A deadly volcano that gave no warning. Normally, scientists see signs a mountain will blow. Not at Nyiragongo in 2021.

Last year, one of the most dangerous volcanoes in Africa erupted without any warning.

In a sense, Nyiragongo, a vertiginous volcano in the Democratic Republic of Congo, is always erupting.. The mountain is crowned with a rare, persistent lava lake constantly fed by churning magma below.

But on May 22, 2021, its molten innards found another route to the surface. They oozed from the fractures on the volcano's flanks towards the metropolis of Goma, leading to the deaths of at least 31 people, injuring 750 others, displacing thousands more and leaving behind a trail of destruction. 

In a new study published in Nature, Delphine Smittarello, a geophysicist at the European Center for Geodynamics and Seismology in Walferdange, Luxembourg, and her colleagues articulated how the eruption managed to ambush everyone.

Most sufficiently monitored volcanoes offer warning signals before erupting. Magma forcing its way through rock generates distinctive types of earthquakes, deforms the land as it ascends and unleashes noxious gases.

Some volcanoes are so active that they are always creating noticeable chaos, but a distinct change in their usual, or ''background'' behaviour foreshadows eruptions.

Not so for Nyiragongo in 2021.To any expert's eyes, it was business as usual. 

''We were not able to detect any dramatic change that could tell us that an eruption will occur,'' said Dr. Smittarello, the lead author of the study.

Her team suspects that before the paroxysm, magma intruded below Nyiragongo's flank. But then, it waited. Not only does immobile magma stay silent, but the molten mass was already so close to the surface that if the flank broke apart, it would have immediately erupted without any usual precursory clamor.

And it was only a matter of time.

This sort of unannounced eruption offers scientists a harsh lesson :  

For every paradigm-shifting secret they extract from their mountainous subjects, ''there are always things that we don't understand,'' said Emily Montgomery-Brown, a geophysicist at the U.S. Geological Survey's Cascades Volcano Observatory who was not involved in the study.

With its unusually fluid, fast-moving lava and its ability to disperse suffocating carbon dioxide gas into its surroundings, Nyiragongo is an extraordinarily perilous volcano that frequently endangers both Goma, in Congo, and Gisenyl, a contiguous Rwandan city. 

''This is a strange volcano,'' said Benoit Smets, a geohazards expert at the Royal Museum for Central Africa in Tervuren, Belgium, and a co-author of the study.

Using traditional monitoring methods on Nyiragongo means that ''you will not be able to detect such kinds of eruptions.'' And that makes this volcano even more dangerous than previously thought.

Nyiragongo's stealth characteristics are not unique. Other volcanoes can let their lava loose from rifting landscapes relatively quietly, while others unleash unexpected blasts of steam.

The hope is that by studying such eccentric eruptions, one day - with the aid of improved technological wizardry - some lifesaving precursors will be spotted.

But it's possible that we will never become perfect prophets of our volcanic futures. ''There may be things we will never be able to forecast,'' Dr. Montgomery-Brown said.

The World Students Society thanks Robin George Andrews.


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