a seismic reflection study of northern baffin bay implication for tectonic evolution reflection profiles offshore of baffin island south of lancaster sound reveal coast parallel half grabens containing flat lying sedimentary sections typical of a rifted margin in northernmost baffin bay adjacent to devon and southern ellesmere islands four sedimentary basins are identified in these basins the sedimentary sections are faulted folded and laterally discontinuous the basement shows linear trends steep faults and abrupt variations in depth in one basin a 50 km long and 10 km wide flower structure is observed a transpressive tectonic regime is suggested to explain the uplifted sedimentary and basement section and the change in depth to basement across it a 150 km long paleoshelf buried by a thickening sedimentary wedge is present offshore of devon island because strike slip and compressional features are observed on seismic profiles north of lancaster sound and extensional features are observed to the south differences in the plate tectonic development are inferred the inte

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

petrology of serra geral parana continental flood basalts southern brazil crustal contamination source material and south atlantic magmatism the serra geral parana continental flood basalt sg cfb province in brazil is associated with the jurassic cretaceous breakup of gondwanaland and the transition of continental to oceanic magmatism during the opening of the south atlantic ocean a suite of 24 samples representative of the sg cfb in rio grande do sul southern brazil shows a compositional continuum from basalt 50 53 wt sio2 mg 60 45 to basaltic andesite to andesite rhyodacite and rhyolite 73 wt sio2 certain compositional aspects of the mafic rocks e g tio2 k2o cao zr nb zr y ti zr resemble those of basaltic dikes and flows associated with the opening of the north atlantic ocean

mapping and facies analysis of paleocene mid eocene seismic sequences offshore southern west greenland abstract new interpretations are reported of the sedimentology and sequence stratigraphy of the palaeogene sediments encountered by the boreholes hellefisk 1 ikermiut 1 kang miut 1 nukik 1 and nukik 2 offshore southern west greenland these interpretations together with new biostratigraphic and palaeoenvironmental interpretations have been used to correlate the boreholes and to calibrate seismic sequences interpreted on a grid of reflection seismic data the interpreted seismic sequences lie between major regional unconformities of danian and mid eocene age the new interpretations show that the area offshore southern west greenland was subject to major uplift and erosion during the danian when latest cretaceous sediments were removed sedimentation restarted in the late danian coevally with major volcanism in central west greenland and the start of sea floor spreading in the labrador sea late paleocene sediments were deposited in a predominantly extensional tectonic environment the extensional stresses continued in most areas during the early eocene but in the northern and northwestern part of the basins a transtensional system developed along the strike slip faults that transferred sea floor spreading movements between the labrador sea and baffin bay sediment input to the basins was predominantly from the north possibly from a major river system flowing out of central greenland lesser amounts of sediment came from the east from the mainland of greenland and minor amounts from the west the thickness of total sediment decreases substantially from north to south the sediments were deposited in environments that ranged from fresh water marginal marine to upper bathyal proximal environments are probably generally sand prone but distal environments probably contain larger amounts of mud some of which could contain a mature source rock for oil basin floor fans syn tectonic wedges and turbidite channel complexes that could act as hydrocarbon reservoirs sealed by surrounding muds have been identified in many of the seismic sequences

rainfall intensity duration threshold and erosion competence of debris flows in four areas affected by the 2008 wenchuan earthquake abstract debris flows in the wenchuan seismic region have caused human casualties and severe damage to local infrastructure consequently the triggering rainfall threshold and erosion capability of post quake debris flows has become an important research topic worldwide in this study we analyze five years of rainstorms and debris flow data from four typical earthquake hit regions in order to examine the local rainfall intensity duration i d thresholds and debris supply conditions it was found that debris flow events in the four seismic areas exhibited different i d thresholds related to local mean annual hourly precipitation and debris flow supply conditions the i d thresholds normalized by mean annual maximum hourly rainfall illustrate that post quake rainfall thresholds were reduced by at least 30 compared to pre quake levels regression analysis revealed a clear linear relationship between the debris supply condition and the empirical coefficient of the i d equation this means that rainfall thresholds of post quake debris flows in different areas are distinctive and are strongly affected by sediment volume different relationships between the entrainment rate and the debris volume per watershed area and its product with the channel gradient illustrate that stream sediments in yingxiu and dujiangyan are more eroded and that local debris flows might persist over a shorter time than in qingping and beichuan in the future finally debris flows in the studied area exhibit no tendency of reduction in erosion competence entrainment rate as found in taiwan which might be indicative of a higher entrainment rate persisting for a longer time

a full coverage high resolution topographic model of greenland computed from a variety of digital elevation data in this paper a new high resolution elevation model of greenland including the ice sheet as well as the ice free regions is presented it is the first published full coverage model computed with an average resolution of 2 km and providing an unprecedented degree of detail the topography is modeled from a wide selection of data sources including satellite radar altimetry from geosat and ers 1 airborne radar altimetry and airborne laser altimetry over the ice sheet and photogrammetric and manual map scannings in the ice free region the ice sheet model accuracy is evaluated by omitting airborne laser data from the analysis and treating them as ground truth observations the mean accuracy of the ice sheet elevations is estimated to be 12 13 m and it is found that on surfaces of a slope between 0 2 and 0 8 corresponding to approximately 50 of the ice sheet the model presents a 40 improvement over models based on satellite altimetry alone on coastal bedrock the model is compared with stereo triangulated reference points and it is found that the model accuracy is of the order of 25 35 m in areas covered by stereo photogrammetry scannings and between 200 and 250 m elsewhere

geomorphic constraints on surface uplift exhumation and plateau growth in the red river region yunnan province china field observations digital elevation model dem data and longitudinal profi le analysis reveal a perched low relief upland landscape in the red river region yunnan province china which correlates to an uplifted regional low relief landscape preserved over the eastern margin of the tibetan plateau as with other major rivers of the plateau margin the red river has deeply incised the lowrelief upland landscape which we interpret to be the remnants of a pre uplift or relict landscape we examine longitudinal river profi les for 97 tributaries of the red river most profi les consist of three segments separated by sharp knickpoints an upper lowgradient channel segment a steeper middle channel segment and a very steep lower channel segment upper channel segments correspond to the relict landscape and have not yet experienced river incision steeper middle and lower segments indicate onset of rapid two phase river incision on the basis of which changes in external forcings such as climate or uplift can be inferred in terms of two end member scenarios two phase incision could be the result of pulsed plateau growth in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth reconstruction of the paleo red river indicates 1400 m river incision 1400 1500 m surface uplift and a maximum of 750 m vertical displacement across the northern red river fault elevating the northern ailao shan range above the surrounding relict landscape on the basis of stratigraphic constraints incision along the red river likely began in pliocene time

impact of chi chi earthquake on the occurrence of landslides and debris flows example from the chenyulan river watershed nantou taiwan abstract the chenyulan river watershed in central taiwan was chosen for evaluating the impact of the chi chi earthquake on the occurrence of landslides and for exploring the initial conditions triggering debris flows interpretations of aerial photographs and spot images as well as field investigations were used to identify landslide and debris flow occurrences precipitation data were then utilized to investigate critical conditions leading to the debris flow comparison of five spot images taken between june 1996 before the july 1996 typhoon herb and september 1999 before the chi chi earthquake shows that the landslide area increased from 7 1 106 to 7 5 106 m2 during that time however by january 2000 after the chi chi earthquake the landslide area almost tripled to 20 8 106 m2 measurement of images taken in march and august 2001 reveals that the landslide area had further expanded to 24 2 106 and 27 5 106 m2 respectively significant differences before and after the earthquake are also noticed in 1 the intensity and amount of precipitation required for triggering debris flow 2 the size of contributing drainage basin in which debris flows occurred and 3 the frequency of debris flows after the chi chi earthquake maximum hourly rainfall intensity and critical accumulated precipitation necessary to initiate debris flow reduced to as low as 1 3 of the pre earthquake figures prior to the chi chi earthquake most debris flows occurred in gullies with slopes greater than 10 and in drainage basins larger than 0 1 km2 conversely after the earthquake debris flows were observed even in gullies with effective drainage area smaller than 0 03 km2 furthermore before the earthquake the debris flow recurrence time in the study area was greater than 5 years whereas six debris flow events have been observed in the 2 years since the earthquake

crustal origin for the parana rhyolites discussion of description and petrogenesis of the parana rhyolites southern brazil by garland et al 1995 our criticisms of the garland et al 1995 paper are introduction three fold and concern 1 the interpretation of oxygen the south atlantic ocean divides what was once a single isotope data on the rhyolites 2 radiogenic isotope large igneous province into the larger parana flood basalt fingerprinting of potential source material 3 the major province of south america and the smaller etendeka element composition of melts produced from potential flood basalt province of namibia the term flood basalt sources in the lower crust province is in this case something of a misnomer because a substantial thickness of silicic volcanic rocks is preserved on both sides of the atlantic the parana rhyolites can be divided into two main types the chapeco high ti oxygen isotopes type which have a high concentration of high field one of the problems of using oxygen isotopes to solve strength elements and low sr isotope ratios sr sr at problems of magma genesis is that oxygen isotope ratios 130 ma 0 705 0 708 and the palmas low ti type are changed during low temperature alteration processes which has lower concentrations of high field strength it is well known that large shifts in do value can occur elements and elevated sr isotope ratios sr sr at 130 in glassy volcanic rocks such as the parana rhyolites e g ma 0 714 0 727 mantovani et al 1985 bellieni et al taylor 1968 cerling et al 1985 these problems can 1986 peate et al 1992 garland et al 1995 suggested be circumvented by analysing fresh phenocrysts such as that the former were produced by partial melting of pyroxene which are unaffected by the alteration process high ti parana basalts whereas the more voluminous harris et al 1990 used the pyroxene do values to palmas rhyolites were produced by prolonged asestimate the magma do values of the palmas low ti similation accompanying crystal fractionation of low ti type rhyolite of the parana to be between 10 1 and parana basalt magmas previous workers have suggested 10 7 with the equivalent low ti magma type in the that the palmas type rhyolites are derived from melting etendeka having do values between 9 7 and 11 2 of pre mesozoic middle to lower crust piccirillo et al these high values led harris et al 1990 to suggest an 1988 harris et al 1990 and we believe that garland et origin by crustal melting al 1995 have overlooked several important lines of garland et al 1995 acknowledged the high do evidence in rejecting the crustal melting hypothesis in values and went on to state that the high do values this comment we will draw on data from the etendeka were used by harris et al 1990 to invoke an entirely province of namibia which was once part of the same crustal origin but it has been argued elsewhere that post eruptive alteration can lead to an increase in do continental flood basalt province

topographical and geological variation of effective rainfall for debris flow occurrence from a large scale perspective abstract understanding the spatial heterogeneity of the debris flow rainfall threshold is meaningful for regional warning systems however regional topographical and geological impacts have not been well quantified using the hengduan mountains with distinct climatic topographical and geological settings as a typical study area this study focused on the geological and topographical variations of effective rainfall for debris flow occurrence from a large scale perspective results showed that the probability of debris flow occurrence was smallest in the cold arid zone and largest in the humid zone the mean dimensionless effective rainfall the ratio of effective rainfall to mean annual precipitation was about 5 2 for an initial warning and 7 7 for serious warnings the contributions to the differences are regional climate geomorphology and geology in sequence of importance the zone with more complex terrain thicker soil and higher sand content would be more beneficial to debris flow formation multiple regression analysis suggested that the geologically related aspects may have a slightly greater effect than topographical factors on effective rainfall in general this work could be in favor of other similar regional national and even global work for debris flow early warning

sequence of instability processes triggered by heavy rainfall in the northern italy abstract northern italy is a geomorphologically heterogeneous region high mountains wide valleys gentle hills and a large plain form a very varied landscape and influence the temperate climate of the area the alps region has harsh winters and moderately warm summers with abundant rainfall the po plain has harsh winters with long periods of subfreezing temperatures and warm sultry summers with rainfall more common in winter geomorphic instability processes are very common almost every year landslides mud flows and debris flows in the alpine areas and flooding in the po flood plain cause severe damage to structures and infrastructure and often claim human lives analyses of major events that have struck northern italy over the last 35 years have provided numerous useful data for the recognition of various rainfall triggering processes and their sequence of development in relation to the intensity and duration of rainfall findings acquired during and after these events emphasise that the quantity and typology of instability processes triggered by rainfall are related not only to an area s morphological and geological characteristics but also to intense rainfall distribution during meteorological disturbances moreover critical rainfall thresholds can vary from place to place in relation to the climatic and geomorphological conditions of the area once the threshold has been exceeded which is about 10 of the local mean annual rainfall mar the instability processes on the slopes and along the hydrographic networks follow a sequence that can be reconstructed in three different phases in the first phase the initial instability processes that can usually be observed are soil slips on steep slopes mud debris flows in small basins of less than 20 km2 in area while discharge increases substantially in larger stream basins of up to 500 km2 in continuous precipitation in the second phase first mud debris flows can be triggered also in basins larger than 20 km2 in area tributaries swell the main stream which is already in a critical condition the violent flow causes severe problems mainly along valley bottoms of rivers with basins up to 2000 km2 in area first bedrock landslides can occur reaching a considerable area density with volumes from a few hundred up to about one to two million cubic meters in continuous precipitation in the third phase basins of more than 2000 km2 in area reach their first critical stage river bed morphology is extensively modified with erosional and depositional processes which can locally undermine the stability of structures and infrastructures waters overflow levees flooding villages and towns to various widths and depths and sometimes claiming casualties some days after an intense rainfall period large landslides involving the bedrock can still take place these processes usually cause the movement of very large rock masses the total duration of rainfall usually has a greater effect on these landslides than does the number of short periods of very intensive precipitation this sequence cannot be divided into separate phases when the events occur simultaneously because of the presence of intense rainfall pulses and the generation of very diffuse surface runoff such situations usually happen during short lasting heavy summer rainstorms or in late spring when snow melt combines with intense rainfall the three phase sequence has been identified in three severe events that are analysed in this paper valtellina lombardy in 1987 tanaro valley piedmont in 1994 and aosta valley in 2000 but this sequence has also been observed during other events that occurred in northern italy in piedmont in 1968 1977 1978 1993 and 2000 in lombardy in 1983 and 1992 in the aosta valley in 1993

the role of debris supply conditions in predicting debris flow activity debris flow frequency and magnitude were determined for 33 basins in southwest british columbia basins were first classifiedaseitherweathering limitedortransport limitedusingadiscriminantfunctionbasedondebris contributingarea an area weighted terrain stability number and drainage density multiple regression was used to predict magnitude peak discharge frequency and activity frequency times magnitude within each group of basins model performance was improved by stratifying the total sample of debris flow basins into weathering and transport limited groups explained varianceincreasedbyanaverageof15percentinthetransport limitedsample indicatingthatsedimentsupplyconditionsin themoreactivebasinsarefundamentalinpredictingdebrisflowactivity anindependenttestoftheregressionmodelswith 11basinsyieldedgenerallygoodresultsfordebrisflowmagnitudeandpeakdischarge predictionofdebrisflowfrequency provedproblematicalinweathering limitedbasins themethodsdevelopedhereprovideestimatesofdebrisflowattributes in basins for which few data on past events are available copyright 1999 john wiley sons ltd

the loch scridain xenolithic sill complex isle of mull scotland fractional crystallization assimilation magma mixing and crustal anatexis in subvolcanic conduits

statistical approaches for the definition of landslide rainfall thresholds and their uncertainty using rain gauge and satellite data abstract models for forecasting rainfall induced landslides are mostly based on the identification of empirical rainfall thresholds obtained exploiting rain gauge data despite their increased availability satellite rainfall estimates are scarcely used for this purpose satellite data should be useful in ungauged and remote areas or should provide a significant spatial and temporal reference in gauged areas in this paper the analysis of the reliability of rainfall thresholds based on rainfall remote sensed and rain gauge data for the prediction of landslide occurrence is carried out to date the estimation of the uncertainty associated with the empirical rainfall thresholds is mostly based on a bootstrap resampling of the rainfall duration and the cumulated event rainfall pairs d e characterizing rainfall events responsible for past failures this estimation does not consider the measurement uncertainty associated with d and e in the paper we propose i a new automated procedure to reconstruct ed conditions responsible for the landslide triggering and their uncertainties and ii three new methods to identify rainfall threshold for the possible landslide occurrence exploiting rain gauge and satellite data in particular the proposed methods are based on least square ls quantile regression qr and nonlinear least square nls statistical approaches we applied the new procedure and methods to define empirical rainfall thresholds and their associated uncertainties in the umbria region central italy using both rain gauge measurements and satellite estimates we finally validated the thresholds and tested the effectiveness of the different threshold definition methods with independent landslide information the nls method among the others performed better in calculating thresholds in the full range of rainfall durations we found that the thresholds obtained from satellite data are lower than those obtained from rain gauge measurements this is in agreement with the literature where satellite rainfall data underestimate the ground rainfall registered by rain gauges

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

the power law relationship between landslide occurrence and rainfall level article i nfo article history zhejiang province is highly prone to the occurrence of landslides during the annual rainy season from may to september we studied the relationship between landslide frequency and rainfall level based on 1414 shallow landslides that have detailed records on the location the date of occurrence and the corresponding daily rainfall data from 1257 rain gauges during the 1990 2003 period in the region cumulative rainfall levels were examined for the periods from the failure day to the prior 10 days the results show that the cumulative frequency of the landslide occurrence correlates well with the landslide triggering rainfall and that their relationship can be described using two power law relations with different scaling exponents for two different ranges of the rainfall level the rainfall level corresponding to the intersection point of two fitted correlation lines can be defined as the upper bound for shallow landslide triggering cumulative rainfall threshold thcr a large number of shallow landslides may be induced when the amount of cumulative rainfall reaches the thcr value the 814 landslides that occurred from 2004 to 2007 in the region are used to examine the method which shows that about 80 of these landslides are induced when the cumulative 1 day rainfall is 200 mm we suggest that the power law relationship between rainfall level and landslide occurrence can be used to estimate the probability of various levels of landslide activity during a rainfall event as a guide for making decisions related to emergency preparedness

subglacial preservation of valley morphology at amundsenisen western dronning maud land antarctica on the high altitude polar plateau of amundsenisen western dronning maud land east antarctica a subglacial valley with a broad horizontal valley floor interpreted as a sediment floodplain or valley delta was studied by radio echo sounding in addition a small probably glacial valley was mapped within the same subglacial massif basal ice temperatures were calculated using field data on precipitation air temperature and ice sheet thickness discoveries of old landforms which have been preserved more or less intact beneath the former fennoscandian and laurentide ice sheets have received increasing attention during the last decade the aim of this study is to investigate whether preservation of landforms occurs under the east antarctic ice sheet and to discuss under that climatological and glaciological circumstances preservation may take place the results show that the ice sheet covering the investigated localities is frozen to bed and therefore has an insignificant erosional capability the observations suggest that a large scale subglacial sediment deposit and a small valley formed by glacial erosion have survived beneath a cold based ice sheet marginal zone for a long time period the process of glacial preservation recognized for bedrock features and tentatively observed for sediment accumulations should act on similar large scale landforms under any cold based ice sheet present or past on the basis of existing studies of the age and stability of the east antarctic ice sheet a middle pliocene age is suggested for the preserved landforms the presence of the presumed sediment filled valley further indicates that no prolonged periods of basal melting have occurred at the amundsenisen study area during the ice sheet history which includes the quaternary glaciation periods finally calculations of basal temperature for localities at different altitudes within the same subglacial massif were used to demonstrate local altitudinal control of glacial preservation 1997 by john wiley sons ltd

calibration and validation of rainfall thresholds for shallow landslide forecasting in sicily southern italy abstract empirical rainfall thresholds are tools to forecast the possible occurrence of rainfall induced shallow landslides accurate prediction of landslide occurrence requires reliable thresholds which need to be properly validated before their use in operational warning systems we exploited a catalogue of 200 rainfall conditions that have resulted in at least 223 shallow landslides in sicily southern italy in the 11 year period 2002 2011 to determine regional event duration cumulated event rainfall ed thresholds for shallow landslide occurrence we computed ed thresholds for different exceedance probability levels and determined the uncertainty associated to the thresholds using a consolidated bootstrap nonparametric technique we further determined subregional thresholds and we studied the role of lithology and seasonal periods in the initiation of shallow landslides in sicily next we validated the regional rainfall thresholds using 29 rainfall conditions that have resulted in 42 shallow landslides in sicily in 2012 we based the validation on contingency tables skill scores and a receiver operating characteristic roc analysis for thresholds at different exceedance probability levels from 1 to 50 validation of rainfall thresholds is hampered by lack of information on landslide occurrence therefore we considered the effects of variations in the contingencies and the skill scores caused by lack of information based on the results obtained we propose a general methodology for the objective identification of a threshold that provides an optimal balance between maximization of correct predictions and minimization of incorrect predictions including missed and false alarms we expect that the methodology will increase the reliability of rainfall thresholds fostering the operational use of validated rainfall thresholds in operational early warning system for regional shallow landslide forecasting

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

cenozoic uplift of nuussuaq and disko west greenland elevated erosion surfaces as uplift markers of a passive margin remnants of a high plateau have been identified on nuussuaq and disko central west greenland we interpret the plateau as an erosion surface the summit erosion surface formed mainly by a fluvial

landslides triggered by the 20 april 2013 lushan earthquake sichuan province china abstract the 20 april 2013 lushan earthquake with a magnitude of m s 7 0 induced widespread landsliding along the southern segment of the longmen shan fault zone this paper presents a preliminary analysis of the characteristics of these co seismic landslides triggered in an area of 13 323 km 2 a total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the lushan earthquake to facilitate the more detailed analysis on the areal frequency of co seismic landslides as polygons we selected an area of 732 km 2 around the epicenter that had the highest density of co seismic landslides the sizes of the landslides are in general much smaller than those that were triggered by the 2008 wenchuan earthquake the most common types of landslides in the study area were rock falls and shallow disrupted landslides from steep slopes which typically involved the top few meters of weathered bedrock and colluvium in this study the relation between the landslide distribution and five main factors was analyzed fault proximity epicenter proximity peak ground acceleration pga slope angle and lithology our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault and the highest landslide concentration is located within a distance of 5 km regarding the distance to the epicenter the largest landslide density is found at a distance between 5 and 10 km the landslide concentration also increases with increasing slope angle until a maximum for the slope class 45 55 in addition results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co seismic landslides in this study we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution this is in contradiction to what has been reported in other earthquake areas such as the wenchuan area

a deep seismic reflection profile across the extinct mid labrador sea spreading center in 1990 a deep multichannel seismic reflection line was shot along a flow line across the labrador sea the results from the central portion of this line between magnetic anomalies 25 and across the extinct central ridge are described here spreading rates in this part of the labrador sea are very low from 10 mm yr to less than 3 mm yr so that the line provides a unique opportunity to examine the relationship between very slow spreading and crustal structure a clear division is observed between two types of crust the oldest crust between dirons 21 and 25 which formed at a mean half spreading rate of 10 mm yr exhibits smoothly undulating basement with only minor normal faulting this region shares many of the reflection characteristics of north atlantic crust formed at moderate to low spreading rates in contrast the younger central region between chrons 21 and 13 which formed at a mean half spreading rate of 3 mm yr displays evidence of intense normal faulting of the crust giving a total extension of about 70 inward facing normal faults on both sides of the extinct ridge with large offsets many of which extend to lower crust or moho depths dominate the seismic section the axial region is characterized by a deep fault bounded median valley these results suggest that mechanical extension plays a more important role in seafloor spreading at low spreading rates than previously documented integration of the reflection data with previous refraction measurements and with gravity modeling of the region shows variations in crustal thickness which can be correlated with spreading rates the region formed at a mean spreading rate of 10 mm yr where about 15 extension is observed exhibits slightly thinner than normal crust 4 8 km or less versus a normal thickness of about 7 km at a lower spreading rate of 3 mm yr across the axial region where extension is about 70 an average crustal thickness of 3 km is obtained thus lower spreading rates are associated with regions of thinner crust and greater amounts of extension while many studies suggest that thin crust at slow spreading rates may result from a reduced magma supply this study suggests that extension is at least equally important and may be responsible for most of the variations in crustal thickness the increased cooling of young oceanic lithosphere formed at these very low spreading rates approximately 3 mm yr may have amplified brittle failure in response to plate separation however the timing of extension is still uncertain and some of it may be related to postextinction tectonics and not to the spreading process the role of extension as a control on crustal thickness needs to be considered further in studies of crustal generation and magmatism at slow spreading ridges extension will decrease the importance of magmatism in generating thin oceanic crust and will favor models of magmatic processes which produce thicker crust

regionalization of rainfall thresholds an aid to landslide hazard evaluation rainfall soil properties and morphology are major factors controlling shallow landsliding a series of meteorological events that triggered soil slips in northern italy were studied to define rainfall thresholds and to evaluate a possible regionalization soil properties triggering rainfall and local lithological and morphometrical settings of different sites were used as input to an infiltration model the approach allows the recognition of several triggering conditions in the piedmont pre alpine and alpine regions this suggests the need for different rainfall thresholds with respect to those derived with other methods intensity versus rainfall duration relationships become particularly important when related to soil permeability and thickness and demonstrate the role of antecedent precipitation events with exceptional water discharge from obstructed road culverts reveal the role played by anthropic structures in triggering such phenomena different approaches to slope stability analysis are shown taking into account bedrock lithology topography seepage and local saturation conditions

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

a warning system for rainfall induced shallow failures abstract it is widely recognised that soil slips and debris flows are triggered by short intense storms owing its geologic geomorphologic and climatic settings the piedmont region nw italy is highly prone to the occurrence of this kind of landslides in the last two centuries in fact a total of 105 severe meteoric events which triggered shallow failures occurred and of these 18 events took place from 1990 to 2002 a fair number of rainfall thresholds have been proposed in the literature defined both on empirical or on physical bases empirical thresholds are defined collecting rainfall data for landslide meteoric events and for events without landslides while physical thresholds are based on numerical models that consider the relation between rainfall pore pressure and slope stability the main objective of this paper is the identification of the empirical triggering thresholds for the piedmont region four meteoric events were selected and analysed november 4 5 1994 july 7 8 1996 april 27 30 2000 october 13 16 2000 because they supply a wide range of variation for both rainfall parameters duration intensity cumulative rainfalls and the number of induced landslides in the intensity duration plot the critical limit is described by the equation i 19d 0 50 where i rainfall intensity expressed in mm h and d rainfall duration expressed in hours such a limit is traced to envelop 90 of the points on the graph in the ni d diagram the triggering thresholds are given by the equations ni 0 76d 0 33 and ni 4 62d 0 79 where ni normalised intensity with respect to the annual precipitation map expressed in mm h pma 100 in the article the different meaning of these thresholds is discussed finally the diagram ni ncr is proposed the triggering threshold is given by the expression ni 0 09ln ncr 0 54 where ncr is the normalised cumulative critical rainfall mm pma 100 the application of the triggering thresholds as a fundamental element in a warning system dedicated to the safeguarding of population in landslide prone areas is discussed in detail an operating procedure which is presently being verified and tested in the studied area is described

rainfall thresholds for possible landslide occurrence in italy abstract the large physiographic variability and the abundance of landslide and rainfall data make italy an ideal site to investigate variations in the rainfall conditions that can result in rainfall induced landslides we used landslide information obtained from multiple sources and rainfall data captured by 2228 rain gauges to build a catalogue of 2309 rainfall events with mostly shallow landslides in italy between january 1996 and february 2014 for each rainfall event with landslides we reconstructed the rainfall history that presumably caused the slope failure and we determined the corresponding rainfall duration d in hours and cumulated event rainfall e in mm adopting a power law threshold model we determined cumulated event rainfall rainfall duration ed thresholds at 5 exceedance probability and their uncertainty we defined a new national threshold for italy and 26 regional thresholds for environmental subdivisions based on topography lithology land use land cover climate and meteorology and we used the thresholds to study the variations of the rainfall conditions that can result in landslides in different environments in italy we found that the national and the environmental thresholds cover a small part of the possible de domain the finding supports the use of empirical rainfall thresholds for landslide forecasting in italy but poses an empirical limitation to the possibility of defining thresholds for small geographical areas we observed differences between some of the thresholds with increasing mean annual precipitation map the thresholds become higher and steeper indicating that more rainfall is needed to trigger landslides where the map is high than where it is low this suggests that the landscape adjusts to the regional meteorological conditions we also observed that the thresholds are higher for stronger rocks and that forested areas require more rainfall than agricultural areas to initiate landslides finally we observed that a 20 exceedance probability national threshold was capable of predicting all the rainfall induced landslides with casualties between 1996 and 2014 and we suggest that this threshold can be used to forecast fatal rainfall induced landslides in italy we expect the method proposed in this work to define and compare the thresholds to have an impact on the definition of new rainfall thresholds for possible landslide occurrence in italy and elsewhere

crustal signatures in the serra geral flood basalt province southern brazil o and sr isotope evidence strontium and oxygen isotopes in igneous rocks from a 35 000 km 2 region of the serra geral parana continental flood basalt province southern brazil indicate that certain mantle derived magmas that formed during the rifting and breakup of gondwana incorporated continental crust sr o and trace element assimilation fractional crystallization models point to variable amounts and types of warm archean granulitic crust 18 o 11 15 and 87 sr 86 sr i 0 735 having contaminated ascending mafic magmas resulting products include evolved rocks basaltic andesite to rhyolite that have 18 o 11 to 15 and 87 sr 86 sr i 0 714 to 0 729 and basaltic rocks that have 18 o 8 to 10 and 87 sr 86 sr i 0 710

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

rainfall control of debris flow triggering in the real torrent southern french prealps abstract this paper investigates the occurrence of debris flow due to rainfall forcing in the real torrent a very active debris flow prone catchment in the southern french prealps the study is supported by a 4 year record of flow responses and rainfall events from three high frequency monitoring stations equipped with geophones flow stage sensors digital cameras and rain gauges measuring rainfall at 5 min intervals the classic method of rainfall intensity duration id threshold was used and a specific emphasis was placed on the objective identification of rainfall events as well as on the discrimination of flow responses observed above the id threshold the results show that parameters used to identify rainfall events significantly affect the id threshold and are likely to explain part of the threshold variability reported in the literature this is especially the case regarding the minimum duration of rain interruption mdri between two distinct rainfall events in the real torrent a 3 h mdri appears to be representative of the local rainfall regime a systematic increase in the id threshold with drainage area was also observed from the comparison of the three stations as well as from the compilation of data from experimental debris flow catchments a logistic regression used to separate flow responses above the id threshold revealed that the best predictors are the 5 min maximum rainfall intensity the 48 h antecedent rainfall the rainfall amount and the number of days elapsed since the end of winter used as a proxy of sediment supply this emphasizes the critical role played by short intense rainfall sequences that are only detectable using high time resolution rainfall records it also highlights the significant influence of antecedent conditions and the seasonal fluctuations of sediment supply

anomalous isotopic compositions of sr ar and o in the mesozoic diabase dikes of liberia west africa the mesozoic diabase dikes of liberia are tholeiites whose 87sr 86sr and 87rb 86sr ratios scatter widely on the rb sr isochron diagram the problem is attributed to differences in the initial 87sr 86sr ratios of these rocks which range from 0 70311 to 0 70792 assuming a uniform age of 186 ma for the dikes and using 87rb 1 42 10 11y 1 the range of values is similar to that observed in the mesozoic basalt flows and dikes of other gondwana continents

development of the continental margins of the labrador sea a review abstract the labrador sea is a small oceanic basin that developed when the north american and greenland plates separated an initial period of stretching in early cretaceous time formed sedimentary basins now preserved under the continental shelves and around the margins of the oceanic crust the basins subsided thermally during late cretaceous time and a second episode of tectonism took place during latest cretaceous and early paleocene time before the onset of sea floor spreading in mid paleocene time around the northern labrador sea davis strait and in southern baffin bay voluminous picrites and basalts were erupted at and shortly after the commencement of sea floor spreading volcanism occurred again in early eocene time at the same time as sea floor spreading commenced in the northern north atlantic farther southeast along the labrador and southern west greenland margins oceanic crust is separated from continental crust by highly stretched but non magmatic transition zones which developed before sea floor spreading a complex transform zone which developed during sea floor spreading in late paleocene and early eocene time separates continental and oceanic crust along the baffin island margin the greenland and labrador ocean continent transitions are asymmetric across the only available conjugate cross sections however a cross section through the labrador margin farther north resembles the greenland cross section in the conjugate pair more than it does the labrador cross section of this pair consideration of the geological history of the area suggests that the non magmatic transition zones may have formed by slow extension of a few millimetres per year through a period of 53 ma during cretaceous and early paleocene time

regional variations within the parana flood basalts southern brazil evidence for subcontinental mantle heterogeneity and crustal contamination abstract continental flood volcanism of the parana basin lower cretaceous is represented by two pyroxene tholeiitic basalts 90 vol the northern parana province npp is dominated by basalts high in tio2 and incompatible elements htib while the southern parana province spp is dominated by basalts low in tio2 and incompatible elements ltib npp basalts show relatively small variations of initial 120 ma 87 sr 86 sr r0 and 143 nd 144 nd nd ratios r0 0 7051 0 7062 and nd 0 5124 0 5125 respectively relative to those occurring in spp r0 0 7046 0 7120 and nd 0 5122 0 5128 respectively the latter basalts show significant positive correlations between r0 vs sio2 k2o rb and ba and negative correlations between r0 vs cr ni and mg value believed to be due to crustal granitic contamination in general the effects of contamination are pronounced in spp and tend to vanish towards npp 18o values range from 6 5 to 10 0 in the basalts from npp and spp and essentially reflect water magma interactions uncontaminated ltib and htib basalts from npp are isotopically distinct from the uncontaminated analogues from spp ltib r0 0 7055 vs 0 7046 nd 0 5124 vs 0 5128 respectively all chemical data consistently indicate distinct sources and a large scale mantle heterogeneity the npp mantle source is expected to have relatively high content of enriched components possibly related to small volume melts and metasomatic fluids tentatively the last stabilization age of the parana mantle heterogeneity is 0 5 1 0 ga old the existence of high and low tio2 basalt suites in both parana and karoo provinces in brazil and southern africa respectively indicates a large scale heterogeneity in the subcontinental mantle and suggests that basalt generation occurred in the lithospheric mantle

the age origin and tectonics of the grao para group and associated rocks serra dos carajas brazil archean continental volcanism and rifting the grao para group which is host to the large serra dos carajas fe deposits is located in the eastern part of the central brazil shield ssw of belem brazil it is composed of a lower sequence of metavolcanic rocks a middle sequence of iron formation carajas formation and an upper sequence of mixed metavolcanic and metasedimentary rocks the grao para group is overlain by an unnamed sedimentary dominantly sandstone unit and unconformably overlies the older xingu complex the lower metavolcanic sequence of the grao para in the region of the serra norte fe deposits is bimodal with dominant metabasalts metabasaltic andesites and metatrachyandesites and subordinate 10 15 metarhyolitic tuffs and flows most of the metavolcanic rocks are at low to medium metamorphic grade with more intense metamorphism and deformation along the northern contact with the xingu complex the thickness of the metavolcanic section is not known but may be 4 6 km the mafic metavolcanic rocks are enriched in rb ba and k with respect to oceanic basalts and basalts of greenstone belts and are relatively depleted in th sr ta ti and p the mafic rocks also show an enrichment in lrees with flat hree patterns the hrees are correlated with mg number u pb zircon analyses of the metarhyolites from the grao para group yield an age of 2758 39 ma rb sr wholerock analyses of the mafic rocks yield an isochron with an age of 2687 54 ma with an initial ratio of 0 7057 0 0010 the results indicate a late archean age of volcanism in the grao para group much older than previously thought rb sr results from the metarhyolites have been partially reset yielding an age 2497 62 ma sm nd analyses from the grao para metavolcanic rocks were too scattered to yield an isochron but nd values relative to chur at 2758 ma indicate values similar to depleted mantle at this time although with some scatter the trace element data and the sr and nd isotopic results from the mafic rocks are consistent with contamination of mantle derived melts by significant but variable amounts of diverse older continental crust the stratigraphy geochemical and isotopic compositions show that the grao para group originated on extending older continental crust during the archean an age terrane boundary must exist between this archean continental terrane and the apparently ensimatic early proterozoic greenstone belts of the northern amazonian craton similarities to other sequences e g the fortescue group australia suggest that similar tectonic settings were widespread at this time many major iron formations were deposited within these environments indicating significant iron formation development on sialic crust in the late archean u ph zircon analyses from the serra dos carajas granite which intrudes the unnamed sedimentary unit overlying the grao para group yield an age of 1820 49 ma in agreement with previous age determinations this age is similar to the ages for the uatuma supergroup volcanic and shallow plutonic rocks which occur throughout the amazonian craton

spatial estimation of debris flows triggering rainfall and its dependence on rainfall return period abstract forecasting the occurrence of debris flows is fundamental for issuing hazard warnings and often focuses on rainfall as a triggering agent and on the use of empirical rainfall thresholds based on rain gauge observations a recognized component of the uncertainty associated with the use of rainfall thresholds is related to the sampling of strongly varying rainfall variability with sparse rain gauge networks in this work we examine the spatial distribution of rainfall depth in areas up to 10 km from the debris flow initiation points as a function of return period and we exploit this information to analyze the errors expected in the estimation of debris flow triggering rainfall when rain gauge data are used in particular we investigate the impact of rain gauge density and of the use of different interpolation methods high resolution adjusted radar rainfall estimates representing the best available spatially distributed rainfall estimates at the debris flows initiation point and in the surrounding area are sampled by stochastically generated rain gauge networks characterized by varying densities debris flow triggering rainfall is estimated by means of three rainfall interpolation methods nearest neighbor inverse distance weighting and ordinary kriging on average triggering rainfall shows a local peak corresponding to the debris flow initiation point with a decay of rainfall with distance which increases with the return period of the triggering rainfall interpolation of the stochastically generated rain gauge measurements leads to an underestimation of the triggering rainfall that irrespective of the interpolation methods increases with the return period and decreases with the rain gauge density for small return period events and high rain gauge density the differences among the methods are minor with increasing the return period and decreasing the rain gauge density the nearest neighbor method is less biased because it makes use only of the closest rain gauge to the debris flow initiation point on the contrary inverse distance weighting and ordinary kriging which are using rain gauges located farther from the debris flows in addition to the closest one exhibit negative biases that increase with return period the standard deviation of the interpolated values is larger when the nearest neighbor is used with respect to inverse distance weighting and ordinary kriging for large return period and low rain gauge density the differences among the methods are minor