2022 Hunga Tonga eruption and tsunami

The Hunga Tonga eruption occurred on January 15, 2022, when the underwater volcano Hunga Tonga-Hunga Ha’apai in the South Pacific violently exploded. The blast caused atmospheric shock waves and tsunamis that literally stretched around the world. Scientists compared the Hunga Tonga eruption to some of the most powerful volcanic events in recorded history. The blast was heard as far away as Alaska—6,000 miles (9,650 kilometers) to the north—and sent an ash plume 36 miles (58 kilometers) into the atmosphere, making it the tallest volcanic ash plume ever recorded. The eruption was particularly devastating to the island Kingdom of Tonga, where an estimated 80 percent of the population was impacted by the disaster. The tsunami destroyed several villages and knocked out power and communications across the island. However, because Tonga had extensive tsunami preparedness measures in place, only four people were killed.

Background

The Kingdom of Tonga consists of an archipelago of about 170 islands in the South Pacific, more than 3,200 miles (5,200 kilometers) east of Australia. The nation’s largest island is Tongatapu, which is home to Tonga’s capital of Nuku’alofa. In 2022, the nation had an estimated population of 105,500.

Tonga is in a geologically active region where two giant sections of Earth’s crust are converging. At this junction, the heavier Pacific Plate is slipping under the lighter Kermadec and Tonga plates, creating a series of island ridges and a deep trench known as the Tonga Trench. The region around the Tonga Trench is part of a larger geological feature known as the Pacific Ring of Fire.

The Ring of Fire stretches for about 25,000 miles (40,000 kilometers) in a giant horseshoe shape from the west coast of South America and North America, through the islands of Japan, the Philippines, Indonesia, and down through Tonga and into New Zealand. The ring marks the region where many of Earth’s tectonic plates are interacting with one another. About 90 percent of the world’s earthquakes and 75 percent of its volcanoes are located along the Ring of Fire.

Overview

Prior to 2015, Hunga Tonga and Hunga Ha’apai were two separate islands located about 40 miles (65 kilometers) north of Tongatapu. Both islands were the highest spurs of the caldera, or main crater, of an underwater volcano. The volcano had erupted in 2009 and again in 2014, with the latter eruption creating a land bridge that linked the two islands together. Historically, the volcano’s eruptions were mild and not generally cause for alarm.

The Hunga Tonga-Hunga Ha’apai volcano began another eruption in December 2021. On January 14, 2022, an explosion in the volcano’s main vent destroyed the land bridge between islands. This left the volcano’s main vent below water and set the stage for the devastating eruption that followed.

With the vent below water, scientists believe the added seawater was vaporized by the molten rock of the volcano. The vaporized water combined with volcanic gases to create an incredible amount of pressure that led to a violent explosion on January 15. The blast annihilated the islands and was so loud that it was heard in Alaska. Scientists estimate that the explosion was the loudest ever recorded by instrumentation and was likely the loudest sound on Earth since the 1883 Krakatau eruption in Indonesia.

Scientists use an eight-point scale called the Volcanic Explosivity Index (VEI) to measure the power of eruptions. The Hunga Tonga-Hunga Ha’apai blast was placed at a VEI-6, one of the strongest volcanic explosions ever recorded. In comparison, both the 1883 Krakatau eruption and the 1991 eruption of Mount Pinatubo in the Philippines were rated at VEI-6. The 1815 explosion of Mount Tambora in Indonesia was the largest explosion ever recorded with a VEI-7.

The Hunga Tonga-Hunga Ha’apai explosion also sent a larger cloud of ash and dust shooting into the atmosphere. The ash cloud reached a height of 36 miles, almost two-thirds of the way into space. When the force of the blast hit the thinner air of the atmosphere’s upper levels, it caused wind speeds of 450 miles per hour (720 kilometers per hour). The electrically charged ash cloud also caused an incredible amount of lighting, with an estimated two hundred thousand strikes per hour. During the height of the blast, the volcano’s ash cloud created almost 80 percent of all lightening strikes on the planet’s surface.

The eruption also sent 50-foot (15-meter) tsunami waves crashing into the western coast of Tongatapu and several islands to the north. Tonga was well-prepared for tsunamis and evacuation orders had been issued on January 14, leading to a death toll of only four people. However, the tsunamis damaged numerous villages on the islands, affecting more than 84,000 people in more than 12,000 households. All the homes on Mango Island, which had a population of about fifty people, were destroyed, while homes on the smaller islands of Fonoifua and Namuka were almost completely wiped out. The United Nations (UN) estimated that the tsunami and falling ash contaminated the islands’ water, destroyed a significant amount of crops, and negatively impacted 60 to 70 percent of Tonga’s livestock. The blast also severed an undersea fiber-optic cable that the nation relies on for communications, effectively cutting Tonga off from the outside world.

Typically, volcanic eruptions do not cause major tsunamis, but the Hunga Tonga-Hunga Ha’apai explosion was different in that it generated tsunamis in two ways. The blast itself caused a large tsunami, but others were triggered by atmospheric shock waves created by the force of the explosion. These tsunamis moved much faster than anticipated, catching forecasters off guard. Normally, tsunami waves move at about 660 feet per second (220 meters per second). The tsunamis created by the blast’s shock waves moved at about 984 feet per second (300 meters per second).

The tsunamis spread out along the Pacific, with waves about 6.5-feet (2-meters) high causing damage along the coasts of South America, California, and Alaska. Two people in Peru drowned in high surf caused by the tsunamis. The atmospheric shock waves were so strong that they caused small tsunamis as far away as the Caribbean, an ocean with no physical connection to the South Pacific.

Bibliography

Andrews, Robin George. “Scientists Unravel How the Tonga Volcano Caused Worldwide Tsunamis.” Quanta Magazine, 13 Apr. 2022, www.quantamagazine.org/scientists-unravel-how-the-tonga-volcano-caused-worldwide-tsunamis-20220413/. Accessed 20 June 2022.

Dickie, Gloria. “Tsunami Models Underestimated Shockwave from Tonga Eruption.” Reuters, 28 Jan. 2022, www.reuters.com/world/asia-pacific/tsunami-models-underestimated-shockwave-tonga-eruption-2022-01-28/. Accessed 20 June 2022.

“80 Per Cent of Tonga Population Impacted by Eruption and Tsunami.” United Nations, 20 Jan. 2022, news.un.org/en/story/2022/01/1110162. Accessed 20 June 2022.

“15 January 2022, Hunga-Tonga Hunga-Ha’apai Volcanic Eruption and Tsunami.” International Tsunami Information Center, 2022, itic.ioc-unesco.org/index.php?option=com‗content&view=article&id=2186&Itemid=3265. Accessed 20 June 2022.

Lovett, Richard A. “The Blast Heard Round the World.” Cosmos, 13 May 2020, cosmosmagazine.com/earth/impact-2022-tonga-eruption/. Accessed 20 June 2022.

“The Ring of Fire.” National Geographic, 3 Feb. 2022, www.nationalgeographic.com/science/article/ring-of-fire. Accessed 20 June 2022.

“Ripple Effect: What the Tonga Eruption Could Mean for Tsunami Research.” National Oceanic and Atmospheric Administration, 3 Feb. 2022, www.noaa.gov/news/ripple-effect-what-tonga-eruption-could-mean-for-tsunami-research. Accessed 20 June 2022.

Tasoff, Harrison. “Tonga Eruption.” University of California, Santa Barbara, 29 Mar. 2022, www.news.ucsb.edu/2022/020589/tonga-eruption. Accessed 20 June 2022.