post glacial relative sea level isostasy and glacial history in icy strait southeast alaska usa abstract we use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level rsl history in northern southeast alaska rsl fell below its present level around 13 900 cal yr bp suggesting regional deglaciation was complete by then rsl stayed at least several meters below modern levels until the mid holocene when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby glacier bay this fluctuating rsl rise likely reflects the episodic but progressive advance of ice in glacier bay that started around 6000 cal yr bp after that time rsl low stands probably signaled minor episodes of glacier retreat thinning that triggered isostatic rebound and land uplift progressive down fjord advance of the glacier bay glacier during the late holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly only after the glacier reached an exposed position protruding into icy strait ca ad 1750 did its terminus succumb a century before the climate changes that marked the end of the little ice age to the catastrophic retreat that triggered the rapid isostatic rebound and rsl fall occurring today in icy strait

evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years although old diagrams have been extensively used the recent ones based on discriminant functions of ratio variables with or without log transformation proposed during 2004 2010 for the discrimination of four tectonic settings of island arc continental rift ocean island and mid ocean ridge were newly evaluated to show their high success rates of 57 3 100 and 58 5 100 for major element and immobile element based diagrams respectively for the continental arc of the andes evaluated for its similarity to island arc these four sets of diagrams showed success rates of 62 1 83 8 these four sets of five diagrams per set were therefore used to infer tectonic setting of the mexican volcanic belt mvb los tuxtlas volcanic field ltvf and central american volcanic arc cava using this approach the mvb especially its western central and eastern parts and the ltvf of southern mexico show a dominantly continental rift setting and the cava shows an arc setting the west central part of the mvb is consistent with dual tectonics of arc and rift these results confirm the application of an unusual mantle upwelling rift model for the mexican on land volcanism whereas the conventional plate tectonic subduction model seems to be applicable for the cava from guatemala to north western costa rica

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

late quaternary sea levels and crustal movements coastal british columbia late quaternary sea level fluctuations on the british columbia coast have been established from studies of terrestrial and marine sediments and landforms these studies indicate that the sea level history of mainland british columbia and eastern vancouver island is very different from that of the queen charlotte islands and western vancouver island specifically in the former areas there was a rapid rise of submerged coastal lowlands between about 13 000 and 10 000 years ago emergence culminated about 6000 9000 years ago depending on the locality when the sea relative to the land was 12 m or more lower than at present in some areas during middle and late holocene time relative sea level rose on the mainland coast and at least locally on eastern vancouver island resulting in inundation of coastal archaeological sites and low lying terrestrial vegetation tidal records and precise levelling suggest ongoing submergence of at least part of this region in contrast shorelines on the queen charlotte i

geological perspectives on the monte verde archeological site in chile and pre clovis coastal migration in the americas discovery of the monte verde archeological site in chile overturned the previous consensus that the first americans into the new world from asia were the makers of clovis projectile points and rejuvenated the hypothesis that migration through the americas occurred largely on portions of the pacific continental shelf exposed by pleistocene drawdown in eustatic sea level the postulate of travel along a paleoshoreline now hidden underwater is an attractive means to posit pre clovis human movement southward from beringia to chile without leaving traces of migration onshore geologic analyses of the pleistocene paleoenvironment at monte verde and of the morphology of the potential migration route along the continental shelf raise questions that have not been fully addressed the periglacial setting of monte verde may call its antiquity into question and the narrowness of the pacific continental shelf of the americas makes it unlikely that people could travel the length of the americas without impacting ground still onshore and no farther inland than monte verde itself geological perspectives on monte verde and coastal migration jointly suggest that the clovis first hypothesis for peopling the new world may have been abandoned prematurely

the 1998 casita volcano flank failure revisited new insights into geological setting and failure mechanisms abstract a flank collapse occurred at the casita volcano in nicaragua on 30 october 1998 during hurricane mitch the collapse transformed into a disastrous lahar that completely buried two small towns 6 km downstream killing about 2500 people destroyed small settlements and disrupted the pan american highway based on the knowledge acquired during previous investigations with additional unpublished field data and observations this study provides a comprehensive review of all previous studies published and unpublished on the 1998 casita lahar and new insights into the initial flank collapse and the current stability the knowledge on pre and post failure geometry geology lithology tectonics and stratigraphy of the scarp area is improved and a summary of available geotechnical data is provided lithological characteristics that were significant in the initial flank collapse and failure mechanism were identified the location of the failure surface was more precisely defined and the number and sequence of stages in the initial failure presented in previous studies have been confirmed slope stability analyses were carried out using limit equilibrium methods geological interpretations analysis of digital elevation models and geotechnical back analyses confirmed that the flank collapse took place in three stages involving both the northern and southern areas of the scarp and occurred continuously during a time interval of seconds to a few minutes in the first stage failure initiated in a highly fractured and altered volcanic breccia in the northern area of the scarp which released a volume of 260 000 m3 the flow that developed from this failure removed colluvium deposits at the toe of the slope in the southern part in not more than 40 s this rapid removal of the colluvium triggered a second stage which comprised 640 000 m3 and consisted in the failure of the southern part of the scarp by the sliding of a fractured volcanic breccia over a unit of clay rich pyroclastic deposits the third and final stage consisted in a failure of the remaining breccia and the overlying fractured lavas in the northern area and involved a volume of 690 000 m3 the fact that future events can affect some remaining settlements and the segment of the pan american highway between chinandega and leon motivated an analysis of the stability of the remaining slope using parameters calibrated in the back analyses of the 1998 flank failure the results indicated that the remaining slope is stable as long as groundwater levels in the northern and southern area are deeper than 65 m and 90 m respectively relative to the points of maximum elevation on the analysed section and the colluvium deposits in the southern area are not removed from the toe of the slope

geology of the san cristobal volcanic complex nicaragua abstract the san cristobal volcanic complex is located in northwestern nicaragua near the city of chinandego five volcanic centers occur within this group the youngest and tallest volcano is san cristobal which erupted repeatedly throughout the 16th and 17th centuries renewed low level volcanic activity beginning in 1971 continues to the present examination of prehistoric deposits indicates that strombolian to moderately strong vulcanian eruptions are typical of san cristobal with effusion of lava possible from both the summit and lower flanks of the cone of potential volcanic hazards associated with this mountain the most serious to neighboring urban areas is heavy tephra fall the four other volcanoes of the san cristobal complex are in various stages of development and erosion only la casita shows evidence of possible future eruptive activity extrusive rocks of the volcanic complex are dominantly tholeiitic to calc alkaline basalts and andesites showing chemical affinity with island arc lavas dacitic domes and pumice layers are associated with at least two other volcanoes in the complex

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

unsteady seepage applied to lining design in stilling basins abstractcases of damages experienced in stilling basins and on the toe of chute spillways are recognized to be due to global instantaneous uplift force resulting from imbalance between the instantaneous pressure distribution both above and below slabs the latter is due to pressure fluctuation propagation forced though unsealed slab joints in the past several theoretical approaches were developed to estimate the uplift contribution due to pressure transmission underneath the slabs in the paper a model is presented based on unsteady flow analysis of seepage through porous media that shows that the propagation models proposed in literature are particular cases of this more comprehensive formulation in addition the use of the unsteady seepage model makes it possible to account for finite thickness foundation layers typical in the cases of earth dams rock fill dams and in other dam types whenever the slabs are posed on alluvial substrates experimental results obtained in laboratory facilities as

late pleistocene coastal paleogeography of the queen charlotte islands british columbia canada and its implications for terrestrial biogeography and early postglacial human occupation molluscs sediment lithology and published sub bottom profiles are used to deduce sea levels outline the influence of glacially induced crustal displacement and reconstruct the paleoenvironment of the northeast pacific late quaternary coastline geo spatial modelling shows subaerially exposed land that could have been inhabited by plants and animals and also coastally migrating early north american peoples ice free terrain present by at least 13 790 150 14 c years bp a land bridge and edible molluscs are identified queen charlotte islands qci late pleistocene coastal paleogeography may assist in explaining the biogeography of many terrestrial plant and animal species along the broader northeastern pacific margin and provide evidence for researchers seeking late pleistocene early holocene glacial refugia late pleistocene early holocene coastlines that are not drowned and that may harbour early archaeological sites are identified along the western qci where migrants probably first travelled and the westernmost british columbia mainland where the effects of glacial ice were reduced

plate boundary localization slip rates and rupture segmentation of the queen charlotte fault based on submarine tectonic geomorphology abstract linking fault behavior over many earthquake cycles to individual earthquake behavior is a primary goal in tectonic geomorphology particularly across an entire plate boundary here we examine the 1150 km long right lateral queen charlotte fairweather fault system using comprehensive multibeam bathymetry data acquired along the queen charlotte fault qcf offshore southeastern alaska and western british columbia fine scale analysis of tectonic geomorphology allowed us to identify and reconstruct 184 strike slip piercing points over a 630 km stretch of the qcf age constraints from glacial recession and offshore sedimentation patterns yield a consistent slip rate of 50 57 mm yr since 17 12 ka the fastest rate for a continent ocean strike slip fault on earth these slip rates equal or exceed estimates of pacific north america pa na relative motion from global plate reconstructions indicating that pa na motion is highly localized the qcf cuts the seafloor along a narrow and unusually straight trace for its entire length and multiple fault traces are observed only at local step overs the geometry and behavior of the qcf over many earthquake cycles is simple and typical of mature faults with relatively homogeneous stress fields since the qcf is the primary pa na plate boundary we used the trace of the qcf to define the small circle path for relative plate motion and computed the associated euler pole predicted along strike obliquity variations based on the new pole agree with observed tectonic geomorphology and suggest that previous global plate reconstructions overestimated the degree of oblique convergence along the qcf we also find that subtle long wavelength 75 150 km bends and discrete step overs appear to define the endpoints of m 7 earthquakes suggesting that obliquity and resultant fault geometry may control rupture segmentation and asperity development lastly the agreement between predicted obliquity and tectonic geomorphology along the entire length of qcf compelled a reevaluation of regional tectonic models in the north the eastern yakatat terrane appears to be translating northwest with the pacific plate and slip transferred from the qcf to the fairweather fault results in 20 mm yr of convergence along the southern st elias mountains in the south we predict a reduced rate of convergence along the qcf west of haida gwaii 5 6 mm yr of shortening on average relative to previous studies our results support a model for transpression and strike slip partitioning along the edge of a hot and weak pacific plate leading to crustal thickening and growth of the queen charlotte terrace to the west of haida gwaii

application of seismic stratigraphy and sedimentology to regional hydrogeological investigations an example from oak ridges moraine southern ontario canada hydrogeological models need to be supported by a clear understanding of the subsurface geology to provide effective assessment flow modelling or management of groundwater regimes this paper illustrates how geophysical and sedimentological data can be used to significantly improve watershed scale hydrostratigraphic models by advancing our understanding of the subsurface through regional hydrogeological investigations in the greater toronto area the example of a 3 km shallow seismic reflection survey that traverses a buried channel within bowmanville creek watershed oak ridges moraine ontario illustrates a basis for linking geophysical and sedimentological properties to regional hydrostratigraphic parameters seismic reflection methods plus seismic stratigraphy and a well constrained three dimensional geological framework have helped to i identify regional hydrostratigraphic units ii define properties and trends of these units facies iii improve depositional models that assist hydrogeological

review of the utility of infrared remote sensing for detecting and monitoring volcanic activity with the case study of shortwave infrared data for lascar volcano from 2001 2005 this chapter provides a historical review of the use of infrared remote sensing for the monitoring of volcanic activity it 1 examines the theoretical basis for infrared observations of thermally anomalous volcanic features 2 presents the various sensors that have been used and are currently available and 3 describes the techniques that have been developed to analyse such data the chapter ends with a case study of data derived from advanced spaceborne thermal emission and reflection radiometer shortwave infrared observations of lascar volcano in chile this case study aims to highlight the utility of infrared observations in volcano logical studies assessing the various techniques that can be used and examining the different factors which influence these analyses the chapter ends discussing future prospects for volcanic infrared remote sensing

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

late quaternary geology of eastern graham island queen charlotte islands british columbia a reconnaissance study of quaternary sediments exposed in coastal bluffs on eastern graham island has revealed the presence of two major till units each of which is underlain by glaciomarine stony mud outwash sand and gravel and laminated to massive silt and sand of undetermined origin sediment units below the surface drift are older than the radiocarbon dating limit sediments above this drift provide a nearly continuous record of geologic events from before 16 000 years bp until the present stratigraphic evidence and radiocarbon dates indicate that 1 late wisconsin glaciation of the coastal lowlands of graham island was weak and of short duration and 2 a period of low sea levels during late pleistocene time was followed by a transgression that culminated about 7500 8000 years ago when the sea was about 15 m higher relative to the land than at present marine regression during middle and late holocene time produced wave cut scarps wave cut benches overlain by littoral sediments bars spits and beach and dune ridges

port eliza cave north american west coast interstadial environment and implications for human migrations abstract the timing of late pleistocene glacial advance retreat relative sea level and environmental viability between 25 and 12 5 ka 14 c yrs bp remain a key issue in the feasibility of a coastal migration route for the first north americans this is discussed on the basis of stratigraphic radiometric and faunal data for port eliza cave a raised sea cave on the west coast of vancouver island british columbia ice cover is indicated by the occurrence of 2 m of laminated clay representing deposition in a subglacial lake from immediately below this clay a diverse vertebrate fauna of marmot vole marten cervid and various species of birds and fish was recovered yielding ages of 18 16 ka these dates and others from the region show that ice cover on the outer coast was brief from ca 15 5 14 ka the fish species indicate that relative sea level was close to the cave and that salmon runs were likely present the terrestrial vertebrate fauna is consistent with a cool open parkland environment with maximum summer temperatures cooler than present these conditions lasted until at least 16 ka with a diverse fauna and favorable climate humans could have survived here on a mixed marine terrestrial diet confirming the viability of the coastal migration hypothesis for this portion of the route

monitoring active volcanoes and mitigating volcanic hazards the case for including simple approaches abstract simple approaches to problems brought about eruptions and their ensuing hazardous effects should be advocated and used by volcanologists while awaiting more sophisticated remedies the expedients we advocate have all or many of the following attributes only locally available materials are required no extensive training of operators or installation is necessary they are affordable and do not require foreign aid or exports they are often labor intensive and are sustainable without outside assistance where appropriate the involvement of local residents is advocated examples of simple expedients which can be used in forecasting or mitigating the effects of crises emphasize the relative ease and the less elaborate requirements with which simple approaches can be activated emphasis is on visual observations often by untrained observers simple meteorogical measurements observations of water level in lakes temperature and chemistry of springs and fumaroles new springs and collapse areas and observations of volcanic plumes simple methods are suggested which can be applied to mitigating damage from mudflows nuees ardentes tephra falls and gas discharge a review in hindsight at ruiz includes the use of both chemical indicators and simple mudflow alarms simple expedients are sufficiently effective that any expert volcanologist called to aid in a crisis must include them in the package of advice offered simple approaches are a critical and logical complement to highly technical solutions to hazardous situations

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

late pleistocene terrestrial deposits on the continental shelf of western canada evidence for rapid sea level change at the end of the last glaciation a paleosol with in situ rooted plant remains has been found in a core at a water depth of 95 m on the central continental shelf of british columbia fluvial sediments associated with the paleosol are sharply overlain by lagoonal or shallow pond sediments these in turn are overlain by shallow marine ediments radiocarbon dates on wood fragments and root recovered from the cored sediments indicate that relative sea level was at least 95 m lower 10 500 yr b p and that the core site was rapidly transgressed by the sea shortly thereafter this rapid transgression was contemporaneous with an equally rapid regression at the heads of fiords on the british columbia mainland to the east the two are probably genetically linked and a result of late pleistocene deglaciation and the migration and collapse of a glacial forebulge our evidence indicates that large areas of the british columbia continental shelf were subaerially exposed 11 10 ka this may have facilitated the southward migration of early humans from beringia into mid continental north america at the end of the pleistocene

structurally controlled hydrocarbon seeps on a glaciated continental margin hecate strait offshore british columbia abstract this paper describes structurally controlled gas seeps and their influence on seafloor morphology at sites within queen charlotte basin qcb a sedimentary basin situated offshore british columbia western canada numerous surficial and shallow sediment features related to both ice cover and shallow gas have been identified in high resolution multichannel seismic huntec deep towed seismic multibeam bathymetry and backscatter and piston core data that were acquired over a 10 km by 10 km grid in an eastern part of qcb pockmarks seafloor mounds and iceberg ploughmarks are visible in the multibeam data small scale folds vertical blank zones and acoustic turbidity are observed in the huntec data the multichannel seismic data show a faulted anticline phase reversed bright spots zones of low instantaneous frequency and velocity pull ups one seafloor mound lies directly above a shallow fault that offsets an asymmetric fold the remaining mounds lie either above or in close proximity to asymmetric folds that are faulted bright spots are observed along some fault traces and within a cut and fill sequence at two way travel times between 0 42 and 1 0 s velocity pull ups are observed in the multichannel data below gas expansion voids present in piston cores backscatter data show that seafloor mounds are highly reflective compared to the surrounding seafloor these observations indicate that gas has been migrating upward through the rock column and expelled into the shallow sediments the shallow gas has been biologically mediated to form carbonate sediments within and around seafloor mounds shallow gas has also deformed surficial sediments into positive relief mounds and negative relief pockmarks

metal enrichment and magnetic properties of core sediments from the eastern yellow sea east asia implications for paleo depositional change during the late pleistocene holocene transition abstract to investigate the paleo depositional environments sediment cores yj1 and yj2 from a tidal flat of the eastern yellow sea were analyzed for the vertical variations of metal concentrations particle size clay mineralogy magnetic properties and total organic carbon content toc fe and mn concentrations determined by both partial and total acid extraction increased at 15 m depth in yj1 and 10 m in yj2 the layer directly below these fe rich brownish horizons showed dramatic decreases in clay mineral content and trace metals zn pb cu cr co ni and as but increases in sand fraction magnetic susceptibility and toc all results were inverse in the upper metal rich layer these dramatic changes in multi parameters are likely due to an environmental change during the late pleistocene holocene transition the rapid environmental change sand rich and oxic clay rich and anoxic resulted in aqueous dissolution of redox sensitive metals e g fe and mn from the lower sandy layer materials the dissolved metals diffused upward and concomitantly were immobilized within the upper clay rich layer the reprecipitated fe or mn hydro oxides then scavenged trace metals by coprecipitation and or adsorption this study suggests that metal distribution patterns can provide new insights into the paleo depositional processes during the pleistocene holocene period

delaciation of the prince rupert kitimat area british columbia late wisconsinan sediments in the prince rupert kitimat area of west central british columbia were deposited in an isostatically depressed marine environment affected by grounded tidewater glaciers the most common sediments are 1 massive bedded and laminated muds and 2 stratified sand and gravel the former are accumulations of clay and silt size detritus transported in suspension from the mouths of meltwater streams and possibly in turbidity flows generated by submarine slope failures the muds locally contain scattered ice rafted stones fossil marine molluscs and foraminifera the main sand and gravel deposits are elevated deltas including both small incised fan shaped forms at the margins of the main valleys and enormous ice contact delta sandur complexes on the floor of kitsumkalum kitimat trough the largest valley in the study area delaciation occurred by downwasting and complex frontal retreat between about 13 000 and 10 000 bp the open outer coast became ice free first in response

the skipjack island fault zone an active transcurrent structure within the upper plate of the cascadia subduction complex abstract the skipjack island fault zone has been mapped in the san juan islands between vancouver island canada and the washington state mainland usa a decade ago interpretation of multibeam sonar seafloor imagery revealed that skipjack island an east west striking sedimentary bedrock outcrop was a fault controlled structural feature a major fault separates skipjack island from a deformed sedimentary bedrock outcrop on the seafloor to the north recently the skipjack island fault zone s morphology and extent have been explored both to the west and east of the island using multibeam echosounder bathymetry seismic reflection profiles and sediment cores the character of the skipjack island fault zone is well defined locally by the interpreted seismic reflection profiles which show active faults that displace sediments deposited since the last glacial maximum the central part of the fault zone near skipjack island appears as a near vertical structure in the shallow subsurface that has been subjected to left lateral motion as evidenced by a bedrock exposure on the seabed north of the island where folded strata bend eastward against the fault the result of drag from fault motion interpretations of recent geophysical data suggest an extension of the skipjack island fault zone farther to the west where it trends towards and possibly connects with the fulford fault on vancouver island and to the east where it either terminates north of lummi island or continues eastward onto the mainland the skipjack island fault zone is interpreted to be the northern boundary of the san juan archipelago with the devils mountain fault zone being the southern boundary both fault zones represent the longest continuous faults of the san juan archipelago this newly mapped fault zone and its zone of deformation to the north may represent the northern boundary of the cascadia forearc potential sesimicity of the skipjack island fault zone and its proximity to the steep unstable northeastern side of orcas island and the southern front of the fraser river delta poses a geohazads problem in the form of earthquakes landslides submarine slides and tsunamis

late glacial vegetation dynamics of the queen charlotte islands and adjacent continental shelf british columbia canada abstract ams radiocarbon dates and paleoecological analyses of sediments from the continental shelf between the queen charlotte islands and the british columbia mainland confirm that portions of the shelf were subaerially exposed and ice free between at least 14 330 and 12 860 14c years bp 17 370 14 570 cal years bp pollen analysis suggests that cyperaceae likely formed the dominant plant cover on the exposed shelf at dogfish bank and fossil pediastrum algae confirm the presence of freshwater pollen accumulation rates suggest low plant density on the exposed shelf although this is uncertain due to over and under representation of some pollen types in relation to vegetation abundance on the landscape paleoecological analyses of late glacial sediments at west side pond on the southern queen charlotte islands demonstrate succession from herb tundra dominated by cyperaceae at 13 750 14c years bp 16 830 cal years bp to dwarf shrub tundra with salix and empetrum nigrum after 13 500 14c years bp 16 400 cal years bp pteridophytes increased in abundance during the transition to pinus contorta woodland ca 13 000 14c years bp 15 600 cal years bp fossil conifer stomata suggest that p contorta grew locally as early as 13 040 305 14c years bp alnus crispa was co dominant by 11 500 14c years bp 13 500 cal years bp and picea sitchensis or its hybrids were present as early as 11 400 14c years bp 13 400 cal years bp in the south moresby area

possible refugia in the alexander archipelago of southeastern alaska during the late wisconsin glaciation the interpretation of the extent of late wisconsin glaciation in southeastern alaska has varied between geologists and biologists maps and reports of the region prepared by geologists commonly indicated that late wisconsin ice extended as a large uniform front west to the edge of the continental shelf however the distribution of plants and animals in the region has led many biologists to suggest that there may have been ice free areas that served as refugia during the late wisconsin based on analyses of aerial photographs topographic maps and bathymetric charts in conjunction with a review of previous literature and reconnaissance fieldwork throughout the region this study presents data supporting a limited ice extent in the alexander archipelago during the late wisconsin and identifies possible ice free areas that may have served as refugia these areas include 1 the fairweather ground 2 the herbert graves island area 3 the western coast of southern baranof island and adjacent continental

seismic facies and regional architecture of the oak ridges moraine area southern ontario analysis of over 50 line kilometres of land based shallow seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac

seismic stratigraphy of late quaternary deposits in the eastern skagerrak high resolution seismic profiles from the swedish west coast divide quaternary deposits into six seismic sequences containing 13 different seismic facies documentation of these sequences and facies and their stratigraphic and geographic variability is the first step in a basin fill analysis to interpret depositional environments and major controlling processes the deposits are attributed to one deglaciation cycle the seismic sequences are i bedrock ii coarse glacial deposits iii weichselian glacimarine ice proximal deposits iv weichselian glacimarine ice distal deposits v channel fill deposits and vi holocene marine deposits the major part of the sediment package is the weichselian glacimarine ice proximal deposits deposited during the ice recession period close to or adjacent to the retreating ice typical appearances for these deposits are conformably well stratified deposits with high amplitude the second largest sequence consists of holocene marine deposits and these are mainly found in the southern part of the study area they have typically a near transparent seismic configuration with only weak parallel stratification these two major sequences are separated by a regional nonconformity creating a hiatus of at least 6000 years the hiatus was formed when strong bottom currents related to the cyclonic under water circulation in the skagerrak started to influence the area later the conditions changed reducing the erosional effect of the bottom currents allowing new sedimentation in the southern part while the northern part is still exposed to erosion

seismic facies of glacial deposits from marine and lacustrine environments seismic facies analysis is the interpretation of sedimentary processes and depositional environments from seismic reflection data the technique was primarily developed by the hydrocarbon industry as a predictive indicator of lithology it involves the description and geological interpretation of a number of seismic reflection parameters of which configuration character and external form are the most commonly analysed parameters in recent years the concept of seismic facies analysis has been increasingly used in high resolution seismic reflection studies of late cenozoic marineand lacustrine glacigenic sequences in support of non antarctic resource and development studies e g minerals hydrocarbons fish pipelines etc and high latitude environmental surveys such studies are key to the proper oversight and utilisation of the offshore environments and to understanding the processes associated with the growth and decay of ice sheets as examples the petroleum industry has long had problems drilling on northern glaciated shelves due in part to sub seabed boulder horizons and gas hydrates but also with icebergs furrowing the seabed and impacting on sea floor installations artificial islands constructed as ice protected drilling plat

rapid sea level change and coastal evolution on the pacific margin of canada a rapid regression occurred off the northern pacific margin of canada approximately between 14 600 and 12 500 14c years b p contemporary with the deglaciation of the continental shelf primarily due to the rapid isostatic rebound sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12 400 14c years b p after which a rapid transgression occurred at 12 500 14c years b p the shelf tilt across the northern pacific margin of canada ranged between 50 m of submergence at prince rupert on the british columbia mainland to greater than 150 m of emergence on the western edge of the queen charlotte islands this regressive transgressive cycle lasted only from 5200 to 5500 14c years a result of the development and collapse of a glacioisostatic forebulge sediment supply wave action and tidal current energy are the primary factors that controlled the coastal response to these late quaternary relative sea level changes plate tectonics on the other hand played a secondary role in coastal evolution during deglacial regression extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break during the transgression of the shelf the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits resulting in the formation of drowned wave cut terraces spit platforms and modification of estuarine environments as the sea level rose in steps the present unconsolidated coastline is mostly erosional during the most recent enso event the sea level rise of up to 0 4 m resulted in as much as 12 m of coastal retreat

late quaternary geology and geochronology of the central continental shelf of western canada piston cores and high resolution seismic profiles from queen charlotte sound have yielded new information on the late quaternary history of this part of the western canada continental shelf cores in three major troughs goose island mitchell s and moresby up to 130 km apart sample a similar sedimentary sequence this sequence comprises five units the lowest unit a which is up to 40 m thick is a laminated to massive mud containing coarse ice rafted debris deposited between pre 13 6 ka and 12 9 ka during deglaciation of queen charlotte sound this unit is overlain by a sequence of stratified sediments units b1 b3 up to 20 m thick deposited during the transition from the pleistocene to the holocene unit b1 directly overlies and is similar to unit a but lacks ice rafted detritus unit b2 is sandy mud locally gravelly deposited during a period of lagging and winnowing from about 12 9 to 10 2 ka when sea level in queen charlotte sound was lower relative to the land than it is today unit b3 is a laminated to massive mud similar to unit b1 deposited when water depths in queen charlotte sound rapidly increased at the end of the pleistocene due to the combined effect of eustatic sea level rise and forebulge collapse the sedimentary sequence is capped by up to 10 m of mud unit c which is more organic rich and contains more clay than any of the other units it was accumulating under present day conditions as early as 9 7 k y ago

paleogeography glacially induced crustal displacement and late quaternary coastlines on the continental shelf of british columbia canada abstract subsequent to the last glacial maximum lgm complex isostatic adjustments resulted from deglaciation eustatic sea level change tectonic faulting and a relatively thin flexible lithosphere in the queen charlotte islands qci region a geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the late quaternary northeast pacific continental shelf between 14 2 and 8 7 ka bp wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath queen charlotte qc sound and hecate strait glacial ice 690 m thick began retreating from dixon entrance after 14 5 ka bp 14c years ago and prior to 12 6 ka bp permitting over 100 m of crustal uplift in northern hecate strait a forebulge persisted in hecate strait and qc sound from 13 2 until after 9 7 ka bp implying fixed glacial ice on the british columbia bc mainland until 10 ka bp paleogeographic reconstructions show two emergent ice free terrains one extending eastward from the qci and the other in qc sound by 11 7 ka bp a landbridge connected the bc mainland and the qci

the malpaisillo formation a sequence of explosive eruptions in the mid to late pleistocene nicaragua central america abstract the subduction related volcanic front in nicaragua consists of the tertiary coyol member in the eastern highlands and the quaternary to recent volcanic arc within the nicaraguan depression although the holocene to recent explosive volcanism has been studied extensively no detailed work has been done on the products of explosive volcanism from quaternary volcanic complexes comprising also the malpaisillo and monte galan calderas the focus of this study the 11 km wide malpaisillo caldera and 3 5 km wide monte galan caldera located 50 km northwest of managua are surrounded by tens of meters of rhyolitic tephras these pyroclastic flow and fall deposits extend proximally at least 11 km to the southeast and 23 km to the southwest with observed depositional thicknesses of 16 m for a single ignimbrite unit or 25 m for the entire section distal deposits are found as far as 350 km offshore in the pacific at least twelve highly explosive large volume eruptive phases with corresponding tephra deposits lpt la paz centro tephra ppt punta de plancha tephra lcbt lower chibola tephra gt guacucal tephra ucbt upper chibola tephra fet la fuente tephra st sabanettas tephra mgt miralago tephra tot tolapa tephra lmt mmt umt lower middle and upper maderas negras tephras are distinguished based on geochemical correlations and similar depositional characteristics radiometric 40ar 39ar ages indicate that most activity related to the large malpaisillo caldera occurred between 570 and 420 ka the large pleistocene malpaisillo and monte galan calderas are characterized by a long lived history and if evolved a distinctly alkaline k2o 2 3 3 8 wt na2o 4 0 4 9 wt geochemical signature compared to the other nicaraguan tephra deposits as a result the previously defined malpaisillo formation has been considerably extended and revised our findings contribute to fill a considerable gap in the long term eruptive history of nicaraguan volcanoes with prominent implications for volcanic hazard evaluation for nicaragua

a 14 000 year vegetation history of a hypermaritime island on the outer pacific coast of canada based on fossil pollen spores and conifer stomata abstract pollen and conifer stomata analyses of lake sediments from hippa island on the north coast of british columbia were used to reconstruct the vegetation history of this small hypermaritime island between 14 000 and 13 230 cal yr bp the island supported diverse herb shrub communities dominated by cyperaceae artemisia and salix pinus contorta and picea sitchensis stomata indicate that these conifers were present among the herb shrub communities likely as scattered individuals transition to open p contorta woodland by 13 000 cal yr bp was followed by increases in alnus viridis alnus rubra and p sitchensis after 12 000 cal yr bp pinus dominated communities were replaced by dense p sitchensis and tsuga heterophylla forest with lysichiton americanus and fern understory thuja plicata stomata indicate that this species was present by 8700 cal yr bp but the pollen record suggests that its populations did not expand to dominate regional rainforests along with tsuga and picea until after 6600 cal yr bp conifer stomata indicate that species may be locally present for hundreds to thousands of years before pollen exceed thresholds routinely used to infer local species arrival when combined pollen and conifer stomata can provide a more accurate record of paleovegetation than either when used alone

postglacial evolution of a pacific coastal fjord in british columbia canada interactions of sea level change crustal response and environmental fluctuations results from mona core md02 2494this article is one of a series of papers published in this special issue on the theme polar climate stability network the sedimentary record in a 40 9 m giant calypso piston core md02 2494 raised from the inner basin within effingham inlet british columbia canada during the 2002 marges ouest nord americaines mona campaign spans from 14 360 14 c years bp 17 300 calibrated calendar cal years bp to about nine centuries before present the core ar chives changes in sedimentation and sea level immediately following deglaciation of the late wisconsin fraser glaciation which peaked about 15 000 14 c years bp the presence of the mazama ash in the core anchors a detailed chronology based on 49 radiocarbon dates and seven pleistocene paleomagnetic secular variation correlations diatom assemblages identify a marine freshwater marine transition in the basin which occurred 11 630 14 c years bp 13 500 cal years bp at this time a bedrock sill presently at 46 m depth was briefly exposed as sea level fell and then rose again during iso static crustal adjustments these data constrain a new sea level curve for the outer coast of vancouver island covering the past 12 000 14 c years bp 14 000 cal years bp providing new information on the nature of deglaciation along the west coast of canada and informing interpretations of regional paleoceanographic records and mantle viscosity models

paleoecology of late glacial terrestrial deposits with in situ conifers from the submerged continental shelf of western canada extensive portions of the continental shelf off the coast of british columbia were subaerially exposed during late wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved the woody plant remains confirm that during the latest period of subaerial exposure terrestrial vegetation was established on the continental shelf microscopic identification of fossil wood and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive pinus contorta dominated communities with abundant alnus crispa and ferns grew on the shelf adjacent to and on the queen charlotte islands around 12 200 14c yr b p dwarf shrubs including salix and empetrum and herbaceous plants such as heracleum lanatum and hippuris vulgaris were also important components of the shelf vegetation near northern vancouver island mixed coniferous forests dominated by pinus contorta with picea tsuga spp alnus spp and ferns occupied the shelf at 10 500 14c yr b p

the 1998 debris avalanche at casita volcano nicaragua investigation of structural deformation as the cause of slope instability using remote sensing abstract during hurricane mitch in 1998 a debris avalanche occurred at casita volcano nicaragua resulting in a lahar that killed approximately 2500 people the failure that initiated the avalanche developed at a pre existing cliff part of the headwall of a gravitational slide of approximately 1 8 km 2 in plan view that cuts the southern flank of the volcano structural analysis primarily based on a high resolution dem has shown that this slide is caused by edifice deformation casita s eastern side is spreading radially outwards forming a convex concave profile and steepening original slopes this deformation is possibly facilitated by millennia of persistent hydrothermal alteration of the volcano s core the gravity slide has some typical features of smaller slumps such as steep headwalls an inner flatter area and a pronounced basal bulge fronted by thrusts the headwall is the source of the 1998 avalanche as well as several previous mass movements edifice deformation has led to extensive fracturing of the hydrothermally altered andesitic source rock increasing instability further field evidence indicates that the gravity slide is still actively deforming and with steep headscarps remaining the hazard of future avalanches is increasing the analysis presented here shows how small but highly damaging landslides can occur during the deformation of a volcanic edifice we show that identification of instability is possible with remote sensing data and minimal reconnaissance work implying the possibility of similar efficient and cost effective analysis at other volcanoes known to host extensive hydrothermal systems we demonstrate this with a simple structural analysis of two similar stratovolcanoes orosi costa rica and maderas nicaragua

fluctuating uplift and lining design in spillway stilling basins the paper deals with the characterization and the control of transient uplift generated by turbulent pressure fluctuations in spillway stilling basins theoretical and experimental analyses are presented defining the maximum instantaneous uplift acting on the linings which lead to a design criterion for suitable floor slabs the thickness of concrete linings not accounting for the possible contribution of anchors required for stability is defined in this paper as a function of 1 the incoming kinetic head and or froude number 2 a dimensionless function of the longitudinal and transversal dimensions of the lining slabs the areal extent of extreme turbulent pressure fluctuations and the anisotropic integral scales of the instantaneous spatial correlation of pressure fluctuations 3 the ratio of specific weights of water and immersed concrete and 4 a dimensionless pressure coefficient qualifying the maximum difference of positive and negative pressure fluctuations about the stationary mean value it is concluded that safe design of protection works is significantly affected by the structure of instantaneous spatial distribution of pressures at the bottom of hydraulic jumps consideration of this factor leads to recommendations for the design of slabs in stilling basins

wurmian deglaciation of western lake geneva switzerland based on seismic stratigraphy abstract western lake geneva le petit lac was filled during the quaternary over a major erosion surface truncating the cemented folded and thrusted tertiary sediments of the foreland alpine basin the carving of the lake occurred during quaternary glaciations with ice originating from the rhone valley catchment basin flowing in two branches oriented sw and ne over the swiss plateau lake geneva is situated on the south western branch of this paleo ice cap for the first time a dense grid of high resolution seismic profiles airgun 5 inch3 airgun 1 inch3 and echosounder has imaged the whole quaternary sequence providing a paleoenvironmental interpretation and a detailed reconstruction of the rhone glacier retreat stages during glacial events that led to the formation of western lake geneva the quaternary sequence filling up the bedrock valley is exceptionally thick with up to 220 m of deposits and consists of glacial glacio lacustrine and lacustrine sediments fourteen seismic units have been defined units u1 u14 unit u1 represents the remnants of glacial deposits older than the last glacial cycle preserved in the deepest part of the lake and in secondary bedrock valleys unit u2 represents gravel and sands deposited by meltwater circulation at the bottom of the glacial valley unit u3 is a thick stratified unit marking the beginning of the deglaciation when the rhone glacier became thinner and buoyant and allowed the formation of a subglacial lake younger glacial units units u4 u5 u7 u9 u11 are acoustically chaotic sediments deposited subglacially under the water table undermelt tills while the glacier was thinning these glacial units are bounded by synform erosion surfaces corresponding to readvances of the glacier the transition from a glacial to a glacio lacustrine environment started with the appearance of a marginal esker fan system unit u6 esker formation was followed by a small advance retreat cycle leading to the deposition of unit u7 then the ice front receded and stratified sediments were deposited in a glacio lacustrine environment units u8 u10 and u12 this retreat was punctuated by two readvances coppet unit u9 and nyon unit u11 producing large push moraines and proglacial debris flows finally a lacustrine environment with a characteristic lake current pattern and mass movement deposits took place units u13 and u14 except for unit u1 the sedimentary sequence records the wurmian deglaciation in a fjord like environment occupied by a tidewater glacier with a steep calving ice front the presence of an esker fan system reveals the importance of subglacial meltwater flow in continental deglaciation push moraines and erosion surfaces below the glacier indicate at least 5 readvances during the deglaciation thus revealing that oscillations of ice front are the key process in deglaciation of perialpine fjord lakes the dating of these continental glacier fluctuations would allow correlation with oceanic and ice records and help to understand the climatic mechanisms between oceans and continents

design of anchored slabs in spillway stilling basins this paper characterizes the temporal behavior of uplift force generated by turbulent pressure fluctuations in spillway stilling basins theoretical and experimental analyses are presented that define the magnitude and temporal evolution of the maximum uplift acting on the lining of such basins analyses for the dynamic behavior of anchored floor slabs are also investigated it is concluded that the applicability of the equivalent thickness criterion based on the balance of the forces acting on the slabs in static condition is unsafe for anchored slabs because this criterion yields an inadequate area for the anchor steel the results lead to a recommendation to double the area of anchor steel as computed by the equivalent thickness criterion for the design of slabs in stilling basins

post glacial sea levels on the western canadian continental shelf evidence for rapid change extensive subaerial exposure and early human habitation grounded piedmont type glaciers inundated and isostatically loaded the deep troughs which indent the western canadian continental shelf as far west as the shelf edge glaciers do not appear to have covered the offshore banks east of the queen charlotte islands haida gwaii ice retreated from the shelf at approximately 13 500 14c yr b p rapid emergence of the crust followed the ice retreat and resulted in a relative fall of sea level at 10 400 14c yr b p relative sea level on the continental shelf was more than 100 m below that of today and large areas of the queen charlotte basin were subaerially exposed eustatic sea level rise coupled with subsidence of a glacioisostatic forebulge allowed sea levels to rise very rapidly and reach the present shoreline on the queen charlotte islands haida gwaii by about 9100 14c yr b p dated shoreline deposits shells submerged wood remnants and barnacles on stone tools at elevations between 110 m and 14 m suggest a sea level rise of 6 3 cm per year between 12 200 and 11 000 calender years our reconstructions of the paleogeography and paleoenvironments suggest a hospitable environment for human habitation existed in areas that are now submerged stone tools excavated from intertidal deposits support this interpretation significant local variations in the depth of synchronous shorelines are described and attributed to localized differences in isostatic load the documented rates of crustal adjustment are much greater than those used in conventional geophysical forebulge models regional high resolution seismic reflection data 3400 line km shows little evidence for post glacial faulting and suggest that most crustal adjustments appear to have been isostatically rather than tectonically driven subaerial exposure and subsequent sea level transgression were the dominant post glacial processes that determined the morphology texture and paleoenvironment of the western canadian continental shelf

surficial geology of hecate strait british columbia continental shelf four surficial geological units are defined geophysically for hecate strait on the northern british columbia continental shelf they consist of tertiary bedrock unit 1 unconformably overlain in much of the strait of glacial till unit 2 which is in turn overlain below 200 m water depth by thick silts unit 4 and above 200 m by quaternary sands and gravels unit 3 except in areas where till or tertiary bedrock is at or near surface glacial ice covered most of the strait at some time in the pleistocene but evidence for a late wisconsinan advance is more prevalent in the principal troughs of the strait sea level was as low as the present day 180 m isobath during the late tertiary or early quaternary and possibly as low as 100 m at the end of the pleistocene based on the presence of drainage channels wave cut terraces and both shore oblique and shore parallel sand ridges sedimentary bedforms found ubiquitously above 100 m appear to be in equilibrium with the present hydrodynamic conditions and t

plate boundary adjustments of the southernmost queen charlotte fault abstract a revision of the plate boundary configuration offshore southern haida gwaii which is the locus of the 2012 m w 7 8 thrust earthquake is based on a re evaluation of regional geophysical data and leads to recognition of fault segments critical for seismic hazard analysis off western canada the strike slip queen charlotte fault qcf and revere dellwood fault rdf constitute the transpressive plate boundary between the pacific and north american plates the southernmost 80 km of the qcf strikes at the highest angle 20 to the relative plate motion yet geomorphology adjacent to the fault is the most subdued synthesizing geomorphology seismicity sidescan sonar gravity and seismic reflection profiles indicates that the plate boundary is evolving to a less transpressive configuration than previously interpreted the rdf is 100 km longer than previously mapped it has propagated northward and overlaps the qcf by 120 km propagation is defined by strike slip earthquakes 3 9 m w m w 7 8 and the 1949 m 8 1 earthquakes

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

drowned forests and archaeology on the continental shelf of british columbia canada we have used high resolution digital terrain imaging and sea floor sampling to reveal drowned late glacial to early postglacial terrestrial landscapes at water depths as great as 150 m in situ tree stumps and shellfish rich paleobeaches are present on these drowned landscapes a stone tool encrusted with barnacles and bryozoa was recovered from a drowned delta flood plain now 53 m below mean sea level this is the first tangible evidence that the formerly subaerial broad banks of the western north american continental shelf may have been occupied by humans in earliest holocene and possibly late glacial time analyses 14 c of the drowned terrestrial and intertidal deposits were used to refine the local sea level curve which shows very rapid change within this glacio isostatically dynamic region

an ice age refugium for large mammals in the alexander archipelago southeastern alaska genetic and paleontological evidence are combining to provide a new and surprising picture of mammalian biogeography in southeastern alaska prior to our study the brown and black bears of the alexander archipelago were considered postglacial immigrants that never had overlapping ranges vertebrate fossils from caves on prince of wales island now demonstrate that brown and black bears coexisted there and even inhabited the same caves both before and after the last glaciation differences in mtdna sequences suggest that living brown bears of the alexander archipelago comprise a distinct clade and are more closely related to polar bears than to their mainland conspecifics we conclude that brown bears and perhaps other large mammals have continuously inhabited the archipelago for at least 40 000 yr and that habitable refugia were therefore available throughout the last glaciation

postglacial vegetation history of mitkof island alexander archipelago southeastern alaska abstract an ams radiocarbon dated pollen record from a peat deposit on mitkof island southeastern alaska provides a vegetation history spanning 12 900 cal yr bp to the present late wisconsin glaciers covered the entire island deglaciation occurred 15 400 cal yr bp the earliest known vegetation to develop on the island 12 900 cal yr bp was pine woodland pinus contorta with alder alnus sedges cyperaceae and ferns polypodiaceae type by 12 240 cal yr bp sitka spruce picea sitchensis began to colonize the island while pine woodland declined by 11 200 cal yr bp mountain hemlock tsuga mertensiana began to spread across the island sitka spruce mountain hemlock forests dominated the lowland landscapes of the island until 10 180 cal yr bp when western hemlock tsuga heterophylla began to colonize and soon became the dominant tree species rising percentages of pine sedge and sphagnum after 7100 cal yr bp may reflect an expansion of peat bog habitats as regional climate began to shift to cooler wetter conditions a decline in alders at that time suggests that coastal forests had spread into the island s uplands replacing large areas of alder thickets cedars chamaecyparis nootkatensis thuja plicata appeared on mitkof island during the late holocene

submerged late quaternary terrestrial deposits and paleoenvironment of northern hecate strait british columbia continental shelf canada abstract stratigraphic and paleoenvironmental analyses of sediments recovered from cores on the western canadian continental shelf indicate that areas of the north central shelf were subaerial and supported terrestrial vegetation during the regional late wisconsinan deglaciation paleoecological analyses of now submerged shelf sediments reveal a late quaternary treeless environment locally covered by wet sedge tundra samples from a coeval onshore section on eastern graham island indicate that a dwarf shrub tundra with mosses and willows also occupied lowland areas on the queen charlotte islands between 13 and 14 ka ice free subaerial conditions persisted for a period of at least 3200 years on some parts of the emergent shelf between 13 2 and 10 ka during the same time period clay rich glaciomarine sediment with ice rafted debris was accumulating in the troughs of the shelf low relative sea levels during deglaciation on the continental shelf adjacent to the eastern queen charlotte islands suggest that late wisconsinan ice was thin and limited in extent in this area the presence of a habitable lowland environment during this time interval strengthens the view that a coastal migration of humans from beringia was possible along portions of the exposed continental shelf

new insight into the factors leading to the 1998 flank collapse and lahar disaster at casita volcano nicaragua during unusually high rainfall associated with hurricane mitch in 1998 a flank collapse leading to a disastrous lahar occurred at casita volcano nicaragua the lack of a similar failure during a rainfall event of comparable magnitude in 1982 tropical storm alleta suggests that additional factors influenced the 1998 collapse we have investigated the potential contribution of erosional flank undercutting seismic activity and anthropogenic land cover change at the collapse site except for seismic events prior to mitch which may have increased flank instability none of these factors appears significant instead for failure to occur the following conditions were required 1 highly fractured slope material allowing deep and rapid infiltration of meteoric water 2 a less permeable underlying layer to obstruct drainage 3 strong continuous antecedent rainfall to build up high pore water pressure and 4 episodic high intensity precipitation during mitch to generate recurrent pressure waves prerequisite 1 was provided by edifice wide deformation towards the south east seismic activity and proximity to a prominent fault and local subsidence condition 2 was met by clay rich layers resulting from hydrothermal alteration more than 1 900 mm of rain fell in the 6 months prior to mitch without significant interruption while intense episodic precipitation occurred during the hurricane satisfying conditions 3 and 4 respectively the main difference with alleta was that it occurred at the beginning of the rainy season and therefore without sufficient antecedent rainfall anthropogenic activity including land cover change did not affect slope stability i e the hazard however vulnerability was generated when two towns were established in the lowlands south of casita on top of previous lahar deposits it was greatly increased when approximately 4 km of forest between the collapse site and the towns were cleared paving the way for a largely unobstructed debris flow deforestation also facilitated erosion along the flanks to provide about 78 of the material contained in the lahar when it destroyed the towns killing more than 2 500 people

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

late quaternary paleoenvironments of northwestern north america implications for inland versus coastal migration routes abstract although the long held normative view of new world colonization relies on entrance through an interior ice free corridor by terrestrially adapted big game hunters a recently demonstrated human presence in southern chile dating prior to the existence of the corridor route implies different colonization scenarios which must be seriously considered a renewed focus of archaeological and paleoecological research on early post glacial landscapes in northwestern north america has revitalized the ice free vs coastal corridor controversy geological findings from glacial geology and paleo sea levels support the possibility of coastal migration from beringia to the pacific northwest between about 14 000 and 10 000 bp and preliminary paleoecological data suggest that the coastal landscape was in part vegetated and probably able to support a terrestrial fauna including humans the same cannot be said about the ice free corridor

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

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

modern to late holocene deposition in an anoxic fjord on the west coast of canada implications for regional oceanography climate and paleoseismic history laminated sediments preserved in the anoxic inner basin of effingham inlet on the pacific coast of vancouver island british columbia canada yield a high resolution sediment deposition record spanning about 6000 yr the varying thickness of diatom terrigenous mud varves in sediment cores from the basin can be interpreted in terms of annual changes in surface productivity and freshwater input within the inlet similarly the occurrence of unlaminated mud units homogenites intercalated amongst the laminated sediments can be interpreted in terms of oceanic and climatic changes these units appear to be associated with coastal upwelling events that result infrequently in highly oxygenated oceanic water penetrating to the bottom of the inner and outer basins of the inlet the sedimentary record also contains massive and graded mud units considered to arise from debris flows and turbidity currents some of which were probably initiated by seismic events including a major event about 4500 14 c yr bp which may be earthquake related a total of seventeen oceanographic surveys of the inlet beginning in 1995 characterize the modern seasonal coastal upwelling regime and a unique bottom water oxygenation event which was

design of stilling basin linings with sealed and unsealed joints abstractone of the main causes of lining damage in stilling basins and at the toe of chute spillways is the global instantaneous uplift forces due to the difference in pressure acting on the upper and the lower surface of protection slabs or rock elements spillway stilling basin linings can be built according to two different techniques using sealed joints or unsealed joints in the case of sealed joints the pressure underneath the slab is constant and the uplift force results from the pressure fluctuations acting on the slab in the case of unsealed joints the pressure propagation at the lower surface of the slab being transferred through the joints should also be considered the aim of the paper is to study define and compare the design criteria in these two cases in the present study the pressure field on the slab is evaluated according to a recent method based on the taylor hypothesis whereas the pressure propagation under the slab is computed by a new 3d model based on unsteady flow analys

time of maximum late wisconsin glaciation west coast of canada new data from a deep sea core in the eastern north pacific ocean indicate that the western margin of the late wisconsin cordilleran ice sheet began to retreat from its maximum position after 15 600 yr b p ice rafted detritus is present in the core below the 15 600 yr b p level and was deposited while lobes of the cordilleran ice sheet advanced across the continental shelf in queen charlotte sound hecate strait and dixon entrance the core data are complemented by stratigraphic evidence and radiocarbon ages from quaternary exposures bordering hecate strait and dixon entrance these indicate that piedmont lobes reached the east and north shores of graham island part of the queen charlotte islands between about 23 000 and 21 000 yr b p sometime thereafter but before 15 000 16 000 yr b p these glaciers achieved their greatest late wisconsin extent radiocarbon ages of late glacial and postglacial sediments from queen charlotte sound hecate strait and adjacent land areas show that deglaciation began in these areas before 15 000 yr b p and that the shelf was completely free of ice by 13 000 yr b p

growth rate variation and potential paleoceanographic proxies in primnoa pacifica insights from high resolution trace element microanalysis red tree coral primnoa pacifica is one of the more common habitat forming deep sea gorgonian corals in the northeast pacific ocean growing in colonies up to 2 m high and living for decades to hundreds of years growth characteristics of p pacifica were studied in dixon entrance northern british columbia and the olympic coast national marine sanctuary washington state usa based on samples collected in july 2008 to minimize the impact of scientific sampling on coral populations only dead coral skeletons and dislodged live corals were collected ages and growth rates were measured using band counts and checked against ams 14 c ages of gorgonin rings ba ca mg ca na ca and sr ca ratios in the calcite cortex were measured using radial secondary ion mass spectrometer sims transects with a spot size of 20 m and separation distance of 25 m growth banding was consistent in width between the central mixed zone consisting of calcite and gorgonin and the dominantly calcite cortex average annual radial growth rate of the nine corals analysed ranged from 0 23 to 0 58 mm yr with an average growth rate of 0 32 mm yr in dixon entrance and 0 36 m yr in ocnms these growth rates are slightly higher than p pacifica growth rates from the gulf of alaska and more than four times the growth rates of sister species primnoa resedaeformis in the northwest atlantic primary productivity is likely a more important driver of geographic variation in primnoa growth rates than temperature or current strength both dixon entrance and ocnms are areas with high primary productivity and strong tidal currents lack of post atomic bomb radiocarbon in all but one of the gorgonin samples and long radiocarbon reservoir ages in the northeast pacific made radiocarbon based verification of coral ages and growth rates difficult due to wide errors in calibrated age estimates mg ca and sr ca ratios were inversely correlated in two of the three corals analyzed and showed evidence of interannual variation mg ca ratios ranged from 70 to 136 mmol mol 1 and sr ca ratios from 2 041 to 3 14 mmol mol 1 previously published relationships between gorgonian calcite mg ca and seawater temperature yielded average temperatures matching ambient measurements but the intra and inter annual variation in apparent temperature based on the mg ca ratios was more than double the observed variation in modern seawater temperature ranges in the region annual variation in mg ca and sr ca could be related to seasonal changes in precipitation efficiency which is likely a function of short term fluctuations in coral growth rate in turn related to variation in primary productivity seasonal and interannual variations in food availability driven by primary productivity may affect skeletal growth rate hence mg ca and sr ca ratios primnoid coral skeletal microgeochemistry probably records temporal changes in both temperature and primary productivity

mapping coral and sponge habitats on a shelf depth environment using multibeam sonar and rov video observations learmonth bank northern british columbia canada abstract efforts to locate and map deep water coral and sponge habitats are essential for the effective management and conservation of these vulnerable marine ecosystems here we test the applicability of a simple multibeam sonar classification method developed for fjord environments to map the distribution of shelf depth substrates and gorgonian coral and sponge dominated biotopes the studied area is a shelf depth feature learmonth bank northern british columbia canada and the method was applied aiming to map primarily non reef forming coral and sponge biotopes aside from producing high resolution maps 5 m2 raster grid biotope substrate associations were also investigated a multibeam sonar survey yielded bathymetry acoustic backscatter strength and slope from benthic video transects recorded by remotely operated vehicles rovs six primary substrate types and twelve biotope categories were identified defined by the primary sediment and dominant biological structure respectively substrate and biotope maps were produced using a supervised classification mostly based on the inter quartile range of the acoustic variables for each substrate type and biotope twenty five percent of the video observations were randomly reserved for testing the classification accuracy the dominant biotope defining corals were red tree coral primnoa pacifica and small styasterids of which stylaster parageus was common demosponges and hexactinellid sponges were frequently observed but no sponge reefs were observed the substrate classification readily distinguished fine sediment sand and bedrock from the other substrate types but had greater difficulty distinguishing bedrock from boulders and cobble the biotope classification accurately identified gardens dense aggregations of sponges and corals and primnoa dominated biotopes 67 accuracy but most other biotopes had lower accuracies there was a significant correspondence between learmonth s biotopes and substrate types with many biotopes strongly associated with only a single substrate type this strong correspondence allowed substrate types to function as a surrogate for helping to map biotope distributions our results add new information on the distribution of corals and sponges at learmonth bank which can be used to guide management at this location

interaction between local tectonics and glacial unloading on the pacific margin of canada abstract variations in late quaternary coastal deformation along the pacific margin of canada reflect not only differences in glacial history but also local non glacial tectonics a forebulge developed to the north in the queen charlotte basin qcb from 13 2 until after 9 7 ka bp resulting in exposure of the currently submerged shelf whereas similar exposure was not evident to the south in the georgia basin a semi quantitative effective elastic lithosphere thickness of between 10 and 20 km is estimated for the qcb we propose that this warm relatively thin lithosphere combined with tectonic movement influenced crustal displacement particularly the decoupling of the north american plate along the queen charlotte qc fault which may have allowed the qcb to behave like a hinge in response to glacial unloading this would explain large magnitude crustal tilting 2 1 m km 1 observed adjacent to the qc fault the 50 m of depression observed in the early and mid holocene may imply that the western edge of the north america plate flexed down below present elevation producing a second wave of response to ice loading and unloading

sub surface structures and collapse mechanisms of summit pit craters abstract summit pit craters are found in many types of volcanoes and are generally thought to be the product of collapse into an underpressured reservoir caused by magma withdrawal we investigate the mechanisms and structures associated with summit pit crater formation by scaled analogue experiments and make comparisons with natural examples models use a sand plaster mixture as analogue rock over a cylinder of silicone simulating an underpressured magma reservoir experiments are carried out using different roof aspect ratios roof thickness roof width of 0 2 2 they reveal two basic collapse mechanisms dependant on the roof aspect ratio one occurs at low aspect ratios 1 as illustrated by aspect ratios of 0 2 and 1 outward dipping reverse faults initiated at the silicone margins propagates through the entire roof thickness and cause subsidence of a coherent block collapse along the reverse faults is accommodated by marginal flexure of the block and tension fractures at the surface aspect ratio of 0 2 or by the creation of inward dipping normal faults delimiting a terrace aspect ratio of 1 at an aspect ratio of 1 overhanging pit walls are the surface expressions of the reverse faults experiments at high aspect ratio 1 2 reveal a second mechanism in this case collapse occurs by stopping which propagates upwards by a complex pattern of both reverse faults and tension fractures the initial underground collapse is restricted to a zone above the reservoir and creates a cavity with a stable roof above it an intermediate mechanism occurs at aspect ratios of 1 1 1 2 in this case stopping leads to the formation of a cavity with a thin and unstable roof which collapses suddenly the newly formed depression then exhibits overhanging walls surface morphology and structure of natural examples such as the summit pit craters at masaya volcano nicaragua have many of the features created in the models indicating that the internal structural geometry of experiments can be applied to real examples in particular the surface area and depth of the underpressured reservoir can be roughly estimated we present a morphological analysis of summit pit craters at volcanoes such as kilimanjaro tanzania san cristobal telica and masaya nicaragua and ubinas peru and indicate a likely type of subsidence and possible position of the former magma reservoir responsible for collapse in each case

controls on deglacial changes in biogenic fluxes in the north pacific ocean the subarctic north pacific ocean holds a large co2 reservoir that is currently isolated from the atmosphere by a low salinity layer it has recently been hypothesized that the reorganization of these high co2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation this reorganization would leave some imprint on paleo productivity records here we present 230th normalized biogenic fluxes from an intermediate depth sediment core in the northwest pacific rc10 196 54 7 n 177 1 e 1007 m and place them within the context of a synthesis of previously published biogenic flux data from 49 deep sea cores north of 20 n ranging from 420 to 3968 m water depth the 230th normalized opal carbonate and organic carbon fluxes from rc10 196 peak approximately 13 000 calendar years bp during the bolling allerod b a period our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period increased somewhat in the northwest pacific during heinrich event 1 and reached a maximum across the entire north pacific during the b a period we evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the north pacific including changes in preservation sediment focusing sea ice extent iron inputs stratification and circulation shifts initiated in the north atlantic and north pacific our analysis suggests that while micronutrient sources likely contributed to some of the observed changes the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region wide contemporaneous peaks in export production we argue that paleoobservations are most consistent with ventilation increases in both the north pacific during h1 and north atlantic during b a being the primary drivers of increases in biogenic flux during the deglaciation as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline

uplift pressures below spillway chute slabs at unvented open offset joints abstractthe catastrophic failure of the spillway chute at oroville dam in february 2017 raised concerns throughout the water resources industry regarding design construction and maintenance pract