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why do some volcanoes erupt more violently than others

Some lava oozes out of a volcano s opening and creeps down a slope, burning everything in its path, while some shoots up into the sky and rains fire down onto the life below. Scientists want to know why certain eruptions of molten rock are more violent than others, and they may have found clues in chemistry. Volcanic eruptions are the most spectacular expression of the processes acting in the interior of any active planet. Effusive eruptions consist of a gentle and steady flow of lava on the surface, while explosive eruptions are violent phenomena that can eject hot materials up to several kilometres into the atmosphere. The transition between these eruptions represents one of the most dangerous natural hazards. Understanding the mechanisms governing such transition has inspired countless studies in Earth Sciences over the last decades. In a new study led by Dr Danilo Di Genova, from the University of Bristol's School of Earth Sciences, an international team of scientists provide evidence, for the first time, that a subtle tipping point of the chemistry of magmas clearly separates effusive from explosive eruptions worldwide.

Moreover, they demonstrate that variabilities at the nanoscale of magmas can dramatically increase the explosive potential of volcanoes. Dr Di Genova said: "The new experimental data, thermodynamic modelling and analysis of compositional data from the global volcanic record we presented in our study provide combined evidence for a sudden discontinuity in the flow behaviour of rhyolitic magmas that guides whether a volcano erupts effusively or explosively. "The identified flow-discontinuity can be crossed by small compositional changes in rhyolitic magmas and can be induced by crystallisation, assimilation, magma replenishment or mixing. "Composition-induced flow behaviour variations may also originate from changes in magmas intrinsic parameters such as temperature, pressure or oxygen fugacity. "
These can result in revitalization of a previously "locked" magma chamber via chemical fluidification or may hinder efficient degassing and lead to increased explosive potential via chemical "stiffening" of a magma.

Furthermore, the study showed how the sudden precipitation of iron-bearing nanocrystals, which have been recently found in volcanic rocks, can increase the explosive potential of a magma via both depletion of iron in the melt structure and providing nucleation points for gas bubbles which drive explosive eruption. If Yellowstone were to erupt at that level again, it would send enough ash and gas into the atmosphere to cloak most of the U. S. The above story is based on provided by. While palm trees and cool breezes make Hawaii a vacation favorite, this slice of paradise sits on active volcanoes. Right now, a slow lava flow is making its way to the town of Pahoa, where hundreds of residents and local businesses are keeping an eye on it from just a couple miles away. Hawaii isn't the only place where volcanoes are erupting. Similar activity is happening in Iceland, Indonesia, Ecuador, Mexico and, of course, there was the recent eruption at.

Some volcanic eruptions are more dangerous than others, saysP and an expert on volcanoes. Molten rock, or magma, comes under pressure, but it's how that pressure is released that determines whether the volcano will create a violent, sudden eruption or not, she says. "If the magma is very sticky, very viscus, it will explode. If the magma is not very sticky, the magma can come out slowly and then the volcano is not explosive," says Lopes. "So it really is a matter of the amount of gas in the magma and how easily it can come out. " Lopes, who also studies ice volcanoes on Titan, Saturn's largest moon, says there's lots of interesting and lesser-known facts about how volcanoes work. Its actually possible to walk on a moving flow because the crust at the top is a very good insulator and it will protect you," she said. Though temperatures can get up to 1,200 degrees Celsius, the crust cools quickly.

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