imprints of himalayan thrust tectonics on the quaternary piedmont sediments of the neora jaldhaka valley darjeeling sikkim sub himalayas india abstract geological mapping in the neora jaldhaka valley of the darjeeling sikkim sub himalayan foothill region reveals the presence of discontinuous strands of tectonically active quaternary thrust faults the zones of active faulting coincide with occurrences of deeply incised piedmont deposits and river terraces along an e w trending corridor in order of younging the successive quaternary thrust faults delineated are the gorubathan matiali and chalsa thrusts unequivocal geological evidence of surface rupture faulting however is noted only along the gorubathan thrust where the precambrian daling group of rocks is thrust over the quaternary piedmont sediments along a low northerly dipping plane the presence of deformational features in the quaternary sediments such as anticlines bending moment faults and back tilting of both the piedmont and the incising river terraces along active fault scarps are interpreted to signify the presence of north dipping blind thrusts below the matiali and chalsa scarps radiocarbon dates of organic rich clay components indicate that the gorubathan thrust post dated 33 875 550 ybp and the lower bound age of the chalsa thrust is 22 030 130 ybp successive foreland ward development of these active strands and the increasing spacing between the successive thrust traces are interpreted to be due to foreland propagating blind thrusts of the himalayan ftb fold and thrust belt in the sub himalayan terrain evidences of backthrust movement are also presented along the thaljhora north fault the segmented and variable geometry of these thrusts imply that the mft main frontal thrust is still in its early stage of growth and the lateral linkages between the active fault strands are yet to be established

representative rainfall thresholds for landslides in the nepal himalaya measuring some 2400 km in length the himalaya accommodate millions of people in northern india and pakistan nepal bhutan and parts of other asian nations every year especially during monsoon rains landslides and related natural events in these mountains cause tremendous damage to lives property infrastructure and environment in the context of the himalaya however the rainfall thresholds for landslide initiation are not well understood this paper describes regional aspects of rainfall thresholds for landslides in the himalaya some 677 landslides occurring from 1951 to 2006 were studied to analyze rainfall thresholds out of the 677 landslides however only 193 associated with rainfall data were analyzed to yield a threshold relationship between rainfall intensity rainfall duration and landslide initiation the threshold relationship fitted to the lower boundary of the field defined by landslide triggering rainfall events is i 73 90d 0 79 i rainfall intensity in mm h 1 and d duration in hours revealing that when the daily precipitation exceeds 144 mm the risk of landslides on himalayan mountain slopes is high normalized rainfall intensity duration relationships and landslide initiation thresholds were established from the data after normalizing rainfall intensity data with respect to mean annual precipitation map as an index in which ni 1 10d 0 59 ni normalized intensity in h 1 finally the role of antecedent rainfall in causing landslides was also investigated by considering daily rainfall during failure and the cumulative rainfall to discover at what point antecedent rainfall plays an important role in himalayan landslide processes rainfall thresholds presented in this paper are generalized so they can be used in landslide warning systems in the nepal himalaya 2008 elsevier b v all rights reserved

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

morphological and sedimentological responses of streams to human impact in the southern blue ridge mountains usa abstract morphological and sedimentological responses of streams to basin scale impact have been well documented for intensively agricultural or urban areas sensitivity thresholds of streams to modest levels of disturbance however are not well understood this study addresses the influence of forest conversion on streams of the southern blue ridge mountains a region that has received little attention with respect to human impact on stream channels basins were chosen for this study to represent the end members of the range of human impact in the area with the forest cover of the basin used as a proxy for level of impact ranging from about 70 100 regionally two pairs of lightly impacted 90 forest and moderately impacted 70 80 forest sub basins of the upper little tennessee river were identified for comparison reach characteristics e g slope drainage area and riparian cover were aligned in each pair to isolate contrasting forest cover as the primary driver of any detected differences in morphology and sedimentology a suite of standard cross sectional and longitudinal data was collected for each reach for characterization of the sedimentology and morphology of the streams difference of means tests were conducted to identify parameters significantly differing between the lightly and moderately impacted streams in both pairs consistent and significant differences within both pairs were demonstrated in bankfull width depth ratios baseflow wetted width and particle size on the stream bed both in the thalweg and throughout the channel bed the moderately impacted streams are narrower than the lightly impacted streams and the bed texture of the moderately impacted streams is finer than that of the lightly impacted streams the moderately impacted streams contain a higher percentage of

morphological and sedimentological responses of small stream channels to extreme rainfall and land use in the darjeeling himalayas abstract three pairs of small fourth to sixth order catchments approximately 5 80 km2 draining the margin of the darjeeling himalayas into the piedmont were selected for a comparison of the land use impact on the morphology and sedimentology of their stream channels each pair experienced similar annual rainfall and comprised similar metamorphic bedrock steep topography and brown soils the members of each pair contrast with respect to their land use structure as they comprise large forest cover forest 90 and a significant contribution of agricultural land with tea plantations forest

geomorphology of medium high mountains under changing human impact from managed slopes to nature restoration a study from the sudetes sw poland in the last few hundred years medium high mountain geomorphic systems of the east sudetes central europe have evolved under varying human impacts and have shown distinctive behaviours depending on the nature and intensity of human activities the general trend within this period has been from initial disturbance brought about by the spread of agriculture through managed rural landscapes in the 19th and early 20th century to gradual restoration of natural conditions observed in the last few tens of years concurrent with considerable population decline in the mountain valleys accelerated soil erosion was successfully mitigated by the introduction of agricultural terraces in the 19th century and most sediment could have been stored within the slopes the current phase of nature restoration is understood as a return to general slope stability weak coupling between slopes and channels and limited sediment transfer across and out of mountainous drainage basins which typified most of the holocene prior to human colonization copyright 2006 john wiley sons ltd

buffers barriers and blankets the dis connectivity of catchment scale sediment cascades abstract catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency this paper introduces the concept of landform impediments termed buffers barriers and blankets that impede sediment conveyance by limiting the connectivity between landscape compartments buffers restrict sediment delivery to channels barriers inhibit sediment movement along channels and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment these features operate as a series of switches which turn on off processes of sediment delivery determining the effective catchment area at any given time using previously documented examples the role of these features in affecting the operation of sediment cascades in a low relief passive landscape setting such as the australian landmass is contrasted to examples from high relief uplifting settings in new zealand the australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since european settlement have impacted upon landscape sensitivity and prospects for river recovery this approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting

extreme rainfalls in eastern himalaya and southern slope of meghalaya plateau and their geomorphologic impacts this paper presents the detailed rainfall characteristics of 3 key areas located in the eastern monsoon india the margin of darjeeling himalaya the margin of bhutanese himalaya and the cherrapunji region at the southern slope of meghalaya upland all these areas are sensitive to changes but differ in annual rainfall totals 2000 4000 mm 4000 6000 m and 6000 23 000 mm respectively and in the frequency of extreme rainfalls therefore the response of geomorphic processes is different also due to various human impact in the darjeeling himalaya the thresholds may be passed 2 3 times in one century and the system may return to the former equilibrium at the margin of western bhutanese himalaya in 1990s the clustering of three events caused an acceleration in the transformation and formation of a new trend of evolution especially in the piedmont zone in the cherrapunji of meghalaya region in the natural conditions the effects of dozens of extreme rainfalls every year were checked by the dense vegetation cover after deforestation and extensive land use the fertile soil was removed and either the exposed bedrock or armoured debris top layer protect the surface against degradation and facilitate only rapid overland flow a new sterile system has been formed

geomorphic responses of lower bega river to catchment disturbance 1851 1926 abstract prior to significant european settlement of the area in the 1850s lower bega river on the south coast of nsw had a narrow relatively deep channel lined by river oaks the river had a suspended or mixed load with platypus habitat available in pools banks were fine grained and relatively cohesive silts and clays as was the floodplain which graded to a series of valley marginal swamps and lakes extensive evidence from maps and portion plans archival photographs bridge surveys and anecdotal sources complemented by field analysis of floodplain sedimentology including radiocarbon dated samples and vegetation remnants are used to document the dramatic metamorphosis in the character and behaviour of lower bega river in the latter half of the nineteenth century by 1926 the channel had widened extensively up to 340 and shallowed in association with bed aggradation by coarse sandy bedload floodplain accretion was dominated by fine to medium sands with some coarse sand splays in contrast with most other studies of channel metamorphosis in australia which have emphasised river responses to climatically induced flood histories relegating human impacts to a secondary role the profound changes to the geomorphic condition and behaviour of bega river reflect indirect human disturbance of bega catchment and direct but non point source disturbance to the channel extensive clearance of catchment floodplain and channel marginal vegetation occurred within a few decades of european settlement altering the hydrologic and sediment regime of the river and transforming the geomorphic effectiveness of floods although this study is situated in a relatively sensitive granitic catchment catchment clearance is likely to have induced equally significant responses in many other river systems in eastern australia in some instances the diffuse aspects of human disturbance on landscapes induce impacts on river character that are just as profound as major direct disturbances of river channels this may have profound implications in understanding and hence managing the geomorphic consequences of river behaviour in australia and elsewhere

reach scale channel geometry of mountain streams abstract the basic patterns and processes of steep channels remain poorly known relative to lower gradient channels in this analysis characteristics of step pool plane bed and pool riffle channels are examined using a data set of 335 channel reaches from the western united states nepal new zealand and panama we analyzed differences among the three channel types with respect to hydraulics channel geometry boundary roughness and bedforms step pool channels have significantly steeper gradients coarser substrate higher values of shear stress and stream power for a given discharge and larger ratios of bedform amplitude wavelength h l pool riffle channels have greater width depth ratios and relative grain submergence r d84 than the other channel types plane bed channels tend to have intermediate values for most variables examined relative form submergence r h is statistically similar for step pool and pool riffle channels despite the lesser relative grain submergence and greater bedform amplitude of step pool channels mean values of darcy weisbach friction factor do not change in response to changes in relative grain submergence these patterns suggest that adjustments along mountain streams effectively maximize resistance to flow and minimize downstream variability in resistance among the different channel types

viscosity of the lower mantle as inferred from rotational data until recently most estimates of the deep mantle viscosity were based on analyses of postglacial uplifts and there were no serious estimates of the sensitivity of the derived viscosity solutions to variations of the input parameters such as those associated with the surface loading in this paper the viscosity of the lower mantle is arrived at by making comparisons of the observed secular motions of the earth s rotation axis with theoretical results from a layered viscoelastic rotating earth which has been subjected to glacial forcing our model consisting of an elastic lithosphere a two layer adiabatically stratified viscoelastic mantle and an inviscid core is essentially analytical and this makes it economically feasible to use as an aid in conducting an extensive sensitivity analysis of the lower mantle viscosity from changes in the parameters connected with the deglaciation phenomenon both sets of rotational data polar wander and nontidal deceleration of the length of the day have been employed to constrain the viscosity structure on the basis of this type of investigation the viscosity of the lower mantle is found invariably to be larger than that of the upper mantle and lies between 1 and 4 1022 p our results which just rely on the second degree harmonic of the strain field also lead to a determination of an upper bound to the thickness of the globally averaged lithosphere this value ranging between 130 and 190 km suggests that strong lateral heterogeneities between oceanic and continental plates may extend a few hundred kilometers into the upper mantle

glaciation induced perturbations in the earth s rotation a new appraisal we revisit the theory and predictions of glaciation induced perturbations in both the rotation rate of the earth or j 2 and the wander of the rotation pole with respect to the surface geography the two most common theoretical formulations associated with polar wander driven by the surface loading of a viscoelastic earth e g sabadini et al 1982 wu and peltier 1984 appear to disagree by one on the number of rotational normal modes associated with a surface gravitational response having n normal modes we show using a generalized theory that the two formalisms yield essentially equivalent predictions we next consider a benchmark comparison of recent predictions of present day polar wander speed due to glacial isostatic adjustment henceforth gia these comparisons confirm the validity of certain previous analyses e g spada et al 1992a they also reveal that predictions of polar wander speed can be sensitive to an assumption of incompressibility previous studies have noted that predictions of j 2 rotation rate as a function of lower mantle viscosity differ significantly in form from analogous predictions of polar wander speed we investigate these differences by considering the contribution to the predicted anomalies from the individual normal modes of relaxation we find that the normal mode structure of the j 2 rotation rate predictions is fundamentally different from that which characterizes the polar wander response and this difference reflects the distinct physical mechanisms which govern these anomalies finally using a large suite of forward computations as well as the calculation of a set of frechet kernels we investigate the sensitivity of our predictions to variations in the viscoelastic earth model we find for example that a previously noted sensitivity of polar wander speed predictions to variations in lithospheric thickness is only valid for earth models with relatively weak lower mantle viscosities 5 x 10 21 pa s

effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central japan landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention we examined the effects of forest harvesting on the frequency of landslides and debris flows in the sanko catchment central japan using nine aerial photo periods covering 1964 to 2003 these photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912 geology and slope gradient are rather uniformly distributed in the sanko catchment facilitating assessment of forest harvesting effects on mass wasting without complication of other factors trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10 fold higher than in control sites total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5 8 10 3 m 3 km 2 compared with 1 3 10 3 m 3 km 2 in clearcuts 25 yr indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability because landslide scars continue to produce sediment after initial failure sediment supply from landslides continues for 45 yr in the sanko catchment to estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions copyright 2007 john wiley sons ltd

marginal faunal belts and their structural implications with examples from the lower palaeozoic fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms on a global scale the identification of exterior oceanic biofacies may be of use in discriminating the course of former continental margins the isograptid graptolite biofacies early to middle ordovician can be distinguished from contemporary epicratonic graptolite biofacies its worldwide occurrence corresponds with continent margins reconstructed from other criteria hence a new isograptid record from irian jaya e new guinea although based on a small sample suggests that there may have been an ordovician oceanic site there on a continental scale the tectonic juxtaposition of different biofacies or of different stratigraphical packages contributes to an understanding of tectonics and can serve to quantify displacement the accretionary prism hypothesis for the southern uplands of scotland is supported and contrasted with the rearrangement of biofacies in the cambro ordovician cow head group of western newfoundland which reveals not only the original shelf margin slope topography now vanished but also provides an estimate of the movement involved in the emplacement of one taconic allochthon on a more local scale faunal evidence is used in assessing the original position of 9suspect9 marginal areas using the simplest possible model this shows for example that anglesey was not greatly separated from gondwana in the early ordovician but strike slip movement cannot be disproved local changes in relative sea level are determinable from sediments and faunas in marginal belts these may differ from the global eustatic curve and when this happens it is a measure of local tectonic activity particular sea level curves may serve to define structurally coherent units within mobile belts new sea level curves are contrasted for a segment of n wales north of the bala fault with that for central sw wales arenig llandovery the s welsh area mostly responded passively to the eustatic curve which can adequately account for shifts in facies and faunas while n wales had a curve often at odds with eustasy and reflecting its structural history

grim gravity model improvement using lageos grim3 l1 improved modeling of the earth s geopotential is one of the major tasks of satellite geodesy the availability of a new set of precise lageos satellite laser ranging slr data as well as seasat acquired observations enabled us to compute an improved solution in the grim model series the new geopotential grim3 l1 recombined the satellite perturbation normals of the former grim3 solution with new normal equation subsystems derived from an additional 16 months of lageos slr data oceanic 1 1 mean free air anomalies recovered from seasat altimetry an updated set of terrestrial 1 1 mean free air anomalies and several condition equations for zonal and resonant harmonics the combined normal equations were solved for a complete set of spherical harmonics up to degree and order 36 and the coordinates of 109 tracking stations comparisons with altimetry derived quantities terrestrial gravity anomalies from satellite to satellite tracking longitude accelerations of 24 hour satellites and satellite orbit fits show a substantial improvement over previous grim solutions and indicate that the lageos data have contributed considerably to the reliable estimation of the long wavelength portion of the gravity field

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

a reassessment of facies and faunas in the type llandeilo ordovician wales abstract detailed analysis of the lithological and faunal successions of the type llandeilo forms the basis of an evaluation of the sequence of depositional environments and a quantitative description of the entombed faunas comprising mainly brachiopods trilobites and ostracods recorded distribution patterns confirm the validity of the existing trilobite trinucleid biostratigraphic zones but emphasize the importance of benthic bivalved taxa which are particularly abundant in the lower llandeilo groups of assemblages comprising localized faunules or associations despite exhibiting evidence of transportation are readily identified as representative of more widespread contemporary palaeocommunities recently described from wales and the welsh borderland the relationship between these palaeocommunities and the transgressive llandeilo sequence indicates a shoreface to open shelf zonation of ecosystems controlled primarily by substrate conditions rather than depth

which dem is best for analyzing fluvial landscape development in mountainous terrains abstract regional studies of fluvial landforms and long term quaternary landscape development in remote mountain landscapes routinely use satellite derived dem data sets the srtm and aster dems are the most commonly utilised because of their longer availability free cost and ease of access however rapid technological developments mean that newer and higher resolution dem data sets such as alos world 3d aw3d and tandem x are being released to the scientific community geomorphologists are thus faced with an increasingly problematic challenge of selecting an appropriate dem for their landscape analyses here we test the application of four medium resolution dem products 30 m srtm aster aw3d 12 m tandem x for qualitative and quantitative analysis of a fluvial mountain landscape using the dades river catchment high atlas mountains morocco this landscape comprises significant dem remote sensing challenges notably a high mountain relief steep slopes and a deeply incised high sinuosity drainage network with narrow canyon gorge reaches our goal was to see which dem produced the most representative best fit drainage network and meaningful quantification to achieve this we used arcgis and stream profiler platforms to generate catchment hillshade and slope rasters and to extract drainage network channel long profile and channel slope and area data tandem x produces the clearest landscape representation but with channel routing errors in localised high relief areas thirty metre dems are smoother and less detailed but the aw3d shows the closest fit to the real drainage network configuration the tandem x elevation values are the closest to field derived gps measurements long profiles exhibit similar shapes but with minor differences in length elevation and the degree of noise smoothing with aw3d producing the best representation slope area plots display similarly positioned slope break knickpoints with modest differences in steepness and concavity indices but again best represented by aw3d collectively our study shows that despite the higher effective resolution of tandem x 12 m the aw3d 30 m data performs strongly across all analyses suggesting that it currently offers the greatest potential for regional mountain geomorphological analyses

definition of the tremadoc series and the series of the ordovician system in britain the tremadoc series and series of the ordovician system are widely used in international correlations and this review explains and summarizes how the base of each of these series is recognized in britain no type section in which the base of any one of them is displayed has ever been selected and formally designated hence the basal horizon of each series is a matter of general understanding rather than precise definition this general understanding is of particular biozones or of assemblages of fossils and their relative ages the geographical separation between type sections of series and differences in facies complicate the understanding of relative ages of biozones brachiopod and trilobite faunas of the llandeilo caradoc and ashgill series have been studied in detail in recent years and biozones proposed these biozones have proved difficult or impossible to recognize outside their type areas in britain and brachiopod trilobite faunas of the tremadoc arenig and llanvirn series are likewise highly provincial thus for correlation within and outside britain attention has been focused on the standard graptolite biozones particularly since such conodont faunas as have been found have not proved useful yet there are problems associated with these standard biozones for example the tetragraptus approximatus biozone is unknown in wales or england the relationship between the base of the glyptograptus teretiusculus biozone and the earliest llandeilo shelly faunas requires clarification and at what level the base of the caradoc series may lie in the nemagraptus gracilis biozone is unknown thus to bring precision to definitions of ordovician series in britain the identification of continuous fossiliferous sequences that will serve as stratotypes is required such a section for the basal portion of the tremadoc series has recently been proposed systematic studies related to particular biozones are needed for example early caradoc and early ashgill brachiopods and graptolites of the didymograptus bifidus and glyptograptus teretiusculus biozones the stratigraphical ranges and abundances of species in particular sections require documentation so that the type of biozone assemblage acme concurrent range etc may be recognized such work could lead towards chronostratigraphy the provision of a standard stratigraphical scale in britain for the tremadoc series and ordovician series

high resolution correlation of anglo welsh middle to upper ordovician sequences and its relevance to international chronostratigraphy abstract continuously fossiliferous sections in south wales and shropshire spanning the base of the upper ordovician permit precise correlation of the nemagraptus gracilis biozone a horizon currently under scrutiny for the selection of a global stratotype section and point gssp using graphic correlation we have compiled a new composite global standard for the middle upper ordovician which shows that the first occurrence of the key graptolite n gracilis is not everywhere of the same age appearing earlier in north american successions than it does in britain species of dicellograptus by contrast appear to be almost synchronous in their first appearance the status and correlation of standard british biozones through the llandeilian caradoc interval based on graptolites and trilobites are revised suitable sections for the definition of bases of biozones are proposed if the base of the n gracilis biozone is accepted internationally as the base of the upper ordovician this biozone being coincident with the base of the caradoc series there are sections suitable for its precise definition in the british succession

excitation of the earth s rotational axis by recent glacial discharges we study the effects of present day glacial dis charges and the growth of the antarctic ice sheet on exciting the earth s rotational axis glacial forcing could cause a maximum change in j of about one third of the observed amount for the maxwell rheology and for burgers body models with a long term lower mantle viscosity greater than about 1023p for transient rheologies the amount of excitation due to glacial melting decreases polar wander is not much excited by recent glacial melting for the various types of rheologies examined

determination of oceanic dynamic barometer corrections to atmospheric excitation of earth rotation the excitation of earth s rotation by atmospheric pressure fluctuations on timescales from days to years is modified by the oceanic response to the pressure load that response has often been approximated as a static inverted barometer ib change in sea level but evidence from theory and both tide gauge and altimetric data suggests that the ib poorly models the sea level response at short periods static models also fail to account for the currents induced by the pressure loading the actual dynamic response of the oceans to barometric loads depends on frequency and on the spatial structure of the loading this work presents a green s function approach to determining the rotational effects of that oceanic response the green s functions characterize the rotational effects of the oceanic response to pressure loads described spatially by individual spherical harmonics for each harmonic of forcing they were computed at nine periods ranging from 4 days to 18 years and interpolated at intermediate periods computations were based on solutions to the author s dynamic spherical harmonic ocean tide model the effects on rotation of the dynamic barometer oceanic response are obtained by a convolution type combination of the green s functions with actual atmospheric pressure data results for data spanning the past decade will be illustrated using harmonically decomposed national center for environmental prediction ncep and european centre for medium range weather forecasts ecmwf pressure fields

taphonomic windows and molluscan preservation recent studies on silicified fossil biotas have suggested that substantial skewing of the molluscan record resulted from early aragonite dissolution in mid outer carbonate ramp settings if those rare skeletal lagerstatten are representative then the quality and completeness of the molluscan record are thrown into doubt yet database studies suggest that the bivalve fossil record is actually relatively complete if so then biodiversity must be captured by other processes that preserved shells vulnerable to early dissolution and which operated on a relatively high frequency i e less than the species duration for bivalves storm beds shell plasters and submarine hardgrounds are identified as fossil deposits that can preserve the labile aragonitic component of the fauna and thus represent potential taphonomic windows many storm event beds include rich accumulations of shelly benthos differences between storm bed faunas and those of the background facies could reflect transportation effects however some storm bed assemblages are rich in originally aragonitic infaunal bivalves that are not represented in background facies or more proximal shelf equivalents and here rapid burial and removal of organic matter by winnowing may be the keys to aragonite shell preservation despite palaeozoic to cenozoic changes in the thickness and frequency of shell beds that reflect the predominant bioclast producers shallow infaunas are commonly concentrated together with epifauna in such deposits some low energy organic rich mud dominated settings are associated with preservation of aragonitic molluscs infaunal bivalves are a prominent component of shell plasters or pavements in such settings linked to episodic bottom water anoxia decaying algal blooms drew the redox boundary up above the sediment water interface and brought populations of infaunal bivalves to the surface where they died isolated from the oxic taphonomically active zone the shells were not dissolved and were buried as thin shell layers in similar settings aragonitic shells were preserved as moulds through early pyritisation or even through preservation of original shell aragonite in oxic environments bioturbational reworking of surface sediment destroyed moulds of aragonitic shells after early dissolution in some hardgrounds these delicate moulds were preserved due to synsedimentary cementation probably using carbonate released by aragonite dissolution the examples included here come from both intervals of calcite and aragonite seas and it is not possible to assess whether the saturation state with respect to aragonite of the ambient sea water played a role in the selective removal of aragonitic shells while taphonomic windows may have captured the diversity of individual groups it is clear from quantitative data involving skeletal lagerstatten that the scale of loss from early aragonite dissolution has drastically altered the trophic composition of some fossil assemblages commonly used as the basis for reconstructions of past communities

monsoonal hillslope processes determine grain size specific suspended sediment fluxes in a trans himalayan river sediments in rivers record the dynamics of erosion processes while bulk sediment fluxes are easily and routinely obtained sediment caliber remains underexplored when inferring erosion mechanisms yet sediment grain size distributions may be the key to discriminating their origin we have studied grain size specific suspended sediment fluxes in the kali gandaki a major trans himalayan river two strategically located gauging stations enable tracing of sediment caliber on either side of the himalayan orographic barrier the data show that fine sediment input into the northern headwaters is persistent while coarse sediment comes from the high himalayas during the summer monsoon a temporally matching landslide inventory similarly indicates the prominence of monsoon driven hillslope mass wasting thus mechanisms of sediment supply can leave strong traces in the fluvial caliber which could project well beyond the mountain front and add to the variability of the sedimentary record of orogen erosion

human impacts to mountain streams mountain streams are here defined as channel networks within mountainous regions of the world this definition encompasses tremendous diversity of physical and biological conditions as well as history of land use human effects on mountain streams may result from activities undertaken within the stream channel that directly alter channel geometry the dynamics of water and sediment movement contaminants in the stream or aquatic and riparian communities examples include channelization construction of grade control structures or check dams removal of beavers and placer mining human effects can also result from activities within the watershed that indirectly affect streams by altering the movement of water sediment and contaminants into the channel deforestation cropping grazing land drainage and urbanization are among the land uses that indirectly alter stream processes an overview of the relative intensity of human impacts to mountain streams is provided by a table summarizing human effects on each of the major mountainous regions with respect to five categories flow regulation biotic integrity water pollution channel alteration and land use this table indicates that very few mountains have streams not at least moderately affected by land use the least affected mountainous regions are those at very high or very low latitudes although our scientific ignorance of conditions in low latitude mountains in particular means that streams in these mountains might be more altered than is widely recognized four case studies from northern sweden arctic region colorado front range semiarid temperate region swiss alps humid temperate region and papua new guinea humid tropics are also used to explore in detail the history and effects on rivers of human activities in mountainous regions the overview and case studies indicate that mountain streams must be managed with particular attention to upstream downstream connections hillslope channel connections process domains physical and ecological roles of disturbance and stream resilience

a comparison of two sets of synthetic reflection seismograms for a complex two dimensional model of the oceanic crust mantle transition the algorithm chosen for the calculation of synthetic seismograms often represents a compromise between the realistic representation of complex geology and economy comparison of synthetic seismic reflection sections calculated using a relatively inexpensive ray theory and a relatively expensive generalized reflectivity algorithm for a complex laterally inhomogeneous model of the oceanic moho demonstrates that ray theory provides a close approximation to the full wave theory the chief difference between the two synthetic sections is the more accurate variation in amplitude with horizontal range predicted by the reflectivity synthetics due to its inclusion of the horizontal smoothing of the reflected amplitudes over the width of the first fresnel zone while this fresnel zone smoothing will become increasingly important with increasing reflector depth the results shown here suggest that inexpensive ray theory synthetics may have sufficient accuracy in many similar applications

downstream coarsening in headwater channels 1 field data from four mountain drainage basins in western washington document systematic downstream coarsening of median bed surface grain size d50 and a subsequent shift to downstream fining at a drainage area of about 10 km2 analyses of network wide patterns of unit stream power derived from both channel surveys and digital elevation models reveal maximum unit stream power that in all four study areas roughly corresponds with both the grain size maxima and an inflection in the drainage area slope relation thought to represent the transition from debris flow dominated channels to fluvially dominated channels our results support the hypothesis that basin wide trends in d50 are hydraulically controlled by systematic variations in unit stream power in addition to lag deposits forced by mass wasting processes the similar relations found in our four study areas suggest that the tendency for downstream coarsening may be ubiquitous in headwater reaches of mountain drainage basins where debris flow processes set the channel gradient

lithological and fluvial controls on the geomorphology of tropical montane stream channels in puerto rico an extensive survey and topographic analysis of five watersheds draining the luquillo mountains in north eastern puerto rico was conducted to decouple the relative influences of lithologic and hydraulic forces in shaping the morphology of tropical montane stream channels the luquillo mountains are a steep landscape composed of volcaniclastic and igneous rocks that exert a localized lithologic influence on the stream channels however the stream channels also experience strong hydraulic forcing due to high unit discharge in the humid rainforest environment gis based topographic analysis was used to examine channel profiles and survey data were used to analyze downstream changes in channel geometry grain sizes stream power and shear stresses results indicate that the longitudinal profiles are generally well graded but have concavities that reflect the influence of multiple rock types and colluvial alluvial transitions non fluvial processes such as landslides deliver coarse boulder sized sediment to the channels and may locally determine channel gradient and geometry median grain size is strongly related to drainage area and slope and coarsens in the headwaters before fining in the downstream reaches a pattern associated with a mid basin transition between colluvial and fluvial processes downstream hydraulic geometry relationships between discharge width and velocity although not depth are well developed for all watersheds stream power displays a mid basin maximum in all basins although the ratio of stream power to coarse grain size indicative of hydraulic forcing increases downstream excess dimensionless shear stress at bankfull flow wavers around the threshold for sediment mobility of the median grain size and does not vary systematically with bankfull discharge a common characteristic in self forming threshold alluvial channels the results suggest that although there is apparent bedrock and lithologic control on local reach scale channel morphology strong fluvial forces acting over time have been sufficient to override boundary resistance and give rise to systematic basin scale patterns copyright 2010 john wiley and sons ltd

river channel response to short term human induced change in landscape connectivity in andean ecosystems the drainage basin of the deleg river 88 km 2 located in the southern ecuadorian andes was studied to assess the geomorphic and hydrologic response of a fluvial system to human induced environmental change in its contributing area historical data on land use channel morphology and sedimentology were collected based on a spatial analysis of aerial photographs 1963 1995 and a field survey 2002 analysis of channel cross sectional profiles and sedimentological data revealed a major change in morphology and sedimentology of the deleg river during the past four decades i the active river channel narrowed by over 45 ii the riverbed incised on average by over 1 0 m and iii the median grain size of the bed surface decreased from 13 2 cm to 4 7 cm the spatial pattern of land cover within the deleg catchment also changed considerably highly degraded agricultural land in the low lying areas was abandoned and partially afforested for timber and wood production whereas secondary upland forest was increasingly cleared for expansion of cropland and pastures notwithstanding large changes in the spatial organization of land use within the catchment the overall land use did not change significantly during the past four decades this suggests that the response of the deleg river to land use change not only depends on the overall land use change but also on the spatial pattern of land use cover change within the catchment although forestation and regeneration of bare gully slopes and floors throughout the catchment only represented a minor part of the total land use change these land use cover changes had a major impact on the hydrological and sediment connectivity in the landscape c 2005 elsevier b v all rights reserved

higher harmonic effects of the earth s gravitational field from post glacial rebound as observed by lageos recently long term orbital data from the artificial satellite lageos have been analyzed to determine the rate of post glacial rebound rubincam has compared the observed values against values derived from two realistic earth models wu peltier l1 l2 working with the second harmonic mode of excitation the data support model l1 with a uniform mantle viscosity of 1022 poise over l2 with a lower mantle viscosity of 1023 poise we find the higher degree harmonic contributions are significant and considerably strengthen the support for model l1 we perform such calculations using the same parameter values for glaciation as rubincam and also values due to peltier and coworkers we also show that a similar analysis of data from the satellite starlette is less likely to be as definitive as analysis of lageos data since there are significant contributions from very high harmonics indicating that the behavior of the earth must be known in much greater detail

present day secular variations in the zonal harmonics of earth s geopotential we develop a new formalism for the prediction of secular variations in the gravitational potential field of a spherically symmetric self gravitating maxwell viscoelastic planetary model subjected to an arbitrary surface load which may include a gravitationally self consistent ocean loading component the theory is applied to generate the most accurate predictions to date of the present day secular variations in the zonal harmonics of the geopotential the so called for degree arising as a consequence of the late pleistocene glacial cycles in this respect we use the very recent ice 3g reconstruction of the last late pleistocene deglaciation event tushingham and peltier 1991 a comparison of these predictions with those generated using simplified disk models of the ice sheets which have been used in all previous studies of the harmonics 2 indicates that the disk model approximation introduces unacceptably large errors at all spherical harmonic degrees except perhaps 2 predictions have also been made using a eustatic loading approximation also used in previous studies in place of a gravitationally self consistent ocean loading component and we have found that the resulting discrepancy is largest at degrees 2 8 and 10 in the case of the magnitude of the error incurred using the eustatic approximation can be as large as order 10 15 of the predicted value we have attributed this discrepancy to the present day net flux of water away from the equatorial regions arising from the remnant present day adjustment associated with the late pleistocene glacial cycles the effect represents a heretofore unrecognized contribution to the harmonics or alternatively the nontidal acceleration of earth s axial rate of rotation in terms of the latter the maximum anomaly in the length of day is approximately 1 7 s yr we also consider the sensitivity of the data to variations in the radial mantle viscosity profile by using a suite of forward calculations and an examination of frechet kernels the theory required for the computation of those kernels is described herein we find that the radial variation in sensitivity can be a strong function of the viscosity model used in the calculations for models with a uniform upper mantle viscosity um of 1021 pa s forward predictions of the harmonics exhibit a pronounced peak when a wide enough range of lower mantle viscosities lm are considered we denote the lm value at this peak as at the lowest degrees 4 frechet kernels computed for a series of increasing lm values 1021 pa s lm 1023 pa s indicate a migration of the dominant sensitivity of the data to variations in viscosity from regions below approximately 1200 km depth for to regions above this depth in the lower mantle for the sensitivity of the data to variations in the viscosity profile in the shallowest parts of the lower mantle for the case is also reflected in a set of forward calculations described herein as an example predictions made using earth models in which the viscosity above 1200 km depth is constrained to be 1021 pa s do not exhibit the multiple solutions characteristic of the um 1021 pa s calculations the same is true of earth models in which the upper mantle viscosity is weakened an order of magnitude to 1020 pa s the theory described herein is also applied to compute the signal 10 arising from the retreat of small ice sheets and glaciers described by meier 1984 and also from any potential variations in the mass of the antarctic and greenland ice sheets the present day signal due to the late pleistocene glacial cycles dominates the signal from meier s sources at all degrees except 3 in contrast the signal arising from mass variations in the antarctic and greenland ice sheets is potentially comparable to the former a comparison of observational constraints on the data with predictions of the postglacial rebound signal described in this paper in order to infer mantle rheology cannot proceed until constraints are placed on the present day mass flux of these large polar ice sheets we show that the constraints required are weakest at degrees 2 and 4 finally we outline a potentially important procedure for incorporating predictions of the signal due to the late pleistocene glacial cycles and meier s sources with an observational constraint on the datum to yield bounds on the present day net mass flux from the antarctic and greenland ice sheets a rigorous application of this procedure must wait until observational constraints on are reestablished in the literature

azimuthal dependence in the gravity field induced by recent and past cryospheric forcings present day glacial activities and the current variability of the antarctic ice volume can cause variations in the long wavelength gravity field as a consequence of transient viscoelastic responses in the mantle we study the azimuthal dependence of the secular variations of the gravitational potential and find that the non axisymmetric contributions are more important for recent glacial retreats than for pleistocene deglaciation changes in land based ice covering antarctica can be detected by monitoring satellite orbits and their sensitivity to variations in gravitational harmonic for degree l greater than 3 resonances in satellite orbits may be useful for detecting these azimuthally dependent gravity signals

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

on transient rheology and glacial isostasy theoretical predictions from analytical self gravitating layered earth models with maxwell burgers body and standard linear solid rheologies are employed to explore the extent to which transient creep may have influenced the inference of long term mantle viscosity from analysis of the various signatures derived from the process of glacial isostatic adjustment the compatibility of the various models is checked by their ability to fit simultaneously the relative sea level free air gravity and the rotational data we conclude that transient creep cannot operate throughout the entire mantle on account of the extreme sensitivity of the uplift and gravity data to any significant departures of the steady upper mantle viscosity from 1021 pa s transient rheology would most likely be unimportant in the upper mantle restricting transient rheology to the lower mantle we find that models with an adiabatic density jump at 670 km depth are not satisfactory because of their inability to produce sufficiently large gravity anomalies and polar wander speeds our calculations show that the preferred models with transient creep in the lower mantle are chemically stratified with a nonadiabatic density change of around 10 the long term viscosities in the lower mantle associated with compatible transient rheological models lie between 5 1022 and 1023 pa s these values are consistent with viscosity estimates derived from correlation of long wavelength geoid anomalies and the density perturbations in the deep mantle

multi scalar controls on channel geometry of headwater streams in new zealand hill country abstract catchment reach and local scale controls upon channel geometry are examined for small headwater streams in adjacent sub catchments with variable land use histories in a typical hill country area of the north island of new zealand although systematic downstream increase in channel cross sectional area is evident in one sub catchment a result of catchment scale controls on geometry including discharge and slope marked local variability in channel geometry in the two other sub catchments reflects non systematic patterns of reach scale controls including the distribution of floodplain pockets and associated bank materials and local scale controls such as bedrock outcrops and wood land use change exerts a primary control upon these relationships for a given catchment area streams in native forest are wider and shallower than streams that flow within pasture or pinus plantations increased hillslope erosion following land clearance has instigated the accumulation of post settlement alluvium psa which has altered the boundary conditions and bank materials within which streams flow significant psa accumulation following native forest clearance in one of the sub catchments has allowed the stream to flow entirely within its own alluvial deposits in this instance catchment scale controls on channel geometry are dominant in contrast local scale controls on channel geometry are more important in the other sub catchments where lesser accumulation of psa reflects differences in land clearance these findings indicate that place based understandings which consider the spatial and historical contexts of landscape settings are required to interpret patterns of channel geometry and to inform river rehabilitation initiatives

the response of slope and channel systems to various types of extreme rainfall a comparison between the temperate zone and humid tropics abstract the mountain slopes and river channels of the temperate zone and of the humid tropics are modelled by various types of extreme rainfall in the flysch carpathians the leading role is played by continuous rains causing floods and landslides rainy seasons wet years mobilizing deep landslides and to a smaller degree by local downpours in the darjeeling himalaya with young relief and uplift tendency the main influence on modelling the mountain slopes and river channels have been the extreme continuous rains separated by several decades of normal rainy season playing the preparatory or relaxation role with simultaneous transformation of slopes and river channels in both cases human impact has caused the acceleration of runoff and mobilization of sediment the higher extremes of precipitation and steep slopes in the humid tropics are balanced to some extent in temperate zones by the lower infiltration rates and lower thresholds of mass mobility on the gentle slopes originated in the periglacial environment

the effects of deforestation on slope and channel evolution in the tectonically active darjeeling himalaya the main indicators of quaternary tectonic uplift are the young mountain slopes of the darjeeling himalaya rising straight above the ganga brahmaputra foredeep fragments of uplifted river terraces and fresh fault scarps evidence for the continuation of the uplift includes downcutting of the tista and other straight rivers in the bedrock continuing aggradation in the plains and overriding of the metamorphic rocks on the alluvia owing to deforestation and extensive land use the earlier natural tendency of a dominance of channel incision over slope degradation has changed to prevailing aggradation even in steep valley reaches caused by intensive slope mass movements and the overloading of the mountain creeks aggradation progresses upstream along the rivers dissecting the mountain front

present day secular variations in the low degree harmonics of the geopotential sensitivity analysis on spherically symmetric earth models 1 we predict present day rates of change of the long wavelength components of the earth s geopotential due to the late pleistocene glacial cycles hereinafter referred to as glacial isostatic adjustment or gia these predictions are generated using spherically symmetric self gravitating maxwell viscoelastic earth models previous studies have generally considered only zonal i e azimuthally independent harmonics or the so called coefficients we extend these efforts to focus on the nonzonal harmonics and explore the sensitivity of our predictions to changes in a variety of model inputs as an example we examine the influence on the gia predictions of ignoring rotational perturbations and assuming an elastically incompressible model and find that these assumptions can have a significant impact on the degree 2 order 1 coefficients while the other harmonics are generally affected by 10 though the gia predictions are generally insensitive to variations in lithospheric thickness and upper mantle viscosity reasonable variations in either lower mantle viscosity or the late pleistocene ice history will have a more significant effect mindful of upcoming dedicated gravity missions we show that predictions of the gia induced changes of the geoid can vary by at least 0 5 mm yr 1 over a plausible range of earth and ice models

polar wandering and the forced responses of a rotating multilayered viscoelastic planet changes in the earth s rotation produced by the waxing and waning of large mobile ice sheets can be used to infer the viscosity of the mantle from a comparison with the recent secular polar drift as revealed in the international latitude service data and also in the estimates of the nontidal acceleration of the length of the day we have developed by using an analytical approach a physical model of a rotating earth consisting of an elastic lithosphere a viscoelastic mantle and an inviscid core forcings from the two major ice sheets laurentide and fennoscandia have been considered sensitivity analysis of the parameters governing the external forcings such as the length and the time of termination of the deglaciation phase show in general that there exist two families of mean mantle viscosities 0 1022 p and 0 1023 p which can match the data satisfactorily however we find it an improvement to incorporate some amount of shrinkage from the antarctic ice sheet obtaining simultaneously a better fit with the two rotational data sets to the lower viscosity solutions hence forcings from the southern hemisphere may be able to remove the ambiguity associated with the extraction of mantle viscosity from rotational data we have also solved the initial value problem of the components of instantaneous angular velocity by means of the laplace transform for applied loads characterizing the continental ice sheets which since the mid pliocene have periodically expanded and contracted over the northern hemisphere in consequence of this continual forcing polar wander of around 5 10 degrees can take place for a mean mantle viscosity 0 1022 p recent reanalysis of paleomagnetic data in conjunction with hot spot tracks have revealed that several degrees of true polar wander could have occurred in the last 5 m y these calculations thus provide a physical explanation for the observed movement of the rotation axis membrane stresses of 0 10 bars can develop from this secular polar motion

channel response to increased and decreased bedload supply from land use change contrasts between two catchments abstract the catchments of pine creek idaho usa 200 km 2 and the drome river in the drome department france 1640 km 2 illustrate contrasting changes in land use bedload sediment production and channel response hard rock mining began in the catchment of pine creek near the end of the 19th century and together with road construction timber harvest and historically heavy grazing of uplands resulted in increased tributary bedload yield increased bedload migrating to the channel combined with removal of large cedar trees on the floodplain resulted in channel instability which propagated downstream over a period of decades on many reaches of pine creek active channel width has increased by over 50 since 1933 over roughly the same time period the drome river catchment was extensively reforested after at least one century of denudation and heavy grazing and numerous check dams were constructed on torrents to reduce erosion as a result the drome river has experienced a reduction in bedload sediment supply since the late 19th century in addition gravel has been extracted from some reaches consequently the channel has degraded and gravel bars have been colonized with woody riparian vegetation channel widths in wide braided reaches decreased from 1947 to 1970 by 60 on pine creek channel instability has resulted in bank erosion exposing contaminated mine tailings and increased flood hazard on the drome river degradation has undermined bridges and embankments and lowered the water table in areas dependent on groundwater for irrigation resulting in loss of 6 million m 3 of groundwater storage since 1960 though they differ in drainage area by nearly an order of magnitude pine creek and the drome river provide an excellent contrast in that they represent two sides of an epicycle of alluvial sedimentation set off in each case by land disturbance in both cases the most recent channel changes though in opposite directions were viewed as negative by river managers on pine creek managers have removed or protected from erosion mine tailings and have attempted to train the stream into a more stable channel and most rock waste piles the principal sediment sources have recently been controlled on the drome river managers have prohibited gravel mining and adopted new policies to permit coarse sediment to migrate through the river system

perturbations of the earth s rotation and their implications for the present day mass balance of both polar ice caps summary the present day perturbations of the earth s rotation are sensitive to the glacial isostatic adjustment gia arising from the late pleistocene glacial cycles and also to the recent mass balance of polar ice caps in this study we evaluate the polar wander and the change of degreetwo harmonic of the earth s geopotential j 2 proportional to the rotation rate for four late pleistocene ice models we examine these perturbations as a function of lower and uppermantle viscosities and lithospheric thickness and rheology elastic or viscoelastic in which a compressible earth model with elasticity and density given by the seismological model prem is used by considering the observations and predictions including the gia process arising from the late pleistocene ice and recent mass balance of polar ice caps we discuss the recent mass balance of the antarctic and greenland ice sheets we also examine the effects of internal processes and the melting of mountain glaciers although this work is only preliminary the results shown below seem to be supported even if these effects are included two solutions are obtained for source areas of the recent antarctic melting we denote an equivalent sea level esl rise mm yr 1 from the greenland and antarctic ice sheets as gl and