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Himanshu Gupta • February 24th, 2022.
We’re bringing you exclusive content from our newsletter, The Forecast, right here on Medium. Sign up here. This feature, called the Weather Corner, takes a deep dive into weird weather around the world, from our Jan. 26 newsletter.
Earlier this month, on Jan. 15, the Pacific island nation of Tonga was rocked by what experts believe to be the world’s biggest volcanic eruption in the last 30 years from the Hunga-Tonga-Hunga-Ha’apai undersea volcano. Like most undersea volcanoes — there are an estimated one million globally — this undersea volcano is located above a very active seismic zone, specifically in the Kermadec-Tonga Ridge in the South Pacific, the convergent boundary where the Pacific Plate is subducted by the Indo-Australian Plate.
This Tonga volcano blast was hundreds of times more powerful than Hiroshima, NASA said. A plume of ash rose into the air more than 30 kilometers (19 miles), but the eruption lasted only about 10 minutes, unlike other big eruptions that can continue for hours.
Tonga reported significant damage across the country, which is home to more than 100,000 people, with the majority living on the main island of Tongatapu, the largest out of the nation’s 170 islands in total, though some smaller ones are uninhabited. Satellite photos show that more than 100 homes have been destroyed, and much of the wreckage, trees, and fields are covered in thick grey ash. Three people have been reported dead so far, but more are still missing. Communications to the island have also been severely affected after the singular undersea cable connecting Tonga to the rest of the world snapped due to impact. There are also likely to be longer-term problems that come from the ash, such as impacts on agriculture and water quality.
The eruption also led to tsunami conditions across the globe — waves emanating from the volcano traveled to Australia, Hawaii, Japan and on the West Coast of the United States. The Peruvian National Police said that at least two people died in Peru due to “atypical waves.” The waves took less than five hours to reach New Zealand, and about 10 to reach Alaska.
Tsunami waves can be far more destructive than normal waves, even when they are not necessarily high, due to the way they are created. A tsunami is a series of extremely long waves, caused by a large and sudden displacement of the ocean (such as an earthquake, landslide, or yes, volcano). Unlike typical wind-propelled waves, which only move through the top layer of the ocean, tsunamis’ waves radiate outwards from the source and travel through the entire water column, from ocean floor to surface.
Experts believe that this volcano was the “Goldilocks” depth for a big explosion, because the crater was about 200 meters (650 feet) below the sea surface. At that depth, seawater streams into the volcano and instantly evaporates into steam, which furthers the eruption’s rapid expansion and energy and bolsters tsunami waves.
Volcanic eruptions can also emit greenhouse gases. Along with the ash released, sulfur dioxide particles, carbon dioxide, and other materials shoot into the sky. Carbon dioxide contributes to global warming, though NASA estimates that human contributions to the carbon cycle are more than 100 times those from all the volcanoes in the world combined.
Sulfur dioxide, though, has an interesting greenhouse effect — if shot up high enough in the atmosphere, it can provide cooling because it reflects sunlight. This happened when the Philippines’ Mount Pinatubo erupted in 1991, pumping about 15–20 million tons of the gas into the air, and leading to the global cooling of about 1 degree Fahrenheit, or half a degree Celsius, for the next two years. (This cooling was also believed to have led to a reduction in Japan’s rice harvest the subsequent season.) But scientists believe that this is unlikely to be the case for this eruption because it was an undersea volcano, so the ocean may have instead absorbed some of the gas.
In addition, climate change is likely to worsen the impacts of tsunamis. Impacts of climate change include sea level rise, more landslides (from glacier and permafrost melt), collapsing ice sheets, and increased earthquakes (from melting glaciers reducing the stability of fault lines), all of which can lead to larger and more deadly tsunamis.
Scientists can take into account these changes in their disaster modeling to ensure that warning systems are accurate and reliable and give enough lead time for impacted communities to evacuate. In addition, investing in more weather-proofed and seismically sound infrastructure is crucial to mitigate these risks. Incorporating sea level rise into building codes for coastline communities is key.