holocene fault scarps near tacoma washington usa airborne laser mapping confirms that holocene active faults traverse the puget sound metropolitan area northwestern continental united states the mapping which detects forest floor relief of as little as 15 cm reveals scarps along geophysical lineaments that separate areas of holocene uplift and subsidence along one such line of scarps we found that a fault warped the ground surface between a d 770 and 1160 this reverse fault which projects through tacoma washington bounds the southern and western sides of the seattle uplift the northern flank of the seattle uplift is bounded by a reverse fault beneath seattle that broke in a d 900 930 observations of tectonic scarps along the tacoma fault demonstrate that active faulting with associated surface rupture and ground motions pose a significant hazard in the puget sound region

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

shear wave velocity correlations for puyallup river alluvium the suitability of selected cone penetration test based shear wave velocity correlations is assessed for use with puyallup river alluvium in puget sound washington the correlation models are found to be biased for puyallup river alluvium however the functional forms of selected correlations were found to be readily adapted to local site conditions the calibration for puyallup river alluvium is presented and is found to perform satisfactorily for both down hole scptu and boring based down hole shear wave velocity derived measurements the distributions of prediction bias are presented for use in reliability studies recommendations are made for calibration of geologic specific correlations using the functional forms of selected statistical shear wave velocity regression models

ocean drilling program leg 169s surficial geology stratigraphy and geomorphology of the saanich inlet area southeastern vancouver island british columbia abstract this paper provides i a descriptive overview of the late pleistocene and holocene geology and geomorphology of the region surrounding saanich inlet and ii the palaeogeographic setting for discussion of the oceanographic record at odp leg 169s sites 1033 and 1034 the dominant deposits and landforms in the saanich inlet area are similar to those of late pleistocene marine influenced glacial environments and modern fjord inlets dominated by retreating tide water glaciers patterns of ice retreat meltwater drainage and sea level change are reconstructed for the interval 4000 15 000 calendar years before present yrbp the flux of meltwater and sediment into saanich inlet was greatest between ca 12 000 and 15 000 yrbp at that time sea level was up to 90 m higher relative to land than today during deglaciation tidewater glaciers occupying chemainus cowichan and koksilah valleys entered a marine embayment that formed in the vicinity of cowichan bay satellite channel saanich inlet and saanich peninsula in the early holocene relative sea level fell to a low stand perhaps tens of metres below the present datum and the surface area of saanich inlet and satellite channel was much reduced by the middle holocene sea level had risen to near its present position and modern drainage patterns and oceanographic conditions were established

holocene history of deep seated landsliding in the north fork stillaguamish river valley from surface roughness analysis radiocarbon dating and numerical landscape evolution modeling documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution while landslide inventories can map spatial distributions lack of dateable material landslide reactivations or time access and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns here we quantify the record of the holocene history of deep seated landsliding along a 25 km stretch of the north fork stillaguamish river valley washington state usa including the 2014 oso landslide which killed 43 people we estimate the ages of more than 200 deep seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness we show that roughness systematically decreases with age as a function of topographic wavelength consistent with models of disturbance driven soil transport the age roughness model predicts a peak in landslide frequency 1 000 ybp with very few landslide deposits older than 7 000 ybp or younger than 100 ybp likely reflecting a combination of preservation bias and a complex history of changing climate base level and seismic shaking in the study area most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments suggesting that lateral channel migration is a primary control on the location of large deep seated landslides in the valley

the impact and significance of tephra deposition on a holocene forest environment in the north cascades washington usa high resolution palaeoecological analyses stratigraphy tephra geochemistry radiocarbon dating pollen and ordination were used to reconstruct a holocene vegetation history of a watershed in the pacific northwest of america to evaluate the effects and duration of tephra deposition on a forest environment and the significance of these effects compared to long term trends three tephra deposits were detected and evaluated mlf t158 and mlc t324 from the climactic eruption of mount mazama mlc t480 from a late pleistocene eruption of mount mazama and mlc t485 from a glacier peak eruption records were examined from both the centre and fringe of the basin to elucidate regional and local effects the significance of tephra impacts independent of underlying long term trends was confirmed using partial redundancy analysis tephra deposition from the climactic eruption of mount mazama approximately 7600 cal years bp caused a significant local impact reflected in the fringe location by changes to open habitat vegetation cyperaceae and poaceae and changes in aquatic macrophytes myriophyllum spicatum potamogeton equisetum and the alga pediastrum there was no significant impact of the climactic mazama tephra or other tephras detected on the pollen record of the central core changes in this core are potentially climate driven overall significant tephra fall was demonstrated through high resolution analyses indicating a local effect on the terrestrial and aquatic environment but there was no significant impact on the regional forest dependent of underlying environmental changes

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

degradation of unconsolidated quaternary landforms in the western north america abstract one of the major goals of geomorphology is to understand the rate of landscape evolution and the constraints that erosion sets on the longevity of land surfaces the latter has also turned out to be vital in modern applications of cosmogenic exposure dating and interpretation of lichenometric data from unconsolidated landforms because the effects of landform degradation have not been well documented disagreements exist among researchers regarding the importance of degradation processes in the dating techniques applied to exposures here we show that all existing qualitative data and quantitative markers of landform degradation collectively suggest considerable lowering of the surface of unconsolidated landforms over the typical life span of quaternary moraines or fault scarps degradation is ubiquitous and considerable even on short time scales of hundreds of years on steeply sloping landforms these conservative analyses are based entirely on field observations of decreasing slope angles of landforms over the typical range of ages in western north america and widely accepted modeling of landscape degradation we found that the maximum depth of erosion on fault scarps and moraines is on average 34 of the initial height of the scarp and 25 of the final height of the moraine although our observations are limited to fault scarps and moraines the results apply to any sloping unconsolidated landform in the western north america these results invalidate the prevailing assumption of no or little surface lowering on sloping unconsolidated landforms over the quaternary period and affirm that accurate interpretations of lichen ages and cosmogenically dated boulder ages require keen understanding of the ever present erosion in our view the most important results are twofold 1 to show with a large data set that degradation affects universally all sloping unconsolidated landforms and 2 to unambiguously show that even conservative estimates of the total lowering of the surface operate at time and depth scales that significantly interfere with cosmogenic exposure and lichen dating

subsolidus evolution and alteration of titanomagnetite in ocean ridge basalts from deep sea drilling project ocean drilling program hole 504b9 leg 83 implications for the timing of magnetization magnetic minerals in six samples of oceanic basalts of the transition zone and upper sheeted dikes from deep sea drilling project ocean drilling program dsdp odp hole 504b leg 83 were studied by methods of rock magnetism and transmission electron microscopy tem tem observations showed that the magnetic mineral in these basalts is end member magnetite tmo of extremely fine grain size 30 100 nm primarily in the range of pseudosingle domain magnetite consistent with the rock magnetic properties including hysteresis parameters curie temperature and low temperature measurements verwey transition magnetite formed by two different processes 1 oxidation exsolution true exsolution and hydrothermal alteration and 2 oxidation exsolution a second stage of oxidation exsolution and hydrothermal alteration the primary titanomagnetite tm60 70 that crystallized from the melt thus evolved to end member magnetite coexisting with titanite sphene kassite ulvospinel tm 87 and ilmenite on a submicroscopic scale on the basis of the formation mechanisms of the magnetic carrier the primary titanomagnetite tm 60 with curie temperature of 180 c did not acquire thermoremanent magnetization trm in these basalts instead the ti bearing magnetite tm 10 20 that formed as oxidized or exsolved lamellae acquired its first thermal chemical remanent magnetization crm at 500 400 c during subsolidus cooling upon the onset of hydrothermal alteration the recrystallized end member magnetite acquired a second crm the natural remanent magnetization of the basalts from the transition zone and upper sheeted dikes is therefore characteristic of crms that were acquired when titanomagnetite altered in part to magnetite during subsolidus cooling and hydrothermal alteration close to the ridge axis

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

constraints on surface deformation in the seattle wa urban corridor from satellite radar interferometry time series analysis summary we apply differential insar dinsar time series techniques to the urban corridor between tacoma seattle and everett wa using 93 interferograms from three satellites ers 1 ers 2 and radarsat 1 between 1992 and 2007 our goal is to study local tectonic geomorphic and groundwater processes consequently we remove long wavelength 50 100 km deformation signals from unwrapped interferograms by comparing surface velocities generated via the time series technique at more than two million points within the overlapping region between two independent ers tracks we estimate the uncertainty of relative surface velocity measurements to be 0 5 mm yr 1 in the vertical we estimate the uncertainty of relative displacement measurements to be 5 4 mm given our comparisons of dinsar derived time series to gps data a result that is consistent both with previous dinsar time series analysis and with the uncertainty expected from gps displacements projected onto the radar line of sight active tectonic deformation at shallow depths on the region s numerous east west structures is absent over the 11 5 yr of sar data examined assuming that the south dipping thrust beneath seattle and tacoma takes up 3 mm yr 1 of north south shortening our data indicate that the fault must be currently locked to a depth of greater than 10 km we also document extensive groundwater related deformation throughout much of the study region most notably we identify sharp linear deformation gradients near federal way wa and running between sumner wa and steilacoom wa these features may mark the locations of previously unmapped fault splays that locally control groundwater movement we find no slow landslide deformation on any of the numerous mapped slide complexes within seattle although regions of known active landsliding such as along perkins lane in seattle exhibit radar phase de correlation these observations are consistent with relatively infrequent and rapid landslide deformation within seattle

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

10be dating of late pleistocene megafloods and cordilleran ice sheet retreat in the northwestern united states during the late pleistocene multiple floods from drainage of glacial lake missoula further eroded a vast anastomosing network of bedrock channels coulees and cataracts forming the channeled scabland of eastern washington state united states however the timing and exact pathways of these missoula floods remain poorly constrained thereby limiting our understanding of the evolution of this spectacular landscape here we report cosmogenic 10 be ages that directly date flood and glacial features important to understanding the flood history the evolution of the channeled scabland and relationships to the cordilleran ice sheet cis one of the largest floods occurred at 18 2 1 5 ka flowing down the northwestern columbia river valley prior to blockage of this route by advance of the okanogan lobe of the cis which dammed glacial lake columbia and diverted later missoula floods to more eastern routes through the channeled scabland the okanogan and purcell trench lobes of the cis began to retreat from their maximum extent at ca 15 5 ka likely in response to onset of surface warming of the northeastern pacific ocean upper grand coulee fully opened as a flood route after 15 6 1 3 ka becoming the primary path for later missoula floods until the last ones from glacial lake missoula at 14 7 1 2 ka the youngest dated flood s 14 0 1 4 ka to 14 4 1 3 ka came down the northwestern columbia river valley and were likely from glacial lake columbia indicating that the lake persisted for a few centuries after the last missoula flood

early wisconsinan mis 4 glaciation on haida gwaii british columbia and implications for biological refugia sea cliffs at cape ball on graham island british columbia expose a thick sequence of pleistocene sediments deposited during at least two glaciations in sequence from the base of the section the units are 1 stony mud 2 till 3 silt sand and peat 4 stony mud 5 laminated sand and silt 6 cross bedded sand and 7 till of special interest is unit 4 a massive to weakly stratified mud containing scattered stones that was deposited during the penultimate pleistocene glaciation marine isotope stage mis 4 this unit contains wood and marine shell fragments that have yielded non finite radiocarbon ages sand and silt with thin stringers of peat unit 3 directly underlie this stony mud and returned an optical age of 57 3 5 7 ka the stony mud is unconformably overlain by ponded sediments unit 5 and advance outwash unit 6 and till unit 7 deposited during the fraser glaciation mis 2 the optically dated unit and a correlative peat and silty sand unit at a nearby exposure have p

pattern of southern laurentide ice sheet margin position changes during heinrich stadials 2 and 1 abstract with concerns over rising global temperatures ice sheet stability and implications for sea level rise the responses of former ice sheets to past climate change provide useful insights into linkages between the atmosphere cryosphere and oceans one example is the behavior of the laurentide ice sheet lis during heinrich stadials times of cooler sea surface temperature sst in the north atlantic using existing cosmogenic surface exposure ages varve chronologies radiocarbon ages and optically stimulated luminescence ages from the southern lis margin this report tests the hypothesis that the southern side of the lis advanced during times of surface cooling of the north atlantic this test reconstructs the timing of local glacial maxima and the times immediately pro and preceding them from multiple areas and compares them to the timing of heinrich stadial 2 hs2 26 6 23 6 ka and to the timing of heinrich stadial 1 hs1 19 3 15 3 ka during hs2 southern sector lobes new england region huron erie lobe lake michigan lobe green bay lobe and the chippewa lobe advanced towards their maximum position except for the des moines lobe for which there is no applicable data during hs1 these same lobes experienced substantial retreat but the des moines lobe advanced thus the southern laurentide margin behaved differently during the two heinrich stadials this pattern may be attributed to differing east west temperature gradients across north america and associated changes in atmospheric circulation

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

latest pleistocene advance and collapse of the matanuska knik glacier system anchorage lowland southern alaska abstract at the end of the last ice age glacier systems worldwide underwent dramatic retreat here we document the advance and retreat of a glacier system with adjacent marine and land based components during the latter part of the termination we utilize three lines of evidence lithologic provenance geomorphic mapping and radiocarbon ages derived from lake cores to reconstruct glacier extent and timing of advance and retreat within our study area centered at n 61 50 w 149 50 just north of anchorage alaska two glaciers sourced in the talkeetna and chugach mountains flowed down the matanuska and knik valleys forming a coalesced lobe that advanced onto the anchorage lowlands and terminated at elmendorf moraine we use the presence of lithologies unique to the matanuska catchment in glacial drift to delineate the paleoflow lines and to estimate the suture line of the two glacier systems the eastern side of the lobe attributed to ice flow from the knik valley was in contact with elevated marine waters within the knik arm fjord and thus retreat was likely dominated by calving geomorphic evidence suggests the western side of the lobe attributed to ice flow from matanuska valley retreated due to stagnation we constrain retreat of the combined matanuska and knik lobe with thirteen new radiocarbon ages in addition to previously published radiocarbon ages and with geomorphic evidence suggesting the retreat occurred in two phases retreat from the elmendorf moraine began between 16 8 and 16 4 ka bp a second faster retreat phase occurred later and was completed by 13 7 ka bp with the 140 km of total retreat occurring over 3000 years or less this pattern of glacial advance and retreats agrees well with the deglacial histories from the southern sectors of the cordilleran ice sheet as well as many other alpine glacier systems in the western u s and northern alaska this consistent behavior of glacier systems may indicate that climate oscillated over western north america early in deglaciation before it was recorded in other proxies such as ice cores furthermore the period in which we note mountain glacier collapse in northwestern north america is synchronous with the worldwide glacial termination raising questions about intrahemispheric linkages

neoglacial fluctuations and sedimentation of an iceberg calving glacier resolved with tree rings kenai fjords national park alaska abstract the mccarty fjord iceberg calving glacier and its land terminating tributaries have fluctuated with some asynchroneity during the past two millennia during advance mccarty glacier shed outwash along the fjord and into ice dammed tributaries inundating forests a radioacarbon framework has revealed at least two major late holocene glacial advances that occurred following a poorly documented expansion about 3600 bp these two later advances are resolved within this fjord with tree ring dating of in situ and transported tree trunks the first event was an early medieval expansion of the mccarty trunk glacier beyond midfjord about 596 a d this followed an interval of tree growth of at least 206 years tributary glaciers probably also advanced at this time however continuous tree growth occurred in the distal southern tributary valleys during this advance while northern tributaries were being dammed by the advancing trunk glacier the down valley extent of this expansion is thus constrained to a position within 12 km of the present contracted ice margin the tree ring refined chronology shows that a second mccarty ice expansion began in the 9th century and reached midfjord by 900 a d and continued to advance through the little ice age in contrast expansions of land terminating glaciers here began after 1300 a d in concert with mountain glaciers worldwide a log from a diamict cross dated with a living tree ring chronology shows that mccarty glacier was advancing within a kilometer of its little ice age maximum at 1790 a d since about 1905 a d dramatic ice retreat has uncovered more than 20 km of mccarty fjord

a holocene sedimentary record of tectonically influenced reduced channel mobility skokomish river delta washington state usa abstract at the skokomish river delta in washington state s puget lowland coseismic uplift and tilting trapped the river against a valley wall resulting in little to no channel migration for the last 1000 years the most recent earthquake occurred before ad 780 990 based on stratigraphic evidence such as sand blows and abrupt facies changes since the hypothesized tilting a 5 km long section of the river has not migrated laterally or avulsed resulting in reduced migration and a muddy intertidal flat that is 2 km wider in the east than on the west side of annas bay a ridge running perpendicular to the river may also have restricted channel mobility the ridge may be either the surface expression of a blind thrust fault or a relict uplifted and tilted shoreline the uplift and tilting of the delta can be ascribed to any of three nearby active fault zones of which the most likely based on the orientation of deformation is the saddle mountain fault zone which produced a surface rupture 1000 1300 years ago the delta has experienced submergence since the earthquake a forest that colonized an uplifted part of the delta about 800 1200 years ago was later submerged by at least 1 6 m and is now a brackish water marsh

late pleistocene stratigraphy and implications for deglaciation and subglacial processes of the flathead lobe of the cordilleran ice sheet flathead valley montana usa abstract the flathead lobe of the cordilleran ice sheet advanced and retreated across the flathead valley a 90 km long by 15 25 km wide basin the glacier terminated at the southern end of the flathead valley during its last glacial maximum i used geologic mapping sedimentologic study and mapping from 3300 descriptive water well logs to define the stratigraphy of glacial and post glacial deposits in the flathead valley and to infer subglacial processes and retreat rates units in the 30 200 m thick stratigraphic sequence include deep sand and gravel proglacial alluvium diamicton till locally gravelly silt and clay coarse grained subaqueous deposits at recessional moraines and glaciolacustrine deposits and surficial sand and gravel outwash and holocene stream deposits a nearly continuous till overlies alluvium and is in turn directly overlain by glaciolacustrine deposits glaciolacustrine shoreline indicators at altitudes of 940 958 m show that the flathead lobe receded as a proglacial lake expanded in that range of altitudes this lake the ancestral flathead lake was impounded behind bedrock that was downcut 60 78 m since the late pleistocene glaciolacustrine deposits are as much as 180 m thick in discontinuous troughs that locally cut through till to alluvium and bedrock the troughs are mostly 1 5 km in width 6 25 km in length sinuous in plan view and undulatory in longitudinal profile the troughs extend below the elevation of flathead lake and have been below local base level since glaciation these characteristics point to incision by meltwater hydrostatically pressurized beneath the flathead lobe in subglacial tunnel channels sand and gravel at the trough bases and part of the glaciolacustrine fill in the troughs are subglacial deposits tunnel channels that terminate at recessional moraines suggest excavation occurred sporadically during deglaciation the distribution of glaciolacustrine silts indicates that the flathead lobe retreated and the ancestral flathead lake expanded by 87 km before the lake outlet stream could downcut its dam by 500 m year 1

surface roughness dating of long runout landslides near oso washington usa reveals persistent postglacial hillslope instability establishing regional landslide chronologies is necessary to advance from hazard recognition to risk assessment and to understand the evolution of landslide prone terrain despite recent advances in landslide mapping due to the availability of high resolution lidar imagery estimating the timing of slope failures remains a challenge here we present a new integrated approach to dating landslides on a regional scale by augmenting quantitative surface roughness analysis with radiocarbon dating and numerical landscape modeling we calibrate a roughness age curve which we use to date 25 deep seated landslides in glacial sediment surrounding the catastrophic a d 2014 oso landslide along the north fork stillaguamish river in washington state usa lidar bare earth images show a high density of long runout landslides in this region using our roughness age curve we estimate an average holocene landslide frequency of 1 every 140 500 yr and show that the 2014 oso landslide was the latest event in an active history of slope failures throughout the holocene with each landslide substantial sediment is delivered to the north fork stillaguamish river driving shifts in the active channel that ultimately affect the pattern of landslides across the valley the high frequency of landslides in this area where river incision and isostatic uplift rates have dropped dramatically since peaking soon after ice retreated from the region shows that landscapes inundated by glacial sediment do not require dramatic changes in base level to remain highly unstable for tens of thousands of years

pumice in the interglacial whidbey formation at blowers bluff central whidbey island wa usa abstract a new 40ar 39ar age of 128 9 ka and chemical analyses of pumice layers from interglacial alluvium at blowers bluff whidbey island wa show that the deposits are part of the whidbey formation a widespread mainly subsurface unit glass chemistry of the dated dacitic pumice does not match any analyzed northern cascade source but upper pleistocene dacites from glacier peak and early pleistocene silicic rocks from the kulshan caldera are chemically similar the chemistry of pumiceous dacite in younger units including the latest pleistocene partridge gravel is similar to that of the dated material the deep troughs of the modern northern puget lowland must have been filled during deposition of the whidbey formation allowing volcanic rich sediment to reach what is now whidbey island topographic analysis of lidar images demonstrates that extensive erosion occurred during latest pleistocene ice retreat the partridge gravel likely records subglacial fluvial erosion along an ice tunnel and ice marginal deposition into adjacent marine waters pumice in the partridge gravel probably was reworked from stratigraphically and topographically lower deposits including those at blowers bluff

late glacial to holocene radiocarbon constraints on north pacific intermediate water ventilation and deglacial atmospheric co2 sources abstract radiocarbon reconstructions of past ocean ventilation rates constrain oceanic sources and sinks of co2 and mechanisms of subsurface hypoxia here 14c in coexisting benthic and planktonic foraminifera from a sediment core 682 m deep off southeast alaska documents paleoventilation over the past 17 000 years a chronology based on calibrated planktonic foraminiferal dates consistent with independent terrestrial dates for regional glacial retreat yields deglacial projection ages moderately greater than those of the holocene suggesting comparatively limited ventilation the observed holocene increase of apparent ventilation at intermediate depths tracks inundation of the bering strait between 11 800 and 13 200 years ago suggesting that flooding of continental shelves and export of low salinity surface waters to the arctic enhanced intermediate water formation in the north pacific an abrupt increase in the benthic planktonic radiocarbon age gradient implying homogenization of abyssal radiocarbon in deep and intermediate waters aligns with the younger of two episodes of rapid rise of atmospheric co2 and depletion of atmospheric c 14 during deglaciation 11 500 13 000 years ago suggesting the north pacific as a possible pathway for venting of oceanic co2 to the atmosphere during the second half of the deglacial transition

ice free conditions in southwestern british columbia at 16000 years bp new radiocarbon dates on wood from two exposures in chilliwack valley southwestern british columbia indicate that this area was ice free and locally forested 16 000 radiocarbon years ago this suggests that the late wisconsinan cordilleran ice sheet reached its maximum extent in this region after 16 000 years bp the chilliwack valley dates are the youngest in british columbia that bear on the growth of the cordilleran ice sheet

are mima like mounds the consequence of long term stability of vegetation spatial patterning abstract the origins of large 5 m diameter 1 m height and regularly spaced i e over dispersed non anthropogenic earth mounds e g mima mounds heuweltjies nabhkas that occur across all biomes remain unresolved an extensive literature documenting diverse explanations for mound genesis has accumulated that primarily ascribes mound formation to faunal agents recent modeling efforts suggest that both abiotic and biotic processes commonly interact to produce striking vegetation patterning e g spots labyrinths the hypothesis that many earth mounds apart from those with a clear faunal genesis e g termitaria may result from vegetation trapping of sediment or aeolian dust and or protection of soil from erosion is reviewed here the literature on the occurrence and properties of some of these mima like mounds is reviewed and the evidence for their origins evaluated some mounds such as coppice dunes otherwise known as nabkhas clearly form as a consequence of aeolian deposition of sediment around vegetation patches however the clay stone and rock content of some mima like mounds is not consistent with purely aeolian origins instead it is suggested that non aeolian mound over dispersion elongation volumes soil properties and stratigraphy are consistent with vegetation patches protecting soil from erosion resulting in preferential erosional deflation of the inter mound area leaving regularly spaced mounds although mima like mounds around the world are formed in diverse vegetation types climates and edaphic conditions many may be long term products of vegetation spatial patterning in which plant canopies and root systems increase sediment capture and reduce erosional losses

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

accumulation variability and mass budgets of the lambert glacier amery ice shelf system east antarctica at high elevations the temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub basins of the lambert glacier amery ice shelf system las east antarctica at high elevations are assessed using a variety of datasets derived from field measurements and modeling the annual temporal variations of the accumulation rate for four cores from the west and east sides of the las are around 34 decadal fluctuation of the accumulation from the dt001 firn core drops to 10 and the 30 year fluctuation to 5 which is assumed to contain the information about the regional and long term trend in accumulation the 15 point running mean of the annual accumulation rate derived from stake measurements can remove most of the high frequency spatial variation so as to better represent the local accumulation model simulations show that the spatial variability of erosion deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the las mass budget estimates at high elevation sub basins of the las suggest drainage 9 has a negative imbalance of 0 7 0 4 gt a 1 lambert and mellor glaciers have a positive imbalance of 3 9 2 1 and 2 1 2 4 gt a 1 respectively and fisher glacier and drainage 11 are approximately in balance the higher elevation region as a whole has a positive mass imbalance of 4 4 6 3 gt a 1 which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region

diatom inferred aquatic impacts of the mid holocene eruption of mount mazama oregon high resolution diatom stratigraphies from mid holocene sediments taken from fringe and central locations in moss lake a small lake in the foothills of the cascade range washington have been analyzed to investigate the impacts and duration of tephra deposition on the aquatic ecosystem up to 50 mm of tephra was deposited from the climactic eruption of mount mazama 7958 7795 cal yr bp with coincident changes in the aquatic ecosystem the diatom response from both cores indicates a change in habitat type following blanket tephra deposition with a decline in tychoplanktonic fragilaria brevistriata and staurosira venter and epiphytic diatom taxa indicating a reduction in aquatic macrophyte abundance additionally the central core shows an increase in tychoplanktonic aulacoseira taxa interpreted as a response to increased silica availability following tephra deposition partial redundancy analysis however provides only limited evidence of direct effects from the tephra deposition and only from the central core but significant effects from underlying environmental changes associated with climatic and lake development processes the analyses highlight the importance of duplicate analyses fringe and central cores and vigorous statistical analyses for the robust evaluation of aquatic ecosystem change

late glacial and early holocene sea level fluctuations in the central puget lowland washington inferred from lake sediments abstract analyses of sediments diatoms and pollen in a 12 65 m long sediment core taken from lake carpenter in the central puget lowland washington provide detailed information regarding the history of deglaciation and late glacial early holocene sea level changes the lake outlet now 8 2 m above sea level has been lowered 1 1 5 m by postglacial erosion the lithology and pollen record suggest that no lengthy hiatuses in sedimentation have occurred the basal sediments are glacialmarine and contain shell fragments and brackish marine diatoms freshwater sediments above the basal section are interrupted only by a short section containing few fossils most of which are brackish to marine indicators and by the mazama tephra at 9 5 m the pollen record in the basal 4 m reveals a pinus zone ca 13 850 11 000 yr b p with a brief peak of picea at ca 13 700 yr b p and an alnus pseudotsuga zone ca 11 000 6500 yr b p the chronology is based on nine radiocarbon ages a relative lowering of sea level below the 9 5 m threshold is recorded in the core at 12 41 m and dates 13 850 to 13 700 yr b p a marine episode occurred about 13 600 yr b p implying that relative sea level temporarily rose above 9 5 m no subsequent transgressions above the 9 5 m level have been recorded comparison of six radiocarbon dates 13 600 yr b p suggest that the marine reservoir correction of 760 yr currently used for this area may be too high for this time period

climatic influences on sediment deposition and turbidite frequency in the nitinat fan british columbia abstract continental margins in regions influenced by temperate ice sheets experience climate dependent changes in sedimentary processes a new stratigraphy is presented for ocean drilling program hole 888b from the nitinat fan on the vancouver margin in which we examine the relationship between fluctuations in glacial sourced sediment delivered to the continental shelf and turbidite character and frequency glacial interglacial episodes are determined based on 1 core lithology where sandy coarse grained sediment and fine grained clay silty clay represents glacial and interglacial intervals respectively 2 18 o of planktonic foraminifera g bulloides in which higher values indicate warmer sea surface temperatures and lower global ice volume 3 magnetic susceptibility in which higher values indicate coarser grain sizes deposited during glacials and 4 ratios of sinistral n pachyderma to dextral n incompta in which higher proportions of n pachyderma are a sign of cooler sea surface temperatures finally using radiocarbon 14 c dates specific marine isotope stages mis within the top 240 m of core are assigned mis 2 4 2 118 mbsf mis 5 118 157 mbsf and mis 6 213 240 mbsf using this chronology sedimentation rates for the nitinat fan were greater 187 cm kyr during glacial mis 2 4 than interglacial mis 5 69 cm kyr additionally during glacial mis 2 4 thicker turbidites upwards of 150 cm were deposited relatively frequently 75 year periodicity compared with those from mis 5 which are relatively thin up to 27 cm and deposited more rarely 130 year periodicity these results indicate that turbidite frequency and thickness are linked to climate through ice sheet extent since transport of glacimarine sediment to the continental slope promotes turbidity currents that are responsible for the most significant amount of offshore sedimentation this study shows that geological processes influencing turbidite deposition can fluctuate over time and may not necessarily be represented by ongoing processes within the modern depositional setting

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

giant short faced bear arctodus simus from late wisconsinan deposits at cowichan head vancouver island british columbia a giant short faced bear arctodus simus ulna fragment was found at the base of exposed quaternary sediments at cowichan head southern vancouver island british columbia in this paper the ulna fragment and its geological context are described and a reasonable taphonomic trajectory is presented the radiocarbon age of 22 750 140 bp on the bone indicates that these bears were on vancouver island during the late wisconsinan a likely source for the cowichan head a simus was from the mainland to the southeast

first time landslides in vashon advance glaciolacustrine deposits puget lowland u s a abstract advance glaciolacustrine qglv deposits from the last continental glaciation are widespread in the densely populated puget lowland and are prone to shallow landsliding much less frequently in historic time new landslides propagate deeply within intact qglv deposits the exceptional volume and highly mobile nature of the 22 march 2014 state route 530 oso landslide generated considerable uncertainty and public concern about the likelihood for similar deep seated failures initiating from most any slope where these deposits crop out the primary study objectives are to utilize geotechnical data from the small data set of available published and public domain investigations to characterize in general terms hydrogeologic geotechnical and geomorphic factors and their relative contribution to initiating deep seated landslides within intact qglv deposits and to inform future hazard and risk assessments for first time landslides within these deposits qglv deposits are overconsolidated very stiff to hard laminated to massive silt and clay shear strength is anisotropic with cohesion being a significant component of bedding parallel strength and friction dominating strength perpendicular to bedding hydraulic conductivity is likely also anisotropic multi year records of pore pressures within qglv deposits show no to minor seasonal flux only minor pore pressure responses to multi day to multi week episodes of heavy precipitation have been detected back analyses using limit equilibrium methods and peak anisotropic strength under drained conditions demonstrate initial stability of the slopes instability occurs near the fully softened strength we conclude that over the long term loss of cohesive strength rather than hydroclimatic pore pressure response is the more important contributor to diminishing stability and in some cases initiation of first time landslides in qglv deposits the shape and location of the slide surface is strongly influenced by strength anisotropy and stress state sliding surfaces developed near the basal contact of the qglv deposits in all of the five studied landslides higher stress states associated with increasing sequence thickness of the landslide masses decrease stability the length of the basal slide surface and thus the aspect ratio of the landslide mass appears to increase proportionally with sequence thickness of the landslide mass

finding concealed active faults extending the southern whidbey island fault across the puget lowland washington 1 the southern whidbey island fault zone swif as previously mapped using borehole data potential field anomalies and marine seismic reflection surveys consists of three subparallel northwest trending strands extending 100 km from near vancouver island to the northern puget lowland east of puget sound the swif makes landfall between the cities of seattle and everett but is concealed beneath a thick mantle of young glacial deposits and vegetation a 20 km wide northwest trending swath of subparallel low amplitude aeromagnetic anomalies crosses this region of the puget lowland and is on strike with the swif the most prominent aeromagnetic anomaly the cottage lake lineament extends at least 18 km and lies approximately on strike with the swif on whidbey island subtle scarps and topographic lineaments on pleistocene surfaces visible on high resolution lidar topography at a number of locations along the swif lie on or near these magnetic anomalies in the field scarps exhibit northeast side up and vertical relief of 1 to 5 m excavations across several lidar scarps lying on or near magnetic anomalies show evidence for multiple folding and faulting events since deglaciation most likely above buried reverse oblique faults excavations in areas away from magnetic anomalies do not show evidence of tectonic deformation in total paleoseismological evidence suggests that the swif produced at least four earthquakes since deglaciation about 16 400 years ago the most recent less than 2700 years ago

semi automated extraction of longitudinal subglacial bedforms from digital terrain models two new methods abstract relict drumlin and mega scale glacial lineation positive relief longitudinal subglacial bedforms lsbs morphometry has been used as a proxy for paleo ice sheet dynamics lsb morphometric inventories have relied on manual mapping which is slow and subjective and thus potentially difficult to reproduce automated methods are faster and reproducible but previous methods for lsb semi automated mapping have not been highly successful here two new object based methods for the semi automated extraction of lsbs footprints from digital terrain models are compared in a test area in the puget lowland washington usa as segmentation procedures to create lsb candidate objects the normalized closed contour method relies on the contouring of a normalized local relief model addressing lsbs on slopes and the landform elements mask method relies on the classification of landform elements derived from the digital terrain model for identifying which lsb candidate objects correspond to lsbs both methods use the same lsb operational definition a ruleset encapsulating expert knowledge published morphometric data and the morphometric range of lsbs in the study area the normalized closed contour method was separately applied to four different local relief models two computed in moving windows and two hydrology based overall the normalized closed contour method outperformed the landform elements mask method the normalized closed contour method performed on a hydrological relief model from a multiple direction flow routing algorithm performed best for an assessment of its transferability the normalized closed contour method was evaluated on a second area the chautauqua drumlin field pennsylvania and new york usa where it performed better than in the puget lowland a broad comparison to previous methods suggests that the normalized relief closed contour method may be the most capable method to date but more development is required

long term shoreline retreat rates on whidbey island washington usa abstract long term retreat rates of puget sound s unconsolidated sediment shorelines have been difficult to quantify and little systematic research has been completed to constrain retreat in this area we put forward a new application of cosmogenic 10be exposure dating to assess long term shoreline retreat on whidbey island wa by dating lag boulders exposed on the shore platform as the shoreline erodes production of 10be in shoreline boulders is modulated by both tidal submergence and topographic shielding from the retreating bluff by modeling the combined effect of these variables on 10be production the timing of exposure can be determined and used to calculate long term 103 104 yr bluff retreat rates in rare cases retreat rates are underestimated due to inherited 10be within the study area average retreat rates ranged between 0 and 8 cm yr 1 our results demonstrate the utility of cosmogenic nuclides for determining long term shoreline retreat rates in areas with thick sediment cover where large numbers of samples can be collected and where the pre depositional history of the boulders is uncomplicated

latest pleistocene alpine glacier advances in the sawtooth mountains idaho usa reflections of midlatitude moisture transport at the close of the last glaciation mountain glaciers in the sawtooth mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice sheet maximum the glaciers constructed an extensive moraine belt in the southeastern sawtooth mountains allowing determination of a detailed radiocarbon chronology from lake and marsh cores moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late pleistocene ice advances a basal radiocarbon date from marsh cores in the alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca 16 900 calibrated cal yr b p minimum limiting dates on glacial lacustrine sediment in lake and marsh cores from three valleys clustered around 13 950 cal yr b p document the maintenance or reestablishment of extensive ice volume during early late glacial time the ca 16 900 cal yr b p advance postdates the last ice sheet maximum by 4000 yr and is broadly correlative with maximum advances of the north yellowstone outlet glacier and the puget lobe of the cordilleran ice sheet and a near maximum advance of wallowa mountain glaciers these synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice sheet maximum as does the subsequent sawtooth advance during early late glacial time together these responses indicate strong sensitivity of certain ice systems to moisture delivery fluctuations

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

glaciofluvial infilling and scour of the puget lowland washington during ice sheet glaciation the puget lobe the southwesternmost extension of the cordilleran ice sheet last advanced into the puget lowland of western washington at about 15 ka the advancing ice sheet deposited voluminous sediment on a prograding proglacial outwash plain that extended from the olympic mountains to the cascade range herein recognized as the great lowland fill subsequent overrunning by the ice sheet excavated deep linear troughs now occupied by the large lakes and marine waters of puget sound excavation of these troughs and valleys of the puget lowland required the net transport of about 1000 km3 of sediment almost entirely during ice occupation and primarily by subglacial water these landforms of glaciofluvial deposition and erosion define the modern landscape here emphasizing the importance of these processes in the region s geomorphology

coeval brittle and ductile deformation beneath the late wisconsinan puget lobe washington state usa late wisconsinan glacial sediments exposed on whidbey island and camano island puget sound washington state usa were deposited in a proglacial shallow marine outwash environment during northward retreat of the puget lobe of the cordilleran ice sheet sediments mainly comprise massive and cross bedded sand and gravels and rhythmically bedded clay and silt fine sand couplets interbedded with diamictons that were deposited by a range of mass flows of different viscosities although sediment stratigraphy and ice advance retreat patterns are well established for the puget lobe brittle and ductile deformation structures within and separating these sediment units are less well understood these structures record the nature of ice bed interactions taking place in subglacial and proglacial environments this study examines evidence for these processes and environments key deformation structures identified include open to overturned folds normal and reverse faults clastic dikes and hydrofractures and passive loading structures evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes sediment rheology and sediment system responses to changes in strain caused by ice bed interactions

extensive early and middle wisconsin glaciation on the western olympic peninsula washington and the variability of pacific moisture delivery to the northwestern united states abstract large glaciers descended western valleys of the olympic mountains six times during the last wisconsin glaciation terminating in the pacific coastal lowlands the glaciers constructed extensive landforms and thick stratigraphic sequences which commonly contain wood and other organic detritus the organic material coupled with stratigraphic data provides a detailed radiocarbon chronology of late pleistocene ice margin fluctuations the early wisconsin lyman rapids advance which terminated prior to ca 54 000 14c yr b p represented the most extensive ice cover subsequent glacier expansions included the hoh oxbow 1 advance which commenced between ca 42 000 and 35 000 14c yr b p the hoh oxbow 2 advance ca 30 800 to 26 300 14c yr b p the hoh oxbow 3 advance ca 22 000 19 300 14c yr b p the twin creeks 1 advance 19 100 18 300 14c yr b p and the subsequent undated twin creeks 2 advance the hoh oxbow 2 advance represents the greatest ice extent of the last 50 000 yr with the glacier extending 22 km further downvalley than during the twin creeks 1 advance which is correlative with the global last glacial maximum local pollen data indicate intensified summer cooling during successive stadial events because ice extent was diminished during colder stadial events precipitation not summer temperature influenced the magnitude of glaciation most strongly regional aridity independently documented by extensive pollen evidence limited ice extent during the last glacial maximum the timing of glacier advances suggests causal links with north atlantic bond cycles and heinrich events

channel evolution on the dammed elwha river washington usa abstract like many rivers in the western u s the elwha river washington has changed substantially over the past century in response to natural and human forcing the lower river is affected by two upstream dams that are slated for removal as part of a major river restoration effort in preparation for studying the effects of dam removal we present a comprehensive field and aerial photographic analysis of dam influence on an anabranching gravel bed river over the past century with the dams in place loss of the upstream sediment supply has caused spatial variations in the sedimentary and geomorphic character of the lower elwha river channel bed sediment is armored and better sorted than on the naturally evolving bed upstream of the dams on time scales of flood seasons the channel immediately below the lower dam is fairly stable but progresses toward greater mobility downstream such that the lowermost portion of the river responded to a recent 40 year flood with bank erosion and bed elevation changes on a scale approaching that of the natural channel above the dams in general channel mobility in the lowest 4 km of the elwha river has not decreased substantially with time enough fine sediment remains in the floodplain that given sufficient flood forcing the channel position sinuosity and braiding index change substantially the processes by which this river accesses new fine sediment below the dams rapid migration into noncohesive banks and avulsion of new channels allow it to compensate for loss of upstream sediment supply more readily than would a dammed river with cohesive banks or a more limited supply of alluvium the planned dam removal will provide a valuable opportunity to evaluate channel response to the future restoration of natural upstream sediment supply

radiocarbon age constraints on rates of advance and retreat of the puget lobe of the cordilleran ice sheet during the last glaciation abstract calibrated radiocarbon dates of organic matter below and above till of the last fraser glaciation provide limiting ages that constrain the chronology and duration of the last advance retreat cycle of the puget lobe in the central and southeastern puget lowland seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17 420 90 cal yr b p which is the closest limiting age for arrival of the glacier near the latitude of seattle a time distance curve constructed along a flowline extending south from southwestern british columbia to the central puget lowland implies an average glacier advance rate of ca 135 m yr the glacier terminus reached its southernmost limit ca 16 950 yr ago and likely remained there for ca 100 yr in the vicinity of seattle where the glacier reached a maximum thickness of 1000 m ice covered the landscape for ca 1020 yr postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16 420 cal yr b p and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum the average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes

evidence for earthquake induced subsidence about 1100 yr ago in coastal marshes of southern puget sound washington buried forest and high marsh soils indicate abrupt changes in relative sea level at four coastal localities in southern puget sound at little skookum inlet and red salmon creek douglas fir stumps in growth position are buried by salt marsh peat at localities along mcallister creek and the nisqually river high marsh soils are buried by tidal flat mud localized liquefaction coincided with submergence of the high marsh soil at mcallister creek dramatic changes in seed and diatom assemblages across these contacts confirm rapid submergence at little skookum inlet and red salmon creek salt marsh peat immediately above a buried forest soil contains diatoms indicative of low marsh and tidal flat environments at mcallister creek and nisqually river low marsh and tidal flat diatoms are abundant in laminated mud directly over high marsh peat inferences from modern analogs indicate at least 1 m of subsidence at each site and possibly up to 3 m at skookum inlet abrupt burial of lowland soils in southern puget sound is best explained by coseismic subsidence some of the submergence may be the result of coseismic compaction and postearthquake settlement widespread buried soils large amounts of subsidence coeval submergence across a wide area and ground shaking at the time of subsidence all point to a large earthquake between 1150 and 1010 cal yr b p in southern puget sound as the most likely cause of subsidence

pleistocene glacimarine sedimentation on the continental slope off vancouver island british columbia abstract cordilleran ice sheet activity has had a significant influence on glacimarine sediment transport and deposition on the western canadian continental slope resulting in distinct sediment facies here we present lithogenic sediment grain size distributions grains 250 m g 1 63 m 10 to 60 m and 2 to 4 m and mass accumulation rates mar from a marine core md02 2496 collected 50 km offshore of vancouver island british columbia the lithogenic fraction of sediment deposited on the slope increased as grain size decreased and sediment sorting increased at 30 ka when the cordilleran ice sheet grew into southern british columbia during the fraser glaciation as the ice sheet advanced onto the continental shelf near core md02 2496 between 19 and 17 ka the proximal ice margin dramatically increased lithogenic sediment mars glacimarine sedimentation at this time was associated with cyclic deposition of generally coarse poorly sorted sediment an 80 year cyclicity suggests the influence of 1 outburst floods 2 lunar or 3 solar cycles on tidewater outlet glacier discharge rapid ice sheet retreat at 17 ka is indicated by ice rafted debris ird deposition followed by the deposition of fine well sorted silt suggestive of iceberg discharge followed by rock flour in a meltwater plume lithogenic sediment mars decreased dramatically at the bolling with a brief return to coarse poorly sorted sediments during the younger dryas glacimarine sedimentation decreased by 10 ka as the cordilleran ice sheet extent diminished to the areal extent of modern ice fields

36cl dating of the classic pleistocene glacial record in the northeastern cascade range washington and are more degraded seventy six 36 cl dates for the moraines cluster in groups having mean ages 1 of 12 500 500 13 300 800 16 100 1100 19 100 3000 70 900 1500 93 100 2600 and 105 400 2200 years a still older highly weathered and eroded moraine is undated but likely is at least 165 000 years old the moraine ages and relative extent of the icicle creek glacier correspond closely to the ages and relative amplitude of july insolation minima at 47 5 n latitude they also are in accord with ages for glaciations in the european alps that were inferred by milutin milankovitch and colleagues in the 1920s based on calculations of summer insolation evidence that the greatest late pleistocene glacier advance occurred at the onset of the last glaciation during marine isotope substage 5d is consistent with a cooling climate and major glacier advances at that time elsewhere in north america and the eurasian arctic with a dramatic increase in global ice volume and with the shifting track of the jet stream over northwestern united states

beryllium 10 dating of the foothills erratics train in alberta canada indicates detachment of the laurentide ice sheet from the rocky mountains at 15 ka the foothills erratics train consists of large quartzite blocks of rocky mountains origin deposited on the eastern slopes of the rocky mountain foothills in alberta between 53 5 n and 49 n the blocks were deposited in their present locations when the western margin of the laurentide ice sheet lis detached from the local ice masses of the rocky mountains which initiated the opening of the southern end of the ice free corridor between the cordilleran ice sheet and the lis we use 10 be exposure dating to constrain the beginning of this decoupling based on a group of 12 samples well clustered in time we date the detachment of the western lis margin from the rocky mountain front to 14 9 0 9 ka this is 1000 years later than previously assumed but a lack of a latitudinal trend in the ages over a distance of 500 km is consistent with the rapid opening of a long wedge of unglaciated terrain portrayed in existing ice retreat reconstructions a later separation of the western lis margin from the mountain front implies higher ice margin retreat rates in order to meet the younger dryas ice margin position near the boundary of the canadian shield 2000 years later

younger dryas environments and human adaptations on the west coast of the united states and baja california on the pacific coast of the united states and baja california the younger dryas was one component of dynamic late pleistocene and holocene environmental changes changing climate sea level rise and shifting shorelines created ecological challenges for ancient coastal peoples and daunting challenges for archaeologists searching for early coastal sites this paper reviews the evidence for ecological change in this west coast region including shoreline changes that may have submerged or destroyed archaeological sites from this time period examining the regional record of human occupation dating to the younger dryas well dated coastal sites are limited to california s northern channel islands and isla cedros off baja california a small number of fluted points found in coastal areas may also date to the younger dryas but their context and chronology is not well defined review of the implications of these two data sets considers whether the early but discontinuous younger dryas archaeological record from the west coast might result from a migration of maritime peoples from northeast asia into the americas

younger dryas readvance in squamish river valley southern coast mountains british columbia abstract stratigraphy and landforms in the brohm creek basin and lowermost mamquam river valley provide evidence for a readvance of a valley glacier in the southern coast mountains of british columbia during the younger dryas interval at brohm creek till containing wood 10 500 and 10 700 14 c yr old ca 12 500 12 900 cal yr old overlies an ice contact terrace that is correlative with similar terraces at the mouth of mamquam river 11 km to the south and 900 m lower in elevation a line linking the two sites has a slope of 5 which is similar to slopes of termini of present day valley glaciers in the southern coast mountains we used these observations to reconstruct the younger dryas glacier in squamish valley at the head of howe sound the glacier deflected landslide debris derived from steep slopes at the head of cheekye river basin on the west flank of mt garibaldi southward to an ice marginal lake at the mouth of mamquam river foreset bedded sediments in the core of a large fan at the mouth of cheekye river indicate the glacier terminus had retreated up squamish valley beyond cheekye and mamquam rivers by 10 200 14 c yr bp 11 900 cal yr old radiocarbon ages on the oldest postglacial sediments in a kettle on the landslide debris show that stagnant ice in the study area had melted before 10 000 14 c yr bp 11 500 cal yr bp the readvance of the squamish valley glacier during the younger dryas chronozone was probably driven by a regional climate reversal

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

the legacy of pleistocene glaciation and the organization of lowland alluvial process domains in the puget sound region article i nfo alluvial rivers of the eastern puget lowland a landscape shaped by scour and fill from the cordilleran ice sheet continue to respond to patterns of deposition and scour by the last glacial age ice sheet 18 000 years after deglaciation topography revealed by valley cross sections created from high resolution lidar digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post glaciation slope area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts concavity indices in mountain headwaters 0 3b b0 9 compare to those of many world rivers 0 2b b1 0 but in the lowlands these indices differ between valleys created by subglacial fluvial erosion 5b b45 and post glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post glacial sea levels 1b b7 dramatic differences in river pattern landforms and dynamics occur in valleys having contrasting aggrading vs degrading and incomplete responses to pleistocene glaciation creating discrete valley scale hetero geneities in fluvial process domains along and between rivers these results point to the importance of valley scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from pleistocene glaciation they also point to the potential usefulness of slope area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes

large scale dam removal on the elwha river washington usa source to sink sediment budget and synthesis abstract understanding landscape responses to sediment supply changes constitutes a fundamental part of many problems in geomorphology but opportunities to study such processes at field scales are rare the phased removal of two large dams on the elwha river washington exposed 21 3 million m3 or 30 million tonnes t of sediment that had been deposited in the two former reservoirs allowing a comprehensive investigation of watershed and coastal responses to a substantial increase in sediment supply here we provide a source to sink sediment budget of this sediment release during the first two years of the project september 2011 september 2013 and synthesize the geomorphic changes that occurred to downstream fluvial and coastal landforms owing to the phased removal of each dam the release of sediment to the river was a function of the amount of dam structure removed the progradation of reservoir delta sediments exposure of more cohesive lakebed sediment and the hydrologic conditions of the river the greatest downstream geomorphic effects were observed after water bodies of both reservoirs were fully drained and fine silt and clay and coarse sand and gravel sediments were spilling past the former dam sites after both dams were spilling fine and coarse sediments river suspended sediment concentrations were commonly several thousand mg l with 50 sand during moderate and high river flow at the same time a sand and gravel sediment wave dispersed down the river channel filling channel pools and floodplain channels aggrading much of the river channel by 1 m reducing river channel sediment grain sizes by 16 fold and depositing 2 2 million m3 of sand and gravel on the seafloor offshore of the river mouth the total sediment budget during the first two years revealed that the vast majority 90 of the sediment released from the former reservoirs to the river passed through the fluvial system and was discharged to the coastal waters where slightly less than half of the sediment was deposited in the river mouth delta although most of the measured fluvial and coastal deposition was sand sized and coarser 0 063 mm significant mud deposition was observed in and around the mainstem river channel and on the seafloor woody debris ranging from millimeter size particles to old growth trees and stumps was also introduced to fluvial and coastal landforms during the dam removals at the end of our two year study elwha dam was completely removed glines canyon dam had been 75 removed full removal was completed 2014 and 65 of the combined reservoir sediment masses including 8 mt of fine grained and 12 mt of coarse grained sediment remained within the former reservoirs reservoir sediment will continue to be released to the elwha river following our two year study owing to a 16 m base level drop during the final removal of glines canyon dam and to erosion from floods with larger magnitudes than occurred during our study comparisons with a geomorphic synthesis of small dam removals suggest that the rate of sediment erosion as a percent of storage was greater in the elwha river during the first two years of the project than in the other systems comparisons with other pacific northwest dam removals suggest that these steep high energy rivers have enough stream power to export volumes of sediment deposited over several decades in only months to a few years these results should assist with predicting and characterizing landscape responses to future dam removals and other perturbations to fluvial and coastal sediment budgets

stratigraphic and geomorphologic evidence of three mis 2 glacial advances in the south fork hoh river valley olympic mountains washington usa the geomorphology and stratigraphy of the south fork hoh river sf hoh olympic mountains washington allow for greater understanding of marine oxygen isotope stage 2 mis 2 ice fluctuations glacial dynamics and sedimentation age control from optically stimulated luminescence and radiocarbon dating constrains deposited sediments associated with four late pleistocene ice marginal positions that formed under reduced ice volume conditions compared with mis 3 5 glaciers in the same drainage the earliest mis 2 ice margin extended into the main hoh river valley pre sf 1 28 ka to 23 0 ka after retreat the ice occupied three closely spaced ice marginal positions sf 1 3 that range in age from 22 0 ka to shortly after 18 7 ka while the sf 1 and sf 3 positions were previously identified as the twin creeks i and ii positions the intermediate sf 2 position had not been recognized moraines are composed of poorly sorted but stratified sediment and few tills diamicton units show evidence of water reworking this research documents a detailed record of mis 2 glaciation in a maritime setting in western north america and provides evidence of rapid mis 2 ice marginal fluctuations that likely reflect responses to millennial scale climatic fluctuations and may be relevant to understanding other complex mis 2 moraine sequences

the devils mountain fault zone an active cascadia upper plate zone of deformation pacific northwest of north america abstract the devils mountain fault zone dmfz extends east to west from washington state to just south of victoria british columbia in the northern strait of juan de fuca of canada and the usa recently collected geophysical data were used to map this fault zone in detail which show the main fault trace and associated primary and secondary conjugate strands and extensive northeast southwest oriented folding that occurs within a 6 km wide deformation zone the fault zone has been active in the holocene as seen in the offset and disrupted upper quaternary strata seafloor displacement and deformation within sediment cores taken close to the seafloor expression of the faults data suggest that the present dmfz and the re activated leech river fault may be part of the same fault system based on the length and previously estimated slip rates of the fault zone in washington state the dmfz appears to have the potential of producing a strong earthquake perhaps as large as magnitude 7 5 or greater within 2 km of the city of victoria

a record of late quaternary vegetation from davis lake southern puget lowland washington abstract pollen and macrofossil analyses of a core spanning 26 000 yr from davis lake reveal late pleistocene and holocene vegetational patterns in the puget lowland the core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units the late pleistocene pollen sequence records two intervals of tundra parkland vegetation the earlier of these has high percentages of picea gramineae and artemisia pollen and represents the vegetation during the evans creek stade fraser glaciation ca 25 000 17 000 yr b p the later parkland interval is dominated by picea tsuga mertensiana and gramineae it corresponds to the maximum ice advance in the puget lowland during the vashon stade fraser glaciation ca 14 000 yr b p an increase in pinus ontorta pollen between the two tundra parkland intervals suggests a temporary rise in treeline during an unnamed interstade after 13 500 yr b p a mixed woodland of subalpine and lowland conifers grew at davis lake during a period of rapid climatic amelioration in the early holocene the prolonged expansion of pseudotsuga and alnus woodland suggests dry temperate conditions similar to those of present rainshadow sites in the puget lowland more mesic forests of tsuga eterophylla thuja plicata and pseudotsuga similar to present lowland vegetation appeared in the late holocene ca 5500 yr b p

regional and local controls on postglacial vegetation and fire in the siskiyou mountains northern california usa article i nfo the siskiyou mountains of northwestern california and southwestern oregon are a floristic hotspot and the high diversity of conifers there likely results from a combination of geological ecological climatological and historical factors to evaluate how past climate variability has influenced the composition structure and fire regime of the siskiyou forests pollen charcoal and lithological evidence was examined from two lakes along a moisture gradient to reconstruct the vegetation fire and climate history the late glacial period was characterized by subalpine parkland and infrequent fire at both sites during the late glacial early holocene transition period subalpine parkland was replaced by a closed forest of pinus cupressaceae abies and pseudotsuga and more frequent fires a 1000 years earlier at the wetter site and it is likely that reduced pacific ocean upwelling created warmer drier conditions at the coast in the early holocene pinus cupressaceae were less abundant and fire less frequent at the coastal site during a period of increased coastal upwelling and fog production in the late holocene abies pseudotsuga pinus and quercus vaccinifolia increased in the forest at both sites suggesting a widespread response to cooling fewer fires at the wetter site may account for the abundance of picea breweriana within the last 1000 years the comparison of the two records implies that large scale controls in climate during the last 14 000 cal yr bp have resulted in major changes in vegetation and fire regime asynchrony in the ecosystem response of wetter and drier sites arises from small scale spatial variations in effective moisture and temperature resulting from topographically influenced microclimates and coastal to inland climate gradients

post glacial sea level change along the pacific coast of north america abstract sea level history since the last glacial maximum on the pacific margin of north america is complex and heterogeneous owing to regional differences in crustal deformation neotectonics changes in global ocean volumes eustasy and the depression and rebound of the earth s crust in response to ice sheets on land isostasy at the last glacial maximum the cordilleran ice sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore this combined with different tectonic settings along the coast resulted in divergent relative sea level responses during the holocene for example sea level was up to 200 m higher than present in the lower fraser valley region of southwest british columbia due largely to isostatic depression at the same time sea level was 150 m lower than present in haida gwaii on the northern coast of british columbia due to the combined effects of the forebulge raising the land and lower eustatic sea level a forebulge also developed in parts of southeast alaska resulting in post glacial sea levels at least 122 m lower than present and possibly as low as 165 m on the coasts of washington and oregon as well as south central alaska neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea level changes

deglacial ocean warming and marine margin retreat of the cordilleran ice sheet in the north pacific ocean abstract a new high resolution planktonic foraminiferal mg ca based ocean temperature record has been generated for deep sea core md02 2496 sited offshore of vancouver island western canada during the last deglaciation 21 12 ka the relationship between cordilleran ice sheet cis retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in md02 2496 that capture tidewater glacier response to surface ocean thermal forcing at cis maximum extent the marine margin of the ice sheet advanced onto the continental shelf during this interval ocean temperatures recorded by surface dwelling globigerina bulloides remained a relatively constant 7 5 c while subsurface dwelling neogloboquadrina pachyderma s recorded temperatures of 5 c these ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern alaskan tidewater glacial systems during the deglacial retreat of the cis the n pachyderma temperature record shows two distinct warming steps of 2 and 2 5 c between 17 2 16 and 15 5 14 ka respectively coincident with ice rafting events from the cis while g bulloides records an 3 c warming from 15 to 14 ka we hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from cis tidewater glaciers during the initial stages of deglaciation

postglacial rebound at the northern cascadia subduction zone postglacial rebound is the response of the earth to the decay of ice sheets a postglacial rebound model explains crustal tilting and rapid uplift at the northern cascadia subduction zone that occurred during retreat of the cordilleran ice sheet observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13 5 14 ka 14c yr ago and rapid sea level fall land uplift at 12 12 5 ka modelled mantle viscosity values range from 5 1018 to 5 1019 pa s and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes 1018 1019 pa s no lower limit to subduction zone mantle viscosity is apparent from our model but viscosity values equal to or larger than 1020 pa s are de nitely ruled out our modelled subduction zone viscosity values are smaller than most upper mantle viscosity estimates derived from postglacial rebound studies of tectonically less active regions 1020 1021 pa s the rapid observed uplift at 12 ka requires in addition to a low mantle viscosity rapid unloading from a sudden collapse of remaining coastal portions of the southern cordilleran ice sheet the sudden collapse provides 0 18 m of global eustatic sea level rise approximately 0 7 of the sea level rise associated with melt water pulse ia predictions of a global postglacial rebound model ice 3g with a 1021 pa s upper mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle owing to the low viscosity values and resulting rapid recovery of glacial deformation our model predicts present day postglacial rebound uplift rates at least 10 times smaller than ice 3g less than about 0 1 mm yr as the ice 3g adjustments were substantial this indicates the need for re evaluation of the geodetic data 2000 elsevier science ltd all rights reserved

paleoseismic evidence for late holocene tectonic deformation along the saddle mountain fault zone southeastern olympic peninsula washington abstract trench and wetland coring studies show that northeast striking strands of the saddle mountain fault zone ruptured the ground about 1000 years ago generating prominent scarps three conspicuous subparallel fault scarps can be traced for 15 km on light detection and ranging lidar imagery traversing the foothills of the southeast olympic mountains the saddle mountain east fault the saddle mountain west fault and the newly identified sund creek fault uplift of the saddle mountain east fault scarp impounded stream flow forming price lake and submerging an existing forest thereby leaving drowned stumps still rooted in place stratigraphy mapped in two trenches one across the saddle mountain east fault and the other across the sund creek fault records one and two earthquakes respectively as faulting juxtaposed miocene age bedrock against glacial and postglacial deposits although the stratigraphy demonstrates that reverse motion generated the scarps slip indicators measured on fault surfaces suggest a component of left lateral slip from trench exposures we estimate the postglacial slip rate to be 0 2 mm yr and between 0 7 and 3 2 mm yr during the past 3000 years integrating radiocarbon data from this study with earlier saddle mountain fault studies into an oxcal bayesian statistical chronology model constrains the most recent paleoearthquake age of rupture across all three saddle mountain faults to 1170 970 calibrated years cal b p which overlaps with the nearby m w 7 5 1050 1020 cal b p seattle fault earthquake an earlier earthquake recorded in the sund creek trench exposure dates to around 3500 cal b p the geometry of the saddle mountain faults and their near synchronous rupture to nearby faults 1000 years ago suggest that the saddle mountain fault zone forms a western boundary fault along which the fore arc blocks migrate northward in response to margin parallel shortening across the puget lowland

southern hemisphere climate variability forced by northern hemisphere ice sheet topography an antarctic ice core reveals that during the last ice age the topography of northern hemisphere ice sheets shifted tropical pacific convection eastward increasing climate variability in the high southern latitudes during glacial maxima ice covered vast areas of the northern hemisphere and had a broad influence across the global climate system tyler jones and colleagues show that climate variability in the southern hemisphere was influenced by these large northern hemisphere ice sheets and was about twice as high during the last glacial maximum than in the warmer holocene that followed the ice sheets created more elevated and brighter surfaces than at present and this altered the location of tropical convection and the atmospheric pathways that link the tropics to west antarctica the results reveal the intimate climatic link between the high latitudes and the key role of the tropics as an interhemispheric mediator the presence of large northern hemisphere ice sheets and reduced greenhouse gas concentrations during the last glacial maximum fundamentally altered global ocean atmosphere climate dynamics1 model simulations and palaeoclimate records suggest that glacial boundary conditions affected the el nino southern oscillation2 3 a dominant source of short term global climate variability yet little is known about changes in short term climate variability at mid to high latitudes here we use a high resolution water isotope record from west antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the last glacial maximum as during the ensuing holocene epoch the past 11 700 years climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical pacific and west antarctica owing to a shift in the mean location of tropical convection this shift in turn can be attributed to the influence of topography and albedo of the north american ice sheets on atmospheric circulation as the planet deglaciated the largest and most abrupt decline in teleconnection strength occurred between approximately 16 000 years and 15 000 years ago followed by a slower decline into the early holocene

late holocene earthquakes on the toe jam hill fault seattle fault zone bainbridge island washington five trenches across a holocene fault scarp yield the first radiocarbon measured earthquake recurrence intervals for a crustal fault in western washington the scarp the first to be revealed by laser imagery marks the toe jam hill fault a north dipping backthrust to the seattle fault folded and faulted strata liquefaction features and forest soil a horizons buried by hanging wall collapse colluvium record three or possibly four earthquakes between 2500 and 1000 yr ago the most recent earthquake is probably the 1050 1020 cal calibrated yr b p a d 900 930 earthquake that raised marine terraces and triggered a tsunami in puget sound vertical deformation estimated from stratigraphic and surface offsets at trench sites suggests late holocene earthquake magnitudes near m7 corresponding to surface ruptures 36 km long deformation features recording poorly understood latest pleistocene earthquakes suggest that they were smaller than late holocene earthquakes postglacial earthquake recurrence intervals based on 97 radiocarbon ages most on detrital charcoal range from 12 000 yr to as little as a century or less corresponding fault slip rates are 0 2 mm yr for the past 16 000 yr and 2 mm yr for the past 2500 yr because the toe jam hill fault is a backthrust to the seattle fault it may not have ruptured during every earthquake on the seattle fault but the earthquake history of the toe jam hill fault is at least a partial proxy for the history of the rest of the seattle fault zone

mass balance and sliding velocity of the puget lobe of the cordilleran ice sheet during the last glaciation an estimate of the sliding velocity and basal meltwater discharge of the puget lobe of the cordilleran ice sheet can be calculated from its reconstructed extent altitude and mass balance lobe dimensions and surface altitudes are inferred from ice limits and flow direction indicators net annual mass balance and total ablation are calculated from relations empirically derived from modern maritime glaciers an equilibrium line altitude between 1200 and 1250 m is calculated for the maximum glacial advance ca 15 000 yr b p during the vashon stade of the fraser glaciation this estimate is in accord with geologic data and is insensitive to plausible variability in the parameters used in the reconstruction resultant sliding velocities are as much as 650 m a at the equilibrium line decreasing both up and downglacier such velocities for an ice sheet of this size are consistent with nonsurging behavior average meltwater discharge increases monotonically downglacier to 3000 m3 sec at the terminus and is of a comparable magnitude to ice discharge over much of the glacier s ablation area palcoclimatic inferences derived from this reconstruction are consistent with previous independently derived studies of late pleistocene temperature and precipitation in the pacific northwest

glacio isostatic response of the puget sound area washington proglacial lake shorelines in the puget sound area were distorted by the isostatic response associated with recession of the cordilleran ice sheet about 18 000 13 500 yr ago the shorelines which are highest near the east west midpoint of the elongate lowland are upwarped northward with a regression slope of 0 85 0 04 m km 1 departures from the trend may have been caused by holocene tectonic warping calibrating this lacustrine record with data from the everson marine limit permits the actual rather than relative uplift to be estimated and contoured the high degree of isostatic equilibrium attained at least 50 during the brief loading hemicycle suggests that the mantle beneath this part of the cascadia subduction zone has anomalously low viscosity and strength crustal strain associated with the loading unloading cycle in the south central lowland appears to he correlated with the pattern of quaternary faulting and seismicity

two post glacial earthquakes on the saddle mountain west fault southeastern olympic peninsula washington abstract two earthquakes ruptured the western strand of the saddle mountain fault after the cordilleran ice sheet began its retreat from the puget sound lowland about 17 ka the fault system includes multiple northeast trending thrust faults on the southeastern olympic peninsula delineated on light detection and ranging topography by prominent east side up scarps that deform vashon till and extend over 6 7 km the cargill creek trench on the saddle mountain west fault exposed faulted drift and postglacial colluvium below a 1 2 m high scarp steeply dipping northeast striking faults form a 10 m wide zone beneath the scarp structural relations in the trench indicate that two earthquakes produced at least 1 m of vertical separation additional folding or faulting beyond the trench raised the scarp to a total height of 1 7 m aligned cobbles dipping approximately 40 to the north attest to earthquake related tilting a cobble firmly lodged in till and split by a secondary fault indicates that hanging wall deformation involved a dextral component of slip however slip on the master fault may have involved a left lateral component based on slip indicators at adjacent trench sites in the region a single charcoal age and estimates of the onset of ice retreat limit the time of the oldest earthquake to 17 7 7 ka the most recent event occurred after 1 7 ka and may be the same earthquake that dammed price lake about 1100 yr ago known from related studies empirical relations suggest that the most recent earthquake was about m 7 0 2 and produced an estimated total slip of 1 3 1 7 m the total postglacial slip rate ranges from 0 1 to 0 3 m k yr these results support the hypothesis that the saddle mountain fault is part of a larger fault system that accommodates transpressive strain as the puget lowland crust migrates around the eastern flank of the olympic mountains

variable responses of western u s glaciers during the last deglaciation cosmogenic 10 be exposure ages from moraines in the wallowa mountains oregon identify two maximal late pleistocene glaciations at 21 1 6 0 4 ka and 17 0 6 0 3 ka and a minor glacial event at 10 2 6 0 6 ka our new high resolution chronology integrated with other well dated glacial records from the western united states demonstrates sub stantial differences in the synoptic responses of western u s glaciers to climate forcing associated with the global last glacial maximum and subsequent millennial scale events originating in the north atlantic region these variable synoptic glacier responses identify large changes in the relative contributions of regional to global controls on the climate of the western united states that accompanied the deglaciation

high resolution seismic reflection imaging of growth folding and shallow faults beneath the southern puget lowland washington state abstract marine seismic reflection data from southern puget sound washington were collected to investigate the nature of shallow structures associated with the tacoma fault zone and the olympia structure growth folding and probable holocene surface deformation were imaged within the tacoma fault zone beneath case and carr inlets shallow faults near potential field anomalies associated with the olympia structure were imaged beneath budd and eld inlets beneath case inlet the tacoma fault zone includes an 350 m wide section of south dipping strata forming the upper part of a fold kink band coincident with the southern edge of an uplifted shoreline terrace an 2 m change in the depth of the water bottom onlapping postglacial sediments and increasing stratal dips with increasing depth are consistent with late pleistocene to holocene postglacial growth folding above a blind fault geologic data across a topographic lineament on nearby land indicate recent uplift of late holocene age profiles acquired in carr inlet 10 km to the east of case inlet showed late pleistocene or holocene faulting at one location with 3 to 4 m of vertical displacement south side up north of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad tacoma fault zone seismic reflection profiles across part of the olympia structure beneath southern puget sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding directly beneath one of these faults a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw suggesting strike slip motion deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset consistent with strike slip faulting these faults and folds indicate that the tacoma fault and olympia structure include active structures with probable postglacial motion