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

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

the effect of h2o2 treatment on stable isotope analysis δ13c δ18o and δ47 of various carbonate minerals abstract in carbonate isotopic measurements h2o2 treatment is one of the most often used methods to remove organic matter contaminants from carbonate minerals for accurate analysis but the interaction between h2o2 solution and carbonate minerals may also lead to analytical bias in this study we quantitatively tested the effect of h2o2 treatment for 7 types of carbonate minerals and the influences on 47 values of calcium carbonate are systematically discussed for the first time most samples presented 47 offsets within the 2 sd of our analytical precision except the methane derived authigenic carbonate mdac the shift of 47 values in mdacs is attributed to the mixing effect of two types of carbonate minerals original one and isotopically altered one and the magnitude is determined by the differences of both 13c and 18o values between two endmembers regarding biogenic carbonate tested here the analytical bias of h2o2 treatment is relative small in 13c and 18o values and therefore the shift of 47 values is statistically neglectable the 13c and 18o values for most samples tested in this study became positive up to 1 7 after h2o2 treatment apart from previously well discussed mechanisms such as removal of organic contamination isotopic fractionation during the partial dissolution and dissolution of isotopic distinct carbonate compositions in the heterogeneous minerals we experimentally demonstrated carbon and oxygen isotopic exchanges between carbonate minerals and h2o2 solution for the first time the 13c and 18o values of carbonate were influenced by isotopic exchanges with atmospheric co2 in the co2 hco3 co32 system and h2o in h2o2 solution respectively rich transition metals in the authigenic carbonate minerals e g mdac travertine which catalyze h2o2 decomposition can enlarge this effect by altering h2o isotopic compositions though the small shift of 13c and 18o in biogenic carbonate observed here up to 0 6 would not change scientific interpretations and conclusions in most of previous studies cautions should be taken in the future based upon our new experimental results we suggest using a buffered h2o2 solution ph 8 isolated from atmospheric co2 to remove potential organic contaminations in biogenic carbonate for authigenic carbonate h2o2 treatment is not recommended if necessary decreasing the h2o2 concentration shortening the reaction time leaving the solution in a co2 free environment and adjusting the solution to a basic condition will improve the accuracy in isotopic analysis of these minerals

10be and36cl depth profiles in an apollo 15 drill core cosmic ray produced10be t1 2 1 6 106 years and36cl t1 2 3 0 105 years have been measured in the apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry from these experiments the half attenuation length for10be production and36cl production were calculated to be 120 g cm2 and 132 g cm2 150 400 g cm2 region the measured half attenuation length for10be is slightly longer than that predicted by the reedy arnold theoretical model the flatter and somewhat deeper maximum seen in the36cl profile compared to the10be 26al and53mn profiles can be explained by production from secondary thermal neutrons on35cl

remnants of a fossil alluvial fan landscape of miocene age in the atacama desert of northern chile using cosmogenic nuclide exposure age dating we have used cosmogenic nuclides to estimate limits on the surface exposure durations and erosion rates of alluvial fans and bedrock surfaces in the atacama desert in chile the oldest landforms we studied are extensive alluvial fans referred to as atacama gravels with the exception of samples collected in antarctica the cobbles collected on these alluvial surfaces have the lowest erosion rates of any samples as determined by cosmogenic nuclides analyzed to date the oldest cobble has a model surface exposure age of 9 myr based on combined measurements of cosmogenic 10be 26al and 21ne concentrations cobbles from the alluvial fans are eroding slower than the surrounding steep mountainous bedrock surfaces maximum erosion rates for cobbles on alluvial surfaces are uniformly 0 1 m myr the survival of these gravels specifically and more generally the stability of landform features in this geographic area is made possible by the attainment of hyperarid conditions in the atacama desert resulting from global climatic cooling about 15 myr ago combined with the rain shadow effect caused by uplift of the central andes the landform features observed presently in the atacama desert are remarkably stable and despite the inevitable erosion that is detectable using cosmogenic nuclides undoubtedly bear considerable resemblance to conditions as they existed in the miocene over geologic time the atacama landscape is evolving in such a manner as to erode the higher bedrock ridges relative to the more stable but stratigraphically lower depositional surfaces through which clastic detritus now travels occasionally along the floors of incised drainage systems leaving the older permeable alluvial fan surfaces largely intact as widespread remnants of a miocene fossil landscape

cosmogenic 3he in terrestrial rocks the summit lavas of maui we have identified terrestrial cosmic rayproduced 3he in three lava flows on the crest of haleakala volcano on maui 3 km above sea level and 0 5 million years old although these lavas like all oceanic basalts contain primordial 3he from the mantle the cosmogenic component 3hec can be identified unambiguously because it is extractable only by high temperature vacuum fusion in contrast a large fraction of the mantle helium resides in fluid inclusions and can be extracted by vacuum crushing leaving a residual component with 3he 4he ratios as high as 75 those in the atmosphere which can be liberated by melting the crushed grains cosmogenic 3he is present in both olivines and clinopyroxenes at 0 8 1 2 10 12 ml stp g and constitutes 75 5 of the total 3he present the observed 3hec levels require a cosmic ray exposure age of only some 64 000 years much less than the actual age of the lavas if there is no erosion using a model that includes effects of uplift or submergence as well as erosion we calculate an apparent erosion rate of the order of 8 5 m 106 years for the western rim of the summit crater as an example of the application of measurements of cosmogenic rare gases to terrestrial geological problems

application of in situ produced cosmogenic 10be and 26al to the study of lateritic soil development in tropical forest theory and examples from cameroon and gabon abstract depth profiles of in situ produced cosmogenic nuclides including 10 be t 1 2 1 5 10 6 years and 26 al t 1 2 0 73 10 6 years in the upper few meters of the earth s crust may be used to study surficial processes quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations in this paper we discuss the fundamentals of the method and apply it to two lateritic sequences located in african tropical forests

10be and 26al production rates deduced from an instantaneous event within the dendro calibration curve the landslide of kofels otz valley austria surface exposure dating requires the knowledge of cosmogenic nuclide production rates when determining time integrated production rates the exposure ages of the calibration samples need to be accurately known the landslide of kofels austria is very well suited for this purpose it is the largest landslide in the crystalline alps of austria dating back to 7800 100 years bc ams 14c dating of buried wood which is well within the 14c dendro calibration curve exposed quartz veins were sampled from the tops of large boulders from the toe of the landslide for analysis of 10be and 26al to calculate sea level high geomagnetic latitude 60 open sky radionuclide production rates corrections were applied for altitude and latitude for shielding by surrounding mountains for sample geometry vegetation and snow cover and for sample thickness the production rates for an exposure age of 10 000 years are 5 75 0 24 10be atoms yr g sio2 and 37 4 1 9 26al atoms yr g sio2 a 26al 10be ratio of 6 52 0 43 can be calculated the influence of the geomagnetic field on these production rates has been estimated using two different geomagnetic field records our production rates should be a good approximation for the use of surface exposure dating between about 5000 and 13 000 years bp

continental erosion and large scale relief a worldwide investigation of continental erosion is carried out by the study of large drainage basins on the basis of hydrological data environmental factors and basin relief distribution inside each basin mean geochemical and mechanical denudation rates are defined a multicorrelation analysis shows that the mechanical denudation rates ds are uncorrelated with environmental factors and correlated with mean basin elevation h while chemical denudation rates dd are insensitive to relief but correlated with mean annual precipitation furthermore two linear relationships between h and ds are detected 1 ds m 10 yr 419 10 6 h m 0 245 with v explained variance 95 1 this law concerns basins related to orogenies younger than 250 ma the negative intercept is interpreted as a continental sedimentation rate of 245 m m y an alternative model in which one invokes a critical elevation separating erosion from sedimentation is equally successful and leads to lower sedimentation rates 60 110 m m y for both models one derives from the slope of the adjustments erosion time constants on the order of 2 5 m y 2 ds m 10 yr 61 10 6 h m with v 86 5 this law concerns basins related to older orogenies the null intercept suggests the lack of continental storage because of the more important dispersion of the data the erosion time constant is calculated separately for each basin it ranges from 15 to 360 m y the tectonic implications of these results are discussed in particular the short time constant 2 5 m y agrees with orogenic uplift rates on the order of 1 mm yr observed in active mountain chains

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

age of allan hills 82102 a meteorite found inside the ice the recovery of thousands of meteorites in the antarctic since 1969 has not only greatly increased knowledge of the meteorites themselves but has also provided a new tool for glaciology most antarctic meteorites are found on blue ice areas where old ice is continuously ablated a measurement of the age of this ice helps us understand meteorite accumulation mechanisms and the dynamics of ice movement the terrestrial age of a meteorite the time period since the date of meteorite fall can be determined from the reduction in concentration of cosmogenic radionuclides during the time the meteorite has been shielded by the earth s atmosphere here we report the terrestrial age of a meteorite that was recovered from below the surface of the ice and argue that this represents a measurement of the age of the ice itself we measured the cosmogenic radionuclides 10be half life 1 5 myr 14c 5 730 yr 26a1 0 71 myr 36c1 0 30 myr and 53mn 3 7 myr in the meteorite and 10be and 36c1 in the ice we obtained a terrestrial age of 11 000 years for the meteorite which suggests that the snow accumulation area where it fell was only a few tens of kilometres away

contemporary versus long term denudation along a passive plate margin the role of extreme events short term contemporary and long term denudation rates were determined for the blue mountains plateau in the western sydney basin australia to explore the role of extreme events wildfires and catastrophic floods in landscape denudation along a passive plate margin contemporary denudation rates were reconstructed using 40 years of river sediment load data from the nattai catchment in the south west of the basin combined with an analysis of hillslope erosion following recent wildfires long term denudation rates 10 kyr 10 myr were determined from terrestrial cosmogenic nuclides apatite fission track thermochronology and post basalt flow valley incision contemporary denudation rates average several times lower than the long term average 5 5 4 mm kyr 1 versus 21 5 7 mm kyr 1 erosion of sediment following wildfires accounts for only a small proportion 5 of the contemporary rate most post fire sediment is stored on the lower slopes and valley floor with the amount transported to the river network dependent on rainfall run off conditions within the first few years following the fire historical catastrophic floods account for a much larger proportion 35 of the contemporary erosion rate and highlight the importance of these events in reworking stored material evidence for palaeofloods much larger than those experienced over the past 200 years suggests even greater sediment export potential mass movement on hillslopes along valleys incised into softer lithology appears to be a dominant erosion process that supplies substantial volumes of material to the valley floor it is possible that a combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between the contemporary and long term denudation rates copyright 2006 john wiley sons ltd

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

erosion rates in fennoscandia during the past million years abstract the widespread existence of cosmogenic nuclides accumulated in bedrock prior to the last glaciation demonstrates the limited erosional efficacy of the most recent fennoscandian and laurentide ice sheets yet the deeper history of erosion in these landscapes repeatedly blanketed by ice remains essentially unknown here we present the first comprehensive ice sheet wide analysis of cosmogenic 10be data n 953 from the fennoscandian landscape we find 64 of all sampled bedrock surfaces contain 10be inheritance including 85 of blockfields and tors and 50 of ice carved terrain in addition to 27 of ice transported boulders recent ice sheets scoured landscapes well beyond glacial troughs and nuclide inventories reveal a patchy legacy of erosional effectiveness that diminishes at high elevations such that 89 n 55 of bedrock samples retain inheritance above 1600 m we exploit this widespread nuclide inheritance in a markov chain monte carlo based inversion model to estimate long term erosion rates and surface exposure histories from 113 paired 10be 26al bedrock samples nuclide inventories with or without inheritance convey equally important information about the erosional effectiveness of the last ice sheet we define cosmogenic nuclide memory as the residence time of bedrock samples inside the nuclide production window 2 m depth where 80 of the total nuclide production occurs the cosmogenic nuclide memory is set by mean erosion rate and varies from 10 ka for samples eroded 2 m during the last glaciation to 1 ma for the slowest erosion rates we find that mean erosion rates are well constrained compared to the ratio of exposure to burial the inclusion of bedrock erosion in our computations thwarts the capacity to constrain surface exposure history or identify former nunataks from paired 10be 26al data ice carved surfaces reflect diverse erosion histories that are not straightforward to interpret from surficial morphology alone relative to the 10 mm kyr benchmark for polar ice masses we report point based mean erosion rates that vary by more than three orders of magnitude with glacial troughs and areal scour terrain eroding at 1 to 100 mm kyr blockfields at 0 8 16 mm kyr and tors at 0 8 7 7 mm kyr 5th 95th percentiles

landscape evolution in antarctica abstract the extreme aridity of antarctica means that very little water is available for weathering and geomorphic processes the landscape everywhere has been shaped by ice but land exposed after ice retreat has been modified by cold desert weathering processes wind is the main agent for removal and redeposition of weathered material while fluvial action is insignificant as an eroding or transporting agent there are few suitable deposits that allow reliable or accurate dating of events but the dates that are available show that landform evolution has been taking place very slowly soil weathering studies have provided a useful means of extrapolation showing relative ages of surfaces where no dates are available the major weathering processes in antarctica involve patterned ground movement frost action wind salt weathering and soil weathering these combine to form distinctive landscape features the complex nature of landform development is illustrated by considering events that have taken place within wright valley one of the largest ice free areas in antarctica within this valley are land surfaces ranging from those found on late pleistocene up valley tills to high altitude extremely fretted and weathered land surfaces that have been ice free possibly since the early miocene

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

measurements of past ice sheet elevations in interior west antarctica a lateral moraine band on mount waesche a volcanic nunatak in marie byrd land provides estimates of past ice sheet surface elevations in west antarctica helium 3 and chlorine 36 surface exposure ages indicate that the proximal part of the moraine up to 45 meters above the present ice surface was deposited about 10 000 years ago substantially later than the maximum ice extent in the ross embayment the upper distal part of the moraine may record multiple earlier ice sheet high stands a nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at mount waesche relative to the maximum ice extent in the ross sea the glacial geologic evidence coupled with the ice sheet model indicates that the contribution of the ross sea sector of the west antarctic ice sheet to holocene sea level rise was only about 3 meters these results eliminate west antarctic ice as the principle source of the large meltwater pulse during the early holocene

cosmic ray produced neon and helium in the summit lavas of maui a 3he component attributed to cosmic ray induced spallation reactions 3hec in silicate minerals has recently been identified in lava flows on the summit of haleakala volcano on maui1 3 this3hec is observed in the helium extracted by fusion of olivine and pyroxene phenocrysts after first removing almost all of the mantle derived helium by vacuum crushing a procedure which releases the volatiles trapped in fluid inclusions within the phenocrysts cosmic ray produced 3he was found in the high altitude 3 000 m summit lavas which are 500 000 years old but was not observed in sub surface samples which were overlain by younger basalts2 or in a 200 yr old lava flow at sea level on maui1 2 we report here the identification of cosmic ray produced 21nec in addition to 3hec in gases extracted by fusion of olivines and clinopyroxenes after vacuum crushing the observed 3he 21ne c ratios and the ratio of 21nec in olivine to that in clinopyroxene are consistent with an in situ origin of 3hec and 21nec by cosmic ray spallation reactions this component could be important for interpreting helium isotopic data in terrestrial reservoirs geophysical applications could include determinations of erosion rates and exposure histories of terrestrial rocks

late noachian to hesperian climate change on mars evidence of episodic warming from transient crater lakes near ares vallis 1 the ares vallis region is surrounded by highland terrain containing both degraded and pristine large impact craters that suggest a change in climate during the late noachian early hesperian from warmer wetter conditions to colder dryer conditions however the regional occurrence of hesperian age crater outlet channels indicates that this period on mars was characterized by episodic climate fluctuations that caused transient warming facilitating the stability of liquid water at the surface an extensive survey of the morphology and topography of 75 impact basins in the region indicates that of the largest degraded craters 4 were identified with single outlet channels that suggest the former presence of water infill these basins lack inlets indicating that water influx was likely derived from sapping of groundwater a comparison of measured crater rim heights to modeled rim heights suggests that the bulk of the depth diameter reduction on these craters was the result of infilling possibly by sediments crater statistics indicate that crater degradation and infill occurred during a short 200 ma interval in the late noachian from 3 8 ga to 3 6 ga craters that formed after 3 6 ga exhibit a near pristine morphology our results support the hypothesis of rapid climate change at the end of the noachian period however geologic relationships between the crater outlet channels and ares vallis indicate that drainage occurred only after the period of intense crater modification during the hesperian 3 5 2 9 ga this suggests a delay between the time of infill of the craters and the time of drainage

late tertiary history of the antarctic ice sheet evidence from the dry valleys data from the dry valleys antarctica suggest that outlet glaciers of a local ice cap carved primary valley systems on both flanks of the transantarctic mountains while coeval alpine glaciers eroded exposed intervalley mountain ranges subsequently a thick ice sheet overrode the transantarctic mountains at least twice flowing northeastward across major pre existing valleys the youngest overriding episode postdated and the older episode antedated middle to early late miocene time we think that an extensive ice sheet covered east and west antarctica during overriding episodes

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

mechanism of creep movement caused by landslide activity and underground erosion in crystalline schist shikoku island southwestern japan abstract the mechanism of creep movement of the zentoku landslide in crystalline schist has not been studied in detail because of the steepness of the slope very slow movement low population density and complex topographic and geologic characteristics sassa et al 1980 proc interpraevent 1 85 106 and sassa 1984 proc 4th international symp on landslides toronto vol 2 pp 179 184 1985 geotechnical classification of landslides proc 4th international conference and field workshop on landslides tokyo pp 31 40 1989 landslide news japan landslide society no 3 pp 21 24 monitored landslide movement and groundwater level at the zentoku landslide on shikoku island southwestern japan and suggested that the mechanism may be caused by underground erosion to study the influence of underground erosion at this site continual monitoring of suspended sediment and water discharge from a groundwater outlet i e a spring was implemented the locations of groundwater flow paths were determined as were the amounts of discharged sediment slope deformation was monitored by means of a borehole inclinometer the conclusions were as follows 1 the flow paths were found to be on or above the shear zones in which underground erosion has occurred 2 in addition to being a result of precipitation and groundwater discharge sediment discharge is affected by landslide activity and 3 the mechanism of creep movement is an interrelated chain process that combines underground erosion caused by landslide activity with landslide activity caused by underground erosion thus landslide activity increases erosion susceptibility and transportation of soils within the mass and underground erosion causes instability of the landslide mass in turn this mechanism can explain the observed phenomenon that the zentoku landslide not only moves actively during heavy rain but also continues to creep throughout the year

the accumulation of cosmogenic chlorine 36 in rocks a method for surface exposure dating because of the reaction of cosmic rays with elements in minerals chlorine 36 accumulates in rocks exposed at the earth s surface this suggests that the ratio of chlorine 36 to stable chloride can be used as a geochronometer reasonable agreement has been obtained between measurements of chlorine 36 in volcanic rocks of known age and calculations of chlorine 36 production based on rock composition and cosmicray flux the buildup of chlorine 36 should be a useful means for measuring the surface exposure time of young volcanic rocks and geomorphic features in the age range of 10 3 to 10 6 years

rates of surface processes on slopes slope retreat and denudation results taken from 270 publications on rates are summarized and collated with those from 149 publications reviewed previously young 1969 1974 the data are classified by major climatic zone normal or steep relief and consolidated or unconsolidated rocks representative rates and their ranges are given for soil creep solifluction surface wash solution chemical denudation rock weathering slope retreat cliff free face retreat marine cliff retreat and denudation the last being compared with representative rates of uplift solifluction is of the order of 10 times faster than soil creep but both cause only very slow ground loss solution is an important cause of ground loss for siliceous rocks on which it may be half as rapid as on limestones total denudation brought about mainly by surface wash reaches a maximum in the semi arid and probably also the tropical savanna zones acceleration of natural erosion rates by human activities ranges from 2 3 times with moderately intense land use to about 10 times with intensive land use and considerably higher still where there is recognized accelerated soil erosion where there is active uplift typical rates are of the order of 10 times faster than denudation although in some high steep mountain ranges these may approach equality

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

moraine preservation and boulder erosion in the tropical andes interpreting old surface exposure ages in glaciated valleys cosmogenic dating provides a long awaited means of directly dating glacial deposits that pre date the last glacial cycle although the potential benefits of longer chronologies are obvious the greater uncertainty associated with older cosmogenic ages may be less readily apparent we illus trate the challenges of developing and interpreting a long chronology using our data from the peruvian andes we used surface exposure dating with cosmogenic radionuclides crns 10 be and 26 al to date 140 boulders on moraines in valleys bordering the junin plain 11 s 76 w in central peru our chronology spans multiple glacial cycles and includes exposure ages greater than 1 million years which indicate that long term rates of boulder erosion have been very low interpreting the chronology of moraines for glaciations that predate the last glacial cycle is complicated by the need to consider boulder erosion and exhumation surface uplift and inheritance of crns from pre vious exposure intervals as an example we recalculate exposure ages using our boulder erosion rates 0 3 0 5 metres per million years and estimated surface uplift rates to emphasise both the chal lenges involved in interpreting old surface exposure ages and the value of chronological data even with large uncertainties when reconstructing the palaeoclimate of a region copyright 2005 john wiley sons ltd

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval