isotope and trace element evidence for late stage intra crustal melting in the high andes abstract purico chascon is an acid igneous complex less than 1 5 ma old rising to 5800 m in the north chilean andes and consisting of andesite dacite cones and dacite domes on an ignimbrite shield the rocks are subdivided into two groups those from chascon appear to exhibit evidence for magma mixing with more basic material now preserved as xenoliths whereas among those at purico no xenoliths have been found 87sr 86sr 0 7095 0 7081 at purico 0 7079 0 7069 at chascon and 0 7061 0 7057 in the xenoliths from the chascon lavas 143nd 144nd 0 51222 0 51236 overall the purico lavas are characterised by higher sio2 rb sr 87sr 86sr and ree abundances and lower sr nd sr ba and143nd 144nd than most andean igneous suites there is no indication ofselective crustal contamination of sr or any systematic change in isotope ratios during differentiation nonetheless the trend of for example high sr nd and sr contents in rocks with low87sr 86sr 0 704 ecuador to low sr nd and sr and high sio2 in rocks with87sr 86sr 0 7081 0 7095 at purico is interpreted as a shift from subduction zone related magmatism to one with greater crustal affinity the formation of the least evolved purico lavas 60 sio2 is discussed in terms of bulk assimilation of crustal material mixing between crustal and mantle derived magmas and partial melting of pre existing crust although such models are still extremely primitive the simplest explanation of the observed chemical variations is that the purico rocks evolved from parental magmas derived by crustal anatexies thermal considerations suggest that such late stage crustal anatexis is a predictable response to crustal thickening which in the andes is thought to have taken place during the cenozoic

role of subduction erosion in the generation of andean magmas subduction erosion or scraping off of the continental crust by subducting oceanic lithosphere is an important tectonic process along parts of the andean convergent plate boundary estimated rates of subduction erosion increase northward north of the southem andes due to decreasing subduction angle and decreasing sediment supply to the trench west of the central andes subduction erosion may remove as much as 535 km 3 of crust per 1 km of trench per 1 m y or 7 vol of the subducting oceanic lithosphere the higher 87 sr 86 sr ratios of mafic magmas erupted north of the southern andes may be explained by the higher rates of subduction erosion and increased amounts of contamination of the sub arc mantle magma source

the volcanic and magmatic evolution of volcan ollague a high k late quaternary stratovolcano in the andean central volcanic zone abstract volcan ollague is a high k calc alkaline composite volcano constructed upon extremely thick crust in the andean central volcanic zone volcanic activity commenced with the construction of an andesitic to dacitic composite cone composed of numerous lava flows and pyroclastic deposits of the vinta loma series and an overlying coalescing dome and coulee sequence of the chasca orkho series following cone construction the upper western flank of ollague collapsed toward the west leaving a collapse amphitheater about 3 5 km in diameter and a debris avalanche deposit on the lower western flank of the volcano the deposit is similar to the debris avalanche deposit produced during the may 18 1980 eruption of mount st helens u s a and was probably formed in a similar manner it presently covers an area of 100 km2 and extends 16 km from the summit subsequent to the collapse event the upper western flank was reformed via eruption of several small andesitic lava flows from vents located near the western summit and growth of an andesitic dome within the collapse amphitheater additional post collapse activity included construction of a dacitic dome and coulee of the la celosa series on the northwest flank field relations indicate that vents for the vinta loma and post collapse series were located at or near the summit of the cone the vinta loma series is characterized by an anhydrous two pyroxene assemblage vents for the la celosa and chasca orkho series are located on the flanks and strike n55 w radial to the volcano the pattern of flank eruptions coincides with the distribution in the abundance of amphibole and biotite as the main mafic phenocryst phases in the rocks a possible explanation for this coincidence is that an unexposed fracture or fault beneath the volcano served as a conduit for both magma ascent and groundwater circulation in addition to the lava flows at ollague magmas are also present as blobs of vesiculated basaltic andesite and mafic andesite that occur as inclusions in nearly all of the lavas all eruptive activity at ollague predates the last glacial episode 11 000 a b p because post collapse lava flows are overlain by moraine and are incised by glacial valleys present activity is restricted to emission of a persistent 100 m high fumarolic steam plume from a vent located within the summit andesite dome sr and nd isotope ratios for the basaltic andesite and mafic andesite inclusions and lavas suggest that they have assimilated large amounts of crust during crystal fractionation in contrast narrow ranges in 143nd 144nd and 87sr 86sr in the andesitic and dacitic lavas are enigmatic with respect to crustal contamination

geomagnetic and mineral magnetic characterization of the anthropocene geomagnetic and mineral magnetic data provide geological indices that are both independent of human impact i e geomagnetic and respond to human induced environmental impact i e mineral magnetic we provide the first discussion of such magnetic events for help in defining the anthropocene within the holocene a potential geomagnetic marker for the anthropocene is the low dipole latitude at c 2700 cal a bp which is associated with distinct palaeosecular variation features in northerly mid to high latitude sites mineral magnetic records from lake and marine sediments identify major deforestation and soil delivery events from catchment systems in many parts of the world during the last 4000 years in europe clusters of these events occur around both 2600 cal a bp and ad 1100 the former coinciding with a low in geomagnetic field dipole latitude and peak intensity mineral magnetic records in peats and lake sediments can reflect particulate pollution from fossil fuel burning the expansion of major coal burning began c ad 1800 in western europe and eastern north america but around ad 1900 this expanded due to more widely distributed coal use and this event is the most clear mineral magnetic marker for the base of the anthropocene

introduction to the special issue on the 2003 eruption of anatahan volcano commonwealth of the northern mariana islands cnmi 1 introductionanatahan volcano situated in the commonwealthof the northern mariana islands cnmi erupted forthefirst timeinrecordedhistoryonmay10 2003 theeruption prompted a period of intensive study andcollaboration between researchers from a number ofgovernmental agencies institutes and universities andresultedinaspecialsessiondedicatedtotheeruptionatthe fall meeting of the american geophysical union agu in december of thesame year seeeos trans agu 84 46 p 1561 1563 this volume of thirteenpapersgrewoutoftheaguspecialsessionandcoversfour principal themes a geological studies of anata han carried out prior to the may 2003 event includingmapping of both the submarine and subaerial portionsof the volcano and monitoring of the local seismicityfollowing activity in 1990 b geophysical signals ofthe 2003 eruption c petrology and geochemistry ofthe eruptive products of the 2003 eruption and d impacts associated with the 2003 eruption in this briefintroduction we summarize the major findings asso ciatedwitheachofthesethemes wealsooffersugges tionstowhereupdatedmaterialandresultsofon goingstudies can be found at the time of writing january2005 anatahan volcano continues to be active albeit at a lower level compared to the spring of2003 so remains the focus of considerable researchand monitoring efforts 2 anatahan volcano background geologythe island of anatahan is situated about 120 kmnorth of saipan the capital of the cnmi it lies atthe southern end of the 1500 km long izu bonin mariana ibm arc system where the oldest oceaniccrust of the pacific plate is subducting beneath youn ger crust of the philippine plate the island representsthe summit of a large strato volcano which rises fromdepths of 3000 m below sea level to an elevation of788 m

physical volcanology of the submarine mariana and volcano arcs narrow beam maps selected dredge samplings and surveys of the mariana and volcano arcs identify 42 submarine volcanos observed activity and sample characteristics indicate 22 of these to be active or dormant edifices in the volcano arc are larger than most of the mariana arc edifices more irregularly shaped with numerous subsidiary cones and regularly spaced at 50 70 km volcanos in the mariana arc tend to be simple cones sets of individual cones and volcanic ridges are elongate parallel to the trend of the arc or at 110 counterclockwise from that trend suggesting a strong fault control on the distribution of arc magmas volcanos in the mariana arc are generally developed west of the frontal arc ridge on rifted frontal arc crust or new back arc basin crust volcanos in the central mariana arc are usually subaerial large 500 km3 and spaced about 50 70 km apart those in the northern and southern marianas are largely submarine closer together and generally less than 500 km3 in volume there is a shoaling of the arc basement around iwo jima accompanied by the appearance of incompatible element enriched lavas with alkalic affinities the larger volcanic edifices must reflect either a higher magma supply rate or a greater age for the larger volcanos if the magma supply estimated at 10 20 km3 km of arc per million years at 18 n has been relatively constant along the mariana arc we can infer a possible evolutionary sequence for arc volcanos from small irregularly spaced edifices to large over 1000 km3 edifices spaced at 50 70 km the volcano distribution and basal depths are consistent with the hypothesis of back arc propagation into the volcano arc

regional o sr and pb isotope relationships in late cenozoic calc alkaline lavas of the andean cordillera quaternary recent volcanism in the andes has occurred in three regions 45 33 s 28 16 s and 2 s 5 n each of which has a distinct plate tectonic setting and contains volcanic suites with different chemical and isotopic characteristics isotope ratios of o and sr are lowest and those of pb least variable in the southern volcanic zone svz where medium k lavas have isotopic characteristics equivalent to volcanics from intraoceanic arcs where continental crust is absent the svz lavas were probably derived from an asthenospheric mantle source above a shallow benioff zone parental basaltic magmas rose largely unmodified through thin continental crust where differentiation occurred by low pressure crystal fractionation without concurrent modification of isotopic composition the slight enrichment of 206 pb in the northern volcanic zone nvz where the crust is thin and the benioff zone deep suggests a greater subduction zone component for parental medium k magmas the slight 18 o enrichment suggests a small amount of lower crustal interaction isotope ratios of o and sr are highest and those of pb most variable in the central volcanic zone cvz parental magmas in the cvz were probably generated within the same mantle source region as those in the svz and nvz subsequently during transit through the exceptionally thick continental crust of the central andes high k magmas were produced by a combination of bulk contamination in the lower crust and later low pressure fractional crystallization assimilation processes in the upper crust which altered both chemical and isotopic compositions

a stratigraphical basis for the anthropocene recognition of intimate feedback mechanisms linking changes across the atmosphere biosphere geosphere and hydrosphere demonstrates the pervasive nature of humankind s influence perhaps to the point that we have fashioned a new geological epoch the anthropocene to what extent will these changes be evident as long lasting signatures in the geological record to establish the anthropocene as a formal chronostratigraphical unit it is necessary to consider a spectrum of indicators of anthropogenically induced environmental change and to determine how these show as stratigraphic signals that can be used to characterize an anthropocene unit and to recognize its base it is important to consider these signals against a context of holocene and earlier stratigraphic patterns here we review the parameters used by stratigraphers to identify chronostratigraphical units and how these could apply to the definition of the anthropocene the onset of the range of signatures is diachronous although many show maximum signatures which post date1945 leading to the suggestion that this date may be a suitable age for the start of the anthropocene

a combined o sr nd and pb isotopic and trace element study of crustal contamination in central andean lavas i local geochemical variations systematic variations in o sr nd and pb isotopic ratios and in sr nd pb and rb trace element abundances in central andean andesitic lavas are analyzed in terms of combined crustal assimilation and fractional crystallization the results of integrated isotopic model calculations show that observed local isotopic and trace element variations within the arequipa and barroso volcanic groups of southern peru are best fit by a simple model involving shallow or intermediate depth crustal assimilation of charcani gneiss or an equivalent rock accompanied by dominantly plagioclase fractional crystallization a consequence of this result is that the rbsr pseudoisochrons reported for the arequipa and barroso volcanics are wholly artifacts of the combined processes of assimilation and plagioclase fractionation as are all of the pb isotopic variations measured in the same lavas already interpreted by tilton and barreiro 14 to be the result of crustal contamination isotopic and trace element compositions of the primary magmas for the arequipa and barroso volcanic series are obtained by correcting for assimilation and fractional crystallization the starting magmas are characterized over the entire range of permissible primary compositions by high87sr 86sr ratios low143nd 144nd ratios and high sr concentrations relative to normal island arc andesites these results appear to require prior contamination of the magmas but not involving plagioclase fractionation the uncertainty in pb and o isotope ratios computed for possible primary magmatic compositions is sufficiently large however that it is not possible to preclude a subcrustal origin for at least some regional variation in sr and nd isotopic ratios

magnetic mineralogy and its implication of contemporary coastal sediments from south china magnetic parameters have been widely used as a rapid cost effective and non destructive method to assess whether their magnetic properties reflect the development history in the pearl river delta three sediment cores collected from south china coastal waters were selected for magnetic research the results indicate that the predominant ferrimagnetic mineral is magnetite with an additional smaller amount of surprisingly high coercive greigite fine grained superparamagnetic and single domain particles of magnetite and the relative contribution of greigite are increased when the total concentration of ferrimagnetic minerals is higher three well known stages of the chinese history i e iron smelting cultural revolution and the latest phase of opening and reforming were identified in the vertical variation of magnetic concentration parameters although the record of the three cores is not completely consistent the results point out that magnetic concentration parameters can reflect the development and pollution history in surrounding coastal areas

geological aspects of the 2003 2004 eruption of anatahan volcano northern mariana islands anatahan volcano northern mariana islands began erupting in may june 2003 a series of subplinian explosive eruptions of andesite magma began at the eastern crater in the eastern part of the summit caldera on the evening of 10 may brown tephra was sent mainly westward by strong winds small scale pyroclastic surges were discharged eastward outside the caldera in late may an andesite lava dome that had once filled the inner crater was fragmented by phreatomagmatic explosions in the middle of june the phreatomagmatic explosions probably occurred due to interaction of the magma head with groundwater around the crater and abundant very fine ash gray tephra was discharged within the caldera and over most of the island the volume of eruption products of the may june eruption was estimated to be 1 4 x 10 7 m 3 dense rock equivalent erupted pumices and lava are aphyric andesite and are variously colored depending on their vesicularity the sio 2 contents of erupted materials decreased slightly with time the fine gray ash is depleted in alkalies probably due to leaching by acid hydrothermal fluids during explosions seismic activity resumed in late march 2004 and small strombolian like explosions were repeated in may and june 2004 about half of the inner crater was filled with new scoria and lava

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

ages of metamorphic and deformational events in the sierra de ancasti pampean ranges argentina metamorphic rocks of the sierra de ancasti catamarca province northwestern argentina were investigated by means of the rb sr method three phases of metamorphism can be distinguished a first possible homogenization of sr possibly took place 524 m y ago a second one can be subdivided into a mean metamorphism at 472 m y and a statical recrystallization at about 450 m y a last weak metamorphism at about 420 m y can be recognized only by ages of cooling of biotites the relations of the metamorphic rocks to granitic intrusions and regional comparisons support this subdivision similar ages have been reported from various regions of the gondwana continent

holocene sediment dynamics in an upland temperate lake catchment climatic and land use impacts in the english lake district accelerated erosion and transport of fine sediment from upland temperate catchments can reflect increased erosivity and or erodibility due in turn to climatic and or human forcing identification of sediment fluxes and sources over holocene timescales can both enable understanding of the relative impacts of these forcings and provide perspective on recent sediment fluxes here we present a 5500 yr record of sediment fluxes and sources from lake bassenthwaite in the english lake district utilizing magnetic measurements and fuzzy clustering coupled with independent pollen and archaeological records to identify the timing and impact of catchment disturbance this record shows that recent sediment flux increases ie within the last 150 years are unprecedented in scale throughout the mid late holocene and appear to be in response to specific human changes occurring within the catchment earlier episodes of human activity from the mid holocene onwards show no link with increased lake sediment fluxes

the submarine flanks of anatahan volcano commonwealth of the northern mariana islands abstract the submarine flanks of anatahan volcano were surveyed comprehensively for the first time in 2003 and 2004 with multibeam and sidescan sonar systems a geologic map based on the new bathymetry and backscatter data shows that 67 of the volcano s submarine flanks are covered with volcaniclastic debris and 26 is lava flows cones and bedrock outcrops the island of anatahan is only 1 of the volume of the entire volcano which has a height from its submarine base of 3700 m and an average diameter of 35 km ne anatahan is a prominent satellite volcano located 10 km ne of the island but it is only 6 of anatahan s volume 40 km 3 vs 620 km 3 seventy eight submarine eruptive vents are mapped associated with lava flows and cones between depths of 350 and 2950 m and 80 of these vents are located in a cluster on the east flank of the volcano the distribution of cones and lava flows vs depth suggests a possible change in eruptive style from explosive to effusive between 1500 and 2000 m eruptive vents below 2000 m have produced mostly lava flows there is no evidence of major landslides on the submarine flanks of anatahan volcano in contrast to many basaltic islands and seamounts suggesting that mass wasting at felsic oceanic arc volcanoes may be characterized by sediment flows of unconsolidated volcaniclastic debris instead of mass movements of relatively large intact blocks

small scale disequilibrium in a magmatic inclusion and its more silicic host basaltic andesite inclusions and their host dacite from the purico chascon complex in northern chile are isotopically distinct textural characteristics of the inclusions are typical of those resulting from magma mingling serial sectioning across the interface of an inclusion and its host dacite complemented by microdrill sampling and detailed microprobe work has enabled us to examine the scale of mixing and chemical isotopic and trace element disequilibrium the results of this work show that 1 the composition of the inclusion is relatively homogeneous 2 the dacite host is generally higher in 87sr 86sr and lower in 143nd 144nd than the enclave but it is heterogeneous on a small scale and probably a hybrid 3 the isotopic composition in the marginal zone apparently on both host and inclusion sides of the weakly chilled interface actually shows the highest 87sr 86sr and lowest 143nd 144nd 4 large plagioclase crystals in the inclusions and host are xenocrystic with higher 87sr 86sr than any of the other samples these observations are reconciled with a model of magma evolution in a crustal magma chamber in such a scenario the mafic magma is overlain by a cap of rhyolite a partial melt of the dacitic ignimbrites which now underlie the purico chascon complex overturn of such a magma system gives rise to a hybrid dacite containing discrete mafic inclusions

the 2003 eruption of anatahan volcano commonwealth of the northern mariana islands chronology volcanology and deformation abstract the first historical eruption on anatahan island occurred on 10 may 2003 from the east crater of the volcano the eruption was preceded by several hours of seismicity two and a half hours before the outbreak the number of earthquakes surged to more than 100 events per hour at 0730 utc the washington volcanic ash advisory center issued an ash advisory although the eruption lasted for 3 months the majority of erupted material was expelled during the first 2 weeks the opening episode of the eruption resulted in a deposit of juvenile scoria and lithic clasts the latter derived from geothermally altered colluvial fill from the vent area the opening episode was followed by crater enlargement and deepening which produced deposits of coarse reddish brown ash containing a mixture of juvenile and lithic clasts the third episode of the eruption produced coarse ash and lapilli comprised of juvenile scoria and minor amounts of lithics plume heights were 4500 to 13 000 m for the initial three phases the fourth episode from about may 18 through early august was characterized by smaller plume heights of 900 to 2400 m and steam was the dominant component minor amounts of coarse ash and accretionary lapilli ash comprise most of the deposits of the fourth episode although ballistic blocks and bombs of andesite lava are also locally present these andesite blocks were emplaced by an explosion on 14 june which destroyed a small lava dome extruded during the first week of june activity waned as the summer progressed and subsequent ash deposits accumulated in july and early august by which time the eruption had effectively ended in september and october degassing and geothermal activity continued characterized by small geysers boiling water and jetting steam noteworthy deviations from this activity were a surge event in late may early june and the destruction of the lava dome on 14 june we calculated on land tephra fall deposits to have a bulk volume of about 27 5 10 6 m 3 covering an area of 40 6 km 2 we determined the juvenile to lithic content of the deposits and corrected the bulk volume to a juvenile volume of 24 0 10 6 m 3 we use a volume corrected density of 1 32 g cm 3 to convert the juvenile volume of 24 0 10 6 m 3 to a magma volume of 13 2 10 6 m 3 using the methods of fierstein and nathenson 1992 fierstein j nathenson m 1992 another look at the calculation of fallout tephra volumes bull volcanology 54 156 167 we computed the total eruption volume at 45 4 10 6 m 3 deformation surveys recorded large changes surrounding the east crater the modeled volumetric change based on the surveys was 0 82 10 6 m 3 of magma which we estimate corresponds to a minimum intrusion of 10 10 6 m 3 of magma which is in good agreement with our calculated on land magma volume

anatahan northern mariana islands reconnaissance geological observations during and after the volcanic crisis of spring 1990 and monitoring prior to the may 2003 eruption abstract anatahan island is 9 5 km east west by 3 5 km north south and truncated by an elongate caldera 5 km east west by 2 5 km north south a steep walled pit crater 1 km across and 200 m deep occupies the eastern part of the caldera the island is the summit region of a mostly submarine stratovolcano the oldest subaerial rocks stage 1 are exposed low on the outer flanks and in the caldera walls these include thick 10 m and thin 2 3 m lava flows well indurated tuffs and scoria units that make up the bulk of the island rock compositions range from basaltic andesite to dacite and most are plagioclase phyric on the steep north and south flanks of the volcano these rocks are cut by numerous east west oriented few hundred m long lineaments of undetermined origin indurated breccias unconformably overlie scarps cut into stage 1 units low on the south flank intermediate age eruptive units stage 2 include caldera filling lava flows and pyroclastic deposits and on the outer flanks vents and valley filling lava flows the youngest pre 2003 volcanic unit on anatahan stage 3 is a hydromagmatic surge and fall deposit rich in accretionary lapilli prior to 2003 this unit was found over almost the entire island and in many places original depositional surfaces and outcrops could be found in high energy environments along the coast indicating a young but undetermined age during reconnaissance visits in 1990 1992 1994 and 2001 geothermal activity fumaroles as well as pits with boiling sediment laden pools was observed in the southern part of the pit crater in march and april 1990 increased local seismicity a large regional earthquake and reported increased fumarolic activity in the pit crater prompted evacuation of anatahan village at the west end of the island our first field investigation took place in late april 1990 to assess the level of volcanic unrest conduct reconnaissance geological observations collect rock and geothermal water samples and set up a geophysical monitoring network results at this time were inconclusive with respect to determining whether the activity was anomalous water in some of the geothermal pits within the pit crater was boiling and ph values as low as 0 7 were recorded in the field an electronic distance measurement edm network was installed and over a 1 week period up to 9 cm of extension occurred across some lines but not others seismicity was characterized by intermittent local earthquakes but no sustained swarms or tremor a brief visit in june 1990 revealed that the shallow lake near the boiling pits was gone but activity in the pits themselves was similar to that of april 1990 only minor extension had occurred along a single edm line since the previous visit and no earthquakes m2 5 occurred during the visit subsequent 1 to 2 day visits occurred in october 1990 may 1992 may 1994 and june 2001 activity within the geothermal pits was relatively constant during every visit although during this 11 year period the level of the water in each pit decreased in june 2001 a 50 m wide region of mud pots and steaming ground in the central part of the geothermal area had developed no geologic evidence however suggested that an eruption would occur

magnetic signature of heavy metals pollution of sediments case study from the east lake in wuhan china detailed magnetic measurements and geochemical analyses were performed on 114 sediment samples collected from the east lake wuhan city china to establish a possible link between the enhanced concentration of anthropogenic magnetic particles and heavy metals with known sources relatively higher magnetic susceptibility values mass specific 150 10 8 m3 kg 1 were observed for samples near the pollution sources e g the wuhan iron and steel company wisc the qingshan thermal power plant qtpp the banks driveways of the lake and near the sightseeing route of yachts on the lake moreover is positively correlated to the concentration of pb correlation coefficient r 0 682 but negatively or weakly correlated with both zn and cu in contrast anhysteretic remanent magnetization arm is significantly correlated with these major heavy metals r 0 645 for zn arm 0 699 for pb arm and 0 841 for cu arm respectively which indicate that arm serves a better indicator for the pollution of heavy metals in this lake thermomagnetic analysis combined with magnetic hysteresis measurements revealed that magnetites in the pseudo single domain multidomain grain size regions are dominant scanning electron microscopy and energy dispersive x ray examinations of the magnetic extracts showed that these fe rich particles have different morphologies orange peel structure hollow structure with adhered smaller particles zr rich melted like irregular particles pear shaped spherules and spherules with slick surfaces these features are typical for particles produced by anthropogenic activities because of the genetic relationship between the environmental setting of the east lake and the nearby pollution sources this study suggests that in situ magnetic surveys are sensitive to evaluate the environmental pollution on the lake bottom

mercury deposition and methylmercury formation in narraguinnep reservoir southwestern colorado usa abstract narraguinnep reservoir in southwestern colorado is one of several water bodies in colorado with a mercury hg advisory as hg in fish tissue exceed the 0 3 g g guideline to protect human health recommended by the state of colorado concentrations of hg and methyl hg were measured in reservoir bottom sediment and pore water extracted from this sediment rates of hg methylation and methyl hg demethylation were also measured in reservoir bottom sediment the objective of this study was to evaluate potential sources of hg in the region and evaluate the potential of reservoir sediment to generate methyl hg a human neurotoxin and the dominant form of hg in fish concentrations of hg ranged from 1 1 to 5 8 ng l n 15 and methyl hg ranged from 0 05 to 0 14 ng l n 15 in pore water generally were highest at the sediment water interface and overall hg correlated with methyl hg in pore water r 2 0 60 p 0007 n 15 net hg methylation flux in the top 3 cm of reservoir bottom sediment varied from 0 08 to 0 56 ng m 2 day mean 0 28 ng m 2 day n 5 which corresponded to an overall methyl hg production for the entire reservoir of 0 53 g year no significant point sources of hg contamination are known to this reservoir or its supply waters although several coal fired power plants in the region emit hg bearing particulates narraguinnep reservoir is located about 80 km downwind from two of the largest power plants which together emit about 950 kg hg year magnetic minerals separated from reservoir sediment contained spherical magnetite bearing particles characteristic of coal fired electric power plant fly ash the presence of fly ash magnetite in post 1970 sediment from narraguinnep reservoir indicates that the likely source of hg to the catchment basin for this reservoir has been from airborne emissions from power plants most of which began operation in the late 1960s and early 1970s in this region

atmospheric mineral dust in dryland ecosystems applications of environmental magnetism irm mean of 67 samples 6 72 10 3 am 2 kg 1 is more than two orders of magnitude greater than that for underlying paleozoic and mesozoic sedimentary rocks this contrast is mainly caused by the presence of silt size titanium bearing magnetite particles in the surficial deposits and their absence in bedrock because of their size composition and isolated location the magnetite particles represent a component of atmospheric dust likely deposited over the past few centuries the positive correlation of sediment irm values with amounts of potential plant nutrients reveals the importance of atmospheric dust to soil fertility over much of the american southwest subsequent disturbance of landscapes by domestic livestock grazing as an example commonly results in wind erosion which then depletes exposed surfaces of original aeolian magnetite and associated fine grained sediment declines in soil fertility and water holding capacity in these settings can be estimated in some field settings via decreases in magnetic susceptibility relative to nearby undisturbed areas along gentle hillslope gradients of the colorado plateau field measures for aeolian magnetite demonstrate that the redistribution of deposited atmospheric dust influences landscape level patterns in the distribution of invasive exotic plant species our results indicate that environmental magnetism has high potential for assessing the development and degradation of dry landscapes elsewhere

environmental magnetic responses of urbanization processes evidence from lake sediments in east lake wuhan china summary we present a study on the environmental magnetic response to urbanization processes from nine sediment cores from east lake in wuhan china the concentration of magnetic particles heavy metals and organic matter in the upper 2 18 cm of the sediment cores have been significantly elevated due to the input of coarse magnetite grains from industrial e g power generation and steelmaking and other anthropogenic activities e g vehicle emissions concentration related magnetic parameters such as magnetic susceptibility saturation isothermal remanent magnetization and anhysteretic remanent magnetization are significantly correlated with concentration of heavy metals and organic matter for example pearson s correlation coefficients are 0 921 for cu 0 660 for pb and 0 848 for loss on ignition respectively the magnetic properties of the lake sediments document the pollution history caused by human impact on the lake catchment during urbanization the environmental quality of the lake was fairly good before the 1960s magnetic heavy metal and organic matter contents of the sediments were low and relatively constant which indicates relatively stable natural inputs from the lake catchment pollution trends since the 1960s are reflected in downcore magnetic property variations of the lake sediment the concentration of magnetic particles in the lake sediments started to increase since 1957 when the wuhan iron and steel company and the qingshan thermal power plant which are located upwind of the lake were built and put into production lake pollution was further aggravated since the acceleration of industrialization and urbanization in east lake area in the 1980s which is verified by the elevated concentration of heavy metals and organic matter in the sediments the magnetic mineral concentration in the lake sediment increased continuously until it peaked in the 1990s and has remained a high level since then these results suggest that magnetic properties respond sensitively to environmental status and that the magnetic properties of sediments can provide an excellent record of the industrial and anthropogenic history in an urban lake catchment

the stable isotope geochemistry of volcanic lakes with examples from indonesia abstract stable isotope compositions d 18o and 34s of volcanic lake waters gas condensates and spring waters from indonesia italy japan and russia were measured the spring fluids and gas samples plot in a broad array between meteoric waters and local high temperature volcanic gas compositions the d and 18o data from volcanic lakes in east indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high temperature volcanic gases we investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases an elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors providing relatively flat isotope evolution curves in 18o d diagrams a numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters lake water temperature and fluxes of meteoric water volcanic gas input evaporation and seepage losses the same model is used to derive the flux magnitude of the keli mutu lakes in indonesia the calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters several 100 m3 volcanic water day and indicate a water residence time of 1 2 decades the 34s data from the keli mutu lakes show a much wider range than those from gases and springs which is probably related to the precipitation of sulfur in these acid brine lakes the isotopic mass balance and s cl values suggest that about half of the sulfur input in the hottest keli mutu lake is converted into native sulfur

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

the 2003 phreatomagmatic eruptions of anatahan volcano textural and petrologic features of deposits at an emergent island volcano abstract stratigraphic and field data are used in conjunction with textural and chemical evidence including data from scanning electron microscope electron microprobe x ray fluorescence x ray diffraction and instrumental neutron activation analysis to establish that the 2003 eruption of anatahan volcano was mainly phreatomagmatic dominated by explosive interaction of homogeneous composition low viscosity crystal poor andesite magma with water the hydromagmatic mode of eruption contributed to the significant height of initial eruptive columns and to the excavation and eruption of altered rock debris from the sub volcanic hydrothermal system volatile contents of glass inclusions in equilibrium phenocrysts less abundances of these constituents in matrix glass times the estimated mass of juvenile magma indicate minimum emissions of 19 kt so2 and 13 kt cl this petrologic estimate of so2 emission is an order of magnitude less than an estimate from toms similarly inferred magma volumes from the petrologic data are an order of magnitude greater than those modeled from deformation data both discrepancies indicate additional sources of volatiles likely derived from a separate fluid phase in the magma the paucity of near source volcanic tectonic earthquakes preceding the eruption and the dominance of sustained long period tremor are attributed to the ease of ascent of the hot low viscosity andesite followed by a shallow phreatomagmatic mode of eruption phreatomagmatic eruptions are probably more common at emergent tropical island volcanoes where shallow fresh water lenses occur at near sea level vents these relations suggest that phreatomagmatic explosions contributed to the formation of many of the near sea level craters and possibly even to the small calderas at the other mariana islands

holocene and recent sediment accumulation rates in southern lake michigan abstract rates of sediment accumulation in lake michigan are a key component of its geologic history and provide important data related to societal concerns such as shoreline erosion and the fate of anthropogenic pollutants previous attempts to reconstruct holocene rates of sediment accumulation in lake michigan as well as in the other laurentian great lakes have been bedeviled by the effect of refractory terrestrial material on radiocarbon ages from total organic carbon samples of lake sediments ams radiocarbon ages on small samples of biogenic carbonate ostracodes and mollusks in lake michigan provide accurate holocene ages the present bicarbonate reservoir effect is estimated from shells of mollusks collected live before atmospheric nuclear testing to be 250 yr from paired samples of biogenic carbonate and terrestrial macrofossils the past reservoir effect is thought to be less than 500 yr the radiocarbon ages indicate a distinct decrease in sediment accumulation rates throughout the southern basin of lake michigan at about 5 ka about the time when lake level stabilized at the nipissing level after rising rapidly for several thousand years average rates of sediment accumulation for the historic period the last 150 yr can be estimated from radioisotopes 210 pb and 137 cs pollen stratigraphy and changes in sediment properties associated with human activity multiple methods are necessary because at any given site problems arise in the assumptions or applicability of one or more methods in general the mass accumulation calculations suggest that sediments were deposited 4 to 11 times faster in the historic period than before human settlement the character of the sediment did not change in a dramatic way but sediment magnetic properties suggest shifts in the sources of sediment the data suggest that some of the changes in sources and or character of the sediment occurred just before human settlement and were probably related to climatic changes associated with the little ice age

the nevados de payachata volcanic region 18 s 69 w n chile ii evidence for widespread crustal involvement in andean magmatism volcanism extending over 11 ma is represented in the rocks of the nevados de payachata region culminating in the formation of two large composite stratocones within the last 500 000 years chemically distinct mafic magmas are erupted at a number of parasitic centers these cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones two distinct trends are defined by the intermediate and evolved rocks a high lile large ion lithophile element tio2 and ce yb lineage among the youngest rocks including the two major stratocones and a more typical calc alkaline trend among the older 1 ma rock types within individual volcanic centers differentiation involves fractionation of plagioclase pyroxene and hornblende with biotite and k feldspar in the more evolved rock types isotopic compositions sr pb nd o vary little with differentiation from basaltic andesite to rhyolite or with age contamination during differentiation from basalt to rhyolite may occur but the most mafic rocks erupted in the region are already enriched in incompatible trace elements and therefore may be insensitive to the effects of interaction with the crust the majority of data are similar to baseline compositions cenozoic parental magmas from other parts of the central andes and may reflect a relatively homogeneous magma source or source mixture throughout this central volcanic zone cvz which is distinct from the southern and northern andes and from island arc volcanic rocks

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

evolution of the mariana convergent plate margin system the mariana convergent plate margin system of the western pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology the system s relative geologic simplicity and the well exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins the mariana convergent margin s long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the philippine sea plate the trenchward edge of the overriding plate has a relatively sparse sediment cover rocks outcropping on the trench s inner slope are typical of the early formed suprasubduction zone s lithosphere and have been subjected to various processes related to its tectonic history pervasive forearc faulting has exposed crust and upper mantle lithosphere many large serpentinized peridotite seamounts are within 100 km of the trench axis from these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids ocean drilling recovered suprasubduction zone lava sequences erupted since the eocene that suggest that the forearc region remains volcanologically dynamic seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution large portions of uplifted southern forearc are exposed at the larger islands active volcanoes at the base of the eastern boundary fault of the mariana trough vary in size and composition along strike and record regional differences in source composition their locations along strike of the arc are controlled in part by cross arc structures that also facilitate formation of submarine volcano chains extending from the base of the fault westward into the back arc basin the western boundary is the west mariana ridge the western portion of the volcanic arc active prior to formation of the mariana trough the trough evolved in a two stage extension process of rifting and subsequent seafloor spreading the back arc basin varies along strike from rifted arc lithosphere with scattered volcanoes but no real spreading center in the north to a complex mid ocean type spreading center south of 20 n the change from initial rifting to true seafloor spreading is also evident across the mariana trough from rifted topography near the west mariana ridge to spreading ridges in the central to eastern basin south of 20 n this morphologic change indicates an early stage of extension with basin and range type topography predominant and volcanism restricted to fissure eruptions along fault block boundaries the spreading ridges and abyssal hill morphology evolved later as new lithosphere was generated at elongate volcanic ridges located in the center of rift valleys the center of extension intersects the active volcanic front differently at either end of the mariana trough in the north extension is by rifting of arc lithosphere where it intersects the arc in the south a major strike slip fault extends from the trench axis across the forearc through the volcanic arc and into the back arc basin arc magmas apparently leak along this fault zone into the forearc and the back arc spreading center the complexity of interrelated tectonism and magmatism in this convergent margin is daunting but studies of arc systems such as this provide the best hope of interpreting many of the exposed terranes accreted to continents comparison of subaerial terranes with recent studies of intraoceanic convergent margins will add to our understanding of plate interactions and of the evolution of the volcanic arcs and extensional back arc basins generated within such environments

magnetic spherules from recent fluvial sediments in alberta canada characteristics and possible origins magnetic spherules were recently recovered in recent fluvial sediments in alberta canada and have been studied using x ray diffraction electron microprobe scanning electron microscope and neutron activation analysis results show that these spherules are composed of magnetite wustite and hematite some of them contain iron metal cores the similarities in morphology mineralogy and internal structure of these spherules to spherules of extraterrestrial origin found in other environments suggest that some of these spherules from alberta might also be of extraterrestrial origin in spite of their unusual compositions

the eruption of mount pagan volcano mariana islands 15 may 1981 a major explosive eruption occurred 15 may 1981 at mount pagan volcano the larger of two historic eruptive centers on pagan island mariana islands the eruption was preceded by increased numbers of locally felt earthquakes beginning in late march or early april and by new ground cracks new sublimates and increased gas emissions a swarm of felt earthquakes began at 0745h local time uct 10 hours 15 may and at 0915 h closely following a loud sonic boom a strong plinian column issued from the volcano the high altitude ash cloud at least 13 5 km travelled south southeast but ash and scoria deposits were thickest 2 m in the nw sector of the island because of the prevailing low altitude southeasterly winds the early activity of 15 may probably involved magmatic eruption along a fissure system oriented about n10 e however the eruption became hydromagmatic possibly within minutes and was largely restricted to three long lived vents the northernmost of these built a substantial new scoria ash cinder cone flows and air fall deposits consisting almost entirely of juvenile material exceeded 105 106 m3 in volume 75 106 m3 of magma on land and at least 70 100 606 m3 at sea an unknown volume was carried away by stratospheric winds lithic blocks and juvenile bombs as large as 1 m in diameter were thrown more than 2 km from the summit and evidence for base surge was observed in restricted corridors as low as 200 m elevation on the north and south slopes of the volcano neither of these events resulted in serious injuries to the 54 residents of the island nor did the eruption produce serious chemical hazards in their water supply weak eruptions occurred during the ensuing month and some of these were monitored by ground observations seismic monitoring and deformation studies precursory seismicity and possibly deformation occurred with some of the observed eruptions more vigorous eruptions were reported by visiting residents in late 1981 and early 1982 but these were of lesser magnitude than the 15 may 1981 event the 15 may lava is predominantly aa and ranges from 3 to 30 m in thickness in composition it is a high alumina basalt with small 1 mm long phenocrysts of plagioclase and clinopyroxene 7 that is more or less typical of basalt of the northern marianas volcanoes it contains slightly more sio2 52 k2o tio2 and less al2o3 and cao than does the basalt of the last eruptive event of mount pagan volcano in 1925 gas analyses indicate that a large portion of air was introduced into the vent system through the porous volcanic edifice and that the carbon gases were not in equilibrium with the magma or each other

cenozoic polyphase landscape and tectonic evolution of the cordillera occidental southernmost peru landforms on the pacific slope of the cordillera occidental western cordillera in southernmost peru reflect the episodic epeirogenic uplift of the central andes since the earliest miocene in the geomorphic history three major stages are distinguished initial uplift followed a mid tertiary period of tectonic and magmatic quiescence in which a low lying subdued landscape formed through dissection of an eocene subaerial volcano plutonic terrain uplift and resulting erosional beveling of this landscape coinciding in their later stages with the explosive reactivation of the magmatic arc gave rise to the regionally extensive lower miocene altos de camilaca surface i which was mantled soon after its formation by ignimbrites of the huaylillas formation major relief was achieved in the middle and early late miocene when a succession of uplift episodes generated a sequence of four discrete pediments constituting the multiple pediment stage ii uplift was accompanied by widespread eruption of ignimbrites of the chuntacala formation subsequently in the pliocene pedimentation was succeeded as the major erosional process by canyon incision across the lower slopes of the cordillera during this valley and terrace stage iii the immediate littoral margin experienced the development of two major terraces contemporaneous with a transition from ignimbrite eruption to predominantly andesitic volcanism in the high cordillera in the early pleistocene during this time it is probable that epeirogenic uplift rather than glacio eustatic sea level changes exerted the dominant control on landform development in the absence of evidence for large scale crustal compression in this immediate region since the cretaceous it is inferred that neogene uplift resulted from episodic thickening of the continental crust through underplating by basic and or intermediate magmas the neogene chronology of landform development herein defined is remarkably similar to that outlined in other transects of the central andes implying that the continental margin has on a broad scale responded uniformly to plate subduction since the early miocene however the low relief evident in the mid tertiary in the study area and not for instance in northern chile 27 s suggests that crustal thickening through the neogene was more rapid and more extensive in the vicinity of the arica deflection than in transects to the north and south the estimated neogene uplift rate for the transect was in the range 0 06 to 0 19 mm yr

magnetite in sediments as an indicator of coal combustion abstract magnetic susceptibility gives an accurate measurement of the magnetite concentration in sediments in all geographical areas studied the magnetite concentration in recent lake estuarine and ocean sediments has been affected by coal burning which releases magnetite spheres to the atmosphere graphs of percent magnetite and percent spheres vs depth age in the various sediments can be used to give information on the history of coal burning in an area as well as the efficiency of air pollution controlling devices chromium zn ti and fe concentrations in the sediments were affected by the input of magnetic spheres cadmium cu mn ni and pb concentrations were not affected

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