the use of palaeomagnetism and rock magnetism to understand volcanic processes introduction this special publication provides a snapshot of our understanding of volcanic processes through the use of palaeomagnetic and rock magnetic techniques here we provide a context for the book placing individual chapters within the milieu of previous work including some magnetic techniques that were not used in the particular studies described herein thermoremanent magnetization is a powerful tool to understand processes related to heating and cooling of rocks including estimating the temperature of emplacement of pyroclastic deposits which may allow us to better understand the rates of cooling during eruption and transport anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics and allow the interpretation of flow dynamics in dykes lava flows and pyroclastic deposits as well as the location of the eruptive vents rock magnetic characteristics can help in the correlation of volcanic deposits but also provide means to date volcanic deposits and to better understand the processes of cooling of the deposits as the magnetic minerals can change with temperature in addition volcanic rocks may be key recorders of past magnetic fields allowing a better understanding of changes in field intensity and perhaps providing clues of how the magnetic field is formed over the past several decades palaeomagnetic and rock magnetic techniques have been applied to numerous problems in volcanology since aramaki akimoto s pioneering study in 1957 which used natural remanent magnetization nrm data to qualitatively estimate the temperature of emplacement of selected pyroclastic deposits in japan aramaki akimoto 1957 many studies have utilized and refined the approach of using progressive thermal demagnetization data to estimate emplacement temperatures of pyroclastic deposits and have demonstrated the utility of this approach in many settings another extensively utilized technique is that of anisotropy of magnetic susceptibility ams which was first applied to pyroclastic volcanic rocks by ellwood 1982 on ignimbrites in the san juan mountains sw colorado usa to estimate flow fabrics and in that study to infer source locations through triangulation it is staggering to think of the number and diversity of ams studies on volcanic rocks that have been undertaken since that time in a bit more than three decades remanent magnetization characteristics have long been used to correlate volcanic rocks and such data together with rock magnetic properties have been employed to study crystallization and cooling processes e g schlinger et al 1988 wells hillhouse 1989 as techniques have been refined and the sensitivity precision reliability and or speed of measurements for an array of modern instrumentation all have improved workers have been able to study volcanic problems in more detail pulling out details of the processes that have not previously been considered in addition the types of problems addressed have diversified considerably we intend this special publication to provide a representative suite of contributions that help to summarize the current array of studies that apply palaeomagnetism and rock magnetism to volcanic processes and to stimulate further research in this exciting science this book is a result of two sessions on volcanic processes and palaeomagnetism held at the international union of geodesy and geophysics congress in melbourne australia in july 2011 and at the american geophysical union annual meeting in san francisco usa in december 2011 from ort m h porreca m geissman j w eds 2015 the use of palaeomagnetism and rock magnetism to understand volcanic processes geological society london special publications 396 1 11 first published online january 20 2015 http dx doi org 10 1144 sp396 17 2015 the geological society of london for permissions http www geolsoc org uk permissions publishing disclaimer www geolsoc org uk pub ethics angharad hills at the geological society of london graciously and tactfully guided this book and the editors through the entire process from chapter solicitation to publication thermoremanent magnetization in volcanic rocks and emplacement temperature

a miocene coarse volcaniclastic mass flow deposit in the shimane peninsula sw japan product of a deep submarine eruption a subaqueous volcaniclastic mass flow deposit in the miocene josoji formation shimane peninsula is 15 16 m thick and comprises mainly blocks and lapilli of rhyolite and andesite pumices and non to poorly vesiculated rhyolite it can be divided into four layers in ascending order layer 1 is an inversely to normally graded and poorly sorted lithic breccia 0 3 6 m thick layer 2 is an inversely to normally graded tuff breccia to lapilli tuff 6 11 m thick this layer bifurcates laterally into minor depositional units individually composed of a massive lithic rich lower part and a diffusely stratified pumice rich upper part with inverse to normal grading of both lithic and pumice clasts layer 3 is 2 5 3 m thick and consists of interbedded fines depleted pumice rich and pumice poor layers a few centimeters thick layer 4 is a well stratified and well sorted coarse ash bed 1 5 2 m thick the volcaniclastic deposit shows internal features of high density turbidites and contains no evidence for emplacement at a high temperature the mass flow deposit is extremely coarse grained dominated by traction structures and is interpreted as the product of a deep submarine explosive eruption of vesicular magma or explosive collapse of lava

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

identification of magnetic minerals carrying nrm in pyroclastic flow deposits the ikeshiro pyroclastic flow deposit at yufu volcano kyushu in japan is a typical block and ash flow generated by collapse of the ikeshiro lava dome erupted ca 2000 years ago clasts in the ikeshiro pyroclastic flow deposit were found to have a low temperature magnetic component that is parallel to the present earth s magnetic field we carried out paleomagnetic and rock magnetic experiments in order to examine the origin of the component by identifying magnetic minerals as a result the clasts were classified into two types based upon magnetic mineralogy type a is carried by titanomagnetite tc 480 485 c whose grain size is mainly md type b is carried by ti poor titanomagnetite tc 500 580 c hematite and titanohematite fe2 ytiyo3 with y 0 5 tc 215 220 c the low temperature magnetic component of type a was carried by titanomagnetite with very low coercivity whereas that of type b was principally carried by titanohematite the viscous remanent magnetization vrm acquisition and demagnetization results indicated that titanomagnetite with low coercivity in type a acquires vrm easily whereas titanohematite in type b hardly acquires vrm therefore the low temperature magnetic component of type b originates not from vrm but from thermoremanent magnetization whereas a part of the low temperature component of type a originates from vrm emplacement temperature of the ikeshiro pyroclastic flow deposit which is estimated from the unblocking temperature of type b samples is between 220 and 400 c the different magnetic mineral assemblage between the two types reflects the difference in oxidation state samples of type b are strongly oxidized whereas those of type a are not oxidation had probably occurred at the ikeshiro lava dome before generation of the ikeshiro pyroclastic flow

a detailed magnetic and mineralogical study of self reversed dacitic pumices from the 1991 pinatubo eruption philippines 39 dacitic pumice and lithic samples from the 1991 eruption of mount pinatubo were investigated through both magnetic and mineralogical means as in a previous study natural remanent magnetization nrm is found to be reversed for most of the samples with respect to the direction of the actual geomagnetic field direction a few samples amongst them ancient lithics transported by pyroclastic flows show scattered nrm directions from thermal demagnetization of these particular samples it is concluded that their orientation changed after emplacement the emplacement temperature is estimated to be more than 460 c from thermal demagnetization of lithic samples two magnetic minerals with large grain sizes are observed under the optical microscope titanomagnetite tm and haemo ilmenite hem ilm microprobe analyses yield x 0 10 for tm and y 0 52 and y 0 54 for two hem ilm phases in agreement with the observed curie temperatures 480 c for tm and 250 c for hem ilm the hem ilm particles display chemical zonation which seems to be correlated with a change of the domain structure typically a ferrimagnetic fm phase with slightly higher titanium content is observed in the central part whilst the crystal margin which is weakly ferromagnetic wf due to spin canted antiferromagnetism is slightly poorer in titanium two different mechanisms for the origin and formation of the two observed phases are discussed 1 chemical zonation of hem ilm crystals due to a change in conditions in the magma chamber shortly before eruption 2 similar to the microstructures observed from synthetic samples this zonation in the large natural hem ilm could be the result of migration of the wf phase towards the grain boundary during residence below the order disorder transition temperature in the magmatic chamber the room temperature hysteresis loop which seems to be dominated by tm provides multidomain md like parameters jrs js 0 01 and hcr hc 20 the large coercivity of remanence 15 40 mt which is attributed to hem ilm may be intrinsic or due to interactions between wf and fm phases the field dependence of the magnitude of the thermoremanent magnetization trm is not linear it increases first reaches a maximum negative value for an applied field h close to 0 5 mt then decreases steadily by extrapolation it is estimated that the trm should be zero for a field of about 12 mt and become positive beyond this total trm is in fact the sum of several components af demagnetization of trms acquired in different fields shows the presence of at least three components a self reversed sr component that contains both hard and moderately hard components and a soft normal component independently of the value of h the median destructive field of the sr component is of the order of 70 mt which suggests that the fm phase is not entirely locked by exchange interaction with the wf phase and can experience noticeable wall movements however some 20 per cent of the sr trm component remains after af treatment of 220 mt although we believe that exchange interaction plays a key role in the process of sr trm acquisition torque curves in the high field of samples both with and without sr trm do not show clear evidence for unidirectional anisotropy similarly we do not observe any significant shift of major hysteresis loops or non vanishing hysteresis losses two characteristics generally considered as indicative of exchange anisotropy and usually observed for synthetic single domain pseudo single domain sd psd hem ilm indeed in addition to the exchange interaction the magnetostatic coupling must play some role here because of the large size of the hem ilm grains

field and paleomagnetic characterization of lithic and scoriaceous breccias at pleistocene broken top volcano oregon cascades abstract cirque wall exposures of cone forming deposits of pleistocene broken top volcano oregon cascade range reveal that the volcano is composed of unconformity bounded constructional units of coherent lava lava flow cores and breccia coarse grained autoclastic breccias are found above and below lava flow cores and may extend downslope from coherent lava outcrops where they may or may not be associated with thin lava stringers mantle bedded scoria fall breccias are recognized by generally good sorting mantle bedding and presence of aerodynamically shaped bombs these breccias vary considerably in thermal oxidation coloration black red orange purple many breccia layers are unsorted mixtures of scoria and lithic nonvesicular fragments that grade laterally to unambiguous autoclastic breccia or lava flow cores these layers are interpreted as hybrid pyroclastic autoclastic deposits produced by incorporation of falling or fallen tephra into advancing lava flow fronts this latter breccia type is common at broken top and offers particular challenges for clast or deposit classification progressive thermal demagnetization results for selected examples of different breccia types show that most scoria fall and autoclastic breccias are emplaced at elevated temperatures averaging 100 300 c clasts within single deposits record different emplacement temperatures ranging in some cases from 100 to over 580 c indicating a lack of thermal equilibration within deposits magnetization directions for single breccia deposits are more dispersed than data typically reported for lava flows settling and rotation of clasts after cooling or incorporation of colder clasts that are not significantly reheated probably accounts for the relatively high dispersion and suggests that paleomagnetic studies demanding low within site dispersion e g for determining paleomagnetic poles or evaluating tectonic rotation should avoid volcanic breccias

paleomagnetic evidence for hot pyroclastic debris flow in the shallow submarine shirahama group upper miocene pliocene japan the cooling history of coarse andesite blocks erupted and deposited proximally in the shallow marine environment has been investigated by paleomagnetic studies and heat conductivity calculations six to 13 samples were cored and measured from six essential andesite blocks 1 5 m in diameter thermal demagnetization techniques were used to detect the directional change of remanence through demagnetization steps each representing different blocking temperatures tb each sample has three components of remanent magnetization c1 c2 and c3 c1 is characterized by a tb of 250 c and an orientation coincident with the present geomagnetic field c2 has a tb of 250 500 c and shows a consistent direction with reversed polarity c3 has a tb of 500 600 c and its orientation is nearly consistent from samples collected from nearby parts of the same clast and are random from samples from different clasts on the basis of the remanence direction of each component the differing tb and the petrography of the samples c1 is interpreted as secondary viscous remanence whereas c2 and c3 are the partial thermoremanent magnetizations obtained during and immediately after emplacement c3 was probably acquired while the blocks were rolling or sliding downslope and c2 formed during continued cooling of the blocks after they came to rest heat conductivity calculations suggest that the blocks were emplaced less than an hour after being erupted if the eruptive vent was only 2 3 km distant as suggested by field relations a downslope transport rate of less than 36 km h is implied

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

interactions between andesitic magma and poorly consolidated sediments examples in the neogene shirahama group south izu japan abstract the upper miocene lower pliocene shirahama group of south izu japan is a sequence of volcanielastic shallow sea sediments and subaqueous lava flows it is gently warped with indistinct preferred orientation and is cross cut by many andesitic intrusive bodies which range in size from less than a meter to several hundred meters the intrusive bodies exhibit various shapes and weak preferred orientation and often have hyaloclastic and peperitic textures along their peripheries hydrothermally altered and chaotically disturbed zones of host rocks also occur along the contacts the areas where the intrusive bodies are abundant are almost coincident with the areas where the more inclined beds and synsedimentary faults are developed the intrusive bodies dragged the surrounding beds with or without synsedimentary faults some intrusions occurred along the faults conjugate sets of the faults indicate that they were produced under unstable stress conditions these relationships between the beds and the intrusive bodies are assumed to have originated mostly by interaction between hot magma and poorly consolidated wet sediments at a shallow depth beneath the sea floor when the intrusions took place the stress conditions in the beds were irregular and unstable judging from the shapes and orientation of the intrusive bodies and also from the deformation characteristics of the enclosing beds some of the intrusive bodies are probably feeder dikes which supplied lave to the shirahama group

paleomagnetic estimates of temperatures reached in contact metamorphism a paleomagnetic study of some silurian devonian lavas from the lorne plateau scotland locally reheated by the intrusion of small tertiary dikes has shown that a laboratory equivalent of the actual peak temperature reached in the reheating can be accurately determined theoretically derived corrections are applied to the experimentally determined temperatures to obtain an estimate of the actual peak temperatures reached in a series of samples across the contact zones these corrected experimental profiles can be compared with peak temperature profiles calculated from heat conduction models the two profiles fit well when the temperatures of the lavas immediately prior to the intrusion are taken into account ambient temperature estimates of 75 25 c and 150 25 c have been obtained for the lavas before intrusion by a normally magnetized dike and a reversely magnetized dike respectively

secondary welding of submarine pumice lithic breccia at mount chalmers queensland australia very thick units of massive pumice and lithic clast rich breccia in the early permian berserker beds at mount chalmers queensland are deposits from cold water supported volcaniclastic mass flows emplaced in a below wave base submarine setting adjacent to syn volcanic andesitic and rhyolitic sills and dykes the pumice lithic breccia shows a well developed eutaxitic texture the eutaxitic foliation is parallel to intrusive contacts and extends as far as a few metres away from the contact at these sites pumice clasts are strongly flattened and tube vesicles within the pumice clasts are compacted and aligned parallel to the direction of flattening some lenticular pumice clasts contain small 2 mm round quartz filled amygdales and spherulites further away from the sills and dykes the pumice clasts have randomly oriented delicate tube vesicle structure and are blocky or lensoid in shape round amygdales were generated by re vesiculation of the glass and the spherulites indicate devitrification of the glass at relatively high temperatures the eutaxitic texture is therefore attributed to re heating and welding compaction of glassy pumice lithic breccia close to contacts with intrusions in cases involving sills secondary welding along the contacts formed extensive conformable eutaxitic zones in the pumice lithic breccia that could be mistaken for primary welding compaction in a hot primary pyroclastic deposit

tephra dispersal from myojinsho japan during its shallow submarine eruption of 1952 1953 a new and detailed bathymetric map of the myojinsho shallow submarine volcano provides a framework to interpret the physical volcanology of its 1952 1953 eruption especially how the silicic pyroclasts both primary and reworked enlarged the volcano and were dispersed into the surrounding marine environment myojinsho 420 km south of tokyo along the izu ogasawara arc was the site of approximately 1000 phreatomagmatic explosions during the 12 5 month eruption these explosions shattered growing dacite domes producing dense clasts that immediately sank into the sea minor amounts of pumice floated on the sea surface after some of these events the myojinsho cone has slopes of almost precisely 21 in the depth range 300 700 m we interpret this to be the result of angle of repose deposition of submarine pyroclastic gravity flows that traveled downslope in all directions many of these gravity flows resulted from explosions and associated dome collapse but others were likely triggered by the remobilization of debris temporarily deposited on the summit and steep upper slopes of the cone tephra was repeatedly carried into air in subaerial eruption columns and fell into the sea within 1 2 km of the volcano s summit entering water as deep as 400 m because the fall velocity of single particles decreased by a factor of 30 in passing from air into the sea we expect that the upper part of the water column was repeatedly choked with hyperconcentrations of fallout tephra gravitational instabilities within these tephra choked regions could have formed vertical density currents that descended at velocities greater than those of the individual particles they contained upon reaching the sea floor many of these currents probably continued to move downslope along myojinsho s submarine slopes fine tephra was elutriated from the rubbly summit of the volcano by upwelling plumes of heated seawater that persisted for the entire duration of the eruption ocean currents carried this tephra to distal areas where it presumably forms a pyroclastic component of deep sea sediment

subaqueous eruption and emplacement of the shinjima pumice shinjima moeshima island kagoshima bay sw japan abstract the shinjima pumice is a fines depleted pumice lapilli tuff emplaced several thousands years ago at about 100 140 m below sea level this 40 m thick deposit comprises many poorly defined flow units which are 1 10 m thick diffusely stratified and showing upward coarsening of pumice clasts with a sharp to transitional base parallel to wavy diffuse stratifications are commonly represented by alignment of pumice clasts especially in the lower half of the flow units pumice clasts of block to coarse lapilli size commonly have thermal contraction cracks best developed on the surfaces demonstrating that they were hot but cooled down to the ambient temperatures prior to their emplacement these features are suggestive of the direct origin of the shinjima pumice from subaqueous eruptions a theoretical consideration on the behavior of subaqueous eruption plumes and hot and cold pumice clasts suggests that subaqueous eruption plumes commonly collapse by turbulent mixing with the ambient water and are transformed into water logged mass flows

nature and origin of cone forming volcanic breccias in the te herenga formation ruapehu new zealand volcanic breccias form large parts of composite volcanoes and are commonly viewed as containing pyroclastic fragments emplaced by pyroclastic processes or redistributed as laharic deposits field study of cone forming breccias of the andesitic middle pleistocene te herenga formation on ruapehu volcano new zealand was complemented by paleomagnetic laboratory investigation permitting estimation of emplacement temperatures of constituent breccia clasts the observations and data collected suggest that most breccias are autoclastic deposits five breccia types and subordinate coherent lava flow cores constitute nine unconformity bounded constructional units two types of breccia are gradational with lava flow cores red breccias gradational with irregularly shaped lava flow cores were emplaced at temperatures in excess of 580 c and are interpreted as aa flow breccias clasts in gray breccia gradational with tabular lava flow cores and in some places forming down slope dipping avalanche bedding beneath flows were emplaced at varying temperatures between 200 and 550 c and are interpreted as forming part of block lava flows three textural types of breccia are found in less intimate association with lava flow cores matrix poor well sorted breccia can be traced upslope to lava flow cores encased in autoclastic breccia unsorted boulder breccia comprises constructional units lacking significant exposed lava flow cores clasts in both of these breccia types have paleomagnetic properties generally similar to those of the gray breccias gradational with lava flow cores they indicate reorientation after acquisition of some or all magnetization and ultimate emplacement over a range of temperatures between 100 and 550 c these breccias are interpreted as autoclastic breccias associated with block lava flows matrix poor well sorted breccia formed by disintegration of lava flows on steep slopes and unsorted boulder breccia is interpreted to represent channel floor and levee breccias for block lava flows that continued down slope less common matrix rich stratified tuff breccias consisting of angular blocks minor scoria and a conspicuously well sorted ash matrix were generally emplaced at ambient temperature although some deposits contain clasts possibly emplaced at temperatures as high as 525 c these breccias are interpreted as debris flow and sheetwash deposits with a dominant pyroclastic matrix and containing clasts likely of mixed autoclastic and pyroclastic origin pyroclastic deposits have limited preservation potential on the steep proximal slopes of composite volcanoes likewise these steep slopes are more likely sites of erosion and transport by channeled or unconfined runoff rather than depositional sites for reworked volcaniclastic debris autoclastic breccias need not be intimately associated with coherent lava flows in single outcrops and fine matrix can be of autoclastic rather than pyroclastic origin in these cases and likely many other cases the alternation of coherent lava flows and fragmental deposits defining composite volcanoes is better described as interlayered lava flow cores and cogenetic autoclastic breccias rather than as interlayered lava flows and pyroclastic beds reworked deposits are probably insignificant components of most proximal cone forming sequences

grain size distribution of volcaniclastic rocks 2 characterizing grain size and hydraulic sorting quantification of the grain size distribution of sediments allows interpretation of processes of transport and deposition jutzeler et al 2012 developed a technique to determine grain size distribution of consolidated clastic rocks using functional stereology allowing direct comparison between unconsolidated sediments and rocks here we develop this technique to characterize hydraulic sorting and infer transport and deposition processes we compare computed grain size and sorting of volcaniclastic rocks with field based characteristics of volcaniclastic facies for which transport and depositional mechanisms have been inferred we studied pumice rich subaqueous facies of volcaniclastic rocks from the oligocene ohanapecosh formation ancestral cascades washington usa pliocene dogashima formation izu peninsula honshu japan miocene manukau subgroup northland new zealand and the quaternary sierra la primavera caldera jalisco state mexico these sequences differ in bed thickness grading and abundance of matrix we propose to evaluate grain size and sorting of volcaniclastic deposits by values of their modes matrix proportion 2 mm f 1 and d16 instead of median diameter d50 and standard deviation parameters f 1 and d16 can be uniformly used to characterize and compare sieving and functional stereology data volcaniclastic deposits typically consist of mixtures of particles that vary greatly in density and porosity hydraulic sorting ratios can be used to test whether inferred density of mixed clast populations of pumice and dense clasts are hydraulically sorted with each other considering various types of transport under water evaluation of this ratio for our samples shows that most studied volcaniclastic facies are deposited by settling from density currents and that basal dense clast breccia are emplaced by shear rolling these hydraulic sorting ratios can be applied to any type of clastic rocks and indifferently on consolidated and unconsolidated samples

a hot miocene subaqueous scoria flow deposit in the shimane peninsula sw japan abstract a subaqueous scoria flow deposit occurs in the miocene takashibiyama formation in sw japan faunal assemblages in associated sediments suggest an outer shelf to upper bathyal environment with water depth likely between 200 and 1500 m the deposit 5 7 m thick is similar to subaerial scoria flow deposits containing mainly non to moderately vesiculated hyalopilitic basaltic andesite lapilli and coarse ash the essential basaltic andesite clasts are variably vesiculated even within single clasts and are commonly cracked with curviplanar surfaces whereas the inner parts are cracked in a pattern similar to perlitic cracks the clasts are blocky with curviplanar surfaces if non to poorly vesiculated and are fibrous with irregular shapes and flattened by compaction if more vesiculated at one proximal location fines depleted rootless pipes 5 90 cm wide and 1 3 m long occur and spherical to amoebic vesicles 0 01 0 3 mm in diameter and filled with stilbite quartz or greenish brown clay are common in the fine ash matrix and in siltstone clasts contained in the deposit the vesicles represent open spaces once supported by gas and the rootless pipes are interpreted as gas escape pipes magnetization vectors of essential clasts are dispersed not at random but around a single direction suggesting that the clasts gained thermoremanent magnetism mainly during cooling in the flow or during post emplacement cooling and then rotated to some extent by differential movement of the flow or by gas escape in the deposit the vesicularity shape and texture of essential clasts suggest a phreatomagmatic eruption involving magmatic vesiculation and dynamic interaction of magma and ambient water the perlitic cracks in the inside of the essential clasts and the paleomagnetic vectors of the essential clasts indicate that the flow was initially hot and that the deposit cooled slowly internal depositional features change rapidly over only 500 m rootless pipes and vesicles in the fine ash matrix and siltstone clasts are therefore absent at distal locations indicating that an initially cohesionless debris flow quickly became sufficiently turbulent to mix with ambient seawater

constraint envelope analyses of macroecological patterns reveal climatic effects on pleistocene mammal extinctions abstract quantitative analysis of macroecological patterns for late pleistocene assemblages can be useful for disentangling the causes of late quaternary extinctions lqe however previous analyses have usually assumed linear relationships between macroecological traits such as body size and range size range shift that may have led to erroneous interpretations here we analyzed mammalian datasets to show how macroecological patterns support climate change as an important driver of the lqe which is contrary to previous analyses that did not account for more complex relationships among traits we employed quantile regression methods that allow a detailed and fine tuned quantitative analysis of complex macroecological patterns revealed as polygonal relationships i e constraint envelopes we showed that these triangular shaped envelopes that describe the macroecological relationship between body size and geographical range shift reflect nonrandom extinction processes under which the large bodied species are more prone to extinction during events of severe habitat loss such as glacial interglacial transitions hence we provide both a theoretical background and methodological framework to better understand how climate change induces body size biased species sorting and shapes complex macroecological patterns

vesiculation and fragmentation history in a submarine scoria cone forming eruption an example from nishiizu izu peninsula japan an uplifted 50 m thick half dissected submarine emplaced below wave base scoria cone occurs as dipping beds in coastal outcrops at nishiizu on the izu peninsula in japan concentrically outward dipping weakly stratified ungraded framework supported thin to very thick beds consist of brown coarse tuff to scoria lapilli tuff with outsized fluidal bombs throughout accessory lithic clasts chiefly occur in the lowermost visible beds scoria bombs have quenched margins weak bread crust textures and their vesicle number densities decrease inward which is indicative of fast surface cooling composite textures in the scoria bombs indicate recycling and agglutination of quenched and semi molten pyroclasts at the submarine vent in contrast to weak concentric gradations in vesicle size distribution in the bombs lapilli have asymmetrical gradients in vesicle size distribution indicating that they are fragments of coarser quenched lumps three grain size modes characterise the nishiizu brown scoria with coarse magma lumps ejected during magmatic fragmentation and quench jointed upon contact with seawater to be subsequently fragmented into lapilli and coarse ash by various styles of fragmentation where seawater plays a critical role the cone was constructed by slow moving fallout fed granular flow creep fed directly by suspension settling focused at the crater rim but extending onto the cone flanks with only minor resedimentation by granular flows nishiizu deposits yield an exceptional record of eruption and sedimentation dynamics during submarine cone building activity and in this study we compare their vesiculation and fragmentation mechanisms with those of potential subaerial analogues

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

explosive destruction of a pliocene hot lava dome underwater dogashima japan transition from effusive to explosive volcanism is common during subaerial eruptions and here we demonstrate that this behavior is also possible underwater the pyroclastic facies produced underwater are distinctive and can be used to distinguish subaqueous from subaerial eruptions and depositional settings the pliocene dogashima formation izu peninsula japan is a pumice rich succession originally deposited in an open marine below wave base setting jutzeler et al 2014a a thick clast supported gray andesite breccia composed of very coarse dense andesite clasts with quenched margins was sourced from disintegration of an active lava dome overall the gray andesite breccia is gradationally to sharply overlain by thick graded clast supported white pumice breccia chiefly composed of angular pumice clasts and free broken crystals regional setting and distinctive facies show that this succession was produced by a fully underwater magmatic volatile driven pumice forming explosive eruption the gradational contact between the two breccias compositional similarities rare mingled clasts and fluidal textures in the gray andesite clasts suggest that the explosive eruption destroyed a hot lava dome and generated an eruption fed high concentration density current in most places the coarsest hot lava dome fragments were deposited first followed by the lower density white pumice clasts the low amount of fine 2 mm components well developed hydraulically controlled grading and sorting clast angularity and very coarse dome derived clasts some including well defined quenched margins and common fluidal textures distinguish the products of subaqueous effusive to explosive eruptions from their subaerial counterparts

fallout of pyroclastic debris from submarine volcanic eruptions volcanic fallout deposits on land being widespread and accessible for study have received much attention and have revealed a great deal about subaerial eruption mechanisms in contrast virtually nothing is known about equivalent deposits produced by submarine volcanoes despite the probable abundance of such material in today s oceans and in accreted volcanic arc terrains many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns experiments on water saturated pumice and pieces of rock lithics show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters pieces of pumice may be five to ten times as large as codeposited lithic fragments similar material erupted into the air and deposited on land displays less well developed bimodality pumice diameters are generally two to three times as large as associated lithics submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain

was a dacite dome implicated in the 9 500 b p collapse of mt ruapehu a palaeomagnetic investigation constraining the process by which volcanoes become unstable is difficult several models have been proposed to explain the driving forces which cause volcanic edifices to catastrophically collapse these include models for destabilisation of volcanic flanks by wedging due to dyke intrusion and the weakening of mechanical properties by pressurisation of pore fluids it is not known which if any of the models are relevant to particular sector collapse events recent developments in the palaeomagnetic estimation of emplacement temperatures of volcaniclastic rocks have shown that even relatively low emplacement temperatures can be recorded by volcaniclastics with high fidelity we have carried out a palaeomagnetic study of emplacement temperatures to investigate the role of igneous activity in the initiation of the 9 500 b p murimotu sector collapse of mt ruapehu new zealand this debris avalanche deposit has three fades which are stratigraphically superimposed and the lowermost fades contains three lithological assemblages representing different segments of the edifice which were transported with little internal mixing within the flow we have determined that some of the dacite bearing assemblage 1 fades 1 was hot 350 c during transport and emplacement whereas none of the other lithological assemblages of fades contained hot material our interpretation is that a dacite dome was active on the ancient ruapehu edifice immediately prior to the murimotu sector collapse the partially cooled carapace of the dome and material shed from this part was incorporated into the avalanche deposit along with cold lavas and volcaniclastics we have not found evidence for incorporation of material at or close to magmatic temperatures at least in the sampled locations our palaeomagnetic work allows us to develop a comprehensive new palaeomagnetic classification of volcaniclastics

more than three million years of community evolution the temporal and geographical resolution of the plio pleistocene western eurasia mammal faunas abstract in this study we collected in a database faunal lists for more than 800 eurasian fossil localities yielding large mammal remains so as to produce continental level ecologic evolutionary units eurasian paleocommunities ea pcoms via bootstrapped cluster analysis ea pcoms are meant to represent taxonomically distinct assemblages of species ea pcoms allow the evolution of large mammal assemblages to be traced both in time and space this latter attribute spatial resolution represents the most important innovation here and contrasts with classic biochronologic schemes from which ea pcoms clearly depart the merits and limitations of this innovation are discussed in detail

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

submarine eruption fed and resedimented pumice rich facies the dogashima formation izu peninsula japan in the izu peninsula japan the pliocene pumice rich dogashima formation 4 55 0 87 ma displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave base marine setting it includes high concentration density current deposits that contain clasts that were emplaced hot indicating an eruption fed origin the lower part of the dogashima 2 unit consists of a very thick sequence 1 m pumice and ash rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension in dogashima 1 and 2 thick cross and planar bedded facies composed of sub rounded pumice clasts are intercalated with eruption fed facies implying inter eruptive mass wasting on the flank of a submarine volcano and reworking and resedimentation by high energy tractional currents in a below wave base environment

silicic magmas in the izu bonin oceanic arc and implications for crustal evolution abundant rhyolitehaseruptedfromthe izu bonin marianavolca nic arc ibm arc from its earliest stage eocene to the present geochemically three types of quaternary rhyolites exist in the izu bonin arcfront and theyare closely related tovolcanotypeand crus tal structure the dominantly basaltic islands of the volcanic frontproduce small volumes of rhyolites that we call r1 the submarinecalderas of the volcanic front erupt mostly rhyolite that we call r2 seamounts knolls and pillow ridges in thebackarcextensionalzoneare mostly basaltic but also contain rhyolites that we call r3 thethickest total crust and the thickest intermediate compositionmiddle crust occurs below the dominantly basaltic volcanoes whereas the intermediate composition middle crust tends to be thin nerbeneaththesubmarinecalderas r1rhyolitesmaybederivedfromquaternary andesitic sources whereas r2 and r3 rhyolites may bederivedfromoligoceneones thehighercao al

bacteriohopanepolyol distribution in yenisei river and kara sea suspended particulate matter and sediments traces terrigenous organic matter input abstract bacteriohopanepolyols bhps are ubiquitous bacterial membrane lipids encountered in soils river and marine suspended particulate matter spm and sediments their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil derived bacterial organic matter om and in some cases the presence of bacterial groups and their activities in aquatic systems we have studied the bhp distribution in the spm of a major siberian river yenisei river that crosses a large latitudinal gradient draining a large part of mongolia and siberian russia the yenisei river is the main river to flow into the kara sea a shelf sea of the arctic ocean we show that the bhp distribution and concentration of spm and surface sediments of the yenisei outflow in the kara sea allow to trace soil marker bhps and evaluate the performance of the r soil index a proxy developed to trace bacterial soil derived om soil marker bhps are present in the yenisei river and their concentration decreases from the yenisei river outflow into the offshore marine sediments the r soil correlates well with an independent proxy for bacterial om the bit index r2 0 82 and has a moderate correlation with the 13corg values a bulk om proxy for terrigenous input r2 0 44 consequently the r soil index performs well in the kara sea strengthening its application for tracing bacterial om in the arctic ocean both in modern and downcore sediments furthermore a suite of bhps that are characteristic for methanotrophic bacteria i e 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol and 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol is encountered in the yenisei outflow sediments these components are partly sourced from terrigenous sources but are likely also produced in situ in the marine sediments the distribution of the pentafunctionalized cyclitol ether bhp in the marine systems is noteworthy and indicates that it can possibly be applied as a marker for cyanobacterial biomass in marine sediments

remelting of an andesitic crust as a possible origin for rhyolitic magma in oceanic arcs an example from the izu bonin arc

the influence of climate on species distribution over time and space during the late quaternary abstract understanding the effect of climate on the composition of communities and its change over time and space is one of the major aims in ecology and paleoecology herein we tackled on this issue by studying late quaternary large mammal paleocommunities of eurasia the late quaternary was a period of strong environmental instability especially characterized by the occurrence of the last glacial maximum lgm we used community phylogenetics and joint species distribution models in order to understand the factors determining paleocommunity composition in the late quaternary our results support the existence of strong climatic selection operating on the lgm fauna both through the disappearance of warm adapted species such as elephas antiquus hippopothamus amphibious and stephanorhinus hemitoechus and by setting the stage for the existence of a community characterized by cold adapted large mammals patterns of abundance in the fossil record co occurrence between species pairs and the extent of climatic forcing on faunal composition differ between paleocommunities but not between extinct and extant species which is consistent with the idea that climate change rather than the presence of humans exerted a major effect on the survival of the late quaternary megafauna

on the emplacement of ignimbrite in shallow marine environments abstract the emplacement of primary pyroclastic flow deposits on the sea floor can occur 1 by nonturbulent dense flows that conserve their heat under water or 2 because the flow either turbulent or nonturbulent temporarily pushes back the shoreline the feasibility of the second mechanism has been investigated theoretically and experimentally using a simple analogue system the experiments involved sustained turbulent saline currents of different densities flowing into a sectorial tank of ambient fluid that was either lighter or denser than the current the currents in all cases displaced the entire layer of ambient fluid up to a distance r irrespective of whether they were denser or lighter r is analogous to the shoreline displacement distance up to which hot ignimbrite can be emplaced by a pyroclastic flow entering the sea by varying flow rate density contrast and depth of the ambient fluid layer a simple equation for r is found that is in good agreement with the experimental data the effect of seawater boiling on shoreline displacement was also investigated by experiments using currents of carbonate solution that produced gas when flowing into a layer of ambient acid the distance r was not reduced in these experiments the equations show that pyroclastic flows of about 10 km 3 or more are capable of pushing back the sea at least a couple of kilometres and possibly more in areas of extensive shallow water enabling hot ignimbrite to be laid down on the seabed at depths corresponding to a few tens of metres shoreline displacement is thus a feasible mechanism for the emplacement of welded ignimbrite in shallow marine settings emplacement of subaerially erupted ignimbrite below storm wave base is not ruled out by the calculations but requires a combination of high discharge rate sustained eruption low density contrast between flow and water steep bathymetric gradient and small island volcano application of the model to the 1883 krakatau eruption suggests that seawater displacement may explain the occurrence of primary ignimbrite on the seabed 10 km northwest of the volcano