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A mighty underwater volcano recently erupted on the Pacific Island of Hunga Tonga-Hunga Ha’apai. The island is part of the nation of Tonga. Millions of people around the world saw video of the spectacular explosion. The event was caught by the GOES West satellite. This U.S. operated satellite has the mission of observing our planet. The video shows a vast ash cloud in the shape of a giant mushroom rising high into the atmosphere. A shockwave caused by the explosion is seen moving outward from Hunga Tonga-Hunga Ha'apai. The eruption caused a four-foot tsunami that hit Tonga’s capital of Nuku’alofa. which is about 65 kilometers south of the volcano. A sonic boom from the eruption was heard across the Pacific Ocean, reaching as far away as Alaska. Reports said Nuku’alofa was covered in a thick layer of volcanic dust.

Most volcanoes on our planet are indeed underwater. This is nothing peculiar. They just erupt very quietly so nobody takes notice. But Tonga’s violent underwater volcanic eruption in mid-January has drawn people’s attention to volcanoes beneath the ocean. Actually, there is no real difference in how submarine (underwater) and subaerial (on land) volcanoes are formed. They are created when molten rock is produced in the second layer of the Earth's interior and makes its way through the crust.

The impact of an underwater volcanic eruption depends on how close it is to the water's surface. At two kilometers and below, seawater is quite cold. Any molten rock exposed here cools very quickly. The water will get hot, but it won't turn into steam. But, where the water is shallower, magma can heat the water to the point that it converts to steam. This creates a large change in volume. Steam explosions are quite destructive because a small volume of water turns into a huge volume of steam. Aside from the risk of tsunamis, the ash thrown into the air when a volcano erupts in shallow water can have a serious impact on people’s health. The falling ash and released gases not only pollute the air but can affect access to electricity and clean water.

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