crustal thickness beneath mt merapi and mt merbabu central java indonesia inferred from receiver function analysis abstract in this study we analysed 2708 receiver functions rfs using data recorded by 53 seismographic stations that surround mt merapi and mt merbabu two volcanos in central java to map the boundary between earth s crust and upper mantle we observe that a number of rfs from this new dataset have complex signals and do not exhibit typical rf characteristics in particular where the converted ps signal from the moho discontinuity is the clearest and strongest amplitude arrival following the p onset this effect may be related to complex shallow velocity structure due to the presence of magmatic rocks and sediments further analysis of the rf results using the h method suggests that moho depth varies between 27 and 32 km beneath the array with no apparent correlation between crustal thickness and surface topography as one might expect from airy isostacy for instance the moho is quite shallow beneath mt merapi up to 27 km depth despite its elevation of nearly 3 km this may be a consequence of dynamic support from an active upper mantle coupled with erosion and or weakening of the lower crust due to the active volcanic plumbing system to the north of mt merapi the moho is deeper 30 31 km depth below mt merbabu vp vs ratio estimates from the h method are relatively high 1 9 beneath the mt merapi and kendeng basin area which may indicate the presence of a zone of hydrous and active partial melting in the underlying crust lower vp vs ratios 1 7 are found beneath mt merbabu which may be due to its relative lack of volcanic activity compared to mt merapi

sedimentary architecture and 3d ground penetrating radar analysis of gravelly meandering river deposits neckar valley sw germany sedimentological outcrop analysis and sub surface ground penetrating radar gpr surveys are combined to characterize the three dimensional sedimentary architecture of quaternary coarse grained fluvial deposits in the neckar valley sw germany two units characterized by different architectural styles are distinguished within the upper part of the gravel body separated by an erosional unconformity i a lower unit dominated by trough shaped depositional elements with erosional concave up bounding surfaces that are filled by cross bedded sets of mainly openwork and filled framework gravel and ii an upper unit characterized by gently inclined sheets of massive and openwork gravels with thin sandy interlayers that show lateral accretion on a lower erosional unconformity the former is interpreted as confluence scour pool elements formed in a multi channel possibly braided river system the latter as extensive point bar deposits formed by the lateral migration of a meandering river channel the lateral accretion elements are locally cut by chute channels mainly filled by gravels rich in fines and by fine grained abandoned channel fills the lateral accretion elements are associated with gravel dune deposits characterized by steeply inclined cross beds of alternating open and filled framework gravel floodplain fines with a cutbank and point bar morphology cover the gravel deposits the gpr images revealing the three dimensional geometries of the depositional elements and their stacking patterns confirm a change in sedimentary style between the two stratigraphic units the change occurred at the onset of the holocene as indicated by 14 c dating of wood fragments and is related to a re organization of the fluvial system that probably was driven by climatic changes the integration of sedimentological and gpr results highlights the heterogeneity of the fluvial deposits a factor that is important for modelling groundwater flow in valley fill aquifers

geophysical imaging of the inner structure of a lava dome and its environment through gravimetry and magnetism volcanic lava domes are compound edifices resulting from complex growth processes including intrusion and extrusion phases explosions and collapses here we present the study of a complex volcanic system located in the chaine des puys volcanic field french massif central france and centred on the puy de dome volcano an 11 000 years old volcano our approach is based on a morpho structural analysis of a high resolution dtm 0 5 m and geophysical imaging methods both gravity and magnetic high resolution surveys have been carried out on the lava dome and the nearby volcanic structures we computed 3d inverse and 2d forwards models based on our current knowledges about volcanic dome structure the geophysical models allow us to propose a synthetic geological model of the inner structure of the puy de dome and surrounding areas this model suggests a scenario for the formation of the lava dome and the inferred intrusions located on both sides the puy de dome could possibly be the southern tip of the northern intrusion

evolution of mid channel bars in a braided river and complex response to reservoir construction an example from the middle hanjiang river china using the middle hanjiang river as an example this paper deals with the development of mid channel bars in a braided river as controlled by channel boundary conditions runoff and sediment load as well as reservoir construction relations have been established between indices describing the mid channel bars and the controlling variables such as the channel width the percentage silt clay content in the channel boundary and the energy expenditure of flowing water bank erosion provides space and material for mid channel bar formation so bank erosion rate can be closely related to mid channel bar indices the middle channel bars exhibit a complex evolutionary response to the reservoir regulated hydrological regime in the middle hanjiang river a descriptive model showing the complex response has been established 1997 john wiley sons ltd

bedload path length and point bar development in gravel bed river models low sinuosity meandering gravel bed flume experiments were employed to investigate spatial patterns of deposition which point to patterns of channel development related to the pool and bar morphology at channel forming discharges fluorescent bedload tracers indicate that deposition is typically focused around the point bar apex downstream of the apex contributing to downstream bar migration and at the bar head riffle surface seven flume experimental runs illustrate a sequence of point bar development related to the spatial patterns of tracer deposition and the related path length distribution at early stages of bar formation transport is from the scour zone across the point bar head to the bar apex and bar margin downstream of the apex as the point bar develops bedload transport across the bar decreases as transport along the channel thalweg increases and sediment is deposited along the bar margin deposition cells appear to move from downstream to upstream of the bar apex as this sequence of bar formation progresses at low non channel forming discharges transport occurs to the bar head riffle surface with very little material being transported to the apex region or point bar interior the implication is that there is an inherent connection between the loci of particle deposition and point bar formation largely controlled by the morphology of the channel

river channel adjustment to meander cutoffs on the river bollin and river dane northwest england morphological adjustment of a channel after cutoff should be expected but rarely has the mode and timescale of adjustment in natural channels been measured four natural cutoffs which have occurred since 1980 on two rivers in northwest england have been monitored from pre cutoff stage two of the cutoffs were neck cutoffs of large loops two were chute cutoffs in which significant bend curvature remained all the cutoffs were the terminal result of progressive bank erosion and or scour of the floodplain rather than overflow and all the cutoffs took place in peak flow events though two of these were of relatively low magnitude high frequency rapid widening and sedimentation took place within the straight channels produced by neck cutoffs immediately after breaching adjustment was mainly by formation of multiple riffles and bars producing a variable morphology in the first 2 4 years subsequently the morphology became more regular and in one case had stabilised within about eight years progressive steepening and acceleration of bank erosion appears to have been propagated upstream in one case but in the other cases erosion was very localised rates of vertical accretion at the entrances to the old channel were much higher than most quoted in the literature rates of change in all morphological sedimentary and biotic components exhibit an exponential decline with time but with slightly differing timescales on these active gravel bed streams major adjustment within the new channels may be completed within 6 12 years though lakes persist in the abandoned channels for much longer

significance of dar zarrouk parameters in the exploration of quality affected coastal aquifer systems the interpreted earth subsurface resistivity layer parameters of 55 vertical geoelectrical soundings are analyzed over a fan shaped area of 1 700 km2 from pipli astrang bhramgiri orissa india in this study dar zarrouk d z parameters namely the longitudinal conductance s transverse resistance t and longitudinal resistivity rs are analyzed and we encountered the resistivity regime of the clay layers saline and fresh water bearing formations the significance of these parameters in establishing an easily decipherable vision about the occurrence and distribution of fresh and saline water aquifers while dealing with complicated situations of intermixing of the resistivity ranges of saline and fresh water aquifers has been illustrated the results show that the dar zarrouk d z parameters provide a useful and confident solution in delineating the saline and fresh water aquifers the behavior of the d z parameters s t and rs and its patterns in space over large areas with respect to the occurrence of saline water and fresh water aquifer systems in the deltaic coastal aquifer system has been demonstrated

deep volcanic morphology below lanzarote canaries from gravity inversion new results for timanfaya and implications abstract the deep roots of oceanic island volcanoes are poorly known and geophysical models can help to constrain processes such as magma storage and transport before and during eruptions lanzarote canary islands is a volcanic island in post erosional phase where in the 18th century one of the most important historical eruptions considering duration and volume of the canary islands took place in the timanfaya area to improve the knowledge on the structure of lanzarote and in timanfaya area we carry out a gravity determination of the subsurface anomalous 3d density structure using an improved quasi automatic inversion methodology the obtained model presents a 3d morphology of anomalous density bodies we describe the improvements of the inversion methodology the adjusted model and interpretative conclusions corresponding to the structure and the long term cumulative magmatic plumbing system of the island three high density sources are described as resulting in the inference of three main volcanic complexes a large central complex san bartolome and two smaller complexes one in the ne and a third smaller one located in the sw close to the timanfaya area the outcrops of miocene lava flows from the center of the island can be attributed to the top of the central intrusive model we infer the local plumbing system for timanfaya volcano area by means of strongly tilted successive branches of magma departing from the sw intrusive body the structural results show no evidence of any magma chamber below timanfaya as proposed by previous works we also present a comparison of the gravity results and geological observations showing different cases of correlation in the island they go from a good match between the gravity anomaly and the position of the central volcanic structure to no anomaly associated to the fissural quaternary volcanic activity

on application of three dimensional interactive modeling in gravity and magnetics by h j gotze and bernd lahmeyer geophysics 53 1096 1108 august 1988 gotze and lahmeyer present the main principles and results new automatic system for the interactive modeling of three dimensional 3 d gravity and magnetic fields the high efficiency of the system is demonstrated convincingly on a practical example of a geologic study in the northwest german basin the importance and timeliness of this work are beyond doubt nonetheless a few remarks on the analytical results seem to be appropriate

sedimentology of the cretaceous maha sarakham evaporites in the khorat plateau of northeastern thailand abstract evaporites of the cretaceous to early tertiary maha sarakham formation on the khorat plateau of southeast asia thailand and laos are composed of three depositional members that each include evaporitic successions each overlain by non marine clastic red beds and are present in both the khorat and the sakon nakhon sub basins these two basins are presently separated by the northwest trending phu phan anticline the thickness of the formation averages 250 m but is up to 1 1 km thick in some areas in both basins it thickens towards the basin centre suggesting differential basin subsidence preceding or during sedimentation the stratigraphy lithological character and mineralogy of the evaporites and clastics are identical in both basins suggesting that they were probably connected during deposition evaporites include thick successions of halite anhydrite and a considerable accumulation of potassic minerals sylvite and carnallite but contain some tachyhydrite and minor amounts of borates during the deposition of halite the basin was subjected to repeated inflow of fresher marine water that resulted in the formation of anhydrite marker beds sedimentary facies and textures of both halite and anhydrite suggest deposition in a shallow saline pan environment many halite beds however contain a curious sieve like fabric marked by skeletal anhydrite outlines of gypsum precursor crystals and are the product of early diagenetic replacement by halite of primary shallow water gypsum the 34s isotopic values obtained from different types of anhydrite interbedded with halite range from 14 3 to 17 0 cdt suggesting a marine origin for this sulphate bromine concentration in the halite of the lower member begins around 70 ppm and systematically increases upward to 400 ppm below the potash rich zone also suggesting evaporation of largely marine waters in the middle member the initial concentration of bromine in halite is 200 ppm rising to 450 ppm in the upper part of this member the bromine concentration in the upper member exhibits uniform upward increase and ranges from 200 to 300 ppm the presence of tachyhydrite in association with the potassic salts was probably the result of 1 the large volumes of halite replacement of gypsum on a bed by bed basis releasing calcium back into the restricted waters of the basin and 2 early hydrothermal input of calcium chloride rich waters the borates associated with potash rich beds likely resulted from erosion and influx of water from surrounding granitic terrains however hydrothermal influx is also possible interbedded with the evaporites are non marine red beds that are also evaporative with displacive anhydrite nodules and beds and considerable amounts of displacive halite the 34s isotopic values of this anhydrite have non marine values ranging from 6 4 to 10 9 cdt these data indicate that the khorat and sakhon nakhon basins underwent periods of marine influx due to relative world sea level rise but were sporadically isolated from the world ocean

interpretation of long offset transient electromagnetic data from mount merapi indonesia using a three dimensional optimization approach in the years 1998 2000 and 2001 long offset transientelectromagnetic lotem surveys were carried out at the active volcanomerapi in central java the measurements investigated the conductivitystructure of the volcanic edifice our area of interest which is belowthe summit and the upper flanks was investigated using horizontal andvertical magnetic field time derivative data from seventransmitter receiver setups because of topography and athree dimensional 3 d underground structure a 3 d interpretation isused the method optimizes few parameters of a 3 d model by a stableleast squares joint inversion of the data providing sufficientresolution capability reasonable data fits are achieved with anonhorizontally layered model featuring a very conductive basement belowdepths of 1 5 km while hydrothermal alteration is also considered wetentatively explain the high conductivities by aqueous solutions withrelatively high salt contents a large magma body or a small superficialreservoir below merapi s central volcanic complex as discussed by otherauthors cannot be resolved by the lotem data

architecture of channel belt deposits in an aggrading shallow sandbed braided river the lower niobrara river northeast nebraska abstract architecture of recent channel belt deposits of the niobrara river northeast nebraska usa records the response of a sandy braided river to rapid base level rise up to 3 m of aggradation has occurred within the lower 14 km of the niobrara river since the mid 1950s as a result of base level rise at the confluence of the niobrara and missouri rivers aerial photographs and channel surveys indicate that the lower niobrara has evolved from a relatively deep stable channel with large bank attached braid bars to a relatively shallow aggrading channel with braid bars and smaller secondary channels architecture of channel belt deposits associated with the recent aggradation has been defined using ground penetrating radar gpr and vibracores the channel belt deposits exhibit a series of amalgamated channel fills and braid bar complexes i e macroforms radar facies identified in the gpr data represent architectural elements of the braid bar complexes large and small bedforms two dimensional 2 d and three dimensional 3 d dunes and channels individual braid bars appear to consist of basal high flow and upper low flow components preservation of the complete high flow bar geometry is generally incomplete due to frequent migration of smaller scale secondary channels within the channel belt i e braided channel network at low discharges the large scale stratification of the braid bar deposits is dominated by cross channel and upstream accretion elements of downstream accretion are also recognized these accretion geometries have not been documented previously in similar sandy braided rivers braid bar deposits with low flow modification e g incision by secondary channels are recognized in the deeper portions of the deposits imaged by gpr preservation of braid bars with both high and low flow components is a result of the rapid base level rise and channel bed aggradation experienced by the niobrara river over the past 45 years recent avulsion of the river channel allowed preservation of the upper low flow component of the braid bar deposits i e bar top sequences the relative abundance and stratigraphic position of the amalgamated channels and braid bar complexes within the channel belt deposits constitute a signature of the recent base level rise

using dc resistivity method to characterize the geometry and the salinity of the plioquaternary consolidated coastal aquifer of the mamora plain morocco the direct current resistivity method was applied to the consolidated coastal plioquaternary aquifer of mamora plain located on the atlantic coast of morocco the aim is to determine the depth of the base of the saturated zone in the aquifer and to help in imaging lateral and vertical distribution of groundwater salinity the geoelectric survey showed four geoelectric formations with the following electrical resistivities from top to bottom 20 80 200 2000 200 300 and 5 70 ohm m the latter designates the basement of the aquifer constituted of marls and sandy marls the mean resistivity of 250 ohm m designates the aquifer formation it decreases to less than 25 of its initial values for the soundings near the shore reflecting the oceanic impact on the aquifer formation resistivity the contour map shows that the basement of the saturated zone in the aquifer is deeper in the northwest near the sebou river estuary with values up to 70 m below sea level this results in a larger thickness of the saturated zone of the aquifer leading to a consequent hydraulic potential on the other hand it has been deduced that the extent of marine intrusion inside the continent can be governed by human activities natural properties and substratum geometry of the aquifer as well as by ecological factors an optimal network of electrical soundings has been proposed for the monitoring of saltwater intrusion

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

joint inversion of active and passive seismic data in central java seismic and volcanic activities in central java indonesia the area of interest of this study are directly or indirectly related to the subduction of the indo australian plate in the framework of the merapi amphibious experiments meramex a network consisting of about 130 seismographic stations was installed onshore and offshore in central java and operated for more than 150 days in addition 3 d active seismic experiments were carried out offshore in this paper we present the results of processing combined active and passive seismic data which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles the inversion was performed using the updated lotos 06 code that allows processing for active and passive source data the joint inversion of the active and passive data set considerably improves the resolution of the upper crust especially in the offshore area in comparison to only passive data the inversion results are verified using a series of synthetic tests the resulting images showan exceptionally strong low velocity anomaly 30 per cent in the backarc crust northward of the active volcanoes in the upper mantle beneath the volcanoes we observe a low velocity anomaly inclined towards the slab which probably reflects the paths of fluids and partially melted materials in the mantle wedge the crust in the forearc appears to be strongly heterogeneous the onshore part consists of two high velocity blocks separated by a narrow low velocity anomaly which can be interpreted as a weakened contact zone between two rigid crustal bodies the recent java mw 6 3 earthquake 2006 05 26 utc occurred at the lower edge of this zone its focal strike slip mechanism is consistent with the orientation of this contact

salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods a case study from north kelantan malaysia integrated hydrogeochemical and geophysical methods were used to study the salinity of groundwater aquifers along the coastal area of north kelantan for the hydrogeochemical investigation analysis of major ion contents of the groundwater was conducted and other chemical parameters such as ph and total dissolved solids were also determined for the geophysical study both geoelectrical resistivity soundings and reflection seismic surveys were conducted to determine the characteristics of the subsurface and groundwater contained within the aquifers the ph values range from 6 2 to 6 8 indicating that the groundwater in the study area is slightly acidic low content of chloride suggests that the groundwater in the first aquifer is fresh with an average concentration of about 15 8 mg l and high geoelectrical resistivity 45 ohm m on the other hand the groundwater in the second aquifer is brackish with chloride concentration ranging from 500 mg l to 3 600 mg l and very low geoelectrical resistivity 1 000 mg l the groundwater in the third aquifer is fresh with chloride concentrations generally ranging from 2 mg l to 210 mg l and geoelectrical resistivity of greater than 45 ohm m fresh and saltwater interface in the first aquifer is generally located directly in the area of the coast but for the second aquifer both hydrogeochemical and geoelectrical resistivity results indicate that the fresh water and saltwater interface is located as far as 6 km from the beach the considerable chloride ion content initially suggests that the salinity of the groundwater in the second aquifer is probably caused by the intrusion of seawater however continuous monitoring of the chloride content of the second aquifer indicated no significant changes with time from which it can be inferred that the salinity of the groundwater is not affected by seasonal seawater intrusion schoeller diagrams illustrate that sulphate concentrations of the groundwater of the second aquifer are relatively low compared to those of the recent seawater therefore this result suggests that the brackish water in the second aquifer is probably from ancient seawater that was trapped within the sediments for a long period of time rather than due to direct seawater intrusion

revision of platte river alluvial facies model through observations of extant channels and barforms and subsurface alluvial valley fills abstract the platte river of nebraska central usa has been used by sedimentologists as a type example of a sandy braided river system for some forty years despite this designation however the details of the river s subsurface stratigraphy have never been evaluated and so the extant facies model for the platte river remains unvalidated this paper analyzes the holocene stratigraphy of the central and lower platte river it utilizes newly acquired data from wireline logs sediment cores aerial photography and ground penetrating radar gpr traverses to characterize subsurface geology in addition to surface sediment and geomorphic mapping sampling and analysis of serial aerial imagery cores and gpr profiles show that the lithosome of the active platte is 6 8 m in thickness and consists predominantly of medium sand although macroform features are common on the surface of the modern active central and lower platte river in nebraska the shallow subsurface stratigraphy is dominated by mesoform cross bedding and planar stratification overlying channel scour fills this differs markedly from the vertical succession predicted by the platte river facies model of miall 1977 data from inactive portions of the central and lower platte river however show macroform cross bedding indicative of the downstream and cross stream migration of linguoid and transverse bars which would be predicted by the published model the typical architecture of the holocene channel belt sand body in the areas studied thus comprises a lower unit dominated by macroform scale cross bedding overlain by an upper unit dominated by mesoform scale cross bedding and scour fills furthermore time series analysis of aerial photography of the river in the vicinity of grand island nebraska shows that 1 the river has become dominated by aggressively vegetated subaerially exposed channel bed domains termed vegetated channel islands that superficially resemble bars and 2 that this stretch is no longer dominated by downstream accreting macroform bars which were abundant in the 1960s and 1970s contraction of the active channel in this region has accompanied these changes somewhat independently of discharge variation new vertical sequence facies models are presented to account for these differences our data show the futility of seeking to characterize a fluvial system by means of a single vertical sequence model and furthermore indicate that the holocene facies architecture of the sandy braided platte river varies both in space and in time the dominance of mesoform scale structure in the shallow subsurface of the central and lower platte river likely reflects the ongoing process of gradual abandonment of the system it further highlights the need for caution in interpreting subsurface structure from surface geomorphology in fluvial systems

3 d modeling of the deep electrical conductivity of merapi volcano central java integrating magnetotellurics induction vectors and the effects of steep topography we derive a 3 d model of the electrical conductivity structure of merapi volcano in central java from magnetotelluric mt sounding curves and geomagnetic induction vectors topography has been considered explicitly in the model the overall magnitude of the conductivities is constrained by mt measurements while lateral variations are mainly derived from geomagnetic induction vectors the resulting model is consistent with both the mt transfer functions apparent resistivities and phases and the magnetic transfer functions induction vectors the final model consists of two 3 d structures i e a central conductor and a second conductor lying to the southwest of the summit the high conductivity material is probably hot saline water as suggested by position and lateral extent of the high conductivity material

three dimensional sedimentary architecture of a large mid channel sand braid bar jamuna river bangladesh the three dimensional subsurface alluvial architecture of a large approximately 3 km long 1 km wide 12 m high mid channel sand braid bar in the jamuna river bangladesh is described evolution of the bar and its depositional characteristics are assessed from a unique combination of ground penetrating radar surveys vibracoring and trenching that are allied to a series of bathymetric surveys taken during growth of the bar over a 29 month period this methodology permits identification of the formative processes of different packages of braid bar sedimentation and provides a facies model for deposition within the entire bar mid channel bar growth occurred in a region of flow expansion and was probably initiated by the stalling and amalgamation of large dunes these dunes created a bar core that grew by i propagation of a downstream accreting slipface ii vertical accretion through stacking of dunes on both bar stoss and top and iii lateral accretion on the bar margins during recession of the flood hydrograph braid bar sedimentation is dominated by four radar facies 1 large scale predominantly planar dipping reflections interpreted as cross stratification up to 8 m in height and greater than 100 m in width that is produced by the cross channel migration of bar margins 2 medium scale trough shaped and planar discontinuous reflections interpreted as cross stratification up to 4 m in height and 300 m wide that is deposited from large sinuous crested sand dunes 3 discontinuous reflections up to 2 m high and 30 m wide interpreted as small scale trough cross stratification that is the product of smaller sinuous crested dunes and 4 high amplitude undulating reflections interpreted as mud drapes deposited in regions of slow flow often in the bar tail region at low stage dune size decreases vertically within the bar in response to the progressively shallower flows on the emerging bar top later evolution of the bar as one anabranch channel became dominant created a 1 5 km extension to the bar tail with an 8 m high angle of repose bar margin slipface formed by flow transverse to the long axis of the bar seven styles of deposition can be defined that constitute the alluvial architecture bar margin slipface vertical accretion in channel bar top vertical accretion upstream accretion lateral accretion downstream accretion and low stage mud drapes a model of braid bar sedimentation is presented that shares many similarities with previous studies of smaller sand bed braid bars with the dominance of dune scale cross stratification the presence of large scale bar margin cross stratification and the occurrence of lateral vertical upstream and downstream accretion however the contribution of the bar margin facies to the preserved stratigraphy highlighted herein may have been underestimated in previous models of braided rivers in which the braid bars were migrating slowly this study suggests a scale invariance in several aspects of mid channel bar sedimentation in sand bed rivers and proposes a model of braid bar sedimentation that may be applied widely within studies of braided alluvial architecture

new results on the resistivity structure of merapi volcano indonesia derived from three dimensional restricted inversion of long offset transient electromagnetic data three long offset transient electromagnetic lotem surveys werecarried out at the active volcano merapi in central java indonesia during the years 1998 2000 and 2001 the measurements focused on the general resistivity structure of the volcanic edifice at depths of 0 5 2 km and the further investigation of a southside anomaly the measurements were insufficient for a full 3d inversion scheme which could enable the imaging of finely discretized resistivity distributions therefore a stable damped least squares joint inversion approach is used to optimize 3d models with a limited number of parameters the mode ls feature the realistic simulation of topography a layered background structure and additional coarse 3d blocks representing conductivity anomalies twenty eight lotem transients comprising both horizontal and vertical components of the magnetic induction time derivative were analyzed in view of the few unknowns we were able to achieve reasonable data fits the inversion results indicate an upwelling conductor below the summit suggesting hydrothermal activity in the central volcanic complex a shallow conductor due to a magma filled chamber at depths down to 1 km below the summit suggested by earlier seismic studies is not indicated by the inversion results in conjunction with an anomalous density model derived from arecent gravity study our inversion results provide information about the southern geological structure resulting from a major sector collapse during the middle merapi period the density model allows to assess a porosity range andthus an estimated vertical salinity profile to explain the high conductivities on a larger scale extending beyond the foothills of merapi

sedimentary facies and paleoenvironment of a pleistocene fossil site in nakhon ratchasima province northeastern thailand quaternary fauna and flora fossils were found in situ in a sand pit at the khok sung village of khok sung subdistrict muang district nakhon ratchasima province six lithostratigraphic units from unit 1 to unit 6 in ascending order were recognized in the sand pit the sediments in the khok sung sand pit were deposited as two meandering channel sets units 1 2 and 3 form the lower channel sequence and units 4 5 and 6 form the upper channel sequence the lower channel unconformably overlies bedrock and generally flowed northward whereas the upper channel flowed eastward the parent rocks of the khok sung sediments crop out in the western margins of the khorat plateau the flora fossils include fruits ziziphus khoksungensis rhamnaceae dipterocarpus costatus dipterocarpaceae melia azedarach and dracontomelon dao anacardiaceae seeds leaves wood tubers cyperus or bolboschoenus cyperaceae amber and pollen this assemblage suggests the presence of tropical mixed deciduous and dry evergreen forests the fauna fossils include fish gavial gavialis cf bengawanicus tortoise batangur cf trivittata heosemys annandalii heosemys cf grandis and malayemys sp soft shell turtle chitra sp and cf amyda sp bovids rhinoceros deer an advanced form of stegodon and hyena the fauna indicate that the climate differed from today with heavier rainfall and more extensive grassland areas during the pleistocene

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

large scale structure of calamus river deposits nebraska usa revealed using ground penetrating radar the large scale i e bar scale structure of channel deposits of the braided low sinuosity calamus river nebraska is described using ground penetrating radar gpr profiles combined with vibracores basal erosion surfaces are generally overlain by medium scale trough cross stratified sets 3 25 cm thick very coarse to medium sands that are associated with relatively high amplitude discontinuous gpr reflectors overlying deposits are bioturbated small scale cross stratified sets 3 cm thick and vegetation rich fine to very fine sands that are associated with low amplitude discontinuous reflectors near surface peat and turf have no associated gpr reflectors in along stream profiles through braid and point bars most gpr reflectors dip downstream at up to 2 relative to the basal erosion surface but some reflectors in the upstream parts of bars are parallel to the basal erosion surface or dip upstream in cross stream profiles through bars gpr reflectors are either approximately parallel to bar surfaces or have low angle inclinations up to 6 towards cut banks of adjacent curved channels basal erosion surfaces become deeper towards cut banks of curved channels these structures can be explained by lateral and downstream growth of bars combined with vertical accretion convex upwards forms up to 0 5 m high several metres across and tens of metres long represent episodic accretion of unit bars scroll bars and bar heads stratal patterns in channel fills record a complicated history of erosion and deposition during filling including migration of relatively small bars a revised facies model for this type of sandy braided river has been constructed based on this new information on large scale bedding structure

depositional and erosional architectures of gravelly braid bar formed by a flood in the abe river central japan inferred from a three dimensional ground penetrating radar analysis abstract we conducted a ground penetrating radar gpr survey of gravelly braid bars in the abe river central japan to clarify the three dimensional 3d variations in their depositional facies under various geomorphologic conditions in september 2011 a ten year return period flood in the study area reworked and deposited braid bars after the flood we surveyed three bars with different geomorphologies using a gpr system with a 250 mhz antenna and identified seven fundamental radar depositional facies inclined reflections facies ia and ib horizontal to subhorizontal reflections facies iia and iib discontinuous reflections facies iiia and iiib and facies assemblage with a large scale channel shaped lower boundary facies iv combinations of these facies in dicate bar formation processes channel filling lateral aggradation and lateral and downstream accretion in the abe river aerial photographs and airborne laser scanning data were obtained before and after the flood the observed changes of the surface topography are consistent with the subsurface results seen in the gpr sections this study demonstrated that the erosional and depositional architecture observed among bars with different channel styles was related to river width and represented depositional processes for high sediment discharge the quantitative characterizations of the sedimentary architecture will be useful for interpreting gravelly fluvial deposits in the rock record

ground penetrating radar images of selected fluvial deposits in the netherlands ground penetrating radar gpr surveys have been carried out in order to characterise reflection patterns and to assess the method s potential for imaging palaeofluvial sediments in the mass rhine former confluence area in the southern netherlands the results show that the deposits of meandering braided and transitional river types produce characteristic radar facies representative examples of each of these river types were selected where the gpr data could be directly correlated with sedimentary information derived from exposures and detailed drilling and geomorphological data could be supplied individual channels may be distinguished by the radar facies of their fills the floodplains of the different river types also show a characteristic radar facies in gpr data from the meander floodplain parallel dipping reflections represent point bar structures while irregular intersecting small channel patterns that alternate with parallel continuous reflections are more typical in the braid plain a transitional river type shows characteristics of both of these types typical examples of gpr sections recorded in each of the different fluvial palaeoenvironments are presented in an interpretative radar facies chart

geomorphic criteria for distinguishing and locating abandoned channels from upstream part of mun river khorat plateau northeastern thailand in order to develop geomorphic criteria for distinguishing and locating abandoned channels and meandered belts in this paper we examined geomorphologic characteristics from the mun river one of the main rivers in the khorat plateau northeastern thailand upstream of mun river originated at southwestern rim of the khorat plateau where the river now cuts through sandstone basement meandering process shaped meander from upstream ending at low lying plain about 30 km downstream from the mun bon dam reservoir and this process displays given values of geomorphic parameters including sinuosity index si channel width w and radius of curvature rc sinuosity index was calculated to express the sinuosity of the channel the relationship between w and rc helps to predict channel stability and also comprehend the possibility of cutoff process as a result paleo and recent flow directions of the mun river are similar from southwest to northeast geomorphic parameters from eight river reaches have changed through time since 1974 2015 two abandoned channel belts were identified and they own an average channel width of 35 and 16 m whereas the mun river nowadays is of 12 7 m si values of two abandoned channel belts are categorized as meandering river system relationship between meander migration rate and bend curvature suggests that the mun river possesses low erosion rate between 0 71 and 2 64 m year since 1974 to the present this rank of rc w ratio suggests stable state of river bank migration different migration indicates discontinuous meandering process from individual belt lateral migration rate was also decreased after mun bon dam was constructed upstream

10 000 years of explosive eruptions of merapi volcano central java archaeological and modern implications abstract stratigraphy and radiocarbon dating of pyroclastic deposits at merapi volcano central java reveals 10 000 years of explosive eruptions highlights include 1 construction of an old merapi stratovolcano to the height of the present cone or slightly higher our oldest age for an explosive eruption is 9630 60 14 c y b p construction of old merapi certainly began earlier 2 collapse s of old merapi that left a somma rim high on its eastern slope and sent one or more debris avalanche s down its southern and western flanks impoundment of kali progo to form an early lake borobudur at 3400 14 c y b p hints at a possible early collapse of merapi the latest somma forming collapse occurred 1900 14 c y b p the current cone new merapi began to grow soon thereafter 3 several large and many small buddhist and hindu temples were constructed in central java between 732 and 900 a d roughly 1400 1000 14 c y b p explosive merapi eruptions occurred before during and after temple construction some temples were destroyed and or buried soon after their construction and we suspect that this destruction contributed to an abrupt shift of power and organized society to east java in 928 a d other temples sites though were occupied by caretakers for several centuries longer 4 a partial collapse of new merapi occurred 14 c y b p eruptions 700 800 14 c y b p 12 14th century a d deposited ash on the floors of still occupied candi sambisari and candi kedulan we speculate but cannot prove that these eruptions were triggered by the same partial collapse of new merapi and that the eruptions in turn ended caretaker occupation at candi sambisari and candi kedulan a new or raised lake borobudur also existed during part or all of the 12 14th centuries probably impounded by deposits from merapi 5 relatively benign lava dome extrusion and dome collapse pyroclastic flows have dominated activity of the 20th century but explosive eruptions much larger than any of this century have occurred many times during merapi s history most recently during the 19th century are the relatively small eruptions of the 20th century a new style of open vent less hazardous activity that will persist for the foreseeable future or alternatively are they merely low level background activity that could be interrupted upon relatively short notice by much larger explosive eruptions the geologic record suggests the latter which would place several hundred thousand people at risk we know of no reliable method to forecast when an explosive eruption will interrupt the present interval of low level activity this conclusion has important implications for hazard evaluation

towards more realistic values of elastic moduli for volcano modelling abstract the accuracy of elastic analytical solutions and numerical models widely used in volcanology to interpret surface ground deformation depends heavily on the young s modulus chosen to represent the medium the paucity of laboratory studies that provide young s moduli for volcanic rocks and studies that tackle the topic of upscaling these values to the relevant lengthscale has left volcano modellers ill equipped to select appropriate young s moduli for their models here we present a wealth of laboratory data and suggest tools widely used in geotechnics but adapted here to better suit volcanic rocks to upscale these values to the scale of a volcanic rock mass we provide the means to estimate upscaled values of young s modulus poisson s ratio shear modulus and bulk modulus for a volcanic rock mass that can be improved with laboratory measurements and or structural assessments of the studied area but do not rely on them in the absence of information we estimate upscaled values of young s modulus poisson s ratio shear modulus and bulk modulus for volcanic rock with an average porosity and an average fracture density quality to be 5 4 gpa 0 3 2 1 gpa and 4 5 gpa respectively the proposed young s modulus for a typical volcanic rock mass of 5 4 gpa is much lower than the values typically used in volcano modelling we also offer two methods to estimate depth dependent rock mass young s moduli and provide two examples using published data from boreholes within k lauea volcano usa and mt unzen japan to demonstrate how to apply our approach to real datasets it is our hope that the data and analysis presented herein will assist in the selection of elastic moduli for volcano modelling to this end we provide a microsoft excel spreadsheet containing the data and necessary equations to calculate rock mass elastic moduli that can be updated when new data become available the selection of the most appropriate elastic moduli will provide the most accurate model predictions and therefore the most reliable information regarding the unrest of a particular volcano or volcanic terrain

morphological and structural changes at the merapi lava dome monitored in 2012 15 using unmanned aerial vehicles uavs abstract dome building volcanoes undergo rapid and profound topographic changes that are important to quantify for the purposes of hazard assessment however as hazardous lava domes often develop on high altitude volcanoes that exhibit steep sided topography it is challenging to obtain direct field access and thus to analyze these morphological and structural changes merapi volcano in indonesia is a type example of such a volcano as soon after its 2010 eruption a new lava dome developed this dome was partially destroyed during six distinct steam driven explosions that occurred between 2012 and 2014 here we investigate the topographic and structural changes associated with these six steam driven explosions by comparing close range photogrammetric data obtained before and after these explosions to accomplish this we performed two uav campaigns in 2012 and 2015 by applying the structure from motion sfm technique we are able to construct three dimensional point clouds assess their quality by comparing them to a terrestrial laser scanning tls dataset and generate high resolution digital elevation models dems and photomosaics the comparison of these two dems and photomosaics reveals changes in topography and the appearance of fractures in the 2012 dataset we find a dense fracture network striking to the nnw sse in the post eruptive 2015 dataset we see that this nnw sse fracture trend is much more strongly expressed we also detect the formation of aligned and elongated explosion craters which are associated with the removal of over 200 000 m3 of dome material most of which 70 was deposited outside the crater region therefore this study suggests that the locations of the steam driven explosions at merapi volcano were controlled by the reactivation of preexisting structures moreover some of the newly developed and reactivated fractures delineate a block on the southern slope of the dome which could become structurally unstable and potentially lead to rock avalanche hazards this study therefore demonstrates the significance of characterizing structural fingerprints during the development of lava domes and exemplifies the value of topographic and fracture mapping which is becoming increasingly feasible when using uavs even on high and steep stratovolcanoes

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

dynamic velocity and seismic characteristics of gravitational rockfalls at the merapi lava dome abstract gravitational instability of discrete lava lobes in an active dome building volcano may generate rockfalls that travel up to hundreds of meters from the summit understanding the behaviour of rockfalls is important for volcanic hazard assessment as rockfalls can precede large dome collapses that generate pyroclastic flows here we investigate the mechanisms trajectory velocity and seismic characteristic of rockfalls at the merapi volcano through high resolution video and seismic spectrum frequency analysis high resolution videos of rockfall events were converted to images for every second and were scaled with a georeferenced 3d point cloud to convert pixels into scaled units on the order of a meter the scaled images were analysed using pixel tracking to investigate the mechanism trajectory and velocity of rockfalls results illustrate that the rockfall mechanisms include gravitational free fall rolling and bouncing airborne rotation and rolling over high friction basal surfaces the dynamic mechanisms of gravitational rockfalls at merapi are strongly controlled by the topography and the condition of the basal surface which is responsible for the continuous fluctuations in rockfall velocity maximum rockfall velocity occurs when rocks become airborne while rotating over the steepest area with velocity up to 90 m s material rolling over gently sloping high friction basal surfaces can significantly reduce the rockfall velocity to 2 m s which then ceases the rock movement our high resolution video documents the relatively short durations of gravitational rockfall events at merapi in the range of 24 61 s and has different time duration with the short period seismic signals as the movement of small rock fragments over sandy area is not detected by seismic signal spectral analysis of seismic frequencies indicates that gravitational rockfalls at merapi are characterized by high frequencies with a range of 4 17 hz this study provides new insights and improves our understanding of the dynamic mechanism of rockfall events at dome building volcanoes

scattering behaviour at merapi volcano java revealed from an active seismic experiment summary the seismic structure of the stratovolcano merapi java indonesia was studied using an active seismic experiment three 3 km long seismic profiles each consisting of up to 30 three component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level the detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting the seismic experiment at merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome where the sources of most of the natural volcanic seismic events are located the cone of merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material additionally the topography of the erosion valleys leads to an irregular deposition which cannot be described by a simple 1 d layering these inhomogeneities have a strong influence on seismic signals the direct p and s waves are attenuated quickly and show only small amplitudes on seismograms the energy lost from the direct waves however is not changed into heat but scattered and can be observed as seismic coda following the direct waves the observed seismograms show a spindle like amplitude increase after the direct p phase this shape of the envelope can be explained by the diffusion model according to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves besides the envelope the coherence and polarization properties of the wavefield also indicate strong scattering only the first onset shows coherence over a station spacing of 100 m whereas the late phases carrying the major part of the energy are mainly incoherent the horizontal components of the seismograms have larger amplitudes than the vertical component but within the horizontal plane the polarization is almost arbitrary corresponding to waves arriving from scatterers located arbitrarily in space as a result of the inversion using the diffusion model we obtain values of the s wave scattering attenuation coefficient gs and the s wave intrinsic absorption coefficient gi in the frequency range of 4 20 hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption gs gi the mean free path of s waves is as low as 100 m gs1 100 m the scattering coefficient is independent of frequency gsyf 0 0 whereas the coefficient of intrinsic attenuation increases with increasing frequency giyf 1 6 the natural seismic signals at merapi volcano show similar characteristics to the artificial shots the first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves therefore these signals appear to be strongly affected by multiple scattering also

fluid ascent and magma storage beneath gunung merapi revealed by multi scale seismic imaging abstract magma is fed to a volcano through a complex plumbing system that involves not only shallow structures beneath the volcano edifice but also deep structures and processes within the underlying crust and upper mantle this paper summarizes seismic experiments carried out over many years at gunung merapi in central java these have resolved the 3d seismic velocity structure of the merapi edifice and provided a 3d structural image of the lithosphere and subduction zone beneath central java earthquake locations reveal that with distance from the trench the dip of the subducting slab steepens from nearly horizontal 0 150 km through 45 150 250 km to 70 250 km the slab appears as a 30 km thick double layer of seismicity in a depth range of 80 km to 150 km and it can be identified seismically to a depth of more than 600 km the active volcanoes of merapi sumbing and lawu are located at the edge of a large low velocity body that extends from the upper crust to the upper mantle beneath central java shear wave signals recorded above this anomaly are strongly attenuated compared to neighboring areas the anomalous body has a detected volume of 50 000 km3 and a decrease in p and s velocities relative to adjacent regions of up to 30 the resulting vp vs ratio of up to 1 9 is unusually high for lower crust additionally the anomaly extends along a 45 degree slope downward from beneath the volcanic arc and meets the slab at 100 km depth we interpret this sloping anomaly as a pathway for fluids and partial melts increased seismicity is observed at depths of 100 km possibly as a result of dehydration of the subducting slab with related fluid releases causing partial melting of overlying mantle material the large velocity reduction and high vp vs ratio in the region are consistent with an increase in temperature a reduction of shear strength and the presence of fluids or melts of 13 to 25 vol the detected strong anomaly beneath central java is unique in size and amplitude compared to other subduction zones the geophysical evidence suggests that this segment of the arc has a high magma flux and is thus capable of developing even larger shallow crustal reservoirs and more voluminous explosive eruptions in the future

sar and gravity change based characterization of the distribution pattern of pyroclastic flow deposits at mt merapi during the past 10 years mt merapi indonesia is one of the most active and dangerous volcanoes in the torrid zone this volcano has erupted frequently and has produced pyroclastic flows following the collapse of the summit lava dome we used synthetic aperture radar sar data acquired by jers 1 and radarsat 1 satellites from april 1996 to july 2006 to clarify the distribution patterns of the pyroclastic flow deposits the extent of the deposits termed p zones was accurately extracted by ratio operation and low level feature extraction from sar intensity images these images highlighted temporal changes of the distribution area perimeter flow distance included angle and collapse direction to validate the image processing results reflectance spectra of the rock samples collected after the eruption in june 2006 were measured in a laboratory the reflectance spectra of all samples showed similar characteristics to the reference spectra which were derived from atmospheric correction of hyperion sensor image data covering the lava dome at the summit therefore p zones were confirmed to be the pyroclastic flow deposits originating from destruction of the lava dome at the summit the image processing results clarified that the extent of the distribution areas perimeter flow distances and included angle of the p zones were variable among the eruptions while the collapse direction had a constant pattern the collapse pattern followed a clockwise change from the south toward the west by comparing the ratio maps of bouguer gravity anomaly data in two periods the change was interpreted to originate from the inclination of the conduit and the formation of shallow and deep magma reservoirs

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

volcano tectonic control of merapi s lava dome splitting the november 2013 fracture observed from high resolution terrasar x data abstract volcanism at active andesite dacite volcanoes is often associated with the formation and collapse of circular shaped protrusions of extruded highly viscous lava the so called domes which are emplaced in the near summit region growing domes may experience stable and instable structural phases with a gradual transition in between dome collapse and the break off of instable blocks of viscous lava may lead to pyroclastic flows one of the most lethal hazards at stratovolcanoes at merapi volcano indonesia a new dome started growing in the summit region in the amphitheater formed in the course of the climactic 2010 eruption three years later the dome reached a height of approximately 100 m and diameters of 220 and 190 m with a plateau like surface area of 40 000 m2 approximately on 18 11 2013 an explosion occurred without identified precursors leaving a major fracture cutting the complete dome structure based on high resolution terrasar x satellite radar imagery we could identify the linear fracture traceable over 200 m in the long axis up to 40 m wide after geocoding of the radar amplitude imagery the fractures azimuthal trend could be compared to other structural lineaments indicative of a significant nnw sse structural direction that has formed on merapi volcano in the past the merapi dome fractured in a nw se direction and is consistent with the alignment of regional tectonic structures and of anticipated directions of pyroclastic flows the fracture may be part of a larger volcano tectonic system and may affect the dynamics and the stability of the merapi dome

constraints on magma flux from displacements data at merapi volcano java indonesia the displacement field has been monitored in the vicinity of the crater rim at mount merapi indonesia from 1993 to 1997 during this period the volcanic activity has been quasicontinuous with dome growth explosions and pyroclastic flows we measured a nine point network every year with the global positioning system static method interpretation of results is conducted with a three dimensional elastostatic boundary elements code that takes into account topography fractures and complex magma source geometry the inversion technique yields an estimate of the variation with time of the boundary conditions at the magma duct interface together with the probability associated with the best model the young s modulus of the equivalent continuum is found to be very low of the order of 1 gpa a feature which suggests that a viscoelastic behavior may be more appropriate for this rock mass given the observed seismic velocities for the domain of interest a striking compatibility is outlined between observed deformations and the rate of occurrence of multiphase seismic events once the main fractures of the structure have been taken into consideration this suggests that the summit elastic or viscoelastic deformation field is controlled by the magma flux within the duct rather than by magma pressure variations in addition a nonelastic displacement has been identified at the westernmost point of the network this was considered critical for the stability of the summit structure a concern whose validity has been verified a posteriori by the july 1998 explosion

textural and micro petrological variations in the eruptive products of the 2006 dome forming eruption of merapi volcano indonesia implications for sub surface processes the interplay between magma ascent degassing and changing magmatic properties are widely recognized as critical factors controlling the style of silicic volcanic eruptions microlite textures in samples from the prolonged dome forming eruption of merapi in 2006 provide a record of changing magmatic ascent conditions and shallow conduit processes throughout the eruption analysis of microlite textural parameters including measurements of areal number density na mean microlite size crystal aspect ratio and groundmass crystallinity combined with the monitoring record and field observations indicate that magma ascent paths change between continuous ascent at varying rates from a deeper magma storage region to ascent being temporarily stalled at shallow depths in the latter stages of the eruption supporting the idea of an ephemeral shallow magma storage region at merapi plagioclase microlite compositions show evidence of decompression induced degassing often displaying rims of anorthoclase and more k rich alkali feldspar sanidine anorthite contents also support the textural data of later erupted magma being temporarily stalled at shallow depths crystal size distributions csds are interpreted to show that both growth dominated and nucleation dominated crystallisation regimes existed during the 2006 eruption resulting from changing conditions of undercooling t during variable magma ascent paths by contrast microlite textural analysis and feldspar microlite compositions of samples from the fast growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5 november indicate faster ascent rates a crystallisation regime more strongly dominated by nucleation due to high t and interaction of the 2010 magma with more hotter magma from depth

electromagnetic evidence for an ancient avalanche caldera rim on the south flank of mount merapi indonesia abstract long offset transient electromagnetic lotem data and vibrotem data from the south flank of mount merapi on java island indonesia are interpreted with one dimensional 1d inversions as well as two dimensional 2d forward modelling one dimensional joint inversions of several components of the electromagnetic field with occam s method reduce the number of equivalent models which were derived from inversions of single components and fit the data to a similar misfit the 1d results together with results from other geophysical measurements serve as the basic model for further 2d forward modelling the final model depicts a layering that follows the topography of the strato volcano in the depth range of 500 m to 1000 m the resistivity of the layers decreases rapidly downwards into a good conductor with resistivities below 10 m the deepest layer has a resistivity of 0 4 m which is quantitatively explained with a combination of saline fluids and hydrothermally altered minerals furthermore the final model supports a hypothesis from the interpretation of central loop tem transient electromagnetic data that there is a fault structure below the southern flank approximately 7 3 km south of the summit to the north of the fault the top of the good conductor is lowered from a depth of 500 m to 1000 m we propose that the fault structure coincides with an ancient avalanche caldera rim

constraints from phase equilibrium experiments on pre eruptive storage conditions in mixed magma systems a case study on crystal rich basaltic andesites from mount merapi indonesia mount merapi is one of indonesia s and the world s most hazardous volcanoes existing constraints on the location and the crystallization conditions of its pre eruptive magma reservoir based on mineral and glass thermobarometry and geophysical surveys are inconclusive yet of immediate importance for future hazard mitigation here we use two series of phase equilibrium experiments to quantify the conditions of pre eruptive magma storage and magma recharge in merapi s upper crustal reservoir 1 to characterize crystallization at total equilibrium conditions 2 to characterize crystallization at local equilibrium conditions between crystal rims and host melt we demonstrate that this experimental approach can constrain pre eruptive crystallization conditions and their variation in crystal rich mixed magma systems such as that of merapi for which standard crystallization experiments and mineral thermobarometry fail in agreement with geophysical estimates we infer that mount merapi s pre eruptive reservoir partially crystallizes at 100 200 75 mpa and thus at relatively shallow depths of c 4 5 to 9 km magmas are stored at 925 950 25 c with a melt h2o content of 3 4 wt and a vapour phase with an xh2o h2o h2o co2 of 0 5 0 6 0 1 pre eruptive recharge magmas in contrast have a temperature 950 to 1000 c a higher melt h2o content of 4 5 wt and a vapour phase with a higher xh2o of 0 8 0 1 we hypothesize that these variations in melt h2o content and vapour xh2o between resident and pre eruptive recharge magmas relate to variable degrees of open system degassing of magma parcels en route into the reservoir rather than to variations in volatile fluxing of the stored magmas

an overview of the seismicity of merapi volcano java indonesia 1983 1994 abstract from 1982 to 1995 merapi volcano java indonesia experienced two main eruptive cycles from 1984 to 1986 and from 1992 to 1994 each cycle had a duration slightly larger than 2 years four major eruptive events occurred in 1984 1986 1992 and 1994 these eruptions were monitored by a telemetered seismic network we present an overview of the seismicity observed between 1983 and 1995 from seismological observations several types of characteristic events are recognised volcanotectonic earthquakes are standard microearthquakes either shallow an aseismic zone is situated between two seismic zones at a depth between 1 5 and 2 5 km below the summit we postulate that it is a small shallow magma reservoir where magma injected from below can be stored temporarily we try to relate seismic observations during both eruptive cycles to the initial injection of deep magma to the superficial magma system the first eruption in each case seems to involve magma enriched in gas that extrudes the content of the conduit and explodes the old dome a regular outflow of magma follows the initial explosion and gradually a dome is building up then it stops and a period of repose is observed later a second episode of dome growth occurs the height of the dome reaches a maximum corresponding to a state of lithostatic equilibrium the time delay of more than 2 years between the beginning and the end of a cycle may result from crystallisation in a volatile rich magma and from the building up of pressure in the superficial magma pocket some important events like the collapse of the dome on 22 november 1994 are not preceded by any seismic precursor when it reaches a large volume the dome is not stable and is likely to collapse by gravity for instance after the sudden influx of matter or gas or after a heavy rain on merapi tremors are observed but do not always precede a dangerous event

merapi central java indonesia an outline of the structural and magmatological evolution with a special emphasis to the major pyroclastic events abstract merapi volcano in the central part of java is regarded as the most active and most dangerous volcano in indonesia on the basis of field studies and geochronological data its history is divided into four periods ancient middle recent and modern merapi according to our preliminary age data the ancient period may have begun around 40 000 y bp and lasted until 14 000 y bp when the middle period begun the recent period begun around 2200 y bp and was replaced by the modern period after the eruption of 1786 during the middle merapi stage a mount st helens type edifice collapse occurred our data suggest that his event is younger than 6700 y bp and older than 2200 y bp during the recent merapi stage violent magmatic to phreatomagmatic eruptions twice interrupted the growth of the volcano the older gumuk phreatoplinian deposits cover the entire cone charcoal found within these deposits gave 14c ages of 2200 and 1470 y bp the overlying sambisari ash deposits were emplaced by violent pyroclastic surges directed towards the south i e to the present location of the town of yogyakarta they buried the shivaitic temple of sambisari at the start of the 15th century modern merapi is characterised by the persistent growth of a summit dome periodically interrupted by partial or total collapse of the dome to generate frequent merapi type nuees ardentes blocks and ash flows and associated surges or more exceptionally fall back st vincent type nuees ardentes scoria flows in contrast previous stages were characterised by effusion of long lava flows alternating with violent explosive phases generating essentially st vincent type nuees ardentes merapi lavas are calc alkaline with a compositional range between 49 5 and 60 5 wt sio2 moreover high k basaltic andesites represent about 90 of merapi lavas disequilibrium features are common in the mineralogical assemblage plagioclase orthopyroxene clinopyroxene olivine amphibole titanomagnetite scarce alkali feldspar macroscopic and microscopic textural heterogeneities are related to magma mixing that may have buffered the compositions of lavas and caused the restricted range of compositions our studies of past activity at merapi provide some insights into future activity and to related volcanic hazards it is clear that merapi has the potential of eruptions much more powerful than observed during the historic period

gravimetric determination of an intrusive complex under the island of faial azores some methodological improvements summary we present some improvements of a gravity inversion method to determine the geometry of the anomalous bodies for priori density contrasts the 3 d method is based on an exploratory process applied not for the global model but for the steps of a growth approach the positive and or negative anomalous structure is described by successive aggregation of cells while its corresponding gravity field remains nearly proportional to the observed one moreover a simple e g linear regional trend can be simultaneously adjusted the corresponding program is applied to new gravity data on the volcanic island of faial azores archipelago the inversion approach shows a subsurface anomalous structure for the island the main feature being an elongated high density body the body is interpreted as a compact sheeted dyke swarm emplaced along faial pico fracture zone a leaky transform structure that forms the current boundary between eurasian and african plates in the azores area the new results in this paper are 1 a bouguer gravity anomaly map 2 several improvements in the inversion process robust process optimal balance fitness model magnitude 3 a new gravimetric method for estimating the mean terrain density 4 a 3 d model for subsurface mass anomalies in faial and 5 some interpretative conclusions about a main intrusive complex detected under the island as a wall like structure extending from a depth of 0 5 to 6 km b s l with a n100 e trend

modeling the density at merapi volcano area indonesia via the inverse gravimetric problem 1 merapi is a high risk andesitic volcano in central java indonesia very little information is known about the detailed regional density structure around merapi and its neighbor volcano merbabu we compute a subsurface three dimensional 3 d model of anomalous density for the volcanoes merapi and merbabu in central java indonesia by inversion of the gravity field as input for the inversion methodology gravity observations from 443 points whose 3 d coordinates are determined by gps are used the inversion algorithm is based on an explorative approach to fit a least squares condition including a balancing factor between the minimization of the residuals and the anomalous mass a mean density about 2242 kg m3 for the region of merapi and merbabu has been computed by least squares adjustment results of the inversion show major low density contrasts up to 242 kg m3 and positive structures about 264 kg m3 referred to the determined mean density a density anomaly relative high with densities up to 264 kg m3 is connecting the volcanoes in a 152 course from nw to se and might be built of older basaltic lava low density contrasts about 242 kg m could be found in agreement with magnetotelluric and electromagnetic results generally the identified high and low density bodies are in agreement with the results of other geophysical methods such as electromagnetic and magnetotelluric prospecting or geological formations and structures a porosity about 21 is derived for the largest negative density bodies about 242 kg m3 furthermore the density model gives some new information about the controversial origin of a hill formation near merapi and is also used to discuss the possible existence of a shallow magma chamber which is also a controversial subject generally the density model serves as basic information for the interpretation of geodetic and geophysical observations and confirms existing results from magnetotellurics electromagnetics and seismic data interpretation

the role of excess co2 in the formation of trona deposits abstract the prevailing theory for the formation of trona na3 co3 hco3 2 h2o relies on evaporative concentration of na hco 3 water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments given the abundance of closed drainage basins dominated by volcanics it is puzzling that there are so few trona deposits and present day lakes that would yield dominantly na co3 minerals upon evaporation groundwater in the san bernardino basin southeastern arizona usa and northeastern sonora mexico would yield mainly na co3 minerals upon evaporation but waters in the surrounding basins would not analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology but the injection of magmatic co2 many major deposits of trona and na co3 type lakes appear to have had excess co2 input either from magmatic sources or from the decay of organic matter it is proposed that along with the presence of volcanics addition of excess co2 is an important pre condition for the formation of trona deposits

an experiment of muon radiography at mt etna italy interactions of conduit geometry with gas liquid flows control volcanic activity implying that the evaluation of volcanic hazards requires quantitative understanding of the inner structure of the volcano the more established geophysical imaging techniques suffer from inherent ambiguity may require spatially dense measurements in active areas and may not provide sufficient spatial resolution in the uppermost part of the conduit system it is thus desirable to develop new imaging techniques allowing a better spatial resolution of a volcano s upper feeding system with reduced ambiguity and a low level of risk for operators muon particles can be utilized to image the internal density distribution of volcanic structures the principle of muon radiography is essentially the same as x ray radiography except for substituting penetrating particles in place of photons muons are more attenuated by higher density parts inside the target and thus information about its inner structure are obtained from the differential muon absorption we report on a muon imaging experiment that was conducted at mt etna in 2010 the target structure was one of the summit craters of the volcano this experiment was performed using a muon telescope suitably designed to withstand the harsh conditions in the summit zone of a high volcano we found a marked difference between synthetic and observed attenuation of muons through the target this discrepancy is likely due to the bias on the observed flux arising from false muon tracks they are caused by low energy particles that by chance hit simultaneously the two matrixes of the telescope leading to detection of a false positive we separated the useful from the unwanted signal through a first order model of the background noise the resulting signal is compared with the corresponding synthetic flux eventually we found regions of higher and lower than expected muon flux that are possibly related to inner features of the target crater

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

permeability and porosity images based on p wave surface seismic data application to a south florida aquifer 1 p wave surface seismic reflection data acquired from a carbonate aquifer in southeastern florida are used to delineate flow units in a proposed aquifer storage and recovery asr horizon the impedance image determined by inversion from p wave reflection data captures most of the boundaries between hydraulic facies the hydraulic facies properties are based on integration of the well logs and the lithology which consists of vuggy carbonate units and sandstones within the proposed asr horizon located in the upper floridan aquifer low permeability zones consist of sandstones and highly permeable zones are carbonates with interconnected vuggy porosity high resolution porosity permeability and impedance images based on cross well reflection and well logs help us evaluate the p wave seismic reflection results we use well logs and cross well seismic data to support whether two dimensional seismic reflection measurements detect important flow units delineated by cross well high resolution seismic data the data analysis demonstrates that major flow units are resolved and imaged with two dimensional seismic reflection techniques although not as clearly as in the high resolution cross well data the results suggest that the surface seismic reflection method integrated with well logs and geology provides the tools to assess water resources in this south florida carbonate aquifer however we recommend conducting a cross well survey in areas where an understanding of the petrophysics is imperative to relating the seismic attributes to rock and fluid properties this can be a critical step for planning purposes when considering a large surface oriented seismic survey

quaternary meandering evolution and architecture of a point bar in the mun river on the sandstone dominated khorat plateau from northeastern thailand abstract the mun river the main right bank tributary of the mekong river meanders and flows eastwards across the flat and sand dominated low lying plain of the khorat plateau northeastern thailand the mun river expresses its evolution with a spectacular trace of its meander landforms on the floodplain surface this paper reveals for the first time the three dimensional shallow subsurface sedimentary architecture inside a part of a sandy point bar deposit of the mun river based on ground penetrating radar gpr in comparison with outcrop observation from a road cut along the gpr line survey as a result we recognized subsurface scroll bars where the expansion rotation and transformation types corresponded well with the sedimentary structures exposed on the road cut dominant gpr radar facies included hummocky wavy group of fitful waves shingled curved down pattern 15 45 degree of reflection angle sigmoid sets of en echelon or sigmoid concaved upward and isolated trough shape parallel horizontally continuous layers and parabolic facies these gpr facies possibly inferred the sedimentary structures of trough cross bedded channel fills side bar deposit erosion surface of channel or chute cut off secondary channel scours and fills horizontal sand bedded and sheet flood sand both gpr facies and lithofacies revealed the meandering evolution of a bar parallel and bar transverse mid channel bar with small braided channels on the bar top and showed the lateral migration of the point bar

p and s velocity structure of the crust and the upper mantle beneath central java from local tomography inversion here we present the results of local source tomographic inversion beneath central java the data set was collected by a temporary seismic network more than 100 stations were operated for almost half a year about 13 000 p and s arrival times from 292 events were used to obtain three dimensional 3 d vp vs and vp vs models of the crust and the mantle wedge beneath central java source location and determination of the 3 d velocity models were performed simultaneously based on a new iterative tomographic algorithm lotos 06 final event locations clearly image the shape of the subduction zone beneath central java the dipping angle of the slab increases gradually from almost horizontal to about 70 a double seismic zone is observed in the slab between 80 and 150 km depth the most striking feature of the resulting p and s models is a pronounced low velocity anomaly in the crust just north of the volcanic arc merapi lawu anomaly mla an algorithm for estimation of the amplitude value which is presented in the paper shows that the difference between the fore arc and mla velocities at a depth of 10 km reaches 30 and 36 in p and s models respectively the value of the vp vs ratio inside the mla is more than 1 9 this shows a probable high content of fluids and partial melts within the crust in the upper mantle we observe an inclined low velocity anomaly which links the cluster of seismicity at 100 km depth with mla this anomaly might reflect ascending paths of fluids released from the slab the reliability of all these patterns was tested thoroughly

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use