new insights into source and dispersal of mediterranean s1 tephra an early holocene marker horizon erupted at mt erciyes turkey abstract deposition of early holocene eastern mediterranean s1 tephra and a black sea cryptotephra coincides with cultural transitions in the fertile crescent termed the neolithic revolution as well as sapropel formation during climate variability of the african humid period classifying them as paramount regional marker horizons for archaeology as well as paleoclimatology their correlations with specific eruptions of the mt erciyes stratovolcanic complex central anatolia remained inconclusive though here we use zircon double dating by u th he and u th disequilibrium methods major and trace element tephra glass geochemistry and probabilistic modeling of tephra dispersal in an attempt to characterize all major late quaternary proximal tephras of mt erciyes and to correlate them with distal deposits furthermore we discuss contrasting proximal and distal tephra dispersal three nearly coeval rhyolitic satellite domes dikkartin perikartin and karagullu erupted at mt erciyes in the early holocene and their dome extrusions were all preceded by explosive phases producing pyroclastic material that formed tephra fall and pyroclastic flow deposits the new eruption age of 9 03 0 55 ka 1 uncertainty here and elsewhere for proximal dikkartin pumice is consistent with 14c based s1 tephra chronologies in distal locations averaging 8 92 0 03 cal ka bp perikartin pyroclastic flow deposits predate s1 tephra by ca 0 8 ka according to a pair of published 14c ages and stratigraphically overlie karagullu fall out here dated to 8 2 1 8 ka previously undated proximal tephras of mt erciyes erupted in the late 85 2 4 9 ka and middle pleistocene 154 5 5 3 ka s1 tephra glass is chemically similar to that of dikkartin fall out but also indistinguishable from that of perikartin fall out karagullu pumice is characterized by a distinct glass chemical composition which correlates with that of unnamed cryptotephra reported for the southeastern black sea instead where these results call for a re evaluation of existing age models maximum lithic clast size isopleths for proximal dikkartin fall out indicate eastward dispersal of a 20 5 km high eruption plume by stratospheric winds in agreement with results of probabilistic tephra dispersal modeling this azimuth contrasts with the known distribution of s1 tephra at distal locations that are all south of mt erciyes significant tephra occurrences at up to 1300 km distance and orthogonal to prevalent stratospheric wind directions either result from very atypical wind conditions probability 10 or are caused by tephra transport by prevailing low altitude winds two scenarios are proposed for low altitude transport eolian reworking of primary fall out more likely from the more widespread dikkartin deposits or co ignimbrite ash cloud dispersal more likely from the perikartin eruption which predominantly produced pyroclastic flows because s1 tephra is chemically indistinguishable from both dikkartin and perikartin by major and trace element glass compositions its exact source and dispersal mechanism remain ambiguous although existing 14c ages for perikartin predating those for s1 tephra favor dikkartin as its source

mound development as an interaction of individual plants with soil water erosion and sedimentation processes on slopes in the mediterranean region semi natural shrubland communities named matorral often present a discontinuous cover where isolated perennial plants alternate with bare inter plant areas in such ecosystems the patchy distribution of the vegetation is usually associated with microtopographic sequences of mounds that develop under isolated plants and break the overall slope continuity in this study the influence of three representative species of the mediterranean matorral rosmarinus officinalis stipa tenacissima and anthyllis cytisoides on slope microtopography is determined and the processes that take part in the development of microtopographic structures beneath the plant canopy are identified the influence of slope gradient plant species and plant parameters on the shape and height of microtopographic structures is also studied the shape of the microtopographic structures is described by using a two dimensional microprofilemeter and mound height is determined by measuring in the field a mound height index defined as the distance from the top to the bottom of the mound the results obtained show that plant species play a major role in the shape and height of the microtopographic structures whereas terrace type structures generally develop under anthyllis shrubs microtopographic forms associated with rosmarinus and stipa plants vary with slope gradient the almost symmetric mound type structures that develop under these two species on gentle slopes change into terrace type structures as slope gradient increases moreover statistically significant differences exist between the three species with regard to mound height mean values of mound height are 19 4 14 6 and 4 3 cm under the canopy of stipa rosmarinus and anthyllis respectively plant parameters essentially roughness and slope gradient have a significant influence on mound height index four main processes were identified as affecting mound development in the studied field site sedimentation differential interrill erosion differential splash erosion and bioturbation plant species interact in different ways with these processes according to their morphologies since stipa and rosmarinus plants are more efficient than anthyllis shrubs in controlling water erosion in retaining sediments and in modifying soil properties under their respective canopies they give rise to higher microtopographic structures that facilitate water and nutrient storage by plants on slopes copyright 2000 john wiley sons ltd

tephra transformations variable preservation of tephra layers from two well studied eruptions volcanologists often use terrestrial tephra layers to reconstruct volcanic eruptions however the conversion of fresh tephra deposits into tephra layers is poorly understood to address this knowledge gap we surveyed tephra layers emplaced by the 1980 eruption of mount st helens usa msh1980 and the 1947 eruption of hekla iceland h1947 we compared our measurements with observations made shortly after the 1947 and 1980 eruptions to calibrate the subsequent transformation of the tephra deposit we expected the tephra layers to retain the broad characteristics of the original deposits but hypothesized a changes in thickness and mass loading due to re working and b positive correlations between thickness and vegetation density we observed some systematic changes in tephra layer properties with distance from the vent and the main plume axis however the preservation of the layers varied both between and within our survey locations closed coniferous forest appeared to provide good conditions for the preservation of the msh1980 tephra as expected preservation of the h1947 deposit in sparsely vegetated parts of iceland was much more variable however preservation of the msh1980 deposit in sparsely vegetated areas of eastern washington state was also excellent possibly due to biocrust formation we concluded that the preservation of tephra layers is sensitive to surface conditions at the time of the eruption these findings have implications for the reconstruction of past eruptions where eruption plumes span regions of variable surface cover

the plinian fallout associated with quilotoa s 800 yr bp eruption ecuadorian andes abstract large volcanic eruptions at dacitic or rhyolitic volcanoes often generate exceptional volumes of fine ash that mantles an area up to a million km 2 these eruptions are characterized by extreme fragmentation of the magma and hence extraordinary dispersal of ash and are categorized as plinian ultraplinian or phreatoplinian events large volume co ignimbrites or co plinian ashes are often produced by such eruptions high fragmentation indices of 90 are attributed to the violent eruption of silicic magma especially if augmented by fuel coolant reactions produced when abundant external water interacts with the magma the present study documents a case where the fine ash 1 mm diameter fall deposit related to the plinian phase of the eruption comprises the overwhelming bulk about 87 wt of the eruptive products this is another example demonstrating the predominance of a widespread fine grained co plinian ash which follows the initial coarser lapilli fall historical eruptions at two other andean volcanoes quizapu chile and huaynaputina peru and at santa maria guatemala and novarupta alaska produced similar ash fall sequences quilotoa s 800 yr bp eruption in the ecuadorian andes is an example of a powerful plinian eruption at a small dacitic volcano it produced a crystal rich fine grained ash layer which mantled an extrapolated 810 000 km 2 with 1 mm thickness and has a bulk magma volume of about 18 3 km 3 stratigraphic and petrographic studies as well as granulometric and density analyses were employed to investigate these eruptive products particularly the distal co plinian fall deposits the eruptive cycle consisted of a phreatomagmatic triggering the establishment of a powerful sustained plinian column and subsequently partial column collapses leading to widespread surge and ash flow activity quilotoa s 800 yr bp eruption has a vei volcano explosivity index 6 and generated a maximum column height of about 35 km and a mass discharge rate of 2 10 8 kg s in comparison pinatubo s 1991 eruption had similar column heights and discharge rates but smaller erupted volumes factors that possibly contributed to the extreme explosiveness and resulting fine grained ash production include inferred volatile overpressures in the crystal dominated dacite magma a rapid eruption onset a forceful and sustained plinian column possibly through a crater lake thus promoting extreme fragmentation of the magma but without leaving evidence of wet phreatoplinian type deposits

illness and elevated human mortality in europe coincident with the laki fissure eruption grattan j durand m taylor s illness and elevated human mortality in europe coincident with the laki fissure eruption in volcanic degassing geological society special publication 213 oppenheimer c pyle d m and barclay j eds geological society london special publications 410 414 2003

bioprotection and disturbance seaweed microclimatic stability and conditions for mechanical weathering in the intertidal zone as well as their destructive roles plants animals and microorganisms contribute to geomorphology and ecology via direct and indirect bioprotection which can reduce weathering and erosion for example indirect bioprotection can operate via biotic influences on microclimate whereby physical decay processes associated with fluctuations in temperature and moisture salt crystallization thermal fatigue and wetting drying are limited in the intertidal zone the spatial and temporal distribution of macroalgae seaweeds is patchy related to physical and ecological conditions for colonization and growth and the nature and frequency of natural and anthropogenic disturbance we examined the influence of seaweed canopies fucus spp on near surface microclimate and by implication on conditions for mechanical rock decay and under canopy ecology monitoring on hard artificial coastal structures in south west england uk built from limestone and concrete showed that both the range and maxima of daily summertime temperatures were significantly lower by an average of 56 and 25 respectively in areas colonized by seaweed compared to experimentally cleared areas short term microclimatic variability minutes hours was also significantly reduced by an average of 78 for temperature and 71 for humidity under algal canopies during low tide events using seaweed as an example we develop a conceptual model of the relationship between biological cover and microclimate in the intertidal zone disturbance events that remove or drastically reduce seaweed cover mediate shifts between relatively stable and unstable states with respect to mechanical decay and ecological stress associated with heat and desiccation in urban coastal environments where disturbance may be frequent facilitating the establishment and recovery of canopy forming species on rocks and engineered structures could enhance the durability of construction materials as well as support conservation planning and policy targets for biodiversity enhancement

woody vegetation and channel morphogenesis in low gradient gravel bed streams in the ozark plateaus missouri and arkansas woody vegetation affects channel morphogenesis in ozark streams of missouri and arkansas by increasing local roughness increasing bank strength providing sedimentation sites and creating obstructions to flow variations in physiographic controls on channel morphology result in systematic changes in vegetation patterns and geomorphic functions with increasing drainage basin area in upstream reaches streams have abundant bedrock control and bank heights that typically are less than or equal to the rooting depth of trees in downstream reaches where valleys are wider and alluvial banks are higher vegetation has different geomorphic functions at drainage areas of greater than 100 200 km2 ozarks streams are characterized by longitudinally juxtaposed reaches of high and low lateral channel migration rates referred to as disturbance reaches and stable reaches respectively whereas stable reaches can develop stable forested floodplains if they are not farmed disturbance reaches are characterized by dynamic vegetation communities that interact with erosion and deposition processes disturbance reaches can be subdivided into low gradient and high gradient longitudinal zones low energy zones are characterized by incremental unidirectional lateral channel migration and deposition of gravel and sand bars the bars are characterized by prominent bands of woody vegetation and ridge and swale topography channel monitoring data indicate that densely vegetated bands of woody vegetation formed depositional sites during bedload transporting events the same floods caused up to 20 m of erosion of adjacent cutbanks scoured non vegetated areas between vegetation bands and increased thalweg depth and definition in high energy or riffle zones channel movement is dominantly by avulsion in these zones vegetation creates areas of erosional resistance that become temporary islands as the channel avulses around or through them woody vegetation on islands creates steep root defended banks that contribute to narrow channels with high velocities calculation of hydraulic roughness from density and average diameter of woody vegetation groups of different ages indicates that flow resistance provided by vegetation decreases systematically with group age mainly through decreasing stem density if all other factors remain constant the stabilizing effect of a group of woody vegetation on a gravel bar decreases with vegetation age

late holocene land surface change in a coupled social ecological system southern iceland a cross scale tephrochronology approach this work is supported by a uk natural environment research council nerc phd studentship ne f00799x 1

reconceptualising the role of organisms in the erosion of rock coasts a new model attempts to understand the morphodynamics of rock coasts focus on the nature and rate of erosion and how this influences the evolution of coastal profiles over century to millennial timescales biological contributions to this process are often ignored or treated in a rather simplistic way as merely producing microscale decreases in rock strength using a combination of field observations and literature review we address two key issues hampering a more rounded assessment of biological impacts erosion of coastal rocks firstly we reconceptualise the biological contributions to erosion of rock coasts into direct and facilitative types and secondly we discuss the need for more appropriate reporting of rates of bioerosion for direct bioerosion this means clearly documenting the percentage of platform surfaces affected by bioerosive agents and quantifying the volume of material eroded and the amount of fine sediment produced for facilitative bioerosion we must quantify the roles of biota in changing the material properties of rocks creating or altering surface morphologies and or weakening joint boundaries in this way facilitative bioerosion is one of several processes mediating geomorphic alteration of rock surfaces contributing to the production of landforms and or reducing the resisting force of rock subsequently we build on these ideas to produce a new conceptual model which more accurately portrays the multiple and cross scalar ways that biological processes notably bioerosion influence the resistance of coastal rocks to erosive forces such a model provides a stronger basis for numerical modelling and understanding the morphodynamics of rock coasts in the future and allows a quantitative assessment of the role of biota

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

two millennia of glacier advances from southern iceland dated by tephrochronology two glaciers at eyjafjallajokull south iceland provide a record of multiple episodes of glacier advance since the sub atlantic period ca 2000 yr ago a combination of tephrochronology and lichenometry was applied to date ice marginal moraines tills and meltwater deposits two glacier advances occurred before the 3rd century ad others in the 9th and 12th centuries bracketing the medieval warm period and five groups of advances occurred between ad 1700 and 1930 within the little ice age the advances of eyjafjallajokull before the norse settlement ca ad 870 were synchronous with other glacier advances identified in iceland in contrast medieval glacier advances between the 9th and 13th centuries are firmly identified for the first time in iceland this challenges the view of a prolonged medieval warm period and supports fragmentary historical data that indicate significant medieval episodes of cooler and wetter conditions in iceland an extended and more detailed glacier chronology of the mid and late little ice age is established which demonstrates that some small outlet glaciers achieved their little ice age maxima around ad 1700 while little ice age advances across iceland appear to synchronous the timing of the maximum differs between glacier type and region

ash mists and brown snow remobilization of volcanic ash from recent icelandic eruptions recent eruptions in iceland and chile have demonstrated that volcanic ash problems persist long after an eruption for this reason ash dispersion models are being extended to include ash remobilization critical to these models is knowledge of the ash source and the particle sizes that can be mobilized under different wind and moisture conditions here we characterize the physical and chemical characteristics of ash deposited on new snow in reykjavik iceland following a blizzard on 6 march 2013 morphological textural and compositional analyses indicate resuspension from multiple eruptive deposits including both grimsvotn 2011 and eyjafjallajokull 2010 eruptions grain size measurements show a mode of 32 63 m with particles as large as 177 m there is little mass in the very fine fraction 10 m pm10 we compare our observations to predictions using the lagrangian particle dispersion model name uk met office the model output is consistent with observations in that it forecasts resuspension from both eyjafjallajokull and grimsvotn source regions and shows ash deposition coincident with the timing of observed deposition in reykjavik the modeled deposit in reykjavik predicts however a substantially lower proportion of grimsvotn ash than observed this discrepancy has highlighted the need to reassess the assumptions used in the simulations particularly regarding the source area and precipitation thresholds furthermore we suggest that modification of ash deposits in the form of erosion redeposition compaction or cementation may influence the dynamics of resuspension over time thus influencing the ability of model simulations to accurately forecast remobilization events

evolution of lacustrine systems along the miocene mur murz fault system eastern alps austria and implications on source rocks in pull apart basins tectonically controlled lakes developed during miocene lateral extrusion of the eastern alps mineralogy and the inorganic and organic geochemistry of rocks from three boreholes were investigated to reconstruct the evolution of lake ingering and lake groisenbach and to study the distribution of source rocks in pull apart basins gas prone coal and oil prone sapropelic shale accumulated during the initial shallow stages of lake ingering thereafter the lake deepened rapidly 125 m thick prodelta shale containing a type ii kerogen was deposited in the brackish several hundred meter deep hydrologically closed lake afterwards decreasing subsidence allowed the filling of the lake by prograding deltas during the advance of the deltaic systems the lake became shallower hydrologically open and the brackish influence terminated source rock quality decreased significantly during the filling stage of the lake a consequence of dilution of autochthonous organic matter and of enhanced input of land plants despite its considerable dimensions formation and filling of lake ingering lasted only two million years lake groisenbach was considerably smaller and more susceptible to high frequency changes in lake chemistry although the water body was temporarily oligosaline brackish conditions did not occur high sulphur contents were due to anoxic events and the inflow of ca rich waters abundant dissolved silica favoured diatoms blooms

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

the onset of the palaeoanthropocene in iceland changes in complex natural systems this study was financially supported by the carnegie trust for the universities of scotland the national science foundation of america through grant 1202692 comparative island ecodynamics in the north atlantic and grant 1249313 tephra layers and early warning signals for critical transitions and the leverhulme trust study abroad fellowship to ajd

how does tephra deposit thickness change over time a calibration exercise based on the 1980 mount st helens tephra deposit abstract tephra layers are frequently used to reconstruct past volcanic activity inferences made from tephra layers rely on the assumption that the preserved tephra layer is representative of the initial deposit however a great deal can happen to tephra after it is deposited thus tephra layer taphonomy is a crucial but poorly understood process the overall goal of this research was to gain greater insight into the taphonomy of terrestrial tephra layers specifically the extent to which deposit thickness is altered over time with implications for tephra volume estimation we approached this by a conducting a new survey of the tephra layer from the recent well studied eruption of mount st helens on may 18th 1980 msh1980 b modelling the tephra layer thickness using a mathematical technique and c comparing our results with an equivalent model based on measurements taken immediately after the eruption in this way we aimed to quantify any losses and transformations that have occurred during our study we collected measurements of tephra layer thickness from 86 locations ranging from 600 km from the vent geochemical analysis was used to identify tephra of uncertain origin our results indicated that the extant tephra layer at undisturbed sites was representative of the original deposit overall preservation in these locations in terms of thickness stratigraphy and geochemistry had been remarkably good however the isopach maps generated from our measurements diverged from isopachs produced in the same way but derived from the original survey data furthermore our estimates of the quantity of tephra produced during the eruption greatly exceeded previous estimates of the fallout volume in our study inaccuracies in the modelled fallout arose from issues of sampling strategy rather than taphonomy our results demonstrate the sensitivity of volcanological reconstructions to measurement location and the great importance of reliably measured low zero values in reconstructing tephra deposits

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

sources of uncertainty in the mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale this study uses the tephra from the caldera forming eruption of mount mazama crater lake or usa to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude we combine 250 mazama tephra occurrences reported by a range of disciplines including archaeology paleoclimatology and volcanology with new field studies to better understand the extent of the distal tephra we find that the mazama tephra has been remobilised to varying degrees over the past 7000 years so each tephra locality was appraised for the likelihood that it records primary tephra fallout we designated 45 of the distal 100 km from source tephra sites as suitable for use in the production of isopachs using a spline fitting method the new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic mazama eruption to 176 km3 61 km3 dense rock equivalent dre this study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit interpreting remobilised deposits can provide insight into post eruptive processes that could potentially pose secondary hazards following large magnitude eruptions we also show that in some circumstances remobilised deposits preserve important physical properties such as grain size

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

seasonality of the late pleistocene dawson tephra and exceptional preservation of a buried riparian surface in central yukon territory canada abstract the late pleistocene dawson tephra was deposited by one of the largest quaternary eruptions in northwestern north america its distribution is known sparsely from sites near the source area in southwestern alaska and central yukon territory where more than 20 occurrences are documented in the klondike region dawson tephra erupted about 25 300 14 c yr bp near the onset of the last glaciation and provides a stratigraphic marker across eastern beringia we report radiocarbon ages paleobotanical data and cryostratigraphic observations from a new dawson tephra locale at goldbottom creek in the klondike region of yukon territory which collectively indicate that the eruption occurred in the late winter or early spring multiple fining upward tephra rich ice beds are interpreted as remnants of surface icings which presently are common in the region during spring a buried in situ riparian meadow preserved below the icing and tephra consists of abundant tufted hair grass deschampsia caespitosa with interspersed horsetails equisetum cf palustre and mosses detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits consistent with a late season surface when the icing was active the extraordinary thickness of dawson tephra in central yukon likely reflects reworking of a winter deposited tephra by snow melt in the spring following the eruption indicating that the primary thickness may be overestimated at valley bottom sites winter deposition of the tephra may have in part minimized the terrestrial ecological impacts of the eruption on zonal steppe tundra vegetation through the retransportation of tephra from hillslopes to the riparian areas where the tephra became incorporated into local fluvial systems

holocene tephrochronology record of large explosive eruptions in the southernmost patagonian andes for regionally widespread holocene tephra layers in southernmost patagonia correlations based on both chemical and chronological data indicate their derivation from five large volume 1 km3 explosive eruptions of four different volcanoes in the southernmost andes bulk tephra and tephra glass major and trace element chemistry and sr isotopic ratios unambiguously distinguish different source volcanoes and imply that two of the regionally widespread tephra mb1 and mb2 were derived from mt burney 52 s one r1 from reclus 51 s one a1 from aguilera 50 s and one h1 from hudson volcano 46 s the h1 tephra derived from the hudson volcano which is located at the southern end of the andean southern volcanic zone svz 33 46 s contains distinctive greenish andesitic glass with feo 4 5 wt and tio2 1 2 wt in contrast rhyolitic glass in tephra derived from the eruptions of mt burney reclus and aguilera volcanoes which are located in the andean austral volcanic zone avz 49 55 s is clear and transparent and has significantly lower feo and tio2 tephra derived from these three avz volcanoes all contain plagioclase orthopyroxene minor clinopyroxene and amphibole biotite occurs only in the aguilera a1 tephra which also has the highest bulk tephra and tephra glass k2o and rb contents averages of new and published 14c ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated 14c age of the r1 eruption of reclus volcano to 12 685 260 years bp the mb1 and mb2 eruptions of mt burney to 8 425 500 and 3 830 390 years bp the hudson h1 eruption to 6 850 160 years bp and the a1 eruption of aguilera volcano to 3 000 100 years bp the volume of the largest of these eruptions h1 of the hudson volcano is estimated as 18 km3 the volume of the reclus r1 eruption is estimated at 10 km3 the aguilera a1 eruption at between 4 and 9 km3 and the younger mt burney mb2 eruption at 2 8 km3 the volume of the older mb1 mt burney eruption is the least well constrained but must have been larger than the younger mb2 eruption the data indicate that the frequency of explosive activity of volcanic centers in the avz is lower than in the southern svz

ecosystem engineers and geomorphological signatures in landscapes abstract biogeomorphologists study the roles of biota in landscape formation and decay ecologists interested in ecosystem engineering study environmental change caused by biota and the consequences for the engineer other organisms and ecological processes the interface is geomorphological change an interface both are aware of but study somewhat independently and differently interaction and integration among the two fields is the goal of this special issue here i take an ecological perspective of geomorphological change caused by ecosystem engineers in patches within landscapes that i hope can help facilitate this goal i ask the following general questions when will an ecosystem engineering species create a geomorphological signature in a landscape what in qualitative terms is such a signature how can the signature be estimated and how long will it last what engineer attributes and ecological factors will determine signature change what creates complications how do the answers inform whether or not life leaves a geomorphological signature to attempt answers i develop a provisional general theory of ecosystem engineering signatures that draws on and integrates a geomorphological foundation of balance between formation and decay landscape patch dynamics a general framework for ecosystem engineering and empirical studies i treat a landscape engineering signature as the balance of rates of formation f and rates of decay d across patches whose ratio value f d can be transformed 1 intermediate 1 or untransformed

widespread dispersal of icelandic tephra how does the eyjafjoll eruption of 2010 compare to past icelandic events widespread dispersal of icelandic tephra how does the eyjafjoll eruption of 2010 compare to past icelandic events

geochemistry dispersal volumes and chronology of holocene silicic tephra layers from the katla volcanic system iceland at least 12 silicic tephra layers silk tephras erupted between ca 6600 and ca 1675 yr bp from the katla volcanic system have been identified in southern iceland in addition to providing significant new knowledge on the holocene volcanism of the katla system which typically produces basaltic tephra the silk tephras form distinct and precise isochronous marker horizons in a climatically sensitive location close to both the atmospheric and marine polar fronts with one exception the silk tephras have a narrow compositional range with sio2 between 63 and 67 geochemically they are indistinguishable from ocean transported pumice found on beaches in the north atlantic region although they differ significantly from the silicic component of the north atlantic ash zone one naazo volumes of airborne silk tephra range from 0 05 to 0 3 km3 we present new isopach maps of the six largest layers and demonstrate that they originate within the katla caldera the apparently stable magma system conditions that produced the silk tephras may have been established as a consequence of the eruption of the silicic component of naazo ca 10 3 ka and disrupted by another large scale event the tenth century ad eldgja eruption ca 1 ka despite the current long repose silicic activity of this type may occur again in the future presenting hitherto unknown hazards copyright 2001 john wiley sons ltd

cooling of the south china sea by the toba eruption and correlation with other climate proxies 71 000 years ago the toba tephra layer has been identified in core md972151 in the southern south china sea scs northeast of the indonesia toba caldera this affords us an opportunity to directly determine a 1 c cooling for ca 1 kyr on the scs following the toba eruption 71 ka during the marine isotope stage 5a 4 transition using century scale sea surface temperature records this cooling event in the scs is well correlated with several coeval proxies such as increased east asia winter monsoon intensity increased ice rafted detritus in the north pacific ocean sediments and decreased 18 o in greenland ice core such correlation suggests a climate change where cold climate signals originated in the northern hemisphere ice sheets transferred southward by the winter monsoon and cooled the scs

the role of vegetation cover and slope angle in tephra layer preservation and implications for quaternary tephrostratigraphy financial support was provided by the national science foundation of america through grant 1202692 comparative island ecodynamics in the north atlantic and grant 1249313 tephra layers and early warning signals for critical transitions and the support of the carnegie trust for the universities of scotland

toba ash on the indian subcontinent and its implications for correlation of late pleistocene alluvium the toba ash occurs extensively in the indian subcontinent and marks a ca 74 000 yr old event in the bay of bengal and indian ocean it is about 10 cm thick whereas in several alluvial basins it is usually 1 3 m thick the latter occurs in a partly reworked state but as nearly chemically pure first cycle sediments the ash has a broad northwesterly dispersal pattern samples of ash from the indian subcontinent compare closely with the youngest 74 000 yr b p toba tuff and the deep sea toba ash in bulk chemical composition ree signature and bubble wall shard morphology however a more proximally located and thicker 2 5 m ash bed from the alluvial basins in the gneissic area and close to east coast has a lower magnitude negative eu anomaly possibly because of minor contamination by feldspathic silt quaternary sediments in the central narmada and middle son basins contain rich late and middle pleistocene mammalian and cultural records based on the presence of the ash layer marker and stratigraphic relations late pleistocene sediments within the subcontinent can be correlated with those from central india and the deep sea