evolution of midplate hotspot swells numerical solutions the evolution of midplate hotspot swells on an oceanic plate moving over a hot upwelling mantle plume is amenable to numerical simulation in our model the plume supplies to the lithosphere a gaussian shaped thermal perturbation and dynamic support dominated by thermal buoyancy we consider the two fundamental mechanisms of transferring heat conduction and convection during the interaction of the lithosphere with the mantle plume the transient heat transfer equations with boundary conditions varying in both time and space are solved in cylindrical coordinates using the alternating direction implicit finite difference method on a 100 100 grid the topography geoid anomaly and heat flow anomaly of the hawaiian swell and the bermuda rise are used to constrain the models our results confirm the conclusion from previous work that the hawaiian swell can not be explained by conductive heating alone even if an extremely high thermal perturbation is allowed on the other hand the model of convective thinning predicts successfully the topography geoid anomaly and the heat flow anomaly around the hawaiian islands as well as the changes in the topography and anomalous heat flow along the hawaiian volcanic chain the model constrains the hawaiian plume to have a half wavelength of about 500 km a center heat flux 5 6 times the background value and a convective current velocity 3 10 times that of the background convective current comparatively the mantle plume for the bermuda rise is much weaker conductive heating is probably the dominant mechanism for the evolution of the bermuda rise

thermal response of a moving lithosphere over a mantle heat source the mid ocean bathymetric swells observed around some volcanic island chains can be modeled using the thermal conduction equations of an oceanic lithosphere moving over a heat source located at the base of the plate some previous studies of this problem have suggested that the heat source must lie well within the lithosphere in order to explain the observed bathymetry and surface heat flow these conclusions are based on an isothermal boundary condition at the base of the lithosphere but this choice requires that the heat source is maintained above this boundary and can actually lead to a flux of heat back into the mantle particularly in the vicinity of the heat source if the lower boundary is insulated insofar as the anomalous temperature field is concerned flux from the heat source back into the mantle is prevented resulting in a more rapid uplift of and in an increased heat flow across the seafloor previous solutions have considered only the steady state solutions whereas the present model also evaluates transient solutions for rapidly moving oceanic plates the transient effects can be neglected provided that the heat source has been active for at least 107 years and that the direction of motion and the intensity of the heat source have remained constant in this interval solutions with the heat source located near the base of the conductive layer of the conduction equations for heat flow bathymetry and geoid heights in the spatial domain reproduce the principal observational characteristics of the hawaiian swell at distances away from the immediate origin of the swell and this part of the swell can be used to estimate the thermal conduction model parameters the model does not wholly explain the observations near the origin and the mismatch may reflect a dynamic component in the support of the swell

uplift of the sierra nevada of california gravity and most seismic interpretations agree that the sierra nevada is at present isostatically compensated by a crustal root the most reasonable timing for emplacement of the root was during mesozoic batholithic intrusions this is difficult to reconcile with the evidence that major uplift of the mountains occurred in the past 10 m y a simple quantitative model for flexural isostasy of an elastic plate before and after breaking resolves this problem and explains the tilt of the sierra nevada block and variations in topography along the range we postulate that cooling and elastic strengthening of the mesozoic magmatic arc prevented its reaching local isostatic equilibrium during erosion in the cenozoic thus an overcompensated residual mountain range was held down elastically until basin and range extension broke the elastic plate along the owens valley and allowed rapid uplift the moho density contrast that best models the amplitude of both late cenozoic uplift and prior topography is slightly larger than seismic and gravity models suggest this implies that up to 20 of the uplift may be driven by density contrasts in the upper mantle the idea of overcompensated erosional remnants and their release upon lithospheric faulting has a more general application to anorogenic uplift of mountain blocks

mechanisms of uplift preceding rifting abstract mareschal j c 1983 mechanisms of uplift preceding rifting in p morgan and b h baker editors processes of continental rifting tectonophysics 94 51 66 the feasibility of three mechanisms that have been proposed to account for the uplifts and heat flow anomalies which might precede rifting is examined the conductive heating following an increase in the heat flux at the base of the lithosphere could result in large scale uplifts 1000 m for 15 mw m2 change in heat flux on a time scale of 108 years a pulse of additional heat flow could induce a more rapid uplift but not the surface heat flow anomaly which is always delayed the advection of heat by magma intrusion into the lithosphere could also produce the uplift and heat flow anomaly if magmas are injected at a steady rate an uplift of the order of 1000 m can be induced in about 50 106 years but it requires the rate of magma injection to be equivalent to 0 3 of the total volume of the lithosphere per 106 years a short intense episode of magma invasion could explain a rapid uplift and change in surface heat flow but it requires the replacement of about 30 of the total volume of the lithosphere the complete replacement of the lithosphere by the rise of a diapir of lighter and hotter asthenospheric material has been modelled numerically the model indicates that the rise of the asthenospheric diapir can take place in a very short time 3 106 years and produce the surface uplift and the crustal thinning observed in rift systems provided that following heating the lower lithosphere viscosity is reduced to 1021 pa s

an extensive region of off ridge normal faulting earthquakes in the southern indian ocean an unusually large number of off ridge earthquakes have occurred within a broad region astride the southeast indian ridge the source mechanisms of nine of these earthquakes in lithosphere from 4 to 27 m y old have been determined with a formal inversion technique based on matching observed and synthetic p and sh waves all events occur in the oceanic mantle from 8 to 22 km below the seafloor the seismic moment and duration of faulting obtained from the inversion constrain the stress drop to lie between a few tens of bars and a few hundred bars for most of the events all of the off ridge earthquakes are characterized by normal faulting mechanisms with the t axes nearly parallel to the nearby ridge axis in sharp contrast to typical mid ocean ridge or intraplate earthquakes a variety of possible tectonic processes which might produce normal faulting in young oceanic lithosphere are considered as possible causes including bending stresses thermal stresses of various origins differential subsidence at a fracture zone off ridge volcanism latitudinal plate motions on a nonspherical earth basal shear stress from small scale convection and plate wide perturbations of the stress field due to the continental collision between india and asia no single mechanism is adequate to explain all the observed off ridge normal faulting earthquakes an apparent asymmetry in the observed seismicity with respect to the ridge suggests that the earthquakes on the antarctic and indian plates are caused by different processes the antarctic plate events can be satisfactorily attributed to the release of thermal and bending stresses associated with a residual depth anomaly between the kerguelen plateau and the southeast indian ridge a region which has been suggested as the site of a horizontal pipe for flow in the asthenosphere from the kerguelen hot spot to the vicinity of amsterdam and st paul islands on the southeast indian ridge the off ridge earthquakes in the indian plate are speculatively attributed to part of the plate wide response of the lithosphere to the ongoing continental collision

constraints on thermal models of the basin and range province abstract several mechanisms that have been proposed to explain the high heat flow in regions of tectonic extension are examined the transient thermal regime is computed and the results are discussed conductive heating of the lithosphere from below requires a time of at least 75 ma to affect the surface heat flow advective heating by the injection of magmas into the lithosphere does not produce steady state conditions before 75 to 300 ma depending on boundary conditions only mechanical stretching of at least the shallow lithosphere can explain the increase in surface heat flow in a time of the order of 30 to 50 ma the heat flow data are compatible with several mechanisms for the extension of the lower lithosphere underplating or dike injection and other geologic and geophysical data are needed to constrain the models

uplift by thermal expansion of the lithosphere summary green s function solutions are derived for the surface heat flow and the uplift caused by conductive heating when axially symmetric variations in heat flow occur at the base of the lithosphere the solutions determined for different space time dependence of the heat flux into the lithosphere illustrate that 1 when the lateral variations in heat flux occur over short distances in comparison to the lithospheric thickness the amplitude of the uplift and of the anomalous surface heat flow are attenuated in comparison to the changes that would follow uniform variations this effect is slightly more important for the surface heat flow which spreads out over larger distances 2 there is a time lag between the uplift which starts instantly and the change in the surface heat flow it is suggested that the model could be applied to the study of plateaux uplift of moderate amplitude such as the black hills or the adirondacks and possibly to the heating event and uplift that may have preceded the subsidence of intracontinental basins

instability in eight sub basins of the chilliwack river valley british columbia canada a comparison of natural and logging related landslides logging causes increased landslide frequency in british columbia in this study the slope type initiation location aspect rate bedrock geology and size of mass movements located in eight logged tributary valleys of the chilliwack river valley are investigated a landslide inventory was created by digitizing landslides identified on aerial photographs dating from 1941 to 2002 this database was analysed using qualitative observations and simple statistical tests and a comparison between natural and logging related landslides was made slope tests displayed a significant difference between natural and logging related events indicating that on average logging related landslides require lower slope gradients to initiate than natural events although aspect initiation location and landslide type did not show a significant relationship between natural and logging related landslides they do suggest subtle differences landslide rate was calculated and compared for natural and logging related landslides it was significantly higher for logging related events attaining a maximum of 31 times the natural rate in 1978 and an overall average increase of nine times the natural rate logging related landslides were on average smaller than natural landslides but this nevertheless resulted in a 3 1 times increase in area affected by logging related landslides compared to natural landslides geology may influence landslide frequency as well it appears to be higher over the less resistive sedimentary rocks of the cultus formation and chilliwack group and lower in granodioritic areas finally roads affected slope stability more than clearcuts in the early decades of the study but this effect decreased over time suggesting a correlation with improved road construction

flow resistance in steep mountain streams resistance to flow at low to moderate stream discharge was examined in five small 12 77 km2 drainage area tributaries of chilliwack river british columbia more than half of which exhibit planar bed morphology the resulting data set is composed of eight to 12 individual estimates of the total resistance to flow at 61 cross sections located in 13 separate reaches of five tributaries to the main river this new data set includes 625 individual estimates of resistance to flow at low to moderate river stage resistance to flow in these conditions is high highly variable and strongly dependent on stage the darcy weisbach resistance factor ff varies over six orders of magnitude 0 29 12 700 and manning s n varies over three orders of magnitude 0 047 7 95 despite this extreme range both power equations at the individual cross sections and keulegan equations for reach averaged values describe the hydraulic relations well roughness is divided into grain and form considered as all non grain sources components form roughness is the dominant component accounting for about 90 of the total roughness of the system i e form roughness is on average 8 6 times as great as grain roughness of the various quantitative and qualitative form roughness indicators observed only the sorting coefficient d84 d50 correlates well with form roughness copyright 2008 john wiley sons ltd

phase change and thermal subsidence of the williston basin summary a mechanism of subsidence for the williston basin is proposed and tested the mechanism combines cooling and thermal contraction of the lithosphere with a phase transformation in the lower crust the cooling and the phase boundary movement following a sudden change in the thermal boundary condition at the base of the lithosphere are calculated isostatic adjustments and sea level variations are included to determine subsidence and sediment accumulation at the basin s centre which are compared with the data the subsidence record could not be explained by temperature boundary conditions the calculations show that 1 the heat flow boundary condition explains the long duration more than 350 myrs of subsidence of the williston basin and 2 the delay of the phase change subsidence about 40myrs explains an acceleration of subsidence in the early stages of the basin s evolution when isostatic adjustments and the effect of sea level variations are included the calculated sediment accumulation history fits well the sediment record of the williston basin

a 1 d morphodynamic model of postglacial valley incision chilliwack river is typical of many cordilleran valley river systems that have undergone dramatic holocene degradation of valley fills that built up over the course of pleistocene glaciation downstream controls on base level mainly blockage of valleys by glaciers led to aggradation of significant glaciofluvial and glaciolacustrine valley fills and fan deposits subsequently incised by fluvial action models of such large scale long term degradation present a number of important challenges since the evolution of model parameters such as the rate of bedload transport and grain size characteristics are governed by the nature of the deposit sediment sampling in the chilliwack valley reveals a complex sequence of very coarse to fine textural modes we present a 1 d numerical morphodynamic model for the river floodplain system tailored to conditions in the valley the model is adapted to dynamically adjust channel width to optimize sediment transporting capacity and to integrate relict valley fill material as the channel incises through valley deposits sensitivity to model parameters is studied using four principal criteria profile concavity rate of downstream grain size fining bed surface sand content and the timescale to equilibrium model results indicate that rates of abrasion and coarsening of the grain size distributions exert the strongest controls on all of the interrelated model performance criteria while there are a number of difficulties in satisfying all model criteria simultaneously results indicate that 1 d models of valley bottom sedimentary systems can provide a suitable framework for integrating results from sediment budget studies and chronologies of sediment evacuation established from dating

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

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

deglaciation of chilliwack river valley british columbia quaternary sediments and landforms in chilliwack river valley southwestern british columbia provide a detailed record of deglaciation of this area between 12 000 and 11 000 years bp stratigraphic sedimentological and radiocarbon data show that a large glacier in eastern fraser lowland part of the cordilleran ice sheet blocked the mouth of chilliwack valley at a time when the middle reaches of the valley were ice free a lake existed between the ice dam in the lower part of the valley and a delta sandur complex west of chilliwack lake in the upper part of the valley two relatively minor advances of the fraser lowland ice lobe into lower chilliwack valley occurred about 11 500 and 11 200 years bp these were separated by a brief period of recession during which tephra was deposited and a coniferous forest and soil developed on freshly deglaciated terrain shortly after 11 200 years bp a glacial lake formed in cultus lake basin two sets of terraces in lower chilliwack valley are graded to diffe

thermotectonic history of the maastrichtian reservoir in campos basin abstract the present study of the carapebus formation on well samples refines our understanding of the thermotectonic history of the maastrichtian oil reservoir in campos basin our investigations are based on the thermal analysis of 55 cuttings samples of which 45 have also been analyzed with apatite fission track aft dating in addition to eleven cores analyzed for vitrinite reflectance vr and spore color the apatites are partially annealed and the aft central ages does not provide precise information on exhumation and thermotectonic events that occurred in the source terrain whereas the youngest aft ages provide a minimum age of 45 9 5 5 ma due to significant track annealing in the rocks the vr 0 37 0 48 ro spore color and thermal alteration index tai data correspond to the immature zone of hydrocarbons the thermal history integrated with seismic profiles demonstrate that two phases of heating happened to reservoir separated by a cooling event 65 37 ma the first heating phase started after deposition of the carapebus formation until 65 ma and the second during late eocene and reflect the subsidence at the basin the cooling event shows a strong correlation with subaerial unconformity related in the basin and an important thermal uplift coeval with the last volcanic pulses of the trindade mantle plume in the basin during the uplift phase the generation of hydrocarbon in reservoir was ceased and no more generation occurred until the recent

postglacial sediment budget of chilliwack valley british columbia the paraglacial reworking of glacial sediments by rivers and mass wasting is an important conditioning factor for modern sediment yields in mountainous catchments in formerly glaciated regions catchment scale and patterns of sediment storage are important influences in the rate of postglacial adjustment we develop a quantitative framework to estimate the volume sediment type and fractional size distribution of legacy glacial materials in a large 1230 km2 watershed in the north cascade mountains in south western british columbia canada chilliwack valley is exceptional because of the well dated bounds of deglaciation interpolation of paleo surfaces from partially eroded deposits in the valley allows us to estimate the total evacuated sediment volume we present a chronology of sediment evacuation from the valley and deposition in the outlet fan based on infrared stimulated luminescence irsl and 14 c dating of river terraces and fan strata respectively the effects of paraglacial sedimentation in chilliwack valley were intensified through a major fall in valley base level following ice retreat the steepened mainstem valley gradient led to deep incision of valley fills and fan deposits in the lower valley network the results of this integrated study provide a postglacial chronology and detailed sediment budget accounting for long term sorting of the original sediments lag deposit formation in the mainstem deposition in the outlet fan and approximate downstream losses of suspended sediment and wash load the mass balance indicates that a bulk volume of approximately 3 2 km3 of glacial material has been evacuated from the valley copyright 2012 john wiley sons ltd

vashon drift definition of the formation in the georgia depression southwest british columbia vashon drift was deposited during the fraser glaciation late wisconsinan at the time of maximum expansion of the southwestern part of the cordilleran ice sheet when it filled the georgia depression about 14 500 years ago the drift is present throughout the depression and comprises till and glaciofluvial and glaciolacustrine sediments derived from source areas surrounding the coastal trough it is overlain by capilano sediments and underlain by quadra sand also of fraser age drift deposition was diachronous and complex probably caused by alpine glaciers coalescing in the trough with the ice margin repeatedly grounding and floating in seawater studies of bedrock striae till fabrics and clast provenance reveal that vashon ice movement was generally southward although locally controlled by topography a time space diagram is presented that confirms the long held hypothesis that advance and decay of vashon ice were rapid

thermoelastic bending of the lithosphere implications for basin subsidence summary thermoelastic stresses are capable of producing significant lithospheric deflection a systematic approach to modelling this effect is presented in which the lithosphere is presumed to behave as a thin elastic or viscoelastic plate on a fluid substrate and lateral variations in basal heat flow induce both vertical buoyant loads and thermoelastic bending moments the amount of uplift or subsidence produced by a given heat source depends on a number of factors including the strength duration and lateral extent of the thermal anomaly and the thickness density rigidity and viscosity of the plate the mechanical response of the plate is characterized by two distinct length scales one for shearing the other for bending and the deformation produced depends critically on the scaled width of the heat source the plate acts as a low pass spatial filter in response to thermal loads but has a narrow band pass filter response to applied moments the temporal response to an abrupt change in basal temperature or heat flow also depends on the ratio of the thermal diffusion time for the plate versus the viscoelastic relaxation time of the material a rapid localized increase in basal heat flow will initially produce a central depression and a peripheral uplift thus while it is often assumed that the main depositional phase in platform basins is associated with the cooling and contraction of the lithosphere following an earlier thermal doming event it is shown that if conditions are right a basin may also form in direct response to the initial heating event either way subsequent thermal equilibration and viscous stress relaxation will tend to modify the initial deflection profile

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

timing and extent of allerod and younger dryas age ca 12 500 10 000 14c yr b p oscillations of the cordilleran ice sheet in the fraser lowland western north america the use of shaded digital topographic models to visualizes suites of topographic features stratigraphy and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the cordilleran ice sheet in the fraser lowland along the western washington british columbia border morphologic features show the extent of ice represented by sumas drift ca 11 600 10 000 14c yr b p following ca 3000 yr of retreat from the glacial maximum fraser glaciation positions 80 km south of seattle and in the strait of juan de fuca the paleogeography of the ice margin and timing of ice retreat during the sumas stade is reconstructed and bracketed by 70 radiocarbon dates 24 on marine shells 46 on wood and peat which are secured by morphologic and stratigraphic evidence four topographically distinct phases of the sumas deglaciation model are suggested phase si 11 600 11 400 14c yr b p outermost drift scattered remnants of ice contact deposits phase sii 11 600 11 400 14c yr b p glacier readvance building prominent moraine followed by glacier retreat phase siii 10 980 10 250 14c yr b p glacier readvance building of multiple moraines followed by glacier retreat phase siv 10 250 10 000 14c yr b p glacier readvance building of inner moraine followed by glacier retreat

geomorphology of a cordilleran ice sheet drainage network through breached divides in the north cascades mountains of washington and british columbia the skagit river valley in northern washington and southern british columbia contains long interconnected valleys barbed tributaries underfit streams and low elevation mid valley divides quantitative measures of connectivity between valleys draining through breached mountain divides aerial photographs and a field verified process form model were used to assess the impact of continental glaciation on the drainage pattern and geomorphology of the watershed structural control on drainage patterns and intense repeated continental glaciation rendered the skagit an extremely interconnected valley with meltwater routes opening it to the fraser and okanagan watersheds divide elimination by drainage of large proglacial lakes led to several hundred meters of erosion at 10 breached divides other geomorphic effects of recurrent continental glaciation include the bisection of a major mountain valley divide migration of as much as 50 km erosion of canyons 15 30 km downstream of breached divides and deposition of exceptionally large alluvial fans at canyon mouths drainage patterns established in the tertiary were reorganized to accommodate southern drainage of glacial meltwater trapped in mountain valleys at the southern margin of the cordilleran ice sheet the skagit basin is now a regional focus for drainage to puget sound from the northernmost north cascades and parts of southern interior british columbia the key to establishing this system was the elimination of a regional divide in what is now skagit gorge which resulted in the capture of the upper skagit valley by the lower skagit river patterns of drainage modification caused by continental glaciation in the skagit basin are similar to those in other mountain areas the skagit s interconnected valleys are similar to the great through valleys of scotland transmountain valleys of british columbia and ice portals of scandinavia

correlation between the geologic record and computed plate motions for central california we have attempted to correlate geologic events in part of central california with computed motions of oceanic plates relative to cratonic north america three composite terranes are considered 1 the sierra nevada 2 the coast ranges northeast of the san andreas fault and 3 the salinian block in the sierra nevada jurassic plutonism ending about 147 m y b p and cretaceous plutonism 120 80 m y b p correlate with deduced farallon north america fa na convergence as does the nevadan orogeny 158 153 m y b p however the gap in plutonism 146 121 m y b p outlasted by far an apparent minimum in convergence 145 135 m y b p magmatism ceased in the sierra and uplift slowed during the laramide orogeny 75 45 m y b p when tectonic activity had moved east to the site of the rockies presumably because of a low angle of subduction but volcanisin resumed in the sierra about 33 m y b p indicating that a steeper angle was reestablished apparently east west compression slackened when the pacific north america pa na transform regime developed basalt was erupted in the southern sierra 12 3 m y b p and during this same time the range started its most rapid rise as a normal fault bounded block the coast ranges north east of the san andreas fault are underlain by the franciscan complex the older parts of the complex were probably assembled in a subduction zone far south of their present location but we believe that the same fa na convergence that was cited for sierran plutonism was responsible despite the disparity in latitude as the farallon plate was probably in contact with most of the western margin of north and south america a perceived strong pulse in convergence 100 85 m y b p evidently produced the coast range thrust which on geologic grounds alone most likely originated between 96 and 88 m y b p some of the northwesterly transport of franciscan rocks relative to north america is ascribed to oblique kula north america ku na convergence 85 43 m y b p during which period the coast range thrust was revived about 60 m y b p the farallon plate again influenced the california margin after the kuia plate had moved northward and fa na convergence caused the accretion of the coastal belt and king range terranes of the neo franciscan the advent of pacific north america pa na interaction was marked by local volcanism which advanced from the southeast toward the northwest in consonance with the passage of the mendocino triple junction dickinson and snyder 1978 in the salinian block plutons 107 82 m y old can be ascribed to the same fa na convergence as the contemporary cretaceous plutons of the sierra nevada although the salinian intrusives originated much farther south paleomagnetic results champion et al 1980 from the salinian related pigeon point formation 75 71 m y in age suggest about 2500 km of poleward essentially coastwise movement this postulated large movement during part or all of the last 75 m y poses the greatest dilemma in our study the kuia is the only known plate whose computed obliquely convergent motion is appropriate for the late cretaceous paleogene part of the migration and even this motion is inadequate for the estimated transport within the most likely time window furthermore the farallon plate seems ideally suited for the laramide orogeny 70 45 m y b p both plates could not have been in contact with the same part of the margin at the same time oblique convergence of the kula plate could possibly have caused large coastwise transport and also the laramide orogeny the coast ranges northeast of the san andreas fault and the salinian block both experienced strike slip faulting and en echelon folding correlative with pa na interaction indicating that they were close together by neogene time faulting and folding have been particularly marked since the inception of spreading in the gulf of california and attachment of westernmost california to the pacific plate about 4 m y b p the rise of individual coastal ranges commencing 3 1 m y b p may possibly have been caused by slight convergence which appears in computed pa na relative motions from 5 m y b p to the present

models of crustal deformation this review is principally concerned with theoretical models of crustal deformation developed during this quadrennium observational data as well as topics in lithospheric flexure and isostasy are covered in companion reviews in this volume progress has been made toward constructing both new inelastic and inhomogeneous elastic models of earthquake induced crustal deformation most of the inelastic models involve dislocations or green s functions in an elastic or anelastic lithosphere which overlies a maxwell viscoelastic asthenosphere

record of large late pleistocene outburst floods preserved in saanich inlet sediments vancouver island canada abstract two anomalous gray silty clay beds are present in odp cores collected from saanich inlet vancouver island british columbia canada the beds which date to about 10 500 14c yr bp 11 000 calendar years bp contain tertiary pollen derived from sedimentary rocks found only in the fraser lowland on the mainland of british columbia and washington just east of the strait of georgia abundant illite muscovite in the sediments supports a fraser lowland provenance the clay beds are probably distal deposits of huge floods that swept through the fraser lowland at the end of the pleistocene muddy overflow plumes from these floods crossed the strait of georgia and entered saanich inlet where the sediment settled from suspension and blanketed diatom rich mud on the fiord floor the likely source of the floods is late pleistocene ice dammed lakes in the fraser and thompson valleys which are known to have drained at about the time the floods occurred

contrasting failure behaviour of two large landslides in clay and silt two large landslides in overconsolidated glaciolacustrine clay and silt located in river valleys in british columbia were found to be quite similar in their main aspects however their failure b

discussion of behavior of pile groups subject to excavation induced soil movement in very soft clay by d e l ong c f leung and y k chow

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

evaluating debris slide occurrence using digital data paraglacial activity in chilliwack valley british columbia debris sliding is one of the most important processes acting to transport sediment within mountainous regions detailed study of debris slide activity at the basin scale typically involves landslide inventories generated from aerial photographs however it has been shown that some types of rapid mass movement can be accurately identified using a combination of high resolution satellite imagery and digital elevation data this approach is beneficial as the digital products allow for a more accurate and efficient data throughput into various types of geomorphic analysis here we demonstrate the use of an automated inventory in the geomorphometric evaluation of debris slide initiation for the chilliwack basin british columbia canada our results indicate that the occurrence of debris sliding is primarily determined by topographical controls for basins that are in equilibrium with the existing climate the frequency of debris sliding should demonstrate a strong relationship to bedrock geology as the production of unconsolidated materials available for failure is a function of weathering rates under these conditions the lack of bedrock control within the chilliwack basin suggests a state of paraglacial relaxation wherein glacial deposits dominate the sediment cascade within the area therefore topographic parameters can be used to discriminate the location of metastable slopes where debris slide erosion will be active the use of digital data in the characterization of debris slide occurrence would seem to be a viable alternative to the more traditional methods

thermal evolution of the sierra nevada tectonic implications of new heat flow data eight new heat flow measurements in the southern sierra nevada constrain models of thermal evolution and lithospheric structure low reduced heat flows 18 to 21 mw m in the southwest sierra nevada are consistent with previous results from the northwestern and central sierra nevada and extend the known region of linear heat flow heat production correlation an additional 150 km to the south isostatic residual gravity and measured rock densities are also linearly correlated in the central sierra nevada suggesting a general association between the upper crustal distribution of density and heat production the linear residual gravity density relation implies that isostatic residual gravity anomalies have upper crustal sources and therefore is evidence against a flexural model of cenozoic sierra nevada uplift new reduced heat flows measured in the southeast sierra nevada are relatively high 32 to 57 mw m and correlate spatially with a region of high seismicity that includes extensional earthquake swarms this correlation supports the view that basin and range extensional tectonics and associated magmatic processes are encroaching on the eastern sierra nevada in the stable southwest sierra nevada as in the central and northwestern sierra nevada the persistence of low reduced heat flow at the surface is consistent with a thermal origin for the cenozoic uplift of the sierra nevada provided the conductive lithosphere is at least 60 to 90 km thick simple order of magnitude calculations show that thermal uplift models combining mechanisms such as advective warming and thinning of the mantle lithosphere advection of basaltic magma and heat into the crust simple thermal expansion and eclogite to basalt phase conversion can account for the timing and amount of cenozoic sierra nevada uplift thermal models do not need the assumptions of unusual lithospheric strength and crustal buoyancy required by mechanical models for cenozoic uplift driven by a mesozoic crustal root

low flow hydraulic geometry of small steep mountain streams in southwest british columbia abstract this investigation explores the at a station hydraulic geometry ahg of small steep mountain streams at low discharge thirteen reaches in five tributaries of chilliwack river british columbia ranging in size from 12 to 77 km 2 are examined the resulting data set is composed of eight to twelve measurements of water surface width mean depth and mean velocity at each of 61 cross sections or 625 unique combinations of the three variables mean velocity in a given cross section responds most rapidly to changing discharge and 31 of the 61 cross sections have velocity exponents that are greater than the water surface width and mean depth exponents combined the velocity exponent m averages 0 51 while the mean water surface width exponent b and mean depth exponent f average 0 20 and 0 29 respectively somewhat surprisingly the ahg of steep mountain streams can be reasonably predicted from just a few measurements of the primary flow variables and stream discharge while conditions at the cross section appear predictable from a few measurements extrapolating the results from one cross section to another in the same reach involves large errors the section to section variability of the exponents and coefficients even when they are located in similar channel units such as riffles prevents accurate extrapolation to unmeasured cross sections

flexure and isostatic residual gravity of the sierra nevada the sierra nevada of california displays an isostatic gravity anomaly of 35 mgal over the western foothills and 45 mgal at the crest of the range a flexural isostatic model designed to explain the rapid neogene uplift of the sierra nevada is consistent with these observations and can explain a portion of both gravity anomalies by contributions from moho depths the present day crustal root causing regional compensation in this model differs from the simple local airy compensation assumed for the sierra in calculating the isostatic residual gravity two dimensional gravity modeling indicates that this difference results in a residual gravity high of 9 mgals over the western foothills which are buoyed up by the excess root to the east and a low of 16 mgals over the crest of the sierra the remainder of the isostatic gravity anomaly is attributed to upper crustal density contrasts because high density rocks underlie the foothills and a low density batholith forms the crest any model for the isostatic residual gravity must assume implicitly or explicitly a flexural response of the lithosphere with the stiff sierran lithosphere the isostatic deflection of the moho due to the upper crustal bodies will be small if a similar gravity model were to assign no stiffness to the lithosphere local airy compensation the mass anomalies of the upper crustal bodies would necessitate a change in depth of the moho to achieve compensation this deflection of the moho would significantly reduce the amplitude of the anomaly produced by the upper crustal block for the unbroken pre uplift case of the sierra nevada of 10 ma our model predicts an isostatic gravity low over the range crest of approximately 80 mgals and a flanking high of 55 mgals these values are larger than would be predicted for a more typical eroded magmatic arc that does not have abnormally low heat flow and consequent high flexural rigidity

axisymmetric finite element analysis of an elastic lithosphere subjected to thermal loading summary an axisymmetric finite element was used to model the lithosphere as an infinite 40 km thick circular elastic plate on an elastic foundation asthenosphere subjected to concentrated thermal loading thermal loading is produced by a point heat source of 4 184 lo8 watts located 60 km beneath the plate within the asthenosphere increased nodal temperatures within the lithospheric finite element mesh were obtained from a solution to the steady state heat conduction equation for a point source in a semi infinite half space vertical as well as radial thermal expansion coefficients of 1 33 x lo k were utilized in the solutions thermoelastic loads as well as isostatic uplift forces are applied as nodal loads in the finite element lithosphere model thermoelastic loads are produced from uneven heating of the lithosphere and differential expansion isostatic uplift forces result from radial expansion and the diminished density of heated lithosphere columns uplift of the lithosphere due to the point heat source and vertical expansion is reduced because of radial expansion and flexure this occurs because material at the base of the lithosphere is closer to the point heat source and experiences greater radial expansion for sediment infdl thermoelastic loading reduces the surface uplift produced by isostatic uplift forces from 3 11 to 192m thermoelastic lithosphere models yield significantly higher radial stress profiles than density models without thermoelastic stresses the neutral plane for radial stress is displaced towards the surface in the thermoelastic models due to greater radial expansion of basal lithosphere material which is closer to the point heat source the finite element model has several advantages over the classical thin plate approach stresses and strains can be evaluated at any point within the lithosphere this capability was used in this study to determine vertical lithosphere expansion thickening non linear variation of stress with depth and the stress neutral plane position

uplift and heat flow following the injection of magmas into the lithosphere summary the thermal effect of a rapid injection of hot magmas into the lower part of the lithosphere is modelled as an increase in heat production through the invaded region the change in surface heat flow and the uplift resulting from the thermal expansion are determined in three dimensional axially symmetric geometry they are expressed as the space time convolutions of a green s function with the anomalous heat production the anomalies with shorter wavelength compared to the lithospheric thickness are attenuated this filtering affects the surface uplift more than the heat flow anomaly the attenuation effect is larger when only the lower part of the lithosphere is invaded the uplift time constant is of the same order as the heat conduction time if the lower lithosphere is invaded by magmas at a moderate rate i e the rate of injection does not exceed the equivalent of 0 1 per cent of the lithospheric volume in 106yr fifty per cent of the total uplift takes place in about 80x 106yr for a lithosphere lookm thick the uplift is slightly faster when the whole lithosphere is invaded the heat flow anomaly is delayed when the lower part of the lithosphere is invaded the spatial extent and the timing of the uplift and heat flow anomalies are critical in determining the mechanism s feasibility magma injections explain rapid uplifts 100 m lo6 yr only if the magma is supplied at a very high rate i e at least 10 per cent of the lithosphere volume per 106yr it is a feasible mechanism for uplifts that occur over longer periods of time 30 x 106yr such as those that seem to have occurred when the african plate came to rest with respect to the mantle

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

phase changes and thermal subsidence in intracontinental sedimentary basins summary a model of tectonic subsidence is developed to explain the late acceleration of subsidence observed in some intracratonic sedimentary basins the proposed mechanism combines the effect of thermal contraction of an initially hot lithosphere with the effect of a subcrustal phase transformation that moves under changing pressure and temperature conditions the subsidence following a sudden change in temperature at the base of the lithosphere is calculated the calculations show that 1 phase changes if present and activated contribute substantially to the subsidence of sedimentary basins 2 because the effect of phase change is delayed subsidence accelerates after a time on the order of 20 myr and 3 the duration of the subsidence is on the order of 100 to 150 myr during the late stages of subsidence the phase change is the dominating mechanism an application to the michigan basin is presented the calculated sediment accumulation history fits the record well when the effect of sea level changes is included in the model

the paraglacial geomorphology of the fraser lowland southwest british columbia and northwest washington abstract the fraser lowland is interpreted as a complex paraglacial landsystem in the sense that all its landform units landform and sediment associations and thus the whole landsystem have been modified by nonglacial processes conditioned by glaciation the late pleistocene and holocene processes of modification include slope erosion glacimarine marine glacifluvial fluvial glacilacustrine lacustrine organic mass movement and aeolian this complex paraglacial landsystem has transitioned from proglacial through marine to its present dominantly fluvial character landforms representative of each sediment redistribution process are described and a conceptual model is developed with relative sea level and sediment source changes as the primary drivers the sediment wave and sediment exhaustion models are compared and illustrated in the context of this paraglacial land system anthropogenic modification during the past century the anthropocene has complicated the paraglacial story and is shown to impact the incidence of natural hazards especially in the context of hydroclimate change

the opening of the atlantic the mesozoic new england igneous province and mechanisms of continental breakup abstract plume and tensionally induced rifting models have been proposed as causes of continental rifting and breakup mantle plumes should produce early lithospheric doming events associated with alkaline magmatism however the triassic alkaline rocks on the east north american e n a margin are structurally localized the uplifts are mostly jurassic in age and voluminous plateau magmatism post dates the initiation of taphrogenesis by 10 to 20 ma in addition there are no chains of anorogenic igneous rocks leading to any of the postulated triassic plumes these facts argue against the plume generated rifting model for the e n a margin but are consistent with the predicted effects of the tensionally induced rifting model the genesis of linear chains of alkaline rocks has been attributed to passage of a lithospheric plate over a mantle plume this explanation has been proposed for the cretaceous monteregian and white mountain intrusive series and the kelvin seamount chain however these rocks are distributed along structurally controlled e w trending lineaments the monteregians are localized by the presence of a paleorift ottawa bonnechere graben in the underlying grenvillian basement and the kelvin seamounts are emplaced along the early jurassic kelvin fracture zone the structures localizing the southern white mountain lineament are less well defined the spatial temporal and geochemical relationships along and between these lineaments are consistent with an origin as a southeastward propagating tensional event the intra plate stresses are probably the result of shifts in the pole of rotation of the north american plate due to irregular northward extensions of seafloor spreading during the cretaceous

a glacial readvance during retreat of the cordilleran ice sheet british columbia central coast descriptions of the cordilleran ice sheet retreat after the last glacial maximum have included short lived readvances occurring during the older and younger dryas stadial periods and into the holocene but identification of these events has been largely limited to southwest and central british columbia and northwest washington state we present evidence of a late pleistocene readvance of cordilleran ice occurring on the central coast of british columbia on calvert island between northern vancouver island and haida gwaii evidence is provided by sedimentological and paleoecological information contained in a sedimentary sequence combined with geomorphic mapping of glacial features in the region results indicate that a cold climate existed between 15 1 and 14 3 cal ka bp and that ice advanced to and then retreated from the western edge of the island between 14 2 and 13 8 cal ka bp these data provide the first evidence of a major fluctuation in the retreating ice sheet margin in this region and suggest that a cold climate was a major factor in ice readvance these data contribute to the understanding of past temperature ice loading and crustal response the nature of ice margin retreat and the paleoenvironment of an understudied area of the pacific northwest

late pleistocene stratigraphy and chronology of lower chehalis river valley southwestern british columbia evidence for a restricted coquitlam stade sediments in lower chehalis valley span middle wisconsin olympia nonglacial interval to holocene time sediments are divided into six units with chronological control provided by 14 new radiocarbon ages fluvial gravel spans the transition from the late olympia nonglacial interval to the early fraser glaciation glaciolacustrine sedimentation represents the first definitive glacial activity in the valley and indicates that vashon ice in the fraser lowland blocked the mouth of the chehalis valley at ca 18 17 ka bp ice then flowed down the chehalis valley the chehalis valley deglaciated while ice persisted in the fraser lowland forming another lake after this lake drained terraces and fans formed this style of glaciation deglaciation is typical of many watersheds peripheral to the fraser lowland in that local valley ice was slightly out of phase with ice in the lowland this resulted in glacial lakes forming during both advance and retreat phases however in contrast to watersheds in the northwestern fraser lowland no definitive evidence of a coquitlam ice advance was found within the chehalis valley although glaciers in the area were likely active and advancing data from the chehalis valley indicates that they were not as extensive as previously thought since ice source areas in the northeastern fraser lowland are in the leeward area of the coast mountains it is suggested that lower precipitation resulted in limited glacier activity there during the coquitlam stade

crustal heterogeneities and the thermal structure of the continental crust the observed linear relationship between surface heat flow q0 and the radiogenic heat production of near surface rocks a0 discovered almost two decades ago has been a primary tool used to infer the distribution of heat production in the continental crust recent evidence on the nature of compositional heterogeneities in the continental crust has led us to reexamine the q0 a0 relationship and the likely implications for the thermal structure of the lower continental crust numerical simulations of crustal thermal models indicate that some interpretations derived from this relation may be flawed in particular the length scale determined from the q0 a0 function normally thought to describe the depth distribution of crustal heat sources is significantly affected by the horizontal scale of crustal heterogeneity as a consequence most estimates of lower crustal heat flow and lower crustal temperatures obtained using heat flow data with the q0 a0 relationship are overestimates this overestimation is proportionally largest in areas of low mantle heat flux such as cratons where basal heat flux may be overestimated by more than a factor of two

variations in the lithosphere thickness and vertical neotectonic movements abstract thermal changes and mechanical deformation of the lithospheric thickness are presumed to cause vertical neotectonic movements it is established that heterochronous fragments of the continental lithosphere respond differently to cenozoic thermotectonic activation lithospheric segments which had consolidated in the archean were less mobile in the cenozoic those of riphean ma and late phanerozoic age were mobile the archean fragments comprise the stable blocks of ancient and young continental platforms the riphean and late phanerozoic fragments comprise orogenic belts these regional differences may be due to different degrees of cratonization of the continental lithosphere

readvance of glaciers in the british columbia coast mountains at the end of the last glaciation abstract late quaternary sediments and landforms at the head of howe sound a fjord in the british columbia coast mountains provide a detailed record of final decay of the southwestern sector of the cordilleran ice sheet at the end of the pleistocene the upper reaches of mamquam river valley a mountain valley at the head of the fjord east of the town of squamish were ice free and locally treed as early as 14 000 years ago 11 900 14 c yr bp folding and faulting of late glacial lacustrine sediments in mamquam valley may record a glacier readvance correlative with the sumas event in the fraser lowland to the southeast by 12 900 years ago 10 690 14 c yr bp the trunk glacier in howe sound had retreated from a sumas age moraine at porteau cove 15 km south of squamish by 12 800 years ago 10 650 14 c yr bp the glacier terminus stood near the present fjord head with the sea at an elevation of about 40 50 m a s l shortly after 12 800 years ago during the younger dryas chronozone the trunk glacier in squamish valley readvanced a short distance and then retreated for a final time tributary valleys were probably completely deglaciated by 11 300 years ago 9920 14 c yr bp and certainly by 10 600 years ago 9360 14 c yr bp relative sea level fell as deglaciation progressed however it did not fall below its present datum in the squamish area until after 11 200 years ago at least 1300 years later than in the fraser lowland

discussion of axial compression of footings in cohesionless soils i load settlement behavior by sami o akbas and fred h kulhawy the discussers would like to commend the authors for their investigation of the characterization and parameterization of the load settlement behavior of axially loaded footings on cohesionless soils because of its importance in geotechnical practice in this discussion the discussers would like to 1 provide the results of a comparative assessment of the performance of loaddisplacement models in approximating the results of a set of fullscale load tests on large footings 2 stress the importance of investigating load displacement uncertainty by addressing quantitatively not only second moment statistics of model parameters but also the correlation between the parameters themselves and 3 examine the adequateness of load displacement models for the generation of multivariate distributions for simulation purposes a database of 30 footings on 12 different sands that were subjected to vertical loading in the field was used for these purposes the origins of these sands included natural marine deposits alluvial sediments aeolian dune sands and compacted sand fills the footings included 18 square 7 rectangular and 5 circular shallow foundations with the equivalent footing width b varying from 0 5 to 6 m only full scale foundations were considered to avert difficulties associated with 1 g model tests and scaling problems e g cerato and lutenegger 2007 a summary of the sand sites test locations sand origin index number in the database footing sizes embedment depth groundwater depth median grain size and cptu net cone tip resistance qnet representative of capacity is given in uzielli and mayne 2010 the applied stress was normalized by qnet settlement s was normalized by foundation width b three load displacement model types were considered

a fluvial record of long term steady state uplift and erosion across the cascadia forearc high western washington state six late quaternary river terraces preserved along the clearwater river in northwestern washington state provide a 140 ka record of long term incision and uplift across the western side of the cascadia forearc high terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio fluvial deposits and the global eustatic curve the terraces overlie flat bedrock surfaces called straths which represent uplifted segments of the river channel bedrock incision is measured by the height of a strath relative to the adjacent modern river channel the straths along the clearwater show an upstream increase in bedrock incision ranging from 0 at the coast to a maximum of 110 m in the headwaters the incision at any point along the profile increases systematically with strath age the calculated incision rates range from 10 ky the clearwater river valley has maintained a steady state profile defined by a long term balance in the rates of incision and rock uplift upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range these results are consistent with other evidence indicating a long term steady state balance between the accretionary influx and the erosional outflux for this part of the cascadia subduction wedge since 14 ma these results help show how terrace deposits form in tectonically active landscapes the dominantly fluvial clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages in turn the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well the fluvial system shows strong forcing by the glacial climate cycle even so the river appears to have returned to the same valley profile during each cycle of strath cutting thus bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle 100 ky but appears to be relatively steady when averaged over longer time scales a simple kinematic model is used to examine how uplift of the cl our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating if accretion occurred entirely at the front of the wedge the present west coast should be moving to the northeast at 3 m ky relative to a fixed puget sound this prediction is in good agreement with offset of a 122 ka sea cliff preserved at the southwest side of the clearwater valley profile in this case the long term margin perpendicular shortening would account for 20 to 35 percent of the geodetically measured northeast southwest shortening across the olympic mountains

scale variation of post glacial sediment yield in chilliwack valley british columbia the holocene volumetric sediment budget is estimated for coarse textured sediments sand and gravel in a large formerly glaciated valley in southwest british columbia erosion is estimated by compiling volumetric loss estimated in digital elevation models dems of gullied topography and by applying a non linear diffusion model on planar undissected hillslopes estimates of steepland yield are based on estimates of post glacial deposition volumes in fans cones and deltas at the outlets of low order tributary catchments erosion of post glacial fans and tributary valley fills is estimated by reconstructing formerly continuous surfaces results are classed by catchment order and compared across scales of contributing area revealing declining specific sediment yield in m3 km 2 a 1 with catchment area for the smaller tributaries 10 km2 and increasing specific sediment yield for larger tributaries and chilliwack valley itself approximately 60 of mobilized sediment is redeposited in first to third order catchments with lesser proportions stored at the outlets of higher order catchments a simple network routing model emphasizes the significant sediment flux contributions from colluvium drift blankets and gullies in steeper terrain as this material is deposited at junctions within the lower drainage network an increasing proportion of material is derived from remnant valley fills and para glacial fans in the major valleys yield from lower order steepland catchments tends to remain in storage indefinitely sequestered on footslopes these observations have implications for modelling the post glacial sediment balance amongst catchments of varying size after 104 years the system remains in disequilibrium the critical linkage lies between low order hillslope catchments fourth order and the larger valleys with more complex fluvial systems copyright 2010 john wiley sons ltd

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