a parametrization based on sea ice morphology of the neutral atmospheric drag coefficients for weather prediction and climate models 1 a hierarchy of parametrizations of the neutral 10 m drag coefficients over polar sea ice with different morphology regimes is derived on the basis of a partitioning concept that splits the total surface drag into contributions of skin drag and form drag the new derivation which provides drag coefficients as a function of sea ice concentration and characteristic length scales of roughness elements needs fewer assumptions than previous similar approaches it is shown that form drag variability can explain the variability of surface drag in the marginal sea ice zone miz and in the summertime inner arctic regions in the miz form drag is generated by floe edges in the inner arctic it is generated by edges at melt ponds and leads due to the elevation of the ice surface relative to the open water surface it is shown that an earlier fit of observed neutral drag coefficients is obtained as a special case within the new concept when specific simplifications are made which concern the floe and melt pond geometry due to the different surface morphologies in the miz and summertime arctic different functional dependencies of the drag coefficients on the sea ice concentration result these differences cause only minor differences between the miz and summertime drag coefficients in average conditions but they might be locally important for atmospheric momentum transport to sea ice the new parametrization formulae can be used for present conditions but also for future climate scenarios with changing sea ice conditions

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

ice floe distribution in the sea of okhotsk in the period when sea ice extent is advancing 1 ice floe distribution in the sea of okhotsk during a cold air outbreak was investigated by analyzing several thousand of sea ice images obtained by the aircraft observation on 18 february in 2000 the effective floe size became small from 10 m to 2 m within the marginal ice zone miz the scaling properties of floe distribution are demonstrated by a cumulative number frequency which follows a power law scaling with an exponent the value of increased from 1 5 within the internal ice zone to 2 1 within the miz which means that relatively small ice floes dominate in the miz the effective width of the miz estimated by a wave attenuation theory agreed with the observed width suggesting that the flexural stress of waves penetrating into the ice is one of the possible mechanisms which cause the difference in the scaling property

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

engineering geology of the tropical volcanic soils of la laguna tenerife abstract geological factors controlling the engineering properties of the volcanic soils of la laguna have been analysed emphasis has been placed on the influence of mineralogy and fabric on the strength and deformation properties and particularly on the results of the classification test the unusually high strength and low compressibility in relation to the high plasticity fine particle size and active mineral composition has been explained the soil fabric is considered to be the main factor leading to these unusual properties but geochemical environment and associated mineralogy also play an important part since la laguna soils show similar engineering geological characteristics to other widely distributed tropical volcanic soils a review has been made of the different hypotheses which attempt to explain the abnormal properties of these soils

mechanistic approach to the shear strength behaviour of allophanic soils abstract the presence of allophane minerals imparts special engineering features to the volcanic ash soils this study examines the reasons for the allophanic soils exhibiting unusual shear strength properties in comparison to sedimentary clays the theories of residual shear strength developed for natural soils and artificial soil mixtures and the unusual surface charge properties of the allophane particle are invoked to explain the high shear strength values of these residual soils the lack of any reasonable correlation between effective stress strength parameter and plasticity index values for allophanic soils is explained on the basis of the unusual structure of the allophane particle the reasons as to why natural soil slopes in allophanic soil areas example dominica west indies are stable at much steeper angles than natural slopes in sedimentary clay deposits london clay areas are explained in light of the hypothesis developed in this study

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

soil pipes and their role in runoff generation and chemical denudation in a humid tropical catchment in dominica numerous soil pipes are reported from a small catchment in an area of kandoid kaolin rich soils and 2375 mm annual rainfall in the humid tropical volcanic island of dominica west indies two spot surveys in august 1982 at baseflow during the wet season indicated that pipes contributed at least 14 16 per cent of streamflow sampled pipeflow was of similar chemical composition to the baseflow dominated streamwater specific conductance 249 420 s cm 1 and silica 75 mg l 1 levels of pipeflow were high and suggested that the pipes tapped solute rich water close to the soil rock interface the principal pipes flow perennially and showed little response to daily rainfalls of up to 43 mm during the monitoring period

power scaling and seasonal changes of floe areas in the arctic east siberian sea the cumulative number versus floe area distribution of seasonal sea floes from six satellite images of the arctic ocean during the summer breakup and melting is fit by two scale invariant power law scaling regimes for floe areas ranging from 30 to 28 400 000 m2 scaling exponents for larger floe areas range from 0 6 to 1 0 with an average of 0 8 scaling exponents for smaller floe areas range from 0 3 to 0 6 with an average of 0 5 the inflection point between the two scaling regimes ranges from 283 102 to 4850 102 m2 and generally moves from larger to smaller floe areas through the summer melting season the stability of the power scaling results is demonstrated for two of the images by dividing each in half and analyzing each half separately with the result that the scaling exponents and the size of the inflection points are nearly the same for each half as for the whole image we propose that the two scaling regimes and the inflection between them are established during the initial breakup of sea ice solely by the process of fracture the distributions of floe size regimes retain their scaling exponents as the floe pack evolves from larger to smaller floe areas from the initial breakup through the summer season due to grinding crushing fracture and melting the scaling exponents for floe area distribution are in the same range as those reported in previous studies of arctic floes and for the single scaling exponents found for crushed and ground geologic materials including streambed gravel lunar debris and artificially crushed quartz the single scaling exponent found for fault gouge falls below the range for floes possibly because the fracturing and grinding process in fault gouge takes place under high confining pressure a probabilistic model of fragmentation is proposed that generates a single power law scaling distribution of fragment size

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

the effect of a storm on the 1992 summer sea ice cover of the beaufort chukchi and east siberian seas for the summer beaufort chukchi and east siberian seas a variety of active and passive microwave satellite data are used to determine the response of the ice edge and interior to a storm specifically the study concentrates on a low pressure system that passed over the region between august 14 and 20 1992 with peak geostrophic winds of about 18 m s 1 through the use of the ers 1 imaging radar and the special sensor microwave imager the ice response is examined at two locations at the ice edge for a nearly stationary location in the chukchi sea and in the ice interior along three swaths in the beaufort chukchi and east siberian seas the ice edge observations show that the storm fractures the large floes into small floes some of which are advected into the adjacent warm water the ice interior observations show that the storm caused an increase in the open water amount and a shift in the floe size distribution toward smaller floes in the ice interior application of the cumulative number distribution n d where n is the number of floes per unit area that are no smaller than some floe diameter d shows that for d 1 km n behaves like d where lies in the range 1 8 2 9 our analysis also shows that this slope is not affected by the storm and is slightly larger near the ice edge

the mechanics of small tropical flowslides in dominica west indies abstract investigation of landslides in the tropical clay soils of dominica revealed that the debris travelled great distances across low angle slopes the initiating mechanism was a shallow rotational or translational slide but the high soil pore water contents invariably led to a flowslide the tropical clays of dominica exhibit unusual geotechnical and hydrological properties the values of residual shear strength exceed what would be expected when comparing them with temperate clays the soilsare more akin to temperate granular materials in their shear strengths even allowing for this the pore waterpressures need to be close to zero for stability of high angle slopes a detailed understanding of runoff processes and subsoil flow is necessary to explain the high flow rates in soils of high water retention capacity only rainfalls of exceptionally prolonged high intensity can elevate pore water pressures and induce landslides there is therefore a vast amount of soil water available to form flow slides when movement commences

phreatic activity and hydrothermal alteration in the valley of desolation dominica lesser antilles phreatic eruptions are possibly the most dramatic surface expressions of hydrothermal activity and they remain poorly understood the near absence of precursory signals makes phreatic eruptions unpredictable with respect to both time and magnitude the valley of desolation vod dominica located close to the boiling lake the second largest high temperature volcanic crater lake in the world hosts vigorous hydrothermal activity with hot springs mud pools fumaroles and steaming ground a phreatic or phreatomagmatic eruption from this site is considered to be the most likely scenario for future volcanic activity on dominica yet there is little information regarding the trigger mechanisms and eruption processes of explosive events at this active hydrothermal center and only a very small number of studies have investigated hydrothermal activity in the vod we therefore conducted two field campaigns in the vod to map hydrothermal activity and its surficial phenomena we also investigated alteration processes and their effects on degassing and phreatic eruption processes we collected in situ petrophysical properties of clay rich unconsolidated samples and together with consolidated rock samples we investigated the range of supergene and hydrothermal alteration in the laboratory in addition we performed rapid decompression experiments on unconsolidated soil samples our results show that alteration leads to an increasing abundance of clay minerals and a decrease in both strength and permeability of the rocks in the immediate vicinity of degassing acid sulfate fluids advanced argillic alteration yields a mineral zoning which is influenced by meteoric water the water saturated basal zone is dominated by kaolinite run 0whereas alunite formation is favored at and above the groundwater table where atmospheric oxidation of h2s to h2so4 occurs e g steam heated alteration alteration effects may in turn inhibit degassing at the surface increasing the potential for pressurization in the subsurface and thus lead to phreatic eruptions rapid decompression experiments together with ballistic trajectory calculations constrain estimates of the conditions prior to the 1997 small scale phreatic event in the vod the results presented here may serve as a contribution to the understanding of the hazard potential of ongoing hydrothermal activity within the vod on a broader perspective our results will help evaluate hydrothermal activity in similar areas worldwide which might also have the potential for phreatic eruptions for instance poas costa rica or tongariro and waimangu new zealand

characteristics of sea ice floe size distribution in the seasonal ice zone 1 the size distribution of sea ice floes was observed by coordinated landsat imagery and video monitoring conducted from an icebreaker and a helicopter for an area 38 km 26 km in seasonal sea ice in the southern sea of okhotsk in february 2003 the combination of imagery on several scales allowed measurements of ice floes over three orders of magnitude from 1 m to 1 5 km two different regimes were observed floes larger than about 40 m have a power law number density with an exponent of 1 87 in the lower range of earlier results below 40 m the power law exponent is 1 15 the cause of these two different regimes is hypothesized to lie in the effects of swell on floes of different sizes and thicknesses the importance of the floe size distribution for lateral melting is elucidated

assessing internal stress evolution in unsaturated soils 1 internal stresses in soils evolve as a result of the various interactions among soil particles and the pore fluids in response to natural or human induced activities whether attributed to suction structure or the various physicochemical forces that may develop assessing the internal stresses in soils has been an active area of research in soil science and engineering this paper presents the restrained ring method as an experimental tool for measuring the stresses that develop in a drying soil when it is restrained from shrinking freely the internal stress that develops can be related to the water content of the soil this method is validated using results for both silty clay loam and clay loam soils tensile stress at failure estimated from the restrained ring method was compared to tensile strength ranges of similar soils and a good correlation was observed moreover internal stresses measured by the restrained ring method were compared with existing empirical relationships using suction and degree of saturation this comparison concluded that suction is not the sole contributor to the soil s internal stress

observations and analyses of an intense waves in ice event in the sea of okhotsk 1 ice draft ice velocity ice concentration and current profile data gathered at an array of eight continental shelf monitoring sites east of sakhalin island were analyzed in conjunction with regional meteorological data to document and explain intense wave occurrences several hundred kilometers inside the sea of okhotsk ice pack the studied event was associated with the 19 21 march 1998 passage of an intense cyclone which produced waves with amplitudes in excess of 1 m at the most offshore monitoring location the relatively monochromatic character of the waves allowed extraction of wave intensity time series from ice draft time series data spatial and temporal variations in these data were used to establish directions and speeds of wave energy propagation for comparisons with an earlier interpretation liu and mollo christensen 1988 of an antarctic intense waves in ice event it was concluded that although both events are compatible with a two stage process in which initially slowly advancing wave activity increases subsequent ice cover wave transmissivity the first stage of the sea of okhotsk event was not explicable in terms of the static stress induced changes in the waves in ice dispersion relationship proposed by liu and mollo christensen an alternative explanation is offered that eschews the linkage between wave group velocities and the observed slow rates of wave energy propagation and attributes the subsequent transition to more normal wave propagation behavior to ice pack divergence

a framework for unsaturated soil behaviour a framework is put forward which explains the shear behaviour of an unsaturated soil in terms of the total stresses and suctions acting within the soil it is based on the critical state model for

mechanisms for the variation of sea ice extent in the northern hemisphere using daily sea ice data derived from satellite borne sensors and atmospheric data we examined processes controlling the variation of sea ice extent in the northern hemisphere the daily ice motion field was computed from imagery of the defense meteorological satellite program dmsp special sensor microwave imager ssm i for seven winters december to april from 1991 1992 to 1997 1998 by employing the maximum cross correlation method in order to examine mechanisms of the temporal variation of the ice extent we analyzed 50 specified lines across the daily ice edge although a high correlation between the ice motion and the geostrophic wind speed was observed in all the ice edge areas the degree for correlation between the speed of the ice edge displacement and the wind speed varied with region the degree for response of the ice edge speed to the wind speed largely depended upon that of the ice edge speed to the ice motion the following mechanisms controlling the variation of ice extent for regions in the northern hemisphere were anticipated in the barents sea bering sea and the sea of okhotsk the ice extent advances by wind driven ice advection and the daily scale variation of the ice extent were also controlled by the variation in wind speed in contrast the ice extent in the labrador sea and the greenland sea seemed to be considerably affected by oceanographic factors such as the location of the thermal front and was not related to the variation in wind speed the regional difference of the variation mechanism was also reflected in the interannual variation in maximum ice extent

an experimental investigation of the mechanical behavior and microstructural features of a volcanic soil isparta turkey and stability of cut slopes in this soil abstract volcanic soils are widely distributed group of soils which cover significant parts of the world s surface and include areas occupied by urban settlements structures and infrastructures and may create geo engineering problems these soils exhibit a distinctive behaviour that is a consequence of their formation history mineralogy and structure some part of the subsoil of a large area surrounding the city of isparta western turkey mainly consists of volcaniclastic deposits this paper presents the results of the part of a research programme aiming at geotechnically characterizing the uppermost layer of this volcaniclastic sequence particularly focusing on its collapse potential shear behaviour and the influence of microstructure on these behaviours in addition its main futures were compared with those of some similar volcanic soils at different parts of the world and the stability of sub vertical cuts in this soil was also assessed the experimental investigation mainly consisted of index and classification tests double oedometer and direct shear box tests to assess the collapse potential and shear behaviour of the soil respectively matric suction of the samples was also determined for preliminary evaluation of the influence of suction on collapse and shear behaviours of the soil in addition thin section studies and x ray diffraction xrd and scanning electron microscopy sem analyses were also conducted to determine mineralogical and microstructural features and to evaluate their influences on the mechanical behaviour of the volcanic soil the deposit is composed of weakly bonded firm silty sand with an open structure low unit weight and high porosity generally unsaturated in situ the results of the double oedometer tests suggest that the volcanic soil generally falls in the category of slight collapse potential at normal stresses ranging between 5 and 100 kpa while at normal stresses greater than 100 kpa its collapse potential increases and ranges between moderate and moderately severe collapse potential classes at normal stresses lower than 100 kpa matric suction may have an effect on collapse behaviour the direct shear box test results indicated that the volcanic soil has two different types of shear strength behaviour represented by bi linear failure envelopes in other words the shear strength parameters of the volcanic soil within a low normal stress range generally between about 6 and 200 kpa exceed those of determined at higher normal stresses since no matric suction was measured during the direct shear box tests it could not be possible to evaluate the effect of suction on the bi linear failure envelopes however some differences between the suction and degree of bonding of the samples taken from different locations might probably have been contributed to the separation of the bi linear behaviour at different normal stress levels the destruction of the bonding cementation between the particles is probably more responsible from the bi linear form of the failure envelope comparisons between the sem micrographs taken from natural and tested specimens revealed that the mechanical behaviour of the volcanic soil is strongly influenced by the bonding material the results of the stability analyses showed a good agreement with the current situation of the cut slopes observed in the study site and suggested that vertical cut slopes with a height of 14 15 m will maintain their stability based on a reasonable factor of safety such as 1 5

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

relationship between the upper ocean and sea ice during the antarctic melting season during the antarctic ice melting season high resolution sea ice data were collected with the video monitoring system aboard the icebreaker shirase along with the monitoring of temperature and salinity in the upper ocean on the basis of these data relationships among sea ice concentration temperature and salinity are investigated in the ice interior region away from the ice free ocean ice concentration is negatively correlated with temperature and positively correlated with salinity for the spatially averaged data which suggests that the local balances of heat and salt nearly hold in a bulk area at the ice margin ice concentration is negatively correlated with both temperature and salinity suggesting that the local balances are overwhelmed by the effects of ice advection the expendable bathythermograph profiles at the ice margin also show that a considerable amount of sea ice was advected into the ice free ocean and subsequently melted there it is pointed out that a polynya works as an ice melting factory in summer it absorbs solar radiation during the period of opening and then melts the ice advected there prom a heat budget analysis and ocean structure in the melting season we propose a simple ice upper ocean coupled model in which sea ice melts on the bottom and lateral faces with the heat source supplied to the open water area by solar radiation the relations among ice concentration temperature and salinity derived from the model are consistent with the observed relations the analytic solution for the no lateral melting case shows that the concentration temperature relation converges to a certain asymptotic curve with time which explains that the temperature concentration plot shows a similar relation for any region dependence of the relations among ice concentration temperature and salinity on the spatial scale is also discussed

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

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

overview of limex 87 ice observations ice observations results and conclusions are summarized for the march 1987 labrador ice margin experiment limex 87 an international oceanographic study conducted in the pack ice of the grand banks area off the coast of newfoundland included are the ice extent flow size and thickness ice kinematics and rheology ice microwave properties oceanic properties under the ice and penetration of swell into the ice

increase and decrease of sea ice area in the sea of okhotsk ice production in coastal polynyas and dynamic thickening in convergence zones 1 this paper examines the production and reduction of sea ice area in the sea of okhotsk analyses were carried out for 10 winters december april from 1991 1992 to 2000 2001 using daily data of sea ice velocity and concentration derived from images of the defense meteorological satellite program dmsp special sensor microwave imager ssm i first we mapped sea ice divergence which was calculated from the daily ice velocity field in the case of offshore winds high divergence was observed along the coastline while there existed a broad convergence area with inshore winds next we examined local changes in an area of sea ice as in the case of ice divergence ice production and reduction are strongly controlled by wind direction we found that a large amount of sea ice was produced in coastal areas under offshore wind conditions the geographical distribution of the ice production area agrees well with that of the well known coastal polynya areas our estimation shows that 8 7 105 km2 yr 1 of sea ice is produced in the northern coastal area and 3 7 105 km2 yr 1 in the sakhalin coastal area in contrast 7 4 105 km2 yr 1 of the ice area disappeared in shantarskiy bay this reduction of ice area is mainly caused by dynamic deformation of existing ice forming rafted ice or pressure ridges this dynamic deformation plays an important role not only in the reduction of okhotsk sea ice area but also in the thickening of ice

evidence of equilibrium peak runoff rates in steep tropical terrain on the island of dominica during tropical storm erika august 27 2015 abstract tropical storm erika was a weakly organized tropical storm when its center of circulation passed more than 150 km north of the island of dominica on august 27 2015 hurricane hunter flights had difficulty finding the center of circulation as the storm encountered a high shear environment satellite and radar observations showed gyres imbedded within the broader circulation radar observations from guadeloupe show that one of these gyres formed in convergent mid level flow triggered by orographic convection over the island of dominica gauge adjusted radar rainfall data indicated between 300 and 750 mm of rainfall on dominica most of it over a four hour period the result was widespread flooding destruction of property and loss of life the extremity of the rainfall on steep watersheds covered with shallow soils was hypothesized to result in near equilibrium runoff conditions where peak runoff rates equal the watershed average peak rainfall rate minus a small constant loss rate rain gauge adjusted radar rainfall estimates and indirect peak discharge ipd measurements from 16 rivers at watershed areas ranging from 0 9 to 31 4 km 2 using the usgs slope area method allowed testing of this hypothesis ipd measurements were compared against the global envelope of maximum observed flood peaks versus drainage area and against simulations using the u s army corps of engineers gridded surface subsurface hydrologic analysis gssha model to detect landslide affected peak flows model parameter values were estimated from the literature reasonable agreement was found between gssha simulated peak flows and ipd measurements in some watersheds results showed that landslide dam failure affected peak flows in 5 of the 16 rivers with peak flows significantly greater than the envelope curve values for the flood of record for like sized watersheds on the planet gssha simulated peak discharges showed that the remaining 11 peak flow values were plausible simulations of an additional 24 watersheds ranging in size from 2 2 to 75 4 km 2 provided confirmation that the ipd measurements varied from 40 to nearly 100 of the envelope curve value depending on storm total rainfall results presented in this paper support the hypothesis that on average the peak discharges scaled linearly with drainage area and the constant of proportionality was equivalent to 134 mm h 1 or a unit discharge of 37 22 m 3 s 1 km 2 the results also indicate that after the available watershed storage was filled after approximately 450 500 mm of rain fell runoff efficiencies exceeded 50 60 and peak runoff rates were more than 80 of the peak rainfall rate minus a small constant loss rate of 20 mm h 1 these findings have important implications for design of resilient infrastructure and means that rainfall rate was the primary determinant of peak flows once the available storage was filled in the absences of landslide dam failure

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

investigations of andesitic volcanic debris terrains part 2 geotechnical here results of geotechnical investigations for the proposed dominica international airport are presented the main geotechnical investigative method is comprised of boreholes to 30 m depth with standard penetrating testing spt and undisturbed shelby tube and disturbed split spoon soil sampling the geotechnical investigation confirms the findings of a companion geophysical investigation which concludes that bedrock is not likely to be encountered within the proposed depths of excavation for the airport geophysical and geotechnical data correlations are developed seismic velocity and the number n of blow counts with spt spt n appear to be well correlated by a linear model a model relationship between spt and seismic dynamic elastic modulus is developed using seismic velocity spt n is better correlated with the dynamic elastic modulus than with seismic velocity the study shows that the seismic velocity and the derived dynamic elastic moduli can accurately predict soil strength as measured by spt

role of apparent cohesion in the stability of dominician allophane soil slopes this study examines the effect of loss of apparent cohesion from rainwater infiltration upon the stability of partly saturated allophanic soil slopes of dominica west indies the parent material of the dominican allophanic soils are the andesitic and dacitic volcanic rocks from ten volcanic centres of mainly pleistocene age although simplifying assumptions are made to assess the depth of wetting front and magnitudes of true and apparent cohesion values of the partly saturated allophanic soils certain inferences of practical significance emerge from the study matric suction contributes to the effective stress of unsaturated soils and increases the shear strength of these soils by imparting them an apparent cohesion strength component this apparent cohesion strength component of the partly saturated dominican allophanic soils is considered to be related to the matric suction term u a u w by a parabolic relationship the partly saturated allophanic soil slopes of dominica would invariably fail from loss of apparent cohesion upon saturation of the soil mantle by the infiltrating water front only if a the average slope angle beta is greater than or equal to the drained shear strength parameter of the unsaturated soil phi d slopes with beta greater than or equal to phi d are referred to as category 1 slopes in this study and b the drained cohesion parameter c d belonging to the partly saturated soil of the category 1 slope is mainly contributed by matric suction induced apparent cohesion c app and contribution from true cohesion c is absent however the possibility of the category 1 slopes for the case 1 situation failing in the saturated condition from effective stress reduction due to rise in ground water table is shown to be an unfeasible proposition in contrast for the case 1 situation the partly saturated category 2 slopes beta phi d are insusceptible to failure from reduction in effective stress due to loss of matric suction but fail in the saturated condition from effective stress reduction due to rise in ground water table if the allophanic soils were to possess a sufficient magnitude of true cohesion c even the partly saturated category 1 slopes possessing slope angles beta much in excess of their phi d values beta phi d 15 1 degrees would remain stable upon total elimination of the matric suction induced cohesion however partly saturated category 1 slopes possessing a true cohesion component and insusceptible to failure from reduction in effective stress upon loss of matric suction invariably fail in the saturated condition from reduction in effective stress due to rise in ground water table using the methodology developed in this study two previously reported case histories pertaining to rain induced translational landslides in the residual soil areas of brazil are re examined and the results obtained in this study are found to be in agreement with the findings of the previous researchers

determining the floe size distribution of east antarctic sea ice from digital aerial photographs floe size within the antarctic pack ice is an important parameter that affects both the ocean ice atmosphere energy exchange and the mechanical properties of pack ice in this paper we present a computer based algorithm to extract floe size distribution information from digital aerial photographs of antarctic sea ice the algorithm segments digital images of sea ice into distinct floes from which the size of each floe is calculated and floe size distributions are derived through a recursive application of the morphological erosion operator each floe is eroded towards its centre while each pixel s erosion number is recorded this ensures no information is lost while individual floes are identified the algorithm combines image processing techniques with some manual input to accurately identify the boundaries of individual floes within an image to demonstrate the functionality of the algorithm six images representing regions along a 22 km south to north transect through a transitional zone of pack ice near 65 s 140 e have been processed regional variations in the floe size distributions show an increase in the number of smaller floes relative to larger floes and a decrease in the dominant floe size in terms of areal coverage from south to north these results are consistent with ship based observations

volcanic soil properties in dominica west indies abstract the unusual geotechnical and hydrological characteristics of the tropical clay soils involved in landslides in dominica resulting from hurricanes david and frederic in 1979 are examined these highly porous soils exhibit very high field moisture contents 42 180 for allophane latosols void ratios are very high up to 6 for allophanes and therefore field dry unit weights are very low 5 47 10 01 kn m3 for allophanes although predrying does not greatly affect the atterberg limits of kandoids it causes great reductions in the limits of allophane rich soils the degree of difference depending on the allophane content allophane soils also form a distinct group on cassagrande s plasticity chart falling below the a line as liquid limit increases predrying increases the r values by around 7 for kandoids but does not affect the allophanes and smectoids values of r vary with clay mineralogy allophanes 30 38 smectoids 32 35 dry kandoids 33 34 wet kandoids 25 29 all are abovevalues for temperate clays and are more akin to granular soils none of the direct shear tests showed any change of n as n n increased a marked contrast to temperate clays a detailed understanding of runoff processes notably zones of percolation impedance perched saturation and throughflow is essential to explanations of slope failure patterns although topsoil permeabilities and porosities of all dominican soils are extremely high subsurface soil hydrology varies strikingly with soil type impermeable subsoils and pans impede percolation at a shallow depth in smectoid and allophane podzolic soils in kandoids and allophane latosolics two zones of impedance above the b horizon and at the soilk rock interface are important but sufficient vertical development of saturation zonesto initiate landslides can only occur in the exceptionally prolonged high intensity rainfalls of cyclones

prediction of rainfall induced shallow landslides in the loess plateau yan an china using the trigrs model in this work a transient rainfall infiltration and grid based regional slope stability model trigrs was implemented in a case study of yan an city northwest china in this area widespread shallow landslides were triggered by the 12 july 2013 exceptional rainstorm event a high resolution dem soil parameters from in situ and laboratory measurements water table depths the maximum depth of precipitation infiltration and rain gauge corrected precipitation of the event were used as inputs in the trigrs model shallow landslides triggered on the same day were used to evaluate the modeling results the summarized results are as follows i the characteristics and distribution of thirty five shallow landslides triggered by the 12 july 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth area and volume less than 3 m 200 m2 and 1000 m3 respectively ii four intermediate factor of safety fs maps were generated using the trigrs model to represent the scenarios 6 12 18 and 24 hours after the storm event the area with fs 1 increased with the rainfall duration the percentage of the area with fs 1 was 0 2 3 3 3 8 and 5 1 for the four stages respectively twenty four hours after the rainstorm trigrs predicted that 1255 grid cells failed which is consistent with the field data iii trigrs generated more satisfactory results at a given precipitation threshold than sinmap which is ideal for landslide hazard zoning for land use planning at the regional scale comparison results showed that trigrs is more useful for landslide prediction for a certain precipitation threshold also in the regional scale iv analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation copyright 2016 john wiley sons ltd

the shear strength of partly saturated soils a direct shear apparatus is described which could be used to study the shear strength of partly saturated soils under controlled conditions the principle of this device is described and the test results are presented and discussed with this apparatus it is also possible to determine the effect on the shear strength of a change in solute suction

infiltration analysis to evaluate the surficial stability of two layered slopes considering rainfall characteristics abstract shallow slope failures in residual soil during periods of prolonged infiltration are common throughout the world using a one dimensional infiltration model and an infinite slope analysis this study examines an approximate method of determining how infiltration influences the surficial stability of two layered slopes the method extends moore s infiltration model which is based on the green ampt model to cover more general situations including those where water moves upward from a perched water table in decreasingly permeable soil the method has also been used to evaluate the likelihood of a shallow slope failure being induced by a particular rainfall event in making this evaluation the method takes into accounts the rainfall intensity and duration of various return periods in a two layered soil profile a comparison of the results of the infiltration model with the results of numerical analyses shows that with the use of properly estimated input parameters the proposed model compares reasonably well with other model that rely on more rigorous finite element method

stability analysis of unsaturated soil slopes considering water air flow caused by rainfall infiltration abstract even though soil is a mixture of solids with voids that are filled by air and water most previous studies on rainfall infiltration and its influence on slope stability were based on a single phase water flow model by assuming that the pore air pressure was atmospheric the purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope water air two phase flow analyses were conducted to investigate the contribution of pore air pressure on infiltration by rainfall in order to study the infiltration behavior with respect to soil type flow analyses were performed with two types of soil under similar settings results obtained from the two phase infiltration analysis were then used as input to the stability analysis by the strength reduction method infiltration and stability analyses based on a single phase water flow model were also carried out which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope the results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone hence remarkable delaying effects on water flow were induced such water air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope