instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of bruarjokull iceland abstract contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments this study concerns the ice marginal environment of the surge type bruarjokull in iceland the sediment distribution in the glacier forefield as well as the morphology sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment landform associations as a result of substrate bedrock decoupling during the 1890 surge subglacial sediment was dislocated across the bedrock surface and deformed compressively leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone a drop in subglacial porewater pressure at the very end of the surge led to substrate bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate simultaneously the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine ridge construction fine grained and incompetent sediment deformed in ductile manner resulting in a narrow moraine dominated by rooted folds while coarse grained and competent sediment deformed in brittle fashion resulting in a wider moraine dominated by thrust blocks a new sequential model of subglacial and ice marginal processes operating during a glacier surge is proposed illustrating the stepwise formation of a marginal sediment wedge and an end moraine a twofold inseparable marginal end product that formed during the last days of the 1890 surge

soil weathering and accumulation rates of oxalate extractable phases derived from alpine chronosequences of up to 1 ma in age abstract in this study we compare newly developed chemical weathering data with previously published data from soils developed along two chronosequences of glacial deposits in the european alps and the rocky mountains wind river range usa by combining these chronosequences we are able to present a comprehensive dataset that represents a time period of 1 ma we describe weathering trends of important elements using a number of weathering indices e g k ca ti ratio the weathering index b of kronberg and nesbitt 1981 and the open mass transport function further we describe the accumulation of al fe si and mn oxyhydroxides including partially organic phases as a function of time and derive the corresponding accumulation rates we calculated pedogenetically formed oxyhydroxides using an approach based on immobile elements our study represents one of only a few studies that describe rates of soil chemical weathering over a period as long as 1 ma results show that rates of chemical weathering clearly decrease along the chronosequences with increasing age of the soils we find weathering rates are nearly four orders of magnitude lower in the 1 ma old soils than in the young soils our results suggest that the older soils may be reaching a steady state for these chemical properties in their present environments a power function best explains the measured time trends of the index b and k ca ti ratios in the soils the best time trend model for pedogenic weakly to poorly crystalline phases and the relative losses gains based on the open system mass transport function were obtained with an exponential decay model function in terms of the soil system the decreases in the accumulation rate of the oxyhydroxides appears to be influenced not only by the factor of time but by climate as well increased precipitation at higher altitudes slows the decrease in weathering rate over time thus our 1 ma chronosequences also become pedogenic gradients since we describe variations in soil properties along biogenic gradients

the mjauvotn tephra and other holocene tephra horizons from the faroe islands a link between the icelandic source region the nordic seas and the european continent six different tephra horizons were found in peat and lacustrine sediments on the faroe islands in the north atlantic their geochemistry showed that they were of icelandic origin three of these can be correlated with previously described tephra horizons from the faroe islands the saksunarvatn tephra c 9000 bp the hekla 4 c 3800 bp and hekla selsund c 3600 bp a previously unrecorded basaltic tephra dated to c 5700 5300 bp was found in two lacustrine successions this horizon is named the mjauvotn tephra after mjauvotn lake on the island of streymoy two further tephras were recorded the basaltic phase of the landnam tephra viia c ad 870s and the rhyolitic tjornuvk tephra these were found in sediments deposited shortly after the first phase of human settlement at tjornuvik which is ams dated to ad 675 861 calibrated age the faroe islands are an important link between the volcanic sources on iceland and the established tephrochronological frameworks on the british isles scandinavia and germany their position within a sensitive region of the northeastern branch of the north atlantic drift make the faroe islands ideal for registering climate changes during the holocene the establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the nordic seas

hydrometeor enhanced tephra sedimentation constraints from the 18 may 1980 eruption of mount st helens 1 uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits in this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the mount st helens 18 may 1980 msh80 eruption in addition we collate all the data needed to model distal ash sedimentation from the msh80 eruption cloud four particle size subpopulations were present in distal fallout with modes at 2 2 4 2 5 9 and 8 3 settling rates of the coarsest subpopulation closely matched predicted single particle terminal fall velocities sedimentation of particles 100 m was greatly enhanced predominantly through aggregation of a particle subpopulation with modal diameter 5 9 0 2 19 3 m mammatus on the msh80 cloud provided a mechanism to transport very fine ash particles with predicted atmospheric lifetimes of days to weeks from the upper troposphere to the surface in a matter of hours in this mechanism ash particles initiate ice hydrometeor formation high in the troposphere subsequently the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits this work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons

the transport of icelandic volcanic ash insights from northern european cryptotephra records fine ash produced during volcanic eruptions can be dispersed over a vast area where it poses a threat to aviation human health and infrastructure we analyse the particle size distributions geochemistry and glass shard morphology of 19 distal 1000 km from source volcanic ash deposits distributed across northern europe many geochemically linked to a specific volcanic eruption the largest glass shards in the cryptotephra deposits were 250 m longest axis basis for the first time we examine the replicability and reliability of glass shard size measurements from peatland and lake archives we identify no consistent trend in the vertical sorting of glass shards by size within lake and peat sediments measuring the sizes of 100 shards from the vertical sample of peak shard concentration is generally sufficient to ascertain the median shard size for a cryptotephra deposit lakes and peatlands in close proximity contain cryptotephras with significantly different median shard size in four out of five instances the trend toward a greater amount of larger shards in lakes may have implications for the selection of distal sites to constrain the maximum glass shard size for modelling studies although the 95th percentile values for shard size generally indicate a loss of larger shards from deposits at sites farther from the volcano due to the dynamic nature of the controls on tephra transport even during the course of one eruption there is no simple relationship between median shard size and transport distance

high spatial resolution electron probe microanalysis of tephras and melt inclusions without beam induced chemical modification wavelength dispersive analysis of tephra grains and melt inclusions by epma has been carried out using a focused beam of 3 m diameter without detected loss of sodium or potassium in standard glasses including anhydrous basalts a slightly hydrated rhyolite and a sodium rich intermediate composition the ability to make analyses without chemical modification is strongly dependent upon current density at the analysis site analysis with narrow beams requires extremely low beam currents that are normally associated with energy dispersive analysis experiments indicate that a value of 0 1 na m2 must not be exceeded at least for moderately hydrated samples if sodium loss is to be avoided high resolution analysis without beam induced analytical artefacts enables fully quantitative analysis of very distal and or highly vesicular tephras and very small melt inclusions without the need to use post analysis corrections this development has enabled high quality analyses from crypto tephra layers that were pre

weathering and evolution of soils formed on granitic glacial deposits results from chronosequences of swiss alpine environments abstract two soil chronosequences of mountainous ecosystems in switzerland served as the basis to calculate the accumulation of soil organic matter transformation of pedogenic fe and al and net losses of the main elements ca mg k na fe al mn and si by means of mass balance calculations elemental losses due to deglaciation and exposure to the weathering environment were calculated these mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of si major base cations and al particularly from the upper horizons the losses are especially pronounced in the early stages of soil formation in most cases the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering the greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000 4000 years of soil development later the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote we also found that the mean ratio of al t fe d al d fe t of the fine earth of the a e and b horizons is closely linked to the duration of soil development a very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years consequently this ratio could be a good indicator of the age of alpine soils furthermore there is a close relationship between the mass of organic c or n in the whole profile and the soil age the older the soil the higher the corresponding mass per unit area the chronofunctions presented give a first attempt of the chemical soil evolution in the alps however only little data has been available up until now regarding alpine soils and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000 8000 years of soil formation under similar climatic conditions

discovery of early holocene wood and peat on the forefield of the pasterze glacier eastern alps austria during recent years a number of fragments of pinus cembra and larix decidua as well as peat were found in front of the tongue of the pasterze glacier in the eastern alps these were washed out by the stream from under the present ice the wood originates from trees which reached ages of upto 400 years or more radiocarbon dating shows them to come from the early holocene they indicate that between cal bc 8100 and cal bc 6900 the pasterze glacier was smaller than at present the pasterze glacier advanced around cal bc 6900 a lump of peat shows that around cal bc 6300 at the latest the pasterze glacier was again smaller than today the radiocarbon age of the fulvic acid fraction of thepeat suggests that growth could have continued until cal bc 5430 5080 further wood samples dated to around cal bc 4800 and cal bc 3800 show that at these times the pasterze glacier was smaller than at present the pasterze glacier had a relatively limited extent over long periods inthe early holocene thus mostly favou

do peatlands or lakes provide the most comprehensive distal tephra records abstract despite the widespread application of tephra studies for dating and correlation of stratigraphic sequences tephrochronology questions remain over the reliability and replicability of tephra records from lake sediments and peats particularly in sites 1000 km from source volcanoes to address this we examine the tephrostratigraphy of four pairs of lake and peatland sites in close proximity to one another

extractable fe and al in late pleistocene and holocene paleosols on niwot ridge colorado front range summary surface and buried paleosols on niwot ridge in the front range of colorado were analyzed for extractable fe and al to determine if their distributions would assist in the interpretation of past and present soil forming environments extractable fe and al distributions in surface and buried paleosols suggest that leaching is more pronounced in the older paleosols with a considerable difference in soil forming environment between pleistocene interstadial later pleistocene and postglacial paleosols using radiocarbon dated buried a horizons it appears that little pyrophosphate extractable fe and al have been translocated downward into these middle latitude alpine buried paleosols there is no evidence that the na pyrophosphate extractable fe and al were affected by degradation of organic matter following burial however the data suggest that some amorphous fe and al might have been affected by soil water movement over permafrost and by redistribution of preweathered sediments

dates of holocene icelandic volcanic eruptions from tephra layers in irish peats tephra from historic and prehistoric eruptions of oraefajokull and hekla iceland have been found in irish peats using a series of stratigraphically related high precision radiocarbon measure ments the date of a known age eruption has been satisfactorily estimated based on the same techniques the calendrical date of the hekla 4 eruption has been estimated as 2310 20 bc

probabilistic modeling of tephra dispersal hazard assessment of a multiphase rhyolitic eruption at tarawera new zealand 1 the tarawera volcanic complex comprises 11 rhyolite domes formed during five major eruptions between 17 000 b c and a d 1886 the first four of which were predominantly rhyolitic the only historical event erupted about 2 km3 of basaltic tephra fall a d 1886 the youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano a d 1315 kaharoa eruption we have used the kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at tarawera of a similar scale the plinian phase of this eruption consisted of 11 discrete episodes of vei 4 we have developed an advection diffusion model tephra that allows for grain size dependent diffusion and particle density a stratified atmosphere particle diffusion time within the rising plume and settling velocities that include reynolds number variations along the particle fall simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs tephra is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions three different scenarios were investigated for a comprehensive tephra fall hazard assessment upper limit scenario eruption range scenario and multiple eruption scenario hazard curves and probability maps show that the area east and northeast of tarawera would be the most affected by a kaharoa type eruption

tephrabase tephrochronology and the development of a centralised european database tephrabase was launched on the world wide web in 1995 as a tool for tephrochro nological research in order to facilitate the identification correlation and dating of tephra deposits this database may be interrogated through multiple routes including by source volcano date location and tephra chemistry datasets include stratigraphy geochemistry chronology and spatial information currently all the european data refer to late quaternary icelandic sourced tephras post 12 k yr bp the sites 62 where the tephra deposits are found include iceland the united kingdom ireland the faroe islands sweden and russia in addition there are also data on tephra layers in central mexico use of tephrabase highlights the importance of selected geochemical data but this has to be used with care as major element characteristics alone do not always produce unique definitions for single tephra deposits for the most accurate results multiple criteria must be used tephrabase can be found at http www tephrabase org copyright 2007 john wiley sons ltd

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate pedogenically significant chemical extracts of iron aluminum and phosphorus are related mainly to time in chronosequences from baffin island canadian arctic the alpine sierra nevada and wind river range western united states the alpine khumbu glacier area himalaya nepal and the alpine southern alps new zealand based on the accumulation index for fe and al and the depletion index for p in each region the following ranking of chemical pedogenic development is obtained southern alps khumbu glacier area wind river range sierra nevada coastal baffin island inland baffin island the ranking mainly follows regional climate with the greatest accumulation and depletion to the warmest and wettest environment and the least accumulation and depletion in the coldest and driest environment

spatial variability of tephra and carbon accumulation in a holocene peatland abstract microscopic tephra layers cryptotephras represent important age equivalent stratigraphic markers utilised in many palaeoenvironmental reconstructions when used in conjunction with proximal records of volcanic activity they can also provide information about volcanic ash cloud fallout and frequency however the spatial distributions of tephra layers can be discontinuous even within the same region understanding the deposition and post depositional redistribution of tephra is vital if we are to use cryptotephras as records of ash cloud occurrence and chronostratigraphic markers the discrete nature of tephra layers also allows for detailed study into processes of deposition and reworking which affect many palaeoenvironmental proxy records we undertook a multi core study in order to examine the historical tephrostratigraphy of a raised peatland in northern ireland three tephra layers originating from iceland hekla 1947 hekla 1845 and hekla 1510 are present in 14 of the 15 cores analysed this suggests that in areas not influenced by snowfall or anthropogenic disturbance at the time of tephra delivery the presence or absence of a tephra layer is generally consistent across a peatland of this type however tephra shard counts per unit area vary by an order of magnitude between cores these intra site differences may confound the interpretation of shard counts from single cores as records of regional ash cloud mass density bootstrap resampling analysis suggests that total shard counts from multiple cores are required in order to make a reliable estimate of median shard counts for a site the presence of three historical tephras in 14 cores enables a spatio temporal analysis of the long term apparent rate of carbon accumulation larca in the peatland substantial spatial and temporal variations in larca are identified over the last 450 years this high variability needs to be taken into account when designing studies of peatland carbon accumulation

practical limitations on the use of diurnal temperature signals to quantify groundwater upwelling groundwater upwelling to streams creates unique habitat by influencing stream water quality and temperature upwelling zones also serve as vectors for contamination when groundwater is degraded temperature time series data acquired along vertical profiles in the streambed have been applied to simple analytical models to determine rates of vertical fluid flux these models are based on the downward propagation characteristics amplitude attenuation and phase lag of the surface diurnal signal despite the popularity of these models there are few published characterizations of moderate to strong upwelling we attribute this limitation to the thermodynamics of upwelling under which the downward conductive signal transport from the streambed interface occurs opposite the upward advective fluid flux governing equations describing the advection diffusion of heat within the streambed predict that under upwelling conditions signal amplitude attenuation will increase but counterintuitively phase lag will decrease therefore the extinction measurable depth of the diurnal signal is very shallow but phase lag is also short yielding low signal to noise ratio and poor model sensitivity conversely amplitude attenuation over similar sensor spacing is strong yielding greater potential model sensitivity here we present streambed thermal time series over a range of moderate to strong upwelling sites in the quashnet river cape cod massachusetts the predicted inverse relationship between phase lag and rate of upwelling was observed in the field data over a range of conditions but the observed phase lags were consistently shorter than predicted analytical solutions for fluid flux based on signal amplitude attenuation return results consistent with numerical models and physical seepage meters but the phase lag analytical model results are generally unreasonable through numerical modeling we explore reasons why phase lag may have been over predicted by the analytical models and develop guiding relations of diurnal temperature signal extinction depth based on stream diurnal signal amplitude upwelling magnitude and streambed thermal properties that will be useful in designing future experiments

transatlantic distribution of the alaskan white river ash volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and or asynchronous behaviors in earth system and archaeological sciences however it is generally assumed that only exceptionally powerful events such as supereruptions 450 km3 of ejecta as dense rock equivalent recurrence interval of 105 yr distribute ash broadly enough to have an impact on human society or allow us to address geologic climatic and cultural questions on an intercontinental scale here we use geochemical age and morphological evidence to show that the alaskan white river ash eastern lobe a d 833 850 correlates to the ad860b ash a d 846 848 found in greenland and northern europe these occurrences represent the distribution of an ash over 7000 km linking marine terrestrial and ice core records our results indicate that tephra from more moderate size eruptions with recurrence intervals of 100 yr can have substantially greater distributions than previously thought with direct implications for volcanic dispersal studies correlation of widely distributed proxy records and volcanic hazard assessment

neoglacial chronology and floristics in the middle teton area central teton range western wyoming the relative ages of neogfacial deposits above 2900m near cloudveil dome middle teton and teepe glaciers central teton range western wyoming were determined using topographic position weathering features lichenometry vegetation characteristics and soils a three fold deposit sequence is identified and correlated with the gannett peak audubon and indian basin neoglacial advances described elsewhere in the teton and nearby wind river ranges while soil profile morphology proved very useful in distinguishing deposits of different age other age indicators such as clay mineralogy and soil chemistry proved of only marginal value in age discrimination this chronosequence emplaced over the last 5000yr provides an excellent setting upon which to test changes in plant species composition and its use as a relative dating method vascular plant species composition cannot be used to discriminate deposits of the different advances possibly because of random colonisation and establishment combined with extensive mass wasting during the neoglacial however certain vegetation features such as total cover and species densities appear useful as relative dating methods

extractable fe and al as an indicator for buried soil horizons summary reddish brown and associated horizons from several buried soils were analyzed for dithionite oxalate and pyrophosphate extractable fe and al although these methods can be used with surficial soils they are not necessarily applicable to buried soils however on the basis of morphology and the fact that dithionite and oxalate extractable fe and al were always highest for the reddish brown horizon in each profile sequence it was concluded that these horizons were zones of pedogenic accumulation since pyrophosphate extractable fe and al essentially measures only the organic forms of pedogenic fe and al and organic compounds are usually subjected to further degradation after burial it is suggested that for buried soils dithionite and oxalate extractable fe and al are more meaningful comparisons with data in the literature giving typical ranges for the main types of soil horizons allowed both the classification of the profiles sampled and the recognition of past processes such as gleying which are not identifiable morphologically today

14c dating and palaeoenvironment of the historic little ice age glacier advance of nigardsbreen southwest norway moss and grass remains associated with a well developed in situ palaeosol buried beneath a moraine ridge in front of nigardsbreen jostedalsbreen ice cap southern norway have been 14c dated pollen preserved with the plant remains suggests the existence of an agricultural landscape prior to the deposition of the moraine the calibrated dates and the pollen spectra are in close accord with historically documented evidence for the timing and palaeoenvironment of the little ice age advance of the glacier considerable potential is indicated for estimating the maximum ages of moraine ridges and for palaeoenvironmental reconstruction where such documentary evidence does not exist

calendar year ages of three mid holocene tephra layers identified in varved lake sediments in west central sweden three intermediate to rhyolitic icelandic holocene tephra horizons hekla 3 kebister and hekla 4 have been identified in annually laminated varved lake sediments in the province of varmland west central sweden calendar year ages were obtained from varve counts and are supported by additional c 14 dating based on terrestrial plant macrofossils the varve ages of the three tephras are 3295 95 cal bp hekla 3 4030 103 cal bp kebister and 4390 107 cal bp hekla 4 the varve age of hekla 3 refines the former calibrated 14 c age based on studies in the british isles and germany considering the age error estimates associated with the varve chronology and calibrated c 14 ages the ages of kebister and hekla 4 are in agreement with former studies thus the age difference between kebister and hekla 4 is estimated to be ca 400 40 varve years formally estimated to ca 200 c 14 years between hekla 3 and hekla 4 to ca 1135 55 varve years formally estimated to ca 1100 calibrated c 14 years and between hekla 3 and kebister 708 20 varve years less

the spatial distribution of holocene cryptotephras in north west europe since 7 ka implications for understanding ash fall events from icelandic eruptions abstract we present distribution maps for all cryptotephras distal volcanic ash layers younger than 7 ka that have been reported from three or more lakes or peatlands in north west europe all but one of the tephras originates from iceland the exception has been attributed to jan mayen we find strong spatial patterning in tephra occurrence at the landscape scale most but not all of the tephra occurrences are significantly spatially clustered which likely reflects atmospheric and weather patterns at the time of the eruptions contrary to expectations based on atmospheric modelling studies tephras appear to be at least as abundant in ireland and northern scotland as in scandinavia rhyolitic and other felsic tephras occur in lakes and peatlands throughout the study region but andesitic and basaltic tephras are largely restricted to lake sites in the faroe islands and ireland explanations of some of these patterns will require further research on the effects of different methodologies for locating and characterizing cryptotephras these new maps will help to guide future investigations in tephrochronology and volcanic hazard analysis

thin tephra layers in peat revealed by x radiography x radiography has been found to provide a rapid economical non destructive method of locating very thin fine grained tephra of icelandic origin in scottish peats tephra layers form time parallel marker horizons or isochrones that are of great archaeological significance because they cover large areas offer precise chronological control for associated material and occur at times of significant cultural and environmental changes not all of the discrete deposits of recent volcanic fallout in scotland are sufficiently dense to show clearly on x radiographs but those which do provide particularly clear easily located marker horizons with many applications in palaeoenvironmental studies the tephra layer in caithness produced by fallout from a c 4000 by eruption of hekla provides a particularly good example of the use of x radiography to locate volcanic ash the method also reveals other structures of archaeological and palaeoenvironmental significance butler 1992 journal of archaeological science 19 151 161

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

high precision ultra distal holocene tephrochronology in north america far travelled volcanic ashes tephras from holocene eruptions in alaska and the pacific northwest have been traced to the easternmost extent of north america providing the basis for a new high precision geochronological framework throughout the continent through tephrochronology the dating and correlation of tephra isochrons in sedimentary records the reported isochrons are geochemically distinct with seven correlated to documented sources in alaska and the cascades including the mazama ash from oregon w7600 years old and the eastern lobe of the white river ash from alaska w1150 years old these findings mark the beginning of a tephrochronological framework of enhanced precision across north america with applications in palaeoclimate surface process and archaeological studies the particle travel distances involved up to w7000 km also demonstrate the potential for continent wide or trans atlantic socio economic disruption from similar future eruptions

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

sizes and shapes of 10 ma distal fall pyroclasts in the ogallala group nebraska abstract size distributions of distal ashfall particles from correlated 10 ma layers in nebraska measured using laser diffraction methods are lognormal with mode diameters of 90 m this ashfall is 100 bubble wall shards of rhyolite glass and apparently represents a distal ashfall from an eruption 1400 km away measured terminal velocities of these ash particles are 0 2 18 cm s consistent with stokes law settling of spherical particles with diameters of 9 50 m surface area of the ash particles measured with gas adsorption is 20 30 times the surface area of equivalent stokes spheres these results highlight the effects of shape and atmospheric drag in distal ashfalls they also highlight atmospheric transport and fallout of distal ashfall particles because these deposits resemble many other ashfalls preserved in the great plains of north america throughout the tertiary and quaternary because the ashfalls preserve major mammalian death assemblages they demonstrate that deposits with modes of op

ash from the toba supereruption in lake malawi shows no volcanic winter in east africa at 75 ka the most explosive volcanic event of the quaternary was the eruption of mt toba sumatra 75 000 y ago which produced voluminous ash deposits found across much of the indian ocean indian peninsula and south china sea a major climatic downturn observed within the greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the youngest toba tuff ytt these events coincided roughly with a hypothesized human genetic bottleneck when the number of our species in africa may have been reduced to near extinction some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors and furthermore that modern humans may have already expanded beyond africa by this time we report an observation of the ytt in africa recovered as a cryptotephra layer in lake malawi sediments 7 000 km west of the source volcano the ytt isochron provides an accurate and precise age estimate for the lake malawi paleoclimate record which revises the chronology of past climatic events in east africa the ytt in lake malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change implying that the eruption did not significantly impact the climate of east africa and was not the cause of a human genetic bottleneck at that time

a 7000 yr perspective on volcanic ash clouds affecting northern europe the ash cloud resulting from the a d 2010 eruption of eyjafjallajokull in iceland caused severe disruption to air travel across europe but as a geological event it is not unprecedented analysis of peats and lake sediments from northern europe has revealed the presence of microscopic layers of icelandic volcanic ash tephra these sedimentary records together with historical records of holocene ash falls demonstrate that icelandic volcanoes have generated substantial ash clouds that reached northern europe many times here we present the first comprehensive compilation of sedimentary and historical records of ash fall events in northern europe spanning the past 7000 yr ash fall events appear to have been more frequent in the past 1500 yr it is unclear whether this reflects a true increase in eruption frequency or dispersal or is an artifact of the records or the way in which they have been generated in the past 1000 yr volcanic ash clouds reached northern europe with a mean return interval of 56 9 yr the range of return intervals is between 6 and 115 yr probabilistic modeling using the ash records for the last millennium indicates that for any 10 yr period there is a 16 probability of a tephra fallout event in northern europe these values must be considered as conservative estimates due to the nature of tephra capture and preservation in the sedimentary record

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

cryptotephra sedimentation processes within two lacustrine sequences from west central sweden developing age models for recent lacustrine sequences spanning the last 200 years two case studies from west central sweden

the white river ash largest holocene plinian tephra the white river ash is a bi lobate tephra in eastern alaska yukon territory and western northwest territories plinian type eruptions produced the north lobe 1900 years bp and the larger east lobe 1250 years bp 14c years present evidence favors the vent for the east lobe to be beneath the klutlan glacier east lobe pumice is not present atop mt churchill so the pumice there must belong to the north lobe and is also likely to have come from a vent beneath the klutlan glacier isopachs of the east lobe now known to stretch as far east as great bear lake indicate an east lobe volume of 47 km3 thickness and grain size of the east lobe decay in exponential fashion producing straight line plots when the thickness half distance and clast half distance are plotted against the square root of the isopach area the proximal slope being steeper than the distal the east lobe eruption is indicated to have been into a wind of about 10 m s and to have produced an eruptive cloud height of 45 km the erupti

the formation of tephra layers in peatlands an experimental approach abstract tephrochronology provides a valuable method of dating peat deposits but results may be compromised if tephra undergoes significant post depositional movement this study takes an experimental approach to investigate the processes of tephra taphonomy tephra was applied to peats and movement monitored over periods of up to 6 years experiments combined field studies on six british peatlands with rainfall simulation experiments in the laboratory tephra moved up to 15 cm down through the peat but the vast majority remained at the surface at time of deposition forming a layer which accurately recorded the palaeo surface tephra moved both down by shards sinking through the peat and up with shards probably being moved by plant growth or with water table variability the extent of tephra movement most likely depends on the density and porosity of the surface peat there is no simple relationship with wetness there is some indication that the extent of tephra movement depends on the tephra particle size but this will require further work to confirm the taphonomy of tephra is an important issue which should be considered in all tephrochronology studies in peatlands

distal deposition of tephra from the eyjafjallajokull 2010 summit eruption the 2010 eyjafjallajokull lasted 39 days and had 4 different phases of which the first and third 14 18 april and 5 6 may were most intense most of this period was dominated by winds with a northerly component that carried tephra toward europe where it was deposited in a number of locations and was sampled by rain gauges or buckets surface swabs sticky tape samples and air filtering in the uk tephra was collected from each of the phases 1 3 with a combined range of latitudes spanning the length of the country the modal grain size of tephra in the rain gauge samples was 25 mu m but the largest grains were 100 mu m in diameter and highly vesicular the mass loading was equivalent to 8 218 shards cm 2 which is comparable to tephra layers from much larger past eruptions falling tephra was collected on sticky tape in the english midlands on 19 20 and 21st april phase 2 and was dominated by aggregate clasts mean diameter 85 mu m component grains 10 mu m sem eds spectra for aggregate grains contained an extra peak for sulphur when compared to control samples from the volcano indicating that they were cemented by sulphur rich minerals e g gypsum caso4 center dot h2o air quality monitoring stations did not record fluctuations in hourly pm10 concentrations outside the normal range of variability during the eruption but there was a small increase in 24 hour running mean concentration from 21 24 april phase 2 deposition of tephra from phase 2 in the uk indicates that transport of tephra from iceland is possible even for small eruption plumes given suitable wind conditions the presence of relatively coarse grains adds uncertainty to concentration estimates from air quality sensors which are most sensitive to grain sizes 10 mu m elsewhere tephra was collected from roofs and vehicles in the faroe islands mean grain size 40 mu m but 100 mu m common from rainwater in bergen in norway 23 91 mu m and in air filters in budapest hungary 2 6 mu m a map is presented summarizing these and other recently published examples of distal tephra deposition from the eyjafjallajokull eruption it demonstrates that most tephra deposited on mainland europe was produced in the highly explosive phase 1 and was carried there in 2 3 days

latest pleistocene and holocene glacier variations in the european alps in the alps climatic conditions reflected in glacier and rock glacier activity in the earliest holocene show a strong affinity to conditions in the latest pleistocene younger dryas glacier advances in the alps related to younger dryas cooling led to the deposition of egesen stadial moraines egesen stadial moraines can be divided into three or in some cases even more phases sub stadials moraines of the earliest and most extended advance the egesen maximum stabilized at 12 2 1 0 ka based on 10be exposure dating at the schonferwall tyrol austria and the julier pass outer moraine switzerland final stabilization of moraines at the end of the egesen stadial was at 11 3 0 9 ka as shown by 10be data from four sites across the alps from west to east the sites are piano del praiet northwestern italy grosser aletschgletscher central switzerland julier pass inner moraine eastern switzerland and val viola northeastern italy there is excellent agreement of the 10be ages from the four sites in the earliest holocene glaciers in the northernmost mountain ranges advanced at around 10 8 1 1 ka as shown by 10be data from the kartell site northern tyrol austria in more sheltered drier regions rock glacier activity dominated as shown for example at julier pass and larstig valley tyrol austria new 10be dates presented here for two rock glaciers in larstig valley indicate final stabilization no later than 10 5 0 8 ka based on this data we conclude the earliest holocene between 11 6 and about 10 5 ka was still strongly affected by the cold climatic conditions of the younger dryas and the preboreal oscillation with the intervening warming phase having had the effect of rapid downwasting of egesen glaciers at or slightly before 10 5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate between about 10 5 ka and 3 3 ka conditions in the alps were not conducive to significant glacier expansion except possibly during rare brief intervals past tree line data from kaunertal tyrol austria in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the swiss and austrian alps points to long periods during the holocene when glaciers were smaller than they were during the late 20th century equilibrium line altitudes ela were about 200 m higher than they are today and about 300 m higher in comparison to little ice age lia elas the larstig rock glacier site we dated with 10be is the type area for a postulated mid holocene cold period called the larstig oscillation presumed age about 7 0 ka our data point to final stabilization of those rock glaciers in the earliest holocene and not in the middle holocene the combined data indicate there was no time window in the middle holocene long enough for rock glaciers of the size and at the elevation of the larstig site to have formed during the short infrequent cold oscillations between 10 5 and 3 3 ka small glaciers less than several km2 may have advanced to close to their lia dimensions overall the cold periods were just too short for large glaciers to advance after 3 3 ka climate conditions became generally colder and warm periods were brief and less frequent large glaciers for example grosser aletschgletscher advanced markedly at 3 0 2 6 ka around 600 ad and during the lia glaciers in the alps attained their lia maximum extents in the 14th 17th and 19th centuries with most reaching their greatest lia extent in the final 1850 1860 ad advance

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

insights on tephra settling velocity from morphological observations in this study we present a systematic and detailed morphological characterization of tephra particles from different eruptions fontana lapilli masaya nicaragua keanak ko i formation kilauea usa recent dome explosions of soufriere hills volcano montserrat and the calculation of their terminal fall velocity tfv as obtained based on different drag prediction models i e wilson and huang 1979 haider and levenspiel 1989 ganser 1993 and dellino et al 2005 in particular particle sphericity and therefore particle surface area is essential for the calculation of tfv of irregular shape particles but is of complex determination various attempts have been proposed according to our results 2d morphological characterization of volcanic particles is a fast and simple application for a wide range of particle size and provides consistent sphericity and settling velocity values 3d scanning also provides a promising tool for lapilli sized tephra 2 cm in contrast gas adsorption derived surface area is not suitable for the calculation of tfv of volcanic particles mostly because it mainly describes the surface contribution of nanometric pores that are not expected to affect significantly tfv and because bulk sample analysis is representative of neither individual particles nor of the whole particle population settling velocities calculated using values of surface area derived from gas adsorption analyses are up to two orders of magnitude lower than the values obtained through 2d analysis in addition our results also show how the influence of particle shape on tfv increases with particle size in particular calculated tfv converges at small particle sizes 3 regardless of the model applied suggesting that the spherical assumption is appropriate for this size fraction discrepancies with the spherical model are within 10 discrepancies with the spherical model increase with particle size up to about 50 and depend on the choice of both the tfv model and the morphological parameterization used in particular the drag prediction model of ganser 1993 is sensitive to the effect of particle morphology on tfv and is well suited for all sizes and reynolds numbers of typical tephra particles finally our results show how individual size categories whole and half are not associated with individual tfv values but with a range of values which increases with class size nonetheless the half system is associated with a smaller standard deviation than the whole system and is therefore more appropriate for the modeling of tephra dispersal in any case for dispersal modeling purposes it is more appropriate to indicate a range of settling velocities for each size class rather than giving an average value

snapshots in time precise correlations of peat based proxy climate records in scotland using mid holocene tephras mid holocene tephra layers have been located and geochemically analysed from seven ombrotrophic bogs in scotland the tephras found in these scottish peats occur as stratigraphically discrete horizons not visible to the naked eye and originate from volcanic activity in iceland identifying and geochemically typing the tephra layers can enable precise correlations between sites on regional scales depending on the spatial extent of the airfall events dispersal of both the glen garry and hekla 4 tephras is excellent over scotland enabling snapshot views of the past at the time of these tephra depositions palaeoecological analyses have also been undertaken on these bogs providing detailed reconstructions of past changes in bog vegetation and surface wetness a proxy for past climates correlations between the ombrotrophic bogs at the time of the glen garry tephra revealed significant differences between the proxy climate records in the north and the south of scotland suggesting asynchronous changes between northern scotland and the rest of great britain

soils as indicators of the pleistocene and holocene landscape evolution in the alay range kyrgystan abstract soils derived from quaternary glacial glaciofluvial and aeolian deposits in the alay range kyrgystan were studied to reconstruct the pleistocene and holocene landscape evolution geomorphologic studies radiocarbon dating of a horizons in palaeosols and iron fractionation were undertaken during the last glacial maximum lgm the abramov glacier in the alay range advanced down the koksu valley to an altitude of 2500 m asl about 50 km from the modern snout ela lowering about 600 m in addition several frontal moraine complexes could be identified at the valley bottom of the koksu river between 3100 m asl and the modern glacier snout at 3650 m asl the complexes can be assigned to the following glacier advances late glacial ela lowering 200 300 m early holocene to end of late glacial younger dryas ela lowering about 110 m neoglacial ela lowering about 50 m and little ice age ela lowering about 50 m similar glacier advances could be reconstructed according to the soil development on the lateral moraines near the abramov glacier at 3600 4000 m asl determination of pedogenic iron oxides corroborated the morphologic and radiocarbon results

aggregation dominated ash settling from the eyjafjallajokull volcanic cloud illuminated by field and laboratory high speed imaging the recent eyjafjallajokull iceland eruption strikingly underlined the vulnerability of a globalized society to the atmospheric dispersal of volcanic clouds from even moderate size eruptions ash aggregation controls volcanic clouds dispersal by prematurely removing fine particles from the cloud and depositing them more proximally physical parameters of ash aggregates have been modeled and derived from ash fallout deposits of past eruptions yet aggregate sedimentation has eluded direct measurement limiting our ability to predict the dispersal of volcanic clouds here we use field based high speed video analysis together with laboratory experiments to provide the first in situ investigation and parameterization of the physical features and settling dynamics of ash aggregates from a volcanic cloud in may 2010 high speed video footage was obtained of both ash particles and aggregates settling from the eyjafjallajokull volcano eruption cloud at a distance of 7 km from the vent fallout samples were collected simultaneously experimental laboratory determinations of the density morphology and settling velocity of individual ash particles enable their distinction from aggregates the combination of field and experimental analyses allows a full characterization of the size settling velocity drag coefficient and density distributions of ash aggregates as well as the size distribution of their component particles we conclude that ash aggregation resulted in a tenfold increase in mass sedimentation rate from the cloud aggravating the ash hazard locally and modifying cloud dispersal regionally this study provides a valuable tool for monitoring explosive eruptions capable of providing robust input parameters for models of cloud dispersal and consequent hazard forecast

geochemistry and extractable fe and al in cold temperature soils of northwestern siberia the concentrations of major minor and trace elements in three cryosols from north western siberia were analysed to determine profiles of geochemical uniformity element mobility and the release and build up of extractable fe and al the scope of this study involves weathering processes over all or part of the lateglacial to the holocene epoch 10 ka bp q1 in a cold environment the variability of hf content in the horizons is likely silica induced and accounts for much of the concentration variation in the other elements the slight increases of mobile to immobile elements in the b horizons indicate trivial downward movement within the profiles iron and al extracts were investigated to elicit information regarding profile age and palaeoclimate extractable fe and al show slight increases relative to the total concentrations in the soil sola ah bw horizons lattice fe decreases in the ah bw horizons as a result of weathering and production of sesquioxides over time increases of ferrihydrite in the ah horizons and in the parent material of some profiles may indicate perched water tables at some time in the past possibly as sustained yearly water levels in the active layer free iron fed relative to total fe increases in the ah bw horizons compared with the lower horizons where the oxidation potential is weaker low total fe reflects reworked felsic rich deltaic and shallow marine deposits from the permian to the early tertiary thereafter emplaced by episodic flooding of glacial meltwater from the arctic urals and or the kara sea ice sheet organically complexed al alp uniformly low in all soils nevertheless shows trends indicating some downward movement a rather unique occurrence in arctic tundra soils as indicated by the slow increase of oxihydrites it may not be realistic to estimate the age of a profile by its physical characteristics however it appears possible to determine broad age ranges from the isotopic composition of water in soils organic carbon concentrations between and within soil profiles indicate it may be more prevalent in tundra soil than previously thought and may also play a significant role in uploading co2 to the atmosphere as warming and microbial activity q2 progresses copyright 2009 john wiley sons ltd

surface exposure dating of the great aletsch glacier egesen moraine system western swiss alps using the cosmogenic nuclide 10be egesen moraines throughout the alps mark a glacial advance that has been correlated with the younger dryas cold period using the surface exposure dating method in particular the measurement of the cosmogenic nuclide 10 be in rock surfaces we attained four ages for boulders on a prominent egesen moraine of great aletsch glacier in the western swiss alps the 10 be dates range from 10 460 1100 to 9040 1020 yr ago three 10 be dates between 9630 810 and 9040 1020 yr ago are based upon samples from the surfaces of granite boulders two 10 be dates 10 460 1100 and 9910 970 yr ago are based upon a sample from a quartz vein at the surface of a schist boulder in consideration of the numerous factors that can influence apparently young 10 be dates and the scatter within the data we interpret the weighted mean of four boulder ages 9640 430 yr including the weighted mean of two 10 be dates of the quartz vein as a minimum age of deposition of the moraine all 10 be dates from the great aletsch glacier egesen moraine are consistent with radiocarbon dates of nearby bog bottom organic sediments which provide minimum ages of deglaciation from the moraine the 10 be dates from boulders on the great aletsch glacier egesen moraine also are similar to 10 be dates from egesen moraines of vadret lagrev glacier on julier pass in the eastern swiss alps both the morphology of the great aletsch glacier egesen moraine and the comparison with 10 be dates from the inner vadret lagrev egesen moraine support the hypothesis that the climatic cooling that occurred during the younger dryas cold episode influenced the glacial advance that deposited the great aletsch glacier egesen moraine because of the large size and slow response time of great aletsch glacier we suggest that the great aletsch glacier egesen moraine was formed during the last glacial advance of the multiphased egesen cold period the kromer stage during the preboreal chron copyright 2004 john wiley sons ltd

weathering rinds archives of paleoenvironments on mount kenya east africa abstractweathering rind thicknesses on pebble and cobble size sediment have been used for the past half century at least as an age indicator of postdepositional time following a geologic event in mountainous terrain rind thickness is taken as a measurement of weathering over time frames of 0 5 m yr variable thicknesses are used to discriminate relative ages of glacial deposits the effects of chemical and physical weathering that together produce rinds are only rarely considered and most research objectives have centered on lichen alteration of clast surfaces recent microscopic analyses of weathering rinds on volcanic clasts of 70 0 ka to 2 0 m yr age produced new data on weathering products as well as unexpected incorporated biotic materials undergoing diagenesis the question as to how much physical mineral chemical biotic paleoenvironmental data might be archived in rinds is discussed the character and classification of organic materials undergoing diagenesis are also discussed

an outline tephrochronology for the holocene of the north of ireland geochemically typed thin layers of icelandic holocene tephras form a tephrochronology for the north of ireland tephrochronology construction is based on geochemical linkage with dated historic icelandic eruptions and high precision multisample radiocarbon dating comparison with geochemically typed holocene layers at sites throughout scotland and northern england shows that some layers are widespread throughout much of the northern british isles other layers of known historic date have so far been detected only in ireland

a new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments abstract tephrochronology a key tool in the correlation of quaternary sequences relies on the extraction of tephra shards from sediments for visual identification and high precision geochemical comparison a prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes e g chemical exchange in the sedimentary environment and or by laboratory analytical procedures however natural glasses particularly when in the form of small shards with a high surface to volume ratio are prone to chemical alteration in both acidic and basic environments current techniques for the extraction of distal tephra from sediments involve the cleaning of samples in precisely such environments and at elevated temperatures the acid phase of the cleaning process risks alteration of the geochemical signature of the shards while the basic phase leads to considerable sample loss through dissolution of the silica network here we illustrate the degree of alteration and loss to which distal tephras may be prone and introduce a less destructive procedure for their extraction this method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity in trials this method out performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations the implications of this study are highly significant because i the current database of distal tephra records and their corresponding geochemical signatures may require refinement and ii the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures it is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

lgm and late glacial fluctuations in the eastern alps abstract studies of glacier development in the eastern alps around the last glacial maximum lgm for more than a hundred years have created a reasonably well based knowledge of glacier extent sedimentation and palaeoclimate as well as chronology this was obtained from broad and detailed mapping palynological investigations and radiocarbon dating despite a very cold climate between 31 and 21 ka bp topographical constraints meant that glacier extent was limited to tributary valleys of the main trenches until about 24 ka bp then rapid ice build up in the main longitudinal valleys led to extended ice streams and to piedmont glaciers in the foreland this build up virtually ended at ca 21 ka bp according to radiocarbon dates obtained from organic matter embedded in the outwash and periglacial gravels niederterrasse the lgm possibly lasted 3000 4000 years and shows a short maximalstand and a more prolonged hochstand both connected with outwash deposits the ice decay was apparently very fast and the glaciers vanished from the longitudinal valleys probably within some hundreds of years this retreat was interrupted by two short oscillations of active glaciers in contact with huge masses of inactive ice occupying the main valley floors before these became totally ice free these events at the beginning of the oldest dryas ca 16 ka bp were followed by a distinct glacier readvance gschnitz marked by end moraines and outwash fans according to some radiocarbon dates this occurred around 14 ka bp during the bolling interstade the valleys became almost ice free the next two glacier readvances daun and egesen were limited to cirques and the higher parts of the valleys and are dated to the older and younger dryas stades respectively

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

new occurrences of the white river ash east lobe in subarctic canada and utility for estimating freshwater reservoir effect in lake sediment archives abstract the freshwater reservoir effect fre in the canadian subarctic complicates development of high resolution age depth models based on radiocarbon dates from lake sediments volcanic ashfall layers tephras provide chronostratigraphic markers that can be used to estimate age offsets we describe the first recorded occurrence of a visible tephra in a lacustrine sequence in the central northwest territories the tephra observed in pocket lake near yellowknife is geochemically and stratigraphically attributed to the white river ash east lobe wrae 833 850 ce 1117 1100 cal bp which originated from an eruption of mount churchill alaska we also observed the wrae as a cryptotephra in bridge lake 130 km to the ne suggesting that records of this tephra are potentially widespread in cnt lakes the identification of this tephra presents opportunities for use of the wrae as a dating tool in the region and to quantify the magnitude of the fre in order to correct radiocarbon age depth models two well dated sediment cores from pocket lake containing a visible wrae record indicate a fre of 200 years at the time of the ash deposition which matches closely with the estimated fre of 245 years at the lake sediment water interface although additional results from other lakes in the region are required this finding implies that fre estimates for the late holocene in the region may be based either on down core wrae radiocarbon age model offsets or on radiocarbon dates obtained from the sediment water interface

late quaternary icelandic tephras in ireland and great britain detection characterization and usefulness microscopic studies of late quaternary tephras from iceland yield a detailed tephrochronology in deposits of the british isles where the quantities of volcanic glass employed are much less than those used to construct almost any other late quatemary tephrochronology we summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in ireland including those which comprise an outline historic tephrochronology for ireland the paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical tephras in other parts of the british isles and europe are used with those in ireland to demonstrate further applications of tephrochronology especially for dating deposits where other dating methods e g radiocarbon have proved difficult

geochemical stability of fine grained silicic holocene tephra in iceland and scotland this paper tests two assumptions fundamental to the use of fine grained silicic tephras from iceland for creating chronological frameworks in northwest europe it is shown firstly that glass shards can retain their overall chemical integrity on at least a four millennial time scale in contrasting depositional environments in iceland and scotland and secondly that an acid digestion process the most practical method for extracting tephra from peat does not significantly bias the results of major element analysis by electron microprobe the implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic icelandic tephras in northwest europe

late glacial retreat and neoglacial advance sequences in the zillertal alps austria abstract late glacial terrain in the schwarzensteinkees hornkees and waxeckkees forelands of the zillertal alps is dominated by sediments deposited by readvancing ice emplaced in the little ice age starting approximately 550 70 cal 14 c yr bp late glacial ice scoured the massif with remnants of late glacial end moraines fronting lia end moraines and buried paleosols underlying lia end moraines providing scattered evidence of compositional change and weathering since the later dryas the amount of recovered wood from lia moraines indicates that the massif was forested for at least part of mid holocene times most likely during the atlantic chronozone when presumably soil morphogenesis was accelerated details of till composition and weathering history provide a pedostratigraphic reconstruction which includes mid lia readvances between 400 70 cal 14 c yr bp and 350 70 cal 14 c yr bp the heavily convoluted character of underlying early lia or older tills suggests either pre existing strongly active cryoturbation in a thin entisol regosol or active push moraine dynamics of advancing warm ice sem analysis documents differences in glacial dynamics that may be related to ice thickness stick slip motion or clastic load in the ice coupled with rate of movement

re deposited cryptotephra layers in holocene peats linked to anthropogenic activity tephra layers can form useful age equivalent stratigraphic markers for correlating palaeoenvironmental sequences and they provide information about the spatio temporal nature of past volcanic ash f