lightning associated with the 1992 eruptions of crater peak mount spurr volcano alaska abstract lightning occurred associated with the ash clouds of all three eruptions of mt spurr volcano in 1992 lightning was detected on seismograms as simultaneous spikes and simultaneous gain ranging a feature that normally lowers the gain at a station when the signal level begins to saturate spikes had typical durations of 0 04 0 05 s using uniform criteria we found 28 lightning flashes in the june 27th eruption 29 in the august 18th eruption and three in the september 17th eruption we measured peak voltages on station rso 94 km ssw to determine the relative strengths of lightning and found that the august lightning was strongest june weakest and september intermediate based on relative signal strengths at different stations we found evidence for different lightning geometries between the june and august eruptions during which prevailing winds blew the ash clouds to the north and east respectively for all three eruptions the first lightning was recorded 21 26 min after the onset of the eruption suggesting that charge separation occurred in the convecting cloud rather than at the vent data recorded by a bureau of land management lightning detection system for the august eruption showed negative polarities for the first 12 recorded flashes and a positive polarity for the last this suggests a charge separation based on particle size in which negative charge is found for larger particles which fall first and positive charge remains on smaller particles which remain suspended longer all three eruptions had similar durations of 3 5 4 h and tephra volumes of 44 56 million cubic meters the august eruption however produced stronger volcanic tremor 30 cm2 reduced displacement as compared with 16 cm2 for june and greater gas 400 120 kt so2 for august and 200 60 kt for june thus lightning strength correlates with both tremor amplitude and magmatic gas content the august eruption occurred during the lightest winds so the ash cloud and charge separation were vertically oriented and favored cloud to ground lightning the september eruption occurred during the coldest and driest atmospheric conditions which may explain the small amount of lightning in general volcanic lightning is important because it can help confirm that explosive eruptions are in progress although the value of the information may be limited by the long delay from eruption onset to first lightning and the variability of eruptive and atmospheric conditions

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

theory and observations of controls on lightning flash size spectra previous analyses of very high frequency vhf lightning mapping array lma observations relative to the location of deep convective updrafts have noted a systematic pattern in flash characteristics in and near strong updrafts flashes tend to be smaller and more frequent while flashes far from strong vertical drafts exhibit the opposite tendency this study quantitatively tests these past anecdotal observations using lma data for two supercell storms that occurred in oklahoma in 2004 the data support a prediction from electrostatics that frequent breakdown and large flash extents are opposed an energetic scaling that combines flash rate and flash area exhibits a 5 3 power law scaling regime on scales of a few kilometers and a maximum inflashenergyatabout10km thespectralshapeis surprisinglyconsistentacrossarangeofmoderatetolarge flash rates the shape of this lightning flash energy spectrum is similar to that expected of turbulent kinetic energy spectra in thunderstorms in line with the hypothesized role of convective motions as the generator of thunderstorm electrical energy the correspondence between kinematic and electrical energy spectra suggests that advection of charge bearing precipitation by the storm s flow including in turbulent eddies couples the electrical and kinematic properties of a thunderstorm

an experiment to detect and locate lightning associated with eruptions of redoubt volcano abstract a commercially available lightning detection system was temporarily deployed near cook inlet alaska in an attempt to remotely monitor volcanogenic lightning associated with eruptions of redoubt volcano the system became operational on february 14 1990 lightning was detected in 11 and located in 9 of the 13 subsequent eruptions the lightning was generated by ash clouds rising from pyroclastic density currents produced by collapse of a lava dome emplaced near redoubt s summit lightning discharge flash location was controlled by topography which channeled the density currents and by wind direction in individual eruptions early flashes tended to have a negative polarity negative charge is lowered to ground while late flashes tended to have a positive polarity positive charge is lowered to ground perhaps because the charge separation process caused coarse rapid settling particles to be negatively charged and fine slow settling particles to be positively charged results indicate that lightning detection and location is a useful adjunct to seismic volcano monitoring particularly when poor weather or darkness prevents visual observation the simultaneity of seismicity and lightning near a volcano provides the virtual certainty that an ash cloud is present this information is crucial for aircraft safety and to warn threatened communities of impending tephra falls the alaska volcano observatory has now deployed a permanent lightning detection network around cook inlet

a gps based three dimensional lightning mapping system initial observations in central new mexico a gps based system has been developed that accurately locates the sources of vhf radiation from lightning discharges in three spatial dimensions and time the observations are found to reflect the basic charge structure of electrified storms observations have also been obtained of a distinct type of energetic discharge referred to as positive bipolar breakdown recently identified as the source of trans ionospheric pulse pairs tipps observed by satellites from space the bipolar breakdown has been confirmed to occur between the main negative and upper positive charge regions of a storm and found to be the initial event of otherwise normal intracloud discharges the latter is contrary to previous findings that the breakdown appeared to be temporally isolated from other lightning in a storm peak vhf radiation from the energetic discharges is observed to be typically 30 db stronger than that from other lightning processes and to correspond to source power in excess of 100 kw over a 6 mhz bandwidth centered at 63 mhz

observations of volcanic lightning during the 2009 eruption of redoubt volcano abstract observations of volcanic lightning during the eruption of redoubt volcano in march and april 2009 were made with the lightning mapping array during the eruption twenty three distinct episodes of volcanic lightning were observed electrical activity occurred as either a volcanic lightning storm with up to thousands of lightning discharges or as a weak electrical event with only a handful of lightning discharges during the volcanic lightning storms we observed two phases of electrical activity the explosive phase and the plume phase the explosive phase consisted of very small discharges on the order of 10 100 m occurring directly above the vent while an explosive eruption was ongoing whereas the plume phase was comprised of discharges occurring throughout the plume subsequent to the explosive eruption the area of discharges during the explosive phase ranged from less than 1 km2 to 50 km2 or more the electrical activity at the beginning of the plume phase was dominated by small discharges over time the horizontal extent of the flashes increased with the largest flashes occurring at the end of the plume phase the distribution of the horizontal size of the discharges over the lifetime of the storm indicate that the charge structure of the plume evolved from a complex and clumpy structure to a more simple horizontally stratified structure plume height was shown to be a key factor in the quantity of lightning in a storm the volcanic lightning storms occurred in plumes with column heights greater than 10 km the tall plumes may contribute to the efficiency of charge generation through ice collisions by providing strong updrafts from the large thermal energy input from the eruption

local seismic and infrasound observations of the 2009 explosive eruptions of redoubt volcano alaska article i nfo local seismic and infrasound data are used to characterize the march april 2009 eruptions of redoubt volca no alaska data are from a network of ten seismic stations ranging from 2 6 to 21 km from the vent and a single infrasound sensor 12 2 km from the vent measurements were made for more than 30 explosive erup tions including the 19 numbered events that were identified during the eruption response more than 30 smaller explosions were also identified measured parameters include onset time duration reduced dis placement dr pressure seismic energy and acoustic energy results were compared with complementary gas and lightning data based on ratios of pressure to dr and acoustic to seismic energy we find that the initial group of explosive eruptions on 23 24 march was relatively stronger seismically and included the four highest dr values we infer that these represent vent enlargement or stronger coupling between the magma and wall rocks one event at 12 31 ut on 23 march had an extremely high pressure of 250 pa for the initial pulse and was likely weakly seismically coupled a second group of explosive eruptions on 27 29 march was relatively stronger acoustically deposits were finer grained and of different lithology with less scoria and more dense clasts these two groups may represent different modes of gas release cumulative acoustic energy as a function of time correlates well with comparable lightning and so2 data suggesting that all three provide insight regarding different factors of gas release for the eruption as a whole the number of events identified depends on criteria measured and depends on the goals of the investigations overall the eruptions were substantially stronger than recent eruptions in alaska with some durations exceeding 1 h and pressures an order of magnitude higher

did ice charging generate volcanic lightning during the 2016 2017 eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano in alaska injected plumes of ash and seawater to maximum heights of 12 km more than 4550 volcanic lightning strokes were detected by the world wide lightning location network wwlln and vaisala s global lightning dataset gld360 over 9 months lightning assisted monitoring efforts by confirming ash producing explosions in near real time but only 32 out of the 70 explosive events produced detectable lightning what led to electrical activity within some of the volcanic plumes but not others and why did the lightning intensity wax and wane over the lifetime of individual explosions we address these questions using multiparametric observations from ground based lightning sensors satellite imagery photographs acoustic signals and 1d plume modeling detailed time series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level approximated by 20 c temperatures for example on 28 may 2017 event 40 the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms with liquid water contents 5 g m 3 and vigorous updrafts 40 m s 1 in the mixed phase region where liquid water and ice coexist based on these findings we infer that thunderstorm style collisional ice charging catalyzed the volcanic lightning however charge mechanisms likely operated on a continuum with silicate collisions dominating electrification in the near vent region and ice charging taking over in the upper level plumes a key implication of this study is that lightning during the bogoslof eruption provided a reliable indicator of sustained ash rich plumes and associated hazards above the atmospheric freezing level

diverse eruptive activity revealed by acoustic and electromagnetic observations of the 14 july 2013 intense vulcanian eruption of tungurahua volcano ecuador

the 2010 eruption of eyjafjallajokull lightning and plume charge structure six lightning mapping array lma stations were deployed in april 2010 around eyjafjallajokull volcano in southern iceland single station lma observations were made during the first explosive period 14 18 april and three dimensional lma observations were made during the second explosive period 5 22 may the single station observations revealed that continuous rf electrical activity caused by high rates of small vent discharges occurred during the first explosive period but not the second indicating that the strength of vent charging varied between the first and second explosive periods during the second explosive period very little lightning was detected between 5 and 10 may while moderate rates of lightning were detected between 11 and 21 may signaling that another change occurred on 11 may that affected plume electrification the data do not make clear if it was changing eruptive activity or changing meteorological activity that resulted in the sudden onset of lightning the plume charge structure during the second explosive period was inferred from the three dimensional lightning data showing that the dominant charge structure varied between a positive monopole and a negative over positive dipole the predominance of a low altitude region of positive charge and the observation that electrical activity was concentrated near the vent indicate that net positive vent charging was dominating the electrification

using lightning observations as a volcanic eruption monitoring tool lightning commonly occurs in the eruption columns produced by explosive volcanic eruptions there are several different kinds of lightning detection instruments that could be employed to help monitor volcanoes each with their own advantages and disadvantages very low frequency vlf instruments have the ability to detect lightning at long ranges but tend to have low sensitivity due to network geometry and typically can provide only the time and 2 d location of a cloud to ground return stroke or similar high amplitude pulse produced by an intracloud discharge low frequency lf and medium frequency mf instruments typically have more sensitivity than a vlf network but can only be used for detection on a regional scale very high frequency vhf lightning mapping instruments also provide only regional coverage but detect all lightning within their range during the 2009 eruption of redoubt volcano alaska usa each of these types of instruments detected lightning from redoubt s ash plume the vhf system consistently detected lightning before the other two during each distinct explosive event and also detected more lightning than the others by one or two orders of magnitude lightning observations could be used to confirm and in some cases detect explosive volcanic activity the rapid response provided by lightning monitoring is a valuable tool for fast identification of potentially hazardous ash clouds

layered lightning activity the horizontal extent of lightning channels reconstructed acoustically from several storms is significantly larger than the vertical extent furthermore an examination of all the reconstructed lightning structure in each of three storms one in arizona one in colorado and one in florida shows that the lightning activity tends to occur in layers 2 3 km thick in the arizona and florida storms there were two layers of activity temperatures at the lower boundary of the layers were near 4 c and 18 c in the arizona storm and 11 c and 39 c in the florida storm in the colorado storm there was a single layer having a lower boundary near the 0 c isotherm our interpretation is that each of the two layers in the arizona and florida storms is associated with a corresponding charged region in the dipole of the thundercloud charge distribution we suggest that the single layer in the colorado storm was a result of the dipolar regions being closer together in altitude

charge mechanism of volcanic lightning revealed during the 2010 eruption of eyjafjallajokull 1 volcanic lightning has intrigued observers through the centuries several likely processes have been proposed to explain the electrification of volcanic plumes including quenching magma water interactions the fracturing or internal friction of fine grained ash and the freezing of plume water at height scarce measurements of volcanic lightning have not been able to distinguish between proposed ideas the eyjafjallajokull volcanic eruption in iceland in april may 2010 may have revealed its charge mechanism during its 39 days the eruption went through a few phases while the conditions of the ambient atmosphere also changed but at different times the most surprising change in the lightning activity occurred on 11 may with no obvious change in the physical eruption character or strength during 3 10 may there was no lightning recorded by long range networks followed by intense activity 11 20 may the change in lightning activity coincided with a change in the conditions of the ambient atmosphere at this time the altitude of the isotherms for droplet freezing about 20 c dropped drastically below the plume top therefore it appears that the atmospheric conditions around the plume were influencing or even controlling some of the lightning activity the critical plume top temperature which appears to have turned on and off the observed lightning activity during the eyjafjallajokull eruption is estimated to be between 20 and 24 c we conclude that a significant charge generation process of the observed volcanic lightning is probably analogous to processes in meteorological thunderclouds

doppler weather radar observations of the 2009 eruption of redoubt volcano alaska abstract the u s geological survey usgs deployed a transportable doppler c band radar during the precursory stage of the 2009 eruption of redoubt volcano alaska that provided valuable information during subsequent explosive events we describe the capabilities of this new monitoring tool and present data captured during the redoubt eruption the minimax 250 c mm 250c radar detected seventeen of the nineteen largest explosive events between march 23 and april 4 2009 sixteen of these events reached the stratosphere above 10 km within 2 5 min of explosion onset high column and proximal cloud reflectivity values 50 to 60 dbz were observed from many of these events and were likely due to the formation of mm sized accretionary tephra ice pellets reflectivity data suggest that these pellets formed within the first few minutes of explosion onset rapid sedimentation of the mm sized pellets was observed as a decrease in maximum detection cloud height the volcanic cloud from the april 4 explosive event showed lower reflectivity values due to finer particle sizes related to dome collapse and related pyroclastic flows and lack of significant pellet formation eruption durations determined by the radar were within a factor of two compared to seismic and pressure sensor derived estimates and were not well correlated ash dispersion observed by the radar was primarily in the upper troposphere below 10 km but satellite observations indicate the presence of volcanogenic clouds in the stratosphere this study suggests that radar is a valuable complement to traditional seismic and satellite monitoring of explosive eruptions

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

magnetotelluric pulses generated by volcanic lightning at sakurajima volcano japan 1 continuous magnetotelluric mt measurements were conducted at sakurajima volcano japan revealing syn eruption electric pulses and sometimes accompanying geomagnetic pulses movies of the eruptions recorded with timing provided by a gps clock show a large number of volcanic lightning flashes some mt pulses occurred simultaneously with lightning flashes pulses were observed more than 10 seconds after the onset of the eruption and tend to occur during eruptions that emit volcanic ash to high altitudes pulses were more common during mild eruptions rather than during vulcanian eruptions the observations suggest that the dominant mechanism of volcanic lighting is similar to that of lightning in thunderstorms in that it requires the collision of particles and subsequent separation of positive and negative charge

volcanic lightning global observations and constraints on source mechanisms lightning and electrification at volcanoes are important because they represent a hazard in their own right they are a component of the global electrical circuit and because they contribute to ash particle aggregation and modification within ash plumes the role of water substance water in all forms in particular has not been well studied here data are presented from a comprehensive global database of volcanic lightning lightning has been documented at 80 volcanoes in association with 212 eruptions the volcanic explosivity index vei could be determined for 177 eruptions eight percent of vei 3 5 eruptions have reported lightning and 10 of vei 6 but less than 2 of those with vei 1 2 these findings suggest consistent reporting for larger eruptions but either less lightning or possible under reporting for small eruptions ash plume heights 142 observations show a bimodal distribution with main peaks at 7 12 km and 1 4 km the former are similar to heights of typical thunderstorms and suggest involvement of water substance whereas the latter suggest other factors contributing to electrical behavior closer to the vent reporting of lightning is more common at night 56 and less common in daylight 44 reporting also varied substantially from year to year suggesting that a more systematic observational strategy is needed several weak trends in lightning occurrence based on magma composition were found the bimodal ash plume heights are obvious only for andesite to dacite basalt and basaltic andesite evenly span the range of heights and rhyolites are poorly represented the distributions of the latitudes of volcanoes with lightning and eruptions with lightning roughly mimic the distribution of all volcanoes which is generally flat with latitude meteorological lightning on the other hand is common in the tropics and decreases markedly with increasing latitude as the ability of the atmosphere to hold water decreases poleward this finding supports the idea that if lightning in large deep eruptions depends on water substance then the origin of the water is primarily magma and not entrainment from the surrounding atmosphere seasonal effects show that more eruptions with lightning were reported in winter bounded by the respective autumnal and vernal equinoxes than in summer this result also runs counter to the expectations based on entrainment of local water vapor

electrical activity during the 2006 mount st augustine volcanic eruptions by using a combination of radio frequency time of arrival and interferometer measurements we observed a sequence of lightning and electrical activity during one of mount st augustine s eruptions the observations indicate that the electrical activity had two modes or phases first there was an explosive phase in which the ejecta from the explosion appeared to be highly charged upon exiting the volcano resulting in numerous apparently disorganized discharges and some simple lightning the net charge exiting the volcano appears to have been positive the second phase which followed the most energetic explosion produced conventional type discharges that occurred within plume although the plume cloud was undoubtedly charged as a result of the explosion itself the fact that the lightning onset was delayed and continued after and well downwind of the eruption indicates that in situ charging of some kind was occurring presumably similar in some respects to that which occurs in normal thunderstorms

velocity depth trends in mesozoic and cenozoic sediments from the norwegian shelf discussion storvoll et al 2005 present log data from 60 wells on the norwegian shelf to investigate velocity depth trends in sedimentary rocks they present an interesting analysis of e g the sonic log velocities of overpressured jurassic sediments and of source rock intervals the authors do however reach the conclusion that no general velocity depth function can be used when performing more accurate analyses like depth conversion of seismic data pore pressure prediction or basin modeling storvoll et al 2005 p 359 this conclusion is surprising for two reasons first because it is not tested by the authors and second because the article presents very good evidence for the existence of normal velocity depth trends for shale i e functions that describe how sonic velocity increases with depth in relatively homogenous sedimentary formations as porosity is reduced during normal compaction the authors present log data from three areas along the norwegian shelf but no examples of pressure versus depth the northern north sea haltenbanken and the barents sea about 60 n 65 n and 72 n respectively the main figures show velocity measurements versus depth for several wells in the three study areas their figures 6 8 12 the authors compare the data with a linear velocity depth trend v p 1477 0 57 z which is similar to the normal velocity depth trend for marine shale dominated by smectite illite published by japsen 2000 formula 1 where v p is velocity in meters per second and z is depth in meters below seabed or ground level this trend is almost identical to that developed by scherbaum 1982 for lower jurassic shale in the northwest german basin and to that presented by hansen 1996 based on data for cretaceous cenozoic shales on the norwegian shelf for depths less than about 2 5 km 1 6 mi it is interesting that the presented shale 1 embed graphic 1 gif