Science

A new island grows in the Pacific after a volcanic eruption

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The underwater volcano Hunga Tonga, located near the Tonga Islands in the South Pacific, erupted again on January 15. The event caused a tsunami, which caused significant damage to the north coast of Nuku’alofa, the capital of the archipelago located about 65 kilometers away; however, no casualties were reported, according to New Zealand Prime Minister Jacinda Ardern. It is the third time that this volcano has entered the eruptive phase and these successive explosions, throwing large amounts of rocks and volcanic ash, have ended up creating a new island in the Pacific.

The submarine volcano Hunga Tonga emerged from the ocean during its first eruption in 2009: the now visible main crater forms a pseudo-island. Then, a second eruption in 2015 caused an accumulation of volcanic materials, which finally expanded this new continental mass: the island, named Hunga Tonga-Hunga Ha’apai, reached an area of ​​2 km² at the time and its highest point high culminates at 150 meters. Experts then thought that its useful life was limited to a few months, due to the phenomenon of erosion caused by the waves.

In mid-2018, when the island was just over 3.5 years old, NASA organized an expedition to study it a little more closely. The island’s beaches were made up of black gravel and clayey mud, the presence of which puzzled the team, says Dan Slayback, a researcher at Goddard Space Flight Center, who participated in the expedition. But above all, the team was able to observe that the vegetation and several species of birds had already taken over the place. For scientists, these rare terrestrial emergencies are a unique opportunity to study a rapidly changing landscape, both in situ and from space.

Tsunami alert for the entire Pacific coast

A new series of eruptions, which began on December 20, has unfortunately shaken this young island in recent days. And on January 15, the eruption was so powerful that the shock wave was felt as far as Alaska, according to AFP. The event caused tsunamis in several countries, along the Pacific coast, from Alaska to Chile, through California and Mexico, as well as in Japan.

Dave Snider, coordinator for the National Tsunami Warning Center in Palmer, Alaska, told the Washington Post that it was highly unusual for a volcanic eruption to affect an entire ocean basin. The US Geological Survey estimated that the eruption caused the equivalent of a magnitude 5.8 earthquake. French weather stations even recorded strong variations in atmospheric pressure after the eruption!

In Tonga, waves of 1.20 meters swept the capital. The phenomenon caused enormous damage, but the inhabitants having taken refuge on the heights, there are no casualties for the moment – this first assessment is however uncertain knowing that the eruption made communications very difficult, in particular with the small islands. According to the directors of the Southern Cross Cable Network, the archipelago could be deprived of Internet for two weeks, due to the cut of a submarine cable.

The capital, Nuku’alofa, was covered in a thick layer of volcanic dust that contaminated all drinking water supplies, Jacinda Ardern said. Until now, assistance by air was impossible due to the enormous cloud of ash that spread over the area, some 19 kilometers above sea level; a new attempt is due today according to New Zealand authorities. However, rescuers will have to be more vigilant: the Tonga Islands are one of the rare territories that have been spared from the COVID-19 pandemic…

An area almost doubled in a few days

This new eruption will, of course, help extend the Hunga Tonga-Hunga Ha’apai island a little more. The first eruptions in December had already increased its area considerably: a comparison of satellite images of the island taken on November 16 and then on January 2 reveal that its surface has expanded by almost 45%.

In the past century, only two other such events have given rise to new sustainable land masses: the island of Surtsey in Iceland, formed after a volcanic eruption in the 1960s, and the island of Faial in the Azores, part from which comes the eruption. of the Capelinhos volcano in the late 1950s.

In Tonga, several undersea volcano eruptions have raised islands in the past, Dan Slayback says, but they were generally short-lived. The most recent took place in 2009, in the same submarine caldera of Hunga Tonga-Hunga Ha’apai, just one or two kilometers from the current island; but was swept out to the ocean in about six months. If this island is holding up despite erosion, it may be thanks to a larger volume of ejected material, giving it more time to stabilize before waves and rain erosion degrade it, he explains. You can also benefit from the protection of the surrounding islands, which cushion the force of the waves before they arrive.

Volcanologists still do not know if the eruption is over or how the situation and the island, which remains under close surveillance, will evolve. Meanwhile, it offers a new opportunity to observe a rapidly changing landscape from space. In order to understand its past and, above all, predict the future of this island, scientists are now working to better characterize the erosion that it suffers day after day.

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