spaceborne imaging radar c sir c observations of groundwater discharge and wetlands associated with the chicxulub impact crater northwestern yucatan peninsula mexico analyses of spaceborne imaging radar c sir c data and field data from the northwestern yucatan peninsula mexico demonstrate that spaceborne multifrequency polarimetric radars are excellent tools for characterizing patterns of wetland flooding seasonal flooding can be detected in most types of forest and marsh in the radar backscatter magnitude and phase data of both l and c band field observations made in the wet and dry seasons concurrent with the space missions and chemical analyses of floodwaters confirm that flooding is the product of discharge from the yucatan aquifer which consists of a fresh water lens floating on seawater this discharge controls the distribution of wetlands therefore vegetation and flooding patterns mapped with sir c imagery provide valuable information on the hydrogeology of the region radar image maps of wetlands and flooding indicate that there are three major zones of groundwater discharge that correlate with structures of the buried chicxulub crater zone 1 with the peak ring zone 2 with the crater rim and zone 3 with the exterior ring zone 1 has sulfate poor discharge unlike the sulfate rich discharge in zones 2 and 3 the highest discharge is in zone 3 where the buried crater is closest to the surface this groundwater discharge pattern can be explained by tidal pumping of fresh water to the surface through high permeability zones developed in the tertiary carbonates overlying crater faults and escarpments

volcanology of arnus vallis mars abstract arnus vallis av is a 300 km long sinuous rille located on the northeastern flank of the syrtis major volcano on mars observational evidence presented here suggests that av formed as an open lava channel that was at least partly incised into the pre existing terrain the lava source area consists of a sub circular pit at the southwestern end of a 7 km long straight section of channel av trends down slope from this source with an average bottom slope of 0 26 or 0 14 width varies from 1 km at the source to 0 6 km near the distal end with a mean of 0 76 km depth decreases from 180 m at the source to 25 m near the distal end the av terminus is obscured by a large impact crater we suggest that the material that flowed in av must have been a relatively high temperature low viscosity lava dynamically and perhaps compositionally similar to terrestrial komatiite or some lunar basalt lavas if correct this finding has implications for the mode of construction of syrtis major

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

acoustic backscattering from the basin and margins of the arctic ocean sound waves created by high energy explosives were used to measure reverberation and backscattering in the arctic ocean from an ice camp in the beaufort sea signals were backscattered from the continental margin and other major features of the basin an acoustic array was used to analyze the signals in azimuth based on these data we constructed charts of normalized backscatter level which can be compared with known topography of the arctic ocean resolution of this remote sensing technique for our experimental conditions analysis frequency 9 hz averaging time 20 s array size 600 600 m is about 8 in azimuth 15 km in radial extent and 1 km in depth we obtained interpretable signals out to 2700 km for 1000 km or less the backscatter charts provide continuous coverage of the margins and major submerged features strong returns from about 73 2 n 139 0 w indicate one or more prominent features that many contemporary topographic charts do not show but which we believe to be real other strong returns are evident from the northwind escarpment and from the continental slopes of alaska and the canadian archipelago via a backscatter model we estimate the roughness product rms height times correlation radius of these features to be about 4500 m2 on average

forest canopy characterization and vegetation penetration assessment with space borne radar synthetic aperture radar sar images from the national aeronautics and space administration s shuttle imaging radar b sir b mission were used to analyze the effects of radar incidence angle on information content and vegetation penetration three sar data sets using incidence angles of 26 46 and 58 were acquired over the mangrove jungles of southern bangladesh the data sets were digitally processed using 3 3 7 7 and 11 11 spatial filters and geometrically registered to a multisource multilevel corraborative data base consisting of landsat data forest map data and in situ acquired forest enumeration and topographic information analyses revealed that significant vegetation penetration was found at all angles and that tree and canopy structural morphology may exert an influence on this phenomenon

unusual features of negative leaders development in natural lightning according to simultaneous records of current electric field luminosity and high speed video the development of downward and upward leaders that formed two negative cloud to ground return strokes in natural lightning spaced only about 200 s apart and terminating on ground only a few hundred meters away was monitored at morro do cachimbo station brazil the simultaneous records of current close electric field relative luminosity and corresponding high speed video frames sampling rate of 20 000 frames per second reveal that the initiation of the first return stroke interfered in the development of the second negative leader leading it to an apparent continuous development before the attachment without stepping and at a regular two dimensional speed based on the experimental data the formation processes of the two return strokes are discussed and plausible interpretations for their development are provided

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

a quantitative approach for evaluating lava flow simulation reliability lavasim code applied to the 2001 etna eruption an edited version of this paper was published by agu copyright 2009 american geophysical union

strokes of upward illumination occurring within a few milliseconds after typical lightning return strokes 1 correlated data for natural cloud to ground lightning flashes were obtained with a high speed video camera 54000 frames per second five stations of electric field change antennas and a seven station vlf lf lightning network linet along with operational lightning and electric field networks at kennedy space center florida four observed flashes at 25 55 km distance had return stroke like upward illumination ui from the ground just after within 2 ms of a return stroke rs but in a separate channel connection to ground 0 7 to 2 5 km apart the ui events were visible for short duration 0 5 ms or less and short length to 1 7 km altitude or less and they had slow propagation speed 1 6 2 6 107 m s 1 and no apparent connection to the rs channel in one case the rs was no longer visible to the ground when the ui began 1 30 ms later although mid level channel was still distinct in another case the main rs had dimmed over the 0 52 ms interval before the ui but was still visible the remaining two cases had the entire length of the prior rs channel no longer visible for 40 and 240 s before the ui began 1 32 and 1 87 ms later electric field change data for the ui events resemble those of weak return strokes these events were not located by the operational ground strike and vhf detection systems all four ui events were detected by linet as negative ground strokes with small less than 7 ka peak current magnitude

temperature of an active lava channel from spectral measurements kilauea volcano hawaii a narrow band spectroradiometer was used to determine the characteristic temperatures of a very active channeled lava flow for the phase 50 eruption of pu u o o on the east rift zone of kilauea volcano hawaii during the twilight of 19 february 1992 14 spectra of this activity were acquired over a 51 minute interval 18 29 to 19 20 hawaiian standard time hst from which the thermal distribution of energy of two 18 m2 areas one near the center and one near the margin of the flow may be investigated a twocomponent thermal mixing model applied to the data taken of the center of the channel gave in the most powerful instance 1 8x105 w m2 a crust temperature of 940 c a hot component temperature of 1120 c and a hot radiating area of 60 of the total area a simultaneous spectrum acquired near the channeled flow margin yielded a crust temperature of 586 c and a hot area of only 1 2 of the total area radiating at 1130 c average radiant flux densities recorded for the center of the lava channel 1 3x105 w m2 average are much greater than previous measurements of lava lakes 4 9x103 w m2 or recently emplaced lava flows maximum of 7 2x104 w m2 the energetic nature of this eruption is shown by satellite measurements made at 02 33 hst on 22 february 1992 by the advanced very high resolution radiometer in band 2 0 72 1 10 m these show the utility of using existing satellites with moderate resolution 1 km x 1 km pixels and high temporal coverage eight overpasses each day for hawaii as potential thermal alarms for rapidly assessing the hazard potential of large volcanic eruptions

multiscale spectral analysis of bathymetry on the flank of the mid atlantic ridge modification of the seafloor by mass wasting and sedimentation the results of a multiscale spectral analysis of bathymetric data on the flank of the mid atlantic ridge are described data were collected during two cruises using hydrosweep multibeam tens of kilometers to 0 2 km scale range and mesotech scanning pencil beam sonar attached to remotely operated vehicle jason 1 km to 0 5 m scale range these data are augmented by visual data which enabled us to identify bathymetric profiles which are over unsedimented or thinly sedimented crust our analysis therefore is focused primarily on statistical characterization of basement morphology work is concentrated at two sites site b on 24 ma crust in an outside corner setting and site d on 3 ma crust in an inside corner setting at site b we find that an anisotropic band limited fractal model i e the von karman model proposed for abyssal hill morphology by goff and jordan 1988 is not sufficient to describe the full range of scales observed in this study our observations differ from this model in two ways 1 strike and cross strike dip spectral properties converge for wavelengths smaller than 300 m and 2 in both strike and dip directions the fractal dimension changes at 10 m wavelength from 1 27 at larger scales to 1 0 at smaller scales the convergence of strike and dip spectral properties appears to be associated with destruction of ridge parallel fault scarps by mass wasting which develops canyon like incisions that cross scarps at high angles the change in fractal dimension at 10 m scale appears to be related to a minimum spacing of significant slope breaks associated with scarps which are created by faulting and mass wasting at site d although there is no significant abyssal hill anisotropy the spectral properties at all scales are consistent with the von karman model the fractal dimension at this site 1 15 is less than at site b this difference may be reflect different morphology related to crustal formation at inside corner versus outside corner position or more likely differences in the degree of mass wasting the smoothing of seafloor morphology by sediments is evident in hydrosweep periodograms where relative to basement roughness spectral power decreases progressively with decreasing wavelength

the influence of topographic roughness on lava flow emplacement a quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions the influence of topography with a vertical amplitude smaller than flow thickness i e substrate roughness is currently not accounted for in most flow emplacement models and hazard estimates here we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt complementing recent work on the interaction of lava flows with obstacles taller than flow thickness we present results from three sets of analog experiments in which corn syrup polyethylene glycol and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes we find that flow front advance rates are impacted by bed roughness for all materials with decreases in average velocities by up to 50 with increases of substrate grain sizes by 5 100 times ranges analogous with topographic variations found in nature these decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity we interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area the difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established additionally the experimental flow geometry measured by the complexity of the flow external perimeter became increasingly complex with increasing substrate grain size this effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces we propose that flow emplacement models should be modified possibly through a calibrated effective viscosity term to account for bed roughness to increase accuracy in flow prediction and hazard estimation models

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

simulating the thermorheological evolution of channel contained lava flowgo and its implementation in excel flowgo is a one dimensional model that tracks the thermorheological evolution of lava flowing down a channel the model does not spread the lava but instead follows a control volume as it descends a line of steepest descent centred on the channel axis the model basis is the jeffreys equation for newtonian flow modified for a bingham fluid and a series of heat loss equations adjustable relationships are used to calculate cooling crystallization and down channel increases in viscosity and yield strength as well as the resultant decrease in velocity here we provide a guide that allows flowgo to be set up in excel in doing so we show how the model can be executed using a slope profile derived from google tm earth model simplicity and ease of source term input from google tm earth means that this exercise allows i easy access to the model ii quick global application and iii use in a teaching role output is tested using measurements made for the 2010 eruption of piton de la fournaise la reunion island the model is also set up for rapid syneruptive hazard assessment at piton de la fournaise as we show using the example of the response to the june 2014 eruption

estimation of bottom scattering characteristics from acoustic reverberation special research program bistatic data for many years sonar practitioners have used lambert s law on a flat bottom to describe clutter due to bottom reverberation this examination of a subset of the bistatic data from the b site of the arsrp natural laboratory examines the validity of this approximation eight pings transmitted by the cory chouest and received by the alliance were chosen to cover the bistatic angular range of 90 to 90 deg with respect to b transmission loss and area corrections to a flat bottom of representative depth were calculated using the artist ray tracing program these corrections were applied to the data to compute scattering strength in each beam time bin this scattering strength was averaged over areas with similar grazing angle to transmitter grazing angle to receiver and bistatic angle again these are angles to a flat bottom scenario the scattering strength plotted versus these three angles shows that neither lambert s law nor the generalized version by nayar et al describe bistatic scattering resea

three dimensional imaging of upward positive leaders in triggered lightning using vhf broadband digital interferometers 1 upward positive leaders upls in two artificially initiated lightning flashes were imaged in three dimensions using vhf broadband digital interferometers and a high speed video camera with time synchronized channel base current measurements locatable vhf sources of the two upls began at 1 1 km and 1 5 km a few milliseconds after the upl inception and ascended to 2 4 km and 3 7 km respectively with average 3 d speeds on the order of 106 ms 1 the initial stage currents for both flashes were unusually large and had peak values of 6 ka and 18 ka vhf sources associated with positive leader propagation were located when the average current was higher than 3 ka and had significant pulse activity the source altitudes and channel base currents suggest that there might have been a region of significant negative charge at altitudes from 2 to 4 km which is below the freezing level of typical thunderstorms in florida

deterministic reverberation from ocean ridges the deterministic relationship between low frequency reverberation and detailed geomorphology is documented for wide area insonifications of the western mid atlantic ridge charted reverberation registers precisely with extended ridges and has a high correlation with negative transmission loss confirming previous analysis with lower resolution data j acoust soc am 95 1865 1881 1993 for a given ridge prominent returns come from steep escarpments and cliffs that face the bistatic source and receiving arrays this was hypothesized in the above reference but could not be proven without the higher resolution waveforms and more sophisticated charting procedures of the present analysis monostatic and bistatic returns from the same lineated ridge at 1 2 11 2 and 21 2 convergence zone ranges are used to thoroughly document the registration with steep scarps a decrease in resolution of the scattering site is also documented for increasing measurement range ambiguity from the horizontal receiving array is resolved by two independent methods that show close agreement for prominent returns the first is an environmental symmetry breaking esb technique that requires detailed knowledge of bathymetry to be incorporated into a range dependent propagation model the second is a global inversion of reverberation charts obtained from differing receiving array locations and orientations the global inversion requires no a priori environmental information and has not been previously applied to field data

conclusion recommendations and findings of the red seed working group red seed stands for risk evaluation detection and simulation during effusive eruption disasters and combines stakeholders from the remote sensing modelling and response communities with experience in tracking volcanic effusive events the group first met during a three day long workshop held in clermont ferrand france between 28 and 30 may 2013 during each day presentations were given reviewing the state of the art in terms of a volcano hot spot detection and parameterization b operational satellite based hot spot detection systems c lava flow modelling and d response protocols during effusive crises at the end of each presentation set the four groups retreated to discuss and report on requirements for a truly integrated and operational response that satisfactorily combines remote sensors modellers and responders during an effusive crisis the results of collating the final reports and follow up discussions that have been on going since the workshop are given here we can reduce our discussions to four main findings 1 hot spot detection tools are operational and capable of providing effusive eruption onset notice within 15 min 2 spectral radiance metrics can also be provided with high degrees of confidence however if we are to achieve a truly global system more local receiving stations need to be installed with hot spot detection and data processing modules running on site and in real time 3 models are operational but need real time input of reliable time averaged discharge rate data and regular updates of digital elevation models if they are to be effective the latter can be provided by the radar photogrammetry community 4 information needs to be provided in an agreed and standard format following an ensemble approach and using models that have been validated and recognized as trustworthy by the responding authorities all of this requires a sophisticated and centralized data collection distribution and reporting hub that is based on a philosophy of joint ownership and mutual trust while the next chapter carries out an exercise to explore the viability of the last point the detailed recommendations behind these findings are detailed here

topographic analyses of k lauea volcano hawai i from interferometric airborne radar we analyze digital topographic data collected in september 1993 over a 500 km2 portion of k lauea volcano hawai i by the c band 5 6 cm wavelength topographic synthetic aperture radar topsar airborne interferometric radar field surveys covering an 1 km2 area of the summit caldera and the distal end of an 8 m thick a flow indicate that the 10 m spatial resolution topsar data have a vertical accuracy of 1 2 m over a variety of volcanic surfaces after conversion to a common datum topsar data agree favorably with a digital elevation model dem produced by the u s geological survey usgs with the important exception of the region of the ongoing eruption which postdates the usgs dem this dem comparison gives us confidence that subtracting the usgs data from topsar data will produce a reasonable estimate of the erupted volume as of september 1993 this subtraction produces dense rock equivalent dre volumes of 392 439 and 90 106 m3 for the pu u k pa ianah and episode 50 53 stages of the eruption respectively these are 124 89 and 94 of the volumes calculated by staff of the hawaiian volcano observatory hvo but do not include lava of k pa ianah and episodes 50 53 that flowed into the ocean and are thus invisible to topsar accounting for this lava increases the topsar volumes to 124 159 and 129 of the hvo volumes including the 2 m uncertainty derived from the field surveys produces topsar derived volumes for the eruption as a whole that range between 81 and 125 of the usgs derived values the vesicularity and ocean corrected topsar volumes yield volumetric eruption rates of 4 5 4 5 and 2 7 m3 s for the three stages of the eruption which compare with hvo derived values of 3 6 2 8 and 2 1 m3 s respectively our analysis shows that care must be taken when vertically registering the topsar and usgs dems to a common datum because c band topsar penetrates only partially into thick forest and therefore produces a dem within the tree canopy whereas the usgs dem is adjusted for vegetation

carbonate geochemistry and the concentrations of aqueous mg2 sr2 and ca2 western north coast of the yucatan mexico abstract we have measured concentrations of major cations sr 2 and alkalinity in groundwater pore water and surface water samples collected from the western north coast of the yucatan peninsula mexico thermodynamic calculations indicate that almost all water samples from the study area are supersaturated with respect to calcite aragonite high mg calcite hmc and dolomite analysis of the data suggests that the geochemical processes controlling mg 2 sr 2 and ca 2 concentrations differ in different environments mass balance modeling has been used to calculate the amount of dissolution and or precipitation of aragonite low mg calcite lmc and hmc and or dolomite required to produce waters with the observed mg 2 sr 2 and ca 2 concentrations mass balance calculations indicate that hmc and aragonite are dissolving whereas lmc is precipitating from most groundwater and inland surface waters the chemistry of surface waters from an extensive saline coastal swamp suggests that lmc and aragonite in surficial swamp sediments are converted to hmc or dolomite while swamp pore water chemistry suggests that hmc is dissolving and lmc and aragonite are precipitating in deeper swamp sediments the chemistry of pore waters suggests that they are derived from saline surface waters and that fresh to brackish groundwater from the shallow confined aquifer does not flow into swamp sediments

effusion rate trends at etna and krafla and their implications for eruptive mechanisms abstract using effusion rates obtained from ground and satellite based data we build a data set of 381 effusion rate measurements during effusive activity at etna and krafla between 1980 and 1999 this allows us to construct detailed effusion rate curves for six fissure fed eruptions at etna and krafla and four summit fed eruptions at etna these define two trends type i and ii type i trends have effusion rates that rise rapidly to an initial peak before declining more slowly resulting in an exponential decrease in eruption rate and declining growth in cumulative volume type ii trends are characterised by steady effusion and eruption rates and hence a linear increase in cumulative volume the former is typical of fissure eruptions and can be explained by tapping of an enclosed pressurised system the latter are typical of persistent etnean summit eruptions plus one persistent effusive eruption at stromboli 1985 1986 examined here and can be explained by overflow of the time averaged magma supply we use our effusion rate data to assess the magma balance at etna 1980 1995 and krafla 1975 1984 between 1980 and 1995 etna was supplied at a time averaged rate of 6 8 2 3 m 3 s 1 of which 13 was erupted at krafla 817 30 10 6 m 3 was erupted and intruded during 1975 1984 and the ratio of erupted to intruded volume was 0 3 at etna there is evidence for intrusion of the unerupted magma within and beneath the edifice as well as storage in the central magma column at krafla unerupted magma was intruded into a rift zone but an increasing proportion of the supply was erupted from 1980 onwards a result of the rift zone capacity being reached magma intruded prior to an eruptive event may also be entrained and or pushed out during eruption to contribute to the initial high effusion rate phases of type i events the detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data we look forward to analysing satellite derived effusion rate trends in real time using data from current and soon to be launched sensors

numerical simulation of basaltic lava flows in the auckland volcanic field new zealand implication for volcanic hazard assessment monogenetic volcanic fields such as the auckland volcanic field avf new zealand are common on the earth s surface and are typically dominated by basaltic lava flows up to 10 s of km long in monogenetic volcanic fields located in close proximity to human population and infrastructure lava flows are a significant threat in this study lava flow emplacement conditions for some basaltic eruptions of the avf were reconstructed using the thermo rheological magflow model eight existing lava flows in the avf were simulated using magflow and eruptive volumes measured from light detection and ranging lidar derived digital terrain models dtms fitting the simulations to the dimensions of actual lava flows provides insight into their emplacement mechanisms and conditions such as effusion rate and probable eruption durations by looking at emplacement in different settings the likely magma ascent rate for studied avf eruptions is calculated to have been on the order of 0 1 m s in the avf the typical estimated duration of past lava flows was from a minimum of 2 days for small volume flows such as little rangitoto 0 0015 km3 up to 83 days for large volume flows such as three kings 0 078 km3 the three best fitting simulations were used to establish eruption scenarios for future volcanic hazard mapping for the avf inferences of eruption duration that will be useful for developing realistic emergency management plans and recovery scenarios for this densely populated volcanic field are also provided

mexican site for k t impact crater research throughout the caribbean suggests that the geophysical anomalies in the yucatan first noted by penfield and camargo 1981 and called the chicxulub crater could be the site of the impact purported to have caused the k t extinctions a semicircular ring of sink holes known locally as cenotes which correlates with the geophysical anomalies has been identified and it is argued that the origin of the cenote ring is related to postimpact subsidence of the chicxulub crater rim if there is indeed a crater the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km if confirmed as a site of impact the chicxulub crater would be the largest terrestrial impact crater known which is consistent with the uniqueness of the k t global catastrophe

risk evaluation detection and simulation during effusive eruption disasters lava ingress into a vulnerable population will be difficult to control so that evacuation will be necessary for communities in the path of the active lava followed by post event population infrastructural societal and community replacement and or relocation there is a pressing need to set up a response chain that bridges scientists and responders during an effusive crisis to allow near real time delivery of globally standard products for a timely and adequate humanitarian response in this chain the scientific research groups investigating lava remote sensing and modelling need to provide products that are both useful to and trusted by the crisis response community requirements for these products include a formats that can be immediately integrated into a crisis management procedure and b in an agreed and stable standard a review of current capability reveals that we are at a point where the community can provide such a response as is the aim of the red seed risk evaluation detection and simulation during effusive eruption disasters working group this book is the first production of this group and is intended not only as a directory of current capabilities and operational service providers but also as a statement of intent and need while providing a simulation designed to demonstrate how a truly pan disciplinary response to an effusive crisis could work

potentials for change detection using seasat synthetic aperture radar data the use of synthetic aperture radar sar images for detecting change on the earth s surface is highly dependent on target orientation azimuth angle and sensor depression angle sar data can be used for change detection when consistency is maintained in radar wavelength polarization azimuth directions and off nadir depression angle the interaction of these parameters and the imaged surface for change detection are shown in examples drawn from a los angeles ca b southern florida c imperial valley ca d a desert region west of tucson az and e western kansas sar imagery is used to emphasize the geometric form and roughness of the earth s surface as changes in the roughness of the surface occur over time temporal sar images will indicate those differences several guidelines for change detection studies using imaging radar are derived from the examples

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

high speed video observation of stepwise propagation of a natural upward positive leader using a high speed video camera operated at 150 000 frames per second we have documented the upward propagation of an initial positive leader from a 325 m meteorological tower in beijing the stepwise development of the upward positive leader was clearly revealed during its self sustained propagation toward the cloud base providing the first optical evidence for the stepping processes of a positive leader the leader developed with definitive intermittent pauses and re establishment with abrupt jump of the leader top obvious brush like corona zone emitting outward from the leader top was identified in the frame of stepping and the luminosity waves propagated downward along the already formed channel from the leader top immediately following the stepping indicating that a current wave was generated at the leader top and subsequently traveled down the channel the channel luminosity decreased during the leader pause stage with the corona zone dimmed correspondingly the positive leader experienced an average interstep interval of 61 7 s ranging between 30 s and 120 s and an average 2 d speed of 8 1 104 m s the transient speed of the step jump was estimated to be larger than 7 3 105 m s with an average step length of 4 9 m the need of sufficient positive charge accumulation at the leader top could be the main cause for the stepping characteristics

vhf lightning mapping observations of a triggered lightning flash 1 on 3 august 2010 an extensive lightning flash was triggered over langmuir laboratory in new mexico the upward positive leader propagated into the storm s midlevel negative charge region extending over a horizontal area of 13 13 km and 7 5 km altitude the storm had a normal polarity tripolar charge structure with upper positive charge over midlevel negative charge lightning mapping array lma observations were used to estimate positive leader velocities along various branches which were in the range of 1 3 104 m s 1 slower than in other studies the upward positive leader initiated at 3 4 km altitude but was mapped only above 4 0 km altitude after the onset of retrograde negative breakdown indicating a change in leader propagation and vhf emissions the observations suggest that both positive and negative breakdown produce vhf emissions that can be located by time of arrival systems and that not all vhf emissions occurring along positive leader channels are associated with retrograde negative breakdown

when does the lightning attachment process actually begin high speed video and electric field records of 43 first and 7 new ground termination subsequent strokes in negative lightning flashes obtained at the lightning observatory in gainesville florida were examined eighteen 36 of these strokes exhibited faintly luminous formations flfs below the downward leader tip just prior to the return stroke all the 18 flfs were connected to the strike object on the ground with 14 of them being also in contact with the downward leader tip for 11 located events showing flfs in contact with the downward leader tip the flf 2 d length ranged from 51 to 200 m and the time interval between the end of exposure of the flf frame and the return stroke onset ranged from 42 to 106 s we inferred that the flfs mostly consisted of relatively low conductivity streamers based on the following observations and estimates a the rates at which the 11 flfs were replaced by channels capable of guiding return stroke waves ranged from 0 7 106 m s to 2 2 106 m s which is comparable to leader speeds in virgin air in the same records b the overwhelming majority of downward leaders continued stepping while being connected to ground via flfs c the average electric field along flfs is 1 to 2 orders of magnitude higher than expected for hot leader like channels since in all cases the flf determined the strike point we conclude that its inferred initiation up to a few hundreds of microseconds before the return stroke onset signified the beginning of the lightning attachment process

flood mapping under vegetation using single sar acquisitions abstract synthetic aperture radar sar enables 24 hour all weather flood monitoring however accurate detection of inundated areas can be hindered by the extremely complicated electromagnetic interaction phenomena between microwave pulses and horizontal and vertical targets this manuscript focuses on the problem of inundation mapping in areas with emerging vegetation where spatial and seasonal heterogeneity makes the systematic distinction between dry and flooded backscatter response even more difficult in this context image interpretation algorithms have mostly used detailed field data and reference image s to implement electromagnetic models or change detection techniques however field data are rare and despite the increasing availability of sar acquisitions adequate reference image s might not be readily available especially for fine resolution acquisitions to by pass this problem this study presents an algorithm for automatic flood mapping in areas with emerging vegetation when only single sar acquisitions and common ancillary data are available first probability binning is used for statistical analysis of the backscatter response of wet and dry vegetation for different land cover types this analysis is then complemented with information on land use morphology and context within a fuzzy logic approach the algorithm was applied to three fine resolution images one alos palsar and two cosmo skymed acquired during the january 2011 flood in the condamine balonne catchment australia flood extent layers derived from optical images were used as validation data demonstrating that the proposed algorithm had an overall accuracy higher than 80 for all case studies notwithstanding the difficulty to fully discriminate between dry and flooded vegetation backscatter heterogeneity using a single sar image this paper provides an automatic data parsimonious algorithm for the detection of floods under vegetation

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

upward lightning observations from towers in rapid city south dakota and comparison with national lightning detection network data 2004 2010 1 we report on upward lightning observations from ten tall towers 91 191 m in rapid city south dakota usa and compare with national lightning detection network nldn data a total of 81 upward flashes were observed from 2004 2010 using gps time stamped optical sensors and in all but one case visible flash activity preceded the development of the upward leaders time correlated analysis showed that the nldn recorded an event within 50 km of towers and within 500 ms prior to upward leader development from the tower s for 83 67 81 of the upward flashes a preceding positive cloud to ground stroke cg was detected in 57 46 81 of the cases and a preceding positive intracloud flash ic in 23 19 81 of the cases however 8 of the 19 nldn indicated ic events were actually cg strokes based on optical observations preceding negative intracloud flashes ic were recorded for 2 2 81 of the cases analysis also showed that for 44 36 81 of the upward flashes the nldn reported subsequent negative cloud to ground cg strokes and or ic events at one or more tower locations of the 151 subsequent events 70 105 151 were cg reports and 30 46 151 were listed as ic events the geometric mean median location accuracy and peak current for subsequent events were 194 m 206 m and 12 9 ka 12 4 ka respectively these correlated observations suggest that a majority of the upward lightning flashes were triggered by a preceding flash with the dominant triggering type being the cg flash

size and structure of the chicxulub crater revealed by horizontal gravity gradients and cenotes it is now widely believed that a large impact occurred on the earth at the end of the cretaceous period and that the buried chicxulub structure in yucatan mexico is the resulting crater24 knowledge of the size and internal structure of the chicxulub crater is necessary for quantifying the effects of the impact on the cretaceous environment although much information bearing on the crater s structure is available diameter estimates range from 170 to 300 km refs 1a 7 corresponding to an order of magnitude variation in impact energy here we show the diameter of the crater to be 180 km by examining the horizontal gradient of the bouguer gravity anomaly over the structure this size is confirmed by the distribution of karst features in the yucatan region mainly water filled sinkholes known as cenotes the coincidence of cenotes and peripheral gravity gradient maxima suggests that cenote formation is closely related to the presence of slump faults near the crater rim

the length of channelized lava flows insight from the 1859 eruption of mauna loa volcano hawai i a r t i c l e i n f o the 1859 eruption of mauna loa volcano hawai i produced paired a and p hoehoe ows of exceptional length 51 km the a ow eld is distinguished by a long n36 km and well de ned p hoehoe lined channel indicating that channelized lava remained uid to great distances from the vent the 1859 eruption was further unusual in initiating at a radial vent on the volcano s northwest ank instead of along the well de ned rift zone that has been the source of most historic activity as such it presents an opportunity both to examine controls on the emplacement of long lava channels and to assess hazards posed by future ank eruptions of mauna loa here we combine evidence from historical chronicles with analysis of bulk compositions glass geothermometry and microlite textures of samples collected along the 1859 lava ows to constrain eruption and ow emplacement conditions the bulk compositions of samples from the a and p hoehoe ow elds are bimodally distributed and indicate tapping of two discrete magma bodies during eruption samples from the p hoehoe ow eld have bulk compositions similar to those of historically erupted lavas b8 wt mgo lava that fed the a channel is more primitive n8 wt mgo nearly aphyric and was erupted at high temperatures 1194 1216 c we suggest that the physical properties of proximal channel fed lava i e high temperature low crystallinity and low bulk viscosity promoted both rapid ow advance and development of long p hoehoe lined channels critical for the latter was the large temperature decrease 50 c required to reach the point at which plagioclase and pyroxene started to crystallize the importance of phase constraints are emphasized by our dif culty in replicating patterns of cooling and crystallization recorded by high temperature eld samples using common models of ow emplacement placement of the 1859 eruption within the context of historic activity at mauna loa suggests that the formation of radial vents and eruptions of high temperature magma may not only be linked but may also be a consequence of periods of high magma supply e g 1843 1877 flank eruptions could therefore warrant special consideration in models and hazard mitigation efforts

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

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

a microwave scattering model for layered vegetation a microwave scattering model was developed for layered vegetation based on an iterative solution of the radiative transfer equation up to the second order to account for multiple scattering within the canopy and between the ground and the canopy the model is designed to operate over a wide frequency range for both deciduous and coniferous forest and to account for the branch size distribution leaf orientation distribution and branch orientation distribution for each size the canopy is modeled as a two layered medium above a rough interface the upper layer is the crown containing leaves stems and branches the lower layer is the trunk region modeled as randomly positioned cylinders with a preferred orientation distribution above an irregular soil surface comparisons of results obtained using this model with measurements from deciduous and coniferous forests show good agreement at several frequencies for both like and cross polarizations

surface expression of the chicxulub crater analyses of geomorphic soil and topographic data from the northern yucatan peninsula mexico confirm that the buried chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the cenozoic has been influenced by the crater late tertiary sedimentation was mostly restricted to the region within the buried crater and a semicircular moat existed until at least pliocene time the topographic expression of the crater is a series of features concentric with the crater the most prominent is an approximately 83 km radius trough or moat containing sinkholes the cenote ring early tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km respectively two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km the low ridge between the inner troughs corresponds to the buried peak ring the moat corresponds to the outer edge of the crater floor demarcated by a major ring fault the outer trough and the approximately 62 km radius inner trough also mark buried ring faults the ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes these interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km but concentric low relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km

a deep groundwater origin for recurring slope lineae on mars the recurring slope lineae on mars have been hypothesized to originate from snow melting deliquescence dry flow or shallow groundwater except for the dry flow origin these hypotheses imply the presence of surficial or near surface volatiles placing the exploration and characterization of potential habitable environments within the reach of existing technology here we present observations from the high resolution imaging science experiment heat flow modelling and terrestrial analogues which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere at depths of approximately 750 m spatial correlation between recurring slope lineae source regions and multi scale fractures such as joints and faults in the southern mid latitudes and in valles marineris suggests that recurring slope lineae preferably emanate from tectonic and impact related fractures we suggest that deep groundwater occasionally surfaces on mars in present day conditions observations and heat flow modelling suggest that briny groundwater surfacing from fractures forms recurring slope lineae on mars

radar scattering from a diffuse vegetation layer over a smooth surface a simple model is presented for the oblique backscatter and bistatic scatter from a smooth surface overlain by a diffuse layer only single scattering in the diffuse layer is taken into account the model analysis shows that the combination of volume scattering and oblique reflection at the surface may increase appreciably the waves scattering the scattering strongly depends on the properties of the smooth surface these results support some of the observations made with the seasat spaceborne imaging radar over flooded regions with heavy vegetation cover

ring of cenotes sinkholes northwest yucatan mexico its hydrogeologic characteristics and possible association with the chicxulub impact crater a 180 km diameter semicircular band of abundant karst sinkholes ring of cenotes in northwest yucatan mexico coincides approximately with a concentric ring of the buried chicxulub structure a circular feature manifested in cretaceous and older rocks that has been identified as the product of the impact of a bolide the ring expressed in tertiary rocks marks a zone of high permeability as shown by 1 the sinkholes themselves 2 breaks in the coastal dune system and high density of springs where the ring intersects the coast and 3 water level transects characterized by a decline in water level toward the ring any direct relation that exists between the ring of cenotes and the chicxulub structure bears on regional hydrogeology if the layer or zone responsible for the ring is deeply buried it may act as a barrier to the movement of ground water across the main flow direction shallower zones of horizontal permeability could result in less complete diversion of ground water through its influence on yucatan aquifer characteristics the ring may provide a link between modern environmental problems and astrogeology possible origins for the ring of cenotes are 1 faulting perhaps reactivated by post eocene mid miocene basin loading 2 permeability in a buried reef complex developed in the shallow paleocene sea around the crater rim or 3 breccia collapse occasioned by consolidation or by solution of evaporite components if the ring developed on ancient faults it may outline hydrothermal systems and mineral deposits produced during paleocene cooling of the chicxulub melt sheet

emplacement conditions of the c 1 600 year bp collier cone lava flow oregon a lidar investigation a long standing question in lava flow studies has been how to infer emplacement conditions from information preserved in solidified flows from a hazards perspective volumetric flux effusion rate is the parameter of most interest for open channel lava flows as the effusion rate is important for estimating the final flow length the rate of flow advance and the eruption duration the relationship between effusion rate flow length and flow advance rate is fairly well constrained for basaltic lava flows where there are abundant recent examples for calibration less is known about flows of intermediate compositions basaltic andesite to andesite which are less frequent and where field measurements are limited by the large block sizes and the topographic relief of the flows here we demonstrate ways in which high resolution digital topography obtained using light detection and ranging lidar systems can provide access to terrains where field measurements are difficult or impossible to collect we map blocky lava flow units using lidar generated bare earth digital terrain models dtms of the collier cone lava flow in the central oregon cascades we also develop methods using geographic information systems to extract and quantify morphologic features such as channel width flow width flow thickness and slope morphometric data are then analyzed to estimate both effusion rates and emplacement times for the lava flow field our data indicate that most of the flow outline which comprises the earliest and most voluminous flow unit can be well explained by an average volumetric flux 14 18 m3 s channel data suggest an average flux 3 m3 s for a later channel filling flow unit when combined with estimates of flow volume these data suggest that the collier cone lava flow was most likely emplaced over a time scale of several months this example illustrates ways in which high resolution dtms can be used to extract and analyze morphologic measurements and how these measurements can be analyzed to estimate emplacement conditions for inaccessible heavily vegetated or extraterrestrial lava flows

effects of martian conditions on numerically modeled cooling limited channelized lava flows 1 we used the flowgo thermorheological model to examine the effects of martian gravitational and environmental conditions on the cooling limited behavior of lava flowing in a channel the largest effect is due to the lower gravity on mars as compared to earth which causes lava to flow more slowly the lower velocity means that heat loss per distance down a mars channel is greater even though the lower velocity also produces a higher percentage cover of insulating crust gravity alone causes the mars flow to be 65 km shorter than an earth flow with an equivalent volumetric flow rate the cooler ambient mars atmosphere causes a slight increase in heat loss by forced convection this slows the flow a bit more resulting in a very slight increase in heat loss per distance by all mechanisms and decreases the modeled flow length by 1 km a difference well below our model uncertainty replacing terrestrial values of atmospheric density viscosity thermal conductivity heat capacity and cubic expansivity makes convection less efficient and increases flow length by 15 km nevertheless at the same volumetric flow rate lava flows 50 km less far under martian conditions than under terrestrial conditions our specific model flow has a volumetric flow rate of 5000 m3 s 1 and traveled 190 km down a channel on a constant 7 slope this volumetric flow rate is slightly less than the maximum rates during the 1783 1785 laki eruption and is 5 10 times greater than those of typical mauna loa eruptions

morphology and emplacement of a long channeled lava flow near ascraeus mons volcano mars 1 channeled lava flows hundreds of kilometers long are common on the lower flanks of the tharsis montes on mars our analysis of a 690 km long lava flow along the southwest perimeter of ascraeus mons shows that it was emplaced on low local slopes 100 km in length but the maximum effusion rates necessary on earth are essentially the minimum for martian flows on the basis of our calculated effusion rates the eruption duration was 3 to 7 earth months assuming a constant effusion rate and continuous eruption the morphology of the ascraeus mons flow shows similarities to terrestrial and simulated channeled flows downstream changes in morphology resemble those observed in the 1907 flow mauna loa volcano hawaii and channeled polyethylene glycol peg flows braided sections of the channel in the ascraeus mons flow contain islands which are hundreds of meters across and resemble features observed in the 1907 and 1984 flows on mauna loa volcano crosscutting relationships suggest islands in the proximal section were shaped by thermal and mechanical erosion whereas islands in the medial section are inferred to be material rafted by surges of lava through the channel overall understanding the morphology of long lava flows on mars is essential to the interpretation of their emplacement and constraining eruption conditions in the saddle regions of the tharsis volcanoes

size and morphology of the chicxulub impact crater the chicxulub impact in mexico has been linked to the mass extinction of species at the end of the cretaceous period from seismic data collected across the offshore portion of the impact crater the diameter of the transient cavity is determined to be about 100 km this parameter is critical for constraining impact related effects on the cretaceous environment with previous estimates of the cavity diameter spanning an order of magnitude in impact energy the offshore seismic data indicate that the chicxulub crater has a multi ring basin morphology similar to large impact structures observed on other planets such as venus

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

geologic interpretation of space shuttle radar images of indonesia the national aeronautics and space administration nasa space shuttle mission in november 1981 acquired images of parts of the earth with a synthetic aperture radar system at a wavelength of 23 5 cm 9 3 in and spatial resolution of 38 m 125 ft this report describes the geologic interpretation of 1 250 000 scale images of irian jaya and eastern kalimantan indonesia where the all weather capability of radar penetrates the persistent cloud cover the inclined look direction of radar enhances subtle topographic features that may be the expression of geologic structures on the indonesian images the following terrain categories are recognizable for geologic mapping carbonate clastic volcanic alluvial and coastal melange and metamorphic as well as undifferentia ed bedrock regional and local geologic structures are well expressed on the images in the vogelkop region of irian jaya the major tectonic elements tamrau mountains sorong fault kemum block bintuni basin and lengguru foldbelt are readily mapped on the image of the sorong fault geomorphic features offset drainage shutterridges aligned notches provide clear evidence for left lateral strike slip displacement several lineaments on the image correlate with previously mapped faults other lineaments may be the expression of previously unrecognized faults on the image of the mainland of irian jaya a belt of metamorphic and melange terrain marks the zone of collision between the pacific plate and the australian plate the high central range of irian jaya is located south of the metamorphic and melange belt the generally homoclinal structure of the central range is interrupted in the paniai lake region by a series of southward directed thrust plates indicated by belts of carbonate terrain new guinea limestone group that alternate with belts of clastic terrain kembelangan formation in the image of eastern kalimantan several major foldbelts are clearly expressed these limited examples of space shuttle radar images demonstrate their value for geologic interpretation of indonesia it is recommended that future shuttle missions acquire complete radar coverage of the main islands of indonesia for use in geologic mapping and energy exploration shuttle radar images would also be valuable for other cloud covered forested regions

features of upward positive leaders initiated from towers in natural cloud to ground lightning based on simultaneous high speed videos measured currents and electric fields original simultaneous records of currents close electric field and high speed videos of natural negative cg lightning striking the tower of morro do cachimbo station are used to reveal typical features of upward positive leaders before the attachment including their initiation and mode of propagation according to the results upward positive leaders initiate some hundreds of microseconds prior to the return stroke while a continuous uprising current of about 4 a and superimposed pulses of a few tens amperes flow along the tower upon leader initiation the electric field measured 50 m away from the tower at ground level is about 60 kv m the corresponding average field roughly estimated 0 5 m above the tower top is higher than 0 55 mv m as in laboratory experiments the common propagation mode of upward positive leaders is developing continuously without steps from their initiation unlike downward negative leaders upward positive leaders typically do not branch off though they can bifurcate under the effect of a downward negative leader s secondary branch approaching their lateral surface the upward positive leader s estimated average two dimensional propagation speed in the range of 0 06 106 to 0 16 106 m s has the same order of magnitude as that of downward negative leaders apparently the speed tends to increase just before attachment

early phase of lightning currents measured in a short tower associated with direct and nearby lightning strikes 1 records of natural lightning currents of negative downward strokes measured at the base of a 60 m high instrumented tower are presented to denote patterns of their early phase such patterns in the records of five flashes and two upward unconnected leaders are discussed typical profiles of this early phase comprising the pre return stroke pulses of the current flowing upwards the tower in response to the downward stepped leader approaching the ground the concavity in the initial rising part of the return stroke waveform and the abrupt rise around the half peak of the first stroke waveform are remarked statistics are developed for the pre return stroke pulses of current to characterize their amplitude duration interval and risetime for both the first stroke and upward unconnected leaders which proved to be quite similar the ratio of the maximum pulse peak to first stroke peak is typically in the range 0 7 to 2 2 of the analyzed currents different from the value of around 10 found for the distant electric fields radiated by first stroke currents

evolution of lava flow fields at mount etna 27 28 october 1999 observed by landsat 7 etm landsat 7 enhanced thematic mapper etm data are presented which document the thermal characteristics of a series of lava flows emplaced at mount etna volcano sicily during 27 28 october 1999 by examining the composition of the short wave infrared swir signal emitted from the flow surface we identified distinctive flow units the first unit appears to comprise recently active lava flows with relatively cool crusts which by virtue of the integrity of this crust as determined from the etm data we infer are stationary or barely moving the second unit is characterized by much higher levels of swir radiance consistent with a channel fed active flow unit analysis of the swir data confirm that this is fed by a lava channel the properties of which are consistent with vigorously active channels observed on kilauea hawaii model predictions of the maximum length that such flows could attain compare favorably with the actual flow lengths observed in the etm data indicating that the cooler flows had indeed stopped advancing and may have attained a cooling limited rather than volume limited maximum length our observations and modeling provide a physical corroboration for the supposition made by wadge 1978 in his analysis of the shape of lava flow fields on mount etna which in the cooling limited case principal flows are active one after the other and not at the same time

unam scientific drilling program of chicxulub impact structure evidence for a 300 kilometer crater diameter as part of the unam drilling program at the chicxulub structure two 700 m deep continuously cored boreholes were completed between april and july 1995 the peto unam 6 and tekax unam 7 drilling sites are 150 km and 125 km respectively sse of chicxulub puerto near the crater s center core samples from both sites show a sequence of post crater carbonates on top of a thick impact breccia pile covering the disturbed mesozoic platform rocks at unam 7 two impact breccia units were encountered 1 an upper breccia mean magnetic susceptibility is high 55 10 6 si units indicating a large component of silicate basement has been incorporated into this breccia and 2 an evaporite rich low susceptibility impact breccia similar in character to the evaporite rich breccias observed at the pemex drill sites further out the upper breccia was encountered at 226 m below the surface and is 125 m thick the lower breccia is immediately subjacent and is 240 m thick this two breccia sequence is typical of the suevite bunte breccia sequence found within other well preserved impact craters the suevitic upper unit is not present at unam 6 instead a 240 m thick evaporite rich breccia unit similar to the lower breccia at unam 7 was encountered at a depth of 280 m the absence of an upper breccia equivalent at unam 6 suggests some portion of the breccia sequence has been removed by erosion this is consistent with interpretations that place the high standing crater rim at 130 150 km from the center consequently the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias depth and thickness support a 300 km diameter crater model

multitemporal and dual polarization observations of agricultural vegetation covers by x band sar images this paper presents a study of sar images which aims to demonstrate the capability of radar to identify vegetation types and to determine the vegetation canopy parameters the investigations per formed on bi temporal and dual polarizatio n hh and vv x band sar images of an agricultural scene included all the steps involved from sar images to applications 1 the retrieval of radar backscatter val ues from sar images has been possible with the use of external ref erence targets 2 the analysis of the polarization and temporal re sponses of the vegetation covers has highlighted the particular behavior of flooded rice fields 3 the observations of ricefields have been inter preted by a theoretical model during an extended period of rice plant growth the model in agreement with the observations suggests a pos sible use of both hh and vv images for ricefield mapping and moni toring and 4 a result of ricefield mapping with an algorithm based on the above results is presented

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

characteristics of unconnected upward leaders initiated from tall structures observed in guangzhou 1 forty five unconnected upward leaders uuls occurred in 19 downward negative flashes are analyzed each observed uul is initiated by a downward stepped leader before a new strike point is struck for each uul several parameters are determined when possible mainly by using high speed images inception height inception time prior to return stroke rs horizontal distance from the flash s strike point two dimensional 2d distance between the nearest downward leader branch tip and the uul s inception point at its inception time 2d length and 2d average propagation velocity their values range from 40 to 503 m number of samples 45 0 1 to 1 32 ms 38 20 m to 1 3 km 38 99 to 578 m 21 0 48 to 399 m 45 and 5 79 to 33 8 104 m s 1 22 respectively 86 19 22 of the velocities are smaller than 1 7 105 m s 1 no uul with an inception time prior to rs greater than 0 5 ms is initiated from a structure lower than 300 m those uuls with inception heights lower than 300 m seldom exhibit lengths longer than 50 m and only can be initiated by flashes within approximately 600 m while those higher than 400 m can even reach several hundred meters and be initiated by flashes over 1 km away the maximum distances for the downward leaders to attract the uuls with inception heights from 100 to 200 m 200 to 300 m and over 400 m are approximately 350 m 450 m and 600 m respectively

high speed video observations of a natural negative stepped leader and subsequent dart stepped leader 1 we present new high speed video observations of a natural negative stepped leader and a subsequent negative dart stepped leader observations were made at a distance of 770 m using a high speed video camera at 10 000 frames per second a microwave frequency radio receiver a broadband electric field antenna and an avalanche photodiode array lightning leader breakdown was observed in detail for both the negative stepped leader and the subsequent dart stepped leader during the negative stepped leader breakdown detailed images were captured of the discharge structures near the leader tips these structures bear a remarkable resemblance to the corona streamer zone and space leader discharges that have been observed in laboratory generated negative stepped leaders during the dart stepped leader breakdown no corona streamer zone was observed outside of the decaying return stroke channel but small luminous structures that are suggestive of space leaders were observed just ahead of the main dart leader tip two distinct low luminosity zones were observed just ahead of the dart leader tip suggestive of two distinct breakdown regimes a multipath junction was observed in the main channel to ground following the first return stroke but was not observed following the second return stroke finally microwave frequency radio emissions for both leader types and their return strokes were recorded and their time domain behavior is compared and discussed

monostatic and bistatic reverberation statistics west of the mid atlantic ridge monostatic and bistatic reverberation of highly resolved signals from very rough bottoms at one site is statistically analyzed scattering at a mean frequency of about 230 hz from a large number of bottom footprints is considered the reverberation envelope is found to be non rayleigh with the degree of departure from rayleigh dependent upon the bottom grazing angle for two cases considered g 5 and 40 and upon the bistatic angle in the entire range 0 to 180 these rough bottom observations can be explained by adopting a continuous scattering model having a rayleigh envelope added to a discrete scattering model arising from a small number of individual features within the sonar footprint having a distinctly non rayleigh envelope these models plus a heuristic mechanism of self selection within the discrete scattering model arguably explain the observed angle dependence of the reverberation statistics

acoustic backscattering at low grazing angles from the ocean bottom part ii statistical characteristics of bottom backscatter at a shallow water site analyses of the statistical characteristics of bottom backscatter measured in shallow water off san diego ca t g goldsberry s p pitt and r a lamb j acoust soc am suppl 1 72 s74 1982 are presented an experimental sonar operating at 30 khz mounted on the sea bottom was used to gather data over a wide sector of the bottom within its operating range the bottom was comprised of areas of coarse and fine sand the distribution function and probability of false alarm function of the detected envelope of a widebeam and a narrowbeam signal were measured some spatial and temporal correlation functions of the signal amplitudes were measured a limited attempt was made to compare the results with existing theoretical models work supported by navsea 63r and norda code 113

numerical experiments on the dynamics of channelised lava flows at mount cameroon volcano with the flowgo thermo rheological model abstract as for many other effusive volcanoes mount cameroon mc is a volcano for which only limited information exists on lava flow properties and emplacement dynamics for recent eruptions this study provides new quantitative constraints for rheological and dynamic characteristics of lava flow effusion for the 1982 and 2000 eruptive events used to calibrate the flowgo thermo rheological model for these lava flows the flowgo 1 d physical model is used to simulate down flow evolution of the geometry and rheology of channel contained cooling limited lava flows morphometric data from historical lava flows were acquired from the field e g channel geometry levee and background slope in order to estimate lava yield strength velocity and effusion rate lava density and viscosity were also estimated from compositional data and laboratory methods to account for uncertainty in the input rheological and geometrical data three end member scenarios were used to bracket the potential range in lava channel initial dimension initial lava temperature and phenocryst content for each of these scenarios two crustal growth models were used one assuming strong insulation due to lava flow surface crusting the other a much lower crusting rate twelve numerical simulations were made per flow and the results were compared against the channel geometry microlite content yield strength and viscosity estimates from field and laboratory investigations best fit models where obtained for both the 1982 and 2000 lava flows using a low rate of surface crusting high initial temperature and low phenocryst content model predicted lengths were within 5 of the actual lengths modelled mean effusion rates for the 1982 52 64 m 3 s 1 and 2000 10 m 3 s 1 flows closely matched field data derived estimations 26 68 and 9 5 m 3 s 1 respectively flowgo model results are highly sensitive to initial channel dimensions phenocryst content and the flowgo model is unable to reproduce the observed rapid near vent increase in microlite content near vent rapid cooling induced by lava degassing is yet to be fully documented and integrated into numerical lava flow models such as flowgo but obtained results already provide valuable insights for lava flow hazard assessment at mount cameroon

lengths and hazards from channel fed lava flows on mauna loa hawai i determined from thermal and downslope modeling with flowgo using the flowgo thermo rheological model we have determined cooling limited lengths of channel fed i e a lava flows from mauna loa we set up the program to run autonomously starting lava flows from every 4th line and sample in a 30 m spatial resolution srtm dem within regions corresponding to the ne and sw rift zones and the n flank of the volcano we consider that each model run represents an effective effusion rate which for an actual flow coincides with it reaching 90 of its total length we ran the model at effective effusion rates ranging from 1 to 1 000 m3 s 1 and determined the cooling limited channel length for each keeping in mind that most flows extend 1 2 km beyond the end of their well developed channels and that our results are non probabilistic in that they give all potential vent sites an equal likelihood to erupt lava coverage results include the following sw rift zone flows threaten almost all of mauna loa s sw flanks even at effective effusion rates as low as 50 m3 s 1 the average effective effusion rate for sw rift zone eruptions since 1843 is close to 400 m3 s 1 n flank eruptions although rare in the recent geologic record have the potential to threaten much of the coastline s of keauhou with effective effusion rates of 50 100 m3 s 1 and the coast near anaeho omalu if effective effusion rates are 400 500 m3 s 1 the 1859 a flow reached this coast with an effective effusion rate of 400 m3 s 1 if the ne rift zone continues to be active only at elevations 2 500 m in order for a channel fed flow to reach hilo the effective effusion rate needs to be 400 m3 s 1 the 1984 flow by comparison had an effective effusion rate of 200 m3 s 1 hilo could be threatened by ne rift zone channel fed flows with lower effective effusion rates but only if they issue from vents at 2 000 m or lower populated areas on mauna loa s se flanks e g p hala could be threatened by sw rift zone eruptions with effective effusion rates of 100 m3 s 1

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

geologic and environmental aspects of surface cementation north coast yucatan mexico the northernmost part of the fresh water aquifer of yucatan mexico is confined near the coast by a thin flat nearly impermeable calcareous layer the authors think it probable that this confining layer is now developing by a process of sedimentation and precipitation of pore filling cement on and near the surface of older limestone at the landward margin of the swamp that extends virtually continuously along the north yucatan coast it is their interpretation that this caco sub 3 cemented layer which is 0 5 to 1 4 m thick developed in the zone of discharge of the fresh water aquifer the presence of sup 14 c 6 0 plus minus 0 4 modern carbon in a sample of aquitard supports the hypothesis that cementation is an ongoing process further support comes from the remarkable regularity between modern mean sea level and the elevation of the landward boundary between the confining zone and normal karst along 250 km of coast confinement of the aquifer produces an elevation of the piezometric surface to about 0 5 m above mean sea level and a concurrent depression of the fresh water salt water interface to an estimated depth of about 18 m below mean sea level at the coast breaching of the confining layer implicit inmore some development schemes for the region could dramatically decrease the thickness of the fresh water lens a valuable water resource the mixing zone beneath the confined part of the aquifer is a chemically active volume that may be vigorously pumped by tides as evidenced by increased salinity of ground water near the coast thus making this zone a likely place for rock water interaction including perhaps dolomite formation less

topographic control on lava flow paths at mount etna italy implications for hazard assessment 1 assessment of the hazard from lava flow inundation at the active volcano of mount etna italy was performed by calculating the probability of lava flow inundation at each position on the volcano a probability distribution for the formation of new vents was calculated using geological and volcanological data from past eruptions the simulated lava flows from these vents were emplaced using a maximum expected flow length derived from geological data on previous lava flows simulations were run using downflow a digital elevation model based model designed to predict lava flow paths different eruptive scenarios were simulated by varying the elevation and probability distribution of eruptive points inundation maps show that the city of catania and the coastal zone may only be impacted by flows erupted from low altitude vents 2000 m preferentially inundate the northeast and southern sectors of the volcano as well as the valle del bove eruptions occurring in the summit area 3000 m elevation pose no threat to the local population discrepancies between the results of simple hydrological models and those of the downflow model show that hydrological approaches are inappropriate when dealing with etnean lava flows because hydrological approaches are not designed to reproduce the full complexity of lava flow spreading they underestimate the catchment basins when the fluid has a complex rheology