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

mesozoic extension controlling the southern alps thrust front geometry under the po plain italy insights from sandbox models in the southern alps fold and thrust belt east west mesozoic rifting controlled the development of extensional faults the deposition of the sedimentary sequences and the thickness and distribution of the main detachment levels vertical and lateral heterogeneities strongly influenced the structural style of the subsequent north south contractional phase as revealed by surface mapping and by subsurface maps derived from seismic data along the strike of the chain lateral terminations of thrust faults occur at syn rift extensional faults trending normal with respect to the contractional structures from west to east the thrust sheet number decreases and the order of structures and their wavelength changes on a regional scale the effects produced by pre existing heterogeneities on the development of contractional alpine tectonic structures in the external area of the southern alps were evaluated by means of scaled sandbox analogue models modelled lateral heterogeneities produced different wavelength thrust sheets salients and recesses whereas vertical heterogeneities facilitated the development of structures of different orders first order structures detached at the base of the model and second order structures detached at the intermediate relatively weak layers comparison of analogue model results with nature showed good geometrical similarities 2006 elsevier ltd all rights reserved

preservation of valley and ridge topography via delivery of resistant ridge sourced boulders to hillslopes and channels southern appalachian mountains u s a abstract discrete bands of resistant strata found along ridgelines in lithologically controlled geologically heterogeneous landscapes are generally credited with maintaining high topography in these settings however the mechanisms by which these ridge formers prevent erosion and preserve topography are not well described here we propose a new way to conceptualize the landscape scale geomorphic function of ridge forming lithologies not only as units whose intermittent resistant outcrops slow erosion of ridgelines themselves but as producers of large durable boulders that litter adjacent hillslopes and channels extending the caprock s resistant qualities to weaker underlying units and inhibiting channel incision over laterally extensive portions of the landscape this conceptual model is based on observations of boulder distributions in the slowly eroding valley and ridge province of the south central appalachian mountains and is in agreement with recent numerical models exploring the role of large boulders in channel and hillslope evolution though boulders are widely observed in the valley and ridge boulder distributions have not generally been mapped nor has their presence been linked to topographic persistence to examine the potential link between resistant ridge derived boulders and relief preservation in the valley and ridge we use uav imagery and field observations to create detailed maps of boulder distributions along representative hillslopes and channels in sw virginia and document boulder appearance size and strength to make inferences about longevity and geomorphic function we find that boulders cover significant portions of hillslopes up to 9 and are concentrated in channels up to 90 boulders are very large average size 1 m and up to 6 m diameter indicating fluvial immobility and channel armoring and often trap sediment upslope indicating hillslope shielding boulders are entirely sourced from durable ridgeline lithologies and exhibit features indicating longevity e g fracturing extensive lichen coverage rounding we interpret boulders to be relict from pleistocene periglacial conditions when intense freeze thaw cycles likely enhanced boulder production our results are consistent with processes described in numerical models of boulder function and suggest that ridge sourced boulders in this region play an important role in topographic preservation by stabilizing hillslopes and channels challenging the idea that ridge forming units primarily maintain relief by stabilizing the ridgelines themselves in addition the linkage of boulder production to a colder pleistocene climate highlights a mechanism by which past climatic conditions may continue to impact landscape evolution after the transition to a new climatic regime

active fault related folding in the epicentral area of the december 25 1222 io ix mcs brescia earthquake northern italy seismotectonic implications abstract a dense grid of petroleum industry seismic reflection profiles coupled with field mapping exploratory trenching and geomorphic and structural analysis are used to characterize the quaternary growth history of the capriano del colle fault system one of several inferred active buried thrusts that extend across the po plain in northern italy shortening is characterized here by a deeply buried south vergent forethrust and an associated north vergent backthrust whose upward propagation is expressed by fault propagation folding near the surface structural interpretation based on seismic data suggests that strain is accommodated at very shallow levels by secondary flexural slip thrusts and reverse faults developed on synclinal flanks that emanate from active axial surfaces analysis of syntectonic growth strata document maximum rates of dip slip of 3 45 0 66 mm yr 1 6 myr 1 2 myr and 0 47 0 22 mm yr during a more recent time period 0 89 myr present a quarry excavation at capriano del colle allows a preliminary paleoseismologic analysis of coseismic surface faulting and liquefaction exposed near the core of an active mid pleistocene to holocene anticline these features are interpreted to be generated during strong local earthquakes consistent with the environmental effects and ground motions of an event similar to the december 25 1222 brescia earthquake io ix mcs this indicates for the first time that compressive folds and blind thrusts in the po plain are currently accommodating slow rates of modern contraction in an active zone of the southern alps that extends from lake garda to varese we thus argue that earthquakes similar to the december 25 1222 brescia event are likely to occur in this region and pose a direct threat to such a densely populated and developed area

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

from rifting to drifting africa is splitting apart down the east african rift an analysis of the relative motion of the tectonic plates involved allows the rate of continental rifting to be estimated

summit erosion rates deduced from 10be implications for relief production in the central appalachians we have measured erosion rates using 10 be from bare bedrock surfaces exposed at high elevations at dolly sods west virginia a classic appalachian paleoperiglacial plateau the mean erosion rate from nine samples is 5 7 m m y signifi cantly lower than previously estimated periglacial erosion rates in this region measured bare bedrock erosion rates likely represent the rate at which the highest portions of this broad upland are being lowered fluvial incision rates measured in the region over similar time scales are 2 times faster suggesting relief is increasing in this portion of the appalachians this observation of increasing relief is inconsistent with prior work suggesting that the central appalachian landscape is in dynamic equilibrium or currently decreasing in relief we hypothesize that late cenozoic climate change has accelerated fl uvial incision rates creating a disequilibrium landscape with growing relief with hillslopes undergoing adjustment to increased fl uvial incision rates

from present rivers to old terrigenous sediments the evolution of the drainage system in the eastern southern alps terra nova 22 218 226 2010 abstract the eastern southern alps are presently dominated by southward drainage systems feeding the venetian friulian plain confined to the south of the insubric lineament following the assumption that river sediments reflect in the first instance the rocks outcropping in their catchments the comparison between present fluvial and old terrigenous sediments lets us to evaluate changes in provenance since the late miocene when the basement exhumation along the valsugana thrust system took place as indicated by apatite fission track data this tectonic event determined the onset of the main drainage systems the evolution of which has been depicted tracking the petrographic signatures from the present back to the late miocene provenance data show important episodes of stream piracy and watershed migration in response to tectonic uplift in the southern alps as well as to the messinian salinity crisis and the quaternary glaciations terra nova 00 1 9 2010

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

time intervals to assess active and capable faults for engineering practices in italy abstract the time span necessary to define a fault as active and capable can mainly be derived from the framework of the regulations and the literature produced since the 1970s on risk estimation in engineering planning of strategic buildings within this framework two different lines of thought can be determined which have mainly developed in the usa on the one side there is a tendency to produce narrow chronological definitions this is particularly evident in the regulatory acts for the planning of nuclear reactors the much more effective second line of thought anchors the chronological definitions of the terms active and therefore capable to the concept of seismotectonic domain as the domains are different in different regions of the world the chronological definition cannot be univocal i e different criteria are needed to define fault activity which will depend on the characteristics of the local tectonic domain and of the related recurrence times of fault activation current research on active tectonics indicates that methodological aspects can also condition the chronological choice to define fault activity indeed this practice implies the use of earth science methods the applications of which can be inherently limited for example limits and constraints might be related to the availability of datable sediments and landforms that can be used to define the recent fault kinematic history for the italian territory we consider two main tectonic domains a the compressive domain along the southern margin of the alpine chain and the northern and northeastern margins of the apennines which is characterised by the activity of blind thrusts and reverse faults and b the extensional domain of the apennines and the calabria region which is often manifest through the activity of seismogenic normal and normal oblique faults in case a the general geomorphic and subsurficial evidence of recent activity suggests that a reverse blind fault or a blind thrust should be considered active and potentially capable if showing evidence of activity during the quaternary i e over the last 2 6 myr unless information is available that documents its inactivity since at least the last glacial maximum lgm ca 20 ka the choice of the lgm period as the minimum age necessary to define fault inactivity is related to practical aspects the diffusion of the lgm deposits and landforms and to the evidence that ca 20 kyr to assess fault inactivity precautionarily includes a number of seismic cycles in the extensional domains of the apennines and calabria region the general geological setting suggests that the present tectonic regime has been active since the beginning of the middle pleistocene therefore we propose that a normal fault in the italian extensional domain should be considered active and capable if it displays evidence of activation in the last 0 8 myr unless it is sealed by deposits or landforms not younger than the lgm the choice of the lgm as the minimum age to ascertain fault inactivity follows the same criteria described for the compressive tectonic domain

geometric disequilibrium of river basins produces long lived transient landscapes abstract although equilibrium has long been considered the attractor state for landscapes the time required to reach equilibrium or even the possibility of reaching equilibrium is still debated using 10 be based catchment averaged denudation rates topographic analysis and analysis of the basin topology and geometry including its area channel length scaling relationship we show that an ancient postorogenic dome on the north american craton the ozark dome is not in a state of equilibrium the persistent state of disequilibrium on the ozark dome is characterized by nonuniform erosion rates that vary by a factor of three asymmetric drainage divides and evidence for drainage rearrangement via stream capture we find that planform geometric disequilibrium of river basins and drainage area exchange between adjoining basins can hold river networks in a disequilibrium state for potentially hundreds of million years and that when sustained over time erosion rate differences associated with drainage area exchange can lead to transient events such as stream capture and production of relief in the form of elevated low relief surfaces our results suggest that landscapes with slowly moving drainage divides might not reach equilibrium and that river basin dynamics may contribute to setting the large scale morphology of old cratonic landscapes

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

rapid incision of the colorado river in glen canyon insights from channel profiles local incision rates and modeling of lithologic controls the colorado river system in southern utah and northern arizona is continuing to adjust to the baselevel fall responsible for the carving of the grand canyon estimates of bedrock incision rates in this area vary widely hinting at the transient state of the colorado and its tributaries in conjunction with these data we use longitudinal profiles of the colorado and tributaries between marble canyon and cataract canyon to investigate the incision history of the colorado in this region we find that almost all of the tributaries in this region steepen as they enter the colorado river the consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels and their coincidence within a corridor of high local relief along the colorado suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem this analysis makes testable predictions about spatial variations in incision rates these predictions are consistent with existing rate estimates and can be used to guide further studies we also present cosmogenic nuclide data from the henry mountains of southern utah we measured in situ10be concentrations on four gravel covered strath surfaces elevated from 1 m to 110 m above trachyte creek the surfaces yield exposure ages that range from approximately 2 5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m my these incision rates are similar to other rates determined within the high relief corridor available data thus support the interpretation that tributaries of the colorado river upstream of the grand canyon are responding to a recent pulse of rapid incision on the colorado numerical modeling of detachment limited bedrock incision suggests that this incision pulse is likely related to the upstream dipping lithologic boundary at the northern edge of the kaibab upwarp copyright 2009 john wiley sons ltd

block controlled hillslope form and persistence of topography in rocky landscapes rocky hillslopes dotted with boulder sized blocks and covered by a thin nonuniform soil are common in both steep landscapes and arid environments on earth as well as on other planets while the evolution of soil mantled convex upward hillslopes in uniform lithology is reasonably well understood the influence of heterogeneous lithology and geologic structure on hillslope form and evolution has yet to be properly addressed landscapes developed in layered sedimentary rocks feature sharp edged landforms such as mesas and hogbacks that exhibit steep linear to concave upward ramps with scattered blocks calved from resistant rock layers overlying softer strata here we show that blocks can control the persistence of topography and the form and evolution of hillslopes in these landscapes we present a numerical model demonstrating that incorporation of feedbacks between block release interruption of soil creep by blocks and sporadic downslope movement of blocks are necessary and sufficient to capture the morphology and evolution of these landscapes numerical results are reproduced by a simple analytical solution that predicts steady state concave hillslope form and average slope angle from block size and spacing our results illuminate previously unrecognized hillslope feedbacks advancing our understanding of the geomorphology of rocky hillslopes on a landscape scale our findings establish a quantitative method to address the migration of sharp edges and the persistence of topography in layered landscapes

stratigraphic control of landscape response to base level fall young womans creek pennsylvania usa abstract landscapes are thought to respond to changes in relative base level through the upstream propagation of a boundary that delineates relict from adjusting topography however spatially variable rock strength can influence the topographic expression of such transient landscapes especially in layered rocks where strength variations can mask topographic signals expected due to changes in climate or tectonics here we analyze the landscape response to base level fall in young womans creek a 220 km2 catchment on the appalachian plateau usa underlain by gently folded paleozoic sedimentary rocks we measured in situ 10be concentrations in stream sands from 17 nested watersheds and used a spatially distributed model of sediment and 10be production to constrain a threefold increase in the rate of base level fall propagating upstream from the catchment outlet using lidar topography and a nearby detailed stratigraphic section we map the extent of continuous blocky resistant sandstone strata that act as a caprock overlying more easily erodible sandstones and siltstones the caprock influences landscape response in two ways first it serves as a boundary between slowly eroding 11 5 m myr 1 low sloping 3 5 areas of relict topography and lower steeper portions of the landscape adjusting to base level fall second hillslopes supported by the overlying caprock are armored with coarse sediment and are significantly steeper 20 30 than hillslopes where the caprock has been eroded 10 despite having similar erosion rates 36 m myr 1 and bedrock substrate our results illustrate how gently dipping layered rocks engender complicated relationships between lithology topography and erosion rate highlighting the importance of understanding how rock material properties influence surface processes and landscape evolution

timescales of landscape response to divide migration and drainage capture implications for the role of divide mobility in landscape evolution efforts to extract information about climate and tectonics from topography commonly assume that river networks are static drainage divides can migrate through time however and recent work has shown that divide mobility can potentially induce changes in river profiles comparable to changes caused by variation in rock uplift climate or rock properties we use 1d river profile and 2d landscape evolution simulations to evaluate how mobile divides influence the interpretation of river profiles in tectonically active settings we define a non dimensional divide migration number ndm as the ratio of the timescale of channel profile response to a change in drainage area tda to the timescale of divide migration tdm in simulations of headward divide migration ndm is much less than unity with no measurable perturbation of channel profiles only in simulations configured to induce rapid lateral divide migration are there occasional large stream capture events and zones where localized drainage area loss is fast enough to support ndm values near unity the rapid response of channel profiles to changes in drainage area ensures that under most conditions profiles maintain quasi equilibrium forms and thus generally reflect spatio temporal variation in rock uplift climate or rock properties even during active divide migration this implies that channel profile form may not reliably record divide mobility so we evaluate alternate metrics of divide mobility in our simulations and an example in taiwan we find that simple measures of cross divide contrasts in topography are more robust metrics of divide mobility than measures of drainage network topology

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

the influence of bedrock geology on knickpoint development and channel bed degradation along downcutting streams in south central indiana geologic controls on knickpoint development and the mechanics of channel bed degradation were eluci dated by comparison of downcutting streams in south central indiana developed in lithologically homoge neous carbonate units and layered siliciclastic strata knickpoints formed in a single lithologic unit are stepped each step consists of a knickpoint face and tread the height of each step is equal to and controlled by bed thickness spatially knickpoints in homogeneous terrain are limited to jointed strata that dip 1 upstream or 2 downstream at angles less than the channel gradient knickpoints observed in lithologically layered strata are characterized by a single step in which resistant jointed rocks overlie and protect weaker units total knickpoint relief is influenced by thickness of the weaker strata knickpoints in layered siliciclastic strata are spatially limited to bedrock reaches produced by differential rates of channel incision knickpoint distribution is also influenced by joint

quaternary evolution of a hyperarid drainage under climatic fluctuations and rift margin base level fall ne negev israel abstract the long term bedrock incision of streams in the northeastern negev has been dictated since the early pliocene by the subsidence of the dead sea basin however this incision is accompanied by very long intervals of sediment aggradation here we document the quaternary scale fluvial response to changing base level lithology structure and climate along the hyperarid nahal zafit ne negev the oldest 1 2 ma alluvial remnants point to a widespread beveled bedrock pediment at the base of the hazera anticline this pediment like other stream pediment anticline relationships in the region provides the baseline framework into which nahal zafit incises during the early to middle pleistocene this pediment was the base level for all streams emerging out of the anticlines the tectonic subsidence of the regional base level at the rift margin farther downstream has caused incision and upstream migration of bedrock knickpoints triggering the development of a wide incised valley in the mazar syncline adjacent to the hazera anticline since 330 ka fluvial terraces landslides and taluses record intervals of basin wide fluvial deposition under prevailing hyperarid to arid climate despite the general arid climate prolonged fluvial deposition intervals occurred at ca 330 265 230 125 and 110 20 ka rapid and quite short duration bedrock incision occurred in between these much longer intervals of aggradation in addition to the proposed climatic imprint on fluvial aggradation incision cycles and the first order base level control of the rift margin fault the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the quaternary evolution of the ne negev watersheds

low rates of bedrock outcrop erosion in the central appalachian mountains inferred from in situ 10be bedrock outcrops are common on central appalachian mountain ridgelines because these ridgelines define watersheds the rate at which they erode influences the pace of landscape evolution to estimate ridgeline erosion rates we sampled 72 quartz bearing outcrops from the potomac and susquehanna river basins and measured in situ produced 10 be ridgeline erosion rates average 9 1 m m y 1 median 6 m m y 1 similar to 10 be derived rates previously reported for the region the range of erosion rates we calculated reflects the wide distribution of samples we collected and the likely inclusion of outcrops affected by episodic loss of thick slabs and periglacial activity outcrops on main ridgelines erode slower than those on mountainside spur ridges because ridgelines are less likely to be covered by soil which reduces the production rate of 10 be and increases the erosion rate of rock ridgeline outcrops erode slower than drainage basins in the susquehanna and potomac river watersheds suggesting a landscape in disequilibrium erosion rates are more similar for outcrops meters to tens of meters apart than those at greater distances yet semivariogram analysis suggests that outcrop erosion rates in the same physiographic province are similar even though they are hundreds of kilometers apart this similarity may reflect underlying lithological and or structural properties common to each physiographic province average 10 be derived outcrop erosion rates are similar to denudation rates determined by other means sediment flux fission track thermochronology u th he dating indicating that the pace of landscape evolution in the central appalachian mountains is slow and has been since post triassic rifting events

bedrock fracture density controls on hillslope erodibility in steep rocky landscapes with patchy soil cover southern california usa abstract although many steep landscapes comprise a patchwork of soil mantled and bare bedrock hillslopes models typically assume hillslopes are entirely soil mantled or bare bedrock making it challenging to predict how rock properties influence hillslope erodibility and landscape evolution here we study headwater catchments across the san gabriel mountains sgm and northern san jacinto mountains nsjm in southern california two steep landscapes with similar climate and lithology but with distinctly different bedrock fracture densities 5 higher in the sgm we combine new and published detrital in situ cosmogenic 10be derived erosion rates with analysis of high resolution imagery and topography to quantify how the morphology and abundance of bare bedrock and soil mantled hillslopes vary with erosion rate within and between the two landscapes for similar mean hillslope angles 35 46 catchments in the nsjm erode at rates of 0 1 0 6 m kyr 1 compared to 0 2 2 2 m kyr 1 in the sgm in both landscapes bare bedrock hillslopes increase in abundance with increasing erosion rate however more and steeper bedrock is exposed in the nsjm indicating that wider bedrock fracture spacing reduces soil production efficiency and supports steeper cliffs additionally higher erosion rates in the sgm require a 3 higher soil transport efficiency reflecting an indirect control of bedrock fracture density on the size of sediment armoring hillslopes our data highlight how hillslope morphodynamics in steep landscapes depend on the strength of soil and bedrock and the efficiency of soil production and transport all of which are variably sensitive to rock properties and influence the partitioning of soil and bare bedrock on hillslopes

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

the continental crust as a source of sand southern alps cross section northern italy abstract all tectonostratigraphic levels of the continental crust from carbonate platforms in the dolomites to granulites in the ivrea zone are exposed along strike in the world famous southern alps cross section in this extraordinary natural laboratory we studied the composition of modern stream sands shed by each distinct type of source rock in order to improve on existing models of sediment provenance and specifically to reconstruct the step by step changes of detrital signatures ideally produced during unroofing of a continental block detritus from progressively deeper crustal levels of the southern alps changes systematically from lithic sedimentaclastic unmetamorphosed cover sequences to lithoquartzose quartzolithic and quartzofeldspathic metamorphiclastic greenschist facies to amphibolite facies basement units and finally to feldspathoquartzose and feldspathic composition granulite facies basement units six progressively richer types of heavy mineral assemblages ztr brookite garnet

cosmocalc an excel add in for cosmogenic nuclide calculations as dating methods using terrestrial cosmogenic nuclides tcn become more popular the need arises for a general purpose and easy to use data reduction software the cosmocalc excel add in calculates tcn production rate scaling factors using lal stone dunai and desilets methods topographic snow and self shielding factors and exposure ages erosion rates and burial ages and visualizes the results on banana style plots it uses an internally consistent tcn production equation that is based on the quadruple exponential approach of granger and smith 2000 cosmocalc was designed to be as user friendly as possible although the user interface is extremely simple the program is also very flexible and nearly all default parameter values can be changed to facilitate the comparison of different scaling factors a set of converter tools is provided allowing the user to easily convert cut off rigidities to magnetic inclinations elevations to atmospheric depths and so forth because it is important to use a consistent set of scaling factors for the sample measurements and the production rate calibration sites cosmocalc defines the production rates implicitly as a function of the original tcn concentrations of the calibration site the program is best suited for be 10 al 26 he 3 and ne 21 calculations although basic functionality for cl 36 and c 14 is also provided cosmocalc can be downloaded along with a set of test data from http cosmocalc googlepages com

vegetation change in a climatic cycle of early pleistocene age in the leffe basin northern italy abstract the plio pleistocene deposits of the leffe basin in the lombardian pre alps in italy first investigated in quarry and lignite mine shafts by lona in 1950 were recently cored the pollen record of part of this core reveals a sequence of four climatic cycles one of them which is about 1 6 ma old and particularly characteristic is discussed here a long interglacial stage can be identified by the dominance of pollen of deciduous trees of temperate climate it clearly shows a forest succession of a mixed oak forest of dry temperate climate followed by a strong development of a juglandaceae assemblage rich in arcto tertiary elements some of them indicating a wet climate in particular the carya peaks appear to be linked to a warm temperate 14 16 c mean annual temperature humid maritime climate with a long growth season if we compare them with modern and fossil analogs this stage is followed by a cooling leading to a long phase of wet coniferous forest this forest succession is subsequently interrupted by a brief period of open vegetation indicating a drier and colder continental climate followed by a new vegetational cycle the climate evolution is discussed in comparison with other recent pollen successions of uppermost pliocene age in the mediterranean area the cycle described is estimated to have lasted about 30 ka the entire leffe lacustrine succession records eight climatic cycles of moderate amplitude we suggest that this cyclicity has been induced by obliquity forcing correlation of the cold phases with the major glacial events of the southern alps as proposed by venzo 1950 and lona 1950 is excluded

the role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western san gabriel mountains california bedrock rivers set the pace of landscape adjustment to tectonic and climatic forcing by transmitting signals of base level change upstream through the channel network and ultimately to hillslopes river incision is typically modeled as a monotonic function of bed shear stress or stream power modulated by sediment tools and cover effects but these models do not apply in channels with steep or vertical bedrock reaches due to changes in flow dynamics hydraulic geometry and bed cover here we investigate how such knickzones oversteepened channel reaches often containing waterfalls influence the propagation of slope break knickpoints that separate relict from adjusting topography and thus the response times of landscapes to external forcing we use a conceptual long profile model to explore the consequences of waterfalls and knickzones on channel response and compare predictions to light detection and ranging lidar topography field observations and cosmogenic radionuclide data from big tujunga creek a 300 km2 watershed in the san gabriel mountains california three prominent knickzones along big tujunga creek characterized by numerous waterfalls show contrasting behavior for the upper knickzone waterfalls align with bands of harder rock exposed on adjacent hillslopes and between waterfalls the channel is mantled by large 2 m boulders indicating knickzone retreat is slow compared to predictions of slope break knickpoint retreat from stream power models enhancing the preservation of an upstream relict landscape the middle knickzone shows evidence for both fast and slow knickzone retreat as well as significant deviations from predictions of uniform tributary knickpoint elevations derived from stream power models the lower knickzone is characterized by a waterfall and knickzone within an incised inner gorge that provide evidence of rapid retreat relative to background channel incision overall we find a pattern of decreasing knickzone and waterfall retreat rate with distance upstream of the range front beyond decreases predicted by simple area dependent celerity models our results highlight that waterfalls and knickzones can both enhance and inhibit landscape adjustment leading to divergent controls on the pace of landscape evolution

lithologic effects on landscape response to base level changes a modeling study in the context of the eastern jura mountains switzerland landscape evolution is a product of the forces that drive geomorphic processes e g tectonics and climate and the resistance to those processes the underlying lithology and structural setting in many landscapes set the resistance to erosion this study uses a modified version of the channel hillslope integrated landscape development child landscape evolution model to determine the effect of a spatially and temporally changing erodibility in a terrain with a complex base level history specifically our focus is to quantify how the effects of variable lithology influence transient base level signals we set up a series of numerical landscape evolution models with increasing levels of complexity based on the lithologic variability and base level history of the jura mountains of northern switzerland the models are consistent with lithology and therewith erodibility playing an important role in the transient evolution of the landscape the results show that the erosion rate history at a location depends on the rock uplift and base level history the range of erodibilities of the different lithologies and the history of the surface geology downstream from the analyzed location near the model boundary the history of erosion is dominated by the base level history the transient wave of incision however is quite variable in the different model runs and depends on the geometric structure of lithology used it is thus important to constrain the spatiotemporal erodibility patterns downstream of any given point of interest to understand the evolution of a landscape subject to variable base level in a quantitative framework

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

what does a mean mean the temporal evolution of detrital cosmogenic denudation rates in a transient landscape in equilibrium landscapes 10 be concentrations within detrital quartz grains are expected to quantitatively refl ect basin wide denudation rates in transient landscapes though detrital quartz is derived from both the incising adjusting lowland and the unadjusted relict upland the integrated 10 be concentrations still provide a denudation rate averaged across the two domains because fi eld samples can provide only a snapshot of the current upstream averaged erosion rate we employ a numerical landscape evolution model to explore how 10 be derived denudation rates vary over time and space during transient adjustment model results suggest that the longitudinal pattern of mean denudation rates is generated by the river s progressive dilution of low volume high concentration detritus from relict uplands by the integration of high volume low concentration detritus from adjusting lowlands the proportion of these materials in any detrital sample depends on what fraction of the upstream area remains unadjusted because the boundary of the adjusting part of the landscape changes over time the longitudinal trend in cosmogenic nuclide derived erosion rates changes over time these insights are then used to guide our interpretation of geomorphic and longitudinal cosmogenic nuclide data from the south fork eel river sfer in the california coast range united states the northward propagating crustal thickening and rock uplift associated with the passage of the mendocino triple junction generates a mobile wave of uplift that progressively sweeps longitudinally down the sfer the consequences of this forcing can be both replicated in the model environment and observed in the fi eld the sfer contains transient landforms including knickpoints and river terraces along mainstem and tributary channels that defi ne a clear boundary between an incised adjusting lowland and an unadjusted relict upland we report nine nested basin wide denudation rates in the mainstem of the sfer using terrestrial cosmogenic 10 be in river borne sediment we fi nd that denudation rates increase in the downstream direction from 0 2 mm yr in the upper catchment to 0 5 mm yr at the outlet using comparisons to the modeled landscape we show that this pattern of denudation rates paired with the distribution of relict topography throughout the watershed refl ect the immaturity of the landscape s transient adjustment later in this modeled transient the predicted erosion rates decrease downstream before they become uniform this interpretation of our data has potentially far reaching implications for quantifying the uplift history and response time of transient landscapes using cosmogenic nuclides

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

late pliocene and pleistocene small mammal chronology in the italian peninsula the abundant documentation of small mammals in the italian peninsula collected over recent years furnishes a detailed biochronological sequence mainly from the late pliocene onwards an updated stratigraphic framework is here presented based on the european small mammal biozonation the early villanyian is characterized by mimomys hassiacus m stehlini and later poorly documented m polonicus the late villanyian localities are well characterized with m pliocaenicus m pitymyoides and m tigliensis the older part of the early biharian is documented by assemblages containing microtus allophaiomys ex gr pliocaenicus m pusillus m cf ostramosensis and m tornensis while the later part of the early biharian is characterized by advanced microtus allophaiomys species occurring together with m pusillus or m blanci in the late biharian m savini microtus hintoni gregaloides microtus iberomys ex gr huescarensis brecciensis and terricola arvalidens occur the early toringian with a mosbachensis allocricetus bursae pliomys episcopalis and small sized microtus brecciensis and the late toringian with a terrestris in diversified associations are quoted the most important faunal events are calibrated by independent chronological controls thanks to the record of small mammals from lacustrine deposits several figures illustrate the most significant rodent species occurring in the succession of selected italian localities

transport slopes sediment cover and bedrock channel incision in the henry mountains utah 1 field data from channels in the henry mountains of utah demonstrate that abundant coarse sediment can inhibit fluvial incision into bedrock by armoring channel beds the cover effect we compare several small channels that share tributary junctions and have incised into the same sedimentary bedrock unit navajo sandstone but contain differing amounts of coarse diorite clasts owing to the spatial distribution of localized sediment sources bedrock channels that contain abundant clasts diorite rich have steeper longitudinal slopes than tributaries of these channels with smaller drainage areas and less sediment diorite poor the diorite poor tributaries have incised more deeply to lower average slopes and have more reach scale slope variability which may reflect bedrock properties longitudinal sediment sorting and incision at lower sediment supply diorite rich channels have less bedrock exposed and smoother longitudinal profiles than diorite poor channels we find that 1 coarse sediment can mantle bedrock channel beds and reduce the efficiency of incision validating the hypothesized cover effect in fluvial incision models 2 the channel slope needed to transport the sediment load can be larger than that needed to erode bedrock suggesting that the slope of incising bedrock channels can become adjusted to the sediment load 3 when abundant sediment is available transport capacity rather than thresholds of motion can be dominant in setting bedrock channel slope and 4 cover effects can be important even when moderate amounts of bedrock are exposed in channel beds

the influence of sandstone caprock material on bedrock channel steepness within a tectonically passive setting buffalo national river basin arkansas usa bedrock channel profile analysis typically assumes that channels evolve toward a condition of topographic steady state where channel morphology is adjusted to rock erodibility uplift rates and stream power here we use the integral method of channel profile analysis to quantify channel steepness within a large set of tributary channels that incise through layered rocks in the buffalo national river basin in northern arkansas statistical analysis of these channels demonstrates that normalized channel steepness is not a function of local bedrock lithology but is influenced by coarse sediment supply specifically normalized steepness is greatest in reaches of the basin where an interval of pennsylvanian sandstone forms a caprock on the ridges block detachment of the sandstone causes large boulders to be stranded in the upper tributaries where stream power is too low to mobilize or effectively erode the boulders within these channels normalized steepness is correlated with sandstone boulder size and percent boulder coverage rather than local lithology despite strong contrasts in the mechanical strength of the lithologies incised this analysis suggests that removal of caprock material is rate limiting within the landscape and may be responsible for the long term persistence of topography within this tectonically passive setting

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

stratigraphic evidence of a middle pleistocene climate driven flexural uplift in the alps 1 this interdisciplinary study on the subsurface stratigraphy of the po plain northern italy brings new evidence in support of a climate driven erosional unloading of the alps since the middle pleistocene a newly acquired high resolution seismic profile and a critical review of industrial seismic lines were integrated with sedimentologic observations on four magnetostratigraphically dated continental cores to reconstruct a three sequence evolution of the pleistocene clastic infill in the northern po basin during the first sequence ps1 1 4 0 87 ma characterized by sedimentation rates of 34 cm kyr outpacing regional subsidence meandering river systems prograded over the basin passing downstream to a cyclothemic shelfal succession the second sequence ps2 0 87 0 45 ma heralded by a regional unconformity r surface correlated to the onset of the major pleistocene glaciations was characterized by widespread continental sedimentation of generally distal braidplain the third sequence ps3 0 45 ma to present marked at the base by another regional unconformity y surface is characterized by proximal braided fluvial deposition under combined conditions of confinement erosion and bypass we interpret the ps3 sequence as deposited under the effects of a flexural uplift of the northern po plain during the middle pleistocene starting at 0 45 ma in response to the long term erosional unloading of the alps triggered by the waxing and waning of alpine glaciers since the late early pleistocene global cooling 0 9 ma according to our modeling erosion on a relatively limited area of the alpine mountain chain ranging from 1 3 to 1 7 mm yr in the axial sector to 0 1 0 3 mm yr at the margins has been able to trigger rock uplift over a wider area including the proximal peripheral basins

modulation of erosion on steep granitic slopes by boulder armoring as revealed by cosmogenic 26al and 10be cosmogenic 26 al and 10 be in quartz from boulders bedrock and sandy sediment from 21 small watersheds in the diamond mountains batholith ca usa and two small watersheds from the nearby fort sage mountains confirm that exposed granitic bedrock and boulders erode more slowly than the catchments in which they are found exposed bedrock and boulders are more abundant on steep slopes and may play an important role in regulating mountain erosion rates rapid transport of fine sediment on steep slopes exhumes resistant corestones which accumulate on the surface the resulting boulder lag apparently shields the underlying soil and bedrock from erosion even when the bedrock is deeply weathered and friable where steep slopes have an abundant boulder lag they erode as slowly as gentler slopes nearby in contrast steep slopes lacking a boulder lag erode much more quickly than gentle slopes boulder armoring can modulate hillslope erosion such that erosion rates of summits steep mountain flanks and gentle footslopes are indistinguishable thus permitting local relief and steep mountain slopes to persist for long periods of time fl 2001 elsevier science b v all rights reserved

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

evidence for late alpine tectonics in the lake garda area northern italy and seismogenic implications we investigated the recent evolution of the po plain alps system by integrating subsurface geophysical data from the po plain with new stratigraphic and structural observations from the southern alps margin inversion of structural data and chronology provided by stratigraphic constraints led to the definition of three tectonic events since the pliocene namely the intra zanclean the gelasian and the middle pleistocene driven by an axis of maximum compression formerly oriented ne intra zanclean and then to the nnw gelasian and middle pleistocene the associated deformation has been accommodated by two sets of faults consisting of nne trending thrust faults mostly represented in the western sector of lake garda and nw trending strike slip faults observed in the southern and eastern sectors the interplay between these two sets of faults is interpreted to produce short w w 6 5 along the nw trending strike slip faults in this framework the newly defined nogara fault and the sant ambrogio fault all pertaining to the nw trending system are regarded as potential candidates for the seismogenic source of the january a d 1117 event the most destructive earthquake in the po plain

hillslope response to knickpoint migration in the southern appalachians implications for the evolution of post orogenic landscapes the southern appalachians represent a landscape characterized by locally high topographic relief steep slopes and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 ma the fundamental processes responsible for landscape evolution in a post orogenic landscape remain enigmatic the non glaciated cullasaja river basin of south western north carolina with uniform lithology frequent debris flows and the availability of high resolution airborne lidar dems is an ideal natural setting to study landscape evolution in a post orogenic landscape through the lens of hillslope channel coupling this investigation is limited to channels with upslope contributing areas 2 7 km2 a conservative estimate of the transition from fluvial to debris flow dominated channel processes values of normalized hypsometry hypsometric integral and mean slope vs elevation are used for 14 tributary basins and the cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the cullasaja basin and adjacent hillslopes metrics of topography relief slope gradient and hillslope activity landslide frequency exhibit significant downstream increases below the current position of major knickpoints the transient effect of knickpoint driven channel incision on basin hillslopes is captured by measuring the relief mean slope steepness and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the cullasaja river a conceptual model of area elevation and slope distributions is presented that may be representative of post orogenic landscape evolution in analogous geologic settings importantly the model explains how knickpoint migration and channel hillslope coupling is an important factor in tectonically inactive i e post orogenic orogens for the maintenance of significant relief steep slopes and weathering limited hillslopes copyright 2011 john wiley sons ltd

new constraints on bedrock erodibility and landscape response times upstream of an active fault abstract considerable progress has been made in modelling the response of rivers to tectonic perturbation in order to decode the tectonic signals embedded in river long profiles and planform geometry whilst studies have showed the importance of rock type on the morphology of rivers responding to tectonics on a local scale these effects are often not captured in landscape evolution models in fact current models of fluvial response to tectonic perturbation such as active faulting require carefully collected data sets to fully constrain or calibrate key parameters including the effect of bedrock lithology on substrate erodibility and timescales for tectonic signal propagation in bedrock river systems here we constrain the role of bedrock in controlling fluvial incision for a 240 km2 catchment draining into the gulf of corinth which has excellent tectonic constraints and a variety of bedrock lithologies an active normal fault at the downstream end of the catchment the east eliki fault is known to have initiated at 0 7 ma with average quaternary uplift and incision rates of 1 00 1 25 mm yr the initiation of the east eliki fault is recorded in the river as a prominent knickzone 7 16 km upstream of the fault detailed field data collected within this catchment at 500 m intervals along the main channel length at this tectonically well constrained field site show an order of magnitude increase in river channel slopes y x 0 02 to 0 18 and stream powers 1 kwm 2 to 27 kwm 2 at the lithological boundary between weak and resistant bedrock the weak conglomerates and strong limestones have schmidt hammer compressive strengths of ca 30 and 50 respectively based on in situ rock strength measurements consequent erodibility values of 1 8 0 3 10 14 and 5 6 2 10 15 ms2kg 1 show a factor of three to four decrease in erodibility for a two fold increase in rock strength a simple simulation of tectonic signal propagation through the river catchment based on these erodibility values indicates that the observed plan view position of the knickpoint is consistent with our calculated knickpoint positions based on erodibility values derived from incision rate and stream power data however the tectonic signal associated with faulting would have propagated completely through the catchment within 1 ma if it were entirely composed of weak rock for similar climatic and tectonic conditions indicating that lithology has a major control on landscape response times our results help constrain the effect of lithology on river channel geometry and allow erosional parameters to be derived that are crucial for effective modelling of tectonic rates from topography

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