79 ad vesuvius pdc deposits temperatures inferred from optical analysis on woods charred in situ in the villa dei papiri at herculaneum italy abstract determining the deposit temperature of pyroclastic density currents pdcs is a first order priority in the assessment of volcanic hazard for past eruptions in which no direct measurements are possible pdc deposit temperatures have been calculated mainly using magnetic proxies a more recent and innovative approach consists of the determination of the degree of charring of preserved wood fragments by optical analysis in this study we perform optical analyses on wooden beams belonging to the villa dei papiri at the archeological site of herculaneum which was destroyed by pdcs during the 79 ad eruption of vesuvius the new temperature data from this study range between 240 c and 370 c and are in good agreement with literature data for this eruption the large t variation measured can be interpreted as due to the interaction of the pdcs with the local environment i e the impacted buildings of the villa and the sea shoreline the study of in situ charred wood allows to constrain the charring kinetics and to evaluate the sensitivity of the reflectance proxy in recording pdc depositional features we demonstrate that the charcoal reflectance is an excellent proxy for the determination of the pdc deposit temperatures even at a local scale and it can be used in conjunction with or in alternative to other more traditional methodologies especially in case of pre heating effects which may alter the t determinations by thermoremanent magnetization

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

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

interaction of pyroclastic flows with building structures in an urban settlement a fluid dynamic simulation impact model abstract a fluid dynamic model has been used to simulate pyroclastic flow urban settlement interactions the geometrical model used here accounts for part of the torre del greco suburb within the urban sector facing vesuvius the partial differential equations of mass momentum and turbulent energy balance have been integrated using a finite element method on a 3 d domain the simulation has been limited both to the isothermal case and the stationary boundary conditions the results show a partial shielding effect of structures closer to the volcano on structures behind them as well as a total pressure waning pattern along the mean direction of the pyroclastic flow

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

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

structural resistance of reinforced concrete buildings under pyroclastic flows a study of the vesuvian area abstract the analysis of the effects of pyroclastic flows on humans and on buildings represents the main tool to define the boundary of the most hazardous area around an active volcano such as somma vesuvius estimation of the lateral pressure on buildings derived from analogies with the damages observed after a nuclear explosion valentine 1998 j volcanol geotherm res 87 117 140 lead to pressure values and or structural resistance which are not realistic too high recent evidence baxter 2000 human and structural vulnerability assessment for emergency planning in a future eruption of vesuvius final report ec project env4 ct98 0699 young et al 1997 eos trans am geophys union 78 401 have shown that beyond 2 3 km from the vent even after a great eruption resistance to collapse of buildings affected by a pyroclastic flow is still possible neri et al 2000 numerical simulation of pyroclastic flows in human and human and structural vulnerability assessment for emergency planning in a future eruption of vesuvius final report ec project env4 ct98 0699 by means of a numerical model of a collapsing column show that the peak overpressures of the pyroclastic flows range from 1 to 2 kpa at a distance from the vent of about 4 5 km where important historical centres of the vesuvian area are located a detailed analysis of urban settlement of the area cherubini et al 2001 vulnerabilita sismica dell area vesuviana gruppo nazionale per la difesa dai terremoti cnr roma has shown that most of the people live in reinforced concrete r c structures not designed to resist horizontal seismic actions the present work is aimed at analyzing the collapse limit load of r c structures to horizontal pressure for different structural design typologies strong aseismic weak aseismic strong non aseismic weak non aseismic the simulations performed have also taken into account the specific features of the r c structures of the area local building practice the limits of resistance for each typology in case of regular and irregular buildings are provided such limits of resistance are in good agreement with the literature data coming from collapse simulation of buildings under seismic actions

influences of urban fabric on pyroclastic density currents at pompeii italy 1 flow direction and deposition 1 to assess ways in which the products of explosive eruptions interact with human settlements we performed volcanological and rock magnetic analyses on the deposits of the a d 79 eruption at the pompeii excavations italy during this eruption the roman town of pompeii was covered by 2 5 m of fallout pumice and then partially destroyed by pyroclastic density currents pdcs anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental pdcs that entered the town these results integrated with volcanological field investigations revealed that the presence of buildings still protruding through the fallout deposits strongly affected the distribution and accumulation of the erupted products all of the pdcs that entered the town even the most dilute ones were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current the degree of interaction varied mainly as a function of obstacle height and density stratification within the current for examples the lower part of the eu4pf current left deposits up to 3 m thick and was able to interact with 2 to 4 m high obstacles however a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion enabling it to flow over the town it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town

paleomagnetic evidence for low temperature emplacement of the phreatomagmatic peperino albano ignimbrite colli albani volcano central italy the peperino albano approximately 19 36 ka old is a phreatomagmatic pyroclastic flow deposit cropping out along the slopes of the associated albano maar colli albani volcano italy the deposit exhibits lateral and vertical transitions from valley pond to veneer facies as well as intracrater facies we present the results of a paleomagnetic study of thermal remanent magnetization trm of the lithic clasts of the peperino albano ignimbrite that provide quantitative estimates of the range of emplacement temperatures across the different facies of the ignimbrite emplacement temperatures estimated for the peperino albano ignimbrite range between 240 and 350 c with the temperatures defined in the intracrater facies being generally lower than in the valley pond and veneer facies this is possibly due to the large size of the sampled clasts in the intracrater facies which when coupled with low temperature at the vent were not completely heated throughout their volume during emplacement the emplacement temperatures derived from the paleomagnetic results are in good agreement with the presence of un burnt plants at the base of the ignimbrite indicating that the temperature of the pyroclastic flow was lower than the temperature of ignition of wood paleomagnetic results from the peperino albano confirm the reliability of the paleomagnetic approach in defining the thermal history of pyroclastic flow deposits

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

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

event stratigraphy and emplacement mechanisms of the last major caldera eruption on sete cidades volcano sao miguel azores the 16 ka santa barbara formation sete cidades is an active yet dormant central volcano located in the westernmost part of sao miguel island azores archipelago characterized by a 5 km wide multi stage caldera formed in the last 36 ka in this work we present new stratigraphic grain size petrographic and geochemical data of the 16 ka santa barbara formation related to the last stage of caldera formation we define the lithostratigraphy of this pyroclastic sequence into three members based on stratigraphic position lithofacies and distribution of the deposits the preserved deposits outcrop in a narrow area over 5 km between the caldera rim and the coastal cliffs and include ash beds with dispersed lapilli lower member coarse grained pumice and lithic rich lapilli tuffs middle member and pumice fall deposits upper member the minimum bulk volume preserved on land is about 0 03 km3 however the majority of the pyroclastic products were deposited in the ocean the presence of magmatic mafic enclaves 48 wt sio2 within the juvenile pumice clasts 63 wt sio2 is testimony to the injection of trachybasaltic magma into the trachytic magma reservoir shortly prior to eruption the mingling of these two magmas acted as the eruption trigger the eruption history can be divided into three main phases each characterized by different eruption styles and deposit emplacement mechanisms accompanied by enlargement of the caldera the eruption started with a sequence of short lived explosions generating unstable columns that produced ash fallout and generated dilute pyroclastic density currents mostly deposited in the sw sector of the volcano the climax of the eruption was marked by successive low fountaining events that generated high particle concentration pyroclastic density currents emplaced on the sw and ne flanks the final phase of the eruption was characterized by establishment of a sub plinian eruption column that produced pumice fall deposits on the ne flank of the volcano our study allows delineation of eruptive scenarios for future major explosive eruptions at sete cidades a volcano which is located on the most populated island of the azores sao miguel island and can provide a framework for the assessment of volcanic hazards on oceanic islands elsewhere

how coriolis forces can limit the spatial extent of sediment deposition of a large scale turbidity current abstract the rotation rate of the earth controls the deposition scale of turbidity currents when their flow transit time is comparable to one day using laboratory experiments it is shown that the maximum length scale l of deposition is set by the scale where the rossby number of the current is equal to one the dimensionless rossby number is defined as ro u fl where u is a depth averaged velocity of the turbidity current and f is the coriolis parameter in these new laboratory experiments the coriolis parameter is varied by changing the platform rotation rate and there is good agreement between experimental observations and the prediction that the extent of the deposition scales as l 4 1 4 g v f 1 4 where g is the reduced gravity and v the initial volume of the sediment laden material this scaling implies that the depositional patterns will vary with latitude and that at higher latitudes one would expect smaller thicker deposits using this scaling implies that the 200 400 km spatial extent of the turbidite arising during the 1929 grand banks earthquake had ro 1 and so coriolis forces controlled the length scale of the turbidite deposition

archaeomagnetic results from mural paintings and pyroclastic rocks in pompeii and herculaneum abstract this work investigates the magnetic remanence associated with red pigments from murals at pompeii and compares their directions to those of the pyroclastic rocks from the vesuvius ad 79 eruption the remanence of the murals is shown using x ray analyses to be carried by haematite murals in thermae stabianae known to have been painted a few years before ad 79 yield an archaeomagnetic direction d 1 2 i 58 0 95 5 5 indistinguishable from that of a nearby kiln d 358 0 i 59 1 95 1 7 evans and mareschal 1989 probably last used immediately prior to the eruption the directions are also consistent with those of fine grained pyroclastic rocks from the eruption d 351 2 i 57 9 95 3 4 and lithic and tile fragments embedded within them d 358 5 i 60 4 95 8 5 other paintings of the 1st century ad yield similar directions with a lower statistical definition this study shows that murals can retain their remanent magnetization for centuries and demonstrates the viability in principle of pictorial remanence as an archaeomagnetic tool

stratigraphy paleomagnetism and magnetic fabric of the toba tuffs constraints on the sources and eruptive styles the toba depression in north central sumatra is a complex of several overlapping calderas resulting from three major ignimbrite forming eruptions within the depression the upland masses of samosir and northern uluan consist of welded ignimbrite capped by coarse breccia and lacustrine sediment hitherto interpreted to be two parts of a single resurgent dome this study has demonstrated that the welded tuffs of samosir and uluan have different magnetic polarities and therefore at least two different ignimbrites are present the samosir uluan massif may consist of parts of two resurgent domes the first ignimbrite eruption occurred at 0 84 ma and produced a very thick 400 m densely welded unit having a reversed polarity anisotropy of magnetic susceptibility ams flow direction and lithic size data indicate that the source lies in the southern part of the toba depression and the thick deposit of uluan is thought to have ponded in a 40 km wide caldera the second ignimbrite is normally magnetized ams flow direction data indicate two separate source vents one to the north in the haranggaol caldera and another to the south the thick deposit at samosir is thought to have ponded in the southern caldera coarse sediments then accumulated over samosir and northern uluan and were capped by lacustrine deposits a renewed episode of resurgence then uplifted samosir island and possibly the northern part of uluan at approximately 0 075 ma the last and apparently largest ignimbrite eruption occurred from calderas in the north and south parts of the toba depression this ignimbrite is mostly nonwelded and normally magnetized part of the uluan dome was destroyed by collapse of the sibandung caldera and latung graben and concomitant with renewed subsidence of the haranggaol and porsea calderas

sediment slides and turbidity currents on the laurentian fan sidescan sonar investigations near the epicenter of the 1929 grand banks earthquake the epicenter area of the 1929 grand banks earthquake on the continental slope south of newfoundland has been investigated using sea marc i a deeply towed midrange sidescan sonar with a 4 5 khz subbottom profiler shallow slides pass downslope into debris flows on the muddy continental slope east of the epicenter at the head of the eastern valley of the laurentian fan west of the epicenter arcuate slide scars cut undisturbed upper slope sediment and lead downslope to a lineated erosional seabed at a water depth of about 1600 m this erosional seabed passes into extensive fields of 100 m wavelength gravel waves situated on the broad irregular valley floor the gravel waves become better developed downslope and extend at least to water depths of 3000 m all these morphological features appear fresh on the sidescan sonograms suggesting that they date from the 1929 earthquake event and the distribution of slides corresponds to the area of instantaneous cable breaks in 1929 the upper limit of erosion on valley walls suggests that the 1929 turbidity current was less than 300 m thick timing of cable breaks downfan suggests that flow velocities were sufficient to rework gravel deposits into large bedforms during waning flow stages over elevated areas of the valley floor similar cross bedded coarse sands and gravels are common in ancient channel deposits

magnetic fabric flow directions and source area of the lower miocene peach springs tuff in arizona california and nevada we have used anisotropy of magnetic susceptibility ams to define the flow fabric and possible source area of the peach springs tuff a widespread rhyolitic ash flow tuff in the mojave desert and great basin of california arizona and nevada the tuff is an important stratigraphic marker from the colorado plateau to barstow california a distance of 350 km however the location of its source caldera is unknown dated at 18 5 ma by 40ar 39 ar the tuff erupted during the early stages of miocene extension along the lower colorado river the thicker accumulations 100 m occur at kingman arizona and in the piute mountains california on opposite sides of the colorado river extensional corridor our ams studies produced well defined magnetic lineations in 30 of 42 sites distributed throughout the tuff typical ratios of the principal ams axes are 1 01 for the magnetic lineation kmax kint and 1 02 for the foliation kint kmin the bulk magnetic susceptibility of the peach springs tuff averages 2 0 10 3 in the si unit system the subhorizontal lineations which presumably parallel the flow directions form a pattern radiating outward from the approximate center of the outcrop area magnetic foliations define an imbrication that generally dips away from the distal margins and toward the center of the outcrop of the tuff the lineation and imbrication indicate a source region near the southern tip of nevada defining the best intersection of the ams lineations required restoration of major extension strike slip faulting and associated tectonic rotation in the disrupted tuff the optimum intersection of magnetic lineations lies in the southern black mountains of arizona on the eastern side of the colorado river extensional corridor no caldera structures are known from that area but the area contains thick sections of the peach springs tuff above a silicic volcanic center the caldera may be buried under younger deposits in the mohave valley of arizona tertiary granite in the newberry mountains may represent a deeper level of the peach springs tuff vent that has been exhumed by detachment faulting

flow directions in ash flow tuffs a comparison of geological and magnetic susceptibility measurements tshirege member upper bandelier tuff valles caldera new mexico usa this study concludes that the elongation axis k 1 of the ellipsoid of anisotropic magnetic susceptibility ams is a suitable proxy for flow axis in ashflow tuffs 153 oriented samples 176 specimens were studied from 18 sites in the 1 1 ma tshirege member of the bandelier tuff these sites are distributed around the valles caldera at distances of 5 25 km outside of the rim k 1 axes correlate well with postulated radial flow axes at 13 sites k 1 also agrees with measured geological flow indicators mainly imbricated larger clasts at 7 sites at 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredk 1 axes thek 1 axes correspond well with geological flow indicators indicating that the divergence of flow from the predicted radial flow pattern is real two major topographic buttresses are suggested as the cause of flow divergence for the tshirege ash flows the san pedro buttress northwest of the caldera and the san miguel buttress in the southeast in situk 1 axes plunge about 7 toward the source at two thirds of the sites therefore the plunge ofk 1 is a plausible in situ indicator for thedirection of flow multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash flow emplacement these observations raisre the question of how best to represent mean flow directions in ash flow sheets by eigenvector methods by vector sum methods or by modes a method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined imbrication determined in this way at one third of the sites dips toward the source i e up flow the minimum k 3 axis of the ams ellipsoid correlates with the flow foliation rather than with the larger clast imbrication the flow axes of ash flows correspond with thek 1 axes not with the declination ofk 3 axes as suggested by some authors initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction which is reversed with a mean ofd 173 5 i 38 4 95 3 4 n 18 this mean is not different at the 95 confidence level from that of earlier workers the mean pole at 098 0 e 74 8 n a 95 3 3 n 18 is about 15 far sided relative to the expected time averaged geomagnetic pole suggesting a history of emplacement too short to adequately average secular variation

experimental evidence links volcanic particle characteristics to pyroclastic flow hazard abstract pyroclastic flows represent the most hazardous events of explosive volcanism one striking example being the famous historical eruption of vesuvius that destroyed pompeii ad 79 much of our knowledge of the mechanics of pyroclastic flows comes from theoretical models and numerical simulations valuable data are also stored in the geological record of past eruptions including the particles contained in pyroclastic deposits but the deposit characteristics are rarely used for quantifying the destructive potential of pyroclastic flows by means of experiments we validate a model that is based on data from pyroclastic deposits the model allows the reconstruction of the current s fluid dynamic behaviour model results are consistent with measured values of dynamic pressure in the experiments and allow the quantification of the damage potential of pyroclastic flows

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

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

interaction between pyroclastic density currents and buildings numerical simulation and first experiments abstract the interaction between pyroclastic density currents and buildings is investigated by means of numerical simulation and large scale experiments numerical simulation is performed with the euler lagrange approach using a two way coupling between gas and particles of three sizes the collapse of an eruptive column consisting of a mixture of gas and pyroclasts is produced experimentally and the impact of the resulting shear current with mock ups representing buildings is monitored a combination of results from simulations and experiments shows that upon impact with a building the multiphase current develops strong turbulence intensity which significantly affects particle dispersion the flow recirculation around the building induces forced deposition at the front and wake in the back wall with flow reattachment farther away these changes produce a variation in the dynamic pressure which is the most important parameter for assessing the impact of pyroclastic density currents moving over inhabited areas

precursory phenomena and destructive events related to the late bronze age minoan thera greece and ad 79 vesuvius italy plinian eruptions inferences from the stratigraphy in the archaeological areas

volcanoes and human history abstract the study of volcanic hazards leads inevitably to questions of how past cultures have lived in volcanically active regions of the world here we summarize linkages between volcanological archaeological and anthropological studies of historic and prehistoric volcanic eruptions with the goal of evaluating the impact of past eruptions on human populations to better prepare for future events we use examples from papers collected in this volume to illustrate ways in which volcanological studies aid archaeological investigations by providing basic stratigraphic markers and information about the nature and timing of specific volcanic events we then turn to archaeological perspectives which provide physical evidence of the direct impacts of volcanic eruptions such as site abandonment and human migration as well as indirect impacts on local cultures as reflected in human artifacts finally we review anthropological studies of societal responses to past and recent volcanic eruptions we pay particular attention to both the psychological impact of catastrophic events and records of these impacts encoded within oral traditions taken together these studies record drastic short term eruption impacts but adaptation to volcanic activity over the longer term largely through strategies of adaptive land use

the afragola settlement near vesuvius italy the destruction and abandonment of a bronze age village revealed by archaeology volcanology and rock magnetism abstract public works in progress in the campanian plain north of somma vesuvius recently encountered the remains of a prehistoric settlement close to the town of afragola rescue excavations brought to light a bronze age village partially destroyed and buried by pyroclastic density currents pdcs of the vesuvian pomici di avellino eruption 3 8 14c ka bp and subsequently sealed by alluvial deposits volcanological and rock magnetic investigations supplemented the excavations careful comparison between volcanological and archaeological stratigraphies led to an understanding of the timing of the damage the buildings suffered when they were struck by a series of pdcs the first engulfed the village located some 14 km to the north of the inferred vent and penetrated into the dwellings without causing major damage the buildings were able to withstand the weak dynamic pressure of the currents and deviate their path as shown by the magnetic fabric analyses some later collapsed under the load of the deposits piled up by successive currents stepwise demagnetization of the thermal remanent magnetization trm carried by potsherds embedded in the deposits yields deposition temperatures in the order of 260 320 c fully consistent with those derived from pottery and lithic fragments from other distal and proximal sites the fairly uniform temperature of the deposits is here ascribed to the lack of pervasive air entrainment into the currents this in turn resulted from the lack of major topographical obstacles along the flat plain the coupling of structural damage and sedimentological analyses indicates that the currents were not destructive in the afragola area but trm data indicate they were still hot enough to cause death or severe injury to humans and animals the successful escape of the entire population is apparent from the lack of human remains and from thousands of human footprints on the surface of the deposits left by the first pdcs people were thus able to walk barefoot across the already emplaced deposits and escape the subsequent pdcs the rapid cooling of the deposits was probably due to both their thinness and heat dissipation due to condensation of water vapour released in the mixture by magma water interaction

magnetic fabric of ignimbrites a case study from the central anatolian volcanic province the magnetic fabric of the pliocene kizilkaya ignimbrite in the central anatolian volcanic province has been investigated by anisotropy of magnetic susceptibility ams and isothermal remanent magnetization airm seven sections were sampled at various stratigraphic heights within the devitrified portion of the ignimbrite the magnetic mineralogy is complex titanomagnetite occurs as magmatic grains and as inclusions in other phenocryst and glass shards an oxidized phase and hematite occur in deposit levels affected by alteration processes the disturbance produced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than 1 from the site mean value of the density the ams fabric varies along each individual section neither the ams magnetic lineation nor the magnetic foliation plunge clearly define a common area as the vent location the airm fabric of low coercivity minerals mainly represented by free titanomagnetite grains of magmatic origin is consistent between sites and the inferred flow directions converge on a region near derinkuyu in the nevsehir plateau previously reported as the kizilkaya ignimbrite source area this study shows that systematic use of the remanent fabric improves the results given by ams and aids the identification of the primary magnetic fabric related to the ignimbrite emplacement dynamics

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

thermal state and implications for eruptive styles of the intra plinian and climactic ignimbrites of the 4 6 ka fogo a eruption sequence sao miguel azores the 4 6 ka fogo a plinian eruption was a caldera forming volcanic event on sao miguel island azores the deposit succession is very complex composed of a thick trachytic plinian fallout deposit interstratified with two intra plinian ignimbrites named pink ignimbrite and black ignimbrite sequentially the succession ends with a main ignimbrite named dark brown ignimbrite which represents the deposit of complete collapse of the eruption column and the end of the eruption in this work emplacement temperatures of the three ignimbrites are estimated by study of partial thermal remanent magnetization ptrm of lithic clasts a total of 140 oriented lithic clasts were collected from 15 localities distributed along the northern and southern flanks of fogo volcano the paleomagnetic data reveal different emplacement temperatures and thermal histories that were experienced by each ignimbrite the results indicate the presence of five different paleomagnetic behaviours that suggest emplacement temperatures of 350 400 c for the first pink intra plinian ignimbrite temperatures higher than 580 600 c for the second black intra plinian ignimbrite and 250 370 c for the last dark brown climactic ignimbrite the thermal history experienced by each pyroclastic flow and its ignimbrite deposit was also assessed by the use of the magnetite ilmenite geothermometer to determine the pre eruptive magma temperature estimated to be around 900 c we interpret the different emplacement temperatures of the fogo a ignimbrites as being due to a combination of factors these include i collapse from different heights of the eruption column and the resultant different amounts of air entrainment into the gas particle mixture ii variable content of lithic clasts and iii different types of juvenile clasts in the ignimbrites

evidence of two holocene phreatomagmatic eruptions at stromboli volcano aeolian islands from paleomagnetic data 1 we present detailed stratigraphic sedimentological and paleomagnetic analyses of holocene phreatomagmatic deposits at stromboli volcano aeolian islands italy the investigated deposits belong to the secche di lazzaro succession sdl and to the advanced operations center of the department of civil defense coa succession both lying on the neostromboli lavas ca 13 5 ka the two stratigraphic successions have similar stratigraphic position and show a phreatomagmatic origin likely related to catastrophic magma water interaction processes during sector collapse events however the thermal remanent magnetization data of the lava lithics indicate that deposits of the sdl succession were emplaced at very low temperatures less than 140 c whereas the basal part of the coa deposit was emplaced at temperatures between 300 340 c paleomagnetic results indicate that the two investigated deposits may be related to two distinct eruptive events occurred during the holocene recent phreatomagmatic activity at stromboli apparently has occurred more frequently than previously believed consequently we must reconsider the recurrence interval of this dangerous eruptive scenario for stromboli

modelling pyroclastic density currents from a subplinian eruption at la soufriere de guadeloupe west indies france we have used a three dimensional non equilibrium multiphase flow numerical model to simulate subplinian eruption scenarios at la soufriere de guadeloupe lesser antilles france initial and boundary conditions for computer simulations were set on the basis of independent estimates of eruption source parameters i e mass eruption rate volatile content temperature grain size distribution from a field reconstruction of the 1530 ce subplinian eruption this event is here taken as a reference scenario for hazard assessment at la soufriere de guadeloupe a parametric study on eruption source parameters allowed us to quantify their influence on the simulated dynamics and in particular the increase of the percentage of column collapse and pyroclastic density current pdc intensity at constant mass eruption rate with variable vent diameter numerical results enabled us to quantify the effects of the proximal morphology on distributing the collapsing mass around the volcano and into deep and long valleys and to estimate the areas invaded by pdcs their associated temperature and dynamic pressure significant impact temperature 300 c and dynamic pressure 1 kpa in the inhabited region around the volcano is expected for fully collapsing conditions and mass eruption rates 2 107 kg s we thus combine this spatial distribution of temperature and dynamic pressure with an objective consideration of model related uncertainty to produce preliminary pdc hazard maps for the reference scenario in such a representation we identify three areas of varying degree of susceptibility to invasion by pdcs very likely to be invaded and highly impacted susceptible to invasion and moderately impacted and unlikely to be invaded or marginally impacted the study also raises some key questions about the use of deterministic scenario simulations for hazard assessment where probability distributions and uncertainties are difficult to estimate use of high performance computing techniques will in part allow us to overcome such difficulties but the problem remains open in a scientific context where validation of numerical models is still necessarily an incomplete and ongoing process nevertheless our findings provide an important contribution to the quantitative assessment of volcanic hazard and risk at la soufriere de guadeloupe particularly in the context of the current unrest of the volcano and the need to prepare for a possible future reawakening of the volcano that could culminate in a magmatic explosive eruption supplementary information the online version of this article 10 1007 s00445 020 01411 6 contains supplementary material which is available to authorized users

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

impact of the ad 79 explosive eruption on pompeii i relations amongst the depositional mechanisms of the pyroclastic products the framework of the buildings and the associated destructive events abstract a quantitative and qualitative evaluation of the damage caused by the products of explosive eruptions to buildings provides an excellent contribution to the understanding of the various eruptive processes during such dramatic events to this end the impact of the products of the two main phases pumice fallout and pyroclastic density currents of the vesuvius ad 79 explosive eruption onto the pompeii buildings has been evaluated based on different sources of data such as photographs and documents referring to the archaeological excavations of pompeii the stratigraphy of the pyroclastic deposits and in situ inspection of the damage suffered by the buildings the present study has enabled the reconstruction of the events that occurred inside the city when the eruption was in progress in particular we present new data related to the c j polibius house a large building located inside pompeii from a comparison of all of the above data sets it has been possible to reconstruct in considerable detail the stratigraphy of the pyroclastic deposits accumulated in the city to understand the direction of collapse of the destroyed walls and to evaluate the stratigraphic level at which the walls collapsed finally the distribution and style of the damage allow us to discuss how the emplacement mechanisms of the pyroclastic currents are influenced by their interaction with the urban centre all the data suggest that both structure and shape of the town buildings affected the transport and deposition of the erupted products for instance sloping roofs drained a huge amount of fall pumice into the impluvia a rectangular basin in the centre of the hall with the function to collect the rain water coming from a hole in the centre of the roof thus producing anomalous deposit thicknesses on the other hand flat and low sloping roofs collapsed under the weight of the pyroclastic material produced during the first phase of the eruption pumice fall in addition it is evident that the walls that happened to be parallel to the direction of the pyroclastic density currents produced during the second eruptive phase were minimally damaged in comparison to those walls oriented perpendicular to the flow direction we suggest that the lower depositional parts of the pyroclastic currents were partially blocked locally reflected and slowed down because of recurring encounters with the closely spaced walls within buildings locally the percentage of demolished walls decreases down current which has been interpreted as a loss in kinetic energy within the depositional system of the flow however it seems that the upper transport system by passed these obstacles then supplied new pyroclasts to the depositional system that restored its physical characteristics and restored enough kinetic energy to demolish the next walls and buildings further along its path

progressive abandonment and planform changes of the central platte river in nebraska central usa over historical timeframes this paper presents data compiled from aerial photography general land office maps glos and discharge data from the central platte river in nebraska that quantify and provide a new understanding of channel evolution and abandonment in a braided stream analyses of aerial photographs and glos in arcmap show that channel area decreased by an average of 46 from 1938 to 2006 and that channel widths in 1858 were an average of 539 greater than in 2006 annual discharge during 1942 2006 does not show a clear long term relationship with the decrease in channel width and area rather stabilization through vegetation of bars and channel banks is cited as the major contributing factor to channel shrinkage and the development of an anabranching system within the boundaries of the 1858 channel the stabilization of anabranches and the encroachment of vegetation onto banks abandoned channels and islands have significantly impacted the riparian ecosys tem as mobile sandy bars gradually disappeared annual aerial photographs of the platte river from 1984 to 2001 show that the river responds to year to year changes in mean discharge through the formation and disappearance of in channel features such as medium size transverse bars large transverse bars open channels exposed channel surfaces laterally accreted surfaces and vegetated channel islands vegetated channel islands and stable anabranches also increased during 1984 2009 significant change has also occurred since the beginning of the twentieth century on the wood river a local tributary to the platte river the wood river experienced a long term increase in sinuosity after it occupied the abandoned north channel of the platte river which last experienced major sediment transport 350 50 years ago according to an optically stimulated luminescence date the modern wood river is also superimposed on a prehistoric meandering pattern with significantly greater meander amplitude we present the first channel abandonment model to account for the gradual abandonment of the platte river braided stream system and its evolution from a braided to an anabranching system in stage 1 the channel prominently features macroform bars comprising downstream migrating foresets in stage 2 downstream migrating dunes are deposited over channel bed features and in stage 3 there is a shift from a braided stream to a stream dominated by anabranches and only channel bed features e g three dimensional dunes are present our new model characterizes the features expected to be found in abandoned braided channels as well as more temporary features that form and are destroyed through successive stages of abandonment

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