Volcanic gas

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Emission cloud over the Halemaʻumaʻu crater (Hawaii).

As volcanic gases are gases referred to, which in the course of volcanic activity on the Earth's surface to escape. The exit can either take place in narrowly defined areas (e.g. at the volcanic crater , fumaroles , solfataras ), or over a large area diffusely from the flanks of a volcano .

Emergence

When molten rock rises in the chimney of a volcano, due to the decreasing pressure, the gases previously dissolved in the molten rock are released and discharge with more or less (even with 'peaceful' eruptions a lot of gas is released) explosive eruptions. Even in a magma chamber below the volcano, the process of fractional crystallization allows the volatile constituents to be enriched in the residual melt beyond the respective saturation limit, so that they form their own phase in the form of gas bubbles . Due to the difference in density between the gases and the surrounding melt, the gas bubbles rise and can escape from the volcano without simultaneous lava extraction .

composition

Leakage of volcanic gases at the crater of Vulcano (Italy).

Gases released from volcanoes are usually a mixture of different substances. The main components of almost all volcanic gases are water vapor (H 2 O), carbon dioxide (CO 2 ), sulfur dioxide (SO 2 ), hydrogen sulfide (H 2 S), hydrochloric acid (HCl) and hydrogen fluoride (HF). Ammonia , some noble gases , carbon monoxide , methane and hydrogen can also occur in varying percentages . The amount and composition of gas depends heavily on the nature of the molten rock from which it emerges. Gases that are released from basaltic melts are CO 2 -dominated, while rhyolite magmas produce larger amounts of mainly water vapor-dominated gases.

meaning

It was previously believed that there are volcanic gas eruptions that occur without extraction of lava . These were u. a. made responsible for the formation of maars , such as occur in the German Vulkaneifel or the French Auvergne . Volcanologists are now certain that maars are formed when groundwater comes into contact with magma and then evaporates explosively ( phreatomagmatic explosion ).

Effects and dimensions

With their gas emissions, volcanoes exert a great influence on life on earth over long and in individual cases also over short periods of time.

  • Viewed over geological time periods, volcanic CO 2 emissions represent a potential climate feedback mechanism that has likely saved the earth from permanent global icing.
  • Over a period of years, however, the emission of sulfur dioxide and other gases as well as volcanic ash can lead to greatly reduced solar radiation and thus cooling on the ground (→  volcanic winter ). In 1991, in the years following the eruption of the Philippine volcano Pinatubo, a decrease in atmospheric temperatures of around 0.5 degrees was measured.
  • A particularly impressive example of the devastating effect of volcanic eruptions on the climate is the so-called year without a summer (1816), in which North America and Europe suffered catastrophic crop failures and famines. Ash layers from large volcanic eruptions that were associated with reduced temperatures can also be detected in ice cores.

An example of the dimension of gas emissions in volcanic plumes is the Popocatépetl volcano, which is about 60 km away from the 20 million population agglomeration of Mexico City . During periods of increased activity between March 1996 and January 1998, the Popocatépetl had repeated eruptions in which at times over 10,000 tons of sulfur dioxide per day were released into the atmosphere. This corresponded to around a quarter of the total anthropogenic - man-made - sulfur emissions in Europe and around half of the emissions in Central and South America combined.

Volcanoes emit large amounts of halogens such as bromine or chlorine, which are suspected of having a considerable influence on the ozone balance .

Determination of the quantity of the escaping gases

The scientists determine the emission rate of a gas from a volcano by first measuring the total amount of the substance in a cross section of the plume perpendicular to the direction of propagation using the DOAS method and then multiplying this by the wind speed . The emission rate gives z. B. on how much SO 2 is emitted per second, day or year.

The wind speed was previously determined by measuring the wind on the ground or at the crater rim. However, these proved to be complex, imprecise and sometimes even dangerous. The data obtained were also only partially representative of the wind direction and speed actually prevailing in the volcanic plume. Today, the DOAS method is used for the so-called correlation method, whereby the DOAS device is quickly directed to two averted viewing directions. The process takes advantage of the fact that the volcanic plume is not mixed homogeneously and the gases are rather unevenly distributed. This results in a structured time series for each of the viewing directions. Every time a cloud with an increased sulfur dioxide concentration passes, only one measuring point reports a maximum, a short time later the other measuring point. The time offset corresponds to the time it takes for the volcanic plume to move from one direction of view to the other. Due to the knowledge of the angle between the viewing directions and the distance to the volcanic plume, one also knows the distance between the two viewing directions in the plume. The wind speed is calculated from the quotient of distance and time offset.

Development of research

In recent times, the instruments for monitoring volcanic emissions have been significantly improved. In 2001, researchers from the Working Group on Atmosphere and Remote Sensing at the Institute for Environmental Physics at Heidelberg University, together with scientists from Chalmers University of Technology, Gothenburg , Sweden, carried out DOAS measurements in volcanic plumes for the first time. Although spectroscopic measurements of sulfur dioxide in volcanic plumes had been carried out using other methods since the 1970s, the new method allowed the construction of much smaller and therefore more manageable instruments. In addition to sulfur dioxide, the researchers were also able to detect a large number of other trace gases such as halogen and nitrogen oxides for the first time.

The different solution behavior of the various gases in the magma has led to the question of whether changes in gas emissions could provide information about the behavior of the magma, e.g. B. Show ascending processes and thus also announce outbreaks. For this purpose, research was and is taking place using systematic measurements, e.g. B. on Popocatépetl ( Mexico ), Masaya ( Nicaragua ), Etna ( Italy ), Gorely , Mutnovsky (both Kamchatka ) and Nyiragongo ( Congo ). Continuous measuring stations have been set up at Popocatepetl, Masaya and Etna.

The possibilities of measuring volcanic emissions with the help of satellites have also been greatly improved. Since the start of the Global Ozone Monitoring Experiment (GOME) in 1995, the detection limits have been significantly reduced thanks to improved spectral scanning. Other instruments with similar properties ( SCIAMACHY , OMI , GOME-2) were added later. Thanks to this greatly improved detection limits and comprehensive spatial coverage, modern satellite instruments open up considerably expanded access to global monitoring of volcanic activity and quantification of its emissions. For example, the atmospheric transport of volcanic emissions can often be tracked over several days using satellite observations (in individual cases over periods of up to a month). This made it possible to study the effects of volcanoes on a regional to global scale. In addition, volcanoes in remote regions could be measured for the first time by satellite observation.

See also

literature

  • Schmincke HU: volcanism . Scientific Book Society Darmstadt, 2000, ISBN 3-534-14102-4 .
  • AJ Krueger: Sighting of El Chichon sulfur dioxide clouds with the Nimbus 7 Total Ozone Mapping Spectrometer . Science 220: 1277-1379 (1983).
  • C. Seftor, N. Hsu, J. Herman, P. Bhartia, O. Torres, W. Rose, D. Schneider, N. Krotkov: Detection of volcanic ash clouds from Nimbus 7 / total ozone mapping spectrometer. Journal of Geophysical Research 102 (D14), 16749-16759 (1997)
  • N. Bobrowski, G. Hönninger, B. Galle, U. Platt: Detection of bromine monoxide in a volcanic plume . Nature 423, 273-276, doi: 10.1038 / nature01625 (2003)
  • S. Guo, GJS Bluth, WI Rose, IM Watson, AJ Prata: Re-evaluation of SO2 release of the June 15, 1991 Pinatubo eruption using ultraviolet and infrared satellite sensors . Geochemistry, Geophysics, Geosystems 5, Q04001, doi: 10.1029 / 2003GC000654 (2004)
  • MF Khokhar, C. Frankenberg, M. Van Roozendael, S. Beirle, S. Kuhl, A. Richter, U. Platt, T. Wagner: Satellite observations of atmospheric SO2 from volcanic eruptions during the time-period of 1996-2002 . Advances in Space Research 36 (5), Atmospheric Remote Sensing: Earth's Surface, Troposphere, Stratosphere and Mesosphere - I, pp. 879–887, doi: 10.1016 / j.asr.2005.04.114 (2005)
  • N. Theys, M. Van Roozendael, B. Dils, F. Hendrick, N. Hao, M. De Mazière: First satellite detection of volcanic bromine monoxide emission after the Kasatochi eruption . Geophysical Research Letters 36, L03809, doi: 10.1029 / 2008GL036552 (2009).
  • S. Guo, GJS Bluth, WI Rose, IM Watson, AJ Prata: N. Theys, M. Van Roozendael, B. Dils, F. Hendrick, N. Hao, M. De Mazière: First satellite detection of volcanic bromine monoxide emission after the Kasatochi eruption. Geophysical Research Letters 36, L03809, doi: 10.1029 / 2008GL036552 (2009)
  • BW Levin, AV Rybin, NF Vasilenko, AS Prytkov, MV Chibisova, MG Kogan, GM Steblov, DI Frolov: Monitoring of the eruption of the Sarychev Peak Volcano in Matua Island in 2009 (central Kurile islands) . Doklady Earth Sciences 435 (1), 1507-1510 (2010)
  • Christoph Kern, Ulrich Platt: Telegram from the depths , Ruperto Carola, issue 1/2010
  • Leif Vogel: Volcanic plumes: Evaluation of spectroscopic measurements, early detection, and bromine chemistry (German translation of the title: Vulkanfahnen: Evaluation of spectroscopic measurements, early detection and bromine chemistry). Dissertation 2011, permanent URL on the Heidelberg document server: [1]
  • Thomas Wagner, Christoph Hörmann, Marloes Penning de Vries, Holger Sihler: Global monitoring of volcanic emissions with satellite instruments. Research Report 2011 - Max Planck Institute for Chemistry
  • Nicole Bobrowski: Gas emissions, read like hieroglyphics. In: forschung - Das Magazin der Deutschen Forschungsgemeinschaft, 2/2012, pp. 4–9 ( online: PDF; 3.34 MB )

Web links

Individual evidence

  1. ^ A b Thomas Wagner, Christoph Hörmann, Marloes Penning de Vries, Holger Sihler: Global monitoring of volcanic emissions with satellite instruments In: Research report 2011 - Max Planck Institute for Chemistry.
  2. ↑ Christoph Kern, Ulrich Platt: Feuerberg over the megacity. The thing about the volcanic and man-made sulfur dioxide. In: Scinexx as of October 1, 2010; Retrieved December 30, 2012.
  3. ^ Statement by Prof. Dr. Christiane Voigt (Institute for Atmospheric Physics): Research flights: DLR examines the influence of contrails and volcanic emissions on the climate In: Press release of the German Aerospace Center (DLR) from October 7, 2011.
  4. ↑ a b Christoph Kern, Ulrich Platt: In a safe distance ... Volcanic gas measurement far away from the dangerous crater. In: Scinexx , as of October 1, 2010.
  5. ↑ Christoph Kern, Ulrich Platt: Waiting for an emergency. What if the Popocatépetl breaks out? In: Scinexx , as of October 1, 2010; Retrieved December 30, 2012.
  6. ^ Nicole Bobrowski: Gas emissions, read like hieroglyphs. P. 9.