Volcanic gas

As volcanic gases gases are referred to, which emerge at the earth's surface during volcanic activity. The exit can be either in targeted areas (eg at the volcano crater, fumaroles, solfataras ) effected or carried out over a large area diffuse from the flanks of a volcano.

Formation

On the ascent of molten rock in the vent of a volcano are conditionally released by the decreasing pressure, the previously dissolved in the molten rock gases and discharged with more or less (even with ' peaceful ' eruptions is a lot of gas released ) explosive eruptions. Even in a magma chamber beneath the volcano, the volatiles can be enriched to about the respective saturation limit in the residual melt, so they there form a separate phase in the form of gas bubbles through the process of fractional crystallization. Rise due to the density difference between the gases and the surrounding melt to the gas bubbles and can thus also without concomitant Lavaförderung the volcano escape.

Composition

At volcanoes escaping gases are usually a mixture of different substances. Main component of almost all volcanic gases are water vapor (H2O ), carbon dioxide (CO2 ), sulfur dioxide (SO2), hydrogen sulphide (H2S ), hydrochloric acid (HCl) and hydrogen fluoride ( HF). In changing percentages also some noble gases, carbon monoxide, methane and hydrogen, ammonia, occur. The gas quantity and composition is strongly dependent on the nature of the molten rock from which they emerge. Gases, which are released from basaltic melts, CO2 - dominated, while rhyolitic magmas produce greater total amounts of mainly water vapor - dominated gases.

Importance

• Volcanic gases are partially greenhouse gases.
• The water on Earth comes partly volcanic gases.
• The change in the composition of volcanic gases can indicate an impending volcanic eruption.

Previously it was believed that it is volcanic gas eruptions that occur without promotion of lava. These were, inter alia, responsible for the formation of maars, as they occur for instance in the German Eifel or the French Auvergne. Meanwhile, the volcanologists are sure that Maare by the contact of magma with ground water that evaporates explosively formed.

Effects and dimensions

Volcanoes practice long and in individual cases, over short periods with their gas emissions a major impact on life on Earth.

• Over geologic periods of time considered represent volcanic CO2 emissions represent a potential climate feedback mechanism that the earth has probably saved from a permanent global glaciation.
• In the range of years the emission of trace gases and ash can, however, lead to a greatly reduced sunlight and thus cool down on the ground. Thus, a decrease in atmospheric temperatures by about 0.5 degrees in 1991 in the years following the eruption of the volcano Pinatubo Philippine measured.
• A particular striking example of the devastating effect of volcanic eruptions on the climate is the so-called year without a summer is (1816 ) in which there was sometimes catastrophic crop failures and famine in North America and Europe. Even in ice cores can be ash layers of large volcanic eruptions demonstrate that were associated with reduced temperatures.

An example of the dimension of the gas emissions in volcanic plumes is the volcano Popocatépetl 60 kilometers away from the 20 million inhabitants agglomeration Mexico City. In times of increased activity approximately between March 1996 and January 1998, the Popocatépetl had repeated outbreaks, which at times reached more than 10,000 tons of sulfur dioxide per day into the atmosphere. This represented around one quarter of total anthropogenic - manmade - sulfur emissions in Europe and about half of the emissions of Central and South America together.

Volcanoes emit large amounts of halogens such as bromine or chlorine, which have a significant influence on the ozone budget (quote).

Quantification of the effluent gases

The emission rate of a gas from a volcano determine the scientists in that they measure the total amount of the first substance in a cross section perpendicular to the propagation direction of the plume with the DOAS technique, and then multiplied by the wind speed. The emission rate is, for example, how much SO2 per second, day, or year is expelled.

The wind speed was determined earlier by wind measurements on the ground or on the crater rim. However, this proved to be costly, inaccurate and sometimes even dangerous. The data obtained were also only partially representative of the actually prevailing in the Volcanic flag wind direction and speed. Today the DOAS technique for the so-called correlation technique is used, wherein the device is directed in DOAS rapid changes in two downwind viewing directions. The method makes use of the fact that the flag is not volcanic homogeneously mixed and the gases are distributed unevenly. Thus, for each of the viewing directions, a structured time series. Every time a cloud with increased concentration of sulfur dioxide passes, just the other measurement point reports of a short time later at a maximum. The time offset corresponding to the time required for the volcanic flag to move from one direction of view to the other. Based on the knowledge of the angle between the directions of view and the distance to the volcano flag, you know hence the distance between the two viewing directions of each other in the flag. The wind speed is calculated accordingly from the quotient of distance and time offset.

Development of research

More recently, the instruments for observation of volcanic emissions have been significantly improved. Adopted in 2001 before researchers working group atmosphere and remote sensing of the Institute of Environmental Physics, University of Heidelberg, together with scientists from the Chalmers University of Technology, Gothenburg, Sweden the first time DOAS measurements in volcanic plumes. Although spectroscopic measurements of sulfur dioxide in volcanic plumes were carried out with other methods since the 1970s, but the new method allowed the construction of much smaller and thus handier tools. Also, the researchers were able for the first time in addition to sulfur dioxide also detect a variety of other trace gases, such as halogen and nitrogen oxides.

The different solution behavior of the different gases in the magma has led to the consideration of whether changes in gas emissions could provide clues about the behavior of magma, for example, show upgrade processes and thus outbreaks could announce. To this end, found and find research through systematic measurements instead, eg at Popocatepetl (Mexico), Masaya (Nicaragua ), Etna (Italy ), Gorely, Mutnovsky (both Kamchatka ) and Nyiragongo (Congo). At Popocatepetl, Masaya and Etna permanent monitoring stations were set up.

The possibilities have been greatly improved to measure volcanic emissions using satellites. Since the launch of the Global Ozone Monitoring Experiment ( GOME ) in 1995, the detection limits have been significantly reduced by the improved spectral sampling. Other instruments with similar characteristics ( SCIAMACHY, OMI, GOME -2) have been added later. Through this greatly improved detection limits and the comprehensive spatial coverage open modern satellite instruments have a significantly expanded access to global monitoring of volcanic activity and quantification of their emissions. Thus, the atmospheric transport of volcanic emissions may be about often be followed over several days using satellite observations (in some cases over periods of up more than a month ). This influences of volcanoes from regional to global scale to investigate left. In addition, volcanoes could be measured in remote areas through satellite observation at all for the first time.