V33C-01 INVITED
Computer Mapping of Pyroclastic Flow Inundation Probability: Application to the August 2006 Flows at Tungurahua, Ecuador
In the summer of 2006 Tungurahua produced its most intense pyroclastic activity since the current eruptive cycle
began in October 1999. In mid-July and again in mid-August more than 20 pyroclastic flows descended ravines
on the north to west flanks of the volcano causing at least five deaths and destroying property and livestock.
These PFs reached the Chambo River at the base of the volcano and temporarily dammed it. The flows passed
over the major Ambato-Baños highway and came within 2.5 km from the popular El Salado hot springs near
the town of Banos (ca. 20,000 inhabitants).
These August 16 pyroclastic flows provide a good data base for calibrating models used in hazard mapping.
Titan2D is a computational code for volcanic block and ash flows and rock avalanches of various types and
scales. It forms the core of the new Titan environment for volcanic hazards analysis that can integrate modeling,
high-performance computing, database management, visualization, and collaborative environments to a very
sophisticated level. Titan provides a solution to mapping problems by providing a probabilistic calculation of
inundation depth that takes into account many of the critical uncertainties using a PCQ methodology to reduce
computation time. We used TITAN to map potential inundation areas for future block-and-ash flows at
Tungurahua, Ecuador. First the DEM was modified to fill the crater with a tiled plane to avoid back filling of the
simulated flows. For each PCQ analysis we started with a 360° uniform distribution of initial direction of
flow, a flux footprint with a 50 m radius and an initial velocity of velocity of 50 m s-1. Flux rates started at their
maximum value and decreased linearly to zero over time; flux durations ranged between 1 and 5 minutes with
duration being linear in volume. Then we used a flux footprint with a 50 m radius and an initial velocity of velocity of
50 m s-1. Flux rates started from their maximum value and decreased linearly to zero over time, flux
durations ranging between 1 and 5 minutes with duration being linear in volume. Realizations of our probabilistic
hazard mapping used a linear log frequency to log volume distribution similar to flows at Unzen with initial
volumes ranging from 7.5 x 105 to 107 m3. Internal friction is not critical to thin-layer models like
TITAN so we used a value of 35° in all simulations. However, because basal friction angle is a very
sensitive parameter for flow behavior we gave it a uniform probability distribution between 22° and
12°. We generated two sets of maps, one for the probability that the height will exceed 1 m on the next event
and a second that the probability that the height will exceed 0.2 m on the next event. Because multiple flows are
common at Tungurahua, 20 occurred during the August 2006 eruptions, we also mapped the probably inundation
for a set of 12 flows with the same level of uncertainty in the input values. The results for the PCQ analysis
compares closely with the actual mapping of the pyroclastic flows done by the Instituto Geofisico immediately
after the eruptions.
http:www.gmfg.buffalo.edu
V33C-02 INVITED
Volcanic hazards maps of the restless Campi Flegrei caldera in the Neapolitan area (Italy)
Volcanic hazards maps for the restless Campi Flegrei caldera have been constructed using stratigraphical, volcanological, structural and petrological data, and statistical analyses. Although only 4 out of 70 eruptions of the past 15 ka were effusive, it cannot be excluded that the next eruption will be effusive. The past explosive eruptions can be grouped in low-, medium-, and high-magnitude events. A future explosive eruption could likely occur in the north-eastern sector of the caldera floor that is under a tensile stress regime, when the ongoing deformation will generate mechanical failure of the rocks. A vent could open also in the western sector, at the intersection of two fault systems contemporaneously activated, as happened in the last eruption at Monte Nuovo, in 1538 AD. The eruption could likely be preceded by precursors apparent to the population, such as ground deformation, seismicity and increase in gas emissions. It will probably alternate between magmatic and phreatomagmatic phases with the generation of tephra fallout, and dilute and turbulent pyroclastic currents. In order to perform a zoning of the territory in relation to the expected volcanic hazards, we have constructed hazards maps in which the areas at variable probability of opening of a new vent, those which could be affected by variable load of fallout deposits, and those over which pyroclastic currents could flow, are delimited. The areas in which a vent could likely open have been defined on the basis of the dynamics of the ongoing deformation of the caldera floor, and of a statistical analysis of critical elements. To construct the fallout hazard map we have used the frequency of deposition of fallout beds, the frequency of load on the ground by tephra fallout and the direction of dispersal axes of the deposits of the last 5 ka, and the limit load of collapse for the variable types of roof construction. The pyroclastic-current hazard map has been based on the areal distribution and frequency of the pyroclastic-current deposits of the last 5 ka.
V33C-03
APOLLO: AN AUTOMATIC PROCEDURE TO FORECAST TRANSPORT AND DEPOSITION OF TEPHRA
Volcanic ash fallout represents a serious threat to communities around active volcanoes. Reliable short term predictions constitute a valuable support for to mitigate the effects of fallout on the surrounding area during an episode of crisis. We present a platform-independent automatic procedure aimed to daily forecast volcanic ash dispersal. The procedure builds on a series of programs and interfaces that allow an automatic data/results flow. Firstly the procedure downloads mesoscale meteorological forecasts for the region and period of interest, filters and converts data from its native format (typically GRIB format files), and sets up the CALMET diagnostic meteorological model to obtain hourly wind field and micro-meteorological variables on a finer mesh. Secondly a 1-D version of the buoyant plume equations assesses the distribution of mass along the eruptive column depending on the obtained wind field and on the conditions at the vent (granulometry, mass flow rate, etc.). All these data are used as input for the ash dispersion model(s). Any model able to face physical complexity and coupling processes with adequate solving times can be plugged into the system by means of an interface. Currently, the procedure contains the models HAZMAP, TEPHRA and FALL3D, the latter in both serial and parallel versions. Parallelization of FALL3D is done at two levels one for particle classes and one for spatial domain. The last step is to post-processes the model(s) outcomes to end up with homogeneous maps written on portable format files. Maps plot relevant quantities such as predicted ground load, expected deposit thickness or visual and flight safety concentration thresholds. Several applications are shown as examples.
V33C-04
Lava Flow Invasion Hazard map of the Southern Rift (Mount Etna, Italy)
We present an integrated approach and a multidisciplinary methodology to compile volcanic hazard map for lava flow invasion. In addition we display an application of the proposed methodology to a sector of Mount Etna, the Southern Rift, one of the most active areas of the Volcano (Behncke & Neri, 2003). The basis and the starting point are a detailed geological and structural survey and a high-resolution stratigraphy (at 1:10,000 scale) that allow us to recognize and to map about 30 lava flows along the Southern Rift. The geological data (lava flow emission point location, relative or historical age, length and outcropping area) are organized in a geographic database. In addition GIS software analyses (Groppelli & Norini, 2005), statistical tests and probabilistic lava flow model (Damiani et al., 2006) are applied. Our methodology rests on five steps. 1) Detailed geological survey and historical descriptions (Branca & Del Carlo, 2004) to produce a geological map identifying recent lava flows and their distribution. 2) GIS analyses of geological data (e.g. lava flow length, eruptive fissure age, qualitative and quantitative spatial probability map that allows to recognize the areas where eruption probability is more relevant based on emission point density, etc.). 3) Testing of a lava flow simulation model (ELFM) based on a high resolution DEM to obtain the morphological constraint of the lava flow simulation (Damiani et al., 2006). 4) Preliminary lava flow hazard map computation based on the ELFM combined with the eruption probability of each pixel of the DEM. 5) Hazard map validation based on the geological map and its analyses. We applied the previous described steps to the Southern Rift, from 2002-03 eruptive fissure (2900 m a.s.l.) to Monte S. Leo (1100 m a.s.l.). We recognized in that area three main eruptive areas, each characterized by different frequency of eruptions and length of lava flows. For each area we calculated the probability of eruption in the next 50 years and we performed digital flow simulations with different parameters after a tuning phase. Merging the three resulting hazard maps, we obtained the hazard map for lava flow invasion of the Southern Rift, which can be helpful for land use and urban planning.
V33C-05
November 16th 2006 Lateral Collapse of South-East Crater on Mount Etna Volcano and Hazard Implication
On November 16th 2006 a sector collapse affected the unstable eastern flank of the South-East Crater (SEC) on Mount Etna Volcano. The SEC is located on the Etna volcano summit and is an active steep cone formed by alternated scoria deposits and lava flows traversed by numerous fractures. The collapse occurred during an eruptive event and was probably triggered by effusive and explosive activity on the SEC. The resulting debris avalanche involved both altered and fresh materials, including an active lava flow. The collapse produced a debris avalanche deposit emplaced on the eastern flank of the volcano, extending up to 1.1 km from the source. The deposit is formed by superimposed flow units, suggesting that it is the result of at least two discrete events, the total volume is estimated in the order of 300,000-500,000 m3. A block-facies and a matrix-facies were recognized in the field. The former is composed by blocks up to 1 meters in dimension and has maximum thickness of 4-5 meters. The matrix-facies is mainly composed by a convection-driven flow deposit consisted of fine ash produced by elutriation during emplacement of the block-facies, maximum observed thickness is 30 cm. The reconstruction of the event has been supported by numerical simulations that were executed using TITAN2D, a modeling software for granular avalanches and landslides developed by GMFG at Buffalo. This approach is also useful to estimate the area that would be affected by an eventual similar event that could interest the SEC. The area affected by the lateral collapse of the SEC is a small portion of the summit area of Mount Etna, but the fact that no one was killed or injured should be considered fortuitous. This because the summit and adjacent areas of the volcano are usually visited by several people, especially tourists, not prepared to face this type of events, which was never observed and described during the recent activity of Mount Etna. The collapse of November 16th 2006 underscores the need to prepare for similar events through scientific investigation (analysis of instability, numerical modelling of flows) and development of specific civil protection plans.
V33C-06
Numerical modeling of debris avalanches at Nevado de Toluca (Mexico): implications for hazard evaluation and mapping
The present study concerns the numerical modeling of debris avalanches on the Nevado de Toluca Volcano (Mexico) using TITAN2D simulation software, and its application to create hazard maps. Nevado de Toluca is an andesitic to dacitic stratovolcano of Late Pliocene-Holocene age, located in central México near to the cities of Toluca and México City; its past activity has endangered an area with more than 25 million inhabitants today. The present work is based upon the data collected during extensive field work finalized to the realization of the geological map of Nevado de Toluca at 1:25,000 scale. The activity of the volcano has developed from 2.6 Ma until 10.5 ka with both effusive and explosive events; the Nevado de Toluca has presented long phases of inactivity characterized by erosion and emplacement of debris flow and debris avalanche deposits on its flanks. The largest epiclastic events in the history of the volcano are wide debris flows and debris avalanches, occurred between 1 Ma and 50 ka, during a prolonged hiatus in eruptive activity. Other minor events happened mainly during the most recent volcanic activity (less than 50 ka), characterized by magmatic and tectonic-induced instability of the summit dome complex. According to the most recent tectonic analysis, the active transtensive kinematics of the E-W Tenango Fault System had a strong influence on the preferential directions of the last three documented lateral collapses, which generated the Arroyo Grande and Zaguàn debris avalanche deposits towards E and Nopal debris avalanche deposit towards W. The analysis of the data collected during the field work permitted to create a detailed GIS database of the spatial and temporal distribution of debris avalanche deposits on the volcano. Flow models, that have been performed with the software TITAN2D, developed by GMFG at Buffalo, were entirely based upon the information stored in the geological database. The modeling software is built upon equations solved by a parallel and adaptive mesh, that can concentrate computing power in region of special interest. First of all, simulations of known past events, were compared with the geological data validating the effectiveness of the method. Afterwards, numerous simulations have been executed varying input parameters as friction angles, starting point and initial volume, in order to obtain a global perspective over the possible expected debris avalanche scenarios. The input parameters were selected considering the geological, structural and topographic factors controlling instability of the volcanic cone, especially in case of renewed eruptive activity. The interoperability between TITAN2D and GIS softwares permitted to draw a semi-quantitative hazard map by crossing simulation outputs with the distribution of deposits generated by past episodes of instability, mapped during the field work.
V33C-07
Flow Simulations Reproducing the 1982 Eruption of the el Chichón Volcano, Mexico.
During the March 28, 1982 eruption of El Chichón volcano (México) different types of flows affected several villages, killing more than 2000 people. This disaster showed the need to elaborate a hazard map for this volcano. The observation of the 1982 eruption coupled with the reconstruction of past events, revealed that main hazards at El Chichón consist of block-and-ash flows, surges and lahars. In order to construct a hazard map of the volcano, computer simulations were performed using the pre-1982 topography (10 m in pixel resolution) to mimic past flows and calibrate the different physical coefficients needed as input parameters in the computer routines. Block and ash flow simulations fitted quite well with observed trajectories (FLOW3D with a0: 0.1-0.2) and inundation limits (with TITAN2D, friction angle: 30º, pile volume: 0.01*106-0.1*106 m3). The main uncertainties were in the more distal portions where it was very difficult to obtain reliable results for flow inundation limits and thicknesses. The ENERGY CONE was applied with a H/L of 0.1 giving a distribution for surges consistent with the S1 deposit, the largest surge emplaced during the 1982 eruption. Finally, lahars were reproduced with LAHARZ using volumes of 4, 2 and 1*106 m3, obtaining surprising results on ravines that were not affected during 1982, but that could be threatened in the future. This work evidences that despite some limitations, mainly related to the topography resolution, computer simulations are useful tools during the preparation of volcanic hazards maps. They must be coupled with detailed data obtained by field work, which is crucial to check the reliability of computer simulations.