inversion of aeromagnetic data using digital terrain models although draped magnetic surveys contain more information about the magnetization of the rocks near the surface of the earth than surveys at constant elevation allowance for the effects of the terrain is critical for their correct interpretation a new method for calculating the magnetic effect of the topography from a digital terrain model by integrating analytically in the vertical direction and then numerically in the horizontal plane is presented this method lends itself to the calculation of anomalies when the magnetization of the rocks varies with position and thus is well suited to the inversion of draped aeromagnetic surveys to obtain the apparent magnetization of the surficial rocks this inversion is achieved by repeated use of an approximate inverse function in the form of a two dimensional 2 d filter that is applied to gridded data an example using draped magnetic data collected over white island an active volcanic island of high relief shows that although the anomaly pattern is domina

a heating process of kuchi erabu jima volcano japan as inferred from geomagnetic field variations and electrical structure since august 2000 we have recorded the total intensity of the geomagnetic field at the summit area of kuchi erabu jima volcano where phreatic eruptions have repeatedly occurred a time series analysis has shown that the variations in the geomagnetic field since 2001 have a strong relationship to an increase in volcanic activity these variations indicate thermal demagnetization of the subsurface around the presently active crater the demagnetization source for the early variations until summer 2002 was estimated at about 200 m below sea level for the variations since 2003 the source was modeled on the basis of the expansion of a uniformly magnetized ellipsoid the modeling result showed that the source is located at 300 m above sea level beneath the crater we carried out an audio frequency magnetotelluric survey with the aim of obtaining a relation between the demagnetization source and the shallow structure of the volcano a two dimensional inversion applied to the data detected two good conductors a shallow thin one which is restricted to a region around the summit area while the other extends over the edifice at depths between 200 and 800 m these conductors are regarded as clay rich layers with low permeability which were assumed to be generated through hydrothermal alteration the demagnetization source for the early variations was possibly located at the lower part of the deep conductor and the source after 2003 lies between the two conductors where groundwater is considered to be abundant based on these results as well as on seismological geodetic and geochemical information we propose a heating process of the kuchierabu jima volcano in the initial stage high temperature volcanic gases supplied from the deep seated magma remained temporarily at the level around the lower part of the less permeable deep conductor since the ascent path had not yet been established then when the pathway developed as a result of repeated earthquakes it became possible for a massive flux of volcanic gases to ascend through the conductor the high temperature gases reached the aquifer located above the conductor and the heat was efficiently transported to the surrounding rocks through the groundwater as a consequence an abrupt increase of the gas flux and di ffusion of the heat through the aquifer occurred and the high temperature zone expanded since the high temperature zone is located beneath another conductor which acts as caprock we assume that the energy of the phreatic explosion is accumulated there

eruption mechanism as inferred from geomagnetic changes with special attention to the 1989 1990 activity of aso volcano abstract geomagnetic changes associated with the volcanic activity of aso volcano were detected with a dense network of continuously recording proton precession magnetometers during the period from june 1989 to june 1990 magnetic date clearly indicate that changes in the magnetization within the volcano are most probably caused by temperature changes this activity can be divided into five stages which are characterized by magnetization and demagnetization of the volcano these magnetic changes with durations of a few months are definitely correlated with some typical volcanic events at the crater as well as the volcanic tremor activity the demagnetization stage appears when the vent is covered by a water pool or the volcanic activity is enhanced the magnetization stage follows the opening of a vent and several large explosions which make the vent permeable the source of magnetic changes lies at a depth of about 200 m below the crater rim in the southwestern part of the active crater magnetic moments responsible for observed magnetic changes at stages 1 2 and 4 are 3 4 5 2 and 2 2 wbm respectively the corresponding source volume is estimated as a single sphere of radius 40 50 m or a spherical shell of 100 m or so an effective mechanism of rapid heating cooling exists which is ascribed to the interaction of groundwater and superheated vapor i e a shallow hydrothermal system this hydrothermal system driven by the surface cap of the vent controls every feature of the eruptions at the final outlet of aso volcano

nonstationary analysis of geomagnetic time sequences from mount etna and north palm springs earthquake 1 volcanomagnetic and or seismomagnetic effects are geomagnetic variations generated before eruptions and or seismic events our aim is to analyze geomagnetic time series to detect the volcanomagnetic and or seismomagnetic effects among a number of other variations two advanced signal processing techniques are proposed to analyze the geomagnetic time series the first technique called continuous wavelet transform singularity analysis cwtsa is based on the continuous wavelet transform the second called time variant statistical analysis of nonstationary signals tvans is based on a time varying adaptive algorithm recursive least squares both techniques are very effective in detecting the geomagnetic variations at the time instants likely linked to volcanic and or seismic activity the application of these methodologies to geomagnetic time sequences respectively recorded on mount etna during the volcanic activity of 1981 and in north palm springs during the seismic events of 8 july 1986 yields a good correspondence between events detected by both techniques and volcanic end seismic events the statistical significance of geomagnetic time series was also assessed to verify the obtained results from cwtsa and tvans it was defined at significance level of 95 in the wavelet power spectrum for the difference of the geomagnetic time series aiming at distinguishing the most significant events when they are upon this one

temperature changes at depths to 150 metres near the active crater of aso volcano preliminary analysis of seasonal and volcanic effects abstract two holes were drilled to depths of 150 m and 70 m from the surface about 200 m from the active crater of aso volcano and quartz thermometers were installed in the holes at depth intervals of 30 m and 35 m respectively this series of observations is one of the first measurements of temperature at depth so close to an active crater the ground temperature at a depth of 2 m had an annual variation with a range of about 10 c as expected clearly corresponding to the atmospheric temperature variation but delayed by about 1 month temperatures measured at depths from 30 m to 70 m had very small annual temperature variations the range of temperature at 30 m depth was about 0 04 c the temperature at a depth of 60 m however was particularly stable probably because at this depth the hole is in the middle of a massive lava flow at depths of 70 m or more small less than 0 2 c annual temperature variations were again observed these variations are probably due to the effects of surface water descending to these levels through cracks and fissures at 120 m depth the average temperature is about 17 5 c over 5 c above the surface average temperature and the annual temperature variation has a range of about 2 c out of phase with the atmospheric changes this is probably due to the interaction of rainfall descending from the surface with convecting hotter fluids from below the temperature gradient below 100 m depth is very high with the average temperature at a depth of 150 m being about 31 c the temperature variations at this depth are dominated by long period variations with a steady decline after a peak in november december 1989 overlain by a rather irregular seasonal variation with a range of about 0 5 c october 1989 was the time of most active volcanic activity with strombolian eruptions depositing ash to a distance of 50 km from the crater accompanied by very high amplitude volcanic tremor so the temperature changes at 150 m seem to be mainly the result of volcanic activity the maximum temperature at this depth occurred 1 or 2 months after the peak of observed volcanic activity so it is likely that the temperature variations show a delayed influence of the level of volcanic activity these results show that in the unconsolidated materials often found by active volcanic craters the effects of seasonal atmospheric variations are carried to substantial depths by groundwater flows so that at aso volcano only at the maximum depth of 150 m are the temperature variations clearly dominated by the level of volcanic activity

magnetic history of a dyke on mount etna sicily summary during the 1989 eruption of mount etna two fracture systems trending c n45 e and n150 e opened at the foot of its 3000 m high se crater and propagated quickly downslope to distances of 3 and 7 km respectively the northeastern fracture fed a flank eruption whereas the southeastern fracture remained dry and overed contrasting volcanological and geophysical evidence of the presence of magma at a shallow depth during the opening of this non eruptive fracture system a diverential magnetic network was set up on a short profile across its distant extremity initially the magnetic field did not display any change along the profile between frequent surveys however repeated measurements at intervals of about 3 months for two years revealed the slow build up of a 130 nt anomaly the anomaly vanishes laterally within 0 2 km of the surface expression of the fracture system this exceptional set of observations constrains the location and time of cooling of a shallow dyke the increase in magnetization of the dyke inferred by the rate of growth of the anomaly leads to the interpretation that the dyke was emplaced near the end of the eruption

combined electromagnetic geochemical and thermal surveys of taal volcano philippines during the period 2005 2006 since 1572 33 phreatic to phreatomagmatic eruptions have occurred on taal volcano philippines some of them causing several hundred casualties considering the time delay between two consecutive eruptions there is an 88 probability that taal volcano should have already erupted since 1992 several phases of seismic activity have been recorded accompanied by ground deformation opening of fissures and surface activity the volcanic activity of taal appears to be controlled by dike injections and magma supply buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming in early 2005 a multidisciplinary project was launched for studying the hydrothermal activity to map the hydrothermal system combined surveys were carried out to investigate self potential total magnetic field ground temperature and carbon dioxide soil degassing along with satellite thermal imaging of the main crater lake the elevated temperatures and high concentrations of carbon dioxide as well as electromagnetic anomalies indicate large scale hydrothermal degassing this process is enhanced along the tectonic features e g crater rim and faults of the volcano while active fissures opened along the e w northern flank during the 1992 1994 seismic activity heat and fluids from the hydrothermal system are essentially released in the northern part of the crater which is bounded to the south by a suspected nw se fault along which seismicity seems to take place and dikes are thought to be intruded during the january 2005 surveys a new seismic crisis started and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano repeated surveys show changes of self potential total magnetic field and ground temperature with time without any noticeable spatial enlargement these observations suggest that the northern flank located between the crater rim and the 1992 1994 fissures is connected with a deep thermal source in main crater and is reactivated during seismic crises this sector could be subjected to flank failure

exploring the interplay between infiltration dynamics and critical zone structures with multiscale geophysical imaging a review abstract infiltration is the process of water entering into and routings through the subsurface it has a profound impact on water flux in the earth s critical zone cz influencing phenomena such as overland flow stream generation plant available water and groundwater recharge as well as the associated cz processes and functions of weathering erosion slope stability and food production however reliable measurement of infiltration in structured geomedia soils and regolith with hidden subsurface features remain challenging the increasing availability of geophysical techniques has helped them emerge as viable options for minimally invasive determination of infiltration at the pedon to hillslope or catchment scales geophysical methods replace the educated guesswork of interpreting field data from traditional infiltrometers with direct visualization and quantification this paper provides a comprehensive literature review of various applications of geophysical techniques used to 1 visualize infiltration relevant structures 2 monitor non uniform or preferential infiltration patterns and 3 map soil moisture distribution after infiltration it then proposes a new conceptualization form and function dualism for subsurface hydrology to link preferential infiltration to cz structures with the goal of formulating more realistic infiltration theories related to subsurface structural heterogeneity the characterization of both subsurface structures form and infiltration dynamics function via geophysical imaging should help infiltration models currently emphasizing macroscale behaviors rooted in the continuum concept expand to accommodate the microscale nature of preferential flow integrating multiple geophysical approaches and developments into the new generation of geophysical techniques will further enhance our ability to see into the fabric of the subsurface and capture the dynamics of non uniform infiltration through the hidden half of the cz this approach offers exciting opportunities for understanding the complex interactions between cz structures and cz processes

volcanomagnetic effects observed on piton de la fournaise volcano reunion island 1985 1987 a permanent network of four to six telemetered magnetic stations has been installed on piton de la fournaise volcano in october 1985 and 1986 eight eruptive sequences have occurred since then some of which affected only the summit whereas others affected the whole massif volcanomagnetic variations are observed with each of these volcanic events the geomagnetic field intensity is measured simultaneously every minute at each station with a precision of 0 25 nt nanotesla the main results are the following volcanomagnetic variations observed with eruptions have amplitudes of several nanoteslas to more than 10 nt with characteristic time durations ranging from l min or less to several months a good correlation between the magnetic variations recorded at the different stations is observed spatial and temporal properties of the volcanomagnetic field appear to be controlled by the features of the eruptions several days before the beginning of the december 1985 march july november december 1986 and january 1987 eruptions changes in the intensity differences are observed with amplitudes of a few nanoteslas up to 5 nt at stations located close to the active part of the rift zone variations are also observed in the most remote stations for larger eruptions in march 1986 november december 1986 and january 1987 correlations between magnetic variations ground deformations and seismic activity have been observed for the december 1985 march 1986 november december 1986 and january 1987 events three main mechanisms could account for the observed volcanomagnetic variations piezomagnetic effects electrokinetic effects and electrical resistivity changes since variations in the stress field in the surroundings can modify the induced and natural magnetizations of magnetized rocks the circulation of water through the interconnected pore network microcracks faults aquifers and also the electrical resistivity of geological structures through the modification of the properties of the pore network

the stratigraphy of oxfordian kimmeridgian late jurassic reservoir sandstones in the witch ground graben united kingdom north sea oil bearing upper jurassic oxfordian kimmeridgian sandstones of the sgiath and piper formations are of major economic importance in the witch ground graben united kingdom north sea they form the reservoirs in 14 fields that originally contained 2 billion bbl of oil reserves including scott field which in 1993 will be the largest producing united kingdom north sea oil field to come on stream in more than a decade the sgiath and piper formations represent late jurassic transgressive and regressive phases that began with paralic deposition and culminated in a wave dominated delta system these phases preceded the major graben rifting episode late kimmeridgian to early ryazanian and deposition of the kimmeridge clay formation the principal source rock of the witch ground graben oil fields a threefold subdivision of the middle to upper oxfordian sgiath formation is formally proposed with scott field well 15 21a 15 as the designated reference well the basal skene member consists of thinly interbedded paralic carbonaceous shales coals and sandstones this is overlain by transgressive marine shales of the saltire member the uppermost oxfordian scott member consists of shallow marine sandstones that prograded to the southwest a precursor of the kimmeridgian wave dominated delta sequence of the piper formation which prograded to the south and to the west the contact of the sgiath and piper formations is a basinwide transgressive marine shale i shale which can act as an effective barrier to fluid communication between the sgiath and piper reservoir sandstones the recognition of transgressive marine shales or maximum flooding surfaces is of great use in understanding regional geological history and in solving exploration and development problems

ground deformation patterns at white island volcano new zealand between 1967 and 2008 deduced from levelling data article i nfo since 1967 levelling measurements have been conducted in the main crater of white island volcano interpretation of these data using numerical modelling reveals that shallow pressure sources 200 600 m deep extending up to the subsurface dominated the long term deformation pattern consisting of inflation deflation cycles the time sequence of height changes magnetic changes and fumarole temperature and chemistry reveal that surface changes were caused by increasing temperature below the main crater reflecting the presence of magma at shallow depth the uplift and subsidence are interpreted in terms of increase or decrease in fluid pore pressure in response to changes of the heat and gas flux the subsidence during and following eruptions could be also linked with removal of material at depth to feed the eruptions

a direct comparison of emi data and borehole data on a 1000 ha data set abstract increasingly the frequency domain electromagnetic induction emi method is used to study soil properties and hydrological properties on different scales yet emi data are most often used as they are or with the low induction number approximation moreover reported studies have been fairly small

experimental constraints on phreatic eruption processes at whakaari white island volcano vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at whakaari white island volcano new zealand here we investigate the influence of sample type hydrothermally altered cemented ash tuffs and unconsolidated ash lapilli and fragmentation mechanism steam flashing versus gas expansion on fragmentation and ejection velocities as well as on particle size and shape our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs cemented by alunite and amorphous opal increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs as less energy is consumed by fragmentation fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front neither fragmentation mechanisms nor sample type show a significant influence on the shape our results emphasize that under identical pressure and temperature conditions eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion therefore phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments

artificial magnetic disturbance from the mass rapid transit system in taiwan an obvious magnetic disturbance has been repeatedly observed by magnetometers located outside of urban areas in yangmingshan national park and has affected the monitoring of volcanic activity in the northern region of taiwan the disturbance has amplitudes of approximately 3 5 nanoteslas and regularly appears for approximately 21 hours per day except during the new year period when it is observed continuously for 45 hours this change coincides with the annual extended operation of the mass rapid transit mrt system a 750 volt direct current drives the mrt trains and leaks to the ground with a maximum value of approximately 1000 amperes measured along the routes the disturbance is dominated by the unbalanced supply and return currents resulting from the leakage the daily changes in the magnetic noise levels are correlated with the electricity consumption of the mrt system because the leakage is proportional to the use of electric power

the biostratigraphic calibration of the scottish and outer moray firth upper jurassic successions a new basis for the correlation of late oxfordian early kimmeridgian humber group reservoirs in the north sea basin abstract the combined results of palynological sampling of scottish onshore sections and offshore wells from the outer moray firth and the re appraisal of ammonites extracted from subsurface cores enable a revised unified macropalaeontological palynological correlation scheme to be proposed for the late oxfordian early kimmeridgian regulare mutabilis ammonite zones of the north sea the results contradict previous controversial correlations which were based upon reported ammonite recovery from boreholes in the witch ground graben a component part of the outer moray firth basin it can now be shown that the upper jurassic biostratigraphy of scotland and the north sea is essentially comparable to that of the english counterpart suggesting that no faunal provincialism persisted across the former north sea dome from uppermost oxfordian times onwards having clarified and resolved previous conflicting views the application of the revised scheme should aid exploration and production in the moray firth basin through the construction of more accurate reservoir correlations and robust palaeogeographic play fairway maps

relationship between volcanic activity and shallow hydrothermal system at meakandake volcano japan inferred from geomagnetic and audio frequency magnetotelluric measurements abstract hydrothermal activity at meakandake volcano japan from 2004 to 2014 was investigated by using long term geomagnetic field observations and audio frequency magnetotelluric amt surveys the total intensity of the geomagnetic field has been measured around the summit crater ponmachineshiri since 1992 by kakioka magnetic observatory we reanalyzed an 11 year dataset of the geomagnetic total intensity distribution and used it to estimate the thermomagnetic source models responsible for the surface geomagnetic changes during four time periods 2004 2006 2006 2008 2008 2009 and 2013 2014 the modeled sources suggest that the first two periods correspond to a cooling phase after a phreatic eruption in 1998 the third one to a heating phase associated with a phreatic eruption in 2008 and the last one to a heating phase accompanying minor internal activity in 2013 all of the thermomagnetic sources were beneath a location on the south side of ponmachineshiri crater in addition we conducted amt surveys in 2013 and 2014 at meakandake and constructed a two dimensional model of the electrical resistivity structure across the volcano combined the resistivity information and thermomagnetic models revealed that the demagnetization source associated with the 2008 eruptive activity causing a change in magnetic moment about 30 to 50 times greater than the other sources was located about 1000 m beneath ponmachineshiri crater within or below a zone of high conductivity a few ohm meters whereas the other three sources were near each other and above this zone we interpret the conductive zone as either a hydrothermal reservoir or an impermeable clay rich layer acting as a seal above the hydrothermal reservoir along with other geophysical observations our models suggest that the 2008 phreatic eruption was triggered by a rapid influx of heat into the hydrothermal reservoir through fluid rich fractures developed during recent seismic swarms the hydrothermal reservoir remained hot after the 2008 eruption and heat was sporadically transported upward through its low permeability ceiling

apparent magnetization intensity map on sakurajima volcano kyushu japan inferred from low altitude high density helicopter borne aeromagnetic surveys abstract in november 2005 we conducted the first low altitude high density helicopter borne aeromagnetic survey over sakurajima volcano kyushu japan to provide a baseline for subsequent measurement of changes in magnetic anomalies related to volcanic processes because previously acquired aeromagnetic data cannot resolve small scale geological feature although the observation error was considered to be 5 0 a m were located on the lava around an ei craters and on the northeastern flank of kita dake 2 the lowermost values of apparent magnetization

a water flow model of the active crater lake at aso volcano japan fluctuations of magmatic gas and groundwater fluxes from the underlying hydrothermal system the first crater of nakadake peak of aso volcano japan contains a hot water lake that shows interesting variations in water level and temperature these variations were discovered by precise continuous observa tions of the lake independent of precipitation we devel oped a numerical model of a hot crater lake and compared with observational data for the period from july 2006 to january 2009 the numerical model revealed seasonal changes in mass flux 75 132 kg s and enthalpy 1 840 3 030 kj kg for the fluid supplied to the lake the relation between the enthalpy and mass flux indicates that the bottom input fluid is a mixture of high and low temperature fluids assuming a mixture of high temperature steam at 800 c and liquid water at 100 c we evaluated the liquid and steam fluxes the liquid water flux shows a seasonal increase lagging behind the rainy season by 2 months suggesting that the liquid water is predominantly groundwater the fluctuation pattern in the flux of the high temperature steam shows a relation with the amplitude of volcanic tremor suggesting that heating of the hydrothermal system drives the tremor consequently precise observations of a hot crater lake represent a potential method of monitoring volcanic hydrothermal systems in the shallow parts of the volcanoes keyword aso volcano hot crater lake hydrothermal system groundwater volcanic tremor

paleozoic multiple accretionary and collisional processes of the beishan orogenic collage in the paper by xiao and others american journal of science v 310 p 1553 1594 1 please substitute figure 16 reproduced here for figure 16 that appears between pages 1573 and 1574 the original figure 16 2 was printed at an improper size figure 3 1 lookup volpage 310

mechanism of phreatic eruptions at aso volcano inferred from near field broadband seismic observations broadband seismometers deployed at aso volcano in japan have detected a hydrothermal reservoir 1 to 1 5 kilometers beneath the crater that is continually resonating with periods as long as 15 seconds when phreatic eruptions are observed broadband seismograms elucidate a dynamic interplay between the reservoir and discharging flow along the conduit gradual pressurization and long period 20 seconds pulsations of the reservoir during the 100 to 200 seconds before the initiation of the discharge followed by gradual deflation of the reservoir concurrent with the discharging flow the hydrothermal reservoir where water and heat from the deeper magma chamber probably interact appears to help control the surface activity at aso volcano

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

self potential variations associated with ultra long period seismic signals at merapi volcano 1 we report about self potential sp anomalies registered 150 m from the active lava dome of merapi volcano which are associated with ultra long period ulp seismic signals periods 100 s during a 5 month period of simultaneous sp and seismological measurements 50 ulp events were detected seismologically if sp time series corresponding to ulp events are aligned to the onset times of ulp events and stacked the resulting traces show anomalous sp with an amplitude of 5 20 mv km and 40 60 min duration in contrast the anomalous signals were not present in ground temperature data nor in sp data recorded 1 km from the summit sp anomalies associated with ulp seismicity might be caused by electro kinetic effect of fluid flow in subsurface this result is consistent with the ulp generation model based on seismological observations and adds new information towards the understanding of ulp seismicity

dynamic response of frequent tremors at aso volcano to teleseismic waves from the 1999 chi chi taiwan earthquake abstract teleseismic waves from the 1999 chi chi taiwan earthquake dynamically triggered isolated tremor and micro earthquakes at aso volcano japan which is at a distance of 1400 km immediately after the arrival of the p waves short period tremor spt began to occur more frequently for about 2000 s and during and after the arrival of surface waves 2 micro earthquakes were observed around the crater observations of frequent spt are an indication of triggered isolated tremor which consists of both spt and long period tremor lpt components for the cases of arrivals of seismic waves from other large teleseisms from march 1995 to june 2002 triggering of isolated tremor was observed during 1998 1999 during this period increased thermal supply to the crater was observed while the background activity was relatively low and the volcanic system beneath the crater was more responsive to external stress perturbations

groundwater chemistry patterns in the phreatic aquifer of the central belgian coastal plain the holocene geological evolution of the belgian coastal plain is dominated by a transgression of the north sea silting up of the coastal plain and human intervention impoldering this has led to a typical pattern in groundwater quality which is discussed here for the central part of the coastal plain therefore a database with available groundwater samples is composed water type according to the stuyfzand classification is determined and different hydrosomes and their hydrochemical facies are identified based on this the origin and evolution of the water types is explained using piper plots and geochemical calculations with phreeqc before the impoldering salinising and freshening conditions alternated with a general salinisation of the aquifer after about 3400 bp this results in a dominance of brackish and salt nacl subtypes which are still found in the deeper part of the aquifer the subsequent impoldering resulted in an major freshening of the aquifer leading to nahco3 mghco3 and cahco3 subtypes overall mixing cation exchange carbonate mineral dissolution and oxidation of organic matter are identified as the major processes determining the general water quality the close link between geological evolution water quality and what is still observable today is illustrated with this example of the belgian coastal plain

exploring the potential of multi receiver emi survey for geoarchaeological prospection a 90 ha dataset article i nfo article history the archaeological evaluation of landscapes in the framework of developer led archaeology is often based on extensive trenching programmes complemented with auger surveys in wetland environments during the archaeological evaluation of a 90 ha polder site in the north west of belgium a mobile multi receiver electro magnetic induction emi survey was used as a main prospecting technique the use of a mobile survey allowed to map the entire study area at a very fine resolution over 25 measurements per m 2 incorporating a multi receiver emi instrument enabled measuring the apparent electrical conductivity eca and the appar ent magnetic susceptibility msa of four different soil volumes simultaneously at each location the detailed maps provided insight into the archaeological and geomorphological features of the site among the detected structures were a large medieval farmstead a palaeoriver system and a number of military remains from world war i wwi the vertical discrimination potential added insight into the vertical facies changes which allowed modeling the palaeolandscape and helped determining the depth of detected medieval features the different msa measurements gave additional insight into the wwi structures in this paper we give an overview of the possibilities of combining multiple eca measurements for interpreting vertical soil variability together with an example of the added information from simultaneously gathered msa data more generally the diverse potential of multi receiver emi survey for geoarchaeological research is demonstrated

depth slicing of multi receiver emi measurements to enhance the delineation of contrasting subsoil features abstract mobile multi receiver electromagnetic induction sensors provide simultaneous readings of the apparent electrical conductivity eca from overlapping soil volumes therefore small contrasting features can be difficult to identify because they have a limited contribution to the bulk measurement especially if they are present in the subsoil i e beneath the topsoil integrating eca data from simultaneous measurements with multiple coil configurations has the potential to elucidate the variability within the soil profile as it enables modelling the electrical conductivity ec for distinct depth intervals therefore it was our objective to develop a methodology to enhance the delineation of contrasting subsoil features such as in filled gullies and archaeological features we selected a 3 5 ha study site where contrasting features were expected a three layered build up was taken as the initial ec slicing model after varying the interface depths the shallowest and deepest ec depth slice showed a clear minimum of their combined variances at interface depths of 0 36 m which corresponded to the ploughing depth and 0 86 m this implies that the ec depth slice in between these depths contained a demonstrably higher variability a sub area of 0 85 ha was completely excavated to a depth of 0 7 m revealing the subsoil features and the host material an automated edge detection algorithm showed that the ec depth slice was superior to any individual eca measurement for delineating the contrasting subsoil features therefore we concluded that depth slicing by integrating simultaneous eca signals from a multi receiver emi sensor clearly improved the identification of subsoil features

evaluation methods of heat discharge and their applications to the major active volcanoes in japan abstract the rates at which thermal energy is released by non eruptive mechanisms associated with active volcanoes in japan have been estimated from surface temperature distributions or from shapes of the fumarolic plume rise values of 5 3 x 107 w and 1 2 x 108 w have been calculated for non eruptive release rates in 100 km segments of the northeast and the southwest japan arc respectively it appears that non eruptive heat discharge is of the same order as that caused by eruptions

el nino induced onshore transport in the california current during 1982 1983 persistent 9 month large scale positive temperature 3 4 c negative salinity 0 1 0 3 and positive dissolved oxygen 0 5 1 ml l subsurface anomalies characterize the el nino induced onshore transport in the california current during 1982 83 these anomalies characteristic diagrams and sign reversals in the salinity and oxygen anomalies are consistent only with enhanced onshore transport of subarctic water from the offshore california current onshore transport excludes poleward propagating kelvin waves as a generation mechanism for the 1982 83 californian el nino the data however support the conclusion simpson 1983 that an anomalous basinwide atmospheric circulation produced the californian el nino

biogeography of bathonian to oxfordian jurassic dinoflagellates arctic nw europe and circum mediterranean regions abstract calculations of the koch index of biotal dispersity suggests that the range of dinoflagellate cyst diversity in the arctic nw europe and circum mediterranean regions was relatively high in the studied late bathonian to earliest callovian early to middle callovian late callovian and early oxfordian time intervals although there are no great differences the dispersity values increase from late bathonian to early oxfordian the simpson coefficient of biotal similarity simpson 1960 which has been applied to quantify the variations between the dinoflagellate floras within the different regions suggests that the differences in composition of the dinoflagellate assemblages became less prominent during late callovian early oxfordian time compared to the late bathonian middle callovian during the late bathonian to early oxfordian the true boreal dinoflagellages assemblages sverdrup basin svalbard franz josef land show a southwardly decreasing similarity to the contemporaneousassemblages approaching the tethyan region similarly assemblages in the southernmost tethyan region middle east iberian penninsula show decreasing similarity to the assemblages approaching the boreal areas the dinoflagellate assemblages in the yorkshire east midlands area appear to be intermediate between the true boreal and tethyan marine microfloras altjough they may show a slightly closer similarity to the tethyan than the boreal assemblages this distribution patterns found among the dinoflagellate cysts appears similar to that observed for the ammonities with distinct differences between boreal arctic and the tethyan mediterranian provinces and with a mixing of elements within the sub boreal province from late early callovian times the previous faunal barriers were disrupted and it is possible to make correlations at the ammonite zonal level among the arctic nw central european and sub mediterranean regions the dinoflagellate assemblages are profoundly different between the boreal assemblages i e in the sverdrup basin svalbard and franz josef land and those of the sub mediterranean province southern germany france switzerland and this continued through the middle callovian the late callovian was a period of distinct diversification among the boreal and sub boreal dinoflagellate cyst floras as shown by an increase in number of species compared to the older callovian assemblages observed within the sverdrup basin barents sea region the north sea area and the british jurassic similar to late bathonian early callovia time the west european sub boreal province in late callovian time also represented an area of mixing of boreal and tethyan marine microfloras as evident within the late bathonian early callovian interval a transition between two distinctive dinoflagellate cyst provinces appears as a generally fluctuating line transversing the britain north sea region in overall character the early oxfordian dinoflagellate cyst assemblages are very similar to those of the late callovian time the simpson coefficients for the early oxfordian dinoflagellate assemblages display latitudinally decreasing similarity trends comparable to the older middle jurassic time intervals it is evident from the present study that the increase in the dispersity values and the decreased differences in composition among the dinoflagellate assemblages from late bathonian to early oxfordian times coincided with the disappearance of important land barriers and the establishment of new open marine sea ways between the boreal and tethyan basins these changes in the provinciality of the dinoflagellates also coincide with a period when southward migration of boreal faunas into the paris and lusitania basins and a migration of mediterranean faunas into eastern greenland took place

the oscillation model of hydrothermal dynamics beneath aso volcano southwest japan after small eruption on may 2011 a new understanding model using repeated absolute and relative gravity measurement abstract at the end of 2010 the seismic activity in aso volcano intensely increased and water level in the nakadake crater decreased until early in 2011 then was followed by a small eruption in may 2011 after the eruption and heavy rain the volcanic activity subsided to calm period crater bottom was refilled with water and water level increased in the nakadake crater the next tremor reappeared in 2014 and tracked to eruption in november 2014 this eruptive pattern and water level variation in the crater repeatedly appeared on the surface and it should be related to the hydrothermal dynamics beneath aso volcano we initiated the gravity measurements in relation to hydrothermal dynamics in the subsurface of aso volcano using scintrex cg 5 549 and lacoste romberg type g 1016 relative gravimeter at 28 benchmarks in april 2011 one month before the eruption the repeated gravity measurements continue to monitor aso volcano with a series of the measurement after the eruption in every three months to a half year we analyze the gravity variation from 2011 to 2014 between the time of the phreatic and strombolian eruption the measurements covered the area more than 60 km 2 in the west side of aso caldera a new gravity network was also installed in may 2010 at seven benchmarks using a10 017 absolute gravimeter which re occupied in october 2010 june 2011 and two benchmarks in june 2014 as a result the gravity changes distinguish hydrothermal dynamic in the subsurface which has a direct correlation to water level fluctuation in the crater after the first eruption and before the second discharge the monitoring data notice large gravity changes between the surveys at benchmarks around nakadake crater and kusasenri area the simple 3d inversion models of the 4 d gravity data deduce the density contrast distribution beneath aso volcano the inversion and mass change result generate the oscillation typical as a new understanding model the variation of the mass shows a similar trend with the hydrothermal input rate to the crater of past research the third year monitoring from april 2013 displays a large gravity and mass variation while precipitation data in this period is smaller than the previous season the largest increased mass about 43 million tons by gaussian method occurred between may 2013 and september 2013 according to the three year gravity monitoring the calm period in aso volcano happens after may 2011 eruption until september 2013 which is followed by the active period before the november 2014 eruption this result will contribute to understand the process of eruption

apparent migration of tremor source synchronized with the change in the tremor amplitude observed at aso volcano japan at aso volcano kyushu japan several different types of volcanic tremor have been observed for many years one of them is the continuous tremor the ground vibration which has dominant frequency between 3 and 10 hz and has approximately constant amplitudes without any clear beginning and ending we observed the continuous tremor at aso using short period seismometer arrays for 3 days in 1999 we locate the source of the continuous tremor by seismic array data processing we use the semblance coefficients in order to estimate the arrival azimuth and apparent slowness by grid search the epicenters of the continuous tremor are located around the currently active crater and the source depths are likely to be shallower than 600 m we find that the estimated epicenter clearly migrates synchronized with the change in the tremor amplitude the migration often occurs periodically with a period of about 80 s but aperiodic occurrence of the migration is also often seen in both cases the epicenter is located southeastward northwestward when the amplitude is larger smaller we propose that there are two or more independent tremor sources with fixed locations and that their amplitudes modulate either aperiodically or periodically with periods nearly 80 s the tremor signals from those sources are mixed at the arrays and the estimated epicenter parameters vary according to which signal dominates the seismograms the simplest model is that there are two point sources one at west and the other at south of the crater we call the two sources as nw source and se source respectively and the amplitude of the se source changes with time consequently the se source dominates the seismogram when the observed amplitude is larger whereas the nw source dominates when the amplitude is smaller we generate synthetic seismograms and apply the location technique to them to verify the validity of the two point source model and to search the locations of two sources which can explain the observed synchronization between the amplitude and the apparent epicenter location we find that the distance between the two sources needs to be more than 400 m to agree with the observation we also analyze the seismic array data observed in 2001 and infer that the nw source in 1999 may be identical to the tremor source of the 2001 data

signals recorded by demeter satellite over active volcanoes during the period 2004 august 2007 december more than 1500 volcanoes can potentially enter into eruption but only some tens of them are equipped with monitoring networks most of volcanic eruptions can be predicted by the integration of continuous real time observations data processing and analysing in the electromagnetic field em a long history of ground observations shows that electric magnetic and electromagnetic signals may precede and accompany volcanic eruptions the possibility that volcanic eruptions may also be preceded by transient electromagnetic anomalies in the ionosphere can be analysed on the basis of demeter mission this microsatellite launched by cnes in 2004 covers 14 orbits per day over seismic and volcanic regions of the earth two complementary and systematic studies are presented over the time period 2004 august 2007 december the first study shows that three types of electric and or magnetic anomalies can be observed in the time window of 30 d preceding an eruption and 15 d after on the 74 eruptions occurring on 50 volcanoes under consideration 48 anomalies are recognised along 30 eruptions 41 per cent of the eruptions were accompanied by em signals on board of the satellite 81 per cent of the anomalies are observed before the eruptions for the period 30 d 15 d and 69 per cent for the period 15 d 15 d in the second study the anomalies above three nearby volcanoes lopevi ambrym and aoba are systematically looked for all orbits between 2004 august and 2006 december anomalies are only observed during periods of larger activity on each of them taking into account that no anomaly is observed a long time before an eruption on can allocate the anomalies to each volcano although the database is still limited the study shows that volcanic activity may be preceded by em perturbations of the ionosphere

ζ potential measurement of volcanic rocks from aso caldera 1 we deduced the z potential of various rocks in aso caldera from streaming potential measurements in laboratory in contrast to the conventional observation that the z potential of crustal rocks is mostly negative under typical geologic conditions almost half of the samples equilibrated with dilute kcl solution show positive values of z potential at ph 4 5 5 5 the samples showing positive z are characterized by relatively low sio2 content and abundance of elements having high isoelectric points and found to be localized around the summit of mt takadake where the positive correlation between self potential sp and altitude is observed we emphasize that measurements of z potential of volcanic rocks are very important to give more appropriate interpretations of sp data from volcanic fields index terms 0634 electromagnetics measurement and standards 0925 exploration geophysics magnetic and electrical methods 5199 physical properties of rocks general or miscellaneous 8499 volcanology general or miscellaneous 1832 hydrology groundwater transport citation hase h t ishido s takakura t hashimoto k sato and y tanaka z potential measurement of volcanic rocks from aso caldera geophys res lett 30 23 2210 doi 10 1029 2003gl018694 2003

volcanomagnetic effects at vulcano island aeolian archipelago italy summary the installation of two continuously operating proton magnetometers 2 km apart and sampling simultaneously every 5 min on vulcano island from 1990 november to 1991 december allowed the detection of some transient anomalies thought to result from internal variations in the physical state of the volcano the diverence of mean values in the magnetic field at the two stations underwent a slow variation of 2 nt during the period of measurements the mean values in the total intensity at one station were inversely correlated to the diverence between the mean values of the two stations this suggests that the contribution to the signal generated by the transitory magnetic field may be broken down into two parts one of external origin which is identical for both stations and another of internal origin proportional to the former but dependent on the site following on from this simple description of the magnetic field a method of analysis was developed to distinguish between transients of volcanomagnetic origin and transients generated by strong variations in the external transitory magnetic field an accurate analysis which takes into account the correlation between the measurements at the two stations leads to the singling out of three magnetic anomalies on 1991 april 2 july 18 and december 23 comparison of the experimental data with the list of earthquakes occurring at vulcano during 1991 showed the close temporal correspondence between the magnetic anomalies and earthquakes the amplitude between 2 and 4 nt spatial extent approximately 2 km and polarity of anomalies point to the piezomagnetic evect as the primary physical mechanism driving these transient changes on the other hand the anomaly with respect to the regional field observed over one year is explicable in terms of a thermomagnetic evect detected at both stations the magnetic static anomaly produced by a completely demagnetized spherical source of 250 m radius located under the la fossa crater at a depth of 1300 m is in agreement with the slow changes observed at vulcano

jurassic septarian concretions from nw scotland record interdependent bacterial physical and chemical processes of marine mudrock diagenesis septarian concretions in the staffin shales formation kimmeridgian isle of skye allow controls on concretion rheology and septarian cracking to be investigated stratabound concretions consist of anhedral ferroan calcite microspar enclosing clay and minor pyrite intergranular volumes range from 77 to 88 and calcite 13c and 18o values in most concretion bodies range from 10 0 to 17 3 and 0 3 to 0 6 respectively consistent with rapid and pervasive cementation in marine pore fluids septarian rupture occurred during incipient cementation with a sediment volume reduction of up to 43 crack lining brown fibrous calcite records pore fluid re oxygenation during a depositional hiatus followed by increasing fe content and 13c related to bacterial methanogenesis brown colouration results from an included gel like polar organic fraction that probably represents bacterially degraded biomass a new hypothesis for concretion growth and septarian cracking argues that quasi rigid proto concretions formed via binding of flocculated clays by bacterial extracellular polysaccharide substances eps this provided rheological and chemical conditions for tensional failure subcritical crack growth volume contraction calcite nucleation and incorporation of degraded products into crack lining cements bacterial decay of eps and syneresis of host muds provided internal stresses to initiate rupture at shallow burial development of septarian shrinkage cracks in muds is envisaged to require pervasive in situ bacterial colonization and to depend on rates of carbonate precipitation versus eps degradation and syneresis subsequent modification of septarian concretions included envelopment by siderite and calcite microspar hydraulic fracturing associated with cretaceous shallow burial or palaeogene uplift and cementation by strongly ferroan yellow sparry calcite that records meteoric water invasion of the host mudrocks an abundance of fatty acids in these spars indicates aqueous transport of organic breakdown products and 13c data suggest a predominantly methanogenic bicarbonate source however the wide 18o range for petrographically identical cement 1 3 to 15 6 is difficult to explain

the volcano electric effect 1 the formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical thm disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system we couple electromagnetic theory maxwell equations and thermoporoelasticity biot equations to look at the ground surface electrical signature of these thm disturbances the nature of this coupling is electrokinetic i e associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water mineral interface the groundwater flow disturbance being related here to the thm disturbances in drained conditions a new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi static electrical signals these signals can be used as precursors of a volcanic eruption indeed electromagnetic phenomena recorded at the ground surface of a volcanic system once properly filtered to remove external contributions provide a direct and quasi instantaneous insight into the thm disturbances occurring in the heart of the volcanic structure prior and during a volcanic event tomography of the quasi static electrical field is discussed and applied to self potential profiles performed at the piton de la fournaise volcano during the preparation phase of the march 1998 eruption

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

magnetic and electric field observations during the 2000 activity of miyake jima volcano central japan magnetic and electric field variations associated with the 2000 eruption of miyake jima volcano are summarized for about 1 week prior to the july 8 phreatic explosion significant changes in the total intensity were observed at a few stations which indicated uprising of a demagnetized area from a depth of 2 km towards the summit this nonmagnetic source can be regarded as a vacant space itself electric and magnetic field variations were observed simultaneously associated with the tilt step event which was the abrupt v50 s inflation at a few km depth within the volcano followed by gradual recovery vseveral hours the electric field is ascribed to the electrokinetic effect most probably due to forced injection of fluids from the source while the magnetic field to the piezomagnetic effect due to increased pressure large magnetic variations amounting to a few tens of nt were observed at several stations since july 8 and they turned almost flat after the august 18 largest eruption magnetic changes are explained mostly by the vanishing of magnetic mass in the summit and additionally by the thermal demagnetization at a rather shallow depth a large increase in the self potential by 130 mv was also observed near the summit caldera associated with the august 18 eruption which suggests that the hydrothermal circulation system sustained within the volcano for the past more than 10 years was destroyed by this eruption 9 2002 published by elsevier science b v

molecular organic geochemistry of a proposed stratotype for the oxfordian kimmeridgian boundary isle of skye scotland the composition of the soluble organic matter of the oxfordian kimmeridgian flodigarry shale member isle of skye scotland is presented for the first time a continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of staffin bay this succession is proposed as a potential stratotype of the boundary between the oxfordian and kimmeridgian stages this paper points out the exceptional preservation and very low thermal degradation of the organic matter indeed the molecular composition is characterized by the abundance of unsaturated biomarkers hopenes and diasterenes as well as undamaged bioterpenoids ferruginol and sugiol the abundance of long chain n alkanes characterized by an odd over even predominance reveals a dominant continental contribution this is also attested to by the relatively high amounts of plant biomarkers e g ferruginol sugiol cadalene and retene which suggest a palaeovegetation largely composed of pinophytes especially cupressaceae taxodiaceae and cheirolepidiaceae on the nearest emerged lands the water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part the composition of the organic matter does not significantly change along the flodigarry shale member in other words no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks and it does not allow us to support a precise location for the oxfordian kimmeridgian boundary in the succession

magnetic anomalies of lava fields in the canary islands possible consequences for paleomagnetic records abstract measurements of the total magnetic field have been performed above the surface of 12 lava flows in the canary islands of la palma and tenerife directions can differ by up to 15 and intensity changes reach 20 the mean flow directions do not coincide and the mean flow virtual dipole moments vdms differ by more than 10 the deviations are linked to topographic features at the surface of the flows and should persist during emplacement of the next overlying flow such effects can thus limit the resolution of paleomagnetic records of detailed geomagnetic features and the field intensity variations above the flows and between the mean flow values could explain a significant part of the scatter inherent to many paleointensity studies historical field variations have been recorded from the same flows and are in agreement with the european curve for the same period however there is also some correlation with the present field which suggest that the underlying magnetized bodies could have affected the paleomagnetic records biases induced by the crustal field would increase considerably during periods of reduced field intensity like during reversals and induce erroneous records samplings performed over large distances within each lava flow would provide the best way to average out the contribution of the anomalies in any case such effects should not be neglected in paleomagnetic studies

the role of thermal viscous remanent magnetisation tvrm in magnetic changes associated with volcanic eruptions insights from the 2000 eruption of mt usu japan abstract volcanic eruptions can produce large magnetic field changes by thermomagnetic effects especially when magma cools from high temperatures and acquires a permanent magnetisation from the earth s magnetic field after the 2000 eruption of mt usu japan significant magnetic field changes were observed not only in the vicinity of the magmatic intrusion but also in an area some distance away that was unlikely to be at a temperature near the curie point the magnetic changes in the latter area appear to be caused by thermal viscous remanent magnetisation tvrm in which the elevated subsurface temperatures have accelerated the acquisition of magnetisation parallel to the existing earth s field in the ground material the unusually large changes up to 40 nt yr are probably because of underlying reversely magnetised pleistocene rocks which are being normally remagnetised by exposure to temperatures of over 200 c we made an order of magnitude estimate of the likely effects of tvrm in this case based on some previous laboratory studies which confirms that tvrm is a plausible mechanism for the observed magnetic changes this paper provides probably the first field example in which a natural tvrm process associated with ongoing volcanic activity has been observed this indicates that even when temperatures are well below the curie point significant magnetic changes can occur on active volcanoes in many cases areas of recent volcanism are dominated by normal magnetisation and thus the tvrm only plays a minor role in volcanomagnetic changes it will however be a significant effect when materials with reversed or randomly oriented magnetisation are moderately reheated through volcanic activity we emphasize that separation of thermal viscous magnetisation from thermal magnetisation will sometimes be necessary for properly interpreting magnetic changes around volcanoes especially in relation to ongoing volcanic activities

very long period seismic signals observed before the caldera formation with the 2000 miyake jima volcanic activity japan 1 very long period seismic signals whose waveform consists of an initial impulsive signal and a later oscillatory wave with 0 2 or 0 4 hz in dominant frequency were observed before the caldera formation in the 2000 activity of miyake jima volcano japan the results of waveform inversion show that the initial and later parts can be explained by a northward single force of 1 5 108 n working at a depth of 2 km beneath the summit and a moment tensor solution at a depth of 5 km below and 2 km southwest of the summit with 1012 nm respectively a clear positive correlation of the amplitudes between the two sources strongly suggests that the shallow single force triggers the deeper moment source in spite of the several km distance between the two sources to analyze the source time functions of the moment tensor that do not always oscillate in phase we introduce a new method of moment tensor diagonalization which is performed in the frequency domain according to the analysis the two principal components have similar amplitudes and are greater than the third principal component suggesting an axially symmetric oscillation one of the possible systems is a combination of two cracks intersecting perpendicularly our interpretation is that the single force was generated when magma containing rock blocks suddenly began to move in a choked subsurface magma path and the resultant pressure waves propagated and excited a resonance oscillation of the two cracks

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

mineralogy at the magma hydrothermal system interface in andesite volcanoes new zealand ejecta from phreatomagmatic eruptions of ruapehu and white island andesite volcanoes in new zealand provide insight into the mineralogical reactions that occur when magma invades a vent hosted hydrothermal system at the surface and in ejected blocks from shallow depths hydrothermal alteration mineralogies are dominated by silica polymorphs anhydrite natroalunite and pyrite blocks from greater depths are composed mainly of cristobalite anhydrite halite and magnetite where altered material was heated to magmatic temperatures thermal decomposition reactions produced mullite wollastonite and indialite some ejected breccias contain osumilite cordierite sanidine and hypersthene indicative of reactions occurring near the osumilite cordierite phase boundary at 800 c and water pressure 0 2 kbar hedenbergite wollastonite andradite and magnetite are found in rare skarn fragments possibly formed by metasomatism of silica poor sulfate rich hydrothermal deposits high temperature parageneses of these types have not been reported before in shallow acidic volcano hydrothermal systems however they may be typical of the magma hydrothermal contact zone at many andesite volcanoes

principles of electrography applied to self potential electrokinetic sources and hydrogeological applications 1 the electrical potential field passively recorded at the ground surface of the earth and termed self potential can be analyzed to determine the shape and the depth of the piezometric surface the coupling between hydraulic flow and electrical current density is electrokinetic in nature the electrokinetic coupling coefficient entering into the integral equation relating the depth of the water table to self potential signals is analyzed for various types of porous materials it is simply related to the electrical conductivity of the pore water in steady state conditions each element of the water table can be seen as an elementary dipole with an inclination locally perpendicular to the water table and strength proportional to the water table elevation then we propose three methods to obtain the shape and range of possible depths of the water table from the study of the self potential distribution recorded at the ground surface the nonuniqueness of the solution is removed if one knows either the electrokinetic coupling coefficient or the water table at one location and under the assumption of the spatial homogeneity of the electrokinetic coupling coefficient two field cases are discussed to show the success of the proposed methods for estimating the shape and depth of the water table at two different scales of investigations they concern the study of self potential signals associated with the shape of the water table in the vicinity of a pumping well and in the flank of the kilauea volcano

a preparation zone for volcanic explosions beneath naka dake crater aso volcano as inferred from magnetotelluric surveys abstract the 1st crater of naka dake aso volcano is one of the most active craters in japan and known to have a characteristic cycle of activity that consists of the formation of a crater lake drying up of the lake water and finally a strombolian type eruption recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water mud eruptions and red hot glows on the crater wall temporal variations in the geomagnetic field observed around the craters of naka dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater volcanic explosions act to release the energy transferred from magma or volcanic fluids measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices where energy from various sources accumulates and in investigating the behaviors of magma and volcanic fluids we carried out audio frequency magnetotelluric surveys around the craters of naka dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km the main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption two dimensional inversions were applied to four profiles across the craters revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area in contrast we found no such remarkable conductor at shallow depths beneath the 4th crater which has been inactive for 70 years finding instead a relatively resistive body the distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results this unusual shallow structure probably reflects the existence of a supply path of high temperature volcanic gases to the crater bottom we propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep level magma and as a floor to infiltrating fluid from the crater lake the relatively resistive body found beneath the 4th crater represents consolidated magma these results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within naka dake

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

magnetic features of the magmatic intrusion that occurred in the 2007 eruption at stromboli island italy significant changes in the local magnetic field marked the resumption of eruptive activity at stromboli volcano on february 27 2007 after differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal thermal noise using temperature data we identified step like changes of 1 4 nt coincident with the opening of eruptive fissures in the upper part of the sciara del fuoco the magnetic variations detected at two stations are closely related to the propagation of a shallow ne sw magmatic intrusion extending beyond the summit craters area these observations are consistent with those calculated using piezomagnetic models in which stress induced changes in rock magnetization are produced by the magmatic intrusion no significant magnetic changes were observed when the first fractures opened along the ne crater rim indeed the stress induced magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and or thermal state of the summit area the continuous long term decay characterizing the post eruptive magnetic pattern can be related to a time dependent relaxation process a maxwell rheology was assumed and the temporal evolution of the piezomagnetic field was evaluated this allowed us to estimate the rheological properties of the medium in particular an average viscosity ranging between 1016 and 1017 pa s was a relaxation time of about 38 days

detection of aeromagnetic anomaly change associated with volcanic activity an application of the generalized mis tie control method repeat aeromagnetic surveys may assist in mapping and monitoring long term changes associated with volcanic activity however when dealing with repeat aeromagnetic survey data the problem of how to extract the real change of magnetic anomalies from a limited set of observations arises i e the problem of spatial aliasing recent development of the generalized mis tie control method for aeromagnetic surveys flown at variable elevations enables us to statistically extract the errors from ambiguous noise sources this technique can be applied to overcome the spatial alias effect when detecting magnetic anomaly changes between aeromagnetic surveys flown at different times we successfully apply this technique to asama volcano one of the active volcanoes in japan which erupted in 2004 following the volcanic activity in 2005 we conducted a helicopter borne aeromagnetic survey which we compare here to the result from a previous survey flown in 1992 to discuss small changes in magnetic anomalies induced by volcanic activity it is essential to estimate the accuracy of the reference and the repeat aeromagnetic measurements and the probable errors induced by data processing in our case the positioning inaccuracy of the 1992 reference survey was the most serious factor affecting the estimation of the magnetic anomaly change because gps was still in an early stage at that time however our analysis revealed that the magnetic anomaly change over the asama volcano area from 1992 to 2005 exceeded the estimated error at three locations one of which is interpreted as a loss of magnetization induced by volcanic activity in this study we suffered from the problem of positioning inaccuracy in the 1992 survey data and it was important to evaluate its effect when deriving the magnetic anomaly change

palaeoecology and sedimentology across a jurassic fault scarp ne scotland a detailed palaeoecological and sedimentological analysis of the kimmeridgian coastal outcrops around helmsdale northeast scotland has been related for the first time to a detailed biostratigraphical scheme allowing the depositional history of this important area adjacent to some north sea oilfields to be elucidated a broad shallow marine sub tropical shelf was disrupted by the onset of normal faulting along the helmsdale fault in earliest kimmeridgian times initially water depths remained shallow on the hanging wall reflected by a normal benthic fauna but a rapidly steepening southeast directed palaeoslope produced frequent sediment sliding shoreface sands developed immediately to the west of the fault and were transferred to the hanging wall via a fault transfer zone where they now constitute the allt na cuile formation continued rapid subsidence during the remainder of the kimmeridgian and the portlandian produced deep poorly oxygenated to anoxic benthic conditions on the hanging wall in which a combination of rock slide debris flow turbidity current deposition alternated with hemipelagite deposition to produce the helmsdale boulder bed formation the eathie locality cromarty previously regarded as a deeper more distal setting than helmsdale contains a slightly more diverse benthic fauna implying shallower water the deepest waters were immediately adjacent to the fault scarp as predicted by the standard half graben depositional model

hydrothermal system beneath aso volcano as inferred from self potential mapping and resistivity structure abstract we conducted self potential sp surveys sequentially from part to part over the central cones of aso volcano since august 1998 by december 2001 the compiled sp map revealed large sp anomalies on the central cones the main feature of the sp map is a w shaped profile along the ns transect over the central cones it is probable that this characteristic sp profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect a positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect to evaluate this sp anomaly we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three dimensional resistivity structure a layered structure obtained from a time domain electromagnetic tdem field experiment was used for the resistivity model the estimated current source is 300 a being located in a conductive layer around the sea level meanwhile sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of nakadake this value was used to estimate the equivalent current in either case of electro kinetic ek mizutani h ishido t 1976 a new interpretation of magnetic field variation associated with the matsushiro earthquakes j geomag geoelectr 28 179 188 or rapid fluid disruption rfd process johnston m j s byerlee j d lockner d 2001 rapid fluid disruption a source for self potential anomalies on volcanoes j geophys res 106 b3 4327 4335 this comparison suggests that the former process is preferable to explain the observed sp anomaly from these results we infer a large scale hydrothermal system beneath the central cones of aso volcano in which the fluid flow initiates from the surrounding area converging to the central vent to transport the heat and materials up to the crater lake of nakadake through a vapor filled conduit

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

volcanomagnetic signals associated with the quasi continuous activity of the andesitic merapi volcano indonesia 1990 1995 abstract merapi volcano in java island indonesia is an andesitic stratovolcano which presents long periods of effusive activity during which an endogeneous dome is continuously growing the viscous lava dome gives rise to unstable blocks which collapse or turn into pyroclastic flows when the volcano does not exhibit any surface activity the overpressure within the volcano slowly increases depending on the quietness duration the unrest of the volcano can start with an explosive phase during which the former dome is partly destroyed magnetic variations of different time constant are observed during the 1990 1995 period which includes one gas plume emission on august 26 1990 and two eruptions on january 20 1992 and on november 22 1994 compared with other types of active volcanoes the observed volcanomagnetic variations are very small at the most a few nanoteslas nt to discriminate the variations associated with the global activity from the signals correlated with each unrest phase one has to dissociate the different time constant variations over the six year time span when long term trends are removed from the magnetic field in each station of the network an outstanding correlation between all the magnetic differences is emphasised the midterm variations point out 2 cycles of activity which fit the stress field evolution within the edifice leading to the 1992 and 1994 eruptions a new cycle has started in may 1995 in every identified cycle rapid volcanomagnetic signals are well associated with stress field changes may 1991 september 1991 february 1993 december 1993 some of the volcanomagnetic variations are short term precursory signals as the three months decrease up to 1 3 nt preceding the 1992 eruption the comparison between magnetic data seismicity and surface phenomena implies that the midterm volcanomagnetic variations associated with the cycles of merapi activity are of piezomagnetic origin

the heat source of ruapehu crater lake deductions from the energy and mass balances abstract regular observations of temperature outflow rates and water chemistry of crater lake mt ruapehu new zealand have been made for the last 25 years these data have been used to derive a model of the dynamics of the lake and determine the input of energy mass and chloride from the volcano to the crater lake the recent relatively quiescent state of the volcano when virtually no heat has been input to the lake has also enabled an assessment to be made of the surface heat loss characteristics which play an important role in the model of the lake the modelling suggests that since about 1982 the ratio of the volcanic heat to mass added to the base of the lake is about 6 mj kg which is not compatible with heating of the lake by magmatic steam alone thus only about 50 of the heating has been by magmatic steam it is suggested that heat could be transferred from a magmatic source to the region below the lake by a heat pipe mechanism commonly associated with geothermal systems the simultaneous upward movement of vapour phase and downward movement of liquid phase from condensed vapour allows efficient heat transfer without overall mass transfer the permeability necessary to supply the required heat is of the order of 10 darcy and is consistent with a rubble filled vent for at least the last five years there has been a characteristic pattern in the crater lake temperature record with alternate heating and cooling phases the heating phase generally lasts for one or two months while the cooling phase lasts for six months to a year a possible explanation for this cyclic behaviour is the presence of a layer of liquid sulphur under crater lake acting as a partial barrier between the heat pipe and the lake the unusual variations of the viscosity of liquid sulphur with temperature will mean that at temperatures greater than 160 c the layer of sulphur becomes highly viscous and would block any upwards steam flow and hence stop the heat input to crater lake so producing a cooling phase this blockage would last until the heating from below raised the temperature of the sulphur beyond the high viscosity region so gases could again pass through the sulphur

piezomagnetic fields due to an inclined rectangular fault in a viscoelastic half space an application to the 2002 2003 etna eruption summary time dependent piezomagnetic fields due to inclined rectangular faults embedded in a viscoelastic homogeneous half space were investigated a viscoelastic rheology of the surrounding medium was assumed to relate piezomagnetic changes at the surface to the stress field at depth the viscosity of the medium strongly influences time dependent stress changes especially in volcanic areas rocks near magmatic sources are considerably heated the presence of higher temperatures produces a lower effective viscosity in the crust making it necessary to consider its inelastic properties rocks no longer behave in a purely elastic manner but permanently deform because the viscosity is significantly lowered to determine the time dependent piezomagnetic fields in a viscoelastic medium we applied the correspondence principle to the analytical elastic solutions for dislocation sources among all the possible rheological models we investigated three cases in which the bulk modulus is purely elastic and the shear modulus relaxes as for i a maxwell solid ii a standard linear solid sls and iii a kelvin solid the piezomagnetic field completely vanishes after the relaxation process for a maxwell rheology whereas it is found to decrease over time and reach some finite offset values for sls and kelvin rheologies a real case study concerning the magnetic anomalies observed during the 2002 2003 mt etna eruption is also investigated post eruptive magnetic variations were in general agreement with a viscoelastic relaxation process of a sls rheology undergoing in the volcano edifice

resistivity variations related to the large march 9 1998 eruption at la fournaise volcano inferred by continuous mt monitoring abstract the 2645 m high la fournaise volcano located in the southwest of reunion island indian ocean is a shield basaltic volcano where effusive eruptions generally occur along long fissures starting from the summit alongside major fractures that characterize the eruptions dynamism and effusivity between 1992 and 1998 the volcano underwent a quiet period during which few earthquakes were recorded minor seismic activity returned after 1997 and picked up in march 1998 during the 35 h preceding the march 9 eruption from 1996 two autonomous stations csv and bav were installed on the volcano csv was located inside the enclos fouque caldera while bav was positioned 8 2 km nw of the volcano summit horizontal components of the electric and magnetic fields were sampled every 20 s continuous time series were available from 1996 to 1999 at csv and from 1997 to march 1998 at bav data have been processed using both single station and remote reference processing both results show apparent resistivity variations synchronous to the eruption time lapse impedance estimates are computed on overlapping time windows of about two days at both stations the only major decrease of the observed impedance coincides with the march 1998 eruption at csv the resistivity started to drop about five days before the eruption reached several local minima until april and then slowly increased as the volcanic crisis reduced in activity after the end of the crisis in september 1998 the apparent resistivity recovered its pre crisis value the time lapse results also show variability in directionality sharp and elongated phase tensor ellipse residuals appear during the eruption with a n105 orientation suggesting the emergence of an almost ns striking dyke a 1d background model built from mt soundings performed during the quiet period 1996 to february 1998 on which a 3d ns striking dyke was added shows a good agreement with phase tensor residuals and spatial distribution of the resistivity variations observed during the eruption

magnetic field changes on white island new zealand and the value of magnetic changes for eruption forecasting for about 15 years after their commencement in 1968 magnetic measurements in the crater of white island gave a good indication of the state of activity and the likelihood of an eruption episode commencing during this period magnetic thermal ground level and chemical measurements were all generally consistent with a model in which these surface changes were caused by increasing temperatures under the donald mound area in the central sub crater in more recent times there has not been such a relationship between the changes around the remnants of donald mound and the volcanic activity which has become localised in the west sub crater it appears that changes under the crater especially lowering of the ground surface and the water table at the west end of the crater have meant that eruptions are no longer preceded by heating under donald mound the west sub crater is not easily accessible for repeat surface surveys one way in which we might be able to monitor future volcanic activity at white island would be by repeated aeromagnetic surveys as the magnetic changes are so large that changes of hundreds of nanoteslas are likely to be observed at practical flying heights

long term thermal activity revealed by magnetic measurements at kusatsu shirane volcano japan abstract repeated geomagnetic measurements commenced around the three summit crater lakes of kusatsu shirane volcano yugama mizugama and karegama lakes in 1976 and continuous measurements commenced in 1990 we reviewed and analyzed these geomagnetic data acquired over the 34 years starting in 1978 changes in the geomagnetic field related to eruptions during 1982 1983 were recorded in the repeated geomagnetic measurements from 1982 to 1985 a thermal demagnetization source was estimated to be 400 m below mizugama crater lake during this period although there were no eruptions from 1988 to 1991 there were numerous volcanic earthquakes thermomagnetic signals due to demagnetization of the material beneath the crater lakes were recorded by the repeated magnetic measurements during this period the demagnetized body was estimated to be 600 m below mizugama crater lake at this time previous seismological and geochemical studies attributed these demagnetization events to the ascent of hydrothermal water and volcanic gas the difference between the depths of demagnetized bodies during these two periods of demagnetization may provide important information about the mechanism of the 1982 1983 eruptions in contrast magnetization associated with cooling of rocks beneath the crater lakes was recorded from 1996 to 2012 according to our thermomagnetic modeling of this period the source of the magnetization was 400 to 700 m below an area immediately northeast of yugama crater lake and the cooling migrated gradually to shallower depths during this period based on our modeling seismological data and geochemical monitoring of yugama lake water we consider that the flux of hydrothermal fluid from depth decreased after 1992 and rock magnetization due to cooling began in 1996

characteristics of isolated hybrid tremor hbt during a calm activity period at aso volcano isolated type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed during the fumarolic activity stage at aso volcano these isolated tremors are called hybrid tremors hbt and comprise two parts an initial part named the hf part with a dominant frequency in the high frequency region approximately 10 hz and the following part named the lf part with a dominant frequency in the low frequency region approximately 2 hz the lf part is observed after the hf part and the hbt is accompanied by a long period tremor lpt hypocenters and source parameters are estimated using seismograms recorded at 64 stations around nakadake crater the amplitude distributions of all hf parts have almost similar trends similarly the amplitude distributions of all lf parts have almost similar trends however the amplitude distributions of hf and lf parts are not similar from these results we proposed that the hypocenters and source parameters of hf and lf parts are not common but each of them have common hypocenters and source parameters the hypocenter region of hf parts was estimated to be just beneath the fumarole region south of the 1st crater the volume fluctuation is the major source factor the hypocenter region of lf parts is estimated to be at a depth of approximately 300 m beneath the first crater the strike slip component is the major source parameter the hypocentral depth of lf parts is located at the upper end of the crack estimated to be the source of the lpts the lpts and hbts are observed almost simultaneously we consider that volcanic fluid is involved in the source mechanisms of both hbt and lpt

geophysical studies of the recent 15 year eruptive cycle at poas volcano costa rica abstract the recent eruptive cycle at poas volcano was notable for the dramatic disappearance and subsequent reappearance of the summit crater lake this cycle consisted of discrete phases of activity associated with a range of geophysical and geochemical signatures that illustrate the relative value of the various techniques for identifying precursory phenomena intrusive episodes in 1980 and 1986 1989 at poas were preceded by a type seismicity magma rose close to the surface on both occasions but the focus shifted from the dome 1980 when the lake remained stable to the crater lake 1986 1989 the 1986 1989 event which culminated in the complete loss of the crater lake and explosive eruptions was characterised by concurrent increases in micro gravity on the southern crater floor b type seismicity and lake temperature and by changes in lake geochemistry the calculated mass of magma intruded in this period is far too small to account for the observed increase in surface heat flux and subsequent loss of the lake we suggest that a series of magma filled dendritic conduits intruded beneath the lake facilitated enhanced heat and gas flux from a deeper magma feeder body a model is envisaged where brittle fracture of the magma carapace at about 500 m depth allows magma to rise up through the conduit system beneath the crater and to fall again or solidify in situ when pressure drops whilst active this process transfers heat and gas upwards driven by the convection of buoyant volatile rich magma displacing colder relatively volatile poor magma as magma pressure from below decreases the link between the deeper magma feeder and the upper conduit system is broken and the hydrothermal system resumes its role of cooling the magma feeder the role of the lake as a physical and chemical buffer to the volcanic system was clearly demonstrated when its disappearance in 1989 was accompanied by enhanced eruptive activity and gas emissions with considerable local environmental impact the lake therefore acts as both a moderator and index of volcanic processes at poas

a volcanomagnetic observation on mount st helens washington total magnetic fields were recorded at five sites on mt st helens between 23 october and 11 november 1981 an interval which included an extrusive dome building eruption of the volcano two of the magnetometers located in the volcano s crater measured reversible magnetic changes which correspond to fluctuations in tilt measured nearby however the relationship is highly nonlinear electric fields were measured on the east flank of the volcano near its summit to search for electrokinetic effects they show no correlation with the magnetic changes and in the long term are uncorrelated with eruptive activity our favored interpretation of the magnetic changes is that they result from stress induced changes in the magnetization of the volcano magnetic field values returned to pre anomaly values this reversibility rules out pressure induced magnetization as the dominant mechanism and places an upper limit of 300 bars on the stress changes the limited spatial extent of the magnetic anomaly field places the source of stress at shallow depth beneath the crater floor consistent with models based on strain data

automated system for magnetic monitoring of active volcanoes in order to provide a basis for short term decision making in the forecasting and monitoring of volcanic activity we developed an entirely automated system of data acquisition and reduction for magnetic data the system mag net is designed to provide monitoring and analysis of magnetic data on etna volcano at large distances from the central observatory the mag net system uses data from an array of continuously recording remote stations spread over the volcanic area and linked by mobile phone to the control center at the local observatory at this location a computer receives the data and performs data sorting and reduction as well as limited evaluation to detect abnormal behavior or breakdown of remote sensors communication software called magtalk is also designed to provide data to distant users with a view to using continuous magnetic observations in advanced analysis techniques for volcano monitoring the mag net system also delivers two graphical user interface based applications to provide an interpretation capability the former called madap speeds up all the data reduction processes in order to evaluate the reliability of magnetic signals the latter called vmm is a procedure for modeling magnetic fields associated with tectonic and volcanic activity to facilitate the identification and interpretation of the sources of a wide spectrum of magnetic signals