Numerical models of Plinian eruption columns and pyroclastic flows

Journal Article · Fri Feb 10 04:00:00 EST 1989 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB094iB02p01867· OSTI ID:6399669

Valentine, G A; Wohletz, K H

Numerical simulations of physical processes governing the large-scale dynamics of Plinian eruption columns reveal conditions contributing to column collapse and emplacement of pyroclastic flows. The simulations are based on numerical solution of the time-dependent, two-phase, compressible Navier-Stokes equations for jets in a gravitational field. This modeling effort is directed toward studying the steady discharge phase of eruptions in contrast to our previous models of the initial, unsteady blast phase. Analysis of 51 eruption models covers a wide range of vent exit pressures, inertial and buoyancy driving forces, and coupling of energy and momentum between gas and pyroclasts. Consideration of three dimensionless groups (Richardson and Rouse numbers and thermogravitational parameter) facilitates this analysis and defines conditions leading to column collapse. For eruptions with similar particle size characteristics, exit pressure ratios are also very important in determining column behavior; column behavior is much more sensitive to exit pressure ratio than to the density ratio between the column and the atmosphere. Model eruption columns with exit pressures exceeding atmospheric pressure have diamond-shaped patterns at their bases with internal dynamics that correspond closely to observations of overpressured jets in laboratory experiments. Collapsing fountains form pyroclastic flows that consist of low-concentration fronts, relatively thick heads, vortex development along the top surfaces, and rising clouds of buoyant ash. The presence of coarse-grained proximal deposits primarily reflects tephra size sorting within the eruption column before collapse, as opposed to that which occurs during lateral transport of the material in pyroclastic flows.

• Research Organization: Los Alamos National Laboratory, Los Alamos, New Mexico
• OSTI ID: 6399669
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 94:B2; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580202* -- Geophysics-- Volcanology-- (1980-1989)
ERUPTION
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HYDRODYNAMICS
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NUMERICAL SOLUTION
THREE-DIMENSIONAL CALCULATIONS
TIME DEPENDENCE
VOLCANOES