visco plastic models of isothermal lava domes the dynamics of expanding domes of isothermal lava are studied by treating the lava as a viscoplastic material with the herschel bulkley constitutive law thin layer theory is developed for radially symmetric extrusions onto horizontal plates this provides an evolution equation for the thickness of the fluid that can be used to model expanding isothermal lava domes numerical and analytical solutions are derived that explore the eects of yield stress shear thinning and basal sliding on the dome evolution the results are briefly compared with an experimental study it is found that it is dicult to unravel the combined eects of shear thinning and yield stress this may prove important to studies that attempt to infer yield stress from morphology of flowing lava

the cooling of frontal flow ramps a calorimetric study on the rocche rosse rhyolite flow lipari aeolian islands italy relaxation geospeedometry using differential scanning calorimetry dsc has been applied to quantify the cooling history across the glass transition of flow ramps at the front of the calcalkaline rhyolite rocche rosse flow of lipari aeolian islands italy modelled cooling rates for the obsidian retrieved from two profiles range between 0 2 and 0 03 k min 1 cooling at the flow front appears to be dominated by conductive heat loss of individual flow ramps forming individual cooling units cooling rates of tens of kelvins per day appear to have controlled the last stage of viscous deformation before the entire flow came to rest it is inferred that cooling rates slower than those modelled are required to sustain flow in highly viscous rhyolitic lavas

examining the ladinian crisis in light of the current knowledge of the triassic biodiversity changes abstract several mass extinctions are known from the history of life but knowledge about minor biotic crises remains incomplete the ladinian is the second stage of the middle triassic epoch available reconstructions of the diversity dynamics of fossil organisms across the entire triassic allow the proposed ladinian biotic crisis to be investigated total biodiversity curves both the conventional curve and that based on sampling standardization fail to identify the crisis but this may be explained by low resolution data or noise in fact the global generic diversity of ammonoids brachiopods and tetrapods declined significantly by 1 1 2 5 times during the ladinian as did the species diversity of conodonts bivalves radiated but their origination rate also decreased during the ladinian land plants were apparently unaffected based on the representative regional record for the northwestern caucasus the number of macroinvertebrate genera dropped by 7 5 times and brachiopods almost totally disappeared foraminifers were also affected significantly thus the proposed biotic crisis appears to have been selective it appears the ladinian biotic crisis was a relatively long term event and its magnitude is comparable to that of other minor mass extinctions e g those of the silurian early jurassic or end cenomanian there are several possible explanations for what caused the ladinian biotic crisis it is possible that global climate cooling was responsible although it is unclear why the palaeobiogeographical differentiation was not favourable for a biotic radiation a eustatic explanation for the drop in diversity is unlikely instead the crisis was mostly likely caused by unstable recovery of the earth s biota after the end permian catastrophe

flowgo a kinematic thermo rheological model for lava flowing in a channel we present a kinematic self adaptive numerical model to describe the down flow thermal and rheological evolution of channel contained lava as our control volume of lava advances down a channel it cools and crystallizes an increasingly thick and extensive surface crust grows and its heat budget and rheology evolve by estimating down flow heat and velocity loss our model calculates the point at which the control volume becomes stationary giving the maximum distance lava flowing in the channel can extend modeled effusion rates velocities widths surface crust parameters heat budget cooling temperature crystallinity viscosity and yield strength all compare well with field data collected during eruptions at mauna loa k lauea and etna modeled lengths of 25 27 2 5 5 7 and 0 59 0 83 km compare with measured lengths of 25 27 4 and 0 75 km for the three flows respectively over proximal flow portions we calculate cooling crystallization viscosity and yield strength of 1 10 c km 1 0 001 0 01 volume fraction km 1 103 104 pa s and 10 3 102 pa respectively at the flow front cooling crystallization viscosity and yield strength increase to 100 c km 1 0 1 volume fraction km 1 106 107 pa s and 103 104 pa respectively all of which combine to cause the lava to stop flowing our model presents a means of a analyzing lava flow thermo rheological relationships b identifying important factors in determining how far a channel fed flow can extend c assessing lava flow hazard and d reconstructing flow regimes at prehistoric unobserved or remote flows

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

an abrupt change in the african monsoon at the end of the younger dryas 1 high resolution studies of variations in the elemental and stable carbon and nitrogen isotope composition of organic matter in cores from lakes malawi tanganyika and bosumtwi tropical africa indicate an abrupt change in the wind driven circulation of these lakes that within the limits of available chronologies was contemporaneous with the end of the younger dryas in the northern hemisphere the change was also coincident with shifts in surface winds recorded in cores from off the west and northeast coasts of africa a range of other proxies indicate that these changes in wind regime were accompanied by a marked increase in precipitation in the northern tropics africa south of 5 10 s on the other hand initially suffered drought conditions together the evidence suggests an abrupt northward translation of the african monsoon system at circa 11 5 0 25 ka b p the data assembled here contribute to a growing body of work showing that the younger dryas was a major climatic excursion in tropical africa furthermore they add substance to recent suggestions that climatic events in the southern hemisphere may have played a significant role in the abrupt demise of the younger dryas

oblique photogrammetry with visible and thermal images of active lava flows digital images from hand held cameras are increasingly being acquired for scientific purposes particularly where non contact measurement is required however they frequently consist of oblique views with significant camera to object depth variations and occlusions that complicate quantitative analyses here we report the use of oblique photogrammetric techniques to determine ground based thermal camera orientations position and pointing direction and to generate scene information for lava flows at mount etna sicily multiple images from a consumer grade digital slr camera are used to construct a topographic model and reference associated ground based thermal imagery we present data collected during the 2004 2005 eruption and use the derived surface model to apply viewing distance corrections to account for atmospheric attenuation to the thermal images on a pixel by pixel basis for viewing distances of 100 to 400 m the corrections result in systematic changes in emissive power of up to 3 with respect to values calculated assuming a uniform average viewing distance across an image

identification of structural controls in an active lava dome with high resolution dems volcan de colima mexico monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity internal dome structure and conditions are more difficult to elucidate but also play vital roles here we describe the exposure following an explosion of significant scarps in the active dome at volcan de colima mexico that are interpreted as evidence of brittle failure planes and a complex internal dome morphology in the first use of automated 3d computer vision reconstruction techniques structure from motion and multi view stereo sfm mvs on an active volcanic dome we derive high resolution surface models from oblique and archive photographs taken with a consumer camera the resulting 3d models were geo referenced using features identified in a web sourced orthoimage no ground based measurements were required in december 2010 the dome 2 14 106 m3 had a flat upper surface reflecting an overall ductile emplacement regime between then and may 2011 a period of low explosivity was accompanied by a small volume loss 0 4 105 m3 and arcuate steps appeared in the dome surface suggesting the presence of localized planes of weakness the complex array of summit scarps was exposed following a significant explosion in june 2011 and is interpreted to be the surface expression of fault planes in the dome the 1 m resolution dems indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit and that heterogeneity within the dome may have been important during the june explosion

crease structures indicators of emplacement rates and surface stress regimes of lava flows crease structures are features commonly found on lava flow surfaces and consist of a fracture with curved walls that extend outward from a linear valley these crease structures are found on flows of nearly all compositions and crystallinities we have mapped the distributions of crease structures on many flows in the western united states and found that 1 axial length is not dependent upon composition and crystallinity 2 adjacent crease structures are generally aligned in an en echelon pattern 3 crease structures located adjacent to flow margins are generally perpendicular to these margins and 4 at mount st helens washington large lobe bisecting crease structures are found on lobes situated on slopes of less than 20 degrees a primary surface feature found on many crease structures is striations striations are sets of long stripes on the walls of the crease structure that extend approximately parallel to the axis of the central valley and they appear to be analogous to those found on the faces of cyclically fractured basalt columns observations of developing crease structures on 6 of the nearly 20 mount st helens dome lobes show that they form throughout the extrusion of flows situated on slopes of less than 20 degrees but only at the very beginning and or end of extrusion of flows on steeper slopes these observations imply that crease structures form when the lava flow is forced to spread laterally either as the flow advances over a flat area or as the down slope movement stagnates near the end of extrusion causing the rate of spreading to exceed the downslope rate of flow this lateral spreading of lava results in the concentration of tensile stress along a line oriented perpendicular to the direction of spreading the cooled crust of the extrusion is therefore torn apart about this line of tensile stress concentration forming a central valley that exposes hot ductile material from the flow interior to the atmosphere the presence of striations on many crease structure walls implies that the emplacement mechanism is similar to that suggested for columnar basalts where each striation is produced by incremental fracturing the stress responsible for crease structure formation is due to both cooling and lateral spreading of lava calculations show that stress due to spreading is three orders of magnitude higher than that due to cooling fracture advance times were calculated using a simple one dimensional conductive cooling model adjusted for the special geometry of the crease structure the model closely approximates measured crease structure emplacement times at mount st helens and gives reasonable estimates for crease structures found on older silicic lava flows we then used this model to calculate emplacement times of entire domes that consist of a single crease structure by dividing the dome volume by the formation time we are able to calculate extrusion rates for these older domes these values which include the first flow rate estimates reported for rhyolitic lavas 0 03 106 m 3 s similar to average flow rates of 0 7 40 m 3 s calculated for mount st helens dacite lobes from detailed topographic maps

thermal diffusivity of rhyolitic glasses and melts effects of temperature crystals and dissolved water thermal diffusivity d was measured using laser flash analysis on pristine and remelted obsidian sam ples from mono craters california these high silica rhyo lites contain between 0 013 and 1 10 wt h2o and 0 to 2 vol crystallites at room temperature dglass varies from 0 63 to 0 68 mm 2 s 1 with more crystalline samples having higher d a st increases dglass decreases approaching a constant value of 0 55 mm 2 s 1 near 700 k the glass data are fit with a simple model as an exponential function of temperature and a linear function of crystallinity dissolved water contents up to 1 1 wt have no statistically significant effect on the thermal diffusivity of the glass upon crossing the glass transition d decreases rapidly near 1 000 k for the hydrous melts and 1 200 k for anhydrous melts rhy olitic melts have a dmelt of 0 51 mm 2 s 1 thermal conduc tivity k0d cp of rhyolitic glass and melt increases slightly with t because heat capacity cp increases with t more strongly than density and d decrease the thermal conductivity of rhyolitic melts is 1 5 wm 1 k 1 a nd should vary little over the likely range of magmatic temperatures and water contents these values of d and k are similar to those of major crustal rock types and granitic protoliths at magmatic temperatures suggesting that changes in thermal properties accompanying partial melting of the crust should be relatively minor numerical models of shallow rhyolite intrusions indicate that the key difference in thermal history between bodies that quench to obsidian and those that crystallize results from the release of latent heat of crystallization latent heat release enables bodies that crystallize to remain at high temperatures for much longer times and cool more slowly than glassy bodies the time to solidification is similar in both cases however because solidification requires cooling through the glass transition in the first case and cooling only to the solidus in the second

the distal segment of etna s 2001 basaltic lava flow etna s 2001 basaltic lava flow provided a good example of the distal flow segment between the flow front and stable channel across which the flow evolves from channel contained to dispersed this zone was mapped with meter precision using lidar data collected during 2004 and 2005 these data supported by field mapping show that the flow front comprised eight lobes each 10 to 20 m high the flow front appears to have advanced not as a single unit but as a series of lobes moving forward one lobe at a time primary lobes were centered on the channel axis and marginal lobes were off axis the lobes advanced as breakouts of low yield strength lava from the flow core of the stalled flow front marginal lobes were abandoned and contributed to marginal levees flanking the transitional channel for etna s 2001 flow the transitional channel is 140 m wide 700 m long and fed a 240 m long zone of dispersed flow the change from stable to transitional channel occurred at a major reduction in slope above this the stable channel is 5 2 km long 55 to 105 m wide and bounded by 15 to 25 m high levees and the stable channel is located over a previous channel in a final stage of activity lava ponding at the break in slope that marks the terminus of the stable channel put pressure on the eastern levee causing it to fail liberated lava then fed a final break out to the east similar flow front features occur at other volcanoes indicating that similar processes are characteristic of dispersed flow zones

quantification of extraterrestrial lava flow effusion rates through laboratory simulations we have used carefully controlled laboratory simulations to develop a model which relates lava flow morphology to effusion rate and rheology through comparisons with measured and estimated eruption rates on earth this approach allows us to constrain eruptive styles and compositions of extraterrestrial lava flows by applying this model to lava flows on the moon mars and venus we have determined that all the common flow morphologies domes folds and levees on these planets could have been produced by basalt like or andesite like lavas through either continuous or episodic emplacement the presence of more evolved magma compositions on other planets is not required to explain any of the observed lava flow morphologies

the strain path and emplacement mechanism of lava flows an example from salina southern tyrrhenian sea italy abstract a lava flow from salina southern tyrrhenian sea consists of subcircular to ellipsoidal basaltic enclaves dispersed in a dacitic host a 2d strain and kinematic analysis of the enclaves has been performed in order to determine a the relative contribution of the coaxial and non coaxial components to the bulk flow deformation b the flow vorticity wk c the strain path and d the mechanism of flow emplacement the axial ratio r f and the angle f between the long axis of the enclaves and the transport direction have been measured in 196 sites located at different distances from the vent in the near vent zone whereas further from the vent values were always larger than 1 ranging from 1 6 in the near vent zone to 1 at the front values were between 0 2 at the back and 2 6 at the front wk was between 0 13 and 1 and increased from the back to the front the enclaves result from the injection of basalt into dacite most of the deformation was acquired during the lava flow emplacement and not during the rise in the conduit plug flow the strain path depicted by the enclaves is consistent with that resulting from experimental analogue models and reveals that the lava suffers lateral extension near the vent further from the vent the lava deforms according to an ideal non coaxial model the lava emplacement is mainly controlled by the gravity evidence of deformation induced by the magma pressure is lacking near the vent the lava behaves as a hyperbolic flow whereas at the front it behaves as a simple shear flow the mechanism of flow emplacement is consistent with a mixed viscous gliding spreading transport model at the back and with a viscous gliding model at the front

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

factors influencing lava substrate heat transfer and implications for thermomechanical erosion we develop numerical simulations of basaltic lava flowing laminarly over a basalt substrate in order to examine the details of the lava dynamics and thermal boundary layers and to understand the implications for substrate heating as the initial stage of a larger study of thermomechanical erosion in different planetary environments we aim to understand why erosion occurs on earth why erosion features are not ubiquitous given the high temperatures involved and whether it is a plausible mechanism for the formation of planetary channels such as lunar sinuous rilles and venusian canali here we confine our attention to terrestrial lavas with well known properties and eruption parameters with relatively simple computational fluid dynamic simulations most closely representing tube fed hawaiian basalts for which erosion has been documented we demonstrate the importance of incorporating several key factors in models of lava flow substrate heat transfer which have commonly been neglected in previous treatments by addressing the interaction of the flow dynamics and heat transfer in the lava our work suggests that the development of a temperature gradient in the base of the lava even for undeveloped flow has a significant influence on substrate temperature the sensitivity of the lava substrate interface temperature to the thermophysical properties of the lava and substrate suggests that a delicate balance is required for partial melting to occur thus it might take weeks of continuous flow to initiate partial melting of the substrate at distances of several kilometers from the vent these durations exceed the periods of stability typical of lava flowing in tubes pauses blockages surges and breakouts frequently disrupt the flow however natural irregularities in the flow dynamics or substrate topography might help to initiate and maintain substrate melting on shorter timescales by disturbing the intimately coupled dynamic and thermal boundary layers although a purely thermal mechanism cannot be ruled out our findings support the premise that mechanical erosion may play a key role in reports of erosion based on field evidence

lava channel roofing overflows breaches and switching insights from the 2008 2009 eruption of mt etna during long lived basaltic eruptions overflows from lava channels and breaching of channel levees are important processes in the development of extensive a lava flow fields short lived breaches result in inundation of areas adjacent to the main channel however if a breach remains open lava supply to the original flow front is significantly reduced and flow field widening is favoured over lengthening the development of channel breaches and overflows can therefore exert strong control over the overall flow field development but the processes that determine their location and frequency are currently poorly understood during the final month of the 2008 2009 eruption of mt etna sicily a remote time lapse camera was deployed to monitor events in a proximal region of a small ephemeral lava flow for over a period of 10 h the flow underwent changes in surface elevation and velocity repeated overflows of varying vigour and the construction of a channel roof a required prelude to lava tube formation quantitative interpretation of the image sequence was facilitated by a 3d model of the scene constructed using structure from motion computer vision techniques as surface activity waned during the roofing process overflow sites retreated up the flow towards the vent and eventually a new flow was initiated our observations and measurements indicate that flow surface stagnation and flow inflation propagated up flow at an effective rate of 6 m h 1 and that these processes rather than effusion rate variations were ultimately responsible for the most vigorous overflow events we discuss evidence for similar controls during levee breaching and channel switching events on much larger flows on etna such as during the 2001 eruption

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

using infrared satellite data to drive a thermo rheological stochastic lava flow emplacement model a method for near real time volcanic hazard assessment 1 we combine two flow simulation models to provide a computationally efficient means of predicting the final dimensions of active lava flows by using a stochastic approach to predict all the downhill paths that a lava flow could possibly follow and a thermo rheological model to terminate these paths once the predicted cooling limited length for the flow has been attained this approach allows for rapid assessment of the area likely to be inundated by lava the 1991 1993 eruption of mount etna is used as a case study lava effusion rate exerts a strong control on the maximum length a lava flow can attain and we demonstrate how the model can be driven by time varying effusion rates obtained from infrared satellite data as such data are obtained in near real time this approach allows flow simulations to be updated in a timely manner in response to changing eruption conditions

the changing morphology of an open lava channel on mt etna an open channel lava flow on mt etna sicily was observed during may 30 31 2001 data collected using a forward looking infrared flir thermal camera and a minolta land cyclops 300 thermal infrared thermometer showed that the bulk volume flux of lava flowing in the channel varied greatly over time cyclic changes in the channel s volumetric flow rate occurred over several hours with cycle durations of 113 190 min and discharges peaking at 0 7 m3 s 1 and waning to 0 1 m3 s 1 each cycle was characterized by a relatively short high volume flux phase during which a pulse of lava with a well defined flow front would propagate down channel followed by a period of waning flow during which volume flux lowered pulses involved lava moving at relatively high velocities up to 0 29 m s 1 and were related to some change in the flow conditions occurring up channel possibly at the vent they implied either a change in the dense rock effusion rate at the source vent and or cyclic variation in the vesicle content of the lava changing its bulk volume flux pulses would generally overspill the channel to emplace p hoehoe overflows during periods of waning flow velocities fell to 0 05 m s 1 blockages forming during such phases caused lava to back up occasionally backup resulted in overflows of slow moving a that would advance a few tens of meters down the levee flank compound levees were thus a symptom of unsteady flow where overflow levees were emplaced as relatively fast moving p hoehoe sheets during pulses and as slow moving a units during backup small localized fluctuations in channel volume flux also occurred on timescales of minutes volumes of lava backed up behind blockages that formed at constrictions in the channel blockage collapse and or enhanced flow under around the blockage would then feed short lived wave like down channel surges real fluctuations in channel volume flux due to pulses and surges can lead to significant errors in effusion rate calculations

mapping and downflow simulation of recent lava flow fields at mount etna in recent years progress in geographic information systems gis and remote sensing techniques have allowed the mapping and studying of lava flows in unprecedented detail a composite gis technique is introduced to obtain high resolution boundaries of lava flow fields this technique is mainly based on the processing of lidar derived maps and digital elevation models dems the probabilistic code downflow is then used to simulate eight large flow fields formed at mount etna in the last 25 years thanks to the collection of 6 dems representing mount etna at different times from 1986 to 2007 simulated outputs are obtained by running the downflow code over pre emplacement topographies simulation outputs are compared with the boundaries of the actual flow fields obtained here or derived from the existing literature although the selected fields formed in accordance with different emplacement mechanisms flowed on different zones of the volcano over different topographies and were fed by different lava supplies of different durations downflow yields results close to the actual flow fields in all the cases considered this outcome is noteworthy because downflow has been applied by adopting a default calibration without any specific tuning for the new cases considered here this extensive testing proves that if the pre emplacement topography is available downflow yields a realistic simulation of a future lava flow based solely on a knowledge of the vent position in comparison with deterministic codes which require accurate knowledge of a large number of input parameters downflow turns out to be simple fast and undemanding proving to be ideal for systematic hazard and risk analyses

computer simulations of lava flow paths in the town of goma nyiragongo volcano democratic republic of congo 1 the 17 january 2002 fissure eruption of mount nyiragongo democratic republic of congo produced lava flows which entered and devastated the densely inhabited town of goma the 2002 and previous 1977 eruptions demonstrate the high level of volcanic risk in the area we present an analysis of the susceptibility to lava flow invasion in goma by means of computer simulations based on the steepest descent path and probabilistic computed flow spreading and obstacle overcoming the dem is obtained from a topographic map of goma by using the dest algorithm the numerical results show the distribution of probable lava flow paths from possible vents in the investigated topographic domain numerical simulations are validated through comparison with the mapped paths of the 2002 lava flows in goma the subsequent investigation includes the analysis of 1 hypothetical lava flow paths from ephemeral vents on the edge of the 2002 lava flows 2 paths from venting along the hypothetical extension of the 2002 fissures 3 paths in case of lava flow arrival in town from the north and 4 changes induced by the presence of the solidified 2002 lava field the results show the susceptibility of the different parts of the town of goma to be invaded by future lava flows and reveal the existence of a large area in town with minimum susceptibility and which can be invaded only in case of venting within it the areas destroyed by the 2002 lava flows are predicted to be characterized by maximum susceptibility to lava flow invasion

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

crystallization history of the 1984 mauna loa lava flow during a 3 week eruption in 1984 mauna loa produced vent lavas that increased in crystallinity from 1 to 30 and 27 km long flows that increased in crystallinity as they moved downstream we examined the crystallization history of these lavas using crystal size distribution csd analysis to study the rates of crystallization viscosity increase and latent heating typical average growth and nucleation rates were 5 10 9 cm s 1 and 5 cm 3 s 1 for microphenocrysts 20 to 500 m size crystals nucleated in the rift zone and 5 10 8 cm s 1 and 5 104 cm 3 s 1 for microlites 1 to 20 m size crystals nucleated in the channel these crystallization rates are high compared with those found in other csd studies of igneous rocks probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel growth and nucleation rates decreased with time at the vent and with distance downstream the maximum downstream total crystallinity measured is 39 25 microlites 14 microphenocrysts in a quenched sample 14 km from the vent growth and nucleation rates cannot be calculated for postemplacement samples but they place upper limits of 53 58 on the amount of crystallization in the channel 9 20 km from the vent crystallization could have been mostly responsible for the 105 fold downstream increase in apparent viscosity although degassing and increasing incorporation of solid lava fragments also contributed another effect of crystallization on the lava flow was the sizeable latent heating 0 01 j g 1 s 1 over the first half of the flow length if the crystallinity of downstream quench samples is representative of the hot fluid core which may have been counteracted by entrainment of cooler material measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics

the satah mountain and baldface mountain volcanic fields pleistocene hot spot volcanism in the anahim volcanic belt west central british columbia canada the satah mountain and baldface mountain volcanic fields smvf bmvf comprise more than three dozen small volcanic centers and erosional remnants thereof these fields are located in the chilcotin highland of west central british columbia canada and are spatially associated with the anahim volcanic belt avb a linear feature of alkaline to peralkaline plutonic and volcanic centers of miocene to holocene ages the avb has been postulated to be the track of a hot spot passing beneath the westward moving cordilleran lithosphere we test the avb hot spot model by applying whole rock 40ar 39ar geochronology n 24 and geochemistry whole rock chemical compositions of volcanic rock samples n 59 from these two fields suggest a strong geochemical affinity with the nearby itcha range shield volcano however smvf and bmvf centers are mostly small in volume 1 km3 and differ in composition from one another even where they are in close spatial proximity trace element and ree patterns of mafic avb lavas are similar to ocean island basalts oib suggesting a mantle source for these lavas the age ranges for the smvf n 11 2 21 to 1 43 ma and bmvf n 7 3 91 to 0 91 ma are largely coeval with the itcha range the distribution of volcanoes in these two volcanic fields is potentially consistent with the postulated avb hot spot track eruption rates in the smvf were high enough to build an elongated ridge that deviates from the e w trend of the avb by almost 90 this deviation might reflect the mechanisms and processes facilitating magma generation and ascent through the lithosphere in this tectonically complex region and may also indicate interaction of the potential hot spot with pre existing fracture systems in vicinity of the itcha range

the early eocene rise of the gonjo basin se tibet from low desert to high forest abstract views differ on the uplift history of the se tibetan plateau and causal geodynamic mechanisms yet reliable age constrained paleoaltimetry in this region could test growth models of the entire plateau here we apply carbonate clumped isotope thermometry to well dated carbonate paleosols and marls in the gonjo basin se tibet to reveal the topographic evolution of the basin the sedimentary ages of carbonates of the lower and upper ranmugou formation are constrained to 54 50 ma and 44 40 ma respectively the temperature derived from carbonate clumped isotope thermometry indicates the mean annual air temperature maat of the gonjo basin in the early eocene was 24 c which is consistent with the warm climate indicated by palm fossils the maat of the basin in the middle eocene was 7 c 17 c cooler than in the early eocene carbonate clumped oxygen isotope thermometry based paleoaltimetry shows the gonjo basin experienced a rapid uplift of 3 1 km from 0 7 km in the early eocene to 3 8 km in the middle eocene this rise explains the marked cooling as a cause of this rapid rise and the associated regional climate change transforming the landscape from desert to forest we invoke crustal deformation and thickening induced by intracontinental subduction between the lhasa and qiangtang terranes that comprise the core of the tibet

clinker formation in basaltic and trachybasaltic lava flows clinker is a term used to describe massive or scoriaceous fragments commonly associated with a lava flows clinker is generally considered to form by fragmentation of an upper vesiculated crust due to an increase in apparent viscosity and or to an increase in shear strain rate surface clinker is considered to be transported to the flow front and incorporated at the base by caterpillar motion clinker that we have observed on a variety of lava flows has very variable textures which suggests several different mechanisms of formation in order to study clinker formation we examined several lava flows from the chaine des puys central france where good sections surface morphology and surface textures are widespread and clearly visible we observed basal and surface a clinker that has fragmentation textures similar to those observed in ash formed in eruptions under dry conditions in two p hoehoe flows we have observed basal clinker that formed in situ two other flows display clinker features identical to those commonly observed in phreatomagmatic ash such as adhering particles blocky shapes spherical glass and attached microphenocrysts another p hoehoe flow has a flakey angular basal breccia with microfaulted and abraded clasts these were probably formed at a cooled lava base by large amounts of simple shear and consequent intra lava brittle faulting using these observations we propose three different ways of fragmentation 1 clinker can form at the surface and eventually produce roll over basal breccia 2 water lava interactions can form basal clinker by phreatomagmatic fragmentation water lava ratio variations may produce different clinker structures in a manner similar to observed textural changes in phreatomagmatic eruptions 3 clinker can be formed by brittle brecciation during basal simple shear the different clinker can provide information about the mechanisms and environmental conditions during lava flow emplacement

cristobalite in the 2011 2012 cordon caulle eruption chile cristobalite is a low pressure high temperature polymorph of sio2 found in many volcanic rocks its volcanogenic formation has received attention because 1 pure particulate cristobalite can be toxic when inhaled and its dispersal in volcanic ash is therefore a potential hazard and 2 its nominal stability field is at temperatures higher than those of magmatic systems making it an interesting example of metastable crystallization we present analyses by xrd sem epma laser raman and synchrotron ct of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011 2012 eruption of cordon caulle chile cristobalite was not detected in pyroclasts negating any concern for respiratory hazards but it makes up 0 23 wt of lava samples occurring as prismatic vapour deposited crystals in vesicles and or as a groundmass phase in microcrystalline samples textures of lava collected near the vent which best represent those generated in the conduit indicate that pore isolation promotes vapour deposition of cristobalite mass balance shows that the sio2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass textures of lava collected down flow were modified during transport in the insulated interior of the flow where protracted cooling additional vesiculation events and shearing overprint original textures in the most slowly cooled and intensely sheared samples from the core of the flow nearly all original pore space is lost and vapour deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite vapour deposition and devitrification act concurrently but semi independently both are promoted by slow cooling and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions with insight afforded by the fundamentally different emplacement geometries of flows and domes

examining rhyolite lava flow dynamics through photo based 3d reconstructions of the 2011 2012 lava flowfield at cordon caulle chile during the 2011 2012 eruption at cordon caulle chile an extensive rhyolitic flowfield was created in excess of 0 5 km3 in volume affording a unique opportunity to characterise rhyolitic lava advance in 2012 and 2013 we acquired approximately 2500 digital photographs of active flowfronts on the north and east of the flowfield these images were processed into three dimensional point clouds using structure from motion and multi view stereo sfm mvs freeware from which digital elevation models were derived sequential elevation models separated by intervals of three hours six days and one year were used to reconstruct spatial distributions of lava velocity and depth and estimate rheological parameters three dimensional reconstructions of flowfronts indicate that lateral extension of the rubbly a like flowfield was accompanied by vertical inflation which differed both spatially and temporally as a function of the underlying topography and localised supply of lava beneath the cooled upper carapace compressive processes also drove the formation of extensive surface ridges across the flowfield continued evolution of the flowfield resulted in the development of a compound flowfield morphology fed by iterative emplacement of breakout lobes the thermal evolution of flow units was modelled using a one dimensional finite difference method which indicated prolonged residence of magma above its glass transition across the flowfield we compare the estimated apparent viscosity 1 21 4 03 1010 pa s of a breakout lobe based on its advance rate over a known slope with plausible lava viscosities from published non arrhenian temperature viscosity models and accounting for crystallinity 50 vol there is an excellent correspondence between viscosity estimates when the lava temperature is taken to be magmatic despite the breakout being located 3 km from the vent and advancing approximately nine months after vent effusion ceased this indicates the remarkably effective insulation of the lava flow interior providing scope for significant evolution of rhyolitic flow fields long after effusive activity has ceased

straightforward reconstruction of 3d surfaces and topography with a camera accuracy and geoscience application topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry here we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3d models from field photographs taken with a consumer grade camera the approach integrates structure from motion sfm and multi view stereo mvs algorithms and in contrast to traditional photogrammetry techniques it requires little expertise and few control measurements and processing is automated to assess the precision of the results we compare sfm mvs models spanning spatial scales of centimeters a hand sample to kilometers the summit craters of piton de la fournaise volcano with data acquired from laser scanning and formal close range photogrammetry the relative precision ratio achieved by sfm mvs measurement precision observation distance is limited by the straightforward camera calibration model used in the software but generally exceeds 1 1000 i e centimeter level precision over measurement distances of 10s of meters we apply sfm mvs at an intermediate scale to determine erosion rates along a 50 m long coastal cliff seven surveys carried out over a year indicate an average retreat rate of 0 70 0 05 m a 1 sequential erosion maps at 0 05 m grid resolution highlight the spatio temporal variability in the retreat with semivariogram analysis indicating a correlation between volume loss and length scale compared with a laser scanner survey of the same site sfm mvs produced comparable data and reduced data collection time by 80

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

pressure dependence of viscosity of rhyolitic melts abstract viscosity of silicate melts is a critical property for understanding volcanic and igneous processes in the earth we investigate the pressure effect on the viscosity of rhyolitic melts using two methods indirect viscosity inference from hydrous species reaction in melts using a piston cylinder at pressures up to 2 8 gpa and direct viscosity measurement by parallel plate creep viscometer in an internally heated pressure vessel at pressures up to 0 4 gpa comparison of viscosities of a rhyolitic melt with 0 8 wt water at 0 4 gpa shows that both methods give consistent results in the indirect method viscosities of hydrous rhyolitic melts were inferred based on the kinetics of hydrous species reaction in the melt upon cooling i e the equivalence of rheologically defined glass transition temperature and chemically defined apparent equilibrium temperature the cooling experiments were carried out in a piston cylinder apparatus using hydrous rhyolitic samples with 0 8 4 wt water cooling rates of the kinetic experiments varied from 0 1 k s to 100 k s hence the range of viscosity inferred from this method covers 3 orders of magnitude the data from this method show that viscosity increases with increasing pressure from 1 gpa to 3 gpa for hydrous rhyolitic melts with water content 0 8 wt in the high viscosity range we also measured viscosity of rhyolitic melt with 0 13 wt water using the parallel plate viscometer at pressures 0 2 and 0 4 gpa in an internally heated pressure vessel the data show that viscosity of rhyolitic melt with 0 13 wt water decreases with increasing pressure combining our new data with literature data we develop a viscosity model of rhyolitic melts as a function of temperature pressure and water content

an emergent strategy for volcano hazard assessment from thermal satellite monitoring to lava flow modeling abstract spaceborne remote sensing techniques and numerical simulations have been combined in a web gis framework lav hazard to evaluate lava flow hazard in real time by using the hotsat satellite thermal monitoring system to estimate time varying tadr time averaged discharge rate and the magflow physics based model to simulate lava flow paths the lav hazard platform allows timely definition of parameters and maps essential for hazard assessment including the propagation time of lava flows and the maximum run out distance we used lav hazard during the 2008 2009 lava flow forming eruption at mt etna sicily italy we measured the temporal variation in thermal emission up to four times per hour during the entire duration of the eruption using seviri and modis data the time series of radiative power allowed us to identify six diverse thermal phases each related to different dynamic volcanic processes and associated with different tadrs and lava flow emplacement conditions satellite derived estimates of lava discharge rates were computed and integrated for the whole period of the eruption almost 14 months showing that a lava volume of between 32 and 61 million cubic meters was erupted of which about 2 3 was emplaced during the first 4 months these time varying discharge rates were then used to drive magflow simulations to chart the spread of lava as a function of time tadrs were sufficiently low 3 s that no lava flows were capable of flowing any great distance so that they did not pose a hazard to vulnerable agricultural and urban areas on the flanks of etna

image based measurement of flux variation in distal regions of active lava flows 1 understanding the processes involved with the advance of lava flows is critical for improving hazard assessments at many volcanoes here we describe the application of computer vision and oblique photogrammetric techniques to visible and thermal images of active a flows in order to investigate distal flow processes at mount etna sicily photogrammetric surveys were carried out to produce repeated topographic data sets for calculation of volumetric lava flux at the flow fronts velocity profiles from a distal channel were obtained by rectification of a thermal image sequence and are used to investigate the rheological properties of the lava significant variations of the magma flux were observed and pulses of increased flux arrived within the flow front region on timescales of several hours the pulses are believed to be the distal result of more frequent flux changes observed in the vent region hence they reflect the importance of flow processes which are believed to cause the coalescence of flux pulses along the channel system as well as short period variations in effusion rate in considering advance processes for the individual flow fronts it must be assumed that they were fed by a highly unsteady flux which was volumetrically at least an order of magnitude lower than that observed near the vent