knickzone propagation in the black hills and northern high plains a different perspective on the late cenozoic exhumation of the laramide rocky mountains geomorphic research in the black hills and northern high plains poses an intriguing hypothesis for the cenozoic evolution of this salient of the laramide rockies most recently geologists have appealed to late cenozoic epeirogenic uplift or climate change to explain the post laramide unroofing of the rockies on the basis of field mapping and the interpretation of long valley profiles we conclude that the propagation of knickzones is the primary mechanism for exhumation in the black hills long profiles of major drainages show discrete breaks in the slope of the channel gradient that are not coincident with changes in rock type we use the term knickzones to describe these features because their profiles are broadly convex over tens of kilometers at and below the knickzone the channel is incising into bedrock abandoning a flood plain and forming a terrace above the knickzone the channel is much less incised resulting in a broad valley bottom numerous examples of stream piracy are documented and in each case the capture is recorded in the same terrace level these observations are consistent with migrating knickzones that have swept through black hills streams rearranging drainages in their wake we demonstrate there are two knickzone fronts associated with mapped terraces preliminary field evidence of soil development shows that these terraces are time transgressive in nature our data strongly suggest that knickzone propagation must be considered a viable mechanism driving late cenozoic fluvial incision and exhumation of the northern high plains and adjacent northern rocky mountains

debris flows and debris torrents in the southern canadian cordillera in canada debris torrents also referred to as channelized debris flows occur in parts of british columbia alberta and the yukon at least 17 deaths and an estimated 100 million of damage to bridges and property can be attributed to this natural hazard the debris mainly comprises large boulders rock fragments gravel to clay sized material tree and wood mulch materials that accumulate in the mountain creeks to be susceptible to a debris torrent a creek must have a drainage area within a critical range a profile that is sufficiently steep an accumulation of debris and some form of triggering mechanism the most common triggering mechanism is an extreme water discharge which may result from a very intense rainfall or a temporary damming of the creek in western canada the resulting torrents involve masses of debris typically less than 50 000 m3 that travel down creeks at speeds between 3 and 12 m s several passive and active forms of mitigation can be used to reduce the impact of debris to

holocene vegetation climate and lake level changes in the interior douglas fir biogeoclimatic zone british columbia chilhil phair fishblue and horseshoe lakes in the southern interior of british columbia were cored and analyzed for pollen phair lake was also examined for plant macrofossils and aquatic molluscs two dated volcanic tephras mazama and bridge river are present in three of the four lakes and together with radiocarbon dates provide an absolute chronology for pollen influx calculations and stratigraphic correlation abrupt changes in sediment type at phair lake about 5650 and 2000 years ago correlate with neoglacial advances near the coast interior transition pollen changes suggestive of moister conditions and the presence of an aquatic mollusc valvata sincera helicoidea at phair and chilhil lakes are consistent with the neoglacial evidence of cooler and wetter conditions after about 2400 years ago the driest part of the holocene was the early pre mazama ca 6600 6800 years ago interval when the vegetation was more open and herb rich and the lake levels were lower than at present wetter clima

light toned salty soils and coexisting si rich species discovered by the mars exploration rover spirit in columbia hills 1 light toned soils were exposed through serendipitous excavations by spirit rover wheels at eight locations in the columbia hills their occurrences were grouped into four types on the basis of geomorphic settings at three major exposures the light toned soils are hydrous and sulfate rich the spatial distributions of distinct types of salty soils vary substantially with centimeter scaled heterogeneities at paso robles dead sea shredded and champagne penny a well mixed nature for light toned soils occurring near and at the summit of husband hill and relatively homogeneous distributions in the two layers at the tyrone site aeolian fumarolic and hydrothermal fluid processes are suggested to be responsible for the deposition transportation and accumulation of these light toned soils in addition a change in pancam spectra of tyrone yellowish soils was observed after being exposed to current martian surface conditions for 175 sols this change is interpreted to be caused by the dehydration of ferric sulfates on the basis of laboratory simulations and suggests a relative humidity gradient beneath the surface si rich nodules and soils were observed near the major exposures of s rich soils they possess a characteristic feature in pancam visible near infrared vis nir spectra that may be diagnostic of hydrated species and this spectral feature can be used to search for additional si rich species the exposures of hydrated salty soils within various geomorphic settings imply the potential existence of hydrous minerals in similar settings over a much wider area hydrous sulfates represent one of the candidates that may contribute the high level of water equivalent hydrogen in equatorial regions detected by the neutron spectrometer on mars odyssey

a soil chronosequence study of the reno valley italy insights into the relative role of climate versus anthropogenic forcing on hillslope processes during the mid holocene abstract relatively few soil chronosequences with good age control exist for late pleistocene and holocene deposits in the mediterranean region of europe yet surface soils and their young buried counterparts can provide meaningful information about the timing and processes of landscape response to external forcing such as climate or anthropogenic change here we present the results of a study that examines a well dated chronosequence of nineteen soil exposures in surficial deposits ranging in age from hundreds of years to hundreds of thousands of years located in the reno river valley near bologna italy the soil forming climate of the reno valley sits on a threshold between that which facilitates the accumulation of caco 3 and that which facilitates the translocation and formation of clay minerals and iron oxides once formed secondary iron oxides are relatively immobile in oxidizing conditions in the soil profile and therefore consistently record age trends with feo fed ratios decreasing predictably with soil age for all soils in the chronosequence the morphology of secondary carbonate accumulation and its depth of leaching also vary predictably with soil age but only for soils younger than about 12 000 years in these young soils horizons that contain secondary carbonate progress from relatively shallow stage i bk horizons in late holocene aged soils to deeper stage iii bk horizons in latest pleistocene aged soils in soils older than approximately 12 000 cal ybp however carbonate dissolution during wetter climates and the addition of colluvium and or dust to terrace surfaces become important factors in the preservation of carbonate in the profile and carbonate content is not predictable by age alone without significant depositional additions these older soils become decalcified pedogenic carbonate precipitated during drier climates is susceptible to dissolution during wetter periods as evidenced by discontinuous carbonate coatings on grains in some soils therefore overall measurable pedogenic carbonate content is spatially and temporally variable as a function of input of fresh carbonate and locally controlled soil moisture conditions particle size does not decrease predictably with soil age for reno valley soils and appears to be strongly influenced by parent material variability in younger soils and by dust additions in older soils our detailed examination of soil stratigraphy in the reno valley revealed evidence of significant aggradation of colluvium and tributary fans in the middle holocene between 6000 and 4000 ybp this aggradation pre dates bronze age agricultural expansion and appears to be instead attributable to the climate conditions of the middle holocene that have been documented elsewhere in italy for this time period this study demonstrates that late pleistocene and holocene surface soils in the mediterranean region of europe can effectively help elucidate rates and processes of landscape evolution

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

quantifying differential rock uplift rates via stream profile analysis despite intensive research into the coupling between tectonics and surface processes our ability to obtain quantitative information on the rates of tectonic processes from topography remains limited due primarily to a dearth of data with which to test and calibrate process rate laws here we develop a simple theory for the impact of spatially variable rock uplift rate on the concavity of bedrock river profiles application of the analysis to the siwalik hills of central nepal demonstrates that systematic differences in the concavity of channels in this region match the predictions of a stream power incision model and depend on the position and direction of the channel relative to gradients in the vertical component of deformation rate across an active fault bend fold furthermore calibration of model parameters from channel profiles argued to be in steady state with the current climatic and tectonic regime indicates that 1 the ratio of exponents on channel drainage area and slope m n is 0 46 consistent with theoretical predictions 2 the slope exponent is consistent with incision either linearly proportional to shear stress or unit stream power n 0 66 or n 1 respectively and 3 the coefficient of erosion is within the range of previously published estimates mean k 4 3 10 4 m 0 2 yr application of these model parameters to other channels in the siwalik hills yields estimates of spatially variable erosion rates that mimic expected variations in rock uplift rate across a fault bend fold thus the sensitivity of channel gradient to rock uplift rate in this landscape allows us to derive quantitative estimates of spatial variations in erosion rate directly from topographic data

tectonic and lithologic controls on bedrock channel profiles and processes in coastal california 1 recent theoretical models suggest that topographic characteristics of bedrock channels are products of interactions among tectonics substrate resistance and the climatically modulated erosive ability of the river the degree to which these factors influence the form of channel profiles is poorly quantified at present here we investigate bedrock channels developed across the southern flank of the santa ynez mountains california uniform climate and systematic variations in lithology and rock uplift rate along the range allow comparison of channel morphology between 1 channels eroding rocks of uniform and nonuniform strength and 2 channels experiencing differences in tectonic forcing we combine field observations surveys and analysis of digital data to determine topographic and hydraulic characteristics of bedrock channels at a constant rock uplift rate streams flowing from resistant to less resistant bedrock exhibit highly concave profiles and increased gradients along lower reaches relative to channels developed in uniform bedrock these effects are interpreted as responses to 1 an increase in substrate resistance to channel incision in the upper reaches and 2 transport limited gradients along lower reaches comparisons of channels developed across uniform lithology but experiencing an approximately sevenfold difference in rock uplift rate reveal an approximately twofold increase in gradient and an approximately threefold decrease in width in this landscape the combined channel adjustments of gradient and width are consistent with a fluvial incision model in which channel incision rate is linearly proportional to mean bed shear stress

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

considerations on the seismotectonics of the northern apennines abstract the northern apennines have been subdivided into homogeneous zones on the basis of recent structural evolution and crustal structure in which the earthquake distribution can find a coherent framework these zones whose physiography is in strict connection with their structure are the internal peri tyrrhenian belt the external or main belt the buried belt and the pede alpine homocline earthquake activity has a tendency to cluster along well defined bands particularly in the easternmost border of the peri tyrrhenian belt as well as along the zone between the external belt and the buried belt i e along the padanian margin of the northern apennines a minimum of seismic activity seems to be correlated with some zones of the external belt as well as with the late tertiary and quaternary magmatic province of tyrrhenian southern tuscany the fault plane solutions are coherent with the structural picture a tentative seismotectonic model of the northern apennines is discussed

transient fluvial incision in the headwaters of the yellow river northeastern tibet china 1 we utilize topographic analysis of channel profiles combined with field measurements of erosion rates to explore the distribution of channel incision in the anyemaqen shan a broad mountainous region in the northeastern tibetan plateau tributary channels to the yellow river display systematic downstream increases in channel gradient associated with convex upward longitudinal profiles steep lower reaches of channels are associated with rapid 1 m ka incision rates along the yellow river while upstream reaches are associated with relatively slow 0 05 0 1 m ka erosion of soil mantled uplands covariance between erosion rates and channel steepness indices suggest that channels are adjusted to match long wavelength differential rock uplift across the range geologic constraints indicate that rapid incision downstream of the range is associated with excavation of basin fill driven by changes in relative base level farther downstream the upstream limit of this wave of transient incision is marked by a series of knickpoints that are found at nearly the same elevation throughout the watershed consistent with knickpoint migration as a kinematic rather than diffusional wave tributary channel gradients downstream of knickpoints however display a progressive adjustment to increased incision rates that may reflect the influence of increased sediment flux comparison of observed channel profiles to a stream power model of fluvial behavior reveals that the rate of knickpoint propagation can only be explained if the erosional efficiency coefficient k increases during incision our results thus highlight the utility of channel profile analysis to reconstruct the fluvial response to both active tectonism and external changes in base level

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

effects of orographic precipitation variations on the concavity of steady state river profiles the concavity or curvature of river profiles has long been taken to be a fundamental indicator of the underlying processes governing fluvial erosion and thereby of landscape evolution however erosion laws have generally been derived without accounting for the strong orographically driven gradients in precipitation typically found in mountainous regions in addition field measurements have found discrepancies between the form of measured stream profiles and theoretically derived values introducing a simple physically based feedback we find that orographically induced variations in precipitation strongly affect the curvature of steady state river profiles this feedback complicates efforts to infer the form of erosion laws from observed profile concavities but could help explain discrepancies between observations and theory our results demonstrate a strong feedback through which climate influences the form of river profiles and show how such climatic effects act to limit the relief of unglaciated mountain ranges

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

holocene migration of lodgepole pine pinus contorta var latifolia in southern yukon canada a palynological reconstruction n 25 profiles suggests that the northern extent of lodgepole pine pinus contorta var latifolia engelmann ex s watson occurred between 59 and 60 n latitude in

controls on the channel width of rivers implications for modeling fluvial incision of bedrock on the basis of the manning equation and basic mass conser vation principles we derive an expression for scaling the steady state width w of river channels as a function of discharge q channel slope s roughness n and width to depth ratio a w 5 a a1 2 2 3 3 8 q 3 8 s 23 16 n 3 8 we propose that channel width to depth ratio in addition to roughness is a function of the material in which the channel is developed and that where a river is con fined to a given material width to depth ratio and roughness can be assumed constant given these simplifications the expression emulates traditional width discharge relationships for rivers incis ing bedrock with uniformly concave fluvial long profiles more sig nificantly this relationship describes river width trends in terrain with spatially nonuniform rock uplift rates where conventional discharge based width scaling laws are inadequate we suggest that much of observed channel width variability in river channels confined by bedrock is a simple consequence of the tendency for water to flow faster in steeper reaches and therefore occupy smaller channel cross sections we demonstrate that using conventional scaling relationships for channel width can result in underestima tion of stream power variability in channels incising bedrock and that our model improves estimates of spatial patterns of bedrock incision rates

thrust fold activity at the mountain front of the northern apennines italy from quantitative landscape analysis abstract we document the active tectonics of growing anticlines embedded in the northern apennine mountain front using a quantitative analysis of the topography these structures appear to be growing at rates of 0 1 0 3 mm year more slowly than the long term general rate of emergence of the apennines from the po plain our analysis is dedicated to extract the signal of this tectonic activity recording it primarily by the channel steepness ksn of streams traversing the mountain front and by swath profiles and relief of the topography topographic swath profiles and ksn are consistent with field stratigraphic structural mapping and seismic reflection profile relationships in general the spatial distribution of ksn values of small channels with upstream drainage area quantitatively we use local development of relief as a proxy for rock uplift measured as river incision across the mountain front and anticlines to test the expected linear scaling between rock uplift rates relief and ksn in this low rock uplift setting 0 1 0 3 mm year this predicted scaling relationship is not supported by ksn and topographic data suggesting a condition of transient response of fluvial incision that generates the relief to the tectonic forcing where ksn and relief have not achieved steady state values however a weak linear scaling between rock uplift and ksn may hold for the local highest uplift settings where over 40 m of relief have been generated thus establishing a lower threshold for where the channel steepness approach may be valid in this slowly deforming landscape assuming a state of transient response of fluvial incision to tectonic forcing the high ksn values can be explained as places where the channels are being actively deformed by tectonics but have not yet fully responded by incising and generating relief therefore in the absence of relief generation the spatial distribution of ksn maximum values for small streams can hold for rock uplift and work as a model for indicating locations of strongest anticlinal growth collectively the correspondence among the stratigraphic markers used to define the structures topography and relief as quantified in the swath profiles and the ksn values that indicate active channel adjustments to tectonic forcing support the evidence of continued shortening across the european adria plate boundary and the contemporary slow growth of the structures embedded in the emergent apennines mountain front

when did the northern apennine become a mountain chain abstract the purpose of the present paper is to bracket the age of the initial uplift of the northern apennine chain by means of all the available evidence the collected data show that the age of the lacustrine or fluvio lacustrine units which have aggraded in the intramontane basins is late pliocene in the northwestern tip of the northern apennine and mostly early pleistocene elsewhere the age of the oldest terraced fluvial deposits showing the initiation of incision is mostly middle pleistocene the uplift of the summit areas of low relief most likely took place during the middle pleistocene it is concluded that the uplift occurring during middle and upper pleistocene caused an area of rather low relief to become the northern apennine mountain chain an eastward shift of the uplift through time is likely

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

thrust front segmentation induced by differential slab retreat in the apennines italy new seismic reflection data reveal that the south eastward prolongation of the apennine thrust front in the central adriatic sea is most likely located in a more external position with respect to the traditional interpretation in this new interpretation the apennine thrust front shows a segmented geometry in correspondence to the tremiti lithospheric transfer zone the available data suggest that the north eastward flexural retreat of the subducting adriatic lithosphere and the related frontal accretion of the apennine accretionary prism have acted during the last 5 ma and may be considered still lively in both the po plain and in the central adriatic domain north of the tremiti lineament by analysing the tectonic evolution of the apulo adriatic areas it may be argued that the differential slab retreat between the central and southern sectors of the subducting adriatic plate has been able to induce the segmentation of the apennine thrust front

late quaternary fluvial terraces of the romagna and marche apennines italy climatic lithologic and tectonic controls on terrace genesis in an active orogen abstract we synthesize a new fluvial terrace chronostratigraphy of the bidente and musone rivers cast within a broader european framework which forms the basis of a terrace genesis and river incision model for the northern apennines italy our model supported by terrace long profiles correlation to po foreland sediments 15 new radiocarbon dates and published numeric and relative stratigraphic ages highlights how drainage basin substrate drives concurrent formation of strath terraces in the bidente basin and fill terraces in the musone basin quaternary climate change paces the formative geomorphic processes through unsteady discharges of water and sediment in the weathering limited setting represented by the bidente basin siliciclastic detritus carves broad strath surfaces during glacial climates that are preserved as terraces as the river incises during the transition to an interglacial climate in contrast the transport limited and carbonate detritus dominated musone basin sees valleys deeply buried by aggradation during glacial climates followed by river incision during the transition to an interglacial climate incision of these rivers over the past 1 million years has been both unsteady and non uniform these and all po adriatic draining rivers are proximal to a base level defined by mean sea level and have little room for increasing their longitudinal profile concavities through incision particularly in their lower reaches despite periodic glacio eustatic drawdowns as a result the observed incision is best explained by rock uplift associated with active local fault or fold growth embedded in the actively thickening and uplifting apennine foreland

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

the mendocino triple junction active faults episodic coastal emergence and rapid uplift a complex zone of rapid holocene surface uplift and deformation occurs at the mendocino triple junction the juncture of three plate bounding faults the cascadia subduction zone san andreas fault and mendocino fault within this mountainous structural knot up to 1 4 m of coastal emergence occurred during the 1992 cape mendocino m s 7 1 earthquake surveying and radiometric dating of ancient marine strandlines 7 5 along the cascadia subduction zone megathrust however another plausible interpretation of the data is that multiple earthquakes resulting in smaller amounts of net surface uplift per event similar to the 1992 earthquake occurred closely spaced in time giving the appearance in the geologic record of less frequent and larger events regardless of the number and timing of paleoearthquakes the number of platforms is a minimum of the number of events that resulted in sudden rapid uplift because platform preservation is also a function of rising holocene sea level at present rates and patterns of net surface uplift are better constrained than the timing and magnitude of paleoearthquakes periods of rapid holocene emergence also are identified as far south of the area of 1992 uplift and the mendocino fault as 30 km along the unlocated san andreas fault these also might be associated with coseismic uplift based on new mapping of active faults in the region it is proposed here that this uplift is the result of multiple discontinuous thrust and strike slip fault segments which distribute plate boundary deformation along a restraining bend at the termination of the san andreas fault this interpretation is consistent with the fact that a single prominent strike slip fault has not been identified in the mendocino triple junction region while several small reverse faults crossing holocene deposits and geomorphic surfaces have been mapped and dated

structural constraints on the tertiary plate tectonic evolution of italy abstract eight cross sections six of which were balanced and restored using the principles of thin skinned tectonics demonstrate the reinterpretation of the apennine and sicilian mountains as a detached fold and thrust belt the thin skinned interpretation constrains the extent of the restored continental margins and the amount percentage direction and timing of tectonic shortening allowing the development of a plate tectonic model late cretaceous and paleogene subduction to the north beneath the corsica sardinia calabria csc microplate causes rifting from se france and the development of oceanic crust between the two in the oligo miocene the late oligocene collision of adria and northernmost csc pins the northern edge of the csc plate causing its counter clockwise rotation and its mid miocene suturing between italy and sicily the n s convergence of africa and europe with counter clockwise rotation of italy causes shortening in the nne ssw direction in italy and sicily from 20 10 ma the n s compression extrudes calabria to the se causing mio pliocene compression in southern italy and eastern sicily at the same time as extension and alkaline volcanism in central italy

geomorphological analysis of the drainage system on the growing makran accretionary wedge abstract the morphology of six adjacent major catchments draining the onshore makran accretionary wedge in southeast iran and southwest pakistan was studied to examine how the channel pattern and the length profiles may reflect the recent and active growth of the wedge qualitative field surveys were combined with the quantitative analysis of channel steepness and concavity measured from digital elevation models these profiles were compared with modelled profiles using a stream power approach assuming homogeneously uplifting uniform rock substratum results show a distinct difference between the studied western and eastern catchments the three western rivers are in morphological equilibrium whereas the two eastern rivers exhibit profiles with prominent convexities and knickpoints thus notably diverging from equilibrium concave up shapes all the studied catchments share the same base level flow on similar lithologies and developed under uniform climate conditions therefore we interpret the morphometric differences in terms of differential rock uplift rate as a response to local tectonic activity this interpretation is consistent with both uplift rates of marine terraces along the coast of makran and the recorded seismicity the geomorphological analysis presented here extends coastal information to wide inland areas and documents longer term tectonic behaviour than the seismotectonic record hence the steeper surface slope and faster surface uplift rates recorded by the eastern catchments compared to equilibrium of the western catchments are regional long term signals relevant for a wide part of the makran accretionary wedge we attribute the regional geomorphic difference to quaternary variations in tectonic regimes that forced differential uplift rates of the wedge surface we hypothesize that the different tectonic regimes are related to different subduction rates

late quaternary sequence stratigraphy of the mackenzie delta the late wisconsinan and holocene sequence stratigraphy of the mackenzie delta provides insights into the glacial history of the region the base of the described succession is a hummocky regional reflector interpreted to be a flooding surface formed immediately after retreat of glacial ice from the mackenzie trough above this flooding surface two progradational parasequences are present the first assigned to the transgressive systems tract is correlated with the tutsieta lake readvance of the ice sheet at approximately 13 000 bp a flooding surface forming the upper boundary of this parasequence extends inland to at least inuvik developing as a response to glacial retreat and early holocene relative sea level rise the second parasequence of holocene deltaic deposits is assigned to the highstand systems tract and is characterized by progressive progradation of the delta into the mackenzie trough to a position seaward of the present delta coastline a distinct reduction in gradient of the most recen

the impact of air mass circulation dynamics on late holocene paleoclimate in northwestern north america paleoclimate records from northern british columbia southwestern yukon and adjacent alaska suggest that late holocene climate may have been influenced by specific air mass circulation dynamics the aleutian lowpressure index alpi is a measure of sea level pressure fluctuations in the pacific northwest associated with the aleutian low al pressure system in this study we show that the al has a strong influence on historical climate change in the study area and explore the relationships between alpi polarity and changes in late holocene paleoclimate records analyses of weather station data in the study area indicate positive correlations r 0 63 between mean wintertime december march temperature and alpi values total wintertime snowfall accumulation and total precipitation show moderate and weak negative correlations respectively a late holocene increase in exotic western hemlock tsuga heterophylla pollen has been observed in regional paleoclimate studies a sustained positive alpi phase during the late holocene is considered as a causative mechanism under such conditions warm maritime air masses would more frequently penetrate inland potentially resulting in eastward pollen transfer enhanced growing conditions at coastal sites and an increase eastwards in the range limit of these species this study indicates that apparent conflicts in the timing and magnitude of late holocene climate change may be the result of a strong regional climate forcing mechanism that exhibits both temporal and geographical variation r 2002 elsevier science ltd and inqua all rights reserved

a new active tectonic model for the construction of the northern apennines mountain front near bologna italy 1 we integrate existing and new geologic data retreating trench extension and accretion tectonics retreat project particularly on the origin growth and activity of the mountain front at bologna italy into a new model that explains apennine orogenesis in the context of a slab rollback upper plate retreat process the bologna mountain front is an actively growing structure driving rock uplift 1 mm year cored by a midcrustal flat ramp structure that accommodates ongoing shortening driven by adria subduction at a rate of 2 5 mm year the data we use are assembled from river terraces and associated pleistocene growth strata geodesy including releveling surveys reinterpretation of published reflection lines and a new high resolution reflection line these data constrain a simple trishear model that inverts for blind thrust ramp depth dip and slip apennine extension is recognized both in the foreland as high angle normal faults and modest stretching in the carapace of the growing mountain front and in the hinterland with larger normal faults that accomplish some crustal thinning as the upper plate retreats this coevolution of extension and shortening shares some notable characteristics with other basement involved collisional orogens including the early tertiary laramide orogeny in the american west and the oligocene to miocene evolution of the alps we propose a possible relationship between underplating and the development of the po as a sag basin as a quaternary phenomenon that may also apply to past periods of apennine deformation tortonian continued shortening on the structure beneath the bologna mountain front represents by far the most important and underappreciated seismogenic source in the front of the northern apennines

interpreting quaternary uplift rates at the mendocino triple junction northern california from uplifted marine terraces analysis of the altitudinal spacing of 14 flights of marine terraces indicates a spatial pattern of varying uplift rates that agrees with that determined from previously dated terraces for the past 3 81 ka and temporal changes in uplift rates from 1 m ka to 3 5 m ka that may reflect response to changes in tectonic regime during passage of the mendocino triple junction mtj a possible mechanism for regional uplift is growth of a slab window south of the mtj the region of most rapid uplift is 25 43 km south of the mtj immediately south of the northern boundary of the slab window the coastline is tilted upward to the south in the region directly above the southern edge of the subducted gorda plate at point delgada 55 km south of the present mtj where the northern edge of the slab window passes approximately 300 ka uplift rates have been 1 2 m ka for at least 330 ka more than 1 4 m y after passage of the southern edge of the subducted slab at the mendocino coast uplift rates have been less than 0 4 m ka for at least 330 ka

transient channel incision along bolinas ridge california evidence for differential rock uplift adjacent to the san andreas fault 1 the rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the marin county region of northern california we characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the franciscan terrane in marin county channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls these patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient as incision outpaces soil production rates these differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the san andreas fault relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates our study highlights how landscape analysis can place bounds on the distribution of earth deformation in both space and time and thus lends insight into the processes driving that deformation

channel response to tectonic forcing field analysis of stream morphology and hydrology in the mendocino triple junction region northern california abstract an empirical calibration of the shear stress model for bedrock incision is presented using field and hydrologic data from a series of small coastal drainage basins near the mendocino triple junction in northern california previous work comparing basins from the high uplift zone huz uplift rates around 4 mm year to ones in the low uplift zone luz 0 5 mm year indicates that the huz channels are about twice as steep for a given drainage area this observation suggests that incision processes are more effective in the huz it motivates a detailed field study of channel morphology in the differing tectonic settings to test whether various factors that are hypothesized to influence incision rates discharge channel width lithology sediment load change in response to uplift or otherwise differ between the huz and luz analysis of regional stream gaging data for mean annual discharge and individual floods yields a linear relationship between discharge and drainage area increased orographic precipitation in the huz accounts for about a twofold increase in discharge in this area corresponding to an assumed increase in the erosional efficiency of the streams field measurements of channel width indicate a power law relationship between width and drainage area with an exponent of 0 4 and no significant change in width between the uplift rate zones although interpretation is hampered by a difference in land use between the zones the huz channel width dataset reveals a scaling break interpreted to be the transition between colluvial and fluvial dominated incision processes assessments of lithologic resistance using a schmidt hammer and joint surveys show that the rocks of the study area should be fairly similar in their susceptibility to erosion the huz channels generally have more exposed bedrock than those in the luz which is consistent with protection by sediment cover inhibiting incision in the luz however this difference is likely the result of a recent pulse of sediment due to land use in the luz therefore the role of sediment flux in setting incision rates cannot be constrained with any certainty to summarize of the four response mechanisms analyzed the only factor that demonstrably varies between uplift rate zones is discharge although this change is likely insufficient to explain the relationship between channel slope and uplift rate the calibrated model allows us to make a prediction of channel concavity that is consistent with a previous estimate from slope drainage area data we show that the inclusion of nonzero values of critical shear stress in the model has important implications for the theoretical relationship between steady state slope and uplift rate and might provide an explanation for the observations this analysis underscores the importance of further work to constrain quantitatively threshold shear stress for bedrock incision

paraglacial and postglacial debris flows on a little ice age terminal moraine jamapa glacier pico de orizaba mexico the study area is located on the northern face of pico de orizaba mexico 5700 m asl on the terminal moraine of jamapa glacier which dates from the little ice age large debris flows are recurrent on the proglacial ramp the comparison of lichen colonies growing on the deposits of the flows reveals that two generations of flows are present an old one and a very recent one that occurred between 1994 and 1995 studies were made of the sedimentologic characteristics of the flows and ground temperatures were recorded to a depth of 70 cm on the floor of the channels comparison of the lichen growth on the exposed surfaces of the deposits led to the relative dating of the older debris flow which is associated with the beginning of the retreat of the glacier and the saturation of the terminal moraine deposits by meltwater the more recent flow has less transport capacity and is identified with the formation of an impermeable layer of permafrost that covers the bottom of the channel of the old debris flow the permafrost layer formed when snow accumulations on the bottom of the channel were covered by ash that fell from the slopes

the lillooet terraces of fraser river a palaeoenvironmental enquiry the history of holocene fluvial terraces was investigated by stratigraphic morphological and palaeohydrologic methods the terraces were formed in glaciofluvial and glaciolacustrine sediments by the fraser river degradation alternated with episodes of stability and aggradation the uppermost terraces four nonpaired surfaces were occupied by a braided river vertical stability was controlled either by the water and sediment discharge of the river or by backwater effects from downstream landslides the lower terraces two paired surfaces and associated fluvial sediments provide evidence for at least two cycles of aggradation and downcutting these can be attributed to the effects of landslides that occurred a short distance downstream climatic variations may also have influenced terrace formation but direct evidence is lacking palaeohydraulic investigations based on gravel texture terrace gradients and geometry of palaeochannels provide results that although approximate conform with conclusions

sedimentary processes of the kusawa lake torrent system yukon canada as revealed by the september 16 1982 flood event abstract the kusawa lake torrent system is located in the northern canadian cordillera of southwestern yukon it is holocene in age and consists of a catchment area gorge and alluvial fan complex the north compartment of the catchment is a third order basin covering an area of 13 2 km 2 it is characterized by active slumping of quaternary glacial deposits that supply sediment for the torrent system the gorge is approximately 800 m long and distinguished by 10 m high vertical walls cut into granitic bedrock the fan complex is semiconical in shape and covers an area of 1 52 km 2 the active part of the fan is plano convex in longitudinal profile covers an area of 0 75 km 2 and is subdivided into an upper middle and lower fan based on the occurrence of seven sedimentary facies that were deposited by a catastrophic flood in 1982 the upper fan is characterized by boulder gravel levees and boulder gravel lobes that were deposited by debris flows it is also characterized by sandy boulder gravel that may represent a transition from debris flow to dominantly hyperconcentrated flow processes the middle fan is distinguished by sandy cobble gravel and sandy pebble gravel that is interbedded with horizontally laminated sand these sediments were deposited by hyperconcentrated flows the lower fan is characterized by horizontally bedded and laminated sand that may represent a transition from hyperconcentrated flow to sheetflood dominant processes and by sand channels that represent rechannelized waning flood discharge the fan displays downfan trends in grain size boulders to sand slope style plano concave and slope value 4 1 typical of sheetflood dominated fans the initiation of sedimentation in the kusawa lake torrent system was due to a combination of rainfall flooding and flooding related to catastrophic slope failure in the catchment area slope failure leads to the formation of a landslide dam and lake and when the dam fails the draining lake results in a flood many times larger than a rainfall flood the frequency of these catastrophic flood events may be once every 200 years although the kusawa lake torrent system is now dormant the potential for further landslide dams and subsequent catastrophic floods is high and could result in further damage to a campground and private property in the area

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

holocene debris flows and environmental history hazelton area british columbia debris flow deposits of chicago creek and the sediment pollen and macrofossil records of seeley lake were studied to elucidate the holocene history of the northwest flank of the rocher dcboulc range near hazelton british columbia the chicago creek drainage has experienced numerous rockfalls debris slides and debris flows a large debris flow covering approximately 300 ha occurred about 3580 2 150 bp this flow was two to three orders of magnitude larger than historic debris flows in this drainage it traveled about 3 km down chicago creek and dammed the outlet stream of seeley lake a debris deposit along lower chicago creek is interpreted as the product of debris torrents that formed during or soon after the damming of seeley lake its surface exhibits soil development rubification and profile development comparable to that on the large debris flow suggesting equivalent age pollen and plant macrofossils are described from a core taken in seeley lake this core spans the period from ca 9200 bp to the present a disturbance event in 3380 2 110 bp correlative with the large chicago creek debris flow is recorded by a clastic sediment layer and changes in the microfossil and rnacrofossil assemblages the chicago creek debris flow and debris torrent ca 3500 bp may be the catastrophic event recorded in the story of the medeek an oral history or ada ok of the gitksan people of hazelton

a fluvial record of active fault propagation folding salsomaggiore anticline northern apennines italy 1 fault propagation folds offer the potential to relate folding to underlying fault propagation and slip provided that fold kinematics can be established fluvial terraces have been recognized as kinematic indicators but precise relationships between surface uplift and various folding mechanisms remain largely unexplored this study takes advantage of a well preserved progressively deformed suite of middle pleistocene to recent fluvial terraces above a growing fault propagation fold at the apennine mountain front northern italy to constrain the recent fold kinematics and place them in the context of a longer growth history gleaned from older growth strata the geometry of straths and overlying terrace deposits defines a fixed anticlinal hinge a rolling synclinal hinge proxies for fault tip propagation rates rock uplift rates and tilting rates and how these features and rates vary over the last 800 ka along 15 km of strike length field studies are augmented with dem based quantitative geomorphic analyses that document catchment hypsometry mean anticlinal hinge elevation and long profile form notably long term rock uplift rates using incision as a proxy are uniformly correlated with fault propagation and associated synclinal hinge migration mean anticlinal hinge elevation and variations in catchment hypsometries channels that cross the forelimb at a high angle to the fold hinge generally have higher concavities but channel steepness commonly thought to reflect rock uplift is more strongly adjusted to rock type this study elucidates a new understanding of a complex fold growth history extending back at least 10 ma and provides a novel demonstration of how fluvial terraces may be utilized to constrain fault related fold kinematics

pliocene and pleistocene exhumation and uplift of two key areas of the northern apennines application of different thermochronological methods to two areas of pronounced relief apuane alps and mt falterona of the northern apennines chain documents an average exhumation rate of about 0 7m m yr this result suggests that the general exhumation of the chain is driven mainly by erosion nevertheless the long term exhumation trend seems to be perturbed by shortterm events at higher exhumation rates the time of increased exhumation rates coincides with onset of intramontane sedimentation documenting a contribution of tectonics local normal faulting to the surface uplift the data indicate an eastward shifting of the onset of topographic relief early pliocene in the apuane alps and early pleistocene in the mt falterona area r 2002 elsevier science ltd and inqua all rights reserved

evaluation of garnet discrimination diagrams using geochemical data of garnets derived from various host rocks abstract this work is an attempt to evaluate six different garnet discrimination diagrams one binary diagram and five ternary diagrams commonly used by many researchers the mineral chemistry of detrital garnet is a useful tool in sedimentary provenance studies yet there is no clear cut understanding of what garnet type originates from which host lithology several discrimination diagrams exist for garnet showing distinct compositional fields separated by strict boundaries that are thought to reflect specific types of source rocks for this study a large dataset was compiled n 3532 encompassing major element compositions of garnets derived from various host lithologies including metamorphic igneous and mantle derived rocks in order to test the applicability of the various discrimination schemes the dataset contains mineral chemical data collected from the literature complemented with some new data n 530 from garnet bearing metamorphic and ultramafic rocks in austria and norway discrimination of the tested diagrams only works for a small group of garnets derived from mantle rocks granulite facies metasedimentary rocks and felsic igneous rocks for other garnet types the assignment to a certain type of host rock remains ambiguous this is considered insufficient and therefore the evaluated diagrams should be used with great care we further apply compositional biplot analysis to derive some hints towards future perspectives in detrital garnet discrimination

holocene climate and seasonality of shell collection at the dundas islands group northern british columbia canada a bivalve sclerochronological approach article i nfo to analyze environmental changes and the seasonality of shell collection in british columbia during the ho locene oxygen isotopes were measured from modern and archeological 1337 7438 cal yr bp shells of the butter clam saxidomus gigantea 1697 discrete isotope samples were taken from two modern and 27 arche ological shells with a high temporal resolution sub seasonal up to daily archeological shells were collected from five shell midden sites on the dundas islands group northern british columbia canada the oxygen iso tope data reveal clear annual cycles with the most positive 18 oshell values occurring during the cold season slower growth annual growth line formation and the most negative 18 oshell values during the warm sea son period of faster growth whereas the most positive 18 oshell values remained relatively constant throughout the holocene the warm season 18 oshell values reflected considerable variability summer values observed in the early and late holocene became approximately 1 more negative around 2500 3000 and 5500 6000 bp implying lower salinity during the mid holocene variations in the oxygen isotopic composi tion of marine shells reflect changes in temperature and salinity such large changes in 18 oshell are unlikely being caused by temperature changes alone furthermore the large annual 18