The average temperature of our planet continues to increase. And the first to pay the costs are the glaciers, now in retreat practically in every corner of the globe: billions of tons of ice that disappear every year from our mountains, altering – Game strength – the geological balance of our planet. With sometimes catastrophic results: a study presented in recent days during the Goldschmidt Conference – the main Congress of World Geochimics, held this year in Prague – reveals that in many areas of the earth volcanic eruptions risk becoming more frequent and destructive, precisely because of the retreat of glaciers.
The ice keeps the mountains standing
It is estimated that, leaving out the glacial caps of Greenland and Antarctica, the glaciers of the Earth cover an area of over 700 thousand square kilometers in total, for an ice volume that exceeds 150 thousand cubic kilometers and a total weight of 121 thousand billion tons. An immense quantity, which for millennia (sometimes even more) has been keeping mountain peaks in its grip, guaranteeing stability to the rocks and pressing with its weight on the faults and geological structures below. It is clear, therefore, that once removed from global warming, the situation we knew is destined to change, often unpredictable.
In the case of the volcanoes, the theory is relatively simple: the weight of the glaciers compresses the rocks below and when it is missing, the gases and the underground magma present in the volcanic chambers can expand, causing an increase in pressure that can feed explosive eruptions. It is known that in Iceland at the end of the last glaciation the retreat of glaciers produced an intense volcanic period of volcanic activity, with an eruption number 30-50 times higher than we see today. In that case, however, the island is located right on the border along which the North American tectonic plaque and the Euroasian one move away from each other. Many volcanic systems arise in areas with different characteristics, subduction areas where a tectonic plaque slips under another. And it is not clear whether what is observed in Iceland can be considered valid even in similar situations. For this, researchers from the University of Wisconsin-Madison have decided to look again at the past, looking for clues.
The study on Chilean volcanoes
In the study presented at the Goldschmidt Conference, American researchers dated the past eruptions of six volcanoes located in southern Chile, and then investigated their evolution according to the advance and withdrawal of the Patagonian glacier that covered the southern part of the country at the apex of the last glaciation. Their analysis show that during the period of maximum expansion of the glacier, between 26 thousand and 18 thousand years ago, the frequency of the eruptions was minimal. While at the end of the glaciation, with the withdrawal of the ice, they took to increase, and to become more powerful, veragping the magma reserves accumulated in the previous millennia of less activity.
It is the confirmation that also the subglacial volcanoes located in subduction areas or far from the boundaries of the busty plaques, are influenced by the disappearance of the glaciers. “Our study suggests that the phenomenon is not limited to Iceland, where the increase in volcanic activity has already been observed – explains Pablo Moreno -Yaeger, a researchers from the University of Wisconsin -Madison who participated in the study – but can also happen in Antarctica, and in other continental regions, as part of North America, New Zealand and Russia”.
The danger should not be underestimated: 254 of the most active volcanoes on the planet are buried under the ice, or arise within three kilometers from a glacier. And an increase in eruptions on such a large scale would inevitably have the effect of further fueling the ongoing climate change, because it would release huge quantities of greenhouse gases in the atmosphere, creating a vicious circle, with further increase in temperatures, more ice that melts, and more eruptions.
Earthquakes also increase
Vulcanic eruptions, on the other hand, are not the only growing geological danger linked to climate change. The weight of the glaciers, in fact, is a decisive factor also for the balance of the earth’s crust. When they fail, the weight disappears, the rocks below tend to relax and get up, and the faults in the surroundings are reactivated. It is defined by scientists as “post glacial rebound”, and it is the mechanism that relates global warming, the retreat of glaciers and the increase in the frequency of earthquakes (below, the withdrawal of the Adamello glacier).
The research that support this correlation are now many. The last dates back to last December, by the Colorado State University researchers. In the study, published in the magazine Geology, the complex of the Monti sangre de Cristo, in the south of Colorado, is analyzed, another mountain range that during the last glaciation was completely covered by a now disappeared glacier. By reconstructing the weight of the ice, and the movements of the underlying faults, the American researchers have shown that from the end of the last glaciation the scroll speed speed has fifth, reaching the movement rate of the other faults in the area. And therefore, in all likelihood, earthquakes caused by these movements have also increased.
Read the Sciences section of Toray.it