laurentide cordilleran and montane glaciation in the western peace river grande prairie region alberta and british columbia canada abstract geological investigations over the last decade in the western peace river grande prairie district of northwestern alberta and northeastern british columbia have provided important chronostratigraphic information regarding laurentide cordilleran and montane quaternary glacial events numerous 14 c age determinations as well as stratigraphic and sedimentological analyses of numerous exposures indicate that this area was first glaciated by cordilleran ice sometime before the late wisconsinan during the late wisconsinan ca 22 000 14 000 bp laurentide glacier ice covered much of the area between approximately 15 000 and 10 000 bp montane ice affected only the western part of the peace region there is no evidence for synchroneity of the ice advances and therefore no evidence for ice coalescence in this region the resultant ice free corridor was most likely a laterally fluctuating zone which existed during a several thousand year period in the late pleistocene climatic conditions along the corridor during this period were probably unfavorable for human migration but adequate for some plants and small animals numerous isolated areas along the western foothills of the northern rocky mountains west of the laurentide glaciation limit were never glaciated during the late wisconsinan

distribution of dynamic and static stress changes during 2000 tottori japan earthquake brief interpretation of the earthquake sequences foreshocks mainshock and aftershocks 1 the dynamic and static stress changes during the 2000 tottori earthquake have been recovered from the results of waveform inversion we use the dem to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model the resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions we conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity this suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks the foreshock distribution was confined to a finite localized zone in the central part of the fault suggesting that this zone was bordered by barriers

multiphase flow of the late wisconsinan cordilleran ice sheet in western canada in central british columbia ice flow during the late wisconsinan fraser glaciation ca 25 10 ka occurred in three phases the ice expansion phase occurred during an extended period when glaciers flowed westward to the pacific ocean and east southeastward onto the nechako plateau from ice centers in the skeena hazelton coast and omineca mountains initially glacier flow was confined by topography along major valleys but eventually piedmont and montane glaciers coalesced to form an integrated glacier system the cordilleran ice sheet in the maximum phase a cordilleran ice divide developed over the nechako plateau to 300 km inland from the pacific coast at this time the surface of the ice sheet extended well above 2500 m above sea level and flowed westward over the skeena hazelton and coast mountains onto the continental shelf and eastward across the rocky mountains into alberta in the late glacial phase a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys and restricted accumulation centers to high mountains discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness ice centers probably shifted in response to climate irregular growth in the ice sheet rapid calving ice streaming and drainage of proglacial and subglacial water bodies crosscutting ice flow indicators and preservation of early valley parallel flow features in areas exposed to later cross valley glacier erosion indicate that the ice expansion phase was the most erosive and protracted event

timing of terminal pleistocene deglaciation at high elevations in southern and central british columbia constrained by 10be exposure dating abstract the cordilleran ice sheet cis covered most of british columbia and southern yukon territory at the local last glacial maximum llgm during marine oxygen isotope stage 2 however its subsequent demise is not well understood particularly at high elevations east of its ocean terminating margin we present 10be exposure ages from two high elevation sites in southern and central british columbia that help constrain the time of initial deglaciation at these sites we sampled granodiorite erratics at elevations of 2126 2230 m a s l in the marble range and 1608 1785 m a s l in the telkwa range at the western margin of the interior plateau the erratics at both sites are near ice marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation the locations of the erratics and their relations to meltwater channels ensure that the resulting 10be ages date cis deglaciation and not the retreat of local montane glaciers our sample sites emerged above the surface of the cis as its divide migrated westward from the interior plateau to the axis of the coast mountains two of the four samples from the summit area of the marble range yielded apparent exposure ages of 14 0 0 7 and 15 2 0 8 ka these ages are 1 8 3 0 ka younger than the well established llgm age of ca 17 ka for the puget lobe of the cis in washington state they are 1 7 ka younger than the llgm age for the puget lobe if a snow shielding correction to their uncertainty weighted mean age is applied the other two samples yielded much older apparent exposure ages 20 6 1 4 and 33 0 1 5 ka indicating the presence of inherited isotopes four samples collected from the summit area of the telkwa range in the hazelton mountains yielded well clustered apparent exposure ages of 10 1 0 6 10 2 0 7 10 4 0 5 and 11 5 1 1 ka significant present day snow cover introduces a large uncertainty in the apparent exposure ages from this site a snow shielding correction based on present day snow cover data increases the uncertainty weighted mean exposure age of the telkwa range erratics to 12 4 0 7 ka consistent with deglacial 14c ages from areas near sea level to the west our exposure ages show a thinning of the southern portion of the cis shortly after the llgm and persistence of a remnant mountain ice cap in the central coast mountains into the younger dryas chronozone our data also show that the summit area of the marble range was ice covered during the llgm the presence of an ice body of considerable dimension in north central british columbia until or possibly even after the younger dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the skeena mountains in northwest british columbia and the need for better understanding of the response of the cis to lateglacial climate fluctuations

seismicity precursors to large earthquakes unified in a stress accumulation framework 1 various seismicity patterns before large earthquakes have been reported in the literature they include foreshocks medium term acceleration and short term activation quiescence doughnut patterns and event migration the existence of these precursory patterns is however debated here we develop an approach based on the concept of stress accumulation to unify and categorize all claimed seismic precursors in a same physical framework we first extend the non critical precursory accelerating seismicity theory n c past which already explains most precursors to additionally include short term activation theoretical results are then compared to the time series observed prior to the 2009mw 6 3 l aquila italy earthquake we finally show that different precursory paths are possible before large earthquakes with possible coupling of different patterns or non occurrence of any this is described by a logic tree defined from the combined probabilities of occurrence of the mainshock at a given stress state and of precursory silent slip on the fault in the case of the l aquila earthquake the observed precursory path is coupling of quiescence and accelerating seismic release followed by activation these results provide guidelines for future research on earthquake predictability

determination of elastic wave velocity and relative hypocenter locations using refracted waves ii application to the haicheng china aftershock sequence we located the aftershocks of the 4 february 1975 haicheng china aftershock sequence using an arrival time difference atd simultaneous inversion method for determining the near source in situ velocity and the location of the aftershocks with respect to a master event the aftershocks define a diffuse zone 70 km 25 km trending west northwest perpendicular to the major structural trend of the region the main shock and most of the large aftershocks have strike slip fault plane solutions the preferred fault plane strikes west northwest and the inferred sense of motion is left lateral the entire haicheng earthquake sequence appears to have been the response of an intensely faulted range boundary to a primarily east west crustal compression and or north south extension the calculated upper mantle p wave velocity is 7 6 0 09 km sec and the inferred crustal thickness is between 31 and 32 5 km the low upper mantle velocity and thin crust may be indicative of local lithospheric extension

nunataks and valley glaciers over the mountains and through the ice models of the first peopling of the americas characterize arrival routes either along the coast or through the ice free corridor following the last glacial maximum while the pendulum has currently swung somewhat towards the coastal route archaeological evidence for either entry is lacking in this paper we introduce a third option an icy corridors entry route we argue that the traditionally envisioned corridor is an unnecessary feature for the terrestrial arrival of clovis or clovis predecessors below the ice sheets the recent genomic data is fully compatible with a re envisioned peopling route

waveform analysis of the 1999 hector mine foreshock sequence 1 by inspecting continuous trinet waveform data we find 42 foreshocks in the 20 hour period preceding the 1999 hector mine earthquake a substantial increase from the 18 foreshocks in the catalog we apply waveform cross correlation and the double difference method to locate these events despite low signal to noise ratio data for many of the uncataloged foreshocks correlation based arrival time measurements are sufficient to locate all but three of these events with location uncertainties from 100 m to 2 km we find that the foreshocks fall on a different plane than the initial subevent of the mainshock and that the foreshocks spread out over the plane with time during the sequence as the time of the mainshock approaches

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

the foreshock sequence of the february 4 1975 haicheng earthquake m 7 3 we have examined the locations and radiation patterns of the foreshocks of the february 4 1975 haicheng earthquake m 7 3 using arrival times from six local seismic stations the foreshocks and mainshock were located relative to a master event the foreshocks occurred in a tight cluster that elongated with time before the largest foreshock the activity was located within a small approximately equidimensional volume with a diameter of about 2 km after the largest foreshock the activity spread northwest and southeast forming a 6 km long northwest trending zone first motions and ratios of p to s amplitudes indicate that two different faulting mechanisms occurred during the foreshock sequence the two radiation patterns can tentatively be correlated with different parts of the zone the hypocenter of the mainshock was not located on the same fault as that defined by the foreshocks hypocenters but rather was located 6 km south of and several kilometers shallower than the foreshock cluster we think this large separation between foreshocks and mainshock in a direction perpendicular both to the plane of rupture of the mainshock and to the trend of the foreshocks might be the result of an en echelon step in the fault that slipped during the mainshock an analysis of the change in stress due to slip during the foreshocks shows that the increase in shear stress on the mainshock fault caused by the foreshocks is very small and that direct triggering of the mainshock by the foreshocks is unlikely

laurentide and montane glaciation along the rocky mountain foothills of northeastern british columbia mapping the surficial geology of the trutch map area nts 94g provides new data on the timing of continental and montane glaciations along the foothills of northeastern british columbia striated surfaces on mountain crests were dated to the late wisconsinan substage by cosmogenic dating the striations were produced by eastward flowing ice emanating from the region of the continental divide this ice was thick enough to cross the main ranges and overtop the rocky mountain foothill summits at 2000 m above sea level asl it is argued here that such a flow unhindered by topography could only have been produced by the cordilleran ice sheet and not by local cirque glaciation during this time the cordilleran ice sheet dispersed limestone and schist erratics of western provenance onto the plains beyond the mountain front conversely the laurentide ice sheet did not reach its western limit in the foothills until after cordilleran ice retreated from the area during its maximum the laurentide ice penetra

mapping quaternary paleovalleys and drift thickness using petrophysical logs northeast british columbia fontas map sheet nts 94ithis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers the relatively subdued topography of british columbia s northern interior plains does not reflect the irregular buried bedrock surface many areas have been deeply incised by preglacial rivers tha

reconstructions of mountain glacier profiles northeastern united states ice surface profiles are reconstructed for 37 proposed mountain glacier localities in the northeastern united states including sites in the catskill and adirondack mountains new york the green mountains vermont the white mountains new hampshire and the longfellow mountains and mount katahdin maine the reconstructions determined numerically from the shear stress equation gh sin show estimated ice thickness as a function of valley position and slope in general ice thickness increases from zero at the position of the glacier terminus terminal position is a required input to the model to some equilibrium slab thickness in the upper valley where the slab thickness is inversely proportional to valley slope glacier reconstructions support the empirical evidence for former local glaciation in the catskill and white mountains and in some localities in the adirondack mountains in several proposed glacier locations in the adirondack and green mountains in very shallow basins and in very gently sloping valleys however estimated ice thicknesses exceed the depth of their respective valleys or the elevation of up valley cols suggesting a re evaluation of these localities as sites of local confined ice flow confirmed localities of local glaciation are mostly in valleys with mean gradients greater than about 5 where reconstructed ice thicknesses are less than about 200 m

flow pattern evolution of the laurentide and cordilleran ice sheets across west central alberta canada implications for ice sheet growth retreat and dynamics during the last glacial cycle this paper presents a reconstruction of the geometry dynamics and flow pattern of the laurentide and cordilleran ice sheets along the albertan portion of the eastern canadian rocky mountains during the last glaciation sediment landform associations relating to the evolution of these ice sheets document their initial convergence and mutual deflection across west central alberta the continued advance of laurentide ice locally displaced cordilleran ice westward into the front ranges and deflected trunk ice emerging from the athabasca river valley south eastwards along the foothills these convergent flow patterns remained major features in the regional geometry of both ice sheets throughout the last glacial maximum the onset of deglaciation was characterized by the northward retreat of the laurentide ice sheet which progressively unblocked valleys along the mountain front the configuration of buttress removal initiated the lateglacial expansion and sequential drawdown of the eastern cordilleran ice sheet along fast flowing outlet glaciers subsequent regional retreat of laurentide and cordilleran ice was associated with the development of large proglacial lakes which amplified deglaciation by destabilizing the margins of both ice sheets triggering extensive readvances due to periodic changes in water level associated with the opening and closing of outlets by ice margin fluctuations

coalescence of late wisconsinan cordilleran and laurentide ice sheets east of the rocky mountain foothills in the dawson creek region northeast british columbia canada abstract geomorphic stratigraphic and geochronological evidence from northeast british columbia canada indicates that during the late wisconsinan approximately equivalent to marine oxygen isotope stage mis 2 a major lobe of western sourced ice coalesced with the northeastern sourced laurentide ice sheet lis high resolution digital elevation models reveal a continuous 75 km long field of streamlined landforms that indicate the ice flow direction of a major northeast flowing lobe of the cordilleran ice sheet cis or a montane glacier 200 km wide was deflected to a north northwest trajectory as it coalesced with the retreating lis the streamlined landforms are composed of till containing clasts of eastern provenance that imply that the lis reached its maximum extent before the western sourced ice flow crossed the area since the lis only reached this region in the late wisconsinan the cis montane ice responsible for the streamlined landforms must have occupied the area after the lis withdrew stratigraphy from the murray and pine river valleys supports a late wisconsinan age for the surface landforms and records two glacial events separated by a non glacial interval that was dated to be of middle wisconsinan mis 3 age

landform assemblages produced by the laurentide ice sheet in northeastern british columbia and adjacent northwest territories constraints on glacial lakes and patterns of ice retreatthis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers the laurentide ice sheet reached the canadian cordillera during the last glacial maximum in northeastern british columbia and adjacent northwest territories and all regional drainage to unglaciated areas in the north was dammed by the ice converging ice flow patterns near the mountain front suggest that the laurentide ice sheet likely coalesced with the cordilleran ice sheet during the last glaciation with deglaciation the ice masses separated but earlier ice retreat in the south meant that meltwater pooled between the mountain front and the laurentide margin the level of the flooding was controlled by persistent ice cover on the southern franklin mountains glacial lake liard formed when the laurentide ice sheet retreated east of the southern liard range and at its maximum extent may have impounded water at least as far south as the fort nelson river deglaciation of the plains was marked by local variations in ice flow caused by a thin ice sheet becoming more affected by the topography and formin

quaternary stratigraphy of the prophet river northeastern british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers exposures in the prophet river valley in northeast british columbia provide a unique glimpse into the quaternary history of the northwest canadian boreal plains the region shows evidence of late wisconsinan laurentide glaciation in the form of widespread till containing abundant erratic clasts derived from the canadian shield vertical sections along the prophet river expose non glacial and advance glacial sediments below this till pre late wisconsinan non glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites macrofossils within horizontally laminated organic rich black clay and silt indicate deposition on the floodplain of the paleo prophet river within an oxbow lake the climate during deposition is interpreted to be similar to present supporting a dominantly spruce forest wood obtained from eight sites provided non finite radiocarbon ages and one sample provided an age of 49 300 2000 bp which is also considered non finite glaciolacustrine clays and s

cosmogenic 36cl dating of the foothills erratics train alberta canada the foothills erratics train of alberta was carried into place during coalescence between montane glaciers and the laurentide ice sheet its age has been controversial late wisconsinan and pre wisconsinan ages have been assigned to it cosmogenic 36 cl exposure dating was carried out on erratics over a 130 km segment of the erratics train seven of eight age determinations support emplacement during the late wisconsinan glaciation these ages eliminate the possibility of an ice free corridor during the last glacial maximum they are also consistent with the hypothesis that the laurentide ice sheet was the most extensive of all pleistocene continental ice sheets in western canada

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

reconstructing the confluence zone between laurentide and cordilleran ice sheets along the rocky mountain foothills south west alberta landform mapping near the athabasca valley was fundamental to determining whether the late wisconsinan laurentide and cordilleran ice sheets lis cis coalesced in this paper we examine the detailed landform record using new lidar digital elevation and hillshade models of the area of confluence and eventual desuturing of these ice sheets this work reveals an earlier more extensive cordilleran advance before coalescence with the lis when the ice sheets coalesced the flow pattern was dominated by ice flow along the mountain front with cordilleran ice flowing out of major trunk valleys but laurentide ice flowing into the foothills up smaller valleys this flow pattern implies that when the ice sheets coalesced the cis was already waning or at least was not at its maximum deglaciation was interrupted by several re advances probably related to the destabilizing effect of proglacial lakes along the ice margin

late wisconsinan cordilleran and laurentide glaciation of the peace river valley east of the rocky mountains british columbia in the past researchers have disagreed over the maximum extent of the cordilleran ice sheet in the peace river valley during the late wisconsinan some workers argued that cordilleran ice reached beyond the rocky mountains and briefly coalesced with the laurentide ice sheet on the westernmost interior plains in contrast others asserted that cordilleran ice did not reach beyond the eastern front of the rocky mountains stratigraphic interpretation of three sections within a middle wisconsinan paleovalley and re examination of a previously published regional stratigraphic framework show that western sourced ice likely the cordilleran ice sheet extended east of the mountain front during the late wisconsinan prior to the incursion of the laurentide ice sheet into the area this conclusion has implications for cordilleran ice sheet reconstruction and modelling and provides insight into the interactions between the cordilleran and laurentide ice sheets during the last glaciation

immediate foreshocks time variation of the b value abstract we compare b values in the frequency magnitude law for the foreshocks and long term seismicity foreshocks are considered in two non overlapping time intervals preceding a main shock i last hours ii last days statistical analysis of the regional and global earthquake catalogs shows that in either of these intervals b value drops by a half compared to long term seismicity this extends the previous results by molchan and dmitrieva molchan g dmitrieva o 1990 dynamics of the magnitude frequency relation for foreshocks phys earth planet inter 61 99 112 who have found such a drop a few hours before a mainshock our results concern a statistical regularity not necessarily seen for each individual sequence of foreshocks

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

an assessment of the minimum timing of ice free conditions of the western laurentide ice sheet abstract this study presents an investigation of the minimum timing of retreat of the western laurentide ice sheet which covered parts of canada and the northern united states during the wisconsin glaciation the retreat of the ice sheet is poorly constrained due to low spatial resolution of chronological data that indicate ice free conditions a limitation of radiocarbon and luminescence dating methods is that it is only possible to determine the time when it is certain that ice is absent from a region which may differ substantially from the true date of ice margin retreat the minimum timing of ice free conditions is determined using a model of ice sheet retreat inferred from landforms that formed during the late stages of glaciation and extrapolating the calibrated probability distribution of chronological data in the opposite direction the analysis excludes radiocarbon samples from materials that have been shown to give artificially old ages such as bulk sediments the results of the analysis identify 55 dates that have the most impact on the model the retreat of the western laurentide ice sheet commenced by at least 15 000 cal yr bp while the minimum timing of ice free conditions between the laurentide ice sheet and the cordillera is after 11 000 cal yr bp a lack of data in the keewatin sector prevents the determination of a precise timing of ice free conditions in the last vestiges of the laurentide ice sheet the model provides a guide to where additional samples could improve chronological control on ice margin location

quaternary stratigraphy and glacial history of the peace river valley northeast british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers two cordilleran and three laurentide glacial advances are recorded in quaternary sediments and landforms in the peace river valley northeast british columbia the advances are inferred from fluvial gravels glaciolacustrine sedi ments and tills within nested paleovalleys excavated during three interglaciations and from the distribution of granitoid clasts derived from the canadian shield till of the last late wisconsinan laurentide glaciation occurs at the surface ex cept where it is overlain by postglacial sediments the advance that deposited this till was the most extensive in the study area and the only advance definitively recognized in western alberta south of the study area late wisconsinan cordil leran till has not been found in the study area but cordilleran and laurentide ice may have coalesced briefly during the last glaciation support for this supposition is provided by the inferred deflection of laurentide flutings to the southeast by cordilleran ice the earliest laurentide advance may have been the least extensive of the three laurentide events recog nized in the study area erratics attributed to this advance occur only east of the halfway river beatton river drainage divide

new insights into eruption source parameters of the 1600 ce huaynaputina plinian eruption peru in the central andes large plinian eruptions volcanic explosivity index 5 occur at a relatively high frequency i e average one every 2000 to 4000 years over the past 50 000 years in peru such recurring explosive activity represents a significant challenge for regions typically hosting several million people e g southern peru western bolivia and northern chile with vei 6 the 1600 ce huaynaputina eruption is considered the largest historical eruption in south america we have re examined the first plinian phase of this eruption in order to better assess critical eruption source parameters i e erupted volume plume height mass eruption rate eruption duration the revised bulk volume of the tephra fall deposit associated with the plinian phase is approximately 13 14 km3 almost twice the previous estimate 7 8 km3 within the 1 cm isopach based on methods including power law weibull function and bayesian linear regression tephra was dispersed by strong winds to the wnw as far as 400 km on peruvian territory and then in the pacific ocean seven villages were buried killing 1500 people the revised plume height estimate 32 2 2 5 km is consistent with the early estimations as a result the huaynaputina 1600 ce first eruption phase lies in the upper part of the plinian field close to the ultra plinian transition making this event one of the largest in the past millennium which coincides with results from recent studies on palaeoclimatic impacts

the accumulation of cosmogenic chlorine 36 in rocks a method for surface exposure dating because of the reaction of cosmic rays with elements in minerals chlorine 36 accumulates in rocks exposed at the earth s surface this suggests that the ratio of chlorine 36 to stable chloride can be used as a geochronometer reasonable agreement has been obtained between measurements of chlorine 36 in volcanic rocks of known age and calculations of chlorine 36 production based on rock composition and cosmicray flux the buildup of chlorine 36 should be a useful means for measuring the surface exposure time of young volcanic rocks and geomorphic features in the age range of 10 3 to 10 6 years

advance of alpine glaciers during final retreat of the cordilleran ice sheet in the finlay river area northern british columbia canada abstract sharp crested moraines up to 120 m high and 9 km beyond little ice age glacier limits record a late pleistocene advance of alpine glaciers in the finlay river area in northern british columbia the moraines are regional in extent and record climatic deterioration near the end of the last glaciation several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern cordilleran ice sheet other lateral moraines merge with ice stagnation deposits in trunk valleys these relationships confirm the interaction of advancing alpine glaciers with the regionally decaying cordilleran ice sheet and verify a late glacial age for the moraines sediment cores were collected from eight lakes dammed by the moraines two tephras occur in basal sediments of five lakes demonstrating that the moraines are the same age plant macrofossils from sediment cores provide a minimum limiting age of 10 550 10 250 cal yr bp 9230 50 14c yr bp for abandonment of the moraines the advance that left the moraines may date to the younger dryas period the finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late glacial glacier advances

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

geology of northeast british columbia and northwest alberta diamonds shallow gas gravel and glaciersthis article introduces a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers this special issue reports on some of the results of a multi disciplinary research program conducted in the boreal plains of northwest alberta and northeast british columbia several innovative approaches to conducting geoscientific research in this remote drift covered region are presented including geochemical analysis of bentonites for evaluating kimberlite potential the use of electromagnetic surveys for mapping buried aggregate deposits and paleo topographic mapping techniques to define buried channels results of the program include the discovery of several large aggregate deposits the first kimberlite indicator minerals in northeast british columbia a significant sphalerite dispersal train in northwest alberta the first documented report of kimberlite sourced bentonites and numerous previously unknown interglacial sites together these papers provide a greatly enhanced understanding of the glacial history quaternary stratigraphy and kimberlite geology of northwest alberta and northeast bri

fault geometry and earthquakes in continental interiors abstract although large earthquakes in continental interiors are much less frequent than those along plate boundaries they have been responsible for a disproportionate amount of destruction i present a testable model for strain accumulation and seismicity in the upper crust of continental interiors intersecting faults provide a focus for strain build up resulting in local pockets of high strain accumulation rigid plates typically deform at strain rates 10 10 to 10 9 strain yr 1 but at intersecting fault zones strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr 1 i e the strain rates are comparable with those at plate boundaries the resulting large earthquakes are associated with relatively short return times hundreds of years typically one of the intersecting faults appears to split and to offset the other main fault defined as a fault on which the larger offset occurs forming two parallel strands separated by a jog i also observe a rotation of one leg of the main fault with respect to the other the region of intersection is usually associated with intense fracturing increased microseismicity and uplift

ice streams of the late wisconsin cordilleran ice sheet in western north america abstract the late wisconsin cordilleran ice sheet cis of western north america is thought to have reached its maximum extent 2 5 106 km2 as late at c 14 5 ka most 80 of the ice sheet s bed consists of high mountains but its core zone sited on plateaux of the intermontane belt of british columbia and coterminous parts of the usa shows broad swaths of subglacially streamlined rock and sediment broad scale mapping from new digital imagery data identifies three subglacial bed types 1 hard beds of variably streamlined bedrock 2 drumlinized soft beds of deformation till reworked from antecedent sediment and 3 mixed beds of variably streamlined bedrock protruding through drumlinized sediment drumlins on soft beds appear to be erosional features cut into till and antecedent sediments and identify the catchment areas of paleo ice streams expressed downglacier as flow sets of megascale glacial lineations msgls grooved and cloned drumlins appear to record the transition from drumlins to msgls the location of paleo ice streams reflects topographic funneling of ice from plateau surfaces through outlet valleys and a soft bed that sustained fast flow rock cut msgls are also present locally on the floors of outlet valleys cis disintegrated in

late tertiary to late quaternary record in the mackenzie mountains northwest territories canada stratigraphy paleosols paleomagnetism and chlorine 36 a stratigraphic sequence of unconsolidated sediments ranging in age from late pliocene to late pleistocene is recorded in the canyon ranges of the mackenzie mountains three of the sections katherine creek little bear river and inlin brook expose bedrock and tertiary gravel overlain by colluvium and a multiple till sequence of montane origin separated by paleosols and capped by a till of laurentide origin the sections are correlated on the basis of lithology paleosol development paleomagnetism and chlorine dating of surface boulder erratics a formal stratigraphic nomenclature is proposed for the deposits of this region the sequence of glacial tills separated by paleosols reflects a long record of glacial interglacial cycles soil properties from the oldest paleosol to modern soil show a general decrease in the degree of soil development suggesting a progressive deterioration of interglacial climatic conditions a normal reverse normal sequence of remanent magnetization was determined within th

cordilleran ice sheet mass loss preceded climate reversals near the pleistocene termination the cordilleran ice sheet cis once covered an area comparable to that of greenland previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost canada as late as 12 5 thousand years ago ka new data indicate that substantial areas throughout westernmost canada were ice free prior to 12 5 ka and some as early as 14 0 ka with implications for climate dynamics and the timing of meltwater discharge to the pacific and arctic oceans early bolling allerod warmth halved the mass of the cis in as little as 500 years causing 2 5 to 3 0 meters of sea level rise dozens of cirque and valley glaciers along with the southern margin of the cis advanced into recently deglaciated regions during the bolling allerod and younger dryas

the pattern and style of deglaciation at the late wisconsinan laurentide and cordilleran ice sheet limits in northeastern british columbia this paper reports on the landform assemblages at the northern confluence of the late wisconsinan laurentide and cordilleran ice sheets with montane and piedmont glaciers in the northern rockies and southern mackenzie mountains recent observations in northeastern british columbia refine our knowledge of the pattern and style of ice sheet retreat glacial lake formation and meltwater drainage at the onset of deglaciation confluent laurentide and cordilleran terminal ice margins lay between 59 n 124 30 w and 60 n 125 15 w from this terminal limit ice sheets retreated into north central british columbia and yukon territory with remnant cordilleran ice and montane glaciers confined to mountain valleys and the liard plateau distinctive end moraines are not associated with the retreat of cordilleran ice in these areas laurentide ice retreated northeastward from uplands and the plateaus then separated into lobes occupying the fort nelson and petitot river valleys ice retreat landforms include recessional end moraines sometimes overridden and drumlinized hill hole pairs crevasse fill deposits de geer like ribbed till ridges hummocky moraines kames meltwater features and glacial lake deposits that fall within the elevation range of glacial lake liard and glacial lake fort nelson ca 840 380 m meltwater and sediment transport into glacial lakes fort nelson liard nahanni and mackenzie was sustained by remnant ice in the liard river and fort nelson river drainage basins until the end of glaciation optical dating of sand from stabilized parabolic dunes on the liard plateau indicates that proglacial conditions lake formation and drainage began before 13 0 0 5 ka calendar years the petitot fort nelson and liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes peace and hay