little ice age glacial activity in peter lougheed and elk lakes provincial parks canadian rocky mountains dendrochronological lichenometric and i4c studies at 14 glacier sites in peter lougheed and elk lakes provincial parks were used to develop a chronology of little ice age glacial events the earliest indications of glacial activity are represented by moraines deposited prior to the 16th century a major glacial expansion in the 17th century is recorded at three sites where i4c dates show glaciers reached their maximum down valley positions lichenometric dates and tree growth suppression records show a phase of glacial activity early in the 18th century for which there is only sparse morainic evidence most moraines in the area date from a glacial advance culminating in the mid 19th century and moraine formation was complete everywhere by the late 1800 s recessional moraines are rare in the study area and indicate that ice front retreat has been relatively continuous since the 19th century the glacial chronology developed in this work is comparable to that reconstructed for both the main ranges of the canadian rockies and the coast ranges of the southern cordillera resum6 les ctudes dendrochronologique 1ichcnomctrique et radiomktrique au i4c de 14 sites rcalisces dans les parcs provinciaux de peter lougheed et de elk lakes ont servi a ctablir une chronologie des cvbnements glaciaires survenus durant le petit bge glaciaire les plus anciens indices de l activitk glaciaire sont reprcsentcs par les moraines dcposces anttrieurement au xvie sibcle une expansion glaciaire majeure durant le xviie sibcle est enregistrke sur trois sites ou les dates au 14c rcvklent la prksence de glaciers avec leurs positions de progression maximale vers le bas de la vallce les datations fondces sur la 1ichcnomctrie et sur les registres de cessation de la croissance des arbres montrent la prcsence d une phase d activitk glaciaire au debut du xviiie sibcle qui a iaissc peu de dcp8ts morainiques dtcelables la plupart des moraines qui apparaissent dans la rcgion datent d une avancce glaciaire qui avait atteint son apogce d extension au milieu du xixe sikcle et leur construction fut complctce vers la fin des annces 1800 les moraines de rkcession sont rares dans la rcgion ctudik cependant elles indiquent que depuis le xixe sibcle il y a eu un retrait relativement continu du front glaciaire la chronologie glaciaire ktablie dans la prcsente ctude est analogue i celle reconstruite pour les chaines principales des rocheuses du canada et pour le domaine c8tier de la cordillbre mkridionale traduit par la raaction

tree ring evidence of little ice age glacier advances in southern tibet the history of late holocene glacier fluctuations in eastern tibet was studied by determining the ages of trees growing on glacier deposits maximum tree ages yield minimum ages of ad 1760 and 1780 for moraine formation at the maximum extent of the little ice age glacier advances in two glacier forefields subsequent moraines could be dated to the beginning of the nineteenth and the beginning of the twentieth century larch trees from a third glacier forefield in southeastern tibet show evidence of glacier activity from 1580 to 1590 from the end of the eighteenth to the beginning of the nineteenth century and from 1860 to 1880 one glacier at mt gyalaperi recently advanced in both 1951 and 1987 periods of glacier advances can partly be correlated with periods of growth reductions in chronologies of total ring width and maximum latewood density derived from trees growing on slopes above the glacier valleys correlation functions with meteorological data suggest that maximum latewood density of subalpin

the little ice age maximum in the southern alps new zealand preliminary results at mueller glacier lichenometric dating studies using the yellow green rhizocarpon subgenus at mueller glacier in the region of mt cook southern alps new zealand reveal a little ice age maximum about ad 1725 1730 differences from previous studies are shown to result from different methods especially the type of mathematical functions used for calculating the lichenometric dating curves previous work also used variable sample sizes distal moraine slopes and to some extent different fixed points schmidt hammer measurements enable the differentiation of little ice age from pre little ice age frontal moraines in the outer glacier foreland and confirm the status of the little ice age as a separate glacier advance among several advances during the holocene

abrupt holocene climate change and potential response to solar forcing in western canada several abrupt climate events during the holocene including the widely documented oscillation at 8 2 thousand years before present ka are attributed to changes in the north atlantic thermohaline circulation additional mechanisms such as interactions between atmospheric circulation ice sheet dynamics and the influence of solar irradiance also have been proposed to explain abrupt climatic events but evidence remains elusive this study presents evidence from multi proxy analyses on the holocene sediments of eleanor lake interior british columbia climatic inferences from our decadal resolution record of biogenic silica bsi abundance are supported by changes in diatom and pollen assemblages from the same core and correlations with existing regional climate records the bsi record reveals abrupt and persistent climatic shifts at 10 2 9 3 and 8 5 ka the latter two of which are coeval with major collapses of the laurentide ice sheet the record also reveals a short term cooling at 8 2 ka that is distinct from the 8 5 ka event and similar in magnitude to several other late holocene coolings bsi is correlated with solar irradiance indices r 0 43 0 61 but the correlation is opposite in sign to that expected from direct solar forcing and weakens after 8 ka possible mechanisms causing the abrupt and persistent climate changes of the early holocene include 1 sudden losses of ice and proglacial lake extent causing a shift in the meridional structure of atmospheric circulation 2 a possible link between solar minima and el nino like conditions that are correlated with warm spring temperature in interior british columbia and 3 the influence of solar irradiance variability on the position of the polar jet possibly via effects on the strength of the glacial anticyclone

glacier fluctuation and tree ring records for the last millennium in the canadian rockies tree ring series and records of alpine glacier fluctuations provide complementary evidence to reconstruct decade to century climate fluctuations over the last millennium in the canadian rockies tree line ring width chronologies in this area are temperature sensitive and long ca 900 years series from sites adjacent to bennington and athabasca glaciers show synchronous declines in ring width during the periods ca 1170 1180 1280 1290 1330 1350 1430 1450 1530 1540 1690 1705 and 1810 1825 a d the latter two events are replicated in many shorter tree ring chronologies and immediately precede the two major periods of moraine development ca 1700 1725 and 1825 1875 a d during the little ice age dendrochronological dating of glacially overridden trees 0 5 1 0 km upvalley of 18th century maximum positions indicate that robson and peyto glaciers were advancing between 1150 and 1350 a d during the earliest phase of the little ice age in the canadian rockies available tree ring data suggest that the level and pattern of climate variability during the 18th and 19th centuries extends back over the last milennium it is also hypothesised that glaciers attained their maximum holocene extent during the little ice age because of the interaction between these decade to century scale fluctuations and the progressive long term decline of incoming summer solar radiation in the northern hemisphere over the last 10 000 years

holocene tephrostratigraphy and glacial fluctuations in waterton lakes and glacier national parks alberta and montana waterton lakes national park in alberta and glacier national park in montana lie along adjacent sections of the continental divide in the rocky mountains in cirques or near divides there is evidence for two ages of glacial deposits younger deposits are generally well preserved poorly vegetated and bear no tephra and no or very small lichens older deposits are more poorly preserved better vegetated bear rhizocarpon sp lichens at least up to 92 mm in diameter and bear tephra the tephra often occurs in two different coloured horizons but both are compositionally equivalent to mazama tephra the older advance has a minimum age of about 6800 14c years bp and a probable maximum age of about 12 000 14c years bp it is correlated with the pre mazama crowfoot advance of the canadian rockies deposits of the younger advance are probably not too much older than mid 19th century because some glaciers began retreating from the deposits about then the younger advance is correlated to the cavell advance of t

geomorphic and climatic change over the past 12 900 yr at swiftcurrent lake glacier national park montana usa abstract glaciated alpine landscapes are sensitive to changes in climate shifts in temperature and precipitation can cause significant changes to glacier size and terminus position the production and delivery of organic mass and in the hydrologic energy related to the transport of water and sediment through proglacial environments a sediment core representing a 12 900 yr record collected from swiftcurrent lake located on the eastern side of glacier national park montana was analyzed to assess variability in holocene and latest pleistocene environment the spectral signature of total organic carbon content toc since 7 6 ka matches that of solar forcing over 70 500 yr timescales periodic inputs of dolomite to the lake reflect an increased footprint of grinnell glacier and occur during periods when sediment sinks are reduced glacial erosion is increased and hydrologic energy is increased grain size carbon nitrogen c n ratios and toc broadly define the termination of the younger dryas chronozone at swiftcurrent lake as well as major holocene climate transitions variability in core parameters is linked to other records of temperature and aridity in the northern rocky mountains over the late pleistocene and holocene

an evaluation of bagnold s dimensionless conefficient of proportionality using measurements of sandwave movement abstract only a few observations are currently available from the tidal marine environment which can be used to evaluate sediment transport formulae research carried out on sandwave movement indicates that most of the sediment transport is restricted to the crestal area mean rates of sediment transport were calculated from volumetric changes between successive slack waters over a nine day period spanning spring tides the results were used in conjunction with boundary layer flow measurements to calculate the threshold velocity for the movement of sediment and also to evaluate bagnold s 1963 dimensionless coefficient of proportionality k comparisons are made with the flume data of guy et al 1966 for the appropriate sediment grain size the dependence of k upon normalised excess shear stress was found to be weaker than that suggested by sternberg 1972 within the range of flow velocities considered there was no indication that k tended towards a constant at high flow velocities

the holocene history of the columbia icefield canada abstract the columbia icefield is the largest icefield in the canadian rockies and feeds eight major glaciers that drain to three different oceans previous glacier studies have focused on athabasca and saskatchewan glaciers primarily due to their easy access this paper reviews evidence of the holocene history from all eight glaciers maximum holocene glacier extent was during the little ice age lia with dating based mainly on minimum tree ring estimates from trees growing on the moraines or from trees scarred tilted or killed by the glaciers the lia maximum advance was during the 19th century at athabasca 1843 4 dome 1846 saskatchewan 1862 and castleguard 1271 and detrital wood from lateral moraines at columbia ca 0 8 0 7ka two overridden stumps at columbia glacier indicate a previously unidentified advance ca 1500 a d these four phases of lia coincide with major reductions in summer temperatures reconstructed at the icefield there are also undated pre 1600 possibly pre lia moraines at kitchener glacier less extensive neoglacial glacier events are documented by an in situ forest bed buried by the saskatchewan glacier ca 2 90 3 4 ka equivalent to the peyto advance and stumps buried by till ca 4 2ka at boundary glacier detrital wood recovered from till at columbia glacier indicates at least one glacier advance ca 2 0 2 2ka till exposed between the bridge river and mazama tephras at stutfield glacier includes detrital wood dating 2 22 2 70 ka that possibly indicates a glacier advance immediately prior to the bridge river tephra regional paleoenvironmental data indicate warmer conditions and higher treelines in the early holocene detrital wood washed out of dome and athabasca glaciers indicates trees were present in these valleys ca 6 7 and 9ka upvalley of present glacier snouts evidence from castleguard cave indicates upstream entrances below the present icefield were probably ice free ca 9 5ka indicating the icefield was much reduced in extent at that time the detrital wood may represent wood killed and reworked by limited glacier advances from the icefield far upstream of present glacier fronts at these times

sediment pathways and transport rates through a tide dominated entrance rangaunu harbour new zealand bed load sediment traps were deployed at two sections across channels in rangaunu harbour entrance traps were inspected and emptied by divers at hourly intervals through both spring and neap tidal cycles for a total of 292 trap deployments current velocities were measured simultaneously with the trap inspections transport is concentrated in sandy megaripple fields on the channel banks and sub tidal platforms flanking the channels there transport is almost continuous throughout the tidal cycle increasing with flow velocity but lagging by approximately one hour the channel floors are lined with shell gravel lag across which bedload transport rates are low and discontinuous tidal asymmetry produces a net seaward transport through the channel troughs and a net landward transport across the channel banks and flanking sub tidal platforms sediment leaving the harbour recirculates in anticlockwise gyres across the ebb tide delta to re enter the harbou and maintain the supply of sand to the megaripple field transport during spring tides is typically 25 30 times that during neaps predictions of transport rates from a method developed by black healy utilizing the yalin bedload equation produced transport rates similar to the traps over sand beds transport over shell lag surfaces appears independent of near bed velocity and more dependent on the passage of ribbons of sand across the lag surface

a high resolution reconstruction of storglaciaren mass balance back to 1780 81 using tree ring data and circulation indices storglaciaren in northernmost sweden has the world s longest ongoing continuous mass balance record starting in 1946 to extend this massbalance record we have reconstructed summer bs and winter bw mass balances separately back to the mass balance year 1780 81 with annual resolution we used tree ring data for bs and a set of circulation indices based on the sea level pressure for bw both proxies have correlation coefficients with respective mass balance components of ca 0 7 the reconstructed net balance bn of storglaciaren was well correlated to the observations during 1946 1980 r 0 8 p 0 05 our reconstruction agrees well with previously obtained results of northern sweden glacier variability where the predominantly positive bn years between 1890 and 1910 correspond to the well documented post little ice age advance of storglaciaren furthermore the results suggest that bs as a function of summer temperatures is more important than bw in determining the bn which is contrary to glaciers in the maritime parts of western scandinavia in general bn has been negative over the last 220 yr suggesting a predomination of continental conditions over northern sweden however the influence of bw increased in the late twentieth century indicating a shift to a more oceanic climate regime

dendrohydroclimate reconstructions of july august runoff for two nival regime rivers in west central british columbia lengthy records of river discharge are necessary to comprehensively assess the long term connection between synoptic climate forcings and nival regime systems in british columbia a regional multispecies network of tree ring width and ring density chronologies was built for west central british columbia with the intention of dendrohydrologically extending short runoff records in this area extended records of july august mean discharge anomalies for the skeena and atnarko rivers were reconstructed back to ad 1660 low flow events represented during the late 1600s early 1700s and late 1800s lie beyond those experienced during the recent instrumental period for these basins the documentation of extreme events of this magnitude necessitates consideration when planning for future water resources in this region supplementary dendroclimatic reconstructions of the winter pacific north american pna pressure anomaly pattern and records of mean summer temperature and end of winter snow water equivalent were also constructed these ancillary climate records provide insight into the long term climate drivers of annual discharge dynamics within these nival basins correlation and wavelet analyses confirm the persistent relationship of synoptic climate regimes described by the southern oscillation index nino 3 4 pacific decadal oscillation and pna indices on runoff in west central british columbia copyright 2012 john wiley sons ltd

grains in motion a review abstract this review paper aims to present a practical integrated procedure for the prediction of sediment transport rates in both the continental and marine environment based on the settling velocity of particles such studies have important applications in diverse fields such as civil and coastal engineering sedimentology and environmental geology where they can assist in flood control and the prevention of contaminant dispersal by wind and water as well as the siltation of dams and harbours the formation of placer deposits including gold diamonds and other heavy minerals is also controlled by sediment transport processes so that these studies can form the basis for more efficient exploration programs the first part of the paper discusses some basic principles important in sediment transport followed by an overview of published methods to determine the settling velocity of differently shaped particles including natural grains the application of settling velocity to predict the entrainment threshold of sediments on plane horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed which finally leads to the determination of sediment transport rates over plane and rippled beds the validity of this approach to natural conditions is tested against published field data where possible other widely used methods are also critically discussed pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments

analysis of analogue models by helical x ray computed tomography the aim of analogue model experiments in geology is to simulate structures in nature under specific imposed boundary conditions using materials whose rheological properties are similar to those of rocks in nature in the late 1980s x ray computed tomography ct was first applied to the analysis of such models in early studies only a limited number of cross sectional slices could be recorded because of the time involved in ct data acquisition the long cooling periods for the x ray source and computational capacity technological improvements presently allow an almost unlimited number of closely spaced serial cross sections to be acquired and calculated computer visualization software allows a full 3d analysis of every recorded stage such analyses are especially valuable when trying to understand complex geological structures commonly with lateral changes in 3d geometry periodic acquisition of volumetric data sets in the course of the experiment makes it possible to carry out a 4d analysis of the model i e 3d analysis through time examples are shown of 4d analysis of analogue models that tested the influence of lateral rheological changes on the structures obtained in contractional and extensional settings

multicentury glacier fluctuations in the swiss alps during the holocene subfossil remains of wood and peat from six swiss glaciers found in proglacial fluvial sediments indicate that glaciers were smaller than the 1985 reference level and climatic conditions allowed vegetation growth in now glaciated basins an extended data set of swiss glacier recessions consisting of 143 radiocarbon dates is presented to improve the chronology of glacier fluctuations a comparison with other archives and dated glacier advances suggests 12 major recession periods occurring at 9850 9600 93008650 85508050 77007550 74506550 61505950 57005500 52004400 43003400 28002700 21501850 14001200 cal yr bp it is proposed that major glacier fluctuations occurred on a multicentennial scale with a changing pattern during the course of the holocene after the younger dryas glaciers receded to a smaller extent and prolonged recessions occurred repeatedly culminating around 7 cal kyr bp after a transition around 6 cal kyr bp weak fluctuations around the present level dominated after 3 6 cal kyr bp less frequent recessions interrupted the trend to advanced glaciers peaking with the prominent little ice age this trend is in line with a continuous decrease of summer insolation during the holocene

proxy data reconstructions of the storglaciaren sweden mass balance record back to ad 1500 on annual to decadal timescales regional summer temperatures t s derived from tree rings and large scale atmospheric circulation indices north atlantic oscillation nao were used to infer the mass balance of storglaciaren sweden on annual and decadal timescales back to ad 1500 winter january march nao was not a suitable proxy for interannual winter balance variability but seemed to have substantial influence on decadal timescales t s were highly correlated to the summer balance but also to the annual net balance this association was much weaker on decadal timescales mainly because of the increased maritime climate around 1980 storglaciaren net balance was modelled back to ad 1500 with annual resolution using t s as a predictor and ad 1664 with decadal resolution using t s and nao as predictors both reconstructions displayed similar evolution negative mass balances dominated most of the 16th century followed by a longer period of predominantly positive mass balance years culminating in about 1750 this is in agreement with previous suggestions of holocene maximum expansion of storglaciaren at that time subsequently the mass balance is highly variable with an increased number of negative years the build up to the well documented early 20th century advance is evident as mass balance becomes progressively more positive towards the early 20th century

dendroglaciological evidence for holocene glacial advances in the todd icefield area northern british columbia coast mountains accelerated glacial recession and downwasting in pacific north america is exposing land surfaces and fea tures buried by glacial advances that in many locations predate the recent little ice age lia dendrochronologic analyses of increment core samples from living trees abies lasiocarpa tsuga mertensiana and samples of subfossil wood collected in the todd icefield area boundary ranges british columbia coast mountains provide the basis for a dendroglaciological and radiocarbon based reconstruction of late holocene glacier activity five intervals of glacier ex pansion were recorded by trees killed or buried by advancing glaciers 1 an advance prior to 3000 14 c years bp 2 an advance at 3000 14 c years bp that coincides with the regional tiedemann advance 3 an unattributed advance at 2300 14 c years bp 4 a two phase advance at 1700 and 1450 14 c years bp that corresponds with the regional first millennium advance 5 an advance with three phases of expansion that began prior to 750 14 c bp and is con sistent with the regional early lia interval and a two phase interval of late lia expansion culminating after 240 and 100 years bp this chronology of late holocene glaciation matches that emerging from similar investigations in the coastal cordillera of pacific north america and provides additional support for the regional significance of both the tiedemann and the first millennium advances resume une recession et une fonte glaciaire accelerees dans l ocean pacifique en amerique du nord exposent des sur faces de terrain et des traits caracteristiques enfouis sous des avancees glaciaires lesquelles dans bien des cas datent d avant le recent petit ge glaciaire des analyses dendrochronologiques d echantillons proportionnels de carottes pris

textural and compositional characterization of recent sediments along a paraglacial estuarine coastline maine usa abstract textural and mineralogical characteristics of bottom sediments collected from the lower kennebec river estuary maine and adjacent nearshore region were used to differentiate subtidal sedimentary environments five depositional environments defined on the basis of bottom morphology bathymetry and dominant sedimentary processes estuarine channel channel margin outer bar shoreface and offshore possess distinct sedimentological characteristics trends in textural characteristics of these environments and those along the adjacent barrier beach include 1 systematic decrease in mean grain size from the estuarine channel to the offshore facies 2 similarity between the outer bar and estuarine channel sands 3 increase in sediment sorting from the channel margin and offshore to shoreface facies and 4 fining of the low tide terrace beachface and berm samples away from the bar welding region the fine grained nature of the offshore facies is the result of deposition of suspended sediment delivered to the coast during large flood events whereas the coarse fraction is contributed through the attrition of carbonate tests of the local macrofauna results of compositional analyses reveal 1 a decrease in shell fragments from the estuarine channel 50 to the offshore

lichenometric dating of the little ice age maximum in mt cook national park southern alps new zealand lichenometric dating studies using the yellow green rhizocarpon subgenus at the eugenie hooker mueller and tasman glaciers in mt cook national park southern alps new zealand reveal a little i

computerized tomographic analysis of displacement trajectories and three dimensional fold geometry above oblique thrust ramps computerized tomographic analysis of physical models of fold thrust structures permits nondestructive systematic analysis of variations in displacement trajectories and variations in three dimensional fold geometry as a function of thrust fault geometry the authors studied models in which sand layers with embedded transport parallel marker lines were shortened incrementally up to a maximum of 24 over rigid footwall fault templates these templates simulated a right stepping oblique ramp connecting two ramps perpendicular to the shortening direction in response to movement over the oblique ramp templates overturned folds formed and marker line deflections indicative of out of plane strains developed marker lines within layers originally truncated by fault templates were deflected leftward away from the right stepping oblique ramp during deformation whereas marker lines within sand layers that originally extended across the upper flat of the fault template were deflected in a more radial pattern differences in marker line deflections imply that displacement trajectories within natural thrust sheets may vary as a function of overburden and structural position furthermore their tomographic studies graphically demonstrate that out of plane strain and differential rotation of layers within thrust sheets occur in the vicinity of oblique ramps

fault development and interaction in distributed strike slip shear zones an experimental approach analogue model experiments using both brittle and viscous materials were performed to investigate the development and interaction of strike slip faults in zones of distributed shear deformation at low strain bulk dextral shear deformation of an initial rectangular model is dominantly accommodated by left stepping en echelon strike slip faults riedel shears r that form in response to the regional bulk stress field push up zones form in the area of interaction between adjacent left stepping riedel shears in cross sections faults bounding push up zones have an arcuate shape or merge at depth adjacent left stepping r shears merge by sideways propagation or link by short synthetic shears that strike subparallel to the bulk shear direction coalescence of en echelon r shears results in major through going faults zones master faults several parallel master faults develop due to the distributed nature of deformation spacing between master faults is related to the thickness of the brittle layers overlying the basal viscous layer master faults control to a large extent the subsequent fault pattern with increasing strain relatively short antithetic and synthetic faults develop mostly between old but still active master faults the orientation and evolution of the new faults indicate local modifications of the stress field in experiments lacking lateral borders closely spaced parallel antithetic faults cross faults define blocks that undergo clockwise rotation about a vertical axis with continuing deformation fault development and fault interaction at different stages of shear strain in our models show similarities with natural examples that have undergone distributed shear

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

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

evidence for a neoglacial advance of the boundary glacier banff national park alberta direct evidence for an early neoglacial advance in the canadian rocky mountains is presented radiocarbon dates from buried peat and tree remains at boundary glacier suggest limiting dates for this advance of between 3800 and 4200 years bp these data from boundary glacier are consistent with previously published dates for the onset of the neoglacial and an early neoglacial advance

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

reconstruction of holocene changes in alpine vegetation and climate in the maligne range jasper national park alberta abstract pollen macrofossil logs and needles and oxygen isotope data from tree rings are presented for three alpine bog sites in the maligne range of the canadian rockies organic sedimentation at the watchtower site began prior to ca 9500 14 c yr b p and by 8770 yr b p timberlines were at least 100 m above present levels the two pollen records are dominated by pinus and subsequent changes in timberlines are inferred from pollen ratio data abies pinus and from macrofossils the recovered records indicate two periods of high hypsithermal timberlines ca 8800 7500 and 7200 5200 yr b p separated by a short interval ca 7300 7400 yr b p when timberline approached modern levels after ca 4500 yr b p timberlines have been similar to or lower than present reaching minimum values in the last 500 yr 18 o determinations from the cellulose of samples of 5 or 10 annual rings cut from contemporary picea englemannii at timberline show strong correlations with mean annual temperatures at jasper isotopic determinations from hypsithermal age logs recovered from sites above present timberline indicate mean annual temperatures were at least 0 5 c warmer ca 8060 and 8770 yr b p than at present at the watchtower site data from logs at the maligne pass site suggest that temperatures were about 1 2 and 1 6 c warmer ca 6000 and 5300 yr b p estimates of temperature from the pollen ratio data are more conservative and suggest maximum differences of ca 1 0 c in july temperatures over the last 8000 yr

sand dynamics at the mouth of a rock bound tide dominated estuary abstract the lowermost kennebec river is a relatively narrow deep bedrock cut estuary situated along the highly indented central coast of maine a large tidal prism and strong tidal currents control bedload sediment transport at the estuary mouth riverine sediment is introduced to the estuary during spring freshets when freshwater discharge may increase by an order of magnitude during the same time some of the existing estuarine sediment is exported to the nearshore a barrier adjacent to the estuary is the product of an abundant riverine sand supply and numerous bedrock ridges which anchor this sand deposit a variety of sedimentologic geomorphic and hydraulic data collected over a 14 year period document a clockwise sand circulation cell that involves the exchange of bedload among the entrance channel to the estuary adjacent beaches nearshore and offshore region tidal currents transport sand from the estuary through a subsidiary channel bordered on both sides by bedrock islands to an offshore subtidal bar northeast storm waves breaking along this outer bar move sand westward and landward toward the beach leading to the development of large bar complexes the welding of a bar complex to the western end of hunnewell beach occurs every 6 9 years and adds 2 300 000 m3 of sand to the shoreline sediment transport calculations along the outer bar are consistent with this volume of sand the sediment gyre is completed as beach sands are moved eastward along the beach and dumped into the estuarine channel this movement of sand is produced by wave action and tidal currents that enter the estuary peripherally during the flooding tide during the ebb cycle strong tidal currents flowing seaward through the subsidiary channel advect water from along the beach which enhances sand transport into the estuary thirteen years of beach profile surveys demonstrate a good correspondence between bar welding events and short term 1 4 years accretionary shoreline changes however the volumetric changes of hunnewell beach cannot be accounted for by bar welding alone the apparent movement of sand between hunnewell beach and other sand is further evidenced by the 135 year record of historical shoreline changes that reveal up to 200 m of shoreline excursions over a 26 year period these data suggest that erosional depositional trends along hunnewell beach are complex and the result of the exchange of sand among the adjacent beaches nearshore zone fox and wood island tombolos kennebec river channel and offshore region the effects of major spring floods and strong bedrock influences produce patterns of sedimentation and a distribution of sand bodies at the mouth of kennebec river that differ markedly from accepted estuarine models that are based on the relative importance of wave and tidal energy this study demonstrates the need to consider structural controls when using these models

the relationship of sediment transport rates and paths to sandbanks in a tidally dominated area off the coast of east anglia u k sand transport measurements of bedload and suspended load in the sizewell dunwich banks area east anglia have shown that the suspended mode is dominant the depth integrated spring tidal residual is 5 66 g cm 1 sec 1 although the neap rate is only one fifth of this the calculated bedload transport rates also vary from 0 012 to 0 040 g cm 1 sec 1 correlating with changing meteorological conditions in order to predict the bedload sediment circulation pattern from midwater current meter measurements five sediment transport equations were calibrated using fluorescent dyed sand yalin s relationship gave the best estimates the bed shear stress was determined by extrapolating the velocity profile as a power law relationship with an exponent equal to 0 1 from midwater down to 2 m and as a lognormal profile from 2 m to the sea bed roughness length values appropriate to the substrate were used although bedload transport residuals are mainly to the south the banks trend northwards from the coast and have also elongated in this direction this is thought to be in response to the dominance of the suspended sediment transport it is suggested that a tidal residual eddy mechanism is responsible for the banks maintenance similar to the process operating in start bay devon the well documented westward movement of the banks is likely to be related to wave processes

tree ring derived little ice age temperature trends from the central british columbia coast mountains canada abstract most glaciers in the british columbia coast mountains reached their maximum holocene extent during the little ice age early and late little ice age intervals of expansion and retreat fluctuations describe a mass balance response to changing climates although existing dendroclimatic records provide insights into these climatic fluctuations over the last 400 yr their short durations prohibit evaluation of early little ice age climate variability to extend the duration of these records submerged coarse woody debris salvaged from a high elevation lake was cross dated to living chronologies the resulting chronology provides the opportunity to reconstruct a regional june july air temperature anomaly record extending from ad 1225 to 2010 the reconstruction shows that the intervals ad 1350 1420 1475 1550 1625 1700 and 1830 1940 characterized distinct periods of below average june july temperature followed by periods of above average temperature our reconstruction provides the first annually resolved insights into high elevation climates spanning the little ice age in this region and indicates that little ice age moraine stabilization corresponds to persistent intervals of warmer than average temperatures we conclude that coarse woody debris submerged in high elevation lakes has considerable potential for developing lengthy proxy climate records and we recommend that researchers focus attention on this largely ignored paleoclimatic archive

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

fire and vegetation history during the last 3800 years in northwestern montana abstract foy lake in northwestern montana provides a record of annual to decadal scale landscape change sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years which were then compared to similar records from ad 1880 to 2000 the long term record at foy lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change fire activity inferred from the frequency of charcoal peaks averaged 18 fire episodes 1000 years from 3800 to 2125 cal year bp and increased from 16 fire episodes 1000 years at 2125 cal year bp to 22 episodes 1000 years at 750 cal year bp a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover between 2125 and 750 cal year bp increased forest cover produced more background charcoal than before and after this period when vegetation was dominated by steppe between 750 and 75 cal year bp steppe has expanded and fire episode frequency averaged 33 episodes 1000 years increasing to a maximum of 40 episodes 1000 years at ca 300 cal year bp and then decreasing to present levels since ad 1880 the pollen record indicates an increase in shrubs and grasses from ad 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing no fires have been documented in the foy lake watershed since ad 1880 charcoal from the extralocal fires of ad 1910 burning over 4 111 249 ha in idaho montana and wyoming however is present in foy lake between ad 1970 and 2000 increased arboreal pollen in the record is consistent with observations that the forest has become more closed the activities of euro americans have led to a decline in forest cover between ad 1880 and 1970 followed by a recent increase as trees are now growing in areas previously occupied by steppe euro americans are likely the cause of a reduction in fire activity in watershed since ad 1880

recent glacier advances in the premier range british columbia aerial photography 1948 1985 and field investigations are used to reconstruct recent ice front fluctuations for 27 glaciers size range 0 63 17 9 km2 in the premier range british columbia rapid rates of frontal recession between ca 1930 and the mid fifties were followed by glacier readvance at many sites culminating in the 1973 1976 period when 90 of the monitored ice fronts were either advancing 68 or stable maximum downvalley advance was about 0 5 km median 90 m and 14 glaciers formed new terminal or lateral moraine ridges between 1970 and 1985 nine of these postdate 1976 one is dated to the 1980 1981 winter using tree rings the glacial advance is attributed to significant mass balance changes inferred from periods of increased winter precipitation ca 1951 1976 and low summer temperatures 1954 1968 measured at valemount warmer summers and reduced winter precipitation after 1976 account for the slight recession of ice fronts from maximum downvalley positions in the last few years

little ice age glacial activity in strathcona provincial park vancouver island british columbia canada dendroglaciological and lichenometric techniques are used to establish the little ice age lia history of two glaciers colonel foster and septimus in strathcona provincial park vancouver island british columbia our lichenometric investigations were preceded by the development of a locally calibrated rhizocarpon geographicum growth curve 1708 1998 a d documentation of a 3 4 year ecesis interval for both trees and lichen greatly reduces one of the main uncertainties in using geobotanical methods for dating lia landforms the moraine dates provided therefore give a good approximation of the shift in climate conditions that lead to the retreat of the glaciers and subsequent moraine stabilization geobotanical evidence records three synchronous episodes of lia moraine deposition at both glaciers two prominent moraines at each site are dated to the early 1700s and late 1800s with a third smaller moraine dated to the mid 1930s moraines deposited prior to 1397 a d were also recorded at colonel foster glacier however precise dating of these moraines was not possible the moraine records from strathcona provincial park suggest two possible modes of glacier response i synchronous responses to larger scale climatic forcing and ii asynchronous responses to local factors such as microclimate topography and glacier geometry the vancouver island lia record was evaluated in the context of lia results from the pacific north american pna cordillera it compares well with regional moraine records from coastal british columbia washington alaska and the canadian rocky mountains suggesting a regional response of pna glaciers to climate change associated with the lia

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

initiation of sand transport over coarse beds in tidal entrances abstract a tidal entrance often acts as a source or a sink for sand in the littoral zone at many entrances in biologically productive regions the bed in the vicinity of the throat section minimum flow area is composed of sediment containing coarse material including large shells with sand occurring in the interstitial regions between the shell defined roughness elements a stochastic relationship giving the critical bed shear stress for the initiation of sand transport under these conditions is applied to hydraulic and sedimentary data obtained from two entrances in florida the results agree well with the critical bed shear stresses derived from data based on the observation of sand movement at the bed the entrainment function based on observations is found to be approximately three times the value obtained from shields criterion a practical implication is that the use of shields criterion in the computation of the rate of sand transport will in general overpredict the rate through the entrance

a fine resolution palaeoclimatic reconstruction of the last 2000 years from lake keilambete southeastern australia a fine resolution analysis of pollen charcoal magnetic susceptibility sediment fractions and total carotenoids was used to investigate the last 2000 years of environmental history at lake keilambete in western victoria australia the chronology of sedimentation was based on three radiocarbon dates supplemented by inferences from 22 previous radiocarbon ages from the site spanning approximately the last 7500 years changes in the analysed parameters infer a relatively higher effective moisture from approximately 2000 to 1800 cal bp increased instability in the lake keilambete catchment from 1750 to 1425 cal bp may reflect a decreased moisture availability and cooler temperatures at about 1450 cal bp a period of considerable environmental change is suggested at lake keilambete warmer temperatures or an increased moisture supply seem likely between 1415 and 1320 cal bp from around c 1150 until 800 cal bp overlapping the medieval warm period a series of changes in the composition of the la

a holocene alluvial sequence in the lower tyne valley northern britain a record of river response to environmental change palaeoenvironmental investigations have been made of late quaternary sediments infilling the lower tyne valley at scotswood newcastle upon tyne 18 km upstream from the mouth of the river attention has focused on the holocene alluvial sedimentary sequence using sedimentological geochemical and palynological analyses holocene valley floor development from c 7500 bp has been largely dominated by a tendency towards river aggradation with some limited lateral and vertical reworking of sediments four alluvial fills have been identified and dated to 1 c 7500 4800 bp 2 from c 2590 bp up to the early first millennium ad and possibly as late as medieval times 3 between the medieval period and the early seventeenth century and 4 between the seventeenth and nineteenth centuries episodes of incision are dated to c 4800 2590 bp and to the period following the early seventeenth century marked variations in the rates and nature of sedimentation and erosion appear to coincide with rising post glacial

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

holocene fluctuations of a meromictic lake in southern british columbia abstract holocene deposits of mahoney lake a meromictic saline lake located in a closed basin in the semi arid okanagan valley contain evidence of frequent and marked changes in lake depth up to 12 m 10014c yr probably caused by short term changes in effective precipitation we studied a 5 45 m long core comprising a basal layer of inorganic mud overlain by a succession of layers of calcareous laminated and nonlaminated organic mud marl and sand we used mazama tephra to adjust nine radiocarbon ages for the hardwater effect meromixis developed ca 900014c yr b p and the lake has been episodically meromictic for about half the time since because of close linkages between sediments and depositional environments in meromictic and saline lakes we infer that laminated sediments indicate meromictic conditions and high lake levels ca 12 m water depth whereas thick marl layers and nonlaminated sediments indicate nonmeromictic conditions and thus low lake levels

a late holocene and prehistoric record of environmental change from lake waikaremoana new zealand further evidence in support of a late pre european polynesian settlement of new zealand is pro vided by an 1850 year long tephropalynological record from a remote region in new zealand s north island the earliest unequivocally anthropogenic forest clearance is estimated from sedimentation rates to have occurred c 375 14 c years bp c ad 1523 1631 although the radiocarbon chronology shown by tephrochron ology to be erroneous due to hard water effects suggested this occurred c 900 years earlier delineation of the anthropogenic era and the distinction between human activity and other agents of environmental change in the pollen spore diagram are supported by cluster analysis and detrended correspondence analysis two distinct phases of forest clearance are evident during the pre european era reflecting local changes either in population pressure or settlement patterns we note that the lull between the two phases of forest clearance coincides with the maximum of the little ice age within the period c late ad 1600s to early 1800s

experiments on faulting in zones of oblique shortening geoscientists have long used analog models to simulate various kinds of structures in nature because this approach offers the opportunity to determine which parameters control their geometry and evolution the models use materials whose mechanical properties are similar to those of rocks less than a decade ago a breakthrough occurred when analog models were first analyzed by x ray computerized tomography ct a technique which makes it possible to visualize the interior of an analog model without destroying it this opened new perspectives for analyzing the 3 d geometry of structures in models and especially their evolution through time

a 263 year record of summer temperature for northern quebec reconstructed from tree ring data and evidence of a major climatic shift in the early 1800 s abstract tree ring data are used to reconstruct 263 years of summer temperatures at a site located near the northern tree line in central western quebec a chronology comprising 20 ring density time series is used in conjunction with a chronology comprising 20 ring width time series in the regression analyses the increased precision of the temperature estimates obtained by using density data as an additional proxy time series places the reconstruction and its interpretation on a firmer basis than it is when only ring width data are used the results are considerably improved over the use of either tree ring parameter alone the temperature reconstruction reflects a major cooling event in the early nineteenth century comparisons with other temperature and proxy data series support the idea of a global cooling event with a persistence of the cool period of about three decades in high latitude north america and of much shorter duration in other regions of the world volcanic activity in the early 1800 s is suggested as partially responsible for the cooling event but is considered inadequate as cause for the extended period of low temperatures in the locale of this reconstruction

experiments on strike slip faulting and block rotation analogue model experiments investigating strike slip faulting in zones of distributed shear deformation show that fault orientations and fault evolution indicate modifications of the stress field with increasing bulk shear strain dextral bulk shear deformation at low strain is accommodated dominantly by synthetic strike slip faults riedel shears at higher strain secondary antithetic and synthetic faults develop mostly between earlier formed major riedel shears closely spaced parallel antithetic faults cross faults delimit domains that rotate about vertical axes with continuing shear deformation rotation of fault bounded domains results in sigmoidal antithetic faults that have a dip slip component and a dip direction that changes along strike there is good agreement between models and natural examples of distributed shear zones where block rotations about vertical axes have been documented

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

the little ice age in the canadian rockies abstract this paper reviews the evidence and history of glacier fluctuations during the little ice age lia in the canadian rockies episodes of synchronous glacier advance occurred in the 12th 13th early 18th and throughout the 19th centuries regional ice cover was probably greatest in the mid 19th century although in places the early 18th century advance was more extensive glaciers have lost over 25 of their area in the 20th century selective preservation of the glacier record furnishes an incomplete chronology of events through the 14th 17th centuries in contrast varve sequences provide continuous annually resolved records of sediments for at least the last millennium in some highly glacierized catchments such records have been used to infer glacier fluctuations evaluation of recent proxy climate reconstructions derived from tree rings provides independent evidence of climate fluctuations over the last millennium most regional glacier advances follow periods of reduced summer temperatures reconstructed from tree rings particularly ca 1190 1250 1280 1340 1690s and the 1800s reconstructed periods of higher precipitation at banff alberta since 1500 are 1515 1550 1585 1610 1660 1680 and the 1880s glacier advances in the early 1700s the late 1800s and in places the 1950 1970s reflect both increased precipitation and reduced summer temperatures negative glacier mass balances from 1976 to 1995 were caused by decreased winter balances the glacier fluctuation record does not contain a simple climate signal it is a complex response to several interacting factors that operate at different timescales evaluation of climate proxies over the last millennium indicates continuous variability at several superimposed timescales dominated by decade century patterns only the 19th century shows a long interval of sustained cold summers this suggests that simplistic concepts of climate over this period should be abandoned and replaced with more realistic records based on continuous proxy data series the use of the term lia should be restricted to describing a period of extended glacier cover rather than being used to define a period with specific climate conditions

what were the primary forcing mechanisms of high frequency holocene climate and glacier variations a compilation of holocene glacial advances throughout the world is compared with summer solar insolation integrated over the northern hemisphere and the magnitudes of global acid fallout from volcanic eruptions north of 20 s estimated from the acidity signal of annual ice layers in the crete and camp century ice cores in greenland correlation analysis between glacial advances versus volcanic eruptions yielded a correlation coefficient of r 0 71 a climatic forcing curve solar insolation and volcanic eruptions weighted 1 1 versus glacial advances increased the correlation coefficient to r 0 90 this suggests that the combined effect of volcanic aerosols and orbital related northern hemisphere summer insolation may have been the primary forcing mechanism of worldwide climate and glacier fluctuations throughout the holocene

neoglacial glacier fluctuations in the canadian rockies abstract the little ice age was the most extensive neoglacial glacier advance in the canadian rockies evidence of earlier less extensive neoglacial glacier advances is based on wood recovered from several glacier forefields wood flushed out of athabasca glacier 7550 8230 yr b p three dates and dome glacier 6120 6380 yr b p two dates indicates that forests occurred upvalley of present glacier termini during the hypsithermal detrital logs from peyto 14 dates saskatchewan 3 dates robson 3 dates and yoho 1 date glaciers plus in situ slumps at peyto and robson glaciers have yielded 14 c dates between 2490 and 3300 yr b p 12 dates between 2800 and 2990 this wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca 3100 and 2500 yr b p treeline was higher than present immediately prior to this advance this advance which did not extend beyond the little ice age maximum position is designated the peyto advance and correlated with the tiedemann advance in western british columbia earliest little ice age advances at peyto and robson glaciers are dated ca 800 600 yr b p at positions ca 500 m upvalley from little ice age limits

persistent millennial scale shifts in moisture regimes in western canada during the past six millennia inferences of past climatic conditions from a sedimentary record from big lake british columbia canada over the past 5 500 years show strong millennial scale patterns which oscillate between periods of wet and drier climatic conditions higher frequency decadal to centennial scale fluctuations also occur within the dominant millennial scale patterns these changes in climatic conditions are based on estimates of changes in lake depth and salinity inferred from diatom assemblages in a well dated sediment core after periods of relative stability abrupt shifts in diatom assemblages and inferred climatic conditions occur approximately every 1 220 years the correspondence of these shifts to millennial scale variations in records of glacial expansion recession and ice rafting events in the atlantic suggest that abrupt millennial scale shifts are important to understanding climatic variability in north america during the mid to late holocene unfortunately the spatial patterns and mechanisms behind these large and abrupt swings are poorly understood similar abrupt and prolonged changes in climatic conditions today could pose major societal challenges for many regions

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

postglacial fire vegetation and climate history in the clearwater range northern idaho usa the environmental history of the northern rocky mountains was reconstructed using lake sediments from burnt knob lake idaho and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large scale climate changes during the holocene vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold dry conditions from 14 000 to 12 000 cal yr b p abundant pinus pollen suggests warmer moister conditions than the previous period most sites record the development of a forest with pseudotsuga ca 9500 cal yr b p indicating warm dry climate coincident with the summer insolation maximum as the amplification of the seasonal cycle of insolation waned during the middle holocene pseudotsugawas replaced by pinus and abies suggesting cool moist conditions the fire reconstructions show less synchroneity in general the sites west of the continental divide display a fire frequency maximum around 12 000 8000 cal yr b p which coincides with the interval of high summer insolation and stronger than present subtropical high the sites on the east side of the continental divide have the highest fire frequency ca 6000 3500 cal yr b p and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late holocene this study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher than present fire frequency occurred in the past

a 1000 year record of forest fire drought and lake level change in southeastern british columbia canada high resolution charcoal analysis of lake sediments and stand age information were used to reconstruct a 1000 year fire history around dog lake which is located in the montane spruce zone of southeastern british columbia macroscopic charcoal 125 um accumulation rates char from lake sediment were compared with a modern stand origin map and fire scar dates in the kootenay valley to determine the relative area and proximity of fires recorded as char peaks small fires close to the lake and larger more distant fires appear as similar sized peaks in the record this information reinforces previous findings where char peaks represent a complex spatial aggregation of local to extra local fires around a lake site char peaks indicate frequent stand destroying fires during the mediaeval warm period ad 1000 1300 and other significant fires at c 1360 1500 1610 and 1800 we also present a proxy measure of lake level changes based on a comparison of accumulation rates of chara globulanis type oospores

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

comparisons of measured and predicted sediment transport rates in tidal currents abstract this paper describes bedload transport measurements in a large scale sedimentary system on the british continental shelf steady flow sediment transport theories are applied to oscillatory tidal currents and various equations are compared with measured transport rates from tracer dispersion experiments the effects of waves on both measured and predicted rates are briefly considered and the predicted directions of sediment movement compared with those inferred from sedimentological data

abiotic versus biotic controls on the development of the fairmont hot springs carbonate deposit british columbia canada the relict fairmont hot springs deposit formed largely of carbonates covers an area of 0ae 5k m 2 and is up to 16 m thick the triangle shaped discharge apron which broadens down valley is divided into a proximal part with beds dipping at 10 and a distal part with beds dipping at 10 to 15 the deposit is formed of the 1 basal macrophyte 2 lower carbonate 3 middle clastic 4 upper carbonate and 5 upper clastic sequences two charcoal samples embedded in the lower carbonate sequence yielded dates of 8690 90 and 8270 70 cal yr bp indicating that much of the deposit formed post glacially during the early to mid holocene deposit aggradation ceased in the mid to late holocene when the fairmont creek valley was incised the lower and upper carbonate sequences which are the thickest sequences are composed of nearly equal parts of travertine abiotic and tufa biotic with feather dendrite travertine radiating dendrite travertine and stromatolite tufa dominating competition between calcite precipitation rates and biotic growth rates controlled the distribution of tufa and travertine across the discharge apron calcite and biotic growth rates were controlled largely by flow velocity across the apron which in turn was controlled by topography and regular fluctuations in spring water discharge volume during times of high spring discharge slow sheet flow over the proximal part of the apron promoted stromatolite growth whereas fast turbulent flow on the distal part of the apron induced rapid feather dendrite formation during times of low spring discharge quiescent shallow evaporative pools conducive to radiating dendrite formation formed on the proximal part of the apron whereas slow flow on the distal part promoted stromatolite growth facies with high calcite supersaturation experienced rapid abiotic dendrite growth that precluded most biotic growth

late holocene environmental change at treeline in the northern coast mountains british columbia canada an integrated stratigraphic paleoecological and geochronological study of lake and fen sediments just beyond the terminus of berendon glacier provides insights into late holocene climate vegetation and glacier change in the northern coast mountains of british columbia cores collected from two small lakes in the foreland of berendon glacier and pits dug in a nearby fen record little lee age and older glacier advances the first little ice age advance in this area began more than 500 years ago and peaked in the early 17th century an earlier neoglacial advance began about 2800 3000 cal yr ago and may have lasted for hundreds of years there is also evidence for an intervening advance of even smaller magnitude around 1200 1300 cal yr ago the advances are broadly synchronous with those in other parts of western north america indicating that they were caused by regional possibly global changes in climate plant communities within the study area did not change dramatically during the late holocene the ranges of some plants however likely retracted or extended near treeline in response to changes in mean temperatures of perhaps 1 2degreesc as a well as changes in summer snow cover the greatest changes in vegetation occurred within and just beyond the forefields of berendon frank mackie and other nearby glaciers the largest climate shifts of the last 3000 years took place during the late little ice age and the last century climate warmed about 1 2degreesc during the 20th century accompanied by a rise in treeline an increase in coniferous tree cover in the subalpine zone and an increase in the temperature and biological productivity of ponds these trends are likely to continue if climate as expected continues to warm c 2004 elsevier ltd all rights reserved less