12.06.2012

DESY X-ray light reveals ozone killer from volcanic eruptions

Volcanic eruptions can cause large holes in the ozone layer. This is the conclusion from a study of Nicaraguan volcanic minerals by a team of Helmholtz scientists from Kiel and Hamburg. Using a new X-ray technology at DESY in Hamburg, the scientists were able to estimate the amount of bromine in volcanic gases.

Microscope image of a slice of volcanic material with inclusion (top) and the bromine concentration within this inclusion (bottom)

The team headed by Steffen Kutterolf from GEOMAR Helmholtz Centre for Ocean Research in Kiel studied 14 volcanic eruptions in Nicaragua that happened in the past 70,000 years. Their main focus was on the amount of chlorine and bromine in the volcanic gases. Both elements are halogens that deplete the ozone layer when they reach the upper level of the stratosphere.

With the DESY X-ray source DORIS, the scientists X-rayed tiny glass inclusions in minerals which had crystallised in the volcanoes’ magma chambers during past eruptions. These inclusions, which are often smaller than 0.1 millimetres, store the composition of the melt at that time.

“The X-ray light stimulates the chemical elements in the inclusions to emit light,” DESY scientist Karin Appel explains the experiment. “Each element fluoresces at different and typical wavelengths – this way we can identify what it is. The intensity of the light allows us to determine the element contents.” The scientists compared the results with the composition of lava rocks which had formed at the corresponding eruptions. From the difference they were able to calculate the gas content.

The analysis of 14 Nicaraguan eruptions showed that the bromine and chlorine concentrations in the stratosphere jumped to levels that are equivalent to twice or three times the amount of the 2011 concentrations of those gases. The Upper Apoyo eruption 24,500 years ago, for example, released 120 megatons of chlorine and 600 kilotons of bromine into the stratosphere.

“When a prehistoric eruption releases bromine and chlorine together with sulfate aerosols into the atmosphere, this can lead to a massive depletion of the ozone layer,” GEOMAR meteorologist Kristin Krüger emphasises, who recently presented the studies at a scientific conference in Iceland.

Ozone depletion can affect large areas of the world because the volcanic gases are carried across the globe – even to polar regions. “The intensity of the chemical ozone layer depletion is a question for future research to address,” said Krüger. Some volcanic gases can remain in the stratosphere for up to six years, she added, although the most significant impacts from eruptions like Mount Pinatubo in 1991 in the Philippines happened within the first two years.

“The next step in the research is to investigate how much damage the volcanic gases caused to the ozone layer in the past to determine the damage that future subduction eruptions might produce,” Kutterolf points out.