V11D-0808
Satellite-based Morphotectonics of the Tibesti Lineament and its Relationship to Volcanism, Tibesti Massif, Chad
Intra-plate volcanism on continental often occurs at 'hotspots' where the crust has been weakened and reworked by either thermal or tectonic processes. We investigate the relationship between intraplate volcanism and faulting along the Tibesti Lineament, northern Chad. Forty-two digital elevation models (DEMs) extracted from Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) datasets provided the basis for much of our analysis. The DEMs were used to create shaded relief maps, three-dimensional perspectives, and topographic profiles. Rose diagrams based on hill shade drainage and joint patterns delineate dominant Precambrian and younger lineation fabrics. Shaded relief images were also used to establish relative ages of volcanic shields, calderas, and scoria fields. Our results indicate a recent (Cenozoic) NW-SE trending normal fault where the Tibesti Lineament traverses the study area. The normal fault herein defined as the Tibesti Fault may be a reactivated reverse fault. The most recent volcanism of sizable volume lies near the intersection of the Tibesti Fault and a newly recognized fault oriented perpendicular to it. Morphotectonic analysis of that region indicates uplift near the intersection of the two faults acted as a mechanism that may have enabled decompression melting. This suggests that extension played a active role in Eocene-Holocene volcanism at Tibesti.
V11D-0809
Investigations of CO2 Emissions From Holocene Volcanic Features of Mono Lake and the Mono Craters Volcanic Chain in Eastern California
Magmatic CO2 emissions have been well studied at the Long Valley caldera in eastern California, but not along the much younger and voluminous Mono Craters volcanic chain 10 to 20 km to the north. A June 2007 field investigation to identify and quantify emissions of magmatic CO2 focused on some of the youngest eruptive features in the chain and on Paoha Island in Mono Lake. North Coulee (NC) is one of the larger late-Holocene volcanic features in the Mono Craters chain and is composed primarily of a glassy rhyolite flow that is partially blanketed on the west by tephra deposits. There is no soil development at NC, and vegetation is generally limited to a few scattered pine trees. Portions of NC contain discrete zones of discolored altered rock that provide evidence of former fumarolic activity; however in this study, only one small area displayed temperatures greater than 40° C. CO2 flux was measured at 224 sites over a ~ 244, 000 m2 area that included many of the alteration zones. The CO2 flux at most sites was anomalously high, with an average flux over the entire study area of 109 gm-2d-1. The estimated discharge of CO2 is around 27 t d-1. Biogenic CO2 emissions at NC should be essentially zero because of the scarcity of soil and vegetation. Given that 63 sites had fluxes below detection limits this supposition is well supported. Additional gas chemistry and isotope work will help determine if all the CO2 is derived from magma. If so, then the magmatic CO2 output from NC is comparable to the CO2 output from the Long Valley hydrothermal system. Diffuse CO2 emissions were also measured at two locations on Paoha Island: around the young cinder cone on the north end of the island, and over dacite flows adjacent to Hot Springs Cove (HSC) on the east. The survey revealed no detectable flux of CO2 around the cinder cone. At HSC, CO2 emissions were localized around steam vents and were generally low. The average flux from 25 sites was less than 8 gm- 2d-1 with only 4 sites displaying an anomalous flux greater than 15 gm-2d-1. These data are in agreement with results from gas samples collected from bubbling springs along the shore of HSC, which contain predominantly C1 through C6 hydrocarbons and N2 with less than 4% CO2.
V11D-0810
Igneous Activity at Yucca Mountain: Technical Basis for Decision Making
Eighty thousand years ago a small-volume basaltic volcano erupted 20 km south of the Department of Energy's (DOE) proposed high-level radioactive waste repository at Yucca Mountain, Nevada. Lathrop Wells is one of the infrequent basaltic volcanoes that have occurred near Yucca Mountain during the past 10 million years. The Advisory Committee on Nuclear Waste and Materials (ACNW&M) has prepared a summary and analysis of the technical views on the nature, likelihood and potential consequences of future igneous activity at the proposed repository. The technical views have been abstracted from public literature and agency reports. Alternate views reflect uncertainties of the igneous processes that have occurred in the region and those that are likely to occur, as well as the interaction of these processes with the proposed repository. There is general agreement that either extrusive or intrusive igneous activity may occur. The extrusive scenario is likely to cause a larger risk and the effect is greatest within the first thousand years. The nature of igneous activity that could occur will probably be similar in composition, structure, and style to the Lathrop Wells volcano. Certain styles of volcanism, like explosive phreatic eruptions (maar volcanism) are not expected because conditions necessary for these do not exist at Yucca Mountain. The volcanic record, particularly during the past 5 million years, suggests a variety of models for evaluating the probability of future igneous activity. The anticipated range of probability of an igneous event intersecting the proposed repository is low, between 1E-9 and 1E-7/yr. An ongoing DOE expert elicitation incorporating the latest geophysical and drilling data will provide an up-to-date, credible estimate of the probability of volcanic intersection. An understanding of the processes involved in interaction between magma and drifts, waste packages, and waste is evolving and providing new insights. As a result, there is limited consensus regarding the consequences of igneous activity in either the extrusive or intrusive scenario. The proposed alternative models differ significantly. The application of magma physics will reduce differences and conservatisms, and suggests that the ability of magma to intrude waste drifts could be limited. Variability and uncertainty exist in evaluating conceptual models in estimating the probability of an igneous event intersecting the repository, and in estimating the consequences of such an event, particularly in the intrusive scenario. Assessment of the performance of the proposed repository as a result of igneous activity requires evaluation of a range of credible views on both the extrusive and intrusive scenarios and the range of parameter uncertainty. These analyses will be useful in evaluating risk from the repository as well as those aspects of igneous activity that are important to risk and thus worthy of further investigation to reduce uncertainties. The ACNW&M report is available online at: http://www.nrc.gov/reading-rm/doc-collections/acnw/letters/2007/.
V11D-0811
Evaluating Consequences of Volcanism for Spent Nuclear Fuel at Yucca Mountain, Nevada
The likelihood that a volcanic dike could intersect a high-level waste (HLW) repository at Yucca Mt. is very small, 1E-9/yr to 1E-7/yr. The intersection of a cone-forming conduit is even less likely. Realistic insights about the fate of HLW in a volcanic conduit suggest that fewer waste packages may be affected and particle sizes of ejected spent fuel may be larger than previously assumed. Most HLW consists of fractured ceramic pellets of UO2 about a cm in diameter, with a melting point >2800C, much higher than magma temperatures of 1000-1200C. Spent fuel would not dissolve in magma; therefore the size range of transported fragments would largely be determined by pre-existing particle sizes in fuel rods. This range would differ from that of volcanic ejecta. The expected travel time in a conduit from repository depth to the surface would be short, allowing little time for erosion of ceramic pellets but permitting rapid quenching of magma on the relatively cold waste packages and their contents. Quench rinds would protect waste fragments during rapid transit to the surface in a column of frothy magma. Xenoliths and crush-impact studies constrain the size of spent fuel particles that may be incorporated in volcanic ash. Estimates of fuel particle size have used a log triangular distribution from 1-100 microns. For comparison, grains of table salt are 100 microns across. Talcum powder is 10 microns. One micron is the wavelength of near infrared light. However, it is unlikely that spent fuel could be reduced to this minute size range. At Lathrop Wells, tuff xenoliths eroded from conduit walls are common in the scoria cone. They vary in size from a fraction of a cm up to 30 cm and have quenched basalt rinds, providing evidence that large spent fuel fragments could survive intact over the short travel distance to the surface. Crush-impact studies at energies up to 1000 J/gram on spent fuel show less than 30% of the fuel mass reduced to <100 microns and less than 10% to <10 microns. Hypothetical doses are sensitive to assumptions about particle size because respirability decreases sharply as particles increase beyond 10 microns. In performance assessment, using a particle size range of 100-10000 microns reduces dose 200-fold compared to a range of 1-100 microns. There is a strong basis to assume that only a fraction of spent fuel entrained in a conduit would be ejected as tephra. The relative volume of ash vs. scoria cone and lava flows can be used to estimate practical limits on the fraction of ejected waste in ash that could be transported by water and wind. Compared with ash, waste in lava flows or scoria cones would be protected from erosion and transport for hundreds of thousands of years, as shown by the million-year-old cones and flows in Crater Flat near Yucca Mt. Also, it is likely that only a limited number of waste packages could be entrained because volcanic conduits would be smaller at the repository depth of 300 m than at ground surface. Lithostatic pressure keeps conduits smaller at depth, possibly <10 m in diameter. It is also possible that a conduit could form between drifts, and no waste would be entrained. Dikes are more likely to intrude pre-existing faults. Conduits form along dikes, so keeping drifts set back from larger faults would reduce the chance of a conduit intersecting the repository. In sum, only a limited number of waste packages is likely be entrained in a volcanic conduit, and there is strong evidence that a large fraction of the HLW content would not be reduced to very small particles. For more information, see the report by NRC's Advisory Committee on Nuclear Waste and Materials [http://www.nrc.gov/reading-rm/doc-collections/acnw/letters/2007/].
V11D-0812
Airborne Radiative Transfer Spectral Scanner: A new airborne hyperspectral imager for hyperspectral volcano observations
In 2006, a new airborne hyperspectral imager, the Airborne Radiative Transfer Spectral Scanner (ARTS), was developed for hyperspectral volcano observations. ARTS provides hyperspectral images to support developing algorithms for the remote sensing of the geothermal distribution, the ash fall areas, and the volcanic gasses columnar content from the air. ARTS will be used mainly to assess volcanic activity and to mitigate volcanic disasters. ARTS is a pushbroom imaging spectrometer covering wavelengths from 380 to 2450nm and 8000 to 11500nm with 421 bands. The ARTS imaging spectrometer consists of three sensor head units (SHUs). These SHUs are the visible - near infrared (VNIR) SHU, the shortwave infrared (SWIR) SHU, and the long-wave infrared (LWIR) SHU. These sensor head units operate as a line scanner in the pushbroom mode from an aircraft. The VNIR SHU covers wavelengths from 380 to 1050nm with 288 spectrum bands. The field of view (FOV) is 40 degrees, and the image of this SHU is 1500 pixels wide cross-track, making the instantaneous field of view (IFOV) 0.49mrad. The SWIR SHU covers wavelengths from 900 to 2450nm with 101 spectrum bands. The LWIR SHU covers wavelengths from 8000 to 11500nm with 32 spectrum bands. SWIR SHU and LWIR SHU have FOVs of 40 degrees and 600-pixel-wide images cross-track, giving them an IFOV of 1.2mrad. ARTS has precise position and attitude measurement systems (GPS/IMU). Direct, accurate geo-corrections of each SHU image can be made using the GPS/IMU systems. ARTS will be used for the operational volcano observation beginning in 2008. We are now validating the in-flight performance of this sensor. In this study, we describe the ARTS optical, electrical, and mechanical systems; its data acquisition and system design; and present some preliminary in- flight performance test results obtained from measurements acquired aboard the Beechcraft King Air B200 aircraft. The validation results indicate that the geo-correction accuracy is typically less than a 2-pixel difference (RMS) for each SHU, and there was the good agreement between the predicted radiance at the sensor and the measured radiance at the sensor at a flight altitude of 1000m AGL. We expect that ARTS will be a well-calibrated instrument for assessing volcanic activity.
V11D-0813
Thermography of volcanic areas on Piton de la Fournaise, Reunion Island : Mapping surface properties and possible detection of convective air flow within volcanic debris
We report on the detection of air convection in a couple of quasi circular cavities forming the 300 years old volcanically inactive cone of Formica Leo (Piton de la Fournaise, Reunion Island) [1]. Infrared thermal images of the cone have been acquired in 2006 from a hand held camera at regular time interval during a complete diurnal cycle. During night and dawn, the data display hot rims and cold centers. Both the conductivity contrasts of the highly porous soils filling the cavities and their 30° slopes are unable to explain the systematic rim to center temperature drop. Accordingly, this signal could be attributed to an air convection dipping inside the highly porous material at the center of each cavity, then flowing upslope along the base of the soil layer, before exiting it along the rims. Anemometrical and electrical data acquired in 2007 allow for the first time the direct detection of this air flow on the field: dipping gas velocities are measured at the center of the cone and self-potentials anomalies [2] generated by the humid air flow in the porous medium are detected. To quantify this process, we present 2D/3D numerical models of air convection in a sloped volcanic soil with a surface temperature evolving between day and night and taking into account electrical phenomena created by the air flow. At this present stage, this work constitutes a first step to investigate the deep structure of the active caldera of Bory-Dolomieu. The detection of the air flow at the surface could be of paramount importance for the understanding of volcanic hazards of the Reunion volcano. [1] Antoine et. al, submitted to G-Cubed [2] Darnet, PhD, Université Louis Pasteur (2003)
V11D-0814
In-situ spectroscopy of the surface of Mount Etna for remote sensing data validation and interpretation
Mount Etna volcano is the tallest and most active of European volcanoes. It is characterised by four craters (Northeast Crater, Voragine, Bocca Nuova, Southeast Crater) with a highest point at 3315m elevation. Eruptions are frequently observed on Etna, and are typical of basaltic volcanism, consisting of voluminous lava flows and ash-generating explosions. Since the late 1970s, summit eruptions have shown an increase in their intensity, with a high rate of short-lived paroxysmal eruptive episodes. Such events commonly produce lava fountains that reach heights of many hundred metersand are accompanied by the generation of abundant tephra and scoriae that can fall tens of kilometers away from the volcano. The surface of Etna is highly dynamic, changing rapidly as lava flows are emplaced, ash falls deposit and pyroclastic cones grow. Such a system has naturally become the focus of air- and space-borne remote sensing studies, focussed on detecting thermal anomalies and measuring volcanic gas emissions. The efficicacy of such studies is strongly dependent on accurate studies of the wavelength-dependent emissivity and reflectance of surface rocks. In order to obtain improved constraints on these parameters for Etna we conducted a campaign of on-situ measurements on Etna in July, 2007. A series of target sites, representative of the both the present-day and oldest volcanic surfaces, were geologically and spectrally characterized. Measurements were made using an ASD FieldSpec Pro portable spectrometer operating in the 300-2500nm wavelength range for reflectance while an FTIR Bruker OPAG-22 was used for emissivity measurements. Here we present the preliminary results of the campaign and compare with satellite data.
V11D-0815
Using Ground Penetrating Radar to Help Delineate Lahar Hazard Zones at Cotopaxi Volcano, Ecuador
Cotopaxi (5897 m) is located in the Eastern Cordillera of the Ecuadorian Andes about 80 km south of Quito and is one of the most active Ecuadorian volcanoes. Over the last 2000 years, Cotopaxi has had at least one eruption of Volcano Explosivity Index (VEI) 3 or larger per century. Many of these past eruptions melted parts of the glaciers on Cotopaxi, generating large volume debris flows. These flows rapidly descended along the three main drainage systems of the volcano towards the North, East and Southwest resulting in considerable destruction. The focus of this work is the study of a debris flow fan covering an area of 2.8 km2. The fan is situated within the confluence area of three quebradas; the San Lorenzo, the San Diego and the Burrohuaycu, that form part of the southwest drainage system 13 km downslope from the volcano summit. In order to estimate extent and thickness of recent lahar deposits, we used a Ground Penetrating Radar (GPR) survey that covers the fan surface in a grid pattern. Transects are perpendicular and parallel to the flow direction of the quebradas. The total length of all transects is 10 km. Regular common mid-point surveys (CMP) at different sites along the lines ensure wave velocity control on wet and dry ground. Global Positioning System Rover measurements along the transects yield X, Y and Z topographic control with an accuracy of decimeters that are used to correct the vertical exaggeration of the GPR profiles. We chose 200 MHz antennas having an average penetration depth of 6 m assuming a velocity of 0.09 m/ns, helping us detect even relatively small changes in outcrop morphology and stratigraphy over short distances. Subsurface control of the surficial geology comes from outcrop sections, quarry faces and excavated trenches that are distributed across the fan area. The identification of a paleo-lahar topography and the integration of GPR data are primary components of this ongoing lahar flow modeling study.
V11D-0816
Optimized Autonomous Space - In-situ Sensorweb: A new Tool for Monitoring Restless Volcanoes
An interagency team of earth scientists, space scientists and computer scientists are collaborating to develop a real-time monitoring system optimized for rapid deployment at restless volcanoes. The primary goals of this Optimized Autonomous Space In-situ Sensorweb (OASIS) are: 1) integrate complementary space and in-situ (ground-based) elements into an interactive, autonomous sensorweb; 2) advance sensorweb power and communication resource management technology; and 3) enable scalability for seamless infusion of future space and in-situ assets into the sensorweb. A prototype system will be deployed on Mount St. Helens by December 2009. Each node will include GPS, seismic, infrasonic and lightning (for ash plume detection) sensors plus autonomous decision making capabilities and interaction with EO-1 multi-spectral satellite. This three year project is jointly funded by NASA AIST program and USGS Volcano Hazards Program. Work has begun with a rigorous multi-disciplinary discussion and resulted in a system requirements document aimed to guide the design of OASIS and future networks and to achieve the project's stated goals. In this presentation we will highlight the key OASIS system requirements, their rationale and the physical and technical challenges they pose. Preliminary design decisions will be presented.
V11D-0817
ASTER Observations of Recent Thermal Activity and Explosive Eruption at Oldoinyo Lengai, Tanzania
Oldoinyo Lengai (OL) is the only active volcano in the world that produces natro-carbonatite lava. These carbonate-rich lavas are unique in that they have relatively low temperatures (500-600 C) compared with typical silicate lavas (600-1100 C), and they have a low viscosity, behaving more like a mud flow than a lava flow. OL has been erupting on and off since 1983, mostly resulting in small lava flows, pools and spatter cones (hornitos) confined to the summit crater. Explosive, ash-producing eruptions here are rare, however, an ASTER observation from September 4, 2007 caught the first satellite image of an ash plume erupting from OL, which may be indicative of a new phase of more silica-rich products and explosive activity that has not occurred here since the 1960s. Thermal infrared satellite monitoring has detected an increasing number of thermal anomalies around OL in recent months. MODIS MODVOLC data detected >30 hot spots in the last week of August and first week of September 2007, some of which may have been brush fires started by lava flows or spatter; ASTER detected the appearance of an anomalous hot spot at the summit of OL as early as mid-June. We will present up-to date information about the progress of the eruption and results from the analysis of the spectral composition of new eruption products and thermal anomalies that occurred prior to the recent explosive eruption. OL is one of many volcanoes in the world, and especially Africa, that is not regularly monitored. It is only through sporadic reports from locals or tourists in the area, and satellite data that we know anything at all about this volcanic eruption. Continued satellite monitoring along with studies of past thermal activity will help determine how future eruptions may be forecasted.
V11D-0818
Rapid Objective Rapid Delineation of Areas At Risk From Block-and-Ash Pyroclastic Flows
Assessments of pyroclastic flow (PF) hazards are often based on mapping of PF and surge deposits and estimation of inundation limits, and/or computer models of varying degrees of sophistication. These methods are often limited, due to poor exposures and large uncertainties on dynamic parameters. In volcanic crises a hazard map is sorely needed, but limited time, exposures, or safety aspects may preclude field work, and insufficient time or baseline data are available for reliable dynamic simulations. We have developed a statistically constrained simulation model for PFs calibrated with data from many volcanoes to estimate potential areas of inundation from PFs, following Iverson, Schilling and Vallance (1998). The predictive equations for block-and-ash PF inundation are given by A = (0.05-0.1)V 2/3 , B = (35-40)V 2/3, where A is cross-sectional area of inundation and B is planimetric area. The proportionality coefficients were obtained from statistical analysis, and comparison of simulations to mapped deposits. The method embeds predictive equations in a GIS program coupled with DEM topography, using the LAHARZ program of Schilling (1998). Although the method is objective and reproducible, any PF hazard zone so computed should be considered as an approximate guide only, due to uncertainties on average coefficients with respect to individual PFs, DEM details, and release volumes. The gradational nested hazard maps reflect in a sense these types of uncertainty. The model does not explicitly consider dynamics aspects, which can be important. Surge impacts must be extended beyond PF hazard zones and we have explored several approaches to do this. The method has been used to quickly supply PF hazard maps in two crises, Merapi 2006, Montserrat 2006-2007. We have also compared our PFz maps (using the term coined by C. Newhall) to actual recent PF deposits, and to maps generated by several other model techniques. NSF support.