investigation of the relationships between basin morphology tectonic uplift and denudation from the study of an active fold belt in the siwalik hills central nepal the present study investigates correlations between an extensive range of geomorphic properties that can be estimated from a digital elevation model and the uplift rate on geological timescales the analysis focuses on an area in the siwalik hills central nepal where lithology and climate can be considered as uniform this area undergoes rapid tectonic uplift at rates of up to 15 mm yr 1 which are derived from the geometric pattern of a fault bend model of fold growth the selected geomorphic properties can be divided in two categories depending on whether or not the vertical dimension is taken into account none of the planar properties are significantly correlated to uplift rate unlike those that include the vertical dimension such as the mean elevation of basins hypsometric curve and hypsometric integral and relief defined by the amplitude factor of length scaling analysis correlation between relief and uplift rate is observed for all length scales of topography shorter than 600 m which suggests that all orders of the streams are able to adjust to the tectonic signal simple mass balance considerations imply that the average elevation is only 10 of surface uplift suggesting that a dynamic equilibrium has been reached quite rapidly using a simple two process model for erosion we find that fairly high diffusion coefficients order of 10 m 2 yr 1 and efficient transport of the material by rivers are required this unusually high value for mass diffusivity at small length scales may be obtained by either a very efficient linear diffusion or by landsliding actually both processes may be active which appears likely given the nature of the unconsolidated substratum and the favorable climatic conditions local relief in the study area may therefore be used to predict either uplift or denudation but the prediction is calibrated only for that specific climatic and lithologic conditions and cannot be systematically applied to other contexts

the effects of rock uplift and rock resistance on river morphology in a subduction zone forearc oregon usa relationships between riverbed morphology concavity rock type and rock uplift rate are examined to independently unravel the contribution of along strike variations in lithology and rates of vertical deformation to the topographic relief of the oregon coastal mountains lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology volcanic and sedimentary rocks are the principal rock types underlying the northern oregon coast ranges between 46 30 and 45 n where mixed bedrock alluvial channels dominate average concavity is 0 57 in this region in the alluviated central oregon coast ranges between 45 and 44 n values of concavity are on average the highest 0 82 south of 44 n however bedrock channels are common and 0 73 mixed bedrock alluvial channels characterize rivers in the klamath mountains from 43 n south 0 64 rock uplift rates of 0 5 mm a 1 mixed bedrock alluvial channels and concavities of 0 53 0 70 occur within the northernmost coast ranges and klamath mountains for rivers flowing over volcanic rocks 0 53 and 0 72 for reaches crossing sedimentary rocks whereas channel type and concavity generally co vary with lithology along much of the range rivers between 44 5 and 43 n do not follow these trends concavities are generally greater than 0 70 alluvial channels are common and river profiles lack knickpoints between 44 5 and 44 n despite the fact that lithology is arguably invariant moreover rock uplift rates in this region vary from low 0 5 mm a 1 to subsidence 0 mm a 1 these observations are consistent with models of transient river response to a decrease in uplift rate conversely the rivers between 44 and 43 n have similar concavities and flow on the same mapped bedrock unit as the central region but have bedrock channels and irregular longitudinal profiles suggesting the river profiles reflect a transient response to an increase in uplift rate if changes in rock uplift rate explain the differences in river profile form and morphology it is unlikely that rock uplift and erosion are in steady state in the oregon coastal mountains copyright 2006 john wiley sons ltd

aminostratigraphy and faunal correlations of late quaternary marine terraces pacific coast usa recent studies using the extent of racemization of amino acids to date fossil mollusc shells in the arctic1 the british isles2 and on the atlantic3 4 and pacific5 13 coasts of north america have relied mainly on theoretical kinetic models of racemization ages generated in this fashion are highly model dependent and require estimates of integrated long term diagenetic temperatures we present here an alternative empirical approach to aminostratigraphy in which we plot amino acid enantiomeric ratios versus latitude for localities along the pacific coast of the united states and generate isochronal correlations by connecting data points of geographically proximal localities that have similar d l ratios and zoogeographic aspect isochrons are calibrated at a few localities by independent radiometric dates the diagenetic temperature effect on racemization is reflected in the slope of the isochrons but the need to quantify temperature is eliminated

coastal landscape evolution as a function of eustasy and surface uplift rate cascadia margin southern oregon we explore the relative importance of eustatic versus tectonic factors in sculpting preserving and modifying coastal landforms the study area is a 30 km coastal reach in southern oregon using degree of soil development as a means of correlating wave cut platforms along the coast we document that surface uplift rate is variable in a shore parallel sense variability being a function of differential vertical displacement of crustal blocks along faults and flexures in the upper plate of the cascadia subduction zone a consequence of this variability is that in areas of moderate uplift rate 0 7 0 9 m k y flights of up to seven emergent wave cut platforms are preserved along the interfluves of coastal drainages whereas in areas of low uplift rate 0 05 0 2 m k y only one wave cut platform commonly exists within a few meters of present sea level preservation of shore platforms in both areas is the result of the inter action of tectonic uplift and eustatic sea level changes operating on a high energy coast subject to platform planation platform reoccupation can be a consequence of late pleistocene eustatic sea level changes operating on low up lift rate coasts particularly in the cases of the 200 ka and 125 ka high sea stands reoccupation by the later highstand is probable when coastal uplift rates are about 0 2 m k y the same eustatic history operating on a higher uplift rate section of the coast results in multiple emergent platforms and no instances of reoccupation coastal drainage basins in the size range of 5 10 km2 have different hypsometries reflecting whether platforms in coastal basins are preserved over a range of altitudes or only near sea level the hypsometric differences are thus a product of differences in uplift rate the dominant mechanism of base level fall varies between the two areas coastal retreat during sea level highstands drives baselevel fall in lower uplift rate basins whereas tectonic uplift mainly drives base level fall in moderate uplift rate basins even though the magnitude of coastal retreat may be about the same in the two areas where coastal retreat largely provides the mechanism for base level fall steep coastal drainages discharge their debris onto coastal piedmonts benches and the resultant alluvial fans prograde over marine deposits in southern oregon the alluvial fan building episode was relatively short about 2 20 k y in duration fan aggradation ceased as a consequence of fan entrenchment most likely brought on by buildup and steepening of the fan over time

systematic variation of bedrock channel gradients in the central oregon coast range implications for rock uplift and shallow landsliding abstract in tectonically active regions bedrock channels play a critical role in dictating the pace of landscape evolution models of fluvial incision into bedrock provide a means of investigating relationships between gradients of bedrock channels and patterns of active deformation variations in lithology orographic precipitation sediment supply and erosional processes serve to complicate tectonic inferences derived from morphologic data yet most tectonically active landscapes are characterized by these complexities in contrast the central oregon coast range ocr which is situated above the cascadia subduction zone has experienced rock uplift for several million years did not experience pleistocene glaciation boasts a relatively uniform lithology and exhibits minor variations in precipitation although numerous process based geomorphic studies suggest that rates of erosion across the ocr are relatively constant it has not been demonstrated that bedrock channel gradients in the region exhibit spatially consistent values analysis of broadly distributed small drainage basins 5 20 km in the central ocr enables us to explore regional variability in bedrock channel gradients resulting from differential rock uplift or other sources consistent with previous studies that have documented local structural control of deformed fluvial terraces in the western portion of our study area our data reveal a roughly 20 km wide band of systematically elevated channel slopes roughly twice the background value roughly coincident with the strike of n s trending mapped folds although many factors could feasibly generate this pattern including variable rock strength precipitation gradients or temporal or spatial variations in forearc deformation the elevated bedrock channel slopes likely reflect differential rock uplift related to activity of local structures importantly our analysis suggests that rock uplift and erosion rates may vary systematically across the ocr although our calculations were focused on the fluvial dominated portion of study basins our results have implications for upstream areas including unchanneled valleys that often serve as source areas for long runout debris flows zero order basins or topographic hollows within the n s trending band of elevated channel slopes tend to be steeper than adjacent areas and may experience more frequent evacuation by shallow landsliding thus this region of the ocr may be highly sensitive to land use practices and high intensity rainstorms

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

fluvial landscape response time how plausible is steady state denudation whether or not steady state topography and denudation are probable states depends on the timescale of system response to tectonic and climatic perturba tions relative to the frequency of those perturbations this paper presents analytical derivations of algebraic relations for the response time of detachment limited fluvial bedrock channel systems both to tectonic and climatic perturbations detachment limited fluvial erosion is described by the stream power incision model and the derivations are limited to the applicability of that model all factors likely to influence system response time that are not adequately captured by the stream power incision model will tend to increase the response time the calculations presented thus provide minimum estimates of landscape response time and therefore over predict the prob ability of attaining and sustaining steady state topography and denudation the central range of taiwan is used as a case study to estimate response times in a landscape often argued to be in steady state model parameters are fit to modern stream profiles by assuming that the topography represents a quasi steady state form estimated response times generally range from 0 25 to 2 5 ma depending on the non linearity of the incision rule and the magnitude and type of perturbation thus it may be reasonably argued that steady state topography and denudation are likely to prevail during periods of climatic stability response time is sufficiently short compared with plate tectonic timescales however rapid climatic fluctuation in the quaternary appears to preclude the attainment of steady state conditions in modern orogens motivation

characterizing structural and lithologic controls on deep seated landsliding implications for topographic relief and landscape evolution in the oregon coast range usa in mountainous areas landslides regulate temporal variations in sediment production and may suppress simple linkages between topographic development and tectonic forcing rates and mechanisms of mass wasting depend on lithology bedrock structure and climatic and tectonic setting these factors tend to vary signifi cantly in active tectonic regions thus clouding our ability to predict how landsliding modulates topographic development over human and geological time scales here we use a novel dem based technique to document the distribution of large landslides in the oregon coast range ocr and quantify how they affect topographic relief we developed an automated algorithm that exploits the distinctive topographic signature specifi cally the relationship between curvature and gradient of large landslides to map their distribution within the gently folded tyee formation eocene deltaicsubmarine ramp sediments in contrast to steep and highly dissected terrain frequently identifi ed as characteristic of the ocr which exhibits steep planar sideslopes and highly curved low gradient ridgetops and valleys terrain prone to large landslides tends to have low values of both drainage density and curvature and gradient values that cluster between 0 16 and 0 44 the distribution of failure dominated terrain in our 10 000 km2 study area is infl uenced by systematic variations in sedimentary facies and bedrock structure the fraction of terrain altered by large landslides 0 1 km2 varies from 5 in the sand rich delta slope and proximal ramp facies southern section of our study area to 25 in the north distal ramp facies coincident with an increase in the thickness of siltstone beds and a decrease in the sandstone siltstone ratio local relief declines progressively northward suggesting that deep seated landsliding is sensitive to the thickness and frequency of low shearstrength siltstone beds and may serve to limit topographic development in the ocr structural controls are superimposed on facies related variations as deep seated landslides are frequently found on slopes whose downslope aspect corresponds to the bedrock dip direction for 1516 strike and dip measurements in our study area we calculated the fraction of proximal terrain 2 5 km altered by deep seated landsliding in the sand rich southern region the proportion of proximal slide dominated terrain increases modestly with bedrock dip in the silt rich northern region terrain altered by deep seated landsliding is pervasive and an increase in dip from 0 to 16 corresponds to a change in the fraction of slide prone terrain from 10 to 28 our technique for mapping large landslides has utility for hazard analysis and land management over million year time scales the progradational character of the tyee formation suggests that continued uplift and exhumation of the ocr should result in a southward propagation of slide prone silt rich distal facies as a result deep seated landsliding will become increasingly prominent and topographic relief in the central and southern ocr will progressively decline whereas spatial variability in climatic or tectonic forcing is often invoked to explain systematic variations in topographic development our results emphasize the importance of structural and intraformation lithologic controls on landsliding as such analyses linking surface processes climate tectonics and landscapes should be couched in the context of diverse geologic and topographic data

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

evidence for regional stream aggradation in the central oregon coast range during the pleistocene holocene transition abstract low nearly continuous terraces of similar age are present along streams in drainage basins that range in size from drift creek 190 km 2 to the umpqua river 11 800 km 2 in the oregon coast range radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000 11 000 14 c yr b p beveled bedrock surfaces straths that underlie the fluvial sediments are 1 8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied where exposed the bedrock straths are overlain by 2 11 m of fluvial sediment that consists of a bottom stratum channel facies of sandy pebble cobble gravel and a top stratum overbank facies of sandy silt or silt eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in coast range drainage basins during the pleistocene holocene transition the cause of such widespread aggradation is unknown but may be related to climate induced changes in the frequency of evacuation of colluvium from hollows which are common in all drainage basins in the region

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

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

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

late quaternary deformation of marine terraces on the cascadia subduction zone near cape blanco oregon the cape blanco region of south coastal oregon sits on the upper plate of the cascadia subduction zone about 60 70 km east of the base of the continental slope though the region has no historic coseismic deformation late quaternary deposits and landforms show abundant evidence of uplift folding and faulting a set of five late quaternary marine terraces and one uplifted holocene beach berm are preserved in the cape blanco region stratigraphic and altitudinal surveys of these physiographic features combined with several numerical and correlation age determinations permit a reconstruction of tectonic deformation near cape blanco in approximately the last 200 000 years the most cogent aspects of the neotectonics in this part of the cascadia subduction zone are that an east west trending anticline deforms the lower three terraces 80 125 ka as well as accounting for uplift of the holocene storm berm latest movement on the anticline was no more than 2 000 years ago but the anticline also deforms sediments as old as middle miocene the anticline is consistent with a north south principal contraction axis at cape blanco in about the last 100 000 years an older terrace at cape blanco approximately 200 ka is offset by two reactivated faults whose movements prior to the eocene served to suture several terranes to the north american continent tectonic tilting in the older terrace is not consistent with a north south principle axis of contraction but the axis of tilt is parallel to north northwest striking structures developed in the quaternary fold belt offshore on the continental shelf the observed deformation indicates that regional stress in the vicinity of cape blanco in the late quaternary has been accommodated by a variable pattern of strain

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

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

timescales of orogeny jurassic construction of the klamath mountains an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 94ycj2454 timescales of orogeny jurassic construction of the klamath mountains b r hacker m m donato c g barnes m o mcwilliams and w g ernst diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order classical interpretations of orogeny were based on relatively imprecise biostratigraphic and isotopic age determinations that necessitated grouping apparently related features that may in reality have been greatly diachronous isotopic age techniques now have the precision required to resolve the timing of orogenic events on a scale much smaller than that of entire mountain belts forty five new 40ar 39ar ages from the klamath mountains illuminate the deformation metamorphism magmatism and sedimentation involved in the jurassic construction of that orogen leading to a new level of understanding regarding how preserved orogenic features relate to ancient plate tectonic processes the new geochronologic relationships show that many jurassic units of the klamath mountains had 200 ma or older volcanoplutonic basement subsequent formation of a large 170 ma arc was followed by contractional collapse of the arc collision with a spreading ridge may have led to large scale nw se extension in the central and northern klamaths from 167 to 155 ma coincident with the crystallization of voluminous plutonic and volcanic suites marked cooling of a large region of the central klamath mountains to below 350 c at 150 ma may have occurred as the igneous belt was extinguished by subduction of colder material at deeper structural levels these data demonstrate that the klamath mountains and perhaps other similar orogens were constructed during areally and temporally variant episodes of contraction extension and magmatism that do not fit classical definitions of orogeny

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

analysis of hillslope erosion rates using dated colluvial deposits hollows are sites of long term deposition of colluvium and contain a valuable record of the timing and rates of hillslope erosion a model is presented that uses measured depositional rates of colluvium in hollows to calculate transport rates of colluvium and bedrock lowering rates on the surrounding slopes this model has been applied to eight dated colluvial deposits in the clearwater river basin of western washington the calculated average transport rate is about 34 cm 3 cm yr and the calculated average bedrock lowering rate is about 0 04 mm yr equivalent to an average sediment yield of 90 t km 2 yr for the holocene there is significant variability in erosion rates between sites which may be due to local lithologic variations although the average values are similar to an independent estimate of modern erosion rates for this area multiple stratigraphic levels have been dated in five deposits and document that the deposits are cumulative and that deposition has been active through the

principal components of quiet time temporal variability of equatorial and low latitude geomagnetic fields diurnal variations of the horizontal component of the geomagnetic field h on international quiet days of 1999 2012 measured hourly at two stations in the same longitude zone in the northern hemisphere near and away from the dip equator have been subjected to principal component analysis this technique is also applied to the difference heej of h at these two stations which is attributed to the equatorial electrojet eej the first three principal components pc1 pc2 and pc3 account for 91 96 of the variances in the data maximum contribution to the quiet day variations in h around its peak in the morning hours at both the stations and in the eej comes from the day to day variation of the amplitude of pc1 patterns of day to day variations of pc1 amplitudes for the equatorial station and the eej are essentially semiannual modulated by solar euv flux superimposed on a longer time scale solar euv flux dependent trend contributions from pc2 and to a lesser extent from pc3 are seen to be responsible for the absence of semi annual variations in h in the afternoon hours at the equatorial station distribution of amplitudes of pc2 and pc3 for heej for weak electrojet days shows seasonal features in accordance with greater occurrence of afternoon morning counter electrojet during june december solstice during the extended solar minimum pc3 amplitudes for h at the equatorial station and for the eej display annual variation possible sources for these seasonal features in the variations of equatorial h are discussed

controls on pool characteristics along a resistant boundary channel abstract the north fork poudre river in phantom canyon has a pool riffle sequence formed in granitic bedrock we address two questions what controls downstream pool spacing within a pool what factors control pool dimensions we hypothesize that both pool spacing and pool geometry could be governed by available flow energy or by substrate characteristics these hypotheses were addressed using channel bed and water surface gradients surveyed under moderate flow selby rock mass strength at vertical outcrops forming lateral pool constrictions and at other vertical outcrops and joint density measured from high resolution digital images of the bedrock outcrop along each of 10 pools the downstream length between pools is quite variable documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fonten

erosion rates in the southern oregon coast range evidence for an equilibrium between hillslope erosion and sediment yield the relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes in landscapes containing hillslopes crenulated by alternating topographic noses and hollows estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows hollows act as local traps for a portion of the colluvium transported down hillslopes and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area analysis of colluvial deposits in nine oregon coast range hollows has yielded average colluvial transport rates into the hollows of about 35 cm3cm 1yr 1 and average bedrock lowering rates of about 007 mm yr for the last 4000 to 15000 yr these rates are consistent with maximum bedrock exfoliation rates of about 0 09 mm yr calculated from six of the hollows supporting the interpretation that exfoliation rates limit erosion rates on these slopes sediment yield measurements from nine coast range streams provide similar basin wide denudation rates of between 0 05 and 0 08 mm yr 1 suggesting an approximate steady state between sediment production on hillslopes and sediment yield in addition modern sediment yields are similar in basins varying in size from 1 to 1500 km2 suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape

geomorphic observations of rivers in the oregon coast range from a regional reconnaissance perspective abstract changes in long profile gradient gradient index pseudo hypsometric integral valley incision and sinuosity fractal dimension for rivers in western oregon were studied to determine their usefulness in assessing an hypothesis of differential uplift within the coast range all data were gathered from topographic quadrangles and geologic maps and so the results of this paper are limited to the description of river forms with only limited interpretations rivers were naturally divided into three groups those in the western coast range the eastern coast range and the klamath and cascade ranges and differences in river morphometry were generalized rivers in the western coast range had more divergent characteristics whereas those in the other groups were more similar within each group for example long profiles of western coast range rivers had diverse forms but in the other groups long profiles were similar within the group pseudo hypsometric integrals had a wide scatter in the western coast range but in the other ranges the pseudo hypsometric integral was more narrowly defined valley entrenchment and high sinuosity were common in the western coast range and were less visible in the eastern coast range these regional generalizations do not hold for the central coast range near 44 5 n where the yaquina and marys rivers are located in the eastern coast range the marys river is unique in that it has a convex bulge in its long profile does not have an increasing valley floor width to valley height ratio downstream and has a high sinuosity fractal dimension in the western coast range the yaquina river is unique in that it has a smoothly decreasing long profile has a very low pseudo hypsometric integral and does not have a decreasing valley floor width to valley height ratio downstream there may be many explanations for these observations but these observations are also consistent with tectonic interpretations that the central western coast range is the locus of synclinal tilting and that the entire oregon coast is experiencing landward tilting and uplift

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

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

topographic form of the coast ranges of the cascadia margin in relation to coastal uplift rates and plate subduction the coast ranges of the cascadia margin are overriding the subducted juan de fuca gorda plate we investigate the extent to which the latitudinal trend in average topography of the coast ranges is a function of the latitudinal change in attributes related to the subduction process these attributes include the variable age of the subducted slab that underlies the coast ranges and average vertical crustal velocities of the western margin of the coast ranges for two markedly different time periods the last 45 years and the last 100 kyr these vertical crustal velocities are computed from the resurveying of highway bench marks and from the present elevation of shore platforms that have been uplifted in the late quaternary respectively topography of the coast ranges is in part a function of the age and buoyancy of the underlying subducted plate this is evident in the fact that the two highest topographic elements of the coast ranges the klamath mountains and the olympic mountains are underlain by youngest subducted oceanic crust the subducted blanco fracture zone in southernmost oregon is responsible for an age discontinuity of subducted crust under the klamath mountains the northern terminus of the topographically higher klamaths is offset to the north relative to the position of the underlying blanco fracture zone the offset being in the direction of migration of the fracture zone as dictated by relative plate motions vertical crustal velocities at the coast derived from bench mark surveys are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms this uplift rate discrepancy indicates that strain is accumulating on the plate margin to be released during the next interplate earthquake in a latitudinal sense average coast range topography is relatively high where bench mark derived short term vertical crustal velocites are highest because the shore platform vertical crustal velocites reflect longer term permanent uplift we infer that a small percentage of the interseismic strain that accumulates as rapid short term uplift is not recovered by subduction earthquakes but rather contributes to rock uplift of the coast ranges the conjecture that permanent rock uplift is related to interseismic uplift is consistent with the observation that those segments of the subduction zone subject to greater interseismic uplift rates are at approximately the same latitudes as those segments of the coast ranges that have higher magnitudes of rock uplift over the long term

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

quaternary upper plate deformation in coastal oregon the leading edge of the north american plate along the cascadia subduction zone is deforming and rotating clockwise as a consequence of both underthrusting of the gorda juan de fuca plate and collision of the north american plate with the pacific plate the details of late quaternary 125 ka upper plate deformation resulting from these plate interactions are largely obscured because the most recent deformation overprints earlier deformation in the tertiary rocks of the coast range however by mapping uplifted wave cut platforms formed during times of high sea level in the past 500 000 yr we identify faults and folds active in the late quaternary in central coastal oregon through a long coast correlation of these platforms using elevation and soil development we infer that several major faults have vertically offset platforms at rates as high as 0 6 m k y for the past 125 k y we regionally extend our analysis by incorporating all known faults and folds in southern and central coastal oregon that deform wave cut platforms most platforms along the southern and central oregon coast have been uplifted at rates of 0 1 0 3 m k y since the late pleistocene however platform uplift rates approach 1 m k y in the vicinity of faults the trend and distribution of these upper plate coastal faults are consistent with their interpreted role as left lateral strike slip block bounding structures accommodating clockwise rotation we speculate that these upper plate faults have a component of dip slip because of their association in many instances with localized uplift if these faults bound rotating blocks the dip slip component of displacement may be either contractional or extensional depending on the orientation of the fault relative to the north south trend of the plate margin

late quaternary tectonic deformation in the cape arago bandon region of coastal oregon as deduced from wave cut platforms the cape arago region of south central oregon sits on the upper plate of the cascadia subduction zone about 80 km east of the base of the continental slope the style of late pleistocene deformation along the cascadia forearc near cape arago is well expressed by the altitudinal variation of a set of five uplifted wave cut platforms these platforms record open folding with a half wavelength of about 6 7 km as well as late quaternary offset on flexural slip reverse faults that parallel bedding in the underlying bedrock the folds have produced both landward and seaward tilts to the uplifted wave cut platforms because the folds cut obliquely across the coastline the magnitude of coastal uplift is variable in the case of the lowest 80 ka wave cut platform this variable uplift has resulted in coastal deformation ranging from subsidence to a maximum uplift of 0 8 m kyr quantitative analysis of the mechanism of flexural slip folding for the south slough syncline near cape arago indicates that the late quaternary strain rate has decreased in the last 200 kyr evidence of past great subduction style earthquakes such as regional uplift and regional landward tilting of wave cut platforms or regional submergence of coastlands is lacking inmore the cape arago region instead the deformational style is controlled by folding though localized folding is dominant the occurrence of great subduction style earthquakes is not precluded because localized folding could occur concurrently with regional coseismic deformation less

gps deformation in a region of high crustal seismicity n cascadia forearc we estimate the rate of crustal deformation in the central and northern cascadia forearc based on a combination of existing global positioning system gps velocity data along the cascadia subduction zone gps strain rates and velocities show that the northwestern washington southwestern british columbia region is currently shortening at 3 3 5 mm yr 31 in a n s direction in good agreement with inference from crustal earthquake statistics on the longterm the shortening rate is 5 6 mm yr 31 providing that the subduction related interseismic loading of the margin is purely elastic compared to the velocity of the oregon forearc with respect to north america v 7m m yr 31 this indicates that most of the forearc motion is accommodated in the puget georgia basin area corresponding to the main concentration of crustal seismicity the difference between the current and long term shortening rates may be taken up during subduction megathrust earthquakes thus these events could produce a sudden increase of n s compression in the puget sound region and could trigger major seattle fault type crustal earthquakes published by elsevier science b v

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

the importance of spatially heterogeneous erosivity and the cumulative area distribution within a basin evolution model abstract topography reflects the terrain composition and the forces to which it is exposed the elements that control this shape are intuitive precipitation wind soil composition geologic activity lithology and vegetation each of these elements varies naturally in space a model of basin evolution is shown to produce quantitatively different topography for different relative magnitudes of diffusive and incisive erosion processes spatial heterogeneities in erosivity also influence the simulated topography the calibration of this evolution model is compared to observed topography the calibration process ultimately hinges on quantification of the aggregation pattern of the basin through analysis of the cumulative area distribution the effect of spatially heterogeneous erosivity is shown to be crucially important to reproduce the cumulative area distribution of observed topography

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

effects of melt loss melt retention and protolith composition on differentiation of anatectic metapelites a case study of the wet mountains colorado abstract two metasedimentary migmatite samples from the same outcrop in the northern margin of the oak creek pluton in the wet mountains colorado have distinct mineralogy textures and major and trace element geochemistry sample w6 a garnet biotite migmatite has trace element characteristics consistent with a sedimentary protolith this sample is also rich in silica and lacks sillimanite and cordierite sample w6a a garnet sillimanite cordierite migmatite has strong heavy rare earth element hree enrichment low silica and contains abundant aluminum rich minerals both rocks are relatively oxidized consistent with sedimentary protoliths for both based on textural and geochemical evidence we interpret the differences in mineralogy between the two samples to be the result of differing degrees of melt extraction and variations in protolith composition such differences were assessed using isocon analysis and calculated p t phase diagrams melt retention in sample w6 resulted in the absence of sillimanite and cordierite and back reaction between minerals and melt in the peak assemblage by contrast melt extraction in w6a left garnet in the residuum and imparted a strong heavy rare earth element enrichment on the sample allowing preservation of the peak mineral assemblage consequently w6a records peak conditions of 743 c and 7 6 kbar whereas w6 yields lower p t estimates that may represent the prograde and retrograde metamorphic paths our results indicate that melt extraction can be heterogeneous even at outcrop scale and differing mineralogy may reflect variable proportions of melt loss and local variations in the composition of the protolith moreover at least at small scale migmatization of iron rich protoliths is a plausible mechanism for the production of ferroan alkaline granitic magmas

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

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

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

present day vertical deformation of the cascadia margin pacific northwest united states we estimate present day uplift rates along the cascadia subduction zone in california oregon and washington in the pacific northwest united states by utilizing repeated leveling surveys and tide gauge records these two independent data sets give similar profiles for latitudinal variation of contemporary uplift rates along the coast uplift rates are extended inland through east west leveling lines that connect the north south line along the coast to the north south line along the inland valleys just west of the cascades the results are summarized as a contour map of present day uplift rates for the western pacific northwest we find that rates of present day uplift vary latitudinally along the coast and inland valleys as well as longitudinally along transects connecting the coast to the inland valleys long term tidal records of neah bay astoria and crescent city indicate uplift of land relative to sea level of 1 6 0 2 0 0 0 2 and 0 9 0 2 mm yr respectively 1 standard error unlike previous estimates of relative sea level change at astoria we adjust for discharge effects of the columbia river including human management influences after approximating an absolute framework by using 1 8 0 1 mm yr to compensate for global sea level rise results indicate that much of the western pacific northwest is rising at rates between 0 and 5 mm yr the most rapid uplift rates are near the coast particularly near the olympic peninsula the mouth of the columbia river cape blanco and cape mendocino two axes of uplift are identified one trends northeast from the southwest oregon coast and the other trends south southeasterly from the olympic peninsula to the columbia river the puget sound vicinity and a small east west region from the north central oregon coast to the inland willamette valley are subsiding at rates up to 1 mm yr we interpret the overall pattern of rapid present day uplift to be generated by interseismic strain accumulation in the subduction zone this interseismic elastic strain accumulation implies significant seismic hazard

sandstone diagenesis reservoir potential and sequence stratigraphy of the eocene tyee basin oregon abstract sandstone petrography and diagenetic analysis within a sequence stratigraphic framework provides a better understanding of the reservoir characteristics in the eocene tyee basin an accretionary and forearc sequence southern oregon coast range detailed comparison of relative abundance of major detrital framework grains documents a marked difference of sandstone composition in each depositional sequence such a difference is mainly due to an abrupt change in provenance from a local klamath mountains metasedimentary source to a more distant extrabasinal idaho batholith clarno volcanic arc source furthermore the composition of framework grains varies systematically from the lowstand systems tract to the highstand systems tract within a depositional sequence this suggests that the patterns of sedimentation and sandstone composition can be affected by relative changes in sea level and tectonic uplift in the source area in addition the eocene tyee basin sandstones exhibit a down section distribution of authigenic minerals consisting of early formed zeolites and late stage quartz as well as a change in the abundance of smectite to mixed layer chlorite smectite with increasing burial depth the down section distribution of authigenic minerals is also causally linked to the compositional variation of detrital framework grains in each depositional sequence with increasing burial temperature much primary porosity has been filled with these authigenic minerals thus diminishing the permeability of potential reservoir rocks secondary porosities and permeabilities of reservoir quality averaging 10 80 2 76 md however are present locally in some highstand delta front sandstone facies in the southern part of the basin as well as in lowstand turbidite sandstones in the deeper part of the basin to the north the development of these reservoir quality sandstones within the eocene tyee basin sequence is due to a complex burial diagenesis which is directly related to temporal and spatial variations in original detrital mineralogy in sedimentation pattern and in burial temperature in the basin

the influence of debris flows on channels and valley floors in the oregon coast range u s a debris flows are one of the most important processes which influence the morphology of channels and valley floors in the oregon coast range debris flows that initiate in bedrock hollows at heads of first order basins erode the long accumulated sediment and organic debris from the floors of headwater first and second order channels this material is deposited on valley floors in the form of fans levees and terraces in channels deposits of debris flows control the distribution of boulders the stochastic nature of sediment supply to alluvial channels by debris flows promotes cycling between channel aggradation which results in a gravel bed morphology and channel degradation which results in a mixed bedrock and boulder bed morphology temporal and spatial variability of channel bed morphology is expected in other landscapes where debris flows are an important process

late quaternary stream incision and uplift in the forearc of the cascadia subduction zone western oregon documentation of a latest pleistocene earliest holocene episode of strath formation and fluvial aggradation in the oregon coast range provides a datum from which long term bedrock stream incision rates are determined variations in long term incision rates probably reflect cumulative differential uplift in the forearc of the cascadia subduction zone although factors such as bedrock and climatic controls and isostatic adjustments to erosion obscure the precise relationship between surface uplift and stream incision patterns of differential incision are most striking near the latitude of newport where a steep gradient divides a region of higher rates 0 6 0 9 mm yr in the northern coast range from a region of lower rates 0 1 0 3 mm yr in the central coast range the steep incision gradient is nearly coincident with abrupt changes in marine terrace 80 125 kyr uplift rates the locations of quaternary faults and the southern flank of a saddle of low historic 40 70 years uplift the exact causes of these variable patterns of incision uplift are unknown analogies with uplift patterns in other subduction zones and comparisons with other neotectonic data in the region indicate that patterns of differential incision probably are caused by variations in permanent strain accumulation along the cascadia subduction zone such variations may be related to differences in seismic moment release during individual earthquakes to changes in plate geometry or rates of wedge accretion to segmentation of earthquake ruptures and or to deformation on active structures in the north american plate and accretionary wedge

sedimentary record of subduction to forearc transition in the rotated eocene basin of western oregon systematic changes in compositions of eocene sandstones in the southern part of the oregon coast range constrain proposed models of tectonic accretion and rotation of this crustal fragment three basic petrofacies of lithic arkosic and volcanolithic composition can be defined sequentially from the base to the top of the section the lithic petrofacies was deposited prior to rotation and was derived from the nearby klamath mountains during collision of the subjacent seamount terrane the transition to arkosic composition coincided with the end of collision and the initiation of forearc basin subsidence the arkosic sands contain muscovite and potassium feldspar derived from a continental plutonic source area their presence in the forearc sequence suggests that the coast range block lay farther to the east and closer to interior parts of the mesozoic batholith belt prior to tectonic rotation volcanolithic sandstones were deposited after rotation of the coast range had begun and they mark the beginning of volcanic activity in the adjacent cascade arc

geomorphic response of coastal streams to low intermediate and high rates of uplift medocino triple junction region northern california analysis of three dimensional morphological properties of 24 coastal drainage basins that have evolved in areas of low 3 m 1 000 yr rates of uplift near the mendocino triple junction mtj coastal northern california identified channel gradients as the best indicator of tectonism in the landscape lower order tributaries best reflect tectonically controlled differences the largest streams examined of third order are able to adjust to most base level change and maintain their profile form whereas lower order streams farther upstream tend to accumulate the effects of net base level fall and have steepest profiles in the areas of highest uplift rates variations in steepness of first order channel gradients indicate that 1 high uplift rates in the wake of the mtj have existed for at least 73 000 yr and 2 differential tilt of the region to the north and south of the current locus of highest uplift rate is occurring in association with regional uplift although first order streams are excellent indicators of areas of both high uplift rates and regional differential tilting they are less useful in distinguishing between areas of low and intermediate uplift rate analysis of the longitudinal profile of the main trunk stream of ten of the 24 drainage basins using the stream gradient index was more useful to categorize broadly the uplift rates and to distinguish between streams in low and intermediate uplift rate areas although the hypotheses tested herein do not identify the exact mechanism off uplift in the mtj region they do indicate that the nature of deformation is most likely regional tilt rather than crustal shortening with localized compressional folding and thrust faulting they also indicate that geomorphic responses trail in the wake of the uplift rate response caused by development of a slab window beneath the north american plate 1 maximum uplift rates occur 9 km south of the northern boundary of the slab window 2 maximum mean first order channel gradient occurs 16 km south of the northern edge of the slab window and 3 maximum drainage basin relief occurs 20 km south of the northern edge of the slab window associated lag times between passage of the southern edge of the subducted gorda plate slab and geomorphic responses are 160 000 yr for maximum uplift rates 290 000 yr for maximum channel gradients and 370 000 yr for maximum relief