directional response of wind waves to a large wind shift abstract the directional response of a fully arisen sea to a 90 wind shift is studied using a combination of airborne radar and in situ directional wave observations the observations were made in february 1991 as a part of the surface wave dynamics experiment radar and buoy mean wave directions in several frequency bands are polynomial smoothed in fetch and duration coordinates and analyzed for the directional relaxation parameter b by using finite differences of the gridded smoothed data in a one dimensional advection equation for the mean wave direction the analysis is carried out using several different sets of buoy wind and wave data in an event window of 40 h in duration by 200 km in fetch 100 300 km offshore for the most well populated and reliable inverse wave age class in the study 1 2 u c 1 6 the authors find b 3 3 0 1 10 5 the data do not support any inference as to possible wave age dependence other than perhaps the null hypothesis b const u c frequencies near the

analysis of a rock slide stabilized with a toe berm a case study in british columbia canada abstract practical experience has shown that slope movement can be controlled by the placement of a berm near the toe of the moving mass during construction of the revelstoke project british columbia canada excavation of a large highway rock cut triggered movement of a 250 000 m 3 rock slide a 15 000 m 3 toe berm was used as a temporary measure to control the displacements of the slide and allow permanent remedial measures to be completed the rock slide was extensively investigated and monitored the sarma limit equilibrium method and the three dimensional distinct element program 3dec were used to investigate the stabilizing effect of the toe berm on the slope deformations in addition 3dec was used to investigate the effect of internal discontinuities on slope displacements the numerical model responded in a manner that is in general agreement with field observations and supported the observations that a small toe berm can be an effective remedial measure in controlling slope displacements

composite tuff ring cone complexes in jeju island korea possible consequences of substrate collapse and vent migration hydromagmatic volcanoes tuff rings and tuff cones in jeju island korea are divided into holocene volcanoes that were constructed upon rigid plateau forming lavas and early to middle pleistocene volcanoes that underlie the lavas and were constructed upon fragile unconsolidated sediments the older volcanoes are distinguished from the holocene volcanoes in that the former have irregular morphologies the irregular morphologies resulted from superposition or juxtaposition of multiple rim deposits of partial tuff rings and or tuff cones that have contrasting lithofacies characteristics bed attitudes and paleoflow directions the rim deposits are bounded by laterally persistent truncation surfaces which suggest large scale collapse of the substrate together with the overlying tephra piles and or erosion during a break in eruptive activity collapse was probably caused by the instability of the friable sedimentary substrate removal of lateral support because of downward quarrying of volcanic conduits and liquefaction of the water saturated substrate by volcanic seismicity the path of magma supply was diverted in some cases after collapse giving rise to migration of the active vent in other cases the eruption style changed abruptly from cone forming fallout dominated to ring forming surge dominated eruptions after collapse the resultant volcanic edifices thus consist of multiple rim beds of partial tuff rings and or tuff cones commonly with non circular morphologies substrate collapse and lateral vent migration as observed in jeju island appears to be an important phenomenon in hydromagmatic volcanoes because they are commonly constructed upon unstable sedimentary substrates substrate collapse and vent migration needs to be taken into account as an important control on volcano morphology and structures and as a means of lateral enlargement of terrestrial submarine or extraterrestrial volcanoes

compositional evolution of magma from paricutin volcano mexico the tephra record the birth of paricutin volcano mexico in 1943 provides an unprecedented opportunity to document the development of a monogenetic cinder cone and its associated lava flows and tephra blanket three type sections provide a complete tephra record for the eruption which is placed in a temporal framework by comparing both bulk tephra and olivine phenocryst compositions to dated samples of lava and tephra our data support the hypothesis of luhr 2001 that the first four months of activity were fed by a magma batch phase 1 that was distinct from the magma that supplied the subsequent eight years of activity we further suggest that the earliest erupted vanguard magma records evidence of temporary residence at shallow levels prior to eruption suggesting early development of a dike and sill complex beneath the vent depletion of this early batch led to diminished eruptive activity in june and july of 1943 while arrival of the second magma batch phase 2 reinvigorated activity in late july phase 2 fed explosive activity from mid 1943 through 1946 although most of the tephra was deposited by the end of 1945 phase 3 of the eruption began in mid 1947 with rapid evolution of magma compositions from basaltic andesite to andesite and dominance of lava effusion the combined physical and chemical characteristics of the erupted material present a new interpretation of the physical conditions that led to compositional evolution of the magma we believe that syn eruptive assimilation of wall rock in a shallow complex of dikes and sills is more likely than pre eruptive assimilation within a large magma chamber as previously assumed we further suggest that waning rates of magma supply from the deep feeder system allowed evolved shallowly stored magma to enter the conduit in 1947 thus triggering the rapid observed change in the erupted magma composition this physical model predicts that assimilation should be observable in other monogenetic eruptions particularly those with low pressure melt inclusions and with eruption durations of months to years

volcano structural analysis of la garrotxa volcanic field ne iberia implications for the plumbing system abstract the garrotxa volcanic field is related to the neogene quaternary european rift system and is the youngest representation of monogenetic volcanism in the iberian peninsula it encompasses over 50 eruptive vents most of them well preserved cones in an area of about 600 km2 lying between the cities of olot and girona ne spain in this paper we investigate the relationship between the neogene extensional tectonics and the spatial distribution of the volcanoes in the area the analysis includes the distribution of faults fissures and vents as well as morphostructural lineaments and the morphometrical analysis of volcanic cones and craters in addition we use the location of the regional seismicity recorded since 1978 and the sites of freshwater springs and mantle derived gases as indicators of active faults and open fractures finally we consider the location of ultramafic xenoliths within volcanic deposits as a way of identifying the deepest fractures in the zone and estimating magma ascent velocities the results obtained show that this volcanic area consists of an extensional basin delimited by two principal nw se faults that favoured the ascent of magma from either the source region or from shallower reservoirs located at the base of the crust towards the upper part of the crust magma transport was captured by shallow secondary extensional nnw sse striking faults whose formation is linked to the slight transtensional movement of the main bounding faults our study provides evidence of how the local stress field and contrasts in substrate stratigraphy could have controlled magma migration which suggests that precise knowledge of the stress configuration substrate geology and structural discontinuities in such regions is crucial in the forecasting of monogenetic volcanism

baseline geochemical characteristics of groundwater in the mountainous area of jeju island south korea implications for degree of mineralization and nitrate contamination summary hydrogeochemical characteristics of groundwater were investigated to elucidate baseline quality for basaltic aquifers of a mountainous area dominated by natural land cover in the volcanic island of jeju south korea principal component analysis pca resulted in four principal components pc of which pc1 pc3 and pc4 represented natural mineralization by water rock interaction while pc2 corresponded to anthropogenic contamination from nitrate sources hierarchical cluster analysis hca was performed to assess the effect of the geochemical and hydrologic processes on each sample six sample groups distinguished by total dissolved solids tds nitrate concentration and water type resulted from the hca high altitude springs low mineral water nitrate contaminated water intermediate mineral water and two groups of high mineral water water types were transformed from na mg ca hco 3 for low mineral water to na hco 3 for high mineral water nitrate contaminated water occurred near the boundary of natural and agricultural land uses of the western area high mineral water had higher calcite saturation states than other groups the high mineral water also had tritium 3 h values lower than 1 5 tu indicating a significant contribution of old groundwater in contrast low mineral water had tritium values of about 3 tu which is close to those of rainwater geographically the high mineral water was concentrated in the southwestern area where intermediate mineral water was also found this distribution was likely related to the presence of extensive trachytic rocks which could have formed locally isolated aquifers enabling prolonged water rock interactions the higher location of low permeability hydrovolcanic tuffs in the subsurface of the southern area would also increase chances of tapping aquifers below the hydrovolcanic tuffs the cumulative probability of tds showed two breakpoints of 50 and 150 mg l that distinguished high altitude springs low mineral water and high mineral water the cumulative probability of nitrate provided possible threshold values for anthropogenic contamination of 2 5 and 5 5 mg l that 32 of samples had nitrate concentrations higher than 2 5 mg l indicated high vulnerability to surface contamination sources in this mountainous area hca seems to be more effective for interpreting the baseline chemistry of groundwater than other threshold calculating statistics in that hca revealed geochemical processes including natural mineralization and anthropogenic contamination our study suggests that the cumulative probability and hca are useful as complementary methods for determining threshold values

unravelling the magmatic system beneath a monogenetic volcanic complex jagged rocks complex hopi buttes az usa the jagged rocks complex is the eroded remnant of the plumbing systems of closely spaced monogenetic alkaline volcanic centres in the southern hopi buttes volcanic field az usa it contains different clinopyroxene populations with distinctive textures and geochemical patterns in the northwestern part of the complex which exposes the best developed system of conduits most of the clinopyroxenes consist of large to medium sized resorbed cores overgrown by euhedral rims type 1 small moderately resorbed greenish cores with the same overgrown rims type 2 and phlogopite as an accessory phase by contrast in the southern part of the complex the majority of clinopyroxenes are euhedral with oscillatory zonation type 3 and are accompanied by minor euhedral olivine the differences between these mineral assemblages indicate a composite history of crystallization and magmatic evolution for the two parts of the complex governed by different mechanisms and ascent patterns from a single source at 50 km depth 16 kbar the northwest system preserves a high pressure assemblage that cooled rapidly from near liquidus conditions suggesting direct ascent from the source to the surface at high to moderate transport rates average 1 25 m s by contrast the southern system represents magma that advanced upward at much lower overall ascent rates stalling at times to form small volume mid crustal storage zones e g sills or a network of sheeted intrusions this allowed the re equilibration of the magma at lower pressure 30 km 8 kbar and led to nucleation and growth of euhedral clinopyroxene and olivine phenocrysts

miocene pleistocene volcanism and tectonics in southern korea and their relationship to the opening of the japan sea abstract miocene pleistocene volcanism and tectonics in southern korea are discussed the miocene volcanism and related tectonics are represented by the eoil orogeny which occurred in the yangnam and pohang basins in the southeastern corner of the korean peninsula the yangnam and pohang basins represent the uplifted central part of the pohang ulsan graben which was rifted between the proto korean peninsula and paleo ulleung land probably in late oligocene early miocene times the eoil orogeny is correlated with the green tuff orogeny in japan evidence of pliocene volcanism is observed on ulleung island located in the western part of the central japan sea volcanic and tectonic events represented on ulleung island are in chronological order 1 volcanic eruption 2 subsidence and marine transgression 3 dome like uplift and 4 volcanic eruption evidence of pleistocene volcanism is present on cheju island located at the southwestern entrance to the korea tsushima strait volcanic and tectonic events represented on cheju island are in chronological order 1 volcanic eruption 2 subsidence and marine transgression 3 uplift and volcanic eruption and 4 doming and volcanic eruption three grabens namely the pohang ulsan graben the ulleung basin and the yamato basin were formed in the southern half of the japan sea which was above sea level in early miocene times paleo ulleung land was present between the pohang ulsan graben and the ulleung basin in miocene pliocene times these three grabens are active rifts and the tectonic events that occurred in this region originated from the action of rising magma the extension and deepening of the southern half of the japan sea resulted from the tectonic movements of these active rifts and their surrounding regions thus it is suggested that the opening of the japan sea progressed by diapiric tectogenesis

directional wave spectra measured with the surface contour radar abstract the surface contour radar is a 36 ghz computer controlled airborne radar which generates a false color coded elevation map of the sea surface below the aircraft in real time and can routinely produce ocean directional wave spectra with post flight data processing which has much higher angular resolution than pitch and roll buoys when compared with waveriders and the xerb and edeco pitch and roll buoys there is good agreement among the nondirectional spectra there is also good agreement among the angles associated with a1 b1 and a2 b2 fourier coefficients of the spreading function for xerb endeco and the surface contour radar there are indications that the pitch and roll buoys in this study may have calibration problems with the magnitudes of the fourier coefficients of the spreading function and that the radar system determines the fourier coefficients with significantly less noise and bias the high spatial resolution and rapid mapping capability over extensive areas make the surface

decreasing magmatic footprints of individual volcanoes in a waning basaltic field the distribution and characteristics of individual basaltic volcanoes in the waning southwestern nevada volcanic field provide insight into the changing physical nature of magmatism and the controls on volcano location during pliocene pleistocene times the volumes of individual volcanoes have decreased by more than one order of magnitude as have fissure lengths and inferred lava effusion rates eruptions evolved from hawaiian style eruptions with extensive lavas to eruptions characterized by small pulses of lava and strombolian to violent strombolian mechanisms these trends indicate progressively decreasing partial melting and length scales or magmatic footprints of mantle source zones for individual volcanoes the location of each volcano is determined by the location of its magmatic footprint at depth and only by shallow structural and topographic features that are within that footprint the locations of future volcanoes in a waning system are less likely to be determined by large scale topography or structures than were older larger volume volcanoes

the influence of magma plumbing complexity on monogenetic eruptions jeju island korea terra nova 23 70 75 2011 abstract continuous pyroclastic successions from monogenetic volcanoes in the jeju island volcanic field korea were targeted for detailed geochemical investigations of juvenile ejecta to show that multiple distinct magma pulses may be erupted during a single monogenetic eruption deeply derived and possibly multiply sourced evolving magma pulses may erupt sequentially from the same vent and form generally uninterrupted depositional sequences with continuous chemical trends alternatively pulses can rise independently resulting in breccia horizons and truncation surfaces in depositional sequences and in stepped and mixed chemical trends we infer that uninterrupted eruptions result from clear plumbing systems in which a single large dyke system feeds an eruption and where differently sourced magmas are erupted independently congested plumbing systems consisting of dyke complexes give rise to vent shifts asymmetrical eruptive centres and composite depositional sequences integration of chemical variation and eruptive dynamics provides a powerful means of understanding monogenetic volcanoes

new age constraints for hominid footprints found on jeju island south korea abstract in 2004 numerous hominid footprints along with diverse animal footprints were found in the late quaternary strata of jeju island south korea however the age of the sediments in which the footprints were found is still controversial previous age estimates included radiocarbon ages of ca 15 000 yr bp late pleistocene and quartz optically stimulated luminescence ages of ca 7000 yr bp mid holocene in this study we report on 11 ams 14 c dating results from a new set of samples collected from the footprint bearing strata and from associated sediments despite some variations and age reversal all samples collected from the footprint bearing strata yielded 14 c ages of late pleistocene these ages are comparable with previous radiocarbon dating results furthermore the presence of the proboscidean footprints attributable to woolly mammoths in the footprint bearing strata supports the radiocarbon dating results based on the new radiocarbon dates and the presence of the alleged mammoth footprints the age of the hominid footprints found at jeju island is thought to be late pleistocene about 19 000 25 000 cal yr bp therefore this is the second discovery of hominid footprints dated to the pleistocene age in asia and the first to be discovered in korea

historic hydrovolcanism at deception island antarctica implications for eruption hazards deception island antarctica is the southernmost island of the south shetland archipelago in the south atlantic volcanic activity since the eighteenth century along with the latest volcanic unrest episodes in the twentieth and twenty first centuries demonstrates that the volcanic system is still active and that future eruptions are likely despite its remote location the south shetland islands are an important touristic destination during the austral summer in addition they host several research stations and three summer field camps deception island is characterised by a quaternary caldera system with a post caldera succession and is considered to be part of an active dispersed monogenetic volcanic field historical post caldera volcanism on deception island involves monogenetic small volume vei 2 3 eruptions such forming cones and various types of hydrovolcanic edifices the scientific stations on the island were destroyed or severely damaged during the eruptions in 1967 1969 and 1970 mainly due to explosive activity triggered by the interaction of rising or erupting magma with surface water shallow groundwater and ice we conducted a detailed revision field petrology and geochemistry of the historical hydrovolcanic post caldera eruptions of deception island with the aim to understand the dynamics of magma water interaction as well as characterise the most likely eruptive scenarios from future eruptions we specifically focused on the crimson hill estimated age between 1825 and 1829 and kroner lake estimated age between 1829 and 1912 eruptions and 1967 1969 and 1970 events by describing the eruption mechanisms related to the island s hydrovolcanic activity data suggest that the main hazards posed by volcanism on the island are due to fallout ballistic blocks and bombs and subordinate dilute pdcs in addition deception island can be divided into five areas of expected activity due to magma water interaction providing additional data for correct hazard assessment on the island

the role of phreatomagmatism in a plio pleistocene high density scoria cone field llancanelo volcanic field mendoza argentina abstract the plio pleistocene llancanelo volcanic field together with the nearby payun matru field comprises at least 800 scoria cones and voluminous lava fields that cover an extensive area behind the andean volcanic arc beside the scoria cones in the llancanelo field at least six volcanoes show evidence for explosive eruptions involving magma water interaction these are unusual in the context of the semi arid climate of the eastern andean ranges the volcanic structures consist of phreatomagmatic derived tuff rings and tuff cones of olivine basalt composition malacara and jarilloso tuff cones were produced by fallout of a range of dry to wet tephra the malacara cone shows more evidence for a predominance of wet emplaced units with a steep slump slope characterized by many soft sediment deformation structures such as undulating bedding planes truncated beds and water escape features the piedras blancas and carapacho tuff rings resulted from explosive eruptions with deeper explosion loci these cones are hence dominated by lapilli tuff and tuff units emplaced mainly by wet and or dry pyroclastic surges carapacho is the only centre that appears to have started with phreatomagmatic eruptions with lowermost tephra being rich in non volcanic country rocks the presence of deformed beds with impact sags slumping textures asymmetrical ripples dunes cross and planar lamination syn volcanic faulting and accretionary lapilli beds indicate an eruption scenario dominated by excessive water in the transportational and depositional regime this subordinate phreatomagmatism in the llancanelo volcanic field suggests presence of ground and or shallow surface water during some of the eruptions each of the tuff rings and cones are underlain by thick fractured multiple older lava units these broken basalts are inferred to be the horizons where rising magma interacted with groundwater the strong palagonitization at each of the phreatomagmatic cones formed hard beds resistant to erosion and therefore the volcanic landforms are well preserved

the madinah eruption saudi arabia magma mixing and simultaneous extrusion of three basaltic chemical types during a 52 day eruption in 1256 a d 0 5 km3 of alkali olivine basalt was extruded from a 2 25 km long fissure at the north end of the harrat rahat lava field saudi arabia the eruption produced 6 scoria cones and a lava flow 23 km long that approached the ancient and holy city of madinah to within 8 km three chemical types of basalt are defined by data point clusters on variation diagrams i e the low k high k and hybrid types all three erupted simultaneously their distribution is delineated in both scoria cones and lava flow units from detailed mapping and a petrochemical study of 135 samples six flow units defined by distinct flow fronts represent extrusive pulses the high k type erupted during all six pulses the low k type during the first three and the hybrid type during the first two

stratigraphy petrochemistry and quaternary depositional record of the songaksan tuff ring jeju island korea abstract the songaksan tuff ring str is one of several recent hydrovolcanic centers on jeju island korea which provides an excellent example of proximal to distal facies changes in wet pyroclastic surge deposits a multidisciplinary study has been carried out on the str and adjacent lithostratigraphic units to constrain absolute age geochemical characteristics and quaternary depositional history a number of rock units were identified inside the crater of the str including scoria deposit i trachybasalt lava scoria deposit ii and a late stage basaltic tuff indicative of a rather complex sequence of magmatic and phreatomagmatic eruptions after the construction of the tuff ring petrochemical analysis shows that the str was generated from different magma batches that fractionated from a homogenous magma chamber and the early erupted magma was more evolved and volatile rich reworking of the str commenced shortly after the hydromagmatic eruption in a high energy nearshore environment resulting in deposition of the hamori formation the formation is composed of planar stratified and low to high angle cross stratified tuffaceous pebbly sandstones and occurs up to an altitude of about 4 m above present sea level 14c dating of molluscan shells beneath the formation indicates that it began to be deposited after about 4000 yr bp detailed sedimentary logging reveals that the formation consists of several stratal packages bounded by laterally persistent and distinct lithologic boundaries probably formed by millennial scale sea level fluctuations occurrence of another hydrovolcanic sequence the sinyangri formation on the opposite side of jeju island having similar sedimentary characteristics and ages suggests that the sea level fluctuations as seen in the hamori formation have affected a wide area of jeju island probably related to the high frequency sea level oscillations during the post 6 ka bp regression period in the east asian region it can be concluded that the formation of the str was possible because of the holocene transgression which made the present coastal areas water saturated and adequate for hydrovolcanic eruptions the str in turn contributed to record high frequency sea level fluctuations during the holocene via acting as a local and short lived but affluent source of loose sediment

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

the udo tuff cone cheju island south korea transformation of pyroclastic fall into debris fall and grain flow on a steep volcanic cone slope the udo tuff cone of cheju island south korea is a middle pleistocene basalt tuff cone that has formed by early surtseyan type eruptions and later drier hydroclastic eruptions the tuff cone comprises steep 20 30 and planar beds of lapillistone lapilli tuff and tuff that can be grouped into seven sedimentary facies a g facies a and b comprise continuous to lenticular layers of grain supported and openwork lapillistone that are inversely graded and coarsen downslope they suggest emplacement by grain flows that are maintained by gravity induced stress and grain collisions facies c includes poorly sorted crudely bedded and locally inversely graded lapilli tuff also suggestive of rapid deposition from highly concentrated grain flows facies d includes thinly stratified and mantle bedded tuff that was probably deposited by fallout of wind borne ash other facies include massive lapilli tuff facies e chaotic lapilli tuff facies f and cross bedded tuffaceous sandstone facies g that were deposited by resedimentation processes such as debris flow slide slump and stream flow respectively the grain flows that produced facies a b and c are interpreted to have originated from falling pyroclasts which initially generated highly dispersed saltating avalanches in which momentum was transferred by the particles themselves this transport mechanism is similar to that of debris fall as the slope gradient was too low to maintain a highly dispersed flow the debris fall decelerated and contracted due to a decrease in dispersive pressure the mode of momentum transfer changed to one of collision because contraction of the debris fall resulted in an increase in particle concentration this transport mechanism is similar to that of common grain flows grain segregation occurred in several ways initial segregation of ash from lapilli occurred due to their differing terminal fall velocities and their contrasting degrees of sliding friction with the bed percolation of ash into interstices of lapilli during flow kinematic sieving augmented further segregation of ash from lapilli the latter process along with a dispersive pressure effect gave rise to vertical inverse size grading downdip inverse grading was produced by particle overpassing

sr isotopes of the seoguipo formation korea and their application to geologic age abstract the seoguipo formation cheju island korea is a shallow marine to nonmarine sedimentary formation formed by the earliest stage of volcanism and simultaneous volcanogenic sedimentation of the island the formation contains signatures of glacioeustasy providing an opportunity to study neogene paleoceanographic changes in the northwestern pacific the proposed geologic age of the formation varies widely from pliocene to pleistocene in spite of an abundance of biostratigraphic and paleomagnetic data this situation has hampered establishment of a time framework on which paleoenvironmental interpretations can be based in this study strontium isotopic ratios were measured from diverse macrofossils obtained from the fossiliferous lower part of the formation to constrain the carbonate ages all macrofossils retain the original mineralogy and microstructures negating the possibility of postdepositional diagenesis the stable oxygen and carbon isotopic compositions of the specimens also show little sign of alteration 87 sr 86 sr ratios of the shells display a wide range of values 0 70863 0 70919 categorized into two groups calcitic pectenids brachiopods and an aragonitic bivalve showing high 87 sr 86 sr values greater than 0 70909 and the rest of bivalves and an aragonitic gastropod showing unusually low values the low 87 sr 86 sr ratios of the latter group are interpreted to be due to the local variation of the paleoseawater condition in which the organisms grew probably caused by contemporaneous volcanic activities and weathering of volcaniclastic materials in a restricted environment the average 87 sr 86 sr ratio of the heavy group yields a carbonate age of 0 86 0 40 0 57 ma by the lowess fit to the marine sr isotope curve of howarth and mcarthur j geol 105 1997 441 the sr isotope age in conjunction with radiometric and biostratigraphic ages suggests that the deposition of the seoguipo formation began since the early pleistocene and the surface exposure of the formation belongs mostly to the middle pleistocene 0 86 0 4 ma

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

diatreme evolution during the phreatomagmatic eruption of the songaksan tuff ring jeju island korea the songaksan tuff ring jeju island korea which erupted ca 3 7 ka bp in a coastal setting provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well preserved ejecta beds and well known subsurface geology the tuff sequence can be divided into four units a to d which have distinctly different accidental componentry quartz rich vs quartz poor grain surface features abraded and ash coated vs unabraded and uncoated and chemical compositions of juvenile particles the basal tephra bed of unit a which probably erupted after the removal of the relatively hard shallow level 120 m deep accidental grains suggesting that the early erupted tephra had not yet experienced recycling and pre eruption mixing in the diatreme on the other hand the overlying tephra beds of units a b and d contain an abundance of abraded and ash coated juvenile accidental grains suggesting that the tephra comprised significant proportions of recycled or premixed materials from previous eruptions or subsurface explosions which participated in the explosion driven mixing in the diatreme before eventual ejection from the diatreme unit c is unusual in that it comprises extremely rare accidental grains and ash coated juvenile accidental grains we interpret that the supply of solid materials either accidental or juvenile to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme the diatreme is therefore envisaged to have been filled with a water saturated slurry in which particle abrasion and adhesion were inhibited we also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit c on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit c the ratio of tachylite to sideromelane grains generally increases up section of the tuff sequence with two abrupt drops across the tuff unit boundaries these variations are coincident with the changes in the chemical composition of juvenile particles suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches the textural and compositional variations of the songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring including removal and renewal of the diatreme fill and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust

depositional processes of the suwolbong tuff ring cheju island korea the suwolbong pyroclastic sequence in the western part of cheju island korea comprises partly preserved rim beds of a quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline the sequence consists of breccia lapillistone lapilli tuff and tuff eighteen sedimentary facies are established and organized into six lateral facies sequences lfs and seven vertical facies sequences vfs the lfs 1 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar bedded lfs 1 undulatory bedded lfs 4 or climbing dune bedded lfs 5 lapilli tuff units they are representative of relatively dry base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting the lfs 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent it results from relatively wet base surge in which sorting is poor due to the cohesion of damp ash the lfs 3 comprises well sorted lapilli tuff and stratified tuff further downcurrent suggestive of deposition from combined fall and surge of relatively dry hydroclastic eruption all seven vertical facies sequences generally comprise two facies units of coarse grained fines depleted lapilli tuff and an overlying fine grained tuff these sequences are suggestive of deposition from base surge that consists of a turbulent head and a low concentration tail depositional processes in the suwolbong tuff ring were dominated by a relatively dry base surge the base surge comprises turbulent and high concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport as the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air it develops large scale turbulent eddies and is segregated into coarse grained bedload and overlying fine grained suspension forming thinly stratified units further downcurrent the base surge may be either cooled and deflated or pushed up into the air depending on its temperature the suwolbong tuff ring comprises an overall wet to dry cycle with several dry to wet cycles in it suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise

a case study of wave current interaction near an oceanic front high resolution directional wave spectrum data were obtained from two nasa airborne radars during the frontal air sea interaction experiment fasinex in february 1986 the observations show a significant change in the wave number spectrum across the front on the basis of surveys from a towed sensor and on satellite imagery the front location and current field are estimated a numerical model is developed for the wave current interaction and is used to model the wave refraction across the frontal current a parametric study is performed to demonstrate the effects of current meandering the main consequence of meandering is the formation of caustics and shadow zone regions in which the wave energy is significantly enhanced or reduced spectral simulation along the aircraft track reveals a reduction of more than 60 in wave energy in the shadow zone this is consistent with the observations

high resolution 40 ar 39 ar study of mount avital northern golan reconstructing the interaction between volcanism and a drainage system and their impact on eruptive styles we present a high resolution 40ar 39ar data set of a volcanic complex at mt avital northern golan which experienced a transition from strombolian to phreatomagmatic activity previous studies attributed this transition to a change in the drainage basin of a nearby stream due to the damming by a lava flow which resulted in flooding of the eruption site in this study we determined the age of different volcanic phases and events in the history of mt avital as well as that of the damming flow and examined the cause of the transition in light of the new 40ar 39ar ages the 40ar 39ar results show that the history of mt avital includes two main phases of volcanic activity an early phase at ca 800 600 ka and a late phase at 120 95 ka most of the activity of the late phase was continuous within the 40ar 39ar error including the transition to phreatomagmatic explosions which occurred sometime between 115 107 ka probably between 115 113 ka the age of the damming flow is 115 6 3 1 ka which suggests that the volcanic activity immediately reacted to the change in the drainage basin dynamics the activity culminated with lava flow eruptions the latest at 100 4 ka either due to the establishment of the tuff ring levees which prevented access of water to the eruption site or due to the migration of activity to the northern part and then to the southern part of the complex

mid holocene sea level highstand along the southeast coast of china various sea level curves have been proposed for the coast of china in the past two decades these sea level curves indicate a complex history of holocene sea level and so the debate on whether or not a higher mid holocene sea level highstand exists in the coast of china has continued this paper aims to re examine the holocene sea level history for the low latitude part of the china coast between 18 n and 32 n by re assessing all the sea level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors the reconstructed sea level histories from different coastal sectors of the china coast reveal a certain degree of variability in the timing and height of mid holocene sea level highstand within large river deltas the mid holocene sea level highstand occurred earlier by almost 1000 years than that from other coastal sites the highstand from large river deltas appears also lower in altitude a few metres below the present day sea level due probably to the local factors of subsidence and sediment consolidation in geologically stable coastal sites the highstand is recorded at the same altitude as the present day sea level a 1 2 m higher highstand is found from sites where tectonic uplift is observed

the polycyclic lausche volcano lausitz volcanic field and its message concerning landscape evolution in the lausitz mountains northern bohemian massif central europe abstract the tertiary lausitz volcanic field covers a broad area encompassing parts of eastern saxony germany lower silesia poland and north bohemia czech republic volcanism was predominantly controlled by the volcano tectonic evolution of the oh e rift and culminated in the lower oligocene this paper deals with the highest volcano of this area the lausche hill 792 6 m a s l situated in the lausitz mountains we offer a reconstruction of the volcanic edifice and its eruptive history its complex genesis is reflected by six different eruption styles and an associated petrographic variety furthermore the lausche volcano provides valuable information concerning the morphological evolution of its broader environs the remnant of an alluvial fan marking a middle paleocene lower eocene 62 50 ma palaeo surface is preserved at the base of the volcano the deposition of this fan can be attributed to a period of erosion of its nearby source area the lausitz block that has undergone intermittent uplift at the lausitz overthrust since the upper cretaceous the lausche hill is one of at least six volcanoes in the lausitz mountains which show an eminent low level of erosion despite their oligocene age and position on elevated terrain these volcanoes are exposed in their superficial level which clearly contradicts their former interpretation as subvolcanoes among further indications this implies that the final morphotectonic uplift of the lausitz mountains started in the upper lower pleistocene 1 3 ma due to revived subsidence of the nearby zittau basin it is likely that this neotectonic activity culminated between the elsterian and saalian glaciation 320 ka the formation of the low mountain range was substantially controlled by the intersection of the lausitz overthrust and the oh e rift

genesis mechanism and stability of the dongmiaojia landslide yellow river china abstract bedding plane landslides are common in nature and usually occur in formations with an alternating sequence of soft and hard rock beds the dongmiaojia landslide located near the xiaolangdi hydraulic project on the yellow river is a typical bedding plane landslide formed in an alternating sequence of soft and hard rock beds using field data of this landslide we systematically analyzed the genesis mechanism and stability of this type of bedding plane landslide according to the geological structure and the deformation characteristics we divided the landslide into three parts the front colluvial mass the middle and rear sliding deformation mass and the rear tension deformation mass the failure mode of the dongmiaojia landslide is mainly retrogressive creep deformation under the action of the combined endogenic and exogenic geological processes an improved dda strength reduction method was applied to study the stability and the failure process of the dongmiaojia landslide the analysis results produced a stability coefficient of the landslide equal to 1 07 the numerical simulation analysis showed that the failure mode of the landslide is a compound failure process which consists of forward sliding of the middle part and retrogressive sliding of the rear part with the front colluvial mass acting as a support effect for the down sliding of the whole landslide mass

semi automatic delimitation of volcanic edifice boundaries validation and application to the cinder cones of the tancitaro nueva italia region michoacan guanajuato volcanic field mexico abstract the shape and size of monogenetic volcanoes are the result of complex evolutions involving the interaction of eruptive activity structural setting and degradational processes morphological studies of cinder cones aim to evaluate volcanic hazard on the earth and to decipher the origins of various structures on extraterrestrial planets efforts have been dedicated so far to the characterization of the cinder cone morphology in a systematic and comparable manner however manual delimitation is time consuming and influenced by the user subjectivity but on the other hand automatic boundary delimitation of volcanic terrains can be affected by irregular topography in this work the semi automatic delimitation of volcanic edifice boundaries proposed by grosse et al 2009 for stratovolcanoes was tested for the first time over monogenetic cinder cones the method based on the integration of the dem derived slope and curvature maps is applied here to the tancitaro nueva italia region of the michoacan guanajuato volcanic field mexico where 309 plio quaternary cinder cones are located the semiautomatic extraction allowed identification of 137 of the 309 cinder cones of the tancitaro nueva italia region recognized by means of the manual extraction this value corresponds to the 44 3 of the total number of cinder cones analysis on vent alignments allowed us to identify ne sw vent alignments and cone elongations consistent with a ne sw max and a nw se min constructing a vent intensity map based on computing the number of vents within a radius r centred on each vent of the data set and choosing r 5 km four vent intensity maxima were derived one is positioned in the nw with respect to the volcano tancitaro one in the ne one to the s and another vent cluster located at the se boundary of the studied area the spacing of centroid of each cluster 24 km can be related to the thickness of the crust 9 10 km overlying the magma reservoir

longevity of a small shield volcano revealed by crypto tephra studies rangitoto volcano new zealand change in eruptive behavior of a basaltic field abstract the life span of small volcanoes in terrestrial basaltic fields commonly considered monogenetic can be difficult to assess due to a paucity of datable materials capable of providing a 102 103 year age resolution we have used microscopic tephra layers crypto tephra in lake sediments to determine the longevity of rangitoto volcano a small shield that represents the most recent volcanism in the auckland volcanic field avf new zealand previous studies suggested construction in a relatively short interval at 550 500 cal yrs bp in contrast the tephra record shows evidence of intermittent activity from 1498 140 to at least 504 6 cal yrs bp a longevity of 1000 years rangitoto volcano is thought to represent about half the magma erupted in the 250 ka history of avf thus the avf has experienced a dramatic shift to prolonged and voluminous central vent volcanism in its most recent history this demonstrates the difficulty in determining time erupted volume relationships in such fields previous avf hazard risk modeling based on isolated short lived

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

the al du aythah volcanic cones al madinah city implications for volcanic hazards in northern harrat rahat kingdom of saudi arabia the basaltic al du aythah volcanic cones lie in the northern part of the extensive lava field of harrat rahat and only 13 km from the centre of al madinah city in the kingdom of saudi arabia historical records indicate they may have erupted in ad 641 the four cones are formed by deposits that record a transition from phreatomagmatic to magmatic explosions followed by minor lava effusion three cones display elongated tuff rings at the base and two produced late stage lava flows the cones themselves are symmetrical and constructed mostly by the accumulation of ballistically ejected pyroclasts spherical bombs and lapilli cannonball bombs lapilli occasionally with country rock fragments inside both cored and loaded bombs lapilli are common within the tuff ring deposits lidar data show a total volume of 1 664 10 6 km3 for the four cones 418 10 6 km3 dre whole rock chemical analyses indicate alkali basalt compositions sio2 44 7 45 9 wt with little compositional variation and no relationship between chemistry and eruptive styles small differences in composition may reflect variations in fractional crystallisation of clinopyroxene and olivine a magnetotelluric 2d cross section shows that the cones are located adjacent to a buried sediment filled alluvial channel along a nnw sse fault dipping to the east the al du aythah eruption was related to the ascent of magma through this structure with the first phase of the eruption triggered by the interaction of the magma with water from the northern harrat rahat aquifer that exists in the al madinah basin this initial water source was rapidly exhausted while the eruption progressed roughly from north to south and from west to east the latter motion probably along the fault controlled feeding dyke our work draws attention to the existence of recent explosive phreatomagmatic eruptions in the al madinah basin which despite the hyperarid climate of the area must be considered a potential future eruption hazard

the response of surface gravity waves to changing wind direction abstract the behavior of a wind sea is investigated for wave directions differing from the local wind direction to describe the phenomenon we added the mean wave direction as an additional prognostic quantity to the jonswap parameters used in mathematical models of the wind sea in previous publications hasselmann et al 1976 gunther et al 1979a b a boundary is given for the frequency domain in which the spectral energy responds to a veering wind field

mechanisms of low flux intraplate volcanic fields basin and range north america and northwest pacific ocean we compare two intraplate pliocene pleistocene volcanic fields in different tectonic settings the central basin and range and the northwest pacific ocean both fields are characterized by widely scattered small volume alkali basaltic volcanoes within the fields each volcano apparently originates from a separate volatile enriched parental melt from the upper mantle there is no evidence at either field for locally anomalous heat flow or ongoing introduction of new fluids into the upper mantle such as might occur above a subducting slab we conclude that the volcanic fields reflect deformation driven collection of already existing partial melts in a heterogeneous upper mantle deformation driven melt collection may be an important mechanism for other diffuse intraplate volcanic fields and this is consistent with a tectonically controlled low flux end member for intraplate fields where magmatism is a passive response to regional deformation differences in the degree of fractionation and contamination between the two fields are inferred to be related to flexure induced vertical variations in the orientation of principal stresses in the northwest pacific ocean which cause stalling of ascending dikes in the lithosphere

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

depositional mechanics and sequences of base surges songaksan tuff ring cheju island korea the songaksan mount in the southwestern part of cheju island korea is a taalian tuff ring produced by phreatomagmatic explosions at an aquifer a detailed analysis of proximal to distal facies changes reveals that the tuff ring sequence can be represented by 21 sedimentary facies one lateral facies sequence lfs and three vertical facies sequences vfs the vfs 1 and 2 are representative of facies relationships in horizontal near vent deposits the vfs 1 comprises scour fill bedded tuff inversely graded tuff massive tuff and laminated tuff from base to top the vfs 2 is a variant of the vfs 1 replaced by an inversely graded lapilli tuff unit at the base the sequences suggest traction carpet suspension and minor traction sedimentation from a high concentration near vent base surge the lfs 1 and the vfs 3 are distilled from outward dipping flank deposits both sequences begin with disorganized lapilli tuff followed successively by stratified lapilli tuff dune bedded lapilli tuff very thinbedded tuff and accretionary lapilli they are suggestive of waning base surge which decreases in particle concentration suspended load fall out rate and flow regimes with an increase in traction and sorting these facies sequences suggest that a base surge experiences flow transformation with its flow characters changing with time and space a near vent base surge is turbulent uniformly mixed and highly concentrated and produces scour fill bedded tuff as capacity decreases the surge transforms into a dense and laminar underflow and a dilute and turbulent upper part gravity transformation depositing inversely graded massive and normally graded lapilli tuff ensuing loss of sediment load and mixing of ambient air result in flow dilution surface transformation stratified and dune bedded units are produced by tractional processes of turbulent and low concentration surge further dilution causes deceleration and cooling and results in precipitation of moistened ash and accretionary lapilli from suspension

compaction in a mantle mush with high melt concentrations and the generation of magma chambers abstract most compaction models in the partially molten mantle have addressed the case of low intergranular melt concentrations up to a few percent here we develop a mathematical and numerical formalism adapted to the two dimensional modeling of compaction in mushes with higher melt concentrations up to a few tens of percents experimental data on mantle like mushes olivine crystals basaltic melts suggest that the mush viscosity depends in a complex way on the melt concentration three rheological thresholds occur at melt concentrations of about 5 20 and 40 respectively the first threshold corresponds to the establishment of full interconnectivity of the intergranular melt the second to the formation of a very dense suspension of crystals and the last to the development of crystal clusters in the suspension the present models take into account the stiff and drastic viscosity drops associated with these rheological thresholds intergranular melt migration associated with an initial melt pulse generates a horizon of high melt crystal ratio if the melt concentration in the initial pulse presents a local excess the horizon becomes slightly tilted as a consequence melt percolates upslope inside the tilted horizon pools at its summit and generates a pocket like zone due to the higher melt concentration the upward darcy velocity in the pocket markedly exceeds that in the horizon the result is that the pocket like impregnation is rapidly disconnected from the horizon and a new pocket develops at the summit of the partially fragmented horizon eventually the intergranular melt contained in the horizon is completely redistributed into pockets increasing the background melt concentration in the mush from 5 20 and 40 leads to an increase of the maximum melt concentration of 10 40 and 100 in the transient horizons and of 25 60 and 100 in the pockets these models suggest that magma chambers with a kilometer extent naturally result from the compaction of a mantle mush with an initial melt concentration exceeding 5

observations of wind waves in the gulf stream frontal zone experimental results of a study of wind waves in the gulf stream frontal zone are presented measurements of two dimensional radar spectra of surface waves and surface current were performed during ship crossings of the gulf stream under different wind conditions waves reflected from the gulf stream were observed on the windward side for an along current wind these effects resulted in a widening of the spectrum angular distribution and a deviation of the mean wave direction from that of the wind trapped waves were observed under against current winds depending on wave age the trapped waves were either locally generated developing waves or entered into the jet downstream nearly fully developed waves trapped waves significantly increased the wave energy locally the experimental data are interpreted in terms of wave kinematics and the equation of spectrum evolution in the relaxation approximation

effects of the gulf stream on ocean waves in the present study a third generation numerical wave model is used to study effects of a straight gulf stream and a gulf stream ring on ocean waves in swell and storm conditions the model accounts for all relevant processes of propagation generation and dissipation of the waves including current effects without imposing a priori restraints on the spectral development of the waves the dominating mechanism affecting the waves appears to be current induced refraction even though the short crestedness of the incoming waves tends to mask its effects also in swell conditions depending on wind and wave conditions refraction may trap locally generated waves in the straight gulf stream or it may reflect wave energy back to the open ocean in the gulf stream ring refraction induces a considerable variation in significant wave height and short crestedness but it hardly affects the mean wave direction in storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following current situations

reconstructing the eruptive history of a monogenetic volcano through a combination of fieldwork and geophysical surveys the example of puig d adri garrotxa volcanic field puig d adri is a complex volcano in the garrotxa volcanic field 0 7 0 01 ma the youngest part of the catalan volcanic zone ne iberian peninsula the construction of this volcano involved the superimposition of three volcanic edifices with five lithostratigraphic units in which several strombolian and phreatomagmatic episodes alternated geological and geophysical surveys performed using electrical resistivity tomography and self potential have contributed to revealing the internal structure of the volcano and the succession of deposits the ring cone morphology of the phreatomagmatic part of the structure shows how a number of variables including the way in which magma and water interacted greatly influenced the eruptive dynamics and the mechanisms of formation a further major issue reflected in the final structure of the edifice is the process of vent migration which was controlled by the characteristics of the substrate and its interaction with the magma as it rose supplementary material granulometric and component histograms of the samples not shown in figure 4 are available at http doi org 10 6084 m9 figshare c 3262498

palaeoclimatic and chronostratigraphic interpretations from strontium carbon and oxygen isotopic ratios in molluscan fossils of quaternary seoguipo and shinyangri formations cheju island korea abstract palaeotemperatures and chronostratigraphies of the quaternary seoguipo and shinyangri formations cheju island south korea were investigated in terms of the strontium oxygen and carbon isotopic compositions of carbonate mollusc shells the 87sr 86sr ratios of mollusc shells from the seoguipo formation range from 0 70911 to 0 70914 which yield carbonate ages of 0 5 1 2 ma early to middle pleistocene using the linear equation between ages and 87sr 86sr ratios of quaternary seawater the 87sr 86sr ratio 0 70917 of aragonitic shells from the shinyangri formation provide late pleistocene ages 0 04 ma based on ams 14c dates of mollusc fossil shells from the shinyangri formation the depositional age of the formation has been extended to 1570 yr bp palaeotemperatures calculated on the basis of the oxygen isotopic composition of the calcitic mollusc shells from the seoguipo formation give a range of values from 12 6 to 19 1 c which is lower than the present day shallow seawater temperature 14 9 25 5 c in the vicinity of the seoguipo coast aragonitic mollusc shells from the shinyangri formation provide oceanic temperatures ranging from 22 5 to 29 8 c which is higher than present day seawater temperatures 14 1 23 2 c the calculated palaeotemperatures of the seoguipo and shinyangri formations are inferred to reflect cold and warm currents flowing over cheju island during the pleistocene to holocene

numerical simulation of basaltic lava flows in the auckland volcanic field new zealand implication for volcanic hazard assessment monogenetic volcanic fields such as the auckland volcanic field avf new zealand are common on the earth s surface and are typically dominated by basaltic lava flows up to 10 s of km long in monogenetic volcanic fields located in close proximity to human population and infrastructure lava flows are a significant threat in this study lava flow emplacement conditions for some basaltic eruptions of the avf were reconstructed using the thermo rheological magflow model eight existing lava flows in the avf were simulated using magflow and eruptive volumes measured from light detection and ranging lidar derived digital terrain models dtms fitting the simulations to the dimensions of actual lava flows provides insight into their emplacement mechanisms and conditions such as effusion rate and probable eruption durations by looking at emplacement in different settings the likely magma ascent rate for studied avf eruptions is calculated to have been on the order of 0 1 m s in the avf the typical estimated duration of past lava flows was from a minimum of 2 days for small volume flows such as little rangitoto 0 0015 km3 up to 83 days for large volume flows such as three kings 0 078 km3 the three best fitting simulations were used to establish eruption scenarios for future volcanic hazard mapping for the avf inferences of eruption duration that will be useful for developing realistic emergency management plans and recovery scenarios for this densely populated volcanic field are also provided

ilchulbong tuff cone jeju island korea revisited a compound monogenetic volcano involving multiple magma pulses shifting vents and discrete eruptive phases ilchulbong sunrise peak tuff cone is a united nations educational scientific and cultural organization unesco world heritage site that owes its scientific importance to the outstanding coastal exposures that surround it it is a type locality for the sedimentary evidence of pyroclastic transport and depositional processes that occur during phreatomagmatic basaltic eruptions its classically shaped cone morphology was long considered to result from a single short lived eruption reanalysis of the sedimentary sequence has now revealed two subtle paraconformities in the deposits indicating that the eruption occurred in three separate phases the break between phases i to ii was long i e days to weeks during which erosion and compaction of the lower cone occurred leading to a volcanowide discontinuity surface and reworked deposits in the lower flanks possibly following cooling and solidification of the initial shallow conduit system the phase ii eruption resumed from a new vent location 600 m away before being terminated by a very brief interval and final eruption of phase iii from the same general site the second pause led to a more subtle discontinuity marked by differences in deposit character above and below it and it was associated with a period of seismicity induced slumping and slipping of deposits detailed geochemical study of the juvenile clasts through the sequence reveals that three separate alkali basaltic magma pulses were erupted corresponding directly to the three eruption phases magmas 1 and 3 may be genetically related with the former showing evidence for longer periods of shallow level fractionation whereas magma 2 originated from a slightly different mantle domain although at a similar depth these results demonstrate that breaks in monogenetic eruption sequences may represent deep magma system processes and they raise fundamental questions concerning the mechanisms of triggering and eruption of multiple magma pulses in small volume basaltic volcanoes this study shows the importance of recognizing sedimentary evidence of time breaks in such eruption sequences as potential indications of shifts in eruption chemistry and vent location these have important implications for the controls of vent migration at other monogenetic volcanoes and for hazard planning during future similar eruptions

forecasting transitions in monogenetic eruptions using the geologic record spatial forecasting of volcanism and associated hazards in intraplate monogenetic volcanic fields is subject to large uncertainties in both data and models we demonstrate a novel logistic regression method for mapping phreatomagmatic magmatic eruption transition susceptibility using near surface hydrologic topographic and geologic data the method is illustrated on the auckland volcanic field the location of new zealand s largest city auckland environmental factors examined for possible influence included the thickness of water saturated and porous sediments substrate type and geology vent elevation and distance from the nearest fault by comparing these factors with the volumes and styles of past eruption sequences a location specific eruption sequence forecasting model was constructed recognizing that larger and or longer eruptions are more likely to exhaust vent area sources of water estimating volcanic hazard susceptibility in this way allows more effective planning and improved preeruption preparedness between eruptions and during future volcanic crises

shallow marine records of pyroclastic surges and fallouts over water in jeju island korea and their stratigraphic implications explosive volcanism results in a wide range of volcaniclastic deposits in many of earth9s subaerial and subaqueous environments in this paper we introduce a unique shallow marine volcaniclastic deposit from jeju island korea for which the materials were transported to the water surface by pyroclastic clouds and then settled from the surface as they were entrained in the water the deposition occurred under alternating currents and still waters which is most plausibly attributed to tidal processes mud flasers or drapes intercalated in the deposit which indicate periods of slack water during tidal cycles suggest that the deposit accumulated in a very short period of a fortnight or a month about a million times faster than the adjacent sedimentary strata because of the unusually high sedimentation rate the volcaniclastic deposit could record the usual fair weather processes in the depositional site at a resolution that is almost never provided by ordinary sedimentary deposits this finding highlights the biases in earth9s stratigraphic records and teaches us that volcanic deposits commonly regarded as the products of catastrophic events can in some cases record more faithfully the ordinary and usual processes that nonvolcanic deposits cannot

volcanic geomorphology an overview abstract the review examines the role of geomorphology in analyzing the volcanoes on earth five objectives are stressed first classifications of volcanic landforms should be improved to take care of the complexity in volcanic landform generation as magmatic systems style of eruption and the erupted material all influence the morphology second geomorphology should contribute to the science of volcanology through its capability in reconstructing growth stages in complex volcanoes and also in analyzing the structural factors which contribute to the catastrophic collapse of volcanoes third geomorphology can contribute to physical volcanology by assessing the effects of topography on transport erosion and deposition of volcanogenic flows and identifying the sources and climatic tectonic conditions which govern the emplacement of volcaniclastic deposits fourth volcanic geomorphology a identifies sedimentary facies associations b constructs facies models for dynamic volcano delivery systems and c analyzes the characteristics of sediment gravity flows in order to determine relevant parameters for modelling their behaviour fifth process oriented geomorphology is critical in developing accurate methods for measuring rates of geomorphic processes that shape ephemeral volcanic constructs and for evaluating and comparing geomorphic impacts on disturbed catchments and the related hydrologic response before during and after eruptions this should help to refine parameters for the exponential decay model finally volcanic geomorphology is essential for risk assessment through geomorphic hazard zonation and composite risk zonation such treatments are necessary in order to face the enhanced challenge posed by the combination of natural hazards and the increasing number of people who are at risk around volcanoes

aircraft and satellite measurement of ocean wave directional spectra using scanning beam microwave radars a microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described the technique which employs short pulse noncoherent radars in a conical scan mode near vertical incidence is shown to be suitable for both aircraft and satellite application the technique has been validated at 10 km aircraft altitude where we have found excellent agreement between buoy and radar inferred absolute wave height spectra

the submarine eruption and erosion of surtla surtsey iceland abstract surtla is the site of a short lived submarine vent which built basaltic elastic deposits almost to sea level in 1963 early in the eruption of surtsey since then wave and current activity have eroded the volcanic pile such that in july 1981 its top was a fairly level plateau 45 m below sea level and its surface comprised a lag deposit of sparse blocks of lava in a bed mainly of glass granules this winnowed layer was underlain by a nonreworked poorly sorted and finer deposit of glassy clasts formed by a combination of disruption by magmatic volatiles steam explosions and quench brecciation during the eruption the explosion violence and associated comminution increased as the pile built up to shallower water depths it is argued that at times of continuous effusion a cupola of steam was situated over the vent as indicated by scoriaceous spatter which shows agglutination and bread crust features that can only have developed in conditions more akin to subaerial than hitherto envisaged in a subaqueous eruption

drinking quality assessment of some groundwater sources along the stretch of jhelum river in kashmir himalaya the physicochemical properties and major ion chemistry of the groundwater sources from alluvial aquifers along the stretch 60 km of jhelum river in kashmir himalaya were determined in order to identify hydro geochemical processes and their suitability for drinking purposes the data depicted that calcium and bicarbonates were dominating among the cations and anions the results indicate the trend of cation dominance as ca2 na mg2 k whereas anion dominance was in the order of hco3 cl so4 2 ratio of calcium to magnesium indicated the dissolution of ca2 from caco3 which results in an increased levels of ca2 in the groundwater interpretation of piper trilinear plot understands the various geochemical processes affecting the groundwater quality and shows groundwater was dominated by ca hco3 type the ph was recorded in the slightly alkalinity range 7 2 7 8 and was showing positive correlation with hco3 the chloro alkaline indices revealed 86 of the sources exchange by a type of base exchange reactions rest by cation anion exchange gibbs diagram revealed groundwater sources fall in the category of rock dominance the concentration of the nitrogen compounds was in the progression of no3 n nh4 n no2 n and the po4 fluctuated from 0 12 to 0 22 mg l moreover corrosivity ratio indicated that water from the majority of sources 71 is safe to supply using pipes without any corrosive effects while 29 of sources are corrosive in nature and need non corrosive pipes for transporting and lifting of groundwater the results revealed groundwater samples were within permissible limits as prescribed by international and national standards for drinking purposes the state government and ngo s can show their interest in utilizing such water resources to overcome the shortage of drinking water in a sustainable way for the daily consumption of the people living in the vicinity of jhelum river

dikes sills and stress regime evolution during emplacement of the jagged rocks complex hopi buttes volcanic field navajo nation usa abstract the dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of the simplest volcanic plumbing systems their geometry is controlled by interaction of magma driven cracks with country rock and reveals regional structural and stress patterns at the time of their emplacement the shallow stress field however may change during the time an intrusion complex is emplaced in response to addition or removal of magma and country rock during associated surface eruptions the jagged rocks complex in the miocene hopi buttes volcanic field navajo nation arizona is exposed 300 350 m below the pre eruptive surface it comprises a group of generally nw se striking dikes punctuated in places by buds a saucer like intrusion larger pyroclastic massifs and a diatreme we made measurements of 13 dikes divided into 172 segments with thicknesses from 8 to 122 cm mean 43 cm and lengths of 60 to 780 m several sills and inclined sheets in places are thicker than dikes having mean thicknesses of 48 cm and 73 cm respectively dikes typically show straight parallel and en echelon patterns while sills and inclined sheets are curved the northwestern dikes differ from the rest in containing large mafic crystals and are inferred to have been emplaced after the others we find that the strike of the overall complex dikes and other sheets elongate massifs and aligned sub cylindrical bodies reflects a crystalline basement control that is evident throughout hopi buttes over the period of the complex s emplacement local stress patterns were not stable we infer that excavation of deep maar craters and perhaps the construction of a scoria cone at the surface modified the local stress patterns to favor emplacement of sills and en echelon dikes later in the complex s evolution in contrast to simple straight dikes as the complex first formed

records of palaeo sea level and eruption duration in a coastal tuff ring jeju island korea phreatomagmatic volcanoes and their sedimentary products can preserve high resolution records of earth surface processes because of their high deposition rate songaksan jeju island korea is a phreatomagmatic volcano which erupted c 3 7 ka bp in a coastal setting its tuff ring preserves a record of intertidal to supratidal facies transition in the basal part which reveals the position of palaeo high tide level for at least 13 high tide events and a record of a storm surge event in the middle part of the tuff ring which lasted approximately three tidal cycles based on these features the phreatomagmatic eruption of songaksan is estimated to have taken place over a month the sea level at the time was almost identical to that at present this study shows that coastal phreatomagmatic volcanoes can preserve high resolution records of eruption duration and palaeo sea level and can provide accurately levelled and dated data points to the quaternary sea level curve

occurrence and mobility of major and trace elements in groundwater from pristine volcanic aquifers in jeju island korea abstract major and trace elements in groundwater from basaltic aquifers in pristine conditions were investigated in a volcanic island to evaluate sources sinks and mobility of elements over a wide range of mineralization conditions with total dissolved solids from 50 mg l to 3400 mg l groundwater was highly undersaturated with respect to primary silicate minerals indicating that dissolution of basaltic rocks may continue under conditions with precipitation of calcite and secondary silicates evolution of b cl ratio in groundwater from marine aerosols to basaltic rocks showed that the ratio could be used as a conservative tracer for interactions between water and basaltic rocks relative mobility rm of elements calculated using the concentrations of elements in the local basaltic rocks and those in groundwater showed that mobility decreased in the order of b rb na k mg ca mo v si sr sc p u zn pb cr cu ba ni ti mn al fe co th indicating that oxyanion forming elements and alkali metals had the highest mobility compared to average rm v had decreased mobility and fe and mn had increased mobility in anoxic groundwater while v mo and u had higher mobility in oxic alkaline water the sources of v cr cu and zn in rocks were estimated using the partition coefficients between minerals and basaltic melt and the disparity between sources and mobility indicated that sinks are more important for controlling the concentrations of these elements in groundwater than the contents in the rocks principal component analysis pca of hydrogeochemical parameters in groundwater produced three principal components pc which represent dissolution of basaltic rocks without significant attenuation of released solutes higher degree of water rock interactions resulting in oxic alkaline conditions and attenuation of zn and cu in higher ph respectively spatial distribution of pcs revealed that groundwater with elevated concentrations of mobile elements was concentrated in the southwestern area and that concentrations of v and cr were more scattered which is likely to be controlled by ph and redox states of groundwater as well as degree of water rock interactions

lithofacies and architecture of a basinwide tuff unit in the miocene eoil basin se korea modes of pyroclastic sedimentation changes in eruption style and implications for basin configuration the miocene eoil basin se korea is a small half graben basin that was rifted by both extensional and dextral strike slip deformations during backarc opening of the east sea sea of japan the basin was filled by fluviolacustrine sediments and abundant basaltic and dacitic volcanic deposits the paljori tuff is a 2 20 m thick basinwide dacitic volcaniclastic unit that is intercalated in the topmost part of a fluviolacustrine formation the tuff consists of two pyroclastic units units ii and iii which are underlain and overlain by two resedimented volcaniclastic units units i and iv unit i at the base is composed mainly of fine grained resedimented tephra unit ii is a massive and stratified tuff produced by a dense pyroclastic density current that was ponded in the southwestern part of the basin unit iii is a massive lapilli tuff emplaced by a voluminous and turbulent pyroclastic density current that swept across the basin toward the northeast without ponding or blocking by intrabasinal highs and basin margin relief and unit iv at the top is composed of coarse grained resedimented tephra the general coarsening up of these units the lack of nonvolcaniclastic sedimentary interbeds and the offset stacking of the units toward the northeast suggest an episodic short duration eruption from the southwest that waxed in mass eruption rate and changed eruption style from phreatomagmatic to magmatic these units show basin scale variations in geometry including 1 thick accumulations of unit i in the northeastern and southwestern extremities of the basin 2 ponding of unit ii in the southwestern part of the basin 3 truncation of unit iii in the same area and 4 thickening of unit iv toward the northeastern basin margin these provide important clues to the distribution of and temporal changes in accommodation space and hence the configuration and structural evolution of the eoil basin it is inferred that the greatest subsidence occurred at the southwestern and northeastern corners of the basin the southwest northeast trending axes of the basin plunge gently toward the northeast and the major intrabasinal faults of the basin were produced before the eruption of the paljori tuff the basinwide preservation of the tuff and its fairly uniform thickness suggest that the basin was undergoing rapid extension and subsidence because of the onset of the rift climax the paljori tuff shows that important clues to and high resolution records of the large scale configuration and structural evolution of a sedimentary basin can be obtained from the study of lithofacies variations and the architecture of a single basinwide volcaniclastic unit

dyke diatreme transition in monogenetic volcanoes insights from the hillier bay volcanic complex western australia the factors controlling phreatomagmatism and diatreme formation are still poorly constrained and understood here we describe the field relationships between mafic intrusions and volcaniclastic deposits observed at hillier bay western australia and discuss the implications for the formation of monogenetic basaltic volcanoes involving both phreatomagmatic and magmatic eruption phases the hillier bay volcanic complex consists of a series of basaltic sheeted dykelets and larger dykes injected within the metamorphic basement volcaniclastic lithologies also occur usually trapped between basaltic dykes and the basement these vary between mixtures of juvenile basaltic fragments metamorphic basement fragments and quartz feldspar sand in different relative amounts based on the textures of the clastic lithologies we argue that initial phreatomagmatic phases resulted from sequential injections of thin dykelets due to ascending magma struggling to open a path to the surface the relatively lower magma water ratio maximises the efficiency of premixing leading to phreatomagmatic explosions later as the main body of magma reaches the shallow conduit through wider dykes magma overcomes water availability and the eruption style switches to magmatic effusive this implies that magma flux may be a determining factor controlling eruption style in at least some monogenetic volcanoes

shallow plumbing systems for small volume basaltic volcanoes eruptive dynamics in basaltic volcanoes are controlled in part by the conduit geometry however uncertainties in conduit shape and dike to conduit transition geometry have limited our predictive capability for hazards assessments we characterize the subvolcanic geometry of small volume basaltic volcanoes magmatic volatile driven eruptions 0 1 to 0 5 km3 based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes conduits and vent areas 250 m depth study areas include east grants ridge new mexico usa basalt ridge east basalt ridge paiute ridge and southeast crater flat nevada usa basaltic feeder dikes 250 to 100 m deep have typical widths of 4 12 m with smooth host rock contacts rhyolite tuff at depths less than 100 m heterogeneities in the host rock form preferential pathways for small dike splays and sills resulting in a 30 m effective width at 50 m depth the development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock the overall zone of effect at depths less than 50 m is 110 m wide 220 m elongated along the feeder dike based on comparisons with theoretical conduit flow models the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1 2 m at depths greater than 500 m the flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure balanced flow conditions sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface 50 m depth but at depths greater than 100 m the difference is a factor of 2 to 4 this difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events while theoretical model results define dimensions necessary for a single steady eruption phase the complex details of magma host rock interactions observed at the study areas contact welding brecciation bifurcating dikes and sills and stoping represent the mechanisms by which the lithostatic pressure balanced geometry is attained the similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure balanced modeling approach consistent with the conclusions of wilson and head j geophys res 86 2971 3001 1981 for this type of volcano

shallow seated controls on styles of explosive basaltic volcanism a case study from new zealand abstract the pyroclastic deposits of many basaltic volcanic centres show abrupt transitions between contrasting eruptive styles e g hawaiian versus strombolian or dry magmatic versus wet phreatomagmatic these transitions are controlled dominantly by variations in degassing patterns magma ascent rates and degrees of interaction with external water we use crater hill a 29 ka explosive effusive monogenetic centre in the auckland volcanic field new zealand as a case study of the transitions between these end member eruptive styles the crater hill eruption took place from at least 4 vents spaced along a nne trending 600 m long fissure that is contained entirely within a tuff ring generated during the earliest eruption phases early explosive phases at crater hill were characterised by eruption from multiple unstable and short lived vents later dominantly extrusive volcanism took place from a more stable point source most of the crater hill pyroclastic deposits were formed in 3 phreatomagmatic p and 4 dry magmatic m episodes forming in turn the outer tuff ring and maar crater p1 m1 p2 and scoria cone 1 m2 m4 this activity was followed by formation of a lava shield and scoria cone 2 purely wet activity is represented by the bulk of p1 and p2 and purely dry activity by much of m2 m4 however m1 and parts of m2 and m4 show evidence for simultaneous eruptions of differing style from adjacent vents and rapid variations in the extent and timing of magma water interaction at each vent the nature of the wall rock lithics and these rapid variations in inferred water magma ratios imply interaction was occurring mostly at depths of 80 m and the vesicularity patterns in juvenile clasts from these and the p beds imply that rapid degassing occurred at these shallow levels we suggest that abrupt transitions between eruptive styles in time and space at crater hill were linked to changes in the local magma supply rate and patterns and vigour of degassing during the final metres of ascent

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level

reconstructing paleoenvironment eruption mechanism and paleomorphology of the pliocene pula maar hungary abstract pula maar is a partially eroded pliocene maar diatreme volcano part of the mio pliocene bakony balaton highland volcanic field the surficial remnant of the maar diatreme volcano consists of 1 a distinct depression with a thick post eruptive lacustrine alginite sediment infill interbedded with coarse grained volcaniclastic sediments 2 a narrow marginal zone inside the depression consisting of primary pyroclastic rock units that are interpreted to be partly collapsed and subsided blocks of entire sections from the tephra ring formerly surrounding the maar crater depression and 3 coarse grained volcaniclastic debris flow deposits closely associated with the collapsed primary pyroclastic rock units in the marginal zone the presence of coherent lava rocks below the crater fill units their distribution pattern and their association with scoriaceous beds indicate that after the maar diatreme forming phreatomagmatic explosive activity small 100 m scale scoria and or spatter cones erupted in the maar crater these cones are the likely source of the lava flows that partially filled the maar crater basin the widespread dm to m thick basaltic sand and or silt units at the base of the post eruptive crater filling sedimentary succession are interpreted to be reworked volcaniclastic material from the intra maar scoria spatter cones as well as from the tephra ring based on comparative analyses of 53 core descriptions this study reveals that the original maar crater basin was larger than previously suggested the deep level of the maar crater is reconstructed to be a northeast southwest elongated depression currently forming a c 50 m deep basin geomorphological considerations suggest that most of the phreatomagmatic pyroclastic rocks are composed of base surge and tephra fall deposits around the deep maar depression these allochthonous rock units form a 50 400 m wide zone of proximal tuff ring sequences the formation of this zone is inferred to be a result of a combination of syn eruptive subsidence due to mass deficit in the rigid triassic dolomite basement caused by the phreatomagmatic explosions as well as post eruptive subsidence of the crater and diatreme filling successions due to diagenetic compaction the facies in the centre of the maar lake is a soft laminated alginite mainly botryococcus colonies diatom frustles calcium carbonate crystals clay minerals in the section exposed in the pula open cast mine a single turbiditic layer is present this layer originated in a landslide which possibly could have been caused by either syn eruptive earthquake and or a sudden post eruptive subsidence event of the diatreme fill

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

pahoehoe toe dimensions morphology and branching relationships at mauna ulu kilauea volcano hawai i pahoehoe toe dimensions morphology and branching relationships were analyzed in flows emplaced during 1972 at mauna ulu a satellitic shield on the east rift zone of kilauea volcano hawai i in order to characterize regions within flow fields dominated by networks of pahoehoe toes measurements of toe length width thickness and orientation were completed for 445 toes at 13 sites variations in site characteristics including slope substrate and position in the flow field allow an evaluation of the effects of such parameters on toe dimensions toe surface morphology ropy or smooth local flow lobe position interior or margin and connective relationships between toes were documented in the form of detailed toe maps these maps show the number of branches connecting a given toe to other toes in its local pahoehoe network and illustrate branching patterns statistical analyses of toe dimensions and comparisons of pahoehoe toe study sites and sub populations combined with field observations evaluation of toe maps and qualitative examination of toe dimension size distributions show the following a although there are significant variations at a given site toes typically have mean lengths 101 cm greater than mean widths 74 cm and mean widths greater than mean thicknesses 19 cm sites that have mean widths greater than mean lengths are those with lower slopes b where significant site to site variations in mean values of a given toe dimension were apparent these differences could not be directly related to site characteristics c ropy toes have significantly larger mean values of length width and number of branches than smooth toes and toes with three or more branches have greater lengths widths and thicknesses than toes with two or fewer branches suggesting concentration of flow in these toe types d the skewness of all size distributions of toe length and width to larger values suggests that toes are transitional to larger sheets and channels consistent with field observations and e two distinct types of branching patterns called monolayer and centrally ridged were observed in preserved pahoehoe flow lobes the significant variability in measured toe dimensions at mauna ulu suggests that toe dimensions are influenced by numerous locally defined random factors and that an approach based on stochastic methods can be used to model pahoehoe flow emplacement

record of complex scoria cone eruptive activity at red mountain arizona usa and implications for monogenetic mafic volcanoes abstract scoria cone eruptions are generally modeled as a simple succession from explosive eruption to form the cone to passive effusion of lava generally from the base of the cone sector collapse of scoria cones wherein parts of the cone are rafted on a lava flow is increasingly recognized as common but the reasons that a cone may not be rebuilt are poorly understood red mountain volcano is a pleistocene scoria cone in the san francisco volcanic field of northern arizona usa the cone lies along the trace of a major steeply dipping normal fault that originated during proterozoic tectonism and was reactivated in tertiary time the earliest phase of eruption at red mountain was typical strombolian forming a cone that was followed by or possibly synchronous with lava effusion toward the west from the base of the cone rafting then ensued as the west side of the cone collapsed approximately 15 of the cone is preserved in mounds as much as 30 m high rafting was extensive enough to remove most of the cone over the vent area which effectively reduced the pressure cap on the magma conduit resultant low fountaining fed clastogenic lava flows and minor scoria fallback clastogenic flows traveled as far as 4 km and now form a cliff 30 40 m high at the edge of the lava platform although several possibilities explain the change in vent dynamics and eruptive style we favor the interpretation that an increase in magma rise rate caused collapse of the cone the abrupt removal of 300 m of material over the vent removed a conduit cork and low fountaining began magma that had erupted effusively suddenly became explosive this aspect of scoria cone rafting at red mountain is broadly similar to sector collapse followed by explosive eruption in larger systems a steep walled 150 m high amphitheatre on the northeast side of red mountain exposes weakly to strongly altered scoria cemented by calcite iron and zeolites we suggest that vapor phase alteration was responsible for sealing fine grained ash beds in the cone and a pressurized system developed residual heat from a dike that was emplaced as part of the magmatic activity provided heat that drove groundwater along the regional fault up into the cone eventually the overpressurized system exploded in a phreatic eruption that created the amphitheatre which has subsequently been enlarged by water and wind erosion the combined sequence of events at red mountain illustrates some of the complexities in monogenetic scoria cone eruptions that have received little attention to date

stability analysis and treatment of a reservoir landslide under impounding conditions a case study the muchanghe landslide is located on the left bank of the muchang river in dongping reservoir hubei province china during reservoir impoundment cracking and dislocation deformations occurred at the front and middle parts of the muchanghe landslide once the landslide was triggered the river could be blocked which would lead to a serious threat to upstream flood control safety in this study the engineering geological properties and deformation characteristics of the muchanghe landslide during impoundment were analyzed a 3 d limit equilibrium method was proposed for the stability analysis of this asymmetric landslide based on the proposed 3 d method a visualization program jslope3d was developed and applied to evaluate the stability of the muchanghe landslide the results indicated that the stability of the landslide gradually decreases with the rise of impounding water level in the dongping reservoir when the impounding water level reaches an elevation of 490 m normal pool level the calculated factor of safety predicted that the landslide would be in an unstable state to prevent the generation of a landslide failure a reinforcement scheme involving the cutting back of the slope and backfill was proposed to improve the stability of the landslide using the proposed 3 d method the muchanghe landslide after stabilization was stable at different impoundment water levels and can satisfy the requirements of the design specification

the shallow depth emplacement of mafic intrusions on a magma poor rifted margin an example from the bight basin southern australia abstract three dimensional 3d seismic data has provided important insights into how magma is transported and stored in sedimentary basins much of our understanding is based on volcanic rifted margins in contrast the magma plumbing systems of magma poor rifted margins are less well studied this study uses 3d seismic data to describe the magma plumbing system of the bight basin igneous complex a volcanic province located along the magma poor southern australian margin here magma emplacement occurred in the mid eocene some 40 million years after the onset of seafloor spreading our data images a variety of 5 270 m thick 2 23 km diameter mafic intrusions that are confined to within 1200 m of the paleoseabed intrusions emplaced at 200 m depth formed hybrid and compound sills and are typified by elongate lava flow like morphologies intrusions emplaced at depths of 200 1200 m formed saucer shaped and compound sills as well as laccoliths approximately 60 of the intrusions have lava flows and volcanogenic vents above their shallowest tips as shown from previous studies this suggests that the intrusions played a crucial role in transporting magma to the paleoseabed furthermore many of the intrusions are overlain by forced folds highlighting the role of magma emplacement in inducing overburden deformation the sills and laccoliths rarely form interlinked complexes and instead most commonly occur as isolated bodies this suggests that they were fed by dykes we infer that high rates of magma ascent in the dykes prevented their transition into sills within sediments at 1 2 km depth our study highlights that the magma plumbing system of the bight basin igneous complex contains a diversity of magmatic intrusions the morphology of which is linked to their emplacement depth host sediment rheology and the physical properties of the magma this plumbing system contrasts markedly with those found along better studied volcanic rifted margins

el estribo volcanic complex evolution from a shield volcano to a cinder cone patzcuaro lake michoacan mexico abstract el estribo volcanic complex evc is located in the northern part of the michoacan guanajuato volcanic field within the trans mexican volcanic belt tmvb el estribo is located at the southern edge of the e w patzcuaro fault that belongs to the patzcuaro jaracuaro graben a western extension of the e w morelia acambay fault system stratigraphy geochronology chemistry and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a 100 ka volcanic hiatus a emission of lava flows that constructed a shield volcano between 126 ka and b mixed phreatomagmatic to strombolian activity that formed a cinder cone 28 ka the magmas that fed these monogenetic volcanoes were able to use the same feeding system the cinder cone itself was constructed by strombolian fallouts and remobilized scoria beds followed by an erosion period and by a mixed phreatomagmatic to magmatic phase strombolian fallouts ending with lava flows soft sedimentary deformation of beds and impact sags cross bedding as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase the erupted magmas through time ejected basaltic andesitic lava flows 56 21 58 88 sio 2 that built the shield volcano and then basaltic andesitic scoria 57 65 59 05 sio 2 that constructed the cinder cone although they used the same feeding system the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart therefore the location of el estribo volcanic complex along an e w fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived questioning the classic view of the monogenetic nature of their volcanoes and yielding information about the potential volcanic risk of these settings usually considered risk free

bottomset architecture formed in the troughs of dunes and unit bars abstract bottomsets are formed in the troughs of migrating bedforms the flow and sediment dynamics downstream of bedforms differ and consequently the thickness grain size and internal structure of bottomsets vary greatly a classification of the controls on bottomset formation is proposed related to two and three dimensional processes flow and sediment unsteadiness and pre existing deposits structures and deposits created by flow and sediment unsteadiness as well as pre existing deposits are also considered in relation to changes they can induce in subsequent trough processes the classification is illustrated by observations from laboratory flumes the modern burdekin river australia and the rock record the roaches grit england and hawkesbury sandstone australia in bottomset examples described in this paper internal variability both vertically and laterally was much greater than that within the dominant foreset component complex compound structures were created by the interaction and predominance of different bottomset controls this combined with their high preservation potential makes them a highly useful paleoenvironmental indicator bottomset variation e g changes in the abundance of mud laterally will influence the permeability heterogeneity of fluvial reservoir rocks bottomsets formed under relatively steady conditions are likely to be laterally extensive and have similar characteristics over their entire length they may act as significant barriers to vertical flow conversely bottomsets generated in unsteady regimes tend to be highly variable potentially creating conduits between cross bed sets aiding inter set permeability

primary versus secondary and subaerial versus submarine hydrovolcanic deposits in the subsurface of jeju island korea jeju island is a quaternary shield volcano built upon the yellow sea continental shelf off the korean peninsula decades of borehole drilling reveals that the shield forming lavas of the island are underlain by extensive hydrovolcanic deposits the seoguipo formation which are about 100 m thick and show diverse depositional features this study provides criteria for distinguishing between hydrovolcanic deposits formed by primary pyroclastic and secondary resedimentation processes in subaerial and submarine settings based on the observations of several selected cores from the formation five facies associations are identified including i primary hydrovolcanic deposits formed by pyroclastic surges and co surge fallouts in tuff rings facies association phtr ii primary hydrovolcanic deposits formed by surtseyan fallout and related pyroclastic transport processes in tuff cones facies association phtc iii secondary hydrovolcanic deposits formed by debris flows hyperconcentrated flood flows sheet floods and rill flows in subaerial settings facies association rhae iv secondary hydrovolcanic deposits formed in submarine settings under the influence of waves tides and occasional mass flows facies association rhmar and v non volcaniclastic and fine grained deposits formed in nearshore to offshore settings facies association nvmar the primary hydrovolcanic facies associations phtr and phtc are distinguished from one another on the basis of distinct lithofacies characteristics and vertical sequence profiles these facies differ from the secondary hydrovolcanic and non volcaniclastic facies associations rhae rhmar and nvmar because of their distinctive sedimentary structures textures and compositions the depositional processes and settings of some massive and crudely stratified volcaniclastic deposits which occur in many facies associations could not be discriminated unambiguously even with microscopic observations nevertheless these facies associations could generally be distinguished because they occur typically in packets or sequences several metres to tens of metres thick and bounded by distinct stratigraphic discontinuities and comprise generally distinct sets of lithofacies the overall characteristics of the seoguipo formation suggest that it is composed of numerous superposed phreatomagmatic volcanoes intercalated with marine or non marine volcaniclastic or non volcaniclastic deposits widespread and continual hydrovolcanic activity together with volcaniclastic sedimentation is inferred to have persisted for more than a million years in jeju island under the influence of fluctuating quaternary sea levels before effusion of the shield forming lavas extensive distribution of hydrovolcanic deposits in the subsurface of jeju island highlights that there can be significant differences in the eruption style growth history and internal structure between shelfal shield volcanoes and oceanic island volcanoes

the fekete hegy balaton highland hungary soft substrate and hard substrate maar volcanoes in an aligned volcanic complex implications for vent geometry subsurface stratigraphy and the palaeoenvironmental setting the fekete hegy volcanic complex is located in the centre of the bakony balaton highland volcanic field in the pannonian basin which formed from the late miocene to pliocene period the eruption of at least four very closely clustered maar volcanoes into two clearly distinct types of prevolcanic rocks allows the observation and comparison of hard substrate and soft substrate maars in one volcanic complex the analyses of bedding features determination of the proportion of accidental lithic clasts granulometry and age determination helped to identify and distinguish the two types of maar volcanoes ascending magma interacted with meteoric water in karst aquifers in mesozoic carbonates as well as in porous media aquifers in neogene unconsolidated wet siliciclastic sediments the divided basement setting is reflected by distinct bedding characteristics and morphological features of the individual volcanic edifices as well as a distinct composition of pyroclastic rocks country rocks in hard substrate maars have a steep angle of repose leading to the formation of steep sided cone shaped diatremes enlargement and filling of these diatreme is mainly a result of shattering material by fci related shock waves and wall rock collapse during downward penetration of the explosion locus country rocks in soft substrate maars have much shallower angles of repose leading to the formation of broad bowl shaped structures or irregular depressions enlargement and filling of these diatremes is mainly the result of substrate collapse for example due to liquefaction of unconsolidated material by fci related shock waves and its emplacement by gravity flows the fekete hegy is an important example illustrating that the substrate of a volcanic edifice has to be taken into account as an important interface which can have major control on phreatomagmatic eruptions and the resulting characteristics of the volcanic complex

flow paths and mixing properties of groundwater using hydrogeochemistry and environmental tracers in the southwestern area of jeju volcanic island summary groundwater from springs test boreholes and domestic wells was investigated to assess the flow system of basaltic aquifers at base flow conditions in the southwestern part of jeju island south korea this study utilized hydrogeochemical parameters and environmental tracers of 18 o 2 h 3 h and chlorofluorocarbons cfcs which showed that well connected flow paths exist between coastal springs regardless of flow rates in contrast test boreholes near the coastal springs exhibited various flow paths nitrate concentrations were much higher than baseline values in mountainous groundwater while those decreased in coastal areas was seemingly contributed from nitrate contamination sources and seawater sources were minimal due to low permeability layers near sea level the water stable isotopes indicated little evaporation and were comparable to the local meteoric water line during the rainy season which was confirmed by deuterium excess values demonstrating that effective infiltration primarily occurs during the rainy season from the effects of altitude on 18 o the mean recharge altitudes for both mountainous and coastal springs were estimated as 300 400 m which implies longer flow paths for the coastal springs the relationship of cfc 12 cfc 113 and that of cfc 12 3 h concordantly indicated that the groundwater consists mainly of binary mixtures composed of 15 25 year old young water and old water with ages greater than 60 years lower nitrate levels in the coastal springs were well represented by the mixing models recharge altitudes for coastal springs increased up to 700 m assuming that old water corresponds to high altitude recharge using the binary mixing model integration of hydrochemical and environmental tracer characteristics revealed that pahoehoe lava flows and hydrovolcanic tuffs play key roles in controlling the groundwater occurrence and quality

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

the miocene costa giardini diatreme iblean mountains southern italy model for maar diatreme formation on a submerged carbonate platform in this paper we present a model for the growth of a maar diatreme complex in a shallow marine environment the miocene age costa giardini diatreme near sortino in the region of the iblei mountains of southern sicily has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions vesicular lava clasts accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas rich magma abundant xenoliths in the upper late deposited beds of the ring suggest rapid magma ascent and deepening of the eruptive vent is shown by the change in slope of the country rock the interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount the occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity intrusions of nonvesicular magma forming plugs and dikes occur on the western side of the diatreme and at the margins close to the contact between breccia deposits and country rock they indicate involvement of volatile poor magma possibly during late stages of activity we propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment this allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center a subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water at which time the hyaloclastite was deposited emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated locally forming peperites the sheltered low energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts ultimately lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions

melt extraction and accumulation from partially molten rocks current models for melt segregation and ascent are not adequate to accurately describe transport and accumulation in combination we propose that transport is discontinuous and in batches and that accumulation occurs by stepwise merging of batches a simple numerical model of jostling spheres that merge when they touch was used to represent stepwise accumulation and transport of batches by propagation of hydrofractures results of the numerical model indicate that such a system may quickly develop into a self organised critical soc state in this state the distribution of melt batch volumes can be described by a power law with an exponent m that lies between 2 3 and 1 once a self organised critical state is established the system is capable of discharging any additional melt without further change to itself deformation aids melt extraction efficiency as it increases the mobility of hydrofractures enhances accumulation and hence lowers the exponent m full connectivity of melt needs never to be reached in the system and melt transport and extraction can occur at very low melt fractions the chemical evolution of melt from source to emplacement level will be governed by the discontinuous mixing and mingling of batches each with different histories and possibly different sources if no subsequent homogenisation occurs in a magma chamber or the final emplacement structure the process can be identified by chemical heterogeneity of plutons and volcanic rocks

eruption dynamics at pahvant butte volcano utah western usa insights from ash sheet dispersal grain size and geochemical data shallow to emergent subaqueous basaltic explosive eruptions here referred to as surtseyan are a source of pyroclastic material expelled from subaqueous vents and transferred to the water column and atmosphere they can threaten coastal communities in different ways and one of these is through the generation of pyroclastic density currents travelling over water once the eruption becomes subaerial these may be preceded or accompanied by eruption fed currents moving along the sea lake floor one approach for studying these eruptions is through analysis of their deposits but these are commonly either inaccessible under water or poorly preserved by the time they are exposed subaerially the site selected for this work pahvant butte ut usa avoids these limitations the volcano was formed at 18 600 cal year b p in the giant pleistocene lake bonneville by an eruption initiated at a relatively shallow water depth 85 m the water is now drained and deposits of the edifice and of the ash sheet at medial distances on the old lake floor medial lake are accessible and well preserved the ash sheet deposits allow us to investigate dispersal of ash from a surtseyan eruption including the subaqueous phase of edifice building by comparing edifice deposits with ash sheet deposits correlated using geochemistry and textural analysis results suggest that medial deposited ash from pahvant butte travelled at least 25 km from the vent in eruption fed pyroclastic density currents moving along the lake floor this transport began early in the eruption apparently prior to the volcano s subaerial emergence

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

linking fluid dynamics and olivine crystal scale zoning during simulated magma intrusion the compositional zoning styles of natural crystals produced during magma intrusion can be used to investigate the structure of magmatic plumbing systems and its relation to expressions of volcanic unrest seismic deformation volatiles however magma intrusion is a progressive dynamic process and yields non monotonic heterogeneities in physio chemical variables such as complex spatial variations in temperature and liquid composition with time such changes in variables are difficult to incorporate in models of crystal zoning in natural systems here we take another approach by integrating the results of a numerical multiphase simulation of melt arrival in an olivine rich reservoir with models of chemical re equilibration of olivine we evaluate the diversity of chemical zoning styles and the inferred time scales using fe mg diffusion in olivine for a limited range of system geometries and time composition temperature values although our models are still a large simplification of the processes that may occur in natural systems we find several time dependent and systematic relations between variables that can be used to better interpret natural data the proportions of zoned and unzoned crystals the zoning length scales and the calculated diffusion times from the crystals vary with time and the initial position of the crystal in the reservoir these relationships can be used for example to better constrain the plumbing structure and dynamics of mafic eruptions from monogenetic volcanoes by detailed studies of changes in the zoning of the crystal cargo with eruptive sequence moreover we also find that the time scales obtained from modeling of crystals at a single temperature and boundary condition tend to be shorter about 25 than the residence time which could also be tested in natural studies by combining crystal time scale records with monitoring datasets

stratigraphy sedimentology and eruptive mechanisms in the tuff cone of el golfo lanzarote canary islands the tuff cone of el golfo on the western coast of lanzarote canary islands is a typical hydrovolcanic edifice along with other edifices of the same age it was constructed along a fracture oriented nee sww that coincides with the main structural trend of recent volcanism in this part of the island we conducted a detailed stratigraphic study of the succession of deposits present in this tuff cone and here interpret them in light of the depositional processes and eruptive dynamics that we were able to infer the eruptive sequence is represented by a succession of pyroclastic deposits most of which were emplaced by flow plus a number of air fall deposits and ballistic blocks and bombs we distinguished five different eruptive depositional stages on the basis of differences in inferred current flow regimes and fragmentation efficiencies represented by the resulting deposits the different stages may be related to variations in the explosive energy eight lithofacies were identified based on sedimentary discontinuities grain size components variations in primary laminations and bedforms the volcanic edifice was constructed very rapidly around the vent and this is inferred to have controlled the amount of water that was able to enter the eruption conduit the sedimentological characteristics of the deposits and the nature and distribution of palagonitic alteration suggest that most of the pyroclastic succession in el golfo was deposited in a subaerial environment this type of hydrovolcanic explosive activity is common in the coastal zones of lanzarote and the other canary islands and is one of the main potential hazards that could threaten the human population of this archipelago detailed studies of these hydrovolcanic eruptions such as the one we present here can help volcanologists understand the hazards that this type of eruption can generate and provide essential information for undertaking risk assessment in similar volcanic environments

the eruptive history of the patzcuaro lake area in the michoacan guanajuato volcanic field central mexico field mapping c 14 and 40ar 39ar geochronology abstract monogenetic volcanic fields occur in many tectonic settings representing an unpredictable and uncertain volcanic hazard the patzcuaro lake is located in the central part of the michoacan guanajuato volcanic field mgvf field mapping of an area of 560 km2 stratigraphy and new radiometric ages 40ar 39ar and 14c aided in the identification of 45 individual volcanic landforms formed during the past 3 9 ma these landforms comprise five medium size shield volcanoes 25 scoria cones 10 lava domes two lavas associated to scoria cones one fissural lava flow and two volcanic complexes these volcanic edifices erupted a minimum volume of 20 km3 since pliocene with an output rate of 0 02 km3 ka chemical composition of magmas ranges from 47 6 to 65 3 wt silica being dominantly andesites 76 vol followed by basaltic andesites 12 vol dacites 9 vol and basalts 3 vol volcanic products vary from mainly andesitic during the pliocene basaltic to dacitic during the pleistocene and basaltic andesitic to andesitic during the holocene all these rocks are the result of low dipping slab subduction related magmatism alignment of cones and structures follow ne sw n s and e w directions the youngest faults are associated with the e w morelia acambay fault system with historic earthquake activity the volcanic complexes el estribo and la muela have cone collapses to the north that correspond with the direction of maximum regional extension associated with the e w fault system the 3 9 ma history of monogenetic volcanism around the patzcuaro lake demonstrates that monogenic fields can be long lived volcanic features

origin of temporal compositional variations during the eruption of lake purrumbete maar newer volcanics province southeastern australia the pleistocene lake purrumbete maar eruption sequence of the newer volcanics province of southeastern australia records stratigraphic temporal and geochemical variations that cannot be explained by crustal processes such as fractional crystallisation and crustal contamination samples from the lake purrumbete maar have distinct trace element trends that correlate with stratigraphic height with decreasing incompatible element concentrations from the bottom of the sequence to the top indicating that the most enriched melts were ejected during the earliest eruption stages with the least enriched melts erupted in the final stages variations in rare earth element ratios indicate that these melts were formed by dynamic melting of garnet lherzolite mantle material consistent with other volcanic centres within the basaltic cones subprovince of the newer volcanics province the geochemistry of the erupted units at lake purrumbete also record minor differentiation of the melts by olivine fractionation although these processes alone cannot explain the observed geochemical variations in the eruption sequence further differentiation of the melts by different processes such as deep clinopyroxene fractionation or assimilation of metasomatised lithosphere may be responsible for the observed geochemical trends at lake purrumbete this shows the complexity of the plumbing system of monogenetic volcanoes but also shows the opportunities that these volcanoes provide to study these processes in detail as the geochemical variations that are preserved in this type of volcanism by fast magma ascent through the crust as evidenced by the presence of fresh mantle xenoliths predominantly reflect processes that occurred in the mantle rather than in the crust