Science

Underwater volcanic eruption devastates Tonga

by Ayush Raj (’23) | February 14, 2022

Art by Allyson Wang (’23)

On January 15, an underwater volcano erupted in Tonga, a small Pacific island nation. The force was equivalent to that of a nuclear bomb, and the explosion launched a towering mushroom cloud into the atmosphere that spread 20 kilometers wide and, by one estimate, 39 kilometers high. The blast sent shock waves which continued to ripple through the Earth’s atmosphere even a week later. 

According to volcanologist Christopher Helo at the University of Mainz in Germany, two-thirds of all volcanic activity happens under the sea. Although underwater explosions are generally uneventful, the one that occurred in Tonga was different. The volcanic explosion triggered a rare tsunami that threatened the island of Tongatapu, which was 65 kilometers away from the eruption, and sent residents fleeing. 

According to Helo, there is really no difference between how submarine (underwater) volcanoes and subaerial (land) volcanoes are formed. Submarine volcanoes are created because of the active volcanism along mid-ocean ridges (underwater mountain ranges), where tectonic plates pull apart. The collision of plates can also form a volcano, and if both the plates are under the ocean, the volcano will also develop underwater. The Hawaiian islands are an example of this phenomenon: when there is a hotspot (also known as a “mantle plume”) underneath an oceanic plate, large volcanoes, and therefore, volcanic islands like Hawaii, could be created.

The impact of an underwater volcanic eruption is determined by the eruption’s proximity to the water surface. According to David Pyle, a volcanologist and professor of Earth Science at Oxford, the weight of the overlying water acts as a pressure cap when the eruption occurs deep under the ocean. However, if the water is shallow enough, magma can convert the water into steam, resulting in a significant change in volume. Since a small volume of water turns into a huge volume of steam, steam explosions are usually disruptive. This kind of disruption can result in tsunamis, as was observed recently.

The tsunami was not the only effect of the recent Tongan volcanic eruption. It also highlighted the fragility of the global undersea fiber-optic cable network. Underwater internet cables carry roughly 95 percent of intercontinental internet data traffic, and the cable from Fiji to Tonga was damaged due to the volcanic eruption. Tonga’s communications were cut off from the rest of the world, pushing the issue of underwater cable dependency into the spotlight. Although communications experts have been trying to emphasize this issue for decades, there seems to be no clear path of action. Laying alternate cables is logistically challenging and incredibly expensive. Furthermore, satellite capabilities cannot handle the same amount of data as their fiber-optic counterpart.

Though this volcano may return to a state of dormancy, researchers warn that its eruptive behavior is highly unpredictable, so volcanologists will continue to monitor the site for potential danger moving forward.

Categories: Science

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