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

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

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

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

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

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

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

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

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

effect of sediment density on bed load transport experiments on transport by water of synthetic lightweight sediments of specific gravities 1 0 s 2 5 and uniform grain size d 3 5mm are described the results confirm the dimensional reasoning

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

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

currently active regions of decelerating accelerating seismic strain in central asia 1 accelerating preshock seismic strain in a broad critical region and decelerating preshock seismic strain in a narrower seismogenic region constitute a model for intermediate term prediction of strong main shocks an effort is made in the present work for a forward test of the decelerating accelerating seismic strain d as model by identifying such patterns and estimating the corresponding probably ensuing strong main shocks m 7 0 in central asia 20 n 45 n 42 e 105 e five such patterns have been identified and the origin time magnitude and epicentral geographic coordinates of each of the corresponding main shocks have been estimated predicted model uncertainties of the estimated time magnitude and space parameters of these probably ensuing main shocks as well as appropriate statistical tests against a standard gutenberg richter seismicity distribution are also presented to allow a future objective evaluation of the model s efficiency for intermediate term earthquake prediction

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

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

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

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

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

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

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

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

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

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