orogen response to changes in climatic and tectonic forcing despite much progress many questions remain regarding the potential dynamic coupling between atmospheric and lithospheric processes in the long term evolution of mountain belts as a complement to recent efforts to discover the interrelationships among climate topography erosion and rock deformation under conditions of mass flux steady state we explore orogen response to changes in climate and tectonic influx we derive an analytical model that predicts a powerful climatic control on orogen evolution and distinct potentially diagnostic responses to climatic and tectonic perturbations due to isostatic compensation the near surface rock uplift rate during transients is tightly coupled to climate modulated erosional efficiency system response is approximately exponential with a characteristic response timescale that is inversely proportional to the climate and lithology modulated erosional efficiency and is largely insensitive to initial conditions tectonic influx and both the sign and magnitude of perturbations

greenland flow variability from ice sheet wide velocity mapping using radarsat synthetic aperture radar data we have mapped the flow velocity over much of the greenland ice sheet for the winters of 2000 01 and 2005 06 these maps provide a detailed view of the ice sheet flow including that of the hundreds of glaciers draining the interior the focused patterns of flow at the coast suggest a strong influence of bedrock topography differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes the overall pattern is one of speed up accompanied by terminus retreat but there are also several instances of surge behavior and a few cases of glacier slowdown comprehensive mappings such as these at regular intervals provide an important new observational capability for understanding ice sheet variability

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

nao implicated as a predictor of northern hemisphere mean temperature multidecadal variability 1 the twentieth century northern hemisphere mean surface temperature nht is characterized by a multidecadal warming cooling warming pattern followed by a flat trend since about 2000 recent warming hiatus here we demonstrate that the north atlantic oscillation nao is implicated as a useful predictor of nht multidecadal variability observational analysis shows that the nao leads both the detrended nht and oceanic atlantic multidecadal oscillation amo by 15 20 years theoretical analysis illuminates that the nao precedes nht multidecadal variability through its delayed effect on the amo due to the large thermal inertia associated with slow oceanic processes an nao based linear model is therefore established to predict the nht which gives an excellent hindcast for nht in 1971 2011 with the recent flat trend well predicted nht in 2012 2027 is predicted to fall slightly over the next decades due to the recent nao decadal weakening that temporarily offsets the anthropogenically induced warming

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

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

complex force history of a calving generated glacial earthquake derived from broadband seismic inversion the force applied to the earth by the calving of two icebergs at jakobshavn isbrae greenland has been quantified the source force history was recovered by inversion of regional broadband seismograms without any a priori constraint on the source time function in contrast with previous studies for periods 10 100 s the three component force can be obtained from distant stations alone and is proportional to the closest station seismograms this inversion makes it possible to quantify changes of the source force direction and amplitude as a function of time and frequency a detailed comparison with a video of the event was used to identify four forces associated with collision then bottom out and top out rotation of the first and second icebergs and ice melange motion only the two iceberg rotations were identified in previous studies all four processes are found here to contribute to the force amplitude and variability such a complete time frequency force history provides unique dynamical constraints for mechanical calving models

ice front variation and tidewater behavior on helheim and kangerdlugssuaq glaciers greenland we used satellite images to examine the calving behavior of helheim and kangerdlugssuaq glaciers greenland from 2001 to 2006 a period in which they retreated and sped up these data show that many large iceberg calving episodes coincided with teleseismically detected glacial earthquakes suggesting that calving related processes are the source of the seismicity for each of several events for which we have observations the ice front calved back to a large pre existing rift these rifts form where the ice has thinned to near flotation as the ice front retreats down the back side of a bathymetric high which agrees well with earlier theoretical predictions in addition to the recent retreat in a period of higher temperatures analysis of several images shows that helheim retreated in the 20th century during a warmer period and then re advanced during a subsequent cooler period this apparent sensitivity to warming suggests that higher temperatures may promote an initial retreat off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into deeper water the cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in greenland can advance rapidly greenland s larger reservoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance

dynamics of glacier calving at the ungrounded margin of helheim glacier southeast greenland during summer 2013 we installed a network of 19 gps nodes at the ungrounded margin of helheim glacier in southeast greenland together with three cameras to study iceberg calving mechanisms the network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved data collection covered 55 days and many nodes survived in locations right at the glacier front to the time of iceberg calving the observations included a number of significant calving events and as a consequence the glacier retreated 1 5 km the data provide real time high frequency observations in unprecedented proximity to the calving front the glacier calved by a process of buoyancy force induced crevassing in which the ice downglacier of flexion zones rotates upward because it is out of buoyant equilibrium calving then occurs back to the flexion zone this calving process provides a compelling and complete explanation for the data tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier interpretation of the gps data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating ice downglacier of the flexion zone before calving the flexion zones are probably formed by the exploitation of basal crevasses and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium thus this calving mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in greenland

effects of terrain smoothing on topographic shielding correction factors for cosmogenic nuclide derived estimates of basin averaged denudation rates estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates the scaling methods of cosmic ray intensities and the correction algorithms for skyline snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production while the calculation of surface nuclide production and application of latitude altitude and palaeointensity scaling algorithms are subjects of active research the importance of additional correction for shielding by topographic obstructions snow and vegetation is the subject of ongoing debate the derivation of all additional correction factor for skyline shielding for large areas is still problematic one important issue that has yet to he addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model dem on topographic shielding collection factors topographic metrics scale with the resolution of the elevalion data and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding for rough high relief landscapes the effect of terrain smoothing call easily exceed analytical errors and should be taken into account here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics copyright c 2008 john wiley and sons ltd

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

spatial and temporal variations in greenland glacial earthquake activity 1993 2010 1 glacial earthquakes are anomalous earthquakes associated with large ice loss events occurring at marine terminating glaciers primarily in greenland they are detectable teleseismically and a proper understanding of the source mechanism may provide a remote sensing tool to complement glaciological observations of these large outlet glaciers we model teleseismic surface wave waveforms to obtain locations and centroid single force source parameters for 121 glacial earthquakes occurring in greenland during the period 2006 2010 we combine these results with those obtained by previous workers to analyze spatial and temporal trends in glacial earthquake occurrence over the 18 year period from 1993 2010 we also examine earthquake occurrence at six individual glaciers comparing the earthquake record to independently obtained observations of glacier change our findings confirm the inference that glacial earthquake seismogenesis occurs through the capsize of large newly calved icebergs we find a close correspondence between episodes of glacier retreat thinning and acceleration and the timing of glacial earthquakes and document the northward progression of glacial earthquakes on greenland s west coast over the 18 year observing period our results also show that glacial earthquakes occur when the termini of the source glaciers are very close to the glacier grounding line i e when the glaciers are grounded or nearly grounded

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

rapid and synchronous ice dynamic changes in east greenland two major outlet glaciers in east greenland have suddenly begun to accelerate and retreat the speeds of kangerdlugssuaq and helheim remained steady during the 1990s despite progressive and substantial thinning but have abruptly increased within the last two years more than doubling ice flux to the ocean had it been an isolated example the comparable 1998 speed up of jakobshavn isbra in west greenland might have been explained simply by its chance retreat past a pinning point now that two further greenland outlets have exhibited similar behavior a common process seems likely a remarkable correspondence in the inter annual patterns of speed and ice front variation between kangerdlugssuaq and helheim implies a significant sensitivity to regional environmental factors the period of continued warming and thinning appears to have primed these glaciers for a step change in dynamics not included in current models we should expect further greenland outlet glaciers to follow suit copyright 2006 by the american geophysical union

erosion driven uplift of the modern central alps abstract we present a compilation of data of modern tectono geomorphic processes in the central european alps which suggest that observed rock uplift is a response to climate driven denudation this interpretation is predominantly based on the recent quantification of basin averaged late holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling furthermore a gps data based synthesis of adriatic microplate kinematics suggests that the central alps are currently not in a state of active convergence finally we illustrate that the central alps have acted as a closed system for holocene redistribution of sediment in which the peri alpine lakes have operated as a sink for the erosional products of the inner central alps while various hypotheses have been put forward to explain central alpine rock uplift e g lithospheric forcing by convergence mantle processes or ice melting we show with an elastic model of lithospheric deformation that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading thus erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens rather we suggest that the geomorphic response of the alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift therefore in a non convergent orogen such as the central european alps the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

recent vertical movements from precise levelling in the vicinity of the city of basel switzerland the southern end of the upper rhine graben is one of the zones in switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region therefore in 1973 a control network with levelling profiles across the eastern rhine graben fault was installed and measured in the vicinity of the city of basel in order to measure relative vertical movements and investigate their relationship with seismic events as a contribution to eucor urgent the profiles were observed a third time in the years 2002 and 2003 and connected to the swiss national levelling network the results of these local measurements are discussed in terms of accuracy and significance furthermore they are combined and interpreted together with the extensive data set of recent vertical movements in switzerland jura mountains central plateau and the alps in order to be able to prove height changes with precise levelling their values should amount to at least 3 4 mm 1 the present investigations however have not shown any significant vertical movements over the past 30 years

reverse glacier motion during iceberg calving and the cause of glacial earthquakes nearly half of greenland s mass loss occurs through iceberg calving but the physical mechanisms operating during calving are poorly known and in situ observations are sparse we show that calving at greenland s helheim glacier causes a minutes long reversal of the glacier s horizontal flow and a downward deflection of its terminus the reverse motion results from the horizontal force caused by iceberg capsize and acceleration away from the glacier front the downward motion results from a hydrodynamic pressure drop behind the capsizing berg which also causes an upward force on the solid earth these forces are the source of glacial earthquakes globally detectable seismic events whose proper interpretation will allow remote sensing of calving processes occurring at increasing numbers of outlet glaciers in greenland and antarctica

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

interpretation of earthquake epicenter and cmt centroid locations in terms of rupture length and direction abstract a comparison is made between hypocenter and centroid estimates of shallow earthquakes to investigate whether the difference between these two quantities contains useful information on fault rupture length and direction an initial comparison of international seismological centre isc and harvard centroid moment tensor cmt catalog locations suggests that for earthquakes below mw 6 5 the difference in location is dominated by location errors whilst larger earthquakes appear to show the effect of increasing spatial rupture however for this data set combined location errors greater than 25 km are observed for a majority of earthquakes imposing a limit on interpretation we use these constraints to investigate this approach using a consistent earth model in the re analysis of eight previously well studied events new hypocenter estimates based on teleseismic p wave arrivals from the isc bulletin and a 3 d velocity model of the mantle s p12 wm13 are compared with new centroid locations obtained using the same 3 d model and waveform data from international deployment of accelerometers ida global digital seismic network gdsn and re calibrated high gain long period hglp stations the distance between our new hypocenter and centroid locations is shown to provide reliable information on both the rupture length and direction the rupture lengths and azimuths generally agree with the most recent previous results from other methods and provide an absolute estimate of the location of the rupture

step wise changes in glacier flow speed coincide with calving and glacial earthquakes at helheim glacier greenland this is the publisher s version also available electronically from http onlinelibrary wiley com

possible mechanisms for glacial earthquakes the large glacial earthquakes reported on by ekstrom et al 2003 2006 and tsai and ekstrom 2007 have previously been evaluated in terms of their seismic characteristics in this paper we attempt to take constraints such as known glacial ice properties outlet glacier size calving style and meltwater variability to construct a self consistent physical model of the glacial earthquake process since many glaciological parameters are poorly constrained we parameterize a number of important processes and estimate a wide range of possible values for some properties the range of model outputs is thus fairly large but it is still difficult to match observational constraints under most conditions we find that only a small class of models is able to satisfy the major observational constraints these models are characterized by 1 lost basal resistance coupled to viscoelastic deformation with extensive internal crevassing or with low effective elastic modulus and possibly low effective viscosity or 2 by nonequilibrium calving such as having large icebergs capsize into the glacier front although observational constraints cannot definitively rule out any of the proposed classes of mechanisms the calving model has much stronger support fortunately the various models make different predictions regarding observables that can potentially be measured in the near future

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

rapid changes in ice discharge from greenland outlet glaciers using satellite derived surface elevation and velocity data we found major short term variations in recent ice discharge and mass loss at two of greenland s largest outlet glaciers their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates likely as a result of fast re equilibration of calving front geometry after retreat total mass loss is a fraction of concurrent gravity derived estimates pointing to an alternative source of loss and the need for high resolution observations of outlet dynamics and glacier geometry for sea level rise predictions

seventeen antarctic seismic events detected by global surface waves and a possible link to calving events from satellite images 1 we detect 17 seismic events in antarctica from 1997 to 2009 by applying a surface wave detector to global seismic data we locate these events using a waveform cross correlation method and find that most occurred near the coast of antarctica and are clustered in three regions four events are on the ronne ice shelf close to the location of a 1998 calving event five events are near the vanderford glacier and eight events are near the ninnis glacier the observed rayleigh and love waves for these events have similar amplitudes and a two lobed radiation pattern matching the expected amplitude behavior of a single force source model using such a model we obtain best fitting horizontal force directions for the 14 events that have relatively better signal to noise ratios analysis of coastline changes from modis images before and after the detected events show that two events on vanderford glacier and one event near ninnis glacier are likely associated with calving events moreover the inferred force directions for the seismic events appear consistent with local ice flow directions both satellite observations and modeling results strongly suggest a link between seismic events and calving processes in the two regions however the force directions on the ronne ice shelf are aligned with observed rift propagation directions suggesting that these events may arise from rifting processes

rock type leaves topographic signature in landslide dominated mountain ranges 1 the idea that hillslopes in active mountain belts are limited to a threshold inclination by the rate of landsliding has guided landscape evolution models for over a decade however widely applied topographic diagnostics of threshold hillslopes remain debated and unverified this study relates landslide occurrence to hillslope metrics of several active mountain ranges throughout new zealand which are formed in uniform greywacke and its schist derivative all these ranges share a distinctive peak in hillslope inclination despite order of magnitude variations in rates of rock uplift and precipitation landslide density and extent of quaternary glaciation comparison with landslide dominated terrain in different lithologies highlights this peak as diagnostic of rock type reflecting a conspicuous tendency in hillslope evolution to adjust to rock mass strength irrespective of the intensity of tectonic and climatic forcing this finding expands the model perspective that only undisturbed strength equilibrium slopes may adjust to their rock mass strength

the evolution towards steady state erosion in a soil mantled drainage basin semi quantitative data from a transient landscape in the swiss alps abstract this paper presents semi quantitative data concerning the pattern of erosion under present day humid climatic conditions for a ca 10 km2 large soil mantled drainage basin located in the northern foothills of the central swiss alps the present day pattern of erosion was presumably initiated at ca 15 ka at the time when the last glacial period was terminated present day erosional processes are characterized by fluvial dissection and hillslope mass failure resulting in linear geomorphic features as fluvial dissection proceeds the rivers tend to adapt steady state longitudinal stream profiles in this case the stream profiles display power law relationships between channel gradient and upstream size of the drainage basin our study shows that establishment of steady state longitudinal stream profiles requires a balanced mass flux between processes on hillslopes and in channels this situation is interpreted for locations where the downslope flux of mass on hillslopes does not exceed the erosional potential and the transport capacity in channels consequently the development of steady state drainage systems appears to be controlled by erosional processes in channels as they dictate the elevation of the base level in contrast systems that are at transient states of longitudinal stream profile development very often display non balanced mass flux between processes in channels and on hillslopes specifically low mechanical strength of the bedrock e g glacial till marls results in a downslope flux of mass that exceeds the transport capacity and the erosional potential in the channel causing the elevation of the channel floor to increase in this case processes on hillslopes are not necessarily coupled with erosion in channels and appear to control the evolution of the drainage basin for a limited time interval besides interpretations of controls on surface erosion this paper also estimates post glacial sediment yield for the analyzed drainage basin these estimates are achieved by determination of the difference between the elevation of the glacial and the present day surface the data show that ca 30 of the analyzed drainage basin experiences present day surface erosion furthermore average post glacial sediment yield measures ca 4 6 m ka if the post glacial volume of sediment is related to the area that has experienced surface erosion or ca 1 4 m ka if it is related to the whole drainage basin interestingly the erosional efficiency appears to be significantly higher for systems that display steady state stream profiles than for transient rivers

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

hypsometry of glaciated landscapes hypsometry frequency distribution of elevations is often used to characterize landscape morphology traditionally in the context of the degree of uvial dissection recently the hypsometry of glaciated regions has been used to infer how rates of glacial erosion compare with tectonic uplift rates however many factors other than tectonics can also exert a major in uence on the hypsometry of a glaciated landscape resulting in a wide variety of hypsometries using examples from the eastern sierra nevada california the western sangre de cristo range colorado and the ben ohau range new zealand we demonstrate that all else being equal the hypsometries of neighbouring basins can indicate the relative degree of glacial modi cation in each a selection of drainage basins from the rocky mountains shows that the position of the equilibrium line altitude ela within the drainage basin relief is a dominant variable in determining the hypsometry of a glaciated basin this is a non linear effect once the ela falls to some critical level the glaciers scour deeply below the ela causing a noticeably different hypsometry the hypsometry of an arbitrary region encompassing many drainage basins can disguise the variation present in the hypsometries and thus landforms of the individual basins unique local circumstances such as the presence of a mountain ice eld waiho basin southern alps substantial hanging valleys avalanche creek glacier national park a narrow outlet canyon sawmill creek sierra nevada and isolated geologic structures baker creek sierra nevada can have a major impact on the hypsometry of an individual basin copyright 2004 john wiley sons ltd

cosmogenic nuclide derived rates of diffusive and episodic erosion in the glacially sculpted upper rhone valley swiss alps denudation rates of small tributary valleys in the upper rhone valley of the swiss central alps vary by more than an order of magnitude within a very small distance tens of kilometers morphometric data indicate two distinct erosion processes operate in these steep mountain valleys we determined the rates of these processes using cosmogenic beryllium 10 10be in pooled soil and stream sediment samples denudation in deep glacially scoured valleys is characterized by rapid non uniform processes such as debris flows and rock falls in these steep valleys denudation rates are 760 2100 mm kyr 1 in those basins which show minimal previous glacial modification denudation rates are low with 60 560 mm kyr 1 the denudation rate in each basin represents a binary mixture between the rapid non uniform processes and soil creep the soil production rate measured with cosmogenic 10be in soil samples averages at 60 mm kyr 1 mixing calculations suggest that the debris flows and rock falls are occurring at rates up to 3000 7000 mm kyr 1 these very high rates occur in the absence of baselevel lowering since the tributaries drain into the rhone trunk stream up stream of a knickzone the flux weighted spatial average of denudation rates for the upper rhone valley is 1400 mm kyr 1 which is similar to rock uplift rates determined in this area from leveling the pace and location of erosion processes are determined by the oscillation between a glacial and a non glacial state preventing the landscape from reaching equilibrium copyright 2010 john wiley sons ltd

determination of predevelopment denudation rates of an agricultural watershed cayaguas river puerto rico using in situ produced 10be in river borne quartz accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities to model global geochemical cycles and to examine interactions among climate weathering and uplift we present a simple approach to estimate predevelopment denudation rates using in situ produced cosmogenic 10be in fluvial sediments denudation processes in an agricultural watershed cayaguas river basin puerto rico and a matched undisturbed watershed icacos river basin were compared using 10be concentrations in quartz for various size fractions of bed material the coarse fractions in both watersheds bear the imprint of long subsurface residence times fine material from old shallow soils contributes little however to the present day sediment output of the cayaguas this confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the cayaguas basin and suggests that pre agricultural erosional conditions were comparable to those of the present day icacos

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

active deformation in the eastern swiss alps post glacial faults seismicity and surface uplift abstract post glacial tectonic faults in the eastern swiss alps occur as single lineaments clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend the orientation of the faults reflects the underlying lithology and the pre existing structures joints pervasive foliations within these lithologies most post glacially formed faults in the area around chur which undergoes active surface uplift of 1 6 mm year trend e w and cut across alpine and glacial features such as active screes and moraines additionally there are nnw and ene striking faults reactivating pervasive alpine foliations and shear zones based on a comparison with the nodal planes of recent earthquakes e w striking faults are interpreted as active faults because of very short rupture lengths and mismatches of fault location with earthquake distribution magnitude and abundance the faults are considered to be secondary faults due to earthquake shaking cumulative deformation in post or interseismic periods or creep and not primary earthquake related faults the maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission track data and is therefore a long lived feature that extends well into pre glacial times isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern rather the faults earthquakes and surface uplift patterns suggest that the alps are deforming under active compression and that the aar massif basement uplift is still active in response to ongoing collision

analysis of glacial earthquakes in 2003 ekstrom et al reported on the detection of a new class of earthquakes that occur in glaciated regions with the vast majority being in greenland the events have a characteristic radiation pattern and lack the high frequency content typical of tectonic earthquakes it was proposed that the events correspond to large and sudden sliding motion of glaciers here we present an analysis of all 184 such events detected in greenland between 1993 and 2005 fitting the teleseismic long period surface waves to a landslide model of the source we obtain improved locations timing force amplitudes and force directions after relocation the events cluster into seven regions all of which correspond to regions of very high ice flow and most of which are named outlet glaciers these regions are daugaard jensen glacier kangerdlugssuaq glacier helheim glacier the southeast greenland glaciers the northwest greenland glaciers rinks isbrae and jakobshavn isbrae event amplitudes range from 0 1 to 2 0 10 14 kg m force directions are consistent with sliding in the direction of glacial flow over a period of about 50 s each region has a different temporal distribution of events all glaciers are more productive in the summer but have their peak activity in different months over the study period kangerdlugssuaq has had a constant number of events each year whereas jakobshavn had most events in 1998 1999 and the number of events in helheim and the northwest greenland glaciers has increased substantially between 1993 and 2005 the size distribution of events in kangerdlugssuaq is peaked above the detection threshold suggesting that glacial earthquakes have a characteristic size

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

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

large fluctuations in speed on greenland s jakobshavn isbrae glacier it is important to understand recent changes in the velocity of greenland glaciers because the mass balance of the greenland ice sheet is partly determined by the flow rates of these outlets jakobshavn isbrae is greenland s largest outlet glacier draining about 6 5 per cent of the ice sheet area and it has been surveyed repeatedly since 1991 ref 2 here we use remote sensing data to measure the velocity of jakobshavn isbrae between 1992 and 2003 we detect large variability of the velocity over time including a slowing down from 6 700 m yr 1 in 1985 to 5 700 m yr 1 in 1992 and a subsequent speeding up to 9 400 m yr 1 by 2000 and 12 600 m yr 1 in 2003 these changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter our observations indicate that fast flowing glaciers can significantly alter ice discharge at sub decadal timescales with at least a potential to respond rapidly to a changing climate

analysis of low frequency seismic signals generated during a multiple iceberg calving event at jakobshavn isbrae greenland 1 we investigated seismic signals generated during a large scale multiple iceberg calving event that occurred at jakobshavn isbrae greenland on 21 august 2009 the event was recorded by a high rate time lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus during the event two full glacier thickness icebergs calved from the grounded or nearly grounded terminus and immediately capsized the second iceberg to calve was two to three times smaller than the first the individual calving and capsize events were well correlated with the radiation of low frequency seismic signals 0 1 hz dominated by love and rayleigh waves in agreement with regional records from previously published glacial earthquakes these low frequency seismic signals had maximum power and or signal to noise ratios in the 0 05 0 1 hz band similarly full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus the signals therefore appear to be local manifestations of glacial earthquakes although the magnitudes of the signals twice time integrated force histories were considerably smaller than previously reported glacial earthquakes we thus speculate that such earthquakes may be a common if not pervasive feature of all full glacier thickness calving events from grounded termini finally a key result from our study is that waveform inversions performed on low frequency calving generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving in particular the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude accordingly in our analysis it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

cosmogenic nuclide evidence for low weathering and denudation in the wet tropical highlands of sri lanka 1 some of the lowest weathering and erosion rates in any mountain range in the world have been measured using cosmogenic nuclides in the steep humid tropical highlands of sri lanka the total preanthropogenic denudation rates were measured in creek sediments and soil samples from unperturbed rain forest sites bedrock from mountain crests and bedrock from inselbergs denudation rates are in the range of 5 30 t km 2 yr 1 2 11 mm ky 1 these rates average denudation over the last 50 250 ky weathering exports in rivers draining the mountainous central highlands show that silicate weathering rates are also low varying from 5 to 20 t km 2 yr 1 today 2 7 mm ky 1 but they represent a significant fraction of the total denudation all these observations run contrary to the conventional geomorphologic and geochemical wisdom that would predict rapid erosion for highlands of high relief temperatures and precipitation we speculate that the high relief in sri lanka represents the remnant of a geomorphic block that was uplifted during rifting at 130 ma or even earlier and that was reduced to the interior of the island by rapid receding of escarpments after continental breakup it is possible that throughout this history hillslopes where not exposing bare bedrock were protected by thick weathered profiles such clay rich layers would inhibit silicate weathering by shielding bedrock from weathering agents in the absence of landscape rejuvenation physical erosion rates are low and fresh mineral surfaces are not being supplied the observation that wet steep tropical highlands can have low rates of rock weathering and erosion has some potentially profound implications for the long term controls of atmospheric co2 budgets high temperature and precipitation which are much invoked though controversial agents for silicate dissolution and co2 drawdown become ineffective in promoting weathering in areas that are not tectonically active

changes in ice front position on greenland s outlet glaciers from 1992 to 2007 1 previous studies in greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss raising greenland s contribution to sea level rise we examined ice front changes of 203 tidewater glaciers land terminating glaciers and glaciers terminating with ice shelves to understand greenland glacier behavior over three periods 1992 2000 2000 2006 and 2006 2007 we observed synchronous ice sheet wide increases in tidewater retreat during 2000 2006 relative to 1992 2000 coinciding with a 1 1 c increase in mean summer temperature at coastal weather stations rates of retreat for the southeast and east slowed during 2006 2007 when temperatures were slightly cooler than the 2000 2006 average our work suggests that regional greenland tidewater retreat responds strongly to climate change with higher temperatures corresponding to increasing retreat and helps confirm a link between ice thickness velocity and ice front position

rapid retreat and acceleration of helheim glacier east greenland 1 a significant amount of the measured coastal thinning of the greenland ice sheet may be due to recent acceleration of outlet glaciers using remote sensing we measured two major periods of speedup on helheim glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km yr these speedups coincided with rapid retreats of the calving front totaling over 7 5 km the glacier also thinned by over 40 m from 2001 to 2003 retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area farther up glacier acceleration may be a delayed response to surface draw down and steepening of the glacier s main trunk if the 2005 speedup also produces strong thinning then much of the glacier s main trunk may un ground leading to further retreat citation howat i m i joughin s tulaczyk and s gogineni 2005 rapid retreat and acceleration of helheim glacier east greenland geophys res lett 32 l22502 doi 10 1029 2005gl024737

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

continued evolution of jakobshavn isbrae following its rapid speedup 1 several new data sets reveal that thinning and speedup of jakobshavn isbrae continue following its recent rapid increase in speed as its floating ice tongue disintegrated the present speedup rate of 5 a 1 over much of the fast moving region appears to be a diffusive response to the initial much larger speedup near the front there is strong seasonality in speed over much of the fast flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short typically 6 km floating ice tongue this modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003 analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving major calving only resumes in late winter when much of this ice clears from the fjord the collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea ice concentration in disko bay this decline may have extended the length of the calving season for several consecutive years leading to the ice tongue s collapse

changes in the dynamics of marine terminating outlet glaciers in west greenland 2000 2009 1 recent changes in the dynamics of greenland s marine terminating outlet glaciers indicate a rapid and complex response to external forcing despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along greenland s northwestern margin it is unclear whether west greenland glaciers have undergone the synchronous speed up and subsequent slow down as observed in southeastern glaciers earlier in the decade to investigate changes in west greenland outlet glacier dynamics and the potential controls behind their behavior we derive time series of front position surface elevation and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west greenland from 2000 to 2009 using these data we look for relationships between retreat thinning acceleration and geometric parameters to determine the first order controls on glacier behavior our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales though nearly all glaciers retreated and thinned over the decade we found no direct relationship between retreat acceleration and external forcing applicable to the entire region in regard to geometry we found that following retreat 1 glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and 2 thinning rates declined more quickly for glaciers with steeper slopes overall glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west greenland

glacier fjord and seismic response to recent large calving events jakobshavn isbrae greenland 1 the recent loss of jakobshavn isbrae s extensive floating ice tongue has been accompanied by a change in near terminus behavior calving currently occurs primarily in summer from a grounded terminus involves the detachment and overturning of several icebergs within 30 60 min and produces long lasting and far reaching ocean waves and seismic signals including glacial earthquakes calving also increases near terminus glacier velocities by 3 but does not cause episodic rapid glacier slip thereby contradicting the originally proposed glacial earthquake mechanism we propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving

monitoring greenland ice sheet buoyancy driven calving discharge using glacial earthquakes since the 2000s greenland ice sheet mass loss has been accelerating followed by increasing numbers of glacial earthquakes ges at near grounded glaciers ges are caused by calving of km scale icebergs which capsize against the terminus seismic record inversion allows a reconstruction of the history of ge sources which captures capsize dynamics through iceberg to terminus contact when compared with a catalog of contact forces from an iceberg capsize model seismic force history accurately computes calving volumes while the earthquake magnitude fails to uniquely characterize iceberg size giving errors up to 1 km 3 calving determined from ges recorded ateight glaciers in 1993 2013 accounts for up to 21 of the associated discharge and 6 of the greenland mass loss the proportion of discharge attributed to capsizing calving may be underestimated by at least 10 as numerous events could not be identified by standard seismic detections olsen and nettles 2018 while calving production tends to stabilize in east greenland western glaciers have released more and larger icebergs since 2010 and have become major contributors to greenland dynamic discharge production of ges and calving behavior are controlled by glacier geometry with bigger icebergs being produced when the terminus advances in deepening water we illustrate how ges can help in partitioning and monitoring greenland mass loss and characterizing capsize dynamics

glacial earthquakes in greenland and antarctica glacial earthquakes are a new class of seismic events first discovered as signals in long period seismograms recorded on the global seismographic network most of these events occur along the coasts of greenland where they are spatially related to large outlet glaciers glacial earthquakes show a strong seasonality with most events occurring during the late summer the rateofglacial earthquakeoccurrenceincreasedbetween2000and2005 with a stabilization of earthquake frequency at 2003 2004 levels in 2006 2008 recent observations establish a strong temporal correlation between the distinct seismic signals of glacial earthquakes and large ice loss events in which icebergs of cubic kilometer scale collapse against the calving face linking the seismogenic process to the force exerted by these icebergs on the glacier andtheunderlyingsolidearth asuddenchangeinglacierspeedresultsfrom these glacial earthquake calving events seasonal and interannual variations in glacier terminus position account for general characteristics of the temporal variation in earthquake occurrence glacial earthquakes in antarctica are less well studied but they exhibit several characteristics similar to glacial earthquakes in greenland