changing climate changing process implications for salt transportation and weathering within building sandstones in the uk salt weathering is a crucial process that brings about a change in stone from the scale of landscapes to stone outcrops and natural building stone facades it is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture where repeated oscillations in these parameters can cause re crystallisation hydration de hydration of salts bringing about stone surface loss in the form of for example granular disaggregation scaling and multiple flaking however this traditional view of how salt weathering proceeds may need to be re evaluated in the light of current and future climatic trends indeed there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general building on contemporary research on the deep wetting of natural building stones it is proposed that as stone may be wetter for longer ion diffusion may become a more prominent mechanism for the mixing of molecular constituents and a shift in focus from physical damage to chemical change is suggested data from ion diffusion cell experiments are presented for three different sandstone types demonstrating that salts may diffuse through porous stone relatively rapidly in comparison to for example dense concrete pore water from stones undergoing diffusion experiments was extracted and analysed factors controlling ion diffusion relating to time of wetness within stones are discussed continued saturation connectivity of pores mineralogy behaviour of salts sedimentary structure and potential changes in system dynamics as a result of climate change are addressed system inputs may change in terms of increased moisture input translating into a greater depth of wetting front salts are likely to be stored differently in stones with salt being in solution for longer periods during prolonged winter wetness this has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone especially in more mobile constituents leading to a weakening of the stone matrix grain boundary cementing the output may be mobilisation and precipitation of elements leading to for example uneven cementing in the stone this reduced strength of the stone or compromised ability of the stone to absorb stress is likely to make crystallisation a more efficacious mechanism of decay when it does occur thus a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens

arcades products of stress controlled and discontinuity related weathering abstract weathering patterns on sandstone cliff faces and sloping surfaces were studied from the viewpoint of gravity induced stress combined with the presence of planar discontinuities in the rock critical evaluation of hundreds of photos taken in various regions around the world numerical modelling using finite element method including automatic stress controlled element removal technique of erosion modelling and physical in situ modelling of friable sandstone revealed the formation of a specific sub group of weathering forms related to planar discontinuities due to their striking similarity with elements known from architecture these pits are introduced as arcades or arcade like forms these pits and cavities vary in size but they are similar in shape coalesced into trains along the discontinuities and separated from each other by hourglass shaped pillars in their origin and geometry these forms differ from widely known cavernous weathering forms such as honeycombs and tafoni we have shown that arcade shape and size are controlled by the redistribution of gravity induced stress along planar discontinuities and the resulting stress shadows the stress shadow zones along the discontinuities are characterized by material loss owing to various weathering and erosional mechanisms although overlooked as yet stress controlled weathering along discontinuities has a strong effect on rock surface morphology and arcades can be taken as its principal example

lumped element analysis of subglacial hydraulic circuits observations of the subglacial hydrological system reveal a richness of responses that are thought to reflect variations in the water supply morphology and connectivity of the system to contribute insight into the physical controls that result in qualitative variations in system response a lumped element formalism is developed and used to simulate the behavior of simple hydraulic circuits the circuit elements for an idealized subglacial water system differ from those used to analyze conventional hydraulic flows but the motivation is similar lumped systems are governed by ordinary differential equations whereas continuous systems are governed by partial differential equations the accompanying examples illustrate the capture property of rothlisberger channels the concept of morphological switching the role of water storage geometry in contributing to system nonlinearity and the effects of seasonal variations in storage capacity and hydraulic resistance

upper bounds on subglacial channel development for interior regions of the greenland ice sheet dow c f kulessa b rutt i c doyle s h hubbard a 2014 upper bounds on subglacial channel development for interior regions of the greenland ice sheet journal of glaciology 60 224 1044 1052 embargo until 01 07 2015

simulating the growth of tafoni throughout the world large caves in rocks tafoni are found which originate from salt weathering the mechanisms that control their development are poorly understood the growth of tafoni has been studied with a model that describes how a rock surface containing a small pit disintegrates by salt crystallization during wetting drying cycles in the model the rock is mapped on a grid the migration and crystallization of salts are simulated explicitly in the drying phase of a cycle at the end of each wetting drying cycle the amount of salt deposited at the grid nodes is evaluated and the shape of the rock surface is adjusted by removing nodes the length of the drying period in a single cycle proved to be the key parameter for short drying periods the amount of crystallized salt at the surface is proportional to the drying rate therefore for short drying periods most salts are deposited at the more exterior parts of the rock surface as a result most damage will develop at these parts of the surface which results in smooth surfaces due to the characteristics of the drying process for long drying periods most salts accumulate at regions with low evaporation rates which are the sheltered parts of the rock surface these parts are not exposed to the wind or the sun as a result the pit grows and a tafone develops copyright 2004 john wiley sons ltd

origin of honeycombs testing the hydraulic and case hardening hypotheses abstract cavernous weathering cavernous rock decay is a global phenomenon which occurs in porous rocks around the world although honeycombs and tafoni are considered to be the most common products of this complex process their origin and evolution are as yet not fully understood the two commonly assumed formation hypotheses hydraulic and case hardening were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate mechanical and hydraulic properties of the lips walls between adjacent pits and backwalls bottoms of pits of the honeycombs were determined via a set of established and novel approaches while the case hardening hypothesis was not supported by the determinations of either tensile strength drilling resistance or porosity the hydraulic hypothesis was clearly supported by field measurements and laboratory tests fluorescein dye visualization of capillary zone vapor zone and evaporation front upon their contact demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate while the honeycomb lips remain dry during occasional excessive water flow events however the evaporation front may shift to the lips while the backwalls become moist as a part of the capillary zone as the zone of evaporation corresponds to the zone of potential salt weathering it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed a hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering

a simple theoretical approach to the thermal expansion mechanism of salt weathering abstract the traditional plate theory in solid mechanics is used to estimate the thermal stress caused by a superficial salt layer on a rock substrate this preliminary investigation theoretically demonstrates that the thermal expansion of superficial salt layers is difficult to result in rock breakdown during the process of salt weathering

large artificial water reservoirs in the vicinity of the himalayan foothills and reservoir induced seismicity there are 11 large reservoirs exceeding a capacity of 1 km3 and or the height of the dam being 100 m or more in the vicinity of the himalayan foothills nine of these have been fully impounded only a couple of these reservoirs are adequately instrumented for seismic surveillance while the rest have inadequate instrumentation however there is no incidence of reservoir induced seismicity reported from any of these nine sites nonoccurrence of induced earthquakes is comprehended primarily due to the thrust fault environment generally prevalent in the himalayan foothills which is not conducive for reservoir induced seismicity nevertheless a few normal and strike slip faults oblique and parallel to the general trend of the himalayas have been reported where reservoir induced seismicity could occur all of these dams are located in a highly seismic area where earthquakes of magnitude exceeding 7 have occurred in their vicinity in the past normally occurring earthquakes therefore pose a much more severe threat to himalayan reservoirs than do reservoir induced seismicity

modeling subglacial water routing at paakitsoq w greenland 1 the functioning of the greenland ice sheet s subglacial drainage system and its effect on ice dynamics have been inferred largely from hypothetical hydrology dynamics models and from analysis of satellite data and in situ gps measurements despite this there is still uncertainty about how the surface hydrology interacts with the subglacial drainage system and affects basal water pressures and ice flow especially over annual time scales to address this we developed a high spatial 100 m and temporal 1 h resolution distributed physically based subglacial hydrological model and applied it to the paakitsoq region western greenland the model is driven with moulin input hydrographs calculated by a surface routing and lake filling draining model forced ultimately with distributed hourly runoff calculated by a surface mass balance model key outputs from the model are spatially and temporally varying subglacial water pressures and proglacial stream hydrographs early in the melt season short spikes in water pressure lasting less than a day occur as a result of lake drainage events during midsummer there are sustained periods of high water pressure lasting days to weeks even at times when the subglacial system is inferred to be predominantly efficient later in the summer large diurnal fluctuations in water pressure occur with peaks regularly exceeding ice overburden pressure superimposed on a gradually declining trend these phenomena support the results of previous hypothetical modeling efforts and inferences drawn from gps measurements

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

a modeling study of the effect of runoff variability on the effective pressure beneath russell glacier west greenland basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier base the ongoing increase in surface melting of the greenland ice sheet warrants an examination of its impact on basal water pressure and in turn on basal sliding here we examine the case of russell glacier in west greenland where an extensive set of observations has been collected these observations suggest that the recent increase in melt has had an equivocal impact on the annual velocity with stable flow on the lower part of the drainage basin but accelerated flow above the equilibrium line altitude ela these distinct behaviors have been attributed to different evolutions of the subglacial draining system during and after the melt season here we use a high resolution subglacial hydrological model forced by reconstructed surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors we find that the increase in meltwater production at low elevation yields a more efficient drainage system compatible with the observed stagnation of the mean annual flow below the ela at higher elevation the model indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in meltwater availability which is consistent with the observed increase in ice velocity

aqueous processes at gusev crater inferred from physical properties of rocks and soils along the spirit traverse 1 gusev crater was selected as the landing site for spirit on the basis of morphological evidence of long lasting water activity including possibly fluvial and lacustrine episodes from the columbia memorial station to the columbia hills spirit s traverse provides a journey back in time from relatively recent volcanic plains showing little evidence for aqueous processes up to the older hills where rock and soil composition are drastically different for the first 156 sols the only evidence of water action was weathering rinds vein fillings and soil crust cementation by salts the trenches of sols 112 145 marked the first significant findings of increased concentrations of sulfur and magnesium varying in parallel suggesting that they be paired as magnesium sulfate spirit s arrival at west spur coincided with a shift in rock and soil composition with observations hinting at substantial amounts of water in gusev s past we used the microscopic imager data up to sol 431 to analyze rock and soil properties and infer plausible types and magnitude of aqueous processes through time we show the role played early by topography and structure the morphology texture and deep alteration shown by the rocks in west spur and the columbia hills formation chf suggest conditions that are not met in present day mars and required a wetter environment which could have included transport of sulfur chlorine and bromine in water vapor in volcanic gases hydrothermal circulation or saturation in a briny fluid containing the same elements changing conditions that might have affected flow circulation are suggested by different textural and morphological characteristics between the rocks in the chf and those of the plains with higher porosity proxy higher void ratio and higher water storage potential in the chf soils were used to assess aqueous processes and water pathways in the top layers of modern soils we conclude that infiltration might have become more difficult with time

cavernous weathering in the capitol reef desert utah tafoni and honeycomb weathering are abundant in sandstones at capitol reef national park cavities are particularly common in talus blocks resting on alkali rich soil in vertical walls of desert washes and in sandstones containing calcareous cement chemical analyses x ray diffraction data and field observations suggest that salt weathering is the most important cause of disintegration but dissolution of calcite cement also occurs in calcareous sandstones cavernous weathering at capitol reef produces cavities similar in appearance to features found in arkose outcrops along the coast of northwest washington even though the environmental conditions at these two locations are very different

a multicomponent coupled model of glacier hydrology 1 theory and synthetic examples 1 basal hydrology is acknowledged as a fundamental control on glacier dynamics especially in cases where surface meltwater reaches the bed for many glaciers at midlatitudes basal drainage is influenced by subaerial englacial and subsurface water flow one of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system we present theoretical and computational models that couple glacier surface runoff englacial water storage and transport subglacial drainage and subsurface groundwater flow each of the four model components is represented as a two dimensional vertically integrated layer that communicates with its neighbors through water exchange governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources the numerical exposition of this theory is a time dependent finite difference model that can be used to simulate glacier drainage in this paper we outline the theory and conduct simple tests using an idealized glacier geometry in the companion paper the model is tailored to trapridge glacier yukon territory canada where results are compared with measurements of subglacial water pressure

basal drainage system response to increasing surface melt on the greenland ice sheet surface meltwater reaching the bed of the greenland ice sheet imparts a fundamental control on basal motion sliding speed depends on ice bed coupling dictated by the configuration and pressure of the hydrologic drainage system in situ observations in a four site transect containing 23 boreholes drilled to greenland s bed reveal basal water pressures unfavorable to water draining conduit development extending inland beneath deep ice this finding is supported by numerical analysis based on realistic ice sheet geometry slow meltback of ice walls limits conduit growth inhibiting their capacity to transport increased discharge key aspects of current conceptual models for greenland basal hydrology derived primarily from the study of mountain glaciers appear to be limited to a portion of the ablation zone near the ice sheet margin

mechanisms of englacial conduit formation and their implications for subglacial recharge abstract ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by shreve 1972 movement of water in glaciers journal of glaciology 11 62 205 214 the shreve model is based on three main assumptions 1 englacial drainage is in steady state 2 englacial water will flow along the steepest hydraulic gradient within the glacier and 3 pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls the shreve model has been widely adopted as a fundamental component of englacial drainage theory there is no evidence however that the model provides a realistic picture of actual glacial drainage systems to evaluate shreve s theory we used speleological techniques to directly survey englacial conduits we mapped a total of 8 25 km of passage in 27 distinct englacial conduits in temperate polythermal cold based and debris covered glaciers between 2005 and 2008 new information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176 m using speleological techniques in all cases englacial drainage systems consisted of a single unbranching conduit englacial conduit morphologies were found to be intimately linked to the orientation of a glacier s principal stresses or the presence of pre existing lines of high hydraulic conductivity if a sufficient supply of water is available hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive on unfractured glacier surfaces relatively shallow subhorizontal conduits with migrating nickpoints form by cut and closure provided channel incision is significantly faster than surface lowering conduits can also form along permeable debris filled crevasse traces that connect supraglacial lake basins of different potential our results suggest that shreve type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect or are advected through zones of acceleration

strong feedbacks between hydrology and sliding of a small alpine glacier 1 we report the spatial and temporal pattern of sliding on the 7 km long bench glacier alaska using five continuously recording gps antennas following motion of the surface ice distributed at 1 km spacing along the glacier center line we documented surface ice motion over 50 days during summer 2002 surface speeds in two previous winters constrain the motion component associated with ice deformation allowing isolation of the sliding speed history we observed two speedup events bracketing 2 weeks of steady slow sliding the first event was not associated with a meteorological trigger was more subtle than the second and propagated up glacier at a rate of several hundred meters per day the second event coincided with a warm up valley wind which triggered considerable melt of the glacier surface sliding speeds in this event reached 0 3 m d 1 and began almost simultaneously at all sites in the ablation area both the horizontal and vertical displacement time series can be explained by growth and collapse of cavities in the lee of bumps in the bedrock bed cavities grow during rapid sliding and decay by viscous creep we posit that effective pressure averaged over some large area of the bed is inversely proportional to the sliding speed this effective pressure then controls the collapse rate of cavities whose dimensions are estimated from a plausible stepped bed geometry this model explains well the horizontal and vertical surface displacement history through the first event and beginning of the second event the vertical record demands a substantial and abrupt drop in water pressure that departs from the posited sliding effective pressure relationship we argue that this pressure drop reflects establishment of efficient subglacial drainage also manifested in a nearly simultaneous step increase in water discharge in the exit stream the establishment of an efficient conduit system terminates sliding its maintenance inhibits further sliding over the remainder of the summer

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

cavernous weathering dynamical instability and self organization cavernous weathering may be conceptualized as a self reinforcing process characterized by positive feedback within the weathering system a morphometric study of caverns in the valley of fire state park nevada usa demonstrates the applicability of a dynamically unstable or conditionally unstable model of cavernous weathering systems outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce a paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale caverns tend toward minimum interior surface area by developing a spheroidal form yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface copyright 2004 john wiley sons ltd

one dimensional reference velocity model and precise locations of earthquake hypocenters in the kumaon garhwal himalaya we report an optimum 1d velocity model of the kumaon garhwal himalaya based on analysis of 5000 seismograms generated at 50 digital broadband seismic stations in the region during april 2005 and june 2008 these include data from 385 local earthquakes with azimuth gaps of 180 each of which had a minimum of seven p and five s phase readings this velocity model was then used to map the locations of 1150 earthquakes 1 m 5 that occurred in the region a majority 75 of these earthquakes occurred in the upper 20 km of the crust largely above the main himalayan thrust and forms an 10 km wide band along the surface trace of the munsiari thrust however we also find another parallel band of earthquakes about 70 km to its southwest through the tehri dam in the lesser himalaya and a significant number 15 both in the tethys himalaya and within the flexed crust of the underthrusting indian plate beneath the ganga basin furthermore unlike the reported absence of seismicity in the lower crust of the nepal himalaya and its reappearance in the shallow mantle the kumaon garhwal himalayan crust is found to be seismically active throughout with no event reliably recorded in the shallow mantle of this region during the epoch of our seismic recording online material figures show constrains and distribution of data used in joint inversion and table shows p and s wave corrections obtained from travel time inversion

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

investigations into provenance and properties of ancient building sandstones of the zittau gorlitz region upper lusatia eastern saxony germany

natural stones for monuments their availability for restoration and evaluation this paper represents the introduction to the volume focused on the various aspects of natural stone research from the topic issues studied recently four major aspects are covered 1 availability of certain stone types for monuments 2 strategies aiming to strengthen our knowledge of past resources through the establishment of natural stone databases and inventories 3 evaluation of natural stone properties and assessment of the compatibility of repair stones and 4 decay studies of natural stone on monuments and on natural exposures this paper also aims to highlight the importance of the use of local stone resources a practice that has seriously declined during the 20th century in most of the industrialized countries the availability of natural stone from monuments is also discussed in terms of sandstones and travertine in the czech republic and hungary as a typical example natural stone has become the expression to describe the versatile durable and aesthetically plausible building materials currier 1960 from the very beginning of civilization important structures and monuments were built from or were principally based on natural stone the use of local stone resources was mostly in balance with the local environment although highly durable when properly applied no stone type can be considered immortal schaffer 1932 and most of the stone varieties are affected by a polluted atmosphere winkler 1997 deteriorated stone on monuments should be preferably replaced by stone varieties of the same composition from the same quarries however this is often not possible and so stone having similar properties and appearance must be sourced p ikryl 2007 the main aim of this research is to find compatible stones in terms of appearance and geochemical physical properties this task requires a thorough understanding of both the rock properties and its response to external conditions and weathering agents availability of natural stone

winter motion mediates dynamic response of the greenland ice sheet to warmer summers 1 we present ice velocities from a land terminating transect extending 115 km into the western greenland ice sheet during three contrasting melt years 2009 2011 to determine whether enhanced melting accelerates dynamic mass loss we find no significant correlation between surface melt and annual ice flow there is however a positive correlation between melt and summer ice displacement but a negative correlation with winter displacement this response is consistent with hydro dynamic coupling enhanced summer ice flow results from longer periods of increasing surface melting and greater duration ice surface to bed connections while reduced winter motion is explicable by drainage of high basal water pressure regions by larger more extensive subglacial channels despite mean interannual surface melt variability of up to 70 mean annual ice velocities changed by 7 5 increased summer melting thereby preconditions the ice bed interface for reduced winter motion resulting in limited dynamic sensitivity to interannual variations in surface melting

seismotectonics of the nepal himalaya from a local seismic network the national seismological network of nepal consists of 17 short period seismic stations operated since 1994 it provides an exceptional view of the microseismic activity over nearly one third of the himalayan arc including the only segment between longitudes 78 e and 85 e that has not produced any m 8 earthquakes over the last century it shows a belt of seismicity that follows approximately the front of the higher himalaya with most of the seismic moment being released at depths between 10 and 20 km this belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the higher himalaya the seismic activity is more intense around 82 e in far western nepal and around 87 e in eastern nepal western nepal between 82 5 and 85 e is characterized by a particularly low level of seismic activity we propose that these lateral variations are related to segmentation of the main himalayan thrust fault the major junctions between the different segments would thus lie at about 87 e and 82 e with possibly an intermediate one at about 85 e these junctions seem to coincide with some of the active normal faults in southern tibet lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long lived feature we infer four 250 400 km long segments that could produce earthquakes comparable to the m 8 4 bihar nepal earthquake that struck eastern nepal in 1934 assuming the model of the characteristic earthquake the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years

modeling channelized and distributed subglacial drainage in two dimensions 1 we present a two dimensional glacier drainage system model glads that couples distributed and channelized subglacial water flow distributed flow occurs through linked cavities that are represented as a continuous water sheet of variable thickness channelized flow occurs through rothlisberger channels that can form on any of the edges of a prescribed unstructured network of potential channels water storage is accounted for in an englacial aquifer and in moulins which also act as point sources of water to the subglacial system solutions are presented for a synthetic topography designed to mimic an ice sheet margin for low discharge all the flow is accommodated in the sheet whereas for sufficiently high discharge the model exhibits a channelization instability which leads to the formation of a self organized channel system the random orientation of the network edges allows the channel system geometry to be relatively unbiased in contrast to previous structured grid based models under steady conditions the model supports the classical view of the subglacial drainage system with low pressure regions forming around the channels under diurnally varying input water flows in and out of the channels and a rather complex spatiotemporal pattern of water pressures is predicted we explore the effects of parameter variations on the channel system topology and mean effective pressure the model is then applied to a mountain glacier and forced with meltwater calculated by a temperature index model the results are broadly consistent with our current understanding of the glacier drainage system and demonstrate the applicability of the model to real settings

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

slope retreat rates estimated from chronology of tufa deposits sheltered by inland notches on mt carmel israel abstract inland notches are elongated half tube indentations that develop on the carbonate rocky cliffs of mountainous zones occasionally tufa accumulates within notches as stalactites drapes and crusts covering the cavity backwall or floors in attempt to determine the age of the latest stage of notch formation and calculate the relative rate of slope retreat u th dating was used on 16 tufa samples from 2 notches providing 28 ages tufa grow during the time interval between the backwall erosion and visor collapse and therefore tufa age is an approximation of the timing of the formation of the surface it developed on i e the age of the notch the oldest known tufa sample is 39 0 10 4 ky 2 and the ages of other tufa samples range from 2 1 to 23 3 ky at the nahal oren notch the present day backwall formed by the end of the last glacial period 14 to18 ky whereas the visor in its present form is from the early holocene 7 to10 ky the oldest sample was found 1 m from the backwall suggesting that backwall retreat rate ranges from 20 to 35 mm ky other samples were deposited 50 to 200 cm from the visor edge suggesting that slope retreat order of magnitude ranges from 101 to 102 mm ky the backwall of the nesher notch formed between 10 and 14 ky our results correspond with the rates of tens of meters per million years similar to the magnitude of denudation found by previous studies in the mediterranean zone of israel dating tufa deposits is a good proxy to estimate the rate of erosion in carbonate slope retreat however a precautionary approach should be taken as rock particles from the eroded bedrock might embed within the tufa affecting the age results questionable samples can be identified using cathodoluminescence cl microscopy

tafoni on coastal slopes south devon u k cavernous weathering tafoni development occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level the freshly weathered surfaces of the cavern interiors are irregular in morphology discordant to major rock structure formed by substantially weakened rock and associated with granular weathering debris the weathering debris contains soluble elements in proportions similar to those present in seawater and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0 1 0 2 m is indicated by the presence of chlorine scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries the mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog

decadal slowdown of a land terminating sector of the greenland ice sheet despite warming ice flow along land terminating margins of the greenland ice sheet gis varies considerably in response to fluctuating inputs of surface meltwater to the bed of the ice sheet such inputs lubricate the ice bed interface transiently speeding up the flow of ice greater melting results in faster ice motion during summer but slower motion over the subsequent winter owing to the evolution of an efficient drainage system that enables water to drain from regions of the ice sheet bed that have a high basal water pressure however the impact of hydrodynamic coupling on ice motion over decadal timescales remains poorly constrained here we show that annual ice motion across an 8 000 km 2 land terminating region of the west gis margin extending to 1 100 m above sea level was 12 slower in 2007 14 compared with 1985 94 despite a 50 increase in surface meltwater production our findings suggest that over these three decades hydrodynamic coupling in this section of the ablation zone resulted in a net slowdown of ice motion not a speed up as previously postulated increases in meltwater production from projected climate warming may therefore further reduce the motion of land terminating margins of the gis our findings suggest that these sectors of the ice sheet are more resilient to the dynamic impacts of enhanced meltwater production than previously thought

origins of honeycomb weathering the role of salts and wind honeycomb weathering is a common surface phenomenon affecting a variety of rocks in a range of environments it develops on building stones and it shapes ocean cliffs rocks in hot deserts and arctic landscapes honeycomb weathering may also help alter rocks on other planets such as mars although first noted in the nineteenth century its origins are still not well understood and a dearth of laboratory experiments testing the many theories proposed for its development has added to the ambiguity incipient honeycomb weathering in a homogeneous limestone has been experimentally reproduced by wind exposure and salt crystallization our experiments show that heterogeneous wind flow over a stone surface is important in the development of this weathering pattern wind promotes evaporative salt growth between grains on a stone surface resulting in the development of small randomly distributed cavities a reduction in air pressure within the cavities results in increased wind speed and rapid evaporation a high evaporation rate and evaporative cooling of the saline solution in the cavity leads to more rapid and greater granular disintegration than in the surrounding areas it seems that this local supersaturation and subsequent buildup of salt crystallization pressure ultimately result in the formation of honeycomb features for the first time these experimental results demonstrate the close relationship between salts wind and honeycomb weathering they also offer new ways to understand the genesis of this striking and sometimes harmful weathering pattern

feedbacks between coupled subglacial hydrology and glacier dynamics on most glaciers and ice sheet outlets the majority of motion is due to basal slip a combination of basal sliding and bed deformation the importance of basal water in controlling sliding is well established with increased sliding generally related to high basal water pressure but the details of the interactions between the ice and water systems has not received much study when there is coupling between the systems here we use coupled subglacial hydrology and ice dynamics models within the community ice sheet model to investigate feedbacks between the ice and water systems the dominant feedback we find is negative sliding over bedrock bumps opens additional cavity space which lowers water pressure and in turn sliding we also find two small positive feedbacks basal melt increases through frictional heat during sliding which raises water pressure and strain softening of basal ice during localized speedup causes cavities to close more quickly and maintain higher water pressures our coupled modeling demonstrates that a sustained input of surface water to a distributed drainage system can lead to a speedup event that decays even in the absence of channelization due to increased capacity of the system through opening of cavities which is enhanced through the sliding opening feedback we find that the negative feedback resulting from sliding opening is robust across a wide range of parameter values however our modeling also argues that subglacial channelization is required to terminate speedup events over timescales that are commensurate with observations of late summer slowdown on mountain glaciers

the importance of wind as a driver of earthen heritage deterioration in dryland environments abstract dryland regions are exposed to extreme environmental conditions that create hotspots of weathering and erosion many earthen heritage sites are located in these dryland regions and experience extensive deterioration driven by interactions with environmental processes however previous research has focused largely on the role of rain as a driver of deterioration this study combines approaches from geomorphology with understandings of earthen materials from heritage science to investigate the relative importance of wind and rain in driving earthen heritage deterioration in drylands we use geomorphological signatures to infer the environmental histories of earthen walls with a range of known ages at suoyang ancient city china using semi quantitative deterioration assessments we find rain driven deterioration features to be associated with the loss of larger volumes of material and to have higher persistence than wind driven deterioration features however we argue that the high frequency nature of wind events means that wind is an important initiator of deterioration across the site in addition walls exposed to the prevailing wind are dominated by wind driven deterioration features outcomes from this study present an opportunity for earthen heritage conservation to investigate potential strategies to minimise wind speed at earthen heritage sites in drylands

moulin density controls drainage development beneath the greenland ice sheet this work was funded through a uk natural environment research council doctoral training grant lcag 133 a bowring junior research fellowship st catharine s college cambridge and a leverhulme newton trust early career fellowship all awarded to a f b i j h was supported by a marie curie fp7 career integration grant within the 7th european union framework programme

insar and gps measurements of crustal deformation due to seasonal loading of tehri reservoir in garhwal himalaya india author s gahalaut vk yadav rk sreejith km gahalaut k burgmann r agrawa r sati sp bansal a abstract the authors 2017 we report unique observations of crustal deformation caused by the seasonal water level changes of tehri reservoir in the garhwal region ofnwhimalaya from gps measurements and interferometric synthetic aperture radar insar analysis all gps sites along the himalaya are strongly influenced by seasonal hydrological and atmospheric loading however the gps sitekunrlocated near the reservoir additionally exhibits anomalous variations due to seasonal water loading and unloading by the reservoir our insar analysis confirms that the seasonal filling of the reservoir causes measurable subsidence in its neighbourhood in addition to the elastic deformation caused by the seasonal reservoir loading and the negligible poroelastic deformation caused by associated fluid pressure changes there is an unaccounted biannual deformation in the east component of the gps time series which we suspect to be caused by altered hydrological conditions due to the reservoir operations understanding crustal deformation processes due to such anthropogenic sources helps in separating deformation caused by tectonic hydrological and atmospheric effects from that caused by these activities

evolution of the subglacial drainage system beneath the greenland ice sheet revealed by tracers predictions of the greenland ice sheet s response to climate change are limited in part by uncertainty in the coupling between meltwater lubrication of the ice sheet bed and ice flow1 2 3 this uncertainty arises largely from a lack of direct measurements of water flow characteristics at the bed of the ice sheet previous work has been restricted to indirect observations based on seasonal and spatial variations in surface ice velocities4 5 6 7 and on meltwater flux8 here we employ rhodamine and sulphur hexafluoride tracers injected into the drainage system over three melt seasons to observe subglacial drainage properties and evolution beneath the greenland ice sheet up to 57 km from the margin tracer results indicate evolution from a slow inefficient drainage system to a fast efficient channelized drainage system over the course of the melt season further inland evolution to efficient drainage occurs later and more slowly an efficient routing of water was established up to 41 km or more from the margin where the ice is approximately 1 km thick overall our findings support previous interpretations of drainage system characteristics thereby validating the use of surface observations as a means of investigating basal processes

measured basal water pressure variability of the western greenland ice sheet implications for hydraulic potential the gradient of the hydraulic potential field at the ice bedrock interface beneath the greenland ice sheet gris dictates the routing and energetics of subglacial water thereby influencing drainage system characteristics and sliding dynamics in the ablation zone of the gris variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western gris to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics all borehole sites show pressures with similar seasonality having relatively steady and high values during winter variable and irregular behavior during spring and fall and diurnal cycles that can persist for multiple weeks during the peak melt season despite much higher variability during the melt season the median pressure of the summer period is nearly the same as the median pressure of the winter period however time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods we find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system this leads to a complex hydraulic potential field across regions of similar ice thickness

short term variability in greenland ice sheet motion forced by time varying meltwater drainage implications for the relationship between subglacial drainage system behavior and ice velocity 1 high resolution measurements of ice motion along a 120 km transect in a land terminating section of the gris reveal short term velocity variations 1 day which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface the seasonal changes in ice velocity at low elevations 1000 m are dominated by events lasting from 1 day to 1 week although daily cycles are largely absent at higher elevations reflecting different patterns of meltwater input using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time varying water input to a channelized subglacial drainage system our investigation substantiates arguments that variability in theduration and rate rather than absolute volume of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure and therefore ice velocity we suggest that interpretations of hydro dynamic behavior in land terminating sections of the gris margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion

erratum to magnesium sulphate salts on monuments in saxony germany regional geological and environmental causes a record of mortar and salt analyses from the last 20 years on various monuments in saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame the regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory i e the natural occurrence of dolomite deposits sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution as can be shown by sulphur stable isotope analyses exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones these processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite

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

seasonal changes in ice sheet motion due to melt water lubrication abstract a numerical model is used to calculate how the motion of an idealized ice sheet margin is affected by the subglacial drainage of melt water from its surface the model describes the evolution of the drainage system and its coupling with ice flow through a sliding law that depends on the effective pressure the results predict ice acceleration during early summer when the inefficient drainage system is temporarily overwhelmed the growth of a more efficient drainage system leads to a subsequent slowdown of the ice very close to the margin but high water pressure and ice velocity are maintained through much of the summer further inland annual mean ice velocity increases with the total quantity of melt water except close to the margin where it is almost insensitive to the amount of melting short term variability of melt water input leads to rapid changes in ice velocity that result in a slight increase in the mean velocity relative to a smoother input linked cavity and poroelastic models for the distributed drainage system are compared and their relative merits discussed two different sliding laws are considered and the need for a holistic description of hydraulically controlled sliding is highlighted

core softening in cavernously weathered tonalite tonalite exhibiting cavernous weathering at catavina baja california was investigated to determine the factors which contribute to differential hardness within the rock soft cores have a high degree of chemical weathering as indicated by kaolinite content hematite formed from the leaching of biotite occurs in coatings on rock surfaces but the hardening effect of the coating is insignificant compared to the core softening of the interior the hardness measured by an abrasion resistance hardness tester is inversely correlated with kaolinite content in the tonalite a one dimensional water flow model was developed for core softened cavernously weathered boulders it indicates that during infiltration and dessication the moisture flux is greatest through the cavern interior wall because of changes in the hydraulic conductivities induced by core softening therefore the cavern interior wall should have the greatest weathering rate in the boulder

biogenic origin of coastal honeycomb weathering honeycomb weathering occurs in two environments in late cretaceous and eocene sandstone outcrops along the coastlines of south west oregon and north west washington usa and south west british columbia canada at these sites honeycomb weathering is found on subhorizontal rock surfaces in the intertidal zone and on steep faces in the salt spray zone above the mean high tide level in both environments cavity development is initiated by salt weathering in the intertidal zone cavity shapes and sizes are primarily controlled by wetting drying cycles and the rate of development greatly diminishes when cavities reach a critical size where the amount of seawater left by receding tides is so great that evaporation no longer produces saturated solutions encrustations of algae or barnacles may also inhibit cavity enlargement in the supratidal spray zone honeycomb weathering results from a dynamic balance between the corrosive action of salt and the protective effects of endolithic microbes subtle environmental shifts may cause honeycomb cavity patterns to continue to develop to become stable or to coalesce to produce a barren surface cavity patterns produced by complex interactions between inorganic processes and biologic activity provide a geological model of self organization surface hardening is not a factor in honeycomb formation at these study sites salt weathering in coastal environments is an intermittently active process that requires particular wind and tidal conditions to provide a supply of salt water and temperature and humidity conditions that cause evaporation under these conditions salt residues may be detectable in honeycomb weathered rock but absent at other times honeycomb weathering can form in only a few decades but erosion rates are retarded in areas of the rock that contain cavity patterns relative to adjacent non honeycombed surfaces copyright 2010 john wiley sons ltd

response of glacier basal motion to transient water storage the speed of a glacier is affected most by sudden jumps in the water supply to the glacier but it goes back to previous levels if high water inputs are sustained because the glacier s plumbing system adjusts

new challenges for tafoni research a new approach to understand processes and weathering rates cavernous tafoni type weathering is a common and conspicuous global feature creating artistic sculptures which may be relevant for geochemical budgets weathering processes and rates are still a matter of discussion field evidence in the type locality corsica revealed no trend of size variability from the coast to subalpine elevations and the aspect of tafoni seems to be governed primarily by the directions of local fault systems and cleavage and only subordinately by wind directions or the aspect of insulation rem analysis of fresh tafone chips confirmed mechanical weathering by the crystallization of salts as conchoidal fracturing of quartz is observed the salts are only subordinately provided by sea spray as calcium and sodium sulfates rather than halite dominate even close to the coast characteristic element ratios compare well with aerosols from mixed african and european air masses sulfates are largely derived from sahara dust indicated by their sulfur isotopic composition salt crystals form by capillary rise within the rock and subsequent crystallization in micro cracks and at grain boundaries inside rain protected overhangs siderophile bacteria identified by raster electron microscopy rem analysis of tafone debris contribute to accelerated weathering of biotite and tiny sulfide ore minerals by applying 10be exposure dating weathering rates of large mature tafone structures were found to be about an order of magnitude higher than those on the exposed top of the affected granite blocks copyright 2010 john wiley sons ltd

amplified melt and flow of the greenland ice sheet driven by late summer cyclonic rainfall intense rainfall events significantly affect alpine and alaskan glaciers through enhanced melting ice flow acceleration and subglacial sediment erosion yet their impact on the greenland ice sheet has not been assessed here we present measurements of ice velocity subglacial water pressure and meteorological variables from the western margin of the greenland ice sheet during a week of warm wet cyclonic weather in late august and early september 2011 we find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice sheet interior we suggest that the late season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less efficient winter mode reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western greenland during this time and we observe a corresponding ice flow response at all land and marine terminating glaciers in these regions for which data are available given that the advection of warm moist air masses and rainfall over greenland is expected to become more frequent in the coming decades our findings portend a previously unforeseen vulnerability of the greenland ice sheet to climate change

vertical extension of the subglacial drainage system into basal crevasses water plays a first order role in basal sliding of glaciers and ice sheets and is often a key constituent of accelerated glacier motion subglacial water is known to occupy systems of cavities and conduits at the interface between ice and the underlying bed surface depending upon the history of water input and the characteristics of the substrate full understanding of the extent and configuration of basal water is lacking however because direct observation is difficult this limits our ability to simulate ice dynamics and the subsequent impacts on sea level rise realistically here we show that the subglacial hydrological system can have a large volume of water occupying basal crevasses that extend upward from the bed into the overlying ice radar and seismic imaging combined with in situ borehole measurements collected on bench glacier alaska reveal numerous water filled basal crevasses with highly transmissive connections to the bed some crevasses extend many tens of metres above the bed and together they hold a volume of water equivalent to at least a decimetre layer covering the bed our results demonstrate that the basal hydrologic system can extend high into the overlying ice mass where basal crevasses increase water storage capacity and could potentially modulate basal water pressure because basal crevasses can form under commonly observed glaciological conditions our findings have implications for interpreting and modelling subglacial hydrologic processes and related sliding accelerations of glaciers and ice sheets

subsurface initiation of tafoni in granite terrains geophysical evidence from ne spain geomorphological implications abstract granite cavities in the north east of spain which developed below the weathering front are reported these cavities up to 3 m across and probably filled with water saturated weathered granite have been detected by electrical resistivity tomography ert as low resistivity anomalies enclosed in high resistivity media corresponding to unweathered granite rock the caverns appear as hyperbolic reflections in a radargram obtained by ground penetrating radar gpr and show similar shape and size to the tafoni found in the surrounding granite outcrops data gathered in this study support a subterranean origin of some of the tafoni a new conceptual model for the initiation and growth of granite cavities under subsurface conditions is proposed groundwater flow through vertical and sheet fractures triggers preferential weathering at points where meter sized spheroidal pockets of weathered granite develop erosion of the rock mass leads to the exposure of these pockets evolving under subaerial conditions as typical tafoni

tafoni development in a cryotic environment an example from northern victoria land antarctica tafoni are a type of cavernous weathering widespread around the world despite the extensive distribution of the tafoni their genesis is not clear and is still a matter of debate also because they occur in such different climatic conditions and on so many different types of substrate geomorphological characterization of more than 60 tafoni in three different antarctic sites two coastal and one inland between 74 and 76 s with sampling of weathering products and salt occurrences are described together with thermal data on different surfaces and wind speed recorded in different periods of the year in a selected tafone close to the italian antarctic station the aim of this present study is to provide further information to help understand the processes involved in the growth of tafoni in a cryotic environment and the relationship of these processes to climate with particular attention to the thermal regime and the role of wind the new data presented in this paper suggest that there is no single key factor that drives the tafoni development although thermal stress seems the most efficient process particularly if we consider the short term fluctuations the data also confirm that other thermal processes such as freezing thawing cycles and thermal shock are not really effective for the development of tafoni in this area the wind speed measured within the tafoni is half that recorded outside thus favouring snow accumulation within the tafoni and therefore promoting salt crystallization on the other hand the wind effect on the thermal regime within the tafoni seems negligible while both salt weathering and thermal stress appear active in this cryotic environment these are azonal processes and are therefore active in other climatic areas where tafoni are widespread such as the mediterranean region copyright 2007 john wiley sons ltd

direct observations of evolving subglacial drainage beneath the greenland ice sheet simultaneous observations of moulins and boreholes in western greenland show that water delivery to the base of the ice sheet via moulins affects short term ice velocity fluctuations but not late season ice velocity decelerations increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system seasonal acceleration of the greenland ice sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed1 2 via crevasses and moulins vertical conduits connecting supraglacial water to the bed of the ice sheet as the melt season progresses the subglacial hydrologic system drains supraglacial meltwater more efficiently1 2 3 4 decreasing basal water pressure4 and moderating the ice velocity response to surface melting1 2 however limited direct observations of subglacial water pressure4 5 6 7 mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby 0 3 2 kilometres away boreholes indicating that moulins connect to an efficient channelized component of the subglacial hydrologic system which exerts the primary control on diurnal and multi day changes in ice velocity our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the paakitsoq region of western greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin connected channels to convey supraglacial melt instead these observations suggest that decreasing late season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt season dynamics affect ice velocity beyond the conclusion of the melt season8 9 10

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

quantifying the effects of glacier conduit geometry and recharge on proglacial hydrograph form summary the configuration of glacier hydrological systems is often inferred from proxy data such as hydrographs that are collected in proglacial streams seasonal changes in the peakedness of hydrographs are thought to reflect changes in the configuration of the subglacial drainage system however the amount of information that proglacial hydrographs contain about drainage system configurations depends critically on the degree to which the drainage systems modify recharge hydrographs if the drainage system does not modify recharge hydrographs then proglacial hydrographs primarily reflect the recharge conditions produced by supraglacial inputs here we develop a theoretical framework to determine the circumstances under which glacier drainage systems can modify recharge hydrographs and the circumstances under which recharge pulses pass through glaciers unchanged we address the capability of single conduits simple arborescent conduit networks and linked cavity systems to modify diurnal recharge pulses simulations of discharge through large sets of such systems demonstrate that unless large reservoirs or significant constrictions are present the discharge hydrographs of simple glacial conduit systems are nearly identical to their recharge hydrographs conduit systems tend not to modify hydrographs because the changes in storage within englacial and subglacial conduit networks on short time scales are typically small compared to their ability to transmit water this finding suggests that proglacial hydrographs reflect a variety of factors including surface melt rate surface water transfer and subglacial water transfer in many cases the influence of suglacial processes may be relatively minor as a result the evolution of proglacial hydrographs cannot be used unambiguously to infer changes in the structure or efficiency of englacial or subglacial hydrological systems without accurate knowledge of the nature of the recharge hydrograph driving the flow

application of an s shaped curve model to the temporal development of tafoni of salt weathering origin to describe temporal change in tafone development an s shaped curve equation is proposed z zc 1 n 1 exp t n exp 1 1 n t where z is observed tafone depth zc is ultimate tafone depth t is time and n and are constants the applicability of this model is examined using tafone data selected from seven sites which are categorized into three different salt weathering environments a spray splash dominant occasionally wave affected supra tidal zone aerosol affected coastal regions and inland desert areas the results indicate that the equation can well describe tafone development in each of these environments an investigation based on the values of n and determined through a best fit of the equation to the data suggests that n characterizes site specific environmental conditions and reflects the magnitude of factors controlling the recession mechanism of tafone surfaces it is found that 1 the maximum rate of tafone growth dramatically decreases from supra tidal through coastal to desert environments and 2 the growing mode of tafoni is different depending on the environmental settings the erosional force to facilitate the development of tafoni at supra tidal sites is estimated to be about 400 times greater than that in the general coastal area copyright 2011 john wiley sons ltd

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

on some microearthquakes near tarbela reservoir during three low water stands detailed 3d stress analyses with a simulated model of tarbela reservoir indicate that most nearby seismogenic faults inferred from observations of preimpoundment seismicity in the region should be stabilized even when the reservoir has low water levels during dry seasons we hypothesize that the hypocenters of some microearthquakes occurring close to the reservoir during dry seasons of 1977 1980 and 1981 were located on those of the above faults that are destabilized by accumulation of broadly north south horizontal compressive stresses of plate tectonic origin an order of magnitude analysis shows that the rate of accumulation of these stresses may be sufficiently rapid to overcome the stability imparted to the seismogenic faults by the tarbela reservoir

inland notches lithological characteristics and climatic implications of subaerial cavernous landforms in israel inland notches are elongated concave shape indentations that develop on the carbonate rocky cliffs of mountainous zones down to the desert fringe these rock shelters form as a result of the interaction between specific petrologic characteristics and climatic controls emphasizing the importance of environment upon rock decay inland notches are shaped due to slight differences 1 15 in the porosity of the visor and cavity bed the cavity bed is more porous so more likely to erode by exfoliation and dissolution thus the cavity bed retreats at a faster rate compared to the slower subaerial dissolution of the visor bed until a critical point is reached where the visor collapses in israel inland notches inhabit the same lithostratigraphic units as do large caves the vast majority 71 of inland notches are formed in hard dense and crystalline limestone deposited throughout the turonian age another 27 are cut into the dolomitic sequence of the upper albian and lower cenomanian the rest 2 are dispersed in the various formations of the cenomanian and eocene eras notches are most common in semi arid and in mediterranean climates but mainly in areas with annual rainfall of between 400 mm and 850 mm in more humid areas 900 mm yr notches are negligible or completely absent due to the rapid rate of chemical dissolution of carbonate rocks in the desert fringe 200 300 mm yr mechanical decay is accelerated and notches exhibit disintegration processes visor collapse and rock falls in the desert area 200 mm yr salt decay replaces the chemical decay characteristic of inland notches encouraging tafoni formation in addition notches form through fluvial activity or on account of greater petrophysical differences between consecutive beds i e elongated cavities may form in soft rocks shaded by harder visors or crusts copyright 2017 john wiley sons ltd

initial results from a distributed physically based model of glacier hydrology this paper describes the development and testing of a distributed physically based model of glacier hydrology the model is used to investigate the behaviour of the hydrological system of haut glacier d arolla valais switzerland the model has an hourly time step and three main components a surface energy balance submodel a surface flow routing submodel and a subglacial hydrology submodel the energy balance submodel is used to calculate meltwater production over the entire glacier surface the surface routing submodel routes meltwater over the glacier surface from where it is produced to where it either enters the subglacial hydrological system via moulins or runs off the glacier surface the subglacial hydrology submodel calculates water flow in a network of conduits which can evolve over the course of a melt season simulation in response to changing meltwater inputs the main model inputs are a digital elevation model of the glacier surface and its surrounding topography start of season snow depth distribution data and meteorological data model performance is evaluated by comparing predictions with field measurements of proglacial stream discharge subglacial water pressure measured in a borehole drilled to the glacier bed and water velocities inferred from dye tracer tests the model performs best in comparison with the measured proglacial stream discharges but some of the substantial features of the other two records are also reproduced in particular the model results show the high amplitude water pressure cycles observed in the borehole in the mid melt season and the complex velocity discharge hysteresis cycles observed in dye tracer tests the results show that to model outflow hydrographs from glacierized catchments effectively it is necessary to simulate spatial and temporal variations in surface melt rates the delaying effect of the surface snowpack and the configuration of the subglacial drainage system itself the model s ability to predict detailed spatial and temporal patterns of subglacial water pressures and velocities should make it a valuable tool for aiding the understanding of glacier dynamics and hydrochemistry 1998 john wiley sons ltd

seismicity and the state of stress from investigations of local earthquakes in the kumaon himalaya abstract results of investigations of local earthquakes in the region of the main central thrust mct in the kumaon himalaya between and adjacent to the valleys of the bhagirathi and yamuna rivers are presented records of over 250 earthquakes were analysed and the following facts emerged 1 1 earthquakes in the himalayas occur in specific areas and belts one such belt has been identified in the region under investigation hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt crossing the yamuna river between the villages of barkot and syanachatti 2 2 all but a few epicentres in this middle segment lie to the southwest of the surface trace of the mct in a zone with a width of 10 30 km 3 3 most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface the maximum estimated depth being 32 km using observations of first motion for a composite focal mechanism solution the nodal planes were observed to be near vertical and the compression axis near horizontal and normal to the local strike of the seismic belt and of the mct we conclude that although the main central thrust itself is not seismically active in this region there is considerable activity immediately to the southwest of it furthermore the mode of faulting as inferred from the records of these earthquakes is strike slip