Abstract
Pyroclastic density currents are one of the most devastating volcanic hazards. Understanding their dynamics is a key to develop successful hazard mitigation strategies. The hazard associated with pyroclastic density currents is commonly investigated a posteriori from their deposits or a priori using analogue and numerical experiments. Despite the low probability of observing a natural moving pyroclastic density current, we present the first in-situ analysis of the internal particle velocities of pyroclastic density currents at Volcán de Colima using a Doppler radar. Our data show two Vulcanian explosions, immediately followed by column collapse and a first pyroclastic density current travelling down the south flank with an average speed of 30 m/s (>50 m/s maximum speed) to a distance of 3 km from the crater rim. The direction of the pyroclastic density current coincided with that of the radar beam enabling measurement of velocity spectra (histogram of particle velocities within the radar beam). The measurement geometry enables the simultaneous measurement of the dense undercurrent at the crater rim (with <20 m/s and an increasing echo power over 20 s) and the dilute cloud higher above the topography approaching the radar (with >20 m/s and approximately constant echo power). The presented data set may be used as a benchmark for future experimental and numerical models that simulate the dynamics of pyroclastic density currents. Using the measured velocities of the collapsing column as input for numerical models will permit the validation of the models for the prediction of the true run-out distance, and thus provide valuable information for hazard assessments.
Highlights
IntroductionNumerical models and analogue experiments show that both pyroclastic density currents (PDCs) and snow avalanches are comprised of a dense undercurrent, behaving like a granular flow, overlain by a dilute ash (or snow) cloud controlled by turbulence and entrainment
Numerical models and analogue experiments show that both pyroclastic density currents (PDCs) and snow avalanches are comprised of a dense undercurrent, behaving like a granular flow, overlain by a dilute ash cloud controlled by turbulence and entrainment
The Doppler radar was set up roughly 2,700 m slant distance from the crater rim on the south flank, on a ridge in-between the ravines where the PDCs descended
Summary
Numerical models and analogue experiments show that both pyroclastic density currents (PDCs) and snow avalanches are comprised of a dense undercurrent, behaving like a granular flow, overlain by a dilute ash (or snow) cloud controlled by turbulence and entrainment. Only one comparable Doppler radar measurement exists: it reveals the internal dynamics of a snow avalanche (a controlled experiment) travelling down the flank of a fjord at 120 km/h24 (=33 m/s). This Doppler radar data set has subsequently been used to validate a numerical model for snow avalanches[25], which is still used for hazard assessment[26].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
