the topography and morphology of low shields and associated landforms of plains volcanism in the tharsis region of mars abstract the morphology and topography of volcanic landforms provide critical information to the investigation of their tectonic setting and the physical characteristics e g rheology of their eruption products their investigation is also an important prerequisite for studies of comparative planetology e g the comparison between surface features of the earth and other planetary bodies numerous small and low shield volcanoes on mars and associated vents and lava flows have previously been compared to terrestrial plains style volcanism which is defined as being an intermediate style between flood basalts and the hawai ian shields this study investigates the topography and morphology of martian landforms associated with plains volcanism using mola moc themis hrsc and hirise data low shields and other landforms of plains volcanism on mars display similarities with terrestrial basaltic volcanic fields and we do not observe any features that do not have morphologic analogues on earth the most typical landforms of martian plains style volcanism are low shields defined as volcanic shields with diameters of typically less than 50 km heights of a few hundred meters only and extremely shallow flank slopes of less than 0 5 other surface features related to plains style volcanism on mars are craters fissure vents cinder and spatter cones lava flows that are commonly associated with lava channels and tubes lava inflation features and volcanic rift zones our results reconfirm the viking orbiter based conclusion that plains volcanism in the eastern snake river plains is perhaps the best terrestrial morphological analogue for these martian surface features icelandic shields distinct structures in hawai i and other basaltic landforms also show similarities to martian plains volcanism sinuous rilles previously not described in association with plains volcanism on mars are interpreted as evidence for high eruption rates the extremely shallow flank slopes of the low shields suggest the eruption of shield building lavas with low viscosity which might be the result of high eruption temperatures high effusion rates a low si and a high mg content along with a possible high fe content or a combination of these factors the spatial distribution of low shield clusters in tharsis does not show any obvious association with large scale tectonic features plains volcanism might represent a relatively recent type of volcanism on mars which is not related to mantle plumes but to a zone of partial melting in an anomalously warm mantle underneath a thickened crust schumacher and breuer geophys res lett 34 l14202 doi 10 1029 2007gl030083 2007

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

visualization and comparison of dem derived parameters application to volcanic areas abstract digital elevation models dems are fruitfully used in volcanology as the topographic base for mapping and quantifying volcanic landforms the increasing availability of free topographic data on the web decreasing production costs for high accuracy data and advances in computer technology has triggered rapid growth of the number of dem users in the volcanological community dems are often visualized only as hill shaded maps and while this is among the major advantages in using them the possibility of deriving a very large number of parameters from a single grid of elevation data makes dems a powerful tool for morphometric analysis however many of these parameters have almost the same informative content and before starting to elaborate topographic data it is recommended to know a priori what parameters best visualize the investigated landform and therefore what is necessary and what is redundant in this work we review a number of analytical procedures used to parameterize and represent dems a lidar derived dem matrix acquired over the valle del bove valley on mt etna is used as test case elevation data for deriving the parameters we first review well known parameters such as hill shading slope and aspect curvature and roughness before extending the review to some less common parameters such as sky view factor svf openness and red relief image maps rrim for each parameter a description is given emphasizing how it can be used for identifying and delimiting specific volcanic elements the analyzed surface parameters are then cross compared in order to infer which of them is most uncorrelated and the results are represented in the form of a correlation matrix finally the reviewed dem derived parameters and the correlation matrix are used for analyzing the volcanic landforms of two case studies michoacan guanajuato volcanic field and a phonolitic lava flow at the island of tenerife

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

field and experimental constraints on the rheology of arc basaltic lavas the january 2014 eruption of pacaya guatemala we estimated the rheology of an active basaltic lava flow in the field and compared it with experimental measurements carried out in the laboratory in the field we mapped sampled and recorded videos of the 2014 flow on the southern flank of pacaya guatemala velocimetry data extracted from videos allowed us to determine that lava traveled at 2 8 m s on the steep 45 slope 50 m from the vent while 550 m further downflow it was moving at only 0 3 m s on a 4 slope estimates of effective viscosity based on jeffreys equation increased from 7600 pa s near the vent to 28 000 pa s downflow in the laboratory we measured the viscosity of a representative lava composition using a concentric cylinder viscometer at five different temperatures between 1234 and 1199 c with crystallinity increasing from 0 1 to 40 vol the rheological data were best fit by power law equations with the flow index decreasing as crystal fraction increased and no detectable yield strength although field based estimates are based on lava characterized by a lower temperature higher crystal and bubble fraction and with a more complex petrographic texture field estimates and laboratory measurements are mutually consistent and both indicate shear thinning behavior the complementary field and laboratory data sets allowed us to isolate the effects of different factors in determining the rheological evolution of the 2014 pacaya flows we assess the contributions of cooling crystallization and changing ground slope to the 3 7 fold increase in effective viscosity observed in the field over 550 m and conclude that decreasing slope is the single most important factor over that distance it follows that the complex relations between slope flow velocity and non newtonian lava rheology need to be incorporated into models of lava flow emplacement

new statistics for estimating the bulk rheology of active lava flows puu oo examples downstream changes in lava rheology due to cooling crystallization and vesiculation have a strong influence on the final length and morphology of a lava flow three statistics are proposed to estimate the change in lava rheology with distance along the path of an active flow these statistics correspond to three separate models of the volumetric flow rate dependence on the thickness of the flow each statistic is based on flow dimensions and topographic data that are often available from field measurements or remote sensing one model assumes an elementary laminar newtonian flow a second empirical model often used to describe the flow of complex geologic materials such as lahars sediment laden floods and debris flows is also investigated for comparison a new volume loss model is also proposed to account for stationary components such as levees and stagnant areas the three statistics derived from these flow rate models are applied and interpreted for two well defined lobes from episodes 2 and 18 of the 1983 1984 puu oo eruption the power law dependence of the first two models results only in modest differences in the estimates of rheologic change along the flow path however the removal of lava from the active flow to construct stationary components produces significant differences in both the magnitude of computed rheologic changes and the ability to discern trends in rheologic changes along the path of the flow

monogenetic vulcanism in sierra chichinautzin mexico the variation in the activity patterns of the chichinautzin volcanic rocks is discussed this sequence of lavas and pyroclastic deposits is located in the central part of the mexican volcanic belt directly south of mexico city and is typical of its quaternary monogenetic vulcanism

late pleistocene and holocene paleoenvironments of chalco lake central mexico abstract in order to establish paleoenvironmental conditions during the late quaternary four cores from the basin of mexico central mexico were drilled in chalco lake located in the southeastern part of the basin the upper 8 m of two parallel cores were studied using paleomagnetic loss on ignition pollen and diatom analyses based on 11 14c ages the analyzed record spans the last 19 000 14c yr b p volcanic activity has affected microfossil abundances both directly and indirectly resulting in absence or reduction of pollen and diatom assemblages important volcanic activity took place between 19 000 and 15 000 yr b p when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry cold climate during this interval abrupt environmental changes with increasing moisture occurred from 15 000 until 12 500 yr b p the lake level increased and the pollen indicates wetter conditions the highest lake level is registered from 12 500 to ca 9000 yr b p the end of the pleistocene is characterized by an increase in humidity from 9000 until ca 3000 yr b p chalco lake was a saline marsh and the pollen record indicates warmer conditions after 3000 yr b p the lake level increased and human disturbance dominates the lacustrine record

benchmarking lava flow models prediction of the emplacement of volcanic mass flows lava flows pyroclastic density currents debris avalanches and debris flows is required for hazard and risk assessment and for the planning of risk mitigation measures numerical computer based models now exist that are capable of approximating the motion of a given volume of volcanic material from its source to the deposition area with these advances in technology it is useful to compare the various codes in order to evaluate their respective suitability for real time forecasting risk preparedness and post eruptive response a benchmark compares codes or methods all aimed at simulating the same physical process using common initial and boundary conditions and outputs but using different physical formulations mathematical approaches and numerical techniques we set up the basis for a future general benchmarking exercise on volcanic mass flow models and more specifically establish a benchmark series for computational lava flow modelling we describe a set of benchmarks in this paper and present a few sample results to demonstrate output analysis and code evaluation methodologies the associated web based communal facility for sharing test scenarios and results is also described

a gigantic bezymianny type event at the beginning of modern volcan popocatepetl the history of volcan popocatepetl can be divided into two main periods the formation of a large primitive volcano approximatively 30 km wide on which is superimposed a modern cone 6 8 km in diameter and 1700m high a major event of bezymianny type marks the transition between these two dissimilar periods the activity of the primitive volcano was essentially effusive and lasted several hundred thousands of years the total volume of products ejected by the volcano is of the order of 500 600 km3 its last differentiated magmas are dacitic a gigantic debris flow d f spread on the southern side is related to the bezymianny type event which destroyed the summit area of the ancient edifice an elliptical caldera 6 5 11 km wide was formed by the landslide its deposits with a typical hummocky surface cover 300 km2 for a volume of 28 30 km3 numerous outcrops belonging to this debris flow show slabs of more or less fractured and dislocated rocks that come from the primitive volcano these deposits are compared to two studied debris flows of similar extent and volume the mount shasta and colima s d f this eruption takes a major place in the volcanologic and magmatic history of popocatepetl pyroclastic products of surge type with laminites and crude layers ashflows and pumiceous airfall layers are directly related to this event and begin the history of the modern volcano probably less than 50 000 years ago in addition a second andesitic and dacitic phase rose both from the central vent forming the basis of modern popo and from lateral vents the terminal cone is characterized by long periods of construction by lava flows alternating with phases of destruction the duration of these episodes being 1000 to 2000 years the cone is composed of two edifices the first volcan el fraile began with effusive activity and was partly destroyed by three periods of intense explosive activity the first period occurred prior to 10 000 years b p the second from 10 000 to 8000 years b p and the third from 5000 to 3800 years b p each period of destruction shows cycles producing collapsing pyroclastic flows or nuees of the st vincent type related to the opening of large craters plinian air fall deposits and minor lava flows the second edifice the summit popo produced lava flows until 1200 years b p and since that time entered into an explosive period two cataclysmic episodes each including major pyroclastic eruptions occurred 1200 and 900 1000 years ago during the pre hispanic and historic times effusive activity was restricted entirely to the summit area alternating with plinian eruptions nevertheless despite the quiet appearance of the volcano the last period of pyroclastic activity which started 1200 years ago may not have ended and can be very dangerous for the nearby populations

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

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

isothermal dynamics of channeled viscoplastic lava flows and new methods for estimating lava rheology 1 this study analyses the influence of a viscoplastic lava rheology on the dynamics of lava flows using a multigrid based augmented lagrangian scheme we find a numerical solution for the flow of a bingham fluid in a rectangular channel the numerical results show that an internal viscoplastic rheology significantly modifies the velocity distribution within a lava flow through the development of plug regions whose size is determined by the magnitude of the yield strength the flow rate maximum surface velocity and central plug dimensions are determined as functions of the channel geometry and fluid rheology and comparisons between these and several limiting analytical solutions confirm the accuracy of the numerical method used the results are also compared to incorrect models which have been proposed previously in the literature several algorithms that extend the results to different sets of measured initial parameters are outlined these calculate 1 the flow depth when the fluid rheology viscosity and yield strength and downstream flow rate are given 2 the flow depth when the fluid rheology and maximum downstream surface velocity are given 3 the flow rate and fluid rheology when the flow depth maximum surface velocity and surface plug width are given and 4 the flow depth and rheology when the flow rate maximum surface velocity and surface plug width are given the use of these algorithms is demonstrated by considering the dynamics of a typical lava flow on mount etna using measured rheological parameters and field observations

emplacement of the youngest flood lava on mars a short turbulent story abstract recently acquired data from the high resolution imaging science experiment hirise context ctx imager and compact reconnaissance imaging spectrometer for mars crism onboard the mars reconnaissance orbiter mro spacecraft were used to investigate the emplacement of the youngest flood lava flow on mars careful mapping finds that the athabasca valles flood lava is the product of a single eruption and it covers 250 000 km 2 of western elysium planitia with an estimated 5000 7500 km 3 of mafic or ultramafic lava calculations utilizing topographic data enhanced with mro observations to refine the dimensions of the channel system show that this flood lava was emplaced turbulently over a period of only a few to several weeks this is the first well documented example of a turbulently emplaced flood lava anywhere in the solar system however mro data suggest that this same process may have operated in a number of martian channel systems the magnitude and dynamics of these lava floods are similar to the aqueous floods that are generally believed to have eroded the channels raising the intriguing possibility that mechanical erosion by lava could have played a role in their incision

solidification dynamics in channeled viscoplastic lava flows 1 the influence of a viscoplastic lava rheology on the dynamics of channeled lava flows is analyzed using analogue experiments the experiments used slurries of polyethylene glycol and kaolin which flowed with a constant flux down an inclined channel under water three sets of complementary experiments are presented isothermal cooling and solidifying flows which quantified the effects of the viscoplastic rheology on shear internal convection and surface crust formation the isothermal and cooling experiments showed the formation of unyielded central plug regions which were not broken up by the convective overturning in the solidifying experiments flows fell into one of three regimes a tube regime in which crust covered the entire flow surface a shear controlled regime with a mobile raft of crust in the channel center and open shear zones near the walls and a plug controlled regime where the width of the central crust was determined by the width of the central plug region the crust coverage is parameterized in terms of two dimensionless parameters the ratio wp of central plug region width to channel width and a parameter which characterizes the relative importance of the strain and solidification rates finally the dynamics of typical lava flows on mt etna and the 1984 mauna loa lava flow are examined we show that our parameterization agrees with lava flow crust widths observed in the field and find that even small yield strengths have a major effect on crust coverage

rheology of a long lava flow at pavonis mons mars 1 dimensions of lava flows can be used to unravel the relative roles of viscosity changes and concurrent formation of levees stationary margins and stagnant zones this approach is applied to data derived from the mars orbiter laser altimeter mola experiment for a long lava flow on the plains north of pavonis mons mars we obtain a formula for the relative change in viscosity on the basis of a steady state newtonian flow rate our approach features a new length scale that describes the transfer of lava from the active advancing component to passive components this length scale can be determined from planetary image and topographic data by estimating the volume fraction of lava contained in flow margins relative to the total flow volume we find only modest changes in viscosity over the distal 175 km of the pavonis flow allowing the flow to also lose volume through degassing resulting in a density increase does little to affect the overall viscosity change thickening and widening of the flow with distance are as expected for a single coherent isothermal viscous flow this dynamic regime features a balance between the formation of an outer skin and shedding of lava into stationary zones requirements for attaining such a regime include a thick flow shallow slopes over extended distances and preexisting surface roughness that is small compared to flow thickness this style of emplacement may explain why many of the long thick sheet like flows on the plains of mars often exhibit an unexpected lack of thickening with distance

a laboratory investigation into the effects of slope on lava flow morphology abstract in an attempt to model the effect of slope on the dynamics of lava flow emplacement four distinct morphologies were repeatedly produced in a series of laboratory simulations where polyethylene glycol peg was extruded at a constant rate beneath cold sucrose solution onto a uniform slope which could be varied from 1 through 60 the lowest extrusion rates and slopes and highest cooling rates produced flows that rapidly crusted over and advanced through bulbous toes or pillows similar to subaerial toey pahoehoe flows and to submarine pillowed flows as extrusion rate and slope increased and cooling rate decreased pillowed flows gave way to rifted flows linear zones of liquid wax separated by plates of solid crust similar to what is observed on the surface of convecting lava lakes then to folded flows with surface crusts buckled transversely to the flow direction and at the highest extrusion rates and slopes and lowest cooling rates to leveed flows which solidified only at their margins a dimensionless parameter primarily controlled by effusion rate cooling rate and flow viscosity quantifies these flow types increasing the underlying slope up to 30 allows the liquid wax to advance further before solidifying with an effect similar to that of increasing the effusion rate for example conditions that produce rifted flows on a 10 slope result in folded flows on a 30 slope for underlying slopes of 40 however this trend reverses slightly owing to increased gravitational forces relative to the strength of the solid wax because of its significant influence on heat advection and the disruption of a solid crust slope must be incorporated into any quantitative attempt to correlate eruption parameters and lava flow morphologies these experiments and subsequent scaling incorporate key physical parameters of both an extrusion and its environment allowing their results to be used to interpret lava flow morphologies on land on the sea floor and on other planets

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

morphology of basaltic lava channels during the mt etna september 2004 eruption from airborne laser altimeter data 1 the morphological features of active lava channels acquired over mt etna by means of airborne laser altimeter data are presented the data were acquired on 16th september 2004 using an optech altm 3033 laser altimeter the flight height was about 2000 m above ground during the flight the lava erupted from the eastern part of the mt etna summit area flowed into the valle del bove the measured morphologic features are channel width wc flow width wf levee height hl flow thickness tf and channel depth dc the main lava flow shows a well developed channel with levees the average measured values for the morphologic features of this flow are wc 16 m wf 52 m hl 7 m tf 5 m and dc 2 m the wc parameter shows linear increase from about 7 m near the vent up to about 25 m close to the front 1600 m in length

tephra geochemistry a discussion of some persistent analytical problems distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation this quantitation can involve difficulties not often encountered in more conventional petrology solving these problems is of particular importance in the holocene and late quaternary of northwest europe where numerous tephra layers of icelandic origin have been detected in peat bogs and lake and marine sediments electron probe microanalysis epma has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis standard epma techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature in many previous studies geochemical data of avoidably low quality have been produced and little attention appears to have been directed to modification of epma methods it is suggested that the black box approach to geochemical analysis should be avoided by the consideration of several factors these include

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

standing waves in high speed lava channels a tool for constraining lava dynamics and eruptive parameters abstract estimates of the rheological properties of lava flows are essential for understanding their emplacement and for hazard assessment despite being a well known phenomenon in water hydraulics the formation and presence of standing waves in lava channels is poorly understood standing waves generally located near the vent area have been frequently described at high speed channelized lava flows they are interpreted as hydraulic jumps indicating a flow under supercritical conditions identifying standing waves therefore offers an opportunity to apply open channel hydraulic theory for supercritical flows in order to determine important eruption parameters such as discharge rate and apparent viscosity we use the length and amplitude of standing waves to reconstruct flow dynamics from both observational data and video analysis the geometry of these standing waves allows us to extract the physical properties of the channelized lava velocity discharge rate apparent viscosity to estimate the channel depth and constrain the flow regime with the rapid advances in technology scientists can deploy equipment to enable low cost real time monitoring of these phenomena and constrain eruption discharge rate and apparent viscosity key parameters for volcanic hazard assessment and mitigation

uav based remote sensing surveys of lava flow fields a case study from etna s 1974 channel fed lava flows during an eruption time scales of topographic change are fast and involve vertical and planimetric evolution of millimeters to meters as the event progresses repeat production of high spatial resolution terrain models of lava flow fields over time scales of a few hours is thus a high value capability in tracking the buildup of the deposit among the wide range of terrestrial and aerial methods available to collect such topographic data the use of an unmanned aerial vehicle uav as an acquisition platform together with structure from motion sfm photogrammetry has become especially useful this approach allows high frequency production of centimeter scale terrain models over kilometer scale areas including dangerous and inaccessible zones with low cost and minimal hazard to personnel this study presents the application of such an integrated uav sfm method to generate a high spatial resolution digital terrain model and orthomosaic of mount etna s january february 1974 lava flow field the sfm method applied to images acquired using a uav platform enabled the extraction of a very high spatial resolution 20 cm digital elevation model and the generation of a 3 cm orthomosaic covering an area of 1 35 km2 this spatial resolution enabled us to analyze the morphology of sub meter scale features such as folds blocks and cracks over kilometer scale areas the 3 cm orthomosaic allowed us to further push the analysis to centimeter scale grain size distribution of the lava surface using these data we define three types of crust structure and relate them to positions within a channel fed a flow system these crust structures are i flow parallel shear lines ii raft zones and iii folded zones flow parallel shear lines are found at the channel edges and are 2 m wide and 0 25 m deep zones running along the levee base and in which cracking is intense they result from intense shearing between the moving channel lava and the static levee lava in zones where initial levees are just beginning to form these subtle features are the only marker that delimits the moving lava from the stagnant marginal lava rafts generally form as the system changes from a stable to a transitional channel regime over this 170 m long zone the channel broadens from 8 to 70 m and rafts are characterized by topographically higher and poorly cracked areas surrounded by lower heavily cracked areas we interpret the rafts as forming due to breakup of crust zones previously moving in a coherent manner in the narrow proximal channel reach folded zones involve arcuate cross flow ridges with their apexes pointing down flow where ridges have relatively small clasts and depressions are of coarser grained breccia our folds have wavelengths of 10 m and amplitudes of 1 m are found towards the flow front down flow of the raft zones and are associated with piling up of lava behind a static or slowly moving flow front the very high spatial resolution topographic data available from uav sfm allow us to resolve surfaces where roughness has a vertical and horizontal scale of variation that is less than 1 m this is the case over p hoehoe and a flow surfaces and thus allows us to explore those new structures that are only apparent in the sub metric data moreover during future eruptions the possibility to acquire such information in near real time will allow a prompt analysis of developing lava flow fields and structures therein such as developing lava channel systems so as to contribute to timely hazard assessment modeling and projections

palaeolandforms and volcanic impact on the environment of prehistoric cuicuilco southern mexico city abstract the pedregal lava field covers an area of 80 km 2 in the southern basin of mexico and includes the cuicuilco archaeological site cuicuilco is considered an early urban centre in the basin of mexico constructed during the late preclassic a few centuries bc and abandoned at the beginning of the first millenium ad three new radiocarbon ages together with reinterpretation of previous ages and detailed analyses of the slopes of the cuicuilco s pyramid support the hypothesis that cuicuilco was abandoned long before the xitli eruption xitli lavas followed several river valleys damming some and causing them to silt up magdalena xocotitla puente volado and chicuautitla rivers subsequently deflecting the old drainage from lake xochimilco to lake texcoco upper and lower piedmont and river landscapes are reconstructed on the basis of soil characteristics and lithostratigraphic units palaeolandforms suggest an agricultural environment prior to the xitli eruption

late quaternary lacustrine paleoenvironments in the cuenca de mexico abstract a late quaternary paleolimnological history from the mexican highlands has been obtained by diatom analysis of short cores and stratigraphic sections of lake and marsh sediments from the cuenca de mexico the large endorheic graben basin that holds mexico city the records dated by radiocarbon and tephrochronologic methods extend back to about 30 ka bp and document the presence of extensive saline lakes in the basin until 25 ka bp thereafter lake levels fell and marginal sites became shallow and fresh under the influence of surficial drainage and especially spring discharge a shallow saline lake existed 18 ka bp in texcoco the central and lowest basin in the system reflecting moderately increased effective moisture at that time by 16 ka bp lake texcoco had become so shallow that diatoms were no longer preserved however marginal sites nourished by spring flow recorded changes in the local hydrologic balance resulting from increased infiltration at higher elevations these changes appear to coincide with glacial advances between about 14 and 10 ka bp on the volcanic mountains surrounding the basin dry climates with reduced infiltration characterized the early holocene but by 5 ka bp a modest increase in precipitation established the modern climatic regime these lacustrine records offer important insights for evaluating the paleoenvironmental history of the cuenca de mexico based on other evidence they confirm glaciological stratigraphic and palynologic data that suggest dry climates and the absence of large pluvial lakes in the cuenca de mexico during and after the full glacial but document climates of significantly increased precipitation at least 10 ka prior to 18 ka bp

viscous newtonian laminar flow in a rectangular channel application to etna lava flows we introduce a 3d model for near vent channelized lava flows we assume the lava to be an isothermal newtonian liquid flowing in a rectangular channel down a constant slope the flow velocity is calculated with an analytical steady state solution of the navier stokes equation the surface velocity and the flow rate are calculated as functions of the flow thickness for different flow widths and the results are compared with those of a 2d model for typical etna lava flow parameters the influence of levees on the flow dynamics is significant when the flow width is less than 25 m the model predicts the volume flow rate corresponding to the surface velocity taking into account that both depend on flow thickness the effusion rate is a critical parameter to evaluate lava flow hazard we propose a model to calculate the effusion rate given the lava flow width the topograhic slope the lava density the surface flow velocity and either the lava viscosity or the flow thickness

one two and three phase viscosity treatments for basaltic lava flows 1 lava flows comprise three phase mixtures of melt crystals and bubbles while existing one phase treatments allow melt phase viscosity to be assessed on the basis of composition water content and or temperature two phase treatments constrain the effects of crystallinity or vesicularity on mixture viscosity however three phase treatments allowing for the effects of coexisting crystallinity and vesicularity are not well understood we investigate existing one and two phase treatments using lava flow case studies from mauna loa hawaii and mount etna italy and compare these with a three phase treatment that has not been applied previously to basaltic mixtures at etna melt viscosities of 425 30 pa s are expected for well degassed 0 1 w h2o and 135 10 pa s for less well degassed 0 4 wt h2o melt at 1080 c application of a three phase model yields mixture viscosities 45 crystals 25 35 vesicles in the range 5600 12 500 pa s this compares with a measured value for etnean lava of 9400 1500 pa s at mauna loa the three phase treatment provides a fit with the full range of field measured viscosities giving three phase mixture viscosities upon eruption of 110 140 pa s 5 crystals no bubble effect due to sheared vesicles to 850 1400 pa s 25 30 crystals 40 60 spherical vesicles the ability of the three phase treatment to characterize the full range of melt crystal bubble mixture viscosities in both settings indicates the potential of this method in characterizing basaltic lava mixture viscosity

dynamics and viscosity of a a and pahoehoe lava flows of the 2012 2013 eruption of tolbachik volcano kamchatka russia the 2012 2013 flank eruption of tolbachik volcano kamchatka lasted 9 months and produced 0 54 km3 of basaltic trachyandesite lava thus becoming one of the most voluminous historical lava effusions of basic composition in subduction related environments globally from march to july 2013 the volcano monotonously erupted lava of constant composition sio2 52 wt with a nearly stable effusion rate of 18 m3 s despite the uniform eruptive and emplacement conditions the dominant style of lava propagation throughout that time gradually changed from a a to pahoehoe we report results of instrumental field measurements of the a a and pahoehoe flow dynamics documented with time lapse cameras as well as the lava viscosity determined by flow rate and shear stress using penetrometer methods maximal propagation velocities of the a a fronts ranged from 2 to 25 mm s and those of the pahoehoe from 0 5 to 6 mm s the flow front velocities of both lava types experienced short period fluctuations that were caused by complex flow mechanics of the advancing flow lobes minimal viscosities of lava of the a a lobes ranged from 1 3 105 to 3 3 107 pa s flow rate method and those of the pahoehoe from to 5 103 to 5 104 pa s shear stress method our data include the first ever measured profiles of viscosity through the entire thickness of actively advancing pahoehoe lava lobes we have found that both the a a and pahoehoe flows were fed by identical parental lava which then developed contrasting rheological properties owing to differences in the process of lava transport over the ground surface the observed transition from the dominant a a to the dominant pahoehoe propagation styles occurred due to gradual elongation and branching of the lava tube system throughout the course of the eruption such evolution became possible because the growing lava field composed of semisolidified flows provided an environment for shallow subsurface intrusions and internal migrations of lava that with time developed into branches of the lava tube system based on our data we propose phenomenological models of the a a and pahoehoe flow mechanics

petrology of the younger andesites and dacites of iztaccihuatl volcano mexico i disequilibrium phenocryst assemblages as indicators of magma chamber processes

paving the seafloor volcanic emplacement processes during the 2005 2006 eruptions at the fast spreading east pacific rise 9 50 n 1 the 2005 2006 eruptions near 9 50 n at the east pacific rise epr marked the first observed repeat eruption at a mid ocean ridge and provided a unique opportunity to deduce the emplacement dynamics of submarine lava flows since these new flows were documented in april 2006 a total of 40 deep towed imaging surveys have been conducted with the woods hole oceanographic institution s whoi towcam system more than 60 000 digital color images and high resolution bathymetric profiles of the 2005 2006 flows from the towcam surveys were analyzed for lava flow morphology and for the presence of kipukas collapse features faults and fissures we use these data to quantify the spatial distributions of lava flow surface morphologies and to investigate how they relate to the physical characteristics of the ridge crest such as seafloor slope and inferred dynamics of flow emplacement we conclude that lava effusion rate was the dominant factor controlling the observed morphological variations in the 2005 2006 flows we also show that effusion rates were higher than in previously studied eruptions at this site and varied systematically along the length of the eruptive fissure this is the first well documented study in which variations in seafloor lava morphology can be directly related to a well documented ridge crest eruption where effusion rate varied significantly

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

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

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

non newtonian viscosity of basaltic magma 1 basaltic melt drives most of earth s volcanism understanding its rheology is crucial for any model of magma transport and volcanic eruption basaltic magma is generally treated as a quasi newtonian liquid but there are observations of non newtonian behaviour with a method that allows measurement of non newtonian viscosity of a representative melt molten basaltic rock we found a strong shear rate dependency of viscosity in a wide range of temperatures the temperature viscosity dependency indicates properties of the molten phase as the cause the viscosity data are in good agreement with a power law model

the effect of confining boundaries on viscous gravity currents newtonian viscous gravity currents propagating along horizontal and inclined channels with semicircular and v shaped boundaries are examined similarity solutions are obtained from the governing mathematical equations and compared with closely matching data from laboratory experiments in which the propagation of glycerine along different channels was recorded geological applications of the results are discussed briefly

the influence of cross sectional channel geometry on rheology and flux estimates for active lava flows lava rheology and effusion rate are critical factors in determining the evolution of lava flows however direct and accurate field measurements are difficult to carry out and estimates are usually based on measurements of the flow s surface velocity and assumptions of sub surface geometry using numerical flow models we show that the potential for error due to geometry uncertainty is minimized if a semi elliptical cross sectional channel shape is assumed flow is simulated for isothermal newtonian temperature dependent newtonian and isothermal power law rheology lavas for isothermal newtonian lava we find that the error in channel shape alone can make apparent viscosity estimates 3 5 times too large e g for inappropriate use of the jeffreys equation on a narrow semi elliptical channel for a temperature dependent rheology using an analytical approximation for newtonian flow in a semi elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry for all channel shapes considered including rectangular channels viscosity calculations for real channels on mauna loa and mount etna show that for a newtonian rheology a semi elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while if the lava is shear thinning power law exponent m 0 6 a rectangular approximation is 15 more accurate our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained

channeled flow analytic solutions laboratory experiments and applications to lava flows although channeled lava flows are common in basaltic volcanism relationships between channel morphology eruption and emplacement parameters and lava properties are not well understood several models have commonly been used to constrain these relations but they have not been well tested on natural or simulated lava flows over a wide range of parameter space here we test the accuracy and assumptions of a moderately simple analytic rectangular channel solution by comparing the behavior of well controlled laboratory polyethylene glycol peg channeled flows to the analytic solution for isothermal steady newtonian flow in a rectangular channel with constant dimensions this analytic solution agrees well with laboratory measurements volumetric effusion rates q m3 s 1 calculated from the analytical model using measured peg flows as input yield ratios of qcalculated qpumped of 0 2 to 3 6 and flow rates calculated from a best fit surface velocity profile to measured velocities give more accurate ratios of 0 8 to 1 2 we find a very weak dependence of solution accuracy on slope attributable to flow front effects within the laboratory flows we subsequently apply the solution to several subaerial and submarine terrestrial flows as well as extraterrestrial channeled flows over a wide range of flow parameters viscosity ranges and flow rates obtained using measured channel dimensions and assumed lava properties are plausible interestingly the resulting extraterrestrial estimates of viscosities and flow rates tend to fall closer to known terrestrial measurements and estimates of channel flow than to previous planetary estimates we therefore suggest that the analytic newtonian rectangular channel flow model is a more appropriate physical model for many channeled terrestrial and planetary flows than the newtonian infinite sheet flow and approximation to bingham channel flow widely used previously

geochemical characterization of late pleistocene and holocene tephra layers from the basin of mexico central mexico in order to aid palaeoenvironmental research of late pleistocene and holocene deposits of central mexico tephra layers collected from the sediments of the texcoco and chalco sub basins in the southern part of the basin of mexico are geochemically characterized and used as stratigraphic markers the tephra layers range in composition from basaltic andesites to rhyolites and are calc alkaline the tephras range in age from 34 000 to ca 260014c yr b p new names are used informally to designate correlated tephras the tlahuac tephra is present in chalco at a depth of 18 m in the southeastern part of texcoco at a depth of around 10 m and at the tlapacoya archaeological site where it had been mistakenly described as basaltic this basalt andesite tephra is dated to at least 34 00014c yr b p the tlapacoya 1 tephra is dated to between 15 020 450 and 14 430 190 yr b p and is present in all chalco sections the tlapacoya 2 tephra corresponds to the previously described pomez gruesa con fragmentos de andesita ca 14 400 yr b p and is present in all chalco and texcoco sections the likely source of these three tephras is the volcano popocatepetl tephra ii at chalco dates to 12 520 135 yr b p and correlates with the upper toluca pumice from nevado de toluca volcano these represent the first geochemical glass shard analysis of tephras from the basin of mexico and so further research is necessary before a reliable tephrochronology can be established

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

the emplacement of pahoehoe toes field observations and comparison to laboratory simulations we observed active pahoehoe lobes erupted on kilauea during may june 1996 and found a range of emplacement styles associated with variations in local effusion rate flow velocity and strain rate these emplacement styles were documented and quantified for comparison with earlier laboratory experiments at the lowest effusion rates velocities and strain rates smooth surfaced lobes were emplaced via swelling where new crust formed along an incandescent lip at the front of the lobe and the rest of the lobe was covered with a dark crust at higher effusion rates strain rates and velocities lobes were emplaced through tearing or cracking tearing was characterized by ripping of the ductile crust near the initial breakout point and most of the lobe surface was incandescent during its emplacement this mechanism was observed to generate both smooth surfaced lobes and when the lava encountered an obstacle folded lobes cracking lobes were similar to those emplaced via tearing but involved breaking of a thicker brittle crust at the initial breakout of the lobe and therefore required somewhat higher flow rates than did tearing cracking lobes typically formed ropy folds in the center of the lobe and smooth margins at the highest effusion rates strain rates and flow velocities the lava formed open channels with distinct levees the final lobe morphologies were compared to results from laboratory simulations which were designed to infer effusion rate from final flow morphology to quantitatively test the laboratory results on the scale of individual natural pahoehoe lobes there is general agreement between results from laboratory simulations and natural lavas on the scale of individual pahoehoe lobes but there are disparities between laboratory flows and lava flows on the scale of an entire pahoehoe lava flow field