evidence for postseismic viscoelastic relaxation following the 1959 m 7 5 hebgen lake montana earthquake a 1983 releveling survey conducted by the national geodetic survey combined with previous surveys in 1923 1960 1967 and 1975 provides evidence for ongoing vertical deformation of a broad region diameter of 150 km surrounding the site of the 1959 hebgen lake earthquake deformation consists of relative uplift centered roughly on the coseismic fault and a smaller amplitude zone of relative subsidence south of the fault maximum observed elevation change during the postseismic period 1960 1983 exceeds 30 cm assuming that the entire uplift i e 1923 1983 occurred following the 1959 earthquake i e uplift measured between 1923 and 1960 was entirely postseismic the rate of vertical deformation appears to have decreased exponentially with a characteristic decay time of about 10 years the spatial pattern and time behavior of the observed movements are consistent with simple models of postseismic deformation following normal faulting in an elastic layer thickness of 30 40 km overlying a viscoelastic half space viscosity of 1019 pa s this model may also account for the anomalously large horizontal strain around the hebgen lake region measured by repeated trilateration surveys during the period 1973 1984 the releveling measurements in the hebgen lake region appear to provide the first observations of viscoelastic relaxation in the asthenosphere following an intraplate earthquake in the united states

temporal gravity and height changes of the yellowstone caldera 1977 1994 this paper describes the longest record of gravity measurements in the area of the yellowstone caldera wyoming the temporal gravity changes at the 12 gal 10 8 ms 2 precision level are compared with changes in heights from leveling and gps the gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to 60 2 gal along the caldera axis the gravity field then reversed polarity to increasing values of up to 60 12 gal between 1986 and 1993 the ratio between height and gravity changes varied during the entire time but converged over the latter period following the free air gravity gradient general ground deformation deduced from leveling showed caldera wide uplift of 15 mm a during the period of gravity decrease then from leveling and gps subsidence of 25 mm a during the gravity increase

measuring the sea ice floe size distribution sea ice is broken into floes whose diameters range from meters to a hundred kilometers this fragmentation affects the resistance of the ice cover to deformation and the melting at floe sidewalls in summer floes are broken by waves and swell near the ice edge and throughout the pack by isostatic imbalances thermal cracking winds and currents in winter they are welded together by freezing floe size can be measured by several properties p for instance area or mean caliper diameter two definitions of floe size distribution seem useful f p the fraction of area covered by floes no smaller than p and n p the number of floes per unit area no smaller than p f p can be measured by sets other than areas such as the fraction of a line or of a point set covered by floes no smaller than p if n behaves like for small where is mean caliper diameter must be greater than 2 so that the small floes occupy finite area if 2 1 the perimeter of small floes is infinite several summertime distributions have been measured on a log log graph their slopes local values of range from 1 7 to 2 5 one distribution follows a power law the others have steeper slopes for larger floes and more gradual slopes for smaller floes another sampling strategy is to measure the lengths of line segments on floes the distribution of these chord lengths is equivalent to the distribution of floe diameters the variance of an estimate of the fraction g of area covered by floes in any size range is g 1 g k 1 where k is the equivalent number of independent samples k can be found from the autocovariance of the indicator function for the chosen size range for line sampling of a narrow range of floe diameters k is the ratio of the sample length to the floe diameter

simulated effect of soil depth and bedrock topography on near surface hydrologic response and slope stability this paper explores the effect of hillslope hydrological behavior on slope stability in the context of transient subsurface saturation development and landslide triggering we perform a series of virtual experiments to address how subsurface topography affects the location and spatial pattern of slip surface development and pore pressure dynamics we use a 3d darcy richards equation solver hydrus 3 d combined with a cellular automata slope stability model to simulate the spatial propagation of the destabilized area our results showed that the soil bedrock interface and in particular bedrock depressions played a key role in pore pressure dynamics acting as an impedance for the downslope drainage of perched water filling and spilling of depressions in the bedrock surface microtopography induced localized zones of increased pressure head such that the development of pore pressure fields not predictable by surface topography lead to rapid landslide propagation our work suggests that landslide models should consider the subsurface topography in order to include a connectivity component in the mathematical description of hydrological processes operating at the hillslope scale copyright 2012 john wiley sons ltd

direction of unsaturated flow in a homogeneous and isotropic hillslope 1 the distribution of soil moisture in a homogeneous and isotropic hillslope is a transient variably saturated physical process controlled by rainfall characteristics hillslope geometry and the hydrological properties of the hillslope materials the major driving mechanisms for moisture movement are gravity and gradients in matric potential the latter is solely controlled by gradients of moisture content in a homogeneous and isotropic saturated hillslope absent a gradient in moisture content and under the driving force of gravity with a constant pressure boundary at the slope surface flow is always in the lateral downslope direction under either transient or steady state conditions however under variably saturated conditions both gravity and moisture content gradients drive fluid motion leading to complex flow patterns in general the flow field near the ground surface is variably saturated and transient and the direction of flow could be laterally downslope laterally upslope or vertically downward previous work has suggested that prevailing rainfall conditions are sufficient to completely control these flow regimes this work however shows that under time varying rainfall conditions vertical downslope and upslope lateral flow can concurrently occur at different depths and locations within the hillslope more importantly we show that the state of wetting or drying in a hillslope defines the temporal and spatial regimes of flow and when and where laterally downslope and or laterally upslope flow occurs

arctic ocean mixed layer eddy generation under leads in sea ice 1 convection in the arctic ocean mixed layer occurs under openings in sea ice where new sea ice is formed the process of brine rejection during ice formation creates negatively buoyant fluid at the surface of ice leads when the fluid convects downward the ocean mixed layer below the lead is stirred vertically and through planetary rotational effects along lead flows at the lead edges are induced these vertical and lateral motions have been previously studied using two dimensional numerical ocean models and observed in field programs such as leadex in this paper the generation of arctic ocean eddies through dynamic instabilities is investigated using a three dimensional nonhydrostatic ocean model results suggest that salt enriched vortices can develop at the base of the mixed layer as a consequence of brine rejection but the vortex formation requires a time period of several days a time long enough that the progenitor lead would likely have closed the scale of the eddies is found to depend on the magnitude of the buoyancy forcing the width of the lead and the duration of the buoyancy forcing the number of vortices produced depends on lead width and duration of buoyancy forcing but is less sensitive to the magnitude of the buoyancy forcing vortex sizes scaled appropriately and vortex numbers are compared with those found in recent laboratory studies of convectively driven flows from line segment sources

the diversion capacity of capillary barriers an arrangement of unsaturated fine grained soil overlying unsaturated coarse grained soil along a sloping contact can under appropriate circumstances divert infiltrating water away from the coarser material such an arrangement is called a capillary barrier the water diverted by a capillary barrier flows downdip above the contact the volume of water moving laterally increases in the downdip direction as additional infiltration is diverted by the barrier sufficiently far downdip the laterally moving water wets the contact to the point that an amount of water equal to the infiltration flows downward through the coarse soil the lateral flow at such a point represents the diversion capacity of the capillary barrier because this flow will not increase farther downdip if the width measured in the direction of dip of the system is large enough that total infiltration exceeds the diversion capacity the downdip portion of the barrier will not be effective the diversion capacity can be calculated exactly in the quasi linear approximation where the relationship between relative permeability krel and pressure potential takes the form krel e this calculation shows that an upper bound on the width of capillary barriers is ks tan o q where ks is the saturated hydraulic conductivity of the fine soil o is the dip angle of the contact and q is the infiltration rate

capillary barrier effect from underlying coarser soil layer infiltration tests were conducted on soil columns of silty sand over pea gravel concrete sand over pea gravel and silty sand over concrete sand to investigate the capillary barrier effect of an underlying coarser soil layer water movement across the interface occurred when the suction head at the interface reached the breakthrough head of the coarser lower soil layer defined as the suction head at which the coarser layer first became conductive regardless of infiltration rate or the properties of the overlying finer soil layer thus the coarser lower soil layer controlled breakthrough in this study after infiltration was terminated the suction head near the interface increased above the breakthrough head and the barrier was restored the breakthrough head did not change substantially after eight test cycles of breakthrough and restoration for a capillary barrier with a pea gravel as the coarser lower soil layer the barrier formed with the concrete sand as the coarser layer permitted breakthrough at a greater suction head than did the barrier with the pea gravel indicating that the more uniform and coarse the lower soil layer is the more effective the capillary barrier

submesoscale sea ice ocean interactions in marginal ice zones signatures of ocean eddies fronts and filaments are commonly observed within marginal ice zones mizs from satellite images of sea ice concentration and in situ observations via ice tethered profilers or underice gliders however localized and intermittent sea ice heating and advection by ocean eddies are currently not accounted for in climate models and may contribute to their biases and errors in sea ice forecasts here we explore mechanical sea ice interactions with underlying submesoscale ocean turbulence we demonstrate that the release of potential energy stored in meltwater fronts can lead to energetic submesoscale motions along mizs with spatial scales o 10 km and rossby numbers o 1 in low wind conditions cyclonic eddies and filaments efficiently trap the sea ice and advect it over warmer surface ocean waters where it can effectively melt the horizontal eddy diffusivity of sea ice mass and heat across the miz can reach o 200 m 2 s 1 submesoscale ocean variability also induces large vertical velocities order 10 m d 1 that can bring relatively warm subsurface waters into the mixed layer the ocean sea ice heat fluxes are localized over cyclonic eddies and filaments reaching about 100 w m 2 we speculate that these submesoscale driven intermittent fluxes of heat and sea ice can contribute to the seasonal evolution of mizs with the continuing global warming and sea ice thickness reduction in the arctic ocean submesoscale sea ice ocean processes are expected to become increasingly prominent

groundwater balance estimation in karst by using a conceptual rainfall runoff model summary a conceptual rainfall runoff model is proposed for the estimation of groundwater balance components including the influences of time variant catchment boundaries and intercatchment groundwater flows karst underground is considered as a lumped system that contains 1 soil cover 2 epikarst zone and 3 vadose and phreatic zones the soil cover receives an average rainfall in catchment as the input into the system the epikarst zone is composed of a production store and a routing store the production store contributes to the loss of water in process of evapotranspiration the routing store contributes to the retention of percolated water and the lateral distribution of groundwater recharge between internal runoff and diffuse infiltration the vadose and phreatic zones accumulate groundwater in fissures fractures and vertical shafts and produce the vadose seepage vadose flow and shaft flow components of the karst spring discharge the parameter estimation and calculation procedure assemble the moisture balance and the groundwater balance approaches the rainfall runoff model is divided in two sub models the sub model based on the moisture balance of soil cover and epikarst production store calculates effective rainfalls the sub model based on the groundwater balance of vadose and phreatic zone calculates groundwater recharges the difference between the effective rainfalls and the groundwater recharges represents the contribution of epikarst zone and non conservative and time variant components to the groundwater balance the proposed methodology is applied to the jadro spring located near the city of split in croatia the calculated groundwater balance shows that the jadro spring aquifer contains a significant storage capacity in the vadose and phreatic zones during the year the aquifer may accumulate up to 140 millions m 3 the variability of calculated catchment area is explained with the time variant catchment boundary dependent on groundwater levels and the intercatchment groundwater flows from neighboring catchments the average catchment area of 396 km 2 is estimated by using the average monthly effective rainfalls and the average monthly groundwater recharges

sea ice melting and floe geometry in a simple ice ocean model a coupled sea ice ocean numerical model has been developed that addresses the role of floe geometry during summertime melting the model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration the partition between melting on the top bottom and lateral side surfaces of floes is examined using time dependent simulations with differing initial average floe diameters the different parameterizations for bottom and lateral melting in the literature are also compared and found to vary significantly the results show that lateral melting is important only for floes with diameters less than o 30 m given atmospheric thermal forcing typical of the central arctic in summer this means that the decrease in ice concentration over the summer is a strong function of floe diameter in keeping with simple geometrical arguments in all cases about 80 of the net thermal energy that enters the ocean through leads goes toward melting ice while the rest warms the ocean

crustal deformation and source models of the yellowstone volcanic field from geodetic data 1 geodetic observations comprising interferometric synthetic aperture radar insar global positioning system gps and precision leveling measurements are used to infer volume change in the subsurface associated with the dynamics of the yellowstone volcanic system we focus primarily on the yellowstone caldera and its related magmatic hydrothermal and fault systems it appears that known faults play a significant role in controlling crustal volume increases and decreases due to the migration of volcanic and hydrothermal fluids for example over 5 cm of subsidence from 1992 to 1995 is associated with source volume changes 6 10 km beneath the nw trending elephant back fault zone and a north trending fault cutting across the caldera furthermore we are able to image an episode of fluid intrusion near the northern edge of the caldera the intrusion is elongated in the north south direction and is parallel to the north trending volume decrease the primary intrusion and related hydrothermal activity occurred between 1996 and 2000 though the volume changes appear to have continued shallowed and changed shape between 2000 and 2002 there is evidence that the intrusive activity influenced extensional faults to the north of the caldera

threshold relations in subsurface stormflow 2 the fill and spill hypothesis analysis of subsurface stormflow from 147 storms at the 20 m long trench in the panola mountain research watershed by tromp van meerveld and mcdonnell 2006a showed that there was a distinct 55 mm precipitation threshold for significant subsurface stormflow production this second paper in the series investigates the processes responsible for this threshold response we installed a dense spatial array of maximum rise crest stage gauges and recording wells on the hillslope and studied the temporal and spatial patterns of transient saturation at the soil bedrock interface and its relation to subsurface stormflow measured at the trench face results show that while transient groundwater developed on parts of the hillslope during events smaller than 55 mm it was not until more than 55 mm of rain fell before bedrock depressions on the hillslope were filled water spilled over microtopographic relief in the bedrock surface and the subsurface saturated areas became connected to the trench when connectivity was achieved the instantaneous subsurface stormflow rate increased more than fivefold compared to before the subsurface saturated areas were connected to the trench face total subsurface stormflow was more than 75 times larger when connectivity was achieved compared to when connectivity was not achieved the fill and spill hypothesis presented in this paper is a process explanation for the observed threshold behavior of tromp van meerveld and mcdonnell 2006a thereby linking patterns and processes

granular flow in the marginal ice zone the region of sea ice near the edge of the sea ice pack is known as the marginal ice zone miz and its dynamics are complicated by ocean wave interaction with the ice cover strong gradients in the atmosphere and ocean and variations in sea ice rheology this paper focuses on the role of sea ice rheology in determining the dynamics of the miz here sea ice is treated as a granular material with a composite rheology describing collisional ice floe interaction and plastic interaction the collisional component of sea ice rheology depends upon the granular temperature a measure of the kinetic energy of flow fluctuations a simplified model of the miz is introduced consisting of the along and across momentum balance of the sea ice and the balance equation of fluctuation kinetic energy the steady solution of these equations is found to leading order using elementary methods this reveals a concentrated region of rapid ice flow parallel to the ice edge which is in accordance with field observations and previously called the ice jet previous explanations of the ice jet relied upon the existence of ocean currents beneath the ice cover we show that an ice jet results as a natural consequence of the granular nature of sea ice

steep slope monitoring in unsaturated pyroclastic soils based on monitoring results the paper describes the hydrological response of a steep hillslope covered by unsaturated pyroclastic soils the instrumented site is located just beside an area which experienced a catastrophic flowslide two years prior to the survey monitoring involved rainfall and matric suction measured at different locations and depths investigations focused on the hydrological response of the slope so as to model the effects of rainfall and then predict the onset of slope failure triggered by critical rainfall

a 12 000 year record of vertical deformation across the yellowstone caldera margin the shorelines of yellowstone lake the 600 ka yellowstone caldera exhibits several signs of unrest the most evident of which is historic ground deformation including both uplift and subsidence we document deformation in the area of the southeastern caldera across 12 000 years using the postglacial shoreline terraces of yellowstone lake raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces with an accuracy of 0 5 m of about 11 recognizable terraces the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns shoreline ages are based on minimum and maximum limiting radiocarbon and obsidian hydration dates each terrace is interpreted as representing an episode of uplift 1 kyr 1 of the caldera interior and subsequent subsidence with little net volume change this cyclic behavior may result from magma emplacement and subsequent withdrawal or cooling and crystallization and or episodic trapping and release of magmatic fluids evolved during cooling and crystallization in a self sealing reservoir as hypothesized by dzurisin et al 1990 early postglacial shoreline deformation reveals substantial intracaldera subsidence possibly reflecting cooling and loss of trapped hydrothermal fluids extension along north south trending normal faults and related structures is also apparent in early to middle postglacial deformation both inside and outside of the caldera margin including downwarping and local faulting of hot weak intracaldera crust net deformation over the past 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim relative to the extracaldera region this uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode subtraction of the total estimated magnitude of inflation in this episode suggests that the overall trend of postglacial deformation has been subsidence the cause of this trend is undetermined but is most likely related to the effects of regional extension and long term cooling within the yellowstone caldera

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

characteristics of residual soils in singapore as formed by weathering residual soils are weathering products of rocks that are commonly found under unsaturated conditions the properties of residual soils are a function of the degree of weathering a series of index properties engineering properties mercury porosimetry tests and scanning electron microscope sem examinations were performed on residual soils from two major geological formations in singapore the results indicate that the variation in the index and engineering properties as well as microstructural characteristics of the residual soils with depth can be related to the degree of weathering an increase in the degree of weathering results in an increase in pore volume and produces a larger range of pore size distribution the variation in the pore volume and the pore size distribution through a profile of weathered rock can be used as an indicative measure of the variation in the degree of weathering with depth

physical modeling investigation of rainfall infiltration in steep layered volcanoclastic slopes abstract infiltration processes in layered slopes can be strongly affected by the different hydraulic properties of the soils constituting the layers with potential downslope flow diversion that can have effects on slope stability as well as on runoff generation and groundwater recharge in this respect volcanoclastic soil covers represent a typical example as layers with strongly contrasting textures are deposited during the various eruptive phases in this paper the results of a transient infiltration test carried out in a densely instrumented physical model of a layered volcanoclastic sloping cover are presented the soil cover was constituted by a layer of gravelly pumices interbedded between two layers of finer ashes sandy loams even with such an extreme contrast in texture capable of significantly delaying the advancement of infiltration through the layer of pumices flow diversion occurred only temporarily at the interface between the upper layer of ashes and the pumices in fact although a long lasting intense rainfall was applied into an initially dry soil profile the downslope diverted water volume in form of a subsurface runoff was just a small fraction of the total applied rainfall in fact the accumulation of water above the upper edge of the pumices responsible of the subsurface runoff soon led to the establishment of a large water potential gradient which redirected the infiltrating flow through the pumices and stopped the downslope flow diversion

crustal fissuring on the crest of the southern east pacific rise at 17 15 40 s s with the near bottom dsl 120 andargo ii imaging systems we observe that the youngest lava flows on a relative age scale aresparsely fissured and that there is a cumulative increase in fissure abundance with time thatproduces a strong positive correlation between fissure density and relative age of lava flows average fissure widths were used to estimate fissure depths in the 17 15

assessment of global positioning system measurements for studies of crustal deformation the u s geological survey has been using the global positioning system gps to perform repeated surveys of networks of different sizes since january 1986 the intersite distances from these various networks are 223 km for a single line connecting the palos verdes and vandenberg sites in southern california 30 50 km for a network of three sites south of the san francisco bay near loma prieta 9 30 km for a network located near hebgen lake montana 7 12 km for a network of sites in the vicinity of parkfield california and 240 m for a line located at the goldstone antenna complex in the mojave desert the lengths quoted do not include the intersite distances for the fiducial sites included in the solutions for orbit determination which can be up to 8000 km we have attempted to assess the long term precision and accuracy of determinations of relative site position for a range of line lengths this assessment has consisted of several different studies in assessing precision we have generally investigated repeatability usually about a best fit linear temporal trend the smallest fractional repeatability was yielded by the measurements on the palos verdes to vandenberg line the root mean square rms residual about the best fit line for these determinations was 6 mm 0 03 parts per million or ppm for the north component 11 mm 0 05 ppm for the east component and 40 mm 0 18 ppm for the vertical component for these determinations gps data from 3 4 consecutive days were combined to produce a single estimate of the vector separation we also used the day to day scatter from these measurements to perform an analysis of variance and found that these multiday determinations can be significantly more precise than estimates determined from a single observing session the worst results were obtained for the loma prieta network where we obtained rms residuals of 11 12 mm 0 3 0 4 ppm for north 14 18 mm 0 3 0 6 ppm for east and 18 21 mm 0 4 0 7 ppm for vertical we cannot definitely explain these poor results but we have evidence to indicate that this poor scatter is due to the short observing session 4 5 hours compared to 6 5 hours for the palos verdes to vandenberg results in assessing accuracy we compared the gps results to those from independent techniques at parkfield we compared the gps estimates of fault parallel motion to those from creep meters and alignment arrays and found excellent agreement within 1 2 mm yr 1 not only for the slip but also for the variation of slip along the san andreas fault we compared the loma prieta and hebgen lake line length estimates to those obtained from a geodolite a high precision laser distance measurement device that the u s geological survey has used for 20 years for studies of crustal deformation if we model the geodolite minus gps line length differences l as l l where l is the line length then we find 0 6 0 5 mm and 0 1 0 1 mm km 1 the uncertainties quoted are one standard deviation from this comparison we conclude that at this level of significance there is no detectable difference between lengths determined from geodolite and gps data finally we compared the gps estimates of the palos verdes to vandenberg line length to those obtained from very long baseline interferometry vlbi the mean difference between the six gps estimates of line length and a best fit line through the vlbi estimates was 1 mm and the rms difference was 12 mm 0 05 ppm close to the standard deviation of the gps measurements for this predominantly east west line

stability analyses of rainfall induced landslides the slope stability issues concerning rainfall induced slope failures are investigated and presented specifically the effect of both negative and positive pore water pressures on the stability of initially unsaturated slopes are carefully explained and coupled with infinite slope analysis methods in order to present a predictive formulation of slope failures that occur as a result of rainfall events the formulation serves as a baseline analysis method for evaluating potentially unstable soil slopes that are subject to surface infiltration and explains the various triggering mechanisms that may occur based on individual combinations of the slope geometry soil strength and infiltration parameters a procedural method is outlined for utilizing the analytical formulation to predict the change in the factor of safety for a slope subject to infiltration and a detailed analysis of a case study is presented to verify the method quantitative statements are made concerning the time and depth of failure in relationship to the soil slope and rainfall parameters

contemporary vertical surface displacements in yellowstone national park relative vertical displacements and average relative vertical velocities have been determined for bench marks located throughout yellowstone national park ynp by comparing geodetic leveling measurements made in 1923 second order 1936 third order 1941 third order 1955 third order 1960 first order and 1975 1977 first order the 1923 1975 data indicate uplift greater than 400 mm 7 7 mm yr of an area approximately 15 20 km wide and at least 40 km long which is centered along the northeast trending axis of the 600 000 year old yellowstone caldera the maximum 1923 1975 vertical displacement in this area is 726 mm 14 0 mm yr the existence of a well defined and untilted yellowstone lake terrace implies that the 1923 1975 average vertical velocities cannot have been maintained for more than a few hundred years the 1955 1977 data from central ynp indicate that the northeastern caldera half has risen relative to the southwestern half at an average velocity of about 8 mm yr a similar bias is present in the 1923 1975 data but it is less pronounced the 1923 1960 and 1960 1975 data from northwestern ynp and a 200 mm depression in the 1923 1975 data near norris junction may be interpreted in terms of deformation associated with the 1959 hebgen lake earthquake and the 1975 yellowstone park earthquake a composite profile of the 1936 1977 and 1941 1977 average vertical velocity data which skirts the edge of the yellowstone caldera in northeastern ynp is most easily explained as the result of random leveling error and or bench mark instabilities the apparent youth of the 1923 1975 yellowstone uplift and its close association with the yellowstone caldera suggest that the most likely cause of the uplift is a recent not more than 500 years ago influx of molten material into the upper crust beneath the caldera

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

the influence of the spatial distribution of leads and ice floes on the atmospheric boundary layer over fragmented sea ice the response of the atmospheric boundary layer abl to subgrid scale variations of sea ice properties and fracturing is poorly understood and not taken into account in mesoscale numerical weather prediction nwp model parametrizations in this paper we analyze three dimensional air circulation within the abl over fragmented sea ice a series of idealized high resolution simulations with the weather research and forecasting wrf model is performed for several spatial distributions of ice floes and leads for two values of sea ice concentration 0 5 and 0 9 and several ambient wind speed profiles the results show that the convective circulation within the abl is sensitive to the subgrid scale spatial distribution of sea ice considerable variability of several domain averaged quantities cloud liquid water content surface turbulent heat flux thf is found for different arrangements of floes moreover the organized structure of air circulation leads to spatial covariance of variables characterizing the abl based on the example of thf it is demonstrated that this covariance may lead to substantial errors when thf values are estimated from area averaged quantities as it is done in mesoscale nwp models this suggests the need for developing suitable parametrizations of abl effects related to subgrid scale sea ice features for these models

the evolution of scaling laws in the sea ice floe size distribution the sub gridscale floe size and thickness distribution fstd is an emerging climate variable playing a leading order role in the coupling between sea ice the ocean and the atmosphere the fstd however is difficult to measure given the vast range of horizontal scales of individual floes leading to the common use of power law scaling to describe it the evolution of a coupled mixed layer fstd model of a typical marginal ice zone is explicitly simulated here to develop a deeper understanding of how processes active at the floe scale may or may not lead to scaling laws in the floe size distribution the time evolution of mean quantities obtained from the fstd sea ice concentration mean thickness volume is complex even in simple scenarios suggesting that these quantities which affect climate feedbacks should be carefully calculated in climate models the emergence of fstds with multiple separate power law regimes as seen in observations is found to be due to the combination of multiple scale selective processes limitations in assuming a power law fstd are carefully analyzed applying methods used in observations to fstd model output two important sources of error are identified that may lead to model biases one when observing an insufficiently small range of floe sizes and one from the fact that floe scale processes often do not produce power law behavior these two sources of error may easily lead to biases in mean quantities derived from the fstd of greater than 100 and therefore biases in modeled sea ice evolution

aseismic growth of durmid hill southeasternmost san andreas fault california our 2 27 km leveling line across and normal to the san andreas fault at durmid hill domed upward by 9 mm between september 1985 and december 1991 the flanks of the line tilted more than 1 rad yr implying that the uplift extends beyond the ends of the line and that absolute uplift of the crest of the hill may greatly exceed the measured rate of 1 5 mm yr trilateration measurements sampling 5 km of the fault zone within the hill from 1978 to 1992 yield a mean dextral slip rate of 2 4 0 3 mm yr and fault normal extension of 1 0 3 mm yr the inferred uplift rate during the 5 5 year leveling period as well as from geomorphic samples at 330 years and 35 000 years and from erosion of sedimentary strata younger than 738 000 years in monoclines abutting the fault at durmid hill is remarkably consistent at 1 to 4 mm yr and implies that the current processes may have persisted for millennia we investigate two mechanisms for the deformation that are defined by the symmetry of the observed doming transpression on a vertical or near vertical subsurface san andreas fault or slip on a shallow flat fault or detachment that terminates beneath durmid hill the resultant models suggest that uplift rates of 1 mm yr will result from 6 mm yr dextral shear along a vertical fault together with 1 mm yr horizontal convergence across that fault and this strain field is consistent with the paleoseismic record and our leveling data we conclude that interseismic processes account for most of the growth of durmid hill because the interseismic vertical deformation rates equal or exceed the long term vertical slip rate measured across the fault because dextral shear of 6 mm yr at durmid hill represents a small fraction of the 25 mm yr measured across the entire san andreas fault zone in coachella valley and because the san andreas fault at durmid hill may represent an earthquake nucleation zone the observed deformation processes may be of significant importance for understanding future earthquake rupture initiation or termination

infinite slope stability under steady unsaturated seepage conditions 1 we present a generalized framework for the stability of infinite slopes under steady unsaturated seepage conditions the analytical framework allows the water table to be located at any depth below the ground surface and variation of soil suction and moisture content above the water table under steady infiltration conditions the framework also explicitly considers the effect of weathering and porosity increase near the ground surface on changes in the friction angle of the soil the factor of safety is conceptualized as a function of the depth within the vadose zone and can be reduced to the classical analytical solution for subaerial infinite slopes in the saturated zone slope stability analyses with hypothetical sandy and silty soils are conducted to illustrate the effectiveness of the framework these analyses indicate that for hillslopes of both sandy and silty soils failure can occur above the water table under steady infiltration conditions which is consistent with some field observations that cannot be predicted by the classical infinite slope theory a case study of shallow slope failures of sandy colluvium on steep coastal hillslopes near seattle washington is presented to examine the predictive utility of the proposed framework

brine driven eddies under sea ice leads and their impact on the arctic ocean mixed layer abstract eddy generation induced by a line shaped salt flux under a sea ice lead and associated salt transport are investigated using a three dimensional numerical model the model is designed to represent a typical condition for the wintertime arctic ocean mixed layer where new ice formation within leads is known to be one of the primary sources of dense water the result shows that along lead baroclinic jets generate anticyclonic eddies at the base of the mixed layer and almost all the lead originated salt is contained inside these eddies these eddies survive for over a month after closing of the lead and transport the lead originated salt laterally consequently the lead origin salt settles only on the top of the halocline and is not used for increasing salinity of the mixed layer sensitivity experiments suggest that the horizontal scale of generated eddies depends only on the surface forcing and is proportional to the cube root of the total amount of salt input this scaling of eddy size is consi

on the feedback of ice ocean stress coupling from geostrophic currents in an anticyclonic wind regime over the beaufort gyre abstractbased on analysis of observational data it has been suggested that a negative feedback of ice ocean stress coupling may limit freshwater accumulation in the beaufort gyre bg in this pape

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

tilt observations using borehole tiltmeters 2 analysis of data from yellowstone national park we have installed borehole tiltmeters at five sites in yellowstone national park wyoming and have used these instruments to measure the spatial variation of the amplitude and phase of the principal semidiurnal tide the measured tides vary both with position and azimuth and differ from the sum of the body tide and the ocean load by up to 50 the difference predicted by a finite element model constructed from seismic refraction and gravity data has a maximum value of only 12 although the discrep ancy between our observations and the model is only marginally significant at some sites the disagreement between the model and our observa tions is much larger than we observed using the same instruments at other sites and cannot be attributed to an instrumental effect we have been unable to modify the model to explain our results while keeping it consistent with the previous observations

sea ice switches and abrupt climate change we propose that past abrupt climate changes were probably a result of rapid and extensive variations in sea ice cover we explain why this seems a perhaps more likely explanation than a purely thermohaline circulation mechanism we emphasize that because of the significant influence of sea ice on the climate system it seems that high priority should be given to developing ways for reconstructing high resolution in space and time sea ice extent for past climate change events if proxy data can confirm that sea ice was indeed the major player in past abrupt climate change events it seems less likely that such dramatic abrupt changes will occur due to global warming when extensive sea ice cover will not be present

submesoscale fronts in the antarctic marginal ice zone and their response to wind forcing submesoscale flows in the ocean are energetic motions o 1 10 km that influence stratification and the distributions of properties such as heat and carbon they are believed to play an important role in sea ice impacted oceans by modulating air sea ice fluxes and sea ice extent the intensity of these flows and their response to wind forcing are unobserved in the sea ice regions of the southern ocean we present the first submesoscale resolving observations in the antarctic marginal ice zone miz collected by surface and underwater autonomous vehicles for 3 months in austral summer we observe salinity dominated lateral density fronts occurring at sub kilometer scales surface winds are shown to modify the magnitude of the mixed layer density fronts revealing strongly coupled atmosphere ocean processes we posture that these wind front interactions occur as a continuous interplay between front slumping and vertical mixing which leads to the dispersion of submesoscale fronts such processes are expected to be ubiquitous in the southern ocean miz

groundwater recharge assessment at local and episodic scale in a soil mantled perched karst aquifer in southern italy summary groundwater recharge assessment of karst aquifers at various spatial and temporal scales is a major scientific topic of current importance since these aquifers play an essential role for both socio economic development and fluvial ecosystems in this study groundwater recharge was estimated at local and episodic scales in a representative perched karst aquifer in a region of southern italy with a mediterranean climate the research utilized measurements of precipitation air temperature soil water content and water table depth obtained in 2008 at the acqua della madonna test area terminio mount karst aquifer campania region at this location the aquifer is overlain by ash fall pyroclastic soils the episodic master recession emr method an improved version of the water table fluctuation wtf method was applied to estimate the amount of recharge generated episodically by individual rainfall events the method also quantifies the amount of precipitation generating each recharge episode thus permitting calculation of the recharge to the precipitation ratio rpr on a storm by storm basis depending on the seasonally varying air temperature evapotranspiration and precipitation patterns calculated values of rpr varied between 35 and 97 among the individual episodes a multiple linear correlation of the rpr with both the average intensity of recharging rainfall events and the antecedent soil water content was calculated given the relatively easy measurability of precipitation and soil water content such an empirical model would have great hydrogeological and practical utility it would facilitate short term forecasting of recharge in karst aquifers of the mediterranean region and other aquifers with similar hydrogeological characteristics by establishing relationships between the rpr and climate dependent variables such as average storm intensity it would facilitate prediction of climate change effects on groundwater recharge the emr methodology could further be applied to other aquifers for evaluating the relationship of recharge to various hydrometeorological and hydrogeological processes

earthquake geodesy and hazard monitoring catastrophic events such as major earthquakes and volcanic eruptions result when the earth s crust fails in response to accumulated deformation the accumulation of deformation results from ongoing processes such as aseismic deformation of subcrustal rock associated with relative plate motions or the ascent of magma through a volcanic plumbing system geodetic measurements document the crustal deformation leading to these failures and the deformation resulting from them providing unique insight into the physical processes involved by virtue of the space and time domains of ground deformation detected with geodetic measurements geodesy is a useful tool in monitoring active tectonic and volcanic regimes for a wide range of natural events including earthquakes aseismic fault motions and volcanic events geodetic measurements constrain physical models of the processes that cause such events because these geodetic studies probe the underlying processes leading to and culminating in catastrophic natural events many such studies are directly applicable to earthquake and volcano hazard assessment

funneled flow mechanisms in a sloping layered soil laboratory investigation artificial capillary barriers are being used to divert water away from sensitive underground regions conversely funneled flow over natural capillary barriers may increase the danger of groundwater contamination by decreasing the travel time and contact area there have been relatively few experimental studies of capillary barrier flow patterns in this study water was applied uniformly across the top surface of a backlit tilting chamber 1 cm thick 110 cm high and 180 cm long in which a coarse sand layer was imbedded in a fine sand bedding slope and water application rates were varied between 0 and 12 and 1 and 3 cm h 1 respectively after attaining steady state matric potential was measured along the textural interface and photos of dye traces were taken in order to visualize streamlines the funneled flow was characterized by three discrete regions an initial capillary diversion a breakthrough region and a toe diversion the breakthrough region consisted of a significant zone of partial breakthrough where the vertical flux into the coarse layer was less than the water application rate the lateral distance of the capillary diversion was explained well by previously published relationships when the water entry value at the textural interface was replaced by lower observed matric potential at which breakthrough occurred at the most upslope point the length of the capillary diversion was overpredicted using the air entry value finally the toe of the coarse layer had significant observed effects on funneled flow patterns which have previously received little if any attention the results of this study imply that the slope of the coarse layer and infiltration rate will largely govern the effectiveness of capillary barriers and that capillary barriers are less effective than previously assumed

crustal deformation of the yellowstone caldera from first gps measurements 1987 1989 a global positioning system gps network was established in 1987 in order to measure crustal deformation across the yellowstone plateau centered on the yellowstone caldera and adjacent teton wyoming and hebgen lake montana fault zones forty four gps stations in the yellow stone network were re surveyed in 1989 and station coordinates using broadcast orbits were obtained these results were used to assess the precision and accuracy of the gps surveys and to identify areas of rapid crustal deformation on the yellowstone plateau the gps measured displacements between 1987 and 1989 were calculated relative to a station at the eastern edge of the 100 km wide network the relative horizontal displacements have an average magnitude of 15 10 mm the relative vertical displacements are generally less than 25 mm about an average near zero and with an uncertainty of 20 mm comparisons with leveling and trilateration measurements taken nearly simultaneously suggest that the accuracy of these gps measurements is at the level of the above uncertainties gps measured vertical displacements across the northern part of the yellowstone caldera and 1st order leveling results show up to 20 mm of subsidence between 1987 and 1989 this subsidence is part of a six year period of caldera deflation that began in 1985 in addition up to 66 mm of uplift is observed with gps at the northwest edge of the yellowstone caldera and may be associated with processes following an intense earthquake swarm in 1985 86 and with caldera subsidence

fracture of summer perennial sea ice by ocean swell as a result of arctic storms 1 the arctic summer minimum sea ice extent has experienced a decreasing trend since 1979 with an extreme minimum extent of 4 27 106 km2 in september 2007 and a similar minimum in 2011 large expanses of open water in the siberian laptev chukchi and beaufort seas result from declining summer sea ice cover and consequently introduce long fetch within the arctic basin strong winds from migratory cyclones coupled with increasing fetch generate large waves which can propagate into the pack ice and break it up on 06 september 2009 we observed the intrusion of large swells into the multiyear pack ice approximately 250 km from the ice edge these large swells induced nearly instantaneous widespread fracturing of the multiyear pack ice reducing the large 1 km diameter parent ice floes to small 100 150 m diameter floes this process increased the total ice floe perimeter exposed to the open ocean allowing for more efficient distribution of energy from ocean heat fluxes and incoming radiation into the floes thereby enhancing lateral melting this process of sea ice decay is therefore presented as a potential positive feedback process that will accelerate the loss of arctic sea ice