persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

the 2005 eruption of sierra negra volcano galapagos ecuador sierra negra volcano began erupting on 22 october 2005 after a repose of 26 years a plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a 2 km long curtain of lava fountains the eruptive fissure opened inside the north rim of the caldera on the opposite side of the caldera from an active fault system that experienced an mb 4 6 earthquake and 84 cm of uplift on 16 april 2005 the main products of the eruption were an a a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank the a a flow grew in an unusual way once it had established most of its aerial extent the interior of the flow was fed via a perched lava pond causing inflation of the a a this pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow many of which were subsequently overridden by a a as the crust slowly spread from the center of the pond and tumbled over the pahoehoe the curtain of lava fountains coalesced with time and by day 4 only one vent was erupting the effusion rate slowed from day 7 until the eruption s end two days later on 30 october although the caldera floor had inflated by 5 m since 1992 and the rate of inflation had accelerated since 2003 there was no transient deformation in the hours or days before the eruption during the 8 days of the eruption gps and insar data show that the caldera floor deflated 5 m and the volcano contracted horizontally 6 m the total eruptive volume is estimated as being 150 106 m3 the opening phase tephra is more evolved than the eruptive products that followed the compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2 1 km beneath the caldera floor

a volcano bursting at the seams inflation faulting and eruption at sierra negra volcano galapagos the results of geodetic monitoring since 2002 at sierra negra volcano in the galapagos islands show that the filling and pressurization of an 2 km deep sill eventually led to an eruption that began on 22 october 2005 continuous global positioning system cgps monitoring measured 2 m of accelerating inflation leading up to the eruption and contributed to nearly 5 m of total uplift since 1992 the largest precursory inflation ever recorded at a basaltic caldera this extraordinary uplift was accommodated in part by repeated trapdoor faulting and coseismic cgps data provide strong constraints for improved deformation models these results highlight the feedbacks between inflation faulting and eruption at a basaltic volcano and demonstrate that faulting above an intruding magma body can relieve accumulated strain and effectively postpone eruption

subsidence in the paricutin lava field causes and implications for interpretation of deformation fields at volcanoes abstract assessment of volcanic hazards includes interpretation of ground deformation signal which at polygenetic volcanoes often results from the superposition of deformation due to pressure changes in the magmatic system and due to surficial processes such as cooling of emplaced lava the deformation signal associated with emplaced lava is sometimes considered negligible if fields are decades old but if the lava thickness is great deformation may still be occurring possibly leading to misinterpretation of the observed deformation here i evaluate the 2007 2011 ground motion of the 1943 1952 lava field of the paricutin monogenetic cinder cone mexico interferometric synthetic aperture radar insar time series reveal patchy subsidence restricted to the lava field and following linear rates up to 5 5 cm year there is a clear correlation between subsidence rates and topography suggesting a causal relationship with deposits or lava thickness i estimate these thicknesses in the subsiding areas using pre and post eruption topographic maps and show that they reach up to 200 m a numerical model for lava flow cooling was developed considering radiation and convection from the surface conductive transfer inside the flow and to the ground and vesiculation and latent heat generation at the top and bottom of the flow the model shows that compaction induced by cooling of the thick deposits emplaced 60 years ago explains the observed subsidence when conductive transfer to the ground is considered these results demonstrate that thick deposits can keep deforming significantly even decades after their emplacement emphasizing the importance of considering cooling processes when interpreting deformation fields at polygenetic volcanoes producing massive lava fields

the consequences of fluid motion in volcanic conduits when volcanoes are active there are characteristic signs such as ground movement sounds heat and ejected material each of these signs is a result of and hence an information source for fluid motion in volcanic conduits here we briefly review some of the links between these signs and fluid flow processes and suggest future directions that should allow advancement of eruption forecasting as these links become understood more fully cross fertilization between increasingly realistic numerical and experimental models diverse geophysical data sources and chemical and physical evidence in eruptive products can be achieved by simultaneously applying these approaches to well studied volcanoes

facies characteristics of a proglacial turbiditic sand lobe at svalbard abstract a shallow marine turbiditic lobe inferred to be associated with an ice contact delta was deposited during the last glaciation weichselian at svalbard the norwegian arctic the postglacially raised sandy lobe is exposed in a 200 m long river section and exhibits six units that reflect an early phase of glaciomarine mud deposition followed by three episodes dominated by deposition from sandy turbidity currents the lobe is characterized by a complex pattern of turbidite filled erosional features from thin scour fills reflecting a highly mobile flow pattern to stacked chute fill deposits showing confined flow the sandy turbidites show rhythmic deposition of massive to graded laminae deposited from suspension alternating with faint laminae or ripple cross lamination deposited from tractional transport semi continuous turbidity currents are thought to have been generated by retrogressive slumping of ice proximal well sorted sandy deposits on the delta front and slope the lateral and vertical changes of lithofacies within the sandy lobe are mainly attributed to normal mechanisms of turbiditic lobe growth with only minor effect from synsedimentary glacier terminus movement and minor changes in the meltwater outflow position this detailed mapping of facies changes allows a fairly accurate reconstruction of the axis of the former discharge outlet

high rates of inflation during a noneruptive episode of seismic unrest at semisopochnoi volcano alaska in 2014 2015

seismicity patterns during a period of inflation at sierra negra volcano galapagos ocean island chain basaltic shield volcanoes of the western galapagos islands are among the most rapidly deforming volcanoes worldwide but little was known of the internal structure and brittle deformation processes accompanying inflation and deflation cycles a 15 station broadband seismic array was deployed on and surrounding sierra negra volcano galapagos from july 2009 through june 2011 to characterize seismic strain patterns during an inter eruption inflation period and to evaluate single and layered magma chamber models for ocean island volcanoes we compare precise earthquake locations determined from a 3d velocity model and from a double difference cluster method using first motion of p arrivals we determine focal mechanisms for 8 of the largest earthquakes ml 1 5ml 1 5 located within the array most of the 2382 earthquakes detected by the array occurred beneath the broad 9 km wide sierra negra caldera at depths from surface to about 8 km below sea level although outside our array frequent and larger magnitude ml 3 4ml 3 4 earthquakes occurred at alcedo and fernandina volcano and in a spatial cluster beneath the shallow marine platform between fernandina and sierra negra volcanoes the time space relations and focal mechanism solutions from a 4 day long period of intense seismicity june 4 9 2010 along the southeastern flank of sierra negra suggests that the upward migrating earthquake swarm occurred during a small volume intrusion at depths 5 8 km subsurface but there was no detectable signal in insar data to further constrain geometry and volume focal mechanisms of earthquakes beneath the steep intra caldera faults and along the ring fault system are reverse and strike slip these new seismicity data integrated with tomographic geodetic and petrological models indicate a stratified magmatic plumbing system a shallow sill beneath the large caldera that is supplied by magma from a large volume deeper feeding system the large amplitude inter eruption inflation of the shallow sill beneath the sierra negra caldera is accompanied by only very small magnitude earthquakes although historical records indicate that larger magnitude earthquakes mw 6 occur during eruptions trapdoor faulting episodes without eruptions and large volume flank intrusions

petrology of lavas from sierra negra volcano isabela island galapagos archipelago sierra negra volcano is a voluminous active basaltic shield situated in the western galapagos archipelago a hotspot related chain adjacent to the galapagos spreading center the volcano has erupted fe rich tholeiitic basalts of very limited compositional range comparison of lavas from each of five stratigraphic units covering the entire volcano indicates that the lavas are mineralogically similar and compositionally restricted 4 4 to 6 9 wt mgo the lavas are fe rich and hypersthene normative and plot in both the alkaline and tholeiite fields of the alkali silica diagram rare earth element ree patterns are steep and parallel the major and trace element data indicate a comagmatic relationship by fractional crystallization of the observed phenocryst phases projections into pseudoternary phase diagrams suggest that the magmas cooled and crystallized at pressures between 1 and 3 kbar calculated melt densities range from 2 73 to 2 77 g cm3 which are higher than those of typical mid ocean ridge basalt morb hawaiian tholeiite and other galapagos lavas the high calculated melt densities may be caused by fractionation at greater depths than is ordinary for the other basaltic magmas suppression of plagioclase and olivine crystallization in favor of augite may eliminate the minimum density window that has been proposed for morb fractionation sierra negra lavas have the most radiogenic lead and strontium isotopic ratios in the western galapagos indicating that the magmas have a relatively large contribution of plume material and have been minimally contaminated by entrainment of morb producing mantle magmatic 3he 4he isotopic ratios from sierra negra are approximately 15 times the atmospheric ratio although these ratios clearly indicate plume helium they are not the highest 3he 4he in the archipelago suggesting that helium is decoupled from the heavier isotopes high sm yb ratios light rare earth element lree enrichment and a steep ree slope are consistent with an origin by moderate extents 5 15 of partial melting of a garnet lherzolite source with ree characteristics that are between chondrite and depleted earth mantle sources sierra negra lavas are compositionally monotonous because homogeneous plume rich material has experienced long term exposure to a well regulated sublithospheric thermal environment with additional compositional restrictions imposed in the lithosphere by high magma flux

the may 2005 eruption of fernandina volcano galapagos the first circumferential dike intrusion observed by gps and insar the may 2005 eruption of fernandina volcano galapagos occurred along circumferential fissures parallel to the caldera rim and fed lava flows down the steep southwestern slope of the volcano for several weeks this was the first circumferential dike intrusion ever observed by both insar and gps measurements and thus provides an opportunity to determine the subsurface geometry of these enigmatic structures that are common on galapagos volcanoes but are rare elsewhere pre and post eruption ground deformation between 2002 and 2006 can be modeled by the inflation of two separate magma reservoirs beneath the caldera a shallow sill at 1 km depth and a deeper point source at 5 km depth and we infer that this system also existed at the time of the 2005 eruption the co eruption deformation is dominated by uplift near the 2005 eruptive fissures superimposed on a broad subsidence centered on the caldera modeling of the co eruption deformation was performed by including various combinations of planar dislocations to simulate the 2005 circumferential dike intrusion we found that a single planar dike could not match both the insar and gps data our best fit model includes three planar dikes connected along hinge lines to simulate a curved concave shell that is steeply dipping 45 60 toward the caldera at the surface and more gently dipping 12 14 at depth where it connects to the horizontal sub caldera sill the shallow sill is underlain by the deep point source the geometry of this modeled magmatic system is consistent with the petrology of fernandina lavas which suggest that circumferential eruptions tap the shallowest parts of the system whereas radial eruptions are fed from deeper levels the recent history of eruptions at fernandina is also consistent with the idea that circumferential and radial intrusions are sometimes in a stress feedback relationship and alternate in time with one another

using numerical modeling to explore the origin of intrusion patterns on fernandina volcano galapagos islands ecuador 1 using parameterized finite element models we investigate the emplacement of both radial and circumferential intrusions in the configuration observed at fernandina volcano in the galapagos islands when situated within the edifice at depths consistent with petrological and surface displacement data inflation of a mildly oblate magma reservoir to the point of rupture can initiate either radial or circumferential intrusions in response to minor volcanologically plausible variations in reservoir geometry i e aspect ratio in addition more oblate reservoirs inject lateral sills into an inflation derived stress field consistent with rotation about their propagation axis to form gently dipping radial dikes a mode of behavior recently inferred from insar data at fernandina all three styles of intrusion occur in near surface configurations consistent with field observations

thermomechanics of shallow magma chamber pressurization implications for the assessment of ground deformation data at active volcanoes abstract in this study we utilize thermomechanical models to investigate how magma chambers overpressurize as the result of either magmatic recharge or volatile exsolution by implementing an adaptive reservoir boundary condition we are able to track how overpressure dissipates as the magma chamber expands to accommodate internal volume changes we find that the size of the reservoir greatly impacts the resultant magma chamber overpressure in particular overpressure estimates for small to moderate sized reservoirs 1 10 km 3 are up to 70 lower than previous analytical predictions we apply our models to santorini volcano in greece where recent seismic activity and ground deformation observations suggested the potential for eruption the incorporation of an adaptive boundary condition reproduces mogi flux estimates and suggests that the magma reservoir present at santorini may be quite large furthermore model results suggest that if the magma chamber is 100 km 3 overpressures generated due to the high magma flux may not exceed the strength of the host rock thus requiring an additional triggering mechanism for eruption although the adaptive boundary condition approach does not calculate the internal evolution of the magma reservoir it represents a fundamental step forward from elastic mogi models and fixed boundary solutions on which future investigations of the evolution of the magma can be built

the 2008 eruptive unrest at cerro azul volcano galapagos revealed by insar data and a novel method for geodetic modelling

new insights on the late pleistocene holocene lithic industry in east kalimantan borneo the contribution of three rock shelter sites in the karstic area of the mangkalihat peninsula this paper aims to present some aspects of the late pleistocene holocene lithic industry in the inland east kalimantan region by studying the assemblages found in three rock shelter sites in the karstic area of the mangkalihat peninsula this study analyzes these assemblages in their regional techno complex taking into consideration the environmental components it focuses on certain aspects of stone flaking technology and the trends in the reduction sequences of the assemblages our results shows that the reduction sequences flaking technology and the typology of the blanks and tools persisted across the pleistocene holocene boundary as revealed in liang abu where the lithic artifacts were found throughout the stratigraphic sequence over at least 20 000 years other excavations in liang jon and liang pemalawan have confirmed this continuity until the historical eras in addition this research emphasizes the potential influence of the environmental and climatic stability persistence of the rain forest during at least the last 40 000 years in this region as well as the inland geographical location on the continuity of the local stone flaking technology

an active ring fault detected at tendurek volcano by using insar 1 although ring faults are present at many ancient deeply eroded volcanoes they have been detected at only very few modern volcanic centers at the so far little studied tendurek volcano in eastern turkey we generated an ascending and a descending insar time series of its surface displacement field for the period from 2003 to 2010 we detected a large 105 km2 region that underwent subsidence at the rate of 1 cm yr during this period source modeling results show that the observed signal fits best to simulations of a near horizontal contracting sill located at around 4 5 km below the volcano summit intriguingly the residual displacement velocity field contains a steep gradient that systematically follows a system of arcuate fractures visible on the volcano s midflanks rapideye satellite optical images show that this fracture system has deflected holocene lava flows thus indicating its presence for at least several millennia we interpret the arcuate fracture system as the surface expression of an inherited ring fault that has been slowly reactivated during the detected recent subsidence these results show that volcano ring faults may not only slip rapidly during eruptive or intrusive phases but also slowly during dormant phases

insight into vent opening probability in volcanic calderas in the light of a sill intrusion model the aim of this paper is to discuss a novel approach to provide insights on the probability of vent opening in calderas using a dynamic model of sill intrusion the evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas on the basis of previous studies we think that the intrusion of sills is one of the most common mechanism governing caldera unrest therefore we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability we carried out several numerical experiments by using a physical model to assess the role of the magma properties viscosity host rock characteristics young s modulus and thickness and dynamics of the intrusion process mass flow rate in controlling the stress field our experiments highlight that high magma viscosity produces larger stress values while low magma viscosity leads to lower stresses and favors the radial spreading of the sill also high rock young s modulus gives high stress intensity whereas low values of young s modulus produce a dramatic reduction of the stress associated with the intrusive process the maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it over time in our simulations we find that maximum values of tensile stress occur in ring shaped areas with radius ranging between 350 m and 2500 m from the injection point depending on the model parameters the probability of vent opening is higher in these areas

fumarole plume and diffuse co 2 emission from sierra negra caldera galapagos archipelago measurements of visible and diffuse gas emission were conducted in 2006 at the summit of sierra negra volcano galapagos with the aim to better characterize degassing after the 2005 eruption a total so2 emission of 11 2 t day 1 was derived from miniature differential optical absorption spectrometer mini doas ground based measurements of the plume emanating from the mini azufral fumarolic area the most important site of visible degassing at sierra negra volcano using a portable multigas system the h2s so2 co2 so2 and h2o so2 molar ratios in the mina azufral plume emissions were found to be 0 41 52 2 and 867 9 respectively the corresponding h2o co2 and h2s emission rates were 562 394 and 3 t day 1 respectively the total output of diffuse co2 emissions from the summit of sierra negra volcano was 990 85 t day 1 with 605 t day 1 being released by a deep source the diffuse to plume co2 emission ratio was about 1 5 mina azufral fumaroles released gasses containing 73 6 mol of h2o the main noncondensable components amounted to 97 4 mol co2 1 5 mol so2 0 6 mol h2s and 0 35 mol n2 the higher h2s so2 ratio values found in 2006 as compared to those reported before the 2005 eruption reveal a significant hydrothermal contribution to the fumarolic emissions 3he 4he ratios measured at mina azufral fumarolic discharges showed values of 17 88 0 25 ra indicating a mid ocean ridge basalts morb and a galapagos plume contribution of 53 and 47 respectively

emergence and evolution of santa maria island azores the conundrum of uplifted islands revisited the growth and decay of ocean island volcanoes are intrinsically linked to vertical movements while the causes for subsidence are better understood uplift mechanisms remain enigmatic santa maria island in the azores archipelago is an ocean island volcano resting on top of young lithosphere barely 480 km away from the mid atlantic ridge like most other azorean islands santa maria should be experiencing subsidence yet several features indicate an uplift trend instead in this paper we reconstruct the evolutionary history of santa maria with respect to the timing and magnitude of its vertical movements using detailed field work and 40ar 39ar geochronology our investigations revealed a complex evolutionary history spanning 6 m y with subsidence up to ca 3 5 ma followed by uplift extending to the present day the fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms localized uplift in response to the tectonic regime affecting the southeastern tip of the azores plateau is unlikely since the area is under transtension our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions suggesting that intrusive processes play a significant role even on islands standing on young lithosphere such as in the azores

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

on merging high and low resolution dems from topsar and srtm using a prediction error filter high resolution digital elevation models dems are often limited in spatial coverage they also may possess systematic artifacts when compared to comprehensive low resolution maps here we correct artifacts and interpolate regions of missing data in airborne topographic synthetic aperture radar topsar dems using a low resolution shuttle radar topography mission srtm dem we use a prediction error pe filter to interpolate and fill missing data so that the interpolated regions have the same spectral content as the valid regions of the topsar dem the srtm dem is used as an additional constraint in the interpolation we use cross validation methods to obtain the optimal weighting for the pe filter and srtm dem constraints

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

chronology and phenomenology of the 1982 and 2015 wolf volcano eruptions galapagos archipelago abstract the 1982 and 2015 eruptions were the first at wolf volcano galapagos archipelago with eyewitness accounts and satellite imagery both eruptions were characterized by a rapid and intense initial phase with multiple eruptive vents leading to the formation of large a lava fields and scarce p hoehoe mostly associated with the waning phases the 1982 eruption started on 28 august from an intra caldera vent that produced high lava fountains as well as a radial fissure on the se flank the whole eruption lasted for at least 9 days and generated 52 5e 6 m3 dre dense rock equivalent of lava the 2015 eruption started on 25 may from a circumferential fissure that produced high lava fountains and deposited reticulite scoria on the flanks of the volcano for the first time since the onset of volcano monitoring in galapagos we report cryptotephra from the 2015 eruption reaching and depositing in mainland ecuador 1400 km away from the source lava from the 2015 circumferential vents covered 18 5 km2 on the se and e flanks on 13 june 2015 the eruption switched to an intra caldera vent that was active until 30 june and produced lava flows that covered most of the caldera floor the 2015 eruption lasted 36 days and produced 87e 6 m3 dre of lava making it the fourth largest eruption in galapagos since the eruption of sierra negra in 1979 we use combined ground based geophysical surveillance remote sensing eyewitness accounts and detailed field work to constrain the eruptive dynamics of this remote volcano our approach allows quantification of eruption rates which are critical for understanding volcanic systems and for hazard assessment first order rheological calculations permit us to further constrain the eruption dynamics and emplacement of the lava fields

imaging rapidly deforming ocean island volcanoes in the western galapagos archipelago ecuador using local body wave arrival time tomography methods to determine 3 d seismic velocity structure we imaged the plumbing system of sierra negra volcano galapagos this hot spot volcanic chain includes some of the fastest deforming volcanoes in the world making this an ideal location to study shield volcano plumbing systems we inverted p and s wave arrivals recorded on a 15 station temporary array between july 2009 and june 2011 using an a priori 1 d velocity model constrained by offshore refraction studies with local seismicity from nearby volcanoes as well as the ring fault system the model resolution is good between depths of 3 and 15 5 km the propagation of s waves throughout this volume argues against any large high melt accumulations although a shallow melt sill may exist above 5 km we image a broad low velocity region 25 km laterally below sierra negra at depths 8 15 km no large regional velocity increase is found within the limits of good resolution suggesting that crust is thicker than 15 km beneath the western galapagos archipelago our results are consistent with crustal accretion of mafic cumulates from a large volume magma chamber that may span the boundary between preplume and accreted crust the similarity between our results and those of hawaii leave open the possibility that the crust has also been thickened by under plating

magma degassing as a source of long term seismicity at volcanoes the ischia island italy case transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity this risk is powered by the common belief that volcanic seismicity cannot be forecast even on a long term here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity to this aim we consider ischia volcano italy which suffered similar earthquakes along its uplifted resurgent block we show that this seismicity marks an acceleration of decades long subsidence of the resurgent block driven by degassing of magma that previously produced the uplift a process not observed at other volcanoes degassing will continue for hundreds to thousands of years causing protracted seismicity and will likely be accompanied by moderate and damaging earthquakes the possibility to constrain the future duration of seismicity at ischia indicates that our capacity to forecast earthquakes might be enhanced when seismic activity results from long term magmatic processes such as degassing

joint analysis of displacement time series retrieved from sar phase and amplitude impact on the estimation of volcanic source parameters 1 we study the impact of jointly analyzing the phase and amplitude information of a sar dataset on the interpretation of the surface displacement over time in areas characterized by large dynamics in particular we compute the ground displacement time series over fernandina and sierra negra calderas galapagos islands by applying the small baseline subset sbas and the pixel offset po sbas techniques to 25 envisat sar images acquired between 2003 and 2007 when both volcanoes experienced catastrophic eruptions by merging the sbas and po sbas time series results the spatial density of measurements increased substantially in addition the joint analysis of the time series allows us to better constrain the temporal evolution of the magmatic source volume changes our results show that the joint use of the sbas and po sbas approaches may help for a more correct evaluation of large deformation affecting the earth s surface caused by eruptions earthquakes and landslide phenomena

top down inflation and deflation at the summit of kīlauea volcano hawai i observed with insar 1 we use interferometric synthetic aperture radar insar to study deformation of the summit caldera at k lauea volcano during 2000 2008 which spanned both an east rift zone eruptive event in 2007 and the start of the ongoing summit eruption in 2008 the data set consists of small baseline subset sbas time series generated from 270 acquisitions on three separate beam modes from the radarsat 1 satellite we identify 12 time periods with distinct patterns of displacement that we attribute until late 2003 to secular tectonic driven deformation and from 2004 to 2008 to four different sources in the summit area we model the shallow magmatic system as a spherical reservoir at 1 9 0 1 km depth below the surface to the northeast of halemaumau source 1 and three vertically stacked sills at greater depths in the southern caldera area source 2 at the southern edge of the caldera at 2 9 0 2 km depth source 3 to the south southeast of the caldera at 3 4 0 5 km depth and source 4 south of the caldera at 3 6 0 4 km depth the sequence for filling of and withdrawal from these reservoirs reveals a top down process with sequences of both inflation and deflation initiating in the shallowest source inflation of source 3 is coincident with elevated seismic activity in the upper east rift zone in february 2006 and may 2007 source 4 is elongated toward the southwest rift zone and also shows elevated seismicity that extends toward the southwest rift zone

deformation time series generation in areas characterized by large displacement dynamics the sar amplitude pixel offset sbas technique we exploit the amplitude information of a sequence of synthetic aperture radar sar images acquired at different times in order to generate displacement time series in areas characterized by large and or rapid deformation the size of which is on the order of the image s pixel dimensions we follow the same rationale of the small baseline subset sbas differential sar interferometry dinsar approach by coupling the available sar images into pairs characterized by a small separation between the acquisition orbits we exploit the amplitudes of the selected image pairs in order to calculate the relative across track range and along track azimuth pixel offsets po finally we apply the sbas inversion strategy to retrieve the range and azimuth displacement time series this approach referred to as pixel offset po sbas technique has been applied to a set of 25 envisat sar observations of the sierra negra caldera galapagos islands spanning the 2003 2007 time interval the retrieved deformation time series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that in correspondence to the october 2005 eruption reached several meters moreover by comparing the po sbas results to continuous gps measurements we estimate that the accuracy of the po sbas time series is on the order of 1 30th of a pixel for both range and azimuth directions

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

constraints on magma chamber geometry at sierra negra volcano galapagos islands based on insar observations abstract we investigate the problem of estimating magma chamber geometry using insar observations of sierra negra volcano galapagos ascending and descending interferograms are combined to determine vertical and one horizontal component of displacement the ratio of maximum horizontal to vertical displacement suggests a sill like source spherical or stock like bodies are inconsistent with the data we estimate the geometry of the sill assuming a horizontal uniformly pressurized crack with unknown periphery and depth the sill is discretized into small elements that are either open and are subjected to the pressure boundary condition or remain closed we find the best fitting sill to be located beneath sierra negra s inner caldera at a depth of about 2 km using boundary element calculations we show that any magma chamber with a flat top coincident with the sill model fits the data equally well the data are insensitive to the sides and bottom of the magma chamber

sill intrusion as a source mechanism of unrest at volcanic calderas the interpretation of dynamic processes that occur in volcanic calderas is not simple the ground deformations and the local seismicity which in other volcanic contexts are usually regarded as precursors to eruption in caldera environment in many cases are not followed by any eruption we formulate a general hypothesis that can explain these behaviors our hypothesis is that the intrusion of a sill can be responsible for the dynamics observed during unrest at calderas in order to investigate the reliability of this hypothesis we developed a dynamic model of sill intrusion in a shallow volcanic environment in our model the sill fed by a deeper magma reservoir intrudes below a horizontal elastic plate representing the overlying rocks and expands with axisymmetric geometry the model is based on the numerical solution of the equation for the elastic plate coupled with a navier stokes equation for simulating the dynamics of the sill intrusion we performed a number of simulations with the objective of showing the main features of the model in the experiments when the feeding process stops the vertical movement reverses its trend and the area of maximum uplift undergoes subsidence under certain conditions the subsidence can occur even during the intrusion of the sill the stress field produced by the intrusion is mainly concentrated in a circular zone that follows the sill intrusion front the features predicted by the model are consistent with many observations carried out on different calderas as reported in the scientific literature

on trapdoor faulting at sierra negra volcano galapagos abstract rapid uplift observed during 1992 1997 at sierra negra volcano western galapagos was followed by deformation that we have previously interpreted as trapdoor faulting on an intra caldera fracture system at that time no direct evidence for the trapdoor faulting was available to support this interpretation here we report field evidence of recent faulting at sierra negra and provide direct measurements of the faulting using pixel offsets between satellite radar amplitude backscatter images our field observations carried out in 2001 indicate that recent faulting occurred along the southern part of the intra caldera fault system with maximum offset of at least 0 5 1 m differences between two satellite radar amplitude images show 1 4 0 2 m range change across this fault system this suggests that 1 5 0 2 m of faulting occurred assuming vertical ground displacements consistent with our previous modeling results results of numerical modeling indicate that growing sills can cause faulting of the intrusion roof on outward dipping or nearly vertical faults this occurs at high excess magma pressure when the lateral extent half length of the sill becomes greater than its depth the derived 2 km deep sierra negra sill exhibits trapdoor faulting 3 km south of the center of the sill therefore these modeling results provide a plausible mechanical explanation for the trapdoor fault at sierra negra

results from new gps and gravity monitoring networks at fernandina and sierra negra volcanoes galapagos 2000 2002 gps and gravity networks were established on sierra negra and fernandina volcanoes in 2000 and remeasured in 2001 and 2002 after a decade in which the caldera inflated by over 2 5 m sierra negra s caldera began to subside between 2000 and 2002 at a rate of about 9 cm a neither inflation nor deflation was accompanied by eruption simple elastic modeling indicates that the deformation at sierra negra can be attributed to volumetric contraction of a 2 1 km deep sill beneath the caldera caused by either movement of magma out of the sill or loss of bubbles through degassing precise gravity measurements support but do not prove the former mechanism fernandina volcano is in a phase of slow refilling of the summit reservoir after the 1995 eruption causing lateral expansion of the caldera rim by about 3 cm a our estimate for the depth of the shallowest part of the fernandina magma chamber is 1 to 2 km neither volcano shows evidence of flank spreading

stress interaction between magma accumulation and trapdoor faulting on sierra negra volcano galapagos abstract understanding the state of stress within volcanoes and how it changes with active geophysical processes is important to assess when and where magma may propagate to the surface and initiate an eruption observations of volcanic deformation help to constrain parameters of models that can be used to describe these processes and to calculate the resulting stress changes within volcanoes here i use geodetic observations to constrain elastic dislocation models of magma accumulation and faulting at sierra negra volcano galapagos in the years before the october 2005 eruption which was the first eruption at sierra negra since 1979 both insar and gps data document a remarkable story of 5 m pre eruption uplift during 1992 2005 which was accompanied by at least three trapdoor faulting events on an intra caldera fault system in january 1998 april 2005 and just before the eruption in october 2005 the pattern of uplift observed in the insar data from different time periods during 1992 2005 is consistent with filling and pressurization of a 2 2 km deep sill under the caldera modeling results for the trapdoor faulting in april 2005 on the other hand indicate that slip occurred on a thrust fault that dips steeply 71 in towards the center of the caldera and extends from the surface down to the sill at 2 2 km depth independently the calculated stress changes caused by the inflating sill show that the coulomb failure stress change cfs at the fault s location is maximized on a 72 dipping thrust fault agreeing almost exactly with the deformation modeling result and implying that the inflation triggered the faulting the calculations also show that the cfs for optimally oriented faults any strike and dip is significantly larger in the southern part of the caldera where the faulting took place than at any other location the trapdoor faulting in turn relieved the pressure within the sill but caused compression to the south of the faults this suggests that while the faulting provides a mechanism for the sill to thicken and postpone eruptions it also prevents the sill from growing to the south

4d gravity changes associated with the 2005 eruption of sierra negra volcano galapagos sierra negra volcano the most voluminous shield volcano in the galapagos archipelago and one of the largest basaltic calderas in the world erupted on october 22 2005 after more than 25 years of quiescence gps and satellite radar interferometryinsar monitoring of the deformation of the caldera floor in the months prior to the eruption documented extraordinary inflation rates 1c m day the total amount of uplift recorded since monitoring began in 1992 approached 5 m at the center of the caldera over the eight days of the eruption the caldera floor deflated a maximum of 5 m and subsquently renewed its inflation but at a decelerating rate to gain insight into the nature of the subsurface mass density changes associated with the deformation gravity measurements performed in 2005 2006 and 2007 are compared to previous measurements from 2001 2002 when the volcano underwent a period of minor deflation and magma withdrawal the residual gravity decrease between 2001 2002 and 2005 is among the largest ever recorded atan active volcano950 gal and suggests that inflation was accompanied by a relative density decrease in the magmatic system forward modeling of the residual gravity data in 4d from 2002 to 2005 gives an estimate of the amount of vesiculation in the shallow sill required to explain the observed gravity variations geochemical constraints from melt inclusion and satellite remote sensing data allow us to estimate the pre eruptive gas content of the magma and place constraints on the thickness of the gas rich sill necessary to produce the gravity anomalies observed results suggest that reasonable sill thicknesses 700 800 m and bubble contents 10 50 volume can explain the large decrease in residual gravity prior to eruption following the eruption 2006 and 2007 the deformation and gravity patterns suggest re equilibration of the pressure regime in the shallow magma system via a renewed influx of relatively gas poor magma into the shallow parts of the system