USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
A Compilation of Sulfur Dioxide and Carbon Dioxide Emission-Rate Data from
Mount St. Helens during 1980-88
--
McGee, Kenneth A., and Casadevall, Thomas J., 1994,
A Compilation of Sulfur Dioxide and Carbon Dioxide Emission-Rate Data from
Mount St. Helens during 1980-88:
U.S. Geological Survey Open-File Report 94-212
Introduction
Airborne monitoring of Mount St. Helens by the USGS began in May 1980 for
sulfur dioxide emissions and in July 1980 for carbon dioxide emissions. A
correlation spectrometer, or COSPEC, was used to measure sulfur dioxide in
Mount St. Helens' plume. The upward-looking COSPEC was mounted in a fixed-
wing aircraft and flown below and at right angles to the plume. Typically,
three to six traverses were made underneath the plume to determine the SO2
burden (concentration x pathlength) within a cross- section of the plume.
Knowing the burden along with the plume width and plume velocity (assumed
to be the same as ambient wind speed), we could then calculate the emission
rate of SO2. The use of correlation spectroscopy for determining the sulfur
dioxide output of volcanoes is well established and the technique has been
discussed in detail by a number of investigators (Malinconico, 1979;
Casadevall and others, 1981; Stoiber and others, 1983).
Carbon dioxide in the Mount St. Helens plume was measured by an infrared
spectrometer tuned to the 4.26 µm CO2 absorption band. An external sample
tube was attached to the fuselage of a twin-engine aircraft to deliver
outside air to the gas cell of the spectrometer. The aircraft was then
flown at several different elevations through the plume at right angles to
plume trajectory to define plume area and carbon dioxide concentration in a
vertical cross-section of the plume. These two parameters along with the
density of CO2 for the altitude of the plume and the plume velocity
(assumed as above to be equal to ambient wind speed) were then used to
calculate the CO2 emission rate (Harris and others, 1981).
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07/17/02, Lyn Topinka