Volcano Monitoring with FT-IR

AeroSurvey has been involved in two separate volcano monitoring investigations.  In 1994, we worked with Dr. Peter Francis from the Open University (Milton Keynes, England) to investigate the gaseous emissions from Mt. Etna and Vulcano, a volcanic island in the Mediterranean.  In 1995, we worked with Dr. Philip Kyle from New Mexico Institute of Mining and Technology (Socorro, New Mexico) to study Mt. Erebus in Antarctica.

Why study volcanic gases?

The composition of gases coming from volcanoes can tell us much about the composition of the underlying magma bodies.  Volcanic eruptions may be preceded by changes in the magma bodies and these changes may be detectable as a change in the composition of gases emitted by a volcano.  

Why use FT-IR?

Although other techniques have been used for many years to sample volcanic gases, open-path FT-IR techniques offer a means of actually monitoring the composition of the volcanic gases. In our one-week investigation at Mt. Etna, we were able to collect thousands of spectra over many hours and days, each one providing information on a number of volcanic gas components.  In our Mt. Etna investigation, we used each spectrum to produce a single value representing the ratio sulfur dioxide to hydrogen chloride.  The large number of spectra resulted in a statistically robust data set and provided a high degree of confidence in the average values seen at different locations and on different days.  This data set may be the beginning of a database that will allow volcanologists to know how much variation is "normal". 

How is FT-IR data collected at volcanoes?

FT-IR data may be collected actively or passively, from the air or from the ground, and we tried all of these approaches at some point in our volcano investigations.  Most of the useful data, however, came from ground-level monitoring of plumes with an active set-up.  We would establish an infrared beam along the downwind slope or near the crater rim, over which the plume was passing.  As the plume passed through our beam, molecular components of the plume such as sulfur dioxide and hydrogen chloride would absorb characteristic frequencies of the  infrared beam.  We used the FT-IR instrument to characterize these absorptions in the form of absorbance spectra.  The presence of characteristic absorbance bands confirmed the presence of various gases and the intensities of the bands allowed us to make quantitative assessments.

A look at the data

The top spectrum in the figure above is actually just one section of an infrared absorbance spectrum, collected from the crater rim on Vulcano.  This spectrum is interesting because it reveals the presence of a plume component not previously thought to exist in volcanic gases - silicon tetrafluoride.  Similarly, we found a tremendous amount of unexpected carbon monoxide leaving Mt. Erebus. Most analytical techniques are good at showing us what we are looking for - one of the great things about FT-IR is it's ability to reveal things we may not have been looking for!  

The same spectrum shown above also contained the signature of hydrogen chloride (in another spectral region that we couldn't cram very well into one graphic).  We measured the amount of sulfur dioxide and hydrogen chloride in this spectrum and produced a ratio value (about 1.2, in this spectrum).  We did this for hundreds of spectra collected at this particular site and thus obtained an average ratio of sulfur dioxide to hydrogen chloride.  We found different ratios at different volcanoes and even at the same volcano when sampled at different sites and on different days.  

Want to know more?

The results of our work on the Italian volcanoes have been published in a few different journals.

For information on the FT-IR aspects of the work we suggest:

"Infrared Analysis of Volcanic Plumes: A Case Study in the Application of Open-Path FT-IR Monitoring Techniques," C.T. Chaffin, T.L Marshall, W.G. Fateley, R.M. Hammaker, Spectroscopy Europe, 7/3, 18-24 (1995).

For information on the volcanic aspects of the results, try some of the following articles:

"SO2:HCl ratios in the plumes from Mt. Etna and Vulcano determined by Fourier transform spectroscopy," P.W. Francis, A. Maciejewski, C. Oppenheimer, C.T. Chaffin, and T. Caltobiano, Geophysical Research Letters, 22,13, 1717-1720 (1995). 

"Remote determination of SiF4 in volcanic plumes: a new tool for volcano monitoring," Francis P. W., Chaffin C. T., Maciejewski A. J. H. and Oppenheimer C. . Geophysical Research Letters, 23/3, 1996. 

"New methods make volcanology less hazardous,"  Francis P. W., Maciejewski A. J. H., Oppenheimer C. and Chaffin C. T. . EOS Transactions, 7/41, 1996. 

"Volcanic gas measurements by helicopter-borne Fourier transform spectroscopy," Oppenheimer C., Francis P. and Maciejewski A. . International Journal of Remote Sensing, Vol. 19, Nº. 2, p. 373 - 379, 1998.

Want to see some pictures?

You can click on some of the pictures in the gallery below to enlarge and read more about each one. Some of the photos illustrate the use of FT-IR in these applications while others are included simply because we think they are pretty cool.

Volcanic Monitoring Investigations - Picture Galleries
	Mt. Etna, Sicily A large accessible volcano, Mt Etna allowed us to get thousands of spectra from multiple craters.  Photos in this set illustrate the transportability and ruggedness of the FT-IR instrumentation.
	Vulcano, a volcanic island in the Mediterranean Sea Vulcano is a small volcano, rising only 400' out of the Mediterranean Sea.  We collected a lot of the best data here passively, using the hot rocks around and in the crater as an infrared source for making high-quality absorption measurements.
	Mt. Erebus, Antarctica At 12,444' in the icy frontier of Antarctica, Mt. Erebus is one of the most inaccessible and foreboding sites for volcanic research on Earth.  But we managed to get our equipment down there and it functioned quite well nonetheless.