impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

late cenozoic relief evolution under evolving climate a review abstract the present review paper is an attempt to summarize quantitative evidence of late cenozoic changes in topographic relief different meanings of the word relief as it is commonly used and detail the metrics used to quantify it we then specify methodological tools used to quantify relief change primarily low temperature thermochronometry and terrestrial cosmogenic nuclides and analyze published evidence for different regions our review first shows that relief changes and rates of changes are more important at mid than high or low latitudes and appear to be insensitive to mean precipitation rates it also show that relief change is positive relief increases in most of the reported cases 80 we subsequently define two functional relationships between relief and erosion depending on the chosen definition of relief and propose a conceptual model of landscape memory we conclude following others that erosion rates depend non linearly on relief evolution itself being a function of the spatial distribution and rates of erosion the relief increases documented in this review may be to erosion rate increases during the same timescales lastly we discuss the importance of glacial and periglacial processes on late cenozoic relief and erosion rate changes and stress the importance of frost shattering and glacial erosion at mid and high latitudes

stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

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

cirques have growth spurts during deglacial and interglacial periods evidence from 10be and 26al nuclide inventories in the central and eastern pyrenees cirques are emblematic landforms of alpine landscapes the statistical distribution of cirque floor elevations is used to infer glacial equilibrium line altitude and the age of their frontal moraines for reconstructing glacial chronologies very few studies however have sought to measure cirque floor and supraglacial ridgetop bedrock downwearing rates in order to confront these denudation estimates with theoretical models of quaternary mountain landscape evolution here we use 10 be nuclide samples n 36 from moraines bedrock steps and supraglacial ridgetops among a population of cirques in the east central pyrenees in order to quantify denudation in the landscape and detect whether the mountain topography bears any relevance to the glacial buzzsaw hypothesis minimum exposure ages meas obtained for a succession of moraines spanning the oldest dryas to the holocene produced a deglaciation chronology for three different pyrenean ranges maladeta bassies and carlit based on a series of corrections calibrations and chronostratigraphic tuning procedures meas on ice polished bedrock exposures were further used to model denudation depths at nested timescales during the wurm the younger dryas and the holocene results show that subglacial cirque floor denudation was lower during glacial periods wurm 10 mm ka than during deglacial and interglacial periods tens to hundreds of mm ka the relative inefficiency of glacial denudation in the cirque zone during the wurm would have resulted from i cold based and or ii low gradient glaciers situated in the upper reaches of the icefield and or from iii glacier load starvation because of arrested clast supply from supraglacial rockslopes situated in the permafrost zone denudation peaked during the younger dryas and holocene glacial advances a time when cirque glaciers became steeper warmer based and when frost cracking weakened supraglacial ridgetops thus enhancing sub glacial erosion by providing debris to the sliding glacier base cirques therefore grow faster during more temperate periods of cirque glaciation than under full glacial conditions another key finding was the very low rates of ridgetop lowering averaged over the wurm and holocene 10 25 mm ka a comparison of the denudation rates obtained from the cirque zone with regional estimates of crustal uplift indicates that the alpine topography is not in a steady state the low intensity of glacial denudation failed to bring the topography to a buzzsaw equilibrium state

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

low temperature thermochronologic record of eocene migmatite dome emplacement and late cenozoic landscape development shuswap core complex british columbia exhumed mid to lower crustal rocks offer an opportunity to determine the mechanisms conditions timing and consequences of the ascent of hot rocks from deep to shallow crustal levels we used results of low t thermochronology zircon and apatite u th he apatite fission track to document the very shallow emplacement 1800 m have preserved eocene fission track ages and evidence of rapid cooling 60 c myr this eocene cooling event corresponds to rapid exhumation by upward flow of partially molten crust and final exhumation by detachment faulting samples collected below 1800 m in elevation display a wide range of apatite fission track ages 43 15 ma and track length distributions that reflect prolonged residence in the apatite partial annealing zone these age elevation relations imply that the dome rocks reached the near surface 2 km during initial upward flow and tectonic exhumation in the eocene and that little erosion of the eocene surface has occurred since that time thermal modeling of the lowest elevation samples 600 m and intrasample apatite u th he age variations reveal enhanced erosion and relief production at the onset of continental glaciations at 3 ma our work illustrates the dynamic links between deep and shallow crustal processes and the evolution of topography in a deeply incised hot orogen

a quantification of the glacial imprint on relief development in the french western alps abstract the morphology of the western alps has been strongly influenced by quaternary glaciations on the basis of observations of glacial morphology in the belledonne grandes rousses taillefer and pelvoux ecrins massifs south eastern france we reconstitute the glacial trimline and equilibrium line altitude ela during the most extensive glaciation meg our best estimate of the meg ela is 1800 100m using digital elevation models we compare our glacial reconstruction with the relief structure of nine major catchments draining the massifs modal elevations of the largest catchments occur at 2000 2500m and coincide with minima in plots of mean slope angles as a function of elevation modal elevations and slope minima occur between the modern and meg elas confirming a strong glacial imprint on relief in order to quantify glacial valley carving in the massifs we isolated high elevation low relief surfaces that form rock shoulders adjacent to the glacial valleys from a digital elevation model and constructed an interpolated surface passing through these subtracting the present day topography from this surface allows us to quantify the maximum glacial valley depths maximum valley depths determined in this manner are typically 1000m with spatial maxima occurring around the location of the meg ela in most valleys these numbers do not take into account glacial valley widening and local glacial overdeepenings the also neglect however potential pre glacial fluvial valley incision which could account for 20 50 of the measured valley depths in spite of these problems inferred valley depths are reasonably well correlated with the mean reconstructed ice thickness and constitute about half of the sub ridgeline relief of the studied catchments these results lead us to propose a significant quaternary increase in the relief of the french western alps controlled by climate and associated with the initiation of alpine glaciations for reasonable values of the effective elastic thickness of the lithosphere the isostatic response to glacial valley carving reaches values of 300m across the massifs this number is insufficient to substantially offset topographic lowering due to regional denudation and we conclude that the isostatic response to glacial valley carving has not increased peak elevations significantly

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

dramatic increase in late cenozoic alpine erosion rates recorded by cave sediment in the southern rocky mountains abstract apparent increases in sedimentation rates during the past 5 ma have been inferred at sites around the globe to document increased terrestrial erosion rates but direct erosion rate records spanning this period are sparse modern and paleo erosion rates for a small alpine catchment 3108 m above sea level in the southern rocky mountains are measured using the cosmogenic radionuclides crns 10be and 26al in cave sediment bedrock on the overlying landscape surface and coarse bedload in a modern fluvial drainage the unique setting of the marble mountain cave system allows the inherited erosion rates to be interpreted as basin averaged erosion rates resulting in the first crn based erosion rate record from the rocky mountains spanning 5 myr pliocene erosion rates derived from the oldest cave sample 4 9 0 4 ma for the landscape above the cave are 4 9 1 1 m myr 1 mid pleistocene erosion rates are nearly an order of magnitude higher 33 1 2 7 to 41 3 3 9 m myr 1 and modern erosion rates are similar due to the effects of snow shielding these erosion rate estimates are likely higher than actual rates by 10 15 the most likely explanation for this dramatic increase in erosion rates which likely occurred shortly before 1 2 ma is an increase in the effectiveness of periglacial weathering processes at high elevations related to a cooler and wetter climate during the pleistocene providing support for the hypothesis that changes in late cenozoic climate are responsible for increased continental erosion

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

improved spatial resolution of elemental maps through inversion of la icp ms data laser ablation inductively coupled plasma mass spectrometry la icp ms provides the spatial distribution of elements within crystals and therefore can constrain the rates of geological processes spatial resolution of la icp ms is limited by the requirement to ablate sufficient material to surpass the detection limit of the instrument too little material and the concentration cannot be measured too much material from the same spatial location and the possibility of depth dependent variations in concentration increases because of this requirement and typical analytical setup this commonly places a lower bound on the diameter of an ablation spot size of approximately 20 m for elements with ppm concentration here we present a means to achieve sub spot size resolution using inverse methods we discretize the space sampled in an analysis into pixels and note that the average concentration of the pixels sampled by a spot equals the measured concentration as multiple overlapping spots sample some of the same pixels we can combine discrete expressions for each spot as a system of linear equations through linear inversion with smoothness constraints we can solve for unknown pixel concentrations we highlight this approach with two natural examples in which diffusive processes are important magmatic ascent speeds and u th he noble gas thermochronometry in these examples accurate results require that the true concentration gradients can be recovered from la icp ms data we show that the ability to infer rapid rates of magma ascent is improved from months to weeks and that we are able to interpret previously un interpretable thermochronometric data

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

the influence of alpine glaciation on the relief of tectonically active mountain belts a surface processes model incorporating large scale fluvial processes local hill slope processes and glacial erosion is used to investigate the effect of glaciation on the relief of a fast growing narrow orogen the results of several simulations show that glaciers concentrate erosion near peaks fluvial erosion is reduced downstream of glaciers glaciers with frozen bases can lead to an increase in relief and the net affect of glaciation in the absence of widespread basal freezing is to reduce relief

exhumation along the fairweather fault southeastern alaska based on low temperature thermochronometry 1 the southern alaskan syntaxis marks the spectacular junction between the 1000 km long pacific north america transform margin and the chugach st elias belt where subduction and terrane accretion drive rapid convergent deformation and rock uplift new low temperature thermochronometry reveals that intense orogenic deformation is not restricted to one side of the syntaxis but extends nearly 300 km south along the dextral fairweather fault apatite and zircon u th he ages as young as 0 9 and 2 0 ma suggest maximum exhumation rates of nearly 2 mm a in close proximity 0 5 mm a along the entire plate margin we estimate that long term rock uplift accommodates 3 mm a of fault normal convergence in this area this suggests that the fairweather fault is slightly transpressive and highly partitioned analogous to the central san andreas fault this convergence only accounts for 1 5 of the obliquity between pacific plate motion and the continental margin however implying the deficit is taken up by 1 2 cm a thrust sinistral motion along the offshore transition fault additionally thermochronometry shows a marked increase in bedrock cooling coincident with onset of heavy glaciation similar to what has been observed in other parts of the pacific northwest the tectonically active fairweather corridor is distinguished however by the magnitude of the acceleration and the depth of exhumation since pliocene climate change

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

dating topography of the sierra nevada california using apatite u th he ages the upward motion of rock masses relative to the earth s surface has been documented for most of the main mountain belts using thermochronological and petrological techniques more fundamental to the physical processes of mountain building however is the motion of the earth s surface itself which remains elusive here we describe a technique for estimating the age of topographic relief by mapping the low temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium thorium and helium contents the technique exploits horizontal variations in temperature in the shallow crust that result from range normal river drainages because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges our results from the sierra nevada california indicate that two of the modern transverse drainages the kings and the san joaquin had developed deep canyons by the late cretaceous period suggesting that the high topography of the range is 50 60 million years older than generally thought

glacier advances during the last 400 ka as evidenced in st beatus caves be switzerland abstract while stalagmites within caves are commonly used to obtain information about past climate change little attention has so far been given to the cave its morphology and many other types of deposits contained in it the discontinuous nature of cave sediments and the possibility that caves are re shaped by more recent water circulations has discouraged many researchers despite the fact that it is just this intimate relationship between the cave and surface conditions that makes caves such valuable archives this article presents a method of determining a relative chronology which can then be dated numerically information from st beatus cave and other nearby caves provides evidence of glacial advances that occurred within the following time windows 350 235 180 160 135 114 99 76 54 and 30 16 ka it also describes the following dated periods of valley deepening 805 760 m a s l 350 ka 760 700 m a s l 235 180 ka 700 660 m a s l 160 135 ka and 660 560 m a s l 30 16 ka these dates are new for this part of the alpine arc

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

fjord insertion into continental margins driven by topographic steering of ice fjords line mountainous continental margins where icesheets and glaciers once stood a two dimensional model simulation suggests that fjords can be eroded within one million years primarily in response to topographic ice steering and erosion from ice discharge subsequent glaciers that form on these landscapes are smaller and exhibit greater responses to climate change

ice sheet erosion and the stripping of tertiary regolith from baffin island eastern canadian arctic abstract the erosion of glaciated regions and concomitant changes in ice sheet dynamics through the pleistocene are poorly documented the baffin island landscape which has been shaped by the foxe sector of the laurentide ice sheet lis contains a variety of glacial and proximal glaciomarine sedimentary archives spanning the pleistocene we examine these records to better understand when tertiary regolith was stripped from beneath the foxe sector of the lis till on the interior plateaux of the island in areas with scoured bedrock have low chemical index of alteration cia values low meteoric 10 be 10 be met concentrations and clay mineralogy consistent with erosion from an unweathered bedrock source however in some areas in between fiord onset zones more weathered till is present containing considerably higher cia values high 10 be met concentrations and secondary clay mineral weathering products implying that the till has persisted on the landscape and weathered during successive glaciations using these weathering signatures we analyze the coastal glaciogenic deposits of the clyde foreland formation cff at two sites for evidence of tertiary regolith removal from the interior of baffin island by lis erosion provenance indicators within the cff demonstrate that pleistocene lis ice flow lines across baffin island have remained generally constant the oldest cff glaciogenic unit likely representing one of the first if not the first lis advances across baffin island had high 10 be met concentrations at the time of deposition consistent with extensive regolith erosion evidence of notably weathered sediment is absent in all younger units suggesting that tertiary regolith was likely largely stripped from the interior of the island by 1 6 0 2 ma

controls of initial topography on temporal and spatial patterns of glacial erosion abstract here we investigate the influence of initial pre glacial topography on spatial and temporal patterns of glacial erosion using numerical surface process modelling including a higher order ice sheet model first we consider glacier dynamics when simulating glaciation in two real landscapes representing plateau type topography southeast australia and characteristic steady state fluvial topography southern taiwan we find that the different initial landscape configurations result in distinctly different ice configurations and patterns of basal sliding the sliding patterns are controlled by ice configuration and the resulting basal shear stresses and by the thermal properties at the base of the ice we then investigate how these characteristic patterns of basal sliding control glacial erosion and long term landscape evolution using synthetic representations of the two landscapes the two landscape configurations result in markedly different spatial and temporal patterns of glacial erosion however the resulting landscapes may have similar morphology irrespective of initial landscapes and glacial erosion patterns being significantly different the numerical experiments also suggest that in addition to basal temperature basal shear stress is important in restricting long term glacial erosion which is relevant for the preservation of landforms during glaciations specifically pre glacial landforms may be eroded although they are initially protected by cold based ice when the ice configuration promotes significant basal shear stress glacial erosion at the edge of a plateau like landscape in contrast pre glacial landforms may be preserved irrespective of the ice being warm based when low gradients in the ice surface act to limit basal shear stress

vegetation succession and climate change during the early pleistocene 2 2 1 8 ma in the nihewan basin northern china abstract the nihewan formation northern china is ideal for studying environmental changes during the early pleistocene in conjunction with palaeomagnetic measurements pollen and grain size analyses were conducted on 120 samples from a 24 m long section 2 2 1 8 ma of core nha from the nihewan basin in order to reconstruct past vegetation and climatic changes the pollen assemblages were dominated by pinus indicating that the vegetation was primarily pine forest and that the climate was relatively warm and wet from 2 15 1 92 ma deciduous broad leaved tree pollen significantly increased to 10 of the total showing that more broad leaved trees grew in the study area during the warmest and wettest period in the study section from 1 92 1 78 ma coeval with the olduvai event pinus and broad leaved tree pollen types decreased the percentages of picea 20 artemisia and chenopodiaceae increased indicating that spruce forests expanded the openness of the forested areas increased and the climate became cold and dry the vegetation changes reconstructed during the olduvai period indicates that the climate in the nihewan basin was cold and dry relating to global cooling facilitated by the uplift of the tibetan plateau and the strengthening of the winter monsoon

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

tectonic control on rock uplift exhumation and topography above an oceanic ridge collision southern patagonian andes 47 s chile

extremely low long term erosion rates around the gamburtsev mountains in interior east antarctica the high elevation and rugged relief 3 km of the gamburtsev subglacial mountains gsm have long been considered enigmatic orogenesis normally occurs near plate boundaries not cratonic interiors and large scale tectonic activity last occurred in east antarctica during the pan african 480 600 ma we sampled detrital apatite from eocene sands in prydz bay at the terminus of the lambert graben which drained a large pre glacial basin including the northern gamburtsev mountains apatite fission track and u th he cooling ages constrain bedrock erosion rates throughout the catchment we double dated apatites to resolve individual cooling histories erosion was very slow averaging 0 01 0 02 km myr for 250 myr supporting the preservation of high elevation in interior east antarctica since at least the cessation of permian rifting long term topographic preservation lends credence to postulated high elevation mountain ice caps in east antarctica since at least the cretaceous and to the idea that cold based glaciation can preserve tectonically inactive topography

westernmost grand canyon incision testing thermochronometric resolution the timing of carving of grand canyon has been debated for over 100 years with competing endmember hypotheses advocating for either a 70 ma old or 6 ma young grand canyon several geological constraints appear to support a young canyon model but thermochronometric measures of cooling history and corresponding estimates of landscape evolution have been in debate in particular 4he 3he thermochronometric data record the distribution of radiogenic 4he from the 238u 235u and 232th decay series within an individual apatite crystal and thus are highly sensitive to the thermal history corresponding to landscape evolution however there are several complicating factors that make interpreting such data challenging in geologic scenarios involving reheating here we analyze new data that provide measures of the cooling of basement rocks at the base of westernmost grand canyon and use these data as a testbed for exploring the resolving power and limitations of 4he 3he data in general we explore a range of thermal histories and find that these data are most consistent with a young grand canyon a problem with the recovered thermal history however is that burial temperatures are under predicted based on sedimentological evidence a solution to this problem is to increase the resistance of alpha recoil damage to annealing thus modifying he diffusion kinetics allowing for higher temperatures throughout the thermal history this limitation in quantifying radiation damage and hence crystal retentivity introduces non uniqueness to interpreting time temperature paths in rocks that resided in the apatite helium partial retention zone for long durations another source of non uniqueness is due to unknown u and th distributions within crystals we show that for highly zoned with a decrease in effective u of 20 ppm over the outer 80 of the radius of the crystal the 4he 3he data could be consistent with an old canyon model to reduce this non uniqueness we obtain u and th zonation information for separate crystals from the same rock sample through la icp ms analysis the observed u and th distributions are relatively uniform and not strongly zoned thus supporting a young canyon model interpretation of the 4he 3he data furthermore we show that for the mapped zonation the difference between predicted 4he 3he data for a uniform crystal and a 3d model of the crystal are minimal highlighting that zonation is unlikely to lead us to falsely infer an old grand canyon

4he 3he thermochronometry using classical diffusion theory we present a mathematical technique for the determination of 4he concentration profiles in minerals this approach should prove useful for constraining the low temperature cooling histories of individual samples and for correcting u th he ages for partial diffusive loss the calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3he obtained by proton irradiation shuster et al earth planet sci lett 217 2004 19 32 in minerals devoid of natural helium this isotope allows measurement of he diffusion coefficients in minerals with measurable radiogenic he it permits determination of 4he profiles arising during ingrowth and diffusion in nature the 4he profile can be extracted from stepwise degassing experiments in which the 4he 3he ratio is measured the evolution of the 4he 3he ratio as a function of cumulative 3he released can be compared with forward models to constrain the shape of the profile alternatively we present a linear inversion that can be used to directly solve for the unknown 4he distribution the inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution using either approach we show that stepwise degassing data can yield robust and high resolution information on the 4he profile profiles of radiogenic he are a sensitive function of the time temperate t t path that a cooling sample experienced thus by step heating a proton irradiated sample it is possible to restrict the sample s acceptable t t paths the sensitivity of this approach was explored by forward modeling 4he profiles resulting from a range of realistic t t paths using apatite as an example results indicate that 4he profiles provide rich information on t t paths especially when the profiles are coupled with u th he cooling ages on the same sample samples that experienced only moderate diffusive loss have 4he concentration profiles that are rounded at the edge but uniform in the core of the diffusion domain such profiles can be identified by nearly invariant 4he 3he ratios after the first few to few tens of percent of 3he have been extracted by step heating we show how such data can be used to correct u th he ages for partial diffusive loss

the relative efficiency and influence of glacial and fluvial erosion on tibetan plateau landscapes abstract driven by climate change periods of dominating glacial and fluvial erosion have both sculpted mountain ranges during the quaternary to understand the evolution of mountain landforms there is considerable interest in knowing which erosion agent leads to more incision how glacial thermal regime impacts erosion and landscape development and whether glacial erosion can result in increased relief to investigate the relative efficiency of glacial and fluvial erosion and the influence of glacial thermal regime on topography we compare two different mountain ranges the qionglai shan monsoonal temperate glaciation and lenglongling subcontinental glaciation in western china we use a 1 d model to construct presumptive fluvial longitudinal profiles if glaciation had not occurred and compare these with the actual glacial profiles to obtain relative incision rates of fluvial and glacial erosion results demonstrate that glacial incision is smaller than fluvial incision in lenglongling and larger than fluvial incision in the qionglai shan which may be influenced by different tectonics and glacier types topographic analysis of glacial and fluvial valleys with similar drainage areas show that glacial erosion results in valley widening local valley relief increase induced by isostatic uplift and slope gradient increase in lenglongling however there is no local valley relief and slope increase observed in the qionglai shan which may reflect slope process responses to threshold hillslope limiting the height above valley bottoms

plio pleistocene increase of erosion rates in mountain belts in response to climate change here we review an ensemble of observations that point towards a global increase of erosion rates in regions of elevated mountain belts or otherwise high relief since the onset of northern hemisphere glaciation about 2 3 ma during that period of earth s history atmospheric co2 concentrations may have dropped and global climate cooled and evolved towards high amplitude oscillating conditions that are associated with the waxing and waning of continental ice sheets in the northern hemisphere we argue for a correlation between climate change and increased erosion rates and relief production which we attribute to some combination of the observed cooling onset of glaciation and climatic oscillation at orbital timescales in our view glacial erosion played a major role and is driven by the global cooling furthermore analyses of the sedimentary fluxes of many mountain belts show peaks of erosion during the transitions between glacial and inter glacial periods suggesting that the variable climatic conditions have also played a role

the relationships between tectonics climate and exhumation in the central andes 18 36 s evidence from low temperature thermochronology abstract the central andes between 18 s and 36 s latitude strike north south for 2000 km along the chilean subduction margin cross several climate zones from hyperarid to humid and exhibit mean elevations in excess of 4000 m a s l here we investigate the relationships between tectonics climate and exhumation by inverting low temperature thermochronological data compiled from the literature 824 ages from 549 samples and new data 238 ages from 146 samples to quantify the exhumation rate history of the central andes since 80 ma our inferred exhumation rates west of the drainage divide and between 18 and 32 s did not exceed 0 25 km ma such low exhumation rates are consistent with low shortening rates and arid conditions in this region local pulses of exhumation occurred only during the eocene as response to active deformation and during the miocene probably as response to uplift of the western andean slope east of the drainage divide between 18 and 28 s the observed exhumation pattern reflects the onset and eastward propagation of deformation here exhumation occurred locally since the middle to late eocene in the eastern cordillera and the altiplano puna and subsequently affected larger parts of these regions and the north western sierra pampeanas during the oligocene in the early miocene 20 ma the interandean zone started exhuming and at 12 10 ma exhumation propagated into the subandean zone enhanced shortening rates and intensified precipitation along the eastern deformation front associated with the onset of the south american monsoon led to increased exhumation rates in the eastern interandean and the subandean zones in the plio pleistocene 0 6 km ma higher pleistocene exhumation rates are also observed in the northern sierra pampeanas 1 5 km ma that can be related to rock uplift along steep reverse faults coupled with high precipitation south of 32 s on the western side exhumation rates in the principal cordillera increased from ca 0 25 km ma in the miocene to rates locally exceeding 2 km ma in the pleistocene whereas the tectonic regime in the southern principal cordillera remained unchanged since the late miocene these higher rates are likely associated with enhanced erosion resulting from intensified pleistocene precipitation and glacial growth in this region reinforced by isostatic rock uplift and active tectonics our study shows that the onset of exhumation correlates mainly with the initiation of horizontal shortening and crustal thickening whereas the magnitude of exhumation is largely set by the amount of precipitation and glacial erosion and by the style of deformation which is controlled by inherited structures and the amount of sediments in the foreland

seasonal scale abrasion and quarrying patterns from a two dimensional ice flow model coupled to distributed and channelized subglacial drainage abstract field data and numerical modeling show that glaciations have the potential either to enhance relief or to dampen topography we aim to model the effect of the subglacial hydraulic system on spatiotemporal patterns of glacial erosion by abrasion and quarrying on time scales commensurate with drainage system fluctuations e g seasonal to annual we use a numerical model that incorporates a dual morphology subglacial drainage system coupled to a higher order ice flow model and process specific erosion laws the subglacial drainage system allows for a dynamic transition between two morphologies the distributed system characterized by an increase in basal water pressure with discharge and the channelized system which exhibits a decrease in equilibrium water pressure with increasing discharge we apply the model to a simple synthetic glacier geometry drive it with prescribed meltwater input variations and compute sliding and erosion rates over a seasonal cycle when both distributed and channelized systems are included abrasion and sliding maxima migrate 20 up glacier compared to simulations with distributed drainage only power law sliding generally yields to a broader response of abrasion to water pressure changes along the flowline compared to coulomb friction sliding multi day variations in meltwater input elicit a stronger abrasion response than either diurnal or seasonal variations alone for the same total input volume an increase in water input volume leads to increased abrasion we find that ice thickness commensurate with ice sheet outlet glaciers can hinder the up glacier migration of abrasion quarrying patterns computed with a recently published law differ markedly from calculated abrasion patterns with effective pressure being a stronger determinant than sliding speeds of quarrying rates these variations in calculated patterns of instantaneous erosion as a function of hydrology sliding and erosion model formulation as well as model forcing may lead to significant differences in predicted topographic profiles on long time scales

long term glacial erosion of active mountain belts example of the chugach st elias range alaska an emerging paradigm that equates glaciers to buzz saws of exceptional erosional efficiency has been strengthened by short term 10 2 yr sediment yields from southern alaska new low temperature cooling ages from this area the glaciated chugach st elias mountains constrain long term 10 6 yr exhumation rates vertically averaged exhumation rates reach 3 mm yr but are an order of magnitude lower than rates based on short term sediment yields whereas these exhumation rates are not exceptional for oro genic belts denudation patterns are strongly correlated with the distribution of glaciers and erosion appears to keep pace with con vergence and uplift these findings imply a coupling between gla cially dominated erosion and tectonics

abrupt glacial valley incision at 0 8 ma dated from cave deposits in switzerland glacial erosion dramatically alters mountain landscapes but the pace at which glaciers carve a previously fluvial landscape remains poorly defined because long term valley incision rates are difficult to measure here we reconstruct the lowering history of the aare valley switzerland over the past 4 m y by dating cave sediments with cosmogenic 26al and 10be incision accelerated from 120 m m y to 1200 m m y at 0 8 1 0 ma at least 1 m y after the onset of local glaciation rapid incision may have been triggered by lowering of the equilibrium line altitude at the mid pleistocene climate transition

pleistocene reversal of the fraser river british columbia the fraser river in british columbia canada is the longest non dammed river on the west coast of north america and supplies 20 10 6 t yr of sediment to the pacific ocean abundant geomorphological evidence indicates that the fraser river reversed its course to southward flow in the recent geological past investigation of two volcanic dams at dog creek demonstrates northward flow of the fraser until at least 1 06 ma before reversal and erosion of the 270 km long fraser canyon we propose that the submarine nitinat fan off the coast of british columbia records the reversal and sudden input of coarse continental derived sediment ca 0 76 ma this study confirms reversal of the fraser river and places a firm constraint on the maximum age of that reversal reversal likely followed stream capture in response to enhanced glaciofluvial erosion and uplift of the coast mountains

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

strontium neodymium and lead isotope variations of authigenic and silicate sediment components from the late cenozoic arctic ocean implications for sediment provenance and the source of trace metals in seawater proven ance changes of silicate sediment deposited during the late cenozoic 5 0 ma on the alpha ridge central arctic ocean are determined from variations in strontium lead and neodymium isotope compositions whereas strontium and lead isotope compositions are relatively invariant from 5 to 1 7 ma end values start to increase at 3 ma subsequently s7sr 86sr and 2 6pb z 4pb ratios progressively increase and end values progressively decrease from 1 7 ma to the present day from these isotope variations three different endmember compositions for sediment source regions are defined the two endmember compositions defined by sediment that was deposited by sea ice from 5 to 1 7 ma are consistent with a significant component being derived from the east siberian shelf the progressive change in isotope compositions from 1 7 to 0 ma correlates with an increase in coarse detritus deposited by icebergs over this time period the isotope data are consistent with a progressive increase in the proportion of sediment that was deposited in the central arctic ocean since 1 7 ma having been derived from the northern canada or queen elizabeth island region changes in the strontium neodymium and lead isotope compositions of arctic seawater are determined by analyzing the oxide fractions of fe mn micronodules strontium isotope compositions of the microno dule oxide fractions are similar to published late cenozoic seawater data and indicate that 97 of the sr is seawater derived but minute contributions of sr from silicate detritus prohibit using the hydrogenous fractions for chronostratigraphic purposes neodymium and lead isotope compositions of the micronodule oxide fractions which reflect those of arctic seawater follow the isotope variations of the silicate components throughout the late cenozoic these relations indicate that river water can not be the primary source of rare earth elements and pb to the dissolved reservoir in arctic seawater and that ice rafted detritus by dissolution or exchange processes is an important source of trace elements to seawater in ice covered oceans copyright 1997 elsevier science ltd

arrested development erosional equilibrium in the southern sierra nevada california maintained by feedbacks between channel incision and hillslope sediment production tributary creeks of the southern sierra nevada have pronounced knickpoints that separate the landscape into an alternating sequence of gently sloped treads and steeply sloped risers these knickpoints and the surrounding stepped topography suggest that the landscape is still responding to pleistocene changes in base level on main stem rivers we tested this hypothesis using cosmogenic nuclides and uranium isotopes measured in stream sediment from widely distributed locations catchment scale erosion rates from the cosmogenic nuclides suggest that the treads are relict surfaces that have adjusted to a previous base level nevertheless erosion rates of relict interfluves are similar to canyon incision rates implying that relief is unchanging in the lower kings and san joaquin rivers in addition our results suggest that much of the southern sierra nevada is in a state of arrested development the landscape is not fully adjusted to and moreover is not responding to changes in base level lowering in the canyons we propose that this can be explained by a paucity of coarse sediment supply which fails to provide sufficient tools for bedrock channel incision at knickpoints we hypothesize that the lack of coarse sediment in channels is driven by intense weathering of the local granitic bedrock which reduces the size of sediment supplied from hillslopes to the channels our analysis highlights a feedback in which sediment size reduction due to weathering on hillslopes and transport in channels is both a key response to and control of bedrock channel incision and landscape adjustment to base level change

geospatial analysis and simulation of glacial lake outburst flood hazard in shyok basin of pakistan the upper indus basin uib is prone to glacial lake outburst floods glofs physical monitoring of such a large area on regular basis is a challenging task especially when the temporal and spatial extent of the hazard is highly variable the study has been conducted in the shyok sub basin of uib where there are several human settlements which are endangered due to the glof hazard sudden breaches in the unstable moraine dams adjoining receding glaciers may occur because of rapid and huge accumulation of turbulent water in the glacial lakes the purpose of this study was to map the two potentially dangerous glacial lakes and simulate the associated hazard in the downward settlements using hec ras in the gis environment using landsat 7 remote sensing data the aster digital elevation model dem is utilized to detect flow accumulation of glacial hazard involving slope elevation and orientation of the mountain glaciers the study results have revealed that settlements of the shyok basin are threatened by the glof hazard keeping in view the seasonal growth of the two potentially dangerous glacial lakes of the shyok basin a low discharge of 100 m3 s from both lakes can affect 20 whereas a moderate discharge of 300 m3 s and a high discharge of 500 m3 s respectively can impact 30 and 40 of the barah village habitat the results of the study can provide a platform for the establishment of an early warning and monitoring system to minimize the impact of future glofs

signatures of late pleistocene fluvial incision in an alpine landscape uncertainty regarding the relative efficacy of fluvial and glacial erosion has hindered attempts to quantitatively analyse the pleistocene evolution of alpine landscapes here we show that the morphology of major tributaries of the rhone river switzerland is consistent with that predicted for a landscape shaped primarily by multiple phases of fluvial incision following a period of intense glacial erosion after the mid pleistocene transition 0 7 ma this is despite major ice sheets reoccupying the region during cold intervals since the mid pleistocene we use high resolution lidar data to identify a series of convex reaches within the long profiles of 18 tributary channels we propose these reaches represent knickpoints which developed as regional uplift raised tributary bedrock channels above the local fluvial baselevel during glacial intervals and migrated upstream as the fluvial system was re established during interglacial periods using a combination of integral long profile analysis and stream power modelling we find that the locations of 80 of knickpoints in our study region are consistent with that predicted for a fluvial origin while the mean residual error over 100 km of modelled channels is just 26 3 m breaks in cross valley profiles project toward the elevation of former end of interglacial channel elevations supporting our model results calculated long term uplift rates are within 15 of present day measurements while modelled rates of bedrock incision range from 1 mm yr for low gradient reaches between knickpoints to 6 10 mm yr close to retreating knickpoints typical of observed rates in alpine settings together our results reveal approximately 800 m of regional uplift river incision and hillslope erosion in the lower half of each tributary catchment since 0 7 ma

apatite u th he signal of large magnitude accelerated glacial erosion southwest british columbia alpine glaciers are efficient agents of erosion and capable of significantly modifying topography despite recent advances in theoretical and field studies that quantify glacial erosion processes few studies have documented glacial erosion rates over long 10 6 yr or large more than tens of kilometers scales we use apatite u th he ahe and apatite fission track aft cooling ages to address the late miocene to holocene erosion history across two 60 km long transects of the heavily glaciated southern coast mountains british columbia observed ahe cooling ages from equal elevation samples range between 1 5 and 8 ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1 5 4 0 m y we evaluated temporal and spatial variations in erosion rates using a three dimensional thermal kinematic model that predicted ahe and aft ages at the surface for different erosion histories comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300 over the past 1 5 7 m y coincident with the onset of glaciation of this range

zircon 4he 3he fractional loss step heating and characterization of parent nuclide distribution abstract the radiogenic ingrowth and diffusive loss of 4he in accessory minerals is used to determine the timing of low temperature thermal processes such as shallow tectonic magmatic hydrothermal and geomorphic events while the thermal history experienced by a sample cannot be directly constrained by a single u th he total gas age 4he concentration profiles normalized against irradiation induced spallogenic 3he have been shown to reliably recover continuous thermal history constraints if the parent nuclide distribution is either spatially uniform or can be determined as such 4he 3he thermochronometry has been successfully applied to apatite however individual zircon grains can contain complex parent nuclide zonation using moderately zoned euhedral zircon grains from the rapidly cooled distal fish canyon tuff we investigated the potential of the zircon 4he 3he thermochronometer through combining 4he 3he diode laser fractional loss step heating with detailed analysis of parent element zonation we present a routine method for the quantitative characterization of parent nuclide zonation by la icp ms depth profiling this study also demonstrates the importance of thermal control and avoidance of intra sample thermal gradients during laser step heating fractional loss experiments accurate and stable thermal control was achieved with an optimized sample holder design laser defocusing and pid control loops to minimize temperature overshoot failure to reach set point and temperature drop offs these analytical developments illustrate both the pitfalls and promise of zircon 4he 3he thermochronometry and create a reproducible methodology for 4he 3he thermochronometric applications to zoned and slowly cooled zircon

glacial erosion at the fjord onset zone and implications for the organization of ice flow on baffin island arctic canada abstract organized conduits of fast ice flow at the fringe of present and past ice sheets move the majority of ice from ice sheet interior to periphery these relatively narrow corridors play a critical role in feedbacks between landscape evolution and ice sheet dynamics here we combine bedrock 10 be concentrations with distribution of lakes on baffin island arctic canada to constrain the pattern of glacial modification at a fjord onset zone the region of increasing relief from the continental interior to the fjord head high lake density and a lack of 10 be inheritance in the valley bottom indicate significant glacial scouring for some duration of the last glacial cycle in contrast 10 be inheritance and a lack of lakes at higher elevations indicate a lack of glacial scour and only slight glacial modification despite the entire region being covered by the laurentide ice sheet during the last glaciation this pattern of glacial erosion at the fjord onset zone is similar to what is found in the outer fjords 100 km toward the last glacial maximum ice margin and indicates that ice flow becomes organized well inland from the fjorded coast the relief generating process of selective linear erosion occurs at the fjord onset zone and was responsible for evolving baffin island fjords even in the late quaternary

glacial hydrology and erosion patterns a mechanism for carving glacial valleys article i nfo article history most glacial erosion models assume that erosion rates are proportional to ice sliding velocity while recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion first it suggests that erosion might mainly occur during melting seasons when subglacial water pressure is large and effective pressure is low i e before the channels fully develop and reduce the water pressure at the ice bedrock interface which promotes sliding and erosion second the distribution of erosion is bimodal with a peak at the equilibrium line altitude and as we demonstrate enhanced erosion at much lower altitudes within the ablation area where water due to melting abounds this has important implications because it explains why glacial erosion can simultaneously

canyon incision and knickpoint propagation recorded by apatite 4he 3he thermochronometry abstract in many regions of the world deeply incised canyons demonstrate the net effects of physical processes active at earth s surface in response to surface uplift low temperature thermochronometry can constrain the timing and rates of bedrock incision which is necessary for relating canyon incision to surface uplift over geological timescales we analyzed four samples from the cotahuasi ocona canyon system in southwest peru using 4 he 3 he thermochronometry and we present a new inversion model to identify continuous low temperature cooling histories that are consistent with the observed data derived cooling histories limit the onset of fluvial incision to 13 to 8 ma this is in agreement with previously reported interpretations based on a three dimensional thermal model interpolation to a much larger set of conventional apatite u th he ages however because 4 he 3 he thermochronometry constrains an independent cooling history for each sample the results also permit testing of landscape evolution models with greater spatial variability in exhumation compared to those models that can be tested by a geographically scattered set of conventional u th he ages the different cooling histories of the four samples require asynchronous incision along at least part of the canyon system that is best explained by headward propagation of fluvial incision by knickpoint migration

ice thickness and topographic relief in glaciated landscapes of the western usa abstract the development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes in particular glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice here we summarise a field based test of this hypothesis in two mountain ranges in the western united states the sierra nevada california and the sangre de cristo range colorado these areas exhibit a range of degrees of glacial occupation during the quaternary including some drainage basins essentially unoccupied by ice allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification we mapped last glacial maximum lgm trimlines to estimate the ice thickness at the equilibrium line altitude during the lgm and determined several metrics of relief for drainage basins across the full spectrum of lgm ice extents comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area we extended our study to the bitterroot range in idaho montana and the teton range in wyoming for a more comprehensive understanding of sub ridgeline relief or missing mass this measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers but appears to be influenced by the more active tectonics of the teton range while the effects of glacial modification on the landscape are clear valley widening hanging valley formation the overall change in the relief structure of the mountain ranges studied here is surprisingly modest

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history i theory and conceptual model abstract we determine to what extent low temperature thermochronology data in particular from age elevation profiles provide independent and quantitative estimates on denudation rates and relief development thermochronological age elevation profiles have been widely used to infer exhumation histories however their interpretation has remained inherently one dimensional neglecting potential effects of lateral offsets between samples furthermore the potential effects of transient topography on crustal isotherms and consequently on thermochronological data have not yet been addressed in detail we investigate this problem with the aim of deriving independent estimates of both denudation rates and relief history from low temperature thermochronometers measuring the relative uncertainties on these parameters and finally constraining the timing of potential variations in denudation rate and or relief development we adopt a non linear inversion method combining the three dimensional thermal kinematic model pecube which predicts thermal histories and thermochronological ages from an input denudation and relief history with an inversion scheme based on the neighbourhood algorithm we use synthetic data predicted from imposed denudation and relief histories and quantitatively assess the resolution of thermochronological data collected along an age elevation profile our results show that apatite fission track aft ages alone do not provide sufficient quantitative information to independently constrain denudation and relief histories multiple thermochronometers apatite u th he ahe ages and or track length measurements combined with aft ages are generally successful in constraining denudation rates and timing of rate changes the optimum combination of thermochronometers varying with the input scenario relief change or varying denudation rates however relief changes can only be quantified and precisely constrained from thermochronological age elevation profiles if the rate of relief growth is at least 2 3 times higher than the background denudation rate this limited resolution is due to the depth of the closure isotherm between 70 and 110 c for the aft and ahe systems which only partly record topographic change new thermochronometers such as 4 he 3 he or osl that are sensitive to lower temperatures may be the key for resolving this issue

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

climatic control of denudation in the deglaciated landscape of the washington cascades erosion in the washington cascades mountains was dominated by glacier activity until the end of the last glacial maximum when fluvial incision and mass wasting became the dominant drivers an analysis of millennial scale rates of denudation in the range suggest erosion is sensitive both to spatial variations in precipitation and inherited topography

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

climatic limits on landscape development in the northwestern himalaya the interaction between tectonism and erosion produces rugged landscapes in actively deforming regions in the northwestern himalaya the form of the landscape was found to be largely independent of exhumation rates but regional trends in mean and modal elevations hypsometry frequency distribution of altitude and slope distributions were correlated with the extent of glaciation these observations imply that in mountain belts that intersect the snowline glacial and periglacial processes place an upper limit on altitude relief and the development of topography irrespective of the rate of tectonic processes operating

subglacial extensional fracture development and implications for alpine valley evolution 1 bedrock stresses induced through exhumation and tectonic processes play a key role in the topographic evolution of alpine valleys using a finite difference model combining the effects of tectonics erosion and long term bedrock strength we assess the development of near surface in situ stresses and predict bedrock behavior in response to glacial erosion in an alpine valley the matter valley southern switzerland initial stresses are derived from the regional tectonic history which is characterized by ongoing transtensional or extensional strain throughout exhumation of the brittle crust we find that bedrock stresses beneath glacial ice in an initial v shaped topography are sufficient to induce localized extensional fracturing in a zone extending laterally 600 m from the valley axis the limit of this zone is reflected in the landscape today by a valley shoulder separating linear upper mountain slopes from the deep u shaped inner valley we propose that this extensional fracture development enhanced glacial quarrying between the valley shoulder and axis and identify a positive feedback where enhanced quarrying promoted valley incision which in turn increased in situ stress concentrations near the valley floor assisting erosion and further driving rapid u shaped valley development during interglacial periods these stresses were relieved through brittle strain or topographic modification and without significant erosion to reach more highly stressed bedrock subsequent glaciation caused a reduction in differential stress and suppressed extensional fracturing a combination of stress relief during interglacial periods and increased ice accumulation rates in highly incised valleys will reduce the likelihood of repeat enhanced erosion events

discovery of the southwest dongsha island mud volcanoes amid the northern margin of the south china sea abstract the dongsha basin circling dongsha island that is amid the northern margin of the south china sea is characterized by thin 0 5 km cenozoic sediments veneering on thick up to 5 km mesozoic strata recently several geophysical and geological surveys including multiple channel reflection seismic sub bottom profiling and benthic dredging have been conducted on the slope southwest to the dongsha island where the water depth varies from 400 m to 2000 m a novel discovery is numerous submarine mud volcanoes of various sizes over there typically 50 200 m high and 0 5 5 km wide geophysical profiles document their unusual features e g roughly undulating seafloor high amplitude seabed reflectivity foggy hyperbolic diffractions up to 50 m in water column above seabed and internal reflection chaos and wipe out down to 2 3 km level or deeper below the seabed benthic dredging from the mud volcanoes gives abundant faunas of high diversity e g scleractinian stony coral gorgonian black coral thiophil tubeworm glass sponge bryozoan etc indicating booming chemosynthetic community among which the lophelia pertusa like coral and the euretidae like glass sponges are the first reports in the south china sea concomitantly with them there are also abundant authigenic carbonate nodules and slabs raw brecciated and breccias with bio clasts congregation besides there coexist massive mudflows and allogenic coarse grained quartz feldspar and tourmaline most likely brought out by mud volcanism geochemical analysis of the bottom water samples give dissolved methane concentration up to 4 times higher than the background average these results lend comprehensive evidences for the ongoing and historical mud volcanism the escaping methane gas is inferred to source mainly from the mesozoic strata occupying a large province of the deep water slope ca 1000 km 2 or more the mud volcanoes is prospective for gas hydrate and natural gas for the dongsha basin

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

radiogenic isotope records of quaternary glaciations changes in the erosional source and weathering processes variations of global and regional silicate weathering rates and paleo ocean circulation patterns are estimated by using radiogenic isotope records but the effects of changes in provenance are generally ignored here sediment provenance has been constrained through the use of ar ar ages for individual detrital minerals from the labrador sea which can be compared directly to the radiogenic isotope compositions from the same core material dramatic changes in the radiogenic isotope composition of north atlantic deep water through the quaternary period are shown to reflect discrete changes in both sources and weathering processes accompanying northern hemisphere glaciation changes in the different radiogenic isotope systems reflect the influence of source physical weathering and chemical weathering and not simply changes in the underlying weathering rate or ocean circulation patterns that are typically inferred