paleo sea ice conditions of the amundsen gulf canadian arctic archipelago implications from the foraminiferal record of the last 200 years 1 four boxcores were collected as part of the canadian arctic exchange shelf study cases in the amundsen gulf at water depths of 59 m to 600 m data from these cores help to develop a record of changes in the oceanographic history of the area over the last 200 years with particular reference to the indication of paleo sea ice formation a key element of the arctic ecosystem the four sites cover a range of water depths and environments to provide a basis for comparison the benthic foraminifera of sites ca 06 253 m water depth and ca 18 600 m water depth show an increase in arctic surface water associated agglutinated foraminifera over the last 100 years uppermost 8 to 16 cm these are indicating a decrease in sea ice cover and in cold saline arctic bottom water influence these are similar to canadian arctic archipelago postglacial faunas this contrasts with abundant planktic foraminifera at the same stations suggesting strong oceanic arctic surface influence little freshwater in the central gulf the foraminifera of sites 403b 59 m water depth and 415b 56 m water depth at the outermost edges of amundsen gulf indicate that the present day location of the winter flaw lead has been in place for at least the last 100 years with foraminiferal faunas similar to those of the beaufort shelf additionally station 415 is on an earlier holocene shoreline that is covered with cobbles

impact of riser reconstructions on estimation of secular variation in rates of strike slip faulting revisiting the cherchen river site along the altyn tagh fault nw china abstract slip rates are heavily contested for many of the first order strike slip faults within the indo asian collision zone rates determined geodetically are generally lower than those reported using reconstructions of offset landforms and it is unclear if this discrepancy reflects true secular variation in slip history systematic errors in interpretation or both here i examine the methods used to derive slip rates from reconstructions of displaced fluvial risers and show that such rates are subject to potentially important uncertainties that have largely been overlooked review of published data demonstrates that the slip rate can vary by a factor of 1 2 to 5 for the same site depending on whether the reconstruction uses the age of the upper or lower terrace for the initiation of riser offset to reduce this epistemic uncertainty i have developed six geomorphic indices that can be used to identify the most accurate end member reconstruction 1 comparison of riser offset with inset channel width 2 similarity of riser and tread displacements 3 morphological analysis of the scarp profile 4 riser deflection in plan view 5 diachroneity of terrace abandonment and 6 whether riser crests or bases yield the slip vector without the use of these geomorphic observations the epistemic uncertainty associated with current methods for determining slip rate from offset fluvial risers is likely to be so large that there is no resolvable discrepancy between the gps and geologic rates within the indo asian collision zone application of three of these indices to new field mapping of the cherchen he river site 86 4 e along the central altyn tagh fault yields a revised slip rate of 9 4 2 3 mm yr equivalent within error to the rates previously derived from gps and paleoseismic studies although reinterpretation of published data from the sulamu tagh site 87 4 is consistent with this revised rate additional work is needed to reconcile this result with some of the rates reported near aksay 94 e

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

a theoretical model coupling chemical weathering and physical erosion in landslide dominated landscapes a current theory that links the uplift of the himalayas to the drawdown of atmospheric co2 assumes that rates of chemical weathering are enhanced by accelerated physical erosion due to the increased exposure of fresh minerals although several studies have concluded that weathering rates do increase with erosion rates there is disagreement over the form of that relationship some find a linear relationship between weathering rate and erosion rate others however find that weathering is only approximately proportional to the square root of physical erosion such that changes in erosion rate are not matched by equivalent changes in weathering rate defining the nature of the relationship is critical because it determines the sensitivity of changes in weathering rate to changes in erosion rate in this study a theoretical model that couples erosion by landslides with chemical weathering processes was derived to explore the nature of this relationship in rapidly eroding landscapes results from the model suggest that where landsliding is the dominant erosional process the rate of chemical weathering is only proportional to the erosion rate raised to the 0 6 power therefore even if weathering rate is wholly dependent on erosion rate increases in erosion will not be matched by equivalent increases in chemical weathering 2007 elsevier b v all rights reserved

genesis of streamlined landforms and flow history of the green bay lobe wisconsin usa abstract the distribution of streamlined landforms in southeastern wisconsin suggests that drumlins and flutes formed during several phases of the green bay lobe between 18 and 14 000 bp the largest group of drumlins formed during a still stand of the ice margin during the johnstown phase presumably about 18 16 000 bp flutes and smaller drumlins are superimposed on larger forms and larger drumlins are remolded this indicates that drumlin modification continued during retreat three fields containing smaller drumlins formed after ice re advanced a short distance or stabilized during the green lake rush lake and st anna phases about 16 14 000 bp the drumlin forming process included erosion and deformation of pre existing ice marginal and proglacial sediments drumlins associated with the johnstown phase show an increase in length up glacier this is probably the result of variations in flow velocity length of time of drumlin formation and sediment availability flutes and small drumlins are associated with retreat moraines and formed near a thin retreating ice margin ice surface profile reconstructions suggest that margins were relatively steep during the johnstown milton green lake and early rush lake phases during the lake mills and late rush lake phases when flutes were forming the ice surface slopes were lower and margins were retreating during retreat minor sublobes developed some perhaps resulting from surges into small proglacial lake basins thus steep ice margins and driving stresses on the order of 15 25 kpa were typical during drumlin formation the formation of flutes and the remolding of larger drumlins into smaller forms took place beneath gently sloping ice of retreating margins associated with lower driving stresses

early to late pleistocene history of debris flow fan evolution in western death valley california using cosmogenic 10be and 26al abstract debris flow fans with depositional records over several 10 5 years may be useful archives for the understanding of fan construction by debris flows and post depositional surface modification over long timescales reading these archives however requires that we establish the temporal and spatial pattern of debris flow activity over time we used a combination of geomorphic mapping of fan surface characteristics digital topographic analysis and cosmogenic radionuclide dating using 10 be and 26 al to study the evolution of the warm springs fan on the west side of southern death valley california the 10 be concentrations yield dates that vary from 989 43 to 595 17 ka on the proximal fan and between 369 13 and 125 5 ka on distal fan surfaces the interpretation of these results as true depositional ages though is complicated by high inheritance with a minimum of 65 ka measured at the catchment outlet and of at least 125 ka at the distal fan results from the 26 al measurements suggest that most sample locations on the fan surfaces underwent simple exposure and were not affected by complex histories of burial and re exposure this implies that warm springs fan is a relatively stable landform that underwent several 10 5 years of fan aggradation before fan head incision caused abandonment of the proximal and central fan surfaces and deposition continued on a younger unit at the distal fan we show that the primary depositional debris flow morphology is eliminated over a time scale of less than 10 5 years which prevents the delineation of individual debris flows as well as the precise reconstruction of lateral shifts in deposition as we find it on younger debris flow fans secondary post depositional processes control subsequent evolution of surface morphology with the dissection of planar surfaces while smoothing of convex up interfluves between incised channels continues through time

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

levelling aeromagnetic survey data without the need for tie lines a new methodology that levels airborne magnetic data without orthogonal tie lines is presented in this study the technique utilizes the low wavenumber content of the flight line data to construct a smooth representation of the regional field at a scale appropriate to the line lengths of the survey levelling errors are then calculated between the raw flight line data and the derived regional field through a least squares approach minimizing the magnitude of the error with a first degree error function results in significant improvements to the unlevelled data the technique is tested and demonstrated using three recent airborne surveys

organic remains in finnish subglacial sediments abstract many sites in fennoscandia contain pre late weichselian beds of organic matter located mostly in the flanks of eskers it is a matter of debate whether these fragmentary beds were deposited in situ or whether they were deposited elsewhere and then picked up and moved by glacial ice the till mantled esker of harrinkangas includes a shallow depression filled with sand and silt containing for example several tightly packed laminar sheets of brown moss bryales remains it is argued that these thin peat sheets were transported at the base of the ice sheet or englacially and were deposited together with the silt and sand on the side of a subglacial meltwater tunnel subglacial meltout till subsequently covered the flanks of the esker near the receding ice margin information about the depositional and climatic environments was obtained from biostratigraphic analysis of the organic matter pollen spectra for the peat represent an open birch forest close to the tundra zone a thin diamicton beneath the peat contains charred pine wood recording the former presence of pine forests in western finland the unhumified extremely well preserved peat evidently originated during the final phase of an ice free period most probably the end of the eemian interglaciation it was redeposited in the esker by the last ice sheet reconstructions of the pleistocene chronology and stratigraphy of central fennoscandia that rely on such redeposited organic matter should be viewed with caution

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

subsurface heterogeneity in the geological and hydraulic properties of the hummocky paris moraine guelph ontario the advance and retreat of ice lobe margins of the laurentide ice sheet formed moraines that are a prevalent feature throughout southwestern ontario in contrast to the well studied stratified moraine complexes recessional and end moraines have largely been ignored in the context of hydrogeological studies recent urban growth has led to development pressures on these moraines and a need to better understand their hydrogeology this study presents data sets from the paris moraine near guelph ontario to examine its geomorphology internal composition and the corresponding hydraulic properties of these ice marginal features the moraine s geomorphic elements were mapped using high resolution global positioning system transects aerial photograph analysis and ground truthing nine continuous sediment cores were recovered to determine the nature and distribution of subsurface sedimentary units and their relation to the regional stratigraphic framework cores were described in detail using standard sedime

decorrugation and removal of directional trends of magnetic fields by the wavelet transform application to archaeological areas the problem of removing directional trends frequently occurs in the processing of magnetic data and also in the subsequent steps of data interpretation the so called corrugations are typical directional trends occurring in levelled data which may be removed in several ways classical techniques are based on high pass filtering of the data and successively filtering these transformed data with directional cosine filters other linear features are due to real sources such as pipelines in shallow surveys or dike swarms in regional surveys they should nevertheless be considered as noise due to the fact that their effect is strong and tends to hide the field features related to structures of more interest we deal with both kinds of problem presenting the results of a study in an archaeological area of southern italy decorrugation of magnetic field anomalies is performed using a method based on the excellent space frequency localization properties of wavelet bases allowing a very sharp filtering of the field along a selected direction we compare this technique with the classical one in a synthetic case and find that the wavelet decorrugation is simpler and produces low distortion maps besides the field decorrugation the wavelet approach was also shown to be useful in the subsequent enhancement of the measured field in fact we show that the wavelet analysis offers a unique framework where various filtering problems directional isotropic global or local as well may be easily solved as regards the archaeological case strong noisy effects from elongated sources pipelines were successfully removed in a sharp and local way

late glacial landforms of wollaston peninsula victoria island northwest territories product of ice marginal retreat surge and mass stagnation an analysis of glacial landforms on a regional scale leads to an interpretation of the dynamics of late wisconsinan glaciation on wollaston peninsula victoria island northwest territories the glacial record is dominated by four adjacent belts of landforms i ground moraine till plains and ice marginal drainage features ii hummocky moraine iii lateral and shear moraine and iv streamlined landforms the landform belts are considered as representing four distinct glacial ice conditions or regimes 1 ice margin retreat during extending flow of thin active ice 2 marginal ice stagnation following compressional flow 3 a surging ice margin producing massive shear moraines and 4 large scale flooding and mass ice stagnation following a surge these landform belts were arranged in zones by topographically controlled glacial dynamics the latter two defining a former ice stream glaciological inferences can be extended by examining the sediments and processes that produced each landform set

uncertainties in slip rate estimates for the mission creek strand of the southern san andreas fault at biskra palms oasis southern california this study focuses on uncertainties in estimates of the geologic slip rate along the mission creek strand of the southern san andreas fault where it offsets an alluvial fan t2 at biskra palms oasis in southern california we provide new estimates of the amount of fault offset of the t2 fan based on trench excavations and new cosmogenic 10be age determinations from the tops of 12 boulders on the fan surface we present three alternative fan offset models a minimum a maximum and a preferred offset of 660 m 980 m and 770 m respectively we assign an age of between 45 and 54 ka to the t2 fan from the 10be data which is significantly older than previously reported but is consistent with both the degree of soil development associated with this surface and with ages from u series geochronology on pedogenic carbonate from t2 described in a companion paper by fletcher et al this volume these new constraints suggest a range of slip rates between 12 and 22 mm yr with a preferred estimate of 14 17 mm yr for the mission creek strand of the southern san andreas fault previous studies suggested that the geologic and geodetic slip rate estimates at biskra palms differed we find however that considerable uncertainty affects both the geologic and geodetic slip rate estimates such that if a real discrepancy between these rates exists for the southern san andreas fault at biskra palms it cannot be demonstrated with available data

stable rapid rate of slip since inception of the san jacinto fault california 1 in california where the san jacinto fault sjf and san andreas fault saf accommodate the majority of the dextral shear deformation between the pacific and north american plates initiation of the sjf led to an apparent decline in the slip rate of the saf previous studies suggest that since then slip rate has covaried between these faults possibly due to changes in fault strength variation in topographic loading along a fault or the development of new faults and that presently the sjf is the dominant plate boundary structure however we dated displaced sedimentary deposits and landforms over three distinct time intervals since 700 ka and our results imply a constant slip rate of 12 1 3 4 2 6 mm yr this rate is similar to the fault s lifetime rate and from rates derived from geodesy suggesting that since the sjf initiated its slip rate has remained relatively stable and does not exceed that of the saf

major end moraines of younger dryas age on wollaston peninsula victoria island canadian arctic implications for paleoclimate and for formation of hummocky moraine some of the most extensive and massive end moraines of younger dryas age 11 10 14c ka bp yet recognized in north america occur on wollaston peninsula of victoria island on the western part of the peninsula numerous closely spaced end moraines formed in the interval starting 11 100 100 radiocarbon years ago and ending about 10 500 10 200 years ago net recession was generally slow throughout and was punctuated by moraine building and at least two readvances recession is mapped with a resolution that is approximately decadal the moraines form an orderly nested succession and are consistently associated with westward shedding of meltwater which formed a sequence of marine limit deltas we lack firm independent proxy climate evidence needed to assess whether these moraines formed because of cold younger dryas climate rather than because of controls such as topographic setting and water depth but climatic control seems probable the moraines evidently retain glacier ice cores as do most similarly

dilution of 10be in detrital quartz by earthquake induced landslides implications for determining denudation rates and potential to provide insights into landslide sediment dynamics the concentration of 10be in detrital quartz 10beqtz from river sediments is now widely used to quantify catchment wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10beqtz major landslide triggering events can provide large amounts of low concentration material to rivers in mountain catchments but changes in river sediment 10beqtz due to such events have not yet been measured directly here we examine the impact of widespread landslides triggered by the 2008 wenchuan earthquake on 10beqtz in sediment samples from the min jiang river basin in sichuan china landslide deposit material associated with the wenchuan earthquake has consistently lower 10beqtz than in river sediment prior to the earthquake river sediment 10beqtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence i e with greater than 0 3 of the upstream catchment area affected by landslides because of input of the 10be depleted landslide material but showed no systematic changes where landslide occurrence was low changes in river sediment 10beqtz concentration were largest in small first order catchments but were still significant in large river basins with areas of 104 105 km2104 105 km2 spatial and temporal variability in river sediment 10beqtz has important implications for inferring representative denudation rates in tectonically active landslide dominated environments even in large basins although the dilution of 10beqtz in river sediment by landslide inputs may complicate interpretation of denudation rates it also may provide a possible opportunity to track the transport of landslide sediment the associated uncertainties are large but in the wenchuan case calculations based on 10be mixing proportions suggest that river sediment fluxes in the 2 3 years following the earthquake increased by a similar order of magnitude in the 0 25 1 mm and the 0 25 mm size fractions as determined from 10beqtz mixing calculations and hydrological gauging respectively such information could provide new insight into sediment transfer with implications for secondary sediment related hazards and for understanding the removal of mass from mountains

numerical and analytical models of cosmogenic radionuclide dynamics in landslide dominated drainage basins 1 in many tectonically active regions on earth landslides dominate sediment delivery to channels while cosmogenic radionuclides crn represent a valuable tool to document basin averaged erosion rates a better understanding of crn dynamics in these systems is required before erosion rates can be reliably inferred from crn concentrations the stochastic nature of landslides results in variability of crn concentrations in both alluvial and hillslope samples that is both difficult to document and poorly understood to guide sampling strategies we developed a 2 d plan view model to simulate the influence of landslides on crn dynamics we employ a sediment mixing model in which concentrations of crns from material eroded by both landslides and steady processes are combined to evaluate how best to infer erosion rates from crn concentrations this model is further used to test a new analytical solution for the distribution of crn concentrations on hillslopes in a landslide prone system results suggest that for landscapes dominated by deep 5 m landslides only large drainage basins 100 km2 provide consistently reliable estimates of erosion rates from crn concentrations for landscapes dominated by shallow landslides 0 7 2 m smaller basins can produce reliable estimates results further suggest that the distribution of concentrations from hillslope samples could be used to deduce the relative contribution of material derived from landslide and steady processes these findings underscore the need to consider carefully the sources of natural variability in sampling and analyzing crns if properly done the variability can reveal useful information about geomorphic processes in landslide prone areas

subglacial hydraulic conditions and their possible impact upon subglacial bed formation abstract in reviewing hypotheses of subglacial bed formation it becomes apparent that a close relationship must exist between the development of these bedforms and subglacial hydraulic conditions a speculative classification of subglacial temperate beds is presented subglacial beds are subdivided into h q and m beds h beds are typically hard beds in which upper interface meltwater activity dominates m beds are those in whichd soft mobile subglacial debris conditions prevail and in which advective pervasive f flow of saturated debris occurs in q beds both of the other bed types occur but are of a spatially and temporally transitory nature thus this latter bed type may be the most common beneath ice masses it is under an m bed state that many drumlin subglacial bedforms and associated forms are thought to develop discussion on the processes involved in mobile debris entrainment and the effect of changing rheological parameters are developed it is argued that such bedform initiation occurs due to anisotropic rheological variations within the mobile debris setting up a feedback effect such conditions are thought to be found most likely at the lower interface of a fast moving ice mass possibly typical of an ice stream in using empirical analyses of mobile debris conditions a limited set of relationships between subglacial meltwater flux rates basal ice velocity debris porosity and bed width are established with reference to mobile debris thicknesses using this relationship a set of possible parameter values that would allow bed formation to be achieved are presented the impact of bed formation under these conditions upon possible sedimentological facies and deformation structures is postulated the wider effect of m bedd conditionsd on subglacial sedimentology is introduced and the need to investigate subglacial hydraulic and bed conditions under past glaciations from the evidence of their glacial sediments and landforms emphasised

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

a mechanistic erosion model for cosmogenic nuclide inheritance in single clast exposure ages abstract terrestrial cosmogenic nuclides tcns produced by the bombardment of earth s surface by cosmic rays are widely used for age dating and pacing surface processes sediments carry an inherited tcn concentration useful for quantifying erosion and transport rates but that must be subtracted when age dating sedimentary landforms such as alluvial fans here we present a mechanistic model of inheritance based on the contributions of episodic erosion by landsliding and steady background erosion due to soil formation the balance of these processes revealed by the distribution of inheritance recorded by a population of individual surface clasts affects rates of soil generation and the cycling of material through the earth s critical zone the surficial layer upon which all terrestrial life depends we test our inheritance model on alluvial fan tcn datasets drawn from a global compilation of active fault slip rate studies inheritance corrected landform ages are systematically younger than published ages our results reveal a consistent signature of spatiotemporal clustering of landslides important for quantifying hazard and for understanding the coupling of physical and chemical erosion application of our inheritance model provides a rigorous approach to correcting landform ages for inheritance and reveals information on landslide frequency with broad implications for hazard and land use

aeromagnetic data in the uk a study of the information content of baseline and modern surveys across anglesey north wales a number of modern multiparameter high resolution airborne geophysical surveys termed hires have been conducted over the past decade across onshore uk these were undertaken in part as a response to the limited resolution of the existing uk national baseline magnetic survey data set acquired in the late 1950s and early 1960s modern magnetic survey data obtained with higher precision and reduced line spacing and elevation provide an improved data set however the distinctions between the two available resources existing and new are rarely quantified in this contribution we demonstrate and quantify the improvements that can be anticipated using the new data the information content of the data sets is examined using a series of modern processing and modelling procedures that provide a full assessment of their resolution capabilities the framework for the study involves two components the first relates to the definition of the shallow magnetic structure in relation to an ongoing 1 10 k and 1 50 k geological map revision the second component relates to the performance of the datasets in defining maps of magnetic basement and assisting with larger scale geological and structural interpretation one of the smaller hires survey areas the island of anglesey ynys mon off the coast of nw wales is used to provide a series of comparative studies the geological setting here is both complex and debated and cultural interference is prevalent in the low altitude modern survey data it is demonstrated that successful processing and interpretation can be carried out on data that have not been systematically corrected decultured for non geological perturbations across the survey area a wide number of near surface magnetic features are evident and are dominated by a reversely magnetized palaeogene dyke swarm that extends offshore the average depth to the upper surfaces of the dykes is found to be 44 m the existing baseline data are necessarily limited in resolving features 3 km to upper surface assessments of magnetic basement this further assessment is successfully provided by the larger scale baseline data which locates and defines a mid crustal magnetic basement feature centred beneath the snowdon massif and illustrates that basement of similar characteristic extends beneath much of anglesey

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

late quaternary slip rate along the central bangong chaxikang segment of the karakorum fault western tibet insight into the spatial and temporal changes of slip rate is essential to understand the kinematic role of large strike slip faults in continental collision zones geodetic and geologic rates from present to several million years ago along the karakorum fault range from 0 to 11 mm yr here we determine the first late quaternary slip rate at the southern end of the linear bangong chaxikang segment of the karakorum fault using cumulative offsets 20 200 m of fans and terraces at three sites as well as 74 new 10 be surface exposure ages to constrain the age of these offset geomorphic markers the rate is 3 mm yr at sites gun and chaxikang and it is 1 7 2 2 mm yr at the gar fan site together with rates obtained along the southernmost menshi kailas segment the karakorum fault slip rate seems to increase southeastward from south of bangong lake to kailas from 3 to 8 mm yr these karakorum fault slip rate data 3 8 mm yr together with the total length of the fault 1000 km and its initiation age 13 23 ma confirm that the karakorum fault is the major fault accommodating dextral strike slip motion ne of the western himalayas the dextral karakorum fault in the south and the conjugate left lateral longmu co altyn tagh fault system in the north are thus the major strike slip faults of western tibet which contribute to eastward extrusion of tibet

slip rates on the fish springs fault owens valley california deduced from cosmogenic 10be and 26al and soil development on fan surfaces long term deformation along the fish springs fault in owens valley california is recorded by offset landforms including a previously dated cinder cone 39 ar 40 ar 314

subglacial bedform evidence for a major palaeo ice stream and its retreat phases in amundsen gulf canadian arctic archipelago ascertaining the location of palaeo ice streams is crucial in order to produce accurate reconstructions of palaeo ice sheets and examine interactions with the ocean climate system this paper reports evidence for a major ice stream in amundsen gulf canadian arctic archipelago mapping from satellite imagery landsat etm and digital elevation models including bathymetric data is used to reconstruct flow patterns on southwestern victoria island and the adjacent mainland nunavut and northwest territories several flow sets indicative of ice streaming are found feeding into the marine trough and cross cutting relationships between these flow sets and utilising previously published radiocarbon dates reveal several phases of ice stream activity centred in amundsen gulf and dolphin and union strait a large erosional footprint on the continental shelf indicates that the ice stream ca 1000 km long and ca 150 km wide filled amundsen gulf probably at the last glacial maximum subsequent to this the ice stream reorganised as the margin retreated back along the marine trough eventually splitting into two separate low gradient lobes in prince albert sound and dolphin and union strait the location of this major ice stream holds important implications for ice sheet ocean interactions and specifically the development of arctic ocean ice shelves and the delivery of icebergs into the western arctic ocean during the late pleistocene copyright c 2006 john wiley sons ltd

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

controlled moraines origins characteristics and palaeoglaciological implications abstract controlled moraines are supraglacial debris concentrations that become hummocky moraine upon de icing and possess clear linearity due to the inheritance of the former pattern of debris rich folia in the parent ice linearity is most striking wherever glacier ice cores still exist but it increasingly deteriorates with progressive melt out as a result moraine linearity has a low preservation potential in deglaciated terrains but hummocky moraine tracts previously interpreted as evidence of areal stagnation may instead record receding polythermal glacier margins in which debris rich ice was concentrated in frozen toe zones recent applications of modern glaciological analogues to palaeoglaciological reconstructions have implied that a controlled moraine development can be ascribed to a specific process e g englacial thrusting or supercooling and b controlled moraine preservation potential is good enough to imply the occurrence of the specific process in former glacier snouts e g ancient polythermal or supercooled snouts these assumptions are tested using case studies of controlled moraine construction in which a wide range of debris entrainment and debris rich ice thickening mechanisms are seen to produce the same geomorphic features polythermal conditions are crucial to the concentration of supraglacial debris and controlled moraines in glacier snouts via processes that are most effective at the glacier permafrost interface end moraines lie on a process form continuum constrained by basal thermal regime the morphological expression of englacial structures in controlled moraine ridges is most striking while the moraines retain ice cores but the final deposits landforms tend to consist of discontinuous transverse ridges with intervening hummocks preserving only a weak impression of the former englacial structure these are arranged in arcuate zones of hummocky moraine up to 2 km wide containing ice walled lake plains and lying down flow of streamlined landforms produced by warm based ice a variety of debris entrainment mechanisms can produce the same geomorphic signature spatial and temporal variability in process form relationships will lead to the sequential development of different types of end moraines during the recession of a glacier or ice sheet margin

new marine evidence for a late wisconsinan ice stream in amundsen gulf arctic canada abstract amundsen gulf and adjoining dolphin and union strait and coronation gulf form the southwestern end of the northwest passage adjacent to the beaufort sea extensive high resolution multibeam sonar imagery and sub bottom profiles of the seabed have been acquired primarily in amundsen gulf by arcticnet and the ocean mapping group at the university of new brunswick these data reveal a variety of seabed landforms including mega scale glacial ridge and groove lineations drumlins moraines iceberg scours bedrock outcrops and discontinuous sediment deposits of variable thickness the lineations are widespread especially in southeastern amundsen gulf they resemble modern and paleo bedforms reported from antarctica svalbard greenland and other canadian arctic channels where they have been ascribed to ice streams the glacial sole marks on the seabed in amundsen gulf and regional data from the adjacent mainland and islands outline the configuration of a glacial ice stream from the laurentide ice sheet that occupied amundsen gulf and adjoining waterways during the late wisconsinan part of the northwestward flowing ice stream was deflected around the colville mountains on victoria island and rejoined the main ice stream in amundsen gulf by way of prince albert sound the grounded amundsen gulf ice stream extended northwestward to the outer slope in the beaufort sea where it was buttressed by arctic shelf ice maximum ice stream extent is inferred to have been coincident with the late glacial maximum multi sequence ice contact sediments and stratigraphic relations with glaciomarine sediments indicate that several ice advances and retreats occurred in the northwestern part of the gulf final retreat from the maximum position began prior to 13 000 cal yr bp and terrestrial dates indicate that the retreating ice front had reached dolphin and union strait by about 12 5 cal ka bp

analysis of historical landslide time series in the emilia romagna region northern italy a catalogue of historical landslides 1951 2002 for three provinces in the emilia romagna region of northern italy is presented and its statistical properties studied the catalogue consists of 2255 reported landslides and is based on historical archives and chronicles we use two measures for the intensity of landsliding over time i the number of reported landslides in a day dl and ii the number of reported landslides in an event sevent where an event is one or more consecutive days with landsliding from 1951 2002 in our study area there were 1057 days with 1 dl 45 landslides per day and 596 events with 1 sevent 129 landslides per event in the first set of analyses we find that the probability density of landslide intensities in the time series are power law distributed over at least two orders of magnitude with exponent of about 2 0 although our data is a proxy for landsliding built from newspaper reports it is the first tentative evidence that the frequency size of triggered landslide events over time not just the landslides in a given triggered event like earthquakes scale as a power law or other heavy tailed distributions if confirmed this could have important implications for risk assessment and erosion modelling in a given area in our second set of analyses we find that for short antecedent rainfall periods the minimum amount of rainfall necessary to trigger landslides varies considerably with the intensity of the landsliding dl and sevent whereas for long antecedent periods the magnitude is largely independent of the cumulative amount of rainfall and the largest values of landslide intensity are always preceded by abundant rainfall further the analysis of the rainfall trend suggests that the trigger of landslides in the study area is related to seasonal rainfall copyright 2010 john wiley sons ltd

ice keel seabed features in marine channels of the central canadian arctic archipelago evidence for former ice streams and iceberg scouring abstract the study area lies within the central part of the canadian arctic archipelago a region that was covered by the laurentide ice sheet during the late wisconsinan glaciation and earlier multibeam imagery from widely spaced transects indicates the presence of linear groove and ridge features on the seabed at several localities in peel sound franklin strait northern larsen sound and within m clintock channel these lineations resemble features in antarctica and in several formerly glaciated regions that have been interpreted to be sole marks emplaced beneath fast flowing ice streams based on these analogies a similar origin is inferred for the lineations on the channel floors within the study area the lineations are oriented parallel to the channel axes and margins they occur on all transects within the bathymetrically deeper area at the junction of franklin strait and peel sound northward in peel sound they occur extensively on the western and central transects and more locally on the eastern transect their north south orientation is normal to that of glacial flow features on somerset island and most of eastern prince of wales island which border peel sound to the east and west respectively the trend of the lineations is northeasterly parallel to the channel axis in franklin strait and mainly northerly in larsen sound and m clintock channel elsewhere the seabed imagery commonly displays scours of various sizes and orientations created by the keels of icebergs seabed sediments revealed by 3 5 khz sub bottom profiles are interpreted to consist primarily of ice contact sediments that in part are thinly mantled by draped water lain sediments the age of the lineations has not been established possibly their formation was coincident with an ice stream in the m clintock channel eastern victoria island region which formed an ice shelf in viscount melville sound that grounded on southern melville and byam martin islands at ca 10 4 9 6 14 c ka bp alternatively they could result from later glacial events

millennial scale record of landslides in the andes consistent with earthquake trigger landslide deposits are often interpreted as the consequence of precipitation a millennial scale record of landslides inferred from river cobbles in the arid andes is instead consistent with earthquake triggering

chemical weathering in active mountain belts controlled by stochastic bedrock landsliding in active mountain belts erosion is driven by bedrock landsliding river water chemistry in new zealand s southern alps suggests that stochastic mass wasting processes also enhance chemical weathering in such environments a link between chemical weathering and physical erosion exists at the catchment scale over a wide range of erosion rates1 2 however in mountain environments where erosion rates are highest weathering may be kinetically limited3 4 5 and therefore decoupled from erosion in active mountain belts erosion is driven by bedrock landsliding6 at rates that depend strongly on the occurrence of extreme rainfall or seismicity7 although landslides affect only a small proportion of the landscape bedrock landsliding can promote the collection and slow percolation of surface runoff in highly fragmented rock debris and create favourable conditions for weathering here we show from analysis of surface water chemistry in the southern alps of new zealand that weathering in bedrock landslides controls the variability in solute load of these mountain rivers we find that systematic patterns in surface water chemistry are strongly associated with landslide occurrence at scales from a single hillslope to an entire mountain belt and that landslides boost weathering rates and river solute loads over decades we conclude that landslides couple erosion and weathering in fast eroding uplands and thus mountain weathering is a stochastic process that is sensitive to climatic and tectonic controls on mass wasting processes

depositional history of the north taymyr ice marginal zone siberia a landsystem approach the sediment landform associations of the northern taymyr peninsula in arctic siberia tell a tale of ice sheets advancing from the kara sea shelf and inundating the peninsula probably three times during the weichselian in each case the ice sheet had a margin frozen to its bed and an interior moving over a deforming bed the north taymyr ice marginal zone ntz comprises ice marginal and supraglacial landsystems dominated by thrust block moraines 2 3 km wide and large scale deformation of sediments and ice large areas are still underlain by remnant glacier ice and a supraglacial landscape with numerous ice walled lakes and kames is forming even today the proglacial landsystem is characterised by subaqueous e g deltas or terrestrial e g sandar environments depending on location altitude and time of formation dating results osl c 14 indicate that the ntz was initiated ca 80 kyr bp during the retreat of the early weichselian ice sheet and that it records the maximum limit of a middle weichselian glaciation ca 65 kyr bp during both these events proglacial lakes were dammed by the ice sheets part of the ntz was occupied by a thin late weichselian ice sheet 20 12 kyr bp resulting in subaerial proglacial drainage copyright c 2002 john wiley sons ltd

terrestrial ice streams a view from the lobe abstract the glacial landforms of minnesota are interpreted as the products of the lobate extensions of ice streams that issued from various ice sheds within the laurentide ice sheet low relief till plains trough shaped lowlands boulder pavements and streamlined forms make up the subglacial landsystem in minnesota that is interpreted as having been formed by streaming ice extremely uniform tills are created subglacially in a way that remains somewhat mysterious at the ice margins thrust moraines and hummocky stagnation topography are more common than single crested simple moraines if the ice lobes had repeated advances subglacial drainage features are obscure up ice but are present down ice in the form of tunnel valleys eskers spooner hills and associated ice marginal fans ice streaming may occur when basal shear stress is lowered as a result of high subglacial water pressure subglacial conditions that allow the retention of water will allow an ice lobe to extend far beyond the ice sheet as long as the ice shed also supports the advance by supplying adequate ice even with adequate ice flux however the advance of an ice lobe may be terminated at least temporarily if the subglacial water is drained through tunnel valleys or perhaps a permeable substrate thrust moraines and ice stagnation topography will result from sudden drainage although climate change is ultimately responsible for the accumulation of ice in the laurentide ice sheet the asynchronous advances and retreats of the ice lobes in the mid continent are strongly overprinted by the internal dynamics of individual ice streams as well as the interaction of ice sheds which obscure the climate signal

late quaternary sea level history in the paulatuk to bathurst inlet area northwest territories the paulatuk bathurst inlet region experienced rapid deglaciation in response to marine incursion across isostatically depressed terrain during high relative sea level stands marine limits freq

late pleistocene slip rate of the central haiyuan fault constrained from optically stimulated luminescence 14c and cosmogenic isotope dating and high resolution topography the haiyuan fault is a major left lateral active fault of the india asia collision zone while the 1000 km long fault between hala lake in the west to liupan shan in the east accommodates eastward displacement of northeast tibet relative to the gobi alashan to the north the amount of slip accumulated and its slip rate remain debated we revisit the site of daqing or sangedun at 102 7 e in gaudemer et al 1995 to better constrain the long term slip rate of the haiyuan fault in its central part we used terrestrial lidar to build a high resolution dem and unmanned aerial vehicle to build an aerial photomosaic with 0 1 m resolution to survey the offset terraces their geomorphology and the fault trace we refine the geomorphological interpretation of the site measure riser offsets and determine their relation to terrace formation the well constrained age of the highest terrace t3 at 13 7 1 5 ka determined from the combination of surface and sub surface osl 14 c and terrestrial in situ 10 be cosmogenic nuclide dating associated with the maximum lower terrace riser offset of 88 m yield a minimum slip rate of 6 4 1 2 mm yr over the late pleistocene the age of the intermediate terrace t2 is bracketed between 8 0 ka 14 c and 12 ka 10 be the ages and vertical offsets of the 2 highest terraces is used to infer the age of t2 offset vertically 5 7 m at 5 4 1 ka its 29 2 m offset is consistent with a rate of 6 5 mm yr given the vertical offset youngest terrace t1 of 1 3 0 2 m its age is estimated at 1 2 0 2 ka in agreement with the youngest surface exposure age overall a slip rate of 5 8 mm yr fits all offset and age data at the daqing site the smallest offset of a gully incised into t1 of 6 0 0 5 m is potentially associated with the most recent slip event that occurred in the last millennia

microlevelling procedures applied to regional aeromagnetic data an example from the transantarctic mountains antarctica the extensive application of digital enhancement and filtering as a powerful tool for aeromagnetic interpretation not only of high resolution but also of regional data requires an improved levelling two microlevelling techniques were thus compared in order to find an effective but relatively simple procedure to remove or at least to reduce residual magnetic errors remaining after standard levelling processes this study was carried out on regional aeromagnetic data recently acquired at high magnetic latitudes along the transantarctic mountains in antarctica where it is particularly critical to remove time dependent magnetic variations two dimensional fft filters applied to the gridded data namely the butterworth and a directional cosine filter proved to be more effective than previously proposed one dimensional space domain filters in the reduction of the residual corrugation not removed by statistical levelling tectonic interpretation of trends detected in the total field magnetic anomaly map and in the 3d analytic signal improved after application of frequency domain microlevelling however we also show that when interpreting microlevelled data two factors must be considered i the possible presence of real geological trends aligned along the flight lines ii modifications in the results yielded by depth estimates of magnetic sources due to the fft filters applied during the microlevelling procedure such changes were seen both in the well established 2d fft method based on the slope of the energy spectrum and in the more recent 3d euler deconvolution technique overall our results indicate that microlevelling could profitably be applied to older gridded aeromagnetic data sets in antarctica thus improving the accuracy and geological significance of future regional magnetic compilations as already seen in other continents

subglacial processes of the scandinavian ice sheet in fennoscandia inferred from flow parallel features and lithostratigraphy abstract subglacial processes of the last scandinavian ice sheet in fennoscandia were investigated on two different scales a detailed case study in southwestern finland and a generalized study in the central parts of the ice sheet previously reconstructed time transgressive glacial flow patterns were correlated with different types of glacial flow parallel features and lithostratigraphic units the comparison of orientations of each flow parallel feature with relative ages of different flow patterns enabled estimations of relative distances of the orientation generating processes in relation to the receding ice margin this method was also used to infer sedimentary environments of each lithostratigraphic facies identified generalized lithostratigraphic sequences were compiled in fennoscandia using sections described previously in areas of ice streams a sandy till showing mature deformation structures forms till sheets drumlins and some ribbed moraines the facies is overlain by occasional glaciofluvial deposits and partly washed deformation till both indicating abundant excess water at the ice bed interface in interlobate areas glaciofluvial material is under and overlain by a silty till showing ductile deformation structures in places uppermost thin clayey till interpreted to be a subglacial melt out till mantles underlying till and subglacial glaciofluvial deposits the characteristics of different units are controlled by ice flow velocities subglacial hydrology and deformation type of the substratum the time transgressive origin of till beds and intervening washed sediment as well as divergent ice flow patterns is emphasized ice flow was concentrated in streams which generated marginal fan shaped lobes interstream areas of low basal velocities and melting rates were left between adjacent ice streams in areas of ice streams fast basal ice flow velocities continuously generated heat and meltwater which flowed at first in the sediment and closer to the margin also in thin discontinuous sheets at the ice bed interface excess water may have subsequently formed a linked cavity system and channelized to a tunnel network initiating esker deposition or incision of tunnel channels most processes operated continuously during deglaciation with spatial and temporal differences in their activity the mode of subglacial drainage changed periodically during deglaciation and was probably controlled by the volume of subglacial meltwater available in some periods sheet flow of basal water deposited major marginal complexes and subsequently tunnel networks were re established esker pattern and sedimentation rates of proglacial varved clays indicate that tunnel drainage of subglacial water was partly episodic

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

geochemical methods to infer landscape response to quaternary climate change and land use in depositional archives a review abstract understanding and quantifying the processes and geochemical cycles associated with catchment erosion the development of soils and weathering horizons and terrestrial habitat change beyond the scales of modern observations remain challenging such research however has become increasingly important to help predict future landscape change in light of increasing land use and rapid global warming we herein review organic and inorganic geochemical tools applied to depositional archives to better understand various aspects of landscape evolution on geological time scales we highlight the potentials and limitations of inorganic geochemical analytical methods such as major element geochemistry metal and radiogenic isotopes and in situ cosmogenic nuclides as qualitative semi quantitative and quantitative proxies for the transformation of bedrock material via regolith and soils to sediments we also show how stable isotope geochemistry applied to lacustrine endogenic carbonates can be used to infer rock water interactions vegetation change and soil development in limestone rich catchments proxies focusing on the silicilastic element of sediment formation transport and deposition are ideally combined with organic geochemical proxies for vegetation change and soil organic matter evolution in a catchment to gain a comprehensive picture of the critical zone s evolution over time multi proxy and multidisciplinary research combining organic and inorganic geochemical techniques from several sedimentary archives in the same catchment have high potential to provide comprehensive information on quaternary landscape evolution and thus improve the robustness of associated forecasting models

drumlins products of controlled or uncontrolled glaciodynamic response abstract two schools of thought on the process of drumlin formation have recently developed that have created a controversy within this ara of glacial geology one hypothesis contends that drumlins are in the main developed within a soft mobile subglacial debris zone the other school argues that for those drumlins that contain primary deposited stratified sediment formation during catastrophic subglacial flood events is necessary a classification of subglacial bed types is presented that allows for the accommodation of both schools it is proposed that a new paradigm for subglacial research may be needed in order that a closer relationship between glaciodynamics and sedimentological processes be established in future attempts at explaining glacial processes and froms

airborne geophysical data leveling based on line to line correlations a new technique removes the leveling errors in airborne geophysical data based on an assumption that the data are continuous i e not renulled or recalibrated from line to line a single flight line is selected as a reference to level and tie all survey lines to this continuously varying datum the leveling errors are determined in a least squares sense from the reference line and the adjacent line to be leveled the technique markedly improves the quality of the unleveled raw data and works best if the reference line overlaps most of the line being leveled this method cannot distinguish a linear geologic feature in the direction of flight lines from a leveling error the technique initially was developed for airborne electromagnetic em data in cases where tie line leveling works poorly however it may also be used for airborne magnetic and other data in which case tie lines used in conventional leveling techniques are not needed

leveling total field aeromagnetic data with measured horizontal gradients temporal changes in the earth s magnetic field occur in the frequency band of millihertz to a few hertz amplitudes of variations above 0 1 hz are usually much smaller than 1 nt changes of 50 100 nt over periods of a few hours are not uncommon

seismic stratigraphy sedimentary architecture and palaeo glaciology of the mackenzie trough evidence for two quaternary ice advances and limited fan development on the western canadian beaufort sea margin abstract a comprehensive grid of high resolution 2 d seismic reflection data from the western canadian beaufort sea margin is used to reconstruct past ice stream dynamics within the mackenzie trough eight seismic facies and five sequences divided into two megasequences are identified from the mackenzie trough stratigraphy evidence for two quaternary ice advances to the shelf break is provided by two sequences of acoustically chaotic to semi transparent facies interpreted as subglacial till buried landforms interpreted as lateral moraines and a grounding zone wedge record the positions of still stands or re advances in the ice margin the continental slope beyond the trough is characterised by canyons separated by inter canyon ridges and thin glacigenic debris flows correlation with the onshore record suggests that the older of the two ice advances which excavated the mackenzie trough probably occurred during the illinoian or early wisconsinan glaciations the younger ice stream advance is interpreted to have occurred during the last late wisconsinan glaciation the onset of cross shelf glaciation on the western canadian beaufort sea margin is inferred to have been initiated significantly later than on the eastern beaufort sea and eastern canadian arctic margins which have a longer history of ice advance and were less peripheral to the ice sheet centre the architecture of the slope beyond the mackenzie trough reflects this comparatively short history of ice advance and lacks the progradational architecture and major glacial sedimentary depocentre or trough mouth fan that is characteristic of slopes seaward of cross shelf troughs on formerly glaciated margins

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

meltwater intensive glacial retreat in polar environments and investigation of associated sediments example from pine island bay west antarctica abstract modern pine island and thwaites glaciers which both drain into pine island bay are among the fastest changing portions of the cryosphere and the least stable ice streams in antarctica here we show that the uppermost sediment unit in pine island bay was deposited from a meltwater plume a plumite during the late stages of ice sheet retreat 7 8 6 k cal yr bp and argue that this deposit records episodes of meltwater intensive sedimentation the plumite is a hydraulically sorted glacially sourced draping deposit that overlies proximal glacimarine sediments and thickens towards the modern grounding line the uppermost sediment unit is interpreted as a product of non steady state processes in which low background sedimentation in large bedrock carved basins alternates with episodic purging of sediment laden water from these basins the inner part of pine island bay contains several basins that are linked by channels with a storage capacity on the order of 70 km 3 of stagnant water and significant sediment storage capacity purging of these basins is caused by changes in hydraulic potential and glacial reorganization the sediment mobilized by these processes is found here to total 120 km 3 this study demonstrates that episodes of meltwater intensive sedimentation in pine island bay occurred at least three times in the holocene the most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit we note that the final phase of ice stream retreat in marguerite bay was marked by a similar sedimentary event and suggest that the modern thwaites glacier is poised for an analogous meltwater intensive phase of retreat

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined