03.05.2013

Volcanoes can damage the ozone layer

GEOMAR and DESY scientists suggest that eruptions possibly have an effect on the ozone depletion

The in some areas extremely thin ozone layer discovered in the 1980s was clearly due to manmade emissions. However, there are ozone killing sources also in nature. Scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel and DESY in Hamburg found that giant volcanic eruptions may have large amounts of ozone depleting gases. Their study is published in the internationally renowned scientific journal “Geology”.

The Apoyo Caldera in Nicaragua was the site of a gigantic volcanic eruption 24 500 years ago. New research suggests that this and other eruptions could have released gases that temporarily depleted the ozone layer considerably. Photo: S. Kutterolf, GEOMAR

Mid of the 1980s, atmosphere researchers discovered that the ozone layer in the stratosphere was very thin in some areas. The cause for this “ozone hole” was ozone depleting hydrochlorofluorocarbons manufactured in large amounts for several industrial products, and released into the atmosphere. Ozone in the stratosphere, i.e. in an altitude of 15 to 50 kilometres, is vital for life on earth because it forms a shield against dangerous UV radiation from outer space. For this reason, the international community of states had agreed rather quickly on counteraction and, in fact, the ozone layer is slowly recovering since then. However, it is difficult to make predictions on when the ozone layer will reach the pre-industrial status. Nature too produces ozone depleting substances, e.g. compounds of bromine and chlorine. “These are halogens that love to react with other substances — especially with ozone,” said Kirstin Krüger, a meteorologist with GEOMAR Helmholtz Centre for Ocean Research Kiel.

Volcanoes are major sources of bromine and chlorine compounds which are released at eruptions.  A team of scientists headed by Steffen Kutterolf (GEOMAR) and Karen Appel (DESY, now European XFEL) planned to investigate in Hamburg if and to what extent volcano eruptions had an impact on the depletion of the ozone layer. “We actually found out that giant volcano eruptions may have had a great effect on the ozone layer,” said Kutterolf.

For their study, the scientists selected 14 exemplary giant volcano eruptions which took place on the territory which today is Nicaragua and which were explosive enough to transport gases into the stratosphere. In order to determine the amount of gases released at the eruptions, the scientists analysed gases trapped by minerals crystallising in the magma chambers of the volcanoes already before the eruptions and, to precisely measure trace gases including bromine and chlorine, they used the high-energy radiation of the DORIS storage ring for their analysis. “The X-rays make the trapped chemical elements radiate,” Karen Appel illustrated the investigations. “Each element fluoresces at a different typical wavelength which allows identification. The radiation strength permits the determination of the elemental composition.” The scientists compared the results with the composition of lava rocks which formed at the corresponding eruptions and the difference allowed an estimate of the gas concentration.

With the purpose to determine the possible effect of the identified gas quantities on the stratosphere, the scientists assumed that ten per cent of the released halogens were transported to an altitude of 15 kilometres or higher. In spite of the cautious assumptions, the calculations revealed that, on the basis of the 14 investigated eruptions, the concentrations of bromine or chlorine in the stratosphere were on average two to three times higher than the pre-industrial concentration. 24 500 years ago, the Upper Apoyo eruption, for example, released 120 megatons of chlorine and 600 kilotons of bromine into the stratosphere – an effect that could have caused a massive ozone depletion and which possibly affected large areas of the earth’s atmosphere.

“Now we know that volcano eruptions in past epochs of geologic history had the potential to damage the ozone layer. The next step of research is to find out the actual extent of damage. With this, we are able to make estimates for future eruptions,” said Kutterolf.