volcano ice interactions precursory to the 2009 eruption of redoubt volcano alaska abstract in late summer of 2008 after nearly 20 years of quiescence redoubt volcano began to show signs of abnormal heat flow in its summit crater in the months that followed the excess heat triggered melting and ablation of redoubt s glaciers beginning at the summit and propagating to lower elevations as the unrest accelerated a variety of morphological changes were observed including the creation of ice cauldrons areas of wide spread subsidence punctures in the ice carved out by steam and deposition from debris flows in this paper we use visual observations satellite data and a high resolution digital elevation model of the volcanic edifice to calculate ice loss at redoubt as a function of time our aim is to establish from this time series a proxy for heat flow that can be compared to other data sets collected along the same time interval our study area consists of the drift glacier which flows from the summit crater down the volcano s north slope and makes up about one quarter of redoubt s total ice volume of 4 km 3 the upper part of the drift glacier covers the area of recent volcanism making this part of ice mass most susceptible to the effect of volcanic heating moreover melt water and other flows are channeled down the drift glacier drainage by topography leaving the remainder of redoubt s ice mantle relatively unaffected the rate of ice loss averaged around 0 1 m 3 s over the last four months of 2008 accelerated to over twenty times this value by february 2009 and peaked at greater than 22 m 3 s just prior to the first major explosion on march 22 2009 we estimate a cumulative ice loss over this period of about 35 million cubic meters m m 3

upb dating of fe rich phases using a sequential leaching method a sequential leaching method was developed for upb dating of fe rich phases which uses a series of successively stronger acids the method was applied to date fe rich phases of magmatic origin in the kinsman quartz monzonite new hampshire usa and of sedimentary origin in the dales gorge member of the brockman iron formation hamersley basin australia using the composition of major element released by the acid leaching and combining it with x ray and sem analyses of the residues we were able to identify the relatively pure phases released and use these samples for dating magnetite separates from the kinsman quartz monzonite yielded upb age of 372 34 ma which is consistent with smnd and a rbsr isochron ages determined in previous studies leached whole rock samples of the brockman iron formation yielded a 207pb206pb age of 2213 250 ma which agrees with previously determined pbpb smnd and rbsr isochron ages this age is interpreted as the time of redistribution of u and pb associated with the fe rich phases during regional metamorphism while the potential of the sequential leaching method is demonstrated more work is needed in order to improve the precision of the data this requires further investigation of the nature of the pure phases

intrusion of basalt into frozen sediments and generation of coherent margined volcaniclastic dikes cmvds coherent margined volcaniclastic dikes cmvds are described for the first time from askja dyngjufjoll iceland these dikes display continuous coherent glassy margins 5 cm thick and have a variety of clastic interiors comprising vitric tephra pillow and pillow fragment bearing lapilli tuffs cmvds are interpreted to form when basaltic dikes interact with subglacial ice cemented volcaniclastic sediments formation requires chilling of dike margins drainage of the dike interior and flooding of the cavity by meltwater followed by non explosive mingling of magma clastics and water evidence for ice cementation includes minimal interaction with the host 3 mm peperite local pillowed dike margins and the preservation of continuous glassy coherent margins along the edge of a drained dike cavity cmvds should be present at other volcanic centers with ice cemented sediments including the martian cryosphere

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

a miner s perspective on pb isotope provenances in the western and central mediterranean the conventional approach to ore provenance studies of ancient silver coins and artifacts has been to first analyze and then try to match them to published data about mining districts a difficult task given our incomplete knowledge of these while literary sources are useful to identify possible provenances they potentially bias interpretations proper because of a variety of limitations of their time archeological evidence in the form of mining shafts galleries spoil heaps and tools also provides a tangible and reliable record of mining but dating such activity can be problematic and the record is inconsistent here we propose a new approach driven by pb isotopic data rather than numismatic groups statistical analysis of pb isotopic data is used to identify ore defined isotopic clusters this new method is based on an algorithm that predicts the number of isotopic clusters necessary to fulfill the simple condition that variance within isotopic clusters is minimized whereas inter cluster variance is maximized since each cluster reflects a discrete geological episode within a particular environment broadly datable to a specific pb model age it can be identified as a potential source exploited by ancient miners we explore the potential of this method in two examples using data from coins and ores respectively in the first example roman republican silver coins form three end member clusters sourced in mining districts with cenozoic mesozoic and paleozoic pb model ages the example demonstrates how sources of silver used to mint coinage of the roman republic shifted within 50 years of the end of the second punic war in 201 bce in the second example using aegean galena samples pb isotopes distinguish components with model ages datable to the hercynian basement the recent aegean tectonic province and cyprus noting that significant silver mining districts may remain unidentified in either spain or the aegean world we further clarify a number of potential analytical issues and advocate that users of pb isotopes for tracing archeological artifacts measure all four lead isotopes and inspect the 12 proposed isotope combinations in order to select those that provide the best representation of the data we also emphasize that full advantage should be taken of the geologically informed parameters model age and th u pb relationships to identify the geological context of metal sources

melting of the glacier base during a small volume subglacial rhyolite eruption evidence from blahnukur iceland abstract although observations of recent volcanic eruptions beneath vatnajokull iceland have improved the understanding of ice deformation and meltwater drainage little is known about the processes that occur at the glacier base we present observations of the products of a small volume effusive subglacial rhyolite eruption at blahnukur torfajokull iceland lava bodies typically 7 m long have unusual conical morphologies and columnar joint orientations that suggest emplacement within cavities melted into the base of a glacier cavities appear to have been steep walled and randomly distributed these features can be explained by a simple model of conductive heat loss during the ascent of a lava body to the glacier base the released heat melts a cavity in the overlying ice the development of vapour escape pipes in the waterlogged permeable breccias surrounding the lava allows rapid heat transfer between lava and ice the formed meltwater percolates into the breccias recharging the cooling system and leaving a steam filled cavity the slow ascent rates of intrusive rhyolitic magma bodies provide ample time for a cavity to be melted in the ice above even during the final 10 m of ascent to the glacier base an equilibrium cavity size is calculated at which melting is balanced by creep closure this is dependent upon the heat input and the difference between glaciostatic and cavity pressure the cavity sizes inferred from blahnukur are consistent with a pressure differential of 2 4 mpa suggesting that the ice was at least 200 m thick this is consistent with the volcanic stratigraphy which indicates that the ice exceeded 350 m in thickness although this is the first time that a subglacial cavity system of this type has been reconstructed from an ancient volcanic sequence it shares many characteristics with the modern firn cave system formed by fumarolic melting within the summit crater of mount rainier washington at both localities it appears that localised heating at the glacier base has resulted in heterogeneous melting patterns despite the different rheological properties of ice and firn similar patterns of cavity roof deformation are inferred the development of low pressure subglacial cavities in regions of high heat flux may influence the trajectory of rising magma with manifold implications for eruptive mechanisms and resultant subglacial volcanic landforms

u pb dating of a speleothem of quaternary age we demonstrate that u pb dating is a promising method for secondary carbonate materials of quaternary age and older by obtaining a 206pb 238u age for a speleothem with high u 10 g g 1 and very low pb 10 ng g 1 that is supported by an independent 230th age thermal ionisation mass spectrometry was used to determine the u and pb isotopic ratios and concentrations for subsamples of a stalactite from winnats head cave peak district uk we obtained 206pb 204pb ratios up to 50 and determined a 206pb 238u age of 248 10 ka which is within error of the 207pb 235u age of 333 79 ka and a spectrometric u th age of 255 ka for samples of tertiary and quaternary age the initial state of u series disequilibrium is an important consideration and as with most radiometric dating techniques the mineral must have remained closed to u th pb and all intermediate daughters we show that dense calcite speleothems are ideal in this respect and that no loss of rn has occurred unlike u series disequilibrium methods u pb dating has no upper limit and hence materials of quaternary age older than 0 6 ma can be analysed to investigate landscape development paleoclimate hominid evolution or hydrogeochemistry in carbonate terrains

heat transfer in volcano ice interactions on mars synthesis of environments and implications for processes and landforms we review new advances in volcano ice interactions on mars and focus additional attention on 1 recent analyses of the mechanisms of penetration of the cryosphere by dikes and sills 2 documentation of the glacial origin of huge fan shaped deposits on the northwest margins of the tharis montes and evidence for abundant volcano ice interactions during the later amazonian period of volcanic edifice construction and 3 the circumpolar hesperian aged dorsa argentea formation interpreted as an ice sheet and displaying marginal features channels lakes and eskers indicative of significant melting and interior features interpreted to be due to volcano ice interactions e g sub glacial volcanic edifices pits basins channels and eskers in this context we describe and analyse several stages and types of volcano ice interactions 1 magmatic interactions with ice rich parts of the cryosphere 2 subglacial volcanism represented by intrusion under and into the ice and formation of dikes and moberg like ridges intrusion of sills at the glacier volcano substrate interface and their evolution into subglacial lava flows formation of subglacial edifices marginal melting and channels 3 synglacial ice contact volcanism represented by flows banking up against glacier margins chilling and forming remnant ridges and 4 post glacial volcanism and interactions with ice deposits

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

subglacial lava propagation ice melting and heat transfer during emplacement of an intermediate lava flow in the 2010 eyjafjallajokull eruption during the 2010 eyjafjallajokull eruption in south iceland a 3 2 km long benmoreite lava flow was emplaced subglacially during a 17 day effusive explosive phase from april 18 to may 4 the lava flowed to the north out of the ice filled summit caldera down the outlet glacier gigjokull the flow has a vertical drop of about 700 m an area of ca 0 55 km2 the total lava volume is ca 2 5 107 m3 and it is estimated to have melted 10 13 107 m3 of ice during the first 8 days the lava advanced slowly 100 m day 1 building up to a thickness of 80 100 m under ice that was initially 150 200 m thick faster advance up to 500 m day 1 formed a thinner 10 20 m lava flow on the slopes outside the caldera where the ice was 60 100 m thick this subglacial lava flow was emplaced along meltwater tunnels under ice for the entire 3 2 km of the flow field length and constitutes 90 of the total lava volume the remaining 10 belong to subaerial lava that was emplaced on top of the subglacial lava flow in an ice free environment at the end of effusive activity forming a 2 7 km long a a lava field about 45 of the thermal energy of the subglacial lava was used for ice melting 4 was lost with hot water about 1 was released to the atmosphere as steam heat was mostly released by forced convection of fast flowing meltwater with heat fluxes of 125 310 kwm 2

astronomical frequencies for pre quaternary palaeoclimate studies the sensitivity of the earth s orbital frequencies involved in the astronomical theory of palaeoclimates to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth has been investigated for the last billion years the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for the obliquity and the precession a shortening which is larger for the longer periods these periods of precession and obliquity influenced by the changing earth moon distance length of the day and dynamical ellipticity of the earth have been recomputed for the last 440 million years

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

ice melt rates by steam condensation during explosive subglacial eruptions subglacial volcanism melts cavities in the overlying ice these cavities may be flooded with meltwater or they may be fully or partially drained we quantify for the first time heat transfer rates by condensation of steam on the walls and roof of a fully or partially drained subglacial eruption cavity our calculations indicate that heat fluxes of up to 1 mw m 2 may be obtained when the bulk vapor in the cavity is in free convection this is considerably smaller than heat fluxes inferred from ice penetration rates in recent subglacial eruptions forcing of the convection by momentum transfer from an eruption jet may allow heat fluxes of up to 2 mw m 2 consistent with values inferred for the gjalp 1996 subglacial eruption vapor dominated cavities in which vapor liquid equilibrium is maintained have thermal dynamic responses that are an order of magnitude faster than the equivalent flooded cavities

magnesian calcite cements and their diagenesis dissolution and dolomitization mururoa atoll the most ubiquitous syn sedimentary cements affecting mururoa atoll are composed of magnesian calcite three main types are distinguished fibrous bladed and sparitic on the basis of petrography morphology and mgco3 concentration of the constituting crystals while peloid infills a particular form of hmc chemical precipitation also exist petrographic evidence and isotopic signatures are compatible with marine precipitation mururoa atoll was exposed several times to meteoric diagenesis resulting in varied diagenetic alterations including selective dissolution and partial dolomitization of mg calcite cements these alterations are responsible for substantial modifications of the initial cement fabrics and may introduce unconformities in the diagenetic chronology the first stage of the partial dissolution of mg calcite induces the development of chalky white friable zones within the initially crystalline hard cement layers at ultrascale this is due to the creation of micro voids along the elongate cement fibres advanced dissolution includes total disappearance of cement portions as attested to by large voids within the cement crust and or between superposed cement layers mg calcite dissolution is related to meteoric diagenesis during periods of quaternary exposure the creation of voids within mg calcite layers is due to the mechanical removal of previously altered calcium carbonate a process suggesting marine or non marine water flow probably in the vadose environment selective dolomitization of mururoa cements involves alternations of calcite and dolomite which form successive cement like rinds within primary cavities at mururoa these alternations are the result of selective dolomitization of the pre existing mg calcite cements rather than successive precipitation of calcite and dolomite selective dolomitization of mg calcite cements at mururoa indicates that a given cement succession is not necessarily a simple chronological sequence oxygen isotope values of dolomites are enriched in 186 by about 3 pdb within calcite dolomite pseudo alternations the dolomitizing fluid at mururoa seems similar to present marine water although some mixture with meteoric water is probable to favour dissolution associated with dolomitization

reply to and comment on the usage of 238u 207pb vs 206pb 207pb linear regressions for the la icp ms u pb dating of cassiterite abstract isotope dilution thermal ionization mass spectrometry id tims and laser ablation inductively coupled plasma mass spectrometry la icp ms are two popular analytical methods used to constrain the age of minerals including cassiterite compared to id tims the la icp ms analytical method is often favoured due to its simple analytical procedure and sample preparation although the methodology constantly needs modification our recent paper on dating cassiterite from the baiganhu w sn ore field in nw china based on la mc icp ms and id tims methods has received a response from dr leonid a neymark 2017 definitely neymark is appreciated and his suggestions are helpful to improve the methodology of cassiterite u pb geochronology based on a discussion on the cassiterite u pb dating method we re confirm the validity of the cassiterite u pb ages for the baiganhu w sn ore field the initial non radiogenic 204pb used in the u pb isochron approach can be replaced by the non radiogenic 207pb because the radiogenic 207pb decayed from 235u can be ignored in cassiterite with a high pb content therefore the cassiterite u pb isochron yields an age similar to that obtained from t w concordia for the same sample testifying the validity of the cassiterite 238u 207pb 206pb 207pb isochron method

glaciation on mercury accumulation and flow of ice in permanently shadowed circum polar crater interiors abstract radar bright deposits that coincide with regions in permanent shadow typically found within impact craters at and near the poles of mercury have been interpreted as being composed of water ice we investigate the dynamic properties of these solid water ice deposits glaciers with the goal of constraining their movement flow rates possible deformation and related structures and deposits as an end member we treat the extreme case of maximum ice accumulation where these deposits fill the crater to the shadow line an event we would only expect following maximum accumulation conditions such as a large cometary impact or a comet shower we find that given the extremely cold conditions and the limited thickness of glaciers even under the most favorable accumulation conditions glaciation is cold based ice flow velocities are very low 4 10 8 m yr and with the exception of a sublimation lag deposit glaciation is unlikely to leave any significant impact on the terrain an important accelerator of ice flow is found to be the contribution of lateral heat conduction from the surrounding extremely hot surface terrain 225 k average with up to 450 k maximums which for 55 km craters yields velocities of 10 3 m yr while for smaller 10 km craters velocities may exceed 1 m yr enough to leave a detectable ice deformation imprint such as drop moraines however given that the observed deposits are substantially below their maximum fill capacities these estimates are unlikely to be attained

to the origin of icelandic rhyolites insights from partially melted leucocratic xenoliths we have studied glass bearing leucocratic granitic to qz monzonitic crustal xenoliths from the tindfjoll pleistocene volcanic complex sw iceland the xenoliths consist of strongly resorbed relicts of anorthitic plagioclase k rich feldspar and rounded quartz in colorless through pale to dark brown interstitial glass spongy clinopyroxene and or rounded or elongated crystals of orthopyroxene are in subordinate amount magnetite ilmenite zircon apatite allanite and or chevkinite are accessory minerals the xenoliths more likely are relicts of earlier formed partially melted si rich rocks or quartz feldspar rich crystal segregations which suffered latter interaction with hotter and more primitive magma s icelandic lavas are typically low in 18o compared to mantle derived morb like rocks 5 6 0 2 likely due to their interaction with or contamination by the upper crustal rocks affected by rain and glacial melt waters surprisingly many quartz and feldspar crystals and associated colorless to light colored interstitial glasses of the studied xenoliths are not low but high in 18o 5 1 7 2 excluding three dark brown glasses of 4 5 the xenoliths contain abundant low to high 18o 2 4 6 3 young zircons u pb age 0 2 0 27 0 03 ma u th age 0 16 0 07 ma most of them in oxygen isotope equilibrium with interstitial glasses the 18o values 5 6 recorded in the coexisting zircon quartz feldspar and colorless interstitial glass suggest crystallization from melts produced by fusion of crustal rocks altered by seawater also reflecting multiple melting and crystallization events this suggests that normal 18o silicic magmas may not be ultimately produced by crystallization of mafic basaltic magmas instead our new single crystal laser fluorination and ion microprobe o isotope data suggest addition of diverse partial crustal melts probably originated from variously altered and preconditioned crust

sequence stratigraphy and cyclic development of basal zechstein carbonate evaporite deposits with emphasis on zechstein 2 off platform carbonates upper permian northeast germany abstract although the basal zechstein is classically subdivided into two cycles z1 and z2 lower part it can alternatively be subdivided into three complete third order depositional sequences zs1 zs3 and the associated lowstand systems tract transgressive systems tract of a fourth sequence zs4 third and higher order sea level fluctuations influenced the depositional and diagenetic history of the carbonate evaporite alternations within the basal zechstein the main subject of the present study the zechstein 2 carbonate stassfurt carbonate or ca2 is interpreted to encompass both transgressive predominantly in slope and basinal settings and highstand systems tracts of zechstein sequence zs3 as well as part of the lowstand systems tract of the fourth zechstein sequence zs4 in northeastern germany hydrocarbon reservoirs of the ca2 developed along both northern and southern margins of the southern permian basin on top of the topography of the zechstein 1 cycle z1 this z1 topography resulted from deposition of the werra anhydrite a1 the highstand systems tract of the second zechstein sequence zs2 the northern ca2 carbonate platform is consistently narrow and fringed by coated grain and composite grain bars and shoals it is characterized by a steep fault controlled slope which precluded the formation of in situ shallow water grain dominated carbonates during relative sea level lowstands displaced shallow water coated grain and composite grain packstones wackestones may however occur as slope fan deposits turbidites in contrast the southern carbonate platform is wide tectonically dissected and fringed by grain dominated shallow water carbonates coated grain and composite grain bars and shoals zechstein 2 shallow water carbonates detectable by basal zechstein seismic anomalies also developed on pre existing topographical highs in off platform positions three depositional cycles ca2 cycles i ii and iii most probably reflecting high amplitude fourth order sea level fluctuations can be identified within the stassfurt carbonate our observations suggest that sea level variations possibly reflecting cyclicity in the milankovitch frequency band 0 1 0 4 ma and the pre zechstein topography pronounced during formation of the werra anhydrite were the most important factors in controlling the depositional as well as the diagenetic history of the zechstein 2 carbonate in off platform positions

the anatomy of a sulphate platform and adjacent basin system in the leba sub basin of the lower werra anhydrite zechstein upper permian northern poland the lower werra anhydrite zechstein upper permian deposits of the teba area originated in a deep basin setting in shallow to deep water conditions facies changes occur within small distances and suggest fluctuating boundaries between well defined basins and platforms this pattern of local platforms and adjacent basins developed during deposition in basinal areas the sequence is clearly transgressive whereas on platforms accumulation kept pace with subsidence after an initial transgression nodular anhydrite represents a polygenetic deposit which formed at different times with respect to deposition massive anhydrite with pseudomorphs after upright growth gypsum crystals suggest rapid precipitation in a subaqueous environment and or fluctuating but generally high salinity conditions massive clastic sulphate originated due to periodic high energy events and resedimentation or due to brecciation possibly connected with salinity fluctuations and the dissolution of halite massive textureless anhydrite is locally porous and passes upward into breccia indicating a strongly saline environment bedded anhydrite is considered to form in shallow water environments and laminated anhydrite in deep water bedded anhydrites contain portions which are graded intercalations of sulphate turbidites and upright growth gypsum suggest fluctuating water depths with comparatively deep water during turbidite deposition but shallower conditions during upright growth gypsum deposition the sequence observed in slope zones at platform basin margins detrital parautochthonous sulphate sand to graded beds to basinal laminites indicates that redistribution processes were important at the onset of the lower werra anhydrite deposition bathymetric relief existed between the central part of the basin and its margins where carbonate platforms remained subaerially exposed formation of local platforms and adjacent basins required a relatively high subsidence rate as pre existing relief cannot account for the total accumulated thickness of the lower werra anhydrite deposits one implication of this is that the main argument against the shallow water shallow basin evaporite basin model i e a very fast rate of subsidence may not be valid for the eba lower werra anhydrite basin

lunar nodal tide and distance to the moon during the precambrian the pace of tidal evolution for the past 450 myr implies an earth moon collision some 1 500 2 000 myr bp see ref 1 an event for which there is no corroborating evidence here we present the first direct determination of the lunar distance in the precambrian we interpret a 23 3 0 3 yr periodicity preserved in a 2 500 myr bp australian banded iron formation bif 2 as reflecting the climatic influence of the lunar nodal tide which has been detected with its modern 18 6 yr periodicity in some modern climate records3 10 the lunar distance at 2 500 myr bp would then have been about 52 earth radii the implied history of precambrian tidal friction is in accord with both the more recent palaeontological evidence and the long term stability of the lunar orbit the length of the milankovitch cycles that modulate the ice ages today11 13 also evolve with the earth moon system their detection in the precambrian sedimentary record would then permit an independent determination of the lunar distance

the ascraeus mons fan shaped deposit volcano ice interactions and the climatic implications of cold based tropical mountain glaciation abstract amazonian aged fan shaped deposits extending to the northwest of each of the tharsis montes in the tharsis region on mars have been interpreted to have originated from mass wasting volcanic tectonic and or glacial processes we use new data from mro mgs and odyssey to characterize these deposits building on recent evidence for cold based glacial activity at pavonis mons and arsia mons we interpret the smaller ascraeus fan shaped deposit to be of glacial origin our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat including 1 a ridged facies interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat 2 a knobby facies interpreted to represent vertical downwasting of the ice sheet and 3 complex ridges showing a cusp like structure we also see evidence of volcano ice interactions in the form of 1 an arcuate inward facing scarp interpreted to have formed by the chilling of lava flows against the glacial margin 2 a plateau feature interpreted to represent a subglacial eruption and 3 knobby facies superimposed on flat topped flows with leveed channels interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till we discuss the formation mechanisms of these morphologies during cold based glacial activity and concurrent volcanism on the basis of a mid to late amazonian age 250 380 ma established from crater size frequency distribution data we explore the climatic implications of recent glaciation at low latitudes on mars gcm results show that increased insolation to the poles at high obliquities 45 forces sublimation of polar ice which is transported to lower latitudes and deposited on the flanks of the tharsis montes we assess how local orographic effects the mass balance of the glacier and the position of equilibrium line altitudes all played a role in producing the observed geomorphologies in doing so we outline a glacial history for the evolution of the ascraeus mons fan shaped deposit and compare its initiation growth and demise with those of arsia mons and pavonis mons

interactions between lava and snow ice during the 2010 fimmvorðuhals eruption south central iceland 1 the 20 march 12 april basaltic effusive eruption at fimmvor uhals southern iceland was an important opportunity to directly observe interactions between lava and snow ice the eruption site has local perennial snowfields and snow covered ice and at the time of eruption it was covered with an additional 1 3 m of seasonal snow syn eruption observations of interactions between lava and snow ice are grouped into four categories 1 lava advancing directly on top of snow 2 lava advancing on top of tephra covered snow 3 snow ice melting at lava flow margins and 4 lava flowing beneath snow based on syn and post eruption observations in 2010 11 we conclude that the features seen in the lava flow field show only limited and localized evidence for the influence of snow ice presence during the eruption estimated melting rates from radiant and conductive heating at the flow fronts are too slow on the order of 5 m hr to allow for complete melting of snow ice ahead of the advancing lava flows at least during periods of observed rapid lava advance rates 15 55 m hr thus we conclude that during those periods which largely established the aerial extent of the lava flow field lava advanced on top of snow that this likely was the predominant mode of lava emplacement for much of the eruption is supported by many syn eruption field observations examination of the lava flows subsequent to the eruption has so far only found subtle evidence for interactions between lava and snow ice for example locally lava flows have fractured and are collapsing or have developed marginal rubble aprons from melting of snow banks that were partly covered by lava flow margins

icelandic pseudocraters as analogs to some volcanic cones on mars pseudocraters are rootless vents formed by the interaction of lava flows with surface or near surface water this interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs pseudocraters in several localities in iceland were examined in the field and compared to similar appearing features observed on mars the icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter have summit craters which range from 2 to 28 m in diameter many cones lack craters entirely and have flanks that are either concave up or convex up the size and spacing of icelandic pseudocraters might be a function of the availability of water in which larger closely spaced features result from efficient lava water interaction as suggested by the environments in which the features formed possible martian pseudocrater cones in amazonis planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter a numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and martian conditions the results suggest that explosions forming martian cones require significantly less water calculated masses are less by a factor of 4 to 16 than those forming icelandic pseudocraters despite their larger sizes this is attributed to the low gravity and atmospheric pressure in the mars environment and is consistent with the likely lower abundance of water which might be present as interstitial ice at shallow depths in the regolith locations of potential pseudocraters on mars at latitudes as low as 8 n imply the presence of crustal ice stores at the time of their formation

lava ice interaction on a large composite volcano a case study from ruapehu new zealand ice exerts a first order control over the distribution and preservation of eruptive products on glaciated volcanoes defining the temporal and spatial distributions of ice marginal lava flows provides valuable constraints on past glacial extents and is crucial for understanding the eruptive histories of such settings ice marginal lava flows are well displayed on ruapehu a glaciated andesite dacite composite cone in the southern taupo volcanic zone new zealand flow morphology fracture characteristics and 40ar 39ar geochronological data indicate that lavas erupted between 51 and 15 ka interacted with large valley glaciers on ruapehu ice marginal lava flows exhibit grossly overthickened margins adjacent to glaciated valleys are intercalated with glacial deposits display fine scale fracture networks indicative of chilling against ice and are commonly ridge capping due to their exclusion from valleys by glaciers new and existing 40ar 39ar eruption ages for ice marginal lava flows indicate that glaciers descending to 1300 m above sea level were present on ruapehu between 51 41 and 27 15 ka younger lava flows located within valleys are characterised by blocky flow morphologies and fracture networks indicative of only localised and minor interaction with ice and or snow mainly in their upper reaches at elevations of 2600 2400 m an 40ar 39ar eruption age of 9 3 ka 2 error determined for a valley filling flow on the northern flank of ruapehu indicates that glaciers had retreated to near historical extents by the time of emplacement for this lava flow the applicability of 40ar 39ar dating to ice marginal flows on glaciated andesite dacite composite volcanoes makes this technique an additional proxy for paleoclimate reconstructions

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

heat transfer in volcano ice interactions on earth the very high temperature contrast between magma lava and water ice commonly leads to the assumption that significant melting will take place immediately upon magma lava ice contact yet observations of active flows show little evidence of voluminous melting upon contact we use analytical thermal models to reassess the efficiency with which heat can be transferred from magma to ice in three situations lava flows erupted on top of glacial ice sill intrusions beneath glacial ice evolving into subglacial lava flows and dyke intrusions into the interiors of glaciers we find that the maximum ratios of thickness of ice that can be melted to the thickness of magmatic heat source are likely to be 2 5 for subaerial lava flows encroaching onto glaciers 6 7 for subglacial lava flows and 10 for dykes intruded into glacial ice rates of ice melt production are not linear functions of time and flow thickness however and this may account for the observations of minimal immediate water release from beneath advancing lava flows field observations during future eruptions should be directed at measuring the temperature of released water

tephra deposition on glaciers and ice sheets on mars influence on ice survival debris content and flow behavior we examine the consequences of pyroclastic deposits being emplaced onto ice layers on mars both those in the polar caps and those forming glaciers on the flanks of some of the large shield volcanoes we show that layers of pyroclasts greater than a few meters in thickness whether emplaced cold as fall deposits or hot as pyroclastic density current deposits act almost exclusively to protect ice layers beneath them from sublimation irrespective of whether they are emplaced at high or low elevations or high or low latitudes layers less than about 2 m thick on the other hand can cause significant ice loss by raising the surface temperature due to their low albedo and then transmitting that increased temperature to the underlying ice especially on a diurnal time scale this can have a significant bearing on the emplacement history of polar water ice and on the survival time of glacial ice on shield volcano flanks a key factor in the latter case is the timing of the episodic volcanic activity relative to the cycles of climate change driven by mars obliquity and eccentricity variations

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

dynamics and viscosity of a a and pahoehoe lava flows of the 2012 2013 eruption of tolbachik volcano kamchatka russia the 2012 2013 flank eruption of tolbachik volcano kamchatka lasted 9 months and produced 0 54 km3 of basaltic trachyandesite lava thus becoming one of the most voluminous historical lava effusions of basic composition in subduction related environments globally from march to july 2013 the volcano monotonously erupted lava of constant composition sio2 52 wt with a nearly stable effusion rate of 18 m3 s despite the uniform eruptive and emplacement conditions the dominant style of lava propagation throughout that time gradually changed from a a to pahoehoe we report results of instrumental field measurements of the a a and pahoehoe flow dynamics documented with time lapse cameras as well as the lava viscosity determined by flow rate and shear stress using penetrometer methods maximal propagation velocities of the a a fronts ranged from 2 to 25 mm s and those of the pahoehoe from 0 5 to 6 mm s the flow front velocities of both lava types experienced short period fluctuations that were caused by complex flow mechanics of the advancing flow lobes minimal viscosities of lava of the a a lobes ranged from 1 3 105 to 3 3 107 pa s flow rate method and those of the pahoehoe from to 5 103 to 5 104 pa s shear stress method our data include the first ever measured profiles of viscosity through the entire thickness of actively advancing pahoehoe lava lobes we have found that both the a a and pahoehoe flows were fed by identical parental lava which then developed contrasting rheological properties owing to differences in the process of lava transport over the ground surface the observed transition from the dominant a a to the dominant pahoehoe propagation styles occurred due to gradual elongation and branching of the lava tube system throughout the course of the eruption such evolution became possible because the growing lava field composed of semisolidified flows provided an environment for shallow subsurface intrusions and internal migrations of lava that with time developed into branches of the lava tube system based on our data we propose phenomenological models of the a a and pahoehoe flow mechanics

using u pb ages of miocene tufa for correlation in a terrestrial succession barstow formation california sedimentary rocks and associated fossils are the direct record of past life and its environmental context few methods allow direct and precise dating of this important archive making it diffi cult to correlate climate biologic and tectonic events preserved in terrestrial records we sampled lacustrine tufa calcite from the middle member of the miocene barstow formation to further test the feasibility of uranium lead dating of terrestrial carbonates five samples yield u pb ages 2 of 14 81 0 39 ma 15 30 0 25 ma 15 39 0 15 ma 16 14 0 40 ma and 16 24 0 23 ma these precise ages are consistent with existing ages from k ar and 40 ar 39 ar dating of intercalated volcanic ashes our most precise u pb age on tufa has an uncertainty of 1 150 ka which is equivalent to uncertainties for k ar ages from the same time period our results indicate that u pb dating of carefully sampled and screened sedimentary carbonates provides much needed age constraints in purely terrestrial sequences and can be a powerful tool for correlation even in deposits with structural complexity and rapid facies changes

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

the 1969 subglacial eruption on deception island antarctica events and processes during an eruption beneath a thin glacier and implications for volcanic hazards a short lived eruption of basaltic andesite to andesite on deception island in 1969 occurred from a series of fissures underneath a glacier the glacier was thin c 100 m and the eruption created a large and sudden discharge of meltwater that overflowed the glacier severely damaging buildings on the island the eruption was unusually well documented and it illustrates several features of subglacial eruptions that are only poorly known and not well understood in particular overflowing meltwater is contrary to predictions based on existing simple hydrological models for eruptions beneath thin glaciers the eruption is analysed in this paper and used as a model for the fluid dynamics and thermodynamics of eruptions beneath a thin glacier mainly composed of impermeable ice it is suggested that in eruptions of relatively fluid magmas with a low magma rise rate volatiles and magma are able to decouple and subglacial melting is strongly influenced by the superheated magmatic and hydrothermal gases mainly steam thus melting is much faster than that due solely to coupled conductive magma and convective meltwater heat transfer the influence of gasdriven melting also has an important effect on the shape of the meltwater cavity and may be at least partly responsible for the cylindrical ice chimneys developed above vents on deception island the results of the study are important for reconstructing the shapes of englacial cavities melted above a vent they also highlight the importance of glacier structure and densification rather than simply glacier thickness in determining the hydraulic evolution of an eruption even eruptions beneath thin glaciers can generate significant meltwater floods

quaternary geochronology using the uthpb method abstract we describe a method of uranium thorium lead u th pb isotopic age dating for quaternary rocks the approach uses an instrumental mass discrimination correction for lead isotope ratios which allows small enrichments of radiogenic 206ph and 208ph to be detected at the level of 0 001 igneous rocks hosting minerals with a range in 238 u 204 pb values of 100 can be dated with uncertainties of approximately 15 20 kyr a quaternary rhyolite dated at 1 19 ma by k ar yields a 238u 206ph age of 1 03 0 10 ma a holocene dacite 9 5 ka has uniform 206 pb 207 pb to within 0 0015 in groundmass phases but 1 mm plagioclase phenocrysts have lower 206 pb 207 pb by 0 105 0 002 indicating contamination of the magma after plagioclase crystallization high precision 206 pb 207 ph ratios may be a useful new tool for petrogenetic studies

subglacial to emergent basaltic volcanism at hloðufell south west iceland a history of ice confinement abstract hlo ufell is a familiar 1186 m high landmark located about 80 km northeast of reykjavik and 9 km south of the langkjokull ice cap in south west iceland this is the first detailed study of this well exposed and easily accessible subglacial to emergent basaltic volcano eight coherent and eleven volcaniclastic lithofacies are described and interpreted and its evolution subdivided into four growth stages i iv on the basis of facies architecture vents for stages i ii and iv lie along the same fissure zone which trends parallel to the dominant nne ssw volcano tectonic axis of the western volcanic zone in this part of iceland but the stage iii vent lies to the north and is probably responsible for the present n s elongation of the volcano the basal stage i is dominated by subglacially erupted lava mounds and ridges which are of 240 m maximum thickness were fed from short fissures and locally display lava tubes some of the stage i lavas preserve laterally extensive flat to bulbous steep glassy surfaces that are interpreted to have formed by direct contact with surrounding ice and are termed ice contact lava confinement surfaces these surfaces preserve several distinctive structures such as lava shelves pillows that have one flat surface and mini pillow

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

u pb dating of geodic calcite new insights on western europe major tectonic events and associated diagenetic fluids this study presents the first application of the u pb dating method to highly pb depleted diagenetic geodic calcites of the jurassic formations of the paris basin that leads to a reappraisal of the palaeohydrological history of this region composite u pb ages from multiple geodes combined with 18 o analyses reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events dogger formations recorded a first diagenetic fluid episode at 147 8 3 8 ma i e at the very beginning of the emersion of the basin during the tithonian period and 30 ma earlier than previously assumed 18 o results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the cretaceous period oxfordian formations recorded another major meteoric fluid circulation at 33 5 2 8 ma related to the initial stage of the european cenozoic rift system ecris consequently the porosity of the mesozoic formations of the studied area may have been closed sooner than previously thought before the main ecris rifting phase of oligocene age this study shows that u pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins supplementary material pb pb diagrams 238 u and 235 u series isochron diagrams and effect of blank correction on u and pb isotopic compositions and on ages calculation are available at https doi org 10 6084 m9 figshare c 3886885

genesis of evaporite associated platform dolomites case study of the main dolomite zechstein upper permian leba elevation northern poland dolomitization of the zechstein late permian main dolomite carbonates of northern poland was penecontemporaneous and or very early diagenetic well ordered stoichiometric dolomites are associated with the basinal facies the platform dolomitesare relatively poorly ordered and usually non stoichiometric most samples are highly enriched in 13c as in other zechstein carbonates 6 o values show large variations from 5 l to 7 4 there is an isotope zonation of the examined dolomites the isotope signature indicates that dolomites formed from variable solutions of meteoric water seawater and evaporitic brines of possible marine or continental origin once initiated dolomitization proceeded despite the evolution of dolomitizing brines this evolution explains the occurrence of lagoonal dolomites with common evidence for dissolution in the lower part of sections compared with well developed rhombohedra in the upper part crystal zoning suggests the initiation of dolomite growth in hypersaline water and progressive dilution by fresh water there is isotopic evidence for migration of continental waters into the basin presumably following sea level fall at the end of the deposition of the main dolomite influence of fresh water on syndepositional dolomitization well established in the main dolomite strongly suggests that similar relationships may be characteristic for other evaporite associated dolomites as well

basaltic subglacial sheet like sequences evidence for two types with different implications for the inferred thickness of associated ice abstract subglacially erupted volcanic sequences provide proxies for a unique range of palaeo ice parameters and they are potentially highly useful archives of palaeoenvironmental information particularly for pre quaternary periods they can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies yet they remain largely under utilised basaltic volcanic sequences erupted subglacially consist empirically of two major types corresponding to eruptions under thick and thin ice respectively the latter are called subglacial sheet like sequences and only one generic type of sequence has been described so far however there is now evidence that there are at least two generic types with significantly different implications for interpretations of associated palaeo ice sheet thicknesses one type which is relatively well described is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover 1000 m eruptions that form the dalsheidi type of sequence commence with the injection and inflation of a sill along the ice bedrock interface such interface sills were predicted theoretically but had no known geological example until now subsequent evolution commonly involves floating of the ice cover catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite as cohesionless mass flows and hyperconcentrated flows the water saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying interface sill eruptions are commonly not explosive until their later stages dalsheidi type deposits are outflow sequences probably linked to subglacial pillow volcanoes which in iceland were erupted along fissures they only provide an indication of minimum thicknesses of the associated overlying ice although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m however they are likely to be characteristic products of eruptions under the thick west antarctic ice sheet but are currently inaccessible such eruptions may be capable of destabilising that ice sheet

explosive lava water interactions in elysium planitia mars geologic and thermodynamic constraints on the formation of the tartarus colles cone groups 1 volcanic rootless constructs vrcs are the products of explosive lava water interactions vrcs are significant because they imply the presence of active lava and an underlying aqueous phase e g groundwater or ice at the time of their formation combined mapping of vrc locations age dating of their host lava surfaces and thermodynamic modeling of lava substrate interactions can therefore constrain where and when water has been present in volcanic regions this information is valuable for identifying fossil hydrothermal systems and determining relationships between climate near surface water abundance and the potential development of habitable niches on mars we examined the western tartarus colles region 25 27 n 170 171 e in northeastern elysium planitia mars and identified 167 vrc groups with a total area of 2000 km2 these vrcs preferentially occur where lava is 60 m thick crater size frequency relationships suggest the vrcs formed during the late to middle amazonian modeling results suggest that at the time of vrc formation near surface substrate was partially desiccated but that the depth to the midlatitude ice table was 42 m this ground ice stability zone is consistent with climate models that predict intermediate obliquity 35 between 75 and 250 ma with obliquity excursions descending to 25 32 for lava thicknesses ranging from 30 to 60 m and ground ice fractions ranging from 0 1 to 0 3 an ice volume of 4 23 km3 could have been melted and or vaporized by the time the lava solidified and the associated hydrothermal systems could have retained temperatures 273 k for up to 1300 years

40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited new 40 ar 39 ar age determinations on sanidine from the rhyolite of alder creek california indicate a 1 186 0 006 ma age for the cobb mountain normal polarity subchron the new age is statistically older 0 05 than the previously reported k ar age 1 12 0 02 ma and agrees with the age suggested by the astronomical polarity time scale incomplete extraction of radiogenic 40 ar 40 ar from the sanidine is the most likely reason for the disparity between the 40 ar 39 ar and k ar ages because the cobb mountain subchron is a worldwide short duration event and because no widely used interlaboratory 40 ar 39 ar standard younger than 27 ma exists we propose that sanidine from the rhyolite of alder creek be considered for use as a new quaternary 40 ar 39 ar mineral standard

volcano ice interactions in the arsia mons tropical mountain glacier deposits fan shaped deposits fsd superposed on the sides of the tharsis montes volcanic edifices are widely interpreted to have been formed by cold based glaciation during the late amazonian a period when the tharsis montes were volcanically active we survey the similar to 166 000 km 2 arsia mons fsd using new high resolution image and topography data and describe numerous landforms indicative of volcano ice interactions these include 1 steep sided mounds morphologically similar to terrestrial tindar that form by subglacial eruptions under low confining pressure 2 steep sided leveed flow like landforms with depressed centers interpreted to be subglacial lava flows with chilled margins 3 digitate flows that we interpret as having resulted from lava flow interaction with glacial ice at the upslope margin of the glacier 4 a plateau with the steep sides and smooth capping flow of a basaltic tuya a class of feature formed when subglacial eruptions persist long enough to melt through the overlying ice and 5 low areally extensive mounds that we interpret as effusions of pillow lava formed by subglacial eruptions under high confining pressure together these eruptions involved hundreds of cubic kilometers of subglacially erupted lava thermodynamic relationships indicate that this amount of lava would have produced a similar volume of subglacial liquid meltwater some of which carved fluvial features in the fsd landforms in the fsd also suggest that glaciovolcanic heat transfer induced local wet based flow in some parts of the glacier glaciovolcanic environments are important microbial habitats on earth and the evidence for widespread liquid water in the amazonian aged arsia mons fsd makes it one of the most recent potentially habitable environments on mars such environments could have provided refugia for any life that developed on mars and survived on its surface until the amazonian

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

the table a flat topped volcano in southern british columbia revisited more than 65 years ago w h mathews published a seminal paper in american journal of science describing the table an iconic flat topped volcano in southern british columbia canada the table is recognized as the type example of a glaciovolcanic lava dominated tuya we use field mapping 3 d photogrammetry lithofacies identification and 40ar 39ar geochronology to re examine the emplacement origins of this unique volcanic edifice the table is a steep sided flat topped mass of dense porphyritic andesite preserving a near original outer surface of hackly fractured aphanitic material the age of the edifice is 100 12 ka a new model for the emplacement involves dike injection and endogenous inflation within an overlying ice mass that is estimated to have been 250 to 350 m thick the model assumes that the edifice expanded outwardly as an elliptical cylinder endogenously inflating and melting an equal volume of ice the thermal exchange between the expanding massif and the melting ice operates across a subvertical well drained enveloping carapace of quench breccia for effusion rates of 0 5 to 2 m3 s 1 marginal heat fluxes are 43 to 186 w m 2 implying low overall heat transfer coefficients 0 04 to 0 18 w m 2 k 1 the total volume of ice melted serves as a calorimeter and constrains the average thickness 3 m and properties thermal conductivity 0 1 0 4 w m 1 k 1 of the breccia carapace the heat transfer efficiency of intermediate lava dominated tuyas is significantly lower 2 than reported for other glaciovolcanic systems commonly 45 77 but similar to that found for block lava flows and lava tubes

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

observations on lava snowpack and their interactions during the 2012 13 tolbachik eruption klyuchevskoy group kamchatka russia abstract observations made during january and april 2013 show that interactions between lava flows and snowpack during the 2012 13 tolbachik fissure eruption in kamchatka russia were controlled by different styles of emplacement and flow velocities a a lava flows and sheet lava flows generally moved on top of the snowpack with few immediate signs of interaction besides localized steaming however lavas melted through underlying snowpack 1 4 m thick within 12 to 24 h and melt water flowed episodically from the beneath flows pahoehoe lava lobes had lower velocities and locally moved beneath within the snowpack even there the snow melting was limited snowpack responses were physical including compressional buckling and doming and thermal including partial and complete melting maximum lava temperatures were up to 1355 k 1082 c type k thermal probes and maximum measured meltwater temperatures were 335 k 62 7 c theoretical estimates for rates of rapid e g radiative and slower conductive snowmelt are consistent with field observations showing that lava advance was fast enough for a a and sheet flows to move on top of the snowpack at least two styles of physical interactions between lava flows and snowpack observed at tolbachik have not been previously reported migration of lava flows beneath the snowpack and localized phreatomagmatic explosions caused by snowpack failure beneath lava the distinctive morphologies of sub snowpack lava flows have a high preservation potential and can be used to document snowpack emplacement during eruptions

north german zechstein facies patterns in relation to their substrate an attempt was made to relate the early zechstein facies distribution to the zechstein substrate comparable developments in the hessian trough and along the lower rhine embayment allow for the assumption that the creation of depocenters in the weser ems area are governed by interrelated late saalic tectonic pulses due to differences in the architecture and mobility of the substrate variations in the depositional model must be assumed

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

facies analysis of proximal subglacial and proglacial volcaniclastic successions at the eyjafjallajokull central volcano southern iceland

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

a brief overview of eruptions from ice covered and ice capped volcanic systems in iceland during the past 11 centuries frequency periodicity and implications eruptions from partly ice covered and ice capped volcanic systems constitute nearly 60 of all known historical i e in the past 11 centuries eruptions in iceland since the fourteenth century such eruptions have been reported in contemporary or near contemporary documents at least 120 historical eruptions have broken through the ice on the glaciated parts of five volcanic systems and have left tephra layers in ice and soil or been recorded at the time an unknown number of eruptions did not breach the overlying ice and left no record at all beginning as subglacial eruptions most eruptions break through the ice in minutes hours or days and can last from a few days to several months a single vent or the whole length of a fissure may then emerge to emit highly fragmented tephra in hydromagmatic explosions of varying strength the volume of airborne tephra varies by at least four orders of magnitude with dispersal range varying from near vent to transatlantic in most of the eruptions the magma was of basaltic composition eruption frequency is highest within the grimsvotn system where up to seven eruptions every 40 years have occurred during peaks of activity and at least 70 eruptions over historical time the observed pattern of temporally and spatially close eruptions separated by periods of low or no activity leaves open the question whether pre holocene deposits of several closely spaced subglacial eruptions can be securely distinguished from those formed in a single subglacial eruption

thermodynamics and fluid dynamics of effusive subglacial eruptions we consider the thermodynamic and fluid dynamic processes that occur during subglacial effusive eruptions subglacial eruptions typically generate catastrophic floods jokulhlaups due to melting of ice by lava and generation of a large water cavity we consider the heat transfer from basaltic and rhyolitic lava eruptions to the ice for typical ranges of magma discharge and geometry of subglacial lavas in iceland our analysis shows that the heat flux out of cooling lava is large enough to sustain vigorous natural convection in the surrounding meltwater in subglacial eruptions the temperature difference driving convection is in the range 10 100 c average temperature of the meltwater must exceed 4 c and is usually substantially greater we calculate melting rates of the walls of the ice cavity in the range 1 40 m day indicating that large subglacial lakes can form rapidly as observed in the 1918 eruption of katla and the 1996 eruption of gjalp fissure in vatnajokull the volume changes associated with subglacial eruptions can cause large pressure changes in the developing ice cavity these pressure changes can be much larger than those associated with variation of bedrock and glacier surface topography previous models of water cavity stability based on hydrostatic and equilibrium conditions may not be applicable to water cavities produced rapidly in volcanic eruptions energy released by cooling of basaltic lava at the temperature of 1200 c results in a volume deficiency due to volume difference between ice and water provided that heat exchange efficiency is greater than approximately 80 a negative pressure change inhibits escape of water allowing large cavities to build up rhyolitic eruptions and basaltic eruptions with less than approximately 80 heat exchange efficiency cause positive pressure changes promoting continual escape of meltwater the pressure changes in the water cavity can cause surface deformation of the ice laboratory experiments were carried out to investigate the development of a water cavity by melting ice from a finite source area at its base the results confirm that the water cavity develops by convective heat transfer

accelerated pleistocene coral extinctions in the caribbean basin shown by uranium lead u pb dating ages of corals and shallow marine sequences define rates of marine invertebrate evolution tectonic uplift and paleoclimate change yet accurate ages are difficult to obtain prior to the late pleistocene we report a new approach for combining uranium lead u pb and uranium series dating for middle pleistocene corals from the caribbean side of costa rica two corals have 230 th 238 u in secular equilibrium small excesses in 234 u and 206 pb 238 u ages of 1 02 0 07 ma and 1 288 0 034 ma the latter coral age dates a recognized geomagnetic event to ca 1 3 ma a time at which no polarity events had been identified the new ages also show that the major coral extinction in the caribbean basin occurred shortly after 1 0 0 9 ma much more recently than previously thought this coral extinction now coincides with the global change at 1 0 0 8 ma to the current pattern of glacial interglacial cycles and amplified changes in sea level these factors may have provided a new strong environmental mechanism for rapid habitat modification and coral extinction

the geysers cobb mountain magma system california part 2 timescales of pluton emplacement and implications for its thermal history abstract over 400 ion microprobe u pb isotopic ages measured for zircons extracted from 24 geothermal wells that penetrate the geysers plutonic complex gpc allow us to conclude that the entire known extent of the gpc crystallized during the early pleistocene nine samples of the microgranite porphyry that forms the shallow cupola 100 1 500 m below sea level mbsl of the gpc yield the oldest model u pb age 1 75 0 01 ma after correction for initial u series disequilibrium errors 1 twelve samples from the main intrusive phase orthopyroxene biotite granite present at depths 1 250 mbsl define a crystallization age of 1 27 0 01 ma this coincides with the age determined for a structurally and compositionally distinct body of granodiorite 1 25 0 01 ma n 5 samples that is intruded over a similar depth range two petrographically distinct varieties of orthopyroxene biotite granite yield ages of 1 46 0 03 gpc21 6000 and 1 16 0 02 ma ca5636 74f 21 three samples u pb zircon ages for dikes intruded in metagraywacke country rocks overlap with those obtained from the main body of the gpc and include the youngest material identified dike sample negu2 st1 7700 1 11 0 03 ma overall the u pb results demonstrate that the main body of the gpc 300 km3 was emplaced and crystallized within the upper crust over a short time interval 0 2 ma that overlaps with zircon crystallization ages of overlying silicic volcanic units

remote sensing evidence of lava ground ice interactions associated with the lost jim lava flow seward peninsula alaska thermokarst terrains develop when ice bearing permafrost melts and causes the overlying surface to subside or collapse this process occurs widely throughout arctic regions due to environmental and climatological factors but can also be induced by localized melting of ground ice by active lava flows the lost jim lava flow ljlf on the seward peninsula of alaska provides evidence of former lava ground ice interactions associated geomorphic features on the scale of meters to tens of meters were identified using satellite orthoimages and stereo derived digital terrain models the flow exhibits positive and mixed relief features including tumuli n 26 and shatter rings n 4 as well as negative relief features such as lava tube skylights n 100 and irregularly shaped topographic depressions n 1188 that are interpreted to include lava rise pits and lava induced thermokarst terrain along the margins of the flow there are also clusters of small peripheral pits that may be the products of meltwater or steam escape on mars we observed morphologically similar pits near lava flow margins in northeastern elysium planitia which suggests a common formation mechanism investigating the ljlf may therefore help to elucidate processes of lava ground ice interaction on both earth and mars

insights on lava ice snow interactions from large scale basaltic melt experiments quantitative measurements of interactions between lava and ice snow are critical for improving our knowledge of glaciovolcanic hazards and our ability to use glaciovolcanic deposits for paleoclimate reconstructions however such measurements are rare because the eruptions tend to be dangerous and not easily accessible to address these difficulties we conducted a series of pilot experiments designed to allow close observation measurements and textural documentation of interactions between basaltic melt and ice here we report the results of the first experiments which comprised controlled pours of as much as 300 kg of basaltic melt on top of ice our experiments provide new insights on 1 estimates for rates of heat transfer through boundary layers and for ice melting 2 controls on rates of lava advance over ice snow 3 formation of lava bubbles i e limu o pele by steam from vaporization of underlying ice or water and 4 the role of within ice discontinuities to facilitate lava migration beneath and within ice the results of our experiments confirm field observations about the rates at which lava can melt snow ice the efficacy with which a boundary layer can slow melting rates and morphologies and textures indicative of direct lava ice interaction they also demonstrate that ingestion of external water by lava can create surface bubbles i e limu and large gas cavities we propose that boundary layer steam can slow heat transfer from lava to ice and present evidence for rapid isotopic exchange between water vapor and melt we also suggest new criteria for identifying ice contact features in terrestrial and martian lava flows