Open AccessLarge‐scale experiments on the mechanics of pyroclastic flows: Design, engineering, and first results
Author(s) -
Dellino Pierfrancesco,
Zimanowski Bernd,
Büttner Ralf,
La Volpe Luigi,
Mele Daniela,
Sulpizio Roberto
Publication year - 2007
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2006jb004313
Subject(s) - pyroclastic rock , overpressure , mechanics , turbulence , geology , electrical conduit , shear (geology) , plume , volcano , thermodynamics , petrology , physics , mechanical engineering , seismology , engineering
A newly designed apparatus for experimental studies of pyroclastic flows consists of a cylindrical conduit that is filled with samples of natural volcanic products (tephra). Blowing nozzles in the base plate of the conduit are connected to a volume of highly pressurized gas. Opening of fast solenoid valves results in impulse‐like coupling of the released gas to the sample. The system was designed so that the range of mechanical energy transferred to the particle mass in the conduit reflects the mechanical energy observed and measured during fragmentation experiments with melts of similar composition. Depending on the specific mechanical energy (SME) of the system, which results from Δ PV / m , where Δ P is gas overpressure (i.e., pressure > atmospheric), V is gas volume, and m is sample mass, different behaviors are observed. If SME > 2.6 kJ/kg, a dilute plume develops, and particles are sedimented by fallout exclusively. If SME < 1.5 kJ/kg, the exiting column collapses and develops a shear current similar to a pyroclastic flow. The Reynolds number of the shear currents is >10 6 , implying that flows are fully turbulent and that particle coupling to gas turbulence of natural pyroclastic flows is replicated by the experiments. The measured shear current velocities are proportional to the impact mass flow rate, i.e., the product of mixture density and impact velocity. Experimental data and grain‐size analysis of the produced particle deposits suggest that the scale of the experiment is large enough to reproduce the transport dynamics of natural pyroclastic flows.