discriminating between subglacial and proglacial lake sediments an example from the danischer wohld peninsula northern germany subglacial lakes are common features of contemporary ice masses however they are rarely identified in the geological record this is due to the difficulty in discriminating between subglacial and proglacial lake sediments a proglacial origin is typically preferred as the simplest explanation we hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the danischer wohld peninsula northern germany which have been interpreted to record both proglacial and subglacial sedimentation we identify two major phases of ice activity and associated lake formation during the late weichselian glaciation 1 proglacial lake formation at 23 ka in front of the advancing baltic ice stream this lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent 2 retreat of ice back into the baltic basin at 19 ka and formation of a proglacial lake that persisted for 4 ka we suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka this is based on the presence of aggrading sediment deposits characterised by stratified laminated diamictons and interbedded tabular to channelized sorted sediments the juxtaposition of relatively undeformed waterlain sediment and subglacial till absence of glaciotectonic thrusting and folding or of fining coarsening successions and the geomorphic association with tunnel valleys to the south of the study area the style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments the luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems

sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

the uwekahuna ash member of the puna basalt product of violent phreatomagmatic eruptions at kilauea volcano hawaii between 2800 and 210014c years ago abstract kilauea volcano s reputation for relatively gentle effusive eruptions belies a violent geologic past including several large phreatic and phreatomagmatic eruptions that are recorded by holocene pyroclastic deposits which mantle kilauea s summit area and the southeast flank of adjacent mauna loa volcano the most widespread of these deposits whose original distribution can be reconstructed is the uwekahuna ash member of the puna basalt a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries the first episode occurred between 2770 70 and 2265 50 14 c yr ago it included two major pyroclastic surges each preceded by unusually vigorous lava fountaining from a vent near the volcano s summit before the second eruptive episode 2110 120 14 c yr ago plants had re colonized the rainforest environment northeast of the summit and at least two lava flows from mauna loa had buried parts of the first episode deposits the second episode also began with vigorous lava fountaining followed by widespread lithic ashfall a third major surge and finally a fourth fountaining event before the final pumice deposit could be significantly reworked it was partly buried by picritic basalt flows that are unusual in kilauea s summit area in proximal areas the uwekahuna ash member is more than 1 m thick locally 5 m and includes lithic blocks up to 0 8 m in diameter coarse primarily lithic debris was deposited around the vent by laterally expanding surges fallout deposits accumulated preferentially to the northeast under the influence of high altitude counter tradewinds the area devastated by surges and originally buried by at least 15 cm of the uwekahuna was about 420 km 2 the bulk volume of the deposits was approximately 0 3 km 3 including less than 0 1 km 3 of juvenile material juvenile constituents are olivine tholeiitic basalts similar in major element composition to typical kilauea summit lava flows but variations in both major elements and trace elements suggest that the eruptions tapped more than a single uniform source region we infer that the eruptions which produced the uwekahuna were driven by water interacting with a fluctuating magma column magma withdrawal episodes may have been accompanied by large volume submarine effusive eruptions and by summit collapse the volume extent and character of the uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at kilauea as well as at other basaltic volcanoes

continental transform tectonics great slave lake shear zone ca 1 9 ga northwest canada great slave lake shear zone gslsz is a northeast trending dextral mylonite zone across which the coeval north trending thelon and taltson magmatic zones on the west margin of the churchill province are offset 300 700 km it is proposed that the gslsz is a continental transform structure related to oblique collisional indentation of the active margin of the churchill province by the microcontinental slave province this accounts for geologic and geophysical differences between the thelon and taltson zones and explains the localization of a tibetan type queen maud uplift north of the gslsz and the abrupt loss of slip on the gslsz east of the uplift it also provides a new model for the athapuscow aulacogen analogous to the modern bay of bengal indo burman ranges sagaing transform andaman sea situation

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

correlations of volcanic ash texture with explosion earthquakes from vulcanian eruptions at sakurajima volcano japan abstract we compare the texture of volcanic ash with the maximum amplitude of explosion earthquakes a eq for vulcanian eruptions from sakurajima volcano we analyze the volcanic ash emitted by 17 vulcanian eruptions from 1974 to 1987 using a stereoscopic microscope we classify the glassy particles into smooth surface particles s type particles and non smooth surface particles ns type particles according to their surface conditions gloss or non gloss appearance as an indicator of the freshness of the particles s type particles are further classified into v type particles those including vesicles and nv type particles those without vesicles by means of examinations under a polarized microscopic of polished thin sections cross correlated examinations against seismological data show that 1 the number fraction of s type particles s fraction has a positive correlation with a eq 2 the number ratio of nv type particles to v type particles the n v number ratio has a positive correlation with a eq and 3 for explosions accompanied with bl type earthquake swarms the n v number ratio has a negative correlation with the duration of the bl swarms bl swarms refer to the phenomenon of numerous bl type earthquakes occurring within a few days prior to an increase in explosive activity kamo k 1978 some phenomena before the summit crater eruptions at sakura zima volcano bull volcanol soc japan 23 53 64 the positive correlation between the n v number ratio and a eq could indicate that a large amount of separated gas from fresh magma results in a large a eq plagioclase microlite textual analysis of nv type particles from five explosive events without bl swarms shows that the plagioclase microlite number density mnd and the l w length width ratio have a positive correlation with a eq a comparison between textural data mnd l w ratio crystallinity and the result of a decompression induced crystallization experiment couch s sparks r s j carroll m r 2003 the kinetics of degassing induced crystallization at soufriere hills volcano montserrat j petrol 44 1477 1502 suggests that a plagioclase microlite texture of volcanic ash from eruptions without bl swarms could be generated by a decompression of 100 160 mpa if the mnd is controlled by the water exsolution rate from melt the positive correlation between the mnd and a eq may suggest that a eq becomes large when the effective decompression is large and the water exsolution rate is high from 6 2 10 5 to 1 9 10 4 wt s the estimated magma ascent rate ranges from 0 11 to 0 35 m s which is one order of magnitude faster than that of an effusive eruption and one to three orders slower than those for a sub plinian eruption this suggests that the ascent rate of magma plays an important role in the occurrence of vulcanian eruptions we propose a simple model for vulcanian eruptions at sakurajima volcano that takes into account the correlation between the s fraction and a eq

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

the holocene secche di lazzaro phreatomagmatic succession stromboli italy evidence of pyroclastic density current origin deduced by facies analysis and ams flow directions the edifice of stromboli volcano gravitationally collapsed several times during its volcanic history 100 ka present the largest holocene event occurred during the final stage of the neostromboli activity 13 5 ka and was accompanied by the emplacement of phreatomagmatic and lahar deposits known as the secche di lazzaro succession a stratigraphic and paleomagnetic study of the secche di lazzaro deposits allows the interpretation of the emplacement and the eruptive processes we identify three main units within the succession that correspond to changing eruption conditions the lower unit ua consists of accretionary lapilli rich thinly bedded parallel to cross stratified ash deposits interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents upward the second unit ub of the deposit is more massive and the beds thicker indicating an increase in the sedimentation rate from pyroclastic density currents the upper unit uc caps the succession with thick immediately post eruptive lahars which reworked ash deposited on the volcano s slope flow directions obtained by anisotropy of magnetic susceptibility ams analysis of the basal bed of ua at the type locality suggest a provenance of pyroclastic currents from the sea this is interpreted to be related to the initial base surges associated with water magma interaction that occurred immediately after the lateral collapse which wrapped around the shoulder of the sector collapse scar upward in the stratigraphy upper beds of ua and ub paleoflow directions change and show a provenance from the summit vent probably related to the multiple collapses of a vertical pulsatory eruptive column

large subglacial lake beneath the laurentide ice sheet inferred from sedimentary sequences subglacial lakes identifi ed beneath the antarctic ice sheet belong to a rare category of unexplored environments on earth s surface the key to understanding the origin and longevity of subglacial lakes is likely contained in their sedimentary sequences here we explore the nature of a sedimentary succession in a deep tectonic trough identifi ed as a prime candidate for a large subglacial paleolake the trough is the 100 km long 620 m deep christie bay located in the east arm of the great slave lake canada high resolution seismic refl ection data and short sediment cores collected in the deep trough show a 150 m thick sequence of fi sedimentary lake fi ll separating glacial ice contact deposits from draped holocene lake sediments we interpret this sequence to consist of sediments that accumulated in a subglacial lake that covered an area larger than 130 km 2 the inferred presence of a subglacial paleolake is supported by results from hydrologic modeling of drainage pathways beneath the laurentide ice sheet during the last glacial maximum our data point toward the existence of a dynamic subglacial lake environment where sediments were delivered by discharge of meltwater from a subglacial water system a core sample of the sedimentary lake fi ll in christie bay may elucidate whether living organisms exist in subglacial lakes

thick and fast sedimentation in a pleistocene fiord lake of british columbia canada the central interior plateau of british columbia canada is dissected by numerous elongate glacially overdeepened lake basins akin to coastal fiords an air gun seismic reflection investigation 242 km of trackline of okanagan lake 120 km long 3 5 km wide shows that the pleistocene sediment fill is up to 792 m thick and that bedrock has been excavated by repeated pleistocene glacial erosion to nearly 650 m below sea level the depth of bedrock incision below the surrounding plateau is more than 2000 m exceeding that of the grand canyon in arizona the total volume of sediment infill within the narrow trenchlike basin is more than 90 km 3 and several lines of evidence suggest that this fill accumulated rapidly during a single phase of glaciolacustrine sedimentation during late wisconsin deglaciation of the region after 15 ka similar fiord lake basins up to 100 km long are common in the interior of british columbia if the data from okanagan are representative these basins may represent a major previously unrecognized component of the total glacial sediment flux to the ocean overdeepening below sea level and the focusing of large volumes of glacial sediment and meltwater into such basins are of considerable glaciologic significance and may record the fast unstable flow of ice streams during deglaciation of the cordilleran ice sheet

edifice collapse and related hazards in guatemala abstract guatemalan volcanoes have at least seven debris avalanche deposits associated with cerro quemado fuego pacaya tecuamburro and an unidentified volcano the deposits range in size from less than 0 1 to in excess of 9 km 3 and from 2 5 to in excess of 300 km 2 the avalanches traveled 3 to 50 km from their sources in the guatemalan highlands three of the avalanches occurred in late pleistocene time and four in holocene time two of them within the last 2000 years the avalanches occurred at both andesitic and basaltic stratovolcanoes and at dacitic dome complexes laterally directed phreatic or magmatic pyroclastic explosions were associated with two of the debris avalanches an evaluation of factors that might lead to an edifice collapse in guatemala is based on the case studies presented in this report and a survey of the literature edifice collapses are more apt to occur if zones of weakness exist within the volcanic edifices such as unwelded pyroclastic rocks and pervasively altered rocks further the trench ward side of volcano pairs like fuego and atitlan may be more likely to fail because it may have weak zones along the contact with the older back arc volcano the direction of failure may be influenced by regional slopes which in guatemala generally trend southward toward the oceanic trench and by such structural factors as multiple vents or overly steep slopes reflecting previous activity or erosion debris avalanches are more likely to occur in drainages which have headwaters at two or more volcanoes domes are especially apt to produce small to moderate sized debris avalanches and further if the domes form a coalescing chain are most likely to fail in a direction normal to the chain these factors are used at seventeen major volcanic centers in guatemala to assess their potential for edifice collapse and most probable direction of failure

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

morpho structural setting of stromboli volcano revealed by high resolution bathymetry and backscatter data of its submarine portions the first high resolution bathymetric and backscatter maps of offshore stromboli island are presented together with an interpretation of its volcanic structural and sedimentary features the volcanic edifice is characterized by a sub conical shape with a quasi bilateral symmetry with respect to a ne sw axis the dimensions of the strombolicchio volcanic centre to the ne of stromboli have been restored by redrawing its morphology before wave action that eroded it in late quaternary time on the ne submarine flank of strombolicchio a n64 e structural trend controls the shape of strombolicchio canyon on the southern side of stromboli the submarine flank has a radial structural trend possibly reflecting a volcanic stress regime landslide scars at various scales are ubiquitous on the submarine slopes of stromboli repeated large scale lateral collapses have affected both the northwestern and southeastern unbuttressed flanks of the volcano producing large debris avalanche deposits

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

comment on the comment by m j siegert on a numerical model for an alternative origin of lake vostok and its exobiological implications for mars by n s duxbury et al 1 there is some debate on the origin of subglacial lake vostok and whether the water within the present subglacial lake system contains biota that survived the buildup of the antarctic ice sheet one theory suggests that lake vostok existed as a preglacial lake before glaciation of the continent at around 15 ma ago survived the subsequent period of ice sheet growth and remained stable beneath the thick ice cover to the present day duxbury et al 2001 another hypothesis challenges this view by stating that the early phase of build up would have resulted in ice grounding throughout the trough which the lake now occupies siegert 2004 2 according to duxbury et al 2001 the lake could have survived the growth of the ice sheet as long as the preglacial lake was more than 53 m deep in their model subglacial lake vostok is considered as an approximate closed system however if lake vostok existed as a preglacial lake the closure of the lake vostok system must have happened between the initiation of the ice sheet and the establishment of a stable ice cover in east antarctica siegert 2004 therefore the dynamic evolution of the ice sheet and its interaction with the preglacial lake should be accounted for in determining whether subglacial lake vostok is a direct remnant of a preglacial surficial lake 3 siegert 2004 demonstrates that the preglacial lake could not have survived the buildup of the antarctic ice sheet water flow beneath an ice mass is controlled by the hydraulic potential gradient pg rigas rw ri gab where ri and rw are the density of ice and water and as and ab are the surface and basal slope respectively shreve 1972 if the magnitude of surface slope is larger than one tenth the basal slope water can be driven out of a topographic depression and flow uphill two icesheet model studies huybrechts 1993 deconto and pollard 2003 show that during the inception and growth of the antarctic ice sheet the ice sheet margin was situated close to lake vostok the steep margin of the ice sheet across lake vostok implies high subglacial hydraulic potential gradients which led siegert 2004 to conclude that basal water is evacuated as the steep ice sheet margin progresses over the lake however none of the above models take into account the interaction of the ice sheet with the underlying lake whether it be a preglacial or a subglacial lake and only consider an ice sheet more or less frozen to the underlying bedrock 4 below i present a physical mechanism that allows for subglacial lake vostok to survive the buildup of the ice sheet by taking into account the interaction of the ice sheet with the preglacial subglacial lake this hypothesis is supported by the fact that the surface of a preglacial lake as well as the interface between a subglacial lake and the overriding ice sheet can be regarded as a slippery spot

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

dynamics of surges generated by hydrothermal blasts during the 6 august 2012 te maari eruption mt tongariro new zealand abstract the 6 august 2012 te maari eruption produced violent and widespread cold pyroclastic density currents pdcs following unroofing of the pressurized hydrothermal system despite an erupted volume of only 5 10 5 m 3 and lacking any juvenile component the 340 000 m 3 of pdcs spread over an area of 6 1 km 2 and had mobilities that were on the order of volcanic blasts or blast like pdcs this great mobility was due to strong lateral focussing of explosion energy producing jets with initial velocities 100 m s we present a type stratigraphy for these hydrothermal derived low temperature pdcs that show a tripartite deposit sequence each of the deposit units dominates respectively three outward gradational sedimentary facies reflecting transitions in the propagating pdc transport and depositional mechanisms the largest pdcs directed west and east of the upper te maari area were generated from outer cone breccias and tuffs that were mostly highly hydrothermally altered landsliding and the geometry of the hydrothermal area led to the directed jetting initial particle laden jets laid sheets grading into lobes of proximal massive sand to gravel rich facies dominated by unit a and extending up to 1 km from the vents as the jets were collapsing a vertically and longitudinally stratified pdc developed within the first few hundred metres from source exponential thinning and coarse tail grading dominated fining with radial distance of massive unit a resulted from fast deposition and progressive depletion of the most concentrated flow region behind the pdc head markedly slower tractional sedimentation from the passing pdc body and tail deposited the highly stratified and ripple bedded fine coarse ash of unit b this formed distinctive dune fields of the medial dune bedded ash rich facies upwards in depositional sequences the waning of the current can be seen by replacement of higher energy bedforms to progressively lower ones downstream progressive waning and further depletion are characterised by the development of the distal wavy to planar bedded ash rich facies this is increasingly dominated by the uppermost deposition unit c of laminated fine med ash deposited by gently turbulent dilute phoenix clouds these high energy pdcs sourced from flank hydrothermal systems should be regarded as a serious threat in any multihazard assessment of a stratovolcano even though they may not be one of the major magmatic vent sites in addition further detailed studies of these hydrothermal jetting events and their deposits should be pursued in order to better understand large volume volcanic blasts which appear to be a larger scale sibling phenomenon

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

growth after collapse the volcanic and magmatic history of the neostromboli lava cone island of stromboli italy this study focuses on the holocene neostromboli lava cone which is part of the stromboli volcano aeolian islands italy it represents an important example of the structure and behaviour of lava cone re growth shortly after a large scale volcano sector collapse neostromboli s eruptive style is dominated by extrusion of sheet like a a lava flows and associated autoclastic breccias the lava cone developed during five phases of activity phases a to e representing discrete episodes of lava effusion characterised by rapid changes in magma composition spatial development of the feeder system and physical properties of erupted lavas through time although they all belong to the potassic series ks with sio2 49 55 wt and mgo 2 50 6 25 wt the neostromboli lavas have distinct petrogenetic characteristics ranging from leucite free and low sr shoshonitic basalts phases a and b to leucite bearing shoshonitic basalts with high phase c and intermediate phase d sr contents and to leucite free biotite bearing shoshonites phase e three different batches of mantle derived relatively primitive basic magmas fed the activity of phases a c and d the evolution phases a to b is inferred to have occurred in a continuously replenished tapped and crystallizing rtf magma chamber whereas phase e products were dominantly generated by fractional crystallization from phase d magmas the neostromboli cone shows summit flank and satellite vents and sheet intrusions with different geometry and location through time reflecting the interplay of regional tectonics precursory instability processes and volcano load

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

geological evidence for recurrent collapse driven phreatomagmatic pyroclastic density currents in the holocene activity of stromboli volcano italy abstract we present a multidisciplinary geological study of lithified to unconsolidated ash rich lapilli tuff deposits bearing accretionary lapilli that crop out in scattered sites along the lower slopes of the stromboli volcano southern italy these deposits are related to three pyroclastic successions called semaforo nuovo secche di lazzaro and semaforo labronzo with distinctive lithologic and volcanologic features and different stratigraphic position within the neostromboli volcano stratigraphy holocene their juvenile clasts have slightly different major and trace element compositions whole rock and glass isotopic ratios and mineralogical characteristics although they are all within the most evolved high k shoshonites typical of neostromboli the three successions are independently recognized in distinct sectors of the volcano displaying an asymmetric areal distribution that is interpreted as the result of directed pyroclastic density currents and minor fallout generated from summit eruptive vents lithological characteristics and morphoscopic features of ash particles indicate phreatomagmatic fragmentation combined with mechanisms of volatile exsolution or decompression which is atypical with respect to the dominant strombolian effusive eruptive behaviour of stromboli during the holocene we suggest that the three phreatomagmatic eruptions are linked to different major lateral collapses associated to flank fissure eruptions that occurred along the nw dipping sciara del fuoco collapsed flank it is argued that the collapses have unloaded the magmatic and hydrothermal system enabling magma water interaction and explosive decompression of a shallow magma reservoir the recurrent collapse eruption link with generation of directed pdcs able to reach the lower slopes of the volcano highlights a previously underestimated source of volcanic hazard at stromboli

the geomorphic and paleoenvironmental record in the sediments of atlin lake northern british columbia atlin lake in northern british columbia and southern yukon territory is the largest natural lake in the north american cordillera 791km 2 inflow from the juneau ice field delivers large volumes of sediment to the proximal basins of willison bay and llewellyn inlet sediment is distributed by interflow and underflow through these basins based on acoustic data each of these basins contain holocene deposits about 120m thick representing mean annual accumulation since deglaciation of more than 1cm a cores confirm this except that the formation of a small lake at the toe of llewellyn glacier during about the past 50 years is trapping sediment and has reduced accumulation in llewellyn inlet by an order of magnitude sills separate these basins from the main body of atlin lake and torres channel where accumulation is much less averaging about 1 4mm a during the history of the lake late pleistocene glacilacustrine sediment occurs as a thin patchy deposit and is overlain by up to 10m of holocene lacustrine deposits unlike other large lakes in the cordillera with thick late pleistocene deposits indicating large volumes of sediment contributed by glaciers in the lakes and their basins the pattern in atlin lake documents rapid retreat of glaciers from the lake and much of the drainage basin

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

large scale phreatomagmatic silicic volcanism a case study from new zealand abstract pyroclastic deposits of the 20 000 year old wairakei formation occur in the region surrounding lake taupo in the central north island of new zealand recent advances in the correlation of both proximal and distal equivalents of the wairakei deposits show that they were the result of one large eruption the ash layers once covered most of new zealand they are also present in deep sea cores from the sw pacific and on the chatham islands the dispersal and grain size parameters of the ash fall members indicate that their vent area was within the taupo volcano tectonic depression which for a long period has contained a large lake the wairakei eruption is interpreted to have been phreatomagmatic throughout each phase of the eruption sequence generated its own characteristic deposits the sequence of events can be summarized as follows 1 eruption and deposition of a white fine grained bedded fall deposit 2 eruption and deposition of a medium grained pumice fall deposit 3 generation of ultra fine wet ash clouds with a fall deposit accumulating largely as aggregates and accretionary lapilli accompanied by base surges 4 formation of water cooled pyroclastic flows and deposition of an extensive ignimbrite 5 return to a dominantly vertical eruption column and deposition of a medium grained bedded ash fall immediately followed by another wet ultra fine fall deposit charged with accretionary lapilli finally 6 an ignimbrite less widespread than that of phase 4 was produced co ignimbrite fall deposits of fine vitric dust and medium grained pumice were laid down over a huge area there may have been a short hiatus in activity between phases 4 and 5

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

directed blasts and blast generated pyroclastic density currents a comparison of the bezymianny 1956 mount st helens 1980 and soufriere hills montserrat 1997 eruptions and deposits we compare eruptive dynamics effects and deposits of the bezymianny 1956 bz mount st helens 1980 msh and soufriere hills volcano montserrat 1997 shv eruptions the key events of which included powerful directed blasts each blast subsequently generated a high energy stratified pyroclastic density current pdc with a high speed at onset the blasts were triggered by rapid unloading of an extruding or intruding shallow magma body lava dome and or cryptodome of andesitic or dacitic composition the unloading was caused by sector failures of the volcanic edifices with respective volumes for bz msh and shv c 0 5 2 5 and 0 05 km3 the blasts devastated approximately elliptical areas axial directions of which coincided with the directions of sector failures we separate the transient directed blast phenomenon into three main parts the burst phase the collapse phase and the pdc phase in the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere with much of the expansion having an initially lateral component the erupted material fails to mix with sufficient air to form a buoyant column but in the collapse phase falls beyond the source as an inclined fountain and thereafter generates a pdc moving parallel to the ground surface it is possible for the burst phase to comprise an overpressured jet which requires injection of momentum from an orifice however some exploding sources may have different geometry and a jet is not necessarily formed a major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet or alternatively to dynamic pressures and shocks within the energetic collapse and pdc phases internal shock structures related to unsteady flow and compressibility effects can occur in each phase we withhold judgment about published shock models as a primary explanation for the damage sustained at msh until modern 3d numerical modeling is accomplished but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified pdc this view is reinforced by recent modeling cited for shv in distal and peripheral regions solids concentration maximum particle size current speed and dynamic pressure are diminished resulting in lesser damage and enhanced influence by local topography on the pdc despite the different scales of the blasts devastated areas were respectively 500 600 and 10 km2 for bz msh and shv and some complexity involving retrogressive slide blocks and clusters of explosions their pyroclastic deposits demonstrate strong similarity juvenile material composes 50 of the deposits implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred the character of the magma fragmented by explosions highly viscous phenocryst rich variable microlite content determined the bimodal distributions of juvenile clast density and vesicularity thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater and laterally from the axial region the proximal stratigraphy of the blast deposits comprises four layers named a b c d from bottom to top layer a is represented by very poorly sorted debris with admixtures of vegetation and soil with a strongly erosive ground contact its appearance varies at different sites due to different ground conditions at the time of the blasts the layer reflects intense turbulent boundary shear between the basal part of the energetic head of the pdc and the substrate layer b exhibits relatively well sorted fines depleted debris with some charred plant fragments its deposition occurred by rapid suspension sedimentation in rapidly waning high concentration conditions layer c is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated created by rapid sedimentation under moderate concentration weakly tractive conditions with the uppermost laminated part reflecting a dilute depositional regime with grain by grain traction deposition by analogy to laboratory experiments mixing at the flow head of the pdc created a turbulent dilute wake above the body of a gravity current with layer b deposited by the flow body and layer c by the wake the uppermost layer d of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high rising buoyant thermal plume derived from the sediment depleted pyroclastic density current the strong similarity among these eruptions and their deposits suggests that these cases represent similar source transport and depositional phenomena

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

late glacial drainage systems along the northwestern margin of the laurentide ice sheet abstract the evolution of drainage systems along the retreating northwestern laurentide ice sheet was complex the interaction of ice margin configuration topography and glacioisostasy resulted in a network of meltwater rivers that variably overflowed to the arctic and pacific oceans and to the gulf of mexico glacial lakes also changed dramatically in size and location during the period of deglaciation at the last and all time glacial maximum the ice sheet extended into the eastern cordillera blocking northward and eastward drainage to the arctic ocean some meltwater and most non glacial runoff were diverted through the mountains to the yukon river basin into alaska and the pacific ocean retreat from the glacial maximum prior to 21 ka bp allowed proglacial drainage from the western margin of the ice sheet to flow into the beaufort sea arctic ocean deglaciation was rapid after about 13 ka bp with the present route of the lower mackenzie river established between 13 and 11 5 ka bp continued ice retreat led to significant southward expansion of the mackenzie beaufort drainage basin at about 11 5 ka bp through drainage capture of glacial lake peace which previously had drained southeastward into the missouri river and to the gulf of mexico very rapid ice retreat between 10 5 and 10 ka bp allowed glacial lake mcconnell to expand down slope in contact with the ice margin numerous glacial lakes occurred along the northwestern margin of the ice sheet during the maximum and retreat phases these include ice dammed glacial lake old crow which occupied unglaciated terrain of the northern yukon and glacial lake peace which utilized a number of outlets as it migrated eastward with the ice front along the peace valley the largest glacial lakes in the region were the result of glacioisostatic depression reversing the regional drainage the mackenzie phase of glacial lake mcconnell was the second largest pleistocene lake in north america 215 000 km 2 late glacial and post glacial changes in drainage systems were largely in response to isostatic rebound

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

the secche di lazzaro pyroclastics of stromboli volcano a phreatomagmatic eruption related to the sciara del fuoco sector collapse widespread phreatomagmatic ash deposits secche di lazzaro pyroclastics overlying the lavas of the neostromboli period 13000 to ca 5000 years b p have been identified at stromboli volcano the deposits consist of accretionary lapilli rich ash fall layers and debris flows ash fall layers originated by phreatomagmatic explosive activity from a vent probably located in the uppermost part of the sector collapse scarp sciara del fuoco which formed at the end of neostromboli period stratigraphic position composition of fresh lapilli identical to the neostromboli lavas and an unusually large scale of explosions suggest that the secche di lazzaro pyroclastics were erupted in connection with the sciara del fuoco slope failure characteristics of the deposits are consistent with phreatomagmatic hydrothermal explosivity related to catastrophic decompression of the plumbing hydrothermal system occurrence of multiple ash fall episodes coupled with variation of nature of lithics lithology is suggestive of repeated explosions eventually triggered by multiple backward migrating block detachments

salinity impact on water flow and lake ice in lake vostok antarctica 1 lake vostok isolated from direct exchange with the atmosphere for millions of years provides a unique so far inaccessible habitat by using a numerical model and recent geometry information the lake circulation was investigated for different salinites for freshwater thermally driven circulation occurs resulting from pressure dependent melting point differences at the inclined ice ceiling north to south ice pumping provides a steady supply of glacial water the weak circulation is driven by very small density contrasts but requires no unusual geothermal input for low salinity conditions however circulation intensifies occupying the entire lake the maximum amplitudes of melting freezing increase by about 50 and melting extends further south for both conditions approximately 200 m of refrozen ice accumulates beneath vostok station the lake habitat will be affected clearly by salinity it is essential to establish the specific chemistry for comprehending this unique environment and planning in situ experiments

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

late glacial and holocene sedimentary environments of quesnel lake british columbia abstract at 512 m quesnel lake is the third deepest in north america and at 100 km long its drainage basin spans from the arid interior plateau to the high mountains of the eastern cordillera where small glaciers are a significant source of sediment in most of the lake sediment is 0 to 40 m thick reaching a maximum of just over 100 m thick near the junction of the three arms cores from three locations in the lake provide evidence that the entire holocene record is contained in the upper 4 to 6 m of the sedimentary record where rates of accumulation have been constant or have decreased slowly the highest rates 0 35 to 0 72 mm a occur near points of inflow while the lowest rate 0 22 mm a occurs in a sheltered environment with limited inflow and significant hypolimnic circulation which may flush water and suspended sediment from the water column late pleistocene sediment beneath has a similar acoustic signature to the cored holocene record above suggesting that the sedimentary processes governing its deposition were not greatly different than in the present lake but that extensive glacial and paraglacial sources contributed to a significantly higher rate of accumulation mazama ash analyzed from two locations near points of inflow has an age of 7576 60 cal bp according to our chronology vivianite which is uncommon in lakes of the cordillera occurs in the middle of the cores mainly associated with macroscopic wood fragments and indicates reducing conditions within the sediment

evidence for the long term sedimentary environment in an antarctic subglacial lake lakes beneath the antarctic ice sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments however no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet and understanding of sediment pathways processes and structure in subglacial lake environments remains uncertain here we present an analysis of seismic data from subglacial lake ellsworth showing that the lake bed comprises very fine grained sediments deposited in a low energy environment with low water and sediment fluxes minimum sediment thickness is 6 m the result of prolonged low sedimentation rates based on the few available analogues we speculate this sediment age range is a minimum of 150 ka and possibly 1 ma sediment mass movements have occurred but they are rare and have been buried by subsequent sedimentation we present a new conceptual model of subglacial lake sedimentation allowing a framework for evaluating processes in subglacial lake environments and for determining future lake access locations and interpreting subglacial lake samples

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

the nature origins and distribution of ash aggregates in a large scale wet eruption deposit oruanui new zealand abstract this study documents the processes and products of volcanic ash aggregation in phreatomagmatic phases of the 25 4 ka oruanui supereruption from taupo volcano new zealand detailed textural and stratigraphic relationships of aggregates are examined in six of the ten erupted units which range from relatively dry styles of eruption and deposition units 2 5 to mixed units 6 7 8 and dominantly wet unit 3 aggregate structures and grain size distributions shift abruptly over vertical scales of cm to dm providing diagnostic features to identify deposits emplaced primarily as vertical fallout or pyroclastic density currents pdcs the six categories of ash aggregates documented here are used to infer distinct volcanic and meteorological interactions in the eruption cloud related to dispersal characteristics and mode of emplacement our field observations support the notion of brown et al 2010 origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife geol soc am bull 122 305 320 that deposits bearing matrix supported accretionary lapilli with concentric internal structure and abundant rim fragments are associated with emplacement of pdcs however on the basis of grain size distributions and field relationships it is inferred that these types of ash aggregates formed their ultrafine ash dominantly 100 km from vent it is inferred that ambient meteorological conditions play a more important role in ash fallout in these cases entrainment of moist air and distal subsidence and melting of ice carried by the plume are both likely to have contributed to the observed features of late stage aggregation in the drier phases of eruption these observations suggest that proximal column influenced aggregation processes which weaken with distance from source are overprinted by secondary later stage aggregation mechanisms farther downwind

understanding the collapse eruption link at stromboli italy a microanalytical study on the products of the recent secche di lazzaro phreatomagmatic activity abstract the secche di lazzaro sdl phreatomagmatic activity with the associated neostromboli sector collapse represents the most powerful activity of the last 6 ky at stromboli as revealed by its present day activity stromboli is one of the most eruptive volcanoes in italy and flank instability along its nw flank is a common process volcano instability is often dramatised by explosive eruptions thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself the possible role of pre eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies we studied the juvenile components scoria and pumice of the pyroclastic deposits from the sdl phreatomagmatic activity with the aim to understand the eruption collapse link the sdl pyroclastic sequence has been investigated in three different outcrops at secche di lazzaro sdl sw sequence at vallone del monaco sdl s and along the old path from stromboli village to the active craters sdl n juvenile components are ks shoshonites similar to the most evolved lavas erupted at the end of the neostromboli potassic period our study indicates that the sdl system is strongly heterogeneous and made up by at least two different sequences sdl n and sdl sw sdl s with different textural characteristics of the deposits and composition of the juvenile components mineral chemistry data show a variable presence of recycled crystals antecrysts possibly deriving from the previous neostromboli activity up to 13 ky ago whole rocks are characterised by small but significant differences between the sdl n and the southern samples pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages a clear isotope heterogeneity has been also found and explained by the presence of 10 minimum of less radiogenic antecrysts whereas crustal contamination would have only affected the higher sr radiogenic residual melt these data suggest that the sdl phreatomagmatic eruptions were fed by compositionally distinct potassic magmas which rested and evolved in two shallow magma conduits when the magma supply ceased in the waning phase of the neostromboli activity our results also rule out the occurrence of new arrivals of refreshing magmas in the sdl feeding system as well as other internal magma related causes as triggers for the sdl explosive eruptions accordingly external collapse related causes seem effectively more suitable for triggering the sdl phreatomagmatic eruptions by decompression of the magmatic systems we also suggest the sdl n and sdl sw sdl s sequences are generated by two respective explosive events separated in time and or space they can be respectively related to multiple failures of sciara del fuoco which successively depressurised the sdl n and the sdl sw sdl s magma conduits

major changes in volcano behaviour after a sector collapse insights from stromboli italy in recent years increasing numbers of volcanoes are being recognized as having undergone large sector collapses how far such events can change the succeeding behaviour of the volcano is poorly known despite the importance for natural hazards and economic applications by analysing the last 100 kyr geological history of stromboli italy which has involved multiple collapses this paper illuminates the feedback effect between sector collapse and magma upwelling and emplacement the collapsed zone of stromboli is episodically unbuttressed draining magma preferentially with formation of eruptive centres in the collapse amphitheatre and dyking along the collapse shoulders after a collapse there were no further linear eruptions across the cone on opposing middle lower slopes but these occurred again after rebuilding of the cone the time averaged eruption rate increased immediately before the first collapse and remained higher during the succeeding period of frequent collapses

early paleozoic ca 465 ma eclogites from beishan nw china and their bearing on the tectonic evolution of the southern central asian orogenic belt abstract the beishan orogen is situated in the southern margin of the central asian orogenic belt caob it is connected with the tianshan orogen to the west and the mongolia xing anling orogen to the east this orogen exhibits a well preserved neoproterozoic to late paleozoic sequence containing ophiolites accretionary complexes and eclogites in this paper we provide new geochronological data for eclogites and their country paragneiss to constrain the tectonic evolution of the beishan orogen u pb zircon dating of eclogites yielded two concordant ages 886 4 ma for the cores and 465 10 ma for the rims the zircon cores display bright luminescence with homogeneous or planar sector zoning intermediate th u ratios 0 17 0 47 and hree enriched patterns with negative eu anomalies eu eu 0 16 0 58 these features coupled with their formation temperatures of 680 710 c suggest that the core age represents the time of an earlier upper amphibolite facies metamorphic episode by contrast the zircon rims have dark luminescence with homogeneous or fir tree zoning low th u ratios 12 kbar for the eclogite facies metamorphism on the other hand zircon dating of a paragneiss near the eclogite produced two major groups of ages ca 1450 ma for a magmatic event and ca 900 ma for a metamorphic event it seems that eclogites and their country rocks have suffered the same earlier metamorphic episode based on the available age data obtained for eclogites ophiolites and granitoids from the beishan area a tectonic scenario can be constructed as follows the ca 1000 ma oceanic crust representing by protoliths of the eclogites was involved in early neoproterozoic orogenesis to have formed a microcontinental block during the early paleozoic island arcs and microcontinental blocks were progressively accreted to the northern margin of the tarim craton dunhuang block this was followed by the closure of paleoasian ocean and final amalgamation between the tarim craton and kazakhstan block in the late paleozoic

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

topographic and hydrological controls on subglacial lake ellsworth west antarctica 1 subglacial lake ellsworth sle was identified using reconnaissance data collected in the 1970s here we present more detailed surveys sle lies beneath 3 2 km of ice in a subglacial valley in west antarctica it has an area of only 18 km2 is dissimilar to the large tectonically controlled lakes beneath east antarctica and is a strong candidate for in situ exploration our analysis indicates that the ice above sle is floating on a fluid whose density is 950 1013 kg m 3 this could indicate freshwater but certainly precludes seawater or high salt acid or clathrate content the water in the lake is unlikely to be produced solely by local melt it is more likely delivered via subglacial drainage our surveys show no identifiable hydrological barrier to outflow meaning sle is effectively full new water entering the lake is likely balanced by outflow which would drain into another lake that we have also identified

high resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake lake le bourget northwestern alps france abstract lake le bourget is a deep peri alpine glacial lake originating from the last glacial the wurm the lake has amassed over 250 m of sediment since the last glacial maximum two seismic sparker surveys on the lake revealed the glacial and post glacial sedimentary infill the depth and the morphology of the wurm erosion surface and penetrated the riss wurm interglacial deposits as deep as the underlying riss erosion surface the density of the seismic grid and the high resolution of the data even at greater depths allowed a detailed study of the sedimentary processes and of their evolution throughout the deglaciation five main seismic facies characterise the basin fill they are interpreted as glacial deposits glacio lacustrine sediments proglacial lacustrine fans alluvial fan deltas and authigenic lacustrine drape these occur as a suite of deposits associated with the major lake tributaries and are the result of major changes in sediment supply and style of discharge into the lake the three dimensional facies associations within the basin fill document the history of the basin and its catchment area since the onset of the deglaciation

offshore evidence of large scale lateral collapses on the eastern flank of stromboli italy due to structurally controlled bilateral flank instability abstract new detailed swath bathymetry and long range side scan sonar data on the submerged flanks of stromboli integrated with seismic data and seabed sampling indicate that repeated lateral instability processes occurred on the eastern flank of the volcano although no debris avalanche deposits were known before the high resolution exploration of the seabed this flank of the island is opposite to the northwestern side more evidently affected by repeated flank collapses and this setting is evidence for a structurally controlled bilateral flank instability of the volcanic edifice evidence of at least two large scale lateral collapses is represented by a superficial hummocky megablock field partially outcropping on the middle lower eastern submerged slope and by a chaotic unit estimated volume is 1 2 km3 actually embedded within the volcaniclastic sequence at the foot of the submerged flank a main submarine scar open towards the se is carved in the upper slope on the eastern flank of the island being partially filled with gravity flow deposits owing to the present day depositional setting of the volcano s submerged flank a morphological continuity can be envisaged between this submerged scar and an inferred subaerial one likely encompassing the rina grande depression and several minor nested landslide scars recognized on the eastern stromboli flank a spatial and temporal reconstruction of possible events is proposed the chaotic debris avalanche unit buried within the volcaniclastic apron at the slope base and partially reworked in its distal part within the stromboli canyon floor is thought to be the result of a lateral collapse event called paleostromboli lateral collapse plc as it likely occurred in the earlier stages of the subaerial development of the island affecting a wide sector of the eastern stromboli flank the megablock field might instead result from a more superficial debris avalanche deposit partially eroded by gravity flows currently acting on the seabed it is tentatively related to the recent subaerial scar morphologies affecting the vancori units and for this reason named vancori lateral collapse vlc displaced materials have lower volume and mobility than the plc

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

insights into the october november 2010 gunung merapi eruption central java indonesia from the stratigraphy volume and characteristics of its pyroclastic deposits abstract the 2010 eruption of merapi was the second most deadly in the historic record of this volcano claiming over 380 lives by relating the observations of this eruption with detailed examination of deposit distribution stratigraphy and sedimentology a reconstruction of the properties of the pyroclastic density currents pdcs is presented including the valley controlled block and ash flows bafs and widespread energetic pyroclastic surges the distribution volume and mobility characteristics of all types of pdc during the eruption sequence show evidence for levels of intensity unseen since the large scale 1872 and 1930 eruption phases especially during the climactic events of october 26 and november 5 many tephra falls interbedded with pdc units show that most dome collapse events occurred along with and between explosive vulcanian eruptions the 2010 eruption produced very long runout bafs reaching 16 1 km in the kali gendol on november 5 this runout could be explained by its large volume 20 million m 3 around 10 times that of previous merapi bafs during the last 130 years major avulsion of these dense bafs to form overbank deposits became more common through the eruptive sequence as the valley was progressively filled with successive pdc deposits spreading avulsed bafs were a particular hazard downstream of 10 km where the landscape is less dissected less clear however is why pyroclastic surges extended up to 10 km from the vent on november 5 and 6 4 km on october 26 these expanded much farther from baf margins 2 km than ever seen before at merapi in one location they were decoupled from valley centered bafs with high momentum traveling initially laterally across steep valley systems before draining downslope at this site on the western side of the upper gendol at around 3 km from source surge decoupling was apparently exacerbated by upstream collision and deflection of high flux hot and gas rich bafs against the cliffs of gunung kendil the 1 4 km long cliff face was impacted directly for the first time in 2010 events and may have been responsible for the formation of larger than normal turbulent ash rich clouds above bafs these results imply that future eruption events under the present summit and upper flow path configuration are also highly likely to generate wide dispersal pyroclastic surges and extreme hazard especially now that dense forest has been destroyed on the upper southern slopes of the volcano

transport and deposition processes of the hydrothermal blast of the 6 august 2012 te maari eruption mt tongariro the 2012 eruption of tongariro volcano new zealand produced highly mobile low temperature blast derived pyroclastic density currents after partial collapse of the western flank of the upper te maari crater despite a low volume 340 000 m3 the flows traveled up to 2 5 km from source covering a total area of 6 1 km2 along one of the blast axes freshly exposed proximal to distal sedimentary structures and grain size data suggest emplacement of the fining upward tripartite depositional sequence massive stratified and laminated under a dilute and strongly longitudinally zoned turbulent density current while the zoning formed in the deposit in the first 1500 m of runout the current progressively waned to the extent where it transported a nearly homogenous grain size mixture at the liftoff position our data indicate that after the passage of an erosive flow front massive unit a was deposited under a rapid suspension sedimentation regime unit b was deposited under a traction dominated regime generated by a subsequent portion of the flow moving at lower velocities and with lower sediment transport capacity than the portion depositing unit a the final and slowest flow zone deposited the finest particles under weakly tractive conditions transport and emplacement dynamics inferred in this study show strong similarities between hydrothermal explosions magmatic blasts and high energy dilute pdcs the common occurrence of hydrothermal fields on volcanic flanks points to this hazard being an under appreciated one at stratovolcanoes worldwide

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

the timing of regional lateglacial events and post glacial sedimentation rates from lake superior abstract we analyze both new and previously published paleomagnetic records of secular variation psv from lake superior sediment cores and compare these records to correlated rhythmite varve thickness records to determine post glacial sedimentation rates and to reassess the termination of glaciolacustrine varves in the basin the results suggest that offshore sedimentation rates have exhibited considerable spatial variation over the past 8000 years particularly during the mid holocene we attribute offshore mid holocene sedimentation changes to alterations in whole basin circulation perhaps precipitated by a greater dominance of the gulf of mexico air mass during the summer season nearshore bays are characterized by high sedimentation rates for at least 1000 years after varve cessation and during a period between around 4500 and 2000 cal bp after 2000 cal bp sedimentation rates subsided to earlier rates the increases between 4500 and 2000 cal bp are probably due to lake level fall after the nipissing ii highstand the older glaciolacustrine varve thickness records suggest that the influx of glacially derived sediment ended abruptly everywhere in the lake except near the lake nipigon inlets multiple sediment cores reveal 36 anomalously thick varves previously ascribed to the formation of the nakina moraine which were deposited just prior to varve cessation in the open lake the psv records support the observation that the cessation of these thick varves is a temporally correlative event occurring at 9035 170 cal bp calibrated years before 1950 ca 7950 8250 14 c bp this date would correlate to the eastern diversion of lake agassiz and glacial meltwater into lake ojibway

glacial lake mcconnell paleogeography age duration and associated river deltas mackenzie river basin western canada abstract glacial lake mcconnell lasted from 11 8 to 8 3 ka bp while occupying parts of the great bear great slave and athabasca lake basin the retreating laurentide ice front formed the eastern margin whereas low rolling hills formed the north west and south shorelines three major deltas were deposited at the mouths of the laird peace and athabasca rivers the total extent of all phases of the lake was 240 000 km 2 while the largest extent was 210 000 km 2 at 10 5 ka bp downwarping of the basin by glacial ice was the main cause of the lake whereas sediment blockage between jean marie river and fort simpson was secondary initially glacial lake mcconnell occupied the northwestern corner smith arm of the great bear lake basin and discharged through the hare indian river outlet by 11 5 ka bp the enlarged water body flowed out the great bear river but only for a short period of time the mackenzie river formed the third outlet near jean marie river at 11 ka bp and flow in the great bear river ceased until 9 ka bp at 9 9 ka bp glacial lake mcconnell was impacted by a major flood from glacial lake agassiz with a peak discharge of 2 7 10 6 m 3 sec flood water discharged from glacial lake mcconnell peaking at 0 35 0 57 10 6 m 3 sec and receding flow continued for 30 months the massive influx of floodwater into glacial lake mcconnell caused an abrupt increase of discharge which enlarged the outlet channel to between 6 and 13 km wide between fort simpson and jean marie river at 8 3 ka bp isostatic rebound ended the 3500 year old extensive lake by dividing it into the great slave lake and lake athabasca

documentation of earthquake induced disturbance of lake sediments using subbottom acoustic profiling subbottom acoustic profiling in lakes on the canadian shield and in the canadian cordillera has revealed disruptions in deltaic and lacustrine sediments that can be attributed to large historical earthquakes the timiskaming earthquake of 1935 magnitude 6 25 and the vancouver island earthquake of 1946 magnitude 7 2 triggered extensive slumping and flow of postglacial sediments in lakes located within a few tens of kilometres of the epicentres of these events there is some evidence in one of the surveyed lakes for in situ mobilization of sediment on relatively gentle slopes with minimal horizontal displacement this may be a product of liquefaction induced by coseismic shaking or displacements along faults beneath the basin in another lake widespread coseismic slumping resuspended large amounts of fine sediment which then settled out onto the lake floor to produce a texturally anomalous layer features similar to those produced by the 1935 and 1946 earthquakes can also result from a variety of non

reconstruction of the eruptive activity on the ne sector of stromboli volcano timing of flank eruptions since 15 ka a multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower ne flank of stromboli volcano since 15 ka the oldest flank eruption recognised is roisa which occurred at 15 ka during the vancori period and has transitional compositional characteristics between the vancori and neostromboli phases roisa was followed by the san vincenzo eruption that took place at 12 ka during the early stage of neostromboli period the eruptive fissure of san vincenzo gave rise to a large scoria cone located below the village of stromboli and generated a lava flow most of which lies below sea level most of the flank eruptions outside the barren sciara del fuoco occurred in a short time between 9 and 7 ka during the neostromboli period when six eruptive events produced scoria cones spatter ramparts and lava flows the neostromboli products belong to a potassic series ks and cluster in two differently evolved groups after an eruptive pause of 5 000 years the most recent flank eruption involving the ne sector of the island occurred during the recent stromboli period with the formation of the large highly k calc alkaline lava flow field named san bartolo the trend of eruptive fissures since 15 ka ranges from n30 e to n55 e and corresponds to the magma intrusions radiating from the main feeding system of the volcano

varicolored and vesiculated tuffs from la fossa volcano vulcano island aeolian archipelago italy evidence of syndepositional alteration processes chemical and mineralogical data for samples collected from a surge sequence from la fossa cone vulcano island italy show a wide variety of alteration states between adjoining beds the macroscopic features of which are expressed by various degrees of reddening the effects of the alteration processes on pyroclastic rocks are as follows hydration and oxidation of each component of the pyroclastic rocks to varying degrees formation of authigenic smectite precipitation of a large variety of soluble salts and corrosion on the surface of glass fragments pitting dry surge beds emplaced from a two phase dry steam solid suspension do not show significant alteration by contrast wet surge deposits suggesting an emplacement from free water bearing turbulent flows show an increasing degree of alteration passing from grey to red coloured beds the strict relationship between the present alteration state and the depositional unit rules out any post depositional processes the occurrence of alteration in wet surge beds and the lack of alteration in dry beds shows that the main controlling agent was water condensed from the eruptive cloud and suggests a syn depositional character to the alteration itself these observed differences can be ascribed to the different chemical reactivities of the water probably related to the amounts of acidic species carried by the eruptive cloud and or by the efficiency of their capture during the condensation of the water vapour

basal sediment evacuation by subglacial meltwater suspended sediment transport from haut glacier d arolla switzerland proglacial suspended sediment transport was monitored at haut glacier d arolla switzerland during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater sub seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained under hydraulically inefficient subglacial drainage at the start of the melt season sediment availability was generally high but sediment transport increased relatively slowly with discharge later in the melt season sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity basal sediment availability declined during channelization but increased throughout the remainder of the monitored period resulting in very efficient basal sediment evacuation over the peak of the melt season increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge basal sediment availability therefore appears likely to have been increased by 1 enhanced local ice bed separation leading to extra channel flow excursions and sol or 2 the deformation of basal sediment towards low pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less efficient drainage copyright 2005 john wiley sons ltd

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

a numerical model for an alternative origin of lake vostok and its exobiological implications for mars in connection with recent galileo images of the jovian satellite europa there has been a significantly increased interest in the subglacial lake vostok in central east antarctica since the theoretical prediction by zotikov 1961 of the existence of lakes one of which later was named vostok under 4 km of ice in antarctica and its confirmation by radar measurements from aircraft in 1974 robin et al 1977 and from the ers 1 satellite in 1993 it was tacitly assumed that the lake originated from the basal melting of ice e g zotikov 1961 1977 1986 kapitsa et al 1996 recently zotikov and duxbury 2000 proposed an alternative hypothesis that if lake vostok had existed on the surface before the antarctic perennial glaciation began 5 30 myr ago then it was buried under the thermally protecting ice and never froze all the way to the bottom in this study we support our hypothesis by comprehensive numerical modeling and evaluate its interesting implications for mars and exobiology our numerical experiments on the sensitivity of the freezing depth to different upper boundary temperatures and different internal heat flows and the recent mars global surveyor mars orbiter laser altimeter mola data support our model of the origin of possible subpolar water on mars versus the old basal melting hypothesis we also propose here experimental tests for our hypothesis as a result of our computations we conclude that lake vostok has survived the antarctic glaciation without freezing completely if it were initially an open lake with a surprisingly small water depth greater than 53 m the current water depth at a single point is as much as 500 m verkulich et al 1996 this maximum freezing depth of 53 m was reached in only 3300 years when the total upper ice cover was only 600 m the computed critical water depth is applicable to other antarctic lakes under a thick ice cover for the martian internal heat flow we have computed the critical water depth to be 63 m the existence of the lake before the accumulation of ice in antarctica implies that possible microorganisms and their remnants in the lake can be older than the antarctic ice sheet i e older than 5 30 myr if future observations find water under the martian polar caps this subpolar water according to our model has originated from lakes that were on the martian surface before the formation of mars polar caps and have not completely frozen such environments would be ideal candidates for extant or extinct life on the red planet this argues for a drilling mission at the martian polar caps

pattern recognition of lidar data and sediment anisotropy advocate a polygenetic subglacial mass flow origin for the kemijarvi hummocky moraine field in northern finland abstract object based image analysis and supervised machine learning on a digital elevation model derived from airborne laser scanning data were conducted to assess the aggregate raw material potential over the kemijarvi hummocky moraine field in finnish lapland geomorphometric analysis revealed surface stoniness to be diagnostic of moraine hummocks it was utilized to detect true moraine hummocks from among the potential hummocks delineated using object based image analysis with logistic regression of curvature features derived from the digital elevation model area under the receiver operating characteristics curve auc 0 77 based on the electrical sedimentary anisotropy data the kemijarvi moraine is polygenetic such that the ridges are diagonally and erosionally fluted from sector 280 290 on their surfaces while the ridge cores are deposited from the nw from sector 310 340 the cores are composed of infill gravels and crudely stratified diamict sequences we consider the core of the kemijarvi hummocky moraine field to represent pre existing early weichselian subglacial ridges rather than being generated through monogenetic late weichselian compressional shearing and stacking frozen bed extension or bed ribbing instability mechanisms as presented for ribbed moraines that are transverse to ice flow recently evidence has been presented of multiple slip events earthquakes with moment magnitudes mw 6 7 7 0 up ice from kemijarvi we therefore propose that the genesis of the hummocks may be associated with past early weichselian fault instability within glacio isostatic adjustment s which was able to generate subglacial water bodies possibly lakes and saturated materials that were forced towards the se based on this new geomorphological evidence from mapping using a digital elevation model derived from airborne laser scanning data and azimuthal conductivity surveys combined with the reinterpretation of previously presented geophysics and sedimentological observations we suggest the kemijarvi hummocky moraine field to be reconsidered as the kemijarvi subglacial mass flow field which holds significant potential for construction aggregate materials

hypothesis for mega outburst flooding from a palaeo subglacial lake beneath the east antarctic ice sheet subglacial outburst floods at the margins of the antarctic and laurentide ice sheets have been linked to changes in global ocean circulation and climate the impact of palaeo hydrological systems beneath the east antarctic ice sheet eais has however remained elusive by analysing bed morphology in the wilkes subglacial basin we hypothesise the occurrence of a major palaeo subglacial lake and associated outburst floods in the interior of east antarctica at similar to 70 km wide and over 100 km long the inferred area of outburst flooding is the most extensive in antarctica and the palaeo subglacial lake from which the floods originated is the second largest after lake vostok the scale of inferred outburst flooding is similar to mega floods beneath the laurentide ice sheet we suggest that this major hydrological system developed during expansion of the eais in the middle miocene and probably affected ice sheet stability ocean circulation and climate evolution

stratigraphy and significance of brown tuffs on the aeolian islands southern italy abstract brown tuffs bt are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the aeolian islands and capo milazzo on the northern coast of sicily detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period ca 80 ka bp up to 4 5 ka bp age of the overlying punte nere pyroclastic products on vulcano the most complete bt succession is documented on lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers local volcanic products paleosols and epiclastic deposits and the occurrence of local erosive surfaces inter island occurrence of ischia tephra a widely known tephra layer in the aeolian archipelago dated at 56 ka bp and monte guardia pyroclastics from lipari dated at 22 20 ka bp subdivides the bt succession in upper ubt intermediate ibt and lower bt units lbt which can be correlated at regional level the lbt was emplaced between 80 and 56 ka bp the ibt between 56 and 22 ka bp and the ubt between 20 and 4 5 ka bp on the basis of stratigraphy similarity in lithology and textural features morphology of glass fragments composition and consistency of thickness and grain size variations ubt units correlate with piano grotte dei rossi tuffs on vulcano island they were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the la fossa caldera on vulcano island composition is in agreement with this hypothesis since ubt compositional features match those of vulcano magmas erupted in that period the effect of co ignimbrite ash clouds or associated fallout processes from sustained eruptive columns is seen to explain the presence of ubt in areas further away from the suggested source e g salina and lipari islands and capo milazzo the origin of ubt exposed on panarea island is still a matter of debate due to contrasting compositional data due to large uniformity of lithological textural and componentry characters with respect to the ubt the lower portions of the bt succession lbt ibt are considered to be the result of recurrent large scale hydromagmatic eruptions of similar type moreover for the ibt units the correlation with monte molineddo 3 pyroclastics of vulcano island on the basis of lithological compositional and stratigraphic matching again suggests source s related to the vulcano plumbing system and located within the la fossa caldera

evidence of two holocene phreatomagmatic eruptions at stromboli volcano aeolian islands from paleomagnetic data 1 we present detailed stratigraphic sedimentological and paleomagnetic analyses of holocene phreatomagmatic deposits at stromboli volcano aeolian islands italy the investigated deposits belong to the secche di lazzaro succession sdl and to the advanced operations center of the department of civil defense coa succession both lying on the neostromboli lavas ca 13 5 ka the two stratigraphic successions have similar stratigraphic position and show a phreatomagmatic origin likely related to catastrophic magma water interaction processes during sector collapse events however the thermal remanent magnetization data of the lava lithics indicate that deposits of the sdl succession were emplaced at very low temperatures less than 140 c whereas the basal part of the coa deposit was emplaced at temperatures between 300 340 c paleomagnetic results indicate that the two investigated deposits may be related to two distinct eruptive events occurred during the holocene recent phreatomagmatic activity at stromboli apparently has occurred more frequently than previously believed consequently we must reconsider the recurrence interval of this dangerous eruptive scenario for stromboli

cold intrusions in lake baikal direct observational evidence for deep water renewal we studied cold deep water intrusions in the south basin of lake baikal on the basis of 2 yr of data december 1995 november 1997 from near bottom and near surface thermistor strings monthly conductivity temperature depth ctd profiles and a near bottom current meter all collected near the south basin maximum depth of 1 461 in the data show intrusions into the greatest depths with temperatures of 0 08 0 20degreesc below ambient similar to3 33 to similar to3 38degreesc at maximum depth the intrusions were observed three times per year between january and june when surface water is always cooler than deep water with durations of a few at least 1 3 days the estimated water input ranged from 1 to 10 km 3 per event and the annually accumulated volume was estimated to be 10 30 km 3 which is significantly less than the steady state indirect estimates of 30 70 km 3 yr 1 to the permanently stratified deep water depth 300 in this indicates that not all of the cold intrusions reach the deepest area because the cooling of the near bottom waters was not accompanied by a significant increase in ion or particle content and because deep sediment traps did not contain significant enrichments of minerogenic particles we concluded that selenga river inflow is not a possible source of the cold intrusions two ctd profiles in june 1996 and 1997 showed lower temperature throughout the deep water as expected from thermobaric instabilities the required downwelling is definitely not occurring in the pelagic interior but most probably by near coast counterclockwise currents the source of the regularly occurring deep intrusions is clearly cold surface water but the actual mechanism is uncertain

lgm summer climate on the southern margin of the laurentide ice sheet wet or dry abstract regional climate simulations are conducted using the polar fifth generation pennsylvania state university psu ncar mesoscale model mm5 with a 60 km horizontal resolution domain over north america to explore the summer climate of the last glacial maximum lgm 21 000 calendar years ago when much of the continent was covered by the laurentide ice sheet lis output from a tailored ncar community climate model version 3 ccm3 simulation of the lgm climate is used to provide the initial and lateral boundary conditions for polar mm5 lgm boundary conditions include continental ice sheets appropriate orbital forcing reduced co2 concentration paleovegetation modified sea surface temperatures and lowered sea level the simulated lgm summer climate is characterized by a pronounced low level thermal gradient along the southern margin of the lis resulting from the juxtaposition of the cold ice sheet and adjacent warm ice free land surface this sharp thermal gradient anchors the midtropospheric

basal temperature evolution of north american ice sheets and implications for the 100 kyr cycle 1 we simulate three dimensional ice temperature fields to examine spatial temporal history of the subglacial thermal environment during the last glacial cycle model results suggest that 60 80 of the laurentide ice sheet was cold based frozen to the bed at the lgm and therefore unable to undergo large scale basal flow the fraction of warm based ice increases significantly through the ensuing deglaciation with only 10 20 of the laurentide ice sheet frozen to the bed by 8 kyr bp this basal thermal evolution a function of both climatic and ice sheet history could enable a dynamical switch to widespread basal flow through the deglacial period because basal flow has the capacity to evacuate large amounts of ice from the interior of continental ice sheets creating thin and climatically vulnerable ice masses this switch in flow regime may have played a significant role in glacial terminations and the 100 kyr glacial cycle

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

fast geochemical changes and rapid lava accumulation at stromboli island italy inferred from k ar dating and paleomagnetic variations recorded at 60 and 40 ka abstract forty three lava flows from the vallone di rina stromboli aeolian islands italy have been investigated for paleomagnetic geochemical and k ar analyses k ar dating shows that two fast building stages occurred at 62 1 and 40 2 ka the comparison with archeomagnetic variations for the last 2 kyr shows that the time interval covered by the vallone di rina section is at the most a few thousand years most probably on the order of a few hundred years such high accumulation rate can be related to the stromboli volcanic history which is marked by five to seven successive collapses the rapid effusion rate of these paleo stromboli pst ii lavas suggests that they have been erupted shortly after the paleo stromboli i collapse in response to pressure release due to instantaneous deloading their age of 62 1 ka is thus interpreted here as the age of the paleo stromboli i collapse event similarly the age of 40 2 ka obtained for lavas from paleo stromboli iii can be related with another collapse event as previously recognized major and trace elements of these lava flows show that they are compatible with magma sources of metasomatized mantle origin and various crustal levels of melting and mixing they display recurrent jumps from calc alkaline to high k calc alkaline and shoshonitic series within a very short time span which suggest that several magmatic systems were operating simultaneously finally we have shown that the combined approach of absolute dating provided by the k ar cassignol technique together with high resolution paleomagnetic data compared to historical variations can constrain for high extrusion rates the relative lava emplacements to within a few hundred years

recent eruptive history of stromboli aeolian islands italy determined from high accuracy archeomagnetic dating 1 the large sample method of archeomagnetic dating was applied to stromboli 127 samples 10 sites yielded paleofield directions with 95 confidence intervals less than 2 coupled with a reference curve for secular variation in western europe these allow accurate dating of volcanic events a lava flow underlying san bartolo village gave a minimum age of ad 100 100 a lava overflow predating the last sector collapse was dated from 1350 60 suggesting the recent occurrence of highly hazardous events lava spatters and a hot avalanche high on the northern flank were emplaced during the xxth century lava spatters on the lower flanks could date the onset of the still ongoing phase from ad 550 50 these results are different from those obtained in a recent study probably because traditional paleomagnetic sampling cannot yield sufficient precision considering the characteristics of the archeomagnetic secular variation curve

paroxysmal dome explosion during the merapi 2010 eruption processes and facies relationships of associated high energy pyroclastic density currents an 11 minute sequence of laterally directed explosions and retrogressive collapses on 5 november 2010 at merapi indonesia destroyed a rapidly growing dome and generated high energy pyroclastic density currents pdcs spreading over 22 km2 with a runout of 8 4 km while contemporaneous co genetic valley confined pdcs reached 15 5 km this event formed stage 4 of the multi stage 2010 eruption the most intense eruptive episode at merapi since 1872 the deposits and the widespread devastating impact of associated high energy pdcs on trees and buildings show striking similarities with those from historical volcanic blasts montagne pelee martinique bezymianny russia mount st helens usa soufriere hills montserrat we provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast like deposits in merapi s recent history we used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown the stratigraphy of stage 4 consists of three depositional units u0 u1 u2 that we correlate to the second third and fourth explosions of the seismic record both u1 and u2 show a bi partite layer stratigraphy consisting each of a lower l1 layer and an upper l2 layer the lower l1 layer is typically very coarse grained fines poor poorly sorted and massive and was deposited by the erosive waxing flow head the overlying l2 layer is much finer grained fines rich moderately to well sorted with laminar to wavy stratification l2 was deposited from the waning upper part and wake of the pdc field observations indicate that pdc height reached 330 m with an internal velocity of 100 m s 1 within 3 km from the source the summit s geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused pdc mass towards a major constriction thereby limiting the loss of kinetic energy this favored elevated pdc velocities and high particle concentration promoted overspilling of pdcs across high ridges into other river valleys and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest the merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high energy high velocity pdcs this constitutes a credible high impact scenario for future multi stage eruptions at merapi and at other volcanoes that pose particular monitoring crisis response and risk reduction challenges

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity