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As scientists have found, they only seem predictable.
Shield volcanoes erupt only basaltic lava, which, although may damage, for example, nearby buildings, but is actually quite safe, as is moving around at walking pace. Such volcanoes are considered to be predictable, and therefore relatively safe. Their activity remains unchanged, which is associated with the homogeneity of the magmatic system, and local authorities can quite easily take precautionary measures in case of eruption. At least so it was believed until recently.
But now an international team of scientists led by Dr. Michael Drain from Dublin’s Trinity College found that shield volcanoes are actually not as safe. The researchers examined the basalt lava that is thrown on the surface of the Galapagos volcanoes, and contained microscopic crystals was able to reconstruct the chemical composition and physical characteristics of magma under the earth.
The results showed that despite the homogeneity of lava, of magma under the volcano has a very diverse composition and includes compounds similar to those that triggered the explosion of mount St. Helen in 1980 that killed 57 people and hundreds of square kilometers turned into a desert.
The study’s authors believe that the apparent homogeneity of the lava is provided by a large volume of molten magma beneath the surface and virtually erase the signs of chemical change. This happens when the volcano is close to the mantle plume.
However, finding the depth of a chemically heterogeneous magma under certain circumstances, it is able to rise to the surface, and in this case, the volcano, which thousands of years “quietly” kept up only homogeneous basaltic lava, can dramatically change its activities on the explosive.
“It was completely unexpected, says about the opening of Dr. Drain. — We began this study wanting to understand why these volcanoes are so boring and what processes cause the composition of the lava to remain constant for a long time. Instead, we found that they are not boring — they just hide this secret of magma beneath the surface”.
The study authors say their discovery forces us to reconsider approaches to the assessment of risks associated with solid volcanoes, which are located not only in the Galapagos, but, for example, in Hawaii and in Iceland: “the Fact that they erupted in a certain way in the past, does not mean that you can count on the same continued in the future,” said Dr. Drain.