IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

3A1_3F-O3

Room A3

Date/Time: July 23 9:30-9:45

From field data to volumes: constraining uncertainty for pyroclastic eruptions
Malin Klawonn1 , Bruce F Houghton1 , Donald A Swanson2 , Sarah A Fagents1 , Paul Wessel1 , Cecily JWolfe1
1

University of Hawaii, U.S.A., 2 Hawaiian Volcano Observatory, USGS, U.S.A.
E-mail: klawonn@hawaii.edu

In this study we aim to understand the variability in eruption volume estimates from field studies of pyroclasticdeposits.

Variability arises from three components: site selection in the field, hand-contouring of thickness

measurements, and the selection of methods to integrate data and estimate volume. We distributed paper mapsof the 1959 Kilauea Iki tephra dataset to 101 volcanologists worldwide, who produced hand-drawn contours. The
returned isopach maps show great variety in contour number, spacing and shape. More experienced participantstended towards fewer, smoother, and more elliptical contours. However, these differences do not manifest indifferences in isopach areas for a given thickness value. After excluding outliers we find that isopach area
uncertainty lies around 7% across the well sampled deposit, but increases to over 30% for isopachs that areassociated with the largest and smallest thickness measurements, where there is more uncertainty with the fielddata and hence more subjectivity. We fit exponential, power-law and Weibull functions through the isopach
thickness versus square root area values and find an average standard deviation for total volume of s = 37%.
The volume uncertainty is again largest (s = 58% to 59%) for the most proximal field that is not constrained bymeasurements and the distal field for which measurements are strongly affected by post-depositional processes,
while uncertainty across the densely sampled deposit lies at s = 8%. In case of the Kilauea Iki 1959 eruption we findthat the deposit beyond the 5 cm contour line contains only 1% of the total eruption volume, while the extrapolatednear-source deposit contains 61% and the well-constrained intermediate deposit 38% of the total volume. Thus
the relative uncertainty within each zone impacts total volume estimates differently. The large uncertainties in distaland proximal field are associated with the extrapolation of the empirical functions, and we expect uncertainty for
different eruptions and eruption types to show similar uncertainty trends. Therefore, we suggest a new conventionof stating all three partial volume estimates: one for the deposit that is constrained by measurements extending
to the largest and smallest reasonable isopach, one for the extrapolated deposit above the thickest isopach andone for the extrapolated distal deposit beyond the thinnest contour. This convention allows third parties to better
assess the associated uncertainty of an eruption volume, and is also a useful tool to identify desired measurement
locations during a field campaign in order to improve the accuracy of volume estimate of a given deposit.

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