Did you know that the most colossal waves ever recorded didn’t come from the open ocean? It’s a fact that even surprises scientists. But here’s where it gets even more astonishing: these monstrous waves weren’t born from earthquakes, but from something far less obvious—landslides. Yes, you read that right. When unstable slopes collapse into water, they can unleash tsunamis that rival or even surpass those triggered by seismic activity. And this is the part most people miss: these landslide-triggered tsunamis (LTTs) are not rare occurrences. They account for about 10% of all recorded tsunamis globally and are the second most frequent cause after earthquakes. Some have produced waves towering over 30 meters, and in extreme cases, reaching heights of hundreds of meters. These events are hyper-local, lightning-fast, and still shrouded in mystery.
A groundbreaking global review led by Katrin Dohmen and her team analyzed 317 landslide events that generated 297 tsunamis worldwide. Each case was meticulously documented, detailing the location, trigger, wave height, and impact on human life and infrastructure. The study categorizes these events into six primary causes: earthquakes (44%), volcanic activity (10%), paraglacial conditions (10%), human activity, precipitation, and an unknown cause for nearly one-fifth of cases. But here’s the controversial part: while earthquakes dominate the narrative, human-induced factors like reservoir construction and mining are increasingly playing a role in triggering these catastrophic waves.
The data also reveals where these tsunamis are most dangerous. While one-third occur along open coasts, a staggering 41% happen in enclosed marine environments like bays and fjords, and 25% in inland waters such as lakes and reservoirs. These confined spaces act like amplifiers, trapping wave energy instead of letting it dissipate into the open sea. This is why the highest tsunami run-ups—like the 524-meter wave in Alaska’s Lituya Bay in 1958 or the 260-meter wave in Italy’s Vajont reservoir disaster in 1963—are linked to landslides in narrow basins.
And this is where it gets even more alarming: climate change is adding fuel to the fire. Paraglacial conditions, where landscapes adjust after glaciers retreat, already account for 11% of LTTs. As glaciers melt in places like Greenland and Alaska, steep rock walls lose their frozen support, permafrost degrades, and sediment-rich deltas become increasingly unstable. In 2017, a 45-million-cubic-meter rockslide in Greenland’s Karrat Fjord triggered a tsunami that devastated nearby villages, leaving four people missing. In 2023, another Greenland rockslide sent a 200-meter-high wave down Dickson Fjord, creating a standing wave that reverberated globally. These events are a stark reminder of what a warming climate can unleash in high-latitude fjord coasts.
Humans, too, are creating their own tsunami risks. One in nine documented LTTs is linked to human activity, with reservoirs behind large dams being a major hotspot. Fluctuating water levels alter pore pressure in slopes, making them more susceptible to collapse during heavy rain. The Three Gorges region in China has seen thousands of landslides since its reservoir was filled, though only a few have generated waves. Open-pit mines, quarries, and artificial embankments also pose risks, especially in narrow lakes or flooded pits, where even small landslides can create waves large enough to threaten lives and infrastructure. For engineers and regulators, this isn’t just a theoretical problem—it’s a pressing issue tied to dam safety, shipping routes, and local economies.
But here’s the real challenge: warning systems for these tsunamis are woefully inadequate. Unlike traditional ocean-wide tsunamis, landslide-triggered waves can arrive in minutes, leaving little to no time for sirens or alerts. In 2018, earthquake-triggered landslides in Palu Bay, Indonesia, sent water crashing into the city in just 100 seconds. Adding to the complexity is the uncertainty surrounding these events. Key details like landslide volume, material, and even location are often missing, especially for submarine slides. Public seafloor maps are too low-resolution to identify smaller features that can still generate dangerous waves, making it nearly impossible to predict wave heights or which coastal areas are most at risk.
Existing early warning systems are primarily designed for earthquake-generated tsunamis, which work well in places like Indonesia and Japan. However, when earthquakes trigger underwater landslides, the resulting waves can arrive earlier or higher than predicted. Coastal regions near large strike-slip faults, like Palu Bay or parts of the Sea of Marmara, face a dual threat and require special attention.
So, what needs to change? Scientists argue that the first step is identifying unstable slopes through high-resolution bathymetry, especially in active tectonic zones and around major reservoirs. Landslide susceptibility mapping should also extend to offshore areas, not just hillsides. In some places, like Norway’s Tafjord area, authorities monitor unstable slopes with sensors and alert residents via phone and sirens if a collapse seems imminent. Similar systems exist around Chinese reservoirs. But for most coastlines, protection will rely on public awareness. People living or vacationing near steep fjords, volcanic islands, or large reservoirs must recognize warning signs like strong shaking, visible rockfalls, or a sudden roar near the shore as cues to move to higher ground immediately—no official alert needed.
Landslide tsunamis may not be the most common, but they highlight the intricate connections between mountains, dams, volcanoes, and the sea. When a slope fails at the wrong time in the wrong place, coastal communities can be upended in seconds. Here’s the thought-provoking question: As climate change accelerates and human activity expands, are we doing enough to prepare for these hidden yet devastating threats? Share your thoughts in the comments—let’s spark a conversation about how we can better protect our vulnerable coastlines.
