geochemistry of aliphatic rich coals in the cooper basin australia and taranaki basin new zealand implications for the occurrence of potentially oil generative coals

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

character mass distribution and origin of tephra fall deposits of the 1989 1990 eruption of redoubt volcano south central alaska abstract the 1989 1990 eruption of redoubt volcano spawned about 20 areally significant tephra fall deposits between december 14 1989 and april 26 1990 tephra plumes rose to altitudes of 7 to more than 10 km and were carried mainly northward and eastward by prevailing winds where they substantially impacted air travel commerce and other activities in comparison to notable eruptions of the recent past the redoubt events produced a modest amount of tephra fall deposits 6 10 7 to 5 10 10 kg for individual events and a total volume dense rock equivalent of about 3 5 10 7 m 3 of andesite and dacite two contrasting tephra types were generated by these events pumiceous tephra fall deposits of december 14 and 15 were followed on december 16 and all later events by fine grained lithic crystal tephra deposits much of which fell as particle aggregates the change in the character of the tephra fall deposits reflects their fundamentally different modes of origin the pumiceous deposits were produced by magmatically driven explosions the finegrained lithic crystal deposits were generated by two processes hydrovolcanic vent explosions generated tephrafall deposits of december 16 and 19 such explosions continued as a tephra source but apparently with diminishing importance during events of january and february ash clouds of lithic pyroclastic flows generated by collapse of actively growing lava domes probably contributed to tephra fall deposits of all events from january 2 to april 26 and were the sole source of tephra fall for at least the last 4 deposits

statistical forecasting of repetitious dome failures during the waning eruption of redoubt volcano alaska february april 1990 abstract the waning phase of the 1989 1990 eruption of redoubt volcano in the cook inlet region of south central alaska comprised a quasi regular pattern of repetitious dome growth and destruction that lasted from february 15 to late april 1990 the dome failures produced ash plumes hazardous to airline traffic in response to this hazard the alaska volcano observatory sought to forecast these ash producing events using two approaches one approach built on early successes in issuing warnings before major eruptions on december 14 1989 and january 2 1990 these warnings were based largely on changes in seismic activity related to the occurrence of precursory swarms of long period seismic events the search for precursory swarms of long period seismicity was continued through the waning phase of the eruption and led to warnings before tephra eruptions on march 23 and april 6 the observed regularity of dome failures after february 15 suggested that a statistical forecasting method based on a constant rate failure model might also be successful the first statistical forecast was issued on march 16 after seven events had occurred at an average interval of 4 5 days at this time the interval between dome failures abruptly lengthened accordingly the forecast was unsuccessful and further forecasting was suspended until the regularity of subsequent failures could be confirmed statistical forecasting resumed on april 12 after four dome failure episodes separated by an average of 7 8 days one dome failure april 15 was successfully forecast using a 70 confidence window and a second event april 21 was narrowly missed before the end of the activity the cessation of dome failures after april 21 resulted in a concluding false alarm although forecasting success during the eruption was limited retrospective analysis shows that early and consistent application of the statistical method using a constant rate failure model and a 90 confidence window could have yielded five successful forecasts and two false alarms no events would have been missed on closer examination the intervals between successive dome failures are not uniform but tend to increase with time this increase attests to the continuous slowly decreasing supply of magma to the surface vent during the waning phase of the eruption the domes formed in a precarious position in a breach in the summit crater rim where they were susceptible to gravitational collapse the instability of the february 15 april 21 domes relative to the earlier domes is attributed to reaming the lip of the vent by a laterally directed explosion during the major dome destroying eruption of february 15 a process which would leave a less secure foundation for subsequent domes

the dynamics and thermodynamics of volcanic clouds theory and observations from the april 15 and april 21 1990 eruptions of redoubt volcano alaska on april 15 1990 and april 21 1990 two relatively small explosive eruptions occurred at redoubt volcano alaska lasting about 4 and 8 minutes respectively on both occasions the erupted material travelled as a pyroclastic flow down an ice canyon on the north flank of the volcano using slow scan television recordings of the eruption and the seismic record in both the near and far field we deduce that after a few minutes the upper parts of these pyroclastic flows became buoyant and a large and hot ash cloud ascended off the flow these thermals rose to a height of about 12 km at which point they began to spread laterally as umbrella clouds using a simple thermodynamic model we estimate that the clouds had a temperature in the approximate range 600 700 k as they rose buoyantly from the flow after entraining and heating air and melting and vaporizing ice we also estimate that in each eruption approximately 109 kg of fine ash was injected into the atmosphere during the april 15 eruption a slow scan television camera recorded the ascent of the cloud these observations are described analysed and compared with the predictions of a new model for the dynamics governing the ascent of such clouds in accord with the observations our model predicts that the cloud initially ascended rather sluggishly since it is only just buoyant on rising from the pyroclastic flow as it ascends it entrains and heats up more air and hence generates more buoyancy therefore it accelerates upwards only much higher in the cloud does the velocity decrease again as the thermal energy of the cloud becomes exhausted the model also predicts that the height of rise of such coignimbrite thermals is a function of the initial mass and temperature of the cloud but is almost independent of the initial velocity during the april 21 eruption a sequence of photographs recorded the lateral spreading of the umbrella cloud during an interval of about 10 minutes after the eruption these photographs are analysed and successfully compared with a simple model for the spreading of the umbrella cloud as a gravity current in a stratified environment using an avhrr satellite image of the air fall deposit from the april 15 eruption combined with a simple model we suggest that the primary mechanism of ash dispersal was transport by the ambient wind

syneruptive mixing degassing and crystallization at redoubt volcano eruption of december 1989 to may 1990 abstract the 1989 1990 eruption of redoubt volcano included initial energetic vertical venting of pumiceous tephra followed by shedding of dense pyroclastic flows from successive unstable domes the suite of quenched magmatic materials thus produced coupled with detailed seismic observations provides a record of establishment and subsequent evolution of an active magma column in the upper crust the initial eruptive event involved a dacite magma with rhyolite melt and an andesite magma with dacite melt the dacite magma contains reaction rim free hornblende high cl concentrations 0 12 0 02 wt of melt and is microlite free all evidence for rapid ascent from depth in contrast the andesite component is microlite rich though this characteristic may have arisen by mixing between the two magmas rather than by slow ascent abundant dense juvenile lava like clasts with low h2o 0 1 0 3 wt were ejected in the initial eruption event implying that the magma column had reached the near surface and its upper portion had undergone degassing and bubble collapse prior to explosive disruption later eruptive events contain evidence of progressive blending of the two magmatic components as well as mixing between fresh reservoir derived and old conduit resident magma magma apparently ascended to the surface from the 6 10 km deep source chamber in a series of pulses rather than by steady flow or gradual emptying of a shallowly intruded body increased shallow long period seismicity which may indicate subsurface degassing from the flowing magma column occurred 5 days before each major eruptive event petrologic evidence indicates that each eruption contained some magma that ascended quickly from the chamber with time the proportion of new magma in eruptive batches may have decreased however even the final dome contains magma that left the chamber no more than a few days before extrusion together the pulses apparently record passage of an andesite plume through redoubt s dacite magma reservoir

seismic character and progression of explosive activity during the 2016 2017 eruption of bogoslof volcano alaska bogoslof volcano in the central aleutian arc experienced a major eruption between december 2016 and august 2017 that was characterized by explosive activity volcanic explosivity index 2 to 3 and the extrusion of lava domes the alaska volcano observatory tracked the activity in real time using seismicity observed on distant stations as well as infrasound lightning satellite data and occasional visual observations in this study we measure the duration of seismic signals associated with individual explosive events to track their progression during the two explosive phases of the eruption seismic recordings of bogoslof explosions show complex waveforms that suggest both individual explosive events and sequences of several explosions separated by lower amplitude tremor the lack of local seismic monitoring stations at distances of 1 km to 15 km distance unfortunately limits our ability to closely observe seismicity and to interpret changing conditions at the vent such as position the presence of a lava dome or plug and the role of seawater associated with the eruption we use the rate of explosive activity seismic waveform character and repose time between explosions to infer the conditions within the conduit

analysis of long period events recorded at mount etna italy in 1992 and their relationship to eruptive activity seismic activity recorded at mount etna during 1992 was characterized by long period lp events and tremor with fluctuating amplitudes these signals were associated with the evolution of the eruptive activity that began on december 14 1991 following the occurrence of numerous volcano tectonic earthquakes at the onset of the eruption lp events dominated the overall seismicity starting in january 1992 the lp activity occurred primarily in swarms which were temporally correlated with episodic collapses of the crater floor in the northeast crater source depths determined for selected lp events suggest a source region located slightly east of northeast crater and extending from the surface to a depth of 2000 m based on the characteristic signatures of the time series four families of lp events are identified each family shares common spectral peaks independent of azimuth and distance to the source these spectral features are used to develop a fluid filled crack model of the source we hypothesize that the locus of the lp events represents a segment of the magma feeding system connecting a depressurizing magma body with a dike extending in the sse direction along the western wall of valle del bove toward the site of the mount etna eruption we surmise that magma withdrawal from the source volume beneath northeast crater may have caused repeated collapses of the crater floor some collapse events may have produced pressure transients in the subjacent dike which acted as seismic wave sources for lp events

the 1989 1990 eruptions of redoubt volcano an introduction abstract redoubt volcano located on the west side of cook inlet in south central alaska erupted explosively on over 20 separate occasions between december 14 1989 and april 21 1990 fourteen lava domes were emplaced in the summit area thirteen of which were subsequently destroyed the eruption caused economic losses estimated at over 160 000 000 making this the second most costly eruption in u s history this economic impact provided the impetus for a integrated comprehensive account of an erupting volcano using both modern and classical research and modern techniques which in turn led to advances in eruption monitoring and interpretation research on such topics as dome formation and collapse and the resulting pyroclastic flows elutriated ash lightning tephra and flooding was blended with the rapid communication of associated hazards to a large user group the seismology successes in predicting and monitoring eruption dynamics were due in part to 1 the recognition of long period seismic events as indicators of the readiness of the volcano to erupt and 2 to the development of new tools that allowed the seismicity to be assessed instantaneously integrated studies of the petrology of erupted products and volatile content over time gave clues as to the progress of the eruption towards completion

velocity depth trends in mesozoic and cenozoic sediments from the norwegian shelf sonic velocity density and resistivity log data from 60 wells on the norwegian shelf have been used to investigate velocity depth trends in sedimentary rocks as a function of sediment composition porosity pore pressure burial history and compaction processes a first order linear velocity depth trend line has been estimated from published velocity data the data analyzed in this study however show significant variations from this trend line indicating 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 lower tertiary smectitic sediments from the northern north sea and haltenbanken are characterized by relatively low velocities compared to the overlying pliocene and pleistocene sediments causing a distinct velocity inversion a significant velocity increase at a burial depth corresponding to 70 100c was found and may reflect the alteration of smectite to illite and the initial precipitation of quartz cement in both sandstones and shales overpressured jurassic sediments from haltenbanken have lower velocities than equivalent hydrostatically pressured sequences but no significant porosity difference the reduced velocities may be a direct response to lower effective stresses and thus reduced elastic compaction low velocities in source rocks are mainly attributed to the relatively soft kerogen and resulting velocity anisotropy the high velocity depth ratio of barents sea sediments after correcting for tertiary exhumation is explained by the burial history of the area the subsequent thermal exposure of the sediments over time and thus the amount of quartz cementation

volcano seismology hazards assessment the last few years have seen several impressive examples of seismic monitoring at volcanoes to provide warnings that have saved lives and property changes in the rates and character of volcanic earthquakes provided precursory signs to explosive eruptions of moderate size at redoubt volcano alaska mount unzen japan mount spurr alaska and rabaul caldera papua new guinea as well as the large eruption at mount pinatubo philippines in all these cases information was successfully communicated and put to practical use through broadcasts of public warnings prior to the eruptions and evacuations were initiated for the volcanoes located in populated areas at mount pinatubo probably thousands and possibly tens of thousands of lives were saved

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

regional velocity depth anomalies north sea chalk a record of overpressure and neogene uplift and erosion a normal velocity depth trend for the upper cretaceous danian chalk group is determined by identifying interval velocity data that represent maximum burial in areas unaffected by overpressuring these data are derived from 845 wells throughout the north sea basin data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the north sea basin and reflect regional neogene uplift and erosion of up to 1 km along the present day limit of the chalk a hiatus at the base of the quaternary increases in magnitude away from the basin center where a complete cenozoic succession is found this hiatus is consistent in size with the missing section estimated from chalk velocities when allowance is made for the quaternary reburial of the chalk negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the chalk exceed 10 mpa equivalent to a burial anomaly greater than 1 km relative to the normal trend the chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden therefore the chalk is considered to represent a regional aquitard and the hydrodynamic model of long distance migration within the chalk is rejected the neogene uplift and erosion of the margins of the north sea basin and the rapid late cenozoic subsidence of its center fit into a pattern of late cenozoic vertical movements around the north atlantic

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

seismological aspects of the 1989 1990 eruptions at redoubt volcano alaska the ssam perspective abstract ssam is a simple and inexpensive tool for continuous monitoring of average seismic amplitudes within selected frequency bands in near real time on a pc based data acquisition system during the 1989 1990 eruption sequence at redoubt volcano the potential of ssam to aid in rapid identification of precursory long period lp event swarms was realized and since this time ssam has been incorporated in routine monitoring efforts of the alaska volcano observatory in particular an eruption that occurred on april 6 was successfully forecast primarily on the basis of recognizing the precursory lp activity on ssam of twenty two significant eruptions that occurred between december 14 and april 21 eleven had precursory swarms longer than one hour in duration that could be detected on ssam for individual swarms the patterns of relative spectral amplitudes are distinct at each station and remain largely stationary through time thus indicating that one source may have been preferentially and repeatedly activated throughout the swarm typically a single spectral band dominates the signal at each seismic station for the vigorous one day swarm that preceded the first eruption on december 14 signals were sharply peaked in the 1 9 2 7 hz band at the closest station located 4 km from the vent but were dominated by 1 3 1 9 hz energy at three more distant stations located 7 5 22 km from the vent the tendency for the signals from different swarms recorded at the same station to be peaked in the same frequency band suggests that all of the sources are characterized by a predominant length scale signals from the precursory lp swarms became weaker as the eruption sequence progressed and swarms that occurred in march and april could only be detected at seismographs on the volcanic edifice onset times of precursory lp swarms prior to eruptions ranged from a few hours to about one week but after the initial vent clearing phase that ended december 19 these intervals tended to become progressively shorter for successive swarms these trends in the relative onset times and intensities of successive precursory lp swarms are consistent with an overall depressurization of the magmatic system through time in general each of the swarms had an emergent onset but the intensities did not always increase steadily until the eruptions instead as the time of an eruption approached the intensity usually increased more rapidly before peaking and then declining prior to the eruption for three of the swarms two distinct peaks in intensity were apparent the time intervals between final peaks in swarm intensity and ensuing eruptions ranged from about 2 hours to almost 2 days but the peaks always occurred closer to the eruptions than to the swarm onsets both the onset of lp swarm activity and a decline in intensity prior to an eruption may represent critical points in the process of pressurization that drives the flow of fluids and gas in a sealed magmatic system a notable exception to this pattern is the eruption of march 9 which lacked a detectable precursory lp swarm but was followed by an unusually long period of strong lp seismicity that may have been stimulated by a depressurization of the magmatic system resulting from dome failure on both december 14 and january 2 the spectra of early syn eruptive signals have peaked signatures much like those of the spectra of precursory lp activity from shortly before the eruptions these similarities may indicate that the source of precursory seismicity continued to be active during at least the early part of each eruption in syn eruptive signals from march and april recorded at stations on the volcanic edifice the dominant spectral energy progressively shifts with time during the eruption to lower frequencies at least part of the energy in these signals may have been generated by the debris flows associated with dome failures

seismological aspects of the 1989 1990 eruption at redoubt volcano alaska the materials failure forecast method ffm with rsam and ssam seismic data abstract seismic activity during the december 1989 to april 1990 eruption of redoubt volcano alaska has been tracked by the alaska volcano observatory using real time seismic amplitude measurement rsam and seismic spectral amplitude measurement ssam systems with up to five stations data consist of 10 minute averages of the absolute amplitudes of seismometer output these data have been used to test in hindsight the materials failure forecast method ffm which attempts to define the time of eruption with a time series for precursory phenomena whose rate of change accelerates measurably before events practical application of the method emphasizes inverse rate plots both for early detection of signal emergent from background and for event forecasting eruption windows are determined by graphical or numerical extrapolation of the inverse rate trend and by intersection of a data envelope reflecting data scatter and consistency with an empirical critical rate near the time of eruption prior to the dome destroying eruption of january 2 rate changes were of sufficient consistency duration and intensity for a qualitative or quantitative ffm predictive analysis using either rsam or ssam signal to noise ratio was high for both rsam or ssam data sets and ffm analyses could have provided useful support for decision making following january 2 in association with a rapid succession of dome collapse eruptions signal strength diminished and rsam signal to noise ratio declined the most distinct patterns on rsam reflected noise rather than signal and forecasting exclusively based for rsam would have been misleading by eliminating the noise in excluded frequencies an enhanced signal to noise ratio was generally produced by ssam for banded frequencies near 2 hz after january 2 only ssam exhibited signal to noise ratios suitable for ffm analysis inverse ssam plots could have been informative for early detection of precursory long period seismicity the prospect of combining the ffm approach with spectral amplitudes in selected frequencies offers considerable promise

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

proximal pyroclastic deposits from the 1989 1990 eruption of redoubt volcano alaska stratigraphy distribution and physical characteristics abstract more than 20 eruptive events during the 1989 1990 eruption of redoubt volcano emplaced a complex sequence of lithic pyroclastic flow surge fall ice diamict and lahar deposits mainly on the north side of the volcano the deposits record the changing eruption dynamics from initial gas rich vent clearing explosions to episodic gas poor lava dome extrusions and failures the repeated dome failures produced lithic pyroclastic flows that mixed with snow and glacial ice to generate lahars that were channelled off drift glacier into the drift river valley some of the dome failures occurred without precursory seismic warning and appeared to result solely from gravitational instability material from the disrupted lava domes avalanched down a steep partly ice filled canyon incised on the north flank of the volcano and came to rest on the heavily crevassed surface of the piedmont lobe of drift glacier most dome collapse events resulted in single monolithologic massive to reversely graded medium to coarse grained sandy pyroclastic flow deposits containing abundant dense dome clasts these deposits vary in thickness grain size and texture depending on distance from the vent and local topography deposits are finer and better sorted down flow thinner and finer on hummocks and thicker and coarser where ponded in channels cut through the glacial ice the initial vent clearing explosions emplaced unusual deposits of glacial ice snow and rock in a frozen matrix on the north and south flanks of the volcano similar deposits were described at nevado del ruiz columbia and have probably been emplaced at other snow and ice clad volcanoes but poor preservation makes them difficult to recognize in the geologic record in a like fashion most deposits from the 1989 1990 eruption of redoubt volcano may be difficult to recognize and interpret in the future because they were emplaced in an environment where glacio fluvial processes dominate and quickly obscure the primary depositional record

statistical analysis of intermittent volcanic tremor associated with the september 1989 summit explosive eruptions at mount etna sicily the pattern of volcanic tremor accompanyingthe 1989 september eruption at the south east summit crater of mount etna is studied in specific sixteen episodes of lava fountaining which occurred in the first phase of the eruption are analysed their periodic behaviour also evidenced by autocorrelation allows us to define the related tremor amplitude increases as intermittent volcanic tremor episodes focusingon the reg ular intermittent behaviour found for both lava fountains and intermittent volcanic tremors we tried an a posteriori forecast usingsimple statistical methods based on linear regression and the student t test we performed the retrospective statistical forecast and found that several eruptions would have been successfully forecast in order to focus on the source mechanism of tremor linked to lava fountains we investigated the relationship between volcanic and seismic parameters a mechanism based on a shallow magma batch regularly refilled from depth is suggested 1 2002 elsevier science b v all rights reserved

dome growth and destruction during the 1989 1990 eruption of redoubt volcano abstract much of the six month long 1989 1990 eruption of redoubt volcano consisted of a dome growth and destructive phase in which 14 short lived viscous silicic andesite domes were emplaced and 13 subsequently destroyed the life span of an individual dome ranged from 3 to 21 days and volumes are estimated at 1 10 6 to 30 10 6 m 3 magma supply rates to the vent area averaged about 5 10 5 m 3 day for most of the dome building phase and ranged from a high of 2 2 10 6 m 3 per day initially to a low of 1 8 10 5 m 3 per day at the waning stages of the eruption the total volume of all domes is estimated to be about 90 10 6 m 3 and may represent as much as 60 70 of the volume for the entire eruption the site of 1989 1990 dome emplacement like that in 1966 was on the margin of a north facing amphitheatre like summit crater the domes were confined on the east and west by steep cliffs of pre eruption cone building volcanic rocks and thus were constrained to grow vertically rapid upward growth in a precarious site caused each dome to spread preferentially to the north resulting in eventual gravitational collapse as long as the present conduit remains active at redoubt volcano any dome formed in a new eruption will be confined to a narrow steeply sloping gorge leading to rapid vertical growth and a tendency to collapse gravitationally repetitive cycles of dome formation and failure similar to those seen in 1989 1990 are probably the norm and must be considered in future hazard analyses of redoubt volcano

seismic velocities in sedimentary rocks indicators of subsidence and uplift seismic velocities from the environment of a saltdome on the pompeckj swell were analysed in order to estimate the rates of subsidence and uplift it is shown using geological data that no true movements of the demanded amount can be proved in the study area the apparent uplifts estimated from velocity analysis can be interpreted as a result of the ice load during the pleistocene together with compression caused by the salt

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

seismic observations of redoubt volcano alaska 1989 2010 and a conceptual model of the redoubt magmatic system abstract seismic activity at redoubt volcano alaska has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano s summit major eruptions occurred in 1989 1990 and 2009 and were characterized by large volcanic explosions episodes of lava dome growth and failure pyroclastic flows and lahars seismic features of the 1989 1990 eruption were 1 weak precursory tremor and a short 23 hour long intense swarm of repetitive shallow long period lp events centered 1 4 km below the crater floor 2 shallow volcano tectonic vt and hybrid earthquakes that separated early episodes of dome growth 3 13 additional swarms of lp events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity and 4 a persistent cluster of vt earthquakes at 6 to 9 km depth in contrast the 2009 eruption was preceded by a pronounced increase in deep lp dlp events at lower crustal depths 25 to 38 km that began in mid december 2008 two months of discontinuous shallow volcanic tremor that started on january 23 2009 a strong phreatic explosion on march 15 and a 58 hour long swarm of repetitive shallow lp events the 2009 eruption consisted of at least 23 major explosions between march 23 and april 5 again accompanied by shallow vt earthquakes several episodes of shallow repetitive lp events and dome growth continuing until mid july increased vt earthquakes at 4 to 9 km depth began slowly in early april possibly defining a mid crustal magma source zone magmatic processes associated with the 2009 eruption seismically activated the same portions of the redoubt magmatic system as the 1989 1990 eruption although the time scales and intensity vary considerably among the two eruptions the occurrence of precursory dlp events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths based on the evolution of seismicity during the 1989 1990 and 2009 eruptions the redoubt magmatic system is envisioned to consist of a shallow system of cracks extending 1 to 2 km below the crater floor a magma storage or source region at roughly 3 to 9 km depth and a diffuse magma source region at 25 to 38 km depth close tracking of seismic activity allowed the alaska volcano observatory to successfully issue warnings prior to many of the hazardous explosive events that occurred in 2009