USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Objective delineation of lahar-inundation hazard zones
-- Richard M. Inverson, Steve P. Schilling, and
James W. Vallance, 1998,
Objective delineation of lahar-inundation hazard zones:
IN: Geological Society of America Bulletin, August 1998, v.110, no.8, p.972-984
Abstract
A new method of delineating lahar hazard zones in valleys that
head on volcano flanks provides a rapid, objective, reproducible alternative
to traditional methods. The rationale for the method derives
from scaling analyses of generic lahar paths and statistical analyses
of 27 lahar paths documented at nine volcanoes. Together these
analyses yield semiempirical equations that predict inundated valley
cross-sectional areas (A)
and planimetric areas (B) as functions of lahar
volume (V). The predictive equations
(A = 0.05V2/3 and B = 200V2/3)
provide all information necessary to calculate and plot inundation
limits on topographic maps. By using a range of prospective
lahar volumes to evaluate A and B,
a range of inundation limits can
be plotted for lahars of increasing volume and decreasing probability.
Resulting hazard maps show graphically that lahar-inundation potentials
are highest near volcanoes and along valley thalwegs, and diminish
gradually as distances from volcanoes and elevations above
valley floors increase. We automate hazard-zone delineation by embedding
the predictive equations in a geographic information system
(GIS) computer program that uses digital elevation models of topography.
Lahar hazard zones computed for Mount Rainier, Washington,
mimic those constructed on the basis of intensive field investigations.
The computed hazard zones illustrate the potentially
widespread impact of large lahars, which on average inundate planimetric
areas 20 times larger than those inundated by rock avalanches
of comparable volume.
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11/24/98, Lyn Topinka