continuous h2o co2 222rn and temperature measurements on merapi volcano indonesia abstract a set of analytical instruments consisting of a gas chromatograph for water and carbon dioxide an alpha scintillation counter to measure radon and a temperature sensor was especially designed and constructed to monitor volcanic gases and was successfully operated over weeks in the high temperature fumaroles at the summit of merapi volcano indonesia the analytical unit runs automatically and is remote controlled through a radio link over a period of several weeks concentrations of h 2 o and co 2 were measured every 35 min and rn activity was monitored at about 90 min intervals the fumarole temperatures were continuously recorded every minute from july 2000 to the end of january 2001 the composition and temperature of the gas emitted at merapi volcano show significant variations due to a regular stronger degassing of the magma concentrations of co 2 increase periodically while h 2 o concentrations decrease on the other hand rn activity rises with increasing atmospheric pressure and higher water concentrations after intensive rainfall infiltration of cold meteoric water into the volcanic edifice possibly causes an increase in the concentration of water vapour and a decrease in the temperature of the gases in the fumarole several seismic events recorded at merapi correlate with gas temperature

structure and isostatic compensation of the comorin ridge north central indian ocean summary bathymetry gravity and magnetic data about 9200 lkm of the comorin ridge north central indian ocean were investigated using the transfer function and forward model techniques to understand the mode of isostatic compensation and origin of the ridge the ridge extends for about 500 km in nnw sse direction and associates with low amplitude gravity anomalies ranging from 25 to 30 mgal compared to the ridge relief suggesting that the anomalies are compensated at deeper depths from admittance analysis an airy model or local compensation with an elastic plate thickness t e of about 3 km and crust thickness t of 15 20 km are suggested for the southern part of the comorin ridge south of 5 n whereas for the northern part a flexural plate model with an elastic thickness of about 15 km is obtained admittance analysis together with the results from gravity forward modelling reveal that the south part was emplaced on relatively weak oceanic crust with both surface and subsurface loading while the north part was emplaced on the continental crust based on present studies and published plate kinematic models we interpret that the comorin ridge was evolved at about 90 ma during the rift stage of madagascar from the southwest of india we have also demarcated the continent ocean boundary cob west of sri lanka and southern tip of india which runs across the strike of the ridge placing the northern part of the ridge on continent and southern part on oceanic crust on the southern part of the ridge eastern flank is steep faulted up to 0 6 km and is controlled by the 79 e fz and then by cob

oligocene to present kilometres scale subsidence and exhumation of the ligurian alps and the tertiary piedmont basin nw italy revealed by apatite u th he thermochronology correlation with regional tectonics the ligurian alps segment of the alpine apennine orogen in nw italy is unconformably covered by upper eocene to holocene sediments in the tertiary piedmont basin tpb and po plain these sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin apatite u th he and fission track thermochronology shows that the orogen first subsided and was buried at 4 km from 30 to 26 ma and began its exhumation thereafter from 26 ma to present this upward movement was contemporaneous with subsidence in the northern tpb the couple exhumation in the s and subsidence in the n migrated northwards through time vertical movements in the area are similar to those reconstructed in corsica in both cases the onset of exhumation b

crustal structure and tectonics of the ninetyeast ridge from seismic and gravity studies seismic reflection and refraction gravity and bathymetric data across and along the central part of the ninetyeast ridge were analyzed to determine the crustal structure of the ridge and to understand its tectonics the ridge in the study area rises to 3 5 km above the seafloor of adjacent ocean basins basement is covered by sediments up to 0 8 km thick but exposed at some locations seismic refraction and gravity models of the ridge show that the crustal thickness is 22 km greater than the average thickness 7 km of oceanic crust estimated in the central indian and wharton basins the ridge is compensated by flexure of layers 2a 2b and 3a to the extent of 2 km and by a 12 km thick deep crustal body layer 3b of underplated material upper crustal velocities layer 2a beneath the ridge are lower up to 3 4 km s 1 than in adjacent basins because of weathering process and hydrothermal circulation of the waters in the tectonized blocks while velocities in deep crustal body layer 3b are higher up to 7 8 km s 1 and seem to be resulted from magmatic rocks accreted within the lithosphere steep down ward faulting of 2 km along the eastern flank of the ninetyeast ridge possibly originated because of compressional and extensional stresses applied along the 89 e fracture zone fz the stresses are interpreted as resulting from multiple ridge jumps of wharton spreading centers during the late cretaceous and middle eocene the velocity depth model suggests that the rocks of layers 2a and 2b and layer 3a are exposed on the eastern flank of the ninetyeast ridge and 90 e fz respectively they are consistent with basalt dolerite and gabbro rocks collected from the fault scarps the central part of the ridge between 1 n and 11 s has uniformly deepened by 0 7 km and is bounded by major sublatitudinal deep seated fractures we interpret that the deepened structural block and associated fractures resulted from the activity of the intense deformation of the central indian ocean

the bent prolongation of the 85 e ridge south of 5 n fact or fiction abstract the enigmatic 85 e ridge crosses the bay of bengal from north to south its strong gravity anomaly low is associated with cretaceous hotspot volcanism south of 5 n the gravity low bends into a sw ne orientation and continues as far sw as the afanasy nikitin seamounts this change has been interpreted to represent a bent hotspot track we report new constraints on the crustal structure and genesis beneath the sw trending gravity low based on new refraction seismic reflection seismic and shipborne gravity data our findings show that the crustal structure across the gravity low does not differ significantly from the adjacent 4 5 to 7 km thick oceanic crust no basement ridge significant crustal thickening or magmatic underplating were identified we found no evidence for a southern prolongation of the 85 e ridge instead our p wave velocity and density models reveal the gravity low to express a flexural basin which is a result of widespread mid miocene to recent lithospheric deformation in the indian ocean the 25 mgal negative gravity anomaly is therefore not related to the passage of the indian plate over a mantle plume casting doubt on the possibility that volcanism at the afanasy nikitin seamounts might be related to the same plume as the northern 85 e ridge the northern 85 e ridge may have been generated at the northern prolongation of the 86 e fracture zone

generation of pyroclastic flows and surges by hot rock avalanches from the dome of mount st helens volcano usa several hot rock avalanches have occurred during the growth of the composite dome of mount st helens washington between 1980 and 1987 one of these occurred on 9 may 1986 and produced a fan shaped avalanche deposit of juvenile dacite debris together with a more extensive pyroclastic flow deposit laterally thinning deposits and abrasion and baking of wooden and plastic objects show that a hot ash cloud surge swept beyond the limits of the pyroclastic flow plumes that rose 2 3 km above the dome and vitric ash that fell downwind of the volcano were also effects of this event but no explosion occurred all the facies observed originated from a single avalanche erosion and melting of craterfloor snow by the hot debris caused debris flows in the crater and a small flood that carried juvenile and other clasts north of the crater a second broadly similar event occured in october 1986 larger events of this nature could present a significant volcanic hazard

dynamic in stability of thwaites glacier west antarctica 1 thwaites glacier west antarctica has the potential to directly contribute 1 m to sea level and currently is losing mass and thinning rapidly here we report on regional results for the sea level response to ice sheet evolution searise experiments and investigate the impact of i spatial resolution within existing data sets ii grounding zone processes and iii till rheology on the dynamics of this outlet glacier in addition to the searise data sets we use detailed aerogeophysical and satellite data from thwaites glacier as input to a coupled ice stream ice shelf ocean plume model that includes oceanic influences across a several kilometers wide grounding zone suggested by new high resolution data our results indicate that the ice tongue provides limited stability and that while future atmospheric warming will likely add mass to the surface of the glacier strong ice stream stabilization on bedrock highs narrower than the length of the grounding zone may be ephemeral if circulating waters substantially reduce basal resistance and enhance melting beneath grounded ice within this zone however we find that stability is significantly enhanced by effectively plastic till beds accurate projections of future sea level change relies on correct understanding of the till rheology as well as local basal processes near the grounding line

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

atmospheric storm triggered and intensified by geodynamics case studies from andaman sea and bay of bengal region in the indian ocean the study analyses the possible connection between the onset of cyclone and volcano tectonic seismicity in the andaman region the historical data of the major volcanic seismic and atmospheric events from the region show that several of the geodynamic activities were followed by severe atmospheric disturbances over the region in this study we consider the case of three recent cyclones phailin hudhud and nilam that either originated or were intensified over the andaman sea and bay of bengal and examine their correlation with the volcano tectonic seismic events during the cyclone occurrence the zenith total delay ztd time series derived from global positioning system data from the pbr2 station on andaman island overlapping with the period of the cyclone occurrence were examined to distinguish the onset and intensification of the atmospheric events the comparison of the sharp changes in ztd associated with the cyclone and the seismic events during the period indicates that the atmospheric changes almost coincide or follow the geodynamic activity our study illustrates that volcano tectonics of the region plays a role in the triggering of atmospheric disturbances

geophysical signatures over and around the northern segment of the 85 e ridge mahanadi offshore eastern continental margin of india tectonic implications abstract the nature and origin of the subsurface 85 e ridge in the bay of bengal has remained enigmatic till date despite several theories proposed by earlier researchers we reinterpreted the recently acquired high quality multichannel seismic reflection data over the northern segment of the ridge that traverses through the mahanadi offshore eastern continental margin of india and mapped the ridge boundary and its northward continuity the ridge is characterized by complex topography multilayer composition intrusive bodies and discrete nature of underlying crust the ridge is associated with large amplitude negative magnetic and gravity anomalies the negative gravity response across the ridge is probably due to emplacement of relatively low density material as well as 2 3 km flexure of the moho the observed broad shelf margin basin gravity anomaly in the northern mahanadi offshore is due to the amalgamation of the 85 e ridge material with that of continental and oceanic crust the negative magnetic anomaly signature over the ridge indicates its evolution in the southern hemisphere when the earth s magnetic field was normally polarized the presence of 5 s twt thick sediments over the acoustic basement west of the ridge indicates that the underlying crust is relatively old early cretaceous age the present study indicates that the probable palaeo location of elan bank is not between the krishna godavari and mahanadi offshores but north of mahanadi further the study suggests that the northern segment of the 85 e ridge may have emplaced along a pseudo fault during the mid cretaceous due to kerguelen mantle plume activity the shallow basement east of the ridge may have formed due to the later movement of the microcontinents elan bank and southern kerguelen plateau along with the antarctica plate

wind driven internal waves and langmuir circulations in a numerical ocean model of the southern baltic sea 1 a one dimensional numerical ocean model of the southern baltic sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations the turbulence model is a k e model that includes extra source terms piw and plc of turbulent kinetic energy tke due to unresolved breaking internal waves and langmuir circulations respectively as tides are negligible in the baltic sea topographic generation of internal wave energy iwe is neglected instead the energy for deepwater mixing in the baltic sea is provided by the wind at each level the source term piw is assumed to be related to a vertically integrated pool of iwe e0 and the buoyancy frequency n at the same level according to piw z e0n z this results in vertical profiles of e the dissipation rate of tke and kh the eddy diffusivity according to e n and kh n 2 below the main pycnocline earlier observations are inconclusive as to the proper value of and here a range of values of is tested in hundreds of 10 year simulations of the southern baltic sea it is concluded that 1 0 0 3 and that a mean energy flux density to the internal wave field of about 0 9 0 3 10 3 w m 2 is needed to explain the observed salinity field in addition a simple wind dependent formulation of the energy flux to the internal wave field is tested which has some success in describing the short and long term variability of the deepwater turbulence the model suggests that 16 of the energy supplied to the surface layer by the wind is used for deepwater mixing finally it is also shown that langmuir circulations are important to include when modeling the oceanic boundary layer a simple parameterization of langmuir circulations is tuned against large eddy simulation data and verified for the baltic sea

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

crustal evolution and sedimentation history of the bay of bengal since the cretaceous multichannel seismic reflection gravity magnetic and bathymetric investigations were made along five latitudinal profiles from the eastern shelf of india to the andaman shelf and four nw se profiles in the western basin off madras seismics on three latitudinal profiles in the bay of bengal the trend of the fracture zones the locations of the magnetic chron 34 and the cretaceous magnetic quiet zone suggest that greater india separated from antarctica after a period of transform motion in the early cretaceous that is about polarity chron m0 120 ma and drifted northwestward negative gravity anomalies are associated with basement rises including the 85 e ridge between the continental margin of india and the ninetyeast ridge magnetic reversals and northward trend of the 85 e ridge support a hotspot origin of the ridge and its emplacement most likely after the cretaceous quiet period juxtaposition of high amplitude hyperbolic reflections down faulted continental blocks buried under thick sediments and associated gravity and magnetic anomalies mark the boundary between continental and oceanic rocks at the foot of continental slope about 80 km seaward of the present continental shelf edge eight seismic sequences as thick as 8 5 km overlie the early cretaceous oceanic basement and include four unconformities lower eocene upper oligocene upper miocene and upper pleistocene which have been correlated to the major geologic tectonic events we also interpret the late cretaceous early tertiary features on the eastern flank of the buried 85 e ridge as carbonate reefs the observation of steep subduction of older cold indian plate beneath the burmese plate near the andaman islands suggests the sunda arc in this region as low to intermediate stress subduction zone

automatic hypocenter determination of volcano induced seismic transients based on wavefield coherence an application to the 1998 eruption of mt merapi indonesia in order to monitor the seismic activity of mt merapi indonesia over a long period of time we installed a permanent array of both broadband and short period seismometers during the summer of 1997 considering the requirements of an automatic classification and localization system for seismic monitoring and surveillance at active volcanoes we split this network into three small aperture arrays distributed around the volcano we introduce here a newly developed method to determine the hypocenters in an automatic non linear manner using the coherence of seismic waves observed at the different arrays to test this method we analyze a swarm of vt b events recorded by the network the first step in this algorithm is based on a modified smoothed coherence transform in the second step we perform a semblance analysis applied to the 3d problem evaluating the quality of the estimated relative onset times after more than one year of dormancy mt merapi renewed its activity at the end of june 1998 this gave us the opportunity to analyze all stages of dome growth collapse and new intrusion of magma using the associated seismicity in a post processing sense this also allowed us to calibrate and test our newly developed automatic monitoring system using the more pronounced waveforms of vt b events by detecting and classifying different event types automatically we are able to localize a large number of vt b events which occurred just before the initial eruption we are also able to resolve some properties of the wavefield at mt merapi which are essential for further interpretations finally the results show that the source region of the vt b type seismicity just before the 1998 eruption is closely related to the region of subsequent high volcanic activity and therefore may represent a promising tool to forecast future eruptions

internal wave mixing in the baltic sea near inertial waves in the absence of tides 1 the dynamics of near inertial motions and their relation to mixing is investigated here with an extensive data set including turbulence and high resolution velocity observations from two cruises conducted in 2008 summer and 2010 winter in the bornholm basin of the baltic sea in the absence of tides it is found that the basin scale energetics are governed by inertial oscillations and low mode near inertial wave motions that are generated near the lateral slopes of the basin these motions are shown to be associated with persistent narrow shear bands strongly correlated with bands of enhanced dissipation rates that are the major source of mixing inside the permanent halocline of the basin in spite of different stratification near inertial wave structure and atmospheric forcing during summer and winter conditions respectively the observed dissipation rates were found to scale with local shear and stratification in a nearly identical way this scaling was different from the gregg henyey type models used for the open ocean but largely consistent with the mackinnon gregg scaling developed for the continental shelf

internal structure of the 85 e ridge bay of bengal evidence for multiphase volcanism abstract the 85 e ridge located in the bay of bengal of the northeastern indian ocean is an enigmatic geological feature as it possesses unusual geophysical signatures the ridge s internal structure and mode of eruptions are unknown due to lack of deep seismic reflection and borehole data control here we analyze 10 km of long streamer seismic reflection data to unravel the ridge s internal structure and thereby to enhance the understanding of how the ridge was originated and grew over a geologic time seismic facies analysis reveals the ridge structure consisting of volcanic vent and several stratigraphic units including packs of prograding clinoforms the clinoform sequences are interpreted as volcanic successions and led to the formation of lava delta fronts interpreted features of lava fed deltas and intervening erosional surfaces and mass flows along ridge flanks suggest that the 85 e ridge is a volcanic construct and was built by both subaqueous and multiphase sub marine volcanism during the late cretaceous approximately from 85 to 80 ma at later time from oligocene miocene 23 ma onwards the ridge was buried under the thick sediments of the bengal fan system

deformation and seismic precursors to dome collapse and fountain collapse nuees ardentes at merapi volcano java indonesia 1994 1998 abstract following the eruption of january 1992 episodes of lava dome growth accompanied by generation of dome collapse nuees ardentes occurred in 1994 1998 in addition nuees ardentes were generated by fountain collapse in january 1997 and the 1998 events also suggest an explosive component significant tilt and seismic precursors on varying time scales preceded these events deformation about the summit has been detected by electronic tiltmeters since november 1992 with inflation corresponding generally to lava dome growth and deflation or decreased inflation corresponding to loss of dome mass strong short term days to weeks accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes apart from those of 22 november 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short term precursors because of the combination of populated hazardous areas and the lack of an issued warning about 100 casualties occurred in 1994 in contrast the strong precursors in 1997 and 1998 provided advance warning to observatory scientists enabled the stepped raising of alert levels and aided hazard management as a result of these factors but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas no casualties occurred the nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse whereas those of 1997 and 1998 were influenced by gas pressurization of the lava dome

structure and evolution of the afanasy nikitin seamount buried hills and 85 e ridge in the northeastern indian ocean abstract geophysical data of the afanasy nikitin seamount ans partly buried hills and 85 e ridge in the northeastern indian ocean were studied together with published seismic refraction results to understand genesis and evolution of the structures the ans joins the 85 e ridge through isolated buried hills and intervening subsurface structures and together they form a linear ridge system the gravity signature of the ridge system changes from negative to positive towards south of 5 n which seems to coincide with termination thinning of pre collision continental sediments in the bay of bengal thick pile of bengal fan sediments had great impact on underneath pre collision sediments as well as on basement rocks the process resulted in attaining higher velocities up to 6 6 and 7 1 km s respectively gravity model studies suggest that structures of the ridge system are compensated in different modes the ans is underlain by an 8 km thick deep crustal body of magmatic rocks while beneath other structures oceanic crust is down flexed up to 2 5 km the presence of metasediments more dense than volcanic rocks and flexure of the lithosphere would explain the negative gravity anomaly over the 85 e ridge whereas lack of metasediments and magmatic rocks at depth would explain the compensated positive anomaly over the ans the width of the 85 e ridge the wavelength 190 km and amplitude 2 5 km of the flexed oceanic crust and the intersection of the ridge with the mesozoic fracture zones suggest that the ridge was formed in intraplate position when the lithosphere underneath was approximately 35 myr old initial emplacement of the ans was coeval with the formation of oceanic lithosphere at 80 73 ma the hotspot forming the 85 e ridge had reactivated the ans during the paleocene and brought it to the sea surface then it underwent erosion and subsidence processes the deformation activity had converged the north and south parts of the ans at late miocene and again at late pleistocene and northward buried hills at early pliocene

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

modeling the pathways and ages of inflowing salt and freshwater in the baltic sea abstract a three dimensional eddy permitting ocean circulation model with implemented bottom boundary layer model and flux corrected transport scheme is used to calculate the pathways and ages of various water masses in the baltic sea the agreement between simulated and observed temperature and salinity profiles of the period 1980 2004 is satisfactory especially the renewal of the deep water in the baltic proper by gravity driven dense bottom flows is better simulated than in previous versions of the model based upon these model results details of the mean circulation are analyzed for instance it is found that after the major baltic inflow in january 2003 saline water passing the slupsk furrow flows directly towards northeast along the eastern slope of the hoburg channel however after the baroclinic summer inflow in august september 2002 the deep water flow spreads along the southwestern slope of the gdansk basin further the model results show that the patterns of mean vertical advective fluxes across the halocline that close the large scale vertical circulation are rather patchy mainly within distinct areas are particles of the saline inflow water advected vertically from the deep water into the surface layer to analyze the time scales of the circulation mean ages of various water masses are calculated it is found that at the sea surface of the bornholm basin gotland basin bothnian sea and bothnian bay the mean ages associated to inflowing water from kattegat amount to 26 30 28 34 34 38 and 38 42 years respectively largest mean sea surface ages of more than 30 years associated to the freshwater of the rivers are found in the central gotland basin and belt sea at the bottom the mean ages are largest in the western gotland basin and amount to more than 36 years in the baltic proper vertical gradients of ages associated to the freshwater inflow are smaller than in the case of inflowing saltwater from kattegat indicating an efficient recirculation of freshwater in the baltic sea

mesozoic anomalies in the bay of bengal abstract the analysis of 8200 line km of total magnetic intensity data in the bay of bengal northeastern indian ocean revealed the presence of approximately n30 e trending seafloor spreading type magnetic anomalies these anomalies resemble the mesozoic anomaly series m11 m0 reported elsewhere the oldest anomaly m11 132 5 ma identified close to the east coast of india is followed by the younger series of mesozoic anomalies towards the offshore some of the anomalies are offset by 60 80 km the configuration of the offsets of the isochrons allowed us to propose approximately n120 e trending oceanic fracture zones the mesozoic crust of 132 5 118 ma is estimated to evolve with an average half spreading rate of 3 5 cm yr except for the ocean floor between the m9 and m4 magnetic isochrons this part of the crust appears to be affected by the buried subsurface 85 e ridge

instrumental lahar monitoring at merapi volcano central java indonesia abstract more than 50 volcanic debris flows or lahars were generated around mt merapi during the first rainy season following the nuees ardentes of 22 november 1994 the rainfalls that triggered the lahars were analyzed using such instruments as weather radar and telemetered rain gauges lahar dynamics were also monitored using new non contact detection instrumentation installed on the slopes of the volcano these devices include real time seismic amplitude measurement rsam seismic spectral amplitude measurement ssam and acoustic flow monitoring afm systems calibration of the various systems was accomplished by field measurements of flow velocities and discharge contemporaneously with instrumental monitoring the 1994 1995 lahars were relatively short events their duration in the boyong river commonly ranging between 30 min and 1 h 30 min the great majority 90 of the lahars was recognized at kaliurang village between 13 00 and 17 30 h due to the predominance of afternoon rainfalls the observed mean velocity of lahar fronts ranged between 1 1 and 3 4 m s whereas the peak velocity of the flows varied from 11 to 15 m s under the gardu pandang viewpoint location at kaliurang to 8 10 m s at a section 500 m downstream from this site river slopes vary from 28 to 22 m km at the two sites peak discharges recorded in various events ranged from 33 to 360 m3 s with the maximum value of peak discharge 360 m3 s on 20 may 1995 to improve the lahar warning system along boyong river some instrumental thresholds were proposed large and potentially hazardous lahars may be detected by rsam units exceeding 400 ssam units exceeding 80 on the highest frequency band or afm values greater than 1500 mv on the low gain broad band setting

observations of the deepwater flow into the baltic sea it has earlier been hypothesized that the deep water flowing into the baltic sea forms a bottom pool in the arkona sea just inside the entrance sills the flow from the pool farther into the baltic sea was assumed to be baroclinic geostrophic and controlled by the pool stratification this was supported by a realistic statistical description of the deepwater flow into the baltic sea computed using historical vertical density profiles from a hydrographical station in the arkona sea however basin wide synoptic measurements of density and currents were not available for a direct verification of the pool model a hydrographic survey was undertaken in the arkona sea shortly after a major inflow event in the beginning of 1993 the conductivity temperature depth sections reveal a thick bottom pool of deep water separated by a halocline from the surface water of baltic origin approaching the northern coastal boundary from the central parts of the pool the halocline sank by about 20 m before hitting the bottom the ship mounted acoustic doppler current profiler recorded a complicated current field however subtraction of the assumed barotropic part gives a current field quite similar to the baroclinic geostrophic current field computed from the density distribution thus a dense bottom pool including a baroclinic geostrophic boundary current along the northern flank of the pool is quite evident from our measurements

the negative gravity field over the 85 e ridge an isopach map made from seismic reflection and refraction data in the bay of bengal shows two prominent n s trending features in the basement topography one is the northernmost portion of the ninetyeast ridge which is totally buried by sediments north of 10on the other buried ridge trends roughly n s for 1400 km at 85oe to the latitude of sri lanka and then curves toward the west it has basement relief up to 6 km two free air gravity anomaly profiles across the region show a strong gravity low 60 mgal over the 85oe ridge while the ninetyeast ridge shows a gravity high to understand the negative free air gravity anomaly over the 85oe ridge we model the lithosphere as a thin elastic plate and calculate its flexural and gravitational response to an uneven sediment load a plausible formation history for a buried ridge consists of at least two major episodes the first is the formation of the ridge on a lithosphere with a flexural rigidity of d i at some later time the ridge is buried by an influx of sediments the lithosphere is cooler and the flexural rigidity has increased to d 2 the character of the gravity field depends primarily upon the initial and final values of flexural rigidity these d1 and d2 values are varied to obtain good agreement between the model and observed gravity anomalies best fitting models have a 180 times increase in flexural rigidity between ridge formation and sediment burial an approximate relationship between flexural rigidity and crustal age shows that the 85oe ridge was formed on relatively young lithosphere 5 15 m y old and that it was buried when the lithosphere was 40 80 m y old

a detailed view into the eruption clouds of santiaguito volcano guatemala using doppler radar 1 using doppler radar technology we are able to show that eruptions at santiaguito volcano guatemala are comprised of multiple explosive degassing pulses occurring at a frequency of 0 2 to 0 3 hz the doppler radar system was installed about 2 7 km away from the active dome on the top of santa maria volcano during four days of continuous measurement 157 eruptive events were recorded the doppler radar data reveals a vertical uplift of the dome surface of about 50 cm immediately prior to a first degassing pulse particle velocities range from 10 to 15 m s in the line of sight of the radar in 80 of the observed eruptions a second degassing pulse emanates from the dome with significantly higher particle velocities 20 25 m s again line of sight and increased echo power which implies an increase in mass flux we carry out numerical experiments of ballistic particle transport and calculate corresponding synthetic radar signals these calculations show that the observations are consistent with a pulsed release of material from the dome of santiaguito volcano

radar doppler velocimetry of volcanic eruptions theoretical considerations and quantitative documentation of changes in eruptive behaviour at stromboli volcano italy summary the use of radar doppler velocimetry for the observation of volcanic activity is new we used this method to continuously observe the activity of one vent of stromboli volcano italy from the end of 2000 april until early may during this period we recorded 702 eruptions 132 of which occurred before a strong rain storm passed over the island on april 29 in order to interpret the recorded doppler data we developed a program that simulates different strombolian eruption scenarios for which we then calculate the theoretical doppler spectra comparing our theoretical data with the observed data we are able to show that most of the eruptions are nearly vertical although we did observe only one component of the eruption vector with our doppler radar one of the most interesting features of the data set is a significant change in eruptive behaviour that correlates with the occurrence of the rain storm we find that on average the eruption duration increased by a factor of 2 eruptive velocities were much higher and indirect evidence indicates that the average particle diameter of the erupted material decreased this change may have several causes but the coincidence with the rain storm may be evidence of magma water interaction and feedback on the volcanic activity if the fluid source rain changing the eruptive style is at the surface and in near surface layers then the main control on final eruption dynamics at stromboli volcano must also be in rather shallow regions

modeling and observations of deep water renewal and entrainment in a swedish sill fjord a baroclinically forced deep water renewal event in a small swedish sill fjord is investigated using a one dimensional numerical model and a dataset that resolves temporal variations in salinity and oxygen the observations indicate an almost complete renewal of the basin water within a period of 2 3 weeks the details of the renewal process are emphasized by modeling the sill flow as well as the resulting dense bottom plume with various rates of entrainment it is found that sill mixing is relatively unimportant but that entrainment increases the deep water inflow by a factor of 2 4 different formulas for calculating plume entrainment are compared and the model s sensitivity to variations in sill flow and bottom friction is investigated it is shown that even weak entrainment occurring at shallow depths where the density difference between the plume and the resident water is large has a significant impact entrainment prolongs the time it takes for a complete renewal i e to flush out all resident water and on the moderate timescales considered here yields lower post renewal salinity and oxygen concentrations this implies that entrainment and mixing during renewal may be as important as basin water diffusion in setting the timescale for forthcoming renewal events

efficient flowline simulations of ice shelf ocean interactions sensitivity studies with a fully coupled model abstractthermodynamic flowline and plume models for the ice shelf ocean system simplify the ice and ocean dynamics sufficiently to allow extensive exploration of parameters affecting ice sheet stability while including key physical processes comparison between geophysically and laboratory based treatments of ice ocean interface thermodynamics shows reasonable agreement between calculated melt rates except where steep basal slopes and relatively high ocean temperatures are present results are especially sensitive to the poorly known drag coefficient highlighting the need for additional field experiments to constrain its value these experiments also suggest that if the ice ocean interface near the grounding line is steeper than some threshold further steepening of the slope may drive higher entrainment that limits buoyancy slowing the plume and reducing melting if confirmed this will provide a stabilizing feedback on ice sheets under some circumstances

crumbling of dacite dome lava and generation of pyroclastic flows at unzen volcano recent modelling of volcanic eruptions has shown that the efficiency of subsurface degassing of magmas determines whether magma erupts explosively or effuses quietly1 2 slow uprise of magma is often accompanied by effective degassing leading to the extrusion of lava flows and domes although lava dome extrusion is one of the less explosive modes of eruption it is often accompanied by explosive pyroclastic activities3 5 the 1991 eruption of unzen volcano provided an opportunity to observe at close range several types of small scale pyroclastic flow glowing avalanches originating from lava domes most of the pyroclastic flows are of merapi type caused by blocks falling from a collapsing dome others are of pelean type originating in an explosion from the side of a dome the lavas apparently show variable degrees of self explosivity we suggest that variable degrees of degassing of the magma produced a wide range of excess pore pressures in the extruded lava domes resulting in both merapi type and pelean type pyroclastic flows from the domes

crustal architecture and moho topography beneath the eastern indian and bangladesh margins new insights on rift evolution and the continent ocean boundary the thick sedimentary cover 18 km along the eastern continental margin of india ecmi and over the bay of bengal has hindered understanding of the mechanisms of rifting that operated on the eastern indian and bangladesh margins analysis of multichannel seismic reflection data together with 3d gravity inversion and 2d gravity forward modelling illuminates basement configuration crustal thickness and moho topography thereby revealing the modes of rift evolution and the location of the continent ocean boundary cob along these margins the basement particularly in the shelf and slope regions of eastern peninsular india is traversed by nearly coast perpendicular graben and their seaward continuity is delineated up to 125 km from the coastline three different types of continental margin are present along the ecmi 1 sheared rift on the southern segment of the ecmi up to 14 n latitude offshore the southern granulite terrain 2 hyper extended rift in the central segment between 14 n and 17 n offshore the dharwar craton and 3 hypo extended rift on the northern segment between 17 n and 20 n offshore the eastern ghats mobile belt the graben terminations crustal thickness and moho topography of both the ecmi and offshore bengal basin clearly suggest that the cob runs nearly parallel to the coastline of peninsular india but takes an orthogonal turn offshore in the bengal basin and connects the palaeo continental shelf and the rajmahal sylhet line onshore in the bengal basin crustal thickness 8 10 km and depth to the moho discontinuity 28 km beneath the bangladesh margin are unusual because the crustal thickness increased through interaction of the kerguelen plume with the existing oceanic lithosphere the moho deepened largely due to the load of the bengal fan sediments the absence of rifted crustal blocks on the bangladesh margin and the continuity of the cob into the onshore bengal basin together imply that the present bangladesh region was under marine conditions at least until the beginning of bengal fan sedimentation i e no less than 23 ma

subglacial discharge driven renewal of tidewater glacier fjords the classic model of fjord renewal is complicated by tidewater glacier fjords where submarine melt and subglacial discharge provide substantial buoyancy forcing at depth here we use a suite of idealized high resolution numerical ocean simulations to investigate how fjord circulation driven by subglacial plumes tides and wind stress depends on fjord width grounding line depth and sill height we find that the depth of the grounding line compared to the sill is a primary control on plume driven renewal of basin waters in wide fjords the plume exhibits strong lateral recirculation increasing the dilution and residence time of glacially modified waters rapid drawdown of basin waters by the subglacial plume in narrow fjords allows for shelf waters to cascade deep into the basin wide fjords result in a thin boundary current of shelf waters that flow toward the terminus slightly below sill depth wind forcing amplifies the plume driven exchange flow however wind induced vertical mixing is limited to near surface waters tidal mixing over the sill increases in fjord transport of deep shelf waters and erodes basin stratification above the sill depth these results underscore the first order importances of fjord glacier geometry in controlling circulation in tidewater glacier fjords and thus ocean heat transport to the ice

shelf to basin iron shuttling enhances vivianite formation in deep baltic sea sediments coastal hypoxia is a growing and persistent problem largely attributable to enhanced terrestrial nutrient i e nitrogen and phosphorus loading recent studies suggest phosphorus removal through

revised gravity for offshore india and the isostatic compensation of submarine features abstract high resolution free air gravity data have been derived for offshore india covering the area 60 e to 104 e and 5 s to 26 n using reprocessed radar altimeter data from the geodetic missions of ers 1 and geosat the free air gravity gives enhanced imaging of geological features such as the murray laxmi chagos laccadive 85 e and 90 e ridges these data provide a major improvement compared with the existing satellite derived dataset of sandwell and smith v 9 2 this improvement has been quantified by determining the standard deviation of the difference grid between these two satellite derived gravity datasets which is 10 mgal for the whole study area with a variation of 5 mgal over the active ridges plots of log power spectrum versus wavenumber of these datasets and correlation coefficients between these datasets and marine data confirm the high resolution of the data presented the local airy and regional flexure model of isostasy are tested at 9 locations covering a range of different geological features the northern and southern parts of the eastern continental margins of india blocks 3 and 4 show different flexural responses suggesting they conform to extension and transform type margins respectively whereas the western continental margin and laxmi ridge blocks 8 and 9 have flexural responses conforming more to a fragmented margin the deeper oceanic features of the 90 e and chagos laccadive ridges have distinctly different isostatic responses conforming to flexure and airy type responses respectively this suggests the origin of the 90 e ridge formed on top of a pre existing crust like a hot spot trace whereas the chagos laccadive ridge formed close to an active ridge spreading centre

seasonal dynamics of the system sea strait black sea bosphorus case study abstract the seasonal behaviour of the black sea bosphorus system is studied the one and a half dimensional model of the black sea is used it describes the level and thermohaline structure changes of the sea a one layer sub model is used for the shallow azov sea the black sea model is driven by the seasonal wind heat flux freshwater influx and bottom bosphorus current a quasi stationary hydraulic two layer model of the long strait with bottom and interface friction is used for bosphorus as opposed to most of the earlier models it simulates exchange in terms of the level difference along the strait instead of net barotropic transport the simulations show that the model is able to describe seasonal variations of the vertical structure of the black sea including cold intermediate layer cil formation a set of experiments was carried out to clarify the relative importance of seasonality of main forcing mechanisms freshwater influx heat budget wind and level in the marmara sea on the black sea vertical structure and strait exchange the black sea level follows mainly in the freshwater influx with a delay of 2 months the dependence of the volumetric flow rates in the upper and bottom layers of the strait on the level difference at the strait ends is close to linear the simulations demonstrate sensitivity of exchange through the bosphorus on the seasonal variations of the marmara sea level

generation of subsurface cyclonic eddies in the southeast baltic sea observations and numerical experiments 1 closely spaced ctd transects performed in the summertime reveal simultaneous downward upward bendings of temperature salinity contours in the seasonal thermocline permanent halocline of the stolpe channel and the gulf of gdansk which may be interpreted as geostrophically balanced cyclonic eddies in the intermediate layer to examine processes capable of forming the observed cyclonic eddies a numerical simulation based on the princeton ocean model pom has been initiated the subsurface cyclones in the stolpe channel were satisfactory simulated in model runs under easterly northerly wind conditions their formation was shown to result from the adjustment of the high potential vorticity pv outflow from the bornholm basin via the stolpe sill to low potential vorticity environment by vortex stretching so called the pv outflow hypothesis by spall and price 1998 in accordance with the real wind conditions a cyclonic eddy observed in the intermediate layer of the gulf of gdansk was satisfactorily reproduced in a model run with the westerly wind shutdown which implies westward transport throughout the stolpe channel and thereby excludes the pv outflow hypothesis the subsurface cyclone simulated in the gulf of gdansk was traced to form in the course of relaxation of the coastal downwelling baroclinic jet

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

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

the baltic sea tracer release experiment 2 mixing processes 1 deep water mixing processes in the largest basin of the baltic sea gotland basin are investigated here with the help of long term moored instrumentation and turbulence microstructure measurements budgets for heat and salinity reveal a strong temporal variability in the deep water mixing coefficients that is shown to be coupled to the wind forcing down to time scales of individual wind events consistent with the results from a simultaneously conducted tracer release experiment near boundary turbulence was identified as the key processes for basin scale mixing turbulent bottom boundary layers were found to be thick and stable in the flat deep part of the basin where highest dissipation rates were observed and comparatively thin less energetic and highly variable on the slopes due to a permanent tendency for boundary layer restratification in the absence of internal tides strongly damped basin scale topographic waves with periods of a few days a deep rim current and to a smaller extent near inertial waves were identified as the main energy sources for boundary mixing these results are likely to be relevant also for other medium sized stratified basins

gravity current dynamics and entrainment a process study based on observations in the arkona basin abstract a 19 h time series of dissipation stratification and horizontal velocities has been obtained for a dense gravity current flowing into the arkona basin in the western baltic sea the observations are compared with one dimensional quasi steady theory in which the gravity component in the flow direction is balanced by bottom friction while that in the cross flow direction is balanced by the coriolis force the observations deviate from the theory in that the bottom shear stress is more than 2 times as large as that required to balance the gravity several reasons for this discrepancy are discussed a 1d turbulence model is also compared with the observations profiles of velocity stratification and dissipation rates generally show similar variations with depth as the observations although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed subsequently the model is used to investigate the variation of t

deep water dynamics and boundary mixing in a nontidal stratified basin a modeling study of the baltic sea recent results from a tracer release experiment have shown that similar to many lakes and ocean basins deep water mixing in the baltic sea is largely determined by mixing processes occurring in the energetic near bottom region due to the complexity and small vertical extent of this region however previous modeling studies of the baltic sea have so far not been able to provide a numerically and physically sound representation of boundary mixing here we discuss first results from a nested high resolution simulation of the central baltic sea that aims at a realistic description of the turbulent bottom boundary layer with the help of new numerical techniques adaptive coordinates and state of the art turbulence modeling using a comprehensive data set from the baltic sea tracer release experiment we show that the model is able to reproduce the key dynamical processes near inertial waves topographic waves and a rim current with excellent accuracy boundary mixing triggered by these processes was found to result in simulated basin scale mixing rates in close agreement with observations including a seasonal variability that has been emphasized in previous studies these results may be relevant also for the description of mixing in large lakes and other stratified basins

magma eruption rates of merapi volcano central java indonesia during one century 1890 1992 the magma eruption rates of merapi volcano form 1890 to 1992 are re examined chronologically for this volcano movements of extruded lavas and domes as well as their extrusions are important because they control the modes of the subsequent activities and cause nuees ardentes and lahars the monthly eruption rates varied widely but the cumulative volume of lavas has increased linearly and is expressed as 0 1x106 m3 month the magma production rate of this volcano may have been constant for these 100 years recurrent excessive effusion of lavas is tentatively interpreted by assuming a magma reservoir the averaged eruption rate is small in comparison with other volcanoes such as nyramuragia kilauea and vesuvio however it is remarkable that the activity has been continuous for these 100 years and the total amount of lava discharged during this period reached more than 108 m3 a simple model for the formation of the 1992 lava dome is presented the viscosity of the lavas is probably between 106 and 107 p and the length of the magma conduit is probably less than 10 km

sediment volume and mass beneath the bay of bengal rates of sediment accumulation and the amount of sedimentary fill in depocenters lying downstream of erosion in the himalayas and tibet can provide some insight into tectonics and geological history the objective of this paper is to put on record the best estimates which are possible with existing data of the volume and mass of sediments sedimentary rock and metasedimentary rock beneath the sea floor of the bay of bengal the sedimentary section in the bay of bengal is divided into two parts 1 eocene through holocene sediments and sedimentary rocks which post date the initial india asia collision volume 12 5 106 km3 mass 2 88 1016 t this is most of the bengal fan including its eastern lobe the nicobar fan plus some of the outer bengal delta 2 early cretaceous through paleocene pre collision sedimentary and metasedimentary rocks volume 4 36 106 km3 mass 1 13 to 1 18 1016 t these are interpreted as continental rise and pelagic deposits

oceanography of the black sea a review of some recent results abstract a new synthesis of the black sea oceanography is presented primarily based on studies carried out in the southern black sea as well as on some recent work covering the entire basin obtained in a new era of increasing cooperation between the riparian countries a review of the physical environment is given seasonal and interannual climatic variability of the system are discussed in relation to its hydrology water mass variability and formation are studied with emphasis on the inflow of mediterranean waters pycnocline variability shelf and internal mixing and double diffusive convection the general circulation of the basin and the roles of stratification topography and coastline variations in determining the behaviour of the rapid unstable boundary currents and upwelling along the coast are discussed based on hydrographic data and satellite observations impacts of the physical processes on the ecosystem are discussed

structure and tectonics of 85 e ridge from analysis of geopotential data abstract the bay of bengal bob sedimentary basin is one of the largest offshore sedimentary basins of the world having the thickest accumulation of sediments which mask the underlying crust and it is the geopotential data that offers the unique opportunity of seeing below the thick sediments satellite derived free air gravity fag data marine magnetic data bathymetry available seismic profiles and isopach maps over the bay of bengal are utilized in the present paper to throw light on the nature and tectonics of the bob with particular emphasis on the 85 e ridge combined analysis of gravity and magnetic data along six ew profiles of length varying from 325 to 440 km is undertaken incorporating seafloor spreading anomalies in the model of the several theories put forth for the evolution of the 85 e ridge the present study supports the sagging of the crust and rules out the hotspot trace and magmatic under plating theories the crustal model derived from the magnetic profile analysis suggests that the 85 e ridge does not extend to the north of 15 n latitude and this is supported by the euler solutions of the fag and the long wavelength filtered fag however the intermediate wavelength filtered fag suggests that the 85 e ridge extends up to the ocean continent boundary thereby suggesting that the 85 e ridge thins out dramatically to the north of 15 n latitude analysis of gravity data along 17 n latitude profile predicts that in the northern segment the 85 e ridge is a geo morphological feature within the sediments above the basement whereas to the south of 15 n latitude it is a feature within the oceanic crust below the basement further the reverse magnetization associated with the seafloor spreading anomalies lying on the 85 e ridge belongs either to the albian period or the anomaly a34 a33 the 85 e ridge would be younger than these seafloor spreading anomalies and would have formed due to horizontal compressional forces of the lithosphere preceding development of the subduction zone at the andaman trench

how entraining density currents influence the stratification in a one dimensional ocean basin abstract the sensitivity of ocean stratification to the vertical distribution of plume entrainment is analyzed a large ocean basin supplied by dense water from an adjoining marginal sea is considered the dense water flows into the ocean basin as an entraining density current and interleaves at the bottom or at the level of neutral density where it deposits a mixture of marginal sea and basin water as the basin water i e old plume water is entrained and re circulated in the plume a stratification develops in the basin the mixture deposited at the bottom hence contains an increasing fraction of marginal sea water and the basin density increases with depth as well as with time a stationary solution in which diffusion of buoyancy from above is important is approached asymptotically in time non diffusive solutions to the initial transient adjustment as well as the diffusive asymptotic state have been studied in four different parameterizations of plume entrainment it is shown that in the transient regime the basin stratification and plume density are highly sensitive to how mixing is parameterized the stationary diffusive solution that is approached asymptotically in time is less sensitive to parameterization but depends strongly on basin topography source water density and buoyancy flux at the surface

in situ observation of dome instabilities at merapi volcano indonesia a new tool for volcanic hazard mitigation understanding the mechanism and repetition frequency of dome instability events at high risk dome building volcanoes located near densely populated areas is one crucial piece of information when dealing with volcanic hazard mitigation although some visual in situ observations of such processes have been made at unzen volcano and on montserrat continuous monitoring of dome activity has been severely hampered by weather conditions such as cloud coverage using a newly designed microwave doppler system we are able to continuously monitor in situ processes at active dome systems with our instrument we can determine the velocity of material breaking off an active dome as well as the approximate amount of material passing through the radar beam allowing us to continuously identify different types of dome instabilities a data set collected during a highly active period at the end of oct early nov 2001 at merapi volcano indicates two different instability types a purely gravitational instabilities and b gravitational instabilities that are followed immediately by an explosion such information continuously collected allows tight constrains on the activity status of dome building volcanoes and is an important information for hazard mitigation the number of instabilities detected by the radar during the observational period is larger than the number of rockfall events detected by the seismic network operated at merapi during that time

dynamics of rotating shallow gravity currents passing through a channel part i observation of transverse structure abstract a detailed dataset describing a quasi stationary bottom gravity current approximately 10 m thick and 10 km wide passing through a channel like constriction in the western baltic sea is presented the data include full depth synoptic and highly resolved transects of stratification and turbulence parameters as well as detailed velocity transects across the gravity current at different down channel locations the velocity data reveal a persistent transverse circulation creating a characteristic wedge shaped density structure in the interface a strong asymmetry was also found in the interior of the gravity current where the evolution of a dynamically significant transverse density gradient to the right of the down channel flow was observed spectral analysis of the near bottom velocities showed a surprisingly strong contribution to the bottom stress from low frequency motions with periods up to 30 min that are possibly related to internal wave effects cross channel transects of shear microst

magnetic monitoring at merapi volcano indonesia abstract merapi volcano located 30 km north of the heavily populated city of yogjakarta java is one of the most active of the 129 volcanoes in indonesia about every 2 years a new phase of activity is observed depending on the past activity the unrest gives rise either to an endogenous dome which partly collapses in the southwest direction or to pyroclastic flows which travel as far as 15 km the 1990 1997 period has involved a plume emission on 30 august 1990 an extrusion on 20 january 1992 and a pyroclastic eruption on 22 november 1994 the intensity of the earth magnetic field has been measured simultaneously and digitally recorded at four stations since 1990 two overhauser magnetometers with resolution of 0 01 nt have been installed in the summit area to strengthen the volcano monitoring outstanding magnetic changes appear to correlate with volcanic activity three types of volcanomagnetic signals can be identified long term trends up to 15 nt with period 10 years medium term cyclic variations at most 3 nt in amplitude and with 1 2 years period and small events reaching 1 5 nt lasting a few months and associated with any remarkable volcanic activity merapi volcano began a new cycle of activity in 1995 leading to a dome growth in july 1996 and accompanied by 27 nuees ardentes in august the comparison between magnetic data seismicity and surface phenomena suggests that some long term trends of decade periods could be of thermomagnetic origin while mid term volcanomagnetic variations associated with the cycles of merapi activity could be of piezomagnetic origin short term variations of a few weeks duration less than 1 5 nt are well correlated with the 1995 1996 seismic activity

structure and origin of the 85 e ridge the submerged 85 e ridge in the bay of bengal trends approximately n s between 19 n and 6 n latitudes off the southeast coast of sri lanka it takes an arcuate shape and seems to terminate with the northward extension of the afanasy nikitin seamounts situated around 2 s latitude the ridge is characterized by positive magnetic 100 400 nt and negative free air gravity 60 mgal anomalies with variable widths of 100 180 km magnetic model studies revealed that the rocks of the 85 e ridge are magnetized with reversed polarity the well defined geophysical anomalies and lack of magnetic polarity reversals together with the deep burial nature of the ridge may not favor a hotspot origin two alternative processes for the ridge emplacement have been suggested ridge emplacement may be 1 due to shearing of the lithosphere caused by stretching and compressional forces associated at the time of major plate reorganization immediately after the evolution of the early cretaceous crust in the bay of bengal more precisely at m0 isochron or during the middle albian reversals within the cretaceous long normal polarity k t superchron epoch when the earth s magnetic polarity changed from normal to reversed polarity and or 2 due to sagging followed by deformation produced by the buckling instability of the oceanic plate caused by horizontal compressional forces on the passive continental margin however more marine geophysical data are required to support the postulated coincidence of the ridge with a reversed polarity magnetic anomaly and their associated model further the rajmahal traps normally polarized and the 85 e ridge reversely polarized appear to be associated with two different episodes of eruption that might have been triggered by the kerguelen mantle plume the 85 e ridge seems to extend into the onshore west bengal basin as a subsurface ridge and merges with the reported nne ssw trending zone of strong geophysical anomalies east of rajmahal traps up to 25 n latitude

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

implications of initial conditions and ice ocean coupling for grounding line evolution abstract ice sheet grounding lines are sensitive to initial conditions and to small perturbations in boundary conditions based on new model results coupling ocean and ice flow to study ice ocean dynamics near ice stream grounding lines we couple an ocean plume model that simulates ice shelf basal melting with a two dimensional isothermal model of ice stream and ice shelf flow the notable results of the coupled model experiments are to reveal grounding line migration sensitivities to i specific aspects of modeling derived and history dependent initial conditions ii to the overall melt magnitude and iii to a positive feedback between focused melting and local slopes of basal ice that is eventually stabilized by buttressing for lengthening ice shelves these interactions can lead to multiple steady states for ice flow over a bed that shallows in the along flow direction and have an important bearing on the effects of bedrock bumps when in the vicinity of bedrock highs grounding lines tend to rapidly advance or retreat towards the basal asperity a significant delay or cessation of de glaciation occurs once the grounding line reaches the leeward side of the bedrock crest however while bedrock bumps can offer stability in the grounding zone minor changes in ocean conditions can easily offset their effect through basal melting feedbacks

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

tectonics of the bay of bengal new insights from satellite gravity and ship borne geophysical data abstract recently released satellite derived free air gravity anomalies and the existing ship board geophysical data provide new insights into the tectonics of the bay of bengal with respect to the structure and regional extension of the buried 85 e ridge and the tectonics of the eastern continental margin of india ecmi the 85 e ridge can be visualized extending inland via the mahanadi basin volcanics to the rajmahal traps a large volcanic province in eastern india encompassing the rajmahal and sylhet traps and volcanics in the bengal and mahanadi basins almost on the scale of the deccan volcanic province along the west coast can be envisaged taking into account the occurrences of intrusive and extrusive rocks around the age of 117 ma the 85 e ridge represents the deep ocean volcanic trace of this magmatic activity towards the south the ridge continues in an arcuate manner to the afanasy nikitin seamount at equatorial latitudes in the central indian ocean gravity models of the ridge are indicative of hotspot related crustal underplating processes beneath the ridge the ecmi can be divided into a southern transform and northern rifted segments on the basis of gravity and bathymetry data which bear similarities with the conjugate east antarctica margin

automatic classification of dome instabilities based on doppler radar measurements at merapi volcano indonesia part i summary in this paper we analyse a 3 yr long time series of activity at merapi volcano indonesia which was recorded using a doppler radar system between november 2001 and july 2004 about 57 000 events associated with dome instabilities have been recorded by the radar system because of the huge amount of data an automatic classification system has been developed which identifies different types of instabilities at the lava dome i e sliding material gravitational break offs and explosive outbursts as well as rainfall comparing the record of detected instabilities to rockfall measurements deduced from the seismic network of the volcanological technology research center vtrc we are able to demonstrate the high potential of doppler radar measurements for monitoring of dome activity when aligned to the most active area at the dome the radar detects significantly more events than the seismic system in combination with seismic measurements the doppler radar allows for identifying changes in the location of the most active area at the dome this is particularly helpful since the dome of merapi is covered by clouds about 50 per cent of the time additionally the radar data can help to distinguish between rockfalls and multiphase events in the seismic measurements the different types of instabilities have been analysed for their occurrence frequency in terms of size volume and mean velocity significant temporal changes in the relative occurrence frequencies or the characteristic properties of the different types of instabilities have not been observed however during the period of fastest activity decrease explosive instability events with a gravitational precursor decreased faster than events starting explosively because the radar system is able to observe rainfall the data has been analysed for a link between rain and dome activity throughout the observation period no such link could be found however this might be due to the fact that the activity has been almost continuously decreasing

doppler radar sounding of volcanic eruption dynamics at mount etna besides their common use in atmospheric studies doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field we present the observations made with a mid power uhf doppler radar voldorad during a 7 h strombolian eruption at the se crater of mount etna on 11 12 october 1998 main characteristics of radar echoes are retrieved from analysis of doppler spectra recorded in the two range gates on either side of the jet axis from the geometry of the sounding the contribution of uprising and falling ejecta to each doppler spectrum can be discriminated the temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before during and after its paroxysm moreover during the sharp decrease of eruptive activity following the paroxysm detailed analysis of video from camera recording radar and seismic measurements reveals that radar and video signals start to decrease simultaneously approximately 2 5 min after the tremor decline this delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the se crater detailed analysis of eruptive processes has been also made with voldorad operating in a high sampling rate mode signature of individual outburst is clearly identified on the half part of doppler spectra corresponding to rising ejecta temporal variations of the backscattered power exhibit quasi periodic undulations whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time periodicity of power variations between 3 8 and 5 5 s is in agreement with the occurrence of explosions visually observed at the se vent maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity finally by using a simplified model simulating the radar echoes characteristics we show that when voldorad is operating in high sampling rate mode the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam

gravity anomalies and crustal structure of the bay of bengal abstract the bengal fan is covered afresh by systematic geological and geophysical investigations by national institute of oceanography nio india and a detailed free air gravity map of the fan is prepared the map shows two strong gravity lows one corresponding to the continental shelf and the other to the 85 e ridge the ninetyeast ridge is brought out as a gravity high the anomalies are inverted to determine the anomaly producing interfaces which suggest that the 85 e ridge anomaly could not be explained by an isolated geophysical model invoking a negative density contrast for the ridge material the 85 e ridge anomaly and several other isolated gravity lows are attributed mostly to the depression like structures in the moho each depression of the moho is associated with a basement high the depression beneath the 85 e ridge is about 6 km deep from the regional moho boundary which is at variance to the earlier results it is suggested that the depressions may possibly have developed due to the surface volcanic loads emplaced on already evolved oceanic crust of the bay of bengal

morphology and tectonics of mahanadi basin northeastern continental margin of india from geophysical studies abstract the bathymetry total intensity magnetic and satellite free air gravity data over the eastern continental margin of india between the latitudes 18 30 n and 20 n within the water depths of 25 2300 m between paradip and gopalpur were analyzed and interpreted onshore aeromagnetic and bouguer gravity data over the adjacent coastal region are also supplemented in the present analysis the basement configuration inferred from the bathymetry magnetic and gravity data resembles a series of coast parallel structural highs and depressions and their shearing pattern in the mahanadi offshore basin the chilika offshore lineament and dhamara offshore lineament constitute the southern and northern boundaries of the offshore basin respectively in this sector the inferred continent ocean boundary cob around 170 km from the coast approximately mimics the 2000 m isobath the width of the inferred offshore basin between the chilika offshore lineament and dhamara offshore lineament is around 240 km and it extends approximately up to 170 km from coast to offshore perhaps up to the cob the inferred tectonics of the northeastern continental margin of india suggests pull apart and sheared transform mechanisms during the breakup of india from antarctica the model studies suggest that the northern part of the 85 e ridge abuts the coast at chilika lake the shape of 2000 m isobath over the northeastern continental margin of india closely resembles to that of 2000 m isobath off the lambert graben of east antarctica this inference appears to further support the theory that the eastern continental margin of india and east antarctica are closely aligned in the pre breakup tectonic setting of the eastern gondwanaland

correlation of seismic activity and fumarole temperature at the mt merapi volcano indonesia in 2000 abstract in this paper we present densely sampled fumarole temperature data recorded continuously at a high temperature fumarole of mt merapi volcano indonesia these temperature time series are correlated with continuous records of rainfall and seismic waveform data collected at the indonesian german multi parameter monitoring network the correlation analysis of fumarole temperature and precipitation data shows a clear influence of tropical rain events on fumarole temperature in addition there is some evidence that rainfall may influence seismicity rates indicating interaction of meteoric water with the volcanic system knowledge about such interactions is important as lava dome instabilities caused by heavy precipitation events may result in pyroclastic flows apart from the strong external influences on fumarole temperature and seismicity rate which may conceal smaller signals caused by volcanic degassing processes the analysis of fumarole temperature and seismic data indicates a statistically significant correlation between a certain type of seismic activity and an increase in fumarole temperature this certain type of seismic activity consists of a seismic cluster of several high frequency transients and an ultra long period signal

late quaternary development of the north western baltic proper results from the clay varve investigation within the project late quaternary development of the north western baltic proper a total of 36 piston core samples have been collected the results presented in this study are based on analyses

self potential and ground temperature at merapi volcano prior to its crisis in the rainy season of 2000 2001 abstract rainwater infiltration into the active lava dome of merapi volcano central java has often been suggested as a triggering mechanism for partial dome collapse and subsequent eruptive behavior however the phenomenon has not been systematically investigated we use a multi parametric approach to study the interaction of the hydrologic and magmatic system near the lava dome prior to its crisis in early 2001 we describe the hardware concept for a continuous monitoring system for self potentials u sp and ground temperature t installed in august 2000 at the solfatara woro only 150 m from the active lava dome relating the data from this station to measurements of rainfall air pressure solfatara temperature and seismicity several effects can be distinguished a a long term correlation is observed between electrode temperature difference and sp with estimated coupling coefficients of 2 1 0 5 mv c b after individual rainfall events u t signatures show a typical pattern of positive charge accumulation at the hot electrodes near the fumarolic vents c an exceptional anti correlation between u and t is observed in january 2001 during a period of rapid dome growth prior to the collapse and eruptive crisis d wavelet analysis of sp reveals the sporadic occurrence of periodic fluctuations with a clear 12 h s2 component because of their amplitude of up to 100 mv km and their periodicity s2 but not 24 h or lunar 12 h 25 min these fluctuations are unlikely to be caused by natural magnetic field variation or by earth tides instead they do seem correlated but not in phase with atmospheric pressure changes we discuss effects a d in the framework of source mechanisms related to water lava interactions

a model for the vertial circulation of the baltic deep water abstract the time dependent vertical circulation of the baltic proper is modeled using a horizontally integrated model of high vertical resolution a seasonal pycnocline model computes the properties of the mixed layer below this an advection vertical diffusion model computes the evolution of the salinity and temperature fields a simple model for an entraining dense bottom current which carries the intruding seawater and drives the vertical advection in the basin is developed and used in the derivation of entrainment velocity we it is shown that e we u where u is the speed of the bottom current may be expressed in the well known empirical constants m0 and cd the hypsographic features of the baltic are accounted for in the model the model is forced using realistic meteorological and hydrological time series the inflow of dense seawater to the baltic with large fluctuations in flow rate and salinity is realistically described and constitutes the upstream boundary condition for the bottom current