the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

petrology and geochemistry of lava and ash erupted from volcan colima mexico during 1998 2005 abstract lava n 8 and bulk ash samples n 6 erupted between july 1999 and june 2005 were investigated to extend time series compositional and textural studies of the products erupted from volcan colima since 1869 in particular we seek to evaluate the possibility that the current activity will culminate in major explosive plinian style event similar to that in 1913 lava samples continue to show relatively heterogeneous whole rock compositions with some significant mafic spikes 1999 2001 as have prevailed since 1976 groundmass sio2 contents continue trends to lower levels that have prevailed since 1961 in the direction of the still lower groundmass sio2 contents found in 1913 scoriae importantly ash samples from investigated vulcanian style explosive eruptions in 2005 are devoid of particles with micro vesiculated groundmass textures such textures characterized the 1913 scoriae signifying expansion of in situ magmatic gas as the propellant of the 1913 eruption all magmas erupted since 1913 appear to have arrived in the upper volcanic conduit system in a degassed state the small to moderate vulcanian style explosive eruptions which have been common since 1999 16 000 events have blasted ash clouds as high as 11 km a s l and sent pyroclastic flows out to distances of 5 km these eruptions do not appear to be powered by expansion of in situ magmatic gas new small lava domes have been observed in the crater prior to many explosive eruptions these plugs of degassed lava may temporarily seal the conduit and allow the build up of magmatic gases streaming upward from below ahead of rising and degassing magma in this interpretation when gas pressure exceeds the strength of the plug seal in the upper conduit an explosive vulcanian style eruption occurs alternatively these explosive eruptions may represent interactions of hot rock and groundwater phreato magmatic

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

toward mapping surface deformation in three dimensions using insar 1 one of the limitations of deformation measurements made with interferometric synthetic aperture radar insar is that an interferogram only measures one component of the surface deformation in the satellite s line of sight we investigate strategies for mapping surface deformation in three dimensions by using multiple interferograms with different imaging geometries geometries for both current and future missions are evaluated and their abilities to resolve the displacement vector are compared the north component is always the most difficult to determine using data from near polar orbiting satellites however a satellite with an inclination of about 60 120 would enable all three components to be well resolved we attempt to resolve the 3d displacements for the 23 october 2002 nenana mountain alaska earthquake the north component s error is much larger than the signal but proxies for eastward and vertical motion can be determined if the north component is assumed negligible inversions of hypothetical coseismic interferograms demonstrate that earthquake model parameters can be well recovered from two interferograms acquired on ascending and descending tracks

magmatic architecture of dome building eruptions at volcan de colima mexico changes in the physical chemical and rheological properties of ascending magma regulate the style of volcanic eruptions volcan de colima s eruptive cycles of lava dome growth and explosions have been thoroughly monitored during the period 1998 2010 and provide a remarkable opportunity for deepening our understanding of the underlying processes responsible for the evolution of magma properties here we integrate direct observation with analytical and experimental data to 1 constrain the configuration of the shallow plumbing system and its influence on eruptive activity 2 describe the rheological behaviour of the magma and 3 assess the conditions that lead to fragmentation and ultimately to explosive eruptions the configuration of the shallow plumbing system was inferred from direct observation of extrusion sites and porosity of the erupted products during the ongoing eruptive phase magma was never extruded from a central vent both explosive and effusive activities were restricted to discrete vents inside the crater extensive field based density measurements on 500 blocks in pyroclastic flow deposits reveal a bimodality of porosity at values of 12 and 26 vol the least porous rocks tend to be altered whereas the more porous rocks are pristine this bimodal distribution combined with the lack of a central vent suggests the presence of a central dense altered plug the fragments of which are entrained during explosive eruptions during effusive periods the plug appears to deflect the ascent of magma at a shallow depth and consequently the site of lava extrusion the rheological properties and deformation induced seismogenic behaviour of the magmas were investigated using a uniaxial deformation apparatus instrumented with acoustic sensors the homogeneity in the physicochemical properties of the erupted magma permits the description of a flow law at eruptive temperature and strain rate conditions the crystal rich magma of volcan de colima exhibits a shear thinning rheology and becomes increasingly brittle at higher strain rates complete failure of magma can be predicted using the material failure forecast method which integrates the acceleration of released acoustic energy throughout the deformation rapid decompression experiments of samples pressurised with argon were performed to assess the fragmentation conditions under which explosive eruptions progress in the absence of gas loss due to permeable flow the pore pressure required to fragment volcanic products is inversely proportional to the porosity at volcan de colima a rapid decompression of 6 mpa is required to fragment magma averaging 26 vol pores and to thereby instigate an explosive eruption analysis of ballistic impacts 4 6 km away from the vent from recent explosive eruptions further requires decompression as great as 20 mpa which is sufficient to disrupt the more porous material as well as a fraction of the denser plug the continuing growth of a lava dome and of a larger more impermeable plug could have consequences for the stability of the edifice and development of stronger and more erratic explosive activity at volcan de colima

time averaged discharge rate of subaerial lava at kīlauea volcano hawai i measured from tandem x interferometry implications for magma supply and storage during 2011 2013 differencing digital elevation models dems derived from terrasar add on for digital elevation measurements tandem x synthetic aperture radar imagery provides a measurement of elevation change over time on the east rift zone ezr of k lauea volcano hawai i the effusion of lava causes changes in topography when these elevation changes are summed over the area of an active lava flow it is possible to quantify the volume of lava emplaced at the surface during the time spanned by the tandem x data a parameter that can be difficult to measure across the entirety of an 100 km2 lava flow field using ground based techniques or optical remote sensing data based on the differences between multiple tandem x derived dems collected days to weeks apart the mean dense rock equivalent time averaged discharge rate of lava at k lauea between mid 2011 and mid 2013 was approximately 2 m3 s which is about half the long term average rate over the course of k lauea s 1983 present erz eruption this result implies that there was an increase in the proportion of lava stored versus erupted a decrease in the rate of magma supply to the volcano or some combination of both during this time period in addition to constraining the time averaged discharge rate of lava and the rates of magma supply and storage topographic change maps derived from space based tandem x data provide insights into the four dimensional evolution of k lauea s erz lava flow field tandem x data are a valuable complement to other space air and ground based observations of eruptive activity at k lauea and offer great promise at locations around the world for aiding with monitoring not just volcanic eruptions but any hazardous activity that results in surface change including landslides floods earthquakes and other natural and anthropogenic processes

multidimensional time series analysis of ground deformation from multiple insar data sets applied to virunga volcanic province summary a novel multidimensional small baseline subset msbas methodology is presented for integration of multiple interferometric synthetic aperture radar insar data sets for computation of 2 or 3 d time series of deformation the proposed approach allows the combination of all possible air borne and space borne sar data acquired with different acquisition parameters temporal and spatial sampling and resolution wave band and polarization the produced time series have improved temporal resolution and can be enhanced by applying either regularization or temporal filtering to remove high frequency noise we apply this methodology to map 2003 2010 ground deformation of the virunga volcanic province vvp north kivu democratic republic of congo the horizontal and vertical time series of ground displacement clearly identify lava compaction areas long term deformation of mt nyamuragira and 2004 2006 and 2010 pre and coeruptive deformation providing that enough sar data is available the method opens new opportunities for detecting ground motion in the vvp and elsewhere

post eruptive deformation associated with the 1986 87 and 1989 lava flows of etna detected by radar interferometry we analysed 92 interferograms produced using ers1 sar images taken on etna between may 1992 and october 1993 nineteen show a local subsidence in the eastern flank of the volcano correlated with the location of the 30 october 1986 1 march 1987 and 27 september 9 october 1989 lava flows using fringe unwrapping and data gridding techniques and assuming that over the sampled time window deformation was a linear function of time we derive a map of along range rate of motion the correlation between the deformation field and the area covered by recent lavas suggests that compaction of the lava flows continues several years after the eruptions the area of maximum subsidence 47 mm yr is localised at the narrowing of the 1989 flow between 1500 and 1700 m a s l we observe that subsidence extends outside the lava flows accounting for at least 12 mm yr assuming a relaxation process of the substrate in response to loading produced by recent lavas a simple 1d maxwell visco elastic model predicts a maximum subsidence rate of 25 mm yr and a relaxation time of about 3 5 years the relaxation time agrees with those derived from post eruptive displacements observed by levelling on etna and piton de la fournaise after several eruptions we conclude that at the time of our measurements 25 to 50 of the deformation was related to relaxation of the substrate and the other part due to compaction of the lava flows

measuring large topographic change with insar lava thicknesses extrusion rate and subsidence rate at santiaguito volcano guatemala lava flows can produce changes in topography of the order of 10s 100s of metres a knowledge of the resulting volume change provides evidence about the dynamics of an eruption using differential insar phase delays it is possible to estimate height differences between the current topography and a digital elevation model dem this does not require a pre event sar image so it does not rely on interferometric phase remaining coherent during eruption and emplacement synthetic tests predict that we can estimate lava thicknesses of as little as 9 m given a minimum of five interferograms with suitably large orbital baseline separations in the case of continuous motion such as lava flow subsidence we invert interferometric phase simultaneously for topographic change and displacement we apply this to santiaguito volcano guatemala and measure increases in lava thickness of up to 140 m between 2000 and 2009 largely associated with activity between 2000 and 2005 we find a mean extrusion rate of 0 437 0 06 m

lava flow volume and morphology from digitised contour maps a case study at mount etna sicily abstract the volume and morphology of a lava flow field can be measured by mapping and comparing the topography before and after lava emplacement contour maps are a widely available source of topographic data containing a record of the geomorphological changes at volcanoes due to lava emplacement this paper explores the use of 1 25 000 scale digitised contour maps for mapping two lava flows of diverse eruption history and morphology at mount etna sicily we find that subtracting dems created from these maps gives a good representation of volume and shape for thicker lava flows 10 m mean thickness in the case of the 1983 lava flow however thinner

numerical modeling of lava flow cooling applied to the 1997 okmok eruption approach and analysis 1 throughout february and march of 1997 okmok volcano in the eastern aleutian islands of alaska erupted a 6 km long lava flow of basaltic a a within its caldera a numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling radiation and convection from the surface as well as conduction to the ground were used to transport the flow s heat to its surroundings in the model internally a conduction only approach moved heat from the interior outward vesiculation latent heat generation and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for results indicate that ambient temperature fluctuations on the scale of days to weeks must be taken into account to create an accurate short term prediction of lava surface temperature daily data of rainfall and ambient temperature as opposed to yearly averages greatly increased the accuracy of the model furthermore convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures over a longer cooling period 2 years thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior the model s flexibility allows application to flows other than the 1997 okmok eruption

caldera formation at volcan colima mexico by a large large holocene volcanic debris avalanche abstract about 4 300 years ago 10 km 3 of the upper cone of ancestral volcan colima collapsed to the southwest leaving a horseshoe shaped caldera 4 km in diameter the collapse produced a massive volcanic debris avalanche deposit covering over 1550 km 2 on the southern flanks of the volcano and extending at least 70 km from the former summit the avalanche followed a steep topographic gradient unobstructed by barriers resulting in an unusually high area volume ratio for the colima deposit the apparent coefficient of friction fall height distance traveled for the colima avalanche is 0 06 a low value similar to those of other large volume deposits the debris avalanche deposit contains 40 75 angular volcanic clasts from the ancestral cone a small proportion of vesicular blocks that may be juvenile and in distal exposures rare carbonate clasts plucked from the underlying surface by the moving avalanche clasts range in size to over 20 m in diameter and are brecciated to different degrees pulverized and surrounded by a rock flour matrix the upper surface of the deposit shows prominent hummocky topography with closed depressions and surface boulders a thick coarse grained compositionally zoned scoria fall layer on the upper northeastern slope of the volcano may have erupted at the time of collapse a fine grained surge layer is present beneath the avalanche deposit at one locality apparently representing an initial blast event most of the missing volume of the ancestral volcano has since been restored at an average rate of 0 002 km 3 yr through repeated eruptions from the post caldera cone as a result the southern slope of volcan colima may again be susceptible to collapse over 200 000 people are now living on primary or secondary deposits of the debris avalanche and a repetition of this event would constitute a volcanic disaster of great magnitude ancestral volcan colima grew on the southern trenchward flank of the earlier and larger volcano nevado de colima trenchward collapse was favored by the buttressing effect of nevado the rapid elevation drop to the south and the intrusion of magma into the southern flank of the ancestral volcano other such trenchward younging paired volcanoes are known from mexico guatemala el salvador chile and japan the trenchward slopes of the younger cones are common sites for cone collapse to form avalanche deposits as occurred at colima and popocatepetl in mexico and at san pedro volcano in chile

analysis of active lava flows on kilauea volcano hawaii using sir c radar correlation measurements precise eruption rates of active pahoehoe lava flows on kilauea volcano hawaii have been determined using spaceborne radar data acquired by the space shuttle imaging radar c sir c a coastal site downslope from the pu9u o9o vent was imaged once per day on each of the four days of october 7 10 1994 day to day decorrelation due to resurfacing was determined by interferometric combination of the data at 15 m resolution over a wide area on successive days new lava resurfaced 335700 m 2 368775 m 2 and 356625 m 2 assuming an average pahoehoe flow thickness of 50 cm a mean effusion rate for this period is approximately 2 m 3 s the radar observations show persistent surface activity at each site rather than downslope migration of coherent lava flows

interferometric synthetic aperture radar study of okmok volcano alaska 1992 2003 magma supply dynamics and postemplacement lava flow deformation 1 okmok volcano located in the central aleutian arc alaska is a dominantly basaltic complex topped with a 10 km wide caldera that formed circa 2 05 ka okmok erupted several times during the 20th century most recently in 1997 eruptions in 1945 1958 and 1997 produced lava flows within the caldera we used 80 interferometric synthetic aperture radar insar images interferograms to study transient deformation of the volcano before during and after the 1997 eruption point source models suggest that a magma reservoir at a depth of 3 2 km below sea level located beneath the center of the caldera and about 5 km northeast of the 1997 vent is responsible for observed volcano wide deformation the preeruption uplift rate decreased from about 10 cm yr 1 during 1992 1993 to 2 3 cm yr 1 during 1993 1995 and then to about 1 2 cm yr 1 during 1995 1996 the posteruption inflation rate generally decreased with time during 1997 2001 but increased significantly during 2001 2003 by the summer of 2003 30 60 of the magma volume lost from the reservoir in the 1997 eruption had been replenished interferograms for periods before the 1997 eruption indicate consistent subsidence of the surface of the 1958 lava flows most likely due to thermal contraction interferograms for periods after the eruption suggest at least four distinct deformation processes 1 volcano wide inflation due to replenishment of the shallow magma reservoir 2 subsidence of the 1997 lava flows most likely due to thermal contraction 3 deformation of the 1958 lava flows due to loading by the 1997 flows and 4 continuing subsidence of 1958 lava flows buried beneath 1997 flows our results provide insights into the postemplacement behavior of lava flows and have cautionary implications for the interpretation of inflation patterns at active volcanoes

analysis of topographic decorrelation in sar interferometry using ratio coherence imagery topographic decorrelation due to the local surface slope has been an obstacle to interferometric synthetic aperture radar insar applications a modified spatial decorrelation function is derived as a function of the baseline and topography this function explains the origin of the total topographic decorrelation phenomenon on the slopes directly facing radar illumination and layover which may mislead insar coherence image interpretation the authors define critical terrain slope or critical incidence angle as the angle for which two sar signals completely decorrelate regardless of surface stability it is found that the width of the critical terrain slope increases with the increase of the component of the baseline perpendicular to the radar look direction a new analytical method the ratio coherence imagery is then introduced to highlight total topographic decorrelation against the temporal decorrelation features the applications of this methodology are demonstrated in selected locations in the sahara desert algeria and almer spl inodot spl acute a spain using ers 1 and ers 2 sar data

historical eruptions of merapi volcano central java indonesia 1768 1998 abstract information on merapi eruptive activity is scattered and much is remotely located a concise and well documented summary of this activity has been long needed to assist researchers and hazard mitigation efforts and the aim of this paper is to synthesize information from the mid 1700s to the present a descriptive chronology is given with an abbreviated chronology in a table that summarizes events by year assigns preliminary volcanic explosivity index vei ratings and hartmann classifications and provides key references the history of volcano monitoring is also outlined the study reveals that a major difference in eruption style exists between the twentieth and nineteenth centuries although the periodicity between larger events seems about the same during the twentieth century activity has comprised mainly the effusive growth of viscous lava domes and lava tongues with occasional gravitational collapses of parts of oversteepened domes to produce the nuees ardentes commonly defined as merapi type in the 1800s however explosive eruptions of relatively large size occurred to vei 4 and some associated fountain collapse nuees ardentes were larger and farther reaching than any produced in the twentieth century these events may also be regarded as typical eruptions for merapi the nineteenth century activity is consistent with the long term pattern of one relatively large event every one or two centuries based on the long term eruptive record deduced by others from volcanic stratigraphy it is uncertain whether or not a recurrence time model continues to apply to merapi but if so merapi could soon be due for another large event and its occurrence with only modest or inadequately appreciated precursors could lead to a disaster unprecedented in merapi s history because the area around the volcano is now much more densely populated

tracking lava flow emplacement on the east rift zone of kīlauea hawai i with synthetic aperture radar coherence 1 lava flow mapping is both an essential component of volcano monitoring and a valuable tool for investigating lava flow behavior although maps are traditionally created through field surveys remote sensing allows an extraordinary view of active lava flows while avoiding the difficulties of mapping on location synthetic aperture radar sar imagery in particular can detect changes in a flow field by comparing two images collected at different times with sar coherence new lava flows radically alter the scattering properties of the surface making the radar signal decorrelated in sar coherence images we describe a new technique sar coherence mapping scm to map lava flows automatically from coherence images independent of look angle or satellite path we use this approach to map lava flow emplacement during the pu u kupaianaha eruption at k lauea hawai i the resulting flow maps correspond well with field mapping and better resolve the internal structure of surface flows as well as the locations of active flow paths however the scm technique is only moderately successful at mapping flows that enter vegetation which is also often decorrelated between successive sar images along with measurements of planform morphology we are able to show that the length of time a flow stays decorrelated after initial emplacement is linearly related to the flow thickness finally we use interferograms obtained after flow surfaces become correlated to show that persistent decorrelation is caused by post emplacement flow subsidence

post emplacement dynamics of andesitic lava flows at volcan de colima mexico revealed by radar and optical remote sensing data abstract we used optical and radar remote sensing datasets to map estimate the volume and measure the surface displacements of lava flows emplaced on the flanks of volcan de colima mexico by extrusion of lava dome material from the end of 2014 to early 2016 our main result is that the flow motion of the lava contributes significantly to the recorded displacements several months after its emplacement first we mapped the deposits and estimated their volumes using two digital elevation models dem one derived from radar data acquired before the peak of activity and one derived from optical images acquired just after this peak of activity coherence information derived from the radar dataset added some temporal constraints on the timing of emplacement of various deposits we thus estimated a mean extrusion rate of 1 2 m3 s 1 between november 2014 and february 2015 we then used a new approach to reconstruct the 3d displacement field taking advantage of images acquired by the same satellite on both ascending and descending tracks and using a physical a priori on the direction of horizontal displacements our results show that about 2 cm yr 1 of horizontal motion is still recorded a few months after the emplacement on the sw lava flow which is the only one covered by the two acquisition geometries in order to differentiate the potential causes of the observed displacements we modeled the thermal contraction of the lava flow using a finite element numerical method removing the contribution of thermoelastic contraction from the measured displacements enable to infer both the viscoelastic loading and flow motion effects from the residuals results show that thermal contraction flow motion and viscoelastic loading contribute significantly to the displacements recorded

origin of tin mineralization in the sullivan pb zn ag deposit british columbia constraints from textures geochemistry and la icp ms u pb geochronology of cassiterite

emissivity of terrestrial materials in the 3 5 μm atmospheric window remotely sensed infrared radiance emitted by a surface is a function both of its kinetic temperature and its spectral emissivity consequently assumptions are usually made about the emissivity of earth surface materials to allow their temperatures to be determined or vice versa to increase the accuracy of these assumptions the directional hemispherical spectral reflectance of a wide range of natural earth surface materials has been measured and is summarized here these include igneous metamorphic and sedimentary rocks desert varnish soils vegetation water and ice kirchhoff s law can be used to predict directional spectral emissivity from these data

volumetric characteristics of lava flows from interferometric radar and multispectral satellite data the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos we have used a suite of remotely sensed data numerical lava flow modeling and field observations to determine quantitative characteristics of the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos islands flank lava flow areas volumes instantaneous effusion rates and average effusion rates were all determined for these two eruptions for which only limited syn eruptive field observations are available using data from spot topsar ers 1 and ers 2 we determined that the 1995 fernandina flow covers a subaerial area of 6 5 106 m2 and has a subaerial dense rock equivalent dre volume of 42 106 m3 field observations atsr satellite data and the flowgo numerical model allow us to determine that the effusion rate declined exponentially from a high of 60 200 m3 s 1 during the first few hours to 5 m3 s 1 prior to ceasing after 73 days with a mean effusion rate of 4 16 m3 s 1 integrating the atsr derived exponentially declining effusion rate over the eruption duration produces a total subaerial submarine dre volume of between 27 and 100 106 m3 the range in values being due to differing assumptions about heat loss characteristics only values in the higher part of this range are consistent with the independently derived subaerial volume using spot topsar ers 1 and ers 2 data we determine that the 1998 cerro azul flow is 16 km long covers 16 km2 and has a dre volume of 54 106 m3 flowgo produces at vent velocity and effusion rate values of 11 m s 1 and 600 m3 s 1 respectively the velocity value agrees well with the 12 m s 1 estimated in the field the mean effusion rate total dre volume duration was 7 47 m3 s 1 dike dimensions fissure lengths and pressure gradients along the conduit based on magma chamber depth estimates of 3 5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude the range being due to uncertainty in the magma viscosity dike dimensions and pressure gradient between magma chamber and vent although somewhat consistent with mean effusion rates from other techniques their wide range makes them less useful the exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption as well as time constants of exponential decay during the eruption the results and theoretical relationships combine to indicate that at both volcanoes probably 25 30 of the volumetric increase in the magma chamber erupted as lava onto the surface in both eruptions the lava flow volumes are less than 1 of the magma chamber volume

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

eruptive history of the colima volcanic complex mexico abstract the evolution of the colima volcanic complex can be divided into successive periods characterized by different dynamic and magmatic processes emission of andesitic to dacitic lava flows acid ash and pumice flow deposits fallback nuees ardentes leading to pyroclastic flows with heterogeneous magma plinian air fall deposits scoriae cones of alkaline and calc alkaline nature four caldera forming events resulting either from major ignimbrite outbursts or mount st helens type eruptions separate the main stages of development of the complex from the building of an ancient shield volcano 25 30 km wide up to two summit cones nevado and fuego the oldest caldera c1 7 8 km wide related to the pouring out of dacitic ash flows marks the transition between two periods of activity in the primitive edifice called nevado i the first one which is at least 0 6 m y old was mainly andesitic and effusive whereas the second one was characterized by extrusion of domes and related pyroclastic products a small summit caldera c2 3 3 5 km wide ended the evolution of nevado i two modern volcanoes then began to grow the building of the nevado ii started about 200 000 y ago it settled into the c2 caldera and partially overflowed it the other volcano here called paleofuego was progressively built on the southern side of the former nevado i some of its flows are 50 000 y old but the age of its first outbursts is not known however it is younger than nevado ii these two modern volcanoes had similar evolutions each of them was affected by a huge mount st helens type or bezymianny type event 10 000 y ago for the paleofuego and hardly older for the nevado ii the landslides were responsible for two horseshoe shaped avalanche calderas c3 nevado and c4 paleofuego each 4 5 km wide opening towards the east and the south in both cases the activity following these events was highly explosive and produced thick air fall deposits around the summit craters the nevado iii formed by thick andesitic flows is located close to the southwestern rim of the c3 caldera it was a small and short lived cone volcan de fuego located at the center of the c4 caldera is nearly 1500 m high its activity is characterized by an alternation of long stages of growth by flows and short destructive episodes related to violent outbursts producing pyroclastic flows with heterogeneous magma and plinian air falls the evolution of the primitive volcano followed a similar pattern leading to formation of c1 and then c2 the analogy between the evolutions of the two modern volcanoes nevado ii iii paleofuego fuego is described their vicinity and their contemporaneous growth pose the problem of the existence of a single reservoir or two independent magmatic chambers after the evolution of a common structure represented by the primitive volcano

insar observations of the 1995 fogo cape verde eruption implications for the effects of collapse events upon island volcanoes 1 fogo volcano cape verde islands erupted in april 1995 after 43 years of dormancy about 46 106 m3 of lava erupted during 7 5 weeks from vents on the sw flank of pico do fogo into cha das caldeiras interferograms obtained from 1993 1998 ers sar data show ground deformation due to the feeder dike but lack evidence for any volcano wide deformation related to volume changes of a shallow magma reservoir this suggests that fogo is fed from a relatively deep mantle lithospheric source 16 5 km depth consistent with petrological data this supports the concept that cha das caldeiras is the fill of a collapse scar created by a giant landslide and not a collapse caldera overlying a central shallow magma chamber the disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well developed shallow reservoirs

surface movements of emplaced lava flows measured by synthetic aperture radar interferometry lava flows continue to move after they have been emplaced by flow mechanisms this movement is largely vertical and can be detected using differential synthetic aperture radar sar interferometry there are three main components to this motion 1 movement of surface scatterers resulting in radar phase decorrelation 2 measurable subsidence of the flow surface due to thermal contraction and clast repacking and 3 time dependent depression of the flow substrate these effects act in proportion to the thickness of the lava flow and decay with time although there is a time lag before the third component becomes significant we explore these effects using sar data from the ers satellites over the etna volcano sicily phase decorrelation on young thick a a lava flows persists for a few years and probably results from surface block rotations during flow contraction maximum measured subsidence rates of the 1991 1993 lava flow over a period of 70 days are about 0 7 mm day 1 but are potentially greater in areas of data decorrelation these rates fall to 2 7 10 2 mm day 1 after about 20 years in flows about 50 m thick sooner for thinner flows comparison with measured subsidence rates on kilauean lava lakes suggests that thermal contraction only accounts for about one third of the observed subsidence the remaining motion is thought to come from surface clast repacking during cooling and from creep mechanisms in the flow substrate measurements of postemplacement surface movement provide new constraints on the thermomechanical properties of lava flows and have cautionary implications for the interpretation of interferometric sar data of volcanoes 2001 american geophysical union