ground deformation near gada ale volcano afar observed by radar interferometry radar interferometric measurements of ground surface displacement using ers data show a change in radar range corresponding to up to 12 cm of subsidence near gada ale volcano in northern afar ethiopia that occurred between june 1993 and may 1996 this is the area of lowest topography within the danakil depression 126 m geodetic inverse modeling and geological evidence suggest a volcanic origin of the observed deformation it was probably caused by a combined process of magma withdrawal from a larger reservoir and normal faulting there is no evidence of subaerial eruption this is the only identifiable deformation event during june 1993 october 1997 in the 80 km long erta ale volcanic range indicating surprising inactivity elsewhere in the range

spectral and dynamical hints on the time scale of preparation of the 5 april 2003 explosion at stromboli volcano stromboli volcano is well known for its continuous strombolian activity moreover the volcano occasionally shows effusive phases the latest in 1985 1986 on 28 december 2002 stromboli entered a new effusive phase accompanied by different paroxysmal events that led to considerable hazards for inhabitants and tourists on the island of stromboli on 30 december 2002 a major sector collapse affected the sciara del fuoco slope and initiated a tsunami on 5 april 2003 a powerful explosion which can be compared in size with the most recent explosion in 1930 covered a large part of the normally tourist accessible summit area with bombs as this explosion was not forecasted although the island was by then effectively monitored by a dense deployment of instruments in this paper we tackle the problem of highlighting the time scale of preparation of this event and conduct a search for possible precursors for this purpose we analyze the seismic data preceding the paroxysm with spectral and dynamical methods

decomposition location and persistence of seismic signals recovered from continuous tremor at erta ale ethiopia abstract subband decomposition and reconstruction sdr provides a quantitative semi automated rapid means of analyzing volcanic tremor which can recover signals that dominate different parts of the frequency spectrum while preserving polarization and phase here applied to data from a two week experiment at erta ale in nov dec 2003 we demonstrate that the sdr method can identify signals corresponding to source processes active in several different physical regions of the erta ale caldera different recovered signals suggest that the continuous tremor at erta ale is a composite of several seismic sources including conduit resonance bubble bursting phenomena and degassing at fumaroles these signals are seen throughout the 2003 experiment suggesting that several competing source models of volcanic tremor can produce signals at the same volcanic conduit system simultaneously

spectral discrimination of nts explosions and earthquakes in the southwestern united states using high frequency regional data a high frequency seismic station has been operating since march 1987 near nelson nv records of earthquakes at regional distances from the station show substantially more energy at frequencies above 10 hz than records of nuclear tests of comparable magnitude on the nevada test site this contradicts the predictions made by investigators who have advocated high frequency monitoring for nuclear test detection and identification measuring the slopes of the pg velocity spectra between 4 and 30 hz successfully discriminates 11 nts explosions from 36 earthquakes recorded in the first seven months of operation the spectral differences may result from the respective source depths with the earthquakes occurring deeper and in faster material than the explosions

vorlanite cau6 o4 from jabel harmun palestinian autonomy israel vorlanite cau 6 o 4 fm 3 m a 5 3647 9 a v 154 40 4 a 3 z 2 was found in larnite pyrometamorphic rocks of the hatrurim formation at the jabel harmun locality judean desert palestinian autonomy vorlanite crystals from these larnite rocks are dark gray with greenish hue in transmitted light this color in transmitted light is in contrast to dark red vorlanite fm 3 m a 5 3813 2 a v 155 834 10 a 3 z 2 from the type locality upper chegem caldera northern caucasus heating above 750 c of dark gray vorlanite from the jabel harmun as well as dark red vorlanite from caucasus led to formation of yellow trigonal uranate cauo 4 the unusual color of vorlanite from jabel harmun is assumed to be related to small impurities of tetravalent uranium

lava lake surface characterization by thermal imaging erta ale volcano ethiopia the project sviluppo di sistemi di monitoraggio dipartimento di protezione civile di regione sicilia ingv catania section italy the leverhulme trust the bbc and the ethiopian air force

mechanism of energy transfer in the lava lake of niragongo zaire 1959 1977 abstract heat and mass transfer rates were studied at the niragongo lava lake during two expeditions directed by h tazieff in 1959 and 1972 the results of this study are as follows heat is transferred to the surface of the lake by the movement of lava gas discharge is a result and not the cause of convection the chemical composition of the gases and magma has changed very little between 1959 and 1972 whereas the mass and energy outputs differ by an order of magnitude in 1977 a catastrophic explosion seems to have been caused by tectonic factors stopping the slow convection of magma under the volcano and hence reducing surface manifestations in the form of the lava lake and escaping fumarolic and magmatic gases the gas discharge was in tons day 1 5000 for h2o 11 000 for co2 1000 for so2 in 1959 and in 1972 7700 for h2o 180 000 for co2 and 23 000 for so2 these values correspond to an energy transfer of 0 9 109 w in 1959 and 16 109 w in 1972

locating tremor and shock sources recorded at bromo volcano abstract during a phase of high eruptive activity as well as high tremor activity seismic signals were recorded at bromo volcano east java for almost three months in 1995 the signals generated by the volcano cover a broad frequency range including long period signals with frequencies between 10 and 100 mhz tremor signals at about 5 hz and volcanic shocks with frequencies up to 25 hz seismic signals from volcanoes especially tremors have been classified and categorized in different ways but interpretation has always been limited by the difficulties in determining even approximate source locations volcanic tremor lacks an emergent first onset while the complex structure of the volcano makes it difficult to determine other phases from shock signals than first arrivals if the volcanic signal has been recorded in at least two stations the location of its seismic source can be estimated using a grid search method if we assume the source radiates isotropically in a homogeneous medium applying the grid method to data recorded at mt bromo we determine the locations of the sources of tremor and shock signals the sources for both types of signals are located in the northwestern part of the crater near the open vent and also near the source of long period signals gottschammer 1999 annal geofis 42 465 481

discovery of a recurrent lava lake on saunders island south sandwich islands using avhrr imagery abstract monitoring of the remote south sandwich islands volcanic arc using advanced very high resolution radiometer avhrr data has identified a radiant pixel on channels 3 3 55 3 93 m and rarely 4 10 3 11 3 m the position of the pixel is coincident with mount michael saunders island the active summit crater of a snow covered basaltic stratovolcano with a persistent steam plume the radiant pixel was continuously present in successive avhrr images acquired during intervals of several months in the period examined march 1995 february 1998 although apparently disappearing for similar time intervals more than 5000 images were examined during this study the radiant pixel is interpreted to indicate that the crater has contained a lava lake the first to be recorded in the south sandwich islands the lake appears to persist in the crater for several months at a time at least it may have drained completely at times and was probably absent when the crater was viewed briefly during an overflight in january 1997 persistent or recurring lava lakes are very uncommon world wide and that at mount michael is one of only two recorded in the antarctic region

subband decomposition and reconstruction of continuous volcanic tremor abstract a new method of analyzing volcanic tremor is presented which uses properties of undecimated wavelet packet transforms to filter decompose and recover signals from continuous multichannel data the method preserves many standard properties that are used to characterize tremor such as wavefield polarization and seismic energy in this way we can better understand the potentially many seismic sources that combine to form continuous volcanic tremor and we can specifically address the problem of what causes changing tremor spectral content tests on synthetic data suggest that sdr can recover multiple quasi continuous signals that differ from one another by an order of magnitude even in noisy environments tests on real data recorded at erta ale in 2002 suggest that sdr can recover signals with geophysically meaningful interpretations and corroborates existing seismic and multiparametric work by harris et al 2005 jones et al 2006 and harris 2008 we suggest that this algorithm could effectively detect subtle changes in the time frequency content of volcanic tremor and recover signals from real seismic sources that appear buried in background noise and or partly masked by one another such an algorithm could allow volcanologists much greater insight into the dynamics of volcanic systems and could detect subtle signals that might help address the possibility of unrest

mt niragongo renewed activity of the lava lake abstract on the 21st of june 1982 mt niragongo ended a period of dormancy that had begun on january 11 1977 and fresh lava began to flow into the 800 m deep crater on october 3 a huge lava lake wider and deeper than any previously observed 500 m across and close to 400 m deep rose to within 440 m of the crater rim the observed activity consisted of a large central upwelling fountain of very fluid lava from which concentric lava waves expanded radially numerous small relatively viscous lava flows creeped over the surrounding thin solidified crust that covered about 95 of the lake area these observed features seem to characterize the upper part of a large convective system the persistence of such an extraordinarily large steady state lava lake may be due to the equally exceptional fluidity of the magma rising at the intersection of four different tectonic trends of fractures in the subvolcanic basement

a comparison of regional phases from underground nuclear explosions at east kazakh and nevada test sites abstract analysis of regional data from east kazakh ussr and nevada test site nts underground nuclear explosions suggests possible mechanisms for the generation of both low and high frequency lg spectral characteristics of pn and lg phases from 25 soviet nuclear shots recorded at the chinese digital seismic network cdsn station wmq are analyzed for their dependence on parameters such as m b generally related to shot depth and spatial location shagan versus degelen test sites the observed results are compared with those from the nevada test site nts where the near source conditions are better known the average amplitude ratio pn lg is found to be stable with m b but to vary strongly with frequency for both shagan and yucca flat explosions of similar yield the reduction in amplitude over the frequency range of about 1 to 5 hz is considerably larger for lg than for pn the low frequency lg appears to be generated by the scattering of explosion generated rg into s especially for the shagan river explosions for which good agreement between observation and theory is observed this mechanism also provides a possible explanation for the stability of lg as an estimator of explosive yields because the scattering should be expected to occur over a large region of the shallow crust another important result supported by theory is that the higher frequency lg is strongly dependent on the source medium velocity at higher frequencies 3 to 7 hz the amplitude ratios pn lg for explosions from shagan degelen pahute mesa and yucca flat test sites show significant differences that appear related to differences in their source medium velocities the observed large differences in the relative spectral content of pn and lg from east kazakh and nts explosions are mainly due to the vast differences in the crustal structure of the two test sites

slopes of p to s wave spectral ratios a broadband regional seismic discriminant and a physical model concerns about nuclear proliferation and negotiations toward a comprehensive test ban treaty ctbt emphasize the need for robust seismic monitoring and regional discrimination capabilities especially at low magnitudes standard regional discrimination techniques have many shortcomings for example they cannot always discriminate shallow low magnitude earthquakes or mining related events i show that slopes of p to s wave spectral ratios can be used to discriminate shallow and normal depth earthquakes from explosions and possibly to discriminate explosions from mining related rockburst or collapse events p to s wave slopes and conventional high frequency p to s wave spectral amplitude ratios discriminate even better in combination than alone a comparison of pn and lg spectra from nevada test site nts explosions and earthquakes shows that this method discriminates concentrated explosions from earthquakes and other shallow seismic events such as mine collapses because s waves from explosions decay more rapidly at high frequencies than do s waves from earthquakes spectra of one dimensional reflectivity synthetic seismograms show that frequency dependent attenuation of explosion generated p to s wave converted phases in the near surface layers may be responsible for the differences in lg s wave spectral falloff these simulations also show that absolute amplitudes of earthquake p to s wave spectral ratios are very sensitive to mechanism and depth which may help explain the variable performance of conventional methods

comments on the paper automatic detection and discrimination of volcanic tremors and tectonic earthquakes an application to ambrym volcano vanuatu by daniel rouland denis legrand mikhail zhizhin and sylvie vergniolle j volcanol geotherm res 181 2009 196 206

analysis of phreatic events at ruapehu volcano new zealand using a new som approach abstract we apply self organising maps som to assess the low level seismic activity prior to small scale phreatic events at ruapehu volcano new zealand the som approach allows an automatic pattern recognition virtually independent from a priori knowledge volcanic tremor spectra are randomly presented to the network in a competitive iterative training process followed by a hierarchical clusterization of the som nodes spectra are then projected ordered by time to clusters on the map a coherent time evolution of the data through the clusters can highlight the existence of different regimes and the transitions between them two ruapehu events were examined a phreatic event on 4 october 2006 which displaced the crater lake producing a 4 m high wave on the lake edge and the more energetic 25 september 2007 phreatic eruption the som analysis provides a classification of tremor spectral patterns that clusters into three regimes that we label by colours the pattern for both eruptions is consistent with a pre eruption spectral pattern including enhanced spectral energy in the range of 4 to 6 hz labelled green tremor this gives way to spectra having broader energy between 2 and 6 hz the so called red tremor just prior to the eruption the post eruption pattern includes spectral peaks at generally lower frequencies of 2 to 4 hz the so called blue tremor clusterization into only three groups yields highly non unique solutions which cannot explain the variety of processes operating at ruapehu over long time periods regardless the approach highlights noteworthy similarities that may be explained by a pattern of slow pressurisation under a hydrothermal or magmatic seal green followed by seal failure red and subsequent de pressurisation blue for the two events studied although the application shown here is limited we think it demonstrates the power of this classification approach

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

gas driven lava lake fluctuations at erta ale volcano ethiopia revealed by modis measurements the long lived lava lake of erta ale volcano ethiopia is remotely monitored by moderate resolution imaging spectroradiometers modis installed on satellites the normalised thermal index nti wright et al remote sens environ 82 135 155 2002 is shown to be proportional to the volume of the lava lake based on visual observations the lava lake s variable level can be plausibly related to a stable foam i e a mixture composed of densely packed non coalescing bubbles in suspension within a liquid this foam is trapped at the top of the magma reservoir and its thickness changes in response to the gas flux feeding the foam being successively turned on and off the temporal evolution of the foam thickness and the resulting variation of the volume of the lava lake is calculated numerically by assuming that the gas flux feeding the foam initially constant and homogeneous since december 9 2002 is suddenly stopped on december 13 2002 and not restarted before may 2003 the best fit between the theoretical foam thickness and the level of the lava lake deduced from the nti provides an estimate of both the reservoir radius 155 170 m and the gas flux feeding the foam 5 5 10 3 7 2 10 3 m 3 s 1 when existing this is in agreement with previous estimates from acoustic measurements bouche et al earth planet sci lett 295 37 48 2010 the very good agreement between the theoretical foam thickness and that deduced from modis data shows for the first time the existence of a regime based on the behaviour of a stable foam whose spreading towards the conduit wide conduit condition can explain the long lived activity our predictive model which links the gas flux at the vent to the foam spreading could potentially be used on any volcano with a long lived activity the underlying gas flux and the horizontal surface area of the magma reservoir can then be deduced by combining modelling to continuous measurements of gas flux the lava lake when high often shows regular rise and fall of its level we have recognised a minimum of 26 very well marked cycles between january 2001 and december 13 2002 corresponding to a typical return time of 10 8 2 3 days and a gas volume of 8 3 105 2 0 105 m 3 this corresponds to a gas volume fraction in the reservoir equal to 0 023 0 063 the yearly gas flux estimated between december 13 2002 and september 27 2004 varies between 2 3 10 6 and 5 9 10 6 m 3 s 1 at the depth of the reservoir the long time series provided by infra red sensors mounted on satellites could be used on any persistent volcano to detect potential periodic variations in the level of lava lakes or lava columns providing that the vent has a funnel shape as often and is sufficiently large

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

process of the 1977 nyiragongo eruption inferred from the analysis of long period earthquakes and volcanic tremors abstract the lava lake present in the summit crater of nyiragongo from 1928 to 1977 completely disappeared after the short lived eruption of january 10th 1977 the sequence of events during this eruption was elucidated by analysis of seven long period earthquakes lp events and volcanic tremors recorded at stations lwi nai and bul the seven lp events observed were composed mainly of rayleigh waves with large amplitudes and were classified into two groups one containing three and the other containing four events based on waveform similarities it was determined that the former events were excited by the vertical downward single forces and the latter events by the vertical upward ones the short period seismograms recorded at lwi and nai showed that continuous volcanic tremors began roughly 6 min before the occurrence of the first lp event after the appearance of seven burst type tremor activities tremor amplitudes suddenly increased and then gradually decreased taking the analytical results of seismic events and observed surface activities into consideration we inferred the process of the 1977 nyiragongo eruption to be as follows 1 1 quick draining of the liquid lava through the fissures and disappearance of the long lived lava lake less than 6 min 2 2 large terraces collapsing onto the bottom of crater causing the first three lp events during the next 8 min 3 3 intermittent vesiculation of lava at the top of magma chamber exciting the last four lp events during the next 8 min 4 4 magma flowing in deeper parts of the conduit generating the intense tremors measurable at nai and lasting for roughly 30 min

first recorded eruption of mount belinda volcano montagu island south sandwich islands the modvolc satellite monitoring system has revealed the first recorded eruption of mount belinda volcano on montagu island in the remote south sandwich islands here we present some initial qualitative observations gleaned from a collection of satellite imagery covering the eruption including modis landsat 7 etm aster and radarsat 1 data modvolc thermal alerts indicate that the eruption started sometime between 12 september and 20 october 2001 with low intensity subaerial explosive activity from the island s summit peak mount belinda by january 2002 a small lava flow had been emplaced near the summit and activity subsequently increased to some of the highest observed levels in august 2002 observations from passing ships in february and march 2003 provided the first visual confirmation of the eruption aster images obtained in august 2003 show that the eruption at mount belinda entered a new phase around this time with fresh lava effusion into the surrounding icefield modis radiance trends also suggest that the overall activity level increased significantly after july 2003 thermal anomalies continued to be observed in modis imagery in early 2004 indicating a prolonged low intensity eruption and the likely establishment of a persistent summit lava lake similar to that observed on neighboring saunders island in 2001 our new observations also indicate that lava lake activity continues on saunders island

thermal seismic and infrasonic evidences of variable degassing rates at stromboli volcano abstract during june 1999 we measured the amplitude and rate number of events per second at which gas exited the vent at stromboli volcano as discrete gas bursts or puffs this allowed us to identify two styles of gas burst puffing activity the first is characterized by frequent rapidly rising puffs the second by less frequent slowly rising puffs each style persisted over 5 40 min long durations and was associated with a high and low number of strombolian explosions per hour respectively each period was also associated with characteristic delay times between the arrival of the infrasonic and thermal signals during strombolian explosions the delays were longer during vigorous puffing periods to explain our observations we propose a model in which the degassing process cycles between vigorous and weak degassing phases during vigorous degassing phases bubble layers ascend the conduit at a frequency of 0 5 1 0 s 1 this high degassing level reflects a gas rich magma column and leads to an increased rate in the formation of shallow foams and hence an increase in puffing and explosive activity as well as a higher free surface level and or gas jet velocity during weak phases bubble layers ascend the conduit at a reduced frequency of 0 2 0 3 s 1 during such times the magma column is poor in gas this leads to a decreased rate of foam layer formation and hence a reduction in puffing and explosive activity as well as a lower free surface level and or gas jet velocity variations in puffing activity can thus be used to track changes in the rate at which the shallow system is supplied by fresh gas rich magma our observations indicate that the two degassing styles last from 5 to 40 min and that the switch from one to the other occurs over a matter of minutes

identification of earthquakes and explosions using amplitude ratios the vogtland area revisited identification of seismic events is a major scientific issue in the framework of verification of the comprehensive nuclear test ban treaty ctbt of special interest in this context is the identification of the numerous low yield mining or blasting events especially those occurring in the same area as earthquakes such as the vogtland area in the border region of germany and the czech republic seismic events in this area were investigated by wuster 1993 1995 who achieved complete discrimination using measures of spectral decay and spectral variance at the geress array and a quadratic discrimination function

the little skull mountain nevada earthquake of 29 june 1992 aftershock focal mechanisms and tectonic stress field implications the ml 5 6 29 june 1992 little skull mountain earthquake occurred in the southern nevada test site nye county nevada within 20 km of a potential national nuclear waste repository at yucca mountain nevada while microseismicity in the immediate epicentral vicinity occurred for years prior to the mainshock foreshock activity ml 2 were also sufficiently well recorded to provide local network p wave focal mechanism solutions the mainshock and the majority of the aftershocks through september 1992 display predominantly normal slip focal mechanisms but unambiguous strike slip and oblique slip focal mechanism solutions are also present in the aftershock series the mainshock and immediate foreshock depths were 10 1 km below sea level and depths of focus of aftershocks range from about 6 to 12 km a large subset of the aftershock hypocenters define a southeast dipping structure probably the mainshock fault plane no variation of mechanism style with depth is apparent two mainshock and 84 aftershock focal mechanism solutions were input into gephart s 1990 stressfield inversion program and principal compressional stress directions j j 1 2 3 were determined as well as the stress difference ratio r 1 2 1 3 the results indicate a uniform stress field in which 3 minimum stress is oriented 116 5 azi plunge and 1 maximum stress is oriented 219 69 with r 0 35 the inversion s selection of preferred nodal planes invokes bott s 1959 criterion which states that slip occurs in the direction of resolved shear traction on preexisting fault surfaces for the predominantly normal slip little skull mountain earthquake mechanisms having northeast striking planes the southeast moderately to steeply dipping dip 55 nodal planes are selected however for the dip slip earthquake mechanisms exhibiting more northerly trending strikes shallowly to moderately west dipping 25 dip 65 nodal planes are selected when a coulomb mohr analysis was applied to the focal mechanisms using the above principal stress directions and an assumed ratio 1 3 the ratio of resolved shear stress to normal stress n on the southeast dipping nodal plane of the mainshock exhibited a near maximum level suggesting a high fault strength in contrast a wide range of fault strengths or apparent coefficients of friction was suggested by the n ratios for little skull mountain aftershock preferred nodal planes seismicity on misoriented faults i e those on which shear stress was relatively low may have been the result of a temporarily elevated fluid pore pressure following the mainshock

using so 2 camera imagery and seismicity to examine degassing and gas accumulation at kīlauea volcano may 2010 abstract so 2 camera measurements at k lauea volcano hawaii in may of 2010 captured two occurrences of lava lake rise and fall within the halema um au crater summit vent during high lava stands we observed diminished so 2 emission rates and decreased seismic tremor similar events at k lauea have been described as the result of sporadic degassing following gas accumulation beneath a mostly impermeable lava lake surface incorporation of so 2 camera data into a multi parameter dataset gives credence to the likelihood of shallow gas accumulation as the cause of these high stand events with accumulated gas release upon lake level drop compensating for the gas deficit reached during accumulation

time dependent fisher information measure of volcanic tremor before the 5 april 2003 paroxysm at stromboli volcano italy the investigation of the time dynamics of volcanic tremor recorded at stromboli volcano before the paroxysm occurred on april 5 2003 was performed on the base of a new approach the fisher information measure fim which allows to detect changes in the dynamical behavior of a complex system the particular observed pattern suggests that the signal varies between sets of disordered states small fim and sets of ordered states large fim significant precursory changes in the temporal variation of the fim were revealed at least 42 h before the paroxysm and lasting about 17 h the timescales highlighted are compatible to those found by other authors and could qualify the fim as a good detector of regime changes and possible precursors of anomalous volcanic activity

seismic characteristics of variable convection at erta ʻale lava lake ethiopia abstract the active summit lava lake of erta ale volcano ethiopia offers a unique opportunity to study magma convection in february 2002 we collected a multiparametric set of seismic thermal and video data these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 convection rates typically lasting tens to hundreds of minutes three seismometers placed around the active crater recorded continuous tremor with a dominant frequency of 2 hz and energy at frequencies from 0 8 to 12 hz here we characterize the seismic signature of each regime by its spectral content wavefield polarization and tremor source location for both regimes the wavefield is mostly rectilinear azimuths and incidence angles are consistent with p waves originating in one of two locations the north edge of the active lava lake or a region 100 150 m ene of the lava lake because both regimes are dominated by a low frequency rectilinearly polarized wavefield we investigate the source location using a method that solves for location and isotropic source power by a weighted least squares amplitude based inversion of seismic data we find that tremor source regions are unique to each convective regime although some location overlap exists when tremor is located in short time windows wavefield composition suggests that the convective phases may share a common source process but their differing locations indicate that either the source region is non stationary or a second source skews the location during the high convective phase tremor polarization and location suggests that the low frequency tremor is caused by bubble coalescence and bursting in a conduit whose surface is the lava lake the higher frequency signal associated with the high convective regime is associated with a scattered more complex wavefield superimposed on the low frequency background tremor caused by bubble bursting and cracking of cooled crust at the lava lake surface

the role of large bubbles detected from acoustic measurements on the dynamics of erta ale lava lake ethiopia the activity at the surface of the lava lake on erta ale volcano ethiopia shows that large bubbles are regularly breaking at a fixed position on the lava lake this is also where the small lava fountains are sometimes produced since this location is likely to be directly above the volcanic conduit feeding the lava lake we have done continuous measurements between march 22 and 26 2003 to understand the degassing of a volcano in permanent activity the bubble size has been first estimated from videos which once combined with the acoustic pressure can constrain the source of the sound the gas volume and overpressure stayed roughly constant between 36 700 m3 and 4 103 1 8 104 pa respectively simultaneous thermal measurements showed regular peaks which occurred when the crust was broken by a large bubble hence gave a direct indication on the typical return time between the bubbles 1 h these spherical cap bubbles had a high reynolds number 4600 20000 therefore a wake periodically unstable formed and detached from the bubble bottom the bubbly wake if the detachment occurs close to the surface can explain the duration of lava fountains measured on the videos the periodic arrival of bubbly wakes which mostly detach from the driving spherical cap within the lava lake could explain the absence of cooling at erta ale erebus antartica villarica chile and nyiragongo democratic republic of congo without invoking a convective downflow of magma in the conduit as previously done

a global synthesis of lava lake dynamics abstract active lava lakes represent a variety of open vent volcanism in which a sizable body of lava accumulates at the top of the magma column constrained by the vent and or crater geometry the longevity of lava lakes reflects a balancing of cooling and outgassing occurring at the surface and input of hot and gas rich magma from below due to their longevity and relative accessibility lava lakes provide a natural laboratory for studying fundamental volcanic processes such as degassing convection and cooling this article examines all seven lakes that existed at the time of writing in 2018 located in the pacific antarctica africa and south and central america these lakes span all tectonic environments and a range of magma compositions we focus on analysis of the lake surface motion using image velocimetry which reveals both similarities and contrasts in outgassing and lake dynamics when comparing the different lakes we identify two categories of lake behavior organized erta ale nyiragongo k lauea after 2011 and erebus and chaotic villarrica masaya marum this division does not map directly to lake size viscosity gas emission rate or temperature instead when examined together we find that the lakes follow a linear relationship between average surface speed and the ratio of total gas flux to lake surface area this relationship points to the combined importance of both flux and lake size in addition to the total volume of gas emission and suggests that a shared deep mechanism controls the supply of heat and gas to all lakes on the other hand the differences between chaotic and organized lakes highlight the important role of the geometry of the conduit lake transition which superimposes a shallow signal on that of the deep circulation the spatial patterns of surface motion we document suggest that the release of gas bubbles at chaotic lakes is more efficient i e bubbles are less likely to be retained and recycled compared with organized lakes in addition the data presented here indicate that the solidified crust of organized lakes plays a role in regulating convection and outgassing in lava lakes

regional mb ms lg pg amplitude ratios and lg spectral ratios as criteria for distinguishing between earthquakes and explosions a theoretical study summary theoretical seismograms for point explosion and double couple sources in a uniform plane layered earth are used to evaluate the likely effectiveness of three criteria that have been proposed for distinguishing between earthquakes and explosions the criteria are regional ms ms lg pg amplitude ratios and lg spectral ratios for explosions in material with a high wave speed the near regional mb ms discriminant gives only marginal separation between the two types of source ranging from zero for strike slip earthquakes to on average 0 4 magnitude units for 45d dip slip mechanisms only for explosions in material with a low wave speed do the theoretical data show an overall separation lg pg amplitude ratios successfully separate the source types except for strike slip earthquakes where there is overlap with shallow explosions theoretical lg spectra for deep 1 5 km explosions are depleted in high frequencies when compared with those for earthquakes and shallow explosions discrimination between earthquakes and these deep explosions is therefore possible using the spectral ratio method an important mechanism underlying these lg based discriminants is the interaction of the spherical p wavefront from an explosion with the free surface which generates shear waves with amplitude depending both on frequency and source depth of burial

identification of variable convective regimes at erta ale lava lake abstract during february 17 19 2002 we collected a combined thermal and seismic data set for persistent lava lake activity at erta ale volcano ethiopia these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 surface velocities typically lasting tens to hundreds of minutes these periods of high and low velocity motion define periods of vigorous and sluggish convection respectively spectral analysis revealed that vigorous convection periods were characterized by high frequencies and energies in the thermal data and an increased presence of high frequency energy in the seismic data the data show that vigorous periods were characterized by formation of hot short lived plastic crusts and sluggish periods by cooler longer lived brittle crusts here the higher transit velocity across the lake surface from upwelling zones of crust formation to downwelling zones of crust destruction during the vigorous periods decreases the crust lifetime this in turn decreases the total cooling and thickening experienced by a plate of crust moving across the lake surface two scenarios can be envisaged to explain such convection cycles the first relates variable convection rates to changes in the volume flux and rheology of magma entering the lake in the second cyclic convection is set up by the generation of convective instabilities within the lake in this case cooling of a surface layer generates a slow moving viscous increasingly dense convection layer at the lake surface which is consumed and replaced during overturn

fluctuations in surface height of active lava lakes during 1972 1974 mauna ulu eruption kilauea volcano hawaii an active lava lake is one that forms directly on top of a magma column as opposed to an inactive one formed by passive ponding of lava within a preexisting crater two active lava lakes operating within summit craters of newly constructed volcanic shields at mauna ulu and alae were the longest lived of any observed in a hawaiian rift zone to date small scale fluctuations a few to 20 m in the height of lake surfaces are typically associated with degassing gas piston activity larger fluctuations as great as 200 m reflect major changes in eruptive activity measurements of surface height fluctuations of mauna ulu lake show gross positive correlation with variation in summit tilt which in turn reflects the inflation deflation state of kilauea s summit magma reservoir a more tenuous conclusion is that a sympathetic variation possibly exists between surface heights of the mauna ulu and alae lakes collectively these observations 1 require the existence of a fully engorged connected open and hydraulically efficient magma conduit system linking the summit reservoir with the lava lakes 2 provide additional evidence for the postulated regime of quasi steady state magma transfer that characterized much of the eruption 3 imply that fluctuations in lake surface reflect variation in magma supply rate to the reservoir and or outflow rate from the mauna ulu alae vents and 4 suggest undetected episodes of magma intrusion or storage in kilauea s east rift zone during 1973

inferences on the source of long period seismicity at campi flegrei from polarization analysis and reconstruction of the asymptotic dynamics in the present paper we analyse long period lp events and seismic noise recorded at campi flegrei during the uplift episode of 2004 2006 the results of a detailed polarization analysis indicate that the large number of lps detected during the seismic crisis were accompanied by a sustained activity consisting of very low energy volcanic signals these weak volcanic signals which are usually absent in ambient noise recorded in the studied area and lp events have similar properties namely they are radially polarized towards the same lp source the large dataset analysed allows us to study the statistics of the polarization leading to the extraction of the average properties of the volcanic signals an estimate of the complexity of the system can be provided by the degrees of freedom necessary to describe the asymptotic dynamics in a reconstructed phase space this analysis shows that both lps and low energy signals can be described by a low dimensional dynamical system while ambient noise unrelated to volcanic activity is higher dimensional based on these observations we interpret the phenomena observed during the seismic crisis in the framework of the theory of self oscillating systems in which lps and low energy signals represent self oscillations generated by a persistent hydrothermal source

false alarms and mine seismicity an example from the gentry mountain mining region utah as part of a large discrimination study in the western united states taylor et al 1989 one earthquake was consistently classified as an explosion the magnitude m 3 5 disturbance occurred on 14 may 1981 and was conspicuous in its lack of love waves relative lack of high frequency energy low lg pg ratio and high moment tensor additionally a moment tensor solution by patton and zandt 1991 indicated that the event had a large implosional component the event occurred in the gentry mountain coal mining region in the eastern wasatch plateau utah previous microearthquake studies in the region have demonstrated the existence of numerous small implosional events associated with the mining activities the event is more comparable in appearance at the broadband station at kanab utah knb to the atrisco collapse at the nevada test site nts than to another double couple event near the mining region using a simple source representation we modeled the event as a tabular excavation collapse that occurred as a result of normal mining activities this study raises the importance of having a good catalog of seismic data and information about mining activities from potential proliferant nations this information will be critical in resolving potential false alarms that may be generated from natural mine seismicity

implications of longeval lava lakes for geomorphological and plutonic processes at erta ale volcano afar erta ale volcano sited within the afar triangle of ethiopia is one of the least visited of perennially active subaerial volcanoes satellite images recorded over the past thirty years illustrate the sustained activity of the volcano and complement the few brief periods of field observation we consider that erta ale s lava lakes have probably persisted for 90 years placing them among the longest lived yet recorded despite sustained surface heat fluxes of 100 400 mw the net surface growth rate integrated over the interval 1968 1995 was only 10 kg s 1 we speculate that this minimal lava discharge cannot be used to infer a low magma supply rate to the volcano since heat losses from die lava lakes inhibit eruption by increasing magma density this implies growth of the underlying crust by formation of dikes and sills containing cumulates accommodated and possibly promoted by regional extension and intrusion loading open vent degassing and rift kinematics are clearly reflected in erta ale s morphology which is characterised by very gentle 3 slopes and a summit caldera

a discrimination analysis of short period regional seismic data recorded at tonto forest observatory abstract a new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well the test data consisted of a well constrained set of 30 nevada test site nts explosions and 21 earthquakes located within about 100 km of nts which were recorded on short period seismographs at the tonto forest observatory in central arizona at an epicentral distance averaging 530 km the events in the data set cover a magnitude range from 3 3 to 4 8 m b for which p n p g and l g phases have been analyzed we found that although l g phases from earthquakes are typically more prominent than for explosions with comparable p wave amplitude levels simple time domain l g p amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination however spectral analyses of the data over the frequency band from 0 5 to 5 0 hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant in particular both the p g and l g spectra from earthquakes have been found to be richer in high frequency content than corresponding explosion spectra a discriminant measure defined as the ratio of average l g spectral amplitude level in the 0 5 to 1 0 hz passband to that in the 2 0 to 4 0 hz passband provides good separation of earthquake and explosion populations

discrimination of chemical explosions and earthquakes in central europe a case study both natural and artificial seismicity is observed in the vogtland area at near regional distance 180 km from the geress array this setting offers the opportunity to test various discrimination criteria using a uniform data set of 39 earthquakes and 22 chemical explosions strip mine and quarry blasts from a single epicentral region mostly eliminating wave path and distance effects discriminants used include lg pg and lg rg maximum amplitude ratios spectral peaks and slopes extracted by autoregressive moving average arma modeling master event correlation and the search for time independent frequency structures in sonograms although no single discrimi nant achieves a perfect separation of the two populations a joint discrimination scheme employing simple majority voting reduces misclassifications to 2 future research will focus on possible generalization and the physical basis of the discriminants

discrimination using spectral slopes at frequencies up to 50 hz abstract the spectral characteristics of regional pn waves recorded at the high frequency seismic element hfse at the noress array in southern norway are investigated to determine if spectral slope can be used to discriminate between earthquakes and chemical explosions displacement spectra are calculated for 134 events in southern norway that include 36 known earthquakes and 36 known chemical explosions events range in distance from 230 to 620 km and most have signal above the noise at frequencies over 30 hz the average frequency at the peak signal to noise ratio snr is 15 5 hz spectral slopes are measured on a displacement spectrum calculated with a 2 sec window the slopes range between 1 8 and 5 1 and there is no strong evidence that the slope steepens with distance for this data set according to one theory earthquakes should have steeper slopes than explosions but when this data set is separated into earthquakes and explosions we do not see separation between sources with respect to the slope of the spectrum both source types have events with the same range of spectral slopes and the mean slopes and standard deviations are similar spectra of events at the same locations are often similar however explosions from the blasjo mine in western norway show variability in the spectral slope since the path and distance to hfse are the same for these events the variability must be due to differences in the source mechanism for a set of small earthquakes however the observed variability in spectral slopes appears to be more related to distance and path effects therefore we observe as much variation in spectral slope for one source type as there is between source types the time window over which the spectrum is calculated is varied from 1 to 8 sec to determine if a time window consisting of a pure pn wave was required to discriminate between source types spectral slope usually decreases as the window extends deeper into the coda and the energy content of the signal changes the slopes also become more stable and more reliable as longer windows are used however source discrimination is not possible with any time window

lakargiite cazro3 a new mineral of the perovskite group from the north caucasus kabardino balkaria russia lakargiite cazro3 the zirconium analog of perovskite pbnm a 5 556 1 b 5 715 1 c 7 960 1 a v 252 7 1 a3 z 4 was discovered as an accessory mineral in high temperature skarns in carbonate silicate rocks occurring as xenoliths in ignimbrites of the upper chegem verkhniy chegem volcanic structure the north caucasus kabardino balkaria russia lakargiite forms pseudo cubic crystals up to 30 35 m in size and aggregates up to 200 m lakargiite is associated with spurrite larnite calcio olivine calcite cuspidine rondorfite reinhardbraunsite wadalite perovskite and minerals of the ellestadite group the new perovskite mineral belongs to the ternary solid solution cazro3 catio3 casno3 with a maximum cazro3 content of ca 93 maximum catio3 content of 22 and maximum casno3 content of 20 significant impurities are sc cr fe ce la hf nb u and th raman spectra of lakargiite are similar to those of the synthetic phase ca zr ti o3 with strong bands at 352 437 446 554 and 748 cm 1 lakargiite crystallized under sanidinite facies conditions of contact metamorphism characterized by very high temperatures and low pressures

the seismic noise at las canadas volcanic caldera tenerife spain persistence characterization and possible relationship with regional tectonic events abstract the origin of the continuous seismic noise recorded during the last few years in the volcanic island of tenerife canary islands spain is under debate due to the important implications in terms of hazard the seismic noise is strongly affected by anthropogenic contamination but previous work has shown that nevertheless a significant fraction of this noise has a natural origin an origin that appears to be related to the generation of local tectonic events within or close to the island in this paper the variogram tool is used to characterize the so called persistence of the seismic noise this analysis can quantify how much memory the seismic noise has of its recent past this has important implications in terms of how informative the recorded noise can be about its future evolution and this in turn puts important constraints on how likely it is for the seismic noise to be the source of potential precursors highlighting variations in the volcanic activity that is supposed to generate part of this seismic noise in particular the memory characterization can help to distinguish the naturally generated seismic noise from the anthropogenic contamination although only a few clear examples have been observed until now the possibility that this memory can be affected by the occurrence of local tectonic events is also discussed

seismicity and outgassing dynamics of nyiragongo volcano abstract active lava lakes at volcanoes can be regarded as open windows to their magmatic systems the dynamics of such lakes may therefore provide decisive insights into deeper magmatic processes potentially leading to fundamental theoretical implications and volcano monitoring improvements among the rare volcanoes on earth hosting a persistent lava lake nyiragongo in d r congo directly threatens a massive population of roughly 1 million inhabitants here we analyze close range i e summit and distant around 17 km seismic measurements acquired at this african volcano between 2011 and 2018 in order to better understand the seismic signature of the lava lake activity and how it relates to the deeper volcanic processes both summit and distant seismic records contain a similar continuous tremor pattern attributable to the lava lake activity combining this information with time lapse camera images and lava lake level measurements confirms the mechanism of gas pistoning at nyiragongo which is characterized by short duration a few minutes long and meter scale level variations during the period of observation we also characterize the dominant periodicity of this shallow tremor signature of about a few tens of minutes because this marked periodic pattern varies during a significant one month fluctuation of so2 emissions estimated from space we suggest that this particular seismic periodicity corresponds to the convective lake movement driven by the persistent degassing typical of active open vent volcanoes finally new seismic evidence reveals the effect of deep magmatic intrusion and consequent major pressure changes in the plumbing system resulting in sudden and large drops of the lava lake level associated with strong degassing such transient episodes have similar characteristics to total lava lake drainage associated with flank eruptions already observed at this volcano in 1977 and 2002 or at k lauea volcano in 2018

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

seismic event identification of earthquakes and explosions in germany using spectral lg ratios at the german ndc initial work on seismic event identification has focused on the application of spectral amplitude ratios for lg in order to discriminate naturally occurring seismic events from other events associated with mining and quarry activities only about 10 of all seismic events occurring in germany and adjacent areas are due to natural seismicity and are mostly constrained to the alpine regions and areas along the rhinegraben rhenish massif swabian jura and the bohemian massif vogtland region using data from the broadband grsn network spectral amplitude ratios are calculated from maximum trace amplitudes in the 1 2 hz and 6 8 hz frequency bands which are within the passbands of the deployed sts 2 instruments and the recorded 20 hz data streams these amplitude ratios then must be corrected with an appropriate attenuation model in order to remove propagation paths effects for event identification a scoring scheme is applied across the grsn network based on station dependent scoring thresholds in a case study aimed at testing the identification scheme events are investigated from a quarry in southern germany that provided ground truth information for six events in 1997 to demonstrate the suitability of this identification approach except for one event with a rather strong earthquake signature i e a low spectral lg ratio these events could be screened out from the earthquake population by their large lg ratios in a second step aimed at applying the identification scheme all events in germany and neighboring areas that occurred in 1995 were processed with approximately 800 out of more than 1200 events showing explosion type lg ratios while only 10 remain in the earthquake population however specific mining areas appear to consistently produce earthquake type spectral ratios indicative of particular blasting practices

ambrym vanuatu july august 2000 spectral and dynamical transitions on the hours to days timescale abstract ambrym is a large basaltic volcano with a 12 km wide 1900 year old caldera located in the vanuatu archipelago formerly known as new hebrides two cones are currently active in the caldera marum and benbow each with several active vents that hosted visible lava lakes until 1999 on 26 november 1999 an earthquake m w 7 5 located near the northern part of the island caused important changes to the vent morphology during july 2000 we installed a short period seismic station on the eastern rim of benbow crater in the western side of the caldera the station acquired continuous data for about 1 month during this period volcanic tremor was permanently recorded together with discrete events in this paper first results from these data are discussed focusing attention on the existence of significant transitions in the long term volcano dynamics studied both with spectrally derived dominant and average frequencies and more properly dynamical embedding dimensions and delay time parameters during the observation period on 9 august 2000 another significant earthquake was recorded m b 6 3 about 65 km north of the volcano the influence of this and other regional tectonic events on the volcano dynamics are discussed

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes

multidisciplinary investigation on a lava fountain preceding a flank eruption the 10 may 2008 etna case a multidisciplinary approach integrating a wide data set ranging from bulk rock compositions of the erupted products to volcanic tremor long period events and tilt and gravity signals is used to investigate the source depth and magma dynamics of the 10 may 2008 lava fountain at southeast crater sec of mount etna the investigation was undertaken in the framework of the previous 2007 explosive activity as well as the subsequent effusive eruption beginning 13 may 2008 and lasting up to july 2009 all the data concur in indicating that the 10 may lava fountain was generated by the fragmentation of a foam layer trapped at the top of a shallow reservoir about 1500 1700 m below the summit of sec the shift from the episodic strombolian lava fountain activity occurring in 2007 at sec to the more powerful 10 may 2008 lava fountain is explained by the intrusion of a new more primitive magma into the shallow reservoir data also indicate that an attempted magma intrusion east of the summit area occurred during the 10 may fire fountain this event caused the fracturing and weakening of the surrounding rocks and created a preferential pathway for the penetration of the magma that only 3 days later started to feed the 2008 2009 effusive eruption