experiments on conduit flow and eruption behavior of basaltic volcanic eruptions multiphase flow in basaltic volcanic conduits is investigated using analog experiments and theoretical approaches depending on gas supply large gas bubbles gas slugs may rise through basaltic magma in regimes of distinct fluid dynamical behavior ascent of single slugs supplied slugs fed from the gas source during ascent and periodic slug flow an annular flow regime commences at the highest gas supply rates a first set of experiments demonstrates that the growth of gas slugs due to hydrostatic decompression does not affect their ascent velocity and that excess pressure in the slugs remain negligible the applicability of theoretical formulae describing slug ascent velocity as a function of liquid and conduit properties is evaluated in a second set of experiments a third set of experiments with continuous gas supply into a cylindrical conduit are scaled to basaltic conditions over morton eotvos reynolds and froude numbers gas flow rate and liquid viscosity are varied over the whole range of flow regimes to observe flow dynamics and to measure gas and liquid eruption rates foam generation by slug bursting at the surface and partial slug disruption by wake turbulence can modify the bubble content and size distribution of the magma at the transition from slug to annular flow when the liquid bridges between the gas slugs disappear pressure at the conduit entrance drops by 60 from the hydrostatic value to the dynamic flow resistance of the annular flow which may trigger further degassing in a stored magma to maintain the annular flow regime until the gas supply is exhausted and the eruption ends abruptly magma discharge may also terminate when magma ascent is hindered by wall friction in long volcanic conduits and the annular gas flow erodes all magma from the conduit supplied slugs are found to reach much higher rise velocities than unsupplied slugs and to collapse to turbulent annular flow upon bursting at the surface a fourth set of experiments uses a conduit partially blocked by built in obstacles providing traps for gas pockets once gas pockets are filled rising gas slugs deform but remain intact as they move around obstacles without coalescence or significant velocity changes bursting of bubbles coalescing with trapped gas pockets causes pressure signals at least 3 orders of magnitude more powerful than gas pocket oscillation induced by passing liquid our experiments suggest a refined classification of strombolian and hawaiian eruptions according to time dependant behavior into sporadically pulsating lava fountains driven by stochastic rise of single slugs periodically pulsating lava fountains resulting from slug flow and quasi steady lava fountains oscillating at the frequency of annular flow turbulence

broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

viscous plugging can enhance and modulate explosivity of strombolian eruptions strombolian activity is common in low viscosity volcanism it is characterised by quasi periodic short lived explosions which whilst typically weak may vary greatly in magnitude the current paradigm for a strombolian volcanic eruption postulates a large gas bubble slug bursting explosively after ascending a conduit filled with low viscosity magma however recent studies of pyroclast textures suggest the formation of a region of cooler degassed more viscous magma at the top of the conduit is a common feature of strombolian eruptions following the hypothesis that such a rheological impedance could act as a viscous plug which modifies and complicates gas escape processes we conduct the first experimental investigation of this scenario we find that 1 the presence of a viscous plug enhances slug burst vigour 2 experiments that include a viscous plug reproduce and offer an explanation for key phenomena observed in natural strombolian eruptions 3 the presence and extent of the plug must be considered for the interpretation of infrasonic measurements of strombolian eruptions our scaled analogue experiments show that as the gas slug expands on ascent it forces the underlying low viscosity liquid into the plug creating a low viscosity channel within a high viscosity annulus the slug s diameter and ascent rate change as it enters the channel generating instabilities and increasing slug overpressure when the slug reaches the surface a more energetic burst process is observed than would be the case for a slug rising through the low viscosity liquid alone fluid dynamic instabilities cause low and high viscosity magma analogues to intermingle and cause the burst to become pulsatory the observed phenomena are reproduced by numerical fluid dynamic simulations at the volcanic scale and provide a plausible explanation for pulsations and the ejection of mingled pyroclasts observed at stromboli and elsewhere

crustal and upper mantle structure of stable continental regions in north america and northern europe from an analysis of many seismic profiles across the stable continental regions of north america and northern europe the crustal and upper mantle velocity structure is determined analysis procedures include ray theory calculations and synthetic seismograms computed using reflectivity techniques the p wave velocity structure beneath the canadian shield is virtually identical to that beneath the baltic shield to a depth of at least 800 km two major layers with a total thickness of about 42 km characterize the crust of these shield regions features of the upper mantle of these regions include velocity discontinuities at depths of about 74 km 330 km 430 km and 700 km a 13 km thick p wave low velocity channel beginning at a depth of about 94 km is also present

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

chaotic subduction like downflows in a spherical model of convection in the earth s mantle numerical models of three dimensional nonlinear thermal convection of very viscous fluids have recently been developed in rectangular1 4 and spherical5 12 geometries as analogues of convection in the earth s mantle here we describe model calculations for a compressible fluid in a three dimensional spherical shell with 80 of the surface heat flow generated within the model mantle in agreement with estimates for the earth s mantle13 the rayleigh number and the numerical resolution for these calculations are greater than those of our previous studies9 10 of internally heated convection in a spherical shell our numerical solutions are strongly chaotic with surface planforms dominated by long curvilinear downflows reminiscent of the descending slabs in the earth s mantle although analogy to the earth s mantle is necessarily imperfect owing to for example the absence of variable viscosity and rheology and hence of lithospheric plates our results suggest that descending slabs play an important part in driving mantle convection and that their chaotic evolution may influence the spatial and temporal behaviour of plates and thus the dispersal and aggregation of continents

degassing at low magma viscosity volcanoes quantifying the transition between passive bubble burst and strombolian eruption abstract at many volcanoes low magma viscosities allow persistent degassing over a range of styles from explosive strombolian activity to gas puffing and passive degassing it is generally accepted that strombolian eruptions reflect the bursting of large bubbles gas slugs at the magma surface and that relatively quiescent puffing indicates the presence of significantly smaller bubbles or slugs here we address this qualitative range and derive a dimensionless parameter pslim to quantify and distinguish different regimes of burst vigour for pslim 1 passive activity is anticipated and measurable parameters such as infrasonic amplitude will be small for pslim 1 bursting slugs will be energetic and surface effects are anticipated to increase with increasing pslim various physical parameters recorded during laboratory experiments and simulated through numerical models are shown to demonstrate the same trends when parameterised by pslim hence pslim provides a straightforward relationship between changes in measurable surface effects and the system s subsurface physical parameters and for energetic activity of a particular system burst effects are shown to be proportional to the square root of the gas mass involved effect magnitudes are also shown to be a function of atmospheric pressure and application of pslim parameterisation to planetary scenarios produces results in line with our current understanding of planetary volcanism

terrestrial heat flow in botswana and namibia we report terrestrial heat flow measurements from 25 new sites in botswana and namibia twelve sites from the archean kaapvaal zimbabwe craton and the limpopo belt have a mean of 47 4 mw m 2 standard error of the mean but show a trend of increasing heat flow from less than 40 mw m 2 within the cratonic nucleus to about 60 mw m 2 at its edge thirteen sites in the proterozoic and pan african mobile belts that surround the craton have a mean of 66 3 mw m 2 increasing from about 60 mw m 2 at the cratonic margin to more than 70 mw m 2 several hundred kilometers away radiogenic heat production in near surface basement rocks was measured for four sites on the craton and seven sites in the mobile belts the limited heat flow heat production data from the craton are insufficient to establish a correlation heat flow and heat production data from the mobile belts when combined with published data from six sites in zambia exhibit a linear trend with an intercept of 50 3 mw m 2 and a slope of 5 5 1 1 km some but not all of the observed difference in surface heat flow between the mobile belts and the cratonic nucleus may be due to differences in crustal heat production that part of the regional variation in surface heat flow which originates at greater depths implies a fundamental difference in thermal structure of the lithosphere between the craton and the mobile belts in southern africa

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

dynamics of mild strombolian activity on mt etna abstract here we report the first measurements of gas masses released during a rare period of strombolian activity at the bocca nuova crater mt etna sicily uv camera data acquired for 195 events over an 27 minute period 27th july 2012 indicate erupted so2 masses ranging from 0 1 to 14 kg per event with corresponding total gas masses of 0 1 to 74 kg thus the activity was characterised by more frequent and smaller events than typically associated with strombolian activity on volcanoes such as stromboli events releasing larger measured gas masses were followed by relatively long repose periods before the following burst a feature not previously reported on from gas measurement data if we assume that gas transport within the magma can be represented by a train of rising gas pockets or slugs then the high frequency of events indicates that these slugs must have been in close proximity in this case the longer repose durations associated with the larger slugs would be consistent with interactions between adjacent slugs leading to coalescence a process expedited close to the surface by rapid slug expansion we apply basic modelling considerations to the measured gas masses in order to investigate potential slug characteristics governing the observed activity we also cross correlated the acquired gas fluxes with contemporaneously obtained seismic data but found no relationship between the series in line with the mild form of manifest explosivity

late glacial climatic changes in eastern france lake lautrey from pollen lake levels and chironomids high temporal resolution analyses of pollen chironomid and lake level records from lake lautrey provide multi proxy quantitative estimates of climatic change during the late glacial period in eastern france past temperature and moisture parameters were estimated using modern analogues and plant functional types transfer function methods for three pollen records obtained from different localities within the paleolake basin the comparison of these methods shows that they provide generally similar climate signals with the exception of the bolling comparison of pollen and chironomid based temperature of the warmest month reconstructions generally agree except during the bolling major abrupt changes associated with the oldest dryas bolling allerod younger dryas and the younger dryas preboreal transitions were quantified as well as other minor fluctuations related to the cold events e g preboreal oscillation the temperature of the warmest month increased by not vert similar5 c at the start of bolling and by 1 5 3 c at the onset of the holocene while it fell by ca 3 to 4 c at the beginning of younger dryas the comparative analysis of the results based on the three lautrey cores have highlighted significant differences in the climate reconstructions related to the location of each core underlining the caution that is needed when studying single cores not taken from deepest part of lake basins

modelling the rapid near surface expansion of gas slugs in low viscosity magmas the ascent of large gas bubbles slugs in vertical cylindrical conduits and low viscosity magmas is simulated using 1d mathematical and 3d computational fluid dynamic cfd models following laboratory evidence the 1d model defines a constant rise velocity for the slug base and allows gas expansion to accelerate the slug nose through the overlying fluid during ascent the evolution of rapidly expanding gas slugs observed in laboratory experiments is reproduced well and at volcano scales predicts at surface overpressures of several atmospheres without requiring any initial overpressure at depth the near surface dynamics increase slug nose velocities through the overlying magma by a factor of c 2 5 and the gas expansion results in pre burst magma surface velocities of c 35m s21 to examine pressure distributions and the forces exerted on a conduit 3d cfd simulations were carried out at volcano scales the vertical single forces during final slug ascent to the surface are c 106 n two orders of magnitude smaller than those associated with verylong period seismic events at stromboli this supports a previous interpretation of these events in which they are generated by gas slugs flowing through changes in conduit geometry rather than being the direct result of slug eruption processes

reconstructing the distribution of the paleobiome types in the three river headwaters region in china from the middle holocene this study examined the spatial and temporal patterns of the paleobiome types in the three river headwaters region trhr sanjiangyuan in china from the middle holocene i e 6000 bp existing st

anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose δ13c of hani northeast china abstract significant changes in the global atmospheric and oceanic circulation system occurred during the younger dryas cold period several researchers have demonstrated a weakening of intensity of the indian ocean summer monsoon during that period however the exact characteristics of the east asian summer monsoon still remain vague here we present a late glacial precipitation proxy record of the east asian summer monsoon based on the peat cellulose 13 c found in hani northeast china both the peat cellulose record and a pollen record from lake sihailongwan sediment indicate an abrupt increase in precipitation in the region during the younger dryas period these results support the occurrence of wet conditions in the north and of dry conditions in the south of the chinese mainland during that period by examining the activity of the east asian summer monsoon on an interannual timescale we propose a theory for the anomalous precipitation distribution that we attribute to the occurrence of an el nino like phenomenon in the equatorial pacific ocean during the younger dryas in this case the intensity of the western pacific subtropical high may strengthen and its position over the western pacific ocean may move northward this could cause an enhancement of the east asian summer monsoon and migration of a monsoonal rainbelt towards the northern region of the chinese mainland resulting in a precipitation distribution of wet conditions in the north and dry conditions in the south therefore this anomalous rainfall distribution should be considered to indicate the strengthening of the east asian summer monsoon in anti phase with the indian ocean summer monsoon that weakened during the same period this agrees with the previously revealed anti phase variations of the two monsoons during the ice rafted debris cold events of the north atlantic ocean it appears that in relation to the abrupt temperature drop in the northern hemisphere on centennial to millennial time scales anti phase variations of the two asian summer monsoons occurred

holocene land cover changes on the tibetan plateau information on changes in land surface features on the tibetan plateau tp during the holocene may help our understanding of the forcing of monsoonal circulation we analyse vegetation changes during the last 9000 years from pollen records of four lakes hurleg lake in the qaidam basin qinghai lake on the northeastern tp zigetang lake on the central tp and koucha lake on the eastern tp which represent different regions and vegetation types on the plateau today a set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the holocene pollen records four types of numerical analyses are used to infer different aspects of pollen stratigraphical and inferred vegetation changes biome reconstruction ordination to infer palynological compositional turnover rate of assemblage change analysis and a pollen lai leaf area index transfer function our results show strong regional differences in inferred vegetation change in

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

lessons learned from oxygen isotopes in modern precipitation applied to interpretation of speleothem records of paleoclimate from eastern asia abstract variability in oxygen isotope ratios collected from speleothems in chinese caves is often interpreted as a proxy for variability of precipitation summer precipitation seasonality of precipitation and or the proportion of 18o to 16o of annual total rainfall that is related to a strengthening or weakening of the east asian monsoon and in some cases to the indian monsoon we use modern reanalysis and station data to test whether precipitation and temperature variability over china can be related to changes in climate in these distant locales we find that annual and rainy season precipitation totals in each of central china south china and east india have correlation length scales of 500 km shorter than the distance between many speleothem records that share similar long term time variations in 18o values thus the short distances of correlation do not support though by themselves cannot refute the idea that apparently synchronous variations in 18o values at widely spaced 500 km caves in china are due to variations in annual precipitation amounts we also evaluate connections between climate variables and 18o values using available instrumental measurements of 18o values in precipitation these data from stations in the global network of isotopes in precipitation gnip show that monthly 18o values generally do not correlate well with either local precipitation amount or local temperature and the degree to which monthly 18o values do correlate with them varies from station to station for the few locations that do show significant correlations between 18o values and precipitation amount we estimate the differences in precipitation amount that would be required to account for peak to peak differences in 18o values in the speleothems from hulu and dongge caves assuming that 18o scales with the monthly amount of precipitation or with seasonal differences in precipitation insofar as the present day relationship between 18o values and monthly precipitation amounts can be applied to past conditions differences of at least 50 in mean annual precipitation would be required to explain the 18o variations on orbital time scales which are implausibly large and inconsistent with published gcm results similarly plausible amplitudes of seasonal cycles in amounts or in seasonal variations in 18o values can account for less than half of the 4 5 difference between glacial and interglacial 18o values from speleothems in china if seasonal cycles in precipitation account for the amplitudes of 18o values on paleoclimate timescales they might do so by extending or contracting the durations of seasons a frequency modulation of the annual cycle but not by simply varying the amplitudes of the monthly rainfall amounts or monthly average 18o values amplitude modulation allowing that several processes can affect seasonal variability in isotopic content we explore the possibility that one or more of the following processes contribute to variations in 18o values in chinese cave speleothems different source regions of the precipitation which bring different values of 18o in vapor different pathways between the moisture source and the paleorecord site along which exchange of 18o between vapor surface water and condensate might differ a different mix of processes involving condensation and evaporation within the atmosphere or different types of precipitation each may account for part of the range of 18o values revealed by speleothems and each might contribute to seasonal differences between past and present that do not scale with monthly or even seasonal precipitation amounts

a six hundred year annual minimum temperature history for the central tibetan plateau derived from tree ring width series the recent unprecedented warming found in different regions has aroused much attention in the past years how temperature has really changed on the tibetan plateau tp remains unknown since very limited high resolution temperature series can be found over this region where large areas of snow and ice exist herein we develop two juniperus tibetica kom tree ring width chronologies from different elevations we found that the two tree ring series only share high frequency variability correlation response function and partial correlation analysis indicate that prior year annual january december minimum temperature is most responsible for the higher belt juniper radial growth while more or less precipitation signal is contained by the tree ring width chronology at the lower belt and is thus excluded from further analysis the tree growth climate model accounted for 40 of the total variance in actual temperature during the common period 1957 2010 the detected temperature signal is further robustly verified by other results consequently a six century long annual minimum temperature history was firstly recovered for the yushu region central tp interestingly the rapid warming trend during the past five decades is identified as a significant cold phase in the context of the past 600 years the recovered temperature series reflects low frequency variability consistent with other temperature reconstructions over the whole tp region furthermore the present recovered temperature series is associated with the asian monsoon strength on decadal to multidecadal scales over the past 600 years

reply to the comment by mike r james et al on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity 1 the current paradigm for normal eruptions at stromboli volcano and strombolian type activity more generally posits that each eruption represents the burst of a large pocket of gas commonly referred to as slug at the free surface of themagma column this slug model has been investigated and refined primarily through analog fluid dynamical experiments at the laboratory scale there is no doubt that these studies have advanced our understanding of strombolian eruptions considerably however given the very fundamental status of the slug model for our current thinking about strombolian type eruptions it is paramount to carefully assess all underlying assumptions of the model one important uncertainty lies in the scaling behavior of the observed slug dynamics in the laboratory scale invariance requires all nondimensional numbers to be identical but it is generally not feasible to match all of the nondimensional numbers characterizing the volcanic conduit exactly in a laboratory experiment numerical computations offer a means of directly comparing slug dynamics at drastically different scales suckale et al 2010b we find that the very large slugs in volcanic conduits are more prone to dynamic instabilities and breakup than the comparatively small slugs in laboratory settings this finding in itself does of course not disprove the slug model it merely points to potentially important differences in slug stability at volcanic scales as opposed to laboratory scales 2 being careful and critical of the errors and interpretations of numerical simulations is important similarly the appropriateness of laboratory analogs must also be examined james et al 2011 raise a valid point asking whether our simulations are capable of reproducing stable slug rise in water figure 1 shows a computation performed for the experimental parameters provided by james et al 2011 in agreement with the analog experiments we do indeed find that this slug rises stably in water i e the slug ascends buoyantly within the conduit without experiencing catastrophic breakup as defined by suckale et al 2010b thus the experiments by james et al 2011 do not appear to contradict our computations we also reproduce computationally stable slug flow at finite reynolds number re shown in the experiment specified by jaupart and vergniolle 1989 suckale et al 2010b it is worth noting that in both cases the set of nondimensional numbers characterizing the experiment are not identical to those thought to be representative of the volcanic conduit and thus potential differences in the fluid dynamical behavior are not unexpected 3 that we observe stable slugs in water but not in magma supports an argument raised by james et al 2011 namely that re is an insufficient parameter for comparing slug dynamics at different spatial scales we welcome their discussion of the drawbacks of using a single re to describe slugs focusing on re to characterize our computations was a purely pragmatic decision first re is commonly used for the purpose of comparing fluid dynamical computations at different scales second we were able to use estimates for re characterizing strombolian slugs based on observational data measured at stromboli vergniolle and brandeis 1996 third we observed a correlation between re and breakup within the regime we investigated which is not unexpected since re is an indirect measure of the size of a gas bubble or slug that being said a more comprehensive set of nondimensional numbers is undoubtedly needed to evaluate scaling behavior of slugs for different fluid dynamical regimes including nondimensional criteria that capture the wavelength of potential interface instabilities in relation to the curvature of the interface and the time scale associated with instability growth to the time scale associated with advection of the instability along the interface our study is a first step toward gaining a better understanding of slug stability 4 from a theoretical point of view very large and dynamic gas volumes are not expected to be indefinitely stable the light gas slug moves underneath a column of very heavy magma and this unstable density stratification is prone to the formation of rayleigh taylor instabilities at the essentially flat upper surface of the slug grace et al 1978 developed a semiempirical rationalization of this process that affords rough estimates of maximum stable sizes as listed in table 1 of suckale et al 2010b the appeal of this model lies primarily in its simplicity but this very simplicity also department of earth atmospheric and planetary sciences massachusetts institute of technology cambridge massachusetts usa department of mathematics and statistics mcgill university montreal quebec canada

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

thermal seismic and infrasonic evidences of variable degassing rates at stromboli volcano abstract during june 1999 we measured the amplitude and rate number of events per second at which gas exited the vent at stromboli volcano as discrete gas bursts or puffs this allowed us to identify two styles of gas burst puffing activity the first is characterized by frequent rapidly rising puffs the second by less frequent slowly rising puffs each style persisted over 5 40 min long durations and was associated with a high and low number of strombolian explosions per hour respectively each period was also associated with characteristic delay times between the arrival of the infrasonic and thermal signals during strombolian explosions the delays were longer during vigorous puffing periods to explain our observations we propose a model in which the degassing process cycles between vigorous and weak degassing phases during vigorous degassing phases bubble layers ascend the conduit at a frequency of 0 5 1 0 s 1 this high degassing level reflects a gas rich magma column and leads to an increased rate in the formation of shallow foams and hence an increase in puffing and explosive activity as well as a higher free surface level and or gas jet velocity during weak phases bubble layers ascend the conduit at a reduced frequency of 0 2 0 3 s 1 during such times the magma column is poor in gas this leads to a decreased rate of foam layer formation and hence a reduction in puffing and explosive activity as well as a lower free surface level and or gas jet velocity variations in puffing activity can thus be used to track changes in the rate at which the shallow system is supplied by fresh gas rich magma our observations indicate that the two degassing styles last from 5 to 40 min and that the switch from one to the other occurs over a matter of minutes

comment on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity by j suckale b h hager l t elkins tanton and j c nave

the first second of volcanic eruptions from the erebus volcano lava lake antarctica energies pressures seismology and infrasound 1 we describe a multiparameter experiment at erebus volcano antarctica employing doppler radar video acoustic and seismic observations to estimate the detailed energy budget of large up to 40 m diameter bubble bursts from a persistent phonolite lava lake these explosions are readily studied from the crater rim at ranges of less than 500 m and present an ideal opportunity to constrain the dynamics and mechanism of magmatic bubble bursts that can drive strombolian and hawaiian eruptions we estimate the energy budget of the first second of a typical erebus explosion as a function of time and energy type we constrain gas pressures and forces using an analytic model for the expansion of a gas bubble above a conduit that incorporates conduit geometry and magma and gas parameters the model consistent with video and radar observations invokes a spherical bulging surface with a base diameter equal to that of the lava lake the model has no ad hoc free parameters and geometrical calculations predict zenith height velocity and acceleration during shell expansion during explosions the energy contained in hot overpressured gas bubbles is freed and partitioned into other energy types where by far the greatest nonthermal energy component is the kinetic and gravitational potential energy of the accelerated magma shell 10 9 j seismic source energy created by explosions is estimated from radar measurements and is consistent with source energy determined from seismic observations for the generation of the infrasonic signal a dual mechanism incorporating a terminally disrupted slug is proposed which clarifies previous models and provides good fits to observed infrasonic pressures a new and straightforward method is presented for determining gas volumes from slug explosions at volcanoes from remote infrasound recordings

new constraints on transient lower mantle rheology and internal mantle buoyancy from glacial rebound data a model of mantle rheology which has an explicit transient component of its relaxation spectrum is shown to reconcile two apparently conflicting inferences of lower mantle viscosity if recent analyses of isostatic geoid anomalies are correct in requiring a large increase of viscosity with depth then the weak viscosity stratification demanded by postglacial rebound data implies the importance of such rheological behaviour at least in the earth s lower mantle

the role of large bubbles detected from acoustic measurements on the dynamics of erta ale lava lake ethiopia the activity at the surface of the lava lake on erta ale volcano ethiopia shows that large bubbles are regularly breaking at a fixed position on the lava lake this is also where the small lava fountains are sometimes produced since this location is likely to be directly above the volcanic conduit feeding the lava lake we have done continuous measurements between march 22 and 26 2003 to understand the degassing of a volcano in permanent activity the bubble size has been first estimated from videos which once combined with the acoustic pressure can constrain the source of the sound the gas volume and overpressure stayed roughly constant between 36 700 m3 and 4 103 1 8 104 pa respectively simultaneous thermal measurements showed regular peaks which occurred when the crust was broken by a large bubble hence gave a direct indication on the typical return time between the bubbles 1 h these spherical cap bubbles had a high reynolds number 4600 20000 therefore a wake periodically unstable formed and detached from the bubble bottom the bubbly wake if the detachment occurs close to the surface can explain the duration of lava fountains measured on the videos the periodic arrival of bubbly wakes which mostly detach from the driving spherical cap within the lava lake could explain the absence of cooling at erta ale erebus antartica villarica chile and nyiragongo democratic republic of congo without invoking a convective downflow of magma in the conduit as previously done

the spatial temporal patterns of asian summer monsoon precipitation in response to holocene insolation change a model data synthesis highlights slice and transient simulations of holocene climate change were performed spatial temporal patterns of holocene asian summer precipitation are investigated a tripole pattern of summer precipitation can be seen over monsoonal asia insolation change is a key factor for holocene asian summer monsoon change internal feedbacks are important to holocene asian summer precipitation changes abstract paleoclimate proxy records of precipitation effective moisture show spatial temporal inhomogeneous over asian monsoon and monsoon marginal regions during the holocene to investigate the spatial differences and diverging temporal evolution over monsoonal asia and monsoon marginal regions we conduct a series of numerical experiments with an atmosphere ocean sea ice coupled climate model the kiel climate model kcm for the period of holocene from 9 5 ka bp to present 0 ka bp the simulations include two time slice equilibrium experiments for early holocene 9 5 ka bp and present day 0 ka bp respectively and one transient simulation ht using a scheme for model acceleration regarding to the earth s orbitally driven insolation forcing for the whole period of holocene from 9 5 to 0 ka bp the simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal asia as depicted by the first modes of empirical orthogonal function eof1 of h0k and h9k the transient simulation ht exhibits a wave train pattern in the summer precipitation across the asian monsoon region associated with a gradually decreased trend in the strength of asian summer monsoon as a result of the response of asian summer monsoon system to the holocene orbitally forced insolation change both the synthesis of multi proxy records and model experiments confirm the regional dissimilarity of the holocene optimum precipitation effective moisture over the east asian summer monsoon region monsoon marginal region and the westerly dominated areas suggesting the complex response of the regional climate systems to holocene insolation change in association with the internal feedbacks within climate system such as the air sea interactions associated with the el nino southern oscillation enso and shift of the intertropical convergence zone itcz in the evolution of asian summer monsoon during the holocene

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

characteristics of puffing activity revealed by ground based thermal infrared imaging the example of stromboli volcano italy puffing i e the frequent 1 s ca release of small 0 1 10 m3 over pressurized pockets of magmatic gases is a typical feature of open conduit basaltic volcanoes worldwide despite its non trivial contribution to the degassing budget of these volcanoes and its recognized role in volcano monitoring detection and metering tools for puffing are still limited taking advantage of the recent developments in high speed thermal infrared imaging we developed a specific processing algorithm to detect the emission of individual puffs and measure their duration size volume and apparent temperature at the vent as a test case we applied our method at stromboli volcano italy studying snapshots of 1 min collected in the years 2012 2013 and 2014 at several vents in all 3 years puffing occurred simultaneously at three or more vents with variable features at the scale of the single vent a direct relationship links puff temperature and radius suggesting that the apparent temperature is mostly a function of puff thickness while the real gas temperature is constant for all puffs once released in the atmosphere puffs dissipate in less than 20 m on a broader scale puffing activity is highly variable from vent to vent and year to year with a link between average frequency temperature and volume from 136 puffs per minute 600 k above ambient temperature 0 1 m3 and the occasional ejection of pyroclasts to 20 puffs per minute 3 k above ambient 20 m3 and no pyroclasts frequent small hot puffs occur at random intervals while as the frequency decreases and size increases an increasingly longer minimum interval between puffs up to 0 5 s appears these less frequent and smaller puffs also display a positive correlation between puff volume and the delay from the previous puff our results suggest an important role of shallow bubble coalescence in controlling puffing activity the smaller and more frequent puffing at hotter vents is in agreement with the rapid rise of small gas pockets with only limited coalescence while slower rise allowing more time for coalescence leads to larger but less frequent puffing at colder vents this link between puffing style and vent thermal state points to a feedback between gas flux and magma temperature and viscosity where higher gas flux stirs and heats the magma which by getting less viscous becomes a preferential way for bubble rise such a link has implications for the monitoring of the state of the shallow conduit at open vent volcanoes as well as for determination of their total gas budget relevant for hazard forecast and environmental studies

quantitative climate and vegetation trends since the late glacial on the northeastern tibetan plateau deduced from koucha lake pollen spectra quantitative information on vegetation and climate history from the late glacial holocene on the tibetan plateau is extremely rare here we present palynological results of a 4 30 m long sediment record collected from koucha lake in the bayan har mountains northeastern tibetan plateau vegetation change has been traced by biomisation ordination of pollen data and calculation of pollen ratios the application of a pollen climate calibration set from the eastern tibetan plateau to koucha lake pollen spectra yielded quantitative climate information the area was covered by alpine desert steppe characteristic of a cold and dry climate with 50 less precipitation than today between 16 700 and 14 600 cal yr bp steppe vegetation warm 1 c higher than today and wet conditions prevailed between 14 600 and 6600 cal yr bp these findings contradict evidence from other monsoon influenced areas of asia where the early holocene is thought to have been moist low effective moisture on the northeastern tibetan plateau was likely due to high temperature and evaporation even though precipitation levels may have been similar to present day values the vegetation changed to tundra around 6600 cal yr bp indicating that wet and cool climate conditions occurred on the northeastern tibetan plateau during the second half of the holocene

geoid effects in a convecting system with lateral viscosity variations the geoid signal and the flow patterns of two dimensional steady state convection models with exponential temperature and depth dependent viscosity are compared with results for an equivalent stratified viscosity structure in analogy to richards and hager 1989 the latter are computed by a dynamic response approach the flow fields obtained with this approach are quite different from the full solution the geoid signals are similar but the amplitudes differ significantly the differences are analysed in the horizontal wavenumber domain and in the spatial domain they may lead to an overestimation of the viscosity contrast of the earth s mantle derived by modeling the earth s geoid with dynamic response functions there are implications on the interpretation of observed geoid anomalies in terms of up or downwelling flow structures

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

dynamic surface topography a new interpretation based upon mantle flow models derived from seismic tomography the very long wavelength i e in the degree range l 1 8 dynamic topography at the earth s surface estimated by isostatic reduction of the observed topography is shown to be in good agreement with the topography predicted by a model of viscous flow in the mantle this flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large scale seismic shear velocity heterogeneity in the mantle our estimate and prediction of the long wavelength dynamic surface topography reveals significant depressions 2 3 km of the continental shields relative to their hydrostatic reference positions

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

holocene vegetation history precipitation changes and indian summer monsoon evolution documented from sediments of xingyun lake south west china we present a pollen based precipitation reconstruction and multi proxy records from a 485 cm long sequence from a sediment core from xingyun lake yunnan plateau south west china which depicts the evolution of the indian summer monsoon ism during the last 8500 years pollen and other palaeoenvironmental records document several stages of vegetation history and climate change the warmest and wettest climate in the xingyun lake catchment occurred before 5500 cal a bp and subsequently the climate became gradually drier after 2000 cal a bp the regional environmental conditions became unstable and a wet medieval warm period is probably recorded our reconstruction of the ism is similar to that portrayed by holocene speleothem o 18 records from southern china but is distinctly different from the east asian summer monsoon easm evolution which features a mid holocene maximum our results support the hypothesis that the ism and easm evolved asynchronously during the holocene and imply that the chinese speleothem o 18 records from southern china may principally reflect changes in moisture source from the indian monsoon domain and thus record the history of the ism rather than the easm

volcano infrasonic signals and magma degassing first order experimental insights and application to stromboli we demonstrate the rise and expansion of a gas slug as a fluid dynamic source mechanism for infrasonic signals generated by gas puffing and impulsive explosions at stromboli the fluid dynamics behind the rise expansion and burst of gas slugs in the confines of an experimental tube can be characterised into different regimes passive expansion occurs for small gas masses where negligible dynamic gas over pressure develops during bubble ascent and prior to burst meniscus oscillation forms an important infrasonic source with increasing gas mass a transition regime emerges where dynamic gas over pressure is significant for larger gas masses this regime transforms to fully explosive behaviour where gas over pressure dominates as an infrasonic source and bubble bursting is not a critical factor the rate of change of excess pressure in the experimental tube was used to generate synthetic infrasonic waveforms qualitatively the waveforms compare well to infrasonic waveforms measured from a range of eruptions at stromboli assuming pressure continuity during flow through the vent and applying dimensionless arguments from the first order experiments allows estimation of eruption metrics from infrasonic signals measured at stromboli values of bubble length gas mass and over pressure calculated from infrasonic signals are in excellent agreement with those derived by independent means for eruptions at stromboli therefore providing a method of estimating eruption metrics from infrasonic measurement

an analytical model for gas overpressure in slug driven explosions insights into strombolian volcanic eruptions strombolian eruptions common at basaltic volcanoes are mildly explosive events that are driven by a large bubble of magmatic gas a slug rising up the conduit and bursting at the surface gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals we present a theoretical investigation of slug overpressure based on magma static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts slug length at burst and the depth at which the burst process begins we find that burst overpressure is controlled by two dimensionless parameters v which represents the amount of gas in the slug and a which represents the thickness of the film of magma that falls around the rising slug burst overpressure increases nonlinearly as v and a increase we consider two eruptive scenarios 1 the standard model in which magma remains confined to the vent during slug expansion and 2 the overflow model in which slug expansion is associated with lava effusion as occasionally observed in the field we find that slug overpressure is higher for the overflow model by a factor of 1 2 2 4 applying our model to typical strombolian eruptions at stromboli we find that the transition from passive degassing to explosive bursting occurs for slugs with volume 24 230 m 3 depending on magma viscosity and conduit diameter and that at burst a typical strombolian slug with a volume of 100 1000 m 3 has an internal gas pressure of 1 5 bars and a length of 13 120 m we compare model predictions with field data from stromboli for low energy puffers mildly explosive strombolian eruptions and the violently explosive 5 april 2003 paroxysm we find that model predictions are consistent with field observations across this broad spectrum of eruptive styles suggesting a common slug driven mechanism we propose that paroxysms are driven by unusually large slugs large v

gas slug ascent in a stratified magma implications of flow organisation and instability for strombolian eruption dynamics the canonical strombolian paradigm of a gas slug ascending and bursting in a homogeneous low viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses evidence points to the existence of high viscosity magma at the top of the conduit of strombolian type volcanoes acting as a plug here new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit end member scenarios of a tube fully filled with either high or low viscosity liquid bracket three main flow configurations 1 a plug sufficiently large to fully accommodate an ascending gas slug 2 a plug that can accommodate the intrusion of low viscosity liquid driven by the gas expansion but not all the slug volume so the slug bursts with the nose in the plug whilst the base is still in the low viscosity liquid 3 gas expansion is sufficient to drive the intrusion of low viscosity liquid through the plug with the slug bursting in the low viscosity layer emplaced dynamically above the plug we show that the same flow configurations are viable at volcanic scale through a new experimentally validated 1d model and 3d computational fluid dynamic simulations applied to stromboli our results demonstrate that the key parameters controlling the transition between each configuration are gas volume plug thickness and plug viscosity the flow processes identified include effective dynamic narrowing and widening of the conduit instabilities within the falling magma film transient partial and complete blockage of the conduit and slug disruption these complexities influence eruption dynamics and vigour promoting magma mingling and resulting in pulsatory release of gas

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

constraints on the late quaternary glaciations in tibet from cosmogenic exposure ages of moraine surfaces abstract this contribution provides new constraints on the timing of tibetan glacial recessions recorded by the abandonment of moraines we present cosmogenic radionuclide 10 be inventories at 17 sites in southern and western tibet 32 crests 249 samples and infer the range of permissible emplacement ages based on these analyses individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10 be abundance we consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages 1 erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age and 2 erosion progressively exposes large boulders with little prior exposure and so the oldest sample age records the minimum moraine emplacement age we found that depending on the scenario chosen the moraine emplacement age can vary by 50 for 100 ka old samples we consider two scaling models for estimating the production rates of 10 be in tibet which has an important although lesser effect on inferred moraine ages while the data presented herein effectively increase the database of sample exposure ages from tibet by 20 we find that uncertainties related to the interpretation of the 10 be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies a reanalysis of published data from moraines throughout tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the tibetan moraine age database thus when viewed in a similar way with other samples collected from this area uncertainties within moraine exposure ages obscure attribution of tibetan glacial advances to temperature minima or precipitation maxima our work suggests that more reliable chronologies of tibetan glaciations will come from improvements in production rate models for this portion of the world as well as a better understanding of the processes that form and modify these geomorphic surfaces

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 1 origin of strombolian activity the 1999 basaltic eruption of shishaldin volcano alaska usa displayed both classical strombolian activity and an explosive subplinian plume strombolian activity at shishaldin occurred in two major phases following the subplinian activity in this paper we use acoustic measurements to interpret the strombolian activity acoustic measurements of the two strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column results show that the bubble does not burst at its maximum radius as expected if the liquid film is stretched beyond its elasticity but bursting occurs after one cycle of vibration as a consequence of an instability of the air magma interface close to the bubble minimum radius during each strombolian period estimates of bubble length and overpressure are calculated using an alternate method based on acoustic power we estimate gas velocity to be 30 60 m s in very good agreement with synthetic waveforms although there is some variation within these parameters bubble length and overpressure for the first strombolian phase are found to be c82f11 m and 0 083 mpa for the second strombolian phase bubble length and overpressure are estimated at 24f12 m and 0 15 mpa for the first 17 h after which bubble overpressure shows a constant increase reaching a peak of 1 4 mpa just prior to the end of the second strombolian phase this peak suggests that at the time the magma in the conduit may contain a relatively large concentration of small bubbles maximum total gas volume and gas fluxes at the surface are estimated to be 3 3 10 7 and 2 9 10 3 m 3 s for the first phase and 1 0 10 8 and 2 2 10 3 m 3 s for the second phase this gives a mass flux of 1 2 10 3 and 8 7 10 2 kg s respectively for the first and the second strombolian phases

a global analysis of heat flow from precambrian terrains implications for the thermal structure of archean and proterozoic lithosphere previous studies of heat flow from precambrian terrains have yielded two different relationships a global temporal relationship between heat flow and tectonic age and a regional spatial relationship between heat flow and the proximity of archean cratons we analyze heat flow from tectonically stable precambrian terrains worldwide to address questions associated with these two heat flow patterns 1 is the spatial relationship a global pattern 2 do the two heat flow relationships have a common underpinning in answer to the first question our data analysis reveals a widespread spatial pattern between heat flow and the proximity of archean cratons which is characterized by low heat flow in archean cratons and proterozoic terrains adjacent to cratonic margins and higher heat flow in proterozoic terrains that are more than a few hundred kilometers from a craton to address the second question we examine three previous interpretative models of precambrian heat flow 1 simple cooling of a thermal boundary layer 2 thicker lithosphere in archean terrains than in proterozoic and 3 greater heat production in proterozoic crust than in archean model 1 predicts essentially no change in heat flow in terrains older than 1 5 ga and therefore does not likely provide a common underpinning for the precambrian heat flow patterns models 2 and 3 when combined with the special structural configuration of sutures can independently yield both the spatial and temporal heat flow distributions and thus alone or together may be considered candidates to explain the precambrian heat flow patterns however thermal models of the lithosphere in which the heat flow patterns are explained entirely by variations in crustal heat production cannot satisfy constraints on upper mantle temperatures beneath archean cratons derived from xenolith thermobarometry the thermobarometry constraints can be satisfied by models in which differences in lithospheric thickness are the principal factor controlling the surface heat flow distributions if the heat flow patterns result primarily from variations in lithospheric thickness then a different temporal heat flow relationship for precambrian terrains can be proposed one in which heat flow varies inversely with the age of stabilization of the lithosphere

the dynamics of slug trains in volcanic conduits evidence for expansion driven slug coalescence strombolian volcanism is a ubiquitous form of activity driven by the ascent and bursting of bubbles of slug morphology whilst considerable attention has been devoted to understanding the behaviour of individual slugs in this regime relatively little is known about how inter slug interactions modify flow conditions recently we reported on high temporal frequency strombolian activity on etna in which the larger erupted slug masses were followed by longer intervals before the following explosion than the smaller bursts pering et al 2015 we hypothesised that this behaviour arose from the coalescence of ascending slugs causing a prolonged lag before arrival of the next distinct bubble here we consider the potential importance of inter slug interactions for the dynamics of strombolian volcanism by reporting on the first study into the behaviour of trains of ascending gas slugs scaled to the expansion rates in volcanic conduits this laboratory analogue study illustrates that slugs in trains rise faster than individual slugs and can be associated with aspects of co current flow the work also highlights that coalescence and inter slug interactions play an important role in modulating slug train behaviour we also report for the first time on slug coalescence driven by vertical expansion of the trailing slug a process which can occur even where the leading slug base ascent velocity is greater than that of the trailing slug

pressure changes associated with the ascent and bursting of gas slugs in liquid filled vertical and inclined conduits at basaltic volcanoes the sources of long period and very long period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface to investigate pressure changes associated with these processes two phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase the ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug these dynamic transients generate sub static pressures below the ascending slug in viscosity controlled systems and produce super static pressures when the slug reaches the surface and motion ceases in inertia dominated systems conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two phase flow the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst pressure oscillations are also observed during the release of gas slugs and in their wake region

blast waves from violent explosive activity at yasur volcano vanuatu 1 infrasonic and seismic waveforms were collected during violent strombolian activity at yasur volcano vanuatu averaging 3000 seismic events showed stable waveforms evidencing a low frequency 0 1 0 3 hz signal preceding 5 6 s the explosion infrasonic waveforms were mostly asymmetric with a sharp compressive 5 106 pa onset followed by a small long lasting rarefaction phase regardless of the pressure amplitude the ratio between the positive and negative phases was constant these waveform characteristics closely resembled blast waves infrared imagery showed an apparent cold spherical front 20 m thick which moved between 342 and 405 m s before the explosive hot gas fragments cloud we interpret this cold front as that produced by the vapor condensation induced by the passage of the shock front we suggest that violent strombolian activity at yasur was driven by supersonic dynamics with gas expanding at 1 1 mach number inside the conduit

comment on dynamic surface topography a new interpretation based on mantle flow models derived from seismic tomography by a m forte w r peltier a m dziewonski and r l woodward

a 2000 year dust storm record from lake sugan in the dust source area of arid china 1 arid northwestern china is considered to be a major source of atmospheric dust supply to the northern hemisphere however dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region hydrologically closed lakes in dust source areas act as a trap providing the opportunity to trace the history of dust emission or eolian activity here we present the results of dust storm proxies and a dust storm history from lake sugan in the qaidam basin a dust source area on the northern qinghai tibetan plateau grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred in combination with a sediment chronology generated by counting annual laminations a 2000 year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments frequent and or intensive dust storms occurred during the intervals ad 300 500 ad 1180 1240 and ad 1500 1700 the occurrence of dust storms largely coincided with the strengthening of the siberian high with colder air masses from high latitudes such as during the little ice age frequently encroaching into the dust source areas in northwestern china our results suggest that wind strength plays an important role in dust emissions in arid source areas however dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the qaidam basin

two stage modeling of strombolian type eruptions and quantification of the model parameters insight from the seismic and acoustic signals abstract the seismic signals of majority strombolian explosions show a two phase structure that may be the result of a two stage explosive eruption we quantify the parameters of two proposed stages of strombolian eruptions at volcanoes arenal aso and yasur using 193 seismic records and 18 acoustic signals and considering that the first stage of eruption represents the seismically active process of the gas slug expansion and ascent gsea in the conduit and the second stage is associated with the gas slug burst at the surface it is shown that the radiated seismic energy of strombolian explosions at volcanoes is strongly dependent on the seismic energy radiated during gsea the seismic energy of explosions is correlated also with the duration of gsea process in the interval of durations between 1 3 and 3 7 s for shorter gsea durations the correlation is absent the acoustic energy of explosions is characterized by inverse dependence on the durations of gsea these results demonstrate the influence of the gsea process on the surface manifestations of strombolian explosions

explosive volcanic activity at mt yasur a characterization of the acoustic events 9 12th july 2011 abstract volcanic processes occur in a wide range of temporal and spatial scales however a key step of magma ascent is recognizable in the dynamics of gas and magma in the shallow plumbing system where volatiles play a fundamental role in controlling the eruptive style with the aim of investigating shallow degassing processes an experimental setup was deployed at mt yasur an active volcano located in tanna island vanuatu arc from 9th to 12th july 2011 the setup comprised high speed and thermal cameras as well as a microphone capable of recording both in the infrasonic and audible range the analysis of acoustic signals validated by observing images from the high speed and thermal cameras has enabled characterizing the explosive activity during the investigated period two types of explosions distinct for spectral features and waveforms were observed i minor events corresponding to small overpressurized bursts occurring almost continuously ii major events characterizing the strombolian activity at mt yasur by investigating variation in the occurrence rate of the minor events we found that on a short timescale the dynamics responsible for the two types of explosions are decoupled these results together with previous literature data bring additional evidence of the existence of distinct sources of degassing finally major events can be distinguished as emergent events i e long lasting signals corresponding to ash rich explosions and impulsive events featuring shorter duration and larger amplitude

palaeosol development in the chinese loess plateau as an indicator of the strength of the east asian summer monsoon evidence for a mid holocene maximum the interpretation of the stalagmite delta o 18 record from southern china as an indicator of east asian summer monsoon easm rainfall amount or intensity is strongly debated soil development in the chinese loess plateau clp situated in the modern summer monsoon domain has long been treated as a direct and reliable easm proxy in this study we compiled 81 loess and 229 palaeosol dates from 77 profiles across the clp and synthesized the data statistically in order to investigate the easm history during the holocene the resulting history of holocene loess deposition and palaeosol development demonstrates that 1 loess deposition decreased and palaeosol formation increased across the clp after 11 5 ka 1 ka 1000 cal yr bp revealing a gradually intensified easm during the early holocene 2 numerous palaeosols developed in the clp between 8 8 ka and 3 4 ka indicating a generally strong easm during the mid holocene 3 the number of palaeosol dates decreased rapidly at around 3 ka suggesting a sudden retreat of the easm in the late holocene these trends of easm evolution are broadly consistent with variations in aeolian sand activity in the four main sandlands the mu us otindag horqin and hulun buir sandlands along the modern monsoon fringe in northern china and are supported by a wide range of independent evidence in addition we also found that high loess deposition and stronger aeolian activity occurred at similar to 5 ka representing a weak easm event within the context of an overall strong mid holocene easm the strong mid holocene easm revealed by palaeosol development in the clp and aeolian sand activity in the sandlands in northern china contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china our results are compatible with the proposal that the stalagmite delta o 18 variations in china do not result from changes in easm rainfall amount or intensity but instead reflect changes in moisture source driven by variations in atmospheric oceanic circulation c 2014 elsevier ltd and inqua all rights reserved