comparison of seismicity in the geysers geothermal area with the surrounding region abstract a comparison of seismicity at the geysers and in the surrounding region indicates that the rate of seismicity at the geysers is 45 times the regional rate and that clustering of events in space and time is more prevalent in the region area than at the geysers temporally clustered seismic events that occurred at the geysers from september 1975 through september 1976 appear linked to regional temporal clusters located at the southern end of clear lake during this period a characteristic 2 to 6 day time lapse separated temporal clusters at the geysers from those at clear lake the two areas where these correlated clusters occurred lie on either side of a presumed magma body correlation between clusters in the two areas disappears after september 1976 during the period of correlated seismic episodes regional stress changes may have been transmitted between the two areas by aseismic creep

interactions between complex craters and the lunar crust analysis using grail data a high resolution gravity map over the entire lunar surface has been derived from data acquired by the gravity recovery and interior laboratory grail mission soderblom et al 2015 showed that crater bouguer gravity anomalies scale with crater diameter and porosity for craters in the lunar highlands here we extend this study globally examining complex craters in each of the three lunar terranes highlands maria and the south pole aitken basin we find that craters within south pole aitken basin and in the lunar maria have statistically different bouguer anomalies from those in the lunar highlands these differences are best explained by differences in crustal porosity among the three terranes though there is still much unresolved scatter in the data we find that no other lunar material properties crustal thickness density gradient etc are able to improve our model fit to the data

greenland flow variability from ice sheet wide velocity mapping using radarsat synthetic aperture radar data we have mapped the flow velocity over much of the greenland ice sheet for the winters of 2000 01 and 2005 06 these maps provide a detailed view of the ice sheet flow including that of the hundreds of glaciers draining the interior the focused patterns of flow at the coast suggest a strong influence of bedrock topography differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes the overall pattern is one of speed up accompanied by terminus retreat but there are also several instances of surge behavior and a few cases of glacier slowdown comprehensive mappings such as these at regular intervals provide an important new observational capability for understanding ice sheet variability

source mechanisms of induced earthquakes at the geysers geothermal reservoir at the geysers geothermal reservoir in northern california evidence strongly suggests that activities associated with production of electric power cause an increase in the number of small earthquakes first degree dynamic moment tensors are used to investigate the relationship between induced earthquakes and injection of water into a well as part of a controlled experiment in the northwest geysers the estimation of dynamic moment tensors in the complex shallow crust at the geysers is challenging so the method is described in detail with particular attention given to the uncertainty in the results for seismic events in the moment magnitude range of 0 9 2 8 spectral moduli of dynamic moment tensors are reliably recovered in the frequency range of 1 100 hz but uncertainty in the associated spectral phases limits their use to a few simple results a number of different static moment tensors are investigated with the preferred one obtained from parameters of a model fitted to the spectral modulus of the dynamic moment tensor moment tensors estimated for a group of 20 earthquakes exhibit a range of source mechanisms with over half having significant isotropic parts of either positive or negative sign corner frequencies of the isotropic part of the moment tensor are about 40 larger than the average of the deviatoric moment tensor some spatial patterns are present in source mechanisms with earthquakes closely related in space tending to have similar mechanisms but at the same time some nearby earthquakes have very different mechanisms tensional axes of displacement in the source regions are primarily horizontal while the pressure axes range from near horizontal to vertical injection of water into the well in the center of the study area clearly causes an increase in the number of earthquakes per day but an effect upon source mechanisms is not evident

toward mapping the effective elastic thickness of planetary lithospheres from a spherical wavelet analysis of gravity and topography abstract the effective elastic thickness t e of the lithosphere controls the flexural response to transverse loading and can be used in conjunction with rheological models to remotely estimate surface heat flux of terrestrial planets in the vast majority of studies t e estimation is carried out in a two step process 1 the joint spectra admittance and or coherency of gravity anomalies free air and or bouguer and topography are calculated within finite size windows and 2 the spectra are inverted using a model for the loading of an infinite elastic plate or shell in recent years research in the spatio spectral analysis of cartesian grids and improvements in lithospheric loading models have allowed the mapping of t e on the earth at unprecedented resolution nevertheless the limitations imposed by working with cartesian data and models are hampering further advances in terrestrial t e studies the planetary community on the other hand has traditionally used spatio spectral methods that work directly on the sphere thereby avoiding the undesirable distortions and biases inherent in cartesian studies however the models and methods developed for the earth have never been applied to planetary data therefore also limiting further advances in the mapping of planetary t e this paper reviews the latest developments in t e studies and proposes to combine advances in both terrestrial and planetary studies to allow the mapping of t e of terrestrial planets using a spherical wavelet analysis of gravity and topography data we begin with a review of the recent literature on the challenges and debates concerning t e estimation from joint gravity and topography spectra we then briefly review the implementation of the continuous planar and spherical wavelet transforms cpwt and cswt and demonstrate that both transforms possess exactly the same resolving power however the cswt does not suffer from effects associated with non periodic boundaries we further re derive in a consistent manner the expressions for the admittance and coherency from flexural equations for the loading of thin elastic plates and shells and show that they result in similar spectra except at the longest wavelengths where the shell membrane stresses dominate we then estimate global grids of earth s continental t e by inverting the planar and spherical admittance and coherency functions both separately and jointly using either free air or bouguer gravity anomalies the correspondence between the cartesian and spherical approaches and the similarity of t e results for the earth s continents indicate that the spherical methods are robust results obtained from the joint inversion of admittance and coherency show that simple lithospheric loading models fail to capture the complexity of the data with adverse effects on the estimated parameters finally we extend the analysis to the moon and other terrestrial planets and discuss limitations and future applications of the fully spherical techniques

englacial latent heat transfer has limited influence on seaward ice flux in western greenland surface meltwater can refreeze within firn layers and crevasses to warm ice through latent heat transfer on decadal to millennial timescales earlier work posited that the consequent softening of the ice might accelerate ice flow potentially increasing ice sheet mass loss here we calculate the effect of meltwater refreezing on ice temperature and softness in the p kitsoq near swiss camp and jakobshavn isbrae regions of western greenland using a numeric model and existing borehole measurements we show that in the jakobshavn catchment meltwater percolation within the firn warms the ice at depth by 3 5 c by contrast meltwater refreezing in crevasses cryo hydrologic warming at depths of 300 m warms the ice in p kitsoq by up to 10 c but this causes minimal increase in ice motion 10 m a 1 p kitsoq is representative of western greenland s land terminating ice where the slow movement of ice through a wide ablation zone provides ideal conditions for cryo hydrologic warming to occur we find that only 37 of the western greenland ice flux however travels through such areas overall our findings suggest that cryo hydrologic warming will likely have only a limited effect on the dynamic evolution of the greenland ice sheet

the longevity of lunar volcanism implications of thermal evolution calculations with 2d and 3d mantle convection models abstract lunar volcanism as is generally accepted started well before the emplacement of the mare fill at 3 1 3 9 ga b p and likely extended well into the eratosthenian 3 1 1 1 ga b p the early volcanism is relatively easily understood the extension of the activity to possibly 1 5 ga b p albeit at a decreasing rate poses a problem since a relatively small body such as the moon may be expected to cool rapidly and freeze a partially molten mantle layer quickly we present thermal history models in which a region of partial melt forms in the mantle underneath the lithosphere almost immediately after the start of the model at depths between 300 and 700 km depending on the chosen initial depth of the magma ocean to calculate the thermal histories we use axisymmetric 2d and fully 3d spherical shell convection codes with viscosity depending on the azimuthally averaged temperature the thermal evolution of the moon is found to be characterized by the growth of a massive 700 to 800 km thick lithosphere while the lower mantle and core cool only by 100 200 k the partial melt zone decreases in thickness with time from top to bottom until it vanishes at times between 3 4 and 2 2 ga b p the maximum degree of partial melting is between roughly 10 and 20 the partial melt layer is initially global and is disrupted by cold downwellings as cooling proceeds the melt zone freezes from above due to the thickening of the lithosphere which implies that the source region of volcanic rock proceeds to increasing depth with time this corresponds nicely with the variation of titanium with age of lunar mare basalts mixing of the melt zone with the underlying mantle chemically rejuvenates the melt zone to some degree and thus the source region of the mare basalts

second order moment tensors of microearthquakes at the geysers geothermal field california the geysers geothermal field is the site of intense microseismicity which appears to be associated with steam production it seems that focal mechanisms of earthquakes at the geysers vary systematically with depth but p wave first motion focal mechanism studies have been hampered by inadequate resolution in this study an unconstrained frequency domain moment tensor inversion method is used to over come p wave first motion focal sphere distribution problems and to investigate microearthquake source properties a goal was to investigate the feasibility of using waveforms to invert for the second order moment tensor of microearthquakes in the complex setting of the geysers derived frequency domain moment tensors for two earthquakes were verified by mechanisms estimated from p wave first motions and required far fewer stations for one event 19 p wave first motions were insufficient to distinguish between normal slip and strike slip focal mechanisms but a well constrained strike slip solution was obtained from the waveform principal moment inversion using data from six stations improved waveform focal mechanism resolution was a direct consequence of using p and s wave data together in a progressive velocity hypocenter inversion to minimize green function errors the effects of hypocenter mislocation and velocity model green function errors on moment tensor estimates were investigated synthetic tests indicate that these errors can introduce spurious isotropic and compensated linear vector dipole components as large as 26 per cent for these events whereas principal moment orientations errors were 8 in spite of unfavorable recording geometries and large 0 6 km station elevation differences the results indicate that waveform moment tensor estimates for microearthquake sources can be robust and constrain source mechanisms using data from a relatively small number of stations

measurement and modeling of ablation of the bottom of supraglacial lakes in western greenland 1 we report measurements of ablation rates of the bottom of two supraglacial lakes and of temperatures at different depths collected during the summers of 2010 and 2011 in west greenland to our knowledge this is the first time that such data sets are reported and discussed in the literature the measured ablation rates at the bottom of the two lakes are of the order of 6 cm day versus a rate of 2 5 3 cm day in the case of bare ice of surrounding areas though our measurements suggest the presence of a vertical temperature gradient it is not possible to draw final conclusions as the measured gradient is smaller than the accuracy of our temperature sensors in situ measurements are compared with the results of a thermodynamic model forced with the outputs of a regional climate model in general the model is able to satisfactorily reproduce the measured quantities with rmse of the order of 3 4 cm for the ablation and 1 5 c in the case of water temperature our results confirm that the ablation at the bottom of supraglacial lakes plays an important role on the overall lake volume with the ablation in the case of ice covered by a lake being 110 135 of that over bare ice at nearby locations beside ice sheet hydrological implications melting at the bottom of a supraglacial lake might affect estimates of lake volume from spaceborne visible and near infrared measurements

the morphology of supraglacial lake ogives supraglacial lakes on grounded regions of the greenland and antarctic ice sheets sometimes produce lake ogives or banded structures that sweep downstream from the lakes using a variety of remote sensing data we demonstrate that lake ogives originate from supraglacial lakes that form each year in the same bedrock fixed location near the equilibrium line altitude as the ice flows underneath one of these lakes an image of the lake is imprinted on the ice surface both by summer season ablation and by superimposed ice lake ice formation ogives associated with a lake are sequenced in time with the downstream ogives being the oldest and with spatial separation equal to the local annual ice displacement in addition lake ogives can have decimeter to meter scale topographic relief much like wave ogives that form below icefalls on alpine glaciers our observations highlight the fact that lake ogives and other related surface features are a consequence of hydrological processes in a bedrock fixed reference frame these features should arise naturally from physically based thermodynamic models of supraglacial water transport and thus they may serve as fiducial features that help to test the performance of such models

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

balance mass flux and ice velocity across the equilibrium line in drainage systems of greenland estimates of balance mass flux and depth averaged ice velocity through the cross section aligned with the equilibrium line are produced for each of six drainage systems in greenland the estimates are based on a model equilibrium line fitted to field data and on a revised distribution of surface mass balance for the conterminous ice sheet ice drainage divides and six major drainage systems are delineated using surface topography from ers radar altimeter data ice thicknesses at the equilibrium line and throughout each drainage system are based on the latest compilation of airborne radar sounding data described elsewhere the net accumulation rate in the area bounded by the equilibrium line is 399 gt a 1 and net ablation rate in the remaining area is 231 gt a 1 excluding an east central coastal ridge reduces the net accumulation rate to 397 gt a 1 with a range from 42 to 121 gt a 1 for the individual drainage systems the mean balance mass flux and depth averaged ice velocity at the cross section aligned with the modeled equilibrium line are 0 1011 gt km 2 a 1 and 0 111 km a 1 respectively with little variation in these values from system to system in contrast the mean mass discharge per unit length along the equilibrium line ranges from one half to double the overall mean rate of 0 0468 gt km 1 a 1 the ratio of the ice mass in the area bounded by the equilibrium line to the rate of mass output implies an effective exchange time of approximately 6 ka for total mass exchange the range of exchange times from a low of 3 ka in the se drainage system to 14 ka in the ne suggests a rank as to which regions of the ice sheet may respond more rapidly to climate fluctuations

supraglacial lakes on the larsen b ice shelf antarctica and at paakitsoq west greenland a comparative study we acknowledge the support of the u s national science foundation under grant ant 0944248

moment tensor inversions of m 3 earthquakes in the geysers geothermal fields california microearthquakes have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields hydrofracturing and co2 sequestration sites characterizing and understanding the faulting process of induced earthquakes which is generally achieved through moment tensor inversion could both help in risk prediction and in reservoir development monitoring however this is a challenging task because of their lower signal to noise ratio at frequencies typically used in earthquake source analyses therefore higher resolution velocity models and modeling of seismic waves at higher frequencies are required in this study we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions we utilize a short period seismic network located in the geysers geothermal field in northern california and limit our study to that which would be achieved by industry in a typical reservoir environment we obtain full moment tensor solutions of m 3 earthquakes using waveform modeling and first motion inversions we find that these two data sets give complimentary but yet different solutions some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially this illuminates the presence of fluids at depth and their role for the generation of these small magnitude earthquakes finally since first motions are routinely obtained for all magnitude earthquakes our approach could be extended to small earthquakes where noise level and complex green s functions prohibit using waveforms in moment tensor inversions

higher order gravitational potential gradients for geoscientific applications abstract gravity data have been applied for modelling and interpretation studies in geosciences this contribution reviews currently observable and foreseen gravity data represented by gradients of the gravitational potential functional models linking 3 d mass density distribution functions to potential gradients of up to the third order are formulated using volume integrals of the newtonian type with unitless kernel functions expressed both analytically and using infinite series of associated legendre functions spatial and spectral properties of the kernel functions are analysed and sensitivity of the gradients to particular mass density distributions is studied two particular mass density distribution models are used in numerical experiments a local 3 d mass density model representing shallow mass density variations and a global mass model represented by earth s upper sediments with lateral mass density variations computed values of the gradients demonstrate their different sensitivities to particular mass density distributions which change with an increasing distance of the gradients from gravitating masses third order gradients are particularly useful for studying near subsurface or shallow density structures such as caves caverns salt domes sediment basement morphology continental margins or buried fault systems that could be identified spatially more closely thus higher order gradients would offer an interesting tool for mass density mapping once their observability with the sufficient accuracy and resolution is realized

surface mass balance observations and automatic weather station data along a transect near kangerlussuaq west greenland surface mass balance data from the kangerlussuaq transect k transect located on the western part of the greenland ice sheet near 678n are presented the series covers the period 1990 2003 and is the longest series of surface mass balance measurements in greenland the surface mass balance measurements cover an altitude range of 390 1850m and show a linear increase of the specific mass balance with a mass balance gradient of 3 7 10 3 mm 1 and a mean equilibrium line altitude of 1535ma s l interannual variability shows a weak 4yearly periodicity in addition to the surface mass balance data automatic weather station data at an elevation of approximately 1010m are available for the period 1997 2002 these data are used to explain observed surface mass balance anomalies over the same 5years it is shown that variations in shortwave radiation dominate interannual variability the mean annual cycle of temperature is characterized by a maximum in summer around the melting point leading to a mean summer outgoing longwave radiation of approximately 314wm 2 the mean annual cycle in wind speed shows a maximum in winter on average around 8ms 1 and a minimum in summer on average around 5ms 1 which is characteristic for a katabatic forcing during summer the net radiation is on average about 61wm 2 which is used for ice melting at a rate of typically 2cmw e d 1 net radiation contributes 84 of the total energy used for summer melting averaged over the 5years

band limited bouguer gravity identifies new basins on the moon 1 spectral domain forward modeling is used to generate topography implied gravity for the moon using data from the lunar orbiter laser altimeter instrument operated on board the lunar reconnaissance orbiter mission this is subtracted from selenological and engineering explorer selene derived gravity to generate band limited bouguer gravity maps of the moon so as to enhance the gravitational signatures of anomalous mass densities nearer the surface this procedure adds evidence that two previously postulated basins on the lunar farside fitzgerald jackson 25 n 191 e and to the east of debye 50 n 180 e are indeed real when applied over the entire lunar surface band limited bouguer gravity reveals the locations of 280 candidate basins that have not been identified when using full spectrum gravity or topography alone showing the approach to be of utility of the 280 basins 66 are classified as distinct from their band limited bouguer gravity and topographic signatures making them worthy of further investigation

determination and localized analysis of intersatellite line of sight gravity difference results from the grail primary mission 1 the line of sight los gravity difference between two coorbiting spacecrafts is determined in terms of intersatellite range acceleration measurements available from the gravity recovery and interior laboratory grail the precise orbit data are crucial for retrieving gravity difference from range acceleration and aligning the los data particularly in altitude a relative orbit error of a few centimeters in position and a few tens m s in velocity is commensurate with the grail ranging instrument noise at a few gal in los gravity difference the power spectrum as well as the topography correlation and admittance is quantified by upward continuing the topographic potential forward modeling the los gravity along the spacecraft trajectory i e bouguer correction and comparing with the grail los observations based on the data analysis from the primary grail mission i found that the los gravity difference observation produced near unity correlation with topography potential out to degree 550 higher than the global estimate over the areas covered by the low altitude orbit 20 km the crustal density was estimated to be 2500 2600 kg m3 with regional variations of about 10 by minimizing the bouguer coherence of the grail data at the degree band 150 300 systematic decrease in the density estimates by 3 4 or 100 kg m3 was observed at shorter wavelengths degree band 300 500 it implies the inadequacy of a uniform density model across the entire lithosphere and suggests radial stratification of the bulk density or porosity due to spatially localized characteristic the los gravity difference data are well suited to regional analysis at the highest possible resolution

the constitution and structure of the lunar interior the current state of understanding of the lunar interior is the sum of nearly four decades of work and a range of exploration programs spanning that same time period missions of the 1960s including the rangers surveyors and lunar orbiters as well as earth based telescopic studies laid the groundwork for the apollo program and provided a basic understanding of the surface its stratigraphy and chronology through a combination of remote sensing surface exploration and sample return the apollo missions provided a general picture of the lunar interior and spawned the concept of the lunar magma ocean in particular the discovery of anorthite clasts in the returned samples led to the view that a large portion of the moon was initially molten and that crystallization of this magma ocean gave rise to mafic cumulates that make up the mantle and plagioclase flotation cumulates that make up the crust smith et al 1970 wood et al 1970 this model is now generally accepted and is the framework that unifies our knowledge of the structure and composition of the moon the intention of this chapter is to review the major advances that have been made over the past decade regarding the constitution of the moon s interior much of this new knowledge is a direct result of data acquired from the successful clementine and lunar prospector missions as well as the analysis of new lunar meteorites as will be seen results from these studies have led to many fundamental amendments to the magma ocean model much of what we know from sample analyses has been previously summarized elsewhere and only their most important aspects will be discussed in this chapter the reader is referred to the relevant chapters in the books basaltic volcanism on the terrestrial planets basaltic volcanism study project 1981 the

the impact of injection on seismicity at the geysers california geothermal field water injection into geothermal systems has often become a required strategy to extend and sustain production of geothermal resources to reduce a trend of declining pressures and increasing non condensable gas concentrations in steam produced from the geysers operators have been injecting steam condensate local rain and stream waters and most recently treated wastewater piped to the field from neighboring communities if geothermal energy is to provide a significant increase in energy in the united states the us department of energy goal is 40 000 mw by 2040 injection must play a larger role in the overall strategy i e enhanced geothermal systems egs presented in this paper are the results of monitoring microseismicity during an increase in injection at the geysers field in california using data from a high density digital microearthquake array although seismicity has increased due to increased injection it has been found to be somewhat predictable thus implying that intelligent injection control may be able to control large increases in seismicity

a new ice thickness and bed data set for the greenland ice sheet 2 relationship between dynamics and basal topography new data sets of bed and surface elevation have been combined with balance velocities bed topography and radar reflectivity to investigate the relationship between ice flow and bed conditions it has been found that the bed topography affects the local driving stresses and initiates the onset of streaming flow in specific areas where there are large undulations this onset region only appears significantly inland in three areas the northeast greenland ice stream kangerdlugssuaq gletscher and a region in the southwest associated with abnormally low driving stresses and an apparently unnamed but active glacier bed reflectance values below the northeast ice stream suggest that basal melting could be occurring along its length and it seems likely therefore that the enhanced flow observed inland from the onset of streaming may be due in part to basal sliding

surficial glaciology of jakobshavns isbrae west greenland part i surface morphology jakobshavns isbrae is a large fast moving ice stream outlet glacier in west greenland which ends at a floating calving front it drains about 6 5 of the area of the greenland ice sheet studies of its surface morphology are described in this paper the surface is relatively steep 0 01 0 03 and the thickness is large up to 2600 m along the center line clarke and echelmeyer 1989 indicating very high driving stresses 200 300 kpa the ice stream is about 6 km wide and 85 90 km long all of which is in an area of surface melting the base of the ice stream and of much of the drainage area is below sea level marginal crevasse zones have a width on the order of the width of the ice stream itself unique surficial features are ice blisters and lakes the latter have a sequence of ogive like features on their floating ice cover which can be used to determine velocity there is a pinning point near the terminus which may act as a stabilizing influence possibly playing a role in halting at least temporarily a recent retreat of the terminus ice thickness estimates at the terminus lead to a flux which is less than previously assumed by others e g bindschadler 1984 pelto and others 1989 when estimating jakobshavns isbrae s drainage basin to be nearly in balance the driving stresses on jakobshavns isbrae are an order of magnitude higher than those of the ice streams of west antarctica its crevasse patterns are much less localized its relatively unconfined terminus is more comparable to that of relatively unbuttressed ice streams such as pine island and thwaites glaciers than it is to other west antarctic ice streams which terminate in large confined ice shelves

the fractured moon production and saturation of porosity in the lunar highlands from impact cratering we have analyzed the bouguer anomaly ba of 1200 complex craters in the lunar highlands from gravity recovery and interior laboratory observations the ba of these craters is generally negative though positive ba values are observed particularly for smaller craters crater ba values scale inversely with crater diameter quantifying how larger impacts produce more extensive fracturing and dilatant bulking the bouguer anomaly of craters larger than 93 47 19 km in diameter is independent of crater size indicating that there is a limiting depth to impact generated porosity presumably from pore collapse associated with either overburden pressure or viscous flow impact generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than 30km in diameter consistent with an 8km thick lunar megaregolith whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces

seasonal ice mass balance buoys adapting tools to the changing arctic monitoring the local mass balance of arctic sea ice provides opportunities to attribute the observed changes in a particular floe s mass balance to specific forcing phenomena a shift from multi year to seasonal ice in large portions of the arctic presents a challenge for the existing lagrangian array of autonomous ice mass balance buoys which were designed with a perennial ice cover in mind this work identifies the anticipated challenges of operation in seasonal ice and presents a new autonomous buoy designed to monitor ice mass balance in the seasonal ice zone the new design presented incorporates features which allow the buoy to operate in thin ice and open water and reduce its vulnerability to ice dynamics and wildlife damage while enhancing ease of deployment a test deployment undertaken from april to june 2009 is discussed and results are presented with analysis to illustrate both the features and limitations of the buoy s abilities

evolution of supra glacial lakes across the greenland ice sheet abstract we used 268 cloud free moderate resolution imaging spectroradiometer modis images from 2003 and 2005 2007 to study the seasonal evolution of supra glacial lakes in three different regions of the greenland ice sheet lake area estimates were obtained by developing an automated classification method for their identification based on 250 m resolution modis surface reflectance observations widespread supra glacial lake formation and drainage is observed across the ice sheet with a 2 3 week delay in the evolution of total supra glacial lake area in the northern areas compared to the south west the onset of lake growth varies by up to one month inter annually and lakes form and drain at progressively higher altitudes during the melt season a positive correlation was found between the annual peak in total lake area and modelled annual runoff high runoff and lake extent years are generally characterised by low accumulation and high melt season temperatures and vice versa our results indicate that in a future warmer climate meehl g a stocker t f collins w d friedlingstein p gaye a t gregory j m kitoh a knutti r murphy j m noda a raper s c b watterson i g weaver a j zhao z c 2007 global climate projections in climate change 2007 the physical science basis contribution of working group i to the fourth assessment report of the intergovernmental panel on climate change solomon s d qin m manning z chen m marquis k b averyt m tignor h l miller eds cambridge university press cambridge united kingdom and new york ny usa greenland supra glacial lakes can be expected to form at higher altitudes and over a longer time period than is presently the case expanding the area and time period over which connections between the ice sheet surface and base may be established das s joughin m behn m howat i king m lizarralde d bhatia m 2008 fracture propagation to the base of the greenland ice sheet during supra glacial lake drainage science 5877 778 781 with potential consequences for ice sheet discharge zwally h j abdalati w herring t larson k saba j steffen k 2002 surface melt induced acceleration of greenland ice sheet flow science 297 218 221

formation of band ogives and associated structures at bas glacier d arolla valais switzerland hambrey m j glasser n f goodsell becky 2002 formation of band ogives and associated structures at bas glacier d arolla valais switzerland journal of glaciology 48 161 pp 287 300 keywords europe switzerland geometrical structure three dimensional structure radar observation glacier crevasse models debris interface basal ice glacial tongue stratification glacier

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

the present status of reservoir induced seismicity investigations with special emphasis on koyna earthquakes abstract the status of reservoir induced seismicity ris has been reviewed periodically rothe 1968 1973 gupta and rastogi 1976 simpson 1976 packer et al 1979 in the present paper the significant work carried out during the last three years on ris is reviewed an earthquake of magnitude 5 1 2 occurred on november 14 1981 in the vicinity of aswan lake egypt 17 years after the filling started in 1964 this event occurred 4 days after the seasonal maximum in the reservoir water level and was followed by a long sequence of aftershocks another event of magnitude 4 1 2 occurred in the vicinity of aswan lake on august 20 1982 results of preliminary investigations indicate that this seismic activity is reservoir induced recent analyses of induced seismic events at nurek reservoir u s s r show that the second stage of filling during august to december 1976 increasing the maximum depth from 120 m to 200 m was accompanied by an intense burst of shallow seismic activity an outward migration from the centre of the reservoir possibly associated with diffusion of pore pressure is revealed by the temporal distribution of earthquake foci a variety of investigations including the in situ measurement of tectonic stress pore pressure permeability distribution of faults etc in addition to monitoring seismicity have been undertaken in the vicinity of the monticello reservoir south carolina the largest reservoir induced earthquake is predicted not to exceed magnitude 5 the koyna reservoir india continues to be the most outstanding example of ris three earthquakes of magnitude 5 occurred in september 1980 earthquakes of magnitude 4 occur frequently in the vicinity of koyna the latest being on february 5 1983 events that occurred during the period 1967 1973 have been relocated using better procedures and are found to be much shallower and the epicentres less diffused location of 12 earthquakes of ms 4 0 their foreshocks and aftershocks that occurred during 1973 1976 composite focal mechanism solutions and related studies are consistent with the delineation of a n s trending fault through the reservoir area in a couple of interesting studies it has been demonstrated that earthquakes of magnitude 5 0 in the koyna region are usually preceded by several magnitude 4 earthquakes in the preceding fortnight also a rate of loading of koyna reservoir of at least 40 ft week appears to be a necessary although not sufficient condition for the occurrence of magnitude 5 earthquakes smooth filling emptying appears to be the key to reduce the hazard of ris a map and a table of the reported cases of reservoir induced changes in seismicity through 1982 have been compiled

analysis of synthetic aperture radar data collected over the southwestern greenland ice sheet analyses of the first aircraft multi frequency polarimetric synthetic aperture radar sar data acquired over the southwestern greenland ice sheet are presented data were collected on 31 august 1989 by the jet propulsion laboratory sar using the nasa dc 8 aircraft along with curvilinear patterns associated with large scale morphologic features such as crevasses lakes and streams frequency and polarization dependencies are observed in the p l and c band image products

modelling the delivery of supraglacial meltwater to the ice bed interface application to southwest devon ice cap nunavut canada the transfer of surface generated meltwater to the subglacial drainage system through full ice thickness crevassing may lead to accelerated glacier velocities with implications for ice motion under future climatic scenarios accurate predictions of where surface meltwater accesses the ice bed interface are therefore needed in fully coupled hydrodynamic ice sheet models we present a spatially distributed modelling routine for predicting the location and timing of delivery of surface derived meltwater to the ice bed interface through moulins and supraglacial lake drainage the model is explained as it is applied to the croker bay glacial catchment of devon ice cap canada the formation of moulins drainage of lakes and the transfer of meltwater through the full ice thickness are modelled for the 2004 and 2006 ablation seasons through this case study we assess the model s sensitivity to degree day factors fracture toughness tensile strength and crevasse width and confirm that parameters influencing the rate at which water fills a crevasse are the most significant controls on the ability of a crevasse to reach the bed increased surface melt production therefore has the potential to significantly influence the spatial and temporal transfer of meltwater through surface to bed connections in a warmer climate

topography of the moon from the clementine lidar range measurements from the lidar instrument carried aboard the clementine spacecraft have been used to produce an accurate global topographic model of the moon this paper discusses the function of the lidar the acquisition processing and filtering of observations to produce a global topographic model and the determination of parameters that define the fundamental shape of the moon our topographic model a 72nd degree and order spherical harmonic expansion of lunar radii is designated goddard lunar topography model 2 gltm 2 this topographic field has an absolute vertical accuracy of approximately 100 m and a spatial resolution of 2 5 the field shows that the moon can be described as a sphere with maximum positive and negative deviations of 8 km both occurring on the farside in the areas of the korolev and south pole aitken s p aitken basins the amplitude spectrum of the topography shows more power at longer wavelengths as compared to previous models owing to more complete sampling of the surface particularly the farside a comparison of elevations derived from the clementine lidar to control point elevations from the apollo laser altimeters indicates that measured relative topographic heights generally agree to within 200 m over the maria while the major axis of the lunar gravity field is aligned in the earth moon direction the major axis of topography is displaced from this line by approximately 10 to the east and intersects the farside 24 north of the equator the magnitude of impact basin topography is greater than the lunar flattening 2 km and equatorial ellipticity 800 m which imposes a significant challenge to interpreting the lunar figure the floors of mare basins are shown to lie close to an equipotential surface while the floors of unflooded large basins except for s p aitken lie above this equipotential the radii of basin floors are thus consistent with a hydrostatic mechanism for the absence of significant farside maria except for s p aitken whose depth and lack of mare require significant internal compositional and or thermal heterogeneity a macroscale surface roughness map shows that roughness at length scales of 10 1 10 2 km correlates with elevation and surface age

a dynamic origin for the global asymmetry of lunar mare basalts we propose that the hemispheric asymmetry fig 1 of mare basalts may be explained as a result of hydrodynamic instabilities associated with a layer of mixed ilmenite rich cumulates ic and olivine orthopyroxene opx overlying a metallic core this mixed layer mic should form shortly after the solidification of the magma ocean p c hess and e m parmentier earth planet sci lett 134 1995 501 514 because of gravitational differentiation of chemically dense ic material that is expected to form below the anorthositic crust in the final stages of magma ocean crystallization a e ringwood and s e kesson proc lunar planet sci conf 7 1976 1697 1722 ic material is rich in heat producing elements and thermal expansion due to radiogenic heating causes the mic layer to become less dense than overlying mantle the time required for the mic layer to become thermally buoyant may explain a delay of mare volcanism until about 500 ma after solidification of the magma ocean our analyses of the resulting rayleigh taylor instability and numerical modeling of thermo chemical convection show that the instabilities produce spherical harmonic degree 1 thermal and compositional structure if a lunar metallic core is sufficiently small less than 250 km in radius fl 2000 elsevier science b v all rights reserved

a 1 5km resolution gravity field model of the moon we present a high resolution lunar gravity field model lgm2011 that provides gravity accelerations free air gravity anomalies selenoid undulations and vertical deflections over the entire moon s surface lgm2011 is based on the japanese selene mission that provides the low and medium frequency constituents of the gravity field down to spatial scales of 78 km at spatial scales between 78 km and 1 5 km lgm2011 uses highfrequency topographic information derived from lola laser altimetry to approximate the gravity field signatures of many medium and small size impact craters for the first time for the topography based gravity approximation we use newtonian forward modelling under the key assumptions that the selene and lola data are consistent the high frequency lunar topography is uncompensated and the topographic mass density is constant the short scale component of lgm2011 should not be relied upon in geophysical interpretations lgm2011 can be used as an a priori model for lunar gravity field simulation and inversion studies evaluation of past and future lunar gravity field missions improved topographic mapping

limits to future expansion of surface melt enhanced ice flow into the interior of western greenland moulins are important conduits for surface meltwater to reach the bed of the greenland ice sheet it has been proposed that in a warming climate newly formed moulins associated with the inland migration of supraglacial lakes could introduce surface melt to new regions of the bed introducing or enhancing sliding there by examining surface strain rates we found that the upper limit to where crevasses and therefore moulins are likely to form is 1600m this is also roughly the elevation above which lakes do not drain completely thus meltwater above this elevation will largely flow tens of kilometers through surface streams into existing moulins downstream furthermore results from a thermal ice sheet model indicate that the 1600m crevassing limit is well below the wet frozen basal transition 2000m together these data sets suggest that new supraglacial lakes will have a limited effect on the inland expansion of melt induced seasonal acceleration key points greenland ice sheet meltwater volumes are increasing notably at high elevations low strain rates limit the likelihood of moulin formation at high elevations high elevation meltwater will reach an already wet bed at lower elevations

lunar multiring basins and the cratering process abstract numerous studies of the lunar gravity field have concluded that the lunar moho is substantially uplifted beneath the young multiring basins this uplift is presumably due to the excavation of large quantities of crustal material during the cratering process and subsequent rebound of the impact basin floor using a new dual layered crustal thickness model of the moon the excavation cavities of some nearside multiring basins grimaldi and larger and younger than tranquillitatis were reconstructed by restoring the uplifted moho to its preimpact location the farside south pole aitken spa basin was also considered due to its importance in deciphering lunar evolution restoring the moho to its preimpact position beneath these basins resulted in a roughly parabolic depression from which the depth and diameter of the excavation cavity could be determined using these reconstructed excavation cavities the basin forming process was investigated excavation cavity diameters were generally found to be on the small side of most previous estimates for orientale the modeled excavation cavity lies within the inner rook ring additionally with the exception of the three largest basins serenitatis imbrium and south pole aitken the depth diameter ratios of the excavation cavities were found to be 0 115 0 005 a value consistent with theoretical and experimental results for impact craters orders of magnitude smaller in size the three largest basins however appear to have significantly shallower depths of excavation compared to this trend it is possible that this may reflect a different physical process of crater formation e g nonproportional scaling special impact conditions or postimpact modification processes the crustal thickness model also shows that each basin is surrounded by an annulus of thickened crust we interpret this thickened crust as representing thick basin ejecta deposits and we show that the radial variation in the thickness of these deposits is consistent with scaling laws obtained from small scale experimental studies if multiring basins ever possessed a terraced main crater rim this terraced zone may be presently unrecognizable at the surface due to the emplacement of ejecta deposits that exceed a few kilometers in thickness exterior to the excavation cavity rim we also show that the interiors of many basins were superisostatic before mare volcanism commenced those basins that were closest to approaching a premare isostatic state lie close to or within an anomalous geochemical province rich in heat producing elements

the compensation state of intermediate size lunar craters abstract the compensation state of 49 intermediate size 120 to 600 km diameter lunar craters are investigated using the most recent spherical harmonic models of the lunar topography and gravity truncated at degree n 110 the total mass anomalies per unit area i e the lateral variations of the vertically integrated density perturbations per unit area within an otherwise uniform crust of 60 km thickness are determined such that together with the surface topography give rise to the model gravity anomalies crustal thicknesses of 40 and 80 km are also considered but the general results of this study are not significantly affected excess mass anomalies are obtained by subtracting from the total mass anomalies the mass anomalies that are required for the isostatic compensation of the surface topography the excess mass anomaly of a crater denotes its particular state of compensation dependencies of the excess mass anomalies on crater location size and age are investigated but in general few discernable trends are evident although the vast majority of craters indicate some compensation no correlation exists between age or size and the state of compensation roughly 16 of the craters show no compensation and in some cases have mass deficiencies most likely due to the shock fractured bedrock the breccia lens of lower density the crust in these regions was likely cold and rigid enough at the time of impact to rigidly support the stress caused by crater excavation these features are seen throughout different geological periods demonstrating that the lunar crust cooled quickly and strengthened soon after formation a comparison of the compensation state of craters apollo korolev and hertzsprung suggests that the thermal and mechanical properties of the crust prior to impact had an appreciable effect on the compensation and that crustal thickness may be the single most important factor controlling the compensation of intermediate size craters the characteristics of the excess mass a nomaly profiles of the eight well known near side mascon basins are used to identify new mascon like craters ten newly found mascons are confirmed humboldtianum moscoviense mendel rydberg lorentz hertzsprung korolev schrodinger freundlich sharonov coulomb sarton and schiller zucchius while two more deslandres and dirichlet jackson are very plausible these results show that mare flow is not necessarily required to produce mascon like characteristics

sticky spots and subglacial lakes under ice streams of the siple coast antarctica locations of subglacial lakes discovered under fast moving west antarctic ice streams tend to be associated with topographic features of the subglacial bed or with areas that have strong variations in basal conditions inversion of ice stream surface velocity indicates that basal conditions under ice streams can be highly variable and that there can be widespread regions where basal traction is high to seek an explanation for why lakes appear to be sited near areas with high basal traction we use numerical models to simulate ice stream dynamics thermodynamics and subglacial water flow we demonstrate that the ice flow over high basal traction areas produces favourable conditions for the ponding of meltwater energy dissipation associated with ice sliding over a region with high basal traction constitutes a water source supplying a lake and ice thickness perturbations induced by ice flow over variable traction create local minima in hydraulic potential variations in thermodynamic processes caused by such ice flow could be responsible for limiting the horizontal extent of the subglacial lakes

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

thin elastic shells with variable thickness for lithospheric flexure of one plate planets summary planetary topography can either be modelled as a load supported by the lithosphere or as a dynamic effect due to lithospheric flexure caused by mantle convection in both cases the response of the lithosphere to external forces can be calculated with the theory of thin elastic plates or shells on one plate planets the spherical geometry of the lithospheric shell plays an important role in the flexure mechanism so far the equations governing the deformations and stresses of a spherical shell have only been derived under the assumption of a shell of constant thickness however local studies of gravity and topography data suggest large variations in the thickness of the lithosphere in this paper we obtain the scalar flexure equations governing the deformations of a thin spherical shell with variable thickness or variable young s modulus the resulting equations can be solved in succession except for a system of two simultaneous equations the solutions of which are the transverse deflection and an associated stress function in order to include bottom loading generated by mantle convection we extend the method of stress functions to include loads with a toroidal tangential component we further show that toroidal tangential displacement always occurs if the shell thickness varies even in the absence of toroidal loads we finally prove that the degree one harmonic components of the transverse deflection and of the toroidal tangential displacement are independent of the elastic properties of the shell and are associated with translational and rotational freedom while being constrained by the static assumption degree one loads can deform the shell and generate stresses the flexure equations for a shell of variable thickness are useful not only for the prediction of the gravity signal in local admittance studies but also for the construction of stress maps in tectonic analysis

volume change of jakobshavn isbrae west greenland 1985 1997 2007 following three decades of relative stability jakobshavn isbrae west greenland under went dramatic thinning retreat and speed up starting in 1998 to assess the amount of ice loss we analyzed 1985 aerial photos and derived a 40 m grid digital elevation model dem we also obtained a 2007 40 m grid spot dem covering the same region comparison of the two dems over an area of 4000 km 2 revealed a total ice loss of 160 4k m 3 with 107 0 2 km 3 in grounded regions 0 27 mm eustatic sea level rise and 53 4k m 3 from the disintegration of the floating tongue comparison of the dems with 1997 nasa airborne topographic mapper data indicates that this ice loss essentially occurred after 1997 with 0 7 5 6 km 3 between 1985 and 1997 and 160 7k m 3 between 1997 and 2007 the latter is equivalent to an average specific mass balance of 3 7 0 2 m a 1 over the study area previously reported thickening of the main glacier during the early 1990s was accompanied by similar magnitude thinning outside the areas of fast flow indicating that the land based ice continued reacting to longer term climate forcing

isostasy of the moon from high resolution gravity and topography data implication for its thermal history 1 the lunar prospector line of sight acceleration data after terrain correction have been inverted to the high resolution bouguer gravity anomalies of the lunar nearside lithospheric thicknesses of the early moon were investigated by comparing the gravity anomalies of craters and impact basins of various dimensions the lithosphere was already thick enough to support craters with diameters up to 300 km in the pre nectarian and nectarian periods degree of isostatic compensation of larger impact basins suggested lithospheric thickness of 20 60 km at that time which depended more on localities rather than age differences

a serenitatis origin for the imbrian grooves and south pole aitken thorium anomaly the northwest corner of the moon s south pole aitken spa basin contains a high abundance of thorium and a unique imbrian aged geomorphologic unit that consists of grooves and mounds referred to here as the imbrian grooves because the location of these features are almost antipodal to the imbrium basin where high thorium ejecta and seismic energy are expected to have converged an imbrium origin for these units has long seemed certain by modeling the deposition of impact ejecta on the moon we have investigated whether the convergence of imbrium s ejecta at its antipode could be the origin of both the imbrian grooves and spa thorium anomaly as a result of the moon s rotation our results show that ejecta from this basin should converge more than 12 west of its antipode both the imbrian grooves and thorium anomaly within spa however reside slightly to the east of imbrium s antipode in an attempt to reconcile this disparity the effects of a putative oblique imbrium impact have been qualitatively investigated while this model can distribute ejecta in the general vicinity of the imbrian grooves the planform of our modeled antipodal ejecta is distinctly different from that which is observed as an alternative explanation for the origin of these features we find that the modeled distribution of ejecta from an oblique serenitatis impact is surprisingly similar to the planform of the imbrian grooves with the exception that it is offset directly to the east this eastward offset is likely to be an artifact of our not being able to properly include the effects of the moon s rotation in our oblique impact models we conclude that the imbrium grooves and spa thorium anomaly are most consistent with having an origin from the convergence of ejecta antipodal to the serenitatis basin if this conclusion can be substantiated once quantitative ejecta scaling relations for oblique impacts are determined then this implies that 1 the serenitatis target contained a high abundance of thorium and 2 the convergence of seismic energy at the antipodes of either the imbrium or serenitatis basin was not sufficient to cause substantial surface modification extrapolating this result to mercury suggests that the hilly and lineated terrain antipodal to the caloris basin was formed by the convergence of ejecta and not seismic waves

role of membrane stresses in the support of planetary topography the principal purpose of this paper is to examine whether membrane stresses can support topographic loads on planetary elastic lithospheres it is found that the ability of a spherical shell to support loads through membrane stresses is determined by the nondimensional parameter ed gr2 where d is the thickness of the elastic lithosphere is the density difference between the mantle and crust and r is the radius of the planetary body when this parameter is large membrane stresses can fully support topographic loads without flexure and when it is small the influence of membrane stresses can be neglected solutions of the equation governing the behavior of a spherical shell are obtained for a topographic load expressed in terms of spherical harmonics spherical harmonic expansions of the measured gravity and topography for mars and the moon are compared with the theory it is found that for mars the support of topography is primarily due to membrane stresses for n 8 and for the moon for n 17 for mars the data for 4 n 7 give 0 5 for the moon the data have considerable scatter that is attributed to the mascons but generally correlate with 0 5 if bending stresses are neglected the governing equation for the deflection of the spherical shell is legendre s equation a general solution is obtained for an axisymmetric load this solution is applied to the tharsis region on mars the 60 65 compensation of this region requires that 0 6 the well defined fracture pattern surrounding the tharsis region is attributed to tensional membrane stresses

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

velocity density properties of the lithosphere from three dimensional modeling at the geysers clear lake region california the analysis of travel time delays from 94 teleseisms recorded at the geysers clear lake california region reveals a broad area of delay centered at mount hannah and encompassing the geysers geothermal field a three dimensional velocity inversion of the delays indicates that the source of the delays is a low velocity body largely within the top 30 km of the lithosphere velocity decreases of as much as 20 are observed in the top 15 km near mount hannah and diminish with depth no significant velocity fluctuations are observed below 60 km the block model of velocity perturbations resulting from the teleseismic residual inversion is used to predict the observed bouguer gravity field by solving for the relation between velocity and density perturbation comparison between the predicted gravity and observed gravity indicates that the same body responsible for the teleseismic delays accounts for the long wave length 30 mgal bouguer gravity minima at mount hannah the results of the velocity density modeling suggest that the material beneath mount hannah and the geysers may be partially molten and somewhat more silicic than the surrounding medium supplemental table is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 006 1 00 payment must accompany order

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

lunar prospector overview lunar prospector is providing a global map of the composition of the moon and analyzing the moon s gravity and magnetic fields it has been in a polar orbit around the moon since 16 january 1998 neutron flux data show that there is abundant h and hence probably abundant water ice in the lunar polar regions gamma ray and neutron data reveal the distribution of fe ti and other major and trace elements on the moon the data delineate the global distributions of a key trace element rich component of lunar materials called kreep and of the major rock types magnetic mapping shows that the lunar magnetic fields are strong antipodal to mare imbrium and mare serenitatis and has discovered the smallest known magnetosphere magnetosheath and bow shock complex in the solar system gravity mapping has delineated seven new gravity anomalies and shown that the moon has a small fe rich core of about 300 km radius

fossil figure contribution to the lunar figure abstract the unusual shape of the moon given its present rotational and orbital state has been explained as due to a fossil figure preserving a record of remnant rotational and tidal deformation jeffreys h 1915 mem r astron soc 60 187 217 lambeck k pullan s 1980 phys earth planet interiors 22 29 35 garrick bethell i wisdom j zuber m t 2006 science 313 652 655 however previous studies assume infinite rigidity and ignore deformation due to changes in the rotational and orbital potentials as the moon evolves to the present state we interpret the global lunar figure with a physical model that takes into account this deformation although the moon deforms in response to rotational and orbital changes a fossil figure capable of explaining the observed figure can be preserved by an elastic lithosphere

continued evolution of jakobshavn isbrae following its rapid speedup 1 several new data sets reveal that thinning and speedup of jakobshavn isbrae continue following its recent rapid increase in speed as its floating ice tongue disintegrated the present speedup rate of 5 a 1 over much of the fast moving region appears to be a diffusive response to the initial much larger speedup near the front there is strong seasonality in speed over much of the fast flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short typically 6 km floating ice tongue this modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003 analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving major calving only resumes in late winter when much of this ice clears from the fjord the collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea ice concentration in disko bay this decline may have extended the length of the calving season for several consecutive years leading to the ice tongue s collapse

the relative timing of lunar magma ocean solidification and the late heavy bombardment inferred from highly degraded impact basin structures the solidification of the lunar magma ocean lmo and formation of impact basins are important events that took place on the early moon the relative timing of these events however is poorly constrained the aim of this study is to constrain the formation ages of old impact basins based on inferences of their thermal state most proposed basins formed before pre nectarian pn 5 stage do not exhibit clear concentric features in either topography or gravity suggesting substantial viscous lateral flow in the crust recent geodetic measurements reveal that the lunar crust is thinner than previously estimated indicating that an extremely high crustal temperature is required for lateral flow to occur in this study we calculate lunar thermal evolution and viscoelastic deformation of basins and investigate the thermal state at the

persistent englacial drainage features in the greenland ice sheet 1 surface melting on the greenland ice sheet is common up to 1400 m elevation and in extreme melt years even higher water produced on the ice sheet surface collects in lakes and drains over the ice sheet surface via supraglacial streams and through the ice sheet via moulins water delivered to the base of the ice sheet can cause uplift and enhanced sliding locally here we use ice penetrating radar data to observe the effects of significant basal melting coincident with moulins and calculate how much basal melt occurred we find that more melting has occurred than can be explained by the release of potential energy from the drainage of surface meltwater during one melt season suggesting that these moulins are persistent for multiple years we find only a few persistent moulins in our study area that drain the equivalent of multiple lakes per year and likely remain active over several years our observations indicate that once established these persistent moulins might be capable of establishing well connected meltwater drainage pathways

supraglacial lake spatial structure in western greenland during the 2007 ablation season 1 increases in surface melt rates along the greenland ice sheet margin have accelerated meltwater production resulting in supraglacial lakes that can drain rapidly and enhance basal sliding in this study supraglacial lakes in western greenland are mapped from multitemporal landsat panchromatic imagery during the 2007 melt season the analysis models lake spatial structure and establishes sequencing of drainage from 6 june through 9 august 2007 results indicate high spatial clustering at lower elevations between 100 and 700 m with minimum lake to lake distances of 100 500 m and lake sizes 0 5 km2 at higher elevations 700 1200 m clustering decreases with minimum distances on the order of 900 1400 m and lake sizes between 0 5 and 1 km2 lakes at elevations above 1200 m exhibit less clustering and smaller areas clustering was spatially heterogeneous within elevation bands with high clustering between ice streams and fewer lakes along shear margins spatial patterns of lake drainage throughout the 2007 melt season exhibit strong spatial coherency the magnitude of clustering reveals patterns caused by surface melt production and water routing through surface streams as well as in situ drainage cluster patterns are influenced by proximity to crevasses fields shear margins as well as topographic structure

ancient selenophysical structure of the grimaldi basin constraints from grail gravity and lola topography abstract the grimaldi impact basin is located near the western limb of the moon and lies to the southwest of the oceanus procellarum a clearly visible positive gravity anomaly exists in its low lying inner wall implying a subsurface mass concentration beneath the crater exploration of this basin could extend our meaningful and fundamental understanding of giant impact processes as well as the structure of mare basins craters limited by the low resolution of previous gravity field models it was once impossible to explore the structure beneath grimaldi the recent high resolution gravity data from the gravity recovery and interior laboratory mission make it possible to break through this barrier prior to our investigation of the selenophysical structure around crater grimaldi we developed a flexure model that includes surface and subsurface loads a localized admittance analysis was performed by combining high resolution gravity data with the high resolution topography data obtained from lunar orbiter laser altimeter within 2 std error constraints we estimated the best fit parameters over grimaldi as well as two other places in its neighborhood all the predicted admittances show a goodness of fit with their corresponding observations the large load ratio 9 2 found at the grimaldi is an indirect mirror of the dominant subsurface load consistent with its large positive gravity anomaly in its low lying floor not only the crustal thickness of 48 km but also the crustal density of 2500 kg m 3 found around grimaldi shows a great accordance with the recent results of grail given the best fit parameters of f bc and c the elastic thickness te is found to be around 28 km over grimaldi taking into account the best fit values in its neighborhood a regional elastic thickness of 30 km could be roughly concluded around grimaldi which is completely in the previous ranges 20

remote sounding of greenland supraglacial melt lakes implications for subglacial hydraulics a supraglacial lake depth retrieval function is developed based on the correspondence between moderate resolution imaging spectroradiometer modis reflectance and water depth measured during raft surveys individual lake depth area and volume statistics including short term temporal changes for greenland s southwestern ablation region were compiled for 2000 05 the maximum area of an individual lake was found to be 8 9 km 2 the maximum volume 53 0 10 6 m 3 and the maximum depth 12 2 m sampling over 0 0625 km 2 pixel areas the total lake volume reaches 1 km 3 in this region by july each year the importance of melt lake reservoirs to greenland ice sheet flow may be a feedback between abrupt lake drainage events and ice dynamics lake outburst volumes up to 31 5 10 6 m 3 d 1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment since the overburden pressure at the base of a flooded moulin is greater than that provided by ice lake outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally if water flow in the subglacial environment is constrained laterally considering a moulin with a 10 m 2 cross sectional area basal pressurization can be maintained over lake outburst

progressive inversion for hypocenters and p wave and s wave velocity structure application to the geysers california geothermal field seismicity at the geysers is induced by some aspect of steam production accurate earthquake locations particularly hypocentral depth are needed to determine the relationship between geothermal energy production and seismicity progressive p and s wave velocity hypocenter inversions were done using data from 39 microearthquakes at the geysers to estimate microearthquake locations and determine if the geothermal field has a distinctive seismic signature comparable final vp vs and vp vs velocity models were obtained from four different starting velocity models the elevation interval of maximum steam production coincides with minimum observed vp vs and vp vs increases below the primary production zone suggesting that reservoir rock becomes more fluid saturated with increasing depth a vp vs peak at the condensation zone production zone elevation delineates the top of the stream reservoir earthquake locations are confined to two depth intervals a zone of shallow seismicity occurs immediately below the condensation zone and above maximum depths of steam production a more arealy restricted zone of seismicity is located below maximum production depths and is abruptly terminated at an elevation of 3 7 km

a source model for induced earthquakes at the geysers geothermal reservoir the results of a previous study on source mechanisms of small earthquakes at the geysers geothermal reservoir in northern california are used to investigate an extended crack model for seismic events the seismic events are characterized by their first degree moment tensors and interpreted in terms of a model that is a combination of a shear crack and wing cracks solutions to both forward and inverse problems are obtained that can be used with either dynamic or static moment tensors the model contains failure criteria explains isotropic parts that are commonly observed in induced earthquakes and produces estimates of crack dimensions and maximum amount of slip effects of fluid pressure are easily incorporated into the model as an effective stress the model is applied to static moment tensors of 20 earthquakes that occurred during a controlled injection project in the northwest geysers for earthquakes in the moment magnitude range of 0 9 2 8 the model predicts shear crack radii in the range of 10 150 m wing crack lengths in the range of 2 25 m and maximum slips in the range of 0 3 1 1 cm only limited results are obtained for the time dependence of the earthquake process but the model is consistent with corner frequencies of the isotropic part of the moment tensor being greater than the deviatoric part and waveforms of direct p waves that become more emergent for larger events

fast draining lakes on the greenland ice sheet 1 the rapid drainage of supraglacial lakes around the ablation zone of the greenland ice sheet forms an important link between water at the surface and the ice sheet base allowing surface meltwater to reach the bed and hence increase glacial velocity the conduits formed by lake drainages may remain open during the remainder of the melt season providing a pathway for further meltwater to reach the base we investigated the drainage behavior of lakes from all regions of the greenland ice sheet for the period 2005 2009 we mapped the evolution of 2600 lakes from 3704 modis images detecting a mean of 263 drainage events per year of which 61 occurred in the south west region only 1 of lake drainages occurred in the rapidly thinning south east region our results show marked differences between the hydrology of the different regions of the ice sheet with few lake drainages occurring in the regions where the highest dynamic mass loss is occurring in the south west and north east lake drainages are common and could impact glacier dynamics in the south east they are rare and are thus unlikely to do so