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“I work with bait fishing, and I was at the beach on my way to work when the tsunami hit. While preparing for the day’s work, I heard some kind of noise. Everyone turned and looked toward the sea. I saw it too. The water came as high as a cloud.”
—Arjunan Anjappan, survivor, 2004 Indian Ocean tsunami
“Tsunami: Sea Change for Resilience” UNESCO exhibition
A tsunami, often misunderstood as merely an oversized ocean wave, is one of nature’s most destructive forces. Scripps Institution of Oceanography seismologist Barry Hirshorn is working to provide tsunami warnings to coastal populations as accurately and quickly as possible.
“A tsunami is essentially a gravity wave,” Hirshorn explains. This term, used in scientific communities, emphasizes the role of gravity in the oscillations of water columns. Large displacements are often caused by tectonic activity: The most common source of tsunamis lies in subduction zones, where one tectonic plate slides beneath another. Over time, stress builds along these fault lines, and when released, the sea floor rises or falls, displacing colossal volumes of water.
Hirshorn cites the Dec. 26, 2004 Indian Ocean tsunami as an example: “The sea floor uplifted over a length longer than the state of California, creating a massive column of water … when the water column collapses, this energy radiates outward, creating the tsunami,” he adds. This phenomenon in fact produces not just one wave but a series of waves, which can travel vast distances with immense energy.
It’s more like a steamroller made of water, a fast-moving surge shearing across the land.
Although the energy from a tsunami disperses in all directions, its impact is not uniform. “You get a much stronger tsunami at 90 degrees to the fault,” Hirshorn explains, which is what happened during the 2004 tsunami. This direction of the undersea rupture, which occurred off the coast of Indonesia, determined the intensity and direction of the tsunami, causing disproportionate devastation in certain countries such as Sri Lanka—but damage and deaths as far afield as Tanzania and Thailand.
While the Pacific’s Ring of Fire is a hotbed for tsunamis due to its numerous subduction zones, no ocean is immune. The 1755 Lisbon earthquake generated a tsunami that devastated Europe’s Atlantic coast, a reminder that they can originate anywhere massive undersea activity could trigger one. And these events don’t need to be the movement of entire continental plates. Hirshorn also recounts the record-breaking underwater volcanic eruption in 2022 near Tonga, which created a tsunami and generated waves that circumnavigated the globe.
In the open ocean, a tsunami may seem benign, with a height of less than three feet. However, as it nears the shore, the wave slows and grows exponentially. “The kinetic energy converts into potential energy, creating the towering wall of water that we associate with tsunamis,” Hirshorn says.
One common misconception about tsunamis is that they resemble a single giant, breaking wave. Hirshorn clarifies, “It’s more like a steamroller made of water, a fast-moving surge shearing across the land.” This force allows tsunamis to inundate areas miles inland, causing widespread destruction beyond the coast.
Another strange hallmark of tsunamis is harbors sometimes draining before the wave strikes. “This depends on the position of the harbor relative to the fault,” Hirshorn explains. In some cases, the ocean recedes dramatically, offering a natural warning sign of an impending wave. The 1964 Alaska earthquake caused harbors to empty before a massive wave struck, which Hirshorn recalls as a defining moment in tsunami awareness.
But the 2004 Indian Ocean tsunami stands out for its sheer scale—and the subsequent revolution in tsunami science.
Before 2004, the creation of warning systems often came in response after a given tsunami disaster. After the 2004 tsunami, however, the paradigm shifted to proactive monitoring by building tsunami warnings in more ocean basins. “We can now characterize an earthquake’s magnitude and tsunami potential within minutes,” Hirshorn says. This advance is critical for regions across the globe, including Cascadia in the United States, where a massive tsunami, scientists say, is a matter of when, not if.
Advances in technology and international cooperation have significantly reduced tsunami-related fatalities over the past 20 years. For example, improved communication infrastructure ensures timely warnings even in remote areas. And contemporary tsunami warning systems now leverage differences in wave speeds to provide critical early warnings. Earthquake waves travel faster than tsunamis, allowing scientists to assess the event’s magnitude and potential impact in real time. “The closer populations are warned through seismic data, while distant populations benefit from models predicting tsunami travel times,” Hirshorn says. “We now have the tools to prevent another disaster like 2004.”
However, predicting the exact size and impact of a tsunami remains complex. As is communicating risk to the public. “Public response is critical,” Hirshorn says, highlighting the need for ongoing education and drills. Tsunamis can strike within minutes, leaving no time for hesitation. He emphasizes the importance of public education, noting, “Even in the absence of official warnings, ground shaking is a signal to head inland. It’s better to overreact than underestimate the risk.”
Hirshorn’s insights reveal the dual nature of tsunamis as both awe-inspiring and devastating. Understanding their mechanics, improving prediction, and fostering public preparedness are crucial to mitigating their impact.
To learn more:
Watch Tsunami: Race Against Time; all episodes are streaming now on Disney+ and Hulu.
Or visit the Tsunami: Sea Change for Resilience exhibition at UNESCO Paris until December 31st.
Lead image: Benny Marty / Shutterstock
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