high temperature emplacement of the cerro galan and toconquis group ignimbrites puna plateau nw argentina determined by trm analyses estimates of pyroclastic flow emplacement temperatures in the cerro galan ignimbrite and toconquis group ignimbrites were determined using thermal remanent magnetization of lithic clasts embedded within the deposits these ignimbrites belong to the cerro galan volcanic system one of the largest calderas in the world in the puna plateau nw argentina temperature estimates for the 2 08 ma cerro galan ignimbrite are retrieved from 40 sites in 14 localities 176 measured clasts distributed at different distances from the caldera and different stratigraphic heights additionally temperature estimates were obtained from 27 sample sites 125 measured clasts from seven ignimbrite units forming the older toconquis group 5 60 4 51 ma mainly outcropping along a type section at rio las pitas vega real grande the paleomagnetic data obtained by progressive thermal demagnetization show that the clasts of the cerro galan ignimbrite have one single magnetic component oriented close to the expected geomagnetic field at the time of emplacement results show therefore that most of the clasts acquired a new magnetization oriented parallel to the magnetic field at the moment of the ignimbrite deposition suggesting that the clasts were heated up to or above the highest blocking temperature tb of the magnetic minerals tb 580 c for magnetite tb 600 630 c for hematite we obtained similar emplacement temperature estimations for six out of the seven volcanic units belonging to the toconquis group with the exception of one unit lower merihuaca where we found two distinct magnetic components the estimation of emplacement temperatures in this latter case is constrained at 580 610 c which are lower than the other ignimbrites these estimations are also in agreement with the lowest pre eruptive magma temperatures calculated for the same unit i e 790 c hornblende plagioclase thermometer folkes et al 2011b we conclude that the cerro galan ignimbrite and toconquis group ignimbrites were emplaced at temperatures equal to or higher than 620 c except for lower merihuaca unit emplaced at lower temperatures the homogeneity of high temperatures from proximal to distal facies in the cerro galan ignimbrite provides constraints for the emplacement model marked by a relatively low eruption column low levels of turbulence air entrainment surface water interaction and a high level of topographic confinement all ensuring minimal heat loss

paleomagnetic determination of emplacement temperatures of pyroclastic deposits an under utilized tool paleomagnetic data from lithic clasts collected from mt st helens usa volcan lascar chile volcan de colima mexico and vesuvius italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures at mt st helens the temperature of the deposits tdep at three sites from the june 12 1980 eruption was found to be 532 c 509 c and 510 570 c respectively one site emplaced on july 22 1980 was emplaced at 577 c these new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates lithic clasts from pyroclastic deposits from the 1993 eruption of lascar were fully remagnetized above the respective curie temperatures which yielded a minimum tdep of 397 c samples were also collected from deposits thought to be pyroclastics from the 1913 2004 and 2005 eruptions of colima at colima the sampled clasts were emplaced cold this is consistent with the sampled clasts being from lahar deposits which are common in the area and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit tdep of the lower section of the lithic rich pyroclastic flow lrpf from the 472 a d deposits of vesuvius was 280 340 c this is in agreement with other recently published paleomagnetic measurements in contrast the upper section of the lrpf was emplaced at higher temperatures with tdep 520 c this temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections with the upper section containing a greater proportion of vent derived material that was initially hot our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation

using 14c dating of stable humin fractions to assess upbuilding pedogenesis of a buried holocene humic soil horizon towada volcano japan the genesis of a 40 cm thick buried holocene humic soil horizon in a 6 m high sequence near towada volcano japan was examined by dating stable plant derived humin particles by ams based radiocarbon 14c and by analyzing stable carbon isotope ratios 13c phytolith composition and soil chemical properties the ams dating yielded calibrated ages ranging from 7570 7679 to 6180 6313 cal yr bp we obtained a strong correlation r 0 99 p 0 001 between sample depth and the mean age the now buried humic soil was formed by the incremental accumulation of tephric loess and aeolian dust at a constant rate of 30 mm per century for at least 1200 years whilst the soil surface was slowly rising graminaceous vegetation was supplied at a constant rate so that developmental upbuilding pedogenesis ensued the soil was buried and isolated by the fall of the towada chuseri tephra about 6200 cal yr bp thus the tephra soil sequence near towada volcano represents both developmental and retardant upbuilding pedogenesis

response of sediment to ice sheet loading in northwestern germany effective stresses and glacier bed stability laboratory tests on sediment over ridden by the last ice sheet in northwestern germany reveal very low ice induced pre consolidation and high palaeo pore water pressures sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum generally low permeabilities of the bed caused sustained high pore water pressure in over ridden sediments close to the flotation point this implies a serious possibility of hydraulic lifting of the ice sheet it is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation ice motion was probably focused at the glacier sole by some combination of sliding and ploughing however isolated spots with deformation occur so that the subglacial system in the study area can be characterized as a stable deforming mosaic

the eruptive rate and history of kuju volcano in japan during the past 15 000 years abstract the eruptive history of kuju volcano on kyushu japan during the past 15 000 years has been determined by tephrochronology and 14c dating kuju volcano comprises isolated lava domes and cones of hornblende andesite together with aprons of pyroclastic flow deposits on its flanks kuju volcano produced tephras at roughly 1000 yr intervals during the past 5000 years and 70 of the domes and cones have formed during the past 15 000 years the youngest magmatic activity of kuju volcano was the 1 6 km3 andesite eruption about 1600 years ago which emplaced a lava dome and block and ash flow kuju volcano shows a nearly constant long term eruption rate 0 7 0 4 km3 for 1000 years during the past 15 000 years this rate is within the range of estimated average eruption rates of late quaternary volcanoes in the japanese arc but is about one order of magnitude higher than the eruption rate of unzen volcano kuju volcano has been in phreatic eruption since october 1995 the late quaternary history of kuju indicates that it poses a significant volcanic hazard primarily due to block and ash flows from collapsing lava domes

conduction model for the thermal influence of lithic clasts in mixtures of hot gases and ejecta the thermal influence of lithic clasts in mixtures of hot gases and ejecta produced during explosive eruptions is an important aspect of the dynamics of eruption columns and pyroclastic flows in order to study this aspect we present a heat conduction model which considers both the temperature distributions of the lithic clasts and the exchange of thermal energy between the lithic clasts and other constituents gases and juvenile pyroclasts the model quantifies the thermal energy of the system by means of a characteristic energy function that describes the energy absorbed by each lithic clast using this energy function and considering some hypothetical arrangements of lithic clasts it is possible to calculate by means of heat balance the temperature variations in mixtures of hot gases and ejecta as a function of time volume fraction of particles to gas and thermal diffusivity initial temperature diameter and volume fraction of lithic clasts theoretical results show that in an eruption a volume fraction of 12 of cool lithic clasts 20 100 c whose size is less than 5 cm will cause the mixture of hot gases and ejecta to cool by 300 c we suggest therefore that the thermal effects of lithic clasts should be considered in numerical models of eruption columns and pyroclastic flows

emplacement temperature determinations of proximal pyroclastic deposits on santorini greece and their implications this paper presents the results of a study undertaken to determine emplacement temperatures of volcanic deposits on the volcano of santorini greece using palaeomagnetic methods two types of breccia have been identified on santorini lithic lag breccias and ground breccias they have been interpreted as deposits from pyroclastic flows however where the breccia deposits are not intimately associated with ignimbrite their origin is ambiguous emplacement temperature determinations were carried out on lithic clasts within these deposits to assess the origin and to place constraints on their emplacement mechanisms the results of thermal demagnetization show that all the clasts display at present earth s field component of magnetization the earth s field component indicates that these clasts have cooled from elevated temperatures within the deposits therefore these breccia deposits were emplaced hot verifying their origin as primary products of pyroclastic eruption many of the deposits display a wide range of emplacement temperatures and the lowest temperature at any one location probably represents the equilibrium temperature of the deposit an emplacement temperature determination records the highest temperature experienced by the clast before cooling in situ these clasts may have been heated before during or after the eruption in estimating the emplacement temperature it is important to understand at what stage the clasts were heated thermal modelling was carried out to assess the effects of heating of the clasts a during the eruption and subsequent transport by hot gases and juvenile pyroclasts within pyroclastic flows and b by an overlying hot deposit such as a pyroclastic deposit or lava flow results from this study indicate that many of the clasts were hot before incorporation took place this indicates that clasts were either derived from depth within the volcano or that there were abundant rocks at elevated temperature near or at the surface

origin and mode of emplacement of lithic rich breccias at aso volcano japan geological paleomagnetic and petrological reconstruction abstract takajosan breccia rocks are distributed around the southwestern caldera rim of the aso volcano in japan they are characterized by coarse lithic breccias with a pumiceous matrix the proximal coarse lithic breccias are divided into the lower massive unit and the upper stratified unit the lower massive lithic breccias tend to transform laterally into tuff breccias and pumiceous lapilli tuffs paleomagnetic results showed that all of the deposits were deposited at high temperatures of 175 560 c this was also supported by geological characteristics such as spatter clasts clasts with a bread crust texture and weakly welded parts these features clearly show that the deposits originated from pyroclastic density currents pdcs the dense lithic rich lithofacies low vesicularity of pumice lack of plinian fall deposits and radial distribution indicate that the deposits were derived from boil over pdcs rather than plinian column collapse pdcs the sio2 contents of the matrix glasses of the proximal lower massive breccia showed a progressive decrease from the bottom toward the upper part we interpret that this chemical variation corresponds to chemical zonation of the magma chamber this indicates that the massive deposits aggraded progressively from the base upwards progressive aggradation rather than through en masse freezing the vertical lithofacies changes of the proximal breccias from the lower massive to the upper stratified units indicate that a sustained current in a quasi steady state switched to an unsteady current with the progression of the volcanic activity

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

a 550 year old plinian eruption at el chichon volcano chiapas mexico explosive volcanism linked to reheating of the magma reservoir 1 some 550 years ago 1320 1433 a d a powerful plinian eruption at el chichon volcano in southern mexico produced a widespread pumice fall deposit we subdivided the deposit into three parts on the basis of structural and textural characteristics pumice lithology and density granulometry and petrologic geochemical attributes the deposit covers an area of 1500 km2 within the 1 cm isopach and has a minimum estimated bulk volume of 2 8 km3 1 1 km3 dense rock equivalent dre its eruptive column reached an altitude of 31 km consideration of field evidence the presence and nature of mafic enclaves and chemical data strongly suggest that the 550 year b p eruption is linked with the intrusion of a high temperature basaltic magma into preexisting but stagnated trachyandesitic magma beneath el chichon thorough mixing of the two magmas produced a compositionally uniform hybrid trachyandesite magma average sio2 55 3 wt which subsequently underwent crystal growth and gas exsolution ultimately overpressurizing the zoned magmatic system to erupt explosively on the basis of el chichon s known eruptive history the intrusion mixing event occurred sometime after the 900 year b p eruption the hybrid magma had a preeruption temperature of 820 830 c and was water undersaturated 5 6 wt h2o at pressures of 2 2 5 kbar

developing a holocene tephrostratigraphy for northern japan using the sedimentary record from lake kushu rebun island abstract palaeoclimate records in east asia offer significant potential to further our understanding of monsoon dynamics and can serve as a link between north atlantic and tropical climate systems the sedimentary core from lake kushu rebun island provides the first high resolution palaeoclimate record from northern japan in order for this regionally significant archive to be synchronised to other records and to generate a more detailed holocene tephra lattice for east asia we present the first cryptotephra stratigraphy for northern japan using the kushu rk12 core the detailed rk12 tephrostratigraphy integrates local and far travelled tephras originating from japan russia china north korea and most likely indonesia five key cryptotephra layers have been identified precisely dated and correlated to the specific eruptions or the source region b tm tephra changbaishan volcano sh 12 tephra shiveluch volcano ko g tephra komagatake volcano ma f j tephra mashu volcano and rk12 0819 tephra with possible indonesian origin these tephra horizons are very widely dispersed providing opportunities to synchronise distant palaeoclimate records from the polar region through high northern latitudes to the tropics which facilitate interregional comparison of palaeoclimate and environmental data in addition a number of the geochemically analysed horizons contain other minor numbers of compositionally distinct glass which can also be grouped and correlated to their source volcanoes these minor analyses are of interest since they provide new insight into regional tephra dispersal e g ash dispersal potential of aira and towada and could suggest that there are other potential eruptions that have yet to be identified in the geological record e g potential changbaishan eruptions the integrated lake kushu cryptotephra record extends the ash dispersal of several key tephra horizons in the region the presence of the shiveluch sh 12 tephra in lake kushu ca 1900 km away documents the first example of a russian tephra reaching the japanese archipelago furthermore glass compositions suggest that the core could preserve an eruption event derived from indonesia highlighting the future possibility to significantly extend and interlink the tephra lattice across the entirety of asia this is an essential step for the understanding of how climate changes propagate over large geographical areas indeed several of these tephra markers coincide with significant ecological changes reflected in the pollen proxy record at lake kushu using this high resolution palaeoenvironmental record we however find no significant ecological impact following the large late holocene millennium eruption from changbaishan china north korea

integrating the holocene tephrostratigraphy for east asia using a high resolution cryptotephra study from lake suigetsu sg14 core central japan abstract tephra volcanic ash layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales highly productive arc regions like those in east asia offer a considerable number of widespread isochrons but before records can be confidently correlated using these layers a refined and integrated framework of these eruptive events is required here we present the first high resolution holocene cryptotephra study in east asia using the lake suigetsu sedimentary archive in central japan the holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques which integrates the deposits from explosive eruptions from north korea china south korea and along the japanese arc this lake suigetsu tephrostratigraphy is now the most comprehensive record of east asian volcanism and the linchpin site for correlating sequences across this region major element glass geochemical compositions are presented for the tephra layers in the sequence which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions this study has significantly extended the ash dispersal of many key holocene marker layers and has identified the first distal occurrence of isochrons from ulleungdo and changbaishan volcanoes utilising the high precision lake suigetsu chronology we are able to provide constrained eruption ages for the tephra layers which can be transferred into other site specific age models containing these markers this new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in japan and could be used to precisely assess the regional and hemispheric synchronicity of these events

deposition temperature of some pdc deposits from the 1982 eruption of el chichon volcano chiapas mexico inferred from rock magnetic data abstract thermal remanent magnetization trm analyses were carried out on lithic fragments from two different typologies of pyroclastic density current pdc deposits of the 1982 eruption of el chichon volcano in order to estimate their equilibrium temperature tdep after deposition the estimated tdep range is 360 400 c which overlaps the direct measurements of temperature carried out four days after the eruption on the pdc deposits this overlap demonstrates the reliability of the trm method to estimate the tdep of pyroclastic deposits and to approximate their depositional temperature these results also constraint the time needed for reaching thermal equilibrium within four days for the studied pdc deposits in agreement with predictions of theoretical models sedimentological analysis demonstrates that different thickness of aggrading granular dominated pulses does not affect significantly the estimated tdep for the two studied pdcs the component analysis highlights how the entrapment of a significant amount of pre heated lithic fragments from the dome and the conduit walls reduced the cooling of the pyroclastic mixture

deposition temperature of the ad 472 pollena pyroclastic density current deposits somma vesuvius italy the deposition temperature of the pyroclastic density current pdc deposits emplaced during the ad 472 pollena eruption somma vesuvius italy has been investigated using the thermal analysis of the magnetic remanence carried by lithic clasts embedded within the deposits a total of 310 lithic clasts were collected from all the pdc units in the pollena stratigraphic succession at different distances from the inferred vent and at different stratigraphic levels the temperature reached by each individual clast during residence in the pdc was estimated through stepwise thermal demagnetization with the values from all clasts collected at each site being used to infer the deposition temperature tdep although the sedimentological features of these pdc deposits show some variation the deposition temperature typically falls in the range 300 to 320 c with a maximum range of 260 to 360 c the fairly uniform temperature observed in both the dune bedded and massive deposits points to homogeneity in attainment of tdep for the different deposits and suggests similarity in the depositional regime of the different pdcs and or in heat transfer to lithic fragments similarity in depositional regime was also favoured by the limited control exerted by topography on the distribution of these pdcs with the northern wall of the somma caldera that did not act as a morphological barrier as a result the currents were capable of moving away from the vent without topographic disturbances and thus significant variations in the cooling regime because the pollena eruption is considered similar to the maximum expected event at somma vesuvius the characteristics of its deposits best simulate the likely maximum hazard for the vesuvius region in this regard pollena produced hot dilute pdcs which were able to travel up to 12 km from the vent maintaining high temperatures across this distance

paleomagnetic estimate of the emplacement temperature of the long runout nevado de colima volcanic debris avalanche deposit mexico stoopes and sheridan have mapped a volcanic debris avalanche of nevado de colima which has an exceptionally long runout 120 km and low fall height to length ratio h l 0 04 we present paleomagnetic results from this volcanic debris avalanche deposit which provide evidence that this avalanche was emplaced at elevated temperatures the majority of samples collected from lithic clasts in the volcanic debris avalanche deposit exhibit two component remanent magnetizations with a low temperature component 25 350 c which is well grouped about the geomagnetic field direction at colima and a high temperature component 350 580 c which is randomly oriented although the temperature of the deposit most likely varied with distance from the volcanic source and the thickness of the deposit our results suggest an emplacement temperature of approximately 350 c at intermediate distances 18 26 km from the source in order for the rock clasts 20 40 cm diameter to be heated to these temperatures the avalanche was most likely the results of a magmatic bezymianny type eruption the mixing of hot juvenile gases with the clasts provides an explanation for the high degree of fluidization of this material as evidenced by the long runout of this avalanche deposit

paleomagnetic evidence for high temperature emplacement of the 1883 subaqueous pyroclastic flows from krakatau volcano indonesia the paroxysmal 1883 eruption of krakatau volcano in indonesia discharged at least 6 5 km3 dense rock equivalent of pyroclastic material into the shallow waters of the sunda straits within a 15 km radius of the volcano progressive thermal demagnetization studies of individually oriented pumice clasts from a core sample of the submarine pyroclastic deposits show that 41 out of 47 clasts exhibit single component remanence with mean inclination of 2 4 the partial thermoremanent magnetization components of both pumice and lithic clasts are well grouped in orientation indicating that substantial cooling of clasts must have occurred following deposition estimated subaqueous emplacement temperature for such clasts is greater than 500 c rare two component lithic fragments exhibit inflection points on vector endpoint diagrams that mark the temperature below which the fragments acquired magnetization of similar orientation these inflection points range from 350 to 550 c indicating a minimum subaqueous emplacement temperature of 350 c paleomagnetic evidence for high emplacement temperature supports the hypothesis that proximal 1883 submarine pyroclastic deposits resulted from entrance of hot subaerially generated pyroclastic flows into the sea similar deposits have been interpreted from the geologic record but this is the first documented example of submarine pyroclastic flows from a historic eruption the krakatau deposits thus serve as an important modern analog for the study of pyroclastic flow seawater interactions

reappraisal of the 1982 eruptions of el chichon volcano chiapas mexico new data from proximal deposits additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases iii and iv of the 1982 eruption of el chichon volcano phase iii began on 4 april at 0135 gmt with a powerful hydromagmatic explosion that generated radially fast moving 100 ms 1 pyroclastic clouds that produced a surge deposit s1 due to the sudden reduction in the confining pressure the process continued by tapping of magma from a deeper source causing a new explosion the ejected juvenile material mixed with large amounts of fragmented dome and wall rock which were dispersed laterally in several pulses as lithic rich block and ash flow f1 partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate a series of hydromagmatic explosions that dispersed moisture rich surge clouds and small volume block and ash flows iu up to distances of 3 km from the crater the eruption continued by further decompression of the magmatic system with the ensuing emission of smaller amounts of gas rich magma which with the strong erosion of the volcanic conduit formed a lithic rich plinian column that deposited fallout layer b associated with the widening of the vent an increase in the effective density of the uprising column took place causing its collapse block and ash flows arising from the column collapse traveled along valleys as a dense laminar flow f2 in some places flow regime changes due to topographic obstacles promoted transformation into a turbulent surge s2 which attained minimum velocities of approximately 77 ms 1 near the volcano the process continued with the formation of a new column on 4 april at 1135 gmt phase iv that emplaced fall deposit c and was followed by hydromagmatic explosions which produced pyroclastic surges s3

evolution of the seismic activity from the 1982 eruption of el chichon volcano chiapas mexico we analyzed more than 1700 earthquakes related to the 1982 eruption of el chichon volcano in southern mexico the data were recorded at specific periods throughout the whole eruptive interval of march to april 1982 by three different networks the seismic activity began several months before the first eruption on 28 march during this period the seismicity consisted of hybrid and long period shallow earthquakes most likely related to processes of faulting fracturing and fluid movement underneath the volcano the foci of events occurring before the eruption circumscribe an aseismic zone from approximately 7 to 13 km below the volcano after the eruption the seismic activity consisted of tectonic type earthquakes that peaked at 1200 events h this later activity occurred over a wide range of depths mostly between 5 and 20 km that includes the former aseismic zone and is roughly limited by the major tectonic faults in the area

morphology of ash aggregates from wet pyroclastic surges of the 1982 eruption of el chichon volcano mexico the detailed stratigraphic study of the pyroclastic surge units s1 iu and s3 produced during the most violent phases of the 1982 eruption of el chichon volcano contains a complex succession of hydromagmatic events triggered by the interaction of different proportions of magma and external water component analyses of the horizons within single units reveal that almost all wet and cohesive horizons contain ash aggregates based on their morphology and internal structure four different types of aggregates were distinguished a accretionary lapilli b armored lapilli c irregular aggregates and d cylindrical aggregates the first three types have been described in the volcanological literature field and experimental studies cylindrical forms are reported here for the first time these hollow cylindrical aggregates consist of concentric layers of crystals and glass fragments set in a finer grained matrix they formed around millimeter size foliage fragments that are locally preserved in the interior of the aggregates as scorched or completely carbonized vestiges sem analyses suggest different mechanisms of formation for the four types of aggregates irregular aggregates and armored lapilli formed nearly instantaneously whereas accretionary lapilli and cylindrical aggregates resulted from progressive aggregation of ash in different regions of the eruptive cloud

paleoenvironmental history of post toya ash tephric deposits and paleosols at iwate volcano japan using aeolian dust content and phytolith composition abstract physicochemical mineralogical and geochemical analyses of post toya ash 90 130 ka tephric and aeolian deposits at the foot of iwate volcano northeastern japan revealed the accumulation of deposits of long range aeolian dust transported from the asian continent and interstratified with the tephric deposits oxygen isotopic ratios of quartz in the 1 10 m fractions from two paleosols formed in the aeolian units shibutami cracked layers are 16 2 and 17 0 consistent with this fine grained quartz being of an aeolian origin the accumulation of asian aeolian dust onto tephric deposits in northeastern japan was dominant in the cold stages of the last glacial period 20 34 ka and 50 70 ka we determined the changes in vegetation and climate by using opal phytolith distribution in the tephra and aeolian deposits and associated paleosols similarly we interpreted the paleoenvironmental history of the tephric deposits by relating the vegetation history to the dust flux and fossil periglacial phenomena i e involution observed on tephra beds the paleoclimate sequence obtained coincides closely with the marine oxygen isotope curves indicating that opal phytolith analysis is useful in determining the interglacial glacial cycle recorded in aeolian and tephric deposits

radiocarbon dating of tephra layers recent progress in japan abstract a large number of tephra layers deposited over the past 40 000 years in japan have been studied by means of newly developed techniques as well as the traditional radiocarbon 14 c method the samples for 14 c dating were commonly charcoal and wood directly covered or involved in tephra fall and pyroclastic flow deposits recently the 14 c dates measured for paleosols directly underlying a tephra layer have proved to represent the accurate eruption age of the tephra and have successfully established the high resolution eruptive histories of several volcanoes in addition oceanic and lacustrine sediments have preserved a large number of tephra layers and accelerator mass spectrometry 14 c measurements on terrestrial macrofossils from varved sediments have provided highly accurate ages for tephra layers wiggle matching of 14 c ages from several horizons of peat sediments to intcal98 calibration data that was established by dendrochronology as well as by varve chronology has enabled us to obtain highly accurate ages of tephras intercalated in the peat deposits

the 1982 eruptions of el chichon volcano mexico stratigraphy of pyroclastic deposits abstract following a repose period of 500 to 600 years el chichon volcano in se mexico erupted explosively during the months of march and april 1982 three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 march at 0515 gmt and on 4 april at 0139 and 1110 gmt the first major eruption generated only tephra fall which was dispersed ene in the troposphere over the yucatan peninsula and wsw in the stratosphere towards the pacific ocean the second eruption produced tephra fall and pyroelastic surges and pyroclastic flows by repeated collapse of a lithicrich eruption column the surge and flow activity devastated a roughly circular area 153 km 2 around el chichon to a distance of about 6 km from the vent nine villages within the zone were either partially or completely destroyed and loss of human life was perhaps as high as 2000 pyroclastic flows and surges were also generated during the third eruption although ash fall was the primary activity as a result of both the second and third eruptions tephra was transported ene in the troposphere and wsw in the stratosphere the total volume of material ejected during the three major eruptions 0 50 km 3 d r e is represented by tephra fall 0 37 km 3 pyroclastic surges 0 09 km 3 and pyroclastic flows and debris flows 0 04 km 3 as a result of the eruptions a new 1 km wide and 300 m deep crater was formed by the disruption and excavation of a pre existing summit dome

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

holocene history of intentional fires and grassland development on the soni plateau central japan reconstructed from phytolith and macroscopic charcoal records within cumulative soils combined with paleoenvironmental data from mire sediments phytolith and macroscopic charcoal in cumulative soils on the soni plateau central japan were evaluated to clarify the holocene history of intentional fires and grassland development and to comp

pedogenesis by upbuilding in an extreme leaching and weathering environment and slow loess accretion south westland new zealand abstract soil formation is usually envisaged as acting from the surface downwards in many environments however the accumulation of sediment and soil formation are contemporaneous it is only where the rate of one process far exceeds the rate of the other that assumptions of topdown pedogenesis are appropriate the aspect of upbuilding pedogenesis that distinguishes it from topdown pedogenesis is that each increment of soil below the a horizon has experienced processes characteristic of all horizons above it this study examines the influence of upbuilding soil formation in a high rainfall environment of rapid soil formation and slow loess accretion an environment where upbuilding could have a noticeable influence on soil properties soils formed by topdown soil formation topdown soils are compared with soils formed in loess that accumulated from early last glaciation to the holocene upbuilding soils soils are compared in two environments alaquods on poorly drained terraces and placorthods or dystrochrepts on well drained moraine crests we have assumed that properties of the upbuilding soils inherited during the current topdown phase of pedogenesis beginning in the holocene are analogous to those in the topdown soils in this manner soil properties evolved during upbuilding are distinguished in well drained upbuilding soils on moraines subsoil organic carbon has mineralised so that profile trends are very similar to corresponding topdown soils upbuilding has enhanced weathering in subsoils which is reflected in lower ph lower total p and lower primary inorganic p than in topdown soil counterparts total p concentrations in upbuilding soils are much lower than unweathered loess and constant throughout the subsoil and there is almost no p in primary forms in contrast total p in c horizons of topdown soils reaches concentrations typical of the parent material and more than 30 of this is in a primary inorganic form the differences are attributed to each subsoil increment of upbuilding soils having been part of acid a and e horizons oxalate extractable fe and al data indicate that podzolisation was active during upbuilding poorly drained upbuilding soils on terraces have higher subsoil organic carbon inherited from former a or o horizons than comparable topdown soils buried a and o horizons inherited during upbuilding and preserved in the reducing conditions have acted as sinks for mobile al and now resemble podzolic illuvial bh horizons upbuilding through addition of loess to soils promotes a pedogenic pathway distinct from topdown pedogenesis consequently soil chronosequence studies that include soils on old loess mantled surfaces do not strictly satisfy the assumptions of soil chronosequences the nature and rate of soil processes inferred from these studies need revisiting the findings of this study are transferable to other environments where the rate of soil formation and sediment accumulation are comparable

the 1982 eruptions of el chichon volcano mexico 2 observations and numerical modelling of tephra fall distribution tephra fallout from the a 1 march 29 0532 ut b april 4 0135 ut and c april 4 1122 ut 1982 explosive eruptions of el chichon produced three tephra fall deposits over southeastern mexico bidirectional spreading of eruption plumes as documented by satellite images was due to a combination of tropospheric and stratospheric transport with heaviest deposition of tephra from the ene tropospheric lobes maximum column heights for the eruptions of 27 32 and 29 km respectively have been determined by comparing maximum lithic clast dispersal in the deposits with predicted lithic isopleths based on a theoretical model of pyroclast fallout from eruption columns these column heights suggest peak mass eruption rates of 1 1 108 1 9 108 and 1 3 108 kg s maximum column heights and mass eruption rates occured early in each event based on the normal size grading of the fall deposits sequential satellite images of plume transport and the production of a large stratospheric aerosol plume indicate that the eruption columns were sustained at stratospheric altitudes for a significant portion of their duration new estimates of tephra fall volume based on integration of isopach area and thickness yield a total volume of 2 19 km3 1 09 km3 dre dense rock equivalent or roughly twice the amount of the deposit mapped on the ground up to one half of the erupted mass was therefore deposited elsewhere as highly dispersed tephra

reconciling pyroclastic flow and surge the multiphase physics of pyroclastic density currents abstract two end member types of pyroclastic density current are commonly recognized pyroclastic surges are dilute currents in which particles are carried in turbulent suspension and pyroclastic flows are highly concentrated flows we provide scaling relations that unify these end members and derive a segregation mechanism into basal concentrated flow and overriding dilute cloud based on the stokes number s t the stability factor t and the dense dilute condition d d we recognize five types of particle behaviors within a fluid eddy as a function of s t and t 1 particles sediment from the eddy 2 particles are preferentially settled out during the downward motion of the eddy but can be carried during its upward motion 3 particles concentrate on the periphery of the eddy 4 particles settling can be delayed or fast tracked as a function of the eddy spatial distribution and 5 particles remain homogeneously distributed within the eddy we extend these concepts to a fully turbulent flow by using a prototype of kinetic energy distribution within a full eddy spectrum and demonstrate that the presence of different particle sizes leads to the density stratification of the current this stratification may favor particle interactions in the basal part of the flow and d d determines whether the flow is dense or dilute using only intrinsic characteristics of the current our model explains the discontinuous features between pyroclastic flows and surges while conserving the concept of a continuous spectrum of density currents

holocene tephrostratigraphic framework and monsoon evolution of east asia key tephra beds for synchronising palaeoclimate records abstract in east asia our understanding of holocene climate change forcing mechanisms and propagation require the precise chronological control of palaeoclimate records to allow robust integration of data sets the existing chronologies predominantly based on 14c method however are not sufficient to constrain key questions about abrupt climate shifts that occur within a century in the transitions between states widely dispersed tephra layers allow precise dating and synchronisation of sedimentary archives providing a chronological framework for integrating records especially where the visible tephra record is complemented by the addition of cryptotephra non visible ash despite significant tephra studies in this region however a comprehensive holocene tephra framework is not available to address this issue we carry out a thorough review on holocene tephra investigations undertaken in japan using widespread tephra beds we present an integrated tephra framework and suggest the way forward for establishing this as a wider approach for east asia the framework is based on twenty two ash layers that are mainly from japan and to a lesser extent china n korea s korea and russia each tephra is assessed in terms of chronology geochemistry and distribution the framework is compared with high resolution palaeoclimate records from east asia using this we demonstrate regional variations in monsoon evolution and more importantly the potential of tephra isochrons in constraining such variations given the scarce identification of tephra layers in those well resolved palaeoclimate records we advocate a more systematic employment of the cryptotephra method which would potentially lead to a significant advance in east asian tephrochronology and the correlation of palaeoclimate archives in the region

deposit temperature of pyroclastic density currents emplaced during the el chichon 1982 and colima 1913 eruptions new data on the pyroclastic density current pdc deposit temperature t dep are provided for two prominent eruptions of mexican volcanoes of the twentieth century the 1982 eruption of el chichon and the 1913 eruption of colima in spite of similar lithofacies magma composition and pre eruptive conditions the t dep of the pdcs from the 1982 el chichon and 1913 colima eruptions differ significantly with intervals of t dep of 360 420 c and 250 330 c respectively these new data emphasize that a full understanding of the physical mechanisms responsible for equilibrium temperature attainment within a pyroclastic deposit has not yet been realized the t dep measured for el chichon pdc deposits confirm the preliminary data published elsewhere while colima magnetic temperatures provide different values to those published previously

palaeomagnetic estimates of emplacement temperatures of pyroclastic deposits on santorini greece thermal remanent magnetism provides a method of quantitatively determining the emplacement temperature of individual lithic clasts in a volcaniclastic rock the technique is reviewed and applied to two types of quaternary pyroclastic deposit on santorini emplacement temperature estimates for lithic clasts from two co ignimbrite lithic breccias cape riva and middle pumice eruptions range from 250 c to 580 c showing unambiguously that the breccias were emplaced hot good precision on temperature estimates about 20 c were obtained from the cape riva breccias lithics in a plinian airfall deposit from the middle pumice eruption give less precise results because the primary magnetisation has been partly overprinted by chemical and or viscous remanence and some clasts may have rotated during compaction of the deposit temperatures from proximal airfall are consistent with welding of the deposit within 1 5 km from vent temperature estimates for lithic clasts further from vent scatter but a falloff of temperature away from vent can be recognised if an average emplacement temperature for the whole deposit is identified at each location the study highlights some difficulties in interpreting quantitative temperature estimates for prehistoric pyroclastic deposits

the influence of paleogeomorphology on the stable isotope signals of paleosols abstract the stable carbon and oxygen isotope composition of three different local variations of the same mis5e paleosol horizon were studied in the ver ce loess paleosol sequence hungary these variations developed in local top paleoslope and paleovalley topographic positions with characteristic secondary carbonate features such as hypocoatings hcs based on the 13c 18o enrichment or depletion of the secondary carbonate samples the so called stable isotope matrix sim was established and this was used to characterize stable isotope signals as potential paleoenvironmental indicators to complete the sim box and whiskers plot analysis of 13c and 18o values were elaborated on the pedogenic horizons of the paleosol variations the joint application of the sim and the box and whiskers plot analysis revealed the way in which the climatic stable isotope signal of hcs can be overwritten by the various topographic positions of the hosting paleosols the local top paleosol variation will necessarily have developed under climatic influence the expected transition from cold to warm phases as loess deposition characterized by upbuilding pedogenesis was followed by more effective soil development due to the takeover of topdown pedogenesis was characterized by increasingly negative stable isotope values in the upward succession of genetic horizons in the sequence the same transition was identified by different stable isotope patterns in the case of the other two paleosol variations the paleovalley position implies hydromorphic effects and significant evapotranspiration under denser vegetation cover the paleoslope position was affected by abrupt environmental changes such as run off processes triggered by higher precipitation leading to continuous disturbance in the course of the development of the sequence

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

reworking characteristics of quaternary pyroclastics thera greece determined using magnetic properties abstract the magnetic properties of unwelded poorly consolidated quaternary tephra from thera greece are examined for the evidence on their emplacement particularly the extent to which individual clasts have been reworked after initial deposition most samples have stable remanences with single component magnetization acquired between 350 450 c some from 540 c and 100 150 c indicating that each of these samples was in a fixed position relative to the ambient geomagnetic field when they originally cooled over these temperature ranges the between sample directions within each tephra layer are either a mutually consistent i e within measurement and collection error b grouped but more scattered than expected or c randomly scattered these groupings are interpreted in terms of hot emplacement followed by respectively a no re working b cold internal settlement of individual clasts and c extensive cold reworking in each case the percentage of reworked material within any given layer can be estimated from the scatter of the directions of remanence of individual clasts such estimates are consistent with some but not all volcanological appraisals this magnetic method provides a simple inexpensive method for establishing the degree of cold reworking in such unwelded tephra

sulfur accumulation in melanudands during development by upbuilding pedogenesis since 14 15cal ka to understand the contribution of upbuilding pedogenesis to the accumulation of sulfur s in melanudands we investigated the vertical distribution of s species using k edge x ray absorption near edge structure xanes spectroscopy of s species and vertical variation of 34s values of total s in two japanese melanudands developed above tephra nt s dated at 14 15 cal ka these soils have been developed by upbuilding pedogenesis in which episodic accumulations of volcanic ash and eolian dust transported from the asian continent are added incrementally to the soil surface while topdown pedogenesis occurs concomitantly forming soil horizons the oxidation states of s compounds determined by xanes analysis varied widely in the soil profiles the predominant s species was highly oxidized s in ester sulfates and inorganic sulfates 6 oxidation state proportions of s with reduced and intermediate oxidation states increased episodically to as much as 66 ester sulfate s was found in the soil horizons with estimated ages less than 10 cal ka a close correlation was found between ester sulfate s concentrations and al associated organic s concentrations p 0 05 indeed the concentrations themselves were roughly similar the 34s values of total s increased with depth in the two soil profiles these results suggest that episodic deposits of volcanic ash and eolian dust trapped detritus and humus beneath them during the buildup of the soil surface the organic s compounds in this material might be decayed as topdown pedogenic processes in the soils production of ester sulfate s may be related to the warm and humid climate of the holocene which may have accelerated microbial activity responsible for transformation of reduced to highly oxidized s ester sulfate s might have become al associated forms and accumulated in the soils due to their high pedogenic mineral contents

variations in rates of accumulation of tropospheric fine quartz in tephra loess and associated paleosols since the last interglacial stage tokachi plain northern japan and paleoclimatic inferences abstract terrestrial cover bed sequences comprising loess tephra and associated paleosols are collectively called weathered volcanic ash soils in japan widely distributed these deposits have provided effective records for reconstructions of climatic changes related to glacial interglacial cycles the rates of accumulation of fine material and fine quartz

thermal interactions of the ad79 vesuvius pyroclastic density currents and their deposits at villa dei papiri herculaneum archaeological site italy abstract pyroclastic density currents pdcs can have devastating impacts on urban settlements due to their dynamic pressure and high temperatures our degree of understanding of the interplay between these hot currents and the affected infrastructures is thus fundamental not only to implement our strategies for risk reduction but also to better understand pdc dynamics we studied the temperature of emplacement of pdc deposits that destroyed and buried the villa dei papiri an aristocratic roman edifice located just outside the herculaneum city during the ad79 plinian eruption of mt vesuvius italy by using the thermal remanent magnetization of embedded lithic clasts the pdc deposits around and inside the villa show substantial internal thermal disequilibrium in areas affected by convective mixing with surface water or with collapsed walls temperatures average at around 270 c min 190 c max 300 c where the deposits show no evidence of mixing with external material the temperature is much higher averaging at 350 c min 300 c max 440 c numerical simulations and comparison with temperatures retrieved at the very same sites from the reflectance of charcoal fragments indicate that such thermal disequilibrium can be maintained inside the pdc deposit for time scales well over 24 hours i e the acquisition time of deposit temperatures for common proxies we reconstructed in detail the history of the progressive destruction and burial of villa dei papiri and infer that the rather homogeneous highest deposit temperatures average 350 c were carried by the ash sized fraction in thermal equilibrium with the fluid phase of the incoming pdcs these temperatures can be lowered on short time less than hours and length scales meters to tens of meters only where convective mixing with external materials or fluids occurs by contrast where the villa walls remained standing the thermal exchange was only conductive and very slow i e negligible at 50 cm distance from contact after 24 hours we then argue that the state of conservation of materials buried by pdc deposits largely depends on the style of the thermal interactions here we also suggest that pdc deposit temperatures are excellent proxies for the temperatures of basal parts of pdcs close to their depositional boundary layer this general conclusion stresses the importance of mapping of deposit temperatures for the understanding of thermal processes associated with pdc flow dynamics and during their interaction with the affected environment

deposits and physical properties of pyroclastic density currents during complex subplinian eruptions the ad 472 pollena eruption of somma vesuvius italy small scale pyroclastic density currents pdcs associated with the ad 472 pollena eruption of somma vesuvius italy were generated by both magmatic and phreatomagmatic explosive fragmentation the resulting deposits were emplaced under flow boundary conditions dominated by varying combinations of grain interaction fluid escape and traction processes stratigraphic and lithofacies analysis of these pdcs offers a new perspective on the en masse versus progressive aggradation debate for pdc deposition in particular the analyses indicate that pdcs were density stratified with a basal underflow dominated by grain interactions the underflows comprised trains of self organized granular pulses of variable thickness and magnitude depending on the overall particle concentration and fluid turbulence a change in gradient between the upper and lower slopes of the volcano promoted deposition and the different pulses aggraded sequentially stepwise in this model each pulse stops en masse and the whole deposit aggrades progressively particle concentration density mean velocity and flow height were assessed for the studied pdcs using differaent methods for massive and stratified deposits the calculated mobility of the flows was 0 2 to 0 3 in the expected range for small scale pdcs

palaeomagnetic determination of emplacement temperature of vesuvius ad 79 pyroclastic deposits the city of herculaneum was hurried under 20 m of pyroclastic deposits during the ad 79 eruption of vesuvius whose crater is only 7 km to the east these deposits have been interpreted as the deposits of mudflows1 or hot pyroclastic flows2 5 maury s studies6 of incinerated wood in herculaneum demonstrate heating to at least 400 c we have studied the variation of remanent magnetism with temperature for specimens taken from the deposits including specimens of the matrix material and of embedded lithic fragments we conclude that the temperature of the deposit at emplacement is unlikely to have been greater than 400 c which further supports the interpretation of the pyroclastic deposits at herculaneum as largely ignimbrites hot pyroclastic flow deposits

vegetation dieback as a proxy for temperature within a wet pyroclastic density current a novel experiment and observations from the 6th of august 2012 tongariro eruption abstract the 6th of august 2012 eruption of te maari mt tongariro new zealand generated wet pyroclastic density currents pdcs which caused widespread dieback of vegetation singed brown foliage in their path an absence of significant charcoal formation suggests that pdc temperatures were mostly below 250 c textural evidence for liquid water being present in the matrices during emplacement vesicles suggests that temperatures were

subsurface structure of a maar diatreme and associated tuff ring from a high resolution geophysical survey rattlesnake crater arizona abstract geophysical survey techniques including gravity magnetics and ground penetrating radar were utilized to study the diatreme and tuff ring at rattlesnake crater a maar in the san francisco volcanic field of northern arizona significant magnetic anomalies 1600 nt and a positive gravity anomaly 1 4 mgal are associated with the maar joint modeling of magnetic and gravity data indicate that the diatreme that underlies rattlesnake crater has volume of 0 8 1 km 3 and extends to at least 800 m depth the modeled diatreme comprises at least two zones of variable density and magnetization including a low density highly magnetized unit near the center of the diatreme interpreted to be a pyroclastic unit emplaced at sufficiently high temperature and containing sufficient juvenile fraction to acquire thermal remanent magnetization magnetic anomalies and ground penetrating radar gpr imaging demonstrate that the bedded pyroclastic deposits of the tuff ring also carry high magnetization likely produced by energetic emplacement of hot pyroclastic density currents gpr profiles on the tuff ring reveal long 100 m wavelength undulations in bedding planes elsewhere comparable bedforms have been interpreted as base surge deposits inflated by air entrainment from eruption column collapse interpretation of these geophysical data suggests that rattlesnake crater produced highly energetic phreatomagmatic activity that gave way to less explosive activity as the eruption progressed the positive gravity anomaly associated with the maar crater is interpreted to be caused by coherent bodies within the diatreme and possibly lava ponding on the crater floor these dense magnetized bodies have excess mass of 2 4 10 10 kg and occupy approximately 5 of the diatreme by volume magnetic anomalies on the crater floor are elongate nw se suggesting that the eruption may have been triggered by the interaction of ascending magma with water in fractures of this orientation gpr imaging of the tuff ring also suggests that substantial land slip may have occurred on the western rim perhaps causing part of the tuff ring to collapse into the crater strong radar reflections indicative of well developed weathering horizons are present as well the techniques employed at rattlesnake crater demonstrate the value of combining multiple geophysical techniques in areas where exposures are limited and invasive exploration is not an option

upbuilding pedogenesis under active loess deposition in a super humid temperate climate quantification of deposition rates soil chemistry and pedogenic thresholds abstract although the importance of dust deposition as an integral component of terrestrial biogeochemical cycles is well recognised few studies have directly addressed pedogenic processes associated with dust deposition on the land surface itself and if so mainly as relict features this work addresses this gap by looking at the pedogenic response to an active loess flux gradient in a super humid strong weathering environment on the west coast of new zealand s south island along the gradient seven soil pits were examined for a range of soil physical colour texture bulk density structure roots and chemical properties ph fe o fe d al o soil organic carbon measured to a depth of 50 cm to capture the transitional changes arising from minimal to maximal loess deposition rates maximal deposition rate was estimated to be 28 4 g m 2 y 1 along the gradient towards the highest deposition rate loess free sandy spodosols changed to increasingly more finely textured soils ultimately featuring a two fold increase of silt the pedogenic oxides fe o fe d and al o gradually increased each by 50 and soil organic carbon by 60 these increases were facilitated by continuous accession of loess the loess mixed with organic matter at the surface and became increasingly weathered and leached with the time that it had spent undergoing eluviation subsequently the loess increments were buried within the subsoil as part of an upwardly thickening spodic horizon upbuilding pedogenesis because of the high deposition rates under maximum loess flux spodosol formation became ultimately retarded and an inceptisol formed because loess supply overwhelmed topsoil leaching having also an illuvial subsoil horizon this inceptisol showed the strongest chemical indicators for podzolisation of the gradient soil data from supplementary sites suggested that more developed soils required lower loess fluxes to retard further pedogenic differentiation than younger soils the existence of a loess gradient that is capable of forming distinctive deposits in a super humid environment gives evidence that not only dry arid climates e g during glacials are potentially suitable for the formation of aeolian substrates loess the study indicates enhanced soil organic carbon storage in soils as a result of loess deposition and concomitant pedogenesis

interaction of pyroclastic density currents with human settlements evidence from ancient pompeii integrating field observations and rock magnetic measurements we report how a turbulent pyroclastic density current interacted with and moved through an urban area the data are from the most energetic turbulent pyroclastic density current of the a d 79 eruption of vesuvius italy which partially destroyed the roman city of pompeii our results show that the urban fabric was able to divide the lower portion of the current into several streams that followed the city walls and the intracity roads vortices revealed by upstream particle orientations and decreases in deposit temperature formed downflow of obstacles or inside cavities although these perturbations affected only the lower part of the current and were localized they could represent in certain cases cooler zones within which chances of human survival are increased our integrated field data for pyroclastic density current temperature and flow direction collected for the first time across an urban environment enable verification of coupled thermodynamic numerical models and their hazard simulation abilities

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

forced transport of thermal energy in magmatic and phreatomagmatic large volume ignimbrites paleomagnetic evidence from the colli albani volcano italy abstract few studies have detailed the thermal architecture of large volume pyroclastic density current deposits although such work has a clear importance for understanding the dynamics of eruptions of this magnitude here we examine the temperature of emplacement of large volume caldera forming ignimbrites related to magmatic and phreatomagmatic eruptions at the colli albani volcano italy by using thermal remanent magnetization analysis on both lithic and juvenile clasts results show that all the magmatic ignimbrites were deposited at high temperature between the maximum blocking temperature of the magnetic carrier 600 630 c and the glass transition temperature about 710 c temperature estimations for the phreatomagmatic ignimbrite range between 200 and 400 c with most of the clasts emplaced between 200 and 320 c because all the investigated ignimbrites magmatic and phreatomagmatic share similar magma composition volume and mobility we attribute the temperature difference to magma water interaction highlighting its pronounced impact on thermal dissipation even in large volume eruptions the homogeneity of the deposit temperature of each ignimbrite across its areal extent which is maintained across topographic barriers suggests that these systems are thermodynamically isolated from the external environment for several tens of kilometers based on these findings we propose that these large volume ignimbrites are dominated by the mass flux which forces the lateral transport of mass momentum and thermal energy for distances up to tens of kilometers away from the vent we conclude that spatial variation of the emplacement temperature can be used as a proxy for determining the degree of forced convection flow

development of lithic breccias in the 1982 pyroclastic flow deposits of el chichon volcano mexico abstract pyroclastic flow deposit f1 volume 0 02 km 3 produced during phase iii of the 1982 eruption of el chichon volcano mexico contains basal lithic breccias the breccia layers are well exposed in el platanar gully between 2 and 4 km east of the volcano crater the lithic breccias are inversely graded as defined by lithics dense juvenile blocks and pumice supported in a coarse sandy matrix composed of the same constituents the contact between the main body of the pyroclastic flow deposit and the lithic breccias is generally sharp and planar but not erosive in some outcrops it is gradational and is only shown by an alignment of lithic clasts the origin of these beds is interpreted to be due to a hydraulic jump in the moving pyroclastic flow formed after a pronounced slope break from 11 to 3 at the site where the flow began to be funnelled into the el platanar gully we have investigated the possible modes of formation of the lithic breccias with analog laboratory experiments the experiments show that coarse localized segregations could form through a number of mechanisms the field observations interpreted with the assistance of the laboratory results suggest that pyroclastic flow 1 which produced deposit f1 moved as a kind of density stratified flow with a basal lithic rich zone transporting larger particles and an upper less dense zone transporting smaller particles in suspension at the slope break flow 1 lost competence and dumped the largest particles forming a piled up breccia downstream somewhat smaller lithic particles may have been deposited as ballistics from a low angle jetlike structure comprising a hydraulic jump this deposit thins with distance downstream once the deposit was sufficiently thick on its upstream end particles may have been re entrained into the jet to be deposited further along the flow in a low angle downstream prograding bouldery dune reverse grading in the dune beds may result from kinetic sieving we suggest that planar contacts between the lithic breccias and the associated pyroclastic flow deposit may be the result of strong density and velocity gradients between the two parts of the flow

predicting the block and ash flow inundation areas at volcan de colima colima mexico based on the present day february 2010 status abstract maps of areas potentially affected by block and ash flows and associated ash clouds are here presented for the volcan de colima titan2d 2 0 1 code has been used to simulate block and ash flows using as an input volume that of the actual summit dome assessed at 2 10 6 m 3 while the energy cone model has been used to delimit the possible inundated area from associated ash clouds both merapi and soufriere type block and ash flows were generated using different basal friction angles and maintaining fixed the volume and the internal friction angle the setting of the input parameters takes into account some flow characteristics such as the stepwise aggradation of different pulses that piled up to form the total thickness of the block and ash flow deposits the outputs of the computational routines are reported as two maps describing the total thickness of the final deposits they predict that thick deposits will engulf the ravines descending from the main cone to the west south and southeast with expected maximum runouts between 4 5 and 7 km the associated ash clouds have slightly longer runouts and the model predicts they will inundate some higher grounds that are not affected by the concentrate underflows the presented maps represent useful tools for managing the current block and ash flow hazard at volcan de colima

evidence for welding of a block and ash pyroclastic flow deposit the case of cerro bravo volcano colombia cerro bravo is an active composite volcano located in the san diego cerro machin volcano tectonic province scvtp the northernmost volcanic chain in the colombian andes among the products associated with the volcano there is a peculiar indurated deposit emplaced between 7 and 2 9 ka which resembles a block and ash pyroclastic flow deposit through field observations physical property analyses petrography and scanning electron microscopy sem we demonstrate that this induration is the result of welding processes high density deformed glassy fragments with a common orientation low porosity fiamme and sintering are the most visible characteristics the evidence indicates that welding reached up to rank iv in a i to vi classification scheme we suggest that welding is associated with 1 high emplacement temperature related to the syneruptive destruction of a growing endogenous dome and 2 a low glass transition temperature related to the influence of upward water diffusion after emplacement of the flow over wet ground thus with emplacement temperatures between 670 and 540 c and water contents between 0 5 and 1 2 wt the welding process was unusually efficient calculations made indicate that for the deposit to present the observed characteristics of welding the emplacement temperature needed to exceed the threshold of the glass transition temperature for a time of 5 6 days and have an effective viscosity of 1012 pa s as a result of the welding the deposit decreased its thickness by between 15 and 7 m this work contributes to the knowledge of welding processes and stresses the unusual occurrence of welding in this type of pyroclastic flow deposit which thus requires special emplacement conditions in terms of temperature and water content

palaeomagnetic analysis on pottery as indicator of the pyroclastic flow deposits temperature new data and statistical interpretation from the minoan eruption of santorini greece