21 August, 2001
This morning I met with Dr. Philip Kyle and discussed general principles of volcanism, including the complexities of understanding the magma chamber, and the chemical means that he and his teams have employed to try to get a window on this “heart” of the volcano.
The chemical analysis centers on the gases that are emitted in the plume. The predominant gas is water vapor, followed by carbon dioxide, then carbon monoxide, HCl, and sulfur dioxide. Other compounds that include chlorine and fluorine are included in the list, but at much lower concentrations. Part of the reason that so much effort is devoted to the measurement of the sulfur portion is that it is possible to measure its content remotely using a device called a correlation spectrometer (COSPEC). The device is pointed through the plume at a light source (solar radiation), and the absorption of ultraviolet wavelengths by the sulfur dioxide yields its concentration. This data combined with the area of the cross section of the plume and its rate of ascent yields the number of metric tons of sulfur being emitted into the atmosphere (about 50 to 70 metric tons per day). This is not unlike measuring the cubic feet per second of water flowing in a river. While the emission of sulfur dioxide by Mt. Erebus might give cause for some environmental impact concerns, this volcano’s emissions pale in comparison to the many thousands of tons per day released by other volcanoes around the world.
Phil’s calculations of sulfur emissions are compared to the data collected by Jesse (see 8/20) and other chemical data so that ratios can begin to be generated. Once reliable estimates of the concentrations of a few compounds (or radioactive nuclides) are established, the mathematical calculation of the suspected quantities and concentrations of other compounds can be determined by ratios and fairly simple algebra.
Phil related some interesting stories about his research data and the science and politics of environmentalism. I’ll save that for another entry. In the afternoon I met with Dr. Richard Aster, a seismologist and colleague of Phil’s. Seismology takes a very different approach to the shared goal of everyone studying Erebus (and other volcanoes), which is to understand what is going on in the deep underbelly of the beast. While the chemical data yields a fairly continuous stream of information, the seismic data is episodal. Something has to happen. There are two general categories of seismometers: short period, which registers relatively quick, short-lived tremors, and the broad band seismometers, which detect movements of the earth or volcano wall that have a very long period—from 1 Hz to thirty seconds or more. Seismic events don’t just involve the earth cracking apart or grinding against itself. Within a volcano, lava entering a vacant tube or space can generate vibrations that have a peculiar signature called harmonic volcanic tremor.
There is real-time data from the two currently operating seismometers on Erebus that you can access yourself, if you like. You can find it on the Mount Erebus Observatory Homepage at http://www.ees.nmt.edu/Geop/mevo/mevo.html . Although the data is difficult to interpret without some educated guidance, try clicking on some dates and comparing data. One interesting thing to try is clicking on the data that have been translated into audio frequencies and speeded up so that you can “hear” the seismic event. If you see many small specks in the analog data, you are probably seeing “snowquakes” which are not of interest in this study.
This is a “maintenance year” for the seismic equipment, and I’m sure that I’ll have more to say about the physical setup of this equipment when we’re on the ice.
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