Pyroclastic current dynamic pressure from aerodynamics of tree or pole blow-down

Amanda Clarke, B. Voight

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

The common occurrence of tree and pole blow-down from pyroclastic currents provides an opportunity to estimate properties of the currents. Blow-down may occur by uprooting (root zone rupture), or flexure or shear at some point on the object. If trees are delimbed before blow-down, each tree or pole can be simulated by a cylinder perpendicular to the current. The force acting on a cylinder is a function of flow dynamic pressure, cylinder geometry, and drag coefficient. Treated as a cantilever of circular cross-section, the strength for the appropriate failure mode (rupture, uprooting or flexure) can then be used to estimate the minimum necessary current dynamic pressure. In some cases, larger or stronger standing objects can provide upper bounds on the dynamic pressure. This analysis was treated in two ways: (1) assuming that the current properties are vertically constant; and (2) allowing current velocity and density to vary vertically according to established models for turbulent boundary layers and stratified flow. The two methods produced similar results for dynamic pressure. The second, along with a method to approximate average whole-current density, offers a means to estimate average velocity and density over the height of the failed objects. The method is applied to several example cases, including Unzen, Mount St. Helens, Lamington, and Merapi volcanoes. Our results compare reasonably well with independent estimates. For several cases, we found that it is possible to use the dynamic pressure equations developed for vertically uniform flow, along with the average cloud density multiplied by a factor of 2-5, to determine average velocity over the height of the failed object.

Original languageEnglish (US)
Pages (from-to)395-412
Number of pages18
JournalJournal of Volcanology and Geothermal Research
Volume100
Issue number1-4
StatePublished - Jul 2000
Externally publishedYes

Fingerprint

dynamic pressure
aerodynamics
Poles
Aerodynamics
poles
flexure
flexing
estimates
rupture
stratified flow
turbulent boundary layer
Volcanoes
drag coefficient
Drag coefficient
current velocity
uniform flow
density current
boundary layer flow
drag coefficients
failure modes

Keywords

  • Dynamic pressure
  • Pyroclastic current
  • Tree or pole blow-down

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Pyroclastic current dynamic pressure from aerodynamics of tree or pole blow-down. / Clarke, Amanda; Voight, B.

In: Journal of Volcanology and Geothermal Research, Vol. 100, No. 1-4, 07.2000, p. 395-412.

Research output: Contribution to journalArticle

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