applied stress field by incorporating the criterion into a stress map of the filchner ronne ice shelf derived from a depth integrated finite element model of the strain rate field we have been able to predict regions of potential crevassing these agree well with satellite imagery provided an initial flaw size is assumed in the range 5 50 cm

a low frequency ice penetrating radar system adapted for use from an airplane test results from bering and malaspina glaciers alaska usa ice thickness measurements are needed to calculate fluxes through fast flowing outlet glaciers in greenland alaska patagonia and antarctica however relatively high attenuation of radio waves by dielectric absorption and volume scattering from englacial water hampers detection of the bed through warm deep ice in the past we have had success measuring ice thickness of temperate glaciers using a ground based monopulse radar system operating at low frequencies 2 mhz here we adapt the same system to operate from an airplane test flights over bering glacier alaska usa detected the bed through ice up to 1250 m thick flights across the seward malaspina glacier system alaska resolved the ice thickness of malaspina glacier but strong hyperbolic shaped returns obscured the bed echo through the seward throat it is likely that this clutter in the signal was caused by off nadir returns from chaotic surface crevasses that are ubiquitous in the throat region

degradation of selected terrestrial and martian impact craters degraded craters on mars record the cumulative effects of the complex interplay between erosion transport and deposition by competing intermittent processes fortunately impact craters are instantaneous landforms common to both the earth and mars that are characterized by similar topography and local lithofacies deconvolving the signatures of individual degradation processes around young craters on earth e g drainage scale and density changing wall slope deflation features allows calibrating degradation signatures around craters on mars and places first order limits on controlling processes and perhaps past climates such comparisons are valid despite differences in vegetation cover and time scales over which activity occurs on the two planets analysis of degradation at meteor crater lonar crater and talemzane crater reveals a terrestrial sequence of advancing degradation by fluvial eolian and mass wasting processes at meteor crater fluvial processes currently dominate primary erosion however combined deflation from the ejecta and both alluvium and colluvium make eolian processes most important in overall ejecta degradation lonar and talemzane reveal that advancing fluvial degradation is characterized by larger drainages and decreasing wall slopes at talemzane interior drainages breach the rim crest and pirate headward regions of exterior drainage basins when comparable degradation signatures resolvable at viking resolutions are used in selected areas on mars important differences from the terrestrial sequence are revealed all morphologies of craters in southern ismenius lacus sil are typically incised by small valleys with low drainage densities display rare alluvial deposits possess walls sloped at the angle of repose and are sometimes partially covered by airfall deposit remnants analogy with the terrestrial craters indicates signatures associated with advancing fluvial degradation should be readily detected on mars together with other differences between degraded craters on the two planets the paucity of fluvial signatures in sil implies that mass wasting and eolian activity predominated degradation of martian craters preserved since the hesperian crater statistics for sil indicate most craters were degraded during geologically brief intervals in the noachian and mid hesperian therefore fluvial signatures preserved in sil imply any runoff since the hesperian was short lived locally debouched and unrelated to rainfall

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

a theory of glacier surges we propose a model of glacier flow that is capable of explaining temperate glacier surges the laws of conservation of mass and momentum are supplemented by the prescription of a sliding law that gives the basal shear stress as a function of the basal velocity u and the effective pressure n the effective drainage pressure n is determined by a simple study of the subglacial hydraulic system following rothlisberger we determine n nr for the case of drainage through a single subglacial tunnel alternatively following kamb we find that the corresponding theory for a linked cavity drainage system yields n nk nr furthermore the stability of each drainage system depends on the velocity u such that for large enough u there is a transition from tunnel to cavity drainage consequently one can write n n u we then find that the sliding law u is multivalued and hence so also is the flux depth relation q q h an analysis of the resulting system of equations is sketched for large enough accumulation rates a glacier will undergo regular relaxation oscillations resembling a surge the surge is triggered at the point of maximum stress from this point two hydraulic transition fronts travel up and down glacier to calculable boundary points the speed of propagation is the order of 50 metres an hour at these fronts the tunnel drainage system collapses and a high water pressure cavity drainage system is installed this activated zone has high velocities and quickly relaxes surges to a quasi equilibrium state this relaxation is much like opening a sluice gate in that a large wave front propagates forward behind this wave front the velocity can decay oscillatorily and thus the flow can be compressive we conclude with some discussion of the effects of seasonal variation and of prospects for the current theory s applicability to soft bedded glaciers

seismic noise interferometry reveals transverse drainage configuration beneath the surging bering glacier subglacial drainage systems are known to critically control ice flows but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility here we report a 12 year long monitoring of the drainage underneath bering glacier alaska by correlating ambient noise recorded at two seismic stations on the sides of the glacier we find that the seismic surface waves traveling across bering glacier slowed down by 1 2 during its latest 2008 2011 surge likely due to the switch of the subglacial drainage from a channelized system to a distributed system in contrast to current models the relative amplitude of velocity reductions for rayleigh and love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction we infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges and thus can sustain the high water pressure and ice flow speed

strain localisation and incremental deformation within ice masses framnes mountains east antarctica mesoscale fracture analysis of brittle features has been used to identify zones of localised ductile deformation within an ice stream moving at 20 ma 1 in the framnes mountains east antarctica ground based survey of three strain grids has been integrated with the detailed structural analysis to develop a model of temporal and spatial variation in strain localisation within large high strain zones modelled strain distributions are in good agreement with the occurrence and sense of movement across zones of high ductile strain which have been inferred from observed brittle features the major zone of high strain is 3 km wide and 15 km long and deformed dextrally at a strain rate of 6 17 10 3 a 1 over the two year period of observation despite this constant annual strain rate the internal deformation was incremental localised and temporal in nature resulting in the development of new zones of fracturing

geologic evolution of the east rim of the hellas basin mars abstract geomorphic analyses and crater statistics indicate the distribution of materials on the east rim 27 5 42 5 s 260 275 w of the hellas basin and constrain the timing nature and interactions of geologic processes which have modified the hellas region the discernible geologic history of the area began with the formation of the impact basin and the emplacement of highlands that became heavily cratered during the noachian period the tectonic setting of the region was established at this time and basin structures promoted and influenced subsequent volcanic tectonic and fluvial activity degradation of the highland units by fluvial mass wasting and aeolian processes began in the noachian and continued into the hesperian and amazonian periods sedimentary plains covered low lying regions of the highlands their pitted surfaces in some areas suggest subsidence and the presence of volatiles emplacement of lobate debris aprons shed from highland peaks and possibly facilitated by ice creep occurred in the amazonian period the volcanic history of the east rim of the hellas basin began with the formation of the highland paterae the low dissected shields of hadriaca and tyrrhena paterae formed in the late noachian or early hesperian epochs and are older than or coeval with the ridged plains of hesperia planum volcanic activity continued throughout the hesperian period with the emplacement of the caldera filling materials at hadriaca patera and the lava flows of the flank flow unit of tyrrhena patera outflow channels and related channeled plains of the hesperian and amazonian periods suggest an extensive and complex history of volatile driven erosion and sedimentary deposition dao and harmahkis valles are interpreted to be collapsed regions of the older plains a combination of surface and subsurface flow has removed materials with deposition on the floor of the hellas basin the geologic evolution of the region determined from the observed surface morphology and stratigraphic relationships and refined by crater statistics indicates that a combination of diverse geologic processes acted in the degradation of the hellas basin the effects of volcanism and volatile driven processes were prominent throughout the hesperian and well into the amazonian periods the proposed transition from explosive to effusive volcanism in the hellas region is supported by the relative ages indicated by crater statistics the heat released by volcanism may have resulted in the melting of ground ice and contributed to the development of the channeled plains and outflow channels the presence of wrinkle ridges on units that are inferred to be relatively young from their crater size frequency distributions suggests deformation in the late hesperian or early amazonian epoch

geology of the reull vallis region mars abstract the geology and stratigraphy of the reull vallis region 27 5 47 5 s 245 270 w of the southern highlands of mars are documented through geomorphic analyses and geologic mapping at 1 2 000 000 scale crater size frequency distributions are used to constrain relative ages of geologic units and determine the timing and duration of the various geologic events the origin and evolution of the reull vallis outflow system and the extent to which reull vallis and other fluvial features modified the surrounding highlands are also evaluated rugged highland terrains were formed by repeated impact events and were extensively degraded and embayed by a series of plains highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region reull vallis originates in hesperia planum and dissects units of various types and ages truncated and bisected wrinkle ridges in hesperia planum indicate that the formation of reull vallis postdates ridge formation the morphology of reull vallis suggests it had a long and complex history including subsurface and surface movement of fluids followed by extensive modification by mass wasting volcanic and sedimentary plains units in the region record evidence of erosion by surface flow possibly related to development of reull vallis features produced by mass wasting such as debris aprons and crater fill material and aeolian processes appear to form the youngest deposits exposed in the region

three dimensional seismic refraction tomography of the crustal structure at the ion site on the ninetyeast ridge indian ocean summary we have performed a 3 d seismic refraction tomography of a 48 48 km2 area surrounding odp site 757 which is planned to host an international ocean network ion permanent seismological observatory called the ninetyeast ridge observatory nero the study area is located in the southern part of the ninetyeast ridge the trail left by the kerguelen hotspot on the indian plate the geomar research centre for marine geosciences and the federal institute for geosciences and natural resources acquired 18 wide angle profiles recorded by 23 ocean bottom hydrophones during cruise so131 of r v sonne in spring 1998 we apply a first arrival traveltime tomography technique using regularized inversion to recover the 3 d velocity structure relative to a 1 d background model that was constructed from a priori information and averaged traveltime data the final velocity model revealed the crustal structure down to approximately 8 km depth resolution tests showed that structures with approximately 6 km horizontal extent can reliably be resolved down to that depth the survey imaged the extrusive layer of the upper crust of the ninetyeast ridge which varies in thickness between 3 and 4 km a high velocity anomaly coinciding with a positive magnetic anomaly represents a volcanic centre from which crust in this area is thought to have formed a pronounced low velocity anomaly is located underneath a thick sedimentary cover in a bathymetric depression however poor ray coverage of the uppermost kilometre of the crust in this area resulted in smearing of the shallow structure to a larger depth tests explicitly including the shallow low velocity layer confirmed the existence of the deeper structure the heterogeneity of the upper crust as observed by our study will have consequences for the waveforms of earthquake signals to be recorded by the future seismic observatory

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

volcanic geology of tyrrhena patera mars tyrrhena patera is a large low relief volcano located in the southern cratered highlands of mars on a proposed ring fracture of the hellas basin the volcano is composed of four or possibly five principal units the oldest and most areally extensive of which are suggested to be ash on the basis of their morphology and erosional characteristics lava flows are observed in a flank flow unit extending from the central caldera to the southwest and apparently cap the summit region models derived from the study of terrestrial pyroclastic flows have been applied to the deposits at tyrrhena patera and indicate that the distribution and lengths of the observed deposits are consistent with an origin by the emplacement of gravity driven ash flows generated by hydromagmatic or magmatic explosive eruptions the hydromagmatic case requires considerable quantities of water 7 5 1016 kg however at volumetric water flow rates determined by other investigators 105 m3 s and calculated from the regional slopes in the hesperia planum region 106 m3 s the amounts necessary could be supplied relatively rapidly in geologic time tyrrhena patera represents the earliest central vent volcanism identified on mars and may reflect a transition from the flood style eruptions which dominated early martian history a hydromagmatic origin for tyrrhena patera is in agreement with suggested climatic changes on mars and may explain the absence of this style of volcanism in later eras alternatively a magmatic origin for tyrrhena patera implies an evolution in the types of magmas produced on mars from hesperian to amazonian time during which the prominent shields in the tharsis region formed

interplay between magmatic accretion spreading asymmetry and detachment faulting at a segment end crustal structure south of the ascension fracture zone highlights magmatism detachment faulting and changing symmetry of crustal accretion at a ridge segment end pmps from an occ argue for constant magma production during detachment faulting refraction seismic modelling and pmp events reveal very thin 4 km oceanic crust at a segment end a wide angle seismic section across the mid atlantic ridge just south of the ascension transform system reveals laterally varying crustal thickness and to the east a strongly distorted moho that appears to result from slip along a large offset normal fault termed an oceanic detachment fault gravity modelling supports the inferred crustal structure we investigate the interplay between magmatism detachment faulting and the changing asymmetry of crustal accretion and consider several possible scenarios the one that appears most likely is remarkably simple an episode of detachment faulting which accommodates all plate divergence and results in the westward migration of the ridge axis is interspersed with dominantly magmatic and moderately asymmetric most on the western side spreading which moves the spreading axis back towards the east following the runaway weakening of a normal fault and its development into an oceanic detachment fault magma both intrudes the footwall to the fault producing a layer of gabbro subsequently partially exhumed

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

surface height determination of crevassed glaciers mathematical principles of an autoadaptive density dimension algorithm and validation using icesat 2 simulator simpl data glacial acceleration is a main source of uncertainty in sea level change assessment measurement of ice surface heights with a spatial and temporal resolution that not only allows elevation change calculation but also captures ice surface morphology and its changes is required to aid in investigations of the geophysical processes associated with glacial acceleration the advanced topographic laser altimeter system aboard nasa s future icesat 2 mission launch 2017 will implement multibeam micropulse photon counting lidar altimetry aimed at measuring ice surface heights at 0 7 m along track spacing the instrument is designed to resolve spatial and temporal variability of rapidly changing glaciers and ice sheets and the arctic sea ice the new technology requires the development of a new mathematical algorithm for the retrieval of height information we introduce the density dimension algorithm dda that utilizes the radial basis function to calculate a weighted density as a form of data aggregation in the photon cloud and considers density an additional dimension as an aid in autoadaptive threshold determination the autoadaptive capability of the algorithm is necessary to separate returns from noise and signal photons under changing environmental conditions the algorithm is evaluated using data collected with an icesat 2 simulator instrument the slope imaging multi polarization photon counting lidar over the heavily crevassed giesecke braer in northwestern greenland in summer 2015 results demonstrate that icesat 2 may be expected to provide ice surface height measurements over crevassed glaciers and other complex ice surfaces the dda is generally applicable for the analysis of airborne and spaceborne micropulse photon counting lidar data over complex and simple surfaces

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

bering glacier surge 2011 analysis of laser altimeter data the bering glacier bagley icefield system in alaska is currently surging 2011 large scale elevation changes and small scale elevation change characteristics are investigated to understand surge progression especially mass transport from the pre surge reservoir area to the receiving area and propagation of the kinematic surge wave as manifested in heavy crevassing characteristic of rapid brittle deformation this analysis is based on airborne laser altimeter data collected over bering glacier in september 2011 results include the following 1 maximal crevasse depth is 60 m reached in a rift that separates two deformation domains indicative of two different flow regimes otherwise surge crevasse depth reaches 20 30 m 2 characteristic parameters of structural provinces are derived by application of geostatistical classification parameters include significance and spacing of crevasses surface roughness and crevasse edge curvature indicative of crevasse age a classification based on these parameters serves to objectively discriminate structural provinces indicative of surge progression down glacier and up glacier 3 elevation changes from 2011 and 2010 altimetry show 40 70 m surface lowering in the reservoir area in lower central bering glacier and 20 40m thickening near the front in tashalich arm combining elevation changes with results of crevasse profilometry and pattern analysis the rapid progression of the surge can be mathematically physically reconstructed

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

geostatistical analysis of glacier roughness data in most glaciological and hydrological models surface roughness of snow and ice is an important parameter however roughness is generally used only as an estimated parameter for lack of available observations in this paper we present a method to collect and analyze ice surface roughness data using a specially designed instrument for survey and geostatistical methods for analysis the glacier roughness sensor grs built at the university of trier records variations in microtopography at 0 2 m 0 1 m resolution when pulled across an ice surface global positioning system data are used for location after several processing steps the data are analyzed using geostatistical methods the mathematical tool used to achieve a morphological characterization of ice surface types is the variogram grs data variograms and surface roughness analysis are ideal matches for morphological characterization because none of them requires or provides absolute elevation values morphology is described not by absolute elevation values but by the change of elevation in space which is the derivative of elevation surface roughness values the variogram is calculated from incremental values parameters extracted from variograms of grs data serve to distinguish lake surfaces wind structures ridge and vauey systems melting structures and blue ice areas examples are from jakobshavn isbrae drainage basin west greenland

the correction for the travel time effects of seafloor topography in the interpretation of marine seismic data problems associated with the application of topographic corrections to deep ocean marine seismic data are described synthetic travel time data are used to show that corrections for the delay time introduced by the water column are inferior to corrections for the true water path water path corrections place the shots at the ray entry points on the seafloor require no assumptions about the structure under investigation and maintain the correct distribution of data with range the water path correction can be most accurately applied during the stacking operation that transposes the observed data into intercept time slowness space there is then no requirement to make determinations of slowness and for experiments involving seafloor receiver and surface shots the data may be transposed to the seafloor with complete objectivity water path corrected stacks from different locations may then be compared in the sure knowledge that any observed differences are due to real structural changes and not to topographic correction errors or to invalid assumptions of lateral homogeneity