modeling the mineralogy of atmospheric dust sources the variability of atmospheric dust mineralogy influences the impact of desert dust on the earth s radiative budget and biogeochemical cycles until now atmospheric transport models have assumed that dust was a constant homogeneous mixture hence neglecting this variability the lack of mineralogical data in arid areas prevented a better description of the atmospheric dust composition and we propose here a new formulation to estimate the mineral content of arid surfaces on a global scale first we collect a database of arid soil surface mineralogy for eight major minerals quartz feldspar calcite gypsum illite kaolinite smectite and hematite both for the clay and silt fraction on the basis of this we formulate a mean mineralogical table that relates classical soil types to surface mineralogy we use this table and the geographical distribution of soil types given in the food and agriculture organization soil map of the world to obtain the mineralogy of arid surfaces globally in order to validate these results we present a compilation of measured mineralogical composition of dust samples with identified sources the correlation between observed dust mineralogy and those inferred from soil types in corresponding areas is between 0 70 and 0 94 we then calculate the maps of the single scattering albedo and of the ratio of infrared extinction to visible extinction for the erodible fraction of arid areas mineralogical maps presented here will be used in future studies with an emission scheme in a global transport model

stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

magmatic processes revealed by textural and compositional trends in merapi dome lavas syn eruptive degassing of volcanoes may lead to syn eruptive crystallization of groundmass phases we have investigated this process using textural and compositional analysis of dome material from merapi volcano central java indonesia samples included dome lavas from the 1986 88 1992 93 1994 and 1995 effusive periods as well as pyroclastic material deposited by the november 1994 dome collapse with total crystallinities commonly in excess of 70 phenocrysts 1 microlites the liquids present in merapi andesites are highly evolved rhyolitic at the time of eruption feldspar microlites in dome rocks consist of plagioclase cores ab63an29or8 surrounded by alkali feldspar rims ab53an5or42 compositional pairs which are not in equilibrium a change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition a small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites suggesting that the 1994 collapse event incorporated less degassed partially liquid magma in addition to fully solidified dome rock as decompression drives volatile exsolution rates of degassing and resultant microlite crystallization may be governed by magma ascent rate microlite crystallinity is nearly identical among the 1995 dome samples an indication that similar microlite growth conditions ph2 o and temperature were achieved throughout this extrusive period however microlite number density varied by more than a factor of four in these samples and generally increased with distance from the vent low vent ward microlite number densities and greater microlite concentrations down flow probably reflect progressively decreasing rates of undercooling at the time of crystal nucleation during extrusion of the 1995 dome comparison between dome extrusion episodes indicates a correlation between lava effusion rate and microlite number density suggesting that extrusion slowed during 1995 crystal textures and compositions in the 1992 93 and 1994 domes share the range exhibited by the 1995 dome suggesting that transitions in crystallization conditions i e rates of undercooling determined by effusion rate are cyclic q 2000 elsevier science b v all rights reserved

natural hazards in central java province indonesia an overview central java province indonesia suffers from natural hazard processes such as land subsidence coastal inundation flood volcanic eruption earthquake tsunami and landslide the occurrence of each kind of natural hazard is varied according to the intensity of geo processes it is necessary to learn from the historical record of coastal inundation flood volcanic eruption earthquake tsunami and landslide hazards in central java province to address issues of comprehensive hazard mitigation and management action through the understanding about the nature and spatial distribution of natural hazards treatments can be done to reduce the risks this paper presents the natural hazard phenomena in central java province and provides critical information for hazard mitigation and reduction

sequential plug formation disintegration by vulcanian explosions and the generation of granular pyroclastic density currents at tungurahua volcano 2013 2014 ecuador following 84 years of repose tungurahua volcano ecuador initiated its present eruptive episode in october 1999 but its pdc activity only began in july 2006 a period of highly energetic vulcanian eruptions started in 2012 those of 14 july 2013 18 october 2013 and 1 february 2014 being the most important these eruptions were well monitored by a 5 station broadband seismic and acoustic array repeated repose intervals of 3 5 months between vulcanian events vei 2 suggest that gases in the ascending juvenile magma experienced sequential pressurization cycles as magma of preceding eruptive events solidified to form plugs that sealed the conduit every 34 months plug failure occurred abrupt decompression followed and the resulting vulcanian explosions are associated with the highest seismic and acoustic energies ever registered anywhere small to moderate sized pdc flows associated with the explosions and fountain collapses were generated and traveled 7 km down the steep n nw and w flanks of tungurahua s cone at velocities of 11 to 18 m s although a small lateral blast and its pdc were clocked at 33 m s descending the n flank the explosive fragmentation of the plugs a dense microcrystalline andesite and the juvenile magma a vesiculated glassy andesite comprise the principal rock fragments of the pdc deposits each deposit typically consisting of two layers a thin upper layer of large segregated and abraded clasts with few fines and a thicker lower layer that is fines rich with few large clasts many deposits were studied and photographed within a few days of their formation which are presented

diagenetic history of the surma group sandstones miocene in the surma basin bangladesh abstract this study examines the various diagenetic controls of the miocene surma group sandstones encountered in petroleum exploration wells from the surma basin which is situated in the northeastern part of the bengal basin bangladesh the principal diagenetic minerals cements in the surma group sandstones are fe carbonates with fe calcite dominating quartz overgrowths and authigenic clays predominantly chlorite illite smectite and minor kaolin the isotopic composition of the carbonate cement revealed a narrow range of 18o values 10 3 to 12 4 and a wide range of 13c value 1 4 to 23 1 the 13c vpdb and 18o vpdb values of the carbonate cements reveal that carbon was most likely derived from the thermal maturation of organic matter during burial as well as from the dissolution of isolated carbonate clasts and precipitated from mixed marine meteoric pore waters the relationship between the intergranular volume igv versus cement volume indicates that compaction played a more significant role than cementation in destroying the primary porosity however cementation also played a major role in drastically reducing porosity and permeability in sandstones with poikilotopic pore filling blocky cements formed in early to intermediate and deep burial areas in addition to fe carbonate cements various clay minerals including illite smectite and chlorite occur as pore filling and pore lining authigenic phases significant secondary porosity has been generated at depths from 2500 m to 4728 m the best reservoir rocks found at depths of 2500 3300 m are well sorted relatively coarse grained more loosely packed and better rounded sandstones having good porosities 20 30 and high permeabilities 12 6000 md these good quality reservoir rocks are however not uniformly distributed and can be considered to be compartmentalized as a result of interbedding with sandstone layers of low to moderate porosities low permeabilities owing to poor sorting and extensive compaction and cementation

precambrian paleosols in canada although at least 38 precambrian paleosols have been reported in canada few have received the attention afforded most other geological phenomena the most intensively studied of these are widely distributed early proterozoic paleosols associated with the sub huronian and matonabbee new name unconformities criteria that have been most useful in identifying precambrian paleosols in canada include macrostructures ascending protolith disruption saprolith and corestones micromorphology sepic texture and peds mineralogical changes dissolution transformation geochemical signatures ascending depletion of some elements characteristic weathering indices and distinctive colour contrast diagenetic mechanical and geochemical overprinting of the paleosols evident in many canadian examples includes paleosol compaction veins cutting pedogenic features and widespread alkali and alkaline earth element metasomatism metamorphism and deformation also tend to mask pedogenic features as attested by th

origin of the rajmahal traps and the 85 e ridge preliminary reconstructions of the trace of the crozet hotspot the 85 e ridge is a buried aseismic ridge approximately parallel to and west of the ninetyeast ridge in the northeastern indian ocean it was previously shown to be of probable volcanic origin emplaced on very young oceanic crust but no satisfactory model of emplacement of the rocks was offered we propose a model of origin of the rajmahal traps of northeastern india the 85 e ridge and afanasy nikitin seamount as the trace of the hotspot that now lies beneath the crozet islands in the southern indian ocean this reconstruction places the kerguelen hotspot which formed the ninetyeast ridge at the triple junction between greater india australia and antarctica before the breakup of eastern gondwana

late oligocene to early miocene humidity change recorded in terrestrial sequences in the ili basin south eastern kazakhstan central asia enhanced aridification of central asia driven by the combined effects of orogenic surface uplift paratethys retreat changes in atmospheric moisture transport and global cooling is one of the most prominent cenozoic climate change events of the northern hemisphere deciphering regional long term patterns of central asian hydrology is therefore a key element in understanding the role of northern hemisphere mid latitude drying in the global hydrological system this study characterizes long term palaeoenvironmental conditions between the late oligocene and early miocene in south eastern kazakhstan based on stable isotopes elemental geochemistry and laser ablation uranium lead geochronology from alluvial fluvial and pedogenic deposits sedimentary facies and geochemical weathering indices suggest an increased surface and ground water discharge fed by orographically enhanced precipitation in the tien shan hinterland in contrast pedogenic stable isotope data and elevated rates of magnesium fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification this study posits that pronounced surface uplift of the tien shan mountains during the oligocene miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems this article is protected by copyright all rights reserved

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

toward a revised hazard assessment at merapi volcano central java abstract of 1 1 million people living on the flanks of the active merapi volcano 440 000 are at relatively high risk in areas prone to pyroclastic flows surges and lahars for the last two centuries the activity of merapi has alternated regularly between long periods of viscous lava dome extrusion and brief explosive episodes at 8 15 year intervals which generated dome collapse pyroclastic flows and destroyed part of the pre existing domes violent explosive episodes on an average recurrence of 26 54 years have generated pyroclastic flows surges tephra falls and subsequent lahars the 61 reported eruptions since the mid 1500s killed about 7000 people the current hazard zone map of merapi pardyanto et al 1978 portrays three areas termed forbidden zone first danger zone and second danger zone based on successively declining hazards revision of the hazard map is desirable because it lacks details necessary to outline hazard zones with accuracy in particular the valleys likely to be swept by lahars and excludes some areas likely to be devastated by pyroclastic gravity currents such as the 22 november 1994 surge in addition risk maps should be developed to incorporate social technical and economic factors of vulnerability eruptive hazard assessment at merapi is based on reconstructed eruptive history on eruptive behavior and scenarios and on existing models and preliminary numerical modeling firstly the reconstructed eruptive activity in particular for the past 7000 years and from historical accounts of eruptions helps to define the extent and recurrence frequency of the most hazardous phenomena newhall et al 2000 camus et al 2000 pyroclastic flows traveled as far as 9 15 km from the source pyroclastic surges swept the flanks as far as 9 20 km away from the vent thick tephra fall buried temples in the vicinity of yogyakarta 25 km to the south and subsequent lahars spilled down the radial valleys as far as 30 km to the west and south at least one large edifice collapse has occurred in the past 7000 years newhall et al 2000 camus et al 2000 secondly four eruption scenarios are portrayed as hazardous zones on two maps and derived from the past eruptive behavior of merapi and from the most affected areas in the past thirdly simple numerical simulation based on a digital elevation model a stereo pair of spot satellite images and one 2d orthoimage helps to simulate pyroclastic and lahar flowage on the flanks and in radial valley channels and to outline areas likely to be devastated three major threats are identified 1 a collapse of the summit dome in the short to mid term that can release large volume pyroclastic flows and high energy surges towards the south southwest sector of the volcano 2 an explosive eruption much larger than any since 1930 may sweep all the flanks of merapi at least once every century 3 a potential collapse of the summit area involving the fumarolic field of gendol and part of the southern flank which can contribute to moderate scale debris avalanches and debris flows

clay minerals and their paleoenvironmental interpretation in the baoji loess section southern loess plateau china abstract clay minerals from the loess paleosol section at baoji in north central china were studied by x ray diffraction major components calculated by comparing major peak heights were estimated as follows illite 55 75 kaolinite 10 25 mixed layer chlorite vermiculite 10 20 chlorite

palaeoenvironmental controls on the clay mineralogy of carnian sections from the transdanubian range hungary abstract the upper triassic sediments both in nw europe and in the mediterranean region imply a generally arid climate regime in the carnian however a humid phase with a high input of siliciclastics is assumed carnian pluvial event but its causes are still highly controversial the carnian marine succession of the transdanubian range tr hungary also shows a significant change in sedimentation pelagic carbonate deposition fured limestone formation was followed by the formation of marly sediments veszprem marl and sandorhegy formations in order to understand the environmental changes the clay mineralogy of 240 carnian samples determined by x ray diffraction is discussed in the present paper additionally this set of clay mineral data from four boreholes from the bakony hills bakonysz cs bszu 1 balaton highland balatonfured bfu 1 mencshely met 1 and zsambek basin zsambek zs 14 allows us to test the reliability of clay minerals as palaeoclimatic proxies for the carnian late triassic by reconstructing spatial and temporal variations the first increase in clay content of the studied carnian succession can be detected in the limestone marl couplets of the cordevolian fured limestone its clay fraction is dominated by illite mixed layer illite smectite is and chlorite without kaolinite a good indicator of landmasses with a hot climate and constant humidity thus this compositional change probably related to a sea level drop subsequently the clay mineral assemblages of the veszprem marl sections in the bakony hills and the balaton highland are composed of illite poorly ordered r 0 is with 60 70 expandable component chlorite and kaolinite on the other hand the clay fraction of the samples from the zsambek basin is composed of illite is with an average of 40 50 expandable component and a transitional r 0 to r 1 type of ordering and kaolinite chlorite does not occur in the early julian kaolinite enrichments 10 20 in the clay fraction can be regarded as a manifestation of the climate shift from the prevailing aridity to the more seasonal climate with enhanced humid season the overall presence of abundant illite and accompanying chlorite can indicate a high rate of erosion of moderately weathered rocks while the large amount of smectitic clay transformed to is could be partly derived from transport of weathering products from a distant source area and subordinately from diagenetic alteration of intermediate to basic volcanic rocks spatial variation in the expandability and ordering of the is at least partially could be caused by different degree of the diagenetic overprint

potassium release on drying of soil samples from a variety of weathering regimes and c clay mineralogy in china abstract thirty two soil samples from china were analyzed for exchangeable k before and after drying most soil samples were higher in exchangeable k after air drying and ovendrying 60 c than when wet soil clay minerals especially clay size mica affected k released in air dry and oven dry samples according to composition of clay minerals of air dried samples five classes were recognized soil samples with high mica and montmorillonite have the highest exchangeable k samples that contained higher kaolinite than mica had lower exchangeable k samples with higher kaolinite than quartz and mica had still lower exchangeable k samples of sandy soils contained very low exchangeable k when quartz was the main mineral the samples that had kaolinite and gibbsite as the main clay minerals had very low exchangeable k the degree of weathering weathering mean bore an inverse relationship to the amount of k released on drying in air or at 60 c udults and udalfs red earths of southeastern china because of their high k release on being dried are inferred to have received fine mica from the western desert dust rainout reported to liu et al 1981

high frequency controls on alluvial successions an integrated sedimentological and palaeopedological approach to the plio pleistocene of argentina abstract plio pleistocene palaeosol bearing alluvial strata are continuously exposed along the marine cliffs of southeastern buenos aires province argentina the study interval was deposited by a mixed predominantly suspended load fluvial system outcrops are dominated by floodplain siltstones and mudstones that exhibit a cyclic alternation between calcic and vertic palaeosols this cyclicity is represented by meter scale alluvial cycles that show as a general trend a gradual increase in the proportion of channel fill deposits up section cyclic variations in palaeosols facies and architectural elements can be related to allogenic drivers such as climate and eustasy for the lower punta san andres alloformation the stratigraphic arrangement of the recognised palaeosols and the clay mineral distribution indicate that the palaeoclimate was subhumid average mean annual precipitation map 840 mm seasonal and temperate average mean annual temperature mat 7 85 c for at least 1 ma from ca 2 9 ma to ca 1 8 ma late pliocene early pleistocene with several intervals in which conditions became drier and probably colder even though climate was a major control on palaeosol development it is suggested here that it was not the main control on high frequency cycles variations in the orbital parameters more specifically in insolation were interpreted as having controlled the sedimentation and architectural evolution of the lower punta san andres alloformation depositional systems

unroofing history of the eastern himalaya and the indo burman ranges heavy mineral study of cenozoic sediments from the bengal basin bangladesh abstract upper eocene to neogene fill of the bengal basin provides an earlier unroofing history of the eastern himalaya and indo burman ranges than that provided by drilling of the bengal fan and analysis of heavy minerals in these sequences provides useful provenance constraints quartzose sandstones of the eocene kopili and oligocene barail formations contain only 0 2 heavy minerals comprising abundant opaque minerals and stable minerals such as tourmaline garnet rutile and zircon this assemblage suggests sediment sources dominated by low to intermediate grade metamorphic silicic igneous and metasedimentary rocks the low heavy mineral content and abundance of stable minerals suggest intense chemical weathering these sediments may have been derived in part from incipient uplifts of the proto himalaya and or the indo burman ranges but a more likely source is the indian craton immediately to the west miocene sandstones of the surma group contain more abundant and more diverse heavy mineral assemblages than oligocene sandstones these include abundant opaque minerals and garnet mostly almandine and moderate to minor amounts of tourmaline kyanite zircon calcic amphibole rutile chlorite zoisite staurolite epidote sillimanite and clinopyroxene indicating a broad range of mostly metamorphic source rocks upper strata of the surma group also contain abundant blue green amphibole orthopyroxene and sparse chromite suggesting exhumation of arc and ophiolitic rocks sands and sandstones from the upper miocene to pliocene tipam group and the pliocene to pleistocene dupi tila formation contain assemblages similar to those of the underlying miocene sandstones along with more abundant orthopyroxene and sillimanite in dupi tila sands temporal variations in heavy mineral assemblages in the bengal basin suggest that orogenic detritus first appears in the eastern himalayan foredeep much later early miocene than in the western part of the foredeep eocene the appearance of high pressure phases in upper miocene strata reflects continued unroofing of deeper crustal metamorphic and silicic to ultramafic plutonic rocks

the 1984 nuee ardente deposits of merapi volcano central java indonesia stratigraphy textural characteristics and transport mechanisms for many centuries merapi volcano has generated hot avalanches of blocks lapilli and ashes derived from the destruction of partially solidified viscous lava domes merapi type nuees ardentes on 15 june 1984 at least four nuees ardentes came down the southwest slope of the merapi the first and the last being responsible for more than 99 of the deposits which are now exposed the first nuee ardente a merapi type nuee ardente was produced by the destruction of the dome travelled 7 km from the crater leaving a measured deposit 2 7 m thick 4 km from the crater near its upper depositional limit regularly increasing to a maximum measured thickness of 12 m at the front of the deposit the lower contact is sharp non erosive with pines still rooted in the underlying paleosol the deposit consists of 50 ash 33 lapilli and 17 blocks with two subpopulations one rosin and one normal and is finespoor with less than 4 of fine ash d finer than 4 the deposit displays reverse population grading of both vesiculated and massive clasts and of the maximum grain size the maximum size significantly increases regularly down current over most of the exposed length of unit 1 and bed thickness increases for the entire length of the deposit the deposit of the second nuee ardente is only 6 21 cm thick and of very limited lateral extent it is a normally graded coarse to fine ash with a finespoor base the third unit consists of fines poor normally graded coarse ash exposed in low amplitude 20 40 cm 12 m wavelength dunes the deposit of the fourth nuee ardente rests in sharp erosive contact on the underlying unit increasing in thickness down flow it consists of transitional coarse and fine grained strata 6 130 c cm thick dipping 5 10 down flow the deposit made up of two subpopulations one rosin and one normal is normally graded over the entire bed but coarsegrained strata are reversely graded the relative content of vesiculated clasts increases up bed in both strata types from 12 at the base to 40 at the top the characteristics of unit 1 suggest that it accumulated from a concentrated suspension of cohesionless solids exhibiting non newtonian behavior where dispersive pressure played an important role in the suspension of the clasts units 2 and 3 were probably deposited from dilute turbulent suspensions whereas the upper unit 4 is a classic example of deposition from a high density turbulent suspension leading to the formation of multiple traction carpets driven by the overlying lower density surge the horizontal distance travelled by a hot rock avalanche may be influenced by its transport mechanism debris flows are mobile on very low slopes as low as 1 whereas grain flows even density modified grain flows require relatively high slopes more than 6 at merapi to maintain their mobility if the present merapi dome were to collapse and produce a debris flow its present volume coupled with the minimal 1 5 km vertical drop could travel a distance ranging between 15 and 30 km however if transport were by grain flow mechanisms the mass could come to rest as it reaches a 5 10 slope

silt 2 62 μm 9 4φ the particles in finer grained detrital sediments are usually composed of quartz they fall into two size grades sand 2 mm 62 m and silt 62 m 2 m these size gradings conceal important geological processes since there are geological controls on both the quartz sand and silt populations sand nature is largely controlled by geochemical reactions for example in cooling granite from which it is eventually released by weathering action the quartz is among the last part of the rock system to solidify and the eutectic like reaction which occurs ensures that the quartz exists as small crystalline units each suffering considerable cooling and recrystallisation stresses silt is broken quartz and has traditionally been considered to lack a specific geological control the situation is confused by the large range of materials that fall into the size category but there do seem to be distinguishable modes and possibly comminution limits within the 60 m span the controls operating in this size range are probably the critical concentration of moss defects in the quartz particles moss postulated the formation of specific crystal defects in the quartz formed in granites these affect sand formation and it is possible that they also control the mode size of silt particles within the silt range there may be several usefully definable populations as moss proposed for sand the quaternary appears to be a silt rich period due to tectonic and glacial activity but silt production is apparent throughout the sedimentary record very long term silt producing processes are required to produce silt in nature on a large scale very energetic processes are required many processes that are believed to generate silt particles have been listed however large scale production is essentially due to glacial grinding or to intense weathering processes in high cold tectonically active mountain regions the region of high asia of crustal overlap is a major generator of silt particles these form the productive alluvial soils of north india most of the nation of bangladesh the loess deposits along the syr darya and amu darya rivers in central asia and the great loess deposits of north china some claims have been made for silt production in hot deserts large amounts of very fine aerosolic dust are produced but in terms of loess sized particles this is a small scale process and leads to modest disputed deposits the loess deposits around the sahara usually have smaller mode sizes e g nigeria or larger mode sizes e g libya tunisia than the true chinese mode at 25 m this paper aims to introduce the distinguishing properties of sand and silt discuss in detail the possible processes of silt formation in relation to the evidence of what is produced describe the major silt populations and conclude on the most likely formation process es in particular three silt ranges are discussed in relation to the r size diagram c 2 5 m d1 20 30 m and d2 60 m these can represent canadian quickclay qq chinese loess and the ideal loughborough loess ll and north african loess nal it is intended that this paper will put into context the diverse work in the area and in so doing shed light on what is an often overlooked subject

clay dispersion an important factor in channel runoff generation in a semi arid loess covered area with very low rain intensities abstract overland flow is usually regarded as an important contributor to storm channel flow this observation is certainly applicable to dryland areas where base flow is often irrelevant particularly in small watersheds this study examines channel runoff generation in the extensive loess covered areas that characterize the mildly arid area of western israel where the average annual rainfall is 280 mm hydrological data point to a peculiar hydrological behavior of the ephemeral streams that experience a high frequency of sporadic channel flow events even in extreme rain events peak discharges are exceptionally low indicative of a limited contributing area hydrographs are characterized by very steep rising and falling limbs usually representative of saturated areas located in the vicinity of the runoff recording station based on this observation we advanced the hypothesis that storm runoff originated in the limited area of the active channel with negligible runoff from the adjoining hillslopes we argue that a quasi permanent surface seal at the top of the alluvial deposit drastically limits the hydraulic conductivity of the alluvial fill allowing runoff generation at very low rain intensities the occurrence of the surface seal is ascribed to the combination of two main factors a high clay content 40 where the dominant clays are smectite and illite characterized by a laminar structure and a high water absorption capacity the swelling of the clay particles considerably reduce the porosity of the alluvial material allowing runoff generation at very low rain intensities while limiting the depth of water penetration in the channel itself data presented fit the concept of partial area contribution identified in humid areas however the application of this concept to dryland areas is based on completely different reasons

nuees ardentes of 22 november 1994 at merapi volcano java indonesia nuees ardentes associated with dome collapse on 22 november 1994 at merapi volcano traveled to the south southwest as far as 6 5 km and collectively accumulated roughly 2 5 3 million cubic meters of deposits the damaged area comprises 9 5 km2 and is covered by two nuee ardente facies a conventional merapi type valley fill block and ash flow facies and a pyroclastic surge facies the proximal deposits reflect the accumulation of dozens of nuees ardentes with many subsidiary flow units the distal deposits are more simply organized as only a few individual events reached to distances 3 5 km the stratigraphic relationships north of turgo hill indicate that the surge deposits are a facies of particularly mobile nuees ardentes that also deposited channeled block and ash flow facies they further suggest that the surge facies beyond the channel margins correlate laterally with a finer grained sublayer locally developed at the base of the block and ash flow facies eyewitness reports suggest that the emplacement of the block and ash flow facies in the distal part of the boyong river may have followed by a short time interval the destruction and deposition of the surge facies at turgo village the stratigraphy is in accord with the eyewitness reports the surge facies was emplaced by a dilute surge current detached from the same dome collapse nuee ardente that as a separate flow unit subsequently emplaced the distal block and ash deposit in the boyong valley the detachment occurred at higher elevations likely at or above the slope break at about 2000 m elevation this flow separation enabled the surge current to shortcut over the landscape and to emplace its deposit even as the block and ash flow continued its tortuous southward movement in the boyong channel dome collapse nuee ardente activity formed the bulk of the eruption which was accompanied by virtually no significant vertical summit explosive activity

deposit architecture and dynamics of the 2006 block and ash flows of merapi volcano java indonesia the internal architecture of the 2006 block and ash flow deposits of merapi volcano java indonesia was investigated using data collected from 27 stratigraphic sections measured immediately after flow emplacement and after one and two rainy seasons of erosion identification of different depositional units and their longitudinal and lateral facies variations provide detailed information about i the distribution volumes and sedimentological characteristics of the different units ii flow types and mobility as inferred from associated deposits and iii changes in the dynamics of the different flows and their material during emplacement two main types of block and ash flows short runout to medium runout block and ash flows and long runout block and ash flows are defined based on flow generation mechanism flow volume travel distance deposit morphology distribution lithology and grain size distribution conceptual models for the transport and depositional mechanisms of these two types of block and ash flows are presented variations in the runout distances observed for short runout to medium runout block and ash flows are linked directly to different initial flow volumes degree of fragmentation and material properties of the moving mass during transport with the largest and finer grained flows having the greatest mobility deposition occurs only over a narrow range of basal inclinations close to the angle of repose for pyroclastic material indicating that such flows behave in a similar way to granular free surface flows on unconfined planes the flow mechanisms of long runout block and ash flows at merapi are interpreted to be similar in many respects to unsteady cohesionless grain flows with an inertial flow regime where collisional forces largely overcome frictional forces flow unsteadiness causes the main body to be segmented into different pulses that run closer to each other as the flow moves downslope deposition occurs stepwise with rapid aggradation of stacked sub units from different parts of the major flow pulses in such a model the arrival of each flow pulse front at selected sites in the main river valley controls the generation and development of highly mobile unconfined pyroclastic flows outside valley regions and their associated overbank deposits

sedimentation and tectonics of the sylhet trough bangladesh the sylhet trough a sub basin of the bengal basin in northeastern bangladesh contains a thick fill 12 to 16 km of late mesozoic and cenozoic strata that record its tectonic evolution stratigraphic sedimentologic and petrographic data collected from outcrops cores well logs and seismic lines are here used to reconstruct the history of this trough the sylhet trough occupied a slope basinal setting on a passive continental margin from late mesozoic through eocene time subsidence may have increased slightly in oligocene time when the trough was located in the distal part of a foreland basin paired to the indo burman ranges oligocene fluvial deltaic strata barail formation were derived from incipient uplifts in the eastern himalayas subsidence increased markedly in the miocene epoch in response to western encroachment of the indo burman ranges miocene to earliest pliocene sediments of the surma group were deposited in a large mud rich delta system that may have drained a significant proportion of the eastern himalayas subsidence rates in the sylhet trough increased dramatically 3 8 times from miocene to pliocene pleistocene time when the fluvial tipam sandstone and dupi tila formation were deposited this dramatic subsidence change is attributed to south directed overthrusting of the shillong plateau on the dauki fault for the following reasons 1 pliocene and pleistocene strata thin markedly away from the shillong plateau consistent with a crustal load emplaced on the northern basin margin 2 the shillong plateau is draped by mesozoic to miocene rocks but pliocene and younger strata are not represented suggesting that the massif was an uplifted block at this time 3 south directed overthrusting of the shillong plateau is consistent with gravity data and with recent seismotectonic observations sandstone in the tioam has a marked increase in sedimentary lithic fragments compared to older rocks reflecting uplift and erosion of the sedimentary cover of the shillong plateau if the dauki fault has a dip similar to that of other himalayan overthrusts then a few tens of kilometers of horizontal tectonic transport would be required to carry the shillong plateau to its present elevation uplift of the shillong plateau probably generated a major 300 km westward shift in the course of the brahmaputra river

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

ground deformation at merapi volcano java indonesia distance changes june 1988 october 1995 abstract edifice deformations are reported here for the period 1988 1995 at merapi volcano one of the most active and dangerous volcanoes in indonesia the study period includes a major resumption in lava effusion in january 1992 and a major dome collapse in november 1994 the data comprise electronic distance measurements edm on a summit trilateration network slope distance changes measured to the upper flanks and other data collected from 1988 to 1995 a major consequence of this study is the documentation of a significant 4 year period of deformation precursory to the 1992 eruption cross crater strain rates accelerated from less than 3 10 6 day between 1988 and 1990 to more than 11 10 6 day just prior to the january 1992 activity representing a general asymmetric extension of the summit during high level conduit pressurization after the vent opened and effusion of lava resumed strain occurred at a much reduced rate of less than 2 10 6 day edm measurements between lower flank benchmarks and the upper edifice indicate displacements as great as 1 m per year over the four years before the 1992 eruption the gendol breach a pronounced depression formed by the juxtaposition of old lava coulees on the southeast flank functioned as a major displacement discontinuity since 1993 movements have generally not exceeded the 95 confidence limits of the summit network exceptions to this include 12 cm outward movement for the northwest crater rim in 1992 1993 probably from loading by newly erupted dome lava and movements as much as 7 cm on the south flank between november 1994 and september 1995 no short term precursors were noted before the november 1994 lava dome collapse but long term adjustments of crater geometry accompanied lava dome growth in 1994 short term 2 cm deflation of the edifice occurred following the november 1994 dome collapse

the eruptive history and volcanic hazards of savo solomon islands savo island is the 6 km diameter emergent summit of an andesitic dacitic stratovolcano rising from the iron bottom sound 35 km nw of honiara solomon islands savo has erupted at least three times within recorded history and the 3 000 inhabitants maintain extensive oral traditions of past events through description and interpretation of the volcaniclastic sequences on the island in conjunction with historical accounts and oral traditions we reconstruct the eruptive processes on savo block and ash flow baf deposits are volumetrically dominant on the island within three main depositional environments near vent sequences thick medial channel sequences and distal fan sequences the deposits comprise universally non vesicular and highly porphyritic 40 70 phenocrysts high silica andesite and dacite clasts these appear to have been derived from collapsing lava domes during an 1560 1570 a d eruption however eyewitness descriptions and crater morphology suggest that similar deposits formed from dome explosions or collapses of eruption columns during later eruptions 1830 1840 a d the high sodium magmas ca 5 7 wt na2o apparently crystallised and strongly degassed prior to eruption shallow explosions were possibly caused by entrapment of magmatic gases beneath a dome or conduit plug of highly crystalline near solid magma repeated sealing of the vent may have been due to inward collapse of the highly altered rocks of the surrounding hydrothermal system these rocks probably were saturated due to contemporaneous high intensity rainfall events bafs were hot enough to char vegetation and attain aligned clast trm thermal remnant magnetism up to 3 km from the vent many being accompanied by ash cloud surges changes with distance in the baf deposits appear mostly dependent on flow confinement and are limited to an overall decrease in thickness and maximum clast size and an increased definition of weak planar fabrics in distal fan sequences there is strong evidence for syn and post eruptive redeposition of primary deposits since the savo population is concentrated on coastal volcaniclastic fans we consider the greatest volcanic risk to life is from bafs associated ash cloud surges and lahars hence the main channels and fans are designated as the highest of three relative hazard zones on a simple map prepared to aid local education and planning initiatives on savo

emplacement of pyroclastic flows during the 1998 1999 eruption of volcan de colima mexico after three years of quiescence volcan de colima reawakened with increasing seismic and rock fall activity that reached its peak on november 20 1998 when a new lava dome forced its way to the volcano s summit the new lava rapidly reached the s sw edge of the summit area beginning the generation of merapi type pyroclastic flows that traveled down la lumbre and the el cordoban western and eastern ravines reaching distances of 3 4 5 and 3 km respectively on december 1 1998 the lava flow split into three fronts that in early 1999 had reached 2 8 3 1 and 2 5 km in length advancing down the el cordoban ravines the lava flow fronts disaggregated into blocks forming pyroclastic flows one of the best examples occurred on december 10 1998 as the lava flow ceased moving in early 1999 activity became more explosive strong blasts were recorded on february 10 may 10 and july 17 1999 the last event developed a 10 km high eruptive column from which a pyroclastic flow developed from the base traveling 3 3 km sw from the summit into the san antonio montegrande ravines regardless of the mechanism of pyroclastic flow generation each flow immediately segregated into a basal avalanche that moved as a granular flow and an upper ash cloud in which particles were sustained in turbulent suspension when the basal avalanche lost velocity and eventually stopped the upper ash cloud continued to move independently as a dilute pyroclastic flow that produced a massive pyroclastic flow deposit and an upper dune bedded surge deposit the dilute pyroclastic flow scorched and toppled maguey plants and trees and sandblasted vegetation in the direction of the flow at the end of the dilute pyroclastic flow path the suspended particles lifted off in a cloud from which a terminal ash fall was deposited the basal avalanche emplaced block and ash flow deposits up to 8 m thick that filled the main ravines and consisted of several flow units each flow unit was massive monolithologic matrix supported and had a clast supported steep front ca 1 5 to 2 m thick composed of boulders up to 1 7 m in diameter the juvenile lithic clasts had an average density of 1800 kg m3 the dilute pyroclastic flow emplaced overbank deposits found on valley margins or beyond the tip of block and ash flow deposits they consist from bottom to top of a massive medium to coarse sand size flow layer 2 4 cm thick a dune bedded surge layer 2 10 cm thick and a massive silt size layer 0 5 cm thick the total estimated volume of the pyroclastic flow deposits produced during the 1998 1999 eruption is 24 105 m3

extreme runup from the 17 july 2006 java tsunami 1 the 17 july 2006 magnitude mw 7 8 earthquake off the south coast of western java indonesia generated a tsunami that effected over 300 km of coastline and killed more than 600 people with locally focused runup heights exceeding 20 m this slow earthquake was hardly felt on java and wind waves breaking masked any preceding withdrawal of the water from the shoreline making this tsunami difficult to detect before impact an international tsunami survey team was deployed within one week and the investigation covered more than 600 km of coastline measured tsunami heights and run up distributions were uniform at 5 to 7 m along 200 km of coast however there was a pronounced peak on the south coast of nusa kambangan where the tsunami impact carved a sharp trimline in a forest at elevations up to 21 m and 1 km inland local flow depth exceeded 8 m along the elevated coastal plain between the beach and the hill slope we infer that the focused tsunami and runup heights on the island suggest a possible local submarine slump or mass movement

eruption and deposition of the fisher tuff alaska evidence for the evolution of pyroclastic flows abstract recognition that the fisher tuff unimak island alaska was deposited on the leeside of an 500 700 m high mountain range tugamak range more than 10 km away from its source played a major role in defining pyroclastic flows as momentum driven currents we reexamined the fisher tuff to evaluate whether deposition from expanded turbulent clouds can better explain its depositional features we studied the tuff at 89 sites and sieved bulk samples from 27 of those sites we find that the tuff consists of a complex sequence of deposits that record the evolution of the eruption from a buoyant plume 22 km that deposited 0 2 km3 of dacite magma as a pyroclastic fall layer to erupting 10 100 km3 of andesitic magma as scoria rich pyroclastic falls and flows that were mainly deposited to the north and northwest of the caldera including those in valleys within the tugamak range the distribution of the flow deposits and their welding internal stratification and the occurrence of lithic breccia all su

sedimentology and geomorphology of the deposits from the august 2006 pyroclastic density currents at tungurahua volcano ecuador the deposits of the pyroclastic density currents from the august 2006 eruption of tungurahua show three facies associations depending on the topographic setting the massive proximal cross stratified and distal cross stratified facies 1 the massive facies is confined to valleys on the slopes of the volcano it contains clasts of 1 m diameter to fine ash material is massive and interpreted as deposited from dense pyroclastic flows its surface can exhibit lobes and levees covered with disk shaped and vesicular large clasts these fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved and thus imply a sharp density boundary near the surface of these flows 2 the proximal cross stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse grained layers and cross stratified ash and lapilli bedsets it is interpreted as deposited from a dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and b dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks 3 the distal cross stratified facies outcrops as spatially limited isolated and wedge shaped bodies of cross stratified ash deposits located downstream of cliffs on valleys overbanks it contains numerous aggrading dune bedforms whose crest orientations reveal parental flow directions a downstream decrease in the size of the dune bedforms together with a downstream fining trend in the grain size distribution are observed on a 100 m scale this facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers we suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs and that these diluted currents might rapidly deposit through pneumatic jumps three modes are present in the grain size distribution of all samples independently of the facies which further supports the interpretation that all three facies derive from the same initial flows this study emphasizes the influence of topography on small volume pyroclastic density currents and the importance of flow transformation and flow stripping processes

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

characteristics of pyroclastic deposits at the margin of fond canonville martinique and implications for the transport of the 1902 nuees ardentes of mt pelee abstract the deposits which were studied at fond canonville represent a well defined record of the 1902 eruptions of the montagne pelee the sections are located at the margin of the valley where six eruption units with thicknesses ranging from 8 cm up to 2 m were identified overlying the pre 1902 paleosol the pyroclasts consist of lapilli coarse and fine ash composed of juvenile andesitic fragments of varying vesicularity dust free crystals dust free transparent vesicular glass and accretionary lapilli paleocurrent measurements on cross bedding support the stratigraphic evidence that the flows came down the valley of fond canonville rather than up as was previously proposed most eruption units are made of two or three beds always in sharp contact the basal bed relatively thin contains the coarsest grain size of the unit is massive or normally graded and fine depleted a thin division of parallel laminae may be present at the top the middle bed the thickest in all eruption units has a mean grain size which is intermediate between the lower and upper beds it may be simple or multiple normal grading is generally present on which may be superimposed in the upper portion of the bed 2 4 cm thick strata parallel to the upper bed surface or dipping from it at angles of less than 10 the upper bed the most regular in all units with thicknesses ranging from 2 to 8 cm is made of accretionary lapilli set in a matrix of fine ash a division of parallel and or oblique laminae is generally present at its top the characteristics of the deposits suggest that all three beds accumulated from a stratified turbulent flow normal grading of both coarsest and mean sizes sequences of internal structures including laminae evince that the flows were of relatively low concentration and that traction was an active process during the accumulation of the deposits for these structures to form the flows had to be turbulent for all three beds of the eruption units the thick strata superimposed on the graded middle bed are interpreted as having formed by the migration and aggradation of long wavelength antidunes the relationship between flow velocity and wavelength suggests that subaerial pyroclastic flows can only produce long wavelength antidunes with resulting internal stratification essentially parallel to bedding short wavelength antidunes in subaerial pyroclastic deposits require very high flow density at least close to the bed surface or low velocity which is unlikely considering the grain size present in the deposits

depositional facies of the subsurface neogene surma group in the sylhet trough of the bengal basin bangladesh record of tidal sedimentation the bengal basin in the north eastern part of the indian subcontinent contains a thick 22 km early cretaceous holocene sedimentary succession the neogene succession in the sylhet trough of the basin reaches a thickness of more than 6 km of which the surma group contains important sandstone reservoirs lithologically the group consists of a succession of alternating shales siltstones sandy shales and sandstones with minor conglomerates this research work is a sedimentological analysis of the subsurface neogene succession encountered in the petroleum exploration wells in the sylhet trough of the bengal basin detailed lithologic logs of the cores based on considering texture and sedimentary structure permit a subdivision into eight lithofacies e g a shale dominated facies interbedded fine sandstones and mudstones ripple laminated sandstones parallel laminated sandstones massive sandstones cross bedded sandstones cross bedded sandstones with pebble granule lag and conglomerates characteristic sedimentary structures of the surma group such as flaser wavy and lenticular bedding bipolarity of ripple cross stratification evenly laminated sand silt streaked shales reactivation surfaces within cross bedded sandstone sets mud drapes on foreset laminae and herringbone cross stratification as well as small scale vertical sequences several fining upward cycles are diagnostic for tidal influence on the basis of the lithofacies associations and prograding character of the deposits revealed from the electrofacies associations the surma group sediments have been interpreted as representing deposits of tide dominated deltaic depositional setting

a hydrogeological model for the early diagenesis of late triassic alluvial sediments the late triassic mercia mudstone group of southwest britain a problematic complex arid playa floodplain aeolian deposit contains a variety of mg clays and carbonates recent interpretations have invoked marine waters as a source of mg in clays however both the mg rich clays and other early diagenetic features seen in the late triassic in europe are directly analogous to those found in the inland drainage basins of australia a simple hydrogeological model is offered based on these basins where shallow groundwater evolution takes place within the basin producing a range of early diagenetic products including groundwater dolocretes and mg clays such a model as developed in australia is probably widely applicable to ancient arid alluvial systems the mercia mudstone group is a problematic sequence of predominantly red siltstones and mudstones with minor sand dolomite and limestone intercalations ruffell 1991 it has been extensively studied in outcrops in southwest and southern britain particularly in the bristol channel area the siltstones and mudstones of late triassic age are the distal equivalents to alluvial fan deposits and are associated at least locally with lake margin and spring travertine deposits leslie et al 1992 some workers have favoured a marine influenced setting for the deposition of the mudrocks or playa lakes see review in taylor 1983 most recently they have been interpreted as the deposits of complex floodplain playa systems with a signficant aeolian input talbot et al 1994 extensive evaporites occur locally in the unit including thick halite deposits and have been interpreted as evidence of marine

bomb rich basaltic pyroclastic flow deposit from nakadake aso volcano southwestern japan abstract a bomb rich basaltic pyroclastic flow deposit the izumikawa pyroclastic flow deposit occurs at the northeastern foot of nakadake volcano which is the only active central cone of aso caldera southwestern japan the pyroclastic flow deposit covers a fan shaped area of about 1 9 km2 and the bulk volume is estimated at 9 4 106 m3 the deposit is poorly sorted and consists of subangular faceted clasts and spherical cauliflower bombs set in a sandy non cohesive matrix the deposit forms two different facies a black reversely graded lower unit and a reddish gray reversely graded upper unit the cauliflower bombs which have slightly vesiculated crusts 1 0 1 5 cm thick and denser interiors are more abundant in the lower unit than in the upper unit the presence of cauliflower bombs suggests that the izumikawa pyroclastic flow was generated by an explosion at the source lava lake or conduit which was filled with mixture of solidified and molten lavas we propose the term bomb and ash flow deposit to describe this type of deposit the age of the izumikawa pyroclastic flow deposit was estimated at ca 19 cal ka based on a 14c age obtained from charred wood fragments in the deposit although all recent activity of nakadake has been ash eruptions strombolian eruptions and phreatomagmatic explosions the izumikawa pyroclastic flow deposit underscores the hazard of bomb rich pyroclastic flows that rush down the flanks of the volcano

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

insights into the october november 2010 gunung merapi eruption central java indonesia from the stratigraphy volume and characteristics of its pyroclastic deposits abstract the 2010 eruption of merapi was the second most deadly in the historic record of this volcano claiming over 380 lives by relating the observations of this eruption with detailed examination of deposit distribution stratigraphy and sedimentology a reconstruction of the properties of the pyroclastic density currents pdcs is presented including the valley controlled block and ash flows bafs and widespread energetic pyroclastic surges the distribution volume and mobility characteristics of all types of pdc during the eruption sequence show evidence for levels of intensity unseen since the large scale 1872 and 1930 eruption phases especially during the climactic events of october 26 and november 5 many tephra falls interbedded with pdc units show that most dome collapse events occurred along with and between explosive vulcanian eruptions the 2010 eruption produced very long runout bafs reaching 16 1 km in the kali gendol on november 5 this runout could be explained by its large volume 20 million m 3 around 10 times that of previous merapi bafs during the last 130 years major avulsion of these dense bafs to form overbank deposits became more common through the eruptive sequence as the valley was progressively filled with successive pdc deposits spreading avulsed bafs were a particular hazard downstream of 10 km where the landscape is less dissected less clear however is why pyroclastic surges extended up to 10 km from the vent on november 5 and 6 4 km on october 26 these expanded much farther from baf margins 2 km than ever seen before at merapi in one location they were decoupled from valley centered bafs with high momentum traveling initially laterally across steep valley systems before draining downslope at this site on the western side of the upper gendol at around 3 km from source surge decoupling was apparently exacerbated by upstream collision and deflection of high flux hot and gas rich bafs against the cliffs of gunung kendil the 1 4 km long cliff face was impacted directly for the first time in 2010 events and may have been responsible for the formation of larger than normal turbulent ash rich clouds above bafs these results imply that future eruption events under the present summit and upper flow path configuration are also highly likely to generate wide dispersal pyroclastic surges and extreme hazard especially now that dense forest has been destroyed on the upper southern slopes of the volcano

lahars at merapi volcano central java an overview abstract merapi volcano in central java is one of the most active volcanoes in the world at least 23 of the 61 reported eruptions since the mid 1500s have produced source deposits for lahars the combined lahar deposits cover about 286 km 2 on the flanks and the surrounding piedmonts of the volcano at merapi lahars are commonly rain triggered by rainfalls having an average intensity of about 40 mm in 2 h most occur during the rainy season from november to april and have average velocities of 5 7 m s at 1000 m in elevation a wide range of facies may be generated from a single flow which may transform downvalley from debris flow to hyperconcentrated streamflow because of the high frequency and magnitude of the lahar events lahar related hazards are high below about 450 600 m elevation in each of the 13 rivers which drain the volcano hazard zone maps for lahar were produced by pardyanto et al volcanic hazard map merapi volcano central java 1 100 000 geol surv of indonesia bandung ii 4 1978 and the japanese indonesian cooperation agency master plan for land conservation and volcanic debris control in the area of mt merapi jakarta 1980 but these maps are of a very small scale to meet modern zoning requirements more recently a few large scale maps 1 10 000 and 1 2000 scale and risk assessments have been completed for a few critical river systems

dryland continental mudstones deciphering environmental changes in problematic mudstones from the upper triassic carnian to norian mercia mudstone group south west britain

clay minerals of late pleistocene sites jonzac and les cottes sw france applications of x ray diffraction analyses to local paleoclimatic and paleoenvironmental reconstructions abstract the crystal chemical properties of clay minerals are closely dependent on the physicochemical conditions prevailing at the time when they formed in soils and weathered zones the degree of alteration of primary minerals and the composition of the secondary products are clearly linked to climate and plant cover in particular changes are rapid under temperate conditions which favor the development of thick soils but slow in cold contexts favoring thin and fragile soils in this paper the mineral composition of two pleistocene clay rich deposits is investigated in order to contribute to reconstructing paleoenvironmental changes jonzac charentes sw france and les cottes vienne sw france are two rock shelters with long archaeological sequences which include faunal remains and were recently radiometrically dated the decomposition of xrd patterns at each site allows identification of the principal mineral phases and semi quantitative estimation of their relative proportions the variation of these proportions is analyzed through indexes based on the relative intensities of the decomposed bands the clay fraction of both sites mostly results from the transformation of the minerals forming the sediments in the surrounding area of the rock shelter terrace including contributions from the hillside mineralogical clay data are compared with the faunal spectrum identified at both sites in order to discuss paleoenvironmental implications at jonzac during the quina mousterian period dated to mis4 the environment was cold and dry the dominant mineralogical phases are inherited from the rocks weak pedogenesis this is consistent with the faunal analysis data typical of the mis4 during the mousterian of acheulean tradition period dated to mis3 the mineralogical composition of the clay deposits changed significantly suggesting a less wet environment the aurignacian deposits dated to the end of mis3 early mis2 are rich in mixed layer minerals mlms which are produced by the hydrolysis processes in soils the climatic conditions probably became milder however because no faunal remains were found this evolution is uncertain the les cottes deposits dated between mis3 and early mis2 are mineralogically typical of a cold environment where soil reactions are not very active however some weak variations of the indexes suggest temporary temperate conditions during the les cottes interstadial and in the aurignacian the parallelism between mineral signature and paleontological evidence in recording relatively rapid variations between contrasted climates suggests that clay mineral assemblages from rock shelter deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at a local scale

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

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

sequences climatiques de sols derives de roches volcaniques aux iles canaries abstract soil sequences derived from tertiary and quaternary volcanic rocks in the canary islands have been investigated according to their exposure being to the north or to the south and to altitude some of the soil characteristics are described emphasising the evolution in the sequences and the conditions of genesis the northern sequence is divided into two parallel catenas the differences in which are due to the age of parent materials from top to bottom the old sequence includes ferrallitic soils fersiallitic soils and finally vertisols the recent sequence includes andosols and brown soils thus the distribution is related with climatic altitudinal zonality perhumid at the top then contrasted with alternating humid and dry seasons and finally subarid near the coast this zonality is also reflected by the plant geography the relationships between soils and present day climatic zones are evident for recent formations andosols and perhumid climate brown soils and contrasted climate these relationships seem equally plausible for the more ancient formations the authors suggest a direct lineage between unsaturated andosols and ferrallitic soils on the one hand and between brown soils and fersiallitic soils on the other the southern sequence comprises successively from the top downwards andic brown soils typic brown soils fersiallitic soils vertisols cinnamonic soils and sodic soils because of a much lesser deposition of recent volcanic material only one sequence can be noted the soil distribution is also related to a climatic and vegetational altitudinal zonality moreover the sequence has a greater extension towards the arid pole because the south slope is less rainy than the north the relationships between soil genesis and existing climatic conditions still seem very plausible for the upper part of the sequence especially the andic brown the typic brown and the fersiallitic soils in the lower part of the sequence however the authors suggest that the evolution is related to the fluctuations of quaternary climate at the time of the last fluctuation after a more humid climate favoring clay formation there followed an increasingly arid climate producing calcium carbonate accumulation gypsum and finally sodification of soils as well as genesis of palygorskite

geology and depositional history of cenozoic sediments of the bengal basin of bangladesh abstract the bengal basin lies on the eastern side of the indian subcontinent and occupies the northern part of the bengal geosyncline sedimentation started with the breakup of gondwanaland cretaceous fluvial and deltaic sedimentation was slowly taken over by open marine and deep sea fan sedimentation by the mid eocene the basin was witnessing the maximum marine transgression and most of the stable shelf was in carbonate regime as part of the extended tethyan carbonate shelf the deeper part of the basin was dominated by deep sea fan sedimentation fed by clastic turbidites from the northeast with limited carbonate turbidites from the shelf the collision of the indian plate with the tibetan plate and with the burmese plate in the miocene resulted in a rapid switch in sedimentation pattern in the bengal basin the basin structure and sedimentation were both strongly influenced by the collision pattern of the plates and by the uplift of the himalayas with the miocene collision of the indian plate there was a change from flysch to molasse sedimentation the present day basin configuration with the ganges bramaputra delta on the north and the bengal deep sea fan on the south was established in the pliocene the stratigraphic and tectonic framework of the bengal basin suggest that the deposition of hydrocarbon source rocks was associated with the flysch sedimentation whereas formation of traps and deposition of most of the reservoir rocks in the basin was associated with mid pliocene tectonic movements and with the molasse sedimentation the pre mid miocene sediments now deeply buried in the deeper part of the bengal basin and in the eastern folded belt are the major source of gas of the eastern folded belt of the basin

the proterozoic thelon paleosol northwest territories canada abstract beneath the 1 72 ga thelon formation in the northwestern part of the canadian shield an unmetamorphosed and undeformed paleosol is preserved on a variety of paleoproterozoic and archean protoliths this paper documents the paleosol referred to as the thelon paleosol in four localities where it developed on leucocratic schist gneiss and granite the thelon paleosol is characterized by these ascending changes from fresh protolith through paleosol to the unconformity a saprolitic disruption of the protolith resulting in ped and ferran formation b reddening of the paleosol as a consequence of hematitization c increase in dissolution of feldspar plagioclase alkali feldspar increase in the degree of iron oxidation in biotite chlorite and garnet and an increase in the abundance of neoform kaolinite illite and hematite cement d a loss of tio2 fe2o3 total feo mno mgo cao na2o k2o p2o5 u zr rb sr ba e a gain of fe2o3 and f an increase in cia values the fabric of the parent material appears to be the only soil forming factor that locally influenced paleosol development in comparison to thin profiles developed on massive relatively impervious protoliths thick profiles have developed on metamorphic protoliths in which the fabric has allowed deeper penetration of paleoweathering fluids the behaviour of iron in the profiles particularly profile 2 with a granite protolith and an increase in hematite towards the top of the profiles suggests that the thelon paleosol formed under an oxidizing atmosphere subsequent deposition of quartzose conglomerate and sandstone of the thelon formation has caused compaction of the thelon paleosol and this compaction probably was responsible for the formation of stylocumulates in the paleosol during diagenesis of the thelon formation the influx of diagenetic fluids into the paleosol produced veinlets of quartz and hematite a newly recognized microcrystalline hydrated alumino phosphate sulphate mineral and widespread pseudomorphs of illite after pedogenic vermiform kaolinite

erosion transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at lascar volcano chile abstract investigations have been made on the distribution of pumice and lithic clasts in the lithic rich soncor ignimbrite 26 5 ka and the 1993 pumice flow deposits of lascar volcano chile the soncor ignimbrite shows three main lithofacies which grade into one another coarse lithic breccias range from matrix poor stratified varieties irregular shaped sheets and elongate hummocks in proximal environments to breccia lenses with pumiceous ignimbrite matrix massive lithic rich facies comprise the bulk of the ignimbrite pumice rich facies are bimodal with abundant large pumice clasts often with reverse grading rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys in the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14 whereas pumice rich facies are deposited only on slopes

genesis and diagenesis of paleosols from pliocene volcanics on the golan heights pedogenesis and diagenesis of paleosols that are intercalated amid basalt flows of late pliocene age 3 7 3 1 m y b p have been studied on the southwestern slopes of the golan heights the data obtained suggest that environmental conditions resembled present day ones being characterized by a warm climate with seasonal moisture contrasts all soils show evidence of redeposition as well as stratification of the parent material on very low relief sites vertisols with a large content of smectitic clay influenced by aeolian deposition with a large content of smectic clay formed rubefaction took place as well as clay translocation and possibly also carbonatisation the burial of the soils by lava flows resulted in partial erosion and distinct fritting indicated by compaction cementation and hematization after burial various types of alteration affected the soils such as clay illuviation strong carbonatisation and tectonic movements pedogenic features were preserved very well but have subsequently been overprinted by diagenetic processes especially carbonate precipitation e414c ages of the carbonates indicate continuous rejuvenation by meteoric moisture persistence of smectite indicated that conditions affecting soil solution chemistry had not changed significantly since burial

evolution of reg soils in southern israel and sinai abstract reg soils mostly camborthids and gypsiorthids cover some 15 of the negev and sinai deserts analytical data of seven profiles on depositional surfaces of increasing age in the negev show clear relationships between ages of surfaces and soil profile features exemplified in the development of the cambic salic and gypsic horizons the youngest soil a coarse desert alluvium soil typic torriorthent of dry wadi beds up to a few thousand years old has little profile differentiation and is generally non saline or slightly saline on the higher terraces connected with the lisan formation about 70 000 12 000 years b p clear profile differentiation and the beginning of development of cambic horizons can be discerned evident in their colour textural p differences the soils are already saline and somewhat gypsiferous both soils are not yet defined as regs because of their negligible or restricted profile differentiation reg soils on the older and higher geomorphic surfaces in the arava rift valley several hundred thousand years old have well differentiated profiles with cambic salic and gypsic horizons below their stony desert pavements typical reg soils have light coloured vesicular horizons over mellow very pale brown loam frequently with laminar structure almost completely stone free layers the reddish brown loamy to clay loam b horizons are very saline and show intensive salt weathering of gravels gypsic and petrogypsic horizons occur at depth such reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering

field observations and surface characteristics of pristine block and ash flow deposits from the 2006 eruption of merapi volcano java indonesia abstract a series of pristine block and ash flow deposits from the may june 2006 eruption of merapi represent an exceptional record of small volume pyroclastic flows generated by gravitational lava dome collapses over a period of about two months the deposits form nine overlapping lobes reaching 7 km from the summit in the gendol river valley on the volcano s southern flank which were produced by successive flows generated during and after the major dome collapse event on june 14 both single pulse post june 14 events and multiple pulse pyroclastic flows generated by sustained dome collapses on june 14 are recognised and three types of deposits spread over an area of 4 7 km are distinguished totalling 13 3 10 6 m 3 1 valley confined basal avalanche deposits 11 7 10 6 m 3 in the gendol river valley 2 overbank pyroclastic flow and associated surge deposits 1 4 10 6 m 3 where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and 3 dilute ash cloud surge deposits 0 2 10 6 m 3 along valley margins variations in the distribution surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic flow forming events and varying modes of transport and deposition of the different flows inferred flow velocities of the largest block and ash flows generated on june 14 vary from 43 8 13 5 m s for the basal avalanche and from 62 6 24 2 m s for the ash cloud surge the minimum temperatures range from 400 c for the basal avalanche to 165 c for the overlying ash cloud due to the potential of being re channeled into adjacent river valleys and flowing laterally away from the main river channel the overbank pyroclastic flows are considered the most hazardous part of the block and ash flow system the conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at merapi and similar volcanoes elsewhere

origin of siltstones glacial grinding versus weathering siltstones are unusual rocks they are mainly made up of quartz glacial grinding is considered by some authors to be the main or even the only process generating silt this is supported by 1 the presence of silt in basal tills from present ice caps and above all 2 by the volumetric importance of quaternary loess however ancient glaciogenic sediments contain only a little silt scattered in the matrix of tillites or forming thin intercalations in pro and periglacial deposits these siltstones represent less than 5 of the total volume of upper proterozoic and upper ordovician glaciogenic sequences of west africa on the other hand silt is abundant in weathering profiles of tropical equatorial and mediterranean zones this silt is generated by splitting of minerals mainly quartz inherited from the parent rock quartz grains are partly dissolved in situ and their fragments cemented by iron oxi hydroxides in tropical and equatorial zones and by calcite in mediterranean zones silt is particularly abundant in tropical soils comprising up to 50 75 secondary dissolution of the iron or calcite matrix induces disaggregation of these soils and the release of silt which is later reworked and concentrated by wind or running water weathering processes and especially those operating in tropical zones are the main phenomena generating silt glacial grinding would generate only a little silt a large part of the material of quaternary loess may be derived from glacially reworked weathering profiles

emplacement temperatures of the november 22 1994 nuee ardente deposits merapi volcano java abstract a study of emplacement temperatures was carried out for the largest of the 22 november 1994 nuee ardente deposits at merapi volcano based mainly on the response of plastic and woody materials subjected to the hot pyroclastic current and the deposits and to some extent on eyewitness observations the study emphasizes the turgo kaliurang area in the distal part of the area affected by the nuee ardente where nearly 100 casualties occurred the term nuee ardente as used here includes channeled block and ash flows and associated ash clouds of surge and fallout origins the emplacement temperature of the 8 m thick channeled block and ash deposit was relatively high 550 c based mainly on eyewitness reports of visual thermal radiance emplacement temperatures for ash cloud deposits a few cm thick were deduced from polymer objects collected at turgo and kaliurang most polymers do not display a sharp melting range but polyethylene terephthalate used in water bottles melts between 245 and 265 c and parts of the bottles that had been deformed during fabrication molding turn a milky color at 200 c the experimental evidence suggests that deposits in the turgo area briefly achieved a maximum temperature near 300 c whereas those near kaliurang were

merapi volcano java indonesia and merapi type nuee ardente a particular nuee ardente type merapi type avalanche nuee has been defined at the merapi volcano because of its prominent role in the recent activity of the volcano gravity plays a significant role during the eruption

effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics gunung merapi 2010 eruption in 2010 gunung merapi central java indonesia generated two violent eruption sequences on 26 october and 5 november culminating in widespread pyroclastic density currents pdcs associated with the destruction of lava domes tephra from pdc deposits were analysed to examine pre dome collapse volatile behaviour and evidence of carbonate assimilation secondary ion mass spectroscopy sims depth profiles of plagioclase phenocrysts reveal that the 7 li 30 si ratios in 26 october products are higher in the glass compared to the crystal indicating a build up of li in the groundmass not observed in the 5 november samples higher li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 october explosion which was only captured through the behaviour of quickly diffusing li and not h 2 o following the explosion induced decompression juvenile magma rapidly ascended in great volume to generate extremely destructive pdcs following subsequent dome collapses particularly on 5 november additionally 26 october tephras contain carbonate grains in the ash component and abundant co 2 within the lava lapilli groundmass glass which supports previous studies indicating assimilation of calc silicate lithologies by the merapi magma at depth in the plumbing system prior to the onset of 2010 activity

clay distribution over the landscape of israel from the hyper arid to the mediterranean climate regimes abstract the current study evaluates clay distribution in modern surface sediments mainly soils to which desert dust is a major contributor the mineralogical composition of the clay fraction of seventy seven samples was analyzed by x ray diffraction twenty nine soil and dust samples were also analyzed for their bulk chemical composition the samples are settled dust soils developed on various sedimentary rocks stream and lake sediments they were collected along a climate gradient from hyper arid to mediterranean regimes in israel the purpose of the study is to decipher the main factors that control variable clay distribution along this gradient including annual precipitation substrate type and topography the common clay composition for most samples of all sources is illite smectite is kaolinite illite trace amounts of chlorite palygorskite goethite and quartz might be present pedogenic processes are recognized even under arid climate where loessial soils display kaolinite depletion and more illitic is phases than dust two main processes shape clay composition under a mediterranean climate regime regardless of the parent material a smectitization process occurs in leached low permeable clayey soils and reaches optimum evolution with 90 smectite or smectitic is this evolutionary trend is also recognized in poorly drained soils of catenary chains that are related to other soil types like terra rossa hamra and pale rendzina kaolinitization and apparently illite pedogenic formation occur in well drained red mediterranean soils of the terra rossa and hamra types to the detriment of smectitic is phases of parent materials in the most evolved terra rossa and hamra soils kaolinite becomes the principal mineral and illite is significantly enriched pedogenic evolution of the clay fraction mineralogical composition affects bulk chemical composition of most soil types clay inheritance from the bedrock is rather limited in leached soils it is widely recognized in pale rendzina soils by the presence of smectite or smectite and palygorskite derived from late cretaceous or eocene chalks respectively streams clay composition like that of dust is fairly uniform as streams average various sources across their drainage basins however composition variations can be attributed to local contribution from certain sources

block and ash flow deposition a conceptual model from a gpr survey on pyroclastic flow deposits at merapi volcano indonesia in 2006 a series of block and ash flows swept the southwestern and southern flanks of merapi volcano java indonesia in the k gendol valley near the village of kaliadem we conducted a gpr survey on the most distal lobe of the june 14th second block and ash flow deposit for this 100 m long transect we used a commercial gpr ramac mounted with 100 mhz antennas we measured the topography with a synchronized gps and a laser rangefinder back at the laboratory we processed the dataset with the software reflex data of the subsurface reveals a series of layers separated by strong reflective horizons these horizons are the manifestation of intercalations of fine materials in between more coarse layers the architecture of these layers presents progradation retrogradation and aggradation patterns that we relate to the block and ash flow deposition process based on these observations we proposed a relative chronology of the deposition and a simple conceptual model of the deposition the model show that the block and ash flow can deposit either long close to horizontal single layers or shorter layers that imbricate themselves following different patterns progradation retrogradation or aggradation nevertheless we remained cautious since we only studied a very short portion of the deposit and similar experiences need to be repeated moreover there are reflections in the radargram that we could not identify and further studies need to be conducted

illite in aridic soils desert dusts and desert loess abstract in some desert loess deposits notably those of central asia illite dominates the clay fraction in others such as in the near east and north africa illite is a minor component the interaction between desert loess deposits and aridic desert soils via desert dusts is used to explain the difference in illite contents vertical profile distribution of illite as well as vertical distributions of soluble and exchangeable potassium are taken to indicate that illite forms pedogenetically in the surface horizon of aridic soils once formed it is stable and accumulates it is postulated that the potassium required for the illitazation process is introduced by aeolian dusts the process is facilitated by wetting and drying cycles dusts originating in deserts where they are presently produced by desert weathering of various rocks are defined as primary or juvenile dusts they have low illite contents such are the dusts that are carried from the eastern sahara and sinai peninsula northeast towards the middle east where they form local loess deposits the central asian dusts on the other hand have been subjected to numerous cycles of deflation and deposition resulting in relatively long residence times in the pedogenic environment of aridic soils this results in the enrichment of these dusts with illite the central asian desert loess deposits that interact with these dusts are consequently enriched with illite similar processes of illite enrichment may have operated in other areas such as australia

large sedimentation rate in the bengal delta magnetostratigraphic dating of cenozoic sediments from northeastern bangladesh a 4 3 km thick section of clastic sediments of the surma basin northeastern bangladesh that is exposed along the shari river was sampled for a magnetostratigraphic study miocene through pleistocene ages have been discussed previously however there has been no firm dating through biostratigraphy or radiometric or other methods primary paleomagnetic remanent magnetizations of normal or reversed polarity were determined for most of the 300 collected samples on the basis of assumptions of 1 constant sedimentation rates on average throughout the deposition of the sedimentary sequence 2 no major gaps in sedimentation and 3 a fairly young 2 ma age for the topmost dupi tila deposits we find good agreement between the measured profile and the geomagnetic polarity time scale if the entire sedimentary sequence is between 4 9 and 1 4 ma in age the upper marine shales an important seismic marker horizon are dated as 3 5 ma and are therefore 1 5 m y younger than previously assigned by biostratigraphic results the upper marine shales presumably correspond to the last pre pleistocene sea level highstand the dating of rock units below the upper marine shales is tentative because of a large gap in exposure the inferred sedimentation rate and thus the rate of delta subsidence of 1 2 m k y is much larger than previously assumed it appears to be one of the highest sedimentation rates in earth history that was sustained for millions of years

salt intrusion in coastal and lowland areas of semarang city over a long term semarang coastal and lowland areas have experienced salt water intrusion this condition is accelerated due to land subsidence sea level rise and groundwater exploitation the purposes of this research paper were to highlight the salt water intrusion from 1995 until 2108 based on well log measurement and modfow numerical modeling in coastal and lowland of semarang city sea level rise projection also was considered for salt intrusion projection in the future modflow was used to compute the groundwater flow field mt3d for the salt transport and arcgis environments for coherent geographic visualization a calibration of the model was conducted based on observation best match the results obtained illustrate the development of a forward onshore sea salt water intrusion since 1995 it also showed the 2008 recorded sea water intrusion and provide groundwater sea water contamination projection for the years 2018 until 2108 moreover fresh water distribution near the coast in previous years developed into brackish water then into saline groundwater result showed the movement of saline groundwater from coastline to landward years by years from 2018 2028 2048 2068 2088 and 2108 following high hydraulic conductivity area salt intrusion was also driven by future sea level rise which result to the increase of the fresh water front forward move

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

a paleo brahmaputra subsurface lithofacies analysis of miocene deltaic sediments in the himalayan bengal system bangladesh abstract the bengal foreland basin contains a succession of up to 16 km of dominantly deltaic deposits eroded from the eastern himalayas and the indo burman ranges and carried by major river systems similar to the present day ganges and brahmaputra analysis of electric logs and core descriptions acquired during oil and gas exploration in bangladesh allows construction of lithofacies maps which constrain depositional patterns of miocene strata compilations of sand thickness and sand shale ratio of the miocene surma group show that lower to middle miocene strata of the bhuban formation accumulated in a large elongate trough sand thickness and percentage both decrease markedly away from this depocenter which describes a large scale bend running initially westward from rashidpur northeast bengal basin and curving southward toward the bengal fan middle to upper miocene strata of the boka bil formation show a similar geographic trend in deposition of coarsest and thickest sediment but the major depocenter had shifted northward relative to that of the bhuban formation by some 30 km passing near beani bazar these trends suggest that deltaic deposits of the surma group filled the sylhet trough of the northeast bengal basin from the east published seismic data from western bangladesh show that additional large channels also contributed materials to the bengal basin from the northwest during the late miocene but these channels resulted in very little accumulation in the northwestern part of the basin probably due to restricted subsidence of underlying continental crust this study suggests that there was a major drainage system similar to the modern brahmaputra river during miocene time which carried orogenic sediments eroded from the uplifted terranes of the eastern himalayas and indo burman ranges to the eastern bengal delta

welded block and ash flow deposits from mount meager british columbia canada abstract the 2360 years b p eruption of mount meager british columbia produced a succession of rarely observed welded block and ash flow deposits and non welded equivalents we report on these rhyodacitic block and ash flow deposits by describing the deposits documenting the nature of the welding process and establishing the origins of these pyroclastic deposits variations in welding intensity are tracked by image analysis of field texture maps petrographic study of shard morphology and measurements of sample density and porosity pyroclast oblateness from image analysis of texture maps provides a qualitative record of welding intensity but underestimates the amount of compactional e g volume strain when compared to estimates from physical property measurements e g density porosity unconsolidated deposits have an average matrix porosity of 41 38 45 and clasts have an average porosity of 32 24 40 in unconsolidated deposits isolated porosity is pervasive 50 m shortening of the thickest deposit from 162 m to the current 112 m the pyroclastic flow deposits result from accumulation in a narrow confined river valley the accumulation was sufficiently rapid to keep the deposits above their glass transition temperature thereby allowing the succession to weld as a single cooling unit the nature and distribution of isolated porosity in the juvenile clasts of rhyodacite suggest an explosive rather than effusive origin for these block and ash flow deposits that may be analogous to some vulcanian eruption triggered dome collapse processes observed at soufriere hills volcano montserrat rather than gravitational collapse

modern and late quaternary clay mineral distribution in the area of the se mediterranean sea the present day clay mineral distribution in the southeastern levantine sea and its borderlands reveals a complex pattern of different sources and distribution paths smectite dominates the suspended load of the nile river and of rivers in the near east illite sources are dust bearing winds from the sahara and southwestern europe kaolinite is prevalent in rivers of the sinai in egyptian wadis and in saharan dust a high resolution sediment core from the southeastern levantine sea spanning the last 27 ka shows that all these sources contributed during the late quaternary and that the nile river played a very important role in the supply of clay nile influence was reduced during the glacial period but was higher during the african humid period in contrast to the sharp beginning and end of the african humid period recorded in west african records 15 and 5 5 ka our data show a more transitional pattern and slightly lower nile river discharge rates not starting until 4 ka the similarity of the smectite concentrations with fluctuations in sea surface temperatures of the tropical western indian ocean indicates a close relationship between the indian ocean climate system and the discharge of the nile river

diagenesis and its impact on the reservoir quality of miocene sandstones surma group from the bengal basin bangladesh abstract rapid supply and deposition of 1000 s of meters of miocene and pliocene sediment tend to lead to a different set of controls on reservoir quality than older more slowly buried sandstones here we have studied miocene fluvial deltaic bhuban formation sandstones from the surma group bengal basin buried to 3 000 m and 110 c using a combination of petrographic geochemical and petrophysical methods in order to understand the controls on miocene sandstone reservoir quality to facilitate improved prediction of porosity and permeability the main conclusions of the study are that mechanical compaction processes are the dominant control on porosity loss although early calcite growth has led to locally negligible porosity in some sandstones mechanical compaction occurred by grain rearrangement ductile grain compaction and brittle grain fracturing calcite cement occupying up to 41 intergranular volume was derived from a combination of dissolved and recrystallized bioclasts an influx of organic derived carbon dioxide and plagioclase alteration clay minerals present include smectite illite kaolinite and chlorite the smectitic clay was probably restricted to low energy depositional environments and it locally diminishes permeability disproportionate to the degree of porosity loss kaolinite is probably the result of feldspar alteration resulting from the influx of organic derived carbon dioxide quartz cement is present in small amounts despite the relatively high temperature due to a combination of limited time available in these young sandstones grain coating chlorite and low water saturations in these gas bearing reservoir sandstones reservoir quality can now be predicted by considering primary sediment supply and primary depositional environment the magnitude of the detrital bioclast fraction and the influx of organic derived carbon dioxide

geochemistry and detrital zircon u pb dating of pliocene pleistocene sandstones of the chittagong tripura fold belt bangladesh implications for provenance abstract the bengal basin originated during the collision of india with eurasia and burma the provenance analysis of the chittagong tripura fold belt ctfb which is the folded eastern flank of the bengal basin as well as the neogene belt of the indo burman ranges ibr is key to better understand the possible sources of sediment input from the complex interplay of the indian eurasian and burma plates we report new whole rock geochemical and detrital zircon u pb data from the upper neogene sandstones of tipam dupi tila formations pliocene to plio plestocene succession from the ctfb detrital zircon u pb age spectra show three predominant peaks at

decoupling of small volume pyroclastic flows and related hazards at merapi volcano indonesia the november 1994 eruption at merapi volcano provided good evidence of decoupling of dome collapse pyroclastic flows and of large scale detachment of an ash cloud surge acs component from the basal block and ash flow baf timing and stratigraphic relationships of the largest 1994 acs indicate that this escaped from the valleys travelled well ahead of the baf arrived at the termination tens of seconds before it and deposited a discrete acs deposit beneath the baf unit this suggests that the acs detachment mostly occurred relatively high on the volcano slope likely at the foot of the proximal cone later pyroclastic flow eruptions in january 1997 and july 1998 also showed evidence of acs detachment although to a lesser extent suggesting that acss could be a frequent hazard at merapi volcano based on an extensive review of the available literature and on field investigations of historical deposits we show here that flow decoupling and acs detachment in the way inferred from the 1994 eruption is a common process at merapi the acs related destructions outside valleys were frequently reported in the recent past activity of the volcano i e in at least 16 pyroclastic flow eruptions since 1927 destruction occurred systematically in eruptions where maximum runout of the bafs was 6 5 km or more and occurred rarely for baf runouts of 4 5 km or less the acs deposits have been recognized beneath some valley filling baf units we attribute to some recent destructive eruptions i e the 1930 1954 1961 and 1969 eruptions topographic conditions at merapi volcano favouring acs detachment include a the high slope 30 of the proximal cone leading to high proximal velocities of the pyroclastic flows and thus to the transfer of large amounts of particles into the ash cloud b the strong break in slope at the foot of the proximal cone where the velocity of the basal baf is strongly reduced and a major acs component is thought to form and detach by shearing over the baf and c the small depth of most valleys in the first kilometres beyond the foot of the cone which allows minor acs components to escape from the valleys during travel of the baf however flow decoupling and acs detachment occur for only some of the numerous pyroclastic flows that follow the same path in a given eruption this indicates that topography alone cannot lead to flow decoupling we suggest two factors that control flow decoupling and its extent the main one is flow volume and thus flux as both are correlated in almost instantaneous dome collapse events as suggested by the observed relationship between flow decoupling and the travel distance of the pyroclastic flows the second factor is the amount of available ash in the flow at its early stage which influences the mass and thus momentum of the ash cloud the amount of ash in the pyroclastic flows of merapi may depend on several factors among which are a the physical and thermal state of the part of the active dome that collapses and b the proportion of older cold rocks incorporated in the flow either by undermining of surrounding summit rocks by the current pyroclastic flow activity or by erosion on the upper slopes

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity