a record of post glacial moraine deposition and tephra stratigraphy from otokomi lake rose basin glacier national park montana the sedimentary record of otokomi lake glacier national park montana was studied to determine the age of an adjacent crowfoot moraine the presence of mt st helens jy ash near the bottom of the longest percussion core limits drainage basin deglaciation to before 11 400 14c years before present bp although 14 100 bp is the estimated basal age of the core correlative shifts in loss on ignition coarse 1 mm grain size magnetic susceptibility and x ray gray scale data at a depth of 185 cm are interpreted to be related to a sedimentary change in otokomi lake brought about by the deposition of the adjacent crowfoot moraine the estimated age of the moraine is 10 590 bp which is within the younger dryas interval this information supports the hypothesis that crowfoot moraines represent a regional western north american response to younger dryas cooling

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

radiocarbon dating peatland development key steps in reconstructing past climate in the central appalachian mountains abstract canaan valley in west virginia contains a greater area of peatlands than any other locality in the mid atlantic highlands extensive fieldwork focused on peat stratigraphy combined with high resolution radiocarbon dating was used to evaluate five peatlands within canaan valley national wildlife refuge cvnwr one hundred soil cores were profiled and described 30 with laboratory analysis including 52 radiocarbon dates calibrated basal peat dates from the five peatlands indicate the onset of peat genesis ranged from 18 600 to 15 200 cal yr bp basal peat dates on the two oldest cores are 1800 to 2200 years older than published dates on peat initiation in any other appalachian mountain peatlands peat accumulation rates varied from 0 02 mm yr to 1 34 mm yr with a mean of 0 14 mm yr results of age depth profiles for six well dated cores consistently exhibit rapid accumulation during the late pleistocene heinrich stadial 1 bolling allerod interstadial and younger dryas cold stadial lower accumulation rates in the early holocene greenlandian age even lower accumulation rates during the mid holocene northgrippian age and the most rapid peat accumulation at the onset of the late holocene early meghalayan age a paucity of shallow peat dating younger than 2000 bp may reflect a reduction in peat accumulation or mixing of surface vegetation into near surface soil horizons soil cores from cvnwr suggest a somewhat different peat development history than the process of terrestrialization previously proposed for other peatland ecosystems in the region

circumpolar distribution of holocene marine fossils in antarctic beaches abstract the composite frequency of radiocarbon ages for holocene marine fossils from beaches around antarctica is significantly different than random variations in the frequency of fossil ages coincide with the timing of holocene climate changes inferred from antarctic ice cores sub antarctic lakes polar and alpine moraines and sea level extant antarctic marine species that occur as fossils in beaches may reflect coastal meltwater impacts associated with ice sheet marginal fluctuations that were circumpolar during the holocene

differences in the 14c age δ13c and δ18o of holocene tufa and speleothem in the dinaric karst we studied holocene speleothems and tufa samples collected in numerous caves and rivers in the dinaric karst of croatia slovenia bosnia and herzegovina as well as serbia and montenegro differences in the formation process of tufa and speleothems are discussed in the context of their isotopic composition 14 c 13 c and 18 o as well as the chemistry of surface water rivers lakes and drip water in caves the physical and chemical parameters monitored in the surface water tufa precipitation and drip water speleothem precipitation show that more stable conditions accompany speleothem rather than tufa formation this is particularly obvious in the water temperature variations 2 22 c in surface water and 7 12 c in drip water and in saturation index variation 3 11 in surface water and 1 6 in drip water the range of 14 c ages recorded by holocene speleothems v12 000 yr is wider by several thousands years than that of holocene tufa samples v6000 yr n 13 c values for tufa samples range from 312x to 36x and for speleothem samples from 312x to 3x reflecting higher soil carbon and or vegetation impact on the process of tufa than on speleothem formation the differences in n 18 o values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water the study shows that speleothems from the dinaric karst can be used as global palaeoclimatic records whereas tufa records changes in the local palaeoenvironment 2003 elsevier science b v all rights reserved

8000 year old wood from the athabasca glacier alberta several wood fragments of pinus sp dated at 8230 80 and 8000 90 years bp and abies sp were recovered from the snout of the athabasca glacier this wood derived from an unknown source up valley indicates that the glacier was less extensive than at present during the hypsithermal and that an area up valley of the present snout was tree covered ca 8000 8300 years bp

tephrochronology of late wisconsin deglaciation and holocene glacier fluctuations near glacier peak north cascade range washington abstract tephra layers near glacier peak in the north cascade range provide limiting dates for four periods of alpine glacier advance field relations suggest that late wisconsin alpine glaciers last advanced prior to the eruption of tephra layers from glacier peak about 11 250 yr b p late wisconsin deglaciation in the central north cascades was complete prior to the glacier peak tephra eruptions glaciers again expanded in the early holocene about 8400 8300 yr b p soil formed in alpine meadows during an episode of mild climate in the middle holocene prior to at least two intervals of glacier expansion an older episode between 5100 and 3400 yr b p and a younger episode within the last 1000 yr

bed ribbing instability explanation testing a numerical model of ribbed moraine formation arising from coupled flow of ice and subglacial sediment 1 ribbed moraines are large up to 16 km long ridges of sediment produced transverse to ice flow direction that formed widely beneath palaeo ice sheets since ice sheet stability is sensitive to conditions operating at the bed an understanding of ribbed moraine genesis will provide critical information on ice sheet dynamics currently there is no consensus on ribbed moraine formation and various competing hypotheses have been presented to account for their genesis only one of these theories has been developed into a physically based numerical model that quantitatively describes ribbed moraine formation this theory known as the bed ribbing instability explanation brie argues that ribbed moraines are produced by a naturally arising instability in the coupled flow of ice and till brie demonstrates that transverse subglacial ridges i e ribbed moraine spontaneously grow under certain parameter combinations and it predicts their wavelength spacing between ridges the model represents a significant advance because it is the first time a theory of subglacial bedform generation has been developed to make quantitative predictions which can be formally tested this paper discusses the types of tests that are currently possible and reports the results from the first testing of brie this analysis centers on the ability of brie to predict the primary characteristics of ribbed moraine which are patterning and wavelength results show that brie successfully predicts the correct ribbed moraine pattern and appropriate wavelengths the tests fail to falsify the model and it is concluded that brie remains a viable explanation of ribbed moraine formation

shear resistance and continuity of subglacial till hydrology rules the field observations of g s boulton stimulated widespread interest in deformable beds shear resistance of till in its critical state is insensitive to strain rate and increases linearly with effective pressure during unsteady deformation pseudo viscous shear resistance can be caused by dilation of consolidated tills and resultant pore pressure decline this effect is probably uncommon however because susceptible tills of low hydraulic diffusivity are also those least likely to consolidate significantly during effective pressure transients stick slip motion at whillans ice stream antarctica indicates that its basal till must weaken during rapid slip and strengthen during longer periods of slower slip recurrence intervals for rapid slip episodes there 6 18 hours indicate that till strength variations if driven by changes in pore pressure either related or unrelated to basal freezing are focused in the uppermost several centimeters of the bed ploughing of grains at the bed surface and associated excess pore pressures in adjacent till can account for rate weakening during rapid slip with pore pressure decay causing strengthening between slip episodes by promoting shallow sluggish subglacial water flow and low effective pressure soft beds may help sustain themselves by slowing their own transport soft bed shear resistance kinematics and continuity are problems rooted in subglacial hydrology

insights into alpine moraine development from cosmogenic 36cl buildup dating abstract we have used cosmogenic 36cl surface exposure dating to determine apparent construction ages of late pleistocene moraines in the sierra nevada the white mountains and the wind river range all in the western united states the inferred glacial chronologies from the various localities all exhibit certain characteristics 1 local records are fragmentary and deposits of some glacial advances are always missing no location has deposits of all glaciations and no glacial advance is recorded at all locations this is due either to unfavorable conditions for glacier development at some times or to obliteration of earlier deposits by later more extensive glaciers 2 most moraines have young apparent exposure ages with only a few older than the last glacial cycle this may be due to young true ages of these deposits erosion of moraine surfaces or obliterative overlap and covering of older deposits by younger ones 3 many deposits that were previously correlated e g based on their stratigraphic positions are not correlative they may represent different stades and sometimes even different glaciations similarly some previously uncorrelated deposits have the same exposure ages and may be correlative 4 clusters of several distinct moraines of nearly the same age are present at most locations these clusters suggest that alpine moraines are formed during short deposition episodes that last between several hundred and several thousand years

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

eemian interglacial reconstructed from a greenland folded ice core efforts to extract a greenland ice core with a complete record of the eemian interglacial 130 000 to 115 000 years ago have until now been unsuccessful the response of the greenland ice sheet to the warmer than present climate of the eemian has thus remained unclear here we present the new north greenland eemian ice drilling neem ice core and show only a modest ice sheet response to the strong warming in the early eemian we reconstructed the eemian record from folded ice using globally homogeneous parameters known from dated greenland and antarctic ice core records on the basis of water stable isotopes neem surface temperatures after the onset of the eemian 126 000 years ago peaked at 8 4 degrees celsius above the mean of the past millennium followed by a gradual cooling that was probably driven by the decreasing summer insolation between 128 000 and 122 000 years ago the thickness of the northwest greenland ice sheet decreased by 400 250 metres reaching surface elevations 122 000 years ago of 130 300 metres lower than the present extensive surface melt occurred at the neem site during the eemian a phenomenon witnessed when melt layers formed again at neem during the exceptional heat of july 2012 with additional warming surface melt might become more common in the future

ice stream basal conditions from block wise surface data inversion and simple regression models of ice stream flow application to bindschadler ice stream 1 widespread basal conditions controlling ice stream flows are still beyond the scope of direct observation thus knowledge of their magnitudes and variabilities comes from inversion of surface measurements ice velocities surface elevations and thicknesses we present a new approach to implement a widely accepted inverse method on regular 10 10 km blocks smaller than the whole domain to enhance the spatial resolution of calculated basal conditions inverted basal friction coefficients and calculated shear stress have sharp transitions and large variations in small areas overall the obtained basal shear stress is very small in regions of fast flowing ice the results of the inversion along with the surface variables are used to construct two simple regression models of bindschadler ice stream former ice stream d that reproduce 96 of observed velocity variations while highly idealized these regression models are sufficiently informative to be considered as parameterizations for ice stream flow in large scale ice sheet models which lack the spatial and temporal resolution necessary to simulate ice stream dynamics in detail

rapid erosion drumlin formation and changing hydrology beneath an antarctic ice stream what happens beneath a glacier affects the way it flows and the landforms left behind when it retreats direct observations from beneath glaciers are however rare and the subglacial environment remains poorly understood we present new repeat observations from west antarctica that show active processes beneath a modern glacier which can normally only be postulated from the geological record we interpret erosion at a rate of 1 m a 1 beneath a fast flowing ice stream followed by cessation of erosion and the formation of a drumlin from mobilized sediment we also interpret both mobilization and increased compaction of basal sediment with associated hydrological changes within the glacier bed all these changes occurred on time scales of a few years or less this variability suggests that an ice stream can reorganize its bed rapidly and that present models of ice dynamics may not simulate all the relevant subglacial processes

the basal stress distribution of ice stream e antarctica inferred by control methods the irregular spatial distribution and velocity independence of basal friction derived from landsat measured surface velocity suggests that ice stream flow is not controlled by the properties of a deformable basal till alone rigid bedrock substrata may contact the base of the ice stream in small 100 km2 areas where the velocity field displays strong vorticity and where the ice stream surface appears rumpled in landsat images

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

the early holocene milankovitch thermal maximum and humans adverse conditions for the denali complex of eastern beringia abstract calibration of 14c ages has forced the revision of paleoecological relationships with the milankovitch thermal maximum 10 000 9000 cal bp edwards and barker palaeogr palaeoclimatol palaeoecol 109 1994 127 in eastern beringia paleo geographic factors had dramatic consequences for humans many represented by the late pleistocene early holocene 13 000 7000 cal bp denali complex calibration of 71 radiocarbon ages associated with denali occupations indicates that the earliest precede both the milankovitch maximum and the spread of spruce in interior alaska by 2000 yr some denali occupations co occur with weakly developed forest soil horizons that reflect stabilized surfaces later capped by loess denali occupations peaked during the worldwide temperature decline between 8500 and 8000 cal bp the mesoglacial beget geology 11 1983 389 or the younger younger dryas fewer sites date to the milankovitch maximum and suggest an inverse relationship between warmer climate and human population

rapid intraplate strain accumulation in the new madrid seismic zone remeasurement of a triangulation network in the southern part of the new madrid seismic zone with the global positioning system has revealed rapid crustal strain accumulation since the 1950s this area experienced three large moment magnitudes 8 earthquakes in 1811 to 1812 the orientation and sense of shear is consistent with right lateral strike slip motion along a northeast trending fault zone as indicated by current seismicity detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time

two step deglaciation 14c dated high resolution δ18o records from the tropical atlantic ocean abstract eight box cores from the tropical atlantic were studied in detail with regard to foraminiferal oxygen isotopes radiocarbon and globorotalia menardii abundance a standard atlantic oxygen isotope signal was reconstructed for the last 20 000 yr it is quite similar to the west equatorial pacific signal published previously deglaciation is seen to occur in two steps which are separated by a pause onset of deglaciation is after 15 000 yr b p the pause is centered between 11 000 and 12 000 yr b p but may be correlative with the younger dryas 10 500 yr b p if allowance is made for a scale shift due to mixing processes on the sea floor step 2 is centered near 10 000 yr b p and is followed by a brief excursion toward light oxygen values this excursion the m event may correlate with the gulf of mexico meltwater spike

ocean ventilation during the last 12 000 years hypothesis of counterpoint deep water production abstract available radiocarbon data on selected planktonic foraminifera species suggest that differential dissolution reduces the 14 c c ratio in planktonic tests removing 14c rich specimens from assemblages of surface dwelling species the effect is analogous to that observed for stable isotope composition in planktonic foraminifera other disturbing factors apparently affect benthic radiocarbon data as well thus radiocarbon stratigraphies are difficult to interpret in terms of history of deep water ages that is deep ocean mixing the best data at hand south china sea after corrections for differential dissolution and benthic vital deviations suggest a high variability of deep water mass ages in the late glacial period which is explained in terms of vertical motion of deep water mass boundaries across the recording sites the fluctuations are ascribed to sporadic increases in deep water production in the north pacific during cold periods and to the presence of a glacial bottom water mass which resisted mixing during deglaciation

aseismic fault slip and block deformation in north china in north china the tectonic fault block system enables us to use the discontinuous deformation analysis dda method to simulate the long term cross fault survey and other geodetic data related to aseismic tectonic deformation by the simulation we have found that 1 slips on faults with different orientation are generally in agreement with the ene wsw tectonic stress field but the slip pattern of faulting can vary from nearly orthogonal to pure shear along the strike of the faults this pattern cannot be explained by simple geometric relation between the strike of the fault and the direction of the tectonic shortening this phenomenon has been observed at many sites of cross fault geodetic surveys and might be caused by the interactions between different blocks and faults 2 according to the dda model if the average aseismic slip rate along major active faults is at the order of several tenths of millimeter per year as observed by the cross fault geodetic surveys the typical strain rate inside a block is at the order of 10 8 year 1 or less so that the rate of 10 6 year 1 as reported by observations in smaller areas cannot be the representative deformation rate in this region 3 between the slips caused by regional compression and block rotation there is a possibility that the sense of slip caused by rigid body rotation in two adjacent blocks is opposite to the slip caused by the tectonic compression but the magnitude of slip resulting from the tectonic compression is much larger than that due to the block rotation thus in general the slip pattern on faults as a whole agrees with the sense of tectonic compression in this region that is to say the slip caused by regional compression dominates the entire slip budget 4 based on 3 some observed slips in contradiction to ene tectonic stress field may be caused by more localized sources and have no tectonic significance

implications for deglaciation chronology from new ams age determinations in central west greenland abstract new evidence has been obtained for the age of the umivit keglen and orkendalen moraine systems close to the present ice sheet margin in central west greenland the umivit keglen moraine system is dated at 7500 to 6500 14 c yr b p which is older than the previously assumed date of 7300 to 6000 14 c yr b p the orkendalen system is now dated at 6200 to 5600 14 c yr b p against earlier estimates of 300 to 700 14 c yr b p the new age is based on ams radiocarbon dated organic material within depressions between morainic ridges belonging to the orkendalen system a major implication of the new age is that ice margin positions prevailed for about 6000 years behind the present ice sheet margin the retreat behind the present margin could be substantial and in the light of deglaciation rates prior to the orkendalen phase may be ca 10 s of kilometers rather than kilometers circumstantial evidence is found for the retreat of the ice sheet margin behind its present position during the holocene climatic optimum the results placed into a time frame of deglaciation since the last glacial maximum enable comparison with greenland ice sheet models and ice core records

quaternary forest and climate history of hokkaido japan from marine sediments abstract pollen data from quaternary marine sediments deposited in central hokkaido northern japan provide insight into northeast asian vegetation and climatic changes over the last few million years during the early pleistocene coniferous forest dominated by picea and cryptomeria japonica and taiga composed of larix and picea developed under cool wet and cold dry climates respectively strong climatic contrasts are inferred from late pleistocene interglacial and glacial pollen assemblages which precede the last glacial cycle in the former cool temperate broad leaf forest mainly composed of fagus reflects a warmer and wetter climate than now in the latter taiga similar to that now found in northern sakhalin apparently flourished in hokkaido the composition of pollen assemblages correlated with oxygen isotope stage 5 changed from cool temperate forest of quercus ulmus and juglans substage 5e to picea larix taiga substage 5d cool temperate forest of quercus and ulmus substage 5c and picea abies forest substage 5b compared with present conditions climate during stage 5 in northern japan apparently fluctuated from warmer wetter to colder drier taiga composed of picea pinus and larix indicating colder dry conditions during stage 4 was replaced by picea abies forest and picea larix taiga in stage 3 suggesting relatively cool and cold dry environments taiga and mixed forest with taiga and cool temperate components characterize stage 2 holocene forests with juglans betula and quercus juglans were succeeded by picea and abies during the early holocene warm interval 7000 bp subsequently quercus ulmus and abies alnus assemblages reflect climatic deterioration pan mixed forest has been developed in hokkaido since 2000 bp

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

imaging the active faults with ambient noise passive seismics and its application to characterize the huangzhuang gaoliying fault in beijing area northern china abstract most serious geotechnical problems related to rock engineering are generated by the existence of faults detection of fault especially active faults is the first step to conduct any further in depth studies in faulted rock mass or rock blocks in this paper we investigated the plausibility to image fault zones by passive seismic surveys using recorded ambient noise the test site is in the north suburb of beijing northern china along the south bank of the northwest southeast running wenyuhe river where the nne striking huangzhuang gaoliying fault hgf active in the holocene is crossing in general the results are in good agreement with previous studies using active source seismics conducted in this area along the hgf and existing borehole drillings in the vicinity undoubtedly active source seismic reflection technique is the best technique to image fault in depth with high resolution the drawback is its high cost and the necessity of using explosives a practice usually prohibited in urban settings in contrast passive seismic surveys take the advantage of the ever existing ambient noise source and provide a low cost technique and fast deployment that can locate the fault effectively though the imaging resolution is lower compared to those obtained by active source seismic surveys our passive seismic experiment at the wenyuhe river site demonstrated that this approach is effective especially for those faults with significant normal faulting component and the stratigraphy is significantly different on the two sides crossing the fault line

tectonic stress field of china inferred from a large number of small earthquakes mean principal tress axes were inferred for china using 9621 p wave first motion polarity readings from 5054 small earthquakes 1 ml 5 the area studied was divided into 76 subregions the mean p compressive b intermediate and t relatively tensional axes corresponding to composite focal mechanism solutions of multiple earthquakes for each subregion were determined by a grid test to all possible orientations of the p b and t axes with a step of 5 or 10 in order to get a relatively homogeneous sampling in space we have avoided using the readings from spatially and temporally clustered earthquakes we have rechecked most of the polarity readings by inspection of original seismograms the focal mechanism solutions of large m 6 individual earthquakes are also presented for comparison the results indicate the existence of an overall radial pattern of the present day maximum horizontal stress orientations throughout the continental area of china this pattern is thought to be closely related to indentor models of continental collision between the indian ocean and the eurasian plate

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

radiocarbon dated evidence of worldwide early holocene climate change radiocarbon dated glacial deposits from several different areas of the world indicate that alpine glaciers and ice caps in parts of both the northern and southern hemispheres expanded in response to climate change in early holocene time these data suggest that a worldwide episode of cooler climate similar in scope to the more recent neoglaciation occurred ca 8 500 7 500 yr b p

on the time scale of deglaciation atlantic deep sea sediments and gulf of mexico deglaciation as seen in the 18o record of deep sea sediments starts about 14 000 yrs ago measured bulk 14c ages are too old by 1000 2000 yrs in the central atlantic compared with ages derived from climate correlation this conclusion rests on the observation that deglaciation occurs in two major steps separated by a pause and on the hypothesis that this pause is correlative to the younger dryas cold period the gulf of mexico record is readily correlated with the deep sea record if it is assumed that the appearance of globorotalia menardii is retarded with respect to the tropical atlantic by about 2000 yrs the major meltwater spike then dates near 9000 yrs ago rather than at 13 500 yrs b p as assumed by kennett and shackleton 1975 or 11 500 yrs b p as in emiliani et al 1975

holocene glacier fluctuations in the canadian cordillera alberta and british columbia abstract although the record of holocene glacier fluctuations in british columbia and alberta is still very fragmentary much recent progress has been made in their study dating of end moraines has been supplemented by studies of lateral moraine stratigraphy and dating of glacially overridden organic matter upstream of end moraines dates from sites close to contemporary glaciers indicate that ice had retreated to about its present limits before 10 ka bp prior to deposition of mazama tephra a minor pre hypsithermal readvance the crowfoot advance left deposits in the rockies and the interior of british columbia the earliest known neoglacial advances occurred 5 6 ka bp in the coast mountains and shortly after 4 ka bp in the rockies an advance culminating ca 4 3 ka bp has been reported from bugaboo glacier while evidence of another advance culminating in the period ca 2 5 1 8 ka bp the tiedemann advance is reported from more than one site following a recession the little ice age expansion the cavell advance began shortly after 900 bp this advance culminated in most cases in the 18th or 19th centuries the crowfoot tiedemann and little ice age advances were apparently of roughly the same magnitude the latter was most extensive in most cases but at several sites crowfoot moraines lie slightly farther downvalley than little ice age moraines during the present century ice fronts have generally retreated particularly rapidly in the period 1920 1950 a d although rates of retreat have decreased in the last three decades and some glaciers have readvanced slightly

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

seismic and radar observations of subglacial bed forms beneath the onset zone of rutford ice stream antarctica we present seismic and radar data from the onset region of rutford ice stream west antarctica which show the form and internal structure of a variety of bed forms beneath an active ice stream the ice flow in the area of our survey accelerates from 72 to 200 m a 1 the ice is 2200 3200 m thick and the bed of the ice stream lies up to 2000m below present sea level we have imaged the internal structure of the bed forms with seismic reflection techniques and also observed radar reflections from below the bed in some circumstances we observed a transverse moraine 2 km wide and 1 5 km long beneath the slower flowing part of the ice stream which we interpret to be composed of unconsolidated sediment undergoing active deformation near the ice sediment interface we observed drumlins of classical form with elongation ratios of between 1 1 5 and 1 4 0 where the surface flow speed exceeded 95 m a 1 the conformity of the internal structure of the bed forms with the ice base suggests that the bed forms are active depositional features in congruence with the observation of a contemporary drumlin forming episode in the distal part of the same ice stream these observations provide the first direct evidence of the association between ice stream flow speed and bed form shape

basal hydraulic system of a west antarctic ice stream constraints from borehole observations pressure and tracer measurements in boreholes drilled to the bottom of ice stream b west antarctica are used to obtain information about the basal water conduit system in which high water pressures are developed these high pressures presumably make possible the rapid movement of the ice stream pressure in the system is indicated by the borehole water level once connection to the conduit system is made on initial connection here also called breakthrough to the basal water system the water level drops in a few minutes to an initial depth in the range 96 117 m below the surface these water levels are near but mostly somewhat deeper than the flotation level of about 100m depth water level at which basal water pressure and ice overburden pressure are equal which is calculated from depth density profiles and is measured in one borehole the conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed the thickness of the gap has to be about 2 mm to account for the water level drop on breakthrough and about 4 mm to fit the results of a salt tracer experiment indicating downstream transport at a speed of 7 5 mm s 1 the above gap conduit model is however ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole and also by the large hole to hole variation in measured basal pressure which if present in a gap conduit system with 2 or 4 mm would result in unacceptably large local water fluxes an alternative model that avoids the e objections called the gap opening model involves opening a gap as injection proceeds starting with a thin film the injection of water under pressure lifts the ice mass a round the borehole creating a gap 3 or 4 mm wide at the ice bed interface evaluated quantitatively the gap opening model accounts for the volume of water that the basal watery system accepts on breakthrough which obviates the gap conduit model in order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits of which the most promising type is the canal conduit proposed theoretically by walder and fowler 1994 flat low conduits incised into the till 0 1 m deep and perhaps 1 m wide with a flat ice roof the basal water pressure data suggest that the canals are spaced 50 300 m apart much closer than r tunnel would be the deepest observed water level 117 m i the most likely to reflect the actual water pressure in the canals corresponding to a basal effective pressure of 1 6 bar in this interpretation the shallower water levels are affected by loss of hydraulic head in the narrow passageway s that connect along the bed from borehole to canal s once a borehole has frozen up and any passageways connecting with canals have become closed a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till given enough time for pressure equilibration this pressure varies considerably with time over the equivalent water level range from 100 to 113 m basal pressure sensors 500 m apart report uncorrelated variations whereas sensors in boreholes 25 m apart report mostly but not entirely well correlated variations of unknown origin in part of the record remarkable anticorrelated variations are interspersed with positively correlated one and there are rare abrupt excursions to extreme water levels as deep as 125m and as shallow as 74 m a diurnal pressure fluctuation intermittently observed may possibly be caused by the ocean tide in the ross sea the lack of any observed variation in ice stream motion when large percentagewise variations in basal effective pressure were occurring according to our data suggests that the observed pressure variations are sufficiently local and so randomly variable from place to place that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed

holocene glacier fluctuations in the american cordillera abstract in many areas of the american rocky mountains colorado wyoming utah idaho montana cascade range washington oregon and the sierra nevada california radiocarbon ages suggest that ice receded to near present limits before 10 ka bp a pre altithermal readvance or stillstand left moraines ca 1 3 km beyond and ca 50 300 m below present glacier margins at one locality on glacier peak in washington these deposits are perhaps dated to the early holocene but in general these deposits are probably at least 10 ka old glacial advances during the altithermal ca 8 to 5 ka bp elsewhere are rare radiocarbon evidence for altithermal glacial advances in the colorado front range is questionable the earliest radiocarbon dated neoglacial advances occurred about 5 ka bp in the washington cascades moraines and related deposits believed to be of early neoglacial age i e 5 to 3 ka bp elsewhere are poorly dated for example moraines believed to date to the early neoglacial in colorado triple lakes and wyoming temple lake are actually late pleistocene age based on radiocarbon ages derived from lake sediments at the type localities although relative age data i e lichens rock weathering soils from many areas suggest a three fold neoglacial sequence little supporting radiocarbon evidence is available however tephrochronology distinguishes three neoglacial advances near mount rainier in washington in most mountain ranges of the western united states fresh unweathered sharp crested moraines usually adjacent to present ice margins or near headwalls in empty cirques date to the little ice age of the last several centuries however detailed photographic or other historical records of glacial fluctuations during the last century are rare and detailed mass balance studies rarer still whether or not pre little ice age glacial fluctuations in the american cordillera are synchronous must await better radiometric dating of local moraine sequences

identification and control of subglacial water networks under dome a antarctica 1 subglacial water in continental antarctica forms by melting of basal ice due to geothermal or frictional heating subglacial networks transport the water from melting areas and can facilitate sliding by the ice sheet over its bed subglacial water flow is driven mainly by gradients in overburden pressure and bed elevation we identify small median 850 m water bodies within the gamburtsev subglacial mountains in east antarctica organized into long 20 103 km coherent drainage networks using a dense 5 km grid of airborne radar data the individual water bodies are smaller on average than the water bodies contained in existing inventories of antarctic subglacial water and most are smaller than the mean ice thickness of 2 5 km reflecting a focusing of basal water by rugged topography the water system in the gamburtsev subglacial mountains reoccupies a system of alpine overdeepenings created by valley glaciers in the early growth phase of the east antarctic ice sheet the networks follow valley floors either uphill or downhill depending on the gradient of the ice sheet surface in cases where the networks follow valley floors uphill they terminate in or near plumes of freeze on ice indicating source to sink transport within the basal hydrologic system because the ice surface determines drainage direction within the bed constrained network the system is bed routed but surface directed along flow variability in the structure of the freeze on plumes suggests variability in the networks on long 10s of ka timescales possibly indicating changes in the basal thermal state

morpho sedimentary characteristics and holocene evolution of the emergent part of the ombrone river delta southern tuscany abstract the holocene evolution of the ombrone river delta has been investigated using morphological and sedimentological evidence the delta had a lagoon like prehistoric evolution while seawards the growth occurred mainly in historical times the data obtained together with the available historical and archeological documentation enable a quantitative evaluation of the volume of the emerged part of the delta to be made moreover for the apical area it has been possible to calculate the annual average increase in the volume of deposition during etruscan and roman times as well as during the middle ages and since the renaissance up to now it has been possible to estimate the periods during which wind exerted a more important role in shaping the delta morphology the volume of sediments deposited during the last 6000 years has been estimated at 1766 10 6 m 3 a combination of climatic conditions littoral dynamics and human action appears to have driven the dynamics of the delta growth which however was not continuous but active especially during the last 3000 years during this period about the 80 of the whole delta volume seems to have deposited high rates of sedimentation occurred between the 16th and the 19th centuries a cold and moist period coinciding with the little ice age when the delta took the typical shape of microtidal wave dominated deltas

similarity of organized patterns in driving and basal stresses of antarctic and greenland ice sheets beneath extensive areas of basal sliding the rate of ice transport from the interior of ice sheets to their margins and hence the rate with which it contributes to sea level is determined by the balance of driving stress basal resistance and ice internal deformation using recent high resolution observations of the antarctic and greenland ice sheets we compute driving stress and ice deformation velocities inferring basal traction by inverse techniques the results reveal broad scale organization in 5 20 km band like patterns in both the driving and basal shear stresses located in zones with substantial basal sliding both ice sheets experience basal sliding over areas substantially larger than previously recognized the likely cause of the spatial patterns is the development of a band like structure in the basal shear stress distribution that is the results of pattern forming instabilities related to subglacial water the similarity of patterns on the greenland and antarctic ice sheets suggests that the flow of ice sheets is controlled by the same fundamental processes operating at their base which control ice sheet sliding and are highly variable on relatively short spatial and temporal scales with poor predictability this has far reaching implications for understanding of the current and projection of the future ice sheets evolution

transmission of basal variability to a glacier surface 1 transmission of basal variability to a glacier surface is investigated using analytical models for a linearly viscous medium the three dimensional transient response of the surface to both bedrock undulations and spatial variations in basal slipperiness for perturbations of arbitrary wavelengths is determined using perturbation methods both information transfer toward the surface and lateral transmission of horizontal stresses are strongly affected by the slip ratio that is the ratio of basal sliding to deformational velocity for any mean bedrock slope and above a minimum value of slip ratio the amplitude transfer of bedrock undulations toward the surface has a local maximum at undulation span corresponding to about 3 8 times the mean ice thickness the transmission of basal variability to a glacier surface increases quite significantly with increasing slip ratio this explains why the surfaces of fast flowing ice streams are more undulating than the slower moving bordering areas at slip ratios higher than about 100 the flow of glaciers and ice sheets becomes nonlocal in the sense that surface velocities and buildup and propagation of surface undulations cannot be calculated accurately on the basis of local thickness and slope using linearized long wave theories at these slip ratios instead of the more accurate arbitrary wavelength theory gives estimates of decay times that are an order of magnitude too small and phase velocities several times too large the problem of the propagation and decay of small amplitude surface undulations on glaciers in three dimensions is solved small amplitude surface waves on glaciers are strongly diffusive and dispersive redistribution of mass on ice sheets and glaciers is a diffusion process and it is misleading albeit not mathematically incorrect to describe the reaction of glaciers to surface perturbations in terms of a wave propagation

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

holocene paleoclimatic reconstruction based on mud deposits on the inner shelf of the east china sea abstract we present a paleoclimatic reconstruction of the mid holocene by geochemical analysis of a sediment core mz01 retrieved from the mud area of the inner continental shelf of the east china sea ecs our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes relatively higher ratios of cia ba sr and a lower ratio of cao mgo coincide with major regional warm and humid climate episodes and vice versa therefore these geochemical indicators are useful in reconstructing the paleoclimate in eastern china using the geochemical records of core mz01 which are well constrained by ams 14c dating we found that from 8300 yr bp to 4200 yr bp the regional climate was moderately warm and humid and from 4200 yr bp to 2300 yr bp the climate was cool and dry with large fluctuations between cool dry 3700 yr bp 2850 yr bp and 2400 yr bp and warm wet 3250 yr bp and 2650 yr bp since 2300 yr bp our records indicate that the climate has gradually become warmer although a cold event centered at around 250 yr bp the little ice age lia interrupted this warming trend we also found significant 238 yr cycles in our cia records that imply a possible solar influence on the regional climate changes since the mid holocene

the influence and chronological uncertainties of the 8 2 ka cooling event on continental climate records in china a compilation of early holocene terrestrial records from lacustrine sediments ice cores peat bog palaeosols stalagmites and flood sediments from china indicates that the early holocene climate was unstable and characterized by at least one centennial scale 500 200 years cooling event between 9 0 and 7 6 ka bp the cold period recorded in different settings has been previously linked to the 8 2 ka event suggested by 18o ice from greenland ice cores but the differences in time duration and regional climate conditions have been attributed to monsoon systems inadequate age control and sampling resolution and complex topography in china however our compilation indicates that it is premature to attribute the cold periods recorded at different locations in china simply to the 8 2 ka event let alone to attribute the cause of those anomalies to a freshening of the north atlantic ocean circulation whether there was one synchronous event or not in china where the climate is mainly affected by the mons

basal perturbations under ice streams form drag and surface expression classical sliding theories consider ice sliding over obstacles which are much shorter than the thickness of overlying ice here we present a theory which considers form drag generated under ice streams by large obstacles such as subglacial bedforms which may have lengths comparable to ice thickness we also investigate how perturbations at the surface of an ice stream can be generated by such bedforms and develop a mathematical framework for separating the effects of such local kilometre scale variations in ice flow from the bulk flow of the ice stream

the stability of a viscous till sheet coupled with ice flow considered at wavelengths less than the ice thickness a turbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer ice is modelled as a linearly viscous fluid while the till viscosity has power law dependence on stress and effective pressure a linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till perturbation amplitude can grow this shect flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming bed features this is of great significance for large scale ice shect modelling

holocene and latest pleistocene glacial chronology glacier national park montana moraines of two different age groups have been identified fronting the present day glaciers and snowfields in glacier national park montana the subdued vegetated moraines of the older group have been found at 25 sites mainly in the central part of the lewis range these older moraines are in places overlain by the mazama ash although the exact age of the moraines has not been determined by radiocarbon dating vegetative evidence and correlation with other pre altithermal age moraines in the rocky mountains suggest that these older moraines date from 10 000 bp or earlier whether these moraines are the product of a separate advance after the end of the wisconsin glaciation or are simply the product of the last advance or stillstand of wisconsin glaciers before final deglaciation is not known moraines of the younger group consisting of fresh bouldery rubble are common throughout glacier park tree ring analyses indicate that some of these younger moraines were deposited by advances that culminated du

late quaternary snowline reconstructions for the southern and central sierra nevada california and a reassessment of the recess peak glaciation abstract in the sierra nevada the recess peak glaciation has been previously defined on the basis of deposits exhibiting relative age characteristics intermediate between those of the little ice age deposits and those of early holocene or older moraines in the absence of reliable chronological control the recess peak deposits were assigned an early neoglacial age although numerous moraines in the central and southern sierra have been attributed to this interval regional snowline gradients reconstructed from these deposits lack internal consistency and appear to represent several distinctly different episodes of glacier advance as a basis for comparison with the recess peak data modern and late pleistocene regional snowlines were reconstructed using accumulation area ratios and cirque floor altitudes these reconstructions display regionally consistent gradients rising gradually southward and more steeply eastward based on these data the full glacial late pleistocene snowline depression is estimated to have been 800 m estimates of recess peak snowline depression vary widely ranging from 140 to 500 m and a reconstructed regional gradient rises northward in opposition to the late pleistocene and modern snowlines limited radiocarbon dating and the irregular pattern derived from the recess peak snowline data suggest that even in the type area these deposits resulted from both pre and post hypsithermal glacier advances

latest pleistocene and early holocene fluctuations of glaciers in the canadian and northern american rockies in the canadian and northern american rockies small scale fluctuations of glaciers during and after late wisconsinan deglaciation have been identified using stratigraphy of superimposed glacial deposits geomorphology and records of glacial advance in lake and peat sediments several authors have proposed that valley glacier readvances of relatively modest scale followed the late wisconsinan maximum evidence for some of these is difficult to evaluate from the literature and no deposits recording such readvances have been numerically dated several minimum limiting radiocarbon dates for deglaciation suggest ice had retreated to within a few tens of km of present limits by ca 12 ka bp and to very near present limits by ca 11 ka bp one or more minor glacial advances or stillstands during recession evidently occurred in valley heads prior to 11 ka bp part of the evidence consists of moraines a few km downvalley from subsequently emplaced little ice age and crowfoot moraines the piper lake moraine in the mission mountains of montana is overlain by glacier peak g tephra and thus has a minimum age of 11 200 14c years bp the crowfoot advance a minor advance of about the same magnitude as little ice age advances occurred between ca 11 300 and 10 000 14c years bp and is thought to be related to the younger dryas climatic reversal crowfoot moraines have been found from jasper national park on the north to the mission mountains on the south crowfoot elas were an average of 40 m lower than modern elas around the canada u s border there have been past proposals of significant early holocene glacial advances in the rockies i e after crowfoot time but before the lia but recent evidence indicates that glaciers then were less extensive than at present

subglacial sediments as a control on the onset and location of two siple coast ice streams west antarctica laterally continuous subglacial sediments are a necessary component for ice streaming in the modern onset regions of the ice streams draining the siple coast of west antarctica on the basis of new seismic data combined with previous results we present geophysical results from seismic reflection and refraction experiments in the upper reaches of ice streams c and d that highlight continuous sedimentary basins within and upstream of the current onset regions of both ice streams with streaming ice overlying these sedimentary packages the subglacial environment changes from no sediment to discontinuous sediment to continuous sediment cover along a longitudinal profile from the ice sheet to tributary c1b along this same profile we observe a speedup of ice flow and then full development of the ice stream tributary ice stream d flows above a thick sedimentary package with an uppermost low seismic velocity zone indicative of soft till and the upglacier and lateral extensions of ice stream d are tightly constrained by the extent of continuous sediments the inland termination of these sediments suggests that future migration of high velocity low shear stress ice flow in these regions appears unlikely

a ploughing model for the origin of weak tills beneath ice streams a qualitative treatment abstract glaciological studies of west antarctic ice streams have shown that weak sub ice stream tills provide the basal lubrication that makes fast ice streaming possible under low driving stresses given the significant current interest in time dependent ice stream behavior there is a clear need for a conceptual model of weak sub ice stream tills that treats in a simple but physically correct way the coupling between evolution of till properties and ice stream dynamics as a possible alternative to the previous viscous bed model we propose a ploughing model that is consistent with the experimentally determined coulomb plastic rheology of sub ice stream till in the ploughing model the till is a several meters thick layer of sedimentary material that is disturbed and transported by ploughing that occurs during sliding of a bumpy ice base the thickness of the till layer is determined in the ploughing model by the amplitude of the largest roughness elements ice keels there is no direct proof for the existence of ice bumps and ice keels beneath the modern west antarctic ice streams but bedforms e g megalineations and bundle structures left behind by pleistocene ice streams strongly support our assumption that an ice stream base is irregular generation of new till material occurs when ice keels protrude through the existing till layer and erode the top of the sub till preglacial sediments based on a single tethered stake measurement of engelhardt and kamb j glaciol 44 1998 223 made at the upb camp ice stream b west antarctica fig 1 we estimate that the till flux due to sliding with ploughing is there 3 yr 1 per meter width to balance the estimated till flux in the upb area substrata erosion by ice keels would have to take place at a high but not unreasonable non dimensional rate of 4 assuming 1 contact area in the case of the west antarctic ice streams erosion of sub till materials by ice keels may be particularly fast and unimpeded because these ice streams are overriding unlithified preglacial tertiary sediments the most significant implication of the proposed ploughing model is that it permits treating basal resistance to ice motion as being velocity independent plastic till rheology while allowing subglacial transport of till as in the viscous bed model models of ice streams with a plastic bed exhibit a greater potential for unstable behavior than models of ice streams with viscous beds

latest pleistocene and holocene glacier fluctuations on mount baker washington abstract glaciers on stratovolcanoes of the pacific northwest of north america offer opportunities for dating late pleistocene and holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields we capitalize on this opportunity by examining the holocene glacial record at mount baker an active stratovolcano in northwest washington earlier workers concluded that glaciers on mount baker during the early holocene were more extensive than during the little ice age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes we show that the main argument for an early holocene glacier advance on mount baker namely the absence of ca 10 000 year old tephra on part of the south flank of the mountain is incorrect moreover a lake sediment core indicates that a small cirque moraine previously thought be of early holocene age is also likely older than the tephra and consequently of late pleistocene age lateral and end moraines and wood mats ca 2 km downvalley of the present snout of deming glacier indicate that an advance during the younger dryas interval was little more extensive than the climactic little ice age advance tephra and wood between tills in the left lateral moraine of easton glacier suggest that ice on mount baker was restricted in the early holocene and that neoglaciation began ca 6 ka a series of progressively more extensive neoglacial advances dated to about 2 2 1 6 0 9 and 0 4 ka are recorded by stacked tills in the right lateral moraine of deming glacier intervening retreats were long enough to allow establishment of forests on the moraine wood mats in moraines of coleman and easton glaciers indicate that little ice age expansion began before 0 7 ka and was followed by retreat and a readvance ca 0 5 ka tree ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid 1800s the similarity between glacier fluctuations at mount baker and those elsewhere in the cascades and in british columbia suggests a coherent history of holocene climate change over a broad area of the western cordillera we found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere

melting and freezing beneath the ross ice streams antarctica we have estimated temperature gradients and melt rates at the bottom of the ice streams in west antarctica measured velocities were used to include the effects of horizontal advection and strain heating in the temperature model and to determine shear heating at the bed our modeled temperatures agree well with measured temperatures from boreholes in regions of steady flow we find that ice stream tributaries and the inland ice account for about 87 of the total melt generated beneath the ross ice streams and their catchments our estimates indicate that the ice plains of whillans ice stream and ice stream c even when active have large areas subject to basal freezing confirming earlier estimates that import of water from upstream is necessary to sustain motion the relatively low melt rates on whillans ice stream are consistent with observations of deceleration over the last few decades and suggest a shutdown may take place in the future possibly within this century while there are pockets of basal freezing beneath ice streams d and e there are larger areas of basal melt that produce enough melt to more than offset the freezing which is consistent with inferences of relatively steady flow for these ice streams over the last millennium

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

holocene glacier variations in new zealand a review abstract in the central southern alps of new zealand ice surface lowering has exposed extensive sections of lateral moraines allowing investigation of moraine stratigraphy and genesis the presence of multiple superposed palaeosurfaces within moraine sequences allows recognition of any disturbances displacements or contamination of till layers and interbedded organic material radiocarbon dating of buried wood and soils allows comparison between the holocene glacial history of the eastern ranges and that of the westland region the periodicity of glacier response has been similar to both areas although the precise timing of events has differed due to local climatic and environmental factors in general glaciers in new zealand expanded about 5000 4500 4200 3700 3500 3000 2700 2200 1800 1700 1500 1100 900 700 600 and 400 100 bp

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

glacial deep water properties in the west equatorial pacific bathyal thermocline near a depth of 2000 m abstract the stable isotope stratigraphy of planulina wullerstorfi in three box cores from ontong java plateau in the western equatorial pacific shows that there existed a bathyal thermocline near the depth of 2000 m during glacial time waters below the boundary were colder by about 1 c those above were about the same as now the deep waters were slightly enriched and the upper waters depleted in nutrients compared with present values the differences in 13 c to the present after correcting for the global change are of the order of 0 1 more positive above 2000 m and 0 1 more negative below corresponding to changes in phosphate of the order of 0 1 mol kg less phosphate above and more below the boundary

glacial landforms of extreme size in the keewatin sector of the laurentide ice sheet assemblages of glacial landforms of a mega scale are here identified in the keewatin sector of the laurentide ice sheet large till belts or ridges apparent only on satellite imagery and lyi

mapping basal melt under the northern greenland ice sheet ice sheets in greenland and antarctica are based on continental rock and are coupled strongly to changes in global sea level their beds may be frozen or thawed but it has not been known how much or where basal melt occurs except in special cases where a borehole has reached the bed or where airborne radar has revealed subglacial lakes and reflective ice stream beds in antarctica we have used a previously published technique to detect subglacial melt water in the general case and have here applied it to radar sounder data collected over northern and central greenland we have found extensive subglacial water along between 13 and 20 of the flight paths this paper provides maps of the measured locations and probable extent of subglacial water

quaternary geology of willow creek and some age constraints on prehistoric faulting lost river range east central idaho new data on the geochronology of upper quaternary units in the willow creek drainage bear on the timing of the last prehistoric surface faulting event along the thousand springs segment of the lost river fault surficial effects of this event were paralleled by the 1983 ms 7 3 borah peak earthquake radiocarbon dated till 8 470 160 b p at doublespring pass can be traced to the geomorphically youngest alluvial surface cut by the fault the alluvial surface is related to deglaciation and thus postdates 8 470 b p the faulting also postdates this time aeolian sheetwash sediments draped over the fault scarp are 14c dated as 530 80 b p providing an upper age bracket for faulting geomorphological analysis of presence absence relations of regionally widespread mt mazama tephra 6 850 14c yr b p suggests that the faulting event may postdate this tephra fall and thus lies in the age range 6 850 to 530 b p based on the amount of pre 1983 offset 2 1 to 2 6 m and a maximum of 6 850 yr between events minimum short term slip rates range from 0 3 to 0 4 m 1 000 yr along this segment

stress redistribution and slow earthquakes abstract earthquakes are usually assumed to result when the gradual stress buildup in a region eventually exceeds some initial local strength there are observations which suggest that a number of mechanisms must have a significant role in stress redistribution in active earthquake regions the stress build up could be non linear in time there is evidence that this is so in the case of some major earthquakes one mechanism that might explain non linear strain buildup is a slow earthquake this is similar to a normal earthquake except that the rupture and slip velocities are very low so that negligible energy is radiated in the normally observed seismic frequency band the slow earthquakes studied here have been recorded by a network of sacks evertson borehole strainmeters installed along the seismically active pacific coast of honshu japan larger slow events may have slow foreshocks and aftershocks in a manner similar to that for normal earthquakes the aftershocks appear to have lower stress drops than the foreshocks the static field changes associated with the izu oshima earthquake m 7 of january 1978 were sufficiently large that they were clearly recorded by the nearest three strainmeters interpretation of the records indicate that this earthquake was in essence a normal quake followed by a slow event of similar moment this interpretation is corroborated by reports of ground vibration and faulting on the izu peninsula

holocene glacier variations of blaisen hardangerjokulen central southern norway abstract a 1 m deep gully section 460 m beyond the maximum little ice age marginal moraines of blaisen hardangerjokulen central southern norway revealed alternations of minerogenic and organic sediments the geographical geological settings of the dated section provides a unique on off signal of holocene glacier fluctuations of blaisen lithostratigraphy sediment characteristics and radiocarbon dates from the study section indicate one period of glacier re advance between the late preboreal deglaciation of the inland ice sheet and 8660 100 yr b p a grey sand layer 56 57 cm below the surface is interpreted to be of fluvial colluvial origin and is radiocarbon dated to about 7700 yr b p at 48 cm below the surface a bluish grey sand silt layer is radiocarbon dated to 7590 12 yr b p 6560 6240 b c and interpreted to be glaciofluvial origin a minor glacier oscillation postdates 1130 70 yr b p 810 990 a d the medieval little ice age glacier advance of blaisen beyond its modern extent occurred after 1040 60 yr b p 960 1030 a d calculations of the modern and little ice age equilibrium line altitudes elas on hardangerjokulen suggest an ela depression of ca 130 m during the little ice age maximum