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

upper mantle flow in eastern europe we present and discuss estimates of shear wave splitting in the upper mantle of eastern europe based on sks techniques estimates of the direction of polarization of the fast split wave and the delay of the slow wave t are obtained at seven stations uzh kov and lvv within and near the carpathians sim sev and yal in the crimean peninsula and kiev in the russian plate fast directions at all stations are around 130 close to the values previously found in central europe in the carpathians similar values of t are observed within the pannonian depression where the subcrustal lithosphere if present is very thin and in the foredeep with a thick subcrustal lithosphere this similarity suggests that the observed anisotropy is not inherited from earlier orogenies and preserved in the lithosphere in the crimea the fast direction of anisotropy in the mantle is perpendicular to the strike of the crimean mountains of late jurassic cretaceous age contrary to the expected alignment of the fast direction with the strike of a collisional belt in general the data are consistent with a present day or recent large scale mantle flow in central and eastern europe parallel to the alpine belt

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

variations in erosion intensity and soil maturity as revealed by mineral magnetism of sediments from an alpine lake in monsoon dominated central east china and their implications for environmental changes over the past 5500 years measurements of mineral magnetism were performed on a sediment sequence recovered from foye chi an alpine lake 3410 m a s l on the southern slope of the taibai mountain 3767 m a s l the hig

decoupling of small volume pyroclastic flows and related hazards at merapi volcano indonesia the november 1994 eruption at merapi volcano provided good evidence of decoupling of dome collapse pyroclastic flows and of large scale detachment of an ash cloud surge acs component from the basal block and ash flow baf timing and stratigraphic relationships of the largest 1994 acs indicate that this escaped from the valleys travelled well ahead of the baf arrived at the termination tens of seconds before it and deposited a discrete acs deposit beneath the baf unit this suggests that the acs detachment mostly occurred relatively high on the volcano slope likely at the foot of the proximal cone later pyroclastic flow eruptions in january 1997 and july 1998 also showed evidence of acs detachment although to a lesser extent suggesting that acss could be a frequent hazard at merapi volcano based on an extensive review of the available literature and on field investigations of historical deposits we show here that flow decoupling and acs detachment in the way inferred from the 1994 eruption is a common process at merapi the acs related destructions outside valleys were frequently reported in the recent past activity of the volcano i e in at least 16 pyroclastic flow eruptions since 1927 destruction occurred systematically in eruptions where maximum runout of the bafs was 6 5 km or more and occurred rarely for baf runouts of 4 5 km or less the acs deposits have been recognized beneath some valley filling baf units we attribute to some recent destructive eruptions i e the 1930 1954 1961 and 1969 eruptions topographic conditions at merapi volcano favouring acs detachment include a the high slope 30 of the proximal cone leading to high proximal velocities of the pyroclastic flows and thus to the transfer of large amounts of particles into the ash cloud b the strong break in slope at the foot of the proximal cone where the velocity of the basal baf is strongly reduced and a major acs component is thought to form and detach by shearing over the baf and c the small depth of most valleys in the first kilometres beyond the foot of the cone which allows minor acs components to escape from the valleys during travel of the baf however flow decoupling and acs detachment occur for only some of the numerous pyroclastic flows that follow the same path in a given eruption this indicates that topography alone cannot lead to flow decoupling we suggest two factors that control flow decoupling and its extent the main one is flow volume and thus flux as both are correlated in almost instantaneous dome collapse events as suggested by the observed relationship between flow decoupling and the travel distance of the pyroclastic flows the second factor is the amount of available ash in the flow at its early stage which influences the mass and thus momentum of the ash cloud the amount of ash in the pyroclastic flows of merapi may depend on several factors among which are a the physical and thermal state of the part of the active dome that collapses and b the proportion of older cold rocks incorporated in the flow either by undermining of surrounding summit rocks by the current pyroclastic flow activity or by erosion on the upper slopes

anisotropy gradients from ql surface waves evidence for vertically coherent deformation in the tibet region abstract the india eurasia continental collision has not only caused the high uplift of the tibetan plateau but also created a broad diffuse deformation zone in central asia we relate the well constrained extent of crustal deformation in the tibet region with underlying mantle deformation by interpreting the quasi love ql surface wave scattering in the legacy data of tibet ql waves are waveform anomalies generated from cross mode coupling of earth s free oscillations mainly through azimuthal anisotropy over 50 events with ql observations are identified using recordings in tibet the predominant frequency content of the ql waves is near 10 mhz and reflects peak sensitivity of anisotropy at 150 km depth in the mantle assuming horizontally oriented symmetry axes by calculating the delay times between the ql waves and the main love waves we back project the scatterers to cluster in areas like se tibet sayan mountain and iran noticeably the spatial distribution of these scatterers borders the crustal deformation pattern quite well especially at the deformation limits of central asia this linkage suggests a vertically coherent boundary condition through the crust and the upper mantle for the india eurasia continental collision in central asia

pyroclastic density currents pdc of the 16 17 august 2006 eruptions of tungurahua volcano ecuador geophysical registry and characteristics abstract tungurahua located in the eastern cordillera of the ecuadorian andes is a 5023 m high active volcano notable for its extreme relief 3200 m steep sides and frequent eruptive cycles from 1999 until 2006 tungurahua experienced short periods of low to moderate strombolian activity characterized by fire fountaining explosions frequent ash falls and debris flows and no pdc events without warning tungurahua initiated pdc activity on 15 16 july 2006 which became more intense on the night of 16 17 august 2006 which is the focus of this study continuous monitoring of tungurahua has employed seismic both short period and broadband bb instruments so 2 gas emission cospec and doas and geodetic methods edm tilt meters and gps in addition to thermal imagery airborne and ground based acoustic flow monitors afm installed to monitor lahar activity were important for detecting pdc events acoustic signals were monitored at riobamba 40 km to the sw as well as by infrasound sensors at tungurahua s bb seismic stations based on geophysical parameters visual observations and pdc deposit characteristics four phases of distinct eruptive activity are recognized during the 16 17 august episode phase i 08h37 to 21h13 of 16 aug local time experienced low to moderate strombolian activity with occasional high energy impulsive bursts and small pdc phase ii 21h13 16 aug to 00h12 17 aug was characterized by a number of discrete events with high amplitude seismo acoustic signals followed by the generation of larger pdc that overran monitoring stations and had velocities of 30 33 m s after midnight phase iii 00h12 to 01h14 saw an intense period of unrelenting eruptive activity corresponding to the episode s greatest energy release it was characterized by subplinian activity accompanied by a series of high energy outbursts and constant low frequency jetting that together formed a continuous plume it was during this phase that the largest pdc were produced reaching the surrounding river valleys phase iv after 01h14 followed the cessation of the paroxysmal eruption but witnessed many granular pdc generated by degassed lava spill outs from the crater that developed lobe and channel morphology on the cone s lower flanks hours later a blocky lava flow issued from the crater during these episodes more than 30 pdc events were detected the majority being small flows that remained high on the cone the two largest pdc occurred after midnight probably generated by fountain collapse their descent down the cone s upper steep flanks 28 and 2 4 km in length favored air entrainment resulting in pdc with greater fluidity these flows had volumes of 9 to 17 10 6 m 3 and produced widespread but relatively thin 1 2 m thick normally graded deposits at their distal ends the character and evolution of the pdc activity apparently reflect decreasing volatile contents of the magma and a diminishing magma supply

proxy climate and geomagnetic palaeointensity records extending back to ca 75 000 bp derived from sediments cored from lago grande di monticchio southern italy as part of a multi disciplinary study of maar lake sediments magnetic properties of some 3000 samples from two long cores extracted from the bottom sediments of lago grande di monticchio located in southern italy have been measured and the results connected with lithological palynological and geochemical data obtained from the same cores a time scale based on microlaminations radiocarbon and arar age determinations see companion papers in this special issue of quaternary science reviews dates the base of the longer 51 m core at about 76 ka before the present the strengths of anhysteretic remanence saturation isothermal remanence and susceptibility are highly sensitive to the contrast between stadial and interstadial conditions showing almost flip flop transitions at oxygen isotope stage 5a 4 and stage 2 1 boundaries as previously observed for lac du bouchet another maar lake site located in the haute loire province of france on the other hand these laboratory installed magnetizations vary smoothly through sediment deposited during stadials a prolonged period of heavy modelled precipitation starting at 25 ka bp coincides with a marked decrease in measured magnetic intensities possibly associated with the consequent increase in lake level and lake water chemistry the natural remanent magnetization is dominated by climatic and environmental influences nevertheless a weak signal attributed to variations in the palaeointensity of the geomagnetic field has been isolated and it shows good broad scale agreement with that previously reported for lac du bouchet

the ad 1300 1700 eruptive periods at tungurahua volcano ecuador revealed by historical narratives stratigraphy and radiocarbon dating tungurahua is a frequently active and hazardous volcano of the ecuadorian andes that has experienced pyroclastic flow forming eruption in 1773 1886 1916 18 and 2006 08 earlier eruptions in late pre hispanic and early colonial times have remained poorly known and are debated in the literature to reconstruct the eruptive chronology in that time interval we examine relevant historical narratives recently found in sevilla spain and rome italy and we combine stratigraphic field constraints with 22 new radiocarbon age determinations results show that pyroclastic flow forming eruptions and tephra falls took place repeatedly since similar to 700 c 14 yr bp when the tungurahua region was already populated radiocarbon ages averaging around 625 yr bp reveal a period of notable eruptive activity in the 14th century late integration cultural period the associated andesitic eruptions produced ash and scoria falls of regional extent and left scoria flow deposits on the western flanks of the edifice the fact that tungurahua was known by the puruhas indians as a volcano at the time of the spanish conquest in 1533 perhaps refers to these eruptions a group of ages ranging from 380 to 270 yr bp is attributed to younger periods of activity that also predates the 1773 event and calibration results yield eruption dates from late 15th to late 17th centuries i e inca and early colonial periods the historical narratives mention an early colonial eruption between the spanish conquest and the end of the 16th century followed by a distinct eruptive period in the 1640s the descriptions are vague but point to destructive eruptions likely accompanied by pyroclastic flows the dated tephras consist of andesitic scoria flow deposits and the contemporaneous fallout layers occur to the west these findings reveal that the eruption recurrence rate at tungurahua is at least one pyroclastic flow forming event per century since the 13th century and the occurrence of such eruptions in 2006 08 is thus fully consistent with the rate inferred for the past seven centuries in addition historical chronicles suggest that a notch opened in the crater margin during the 1640 decade as has occurred repeatedly in the past millennium at tungurahua such small volume collapse events represent a previously unrecognized source of hazards which deserve special attention for risk assessment purposes in the context of the currently ongoing eruption c 2008 elsevier b v all rights reserved

mantle deformation and tectonics constraints from seismic anisotropy in the western united states abstract we have examined shear wave splitting in teleseismic shear waves sks skks s from 15 stations in the western united states based on analysis of 123 records from 67 events the varied past and present tectonic styles in this region subduction transform faulting extension and stable domains are expected to cause a wide variety of anisotropic behavior and therefore make it an excellent natural laboratory fast polarization azimuths vary from e w to nearly n s and time delays t range from being barely detectable less than 0 6 s to 1 6 s most stations yielded consistent measurements independent of station event geometry the exceptions were stations situated very close to the san andreas fault which yielded well constrained but inconsistent splitting parameters these have been successfully modeled by two anisotropic layers with different horizontal symmetry axes the upper layer has a fast direction parallel to the fault and t of about 1 s the lower layer with t from 0 6 to 0 9 s is oriented e w near the san francisco bay area and ne sw in the mojave desert other measurements of e w fast are observed as far east as western nevada with large delay times of 1 3 1 5 s but disappear to the north stations in the northwestern basin and range have values of oriented at about 70 with delay times ranging from 0 7 to 1 2 s varies in other regions of the basin and range from 70 in eastern nevada to 20 in the transition zone between the colorado plateau and the basin and range with t of 1 0 s measurements are geographically coherent and in many cases changes correspond to geologic or tectonic boundaries the e w fast feature extends across several tectonic provinces but disappears near the southern boundary of the gorda plate and may therefore be related to the dynamics of plate interactions regional variations in the fast directions of anisotropy within the basin and range suggest that the present extension has not been strong enough to align the fast directions over a great depth extent fast polarization directions within the transition zone between the basin and range and colorado plateau are nearly parallel to the geologic and geophysical boundaries between the two regions and to other geophysical boundaries the size of the delay times suggests that in many of the areas studied either the mantle is almost twice as anisotropic as we estimate or the anisotropy and therefore mantle deformation extends into the sublithospheric mantle we used the two layer method to examine the effect of a postulated lower layer with fast direction parallel to the absolute motion of the north american plate and found the best estimate of contribution from a uniform layer is 0 1 s of t although a contribution of up to 0 7 s cannot be ruled out a value as low as 0 1 s suggests either that olivine is not strongly aligned in a horizontal direction in this layer or that the layer thickness is of the order of 10 km

fabric related seismic anisotropy in upper mantle xenoliths evidence from measurements and calculations the seismic properties and their directional dependence have been measured in four mantle peridotites from picritic tuffs vitim baikal region russia geothermobarometric data suggest a source depth for the xenoliths corresponding to the spinel garnet transition zone 40 90km the experimental data include the measurement of p and s wave velocities and densities at confining pressures to 600 mpa and temperatures to 600 c and the determination of velocity anisotropy and shear wave splitting the measured velocities are compared with velocity calculations based on lattice preferred orientation lpo of olivine orthopyroxene the modal composition of the rocks and the single crystal stiffness coefficients macroscopic velocity anisotropy is strongly controlled by the lpo of olivine measured 600 mpa room temperature and calculated p wave anisotropies compare fairly well although the experimentally determined velocities are markedly lower than the calculated velocities the correspondence between measured and calculated shear wave splitting data is less pronounced this is attributed to grain boundary effects retrogressive reactions interstitial glass incomplete crack closure and to the fact that the lpo of the cpx fraction has not been included in the calculation the magnitude of p wave anisotropy corresponds to that observed in mantle peridotites exposed at the surface ivrea zone northern italy ronda southern spain

eruptive chronology of tungurahua volcano ecuador revisited based on new k ar ages and geomorphological reconstructions abstract this study focuses on the evolution through time of tungurahua volcano ecuador and provides new information regarding its history eighteen new k ar ages constrain its construction and the activity of its three successive edifices we show that the volcano is much younger than expected indeed the older edifice activity only began around 293 10 ka and ended at 79 3 ka after 50 ka of quiescence the second edifice started growing at 29 2 ka after a major sector collapse and itself collapsed at 3 ka since then the third edifice filled the amphitheatre and is still active together with numerical reconstructions of the morphology of the three edifices flanks before erosion these new ages allow us to quantify the magmatic productivity rates during their construction from 0 6 0 3 and 0 9 0 2 km3 ka for the two older edifices to 2 5 1 0 km3 ka for the youngest as well as an erosion rate of 0 2 0 1 km3 ka occurring since the end of tungurahua i construction major and trace element contents of lavas from the three edifices display rather similar trends combined with our new ages the magmatic signature through time does not seem to have been significantly affected either by the sector collapses experienced by the volcano or by changes of the deep magmatic source finally our results show that the k ar dating method by the unspiked cassignol gillot technique performed on groundmass can be successfully applied to lava flows older than the holocene while the uncertainties related to younger units can prevent an accurate age determination particularly this method can be applied to quaternary volcanoes from the ecuadorian arc with many of them remaining without knowledge of the timing of their past activity

radiocarbon ages of holocene pelado guespalapa and chichinautzin scoria cones south of mexico city implications for archaeology and future hazards pelado guespalapa and chichinautzin monogenetic scoria cones located within the sierra del chichinautzin volcanic field scvf at the southern margin of mexico city were dated by the radiocarbon method at 10 000 2 800 4 700 and 1 835 years b p respectively most previous research in this area was concentrated on xitle scoria cone whose lavas destroyed and buried the pre hispanic town of cuicuilco around 1 665 35 years b p the new dates indicate that the recurrence interval for monogenetic eruptions in the central part of the scvf and close to the vicinity of mexico city is 2 500 years if the entire scvf is considered the recurrence interval is 1 700 years based on fieldwork and landsat imagery interpretation a geologic map was produced morphometric parameters characterizing the cones and lava flows determined and the areal extent and volumes of erupted products estimated the longest lava flow was produced by guespalapa and reached 24 km from its source total areas covered by lava flows from each eruption range between 54 chichinautzin and 80 km2 pelado and total erupted volumes range between 1 and 2 km3 cone an average eruption rate for the entire scvf was estimated at 0 6 km3 1 000 years these findings are of importance for archaeological as well as volcanic hazards studies in this heavily populated region

the 15 september 1991 pyroclastic flows at unzen volcano japan a flow model for associated ash cloud surges large scale collapse of a dacite dome in the late afternoon of 15 september 1991 generated a series of pyroclastic flow events at unzen volcano pyroclastic flows with a volume of 1 106 m3 as dre descended the northeastern slope of the volcano changing their courses to the southeast due to topographic control after they exited a narrow gorge an ash cloud surge rushed straight ahead detaching the main body of the flow that turned and followed the topographic lows to the east the surge swept the kita kamikoba area which had been devastated by the previous pyroclastic flow events and transported a car as far as 120 m following detachment the surge lost its force after it moved several hundred meters but maintained a high temperature the deposits consist of a bottom layer of better sorted ash unit 1 a thick layer of block and ash unit 2 and a thin top layer of fall out ash unit 3 unit 2 overlies unit 1 with an erosional contact the upper part of unit 2 grades into better sorted ash at distal block and ash flow deposits the bottom part of unit 2 also consists of better sorted ash and the contact with the unit 1 deposits becomes ambiguous video footage of cascading pyroclastic flows during the 1991 1995 eruption traveling over surfaces without any topographic barriers revealed that lobes of ash cloud protruded intermittently from the moving head and sides and that these lobes surged ahead on the ground surface this fact together with the inspection by helicopter shortly after the events suggests that the protruded lobes consisted of better sorted ash and resulted in the deposits of unit 1 the highest ash cloud plume at the oshigadani valley exit and the thickest deposition of fall out ash over kita kamikoba and ohnokoba indicate that abundant ash was also produced when the flow passed through a narrow gorge in the model presented here the ash clouds from the pyroclastic flows were composed of a basal turbulent current of high concentration main body an overriding and intermediate fluidization zone and an overlying dilute cloud release of pressurized gas in lava block pores due to collisions among blocks and the resulting upward current caused a zone of fluidization just above the main body the mixture of gas and ash sorted in the fluidization zone moved ahead and to the side of the main body as a gravitational current where the ash was deposited as surge deposits the main body which had high internal friction and shear near its base then overran the surge deposits partially eroding them when the upward current of gas fluidization waned better sorted ash suspended in the fluidization zone was deposited on block and ash deposits in the distal places of block and ash deposits unit 2 probably was deposited in non turbulent fashion without any erosion of the underlying layer unit 1

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

testing the suitability of frictional behaviour for pyroclastic flow simulation by comparison with a well constrained eruption at tungurahua volcano ecuador we use a well monitored eruption of tungurahua volcano to test the validity of the frictional behaviour also called mohr coulomb which is generally used in geophysical flow modelling we show that the frictional law is not appropriate for the simulation of pyroclastic flows at tungurahua with this law the longitudinal shape of the simulated flows is a thin wedge of material progressively passing over several hundreds of metres from an unrealistic thickness at the front 1 mm to some tens of centimetres simulated deposits form piles which accumulate at the foot of the volcano and are more similar to sand piles than natural pyroclastic deposits finally flows simulated with a frictional rheology are not channelised by the drainage system but affect all the flanks of the volcano in addition their velocity can exceed 150 m s 1 allowing pyroclastic flows to cross interfluves at bends in the valley affecting areas that would not have been affected in reality and leaving clear downstream areas that would be covered in reality instead a simple empirical law a constant retarding stress i e a yield strength involving only one free parameter appears to be much better adapted for modelling pyroclastic flows a similar conclusion was drawn for the socompa debris avalanche simulation kelfoun and druitt j geophys res 110 b12202 2005

pyroclastic flow erosion and bulking processes comparing field based vs modeling results at tungurahua volcano ecuador pyroclastic density currents pdcs are high temperature and high velocity mixtures that threaten populations in the vicinity of many active volcanoes deciphering the cause of their remarkable mobility is essential for volcanic hazard analysis but remains difficult because of the complex processes occurring within the flows here we investigate the effect of bulking on dense pdc mobility by means of a double approach first we estimate the amount of material incorporated into scoria flows emplaced during the august 2006 eruption of tungurahua volcano ecuador for this we carry out a detailed analysis of 3d corrected digital images of well exposed scoria flow deposits componentry analysis indicates that pdc bulking occurs principally on the steep 25 upper slope of the volcano and the deposits typically comprise 40 50 wt of non juvenile i e accessory and accidental material secondly we develop a simple stress related grain by grain equation of erosion combined with two simple depth averaged geophysical mass flow models that compare the bulking mechanism to a non fluidized and a fluidized flow two behaviors based on coulomb and plastic rheologies are used to reproduce on a first order basis the 2006 tungurahua pdcs cross check comparisons between these modeled cases and the erosion pattern inferred from field based data allow us to evaluate the accuracy of our modeling assumptions regardless of the rheological regime the pdc induced erosion pattern of the 2006 tungurahua eruption can only be reproduced by fluctuations of the flow s basal shear stress during emplacement such variations are controlled by flow thinning thickening processes notably through the formation of a thick non erosive flow body that pushes a thin frictional erosive front during pdc emplacement the input volume of juvenile material as well as the thickness of the erodible layer available prior to the eruption are additional key parameters our work highlights complexities in pdc erosion and bulking processes that deserve further study in terms of hazard assessment our findings reveal that incorporation and bulking translate into increased flow mobility i e the augmented flow mass enhances both flow velocity and runout distance up to 20 these outcomes should be considered closely for hazard analysis at many other andesitic volcanoes worldwide where similar pdc events are common

santorini eruption radiocarbon dated to 1627 1600 b c precise and direct dating of the minoan eruption of santorini thera in greece a global bronze age time marker has been made possible by the unique find of an olive tree buried alive in life position by the tephra pumice and ashes on santorini we applied so called radiocarbon wiggle matching to a carbon 14 sequence of tree ring segments to constrain the eruption date to the range 1627 1600 b c with 95 4 probability our result is in the range of previous less precise and less direct results of several scientific dating methods but it is a century earlier than the date derived from traditional egyptian chronologies

combining insar and seismology to study the 2003 siberian altai earthquakes dextral strike slip and anticlockwise rotations in the northern india eurasia collision zone summary the 2003 september 27 m w 7 2 siberian altai earthquake was the largest to have struck the altai mountains in more than seventy years and was closely followed by two m w 6 2 and 6 6 aftershocks we use radar interferometry seismic bodywaves and field investigations to examine the source processes of these earthquakes the main shock of the initial earthquake ruptured a subvertical nw se striking dextral strike slip fault the fault was previously unrecognised although it approximately follows the southwestern boundaries of two intermontane depressions within the interior northwestern altai it has very little topographic expression a ne dipping m w 6 7 reverse subevent possibly triggered by shear waves from the main shock occurred ten seconds afterwards strike to the southeast the later m w 6 2 and 6 6 aftershocks were dextral strike slip events which contributed further to deformation in the northwest part of the fault zone however interferometric and bodywave models disagree significantly on the source parameters of the earthquakes in particular the total moment released and the dip of the fault planes trade offs of fault dip with moment and centroid depth in the bodywave modelling can account for some but not all of these discrepancies the interferometric data is unevenly distributed containing many more data points on one side of the fault zone than the other however on the basis of calculations with synthetic data we rule this out as a reason for the discrepancies in fault parameters the lower moment predicted by interferometry could be explained by the lack of coherent data close to the faulting if slip was concentrated at very shallow depths the dip yielded by the interferometric modelling might be influenced by lateral changes in elastic properties although these would also affect the bodywave solutions the earthquake sequence occurred close to recent palaeomagnetic measurements of late cenozoic anticlockwise rotations these suggest that the right lateral strike slip faulting that ruptured in the 2003 earthquakes accommodates regional nne ssw shortening by rotating anticlockwise over time the reverse subevent is a rare case of pure shortening perpendicular to the trend of the altai range

age and archaeological implications of xitle volcano southwestern basin of mexico city the pedregal lavas are fresh well exposed basaltic flows erupted from the xitle scoria and cinder cone in the southwestern part of the basin of mexico these lavas cover an area of 70 km 2 and were emplaced over pyramids and other buildings e g cuicuilco and copilco archaeological sites today a part of mexico city including the national university is built on the flows initial strombolian activity produced an ash fallout layer which was immediately followed by effusive emplacement of lava flows the xitle cone grew on the north facing slope of ajusco volcano and lava flowed down to the n ne until it reached the basin floor more than 30 radiocarbon dates have been obtained by several workers on charcoal samples from beneath the lava and several ages for the eruption have been proposed from these dates most dated samples were not directly produced by xitle s eruption but instead are artifacts of human activity that predates the eruption thus these ages mostly about 2000 bp are older than the eruption a new age of 1670 35 years bp ad 245 315 obtained on charcoal samples collected just beneath the lavas is favored for the xitle eruption these samples originated by ignition of vegetation during the emplacement of hot scoriaceous tephra the new age is within the classic period of mesoamerican archaeology whereas the earlier reported ages are at the end of the preclassic the new age carries important implications for the timing of population shifts within the basin of mexico q 2000 elsevier science b v all rights reserved

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

welcoming a monster to the world myths oral tradition and modern societal response to volcanic disasters abstract volcanic eruptions can overwhelm all senses of observers in their violence spectacle and sheer incredibility when an eruption is catastrophic or unexpected neither individuals nor communities can easily assimilate the event into their world view psychological studies of disaster aftermaths have shown that trauma can shake the very foundations of a person s faith and trigger a search supernatural religious or scientific for answers for this reason the ability to rapidly comprehend a traumatic event by accepting the catastrophe as part the observer s world represents an important component of community resilience to natural hazards a relationship with the event may be constructed by adapting existing cosmological ancestral or scientific frameworks as well as through creative and artistic expression in non literate societies communal perceptions of an event may be transformed into stories that offer myth like explanations as these stories make their way into oral traditions they often undergo major changes to allow transmission through generations and in some cases to serve political or religious purposes disaster responses in literate societies are no different except that they are more easily recorded and therefore are less prone to change over time here we explore ways in which the language imagery and metaphor used to describe volcanic events may link disparate societies both present and past in their search for understanding of volcanic catastrophes responses to modern eruptions 1980 mount st helens usa and 1995 present soufriere hills montserrat provide a baseline for examining the progression to older historic events that have already developed oral traditions 1886 tarawera new zealand and finally to oral traditions many hundreds of years old in both the pacific northwest us and new zealand nz we see that repeated volcanism over many generations produces rich webs of cosmology and history surrounding volcanoes nz maori have incorporated volcanoes into the lineage of tribes and individuals thus good and bad outcomes from volcanism are part of long term cycles of reciprocity and equilibrium that link modern maori to their ancestors in both regions cosmologies and mythologies not only document the attempts of past cultures to recover from the impacts of volcanic disasters but also provide a means by which following generations can understand contextualize and therefore recover from future volcanic catastrophes we further suggest that such local traditions can provide a valuable community education tool as well as an important means of aiding the psychosocial recovery of individuals and communities after volcanic disasters

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

tephras and new zealand archaeology establishing an accurate date for earliest polynesian settlement in new zealand is essential for understanding patterns of settlement and associated enviromental impacts and the processes and rates of cultural change in eastern polynesia tephra deposits from five volcanic centres together with exotic sea rafted pumice provide isochronous constraints on the timing of earliest settlement and human impacts in northern new zealand a local basaltic tephra from rangitoto island auckland and locally distributed andesitic tephras from egmont volcano directly date human occupation toc ad 1400 1450 distal andesitic tephras tufa trig formation from mt ruapehu tongariro volcanic centre help constrain the timing of earliest anthropogenic deforestation signals in hawke s bay sea rafted loisels pumice s although of uncertain stratigraphic reliability in places overlies cultural remains that can be no younger thanc ad 1350 along the east coast north island the regionally extensive rhyolitic kaharoa tephra which erupted from okataina volcano between c ad 1300 1390 is the critical settlement layer datum for dating prehistory in the north island no human artefacts are recorded beneath it and the earliest inferred environmental impacts by humans are dated to c ad 1280 just prior to its deposition this maximum date matches the earliest radiocarbon dates derived for both settlement and human impacts from archaeological and natural sites c ad 1250 and implies that the onset of deforestation was essentially contemporaneous with initial settlement the widespread rhyolitic taupo tephra which erupted from taupo volcanoc ad 200 provides an isochronous benchmark well before earliest settlement the tephra may coincide approximately with a putative earlier transient contact in new zealand based on pacific rat bone rattus exulans dates more precise calendrical dates on the tephras via dendrochronology or ice core records or other dating methods would help refine assessment of the timing of earliest settlement while extending the distributional range of critical tephra layers through application of crypto tephra analysis could lead to a greater understanding of settlement patterns

radiocarbon analysis of the early archaeological site of nauwalabila i arnhem land australia implications for sample suitability and stratigraphic integrity abstract this study presents the results of an extensive radiocarbon dating program at the nauwalabila i site in northern australia the results show that the radiocarbon chronology at nauwalabila is reliable to 130 cm depth but below this depth coarse charcoal has been variably altered during a period in the early holocene when an ephemeral groundwater table reached close to the ground surface of the time below 150 cm none of the radiocarbon ages can be considered to indicate reliably the age of deposition of the sediments luminescence dates near the surface and at 110 cm are concordant with the radiocarbon chronology in the upper part of the sequence and hence the aberrant radiocarbon results below 150 cm do not constitute a reason to doubt the accuracy of the luminescence chronology deeper in the stratigraphy a conservative estimate of the age of the sequence based on extrapolation of results from that portion of the sequence where the radiocarbon chronology is considered to be reliable is consistent with the chronology proposed previously from luminescence dating both chronologies therefore suggest occupation of the site before 50 000 years based on sediment characteristics and the distribution of quartz chert quartzite and quartz crystal artefacts there is no evidence that there has been significant vertical displacement of artefacts relative to the surrounding sand matrix both chemical alteration and physical translocation of charcoal contributed to the aberrant ages at depth in the deposit the results point to the need for careful assessment of the suitability of charcoal for radiocarbon dating prior to analysis and to the dangers of relying on a small number of radiocarbon dates in the development robust site chronologies strategies for screening samples for suitability include i microscopic examination ii not analysing samples unless they survive the full abox pretreatment iii not analysing samples unless the material is significantly larger than the sediment matrix iv using chn analysis on both untreated and pretreated material to check for organic contamination and v using stepped combustion to check for concordancy in the ages of carbon released at successively higher temperatures

the kaapvaal craton seismic anisotropy petrophysical analyses of upper mantle kimberlite nodules a dense network of seismic stations has been deployed on the kaapvaal craton south africa to investigate the upper mantle seismic structures in order to bring independent petrophysical constraints we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the earth s surface by kimberlite eruptions seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants despite variations in the nodules compositions microstructures and crystallographic preferred orientations seismic anisotropy is rather homogeneous throughout the craton mean s wave anisotropy is weak 2 64 which is compatible with the small measured sks wave splitting mean delay time of 0 62 s

the baikal rift zone the effect of mantle plumes on older structure abstract the main chain of sw ne striking cenozoic half grabens of the baikal rift zone brz follows the frontal parts of early paleozoic thrusts which have northwestern and northern vergency most of the large rift half grabens are bounded by normal faults at the northwestern and northern sides we suggest that the rift basins were formed as a result of transformation of ancient thrusts into normal listric faults during cenozoic extension seismic velocities in the uppermost mantle beneath the whole rift zone are less than those in the mantle beneath the platform this suggests thinning of the lithosphere under the rift zone by asthenosphere upwarp the geometry of this upwarp and the southeastward spread of its material control the crustal extension in the rift zone this nw se extension cannot be blocked by sw ne compression generated by pressure from the indian lithospheric block against central asia the geochemical and isotopic data from late cenozoic volcanics suggest that the hot material in the asthenospheric upwarp is probably provided by mantle plumes to distinguish and locate these plumes we use regional isostatic gravity anomalies calculated under the assumption that topography is only partially compensated by moho depth variations variations of the lithosphere asthenosphere discontinuity depth play a significant role in isostatic compensation we construct three dimensional gravity models of the plume tails the results of this analysis of the gravity field are in agreement with the seismic data the group velocities of long period rayleigh waves are reduced in the areas where most of the recognized plumes are located and azimuthal seismic anisotropy shows that these plumes influence the flow directions in the mantle above their tails the baikal rift formation like the kenya rio grande and rhine continental rifts achauer u granet m 1997 complexity of continental rifts as revealed by seismic tomography and gravity modeling in jacob a w b delvaux d khan m a eds lithosphere structure evolution and sedimentation in continental rifts proceedings of the igcp 400 meeting dublin march 20 22 1997 institute of advanced studies dublin pp 161 171 is controlled by the three following factors i mantle plumes ii older prerift linear lithosphere structures favorably positioned relative to the plumes and iii favorable orientation of the far field forces

possible late holocene equatorial palaeoclimate record based upon soils spanning the medieval warm period and little ice age loboi plain kenya abstract wetland and floodplain soils in the east african rift of kenya provide a record of changing palaeoclimate and palaeohydrology compatible with climate records for the mid holocene through the late holocene medieval warm period ad 800 1270 and little ice age ad 1270 1850 documented previously in nearby lacustrine sites soils forming from volcaniclastic source materials in both loboi swamp and laterally adjacent kesubo marsh two wetland systems of latest holocene age were investigated using micromorphology whole soil geochemical analysis and stable isotope analysis of soil organic matter som wetland formation was abrupt and possibly related to climate shift from drier conditions associated with the mid holocene and medieval warm period to wetter conditions associated with the little ice age pre wetland sediments are floodplain volcanic sandy silts comprising buried inceptisols som 13c 15 pdb that fine upward to fine silt and clay which are overlain by clays and organic rich sediment peat som 13c 26 pdb stable isotopes record an abrupt shift from 20 to 40 c3 vegetation scrubland mixture of warm season grasses and acacia to 100 c3 wetland dominated by typha that occurred about 680 40 years bp c 14 date from seeds soils developed on the periphery of the wetland show evidence for fluctuations in hydrologic budget including siderite and redoximorphic features formed during wetter phases and vertic shrink swell and clay illuviation features developed during drier phases soils at kesubo marsh located 2 3 km east of loboi swamp consist of two buried mid holocene 4000 4600 years bp two c 14 dates from bulk som inceptisols developed from fluvially derived volcanic sand som 13c 15 pdb and separated from the latest holocene surface soil som 13c 17 5 pdb by an unconformity and prominent stone line both the loboi swamp and kesubo marsh surface soils show increases in zr fe and s relative to buried soils as well as higher leaching indices elevated zr may reflect zircon grain inputs by either aeolian dust during drier climate conditions or fluvial sheetflood inputs whereas higher leaching and elevated fe and s represent pyritization associated with wetter conditions

shear wave splitting beneath the snake river plain suggests a mantle upwelling beneath eastern nevada usa the snake river plain srp a 90 km wide topographic depression in southern idaho is a topographically anomalous feature in the western u s previous seismic studies focused on the northeastern srp to study its relationship with the yellowstone hotspot we present new teleseismic shear wave splitting data from six broadband seismic stations deployed along the axis of the srp from june 2000 to september 2001 we also analyze splitting at hlid a permanent station of the national seismic network located f100 km north of the plain splitting of individual teleseismic phases is consistent at all stations within 2r errors and we favor the interpretation of anisotropy with a single horizontal fast axis although a dipping axis interpretation is statistically permitted at two of the stations our station fast directions as well as shear wave splitting data from numerous other stations throughout the basin and range are best explained by a lattice preferred orientation of olivine due to horizontal shear along the base of the plate associated with the gravitational spreading of buoyant plume like upwelling material beneath eastern nevada into a southwestward flowing asthenosphere with respect to a fixed hotspot reference frame this parabolic asthenospheric flow paf model for the great basin is attractive because it explains the observed high elevations high mantle buoyancy low velocity anomaly beneath eastern nevada high heat flow and depleted geochemistry of some erupted basalts the lack of pliocene recent major volcanism in eastern nevada suggests that a significant amount of the buoyancy flux is due to compositional buoyancy our splitting station delay times vary in a way not predicted by the paf model and can be explained by a zone of aligned magma filled lenses and or partially molten dikes beneath the srp lithosphere a depleted olivine rich residuum underneath the sides of the eastern srp and or the effect of lateral lower crustal flow from beneath the esrp toward its adjacent flanks d 2004 elsevier b v all rights reserved

mongolian plateau evidence for a late cenozoic mantle plume under central asia the 2500 x 700 km mongolian plateau average elevation 2000 m is situated between the altai orogen and the siberian craton and occupies much of mongolia and transbaikalia in russia the plateau is characterized by 1 basin and range topography and two major domes hentai 600 x 300 km and hangai 800 x 550 km where altitudes reach 3905 m 2 lithosphere that is thinner than adjacent areas minimum 50 km 3 elevated heat flow up to 120 mw m2 4 dominantly alkaline basaltic volcanism in the form of cones lava fields and volcanic plateaus mostly of miocene quaternary age and 5 rifts including baikal main evolution in the pliocene quaternary tunka oligocene early miocene and hobsogol pliocene quaternary existing models explain these features in terms of diapiric upwelling of a mantle asthenolith below the main rifts and or as a long distance effect of the india asia collision we propose that the late cenozoic uplift of the whole mongolian plateau and associated rifting magmatism high heat flow and lithospherec thinning are not externally driven by the india asia collision but are the expression of the interaction of a mantle plume with overlying lithosphere some rifts link and interact with major strike slip faults such as the bolnai such faults may be the major expression of the india asia collision in this region

multi method chronometry of the teletskoye graben and its basement siberian altai mountains new insights on its thermo tectonic evolution

the magnetic record of inorganic fly ash deposition in lake sediments and ombrotrophic peats interest in identifying a geological marker signifying the starting point for the anthropocene has prompted an exploration of the stratigraphic record of inorganic particulates generated by industrial activities magnetic measurements of recent lake sediments and ombrotrophic peats are here used to reconstruct the history of deposition of inorganic fly ash spheres resulting mainly from solid fuel combustion and metal smelting the chronologies used have been based on moss increment counting radioisotope dating and pollen analysis the sites come from the united kingdom scandinavia and north america in several cases where detailed chronologies of both fly ash deposition and local industry can be compared the sequence of concentration linked magnetic measurements appears to capture accurately the record of industrial development despite incontrovertible evidence from other peat based records for some selective dissolution of magnetic minerals the dates at which magnetic concentration increases begin range from the 16th century in the peat profiles around the head of morecambe bay south cumbria in north west england where early iron manufacture using charcoal fuelled bloomery hearths is well documented to the mid 20th century at the remotest sites in arctic scandinavia the lake sediment profiles used here come mainly from the united kingdom and in most cases they date increases to the late 19th century or the first decades of the 20th century any attempt to use the magnetic record of fly ash deposition in lake sediments and or peats to mark the date chosen as the onset of the anthropocene would require careful choice of site location and archive bearing in mind the issue of selective magnetic mineral dissolution

structure of the plumbing system at tungurahua volcano ecuador insights from phase equilibrium experiments on july august 2006 eruption products understanding the plumbing system structure below volcanoes and the storage conditions temperature pressure volatile content and oxygen fugacity of erupted magmas is of paramount importance for eruption forecasting and understanding of the factors controlling eruptive dynamics phase equilibria experiments have been performed on a tungurahua andesite ecuador to shed light on the magmatic conditions that lead to the july august 2006 eruptions and the parameters that controlled the eruptive dynamics crystallization experiments were performed on a representative august 2006 mafic andesite product between 950 1025oc at 100 200 and 400 mpa and nno 1 and 2 and water mole fractions in the fluid xh2o from 0 3 to 1 water saturation comparison of the natural phenocryst assemblage proportions and phenocryst compositions with our experimental data indicates that the natural andesite experienced two levels of ponding prior to the eruption during the first step the magma was stored at 400 mpa 15 16 km 1000oc and contained ca 6 wt dissolved h2o in the second step the magma rose to a confining pressure of 200 mpa 8 10 km where subsequent cooling down to 975oc and water degassing of the magma led to the crystallization of reversely zoned rims on pre existing phenocrysts the combination of these processes induced oxidation of the system and overpressure of the reservoir triggering the july 2006 eruption the injection of a new hot volatile rich andesitic magma from 15 16 km into the 200 mpa reservoir shortly before the eruption was responsible for the august 2006 explosive event our results highlight the complexity of the tungurahua plumbing system in which different magmatic reservoirs can co exist and interact in time and are the main controlling factors of the eruptive dynamics

three dimensional structure of lateral heterogeneities in p velocities in the upper mantle of the southern margin of siberia and its preliminary geodynamic interpretation abstract a three dimensional model of lateral variations in p wave velocities in the upper mantle of the southern margin of siberia has been obtained using more than 6000 teleseismic arrival times registered at stations in siberia and kazakhstan the method was based on triangular block parameterization and allows a correlation between output information and the density of input information the inversion stability has been improved significantly compared to traditional approaches special attention was paid to the problem of testing the results obtained the study of the stability of the method sensitivity of results toward noise shows that the reconstruction was stable even if the noise level exceeded the relevant signal another test consisted in a reconstruction using two independent sets of events for these two sets the velocity structures determined were found to coincide satisfactory the preliminary interpretation of the results allows us to suggest some mechanisms of development of the study region according to the tomography images obtained the upper mantle has a clear convective structure two positive velocity anomalies which are interpreted as descending flows are well correlated with regions of recent orogeny altai and sayan three different structures of flows in the upper mantle which could explain the relief observed and the tomographic images obtained are considered qualitatively

analyses of iron oxide assemblages within namib dune sediments using high field remanence measurements 9 t and mossbauer analysis

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

degassing patterns of tungurahua volcano ecuador during the 1999 2006 eruptive period inferred from remote spectroscopic measurements of so2 emissions this paper presents the results of 7 years aug 1999 oct 2006 of so2 gas measurements during the ongoing eruption of tungurahua volcano ecuador from 2004 onwards the operation of scanning spectrometers has furnished high temporal resolution measurements of so2 flux enabling this dataset to be correlated with other datasets including seismicity the emission rate of so2 during this period ranges from less than 100 to 35000 tonnes day t d with a mean daily emission rate of 1458 t d and a standard deviation of 2026 t d average daily emissions during inferred explosive phases are about 1 75 times greater than during passive degassing intervals the total amount of sulfur emitted since 1999 is estimated as at least 1 91 mt mostly injected into the troposphere and carried westwards from the volcano our observations suggest that the rate of passive degassing at tungurahua requires so2 exsolution of an andesitic magma volume that is two orders of magnitude larger than expected for the amount of erupted magma two possible and not mutually exclusive mechanisms are considered here to explain this excess degassing gas flow through a permeable stagnant magma filled conduit and gas escape from convective magma overturning in the conduit we have found that real time gas monitoring contributes significantly to better eruption forecasting at tungurahua because it has provided improved understanding of underlying physical mechanisms of magma ascent and eruption

implications of long term changes in valley geomorphology on the behavior of small volume pyroclastic flows abstract stratigraphic mapping in the lower 3km of the vazcun valley on the ne flank of volcan tungurahua ecuador provides insight into the effects of long term geomorphic changes on pyroclastic flow behavior exposures of deposits in the vazcun valley record activity over the last 2000years during which time significant changes in the geomorphology of the valley have occurred two sets of terraces are present in the lower 2 3km of the valley the older of which grades into a small debris fan at the mouth of the valley each terrace formed during a period of frequent activity that was separated by a long period of quiescence during which the rio vazcun eroded a channel as deep as 40m reaching the previous base level the pyroclastic flows from historical eruptions appear to have been largely contained within the channel that is cut through the higher terraces and debris fan their surface forms the lower terrace located upstream from the head of the debris fan thin pyroclastic deposits exposed within the city of banos are mostly related to ash cloud surges that detached from the main flows as they slowed down within the channel the lower reach of the present channel of the rio vazcun is very sinuous and deeply incised into the two sets of terraces the winding channel would severely impede the mobility of future pyroclastic flows resulting in the deposition of thick deposits detachment of an overriding ash cloud surge could also occur in this region such a surge could be more likely to surmount the channel banks and travel over the surface of the terraces and debris for up to several kilometers from the channel

mountain building strike parallel motion and mantle anisotropy abstract geophysical and geological evidence indicates that tectonic movements parallel to the strike of orogenic belts and suture zones are the most important mode of displacement during continental collision and oblique subduction several hundred to a few thousand kilometers of displacement may have occurred this way resulting in a pervasive ductile deformation of the lithosphere consequently both crustal and mantle fabrics may reflect these movements and their study using both geological and geophysical methods could supply important clues to lithosphere behavior during mountain building on the basis of kinematic analysis of ductilely deformed crustal rocks in zones of movement a variety of tectonic models have been proposed which differ in 1 1 the timing of strike parallel motions early before or during continental accretion or late after accretion was completed 2 2 the geometric pattern of strike parallel displacement zones low angle or high angle and 3 3 the location of orogen parallel movement zones in outboard terranes on the subducting plate along the suture zone or within the continental hangingwall large scale displacements parallel to mountain belts also suggest that they occurred along lithospheric faults rooted in the upper mantle although few studies have been carried out from this view point thermal structural and petrological data support the conclusion that lithospheric faults involving the upper mantle may be discriminated from crustal faults rooted in some crustal decoupling zone where available data on mantle flow beneath orogenic belts are in agreement with mountain parallel displacements inferred from crustal studies this has an important bearing on the seismic anisotropy pattern which can be predicted in the lithospheric mantle below mountain belts the fast velocity direction which is parallel to the flow direction should therefore be recorded parallel to the strike of the belt

magma derived co2 emissions recorded in and content of plants growing in furnas caldera azores abstract the environmental impact of fumarolic and soil emanations of magma derived carbon dioxide across furnas caldera has been investigated by measuring the 14 c and 13 c content of 40 specimens of different c3 plants leaves growing within and outside the degassing areas the results demonstrate a significant to large 14 c depletion in many of the plants due to assimilation of 14 c free endogenous co2 during photosynthesis and leading to artificial radiocarbon ageing of up to 4400 years the extent of 14 c ageing broadly correlates with the intensity of gas manifestations at the sampling sites as inferred from field observations and measurements of excess co2 concentrations in the volcanic ground it also provides a time integrated measure of the amount of volcanic co2 locally admixed to the ambient air at several sites this accounts for 15 to 40 of total co2 420 to 600 ppm in enriched air in some of the plant species azalea camellia and fern 14 c depletion is correlated with an enrichment of 13 c due to assimilation of magma derived co2 with a 4 higher 13 c than normal atmosphere the rate of 13 c enrichment averages ca 0 18 by percent of volcanic carbon fixed in the plant and includes enhanced 13 c discrimination during photosynthesis as a consequence of increased ambient pco2 inferred at 0 0306 per added ppm of volcanic co2 furnas is one of the few volcanoes where clear 13 c enrichment in plants due to endogenous degassing has been evidenced our results can be used to estimate the local intensity of volcanic soil gas fluxes in the emanating areas of furnas caldera they also have implications for radiocarbon dating of past eruptive events in the caldera since plants artificially aged by previous degassing could be trapped in volcanic deposits

basin evolution in a folding lithosphere altai sayan and tien shan belts in central asia abstract central asia is a classical example for continental lithospheric folding in particular the altay sayan belt in south siberia and the kyrgyz tien shan display a special mode of lithospheric deformation involving decoupled lithospheric mantle folding and upper crustal folding and faulting both areas have a heterogenous crust with a long history of accretion collision subsequently reactivated as a far field effect of the indian eurasian collision thanks to the youthfulness of the tectonic deformation in this region peak deformation in late pliocene early pleistocene the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures a review of the paleostress data and tectono stratigraphic evolution of the kurai chuya basin in siberian altai zaisan basin in kazakh south altai and issyk kul basin in kyrgyz tien shan suggests that they were initiated in an extensional context and inverted by a combination of fault controlled deformation and flexural folding in these basins fault controlled deformation alone appears largely insufficient to explain their architecture lithospheric buckling inducing surface tilting uplift and subsidence also played an important role they form typical basins in a folding lithosphere flb their characteristic basin fill and symmetry inner structure folding wavelength and amplitude thermal regime time frame are examined in relation to basement structure stress field strain rate timing of deformation and compared to existing modelling results

upper mantle flow beneath and around the hangay dome central mongolia mongolia represents the northernmost area affected by the india asia collision and it is actively deformed along transpressive belts closely associated with large scale strike slip faults the active and past mantle flow beneath this region is however poorly known in order to investigate deep mantle deformation beneath central mongolia and its relation with the surrounding major structures such as the siberian craton the gobi altay belt and the baikal rift a ns trending profile of broadband seismic stations has been deployed in the summer 2003 from the southern siberian craton to the gobi altay range crossing the entire hangay dome mantle flow is deduced from the splitting of teleseismic shear waves such as sks phases in eastern mongolia the permanent station uln in ulaanbaatar reveals the presence of two anisotropic layers the upper one being oriented ne sw close to the trend of lithospheric structures and the lower one nw se close to the trend of eurasia absolute plate motion along the ns profile in central mongolia seismic anisotropy deduced from sks splitting reveals a homogeneous nw se trending structure fully consistent with the observations made in the altay sayan in western mongolia the observed delay times of 1 5 to more than 2 0 s favor consistent mantle flow over large mantle thicknesses since the lithosphere is less than 100 km thick beneath central mongolia and since the observed fast directions are parallel to the trend of the lithospheric structures but also close to the trend of the absolute plate motion we propose that both the lithosphere and the asthenosphere may join their anisotropic effects beneath central mongolia to explain the large delay times although gps vectors represent the instantaneous displacement of the earth s surface and sks splitting the time and vertical integration of finite strain at depth we use the opportunity of the dense geodetic measurements available in this region to discuss the anisotropy pattern in term of present day deformation in the eurasia fixed reference frame gps and sks both depict a similar trend beneath central mongolia suggesting a lithospheric block escaping toward the east that could orient olivine a axes in the upper mantle within a transpressive tectonic regime a different behaviour is observed in western mongolia the gps vectors trend ns close to the regional compression direction whereas the fast sks directions trend ew suggesting a tectonic regime close to a mode of axial shortening generating the development of an ew trending foliation at depth we therefore propose that mongolia is a place where active and frozen lithospheric deformation may add their effects together with the sublithospheric flow in the three sources of anisotropy inferred a fundamental role is played by the siberian craton that acted as an undeformable core of the continent through time the frozen paleozoic and mesozoic structures wrap around the craton building up the fast anisotropic direction pattern the present day sublithospheric flow induced by the plate motion is likely deflecting around its deep roots finally the present day tectonic regime appears to be controlled by the presence of the craton to the north

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

tomography based mantle flow beneath mongolia baikal area abstract recent progress in seismic tomography of asia allows us to explore and understand more clearly the mantle flow below the mongolia baikal area we present a tomography based model of mantle convection that provides a good match to the residual topography the model provides predictions on the present day mantle flow and flow induced asthenospheric deformation which give us new insights on the mantle dynamics in the mongolia baikal area the predicted mantle flow takes on a very similar pattern at the depths shallower or deeper than 400 km and almost opposite flow directions between the upper shallower than 400 km and lower deeper than 400 km parts the flow pattern could be divided into the simple eastern region and the complex western region in the mongolia the upwelling originating from about 350 km depth beneath baikal rift zone is an important possible drive force to the rifting the seismic anisotropy cannot be simply related with asthenospheric flow and flow induced deformation in the entire mongolia baikal area but they could be considered as an important contributor to the seismic anisotropy in the eastern region of mongolia and around and in sayan baikal orogenic belt

sks splitting beneath continental rift zones we present measurements of sks splitting at 28 digital seismic stations and 35 analog stations in the baikal rift zone siberia and adjacent areas and at 17 stations in the east african rift in kenya and compare them with previous measurements from the rio grande rift of north america fast directions in the inner region of the baikal rift zone are distributed in two orthogonal directions ne and nw approximately parallel and perpendicular to the ne strike of the rift in the adjacent siberian platform and northern mongolian fold belt only the rift orthogonal fast direction is observed in southcentral mongolia the dominant fast direction changes to rift parallel again although a small number of measurements are still rift orthogonal for the axial zones of the east african and rio grande rifts fast directions are oriented on average nne that is rotated clockwise from the n s trending rift all three rifts are underlain by low velocity upper mantle as determined from teleseismic tomography rift related mantle flow provides a plausible interpretation for the rift orthogonal fast directions the rift parallel fast directions near the rift axes can be interpreted by oriented magmatic cracks in the mantle or small scale mantle convection with rift parallel flow the agreement between stress estimates and corresponding crack orientations lends some weight to the suggestion that the rift parallel fast directions are caused by oriented magmatic cracks

between sierra and selva landscape transformations in upper ecuadorian amazonia numerous pre columbian sites with artificial earth mounds have been found in the upano valley at the foot of the andes in the ecuadorian amazon large scale excavations conducted during a franco ecuadorian project helped to reveal techniques in building mound functions chronology of occupation and house plan and associated activities groups of the upano culture built these mound complexes from 500 bc and left the valley ca 400 600 ad these groups transformed the natural landscape building hundreds of earth mound complexes along terraces located at a key area the upano people had strong relationships with the andean highlands where they traded their pottery the most striking aspect is the existence of a spatial pattern organizing the mounds the delimitation of a square or rectangular low and flat plaza is the basis of the spatial pattern in the upano valley it is closed on four sides by mounds modified slopes banks or dug pathways variations occur but the basic pattern is generally the same in several complexes a central mound is built in the center of the plaza with four or six peripheral elevations

comment on shear wave splitting to test mantle deformation models around hawaii by kristoffer t walker gotz h r bokelmann and simon l klemperer

geomorphic evidence of active deformation and uplift in a modern continental wedge top foredeep transition example of the eastern ecuadorian andes abstract the eastern ecuadorian andes appear as a fold and thrust belt adjacent to a continental foredeep represented by one of the world s largest tropical alluvial megafans the pastaza megafan debouching into the amazonian lowland the apex of the pliocene pleistocene megafan situated in the present day wedge top subandean zone has been cut by an erosion surface the western part of which has been uplifted of 500 m along the frontal thrust forming a poorly dissected plateau the mera plateau this erosion surface erased most of the previous fluvial landscape but preserved a large thrust related anticlinal hinge deforming less erodible underlying strata the mirador fold and smaller sized anticlines this surface has been then incised by two antecedent major rivers the pastaza and the napo and few tributaries the plateau edge is marked by a series of large scale gently sloping landslides clustered along a 70 km long concave eastward line associated with the frontal thrust fault the newly formed immature rivers issued from the landslides or sourced within east dipping remnants of the erosion surface downstream of the landslide line constitute the greatest part of the streams feeding the ecuadorian amazonian basin at 70 to 100 km from the landslide line the drainage abruptly changes from highly immature to mature with a well defined hinge line representing the outer limit of landslide and tectonic control the diversions of the pastaza river indicate ongoing fold growth since at least the late pleistocene in the eastern cordillera and the early holocene in the mera plateau the preserved terraces of the pastaza valley are all degradational and are ascribed to periods of tectonic seismic activity alternating with periods of tectonic quiescence or decreased seismic activity rather than to climatic events 14c dating of the plateau erosion surface and of the upper pastaza terraces indicates that the minimum average incision rate since 18 000 years bp varies locally in the upper pastaza valley from 0 5 to 0 67 cm year 1 increasing from 18 000 years bp to now a comparison of these incision rates with fold and thrust fault uplift rates indicates that incision in the upper pastaza valley was a result of rapid uplift up to 1 cm year 1 along the mirador fold and thrust which caused a restoration of the local equilibrium profile of the upper reach combined with smaller local fault uplift along the westernmost thrust faults the uplift of the whole mera plateau with respect to the upper amazonian basin gives a minimum average uplift rate of 2 8 cm year 1 since 18 000 years bp the overall uplift of the mera plateau and the eastern cordillera is likely to have been caused by a regional scale low angle thrust ramp emerging as the frontal thrust fault

lithospheric thermal regimes in europe abstract the heat flow pattern of europe derived from more than 8000 observations is dominated by a general northeast to southwest increase in geothermal activity which is the consequence of the tectonic evolution of the whole continent this paper reviews the history of the geothermal mapping of europe and describes the recently compiled set of geothermal maps of europe surface heat flow is correlated with the age of the last tectonothermal event with the near surface heat production and with the crustal thickness deep temperature distributions within the crust lithosphere are calculated for 1 d 2 d and simple 3 d models characteristic temperature depth curves are given for some of the major tectonic provinces and the results of various techniques are compared the value of the crustal heat contribution is assessed and a regional moho heat flow pattern is proposed the mohorovicic discontinuity is clearly not an isothermal surface neither is the heat flow from below the crust constant

baikal rift zone structure and geodynamics abstract the cenozoic baikal rift zone is superimposed on the caledonian baikal fold belt representing the suture between the precambrian siberian craton and several microcontinents the baikal rift zone consists of a system of disconnected fault bounded basins and extensional and wrench faults that straddles a major arch having a topographic relief of 2 3 km rifting activity commenced during the oligocene and is still active as evident from high seismicity of the baikal rift zone across the baikal rift zone upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8 11 km across the baikal basins as compared to the adjacent unextended areas the discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir indeed geophysical data indicate that the sayan baikal dome coincides with such a diapir the top of which is located at the crust mantle boundary this intrusion is held responsible for oligocene and quaternary doming of the rift zone development of the intra continental baikal rift system is thought to be related to asthenospheric diapirism active rifting however intra plate stresses in conjunction with the himalayan collision may have played some role

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

calibration of shear wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska abstract despite the abundance of measurements of shear wave splitting around the world some fundamental questions about its geological interpretation have not yet been answered in order to constrain 1 i the orientation and magnitude of s wave anisotropy 2 ii the thickness of the anisotropic layer and 3 iii the possible variation of the anisotropy with depth in the subcontinental upper mantle beneath active orogenic belts we have carried out a systematic investigation on shear wave properties of mantle xenoliths from recent alkaline basalts of the canadian cordillera and alaska it is found that the polarization direction of the fast s wave as well as the time delay t between the two arrivals are strongly dependent on the propagation direction with respect to the structural frame at a single station the variations of measured and t values for sks phases from different events can result from this dependence because the average grain size of olivine in upper mantle samples is commonly larger than 0 5 mm dislocation creep prevails over a thickness of at least 250 km and results in olivine lpo and hence anisotropy and shear wave splitting a single thick anisotropic layer in mountain parallel subvertical shear zones may cause high values of tgd while multiple subhorizontal layers will produce multiple splitting making the measurement and interpretation of s wave splitting difficult our results also suggest that the s wave splitting observed in cold old stable cratons such as the canadian shield is likely dominated by fossil anisotropy whereas that observed in hot active orogenic regions such as the northwest american cordillera and the tibetan plateau may be dominated by modern tectonic deformation in the lithosphere and flow in the asthenosphere

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

holocene explosive eruptions of witori and dakataua caldera volcanoes in west new britain papua new guinea abstract witori and dakataua caldera volcanoes have been very active in the middle to late holocene using tephrochronology this paper establishes the chronostratigraphy of these eruptions and their magnitude and the frequency of explosive volcanism at witori and dakataua after a long dormancy witori started explosive activity at ca 5600 conventional radiocarbon years bp producing in the next 4500 years five major tephra layers w k1 to w k4 w g with veis of 5 to 6 after the w g eruption at around 1200 bp the activity decreased in magnitude but increased in frequency with some eruptions forming central cones the major eruption of dakataua began with alternating ejections of phreatomagmatic ashfalls and plinian deposits followed by the cataclysmic eruption resulting in lithic rich pyroclastic flows ca 1100 1200 bp the major tephra layers cover extensive areas in west new britain due to their large volumes and the prevailing easterly winds providing valuable time markers for establishing holocene chronology the largest eruption the w k2 event of ca 3300 bp shaped much of the present landscape with an extensive area significantly devastated by tephra falls and pyroclastic flows obsidian and other artefacts buried by the tephras indicate that the area was repeatedly occupied the major tephra events formed new coastal plains favourable for human occupation

heat flow structure and evolution of the lithosphere of mongolia abstract the geothermal characteristics of mongolia are presented based on heat flow measurements taken in boreholes and at the bottom of lake khubsugul and on heat flow values inferred from 3he 4he isotope ratios in spontaneous spring gases three types of regional heat flow distribution are recognized a narrow linear anomaly in the khubsugul segment of the baikal rift zone an area of regularly varying heat flow controlled by the age of the last tectonomagmatic activity in central mongolia and a zone of anomalously low heat flow in the south mongolian hercynian belt the radiogenic contribution to the terrestrial heat flow is determined a contribution which proved to be different in the southern and northern megablocks of mongolia variations in the thermal regime of the northern central and southern megablocks of mongolia are accounted for by their tectonic evolution

combining historical and 14 c data to assess pyroclastic density current hazards in banos city near tungurahua volcano ecuador pyroclastic density currents pdcs from tungurahua volcano ecuador recurrently rush down the northern vazcun valley and threaten the small tourist city of banos located on its mouth estimating pdc hazards i e pdc return rate and extent is difficult in banos and vazcun because data from the literature are rare and debated while geological exposures are few and vegetated to improve our awareness of pdc hazards in the banos area we examined historical documents conducted new geological research in the vazcun valley and obtained additional 14c data we highlight complex radiocarbon results that may lead to difficulties when interpreting the pdc chronology and offer recommendations to improve sampling strategies for 14c age determinations of pdc deposits overall our results show that the 1640 1773 and 1886 pdc forming eruptions are recorded in the valley while products of the 1918 and 2006 events were likely removed through considering recorded unrecorded bias in the reconstruction of past pdc emplacement in vazcun we calculate a minimal average return rate of 18 pdc forming events for pre columbian and historical eruptions since the devastating 3 ka bp eruption which translates into a maximum average return rate of 150 200 years in the valley however the archives suggest that most pdcs did not affected the now urbanized banos area e g 1918 2006 and we estimate that the city is impacted on average every 350 500 years a duration that is likely perceived as fairly long for people living in the area the banos case study thus raises questions on how to communicate on uncertain threats and impacts and how to improve alert messages in a town where economic incomes are essentially based on tourist activities to better address these issues we plan in future works to focus on cognitive perception of risk and volcanic hazard judgment by populations of banos and nearby rural communities

upper mantle anisotropy beneath the altai sayan region of central asia abstract the altai sayan region of central asia is actively deforming despite its being located several thousands of kilometers away from the collisional front between india and eurasia to add constraints to the role of the upper mantle in this type of tectonic environment we analyzed intermediate period analogue records of sks and skks to determine the state of mantle anisotropy in this region we find that for all stations located in actively deforming areas the fast direction of anisotropy correlates well with indicators of cenozoic to the present day deformation and correlates with older structures only when they happen to align with younger ones the general east northeast trend of the fast direction of anisotropy in active regions also aligns with the principle extensional strain axis determined from earthquake moment tensors at one station nvs located outside of any actively deforming region the n s fast direction may correspond to the long wavelength strain field of the mantle beneath much of siberia these correlations along with the size of the delay times 1 2 s suggest that the anisotropy in the upper mantle beneath the altai sayan is responding to recent tectonic activity

geological and seismological field observations in the epicentral region of the 27 september 2003 mw 7 2 gorny altay earthquake russia abstract the m w 7 2 altay chuya earthquake of 27 september 2003 that occurred in gorny altay southern siberia russia is the first event of this magnitude to occur in the region in historical time the 60 km long surface ruptures of the right lateral event follow a preexisting but previously unmapped northwest southeast fault trace along the northern slope of the north chuya range additional secondary coseismic ruptures were also observed on adjacent faults the earthquake triggered landslides rock falls and liquefaction as well as destruction of houses and other construction in the kurai and chuya basins the 2003 event induced several thousand aftershocks during the years after the mainshock that formed a cloud of epicenters aligned with the main coseismic rupture trace the local earthquake tomography of the event source shows the correspondence between the fault trace at the surface and a long narrow low velocity zone penetrating vertically into the crust down to a depth of 15 17 km if the three dimensional 3d geometry of the aftershock cloud approximates the ruptured fault plane at first order then the fault is mainly vertical or slightly southwest dipping confirming the right lateral reverse kinematics of the fault compatible with northeast southwest shortening accommodated by a combination of right lateral and thrust faults together with the average surface displacement observed in the field u 1 2 m the surface of the fault plane determined by the aftershocks distribution 80 17 km gives a magnitude m w 7 2 in good agreement with the harvard determination natural exposures produced by the 2003 surface faulting together with previous paleoseismic observations across the primary and secondary earthquake induced features have revealed the occurrence of several strong events magnitudes about 7 8 during the last 5000 yr the characteristics of the altay event suggest that the gorny altay region similar to mongolia and gobi is characterized by large infrequent m 7 8 earthquakes along faults moving at rates of a few mm yr or less

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

radiocarbon redating of contaminated samples from a tropical volcano the mansion series of st kitts west indies heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits in addition to easy contamination of this wood by root systems and soluble humic material because the physical nature of the charcoal varies some samples are more prone to contamination two independent studies of the same volcano mt liamuiga on st kitts in the lesser antilles sometimes using samples from the same carbonized tree yielded a systematic difference in radiocarbon ages an exchange of samples and a re investigation of three physically distinct types of charcoal yielded the following results rare hard dense charcoal lacking contamination which had yielded a spurious age of 2860 years bp was redated at 1845 58 years bp common soft friable charcoal with good cellular structure proved to be susceptible to contamination a field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre treatment was used indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets a previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the mansion series contradicted ages older than 41000 years bp from common friable charcoal in the lower mansion series the soft powdery charcoal was re investigated using a sample collected a few centimeters from the original although field decontamination of this sample was not possible more extensive laboratory treatment yielded an age of ca 43000 years bp again proving that routine laboratory pretreatments are inadequate a revised geochronology for the mansion series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits

asymmetric upwarp of the asthenosphere beneath the baikal rift zone siberia in the summer of 1991 we installed 27 seismic stations about lake baikal siberia aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the baikal rift zone and adjacent regions sixty six teleseismic events with high signal to noise ratio were recorded travel time and q analysis of teleseisms characterize an upwarp of the lithosphere asthenosphere boundary under baikal theoretical arrival times were calculated by using the international association of seismology and physics of the earth s interior 1991 earth model and travel time residuals were found by subtracting computed arrival times from observed ones a three dimensional downward projection inversion method is used to invert the p wave velocity structure with constraints from deep seismic sounding data our results suggest that 1 the lithosphere asthenosphere transition upwarps beneath the rift zone 2 the upwarp has an asymmetric shape 3 the velocity contrast is 4 9 in the asthenosphere 4 the density contrast is 0 6 and 5 the p wave attenuation contrast t is 0 1 s

shear wave splitting and small scale convection in the continental upper mantle the deformation of the upper mantle beneath a collisional belt is key to the dynamics of the belt but this deformation is difficult to observe seismic azimuthal anisotropy manifested by shear wave splitting provides the best geophysical evidence of deformation in the upper mantle here we use observations of shear wave splitting to investigate deformation in the upper mantle beneath the tien shan in central asia we find that underneath most of the tien shan the fast direction of azimuthal anisotropy is roughly parallel to the axis of the belt but it deviates by nearly 90 where the upper mantle is anomalously hot the former relationship previously observed in other collisional belts seems to be usual for this environment the anomalous directions however provide evidence of a rising plume beneath the range suggesting more generally that the along strike flow of the mantle beneath collisional belts is a reflection of thermally driven convection

latest pleistocene and holocene vegetation and climate history inferred from an alpine lacustrine record northwestern yunnan province southwestern china abstract reconstructing past changes of the summer monsoon in southwestern china is key to understanding the paleoclimatic dynamics of the indian summer monsoon southwest monsoon a major tropical system with impacts beyond the region high resolution pollen and conifer stoma data are presented from a sediment core tiancai lake located just below treeline in the hengduan mountains northwestern yunnan province of china these data record changes in vegetation and climate for the latest pleistocene and holocene c the last 12 230 cal yr bp and by comparing these results with the pollen records from the nearby erhai lake and lugu lake a regional climate history in yunnan province can be inferred during the period of 12 230 11 510 cal yr bp open alpine meadow around tiancai lake indicates a relatively cold and dry climate corresponding to the younger dryas cold event yd between 11 510 and 10 000 cal yr bp the vegetation types around tiancai lake changed into picea and abies forest and alpine rhododendron shrubland reflecting increases in the temperature and humidity from 10 000 to 6100 cal yr bp tsuga forest expanded persistently toward tiancai lake indicating further climate changed towards warmer and wetter conditions between 6100 and 3410 cal yr bp tsuga forest was the dominant vegetation type nearest to tiancai lake denoting warm and humid climatic conditions corresponding to the holocene climatic optimum in the northwestern yunnan province tsuga forest in mountains around lugu lake shrank quickly at 3410 cal yr bp reflecting significant decline of humidity since 2930 cal yr bp tsuga forest around tiancai lake shrank gradually indicating a fluctuating decrease of temperature these climatic changes reflect changes of the southwest monsoon namely warm and humid climate indicating strong southwest monsoon cold and dry climate denoting weak southwest monsoon