explosive volcanism during the holocene in the upper limay river basin the effects of ashfalls on human societies northern patagonia argentina abstract in order to understand human response to holocene ashfall events tephra layers found in archaeological sites along the upper limay river basin northern patagonia argentina were bracketed with radiocarbon dates and correlated with tephra from a lacustrine sediment core and from outcrops and the archaeological evidence was analyzed a dark tephra associated with seismic activity was identified in the el trebol rockshelter filling interstices between fallen blocks together with remains of human activity and bones of extinct fauna marking a seismo volcanic event occurring between 11 758 and 12 866 cal yr bp this same seismic event affected the cuyin manzano site where the roof collapse made the site uninhabitable for a time a white tephra present in epullan grande epullan chica and traful i caves is correlated with nahuel huapi tephra nht equivalent to laya s rio blanco and rio pereyra members rio pireco formation nht is considered to have been derived from the same eruptive event with dates ranging between ca 1950 2500 cal yr bp a dark tephra from ortega s cave and several tephra from puerto tranquilo i rockshelter ranging between 521 and 2069 cal yr bp show how the mobile hunters gatherers of northern patagonia were able to cope with the changing circumstances

geophysical analysis of transverse ridges and internal structure at lone peak rock glacier big sky montana usa rock glaciers are periglacial alpine landforms that are found in many locations worldwide whereas well developed models of deformation are established for traditional alpine glaciers rock glacier deformation is poorly understood geophysical data from lone peak rock glacier lprg southwest montana usa are paired with lidar bare earth 1m digital elevation model dem analysis to explore potential genetic relationships between internal composition structure and regularly spaced arcuate transverse ridges expressed at the rock glacier surface the internal composition of lprg is heterogeneous with frozen debris and clean ice overlain by an unconsolidated talus mantle upslopedipping clearly distinguished reflectors in the ground penetrating radar gpr longitudinal survey at lprg correspond to transverse ridges the spacing and slope of individual features at the surface and in the subsurface were measured and compared and are found to be similar the structures observed at lprg and other rock glaciers are similar to structures detected in glaciotectonically altered sediment ice cored moraines and other rock glacier settings this finding suggests that transverse ridges on rock glaciers may be used as geomorphic indicators of internal deformation this study contributes to the body of research on the application of gpr to rock glaciers and is the first to directly pair and analyze individual surface topographic features with internal structures

permafrost activity and atmospheric warming in the argentinian andes abstract rock glaciers are permafrost or glacial landforms of debris and ice that deform under the influence of gravity recent estimates hold that in the semiarid chilean andes for example active rock glaciers store more water than glaciers however little is known about how many rock glaciers might decay because of global warming and how much this decay might contribute to water and sediment release we investigated an inventory of 6500 rock glaciers in the argentinian andes spanning the climatic gradient from the desert andes to cold temperate tierra del fuego we used active rock glaciers as a diagnostic of permafrost assuming that the toes mark the 0 c isotherm in climate scenarios for the twenty first century and their impact on freezing conditions near the rock glacier toes we find that under future worst case warming up to 95 of rock glaciers in the southern desert andes and in the central andes will rest in areas above 0 c and that this freezing level might move up more than twice as much 500 m as during the entire holocene 200 m many active rock glaciers are already well below the current freezing level and exemplify how local controls may confound regional prognoses a bayesian multifactor analysis of variance further shows that only in the central andes are the toes of active rock glaciers credibly higher than those of inactive ones elsewhere in the andes active and inactive rock glaciers occupy indistinguishable elevation bands regardless of aspect the formation mechanism or shape of rock glaciers the state of rock glacier activity predicts differences in elevations of toes to 140 m at best so that regional inference of the distribution of discontinuous permafrost from rock glacier toes cannot be more accurate than this in the argentinian andes we conclude that the central andes where rock glaciers are largest cover the most area and have a greater density than glaciers is likely to experience the most widespread disturbance to the thermal regime of the twenty first century

late cretaceous cenozoic intraplate contractional deformation at the norwegian continental shelf timing magnitude and regional implications abstract contractional structures large anticlines and synclines reverse faults and inverted centres of deposition of assumed late cretaceous cenozoic age are common in cretaceous tertiary basins of the northwestern european margin the similarities in style orientation and timing of these structures are striking the present detailed analysis of one anticline the ormen lange dome of the mid norwegian continental shelf indicates that the total contraction is moderate less than 2 3 and that the analysed anticline has been growing almost continuously since its initiation in eocene till present inversion in the barents sea started already in the late cretaceous this episode is suggested to be related to far field effects of active plate margin processes and transfer of stresses across the plate as a consequence of the sub hercynian and paleocene laramide event of the alpine orogeny the development of co axial structures was facilitated by stress focusing along pre existing high relief n s and ne sw trending fault complexes far field plate tectonic stresses originating mainly from the alpine orogeny seem to have been the most important cause of contractional deformation on the nw european shelf in addition ridge push from the north atlantic spreading may have contributed significantly particularly during the neogene

oil and gas developments in western canada in 1989 there were 5513 wells drilled in western canada during 1989 30 fewer than in 1988 total meterage drilled was 6 459 797 m for an average well depth of 1172 m exploratory drilling in 1989 dropped by 13 and development drilling by 40 from 1988 levels british columbia was the only area in western canada with increased activity the industry continued to acquire more acreage for less total bonus at provincial crown sales throughout western canada during 1989 3 564 827 ha were acquired for a total bonus of 484 872 000 footnote 5 although the total disposition of crown lands decreased only 4 the average bonus dropped to 136 ha down 26 from 1988 in alberta the most active exploration areas were the southern and eastern mesozoic gas play the western deep devonian gas play the oil plays on and adjacent to the peace river arch and the middle devonian carbonate oil plays in the northwest in british columbia the most active exploration areas were the mesozoic and paleozoic gas plays in the northeastern portion of the province for the first time in 5 years crown drilling rights were issued within the fraser valley in the southwest there was a focus on gas exploration in the province as pipeline reversal was implemented permitting access to canadian and california markets through the alberta transportation network in manitoba exploration and development activity continued to decline in northern canada exploratory drilling success offering of crown lands for exploration approval of gas exports and indications that many of the native lands claims may be approaching settlement all provided exploration encouragement for the next decade exploration activities occurred throughout the northwest territories from the offshore beaufort to the southern border in saskatchewan active exploration areas were shallow mesozoic gas plays in the western portions of the province and deep paleozoic oil plays in the south

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

late holocene air temperature variability reconstructed from the sediments of laguna escondida patagonia chile 45 30 s climate and environmental reconstructions from natural archives are important for the interpretation of current climatic change few quantitative high resolution reconstructions exist for south america which is the only land mass extending from the tropics to the southern high latitudes at 56 s we analyzed sediment cores from two adjacent lakes in northern chilean patagonia lago castor 45 36 s 71 47 w and laguna escondida 45 31 s 71 49 w radiometric dating 210pb 137cs 14c ams suggests that the cores reach back to c 900 bc laguna escondida and c 1900 bc lago castor both lakes show similarities and reproducibility in sedimentation rate changes and tephra layer deposition we found eight macroscopic tephras 0 2 5 5 cm thick dated at 1950 bc 1700 bc at 300 bc 50 bc 90 ad 160 ad 400 ad and at 900 ad these can be used as regional time synchronous stratigraphic markers the two thickest tephras represent known well dated explosive eruptions of hudson volcano around 1950 and 300 bc biogenic silica flux revealed in both lakes a climate signal and correlation with annual temperature reanalysis data calibration 1900 2006 ad lago castor r 0 37 laguna escondida r 0 42 seven years filtered data we used a linear inverse regression plus scaling model for calibration and leave one out cross validation rmsev 0 56 c to reconstruct sub decadal scale temperature variability for laguna escondida back to ad 400 the lower part of the core from laguna escondida prior to ad 400 and the core of lago castor are strongly influenced by primary and secondary tephras and therefore not used for the temperature reconstruction the temperature reconstruction from laguna escondida shows cold conditions in the 5th century relative to the 20th century mean warmer temperatures from ad 600 to ad 1150 and colder temperatures from ad 1200 to ad 1450 from ad 1450 to ad 1700 our reconstruction shows a period with stronger variability and on average higher values than the 20th century mean until ad 1900 the temperature values decrease but stay slightly above the 20th century mean most of the centennial scale features are reproduced in the few other natural climate archives in the region the early onset of cool conditions from c ad 1200 onward seems to be confirmed for this region

holocene tephrochronology of the hualaihue region andean southern volcanic zone 42 s southern chile late glacial and holocene soils and sediments in southern chile contain an important record of explosive volcanic activity since the end of the last glaciation and have considerable potential for

forced folding and basement detached normal faulting in the haltenbanken area offshore norway triassic evaporites affected the structural development of the haltenbanken area of offshore norway during the late jurassic and early cretaceous by mechanically isolating triassic and younger strata from older strata and basement many folds in the haltenbanken area are forced folds above basement involved normal faults forced folds formed at least in part because triassic evaporites behaved ductilely decoupling overlying strata from underlying faulted strata and basement seismic data show that these forced folds are asymmetric flexures that affect lower cretaceous jurassic and triassic strata strata beneath the traiassic evaporites are faulted some forced folds die out along strike into and are cut by basement involved normal faults folding predominated above salt swells where decoupling was enhanced whereas faulting occurred on the flanks of salt swells where salt thicknesses were reduced and decoupling was less effective many normal faults in the haltenbanken area are basement detached and flatten within the triassic evaporites seismic data show that rollover anticlines and antithetic normal faults affect lower cretaceous jurassic and triassic strata within the hanging walls of these basement detached normal faults strata beneath the evaporites are not affected by this deformation some basement detached normal faults may be secondary structures associated with forced folding others especially thosemore with large displacements may have formed in response to gravity sliding less

morphology and gpr stratigraphy of a frontal part of an end moraine of the laurentide ice sheet paris moraine near guelph on canada abstract during deglaciation the laurentide ice sheet developed lobate ice termini in the great lakes area where the lobes remained quasi stationary for considerable time and sediment was supplied by the glacier end moraines fronted by outwash plains were formed one of the best examples in southern ontario is the paris moraine formed by the lake ontario lobe this study is a detailed examination of the morphology transverse and longitudinal of part of the paris moraine near guelph ontario and an analysis of the stratigraphy as derived from borehole information and ground penetrating radar gpr surveys parts of the northwestern frontal zone of the moraine are characterized by c 30 m high semi isolated hills composed in great part by aprons fans of debris flow and waterlaid sediments to the southeast these hills are backed by moat like depressions similar to those formed by ice push generating hill hole morphology the ice push effect is corroborated by evidence of folding and dislocation in the gpr profiles farther southeastward still the main body of the end moraine is characterized by hummocky topography typical of differential melting of sediment charged stagnant ice

abrupt vegetation changes during the last glacial to holocene transition in mid latitude south america a pollen record from the huelmo site ca 41 30 s shows that vegetation and climate changed at millennial time scales during the last glacial to holocene transition in the mid latitude region of western south america the record shows that a nothofagus parkland dominated the landscape between 16 400 and 14 600 14c yr bp along with magellanic moorland and cupressaceous conifers evergreen north patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14c yr bp following a prominent rise in nothofagus at 14 600 14c yr bp highly diverse closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14c yr bp followed by the expansion of cold resistant podocarps and nothofagus at ca 12 500 and 11 500 14c yr bp local disturbance by fire favoured the expansion of shade intolerant opportunistic taxa between 10 900 and 10 200 14c yr bp subsequent warming pulses at 10 200 and 9100 14c yr bp led to the expansion of thermophilous summer drought resistant valdivian rainforest trees until 6900 14c yr bp our results suggest that cold and hyperhumid conditions characterised the final phase of the last glacial maximum lgm between 16 400 and 14 600 14c yr bp the last ice age termination commenced with a prominent warming event that led to a rapid expansion of north patagonian trees and the abrupt withdrawal of andean ice lobes from their lgm positon at ca 147 000 14c yr bp hyperhumid conditions prevailed between 16 400 and 13 000 14c yr bp what we term the extreme glacial mode of westerly activity this condition was brought about by a northward shift and or intensification of the southern westerlies the warmest driest conditions of the last glacial interglacial transition occurred between 9100 and 6900 14c yr bp during this period the westerlies shifted to an extreme interglacial mode of activity via a poleward migration of stormtracks our results indicate that a highly variable climatic interval lasting 5500 14c years separate the opposite extremes of vegetation and climate during the last glacial interglacial cycle i e the end of the lgm and the onset of the early holocene warm and dry period copyright 2003 john wiley sons ltd

ash storms impacts of wind remobilised volcanic ash on rural communities and agriculture following the 1991 hudson eruption southern patagonia chile tephra fall from the august 1991 eruption of volcan hudson affected some 100 000 km 2 of patagonia and was almost immediately reworked by strong winds creating billowing clouds of remobilised ash or ash storms the immediate impacts on agriculture and rural communities were severe but were then greatly exacerbated by continuing ash storms this paper describes the findings of a 3 week study tour of the diverse environments of southern patagonia affected by ash storms with an emphasis on determining the impacts of repeated ash storms on agriculture and local practices that were developed in an attempt to mitigate these impacts ash storms produce similar effects to initial tephra eruptions prolonged for considerable periods these have included the burial of farmland under dune deposits abrasion of vegetation and contamination of feed supplies with fine ash these impacts can then cause problems for grazing animals such as starvation severe tooth abrasion gastrointestinal problems corneal abrasion and blindness and exhaustion if sheep fleeces become laden with ash in addition ash storms have led to exacerbated soil erosion human health impacts increased cleanup requirements sedimentation in irrigation canals and disruption of aviation and land transport ash deposits were naturally stabilised most rapidly in areas with high rainfall 1 500 mm year through compaction and enhanced vegetation growth stabilisation was slowest in windy semi arid regions destruction of vegetation and

geochemistry of the active azufre planchon peteroa volcanic complex chile 35 15 s evidence for multiple sources and processes in a cordilleran arc magmatic system

dynamics and gpr stratigraphy of a polar rock glacier on james ross island antarctic peninsula we describe field measurements ground penetrating radar gpr geodetic survey and ice core drilling to provide new information on the movement mechanism and internal structure of a polar rock glacier on james ross island antarctic peninsula we collected gpr data along longitudinal and transverse profiles the longitudinal gpr profiles identify inter bedded debris rich layers that dip up glacier similar to the thrust structures in the compression zone of a valley glacier the transverse gpr profiles indicate a syncline structure inclined towards the central part of the rock glacier resembling the transverse foliation of a valley glacier the stratigraphy of two boreholes shows that the rock glacier consists primarily of bubbly ice with thin debris rich layers an internal structure similar to the nested spoons structure common in the interior of valley glaciers these results indicate that the glacier motion is controlled by shear movement common in valley glaciers the geodetic survey confirms that flow velocities decrease towards the lower part of the rock glacier such heterogeneous movement causes longitudinal compression and forms thrusts which then create the debris rich layer by uplifting basal ice and debris pushing of the upstream ice against the downstream ice bends the surface layers forming transverse ridges on the rock glacier surface

short term geomorphological evolution of proglacial systems proglacial systems are amongst the most rapidly changing landscapes on earth as glacier mass loss permafrost degradation and more episodes of intense rainfall progress with climate change this review addresses the urgent need to quantitatively define proglacial systems not only in terms of spatial extent but also in terms of functional processes it firstly provides a critical appraisal of prevailing conceptual models of proglacial systems and uses this to justify compiling data on rates of landform change in terms of planform horizontal motion elevation changes and sediment budgets these data permit us to produce novel summary conceptual diagrams that consider proglacial landscape evolution in terms of a balance of longitudinal and lateral water and sediment fluxes throughout we give examples of newly emerging datasets and data processing methods because these have the potential to assist with the issues of i a lack of knowledge of proglacial systems within high mountain arctic and polar regions ii considerable inter and intra catchment variability in the geomorphology and functioning of proglacial systems iii problems with the magnitude of short term geomorphological changes being at the threshold of detection iv separating short term variability from longer term trends and v of the representativeness of plot scale field measurements for regionalisation and for upscaling we consider that understanding of future climate change effects on proglacial systems requires holistic process based modelling to explicitly consider feedbacks and linkages especially between hillslope and valley floor components such modelling must be informed by a new generation of repeated distributed topographic surveys to detect and quantify short term geomorphological changes

geomorphology internal structure and successive development of a glacier foreland in the semiarid chilean andes cerro tapado upper elqui valley 30 08 s 69 55 w we use geomorphological analysis sedimentological survey remote sensing and ground penetrating radar gpr in order to understand the complex landform assemblage found in front of the cerro tapado glacier in the upper elqui river catchment semiarid andes of chile the geomorphological analysis highlights prominent boundaries dividing the landform assemblage into from the upper part to the lower part an upper latero frontal moraine complex an upper debris covered glacier a lower debris covered glacier two rock glaciers and a lower morainic complex the sedimentological survey highlights the rather small size of the surface debris in general 400 m receding of the glacier occurred along with downslope displacements dm m y 1 of most of the landform units and a significant evolution of the thermokarst features on the debris covered glaciers considerable surface lowering occurred in the upper part of the assemblage while localized bulging is seen along the morphological boundaries in the lower units the gpr profiles highlight spectacular internal structure in the upper debris covered glacier with up to 80 m of buried ice in the other landform units the internal structure is less visible and more heterogeneous the analysis of the radar wave velocity along the gpr profiles reveals the occurrence of air filled and moist zones in the internal structure the geomorphological assemblage is fundamentally characterized by its morphological structural and dynamical boundaries and defined as a young probably 2000 years polygenetic construction with landform units having added to overlapped one another the rock glaciers do not derive from the present debris covered glacier but preexist to it

an inventory driven rock glacier status model intact vs relict for south tyrol eastern italian alps ice presence in rock glaciers is a topic that is likely to gain importance in the future due to the expected decrease in water supply from glaciers and the increase of mass movements originating in periglacial areas this makes it important to have at ones disposal inventories with complete information on the state of rock glaciers this study presents a method to overcome incomplete information on the status of rock glaciers i e intact vs relict recorded in regional scale inventories the proposed data driven modelling framework can be used to estimate the likelihood that rock glaciers contain frozen material potential predictor variables related to topography environmental controls or the rock glacier appearance were derived from a digital terrain model dtm satellite data and gathered from existing data sets an initial exploratory data analysis supported the heuristic selection of predictor variables three classification algorithms namely logistic regression glm support vector machine svm and random forest rf were trained on the basis of the available information on the status of rock glaciers within the territory of south tyrol eastern italian alps the resulting classification rules led to assign a binary label intact or relict to 235 unclassified rock glaciers present in the inventory all models were validated quantitatively on spatially independent test samples spatial cross validation and achieved highly satisfactory performance scores hereby the less flexible statistically based classifier glm performed slightly better than the more flexible machine learning algorithms svm and rf spatial permutation based variable importance assessment revealed that elevation and vegetation cover based on ndvi were the most relevant predictors for more than 80 of the unclassified rock glaciers all of the three models agreed on the spatially predicted rock glacier status only for a minor portion 12 3 one model differed from the remaining two

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

polyphase rift evolution of the voring margin mid norway constraints from forward tectonostratigraphic modeling the mid norwegian voring margin bounding the northern atlantic underwent several rift episodes after the caledonian orogeny permo triassic extension concentrated at the eastern inner margin followed by jurassic cretaceous extension at the center of the margin finally more westward the last rift episode led to continental breakup in the earliest eocene although the general architecture of the margin may be clear the timing and distribution of particularly the oldest rift structures are poorly constrained we use two dimensional forward tectonostratigraphic modeling for better quantitative understanding of the tectonic evolution of the margin two regional profiles crossing the margin have been analyzed modeling of the two profiles integrates the basin shape and fill as well as the underlying crustal structure of the margin the modeling allows us 1 to quantify the distribution and timing of extension of subsequent rift episodes 2 to predict the basin and crustal architecture at deep levels and 3 to test different interpretations of the seismic data the level of lithospheric necking during basin formation is constrained by basement topography and moho depth and lies within the middle crust 20 km furthermore we investigate the migration of the rift axes and the elastic lithospheric strength during the different rift episodes locations of previous extension are not reactivated during renewed rifting instead renewed rifting occurs preferentially in regions where the lithosphere has experienced less extension

geomorphology internal structure and successive development of a glacier foreland in the semiarid chilean andes cerro tapado upper elqui valley 30 08 s 69 55 w reply to discussion by d c nobes abstract we address the criticisms made by nobes 2015 this issue on the study by monnier et al 2014 we reiterate how an air filled cavity was evidenced in a debris covered glacier using ground penetrating radar gpr by calculation of the interval velocity and not only relying on the velocity measured along diffraction events also we show that common mid point cmp measurements were correctly designed and carefully used and interpreted

explosive eruptive record in the katmai region alaska peninsula an overview at least 15 explosive eruptions from the katmai cluster of volcanoes and another nine from other volcanoes on the alaska peninsula are preserved as tephra layers in syn and post glacial last glacial maximum loess and soil sections in katmai national park ak about 400 tephra samples from 150 measured sections have been collected between kaguyak volcano and mount martin and from shelikof strait to bristol bay 8 500 km2 five tephra layers are distinctive and widespread enough to be used as marker horizons in the valley of ten thousand smokes area and 140 radiocarbon dates on enclosing soils have established a time framework for entire soil tephra sections to 10 ka the white rhyolitic ash from the 1912 plinian eruption of novarupta caps almost all sections stratigraphy distribution and tephra characteristics have been combined with microprobe analyses of glass and fe ti oxide minerals to correlate ash layers with their source vents microprobe analyses typically 20 50 analyses per glass or oxide sample commonly show oxide compositions to be more definitive than glass in distinguishing one tephra from another oxides from the kaguyak caldera forming event are so compositionally coherent that they have been used as internal standards throughout this study other than the novarupta and trident eruptions of the last century the youngest locally derived tephra is associated with emplacement of the snowy mountain summit dome 6 ka two tephras 3 700 and 2 700 14c years b p and a summit scoria cone with a crater still steaming today mount katmai has three times produced very large explosive plinian to sub plinian events in 1912 12 16 ka and 23 ka and many smaller pyroclastic deposits show that explosive activity has long been common there mount griggs fumarolically active and moderately productive during postglacial time mostly andesitic lavas has three nested summit craters two of which are on top of a holocene central cone only one ash has been found that is tentatively correlated with the most recent eruptive activity on griggs 3 460 14c years b p eruptions from other volcanoes ne and sw beyond the katmai cluster represented in this area include 1 coignimbrite ash from kaguyak s caldera forming event 5 800 14c years b p 2 the climactic event from fisher caldera 9 100 14c years b p tentatively correlated 3 at least three eruptions most likely from mount peulik 700 7 700 and 8 500 14c years b p and 4 a phreatic fallout most likely from the gas rocks 2 300 14c years b p most of the radiocarbon dating has been done on loess soil and peat enclosing this tephra ash correlations supported by stratigraphy and microprobe data are combined with radiocarbon dating to show that variably organics bearing substrates can provide reliable limiting ages for ash layers especially when data for several sites is available

role of faults and layer interfaces on the spatial variation of stress regimes in basins inferences from numerical modelling abstract the spatial variation of the computed state of stress is studied in a series of numerically solved boundary value problems of basin scale deformation these numerical experiments illustrate simple situations of decollement tectonism under compression the study focuses on the local variation of the state of stress in a sedimentary overburden where major discontinuities such as large scale faults and layer interfaces are present the states of stress are computed using either the distinct element method or the finite element method classic elasto plasticity laws are used for the behaviour of the continuum and the discontinuities are modelled as coulomb contact surfaces a geologic interpretation of the numerical experiments is proposed to highlight the role played by major structural discontinuities in the local variations of the stress regime the models are two dimensional in space and assume plane strain but the full three dimensional stress strain constitutive relation is used therefore the stress regime variations can be represented by constructing the contour map of the wallace bott stress ratio this simple technique together with the construction of diagrams of principal stress magnitude across the model enables us to rapidly examine the stress field pattern and further discuss the deformation modes of faulting and fracturing which may take place at a small scale we have found that the local variations of the stress tensor are in good agreement with common geologic interpretation of brittle deformations in foreland and thrust systems we demonstrate how the presence of layer interface and the difference in mechanical properties of formation lithology may strongly affect the variation of stress in space this modelling approach has important issues when interpreting well tests to gain access to in situ stresses

distal volcanic impacts on peatlands palaeoecological evidence from alaska abstract despite the fact that volcanic ash tephra layers are found preserved in peat deposits around the world comparatively little research has investigated the impacts of distal volcanic emissions on peatlands this study investigates the impacts of several late holocene volcanic eruptions on five peatlands in southern alaska using a palaeoecological approach testate amoebae analysis peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers the humification results were considered unreliable because of a methodological problem a finding which may have implications for other studies using this technique redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras the most likely causes of the impacts are volcanic gases acidic precipitation or tephra derived leachates the finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall these results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change implications of the results for peat based palaeoclimatic studies are discussed as are possible directions for future research

structure and genesis of the thabor rock glacier northern french alps determined from morphological and ground penetrating radar surveys landform analysis and ground penetrating radar gpr were used to investigate the thabor rock glacier in the northern french alps the surface features of the rock glacier were classified and described with emphasis on massive ice exposures the retreat of the former thabor glacier since the little ice age lia was documented through an analysis of historical sources and recent movements of the rock glacier were inferred from orthophoto based measurements two dimensional 2 d models of the radar wave velocity were derived from the raw gpr data using the numerous diffraction hyperbolae for local determinations of the velocity and kriging interpolation techniques subsequently the profiles were migrated through a 2 d kirchhoff migration method using the interpolated velocities the 2 d velocity models exhibit pronounced spatial variations and in several locations high values 0 15 m ns 1 potentially corresponding to massive ice on the other hand while the migrated profiles show numerous layers the internal stratigraphy of the rock glacier is dominated by a few prominent internal boundaries the integration of morphology radar wave velocity and internal stratigraphy allowed us to identify the main structural units of the rock glacier as well as to explain its genesis the rock glacier was formed by the imbrication of a massive ice core originating from the retreat of the former thabor glacier since the lia into pre existing glacial deposits

the last glacial maximum and deglaciation in southern south america abstract this paper models the extent of the patagonian icesheet during the last glacial maximum lgm and its subsequent deglaciation it constrains a new coupled icesheet climate numerical model with empirical evidence and simulates the icesheet at the lgm and at stages of deglaciation under lgm conditions an icesheet with a modelled volume slightly in excess of 500 000 km3 builds up along the andes there is a marked contrast between the maritime and continental flanks of the modelled icesheet with positive mass balance exceeding 2 m in the west and declining tenfold to the east modelled ice velocities commonly reach 400 m yr 1 in the western fjords the model is most sensitive to variations in temperature and good agreement between modelled ice extent and empirical evidence was achieved by applying a temperature decrease of 6 c relative to present day temperatures with constant wind fields over the model domain assuming a stepped start to deglaciation modelled ice volumes declined sharply contributing 1 2 m to global sea level 80 of it within 2000 years the empirical record suggests that such a stepped warming occurred around 17 500 17 150 cal yr ago

faulting fracturing and in situ stress prediction in the ahnet basin algeria a finite element approach abstract many low efficiency hydrocarbon reservoirs are productive largely because effective reservoir permeability is controlled by faults and natural fractures accurate and low cost information on basic fault and fracture properties orientation in particular is critical in reducing well costs and increasing well recoveries this paper describes how we used an advanced numerical modelling technique the finite element method fem to compute site specific in situ stresses and rock deformation and to predict fracture attributes as a function of material properties structural position and tectonic stress presented are the numerical results of two dimensional plane strain end member fem models of a hydrocarbon bearing fault propagation fold structure interpretation of the modelling results remains qualitative because of the intrinsic limitations of numerical modelling however it still allows comparisons with the little available geological and geophysical data in all models the weak mechanical strength and flow properties of a thick shale layer the main seal leads to a decoupling of the structural deformation of the shallower sediments from the underlying sediments and basement and results in flexural slip across the shale layer all models predict rock fracturing to initiate at the surface and to expand with depth under increasing horizontal tectonic compression the stress regime for the formation of new fractures changes from compressional to shear with depth if pre existing fractures exist only sub horizontal fractures are predicted to open thus defining the principal orientation of effective reservoir permeability in models that do not include a blind thrust fault in the basement flexural amplification of the initial fold structure generates additional fracturing in the crest of the anticline controlled by the material properties of the rocks the folding induced fracturing expands laterally along the stratigraphic boundaries under enhanced tectonic loading models incorporating a blind thrust fault correctly predict the formation of secondary syn and anti thetic mesoscale faults in the basement and sediments of the hanging wall some of these faults cut reservoir and or seal layers and thus may influence effective reservoir permeability and affect seal integrity the predicted faults divide the sediments across the anticline in several compartments with different stress levels and different rock failure and proximity to failure these numerical model outcomes can assist classic interpretation of seismic and well bore data in search of fractured and overpressured hydrocarbon reservoirs

changing fire regimes in the temperate rainforest region of southern chile over the last 16 000 yr abstract a high resolution macroscopic charcoal record from lago melli 42 46 s 73 33 w documents the occurrence of forest fires in the lowlands of isla grande de chiloe southern chile over the last 16 000 yr our data suggest that fire activity in this region was largely modulated by the position intensity of the southern westerlies at multi millennial time scales fire activity was infrequent or absent between 16 000 11 000 and 8500 7000 cal yr bp and was maximal between 11 000 8500 and 3000 0 cal yr bp a mosaic of valdivian north patagonian rainforest species started at 6000 cal yr bp along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr bp the modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability suggesting the onset of high frequency variability in summer precipitation regimes starting at 5500 cal yr bp because negative anomalies in summer precipitation in this region are teleconnected with modern el nino events we propose that the onset of el nino like variability at 5700 6200 cal yr bp led to a reshuffling of rainforest communities in the lowlands of isla grande de chiloe and an increase in fire activity

environmental assessment of 1991 hudson volcano eruption ashfall effects on southern patagonia region argentina the august 1991 eruption of the hudson volcano in the southern andean volcanic zone affected an area of 1000 km in radius to the east in the argentine patagonic meseta the thickness of ash ranged from 20 cm in the andean area to less than 1 mm in the atlantic coast zone wind storms reactivated the ash deposits together with terrigenous material more than one year after the eruption in order to assess the potential risk of the ash analyses of concentration size mineralogical composition toxic elements and irritating effects of gases were performed in all samples the percentage of particles of the 2 to 5 m range is below the toxic threshold level trace elements are below the toxic threshold concentration for humans and animals the major impact of the ashfall was on sheep herds about one third of them were lost in the areas close to the volcano soil incorporated the ash layers and a fast recovery of orchards was reported two years later rivers were loaded with sediment in the immediate aftermath but one year later returned to previous conditions along the shores of the buenos aires lake a fresh tephra layer can be distinguished

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

multidisciplinary geophysical investigations over an alpine rock glacier we have performed a multidisciplinary geophysical survey combined with geotechnical investigations over a degrading alpine rock glacier a dense grid of helicopter borne groundpenetrating radar data allowed the 3d shape of the bedrock topography and the gross transition from ice rich to ice poor parts of the rock glacier to be delineated the bedrock topography served as a 2d structural constraint for tomographic inversions of seismic and geoelectric data acquired on coincident profiles parallel and perpendicular to the rock glacier flow direction these profile data were complemented by a small 3d geoelectric tomography experiment only a combined interpretation of all the results allowed reliable and unambiguous interpretation of the tomograms we could distinguish between the active layer bedrock ice bearing rock glacier material and degraded permafrost within the rock glacier the latter could be further distinguished in areas where the ice must have melted only recently and regions that had degraded some time ago additionally high resolution cross hole radar tomography performed in an area of opening crevices allowed small scale structures to be resolved which were indicative of the dominant deformation mechanisms style of the rock glacier the success of our study was primarily based on the availability of 3d data sets that allowed important structures to be traced over larger areas and the integrated interpretation of several data types we have identified the internal structure of the rock glacier to be surprisingly heterogeneous with several small scale features that were judged to be critical for assessing its stability this underpinned the need for comprehensive 3d structural investigations to augment geotechnical measurements linearly with inclinometers or at points in boreholes

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

continuous profiles of electromagnetic wave velocity and water content in glaciers an example from bench glacier alaska usa we conducted two dimensional continuous multi offset georadar surveys on bench glacier south central alaska usa to measure the distribution of englacial water we acquired data with a multichannel 25 mhz radar system using transmitter receiver offsets ranging from 5 to 150 m we towed the radar system at 5 10 km h 1 with a snow machine with transmitter receiver positions established by geodetic grade kinematic differentially corrected gps nominal 0 5 m trace spacing for radar velocity analyses we employed reflection tomography in the pre stack depth migrated domain to attain an estimated 2 velocity uncertainty when averaged over three to five wavelengths we estimated water content from the velocity structure using the complex refractive index method equation and use a three phase model ice water air that accounts for compression of air bubbles as a function of depth our analysis produced laterally continuous profiles of glacier water content over several kilometers these profiles show a laterally variable stratified velocity structure with a low water content 0 0 5 shallow layer 20 30 m underlain by high water content 1 2 5 ice

numerical modeling of cenozoic stress patterns in the mid norwegian margin and the northern north sea numerical modeling of cenozoic stress patterns in the northern north sea and the mid norwegian margin is presented and the sense of potential slip along major fault planes belonging to the two areas is restored we assume that the main regional source of stresses is the atlantic ridge push as demonstrated by previous studies furthermore we also assume a nearly consistent nw se strike for the far field stress from continental breakup between greenland and norway earliest eocene to present day first we applied the commercial two dimensional distinct element method udec to simulate cenozoic stress and displacement patterns in the study area variations in rheology and major fault zones were introduced into the model the more trondelag fault complex and its inferred continuation into the shetland platform forms the major mechanical discontinuity in the model second we used the sortan method developed at the university of paris vi to predict the sense of potential slip along major fault planes the input for the sortan model was constrained by the geometry of the selected fault planes and local principal stress directions extracted from the udec modeling our results show that the more trondelag fault complex and its inferred continuation into the shetland platform act as a weak fault zone this fault zone divides the study area into two different stress provinces the continental margin and the northern north sea this result agrees well with the observed differences in cenozoic structural evolution of the two areas compressive structures are observed along the continental margin whereas relative tectonic quiescence characterizes the northern north sea during the tertiary the restored stress patterns in the northern north sea and the mid norwegian margin also agree well with the observed present day stress configuration our analysis demonstrates a method to reconstruct the sense of slip on major fault planes by combining two complementary numerical tools udec and sortan as a result it is demonstrated that oblique slip motions are mainly expected in particular strike slip and reverse dip slip faulting are simulated

internal structure and composition of a rock glacier in the andes upper choapa valley chile using borehole information and ground penetrating radar this study uses boreholes ground temperature monitoring and ground penetrating radar gpr in order to understand the internal structure and composition of a rock glacier in the upper choapa valley northern chile the rock glacier is a small valley side feature 200 m long and ranging between 3710 and 3780 m a s l two boreholes were drilled down to depths of 20 and 25 m respectively using the diamond drillhole technique an ice rock mixture was encountered in the boreholes with heterogeneous ice content averaging 15 30 data from common midpoint cmp and constant offset co gpr surveys acquired respectively near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar wave velocity the gpr profiles depict a rock glacier constituted of stacked and generally concordant layers with a thickness ranging from 10 m in its upper part to 30 m towards its terminus the cmp analysis highlights radar wave velocities of 0 13 0 16 m ns 1 in the first 20 m of the structure larger vertical and lateral velocity variations are highlighted from co data reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure given the average air temperature registered at the site 0 58c the near melting point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from gpr data it is thought that the permafrost in the rock glacier is currently degrading

towards a late quaternary tephrochronological framework for the southernmost part of south america the laguna potrok aike tephra record abstract a total of 18 tephra samples have been analysed from the composite sediment sequence from site 2 of the laguna potrok aike icdp expedition 5022 from southern patagonia argentina which extends back to ca 51 ka cal bp analyses of the volcanic glass show that all layers but one are rhyolitic in composition with sio2 contents ranging between ca 74 5 and 78 wt and suggest an origin in the austral andean volcanic zone avz 49 55 s nonetheless two main data clusters occur one group with k2o contents between ca 1 5 and 2 0 wt indicating an origin in the mt burney volcanic area and one group with k2o contents between ca 2 7 and 3 9 wt tentatively correlated with viedma lautaro and the aguilera volcanoes in the northern part of the avz the early holocene tephra mb1 and the late pleistocene reclus r1 tephra occur in the upper part of the sequence periods with significant tephra deposition occurred between ca 51 44 ka cal bp and ca 31 25 ka cal bp with a decrease in tephra layer frequency between these two periods

development of tongue shaped and multilobate rock glaciers in alpine environments interpretations from ground penetrating radar surveys abstract rock glaciers occur as lobate or tongue shaped landforms composed of mixtures of poorly sorted angular to blocky rock debris and ice these landforms serve as primary sinks for ice and water storage in mountainous areas and represent transitional forms in the debris transport system accounting for 60 of all mass transport in some alpine regions observations of active flowing alpine rock glaciers indicate a common association between the debris that originates from cirque headwalls and the depositional lobes that comprise them the delivery of this debris to the rock glacier is regulated primarily by the rate of headwall erosion and the point of origin of debris along the headwall these factors control the relative movement of individual depositional lobes as well as the overall rate of propagation of a rock glacier in recent geophysical studies a number of alpine rock glaciers on prins karls forland and nordenskioldland svalbard norway and the san juan mountains of southwest colorado usa have been imaged using ground penetrating radar gpr to determine if a relationship exists between the internal structure and surface morphology results indicate that the overall morphologic expression of alpine rock glaciers is related to lobate deposition during catastrophic episodes of rockfall that originated from associated cirque headwalls longitudinal gpr profiles from alpine rock glaciers examined in this study suggests that the difference in gross morphology between the lobate and tongue shaped rock glaciers can be attributed primarily but not exclusively to cirque geometry frequency and locations of debris discharge within the cirque and the trend and magnitude of valley gradient in relation to cirque orientation collectively these factors determine the manner in which high magnitude debris discharges which seem to be the primary mechanism of formation accumulate to form these rock glaciers

long term mobilisation of chemical elements in tephra rich peat ne iceland this paper presents geochemical profiles of a tephra bearing minerotrophic peat column from ne iceland obtained using various elemental analyses of the solid phase and the pore water the influence of tephra grain size thickness and composition of each tephra on the peat geochemistry was investigated interpretations are supported by a statistical approach in particular by autocorrelation and by microscopy observations minerotrophic peat geochemistry may be strongly dependent upon post depositional mobilization and possible leaching of elements as demonstrated by fe and trace metal concentration profiles chemical elements and more specifically potentially harmful metals can be slowly leached out of volcanic falls during their weathering and re accumulate downwards it is emphasised that a tephra deposit can act as an active geochemical barrier blocking downward elemental movements and leading to the formation of enriched layers in this study the formation of poorly amorphous fe phases above the hekla 3 tephra is shown these poorly crystalline fe phases scavenged ni

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

partial melting of subducting oceanic crust the conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two dimensional thermal models of subduction zones for porosities of 1 containing h20 the amount of partial melt generated at the wet basaltic solidus is limited to 100 mpa can be maintained by rocks close to or above their melting temperatures in the absence of high shear stresses substantial melting of the oceanic crust will only occur during subduction of very young 5 ma oceanic lithosphere partial melting of hydrated basalt amphibolites derived from the mid ocean ridge has been proposed e g 1 3 as being responsible for the generation of certain recent high al andesitic to dacitic volcanic rocks adakites three of these volcanic suites mount st helens southern chile and panama occur in volcanic arcs where oceanic crust 25 ma is being subducted at rates of 1 3 cm yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments however oceanic lithosphere is not currently being subducted beneath baja and new guinea where recent adakites are also present suggesting that some adakite magmas may form by water undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately

the glacial geomorphology and pleistocene history of south america between 38 s and 56 s abstract this paper presents new mapping of the glacial geomorphology of southern south america between latitudes 38 s and 56 s approximately the area covered by the former patagonian ice sheets glacial geomorphological features including glacial lineations moraines meltwater channels trimlines sandur and cirques were mapped from remotely sensed images landsat 7 etm pan sharpened landsat 7 and aster the landform record indicates that the patagonian ice sheets consisted of 66 main outlet glaciers together with numerous local cirque glaciers and independent ice domes in the surrounding mountains in the northern part of the mapped area in the chilean lake district 38 42 s large piedmont glaciers developed on the western side of the andes and the maximum positions of these outlet glaciers are in general marked by arcuate terminal moraines to the east of the andes between 38 s and 42 s outlet glaciers were more restricted in extent and formed alpine style valley glaciers along the eastern flank of the andes south of 45 s a series of large fast flowing outlet glaciers drained the ice sheet the location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes west of the andes at this latitude there is geomorphological evidence for an independent ice cap close to sea level on the taitao peninsula the age of this ice cap is unclear but it may represent evidence of glacier growth during the antarctic cold reversal and or younger dryas chronozone maximum glacier positions are difficult to determine along much of the western side of the andes south of 42 s because of the limited land there and it is assumed that most of these glaciers had marine termini in the south east of the mapped area in the fuegan andes cordillera darwin the landform record provides evidence of ice sheet initiation by adding published dates for glacier advances from the literature we present maps of pre last glacial maximum lgm glacier extent lgm extent and the positions of other large mapped moraines younger than lgm in age a number of large moraines occur within the known lgm limits the age of these moraines is unknown but since many of them lie well outside the established maximum neoglacial positions the possibility that they reflect a return to glacial climates during the younger dryas chronozone or antarctic cold reversal cannot be discounted

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

the tectonic fabric of the ocean basins 1 we present a global community data set of fracture zones fzs discordant zones propagating ridges v shaped structures and extinct ridges digitized from vertical gravity gradient vgg maps we use a new semi automatic fz tracking program to test the precision of our hand digitized traces and find a mean absolute deviation of less than 3 4 km from the raw vgg minima that most clearly delineate each feature and less than 5 4 km from the fz location predicted by fitting model profiles to the vgg data that represent the morphology of the individual fzs these offsets are small considering gravity data only provide an approximation for the underlying basement morphology we further investigate the origin of non fz seafloor fabric by combining published abyssal hill heights computed from gravity anomalies with global half spreading rates a residual abyssal hill height grid with spreading rate effects removed combined with our interpreted tectonic fabric reveals several types of seafloor fabric distinct from typical abyssal hills where discordant zones do not overprint abyssal hill signals residual abyssal hill height anomalies correspond to seafloor that accreted near mantle thermal anomalies or zones of melt depletion our analysis reveals several areas where residual abyssal hill height anomalies reflect pseudo faults and extinct ridges associated with ridge propagation and or microplate formation in the southern pacific ocean

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

crustal sources involved in continental arc magmatism a case study of volcan mocho choshuenco southern chile volcan mocho choshuenco a pleistocene holocene basaltic andesite to dacite shield volcano located at lat 40 s in the southern volcanic zone svz of the andes is built on the thinnest svz continental crust 30 km which consists largely of paleozoic sedimentary and metamorphic rocks and mesozoic plutons sr pb nd and o isotopic ratios of mocho choshuenco lavas 87 sr 86 sr 0 70399 to 0 70422 206 pb 204 pb 18 57 to 18 61 207 pb 204 pb 15 60 to 15 63 208 pb 204 pb 38 45 to 38 57 143 nd 144 nd 0 512787 to 0 512881 18 o 5 8 to 6 8 standard mean ocean water are similar to those of other svz centers and exhibit no correlation with indices of differentiation however incompatible trace element systematics indicate that evolved lavas have been contaminated by crustal plutonic rocks by 5 to 15 rb ba k ba rb la and k la ratios increase with increasing sio 2 content as a result of assimilation of orogenic calc alkalic plutonic rocks enriched in rb and k relative to ba and la xenoliths of plutonic rocks recovered from mocho choshuenco lavas are slightly more radiogenic in 87 sr 86 sr less radiogenic in 143 nd 144 nd and comparable in pb isotopic ratios and they have variable 18 o contents 87 sr 86 sr 0 70482 to 0 70557 206 pb 204 pb 18 60 to 18 64 207 pb 204 pb 15 60 to 15 62 208 pb 204 pb 38 53 to 38 56 143 nd 144 nd 0 512686 18 o 3 3 to 5 5 smow contamination of mocho choshuenco parental magmas by crustal melts with small isotopic contrast imposed little variation on isotopic heterogeneities existing in the parental compositions these heterogeneities probably were produced during magma crust interaction at the crust mantle boundary or in the lower crust

glacier meltwater flow paths and storage in a geomorphologically complex glacial foreland the case of the tapado glacier dry andes of chile 30 s summary the tapado catchment is located in the upper elqui river basin 4000 5550 m in northern chile it comprises the tapado glacial complex which is an assemblage of the tapado glacier and the glacial foreland debris covered glacier rock glacier and moraines although the hydrological functioning of this catchment is poorly known it is assumed to actively supply water to the lower semi arid areas of the elqui river basin to improve our knowledge of the interactions and water transfers between the cryospheric compartment glacier debris covered glacier and rock glacier and the hydrological compartment aquifers streams the results of monitoring of meteorological conditions as well as discharge conductivity and temperature of streams and springs located in the tapado catchment were analyzed the hydrological results are compared to results inferred from a ground penetrating radar gpr survey of the underground structure of the glacial foreland water production from the tapado glacier was shown to be highly correlated with daily and monthly weather conditions particularly solar radiation and temperature the resulting daily and monthly streamflow cycles were buffered by the glacial foreland where underground transfers took place through complex flow paths however the development of a thermokarst drainage network in a portion of the glacial foreland enabled rapid concentrated water transfers that reduced the buffer effect the glacial foreland was shown to act as a reservoir storing water during high melt periods and supplying water to downstream compartments during low melt periods gpr observations revealed the heterogeneity of the internal structure of the glacial foreland which is composed of a mixture of ice and rock debris mixture with variable spatial ice content including massive ice lenses this heterogeneity may explain the abovementioned hydrological behaviors finally calculation of a partial hydrological budget confirmed the importance of the tapado catchment in supplying water to lower areas of the elqui river basin water production from and transfer through cryospheric compartments and its subsequent interactions with hydrological compartments are key processes driving the summer water supply from the tapado catchment

structure of the more basin mid norway continental margin abstract in the more basin offshore mid norway the basis of the cretaceous sequence reaches depths of more than 5000 m the basin is limited on its eastern margin by a system of extensional faults which probably were initiated in the triassic and which were active periodically throughout the aptian the internal basin floor is divided into subbasins by structural highs which are rotated fault blocks presumably rooted in the basement the main structuring of the basin started in late triassic and was followed by accelerating subsidence in the early cretaceous subsidence was interrupted by a mild phase of inversion in the latest cretaceous and a more pronounced inversional phase in the eocene miocene the latter developed folds with wavelengths in the order of kilometers and local low angle reverse faults and the inversion of depocenters

detection of buried ice and sediment layers in permafrost using multi frequency ground penetrating radar a case examination on svalbard abstract we use multi frequency ground penetrating radar gpr to detect and map buried relic glacier ice and sediments in permafrost old aerial photographs 1936 1990 are used to show the origin of a sediment covered ice body and illustrate how it has been buried together with a newly exposed ice sediment cliff this serves as excellent ground truthing for the gpr data empirical gpr frequency dependent relations are established to quantify the loss of the signal power through the layer of sediment the loss through ice is in comparison negligible these relations indicate that the maximum ice pocket detection depth for this sediment type with the different gpr systems used are 90 150 and 200 ns for the 800 500 and 200 mhz systems respectively the electromagnetic em wave velocities calculated from diffractions yield velocities ranging between 0 115 0 135 m ns for the sediment and 0 15 0 17 m ns for the ice with the derived em wave velocities these two way travel twt times correspond to a depth of 6 9 and 13 m respectively this loss cannot be tested for the 200 and 500 mhz systems due to lack of such a deep sediment layer on top of the ice but is consistent with the 800 mhz data

the peopling of the fuego patagonian fjords by littoral hunter gatherers after the mid holocene h1 eruption of hudson volcano abstract early holocene 8500 cal bp littoral sites are well documented along the pacific coast of chile north of 32 s but they do not occur south of this latitude it has been proposed that canoe indians of fuego patagonia the earliest evidence for which is mid holocene punta santa ana 7440 cal bp adapted themselves to the sea from terrestrial hunter gatherer populations already living since 13 000 cal bp in southernmost south america south of 52 s this adaption may have taken place first in the area around seno otway near the earliest maritime cultural sites where transit to and from the interior pampas was relatively easy and forest providing trees for canoes existed seno otway is also the proposed source for green obsidian a distinctive lithic material found in many of the oldest maritime sites including tunel 1 and imiwaia 1 along the canal beagle 300 km to the southeast this green obsidian was previously exploited and transported long distances by terrestrial hunter gatherers as evidenced by its presence in the period iii 9500 7400 cal bp levels of pali aike and fell s cave located 200 km east of seno otway however this obsidian does not occur in period iv after 7400 cal bp when it and other obsidian types from distant sources are absent among the lithic tools found in these two sites this hiatus in the long distant terrestrial transport of obsidian in southernmost patagonia has been attributed to the catastrophic environmental effects of the h1 eruption of hudson volcano 46 s at 7750 cal bp this eruption which was more than five time larger than the 1991 eruption of the same volcano covered much of tierra del fuego with up to 20 cm of tephra and the seno otway area with at least 4 cm of tephra as well as interrupting long distance terrestrial transport of obsidian over all of southernmost patagonia it may have devastated for an extended time period the flora and fauna supporting the local terrestrial hunter gatherers in this area particularly in tierra del fuego which was already isolated by the opening of the strait of magellan at 9240 cal bp here it may have actually extinguished this culture completely however it was unlikely to have affected marine species we propose that this volcanic eruption was a significant trigger to the development of the maritime population from the older terrestrial hunter gatherers

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

arc magma compositions controlled by linked thermal and chemical gradients above the subducting slab 1 global arc magmatism is sustained by a continuous fluid flux that is returned to the mantle in subduction zones despite considerable advances in simulations of melting processes models of arc magmatism remain incompletely tested against erupted products here we show that a suite of primitive volcanic rocks from across the southern chilean arc preserves the signature of a systematic down slab gradient in fluid chemistry the chemical gradient is consistent with predictions from modeling geothermometry and experiments we infer that increasing slab surface temperatures cause the sub arc slab flux to become less water rich and increasingly dominated by hydrous melts over a distance of a few kilometers behind the arc front this change exerts a first order control on magma chemistry and implies discrete melt transport pathways through subduction zones our results replicate patterns in other arcs implying common sub arc slab surface temperature ranges in thermally diverse subduction zones

the caprock of the snorre field norway a possible leakage by hydraulic fracturing abstract the snorre field located on the tampen spur in the west of the viking graben presents a 300 m oil column in triassic and lower jurassic reservoirs and it is characterized by high pressures the caprock is formed by thick shale of cretaceous and palaeocene age some oil shows are found in the caprock up to a few hundred metres above the reservoir and have the same origin as the oil in the reservoirs the secondary migration process seems to be linked to high overpressures within the reservoir the pore pressure at the top of the reservoir reaches about 82 of the total vertical stress which is close to the minimum horizontal stress according to leak off test data hydraulic fracturing probably occurs increasing the shale permeability so that some oil escapes from the reservoirs the snorre field can be considered as a dynamic trap where a constant pressure regime is maintained by several processes linked to the local conditions and particularly to its structural situation and where regulation of the system occurs at the top of the reservoirs the pressure regime and the in situ stress conditions are the key factors in the prospectivity of the traps in this area

modelling the influence of tectonic compression on the in situ stress field with implications for seal integrity the haltenbanken area offshore mid norway exploration for hydrocarbons in overpressured domains is often considered high risk because of the possibility of seal failure and fluid leakage due to natural hydraulic fracturing several of the wells drilled in highly overpressured reservoirs on haltenbanken offshore mid norway have proved to be devoid of hydrocarbons suggesting that ineffective seals are the cause of exploration failure however recent petroleum discoveries within this area demonstrate that fluid pressure is not the ultimate control on entrapment of hydrocarbons we investigate the way in which far field tectonic compression may have influenced the in situ stress conditions on haltenbanken and assess whether tectonic stresses also may facilitate local fracturing of the seal by reducing the retention capacity minimum horizontal stress fluid pressure we have approached the problem by applying a finite element model the elasto plastic model assumes two dimensional plane strain and is constrained from geological and geophysical data the results show that 1 contrasts in the rock s mechanical properties across discontinuities e g sediment interfaces cause rapid shifts in stress magnitudes 2 the differences in stress magnitudes across such discontinuities can be subdued or enhanced under increased horizontal compression and 3 structurally controlled variations in vertical displacements produce local concentrations of highs and lows in the stress field the combined result of these three factors is that the magnitude of horizontal stress may vary quite considerably within spatially restricted areas the implication of these predictions in terms of hydrocarbon preservation potential in highly overpressured regions is that rapid shifts in minimum horizontal stress magnitudes can reduce the retention capacity and therefore facilitate natural hydraulic fracturing

glacier surge mechanisms inferred from ground penetrating radar kongsvegen svalbard deformational structures at the surge type glacier kongsvegen sval bard are displayed at the glacier surface and on a grounded cliff section at the terminus a 300 m665 m grid of 200 mhz ground penetrating radar gpr profiles has been col lected adjacent to the cliff section in order to identify englacial structure two sub horizon tal reflectors have been imaged the upper is interpreted as the glacier bed and represents a transition between glacier ice and frozen subglacial sediments while the lower is inter preted as a transition between frozen and unfrozen subglacial sediment dipping reflec tors corresponding to sediment filled features on the cliff and glacier surface do not cross the glacier bed a small number of reflectors interpreted as thrust faults are visible below the bed reflector a model is developed for structural development which suggests that ice built up in a reservoir zone during quiescence during the surge ice propagated rapidly from this reservoir creating a zone of compression which resulted in thrusting subse quently an extensional flow regime resulted in extensive fracture of the ice we suggest dilated sediment was evacuated into these extensional crevasses from the glacier bed accelerating surge termination

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

lithospheric memory state of stress and rheology neotectonic controls on europe s intraplate continental topography abstract to date research on neotectonics and related continental topography development has mostly focused on active plate boundaries characterized by generally high deformation rates the intraplate sedimentary basins and rifts of the northern alpine foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that europe s intraplate lithosphere is being actively deformed this has major implications for the assessment of its natural hazards and environmental degradation the lithosphere of the northern alpine foreland has undergone a polyphase evolution with an intense interplay between upper mantle thermal perturbations and stress induced intraplate deformation that points to the importance of lithospheric folding of the thermally weakened lithosphere in this paper we address relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography the objectives are to quantify the effects of ongoing alpine collision and atlantic ridge push on the intraplate deformation in europe and its impact on topography evolution and related natural hazards this paper reviews the four dimensional topographic evolution of the european lithosphere through a multi disciplinary approach linking geology geophysics and geotechnology until now research on neotectonics and related topography development of intraplate regions has received little attention our study examines a number of selected natural laboratories in continental europe from orogen through platform to continental margin these natural laboratories include the carpathians pannonian system the northwest european platform iberia and the atlantic continental margin we focus on lithosphere memory and neotectonics with special attention to the thermo mechanical structure of the lithosphere mechanisms of large scale intraplate deformation late neogene anomalies in subsidence and uplift and links with surface processes and topography evolution

gpr survey of a lobate rock glacier in yankee boy basin colorado usa abstract the internal structure of a lobate rock glacier located in the san juan mountains of southwest colorado was investigated using ground penetrating radar gpr a 440 m 25 mhz longitudinal profile oriented along the central axis of the rock glacier shows moderate to strongly coherent reflection horizons or layers that can be recognized clearly to a depth of 30 35 m the layers are interpreted as representing ice supersaturated sediments and coarse blocky rockslide debris that are the result of flow perhaps generated by seasonal snow pack covered by episodic debris flows or high magnitude discharges of talus from the cirque headwall profiles collected at 50 mhz indicate that in the upper 20 m thickness of the rock glacier many of these layers are laterally continuous the total depth of penetration 40 m at 25 mhz was sufficient to detect the rock glacier cirque floor contact which is composed of underlying moraine several prominent reflection events that subdivide the profile into broad 10 15 m thick layers represent contacts between major depositional units these units are believed to be individual flow lobes that were initiated at various cirque headwall locations we interpret this rock glacier to be a composite feature that formed by a process involving the development and subsequent overlap of discrete flow lobes that have over ridden older glacial moraine and protalus rampart materials the latter materials have been incorporated into the present flow structure of the rock glacier

current transition from glacial to periglacial processes in the dolomites south eastern alps abstract a close relationship between glacial and periglacial landforms is frequently observed in alpine environments where a transition from glacial to periglacial processes often took place after the end of the little ice age lia understanding the origin of these landforms is challenging and assessing the current spatial domain of glacial and periglacial processes may be a difficult task in high relief areas where thick and widespread debris cover often characterize rapidly decaying glaciers here we present a comprehensive study of a composite landform located in the dolomites south eastern alps combining geomorphological geophysical and topographic surveys with ground surface temperature measurements results indicate that a debris covered glacier persists in the upper part rather large compared to the lia extent but currently inactive and rapidly losing mass an active rock glacier exists in the lower part surrounded by discontinuous permafrost a frozen body about 10 m thick was detected in the rock glacier and geomorphological evidence suggests that this ice mass is completely detached from the debris covered glacier our findings suggest that the lower part of the composite landform is probably a remnant of the ancient glacier tongue and is currently evolving under periglacial conditions periglacial processes are therefore replacing glacial processes which dominated in this site during the lia

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

tephrochronology of recent events in the andean range northern patagonia spatial distribution and provenance of lacustrine ash layers in the nahuel huapi national park tephrochronology is a powerful tool for dating sedimentary sequences especially in patagonia where a large number of active volcanoes have produced frequent historical eruptions short lacustrine sedimentary sequences were extracted from the lakes moreno oeste and ton cek nahuel huapi national park seventeen volcanic ash layers were identified in both cores 210 pb and 137 cs were used for dating techniques and historical volcanic records were employed for correlation white pumice and glass shards from the tephras were characterised by measuring major and trace element contents by instrumental neutron activation analysis two volcanic sources the cordon caulle and the calbuco volcanoes were recognised as the prevailing systems that impacted the area in the past 800 1000 a the calbuco volcano was mainly responsible for the nine tephras identified in the lake ton cek sequence four of these nine tephras also contained material from the cordon caulle complex and could be interpreted as composite tephras or possible reworked ones the calbuco volcano showed predominant influences in the lake moreno oeste sequence six of the eight tephras identified in such a sequence were from the calbuco volcano and three of these six contained material from the cordon caulle complex the other two were from the cordon caulle complex with contributions from the calbuco volcano in one of them these findings show that the high frequency of volcanic events in the study region demands an accurate characterisation of the products generated by each source as well as an evaluation of their spatial distribution to obtain a consistent framework for dating recent environmental changes copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

tephrostratigraphy of the late glacial and holocene sediments of puyehue lake southern volcanic zone chile 40 s abstract we document the mineralogical and geochemical composition of tephra layers identified in the late quaternary sediments of puyehue lake southern volcanic zone of the andes chile 40 s to identify the source volcanoes and to present the first tephrostratigraphic model for the region for the last millennium we propose a multi criteria correlation model based on five tephra layers identified at seven coring sites the two upper tephras are thin fine grained green layers composed of more than 80 rhyodacitic glass shards and associated to the ad 1960 and ad 1921 22 eruptions of the puyehue cordon de caulle volcanic complex the third tephra is a sandy layer dominated by orthopyroxene and related to the ad 1907 eruption of rininahue maar an olivine rich tephra was deposited at the end of the 16th century and a tephra characterized by a two pyroxene association marks the second half of the first millennium ad in addition we detail the tephra succession of an 11 22 m long sediment core covering the last 18 000 yr the results demonstrate that the central province of the southern volcanic zone has been active throughout the last deglaciation and the holocene with no increase in volcanic activity during glacial unloading

neogene patagonian plateau lavas continental magmas associated with ridge collision at the chile triple junction extensive neogene patagonian plateau lavas 46 5 to 49 5 s southeast of the modern chile triple junction can be related to opening of asthenospheric slab windows associated with collisions of chile rise segments with the chile trench at 12 ma and 6 ma support comes from 26 new total fusion whole rock 40ar 39ar ages and geochemical data from back arc plateau lavas in most localities plateau lava sequences consist of voluminous tholeiitic main plateau flows overlain by less voluminous 2 to 5 million year younger alkalic postplateau flows northeast of where the ridge collided at 12 ma most lavas are syncollisional or postcollisional in age with eruptions of both sequences migrating northeastward at 50 to 70 km ma plateau lavas have ages from 12 to 7 ma in the western back arc and from 5 to 2 ma farther to the northeast trace element and isotopic data indicate main plateau lavas formed as larger percentage melts of a garnet bearing oceanic island basalt oib like mantle than postplateau lavas the highest percentage melts erupted in the western and central plateaus in a migrating slab window model main plateau lavas can be explained as melts that formed as upwelling subslab asthenosphere which flowed around the trailing edge of the descending nazca plate and then interacted with subduction altered asthenospheric wedge and continental lithosphere alkaline postplateau lavas can be explained as melts generated by weaker upwelling of subslab asthenosphere through the open slab window thermal problems of high pressure melt generation of anhydrous mantle can be explained by volatiles h2o and co2 introduced by the subduction process into slab window source region s an oib like rather than a mid ocean ridge basalt morb like source region and the lack of magmatism northeast of where ridge collision occurred at 13 to 14 ma can be explained by entrainment of weak plume s or regional variations in an ambient oib like asthenosphere

topographic migration of georadar data implications for acquisition and processing application of conventional elevation static corrections and migration to wavefield data recorded on irregular surfaces may result in poor reconstructions of complex subsurface features particulary poor images may be obtained at locations where the depths to target structures are comparable to undulations in the surface topography for example topographic relief of only 1 2 m may be important for the processing of georadar data we describe an algorithm that allows georadar data to be migrated directly from gently to highly irregular acquisition surfaces when applied to a variety of complicated synthetic data sets topographically migrated images are observed to be markedly superior to those produced by two standard processing schemes extensive tests demonstrate that topographic migration should be considered in regions characterized by surface gradients 10 i e dips 6 for effective topographic migration lateral and vertical coordinates of the georadar antennas should be determined to better

giant earthquakes in south central chile revealed by holocene mass wasting events in lake puyehue abstract very high resolution reflection seismic profiling 3 5 khz revealed nine holocene mass wasting events in lake puyehue south central chile these events are made up of numerous coeval mass wasting deposits and some homogenites which are radiocarbon dated the two youngest mass wasting events could be attributed to the giant ad 1960 and ad 1575 valdivia earthquakes the most extensive event took place around 1660 cal yr bp evaluation of all possible slope failure processes led us to infer that giant earthquakes roughly comparable to the ad 1960 valdivia earthquake mw 9 5 are the most likely trigger mechanisms of all mass wasting events in lake puyehue these occurred with a mean recurrence rate of 1000 yr although relatively aperiodically ranging between 500 and 2000 yr quantitative comparison of mass wasting events related to historically reported earthquakes ad 1960 and ad 1575 showed significant differences although these earthquakes are assumed to have had a comparable strength a lowered background sedimentation rate could be responsible for this variable earthquake recording which highlights the importance of a thorough assessment of the depositional history before using lacustrine records for quantitative paleoseismic analysis

problems encountered with the 14c dating of peat abstract pairs of neighbouring short columns of peat from two sites in northern england were divided into contiguous 1 cm thick slices that were sub sampled for pollen and plant macro fossil analysis for each slice the remaining peat was then split into humic acid humin and fulvic acid fractions and radiocarbon dated this research demonstrates that significant variations can occur in the radiocarbon content of discrete chemically defined fractions of peat a total of 127 radiocarbon dates was obtained the results from the four columns of peat are highly variable and mutually inconsistent the fulvic acid fraction although normally younger than the corresponding humic acid and humin fractions has very little effect on a combined date in these samples however it is removed from all samples prior to dating in order to remove any carbonates which could contaminate samples the variations in the ages obtained for the humic acid and corresponding humin fractions range from the humin fraction being 630 years older than the humic acid srr 4029 to the humic acid being 1210 years older than the humin fraction srr 4007 even when a two sigma confidence is allowed no correlation was apparent between pollen concentration 13 c enrichment degree of humification and the conventional radiocarbon ages

compositional modeling of petroleum generation and expulsion trial application to a local mass balance in the smorbukk sor field haltenbanken area norway 1 we present an application of a compositional kinetic model of petroleum generation degradation into gas and residue and simultaneous expulsion petroleum composition is described by four carbon fractions c 1 c 2 c 5 c 6 c 14 c 15 and expulsion is related to a petroleum saturation threshold expulsion is important because rapid expulsion of petroleum from source rocks favors oil whereas late expulsion increases the cracking reactions and favors gas accumulation such a model is tested against field data for the first time by applying it to the smorbukk sor field previously named smorbukk greek beta located in the norwegian sea geometrical and one dimensional thermal reconstructions are performed followed by a computation of a mass balance of expelled and unexpelled products for each source rock throughout the drainage area comparison of the model results is made with rock eval data vitrinite reflectance and actual composition of accumulations lower jurassic coals were the main source expelling gas and oil mainly since 5 ma as the present accumulation accounts for less than 10 of total expelled petroleum major petroleum losses probably occurred through the structural spillpoint this migration scheme is supported by the simila composition of the reservoired petroleum and the petroleum expelled since 0 5 ma although various uncertainties are possible this study shows that our model has the capability to quantify expulsion consistently with the observed amounts of unexpelled petroleum in mature source rocks and with the reported composition of the accumulation

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

influence of poroelastic behavior on the magnitude of minimum horizontal stress sh in overpressured parts of sedimentary basins in many sedimentary basins of the world the minimum hori zontal stress s h is greater in overpressured zones than in normally pressured zones at equivalent depths a common explanation is that the frictional slip on listric normal faults keeps the difference between vertical stress s v and s h within certain bounds and the difference is smaller under lower effective stress i e higher pore pressure p p however in the overpressured parts of the central north sea graben united kingdom and the sable subbasin of the scotian shelf canada conventional friction envelopes underestimate the magnitude of s h these data instead indicate that s h increases at a rate proportional to but less than the rate of increase of p p a condition consistent with a p p induced deformation of the rock called poroelastic behavior this paper argues that whereas friction may govern s h in normally pressured basins poroelastic behavior is responsible for the unusually high s h in the overpres sured parts of these same basins data on the p p and s h gradients from these basins suggest that s h p p 0 7

crustal stress in the northern north sea as inferred from borehole breakouts and earthquake focal mechanisms the regional stress field in the northern north sea offshore western norway has been studied through the acquisition and analysis of directions of maximum horizontal compression sh as extracted from borehole breakouts and from earthquake focal mechanism solutions the results indicate that the regional stress field is dominated by nw se compression with good consistency between shallow borehole breakouts 2 5 km depth and deeper earthquakes 10 25 km depth the broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin and the results are in good agreement with the western europe trend found in earlier investigations the tampen spur region in the northern north sea has been subjected to particularly complex deformation with two dominating fault directions trending nw se and ne sw from tampen spur in the west to the sogn graben in the east an anomalous stress field is indicated with ne sw oriented maximum horizontal compressions this anomaly is clearly seen both in the borehole breakout data and in the earthquake data possible sources for this anomaly are discussed and include postglacial uplift and or lateral variations in the physical properties of the crust

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp

a new 3 d thin skinned rock glacier model based on helicopter gpr results from the swiss alps mountainous locations and steep rugged surfaces covered by boulders and other loose debris are the main reasons why rock glaciers are among the most challenging geological features to investigate using ground based geophysical methods consequently geophysical surveys of rock glaciers have only ever involved recording data along sparse lines to address this issue we acquired quasi 3 d ground penetrating radar gpr data across a rock glacier in the swiss alps using a helicopter mounted system our interpretation of the derived gpr images constrained by borehole information results in a novel thin skinned rock glacier model that explains a concentration of deformation across a principal shear zone decollement and faults across which rock glacier lobes are juxtaposed the new model may be applicable to many rock glaciers worldwide we suggest that the helicopter gpr method may be useful for 3 d surveying numerous other difficult to access mountainous terrains