waveform classification of volcanic low frequency earthquake swarms and its implication at soufriere hills volcano montserrat low frequency volcanic earthquakes are indicators of magma transport and activity within shallow conduit systems at a number of volcanoes these events exhibit a high degree of waveform similarity providing a criterion for classification using cross correlation techniques to quantify the degree of similarity we develop a method to sort events into families containing comparable waveforms events within a family have been triggered within one small source volume from which the seismic wave has then travelled along an identical path to the receiver this method was applied to a series of 16 low frequency earthquake swarms well correlated with cyclic deformation recorded by tiltmeters at soufriere hills volcano montserrat in june 1997 nine waveform groups were identified containing more than 45 events each the families are repeated across swarms with only small changes in waveform indicating that the seismic source location is stable with time the low frequency seismic swarms begin prior to the point at which inflation starts to decelerate suggesting that the seismicity indicates or even initiates a depressurisation process a major dome collapse occurred within the time window considered removing the top 100 m of the dome this event caused activity within some families to pause for several cycles before reappearing this shows that the collapse did not permanently disrupt the source mechanism or the path of the seismic waves

seismic hybrid swarm precursory to a major lava dome collapse 9 12 july 2003 soufriere hills volcano montserrat abstract a swarm of 9500 hybrid earthquakes preceded the 12 13 july 2003 dome collapse at soufriere hills volcano montserrat most events had nearly identical waveforms and cross correlation was applied to measure inter event periods as well as phase arrival times to determine accurate relative location hypocenter depths were shallow

upper crustal structure of an active volcano from refraction reflection tomography montserrat lesser antilles to better understand the volcanic phenomena acting on montserrat the sea calipso seis mic experiment seismic experiment with airgun source caribbean andesitic lava island precision seismo geodetic observatory was conducted in 2007 december with the aim of imaging the upper crust and the magmatic system feeding the active soufri ere hills volcano the 3 d survey covered an area of about 50 40 km and involved the deployment of 247 land stations and ocean bottom seismometers obss a subset of the data recorded by four obss and four land stations on a southeast to northwest line has been analysed and traveltimes have been inverted to obtain a 2 d seismic velocity model through the island inverted phases include crustal and sediment p waves and wide angle reflections the resulting velocity model reveals the presence of a high velocity body 3 5 5 5 km s 1 beneath the island with highest velocities beneath the soufri ere and centre hills cor responding primarily to the cores of these volcanic edifices built of a pile of andesite lava domes and subsequent intrusions in the off shore region velocities in the surficial sediment layer vary from 1 5 to 3 0 km s 1 consistent with a mainly calcareous and volcaniclastic composition a wide angle reflector is observed at a depth of 1200 m below the seabed and appears to deepen beneath the island the upper crust beneath this reflector has velocities of 4 0 6 0 km s 1 and is infer red to cor respond to plutonic and hypabyssal rocks and sedimentary material of the old arc the high velocity region beneath the island extends into the crust to a depth of at least 5 km and is believed to be caused by an intrusive complex possibly of intermediate composition a low velocity zone as would be expected in the presence of an active magma chamber was not observed perhaps due to the limited resolution beneath 5 km depth our results so far provide the first wide angle seismic constraints on the upper crustal structure of the island to a depth of 10 km and will help understanding the processes that drive volcanism at montserrat and other island arc volcanoes

swarms of repeating long period earthquakes at shishaldin volcano alaska 2001 2004 abstract during 2001 2004 a series of four periods of elevated long period seismic activity each lasting about 1 2 months occurred at shishaldin volcano aleutian islands alaska the time periods are termed swarms of repeating events reflecting an abundance of earthquakes with highly similar waveforms that indicate stable non destructive sources these swarms are characterized by increased earthquake amplitudes although the seismicity rate of one event every 0 5 5 min has remained more or less constant since shishaldin last erupted in 1999 a method based on waveform cross correlation is used to identify highly repetitive events suggestive of spatially distinct source locations the waveform analysis shows that several different families of similar events co exist during a given swarm day but generally only one large family dominates a network of hydrothermal fractures may explain the events that do not belong to a dominant repeating event group i e multiple sources at different locations exist next to a dominant source the dominant waveforms exhibit systematic changes throughout each swarm but some of these waveforms do reappear over the course of 4 years indicating repeatedly activated source locations the choked flow model provides a plausible trigger mechanism for the repeating events observed at shishaldin explaining the gradual changes in waveforms over time by changes in pressure gradient across a constriction within the uppermost part of the conduit the sustained generation of shishaldin s long period events may be attributed to complex dynamics of a multi fractured hydrothermal system the pressure gradient within the main conduit may be regulated by temporarily sealing and reopening of parallel flow pathways by the amount of debris within the main conduit and or by changing gas influx into the hydrothermal system the observations suggest that shishaldin s swarms of repeating events represent time periods during which a dominant source is activated

determinants of peak discharge in steep mountain catchments case of the rift valley escarpment of northern ethiopia peak discharge is an important hydrological parameter of mountain torrents however due to the flashy and destructive nature of their stream flows it is usually difficult to understand the hydrological behavior of steep mountain catchments through direct measurements of discharges in this study 332 daily peak discharge events from 11 steep 0 27 0 65 m m 1 catchments 0 4 25 km2 were measured in three rainy seasons 2012 2014 with the objective of analyzing runoff response of steep mountain catchments in the western rift valley escarpment of northern ethiopia seven rain gauges were installed at different altitudes 1623 2851 m a s l in and nearby the catchments event peak discharges were calculated using the manning s equation from daily measurements of maximum discharge height at 11 crest stage gauges percentages of land cover classes were detected from high resolution 0 6 m google earth imagery february 1 2014 morphometric characteristics of the catchments were computed both from aster digital elevation model dem and topographic maps correlation analysis between average daily precipitation pd and peak discharge qp showed strong positive relation r2 0 32 0 94 p 0 05 in all the catchments catchment specific peak discharge coefficient cp showed a strong decreasing relation with vegetation cover r2 0 85 p 0 01 relative distance of vegetation cover from the thalweg r2 0 55 p 0 01 combined index of vegetation cover and its relative distance from the thalweg r2 0 76 p 0 01 catchment length r2 0 37 p 0 05 and time of concentration r2 0 43 p 0 05 it was correlated positively with catchment slope gradient r2 0 37 p 0 05 and index of vegetation distribution r2 0 45 p 0 05 a stepwise multiple regression analysis revealed that 99 p 0 01 of the variability of catchment specific peak discharge coefficient in the catchments can be predicted by vegetation cover and infiltration number overall this study demonstrates that in reforesting steep mountain catchments where direct measurement of discharges using the conventional methods is difficult due to the flashy and destructive nature of the stream flows hydrological variability can easily be understood using simple measurements of daily precipitation and peak discharges further runoff response is determined by precipitation event and strongly by percentage of vegetation cover and its strategic location farther from the thalweg in the sloping sides of the catchments

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

an overview of lava dome evolution dome collapse and cyclicity at soufriere hills volcano montserrat 2005 2007 1 the third episode of lava dome growth at soufriere hills volcano montserrat was characterised by higher average magma discharge rates than either previous dome growth episode at this volcano and yet fewer collapses during sustained dome growth at moderate high average rates 6 m3 s we identified 2 6 week discharge pulses that each supplied c 20 mm3 magma from depth our observations are consistent with some existing models but we explain discrepancies by a combination of higher volatile contents and higher ascent rates cycles of c 11 16 days were evident in rockfall lp rockfall and shallow lp earthquake counts related to dome growth and degassing we speculate that degassing at the conduit margins together with stick slip conduit flow may drive these cycles only one major collapse 10 mm3 occurred during the third episode on may 20 2006 as a new magma pulse entered the dome and coincided with heavy rainfall

a space time rainfall disaggregation model adapted to sahelian mesoscale convective complexes a model adapted to the disaggregation of rainfields associated to sahelian mesoscale convective complexes mccs at small time 5 min and space 1 10 km scales is presented spatial and temporal disaggregation have been decoupled in order to simplify the problem the average rain depth over the study area for each storm is first disaggregated in space by using the turning band method a geostatistical technique able to generate spatially correlated fields with a known covariance function the method has been adapted in order to simulate non gaussian rainfall fields including in particular a probability of zero rainfall the movement of the rain system is described by mapping the starting time of the rain event as the convective front moves through the domain finally at each location the temporal disaggregation of the storm rain depth is obtained by using a standard hyetogram model reproducing the typical sequence of a convective front followed by a stratiform trail in its present form the only input of the disaggregation model is the average rain depth over the domain which can be provided either by a general circulation model output or a satellite estimate to perform the various steps of the spatial and temporal disaggregation some knowledge on the climatology of the zone is needed over the sahel this knowledge is provided by the epsat niger data set which contains 170 mesoscale convective systems mcss observed over a 4 year period by a dense recording raingauge network and a weather radar in the niamey area half of these mcss were identified as mccs the analysis of the mccs data set allowed the derivation of a probability distribution and a covariance function of the point storm rain depth it also allowed the calculation of statistics for the average speed and direction of storm displacement and the inference of parameters describing the standard hyetograms a complete example of the use of the model is presented showing that it produces realistic rainfall fields perspectives for further development and validation of the model are given in the conclusion

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

microbial sand chips a non actualistic sedimentary structure abstract microbial mats show a marked decline with the transition from the precambrian to the phanerozoic most likely due to the advent of effective benthic grazing organisms hitherto most aquatic sediments up to sand grade were commonly coagulated by organic material allowing reworking to form intraclasts new term microbial sand chips presence of a microbial mat is indicated 1 by refractory remains of organic matter in the laminated parent sediment 2 by the concentration of early diagenetic pyrite associated with sandy intraclasts in quartzites indicating a concentration of organic matter in the clast and 3 by plastic deformation of the clasts during the erosive event as bioturbation spread into most aquatic depositional environments during the phanerozoic the formation of microbial sand chips became restricted to habitats where bioturbation and grazing are limited by environmental stress and where the preservation potential for microbial sand chips is very low therefore the widespread formation of microbial sand chips in precambrian sandy subaqueous sediments is non actualistic

seismicity associated with dome growth and collapse at the soufriere hills volcano montserrat varied seismicity has accompanied growth and collapse of the lava dome of the soufriere hills volcano montserrat earthquakes have been classified as either volcano tectonic long period or hybrid and daily variations in the numbers of events have mapped changes in the style of eruption repetitive hybrid earthquakes were common during the first months of dome growth in july 1996 the style of seismicity changed and regular short lived hybrid earthquake swarms became common this change was probably caused by an increase in the magma flux earthquake swarms have preceded almost all major dome collapses and have accompanied cyclical deformation thought to be due to a build up of pressure in the upper conduit which is later released by magma moving into the dome

forecasting seismo volcanic activity by using the dynamical behavior of volcanic earthquake rates abstract we present a novel approach for short term forecasting of volcano seismic activity volcanic earthquakes can be seen as a response mechanism of the earth crust to stresses induced by magma injection from this point of view the temporal evolution of seismicity can be represented as a diffusion process which compensates pressure differences by means of this dynamical approach we are able to estimate the system behavior in the near future which in turn allows us to forecast the evolution of the earthquake rate for the next time span from actual and past observations for this purpose we model the earthquake rate as a random walk process embedded in a moving and deforming potential function the center of the potential function is given by a moving average of the random walk s trace we successfully apply this procedure to estimate the next day seismicity at soufriere hills volcano montserrat over a time period of six years when comparing the dynamical approach to the well known method of material failure forecast we find much better predictions of the critical stages of volcanic activity using the new approach

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

multiplets their behavior and utility at dacitic and andesitic volcanic centers 1 multiplets or groups of earthquakes with similar waveforms are commonly observed at volcanoes particularly those exhibiting unrest using triggered seismic data from the 1980 1986 mount st helens msh eruption we have constructed a catalog of multiplet occurrence our analysis reveals that the occurrence of multiplets is related at least in part to the viscosity of the magma we also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at msh and 2007 eruption at bezymianny volcano russia prior to explosions at msh in 2004 and bezymianny in 2007 the multiplet proportion of total seismicity mpts declined while the average amplitudes and standard deviations of the average amplitude increased the life spans of multiplets time between the first and last event were also shorter prior to explosions than during passive lava extrusion dome forming eruptions that include a partially solidified plug like msh 1983 1986 and 2004 2008 often possess multiplets with longer life spans and mpts values exceeding 50 conceptually the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit we infer that such complex stress fields affect the number of concurrent families mpts average amplitude and standard deviation of the amplitude of the multiplets we also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption

the spatial extent of tephra deposition and environmental impacts from the 1912 novarupta eruption the eruption of novarupta within the katmai volcanic cluster south west alaska in june 1912 was the most voluminous eruption of the twentieth century but the distal distribution of tephra deposition is inadequately quantified we present new syntheses of published tephrostratigraphic studies and a large quantity of previously un investigated historical records for the first time we apply a geostatistical technique indicator kriging to integrate and interpolate such data our results show evidence for tephra deposition across much of alaska yukon the northern pacific western british columbia and northwestern washington the most distal tephra deposition was observed around 2 500 km downwind from the volcano associated with tephra deposition are many accounts of acid deposition and consequent impacts on vegetation and human health kriging offers several advantages as a means to integrate and present such data future eruptions of a scale similar to the 1912 event have the potential to cause widespread disruption historical records of tephra deposition extend far beyond the limit of deposition constrained by tephrostratigraphic records the distal portion of tephra fallout deposits is rarely adequately mapped by tephrostratigraphy alone contemporaneous reports of fallout can provide important constraints on the extent of impacts following large explosive eruptions

erosional remnants and pockets evolving from biotic physical interactions in a recent lower supratidal environment abstract sedimentary structures characterizing tidal depositional systems are not in all cases produced by physical dynamics alone the activities of epibenthic cyanobacteria such as biostabilization or surface levelling may also play a significant role in structure formation one example of bio induced structures are erosional remnants and pockets a specific surface morphology that can be observed in the lower supratidal zone of mellum island southern north sea this surface relief rises from partwise erosion of a microbial mat covered and biostabilized tidal surface on the basis of detailed field measurements of the geometric dimensions of the surface relief the tidal current system of the area and the history of formation of the morphology can be reconstructed erosional remnants and pockets are highly facies indicative and fossil occurrences would help in reconstruction paleo environments

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

observations of hybrid seismic events at soufriere hills volcano montserrat july 1995 to september 1996 swarms of small repetitive events with similar waveforms and magnitudes are often observed during the emplacement of lava domes over 300 000 such events were recorded in association with the emplacement of the lava dome at soufriere hills volcano montserrat from august 1995 through august 1996 these events originated 2 3 km deep they exhibited energy ranging over 1 5 4 5 hz and were broader band than typical long period events we term the events hybrid between long period and volcano tectonic the events were more impulsive and broader band prior to compared with during and after periods of inferred increased magma flux rate individual swarms contained up to 10 000 events often exhibiting very similar magnitudes and waveforms throughout the swarm swarms lasted hours to weeks during which inter event intervals generally increased then decreased often several times long duration swarms began about every two months starting in late september 1995 we speculate that the events were produced as the magma column degassed into adjacent cracks

dome growth behavior at soufriere hills volcano montserrat revealed by relocation of volcanic event swarms 1995 1996 abstract we have relocated a subset of events from the digital waveform catalogue of 17 000 volcanic microearthquakes recorded between july 1995 and february 1996 at soufriere hills volcano shv montserrat using a cross correlation based phase repicking technique with a joint location method hypocenters were estimated for 3914 earthquakes having five or more corrected p wave picks the seismic source region collapsed to a volume of 1 km 3 from an initial 100 km 3 relocated events represent 36 swarms each containing nearly identical waveforms having source dimensions of 10 to 100 m in diameter and spatial separations on the order of 500 m or less each swarm occurred over a span of several hours to a few days triggered data appear to miss between 65 and 98 of the events that occur within these swarms based on review of helicorder records visual estimates of summit dome growth show a rough correspondence between episodes of intense swarming and increases in extruded magma although dome observations are too sparse to make a direct comparison for this time period the limited depth range over which dome growth related events occur is consistent with a dynamic model of cyclic plug extrusion behavior in the shallow conduit governed by magma supply rate overpressure buildup and physical properties of the magma and conduit geometry seismic sources may occur in locally overpressured regions that result from microlite formation in a zone of rapid decompression we propose that this zone exists in the vicinity of a detachment plane associated with the cyclic plug extrusion

catastrophic lava dome failure at soufriere hills volcano montserrat 12 13 july 2003 the lava dome collapse of 12 13 july 2003 was the largest of the soufriere hills volcano eruption thus far 1995 2005 and the largest recorded in historical times from any volcano 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows which reached the sea the evolution of the collapse can be interpreted with reference to the complex structure of the lava dome which comprised discrete spines and shear lobes and an apron of talus progressive slumping of talus for 10 h at the beginning of the collapse generated low volume pyroclastic flows it undermined the massive part of the lava dome and eventually prompted catastrophic failure from 02 00 to 04 40 13 july 2003 large pyroclastic flows were generated these reached their largest magnitude at 03 35 when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes the high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge which flowed inland a vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03 35 13 july and four further explosions occurred at progressively longer intervals during 13 15 july 2003 the dome collapse lasted approximately 18 h but 170 of the total 210 million m3 was removed in only 2 6 h during the most intense stage of the collapse

evolution of the december 14 1989 precursory long period event swarm at redoubt volcano alaska abstract the intermittency pattern and evolution in waveforms of long period lp seismic events during the intense 23 h swarm that preceded the december 14 1989 eruption of redoubt volcano are investigated utilizing cross correlation to exploit the high degree of similarity among waveforms a substantially more complete event catalog is generated than was available from near realtime detection based on short term long term amplitude ratios which was saturated by the high rate of activity the temporal magnitude distribution of the predominant lp events is found to have an unusual banded structure in which the average magnitude of each band slowly increases and then decreases through time a bifurcation that appears in the uppermost band shortly after the peak in magnitudes is characterized by a quasi periodicity in intermittency and magnitude that is reminiscent of one of the classic routes to chaotic behavior in some non linear systems the waveforms of the predominant events evolve slowly but unsteadily through time these gradual changes appear to result from variations in the relative amplitudes of spectral peaks that remain stable in frequency which suggests that they are due to differential excitation of a single resonant source two other previously unrecognized repetitive waveforms are also identified but the signals from these secondary events are not clearly recorded at distances beyond the closest station similarities among the spectra of the predominant and secondary events suggest that the signals from these events also could represent different modes of exciting the same source significant changes in the rates and the sizes of the largest of these secondary events appear to coincide with the peak in the size distribution of the predominant lps at least some of the non repetitive lp waveforms in the swarm appear to be the result of the superposition of signals from the rapid repetition of predominant lp source thus placing a constraint on the repeat time of the triggering mechanism for this source a lone hybrid event which has a waveform character intermediate between the predominant lp events and high frequency volcano tectonic events was also identified in the swarm the occurrence of this event provides important evidence that the low frequency character of the lp events is a source rather than a path or site effect

a method for delineating and estimating rainfall fields a geostatistical model has been defined to deal with intermittent rainfall fields the intermittency is represented by a binary random function while inside the rainy areas the rainfall variability is rendered by an intrinsic random function a rain gage data set from the cevennes region france is used to infer the model the inner variability is independent of the intermittency thereby allowing a simple estimation relying on the separate kriging of these two components comparison of the rainfall assessments made by a classic global kriging and the proposed method shows its clear superiority for delineating and estimating rainfall fields

overview of the eruption of soufriere hills volcano montserrat 18 july 1995 to december 1997 the onset of phreatic volcanic activity at the soufriere hills volcano montserrat on 18 july 1995 followed a three year period of heightened volcano seismic activity beneath the island phreatic explosions gave way to continuous eruption of juvenile andesitic magma in the form of a lava dome on or around 15 november 1995 magma production rate has varied leading to changes in eruptive style an explosive eruption on 17 september 1996 followed a period of enhanced dome growth and large scale gravitational collapses from its eastern flank increasing dome volume led to stressing and overtopping of the confining crater walls to the southwest north and west during early 1997 sustained high magma production rate since june 1997 has led to three periods of major gravitational dome collapses followed by vulcanian explosive eruptions dome growth re started immediately after the cessation of the latest of these explosive phases in october 1997 and continues as of december 1997

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

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

identification and calibration of spatial correlation patterns of rainfall abstract the significance of spatial distribution of rainfall and its effects on spatial correlation functions are reviewed a number of statistical terms and properties are explained in depth with reference to the theory of variograms originally adopted in geostatistics this is followed by a detailed analysis of theoretical variogram models effects of meteorological orographic and space time aggregation scales and a discussion on network design areal mean calculations and storm velocities empirical variogram and validation techniques are then examined some applications to two different parts of lombardia the mountainous valtellina catchment and a large part of the flat area of the region in northern italy are given with a discussion of the results in the appendix the technique of kriging is explained with reference to the estimation of the spatial distribution of the random rainfall field

the depositional record of sandy versicolored tidal flats mellum island southern north sea abstract cyanobacteria fix and bind sediments and generate versicolored laminated patterns in quartz sand flats they are developed in the lower supratidal zone between mean high water and mean high water springs the cyanobacteria mats protect the sediments from erosion and desiccation and provide food for marine and terrestrial invertebrates burrowing and grazing polychaetes amphipods and gastropods are present as well as a diverse meiofauna the bioturbation structures are described at some places the population density of the macrofauna averages 20 000 individuals per m2 typical are smooth surfaces and erosional pockets with rippled sand the deposits consist of laminated sand in which organic rich mat generations are intercalated the sediment is medium to fine grained sand the development of versicolored systems by interaction of migrating cyanobacteria and episodic low rate sedimentation was studied in the laboratory the depositional record reveals characteristics from both the terrestrial and the marine surrounding there are bioturbation structures from marine and terrestrial burrowing animals hard skeletal parts from shelled marine organisms and plant roots of halophytes fenestrae produced by burrowing beetles are observed the described mats characterize the type of quartz sandy potential stromatolites

biostabilization of sediments by microbial mats in a temperate siliciclastic tidal flat bahia blanca estuary argentina abstract extensive microbial mats have been found in the siliciclastic tidal flats of the temperate bahia blanca estuary in the atlantic coast of buenos aires province argentina several microbially induced sedimentary structures miss occur especially in the upper intertidal and lower supratidal flats among which the most conspicuous are erosional pockets gas domes microbial mat chips and polygonal oscillation cracks biostabilization processes by epibenthic and endobenthic mats are also analyzed endobenthic mats occur in the upper intertidal area stabilizing ripples that despite the occurrence of severe storms persist in a fixed position for at least 2 months epibenthic mats occurring in the lower supratidal area also protect the substrate forming a thick microbial cover through the studied period this thick cover was only affected by a strong storm that formed areas with erosional pockets and mat pieces nevertheless the loose sediment within the erosional pockets was quickly colonized by microorganisms that developed a thin biofilm layer after a week changes in sediment accumulation were also recorded all over the upper tidal flat during a year showing an important increase due to bioturbation activities of crabs this situation also affected microbial mat growth which evolved from a thin microbial biofilm into a thick stratified microbial mat community in almost 2 years mainly in the lower supratidal areas the results of this study not only help us to better characterize the complex interactions between the microorganisms forming microbial mats the tidal flat sediment and the physical parameters that control this setting but also have important implications for the understanding of analogous fossil sedimentary successions

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

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

a model to describe precursory material failure phenomena applications to short term forecasting at colima volcano mexico some volcanoes exhibit at times accelerating strain and seismicity before eruptions different authors have used this behavior to predict eruptions and to develop materials science models here a linear kelvin voigt viscoelastic model is proposed to describe the observed behavior this model also has applications to other failure phenomena such as landslides the strain rate of a variety of materials under constant stress after an instantaneous elastic response is found to be well described by a general relaxation law dot varepsilon left t right b over 1 st where b and s are parameters depending on the material and its creep state whether the creep regime is primary or tertiary depends upon the sign of s s 0 corresponds to pseudoviscous flow the creep behavior of the viscoelastic body is analyzed for different load histories it is found that the body has an exponential distribution of retardation frequencies that may or may not converge depending on the sign of s according to the model tertiary creep implies material degradation and a critical weakening of the medium leading to a runaway growth of the strain and seismic energy release rates if tertiary creep is detected time of failure predictions may be done from field data through determination of two model parameters for varying loads the model response compare well with reported examples of pre eruptive volcano behavior and with reported results of landslide experiments the model is tested with the july 1994 in hindsight and november 1998 in foresight colima volcano eruptions although this method provides some guidance in estimating the time over which accelerating volcanic precursors may end in an eruption it is emphasized that eruptions may fail to occur at the estimated time or may not occur at all on the other hand eruptions may not be preceded by such a behavior

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

on the feasibility of magma fracture within volcanic conduits constraints from earthquake data and empirical modelling of magma viscosity 1 in the last decade several studies have indicated that magma within volcanic conduits can undergo repeated failure and healing thus providing a realistic source mechanism for the peculiar sequences of low frequency earthquakes that often announce eruptions although geological observations laboratory experiments and numerical modelling support such a hypothesis the links between geophysical observations and the proposed models remain qualitative this study focuses on providing constraints to the relationship between the occurrence of repeating earthquakes and magma fracture at andesite volcanoes empirical modelling of viscosity is incorporated into the fundamental physics of magma fracture in order to assess whether and where the conditions for brittle failure are met within volcanic conduits a case study from the 1995 ongoing eruption of soufriere hills volcano montserrat is presented the locations of earthquakes from a pre eruptive low frequency seismic swarm illuminate a relatively compact source volume at depths of 100 300 meters below sea level viscosity modelling confirms that the soufriere hills magma could rupture at those depths

using a cross correlation technique to refine the accuracy of the failure forecast method application to soufriere hills volcano montserrat prior to many volcanic eruptions an acceleration in seismicity has been observed suggesting the potential for this as a forecasting tool the failure forecast method ffm relates an accelerating precursor to the timing of failure by an empirical power law with failure being defined in this context as the onset of an eruption previous applications of the ffm have used a wide variety of accelerating time series often generating questionable forecasts with large misfits between data and the forecast as well as the generation of a number of different forecasts from the same data series here we show an alternative approach applying the ffm in combination with a cross correlation technique which identifies seismicity from a single active source mechanism and location at depth isolating a single system at depth avoids additional uncertainties introduced by averaging data over a number of different accelerating phenomena and consequently reduces the misfit between the data and the forecast similar seismic waveforms were identified in the precursory accelerating seismicity to dome collapses at soufriere hills volcano montserrat in june 1997 july 2003 and february 2010 these events were specifically chosen since they represent a spectrum of collapse scenarios at this volcano the cross correlation technique generates a five fold increase in the number of seismic events which could be identified from continuous seismic data rather than using triggered data thus providing a more holistic understanding of the ongoing seismicity at the time the use of similar seismicity as a forecasting tool for collapses in 1997 and 2003 greatly improved the forecasted timing of the dome collapse as well as improving the confidence in the forecast thereby outperforming the classical application of the ffm we suggest that focusing on a single active seismic system at depth allows a more accurate forecast of some of the major dome collapses from the ongoing eruption at soufriere hills volcano and provides a simple addition to the well used methodology of the ffm

extensive microbial mats and their influences on the erosional and depositional dynamics of a siliciclastic cold water environment lower arenigian montagne noire france abstract lower arenigian ordovician rocks of the montagne noire france represent a shallow marine environment of a high latitude position along the northern margin of gondwana within the weakly metamorphosed siliciclastics six depositional units were recognized 1 outer shelf 2 foreshore zone below wave base 3 foreshore zone above wave base 4 sand bars of shoreface zone 5 intertidal deposits and 6 lagoonal zone wrinkle structures and various other phenomena were mediated by coherent cyano bacterial mats the structures can be related to the different facies zones of the paleoenvironment whereas the muddy outer shelf and the high energetic sand bars were not overgrown by any mat constructing microbial populations fine sands of the foreshore zone the tidal flats and lagoonal areas were widely colonized restriction of mats due to competition of space by endobenthic macroorganisms or by grazers was low the microbially induced structures are composed of organic material pyrite clay minerals illite chamsonite chlorite and chert the minerals precipitated in situ during degradation of the organic layers by the activity of heterotrophic bacteria at low temperatures because the microorganisms formed a dense organic carpet covering extensive areas of the ancient sea bottom they influenced significantly the erosional and depositional dynamics of the sedimentary system of the local arenigian biostabilization counteracted erosion and baffling trapping and binding enriched mineral particles additionally the in situ formed minerals contributed to the total amount of sediment the biotic influence lead to increased accumulation of sediment within the depositional area the study shows that microbial mats of great extension occur within phanerozoic siliciclastics of cold paleoclimate zones and that preservation of the mat fabrics was possible the significant mats influenced the local sedimentary system an aspect scarcely taken into account for such paleoenvironments