
The consequences of land-based volcanic eruptions are well-documented, as scientists can monitor these events closely. However, more than 3/4 of all volcanic eruptions worldwide occur on the sea and ocean floor. Observing underwater eruptions has been challenging due to the lack of tools and appropriate infrastructure. Given the inaccessibility of underwater eruption sites and the absence of detailed data before and after volcanic activity, the effects of such events often manifest as sudden tsunamis.
In fact, the active study of underwater eruptions and their consequences began just a few years ago, in 2022. In January of that year, the Hunga Tonga volcano, one of the most significant hazards in Oceania, awoke. The region is part of the Pacific Ring of Fire, consisting of a series of powerful underwater volcanoes. The location of the Hunga-Ha’apai underwater volcano near the capital of Tonga enabled the rapid organization of observation and the study of its aftermath.
The Eruption of Hunga-Tonga-Ha’apai
The underwater volcano is situated in the Tonga archipelago between two islands – Hunga and Ha’apai, with an ancient caldera 200 meters in diameter. Monitoring of this periodically active volcano began in 2009, and by 2021, scientists concluded it had entered a dormant phase. However, in January 2022, a sudden eruption occurred. A massive explosion ejected cubic kilometers of water vapor and gases into the mesosphere, reaching an altitude of 50 kilometers (above the stratosphere). This was the highest volcanic plume ever recorded by satellite observations.
The explosion’s energy was 110 Megatons of TNT equivalent, comparable to the eruption of Krakatoa in 1860. When magma came into contact with water, it generated powerful gas flows that poisoned the coastal ecosystem and triggered a tsunami. As the Tongans were well aware of the possibility of large waves resulting from an eruption and responded in a timely manner upon seeing a massive plume of dark emissions over the ocean, the number of casualties was minimal (4 people).
Consequences of the eruption – tsunami
Just minutes after the main explosion of the underwater volcano Hunga-Tonga, waves reaching 18 meters in height hit the nearest islands of the archipelago. The displacement of water masses was caused by the seismic activity accompanying the eruption, the masses of molten lava that poured out of the caldera, and the heated steam that formed when it came into contact with water.
As observations showed, the tsunamis, whose strength did not diminish while traveling across the ocean, reached:
- Fiji, where 150 people went missing;
- the coast of Antarctica;
- the west coast of the USA, where three fishermen were injured;
- New Zealand;
- Peru, where two people died.
New studies by Japanese scientists have shown that the eruption of the underwater volcano Hunga-Tonga caused the appearance of atmospheric gravity waves that circled the planet several times. These waves caused small waves in the ocean, which served as precursors to the incoming tsunami. They reached the coast of Japan several hours before the main waves.
Other consequences
In addition to the tsunami, which brought destruction and casualties to the coastlines of many countries, the eruption of the underwater volcano Hunga-Tonga led to:
- a decrease in air temperature in the region by 4 degrees due to the massive release of steam and sulfur dioxide into the atmosphere, forming aerosols. The cooling lasted for 2 years and was associated with the reduction of sunlight by the eruption products;
- a reduction in the ozone layer caused by secondary circulations of water vapors in the atmosphere;
- a slight change in the Earth’s radiation balance;
- the emergence of a new island in the Tonga archipelago;
- the occurrence of more than 500 thousand lightning strikes.
After the eruption of the Tonga volcano, scientists recorded a rather rare phenomenon – the formation of atmospheric Lamb waves, which cause vibrations in the medium through which they pass. This phenomenon can be compared to an atmospheric earthquake. In the 6 days following the earthquake, the Lamb waves circled the Earth four times in one direction and three times in the opposite direction. Observations and Forecasts
On February 1, 2023, an underwater volcano, East-Epi, erupted near the island of Vanuatu in Melanesia. The eruption sent massive clouds of steam and ash over 100 km into the air, and the movement of the ocean floor resulted in the formation of a tsunami.
Scientists are closely monitoring two powerful underwater supervolcanoes that have become more active in recent years:
- Kuwae, located on the New Hebrides arc, which has erupted 25 times in the past 12,000 years. The last eruption in the 14th century led to a massive tsunami and climate change, resulting in the deaths of 2 million people;
- Taupo, located near the northern coast of New Zealand. It is larger than Yellowstone and last erupted in 232 AD, causing a catastrophic tsunami. The entire territory of New Zealand was covered with ash and buried under pyroclastic flows. The water level in the caldera indicates a gradual increase in magma activity.
Underwater volcanoes are extremely dangerous. Therefore, if you see an explosion in the ocean with the emission of white or dark plumes, act without delay. An underwater volcanic eruption will inevitably lead to a tsunami and other hazardous consequences.