dense water formation in the aegean sea numerical simulations during the eastern mediterranean transient 1 dense water formation processes in the aegean sea eastern mediterranean are studied using a three dimensional numerical ocean model the simulations cover the period 1979 1994 during which major changes that affected the thermohaline circulation of the whole mediterranean sea were recorded sensitivity studies that focus on the role of freshwater budget are presented and the results are evaluated against available hydrological data of the same period the very cold winters of 1987 1992 and 1993 and the extended dry period 1989 1993 that affected the whole eastern mediterranean sea are the main driving mechanisms corresponding to 50 and 32 respectively of the excessive deepwater volume formed in the aegean after 1987 the reduced black sea water outflow during the same dry period was another important forcing mechanism contributing 18 to the total formation while the increased inflow of saline waters from the levantine sea after 1992 was an additional preconditioning factor the locations and mechanisms of water formation processes are identified with combined analysis of data from the march 1987 oceanographic cruise in the aegean sea and the respective model results for that period deep water is found to be formed mainly through open ocean convection in the central and north aegean sea while the contribution of shelf areas is limited intermediate water is also formed through open ocean convection in the southern aegean sea during cold winters as well as in the central and northern aegean during mild winters the total volume of dense water formed during 1979 1994 corresponds to an annual formation rate of 0 24 sv for deep water and 0 34 sv for intermediate water

glassy dynamics of landscape evolution soil creeps imperceptibly downhill but also fails catastrophically to create landslides despite the importance of these processes as hazards and in sculpting landscapes there is no agreed upon model that captures the full range of behavior here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes we find creep for slopes below a critical gradient where average particle velocity sediment flux increases exponentially with friction coefficient gradient at critical gradient there is a continuous transition to a dense granular flow rheology slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials they are described by a two phase flux equation that emerges from grain scale friction alone this glassy model reproduces topographic profiles of natural hillslopes showing its promise for predicting hillslope evolution over geologic timescales

erosional furrows formed during the lateral blast at mount st helens may 18 1980 nearly horizontal quasi periodic erosional features of 7 m average transverse wavelength and of order 100 m length occur in scattered locations from 3 5 to 9 km from the crater at mount st helens under deposits of the lateral blast of may 18 1980 we attribute the erosional features to scouring by longitudinal vortices resulting from flow instabilities induced by complex topography namely by streamline curvature in regions of reattachment downstream of sheltered regions and by the cross flow component of flow subparallel to ridge crests the diameter of the vortices and their transverse spacing inferred from the distance between furrows are taken to be of the order of the boundary layer thickness the inferred boundary layer thickness 14 m at 9 km from the source of the blast is consistent with the running length from the mountain to the furrow locations by using knowledge of ablation patterns on bodies and lofting of dust in high speed flow we are able to infer some features of the flow field within the blast within the furrows the erosion rate was of the order of 9 kg m 2 s 1 about 4 times greater than that expected from laboratory data obtained in flow free of longitudinal vortices the orientation of furrows induced by the cross flow instability can be used to measure the upwash angle and estimate the flow mach number at the central ridge of spirit lake the mach number is inferred to have been about 2 5 and the flow velocity approximately 235 m s the similarities and differences between the furrows reported here and channels observed at other volcanoes are discussed

may 18 1980 mount st helens deposits in south coldwater creek washington beginning at 0832 pacific daylight time pdt mount st helens washington produced a rockslide debris avalanche and a lateral explosion blast that generated a laterally directed pyroclastic surge called here a blast surge the resulting deposits are thickest in the east west trending valley of north fork toutle river immediately north of the volcano but are almost as thick in south coldwater creek a small tributary of the toutle river in the lee of an east west trending ridge johnston ridge just north of the north fork toutle river the avalanche surmounted johnston ridge 300 m relief and flowed down the valley of south coldwater creek closely following the avalanche and in part contemporaneously with it the blast surge left thin up to 0 5 m deposits on johnston ridge and thick up to 15 m deposits in south coldwater creek these deposits have a lower layer layer a1 which is friable massive poorer in fines particles 1 16 mm and more poorly sorted than the upper layer layer a2 layer a2 is less friable because it contains more silt and clay sized material beneath layer a1 is a zone containing a small percentage of debris from the blast surge mixed with products eroded from the underlying surface this zone designated as layer a0 is a poorly mixed layer containing schlieren of soil shattered volcanic fragments and considerable quantities of organic material layer a1 is strongly sorted and fines depleted and is interpreted to have been deposited from just behind the turbulent head of the blast surge layer a2 is interpreted to have been deposited from the body of the blast surge which is believed to have been less turbulent than the head layer a0 is interpreted to have formed by shearing at the base of the head of the blast surge in the region between the front and the back of the head of the blast surge it is concluded that a strongly fines depleted basal layer of a pyroclastic flow or surge deposit underlain by a thin sheared zone is the signature of an extremely high velocity particulate density current

a tracer study of the formation dispersal and renewal of levantine intermediate water the formation and dispersal of levantine intermediate water liw are examined using a series of tracer experiments based on an eddy permitting general circulation model of the mediterranean liw is formed in the region of the rhodes gyre and disperses via both the time mean and time varying circulation tracer released in the rhodes gyre is transferred westward by the time mean circulation but also southward and eastward by the time varying circulation off line tracer experiments suggest that the time varying circulation exhibits both advective and diffusive components where the advective component opposes downgradient transfer in some regions the rate of invasion of tracer into the main thermocline suggests that the renewal timescale is 10 20 years for liw and of order 100 years for eastern mediterranean deep water assuming advection dominates the transfer of tracer the implied annual subduction rate is 0 6 0 1 sv in the rhodes gyre and 0 2 0 1 sv in the adriatic sea the liw mode is found to become cooler and fresher as a result of mixing with the adriatic outflow while its potential vorticity appears well conserved

a sequence of a plinian eruption preceded by dome destruction at kelud volcano indonesia on february 13 2014 revealed from tephra fallout and pyroclastic density current deposits abstract a plinian style eruption with a radially spreading umbrella cloud occurred on february 13 2014 at kelud volcano indonesia we present the sequence of this plinian event based on a geological survey of the eruption products and analysis of satellite images the eruptive deposits were divided into four major depositional units units a b c and d and used to determine the sequence of events the plinian phase was preceded by partial destruction of the existing lava dome and generation of high energy pyroclastic density currents pdcs mainly toward the ne that produced a series of depositional subunits units a 0 2 and blown down trees stage 1 in the main phase of the plinian eruption tephra fallout unit b was widely distributed over east java stage 2 the winds above the volcano significantly affected the tephra dispersal process in stage 3 the plinian column collapsed generating dense pdcs that flowed down the volcano valleys producing pumiceous lobate deposits unit c the declining phase of the eruption produced fine rich fallout tephra layers unit d 1 2 from low level eruption plumes and or ash lofted from pdcs the eruption sequence constructed from field observations is supported by geophysical observations the deposit features and componentry suggest that newly ascended magma triggered the destruction of the lava dome and the generation of high energy pdcs and during the subsequent climactic phase the dome was completely destroyed we estimate a total erupted volume of 0 25 0 50 km 3 bulk deposit volume 0 14 0 28 km 3 in dense rock equivalent and a mass eruption rate of 6 5 2 8 10 7 kg s with a volcanic explosivity index of 4 the eruption sequence and physical parameters of the 2014 eruption will help assess future volcanic activity and hazards at kelud volcano

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

surface deformation and displacement of bed elements during splash model tests abstract the phenomenon of splash is connected with soil erosion occurs commonly and has a complex nature the study presents the results of research in which glass beads dry and saturated beds with a diameter size range of 0 425 0 6 mm were used as a soil model patterns and layers of glass particles beads distinguished by their colour were placed on the surface of the samples displacements of the marked beads were used for the analysis of movement caused by splash the measurements were supplemented with recordings made with high speed cameras and photographs from an x ray microtomograph three types of displacement for dry bed elements were distinguished i displacement inside the surface area wetted with a falling drop of water ii ejection and iii placement on the crater rim as well as two types of displacement for elements from saturated beds i displacement inside the deformation and ii ejection the distance travelled by the beads was related to the specificity their displacement which was associated with the initial location of the beads on the sample surface in the case of dry beds glass beads with an initial location equal to 14 mm or more from the centre of the drop impact were not moved in the case of saturated beds this distance was about 10 mm more than 95 of the beads ejected from dry beds came from the surface layer of the sample all the measurement methods applied show that the deformations of the dry bed surfaces were greater and more diversified than those of the saturated beds the results presented in the study are important for understanding the mechanisms of transport of bacteria fungi and pollutants transferred with ejected soil particles during splash the results can also be used for a physical description of the phenomenon for the computer modelling of both splash and water erosion

mediterranean oceanic response to the interannual variability of a high resolution atmospheric forcing a focus on the aegean sea 1 we investigated the interannual variability of the mediterranean sea thermohaline circulation under present climate conditions using an oceanic model of 1 8 resolution two numerical simulations of 50 year duration were performed in a control simulation the model was forced by a perpetual year forcing inferred from the climatology of the ecmwf fields while in a random simulation the 6 years of the ecmwf fields were randomly applied in this way we were able to test the sensitivity of the thermohaline circulation under an atmospheric interannual variability in particular during the last 10 years of the random simulation a succession of cold winters led to anomalous deep water formation in the aegean sea we focused our analysis on this event this anomalously dense water mostly forms in the central and southern aegean subbasins with a formation rate of about 0 6 sv this led to strong modifications in water mass budgets and circulation with intensified exchanges between these two subbasins the export of those dense waters to the levantine basin remains weak except for a few particular years thus the impact of this event is localized as opposed to the eastern mediterranean transient these results show the possibility for transient events to reoccur in the eastern basin in the forthcoming years

the association of lava dome growth with major explosive activity vei 4 domehaz a global dataset investigation of the global eruptive records of particular types of volcanoes is a fundamental and valuable method of understanding what style of activity can be anticipated in the future and can highlight what might be expected or unusual in particular settings this paper investigates the relationship between large explosions volcanic explosivity index vei 4 and lava dome growth from 1000 ad to present and develops the domehaz database domehaz contains information from 397 dome forming episodes including duration of dome growth duration of pauses in extrusion extrusion rates and the timing and magnitude vei of associated large explosions major explosive activity when associated with dome growth is more likely to occur before dome growth rather than during or at the end of dome forming eruptions in most cases where major explosive activity has been associated with dome growth the eruptions occurred at basaltic andesite to andesitic volcanoes the most common type of dome forming volcano but a greater proportion of dacitic and rhyolitic dome growth episodes were associated with large explosions high extrusion rates 10 m3 s 1 seem to be associated with large explosions and may inhibit degassing or destabilize existing domes leading to explosive decompression large explosions may alternatively be followed by dome growth which represents the clearing of residual magma from the conduit relationships extracted from the global record can be used to construct probability trees for new and ongoing dome forming eruptions or can be used in conjunction with other types of event trees to aid in forecasting volcanic hazards during a crisis especially for volcanoes where data are sparse

the 1968 andesitic lateral blast eruption at arenal volcano costa rica the magmatic andesitic eruption of arenal volcano on july 29 31 1968 after centuries of dormancy produced three new fissural craters a b and c on its western flank and a multilayered pyroclastic deposit emplaced by complex transport mechanisms the explosions were initially triggered by a volatile oversaturated 4 7 wt h2o magma several lines of evidences suggest a small blast surge where a wood rich pyroclastic deposit was emplaced as a ground layer followed by several units of coarse grained md between 0 65 and 5 40 tephra deposits lu lapilli units dau double ash units lu 1 2 3 dau 1 and 2 consist of unconsolidated and well to poorly sorted vesiculated bombs and lapilli of andesite some blocks ash and shredded wood the individual units are possibly correlated with the major explosions of july 29 the thickness of the deposits decreases with the distance from the volcano from 5 6 m to a few centimeters on average 90 of the components are juvenile 10 dense andesite and 90 vesicular these coarse grained beds were deposited in rapid succession by a complex transport process involving normal fallout strong ballistic trajectories with a lateral hot 400 c blast surge lu equivalent to a1 ballistic and coarse tephra sprayed in a narrow 85 area within about 5 5 km from the lowest crater and a high ca 10 km eruption column dispersed airfall fine lapilli ash 100 km from the volcano ashcloud forming explosions producing thin pyroclastic surge and muddy phreatomagmatic fallout deposits flau equivalent to a2 and a3 closed the blast surge sequence the successive explosions on july 30 31 mainly produced block and ash flows and widely dispersed ash fall the total volume of pyroclastic material is calculated as 25 8 5 5 10 6 m 3 9 4 2 0 10 6 m 3 dre a model is proposed to explain the peculiarities of the formation transportation and emplacement of the blast deposits the intrusion of the presumed andesitic cryptodome possibly happened through an active thrust fault favoring not only the formation of the lowest crater a but also the low angle explosive events prior to the eruption several minerals were settling to the bottom of the magma chamber as is suggested by the increase of incompatible elements towards the bottom of the stratigraphic section the major elements indicate that some crystal redistribution occurred and the maximum concentration of al2o3 and eu and sr support plagioclase enrichment in early phases of the eruption top of lu 1 and dau 1 from the about 20 recognized prehistoric and historic blast deposits in the world approximately half were produced by sector collapse of the volcano and the other half by sudden decompression of cryptodomes or lava dome collapses the recent blasts 1888 1990s elsewhere have an apparent recurrence of one event decade compared to just a

cretan deep water outflow into the eastern mediterranean abstract a simple hydraulic model is used to estimate the deep water fluxes of cretan deep water cdw through the cretan arc straits and into the eastern mediterranean basins the input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses data from four hydrographic cruises which took place in 1995 1991 and 1987 are used to estimate the depth of the reservoir above the sill and the density difference the results show a significant cdw outflow of 0 75 106 m3 s 1 in early 1995 the outflow of cdw through kassos strait in the east is 0 53 106 m3 s 1 while 0 22 106 m3 s 1 outflows through the antikithira strait in the west the model results agree with fluxes estimated from current meter observations the cdw outflow has been neither steady nor uniform during the period 1987 95 in the kassos strait the outflow commenced in 1987 and increased rapidly until 1991 since then it appears to have stabilised in the antikithira strait in contrast the outflow has increased steadily since 1987 such modifications in the cdw outflow are associated with changes in its hydrographic characteristics the salinity of cdw increased constantly by approximately 0 1 between 1987 and 1995 while its temperature warmed between 1987 and 1991 and then cooled

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

the role of gravitational instabilities in deposition of volcanic ash volcanic ash is a significant hazard for areas close to volcanoes and for aviation gravitational instabilities forming at the bottom of spreading volcanic clouds have been observed in many explosive eruptions here we present the first quantitative description of the dynamics of such instabilities and correlate this with the characteristics of the fall deposit from observations of the 4 may 2010 eyjafjallajokull iceland eruption gravitational instabilities initially took the form of downward propagating fingers that formed continuously at the base of the cloud and appeared to be advected passively at the crosswind speed measurements of finger propagation are consistent with initial conditions inferred from previous studies of ash cloud dynamics dedicated laboratory analogue experiments confirmed that finger downward propagation significantly exceeded the settling speed of individual particles demonstrating that gravitational instabilities provide a possible mechanism for enhanced sedimentation of fine ash our observations challenge the view that aggregation is the primary explanation of proximal fine ash sedimentation and give direct support for the role of gravitational instabilities in providing regions of high particle concentration that can promote aggregation

stratospheric volcanic ash emissions from the 13 february 2014 kelut eruption mount kelut indonesia erupted explosively around 15 50 ut on 13 february 2014 sending ash and gases into the stratosphere satellite ash retrievals and dispersion transport modeling are combined within an inversion framework to estimate the volcanic ash source term and to study ash transport the estimated source term suggests that most of the ash was injected to altitudes of 16 17 km in agreement with space based lidar data modeled ash concentrations along the flight track of a commercial aircraft that encountered the ash cloud indicate that it flew under the main ash cloud and encountered maximum ash concentrations of 9 3 mg m 3 mean concentrations of 2 1 mg m 3over a period of 10 11 min of the flight giving a dosage of 1 2 0 3 g s m 3 satellite data could not be used directly to observe the ash cloud encountered by the aircraft whereas inverse modeling revealed its presence

directed blasts and blast generated pyroclastic density currents a comparison of the bezymianny 1956 mount st helens 1980 and soufriere hills montserrat 1997 eruptions and deposits we compare eruptive dynamics effects and deposits of the bezymianny 1956 bz mount st helens 1980 msh and soufriere hills volcano montserrat 1997 shv eruptions the key events of which included powerful directed blasts each blast subsequently generated a high energy stratified pyroclastic density current pdc with a high speed at onset the blasts were triggered by rapid unloading of an extruding or intruding shallow magma body lava dome and or cryptodome of andesitic or dacitic composition the unloading was caused by sector failures of the volcanic edifices with respective volumes for bz msh and shv c 0 5 2 5 and 0 05 km3 the blasts devastated approximately elliptical areas axial directions of which coincided with the directions of sector failures we separate the transient directed blast phenomenon into three main parts the burst phase the collapse phase and the pdc phase in the burst phase the pressurized mixture is driven by initial kinetic energy and expands rapidly into the atmosphere with much of the expansion having an initially lateral component the erupted material fails to mix with sufficient air to form a buoyant column but in the collapse phase falls beyond the source as an inclined fountain and thereafter generates a pdc moving parallel to the ground surface it is possible for the burst phase to comprise an overpressured jet which requires injection of momentum from an orifice however some exploding sources may have different geometry and a jet is not necessarily formed a major unresolved question is whether the preponderance of strong damage observed in the volcanic blasts should be attributed to shock waves within an overpressured jet or alternatively to dynamic pressures and shocks within the energetic collapse and pdc phases internal shock structures related to unsteady flow and compressibility effects can occur in each phase we withhold judgment about published shock models as a primary explanation for the damage sustained at msh until modern 3d numerical modeling is accomplished but argue that much of the damage observed in directed blasts can be reasonably interpreted to have been caused by high dynamic pressures and clast impact loading by an inclined collapsing fountain and stratified pdc this view is reinforced by recent modeling cited for shv in distal and peripheral regions solids concentration maximum particle size current speed and dynamic pressure are diminished resulting in lesser damage and enhanced influence by local topography on the pdc despite the different scales of the blasts devastated areas were respectively 500 600 and 10 km2 for bz msh and shv and some complexity involving retrogressive slide blocks and clusters of explosions their pyroclastic deposits demonstrate strong similarity juvenile material composes 50 of the deposits implying for the blasts a dominantly magmatic mechanism although hydrothermal explosions also occurred the character of the magma fragmented by explosions highly viscous phenocryst rich variable microlite content determined the bimodal distributions of juvenile clast density and vesicularity thickness of the deposits fluctuates in proximal areas but in general decreases with distance from the crater and laterally from the axial region the proximal stratigraphy of the blast deposits comprises four layers named a b c d from bottom to top layer a is represented by very poorly sorted debris with admixtures of vegetation and soil with a strongly erosive ground contact its appearance varies at different sites due to different ground conditions at the time of the blasts the layer reflects intense turbulent boundary shear between the basal part of the energetic head of the pdc and the substrate layer b exhibits relatively well sorted fines depleted debris with some charred plant fragments its deposition occurred by rapid suspension sedimentation in rapidly waning high concentration conditions layer c is mainly a poorly sorted massive layer enriched by fines with its uppermost part laminated created by rapid sedimentation under moderate concentration weakly tractive conditions with the uppermost laminated part reflecting a dilute depositional regime with grain by grain traction deposition by analogy to laboratory experiments mixing at the flow head of the pdc created a turbulent dilute wake above the body of a gravity current with layer b deposited by the flow body and layer c by the wake the uppermost layer d of fines and accretionary lapilli is an ash fallout deposit of the finest particles from the high rising buoyant thermal plume derived from the sediment depleted pyroclastic density current the strong similarity among these eruptions and their deposits suggests that these cases represent similar source transport and depositional phenomena

drop shape and erosivity part ii splash detachment transport and erosivity indices the relevance of drop shape for erosivity was tested for different combinations of drop sizes and fall heights for all test combinations together the introduction of the observed drop shape in erosivity parameters only produces minor improvements in the relation between erosivity and detachment and transport by splash this result is attributed to the dominance of oblate shapes in high velocity conditions using small fall heights and low fall velocities as in many rainfall simulators and drop tests it is shown that prolate drops produce a splash detachment which is 2 to 3 times higher than that produced by drops with an oblate shape at impact as drop production in rainulators or for aggregate stability drop tests may result in more or less uncontrolled variations of drop shape it is concluded that in addition to other test conditions drop shape should be specified moreover it is noted that the erosive capability of prolate drops can explain partly the high splash erosion amounts below vegetation

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

observations stratigraphy and eruptive processes of the 1990 eruption of kelut volcano indonesia the february 10 1990 eruption of kelut volcano eastern java reportedly began with seven discrete short lived explosions between 11 41 and 12 35 local times deposits of this initial phreatomagmatic stage include a basal ash fall layer unit a1 widespread pumice surge deposits unit s and related pisolitic ash layer unit a2 the main plinian phase of the eruption lasted about 4 hours from 12 35 and produced pumice flow deposits unit pf overlain by a pumice fallout layer distributed mainly to the southwest unit p and intra plinian scoria flow deposits unit sf uppermost scoria rich ash fall layers unit a3 likely relate to late discrete eruptive pulses a few small explosions resumed on february 11 and 12 leaving no recognizable deposit an embryonic lava dome had formed in the crater bottom by april then was submerged by the new crater lake destruction of the summit area resulted from emplacement of the pre plinian pumice surge up to 4 5 km on the south and west flanks and of the early plinian pumice flows up to 1 2 km radially from the crater before these were channelized in the main valleys to further travel 3 km most of the 32 human deaths resulted from roof collapse under the load of fallout tephra beyond the devastated area which had been evacuated before the eruption began the eruption produced 0 13 km3 of tephra of which 0 12 km3 represent the products of the plinian phase the average eruptive rate of the plinian phase is estimated to have been 7 5 106 kg s magma dre the pumice flows are interpreted to have been formed due to unsteadiness and low velocity of the eruptive column at the beginning of the plinian phase the intra plinian scoria flows incorporate either more degassed or colder juvenile magma they were presumably erupted at the edge of the column due to fluctuations in the mass flux and in pressure in the conduit

how long is a hillslope hillslope length is a fundamental attribute of landscapes intrinsically linked to drainage density landslide hazard biogeochemical cycling and hillslope sediment transport existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope area scaling where the hillslope domain transitions into the fluvial domain here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model dem based on flow directions calculated using pixel aspect until reaching the channel network defined using recently developed channel extraction algorithms through comparisons between these measurement techniques we show that estimating hillslope length from plots of topographic slope versus drainage area or by inverting measures of drainage density systematically underestimates hillslope length in addition hillslope lengths estimated by slope area scaling breaks show large variations between catchments of similar morphology and area we then use hillslope length relief structure of landscapes to explore nature of sediment flux operating on a landscape distinct topographic forms are predicted for end member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient because our method extracts hillslope profiles originating from every ridgetop pixel in a dem we show that the resulting population of hillslope length relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes we find that across a broad range of sites across the continental united states topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

differences in the seismicity preceding the 2007 and 2014 eruptions of kelud volcano indonesia abstract a significant increase in the number of volcano tectonic vt and vb earthquakes preceded the 2007 and 2014 eruptions of kelud volcano indonesia the background seismicity rates at the volcano is generally

the landscape reynolds number and other dimensionless measures of earth surface processes abstract an analogy between turbulent fluid systems and landscape drainage systems parker g haff p k murray a b 2001 eos transactions of the american geophysical union 82 pp f564 is suggested by the observation that transport in both systems can be approximated by diffusion with size proportional effective diffusivities with a cross over at small scales to fickian diffusion the landscape reynolds number of a typical fluvial landscape is estimated to be of order re l 10 6 to 10 9 these large values reflecting the relative efficiency of fluvial transport compared to creep re l is the ratio of the large scale effective diffusivity of rivers to the small scale diffusivity of creep processes on hillslopes the spatial dependence of the effective diffusivity produces rivers with logarithmic long profiles similar to the profiles of many rivers in nature and analogous to the logarithmic dependence of mean fluid velocity on distance from a wall in turbulent flow the landscape example suggests how other generalized reynolds numbers can be constructed as ratios of large scale to small scale diffusivities to measure the efficiencies of complex processes that affect the surface as an example the global airline transportation network is estimated to have an efficacy relative to that of direct human mechanisms for transport of similar goods and materials of about 10 8 as measured by a corresponding technology reynolds number the appearance of such large dimensionless numbers pertaining to the consequences of human invention and design reflects the emergence of the technosphere as an increasingly efficient overlay on the historical domain of biology and surficial geology

granular impact cratering by liquid drops understanding raindrop imprints through an analogy to asteroid strikes when a granular material is impacted by a sphere its surface deforms like a liquid yet it preserves a circular crater like a solid although the mechanism of granular impact cratering by solid spheres is well explored our knowledge on granular impact cratering by liquid drops is still very limited here by combining high speed photography with high precision laser profilometry we investigate liquid drop impact dynamics on granular surface and monitor the morphology of resulting impact craters surprisingly we find that despite the enormous energy and length difference granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters inspired by this similarity we integrate the physical insight from planetary sciences the liquid marble model from fluid mechanics and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid drop imprints in granular media our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes

atmospheric forcing of the eastern mediterranean transient by midlatitude cyclones 1 hydrographic observations indicated a shift of the main deep water formation in the mediterranean sea from its usual location in the adriatic sea to the aegean sea during the late 1980s and early 1990s during winters 1991 1992 and 1992 1993 this event is known as the eastern mediterranean transient emt we report here a connection between emt and specific atmospheric conditions which created anomalously large buoyancy fluxes from the aegean sea during winters 1991 1992 and 1992 1993 the enhanced emt winters we use newly available state of the art datasets with high space and time resolution and show that atypical cyclonic activity in the central mediterranean versus the eastern basin produced the enhanced atmospheric forcing which intensified the emt an abatement of the frequency of cyclones in the central mediterranean during 1992 1993 drastically reduced the northward advection of warm air over the aegean sea compared to more typical years while an increase in the frequency of cyclones in the eastern mediterranean enhanced the southward advection of cold air over the aegean sea especially during 1991 1992 these changes significantly increased buoyancy flux losses from the aegean sea during the enhanced emt winters intensifying deep water production

eyewitness stratigraphy chemistry and eruptive dynamics of the 1913 plinian eruption of volcan de colima mexico abstract based on the stratigraphic record of the deposits analysis of previous works historic archives and eyewitness accounts the 1913 eruption of volcan de colima was reconstructed the eruption started in 17 january and peaked in 20 january 1913 it occurred in three main phases 1 an opening phase with the generation of merapi type pyroclastic flows units f1 f2 f3 and a pyroclastic surge s1 2 a vent clearing phase with strong explosions that produced vulcanian soufriere type pyroclastic flows f4 and a pyroclastic surge s2 which destroyed the summit dome decompressing the magma system and 3 a plinian phase with the establishment of a 23 km high column dispersing a fallout c1 to the ne followed by the collapse of the column that generated a pyroclastic surge s3 and 15 km long pumice rich pyroclastic flows f5 after the eruption remobilization of the pyroclastic material generated lahars in main gullies around the crater fallout c1 blanketed an area of 191 318 km2 covering the cities of guzman guadalajara and saltillo coahuila located at 725 km from the source it had a volume of 1 4 km3 0 57 km3 dre dense rock equivalent the total volume of pyroclastic flow and surge deposits was 0 26 km3 0 07 km3 dre giving a total volume of the eruption of 1 66 km3 0 64 km3 dre the plinian column lasted 4 6 h with a total mass of 1 5 1012 kg and a mass eruption rate of 9 02 107 kg s the column height and the ejected magma volume indicate that the 1913 eruption had a vei 5 being the largest event in the historical record of colima volcano juvenile scoria and pumice consisted of pl opx cpx hbl accessory titanomagnetite ap and ol with reaction rims chemistry of juvenile scoria and pumice samples is andesitic very homogeneous 58 3 0 5 wt sio2 and similar to the 1818 juvenile products 58 9 0 2 wt sio2 the presence of banded scoria olivine phenocrysts with reaction rims and trace element variations strongly suggest that the 1913 eruption was caused by a magma mixing event

the merapi 2010 eruption an interdisciplinary impact assessment methodology for studying pyroclastic density current dynamics abstract the large explosive eruption of merapi volcano indonesia in 2010 presented a key and rare opportunity to study the impacts of a major explosive eruption in a densely populated area pyroclastic density currents pdcs produced throughout the 2010 eruption were unusually destructive causing near complete devastation across a 22 km 2 swath of the densely populated southern flanks and casualties to the end of their runout at 15 5 km from the volcano the majority 120 of the more than 200 fatalities occurred more than 12 km from the volcano where many people were caught in pdcs as they were evacuating the 2010 eruption vei 4 exhibited a range of pdc behaviour in a complex multi stage event that marked a change in eruption behaviour at merapi being the first eruption of this magnitude and style since 1872 this shift in style may mark a change in regime and so understanding the potential impact of such large explosive eruptions is essential for future risk assessment at merapi we describe a new impact assessment methodology that allowed us to collect important empirical geological damage and casualty information and reconstruct impact dynamics associated with the pdcs in contrast to previous pdc impact studies we combined remote field laboratory and gis assessments and were able to enter the affected areas safely and before their disturbance by rains or human activity by integrating the results of our geological damage and medical studies we could reconstruct the spatial and temporal dynamics of the pdcs and their main hazard characteristics our interdisciplinary methods and preliminary findings are discussed here in the areas damaged by pdcs we used empirical damage data and calculations of material and structural resistance to lateral force to estimate approximate dynamic pressures dynamic pressures associated with the 5 november paroxysm exceeded 15 kpa more than 6 km from source and rapidly attenuated over a distance of less than 1 km at the end of the pdc runouts analysis of thermal indicators such as deformed plastic and correlation with information on burns injuries and fires provided estimates of ambient temperatures associated with the pdcs even at the relatively low temperatures estimated for the pdcs 200 300 c they were lethal to people inside as well as outside buildings in part because of the building design that enabled the pdcs to rapidly infiltrate inside such detailed quantitative data can be used to support numerical pdc and impact modelling and risk assessment at dome forming volcanoes providing an improved understanding of the complexity of pdcs and their associated impacts on exposed populations

atmospheric resonant oscillations by the 2014 eruption of the kelud volcano indonesia observed with the ionospheric total electron contents and seismic signals abstract acoustic waves from volcanic eruptions are often observed as infrasound in near fields part of them propagate upward and disturb the ionosphere and can be observed with total electron content tec data from global navigation satellite system gnss receivers here we report tec variations after the 13 february 2014 plinian eruption of the kelud volcano east java indonesia observed with regional gnss networks significant disturbances in tec were detected with six gnss satellites and wavelet analysis showed that harmonic oscillations started at 16 25 ut and continued for 2 5 h the amplitude spectrum of the tec time series showed peaks at 3 7 mhz 4 8 mhz and 6 8 mhz long wavelength standing waves with a wide range of wavelength trapped in the lower atmosphere are excited by the plinian eruption amplitude spectra of the ground motion recorded by seismometers however had frequency components at discrete wave periods the condition for the resonant oscillations between the atmosphere and the solid earth is satisfied only at these discrete wave period and horizontal wavelength pairs therefore efficient energy transfer from the atmospheric standing waves to the solid earth rayleigh waves occurred at discrete periods and resulted in the harmonic ground motion

air density of the permian atmosphere constraints from lithified raindrop imprints abstract in contrast to the composition of earth s ancient atmosphere the corresponding air density is almost unknown a unique method to estimate the palaeo atmospheric density is to use lithified raindrop imprints the size of imprints is amongst other factors controlled by the air density whereas large impacts form in a less dense atmosphere and vice versa this basic relation was used to estimate the near sea level atmospheric density of the permian a period characterised by an icehouse to greenhouse transition and an atmospheric composition comparable to the modern one this makes the permian an important analogue to better understand the current climate and environmental changes in this study we analysed lithified raindrop imprints preserved in permian terrestrial sandstone from the flechting high northern germany following former applications we experimentally determined the relation between raindrop momentum and imprint dimension to estimate the palaeo air density the maximum bound of the permian air density is 2 3 kg m3 assuming that the maximum measured imprint area of 68 1 5 mm2 was formed by the largest naturally occurring raindrop with a diameter of 6 8 mm although we cannot rule out an air density comparable to the present day 1 2 kg m3 more realistic estimates of maximum raindrop diameters for a rainfall rate of 100 mm h are between 3 2 and 4 3 mm yielding air density estimates of 0 3 and 0 85 kg m3 approximately one fourth to three quarters of the present day value this approach is based on a few largest observed imprints and does take the complete raindrop imprint distribution into account the imprint distribution primarily depends on the drop size distribution of the rainfall event that causes the imprints which follow a defined function in this study we present a novel method to further constrain the palaeo air density estimation by comparing the observed distribution of lithified raindrop imprints with modelled imprint distributions for different rainfall rates and drop size distribution functions we observed significant differences theoretical imprint distributions are in general shifted towards smaller imprints which we interpret as a higher probability of larger imprints to be preserved above a threshold imprint area of 10 mm2 observed and modelled distributions match each other suggesting that a major fraction 50 of raindrops did not generate recognisable imprints in the analysed substrate unfortunately no unique rainfall rate fits the observed imprint distribution but instead pairs of rainfall rates and air densities yield reasonable fits palaeo air density estimates therefore depend on an unknown rainfall rate assuming that lithified imprints formed by a rain event with a rainfall rate of

airborne expendable bathythermograph surveys of the eastern mediterranean two extensive airborne expendable bathythermograph axbt surveys of the eastern mediterranean were conducted during december 1991 and july 1992 from a naval oceanographic office rp 3 aircraft larger areas were sampled over shorter periods of time than is possible with conventional surveys carried out by ships the circulation of the eastern mediterranean consists of a collection of subgyres and fronts which show surprising seasonal and interannual variability these surveys help to describe further this variability which is only partially understood in particular the surveys provide additional evidence that a relatively strong anticyclone located adjacent to the southeast corner of crete during the late summer and through fall is a consequence of strong north winds from the aegean the etesians being blocked by crete also notable in both surveys was the absence of a strong mersa matruh gyre an anticyclone or anticyclonic subgyre off the egyptian coast generally considered to be permanent in contrast to published earlier observations the mersa matruh gyre system was more a collection of weaker anticyclones rather than a single sometimes double centered strong feature in both surveys we saw a string of anticyclones off the african coast between about 24 and 32 e in general these eddies did not exhibit a significant surface thermal structure but were most evident in the 200 m to 300 m depth depictions it may be that the formation of a strong southeast crete anticyclone inhibits the formation of a large relatively strong mersa matruh subgyre by interacting with the mid mediterranean jet if so then both the southeast crete anticyclone and the mersa matruh anticyclone could both be recurrent but tend to occur at different times

on the use of remote infrasound and seismic stations to constrain the eruptive sequence and intensity for the 2014 kelud eruption the february 2014 eruption of kelud volcano indonesia destroyed most of the instruments near it we use remote seismic and infrasound sensors to reconstruct the eruptive sequence the first explosions were relatively weak seismic and infrasound events a major stratospheric ash injection occurred a few minutes later and produced long lasting atmospheric and ground coupled acoustic waves that were detected as far as 11 000 km by infrasound sensors and up to 2300 km away on seismometers a seismic event followed similar to 12 minutes later and was recorded 7000 km away by seismometers we estimate a volcanic intensity around 10 9 placing the 2014 kelud eruption between the 1980 mount st helens and 1991 pinatubo eruptions intensities we demonstrate how remote infrasound and seismic sensors are critical for the early detection of volcanic explosions and how they can help to constrain and understand eruptive sequences

estimate of pyroclastic flow velocities resulting from explosive decompression of lava domes apparently benign silicic domes or lava flows can travel for several kilometres and then suddenly collapse to generate pyroclastic phenomena capable of causing widespread destruction as happened recently at mount unzen in japan1 two sources have been proposed for the energy that propels such pelean or merapi type2 pyroclastic flows gravitational col lapse supplemented by heating and expansion of air and sudden expansion of pressurized gases from inside the lava flow if gravity controls the energy transfer then areas likely to be affected can be predicted on the basis of topography3 and the resulting deposits will bear a simple relationship to the part of the lava flow from which they issued but if gas pressure adds a significant contribution hazard assessment becomes more difficult because gas decompression adds velocities beyond those acquired by gravitational forces putting much larger areas at risk and forming pyroclastic deposits that are much more difficult to relate to their source here we estimate the initial velocities of pyroclastic flows generated by dome disintegration for a range of lava compositions and volatile contents and offer a conceptual framework for correlating the dynamics of dome front collapse with the resulting sediment record our results indicate that explosive decompression at distal portions of domes can cause velocities comparable to gravitational collapse especially in cases where volatiles become locally concentrated above equilibrium values

sand detachment under rains with varying angle of incidence abstract in the case of wind driven rain as the angle of rain incidence increases greater force components act parallel to the surface and lower force components act perpendicular to the surface therefore raindrop impact angle could influence the detachment process in the existence of substantial lateral jet development this could be particularly significant for a cohesionless sand surface that has a weaker resistance to the dislodgement by a raindrop impact than a soil surface experiments of simulated wind driven rain were conducted to evaluate sand detachment rates under increased lateral jetting induced by wind velocities of 6 4 10 0 and 12 0 m s 1 at nozzle operating pressures of 75 100 and 150 kpa and incident on windward and leeward slopes of 4 and 9 with these set ups it was possible to have varying angles of incidence and to determine the effect of the compressive stress and shear stress evaluated by the horizontal and vertical kinetic energy fluxes e tx and e tz respectively on the detachment rates from the sand surface at the same vectorwise sum of e tz and e tx the results showed that there was for similar values of e tz and e tx in windward slopes more sand detachment rate however for dissimilar values of e tz and e tx in leeward slopes where e tx was significantly higher than e tz there was less sand detachment rate consequently with certain values of the compressive stress and shear stress the sand detachment rates under wind driven rains peaked and e tz was the limiting component since the rates significantly decreased as e tz particularly decreased in spite of very large values of e tx

modeling the deep convection in the northwestern mediterranean sea using an eddy permitting and an eddy resolving model case study of winter 1986 1987 1 in the northwestern mediterranean sea winter 1986 1987 was particularly cold inducing a strong open ocean convection event in order to investigate the impact of numerical models spatial resolution on the convection representation and the effects of deep convection on the northwestern mediterranean circulation we perform two numerical three dimensional simulations eddy permitting versus eddy resolving models are forced at the surface by the era40 atmospheric fluxes with a simple heat flux correction to better mimic the observed value we examine the characteristics of the deep convection mixed layer water masses characteristics convection zone and mesoscale structures and perform temporal analysis of this event in terms of kinetic energy buoyancy equilibrium and deep water dw evolution the convection characteristics are similarly represented on a global scale by both models and are in good agreement with observations except for the size of the convection region however the eddy resolving model better reproduces the mesoscale structures whose role in the dw formation mixing and transport is shown to be essential the boundary circulation and the overturning are enhanced during the convection event sixty six percent of the dw spreading is due to the bleeding effect into the catalan sea during the convection event whereas 33 is due to the mesoscale structures southwestward advection after the event sixty percent of the restratification with respect of the water column initial structure occurs before july 1987 and is due to light water advection afterward restratification is due to the mixing and is not complete before next year convection

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

transitions between explosive and effusive phases during the cataclysmic 2010 eruption of merapi volcano java indonesia transitions between explosive and effusive activity are commonly observed during dome forming eruptions and may be linked to factors such as magma influx ascent rate and degassing however the interplay between these factors is complex and the resulting eruptive behaviour often unpredictable this paper focuses on the driving forces behind the explosive and effusive activity during the well documented 2010 eruption of merapi the volcano s largest eruption since 1872 time controlled samples were collected from the 2010 deposits linked to eruption stage and style of activity these include scoria and pumice from the initial explosions dense and scoriaceous dome samples formed via effusive activity as well as scoria and pumice samples deposited during subplinian column collapse quantitative textural analysis of groundmass feldspar microlites including measurements of areal number density mean microlite size crystal aspect ratio groundmass crystallinity and crystal size distribution analysis reveal that shallow pre and syn eruptive magmatic processes acted to govern the changing behaviour during the eruption high an up to 80 mol an microlites from early erupted samples reveal that the eruption was likely preceded by an influx of hotter or more mafic magma transitions between explosive and effusive activity in 2010 were driven primarily by the dynamics of magma ascent in the conduit with degassing and crystallisation acting via feedback mechanisms resulting in cycles of effusive and explosive activity explosivity during the 2010 eruption was enhanced by the presence of a plug of cooled magma within the shallow magma plumbing system which acted to hinder degassing leading to overpressure prior to initial explosive activity

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

application of x ray computed microtomography to soil craters formed by raindrop splash abstract the creation of craters on the soil surface is part of splash erosion due to the small size of these craters they are difficult to study the main aim of this paper was to test x ray computed microtomography to investigate craters formed by raindrop impacts measurements were made on soil samples moistened to three different levels corresponding with soil water potentials of 0 1 3 16 and 16 kpa using images obtained by x ray microtomography geometric parameters of the craters were recorded and analysed x ray computed microtomography proved to be a useful and efficient tool for the investigation of craters formed on the soil surface after the impact of water drops the parameters of the craters changed with the energy of the water drops and were dependent on the initial moisture content of the soil crater depth is more dependent on the increased energy of the water drop than crater diameter

low velocity impact cratering experiments in granular slopes abstract low velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle on the crater shape and its scales we use two types of granular matter sand and glass beads former of which has a larger friction coefficient s tan r where r is the angle of repose experiments show that as increases the crater becomes shallower and elongated in the direction of the slope furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side thus forming an asymmetric profile high speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor such asymmetric ejecta dispersal can be explained by combining the z model and a ballistic model using the topographic maps of the craters we classify crater shape regimes i iii which transition with increasing a full rim crater i a broken rim crater ii and a depression iii the critical for the regime transitions are larger for sand compared to glass beads but collapse to close values when we use a normalized slope tan tan r similarly we derive dependences of the scaled crater depth length width and their ratios which collapse the results for different targets and impact energies we compare the crater profiles formed in our experiments with deep craters on asteroid vesta and find that some of the scaled profiles nearly overlap and many have similar depth length ratios this suggests that these vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

the 1902 peleean deposits in the fort cemetery of st pierre martinique a model for the accumulation of turbulent nuees ardentes abstract the ancient fort cemetery located at the northwestern limit of st pierre has been left undisturbed since 1902 and therefore offers a unique opportunity to study the deposits of the eruptions that destroyed the city six eruption units were found overlying the floor of the cemetery leaving an average 1 6 m thick deposit the city was hit by four major nuees which occurred on may 8 20 june 6 and august 30 the may 20 and june 6 eruption units are each made of three beds the basal bed always lacks fines and is generally massive the middle bed is normally graded on which dune type cross bedding is superimposed in the may 20 deposit the upper bed the thinnest has the finest grain size of the eruption unit and is normally graded true parallel laminae were only observed in the upper bed the may 8 eruption unit is essentially made of fines depleted massive lapilli and tuff the evidence strongly suggests that the deposits of the middle and upper beds accumulated from turbulent suspensions the absence of structures in the basal bed is not conclusive evidence of laminar flow deposition and its characteristics are similar to deposits that have accumulated from highly concentrated turbulent suspensions the lack of fines observed only in the basal bed is attributed to gravity segregation helped by vaporization of water present in the underlying deposits and for the may 8 deposit to escaping gas produced by the destruction of the vegetation during or immediately after deposition which could explain the absence of primary structures in the basal bed the fine grained deposits of mt pelee show a primary structure sequence similar to the turbidite sequence and are therefore interpreted in terms of decreasing flow velocity and grain size with time at a fixed site

pyroclastic current dynamic pressure from aerodynamics of tree or pole blow down abstract the common occurrence of tree and pole blow down from pyroclastic currents provides an opportunity to estimate properties of the currents blow down may occur by uprooting root zone rupture or flexure or shear at some point on the object if trees are delimbed before blow down each tree or pole can be simulated by a cylinder perpendicular to the current the force acting on a cylinder is a function of flow dynamic pressure cylinder geometry and drag coefficient treated as a cantilever of circular cross section the strength for the appropriate failure mode rupture uprooting or flexure can then be used to estimate the minimum necessary current dynamic pressure in some cases larger or stronger standing objects can provide upper bounds on the dynamic pressure this analysis was treated in two ways 1 assuming that the current properties are vertically constant and 2 allowing current velocity and density to vary vertically according to established models for turbulent boundary layers and stratified flow the two methods produced similar results for dynamic pressure the second along with a method to approximate average whole current density offers a means to estimate average velocity and density over the height of the failed objects the method is applied to several example cases including unzen mount st helens lamington and merapi volcanoes our results compare reasonably well with independent estimates for several cases we found that it is possible to use the dynamic pressure equations developed for vertically uniform flow along with the average cloud density multiplied by a factor of 2 5 to determine average velocity over the height of the failed object

chronology and pyroclastic stratigraphy of the may 18 1980 eruption of mount st helens washington many timed observations make it possible to subdivide the 9 hour plinian eruption of mount st helens on may 18 1980 into six phases defined by eruption style the phases are correlated with stratigraphic subunits of ashfall tephra and pyroclastic flow deposits the suite of pyroclastic deposits indicates that the eruption became more pumice rich and compositionally diverse with time perhaps owing to concurrent eruption of less evolved gas poor parts of the magma body with the more evolved gas rich parts the paroxysmal phase i 0832 0900 consisted of landslides lithic pyroclastic flows of a lateral blast and other explosions and a weak pre plinian column phase i pyroclastic deposits include lithic ash flow deposits intercalated with and overlying the voluminous debris avalanche deposit and basal pumice lapilli tephra that underlies a pisolitic ash layer the early plinian phase ii 0900 1215 consisted of vertical ejection of tephra with an early pulse of small pyroclastic flows on the upper flanks 1010 1035 a brief period of lithic ash ejection 1035 1100 and a pumice rich pulse that accompanied growth in height of the eruption column 1100 1215 deposits include minor pyroclastic flows on the crater rim and a reversely graded sequence of proximal tephra that include the lower pumice lapilli layer the lower lithic ash layer and the middle pumice lapilli layer all of which consist of evolved white dacitic pumice 63 64 sio2 during the early ash flow phase iii 1215 1500 the height of the eruption column decreased vertical ejection of tephra ceased and pyroclastic flows were fed from intermittent fountains phase iii deposits consist of a poorly exposed sequence 12 m of ash flow tuff that consist of many thin flow units 2 m each containing pumiceous white dacite 63 64 sio2 and denser gray silicic andesite 61 62 sio2 and fine grained ash cloud deposits interbedded with a nongraded middle pumice ash layer the climactic phase iv 1500 1715 developed in two stages fountain fed pyroclastic flows followed by a short pulse 1625 1715 of vigorous vertical ejection of tephra these stages were accompanied by the peak seismic energy release and peak eruption column height respectively climactic deposits consist of a thick 35 m sequence of thick lapilli rich ash flow sheets 4 12 m each with white and gray pumice and streaky scoria bands 60 sio2 in pumice breccia clasts and the reversely graded upper pumice lapilli layer that is interbedded with fine grained ash cloud deposits during the late ash flow phase v 1715 1815 eruption intensity waned but included a brief episode of small pyroclastic flows 1745 1815 phase v deposits consist of small distributary lobes of ash flow tuff containing white and gray pumice and minor fine ash deposits phase vi activity 1815 to may 19 1980 consisted of a low energy ash plume with transient increases in intensity while seismicity continued at depth sustained vertical discharge of phase ii prodeced evolved dacitewith high s cl ratios ash flow activity of phase iii is attributed to decreases in gas content indicated by reduced s cl ratios and increased clast density of the less evolved gray pumice climactic events are attributed to vent clearing and exhaustion of the evolved dacite

insights into eruption dynamics from the 2014 pyroclastic deposits of kelut volcano java indonesia and implications for future hazards abstract on 13 to 14 february 2014 a 4 h long vei 4 eruption occurred at kelut volcano java indonesia pyroclastic density currents pdcs and extensive ash fall led to 7 fatalities and disruption to flights across the asia pacific region new sedimentological descriptions of the pyroclastic deposits from the 2014 eruption were compared with eyewitness and satellite reports to elucidate temporal variations in eruptive dynamics the stratigraphy of the deposits is presented in 3 stages associated with two eruptions that occurred approximately 15 30 min apart stage 1 pdc deposits originate from the smaller onset eruption the pdc deposits from stage 2 and tephra fall deposits from stage 3 originate from the second plinian eruption during the onset eruption stage 1 low energy pdcs were produced that ran out to 70 by vol pdc deposits ran out to 4 7 km from the vent the deposits reflect an increased output of fresh fragmented magma and some conduit widening evidenced by dense lithic fragments vent instabilities and incorporation of dense material into basal margins of the plume led to the marginal collapse and formation of these pdcs stage 3 occurred in the final hour at the peak of the plinian eruption around 01 00 to 02 00 and produced reversely graded lapilli fall deposits with 90 vol pumice from a 26 km high plume this indicates that there was a sustained flux of juvenile magma to the now open vent system and expansion and fragmentation of the gas rich magma was at its most efficient our study of the eruptive sequence of kelut provides some constraints on predicted patterns for future explosive activity critical for further hazard assessment of the volcano since 1901 kelut has erupted on intervals of 1 to 23 years and the 2014 event characterises a typical explosive style of eruption that alternates regularly with effusive dome formation and collapse events this pattern depends on the dynamics of magma renewal to the system and degassing conditions in the shallow magma reservoir and upper conduit if this pattern holds and the next eruption occurs within the next two decades a return of prolonged dome growth could be anticipated

harmonic ionospheric oscillation by the 2010 eruption of the merapi volcano indonesia and the relevance of its amplitude to the mass eruption rate abstract using continuous data from ground based global satellite navigation system gnss receivers in java and sumatra indonesia we studied the response of ionospheric total ionospheric electron content tec to the 2010 nov 5 eruption of the merapi volcano in central java we then compared the results with the case of the 2014 feb 13 eruption of the kelud volcano eastern java the tec showed a quasi periodic oscillation of a frequency 4 mhz with average amplitudes of 0 9 and 1 8 relative to background values lasting for 20 and 120 min for the merapi and kelud eruptions respectively by comparing the two cases together with the 2015 april eruption of the calbuco volcano chile we found the relative tec oscillation amplitude may scale with the mass eruption rate this suggests that the product of such tec oscillation amplitude and the duration provides a new measure for the total volume of the volcanic deposits

crater formation in soils by raindrop impact the process of crater formation by the impact of water drops on soil sand and various other target material was studied craters of various shapes and sizes were observed on different target materials or conditions ranging from circumferential depression to completely hemispherical shape crater shape was dependent upon target material its ow stress or shear strength and the presence and thickness of water on the surface between 5 and 22 per cent of impact energy was spent on cratering but the relationship between crater volume and kinetic energy of a raindrop was curvilinear indicating a lower ef ciency of impact energy in removing target material as the energy increases impact impulse on the other hand showed a more linear relationship with crater volume and the ratio of impulse over crater volume i v remained constant for the entire range of drop sizes impact velocities and surface conditions used in this study surface shear strength represented by the penetration depth of fall cone penetrometer appeared to be a key factor involved in this process an equation was developed which related crater volume to cone penetration depth and impact impulse crater volume which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount can thus be predicted using this equation copyright 2004 john wiley sons ltd

a physically based model of the dispersion of splash droplets ejected from a water drop impact a model has been developed which predicts the dispersion of splash droplets produced by the impact of a water drop on a sloping soil surface experimental results of the ejection velocities and ejection angles of the splash droplets are generalized to a planar slope and the resulting splash distances are calculated taking into account the effects of air resistance the predictions are presented in terms of the numbers of splash droplets from the impact point to surrounding squares arranged in a grid on the slope the model explains many experimentally observed features of raindrop splash in terms of the mechanics of the processes involved and can make predictions of the effects of slope wind raindrop size and soil properties on droplet dispersion the component of the raindrop velocity parallel to the surface of the slope is identified as the main factor determining the degree and the direction of the asymmetry in the splash droplet dispersion by combining the model with a theory of the entrapment of soil in the splash droplets it is possible to extend it to predict the dispersion of soil particles by raindrop impact which is the basis of a model of soil erosion by rainsplash

toward an understanding of deep water renewal in the eastern mediterranean abstract this paper presents a scenario for understanding the unexpectedly large changes of deep waters and thermohaline circulation in the eastern mediterranean during the past decade it is demonstrated as a possible deep water renewal mechanism in the eastern mediterranean in a numerical simulation with a high resolution model which has successfully reproduced the observed 1987 and 1995 regimes as shown by the two meteor cruises a budget study of the model simulation has shown that more than 75 of the salt added to the deep layers of the eastern mediterranean could have come from the top 1000 m by a salinity redistribution process triggered by intensive cooling over the aegean sea a water transformation process analysis is carried out in the model simulation to reveal how colder and fresher dense deep water formed in the aegean is turned into the eastern mediterranean deep water emdw as observed surface heat and freshwater fluxes are diagnosed to show the roles of each component during the trans

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

differences of precursory seismic energy release for the 2007 effusive dome forming and 2014 plinian eruptions at kelud volcano indonesia abstract early warnings of the timing style and size of volcanic eruptions made on the basis of seismic monitoring are important for mitigation of the hazards associated with volcanic eruptions we calculated the rates of seismic energy release at kelud volcano indonesia preceding both the 2007 effusive lava dome eruption and the 2014 plinian eruption for the 2007 eruption there was first a step wise increase in the rate of release of seismic energy followed by a gradual decrease until the eruption for the 2014 eruption the rate of energy release was almost constant until 10 days before the eruption then gradually increased until there was a dramatic acceleration during the last day before the eruption the total seismic energy released by the 2007 and 2014 eruptions were 3 10 8 j and 2 2 10 9 j respectively the relative difference between the ejected volumes of the 2007 and 2014 eruptions is roughly equivalent to that of the total seismic energy released preceding the eruptions we conducted several trials of the material failure forecast method ffm applying it to the square root of the rate of seismic energy released to assess its usefulness for predicting the timing of eruptions the predicted onset of the 2007 eruption was one day earlier than the actual eruption and the seismic energy release preceding the actual eruption did not increase dramatically as suggested by the ffm model several trials of ffm for the 2014 eruption predicted the onset of the eruption to be three days to two weeks later than the actual eruption even as the end time of the ffm time window approaches several hours to 10 min before the actual eruption onset the predicted eruption onset is still 3 h later than the actual onset thus the results of our ffm modeling did not show the method to be useful for predicting eruption times for kelud volcano the differences of the ffm modeling results for the 2007 and 2014 eruptions likely reflect the differences in the rate of energy release immediately before the two eruptions a deceleration before the 2007 eruption and an acceleration before the 2014 eruption these differences may reflect differences in precursory processes for effusive lava dome and plinian eruptions

globally detected volcanic lightning and umbrella dynamics during the 2014 eruption of kelud indonesia abstract volcanic lightning shows considerable promise as a monitoring and research tool to characterize explosive eruptions its key strengths are rapid and remote detection because the radio signals produced by lightning can propagate thousands of km at the speed of light despite these tantalizing properties the scientific work on volcanic lightning has only recently started gaining momentum much more is needed to understand what lightning reveals about the evolution of an eruption in near real time here we examine the timing and energy release of lightning generated by the eruption of kelud volcano in indonesia on 13 february 2014 as detected by the world wide lightning location network wwlln the eruption column reached at least 26 km above sea level representing the highest plume since the advent of global lightning networks in the last decade therefore it provides valuable constraints on the electrification of end member sustained plinian columns we investigate the lightning in context with satellite images photographs and other published studies results show that the earliest satellite detected activity was a thermal anomaly at 15 46 utc corresponding to a directed blast at the onset of eruption and only a few lightning strokes following a brief pause the eruption produced a sustained column and umbrella cloud that spread outward into the tropical stratosphere rates of umbrella expansion provide an average mass eruption rate mer in the range of 8 107 1 108 kg s 1 a more nuanced picture emerges from the time varying mers determined between each satellite pass which show rapid intensification during the first hour of eruption followed by constant mer for about an hour and waning toward the end after 17 50 utc at this stage decreasing flux into the umbrella cloud coincides with column instability and formation of pyroclastic density currents as recorded by photos from the ground 17 45 utc we infer that some of the erupted mass partitioned into ground hugging currents leading to a lower apparent mer interestingly there is not a 1 1 correlation between lightning intensity and mer over the course of eruption stroke rates increase sharply within the first 30 40 min during rapid intensification of the plume and then drop below 2 strokes per min once the mer remains constant this suggests that electrification was controlled by the rate of increase in mer in other words the acceleration of particles out of the vent we also show that lightning stroke rates and energies are greatest within 50 km of the vent even when the ash cloud extends 200 km downwind indicating that lightning was focused in the regions of highest particle concentration and turbulence overall we conclude that abrupt changes in lightning rates are clearly linked to changes in eruption behavior and that rapid detection could aid monitoring efforts to characterize eruption rates or styles

measurements of rain splash on bench terraces in a humid tropical steepland environment soil loss continues to threaten java s predominantly bench terraced volcanic uplands sediment transport processes on back sloping terraces with well aggregated clay rich oxisols in west java were studied using two different techniques splash on bare cropped or mulched sub horizontal 2 3 terrace beds was studied using splash cups of different sizes whereas transport of sediment on the predominantly bare and steep 30 40 deg terrace risers was measured using a novel device combining a gerlach type trough with a splash box to enable the separate measurement of transport by wash and splash processes measurements were made during two consecutive rainy seasons the results were interpreted using a recently developed splash distribution theory and related to effective rainfall erosive energy splash transportability i e transport per unit contour length and unit erosive energy on the terrace risers was more than an order of magnitude greater than on bare terrace beds 0 39 0 57 versus 0 013 0 016 g m j 1 this was caused primarily by a greater average splash distance on the short steep risers 11 cm versus c 1 cm on the beds splashed amounts were reduced by the gradual formation of a protective pavement of coarser aggregates in particular on the terrace beds soil aggregate size exhibited an inverse relationship with detachability i e detachment per unit area and unit erosive energy and average splash length and therefore also with transportability as did the degree of canopy and mulch cover on the terrace risers splash creep and gravitational processes transported an additional 6 50 of measured rain splash whereas transport by wash played a marginal role copyright 2002 john wiley sons ltd

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter

the run out distance of large scale pyroclastic density currents a two layer depth averaged model abstract we have developed a new two layer pyroclastic density current pdc model that considers the effects of the entrainment and thermal expansion of ambient air in the upper dilute layer in order to investigate the dominant factors controlling the run out distance of large scale pdcs numerical simulations show a dilute current spreading radially from the collapsing eruption column edge and forming a thin dense basal current through particle settling i e a two layer pdc forms forward propagation of the two layer pdc stops owing to lift off of the dilute current and or deposition of the dense current and eventually the two layer pdc converges to a steady state our parametric study classifies the flow patterns of steady state two layer pdcs into one of two flow regimes according to the relative magnitude of the run out distances of the dilute and dense currents this relative magnitude critically depends on the ratio of the deposition speed at the base of the dense current d to the speed of particles settling from the dilute current to the dense current ws the run out distance of the whole two layer pdc is determined by that of the dilute current when d ws is large 4 10 3 otherwise when d ws is small 4 10 3 the run out distance of the dense basal current exceeds that of the dilute current the former increases as d ws decreases the run out distance of the dilute current is too short to explain some of the long run out distances of pdcs observed in the field e g the 1991 pinatubo and 2014 kelud eruptions it is suggested that the dense current traveling beyond the lift off point of the parent dilute current plays a significant role in the emplacement of pdcs with such long run out distances

trouble with diffusion reassessing hillslope erosion laws with a particle based model 1 many geomorphic systems involve a broad distribution of grain motion length scales ranging from a few particle diameters to the length of an entire hillslope or stream studies of analogous physical systems have revealed that such broad motion distributions can have a significant impact on macroscale dynamics and can violate the assumptions behind standard local gradient flux laws here a simple particle based model of sediment transport on a hillslope is used to study the relationship between grain motion statistics and macroscopic landform evolution surface grains are dislodged by random disturbance events with probabilities and distances that depend on local microtopography despite its simplicity the particle model reproduces a surprisingly broad range of slope forms including asymmetric degrading scarps and cinder cone profiles at low slope angles the dynamics are diffusion like with a short range thin tailed hop length distribution a parabolic convex upward equilibrium slope form and a linear relationship between transport rate and gradient as slope angle steepens the characteristic grain motion length scale begins to approach the length of the slope leading to planar equilibrium forms that show a strongly nonlinear correlation between transport rate and gradient these high probability long distance motions violate the locality assumption embedded in many common gradient based geomorphic transport laws the example of a degrading scarp illustrates the potential for grain motion dynamics to vary in space and time as topography evolves this characteristic renders models based on independent stationary statistics inapplicable an accompanying analytical framework based on treating grain motion as a survival process is briefly outlined

experimental evidence for hillslope control of landscape scale landscape evolution theory suggests that climate sets the scale of landscape dissection by modulating the competition between diffusive processes that sculpt convex hillslopes and advective processes that carve concave valleys however the link between the relative dominance of hillslope and valley transport processes and landscape scale is difficult to demonstrate in natural landscapes due to the episodic nature of erosion here we report results from laboratory experiments combining diffusive and advective processes in an eroding landscape we demonstrate that rainsplash driven disturbances in our experiments are a robust proxy for hillslope transport such that increasing hillslope transport efficiency decreases drainage density our experimental results demonstrate how the coupling of climate driven hillslope and valley forming processes such as bioturbation and runoff dictates the scale of eroding landscapes

deposits of the 30 march 1956 directed blast at bezymianny volcano kamchatka russia on 30 march 1956 a catastrophic directed blast took place at bezymianny volcano it was caused by the failure of 0 5 km3 portion of the volcanic edifice the blast was generated by decompression of intra crater dome and cryptodome that had formed during the preclimactic stage of the eruption a violent pyroclastic surge formed as a result of the blast and spread in an easterly direction effecting an area of 500 km2 on the lower flank of the volcano the thickness of the deposits although variable decreases with distance from the volcano from 2 5 m to 4 cm the volume of the deposit is calculated to be 0 2 0 4 km3 on average the deposits are 84 juvenile material andesite of which 55 is dense andesite and 29 vesicular andesite on a plot of sorting vs median diameter inman coefficients the deposits occupy the area between the fall and flow fields in the proximal zone less than 19 km from the volcano three layers can be distinguished in the deposits the lower one layer a is distributed all over the proximal area is very poorly sorted enriched in fragments of dense juvenile andesite and contains an admixture of soil and uncharred plant remains the middle layer layer b is distributed in patches tens to hundreds of metres across on the surface of layer a layer b is relatively well sorted as a result of a very low content of fine fractions and it contains rare charred plant remains the uppermost layer layer c forms still smaller patches on the surface of layer b layer c is characterized by intermediate sorting is enriched in vesicular juvenile andesitic fragments and contains a high percentage of the fine fraction and very rare plant remains which are thoroughly charred maximum clast size decreases from layer a to layer c the absence of internal cross bedding is a characteristic of all three layers in the distal zone more than 19 km from the volcano stratigraphy changes abruptly deposit here consists of one layer 26 to 4 cm in thickness is composed of wavy laminated sand with a touch of gravel is well sorted and contains uncharred plant remains the bezymianny blast deposits are not analogous with known types of pyroclastic surges with the exception of the directed blast deposits of the mount st helens eruption of 18 may 1980 the peculiarities of deposits from these two eruptions allow them to be separated into a special type blast surge this type of surge is formed when failure of volcanic edifice relieves the pressure from an inter crater dome and or cryptodome a model is proposed to explain the peculiarities of the formation transportation and emplacement of the bezymianny blast surge deposits

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

rain splash of dry sand revealed by high speed imaging and sticky paper splash targets 1 rain splash transport of sediment on a sloping surface arises from a downslope drift of grains displaced ballistically by raindrop impacts we use high speed imaging of drop impacts on dry sand to describe the drop to grain momentum transfer as this varies with drop size and grain size and to clarify ingredients of downslope grain drift the splash of many grains involves ejection of surface grains accelerated by grain to grain collisions ahead of the radially spreading front of a drop as it deforms into a saucer shape during impact for a given sand size splash distances are similar for different drop sizes but the number of displaced grains increases with drop size in proportion to the momentum of the drop not infiltrated within the first millisecond of impact we present a theoretical formulation for grain ejection which assumes that the proportion of ejected grains within any small azimuthal angular interval dq about the center of impact is proportional to the momentum density of the spreading drop within dq and that the momentum of ejected grains at angle q is on average proportional to the momentum of the spreading drop at q this formulation consistent with observed splash distances suggests that downslope grain transport involves an asymmetry in both quantity and distance more grains move downslope than upslope with increasing surface slope and on average grains move farther downslope this latter effect is primarily due to the radial variation in the surface parallel momentum of the spreading drop surface parallel transport increases approximately linearly with slope

grain scale simulations of loose sedimentary beds the example of grain bed impacts in aeolian saltation sediment transport by wind is one of many processes of interest to the geomorphologist in which grain to grain contacts play an important role in order to illustrate the modelling of collections of frictional inelastic sedimentary grains with the particle dynamics method pdm we use the grain impact process in aeolian saltation as a specific example in pdm all the forces on each particle are evaluated at a sequence of small time steps and the newtonian equations of motion are integrated forward in time interparticle forces at grain contacts are treated as springs with prescribed stiffness normal force and by a coulomb friction law tangential force particle inelasticity is represented by spring damping the granular splash resulting from saltation impacts is assessed for sensitivity to the choice of grain properties and the integration time step we find that for the range of impact speeds and impactor masses relevant to aeolian settings grain splashes are relatively insensitive to grain stiffness grain inelasticity and grain friction and that the pattern of ejection from the bed is largely controlled by bed microtopography a large set of impact realizations involving a variety of impact points on a small set of target beds is used to collect the appropriate statistics for describing the stochastic splash process the splash function representing these statistics is then available for use in calculations over longer time scales such as the evolution of the saltation curtain the details given here will enable the interested reader to adapt pdm modelling to other types of clastic sedimentary systems

paroxysmal dome explosion during the merapi 2010 eruption processes and facies relationships of associated high energy pyroclastic density currents an 11 minute sequence of laterally directed explosions and retrogressive collapses on 5 november 2010 at merapi indonesia destroyed a rapidly growing dome and generated high energy pyroclastic density currents pdcs spreading over 22 km2 with a runout of 8 4 km while contemporaneous co genetic valley confined pdcs reached 15 5 km this event formed stage 4 of the multi stage 2010 eruption the most intense eruptive episode at merapi since 1872 the deposits and the widespread devastating impact of associated high energy pdcs on trees and buildings show striking similarities with those from historical volcanic blasts montagne pelee martinique bezymianny russia mount st helens usa soufriere hills montserrat we provide data from stratigraphic and sedimentologic analyses of 62 sections of the first unequivocal blast like deposits in merapi s recent history we used high resolution satellite imagery to map eruptive units and flow direction from the pattern of extensive tree blowdown the stratigraphy of stage 4 consists of three depositional units u0 u1 u2 that we correlate to the second third and fourth explosions of the seismic record both u1 and u2 show a bi partite layer stratigraphy consisting each of a lower l1 layer and an upper l2 layer the lower l1 layer is typically very coarse grained fines poor poorly sorted and massive and was deposited by the erosive waxing flow head the overlying l2 layer is much finer grained fines rich moderately to well sorted with laminar to wavy stratification l2 was deposited from the waning upper part and wake of the pdc field observations indicate that pdc height reached 330 m with an internal velocity of 100 m s 1 within 3 km from the source the summit s geometry and the terrain morphology formed by a major transversal ridge and a funneling deep canyon strongly focused pdc mass towards a major constriction thereby limiting the loss of kinetic energy this favored elevated pdc velocities and high particle concentration promoted overspilling of pdcs across high ridges into other river valleys and generated significant dynamic pressures to distances of 6 km that caused total destruction of buildings and the forest the merapi 2010 eruption highlights that explosive and gravitational disintegration of a rapidly growing dome can generate devastating high energy high velocity pdcs this constitutes a credible high impact scenario for future multi stage eruptions at merapi and at other volcanoes that pose particular monitoring crisis response and risk reduction challenges

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current

the 2007 eruption of kelut volcano east java indonesia phenomenology crisis management and social response we focus in this paper on the processes and consequences of an unusual volcanic eruption at kelut volcano east java in november 2007 after two months of worrying precursor signs kelut volcano erupted but neither explosions nor the usual hazards observed during the historic eruptions happened e g ash falls volcanic bombs and pyroclastic flows instead of an explosive eruption the 2007 eruption was extrusive given than such an eruption could not be predicted the authorities had to manage a new situation we conducted interviews with nine stakeholders of the crisis management team and undertook a questionnaire based survey in the settlement nearest to the crater in order to understand how the authorities managed the crisis and how people reacted inquiries and questionnaires were carried out shortly after the end of the evacuation process when the volcano was still under surveillance for fear of an explosive phase the results display a real gap in what it takes to manage a crisis or live through a crisis this suggests that the unusual eruption pattern of kelut volcano was not the only factor of the misunderstanding between the authorities and the population these problems stem from more structural causes such as the lack of communication and information when there is a need to adapt to a new scenario in such a situation the inability of the crisis management system to take decisions underscored the intrinsic vulnerability of the population despite a hierarchical and strategic top down crisis management approach

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean