Undersea Eruption of the Hunga Tonga-Hunga Ha’apai Volcano

Kayla Bertholf

S&E Editor


When hearing about volcanoes, one might think of the violent eruptions portrayed as common in the prehistoric world of the dinosaurs, or of the long-ago Pompeii eruption of Mount Vesuvius in 79 CE. However, these geological events are not unique to the past. Volcanic eruptions are common and often undetectable, rarely causing noticeable damage. In fact, there are around 60-80 eruptions every year according to Dr. Meagen Pollock, an earth science professor at Wooster. Despite the common occurrence of eruptions, their “hazards are one really important reason to study volcanoes. Volcanic eruptions can be violent and dramatic.” One recent eruption has made headlines for the damage it caused. 

On Jan. 15, an underwater volcano erupted in Tonga, affecting over 1,200 miles of the surrounding areas directly, sending plumes of gas more than 12 miles into the sky, and causing a nearly 50 foot tsunami with three confirmed deaths. According to NASA, the eruption was more powerful than an atomic bomb. This volcano is mostly underwater with only the top of the crater visible above the ocean surface, yet it still managed to cause widespread destruction. This same volcano has erupted regularly over the past few decades yet rarely causes such destruction. What made this particular event different? Should we be terrified of an impending disaster? 

If you are not a volcanologist, you may first want to know what constitutes a volcano. In the words of Dr. Pollock, a volcano is a vent in the crust of the Earth from which molten rock and hot gasses (magma) are released. Pollock is a professor of earth sciences in the earth sciences department at the College. Volcanoes are formed when magma rises to the surface and escapes through the cracks in the crust. Layers of solidified magma build the classic dome-shape over time. These cracks are often very small and pressure builds as more and more magma is pushed towards the surface. When the pressure is too great, the volcano can erupt. How can we know a volcano is about to erupt? One trigger for an eruption is the movement of tectonic plates as they shift deep below Earth’s surface, causing fissures that act as weaknesses in the Earth’s crust. Other signs of an impending eruption may include small earthquakes, the emissions of steam and gas (often sulfur) and in some cases the rise of lava to the surface. 

What happens during an eruption can vary depending on the type of volcano and types of tectonic boundary they sit on. If a volcano has two tectonic plates moving towards each other with thick lava (a composite volcano), it can become very explosive when erupting, shooting hot ash and rocks high into the air. If a volcano is forming where two tectonic plates are moving away from each other with less viscous lava (a shield volcano), the danger does not come from how explosive it is but rather how quickly the lava can move and cover the ground with fresh molten rock, such as in Hawaii. If a volcano happens to be located in deep water or under a thick layer of glacial ice, the eruption can be gentle. However, if the lava erupts in shallow water or interacts with groundwater at a lower pressure, the heat from the lava causes the liquid water to turn to steam, expanding rapidly and causing a violent fragmentation of lava such as in the Tonga eruption, according to Pollock. 

Perhaps the greatest danger of a volcanic eruption is what happens to the surrounding area afterwards. The lava itself can cause damage to whatever it comes into contact with. The volcanic ash can cause breathing problems and disrupt visibility, especially for airplane pilots, as it lingers in the air. Further, volcanic eruptions can cause the formation of toxic gas clouds, pyroclastic flows, avalanches, tsunamis and mudflows. These can lead to secondary effects such as property and crop loss, and changes to the weather and climate. “Volcanoes near large population centers that erupt violently with little notice are the most destructive and dangerous, said Pollock” 

Are eruptions no more than horrible scenes of death and destruction? Not always. The eruption of a volcano can cause the creation of new land or islands, such as with the Hawaiian Islands. If the layer of ash released is not too thick, it can break down to become fertile farmland. The verdict on if we should all be actively terrified of volcanoes? Probably not.