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

1W_4E-P3

Date/Time: July 21 Poster

The challenge in quantifying magma input and output to active volcanoes—an example
from Kilauea
Michael P. Poland, A. Jeff Sutton, Tim R. Orr
USGS - Hawaiian Volcano Observatory, USA
E-mail: mpoland@usgs.gov

Two of the most fundamental parameters governing volcanic activity are magma supply to and effusion from thevolcanic edifice. Both are especially relevant at persistently active volcanoes, where an imbalance in the two
can result in changes in eruptive activity. Kilauea Volcano, in Hawai‘i—one of the best–studied volcanoes in theworld—provides an excellent example of the challenges in quantifying magma supply and effusion rates.

Magma supply to the volcano has been calculated by combining the volume of effusion with the volume ofstorage as determined from deformation modeling, but that approach assumes all magma storage areas areknown and that models of surface deformation provide accurate volume change estimates. Simple elastic models
of deformation, however, fail to account for magma compressibility, which can bias volume calculations by up to anorder of magnitude. Carbon dioxide emissions provide a means of gauging changes in supply but are only usefulin a relative sense because the CO2 content of the hotspot supplied magma currently remains an estimate.

Numerous techniques have been employed to gauge lava effusion rates, including SO2 emissions basedon a known SO2 content of the magma, lava tube cross-section and flux, topographic change due to lava
emplacement, and thermal measurements. Extensive lava flow fields, however, confound efforts to image thermal
and topographic change, since airborne measurements often lack sufficient areal coverage and satellite monitoring
may not have adequate temporal resolution. In addition, lava that enters the ocean cannot be satisfactorily
accounted for by measuring changes in subaerial topography. If no observable lava tubes are present, geophysicalmethods of determining flux through tubes are not possible.

Finally, equating the rates of lava effusion toSO2 emission assumes that all magma that degasses SO2 also erupts. This assumption does not accountfor pre-eruptive degassing—a process that has been occurring since the start of Kilauea’s summit eruption in2008. Moreover, some magma may degas but not erupt, instead sinking to deeper levels after it has lost its volatiles.

Improved spatial and temporal resolution of satellite measurements can address the effusion rate question.
This technique is best for flows that remain on land and do not enter the ocean. We are currently testing theTanDEM-X topographic mission as a means of mapping the volume change of Kilauea’s Pu‘u ‘O‘o flow field.
Absolute determinations of magma supply, however, will continue to involve numerous assumptions until better
understanding of primary melt composition and magma storage are available. For now, magma supply ratemeasurements remain most useful in a relative sense.

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