surface and bed topography of trapridge glacier yukon territory canada digital elevation models and derived hydraulic geometry measurements of ice thickness and surface elevation are prerequisite to many glaci ological investigations a variety of techniques has been develo ped for inter pret ation of these data including means of constructing regularly gridded digital eleva tion models dem s for use in numcrical studies here we present a simple yet stati sti cally sound method for processing ice pe netr ating radar data and descr ibe a tech nique for interpol ating these data onto a regular grid dems generatcd fort rapridge glacier yukon territory canada are used to derive geometric quantities lhal give pre liminary insights into the underlying basin scale hydrol ogical syste m this simple geo metric analysis suggests that at low water press ures a dendrilic drainage netw ork exists that evolves into a uniaxial morphology as water pressure approaches notation these pre dictions are compared to hydraulic connection probabilities based on bore hole drilling

evolution of a surge type glacier in its quiescent phase kongsvegen spitsbergen 1964 95 kongsyegen is a 102 km 2 sub polar polythermal surge type glacier in northwest spitsbergen svalbard it surged just before 1948 and is currently in its quiescent phase measurements of surface geometry since 1966 show a retreat of the front and strong thinning of up to 75 m in the ablation area and a build up of up to 32 m in the accumulation area present day annual velocities along the glacier are low from 1 4 up to 3 6 m a 1 the measured mean net balance for the period 1987 94 and the balance reconstructed back to 1967 show a weak positive balance of about 0 1 m w e the measured actual ice flux is low and the mass transfer down glacier at the ela is only about 3 20 of that required for steady state thus the glacier is building up towards a new surge the total thickening rate on kongsvegen is somewhat higher than in other cases from svalbard but it is small compared with other well studied surge type glaciers in alaska and he pamirs this relatively low rate of change is a function of the low accumulation rate and the relatively cold climate compared to other areas and is common for surge type glaciers in svalbard

ice bed interface and englacial properties of svalbard ice masses deduced from airborne radio echo sounding data un ensemble de donnees de sondages par echo radio ont ete collectees sur 44 masses de glace au spitsberg et les calottes glaciaires de nordaustlandet svalbard ces donnees ont permis de produire les coefficients de reflexion en puissance pour l interface glace manteau sur une grande etendue de svalbard nord

tidewater glacier surges initiated at the terminus terrasar x data were provided by dlr project oce1503 and funded by the conoco phillips lundin northern area program through the crios project calving rates and impact on sea level c n acknowledges funding from european union erc grant 320816 and esa project glaciers cci 4000109873 14 i nb

enhanced radar scattering from water inclusions in ice it is believed that water filled cavities on the scale of decimetres are present in a number of glaciers in spitsbergen the evidence for this hypothesis comes from airborne radio echo sounding records collected by the scott polar research institute in 1983 the size of these cavities prevents the use of rayleigh scattering theory and requires a more general analysis mie scattering theory is used to investigate the scattered power providing some unexpected results the most significant of which is that for water bodies greater than approximately 0 25 m in radius the returned power from the volume illuminated is greater than that from a perfectly reflecting plane boundary

the role of pedogenesis in palaeosols of mexico basin and its implication in the paleoenvironmental reconstruction abstract most of the paleoenvironmental information for the basin of mexico comes from sedimentary proxies which unfortunately are incomplete for the terminal pleistocene and the holocene in this paper we present a temporal and spatial reconstruction of past soil cover in the south and north of the basin of mexico during the mis 2 and 1 marine isotope stage 2 and 1 palaeosol profiles were selected from three locations cuicuilco copilco and avon in the south basin and compared with soils studied in the teotihuacan valley pachuca and texcoco at north of the basin the results show that the pleistocene soil cover is more homogeneous dominated by the presence of luvisol type soils with secondary carbonates dated to around 20 000 cal yr bp during the holocene the soil distribution changes with andosols developing in the south while vertisols and calcisols form in the north the new soil distribution reflects differing climate conditions during the holocene conditions which characterize the basin today the andosol cover in south basin however represents the result of short term pedogenesis andosols are considered high quality soils that were attractive to settlers and were a factor in the development of sedentary villages

temporal changes in the radiophysical properties of a polythermal glacier in spitsbergen in order to study the seasonal and inter seasonal variations in radio wave velocity rwv radiophysical investigations were made at hansbreen a polythermal glacier in spitsbergen in july august 2003 and april 2004 these investigations included repeated radar profiling 20 and 25mhz along a transverse profile repeated common midpoint measurements continuous radar measurements during 8 days at a fixed site meteorological observations and continuous ice surface velocity monitoring by differential gps seasonal and inter seasonal rwv changes in the temperate ice layer are attributed respectively to rapid water redistribution within it during the summer and to variations in water content from 2 1 in summer to 0 4 in spring the reflection properties of the temperate ice layer correlate well with the air temperature with a nearly semi diurnal time lag the temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography the spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems

glacier surge propagation by thermal evolution at the bed bakaninbreen southern svalbard began a prolonged surge during 1985 in 1986 an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm unfrozen and cold frozen bed ground penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection interpreted as the top of a thick layer of sediment rich basal ice down glacier of the present surge front features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer the base of a permafrost layer and local ice lenses this indicates that this region of the bed is cold up glacier of the surge front a scattering zone above the basal reflection is interpreted as warm ice there is no evidence for this warm zone down glacier of the surge front nor do we see basal permafrost up glacier of it thus as in early surge phase the location of the surge front is now at the transition between warm and cold ice at the glacier bed we suggest that the propagation of the front is associated with this basal thermal transition throughout the surge because propagation of the front occurs rapidly and generates only limited heat basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice bed interface

use of c band ground penetrating radar to determine backscatter sources within glaciers the question of penetration of synthetic aperture radar sar signals at c band frequency into polar glaciers is addressed by comparing ground penetrating radar gpr and sar backscatter signatures profiles of the kongsvegen glacier svalbard were obtained with a c band gpr the received signal is converted to the equivalent radar cross section using the standard radar equation thus mapping the effective scattering sources within the glacier at this frequency the depth of the observed scattering sources is greatest in the superimposed ice where layers are clearly seen to a depth of approximately 14 m the very high scattering properties of the upper firn layers preclude layers deeper than approximately 6 m from being imaged integrating the radar cross sections over the depth gives a single backscatter value that we compare with the backscatter coefficient scattering cross section per unit area of the processed sar data for the same profile the comparison indicates that for coincidentally acquired gpr and sar data the radar cross section measured by the gpr does represent the features that contribute to the sar signal

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

age and archaeological implications of xitle volcano southwestern basin of mexico city the pedregal lavas are fresh well exposed basaltic flows erupted from the xitle scoria and cinder cone in the southwestern part of the basin of mexico these lavas cover an area of 70 km 2 and were emplaced over pyramids and other buildings e g cuicuilco and copilco archaeological sites today a part of mexico city including the national university is built on the flows initial strombolian activity produced an ash fallout layer which was immediately followed by effusive emplacement of lava flows the xitle cone grew on the north facing slope of ajusco volcano and lava flowed down to the n ne until it reached the basin floor more than 30 radiocarbon dates have been obtained by several workers on charcoal samples from beneath the lava and several ages for the eruption have been proposed from these dates most dated samples were not directly produced by xitle s eruption but instead are artifacts of human activity that predates the eruption thus these ages mostly about 2000 bp are older than the eruption a new age of 1670 35 years bp ad 245 315 obtained on charcoal samples collected just beneath the lavas is favored for the xitle eruption these samples originated by ignition of vegetation during the emplacement of hot scoriaceous tephra the new age is within the classic period of mesoamerican archaeology whereas the earlier reported ages are at the end of the preclassic the new age carries important implications for the timing of population shifts within the basin of mexico q 2000 elsevier science b v all rights reserved

estimate of the total volume of svalbard glaciers and their potential contribution to sea level rise using new regionally based scaling relationships we present a set of new volume scaling relationships specific to svalbard glaciers derived from a sample of 60 volume area pairs glacier volumes are computed from ground penetrating radar gpr retrieved ice thickness measurements which have been compiled from different sources for this study the most precise scaling models in terms of lowest cross validation errors are obtained using a multivariate approach where in addition to glacier area glacier length and elevation range are also used as predictors using this multivariate scaling approach together with the randolph glacier inventory v3 2 for svalbard and jan mayen we obtain a regional volume estimate of 6700 835 km3 or 17 2 mm of sea level equivalent sle this result lies in the mid to low range of recently published estimates which show values as varied as 13 and 24 mm sle we assess the sensitivity of the scaling exponents to glacier characteristics such as size aspect ratio and average slope and find that the volume of steep slope and cirque type glaciers is not very sensitive to changes in glacier area

radio echo sounding of spitsbergen glaciers problems in the interpretation of layer and bottom returns comparaison des sondages de glaciers du spitsbezg par un equipement 60 mhz spri mk iv et des sondages sovietiques sur 440 et 620 mhz les fortes differences observees sont attribuees a la forte absorption et grande dispersion sur le lit rocheux des sondages sovietiques

distribution of glaciofluvial sediment within and on the surface of a high arctic valley glacier marthabreen svalbard marthabreen is a 7 8km long valley glacier in sw spitsbergen the glacier is partially covered by a layer of angular debris derived from rockfall in its accumulation area pierced in places by pinnacles and ridges of glaciofluvial sediment these concentrations of glaciofluvial sediment fall into three categories 1 debris pinnacles 2 longitudinal sediment dykes 3 longitudinal ridge accumulations debris pinnacles are slabs of sediment predominantly sands gravels and cobbles elevated to the glacier surface along thrusts longitudinal sediment dykes are low 1m high ridges of sorted sand and gravels which are not associated with penetrative ice structures their occurrence downglacier of sediment dykes and debris pinnacles suggests that they originate as supraglacial or englacial channels or tunnels filled by sediment derived from the dykes or thrusts the presence of large quantities of glaciofluvial sediment on the surface of marthabreen does not imply englacial water flow at high levels within the glacier but is related to ice deformational processes such as thrusting and folding of debris rich stratification copyright 1999 john wiley sons ltd

evidence towards a thermal lag in the response of karsaglaciaren northern sweden to climate change recent topographical and ground penetrating radar gpr surveys of karsaglaciaren which is a small 1 km 2 and thin 56 m mountain glacier in arctic sweden show that there are small areas of temperate ice in the lowermost part of the glacier this is curious because we would expect such a small and thin glacier to have a fully cold ablation zone specifically with our analyses of present glacier geometry and thickness and of the prevailing climate we are unable to explain the presence of temperate ice within the snout of karsaglaciaren using prevailing models of glacier thermal structure this leads us to suggest that the presence of temperate ice within karsaglaciaren is a remnant of a previous polythermal state that existed when the glacier was larger and thicker karsaglaciaren is thus out of synch with current geometry and climate and is exhibiting a thermal lag we propose that with time karsaglaciaren s ablation zone and perhaps the entire glacier may well become fully cold as the temperate zone shrinks further we anticipate that such a thermal lag is likely to be present within other arctic glaciers a thermal lag and an evolution to a fully cold thermal state have significant implications for the dynamic behaviour of small arctic glaciers and for meltwater production from them

late quaternary secular variation data from mexican volcanoes abstract we present 32 new paleomagnetic directions and 21 absolute paleomagnetic intensities pi from 33 volcanoes sampled at 66 sites and covering the last 46 ka of these 29 were radiocarbon dated 3 by thermo luminescence and one is of historical age ad 1793 rock magnetic experiments show that the dominant minerals are magnetite and titanomagnetite of low to intermediate titanium content and of pseudo single domain size paleodirections were determined using stepwise demagnetization protocols and pi by the izzi or thellier coe protocols and strict selection criteria were applied to ensure the reliability of the data previously published data were evaluated to fulfill similar quality criteria as our data resulting in 65 directional data point 18 paleointensity entries from lavas 59 archeointensities are found to be acceptable all accepted data come from a region within an 860 km radius around mexico city paleosecular variation psv curves of the past geomagnetic full vector were established by using the bootstrap resampling algorithm combined with cubic p splines for smoothing and interpolation because of the uneven time distribution of the data this was done for two successive periods between ad 2000 1600 bc and 1600 bc 44000 bc the full vector psv curves are unique for the american continents because of their temporal extension end because they include both directions and absolute pi the recent psv curves the last 3600 years are of high resolutions which certainly have implication for both regional and global geomagnetic field models fast psv change centered around ad 700 and ad 900 separated by a period of much slower psv were observed and rapid pi changes were found around 400 bc and ad 1000 in the period between 1600 bc and 44000 bc psv curves are well defined only within some periods and otherwise only define general psv trends several intensity peaks with values up to 65 t vadm 15 1022 am2 were observed around 250 bc 12000 bc 15000 bc and 27000 bc and intensity lows around ad 700 1200 bc 24000 17000 bc and 34000 bc abnormal directions were found around 26000 bc with negative inclinations down to about 30 which may be related to the mono lake or rockall event a comparison with other psv curves is complicated by the large distance to europe and the hawaiian islands with longitude differences of 99 and 57 respectively lake sediment data from southern texas show more differences than agreements suggesting that either of the data may be affected by systematic errors

vertical ams variation within basalt flow profiles from the xitle volcano mexico as indicator of heterogeneous strain in lava flows abstract the within flow vertical variation of anisotropy of the magnetic susceptibility ams of three basaltic flow profiles from the xitle volcano were investigated in relation to the lava flow induced shear strain rock magnetic properties and opaque microscopy studies have shown that the magnetic mineralogy is dominated by ti poor magnetite with subtle vertical variations in grain size distribution psd grains dominate in a thin bottommost zone and from base to top from psd md to psd sd grains are found the vertical variation of ams principal direction patterns permitted identification of two to three main lava zones some subdivided into subzones the lower zone is very similar in all profiles with the magnetic foliation dipping toward the flow source whereas the upper zone has magnetic foliation dipping toward the flow direction or alternates between dipping against and toward the flow direction the k 1 maximum ams axis directions tend to be mostly parallel to the flow direction in both zones the middle zone shows ams axes diverging among profiles we present heterogeneous strain ellipse distribution models for different flow velocities assuming similar viscosity to explain the ams directions and related parameters of each zone irregular vertical foliations and transverse to flow lineation of a few samples at the bottommost and topmost part of profiles suggest sd inverse fabric levels of intense friction or degassing effects in ams orientations

palaeolandforms and volcanic impact on the environment of prehistoric cuicuilco southern mexico city abstract the pedregal lava field covers an area of 80 km 2 in the southern basin of mexico and includes the cuicuilco archaeological site cuicuilco is considered an early urban centre in the basin of mexico constructed during the late preclassic a few centuries bc and abandoned at the beginning of the first millenium ad three new radiocarbon ages together with reinterpretation of previous ages and detailed analyses of the slopes of the cuicuilco s pyramid support the hypothesis that cuicuilco was abandoned long before the xitli eruption xitli lavas followed several river valleys damming some and causing them to silt up magdalena xocotitla puente volado and chicuautitla rivers subsequently deflecting the old drainage from lake xochimilco to lake texcoco upper and lower piedmont and river landscapes are reconstructed on the basis of soil characteristics and lithostratigraphic units palaeolandforms suggest an agricultural environment prior to the xitli eruption

volcanic impact on the southern basin of mexico during the holocene the interstratification of volcanic and glacial deposits in central mexico has been helpful in correlating the time sequence of these events two glacial advances and many eruptions have occurred during the last 10 000 years although conditions have changed drastically since the last eruptions in the 1920s popocatepetl the origin and evolution of several lakes basin of mexico are related to vulcanism and periods of warmer and colder climatic conditions fifty monogenetic volcanoes have erupted near mexico city during the holocene probably during 20 22 different eruptive periods since some are superimposed vents similar to the jorullo vents which erupted 200 years ago in michoacan mexico the youngest of these volcanoes are chichinautzin and xitle 2030 60 years bp whose lavas covered approximately 80 km each the xitle eruption began with ash emission mainly towards the nw and was later dominated by lava flow fed by tubes this lava covered the cuicuilco prehispanic urban center and the agricultural areas near it the lava dammed and caused silting of the magdalena xicotitla and chicuautitla rivers and deflected the drainage pattern in general the eruption of chichinautzin and the other holocene volcanoes have drastically changed the topography and caused fires as can be seen in the carbonized branches at the base of the flows chichinautzin volcano was formed by successive thin lavas which flowed to the south and by thicker flows to the east west and north older holocene volcanoes are responsible for the formation of the zempoala and xochimico lakes popocatepetl is a 5450 m high stratovolcano to the east of mexico city which has been subject to glacial processes its eruptions have been documented since the 14th century the last being in the 1920s most of these eruptions caused ash fall mainly to the east and northeast but lava emissions and flooding have also been reported larger eruptions in the earlier history produced pyroclastic flows and surges lahars plinian pumice falls and two debris avalanches a preliminary map of the type of volcanism which has affected the different areas and its implications for future hazards is presented

a digital radio echo sounding and navigation recording system the scott polar research institute spri mk iv 60 mhz radio echo sounding res system has proven itself to be a most effective and versatile tool in glaciology during the last 15 years it has been used from a variety of platforms both surface and airborne and over a range of ice thicknesses from 4000 m to 100 m however the photographic recording methods used during this period were felt to be increasingly outdated in the context of modern data handling procedures accordingly in late 1982 the mk iv system was modified to incorporate fast digitizing of the res receiver output with microcomputer controlled magnetic tape recording of both the radar data and navigational inputs drewry and liest 1 1985 the new system will be described along with the improvements in data processing which have resulted from its use

controls on the distribution of surge type glaciers in svalbard we analyzed the possible controls on the distribution of surge type glaciers in svalbard using multivariate logit models including 504 glaciers and a large number of glacial and geological attributes specifically we examined the potential effect of geological boundaries mass balance conditions and thermal regime on surging it was found that long glaciers with relatively steep slopes overlying young fine grained sedimentary lithologies with orientations in a broad arc clockwise from northwest to southeast are most likely to be of surge type no relation between lithological boundaries and surge potential could be established possible explanations for length being conducive to surging are transport distance related substrate properties distance related attenuation of longitudinal stresses and the possible relation between thermal regime and glacier size analysis of glaciers with recorded radioecho sounding reveals that a polythermal regime accumulation area ratios close to balance and a large elevation span increase the surge potential the logit models also enabled us to detect 19 new surge type glaciers to reclassify six glaciers as normal and to identify unusual surge type glaciers our model results suggest that a polythermal regime and fine grained potentially deformable beds are conducive to the surge potential of svalbard glaciers

basal conditions beneath a soft bedded polythermal surge type glacier bakaninbreen svalbard original article can be found at http www sciencedirect com science journal 10406182 copyright elsevier ltd and the international union for quaternary research inqua doi 10 1016 s1040 6182 01 00053 2 full text of this article is not available in the uhra

paleosols beneath a lava flow in the southern basin of mexico the effect of heat on the paleopedological record abstract volcanic activity affects past and present landscapes here we present a case study related to the heat impact of the xitle lava flow on the former soil cover the eruption occurred 1670 years b p in south mexico city the evaluated properties include those related to the soil memory used as tools of paleoenvironmental interpretation in volcanic paleosols macro and micromorphology color grain size distribution magnetic susceptibility and carbon and nitrogen contents changes of these properties by the heat influence are relevant for an adequate paleoenvironmental reconstruction two sites and three soil profiles are selected to show soil modifications by the volcanic activity the two sites represent the following 1 slightly transformed paleosol buried by the lava flow but separated from it by a 10 cm thick volcanic ash layer site cuicuilco enah 2 moderately and strongly transformed paleosols two profiles inside the copilco archeological zone one of the copilco profiles represents a buried paleosol with a very thin 3 cm ash layer on top at the contact with the lava the second profile is the most affected by the lava flow as it is directly beneath the lava all studied paleosols are sandy have a low amount of organic matter narrow c n ratios and very high values of magnetic susceptibility the strongest modifications are observed in the upper horizons which are in contact with the lava however the presence of the ash layer minimizes the heat effect despite the observed modifications it is possible to establish three cycles of soil formation in the paleolandscape the first and the oldest related to the development of a luvisol type soil indicates a longer time of landscape stability during the second cycle a pedosediment with a high concentration of artifacts was formed the last and the youngest cycle includes the ab and the aeb horizons present only in copilco they form by an andosol type pedogenesis which reflects a shorter time of soil development the presence of the aeb horizon is interpreted as the result of the degradation of the ab horizon either due to the heat effect of the lava or to cultivation and irrigation practiced by the pre hispanic communities

mass and enthalpy budget evolution during the surge of a polythermal glacier a test of theory analysis of a recent surge of morsnevbreen svalbard is used to test predictions of the enthalpy balance theory of surging high resolution time series of velocities ice thickness and crevasse distribution allow key elements of the enthalpy internal energy budget to be quantified for different stages of the surge cycle during quiescence 1936 1990 velocities were very low and geothermal heat slowly built up enthalpy at the bed measurable mass transfer and frictional heating began in 1990 2010 then positive frictional heating velocity feedbacks caused gradual acceleration from 2010 to 2015 rapid acceleration occurred in summer 2016 when extensive crevassing and positive air temperatures allowed significant surface to bed drainage the surge front reached the terminus in october 2016 coincident with a drop in velocities ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed surge termination was prolonged however indicating persistence of an inefficient drainage system the observations closely match predictions of the theory particularly build up of enthalpy from geothermal and frictional heat and surface meltwater and the concomitant changes in ice surface elevation and velocity additional characteristics of the surge reflect spatial processes not represented in the model but can be explained with respect to enthalpy gradients

the structural geometric and volumetric changes of a polythermal arctic glacier during a surge cycle comfortlessbreen svalbard various parameters of the most recent surge of the polythermal glacier comfortlessbreen in northwest svalbard have been assessed through a combination of remote sensing and ground observations analysis of a digital elevation model time series shows a marked change in the geometry of the glacier from quiescence 1990 and earlier into the late surge phase 2009 the transfer of 0 74 km3 of ice caused up to 80 m of surface drawdown in the reservoir area above the equilibrium line whilst ice built up in a spatially concentrated manner in the receiving zone below the equilibrium line a ramp of ice c 100 m above quiescent level developed in the lower reaches of the glacier late in the surge also in the lower reaches of the glacier structures attributable to the passage of a kinematic wave are identified and the migration of a surge front on the glacier is thus inferred in a conceptual model we consider that a bend in the valley in which the glacier resides and convergence with tributary glaciers to be significant factors in the style of surge evolution their flow restrictive interference results in slow initial mass transfer and the growth of a surge front within 3 4 km of the terminus copyright 2015 john wiley sons ltd

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

palaeomagnetic study of the xitle pedregal de san angel lava flow southern basin of mexico abstract a detailed study of the 2000 years old xitle pedregal de san angel volcanic field in the southern basin of mexico was undertaken to assess the reliability of the palaeomagnetic record as derived from fresh well preserved and exposed lava flows the xitle vent is on the slope of the ajusco volcano which results in a topographic difference of over 800 m in less than 12 km of horizontal distance most sites present a mean direction with a small within site dispersion around the dipolar direction for the locality but some sites particularly in the basin sector of flat relief away from the vent show shallow inclinations anisotropy of magnetic susceptibility ams shows normal flow fabrics with horizontal foliation planes and small anisotropy degree ams lineations correlate with observed flow directions the magnetic properties vary systematically across flow units but directions do not show a consistent pattern secular variation effects do not apparently contribute to the shallow inclinations or directional scatter some lava structures like pressure crests and blocky fronts give shallow inclinations and scattered directions respectively the resulting overall mean direction is well defined and close to the dipolar direction b 26 dec 359 8 inc 32 8 k 167 95 2 2 but this excludes two apparent directional groups the mean direction for one group with b 19 dec 359 0 inc 35 1 k 247 95 2 1 may be the representative estimate for the field shallow inclinations are considered anomalous and associated to a characteristic specific to given sectors of lava flows palaeointensity determinations have been obtained for six samples from five sites by using the thellier and shaw methods results agree well with previous studies however the standard deviation calculated for the mean value remains high after incorporation of the new data mean palaeointensity based on five new determinations and eight early data is n 13 56 50 6 16 mt and the mean for the overall data set is n 20 60 50 9 21 mt results illustrate some practical considerations and limitations in methodology and the reliability of the palaeomagnetic record in volcanic rocks

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

cold ice in the ablation zone its relation to glacier hydrology and ice water content 1 cold ice within a polythermal ice body controls its flow dynamics through the temperature dependence of viscosity and affects glacier hydrology by blocking water flow paths lakes on the surface linked by persistent deeply incised meltwater streams are hallmark features of cold ice in the ablation zone of a glacier or ice sheet ice radar is a convenient method to map scattering from internal water bodies present in ice at the pressure melting temperature pmt consequently lack of internal scatters is indicative of cold ice we use a helicopter borne 30 mhz ice radar to delineate the extent of cold ice within grenzgletscher zermatt swiss alps the inferred thermal structure is validated with temperature measurements in 15 deep boreholes showing excellent agreement the cold ice occupies 80 90 of the total ice thickness in a 400 m wide flow band along the central flow line quantitative interpretation of ice radar scattering power indicates a decrease of ice water content between pmt and 0 5 k below pmt as predicted by theory and observed in the laboratory the cold ice which emerges at the surface in the lower ablation zone is impermeable to water and is thus devoid of moulins if not crevassed the surface water from melt and rain is routed through deeply incised persistent streams and lakes and cryoconite holes are frequent in stark contrast to the adjacent temperate ice from other tributaries the cold ice thus has a strong control on glacier hydrology but is likely to change due to continued warming

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

geochemical characterization of late pleistocene and holocene tephra layers from the basin of mexico central mexico in order to aid palaeoenvironmental research of late pleistocene and holocene deposits of central mexico tephra layers collected from the sediments of the texcoco and chalco sub basins in the southern part of the basin of mexico are geochemically characterized and used as stratigraphic markers the tephra layers range in composition from basaltic andesites to rhyolites and are calc alkaline the tephras range in age from 34 000 to ca 260014c yr b p new names are used informally to designate correlated tephras the tlahuac tephra is present in chalco at a depth of 18 m in the southeastern part of texcoco at a depth of around 10 m and at the tlapacoya archaeological site where it had been mistakenly described as basaltic this basalt andesite tephra is dated to at least 34 00014c yr b p the tlapacoya 1 tephra is dated to between 15 020 450 and 14 430 190 yr b p and is present in all chalco sections the tlapacoya 2 tephra corresponds to the previously described pomez gruesa con fragmentos de andesita ca 14 400 yr b p and is present in all chalco and texcoco sections the likely source of these three tephras is the volcano popocatepetl tephra ii at chalco dates to 12 520 135 yr b p and correlates with the upper toluca pumice from nevado de toluca volcano these represent the first geochemical glass shard analysis of tephras from the basin of mexico and so further research is necessary before a reliable tephrochronology can be established