Statistics – Computation
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusm.v33c..01s&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #V33C-01
Statistics
Computation
8414 Eruption Mechanisms And Flow Emplacement, 8488 Volcanic Hazards And Risks
Scientific paper
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.
Dalbey K.
Hall Matt
Patra Ayoti
Sheridan Michael F.
Stinton A.
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