Krakatau, a volcanic island in Indonesia, killed more than 30,000 people when it erupted in 1883. Most of the victims died from a tsunami caused by the volcanic eruption, not the volcanic debris itself.
Volcanoes at sea behave differently from those on land. Deep water can suppress explosive eruptions, but near the surface, hot volcanic material and low water pressure combine to produce violent explosions. Scientists still do not fully understand the conditions that trigger a tsunami from an undersea eruption.
An international team of researchers has now focused on the 2022 Hunga eruption in Tonga, which produced one of the most powerful volcanic columns of the century. They found that the rapid collapse of the entire caldera may have amplified the massive tsunami that followed. The discovery raises new questions about the dangers posed by smaller undersea volcanoes.
Hunga’s Date and Scale
Hunga erupted on January 15, 2022. The eruption column soared more than 55 km into the air, pushing vaporized seawater up into the stratosphere. The pressure wave from the explosion was detected across the globe.
The accompanying tsunami reached heights of 40 meters within about 100 km from the source. It is the highest tsunami ever recorded from an underwater volcanic eruption.
Calderas form when the ground above a magma reservoir collapses as the magma drains away. The researchers compared seafloor topography before and after the eruption and found that a roughly 4-kilometer-wide caldera sank by about a kilometer during the eruption. That collapse happened rapidly, and the researchers argue it may have enhanced the massive tsunami.
How Undersea Volcanoes Work
Undersea volcanoes can produce tsunamis through several mechanisms. A sudden collapse of a caldera can push large volumes of water upward, generating a wave. Explosive eruptions can also send shock waves through the water that create a tsunami.
The depth of the water matters. In the deep ocean, high water pressure can suppress explosive volcanic activity, making eruptions less destructive. Closer to the surface, the lower water pressure and the high temperatures of volcanic material can cause violent explosions.
But the exact conditions that trigger a tsunami remain poorly understood. The paper warns: “The dynamics of submarine caldera-forming eruptions and, thus, the hazards they pose are not well understood, owing to the relative inaccessibility of the resulting calderas and eruption products.”
Krakatau’s Deadly Wave
Krakatau offers a grim example of what happens when a volcanic eruption triggers a deadly tsunami. The 1883 eruption produced a tsunami that killed more than 30,000 people.
Many of the victims died from the tsunami rather than the eruption itself.
The Hunga Collapse
The Hunga caldera collapsed rapidly during the eruption. The comparison of seafloor topography before and after the event showed the scale of the collapse: a roughly 4-kilometer-wide caldera sinking by about a kilometer.
The researchers argue that the rapid collapse of the entire caldera may have amplified the massive tsunami. Small calderas like Hunga may be capable of producing a dangerous tsunami depending on how fast and how the collapse unfolds.
This suggests that other underwater volcanoes may also have the potential to generate dangerous tsunamis. The research is a reminder that the world’s oceans contain thousands of undersea volcanoes, many of which have not been closely studied.
The Limits of Our Knowledge
The paper’s warning about the inaccessibility of undersea calderas is worth repeating. The resulting calderas and eruption products are difficult to study, which limits our understanding of how these eruptions unfold.
The Hunga eruption was one of the most powerful volcanic events this century. Its tsunami was the highest ever recorded from an underwater volcanic eruption. Yet the precise mechanics of how the caldera collapse generated that wave remain uncertain.
“The dynamics of submarine caldera-forming eruptions and, thus, the hazards they pose are not well understood, owing to the relative inaccessibility of the resulting calderas and eruption products.”
That uncertainty is the central finding of the research. It is not that undersea volcanoes are harmless; it is that we do not know enough to predict when they will become dangerous.
What This Means for Coastal Communities
The research highlights the need for better monitoring of undersea volcanoes. Many of these volcanoes are located far from populated areas, but their tsunamis can travel great distances.
Coastal communities need early warning systems that can detect undersea eruptions and their associated tsunamis. The Hunga eruption showed that even a relatively small caldera can produce a massive tsunami.
The research also underscores the importance of studying past eruptions. The 1883 eruption of Krakatau and the 2022 eruption of Hunga provide valuable data for understanding how undersea eruptions behave.
The Road Ahead
The research is a step forward, but it is also a call for more work. The international team’s examination of the Hunga eruption has provided new insights into the relationship between caldera collapse and tsunami generation.
The next step is to apply these findings to other undersea volcanoes. The world’s oceans are full of unexplored volcanic features, and many of them have the potential to produce dangerous tsunamis.
The paper’s warning about the inaccessibility of undersea calderas remains a challenge. But each eruption provides new data, and each new study moves us closer to understanding these powerful natural phenomena.
The Hunga eruption was a rare event, but it was not unique. The research shows that even small undersea volcanoes can produce outsized tsunamis. The lesson is simple: when a volcano erupts under the sea, watch the water.
| Event | Date |
|---|---|
| Krakatau eruption | August 26–27, 1883 |
| Hunga eruption | January 15, 2022 |
| Tsunami peak height | 40 meters |
| Record holder | Highest tsunami from an underwater volcanic eruption |
Source material: “Small undersea volcanoes may unleash outsized tsunamis,” Ars Technica.
Get the Notebook.
The day's best stories and every fresh verdict, in plain English, in your inbox by seven. One email a day, no more.