Pyroclast Tracking Velocimetry: A particle tracking velocimetry‐based tool for the study of Strombolian explosive eruptions

Image-based techniques enable high-resolution observation of the pyroclasts ejected during Strombolian explosions and drawing inferences on the dynamics of volcanic activity. However, data extraction from high-resolution videos is time consuming and operator dependent, while automatic analysis is often challenging due to the highly variable quality of images collected in the field. Here we present a new set of algorithms to automatically analyze image sequences of explosive eruptions: the pyroclast tracking velocimetry (PyTV) toolbox. First, a significant preprocessing is used to remove the image background and to detect the pyroclasts. Then, pyroclast tracking is achieved with a new particle tracking velocimetry algorithm, featuring an original predictor of velocity based on the optical flow equation. Finally, postprocessing corrects the systematic errors of measurements. Four high-speed videos of Strombolian explosions from Yasur and Stromboli volcanoes, representing various observation conditions, have been used to test the efficiency of the PyTV against manual analysis. In all cases, >106 pyroclasts have been successfully detected and tracked by PyTV, with a precision of 1 m/s for the velocity and 20% for the size of the pyroclast. On each video, more than 1000 tracks are several meters long, enabling us to study pyroclast properties and trajectories. Compared to manual tracking, 3 to 100 times more pyroclasts are analyzed. PyTV, by providing time-constrained information, links physical properties and motion of individual pyroclasts. It is a powerful tool for the study of explosive volcanic activity, as well as an ideal complement for other geological and geophysical volcano observation systems.

[1]  Lucia Mancini,et al.  Large vesicles record pathways of degassing at basaltic volcanoes , 2008 .

[2]  Maurizio Ripepe,et al.  Detailed analysis of particle launch velocities, size distributions and gas densities during normal explosions at Stromboli , 2012 .

[3]  D. Patanè,et al.  Dynamics of the December 2002 flank failure and tsunami at Stromboli volcano inferred by volcanological and geophysical observations , 2003 .

[4]  W. Melson,et al.  Ejecta velocities, magma chamber pressure and kinetic energy associated with the 1968 eruption of arenal volcano , 1971 .

[5]  Bernard A. Chouet,et al.  Photoballistics of volcanic jet activity at Stromboli, Italy , 1974 .

[6]  Piergiorgio Scarlato,et al.  An analytical model for gas overpressure in slug-driven explosions:insights into Strombolian volcanic eruptions , 2012 .

[7]  S. Vergniolle,et al.  Separated two‐phase flow and basaltic eruptions , 1986 .

[8]  Antonio Cenedese,et al.  Using optical flow equation for particle detection and velocity prediction in particle tracking , 2012, Appl. Math. Comput..

[9]  Matthew R. Patrick,et al.  Dynamics of Strombolian ash plumes from thermal video: Motion, morphology, and air entrainment , 2007 .

[10]  Malte Vöge,et al.  Radar Doppler velocimetry of volcanic eruptions: theoretical considerations and quantitative documentation of changes in eruptive behaviour at Stromboli volcano, Italy , 2003 .

[11]  N. Malik,et al.  Particle tracking velocimetry in three-dimensional flows , 1993 .

[12]  D. Dingwell,et al.  Shallow magma‐mingling‐driven Strombolian eruptions at Mt. Yasur volcano, Vanuatu , 2012 .

[13]  Piergiorgio Scarlato,et al.  High‐speed imaging of Strombolian explosions: The ejection velocity of pyroclasts , 2012 .

[14]  R. Schmid.  Descriptive nomenclature and classification of pyroclastic deposits and fragments: Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks , 1981 .

[15]  Carmela Freda,et al.  Pyroclast Tracking Velocimetry illuminates bomb ejection and explosion dynamics at Stromboli (Italy) and Yasur (Vanuatu) volcanoes , 2014 .

[16]  Wan-Cheng Chiu,et al.  The rate of dissipation of energy and the energy spectrum in a low‐speed turbulent jet , 1956 .

[17]  Antonio Cenedese,et al.  Spatial–temporal improvements of a two-frame particle-tracking algorithm , 2010 .

[18]  Monica Moroni,et al.  Three‐dimensional particle tracking velocimetry studies of the transition from pore dispersion to Fickian Dispersion for homogeneous porous media , 2001 .

[19]  A. Peccerillo.  Geochemical similarities between the Vesuvius, Phlegraean Fields and Stromboli Volcanoes: petrogenetic, geodynamic and volcanological implications , 2001 .

[20]  Armin Gruen,et al.  Particle tracking velocimetry in three-dimensional flows , 1993, Experiments in Fluids.

[21]  G. Waite,et al.  Modeling shock waves generated by explosive volcanic eruptions , 2014 .

[22]  P. Sullivan,et al.  Longitudinal dispersion within a two-dimensional turbulent shear flow , 1971, Journal of Fluid Mechanics.

[23]  Gilberto Saccorotti,et al.  Image processing of explosive activity at Stromboli , 1993 .

[24]  Stephen Self,et al.  Ukinrek Maars, Alaska, II. Deposits and formation of the 1977 craters , 1980 .

[25]  Larry G. Mastin,et al.  A simple calculator of ballistic trajectories for blocks ejected during volcanic eruptions , 2001 .

[26]  M. Moroni,et al.  Physical parameterization of Strombolian eruptions via experimentally‐validated modeling of high‐speed observations , 2012 .

[27]  J. Phillips,et al.  A global study of volcanic infrasound characteristics and the potential for long-range monitoring , 2011 .

[28]  Antonio Cenedese,et al.  Investigation of penetrative convection in stratified fluids through 3D-PTV , 2009 .

[29]  Maurizio Ripepe,et al.  Bombs behaving badly: unexpected trajectories and cooling of volcanic projectiles , 2012, Bulletin of Volcanology.

[30]  M. Alatorre-Ibargüengoitia,et al.  Hazard zoning for ballistic impact during volcanic explosions at Volcán de Fuego de Colima (México) , 2006 .

[31]  Franck Donnadieu,et al.  Mass estimations of ejecta from Strombolian explosions by inversion of Doppler radar measurements , 2008 .

[32]  Sébastien Valade,et al.  Ballistics and ash plumes discriminated by Doppler radar , 2011 .

[33]  Michel Lardy,et al.  Sulphur dioxide emission rates from Yasur volcano, Vanuatu archipelago , 2007 .

[34]  Mauro Coltelli,et al.  Remotely Monitoring Volcanic Activity with Ground-Based Doppler Radar , 2005 .

[35]  L. Wilson,et al.  Explosive volcanic eruptions—IX. The transition between Hawaiian-style lava fountaining and Strombolian explosive activity. , 1995 .

[36]  M. Lardy,et al.  A comparative study of low-frequency seismic signals recorded at Stromboli volcano, Italy, and at Yasur volcano, Vanuatu , 1997 .

[37]  R. Schmid.  Descriptive nomenclature and classification of pyroclastic deposits and fragments , 1981 .

[38]  B. Houghton,et al.  Linking variable explosion style and magma textures during 2002 at Stromboli volcano, Italy , 2007 .

[39]  Antonio Cenedese,et al.  Comparison among feature tracking and more consolidated velocimetry image analysis techniques in a fully developed turbulent channel flow , 2005 .

[40]  A. Weill,et al.  Acoustic sounder measurements of the vertical velocity of volcanic jets at Stromboli Volcano , 1992 .

[41]  Franck Donnadieu,et al.  The geometry of Strombolian explosions: insights from Doppler radar measurements , 2010 .

[42]  Lionel Wilson,et al.  Explosive volcanic eruptions—VII. The ranges of pyroclasts ejected in transient volcanic explosions. , 1993 .