Super volcanic eruptions have been preparing for millions of years: followed by a rapid rise:

Researchers from the University of Bristol and the Scottish Universities Environmental Research Center have found that super-eruptions occur when huge accumulations of magma at the as deeper in the earth’s crust, formed over millions of years, is rapidly moving downward, disrupting pre-existing rock.

Using a crustal flow model, an international team of scientists was able to show that pre-existing plutons – a body of intrusive rock made of magna or solidified lava – formed over a few tens of millions of years before four gigantic tremendous known eruptions. and that the disturbance of these plutons by newly emplaced magmas has occurred with extraordinary rapidity. As the magma fueling the super eruptions takes place over an extended period of time, the magma disrupts the crust and then erupts in just a few decades.

The findings, published today in Nature, explain these extreme differences in time intervals for magma generation and eruption by the flow of hot but solid crust in response to rising magma, which explains the rarity of these eruptions and their huge volumes.

Professor Steve Sparks of the Bristol School of Earth Sciences explained: “The longevity of plutonic and related volcanic systems contrasts with the short time scales for assembling shallow magma chambers before large magnitude eruptions of molten rock. Crystals formed from earlier magmatic pulses, entrained in erupting magmas are stored at near or below solidus temperatures for long periods before eruption and usually have a very short stay in host magmas for a few decades or so. less.

This study casts doubt on the interpretation of prolonged storage of ancient crystals at temperatures high enough for some molten rock to be present and indicates the crystals from plutons (granites) previously emplaced and completely solidified.

Scientists know that volcanic super-eruptions eject crystals derived from older rocks. However, prior to this they were generally thought to have originated from warm environments above the melting points of the rock. Previous studies that show that magma chambers for super-eruptions form very quickly, but there was no convincing explanation for this rapid process. While modeling suggested that supervolcanic eruptions should be preceded by very long periods of emplacement of granitic plutons in the upper crust, evidence for this inference was largely lacking.

Professor Sparks added: “By studying the age and character of tiny crystals that have erupted with molten rock, we can help understand how such eruptions occur.

“The research provides a breakthrough in understanding the geological circumstances that allow super-eruptions to occur. This will help identify volcanoes that have potential for future super-eruptions.”

Such eruptions are very rare and Bristol scientists estimate that only one of these types eruptions occur on earth every 20 000 years. However, such eruptions are very destructive locally and can create severe climate change on a global scale that would have catastrophic consequences.

This project was supported by the mining company BHP and by NERC.

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