How a massive landslide triggered a deadly tsunami in 2007

When earthquakes strike underwater, tsunamis often follow. But what happens when a massive landslide collapses into the sea? This can be a hazardous event that occurs without warning and generates a tsunami that radiates outwards, endangering coastal regions and offshore islands.

On April 21, 2007, a magnitude 6.2 earthquake struck the Aysén fjord region in Chile, triggering massive landslides. These generated a destructive tsunami that killed ten people and wiped out several salmon farms located in the fjord.

This event offered scientists a rare opportunity to test and validate tsunami simulation models in a real-world fjord scenario.

Investigating the massive 2007 tsunami

To understand what happened that day, researchers turned to two advanced simulation tools: NHWAVE and FUNWAVE-TVD. These tools simulate how water behaves when disturbed by sudden movements like landslides.

By applying these simulations to the Aysén event, scientists were able to understand the mechanics behind the landslide-generated tsunami better.

NHWAVE simulated how the waves were generated and moved across the fjord. FUNWAVE-TVD focused on what happened as the waves travelled further out.

Results showed that landslide volume and internal friction angle significantly influenced wave heights. Even minor tweaks to volume estimates led to drastically different results.

The tsunami marked a shift in coastal risk awareness in Chile. It showed that tsunamis are not only caused by earthquakes, but also by landslides above sea level, called subaerial landslides. That realization now plays a crucial role in how experts assess risks and plan for the future.

Predicting landslide tsunamis

Landslide-triggered tsunamis come with a unique set of challenges. Historically, scientists have relied on shallow water theory, which assumes that tsunami wavelengths are much longer than the water depth.

In such scenarios, wave dispersion, a phenomenon where different parts of waves move at different speeds, can be ignored.

Here, wave speed depends only on water depth. However, landslide-generated waves do not follow that rule.

These waves tend to be shorter in length and travel through deep water, making dispersion a critical factor.

That means their speed depends not only on water depth but also on the wavelength itself. This is where things get complicated.

Modeling landslide-generated tsunamis

Modelling landslide-generated tsunamis is challenging due to computational costs. Therefore, researchers often use higher-order Boussinesq-type wave equations (BWEs) instead of simpler shallow-water approaches. BWEs are a set of equations that help model wave behavior in complex situations.

BWEs are often helpful in two-layer systems, where the underwater landslide and the water above are treated as separate layers. These methods are far more accurate, but also demanding in terms of time and resources.

As a result, researchers often face a trade-off between model accuracy and processing time. So, how can we stay one step ahead of these unpredictable waves?

Predicting landslide tsunamis

With better early warning systems in mind, researchers are now turning to data-driven and hybrid models. Many studies have explored the landslide-generated tsunami behavior in fjords or lakes. 

One such study used the Lagrangian nonlinear model, a type of model that tracks water particle motion and can accurately predict coastal flooding.

Another one developed a tsunami early warning system for the island of Crete in the Eastern Mediterranean Basin (EMB). The researchers used data from 12 underwater pressure sensors. 

By combining real-time data with predictive models through data assimilation, the system could forecast earthquake– or landslide-generated tsunamis.

The results show that these types of studies can predict the amplitude and arrival time of tsunamis with impressive accuracy. 

Researchers also used SWASH models, idealized bathymetric profiles, and combined neural networks and statistical regression to develop predictive tools. 

Three-dimensional granular flow models have successfully simulated the entire landslide-to-tsunami process in lake environments. 

Across the board, these efforts point to the same need: we need tailored models and high-resolution data to understand these complex events. And if there is one place where all these forces collide, it is Chile’s Patagonian fjords.

Patagonian fault zone

The Patagonian fjord region is particularly vulnerable to tsunamis due to the combined effects of landslides, earthquakes, and ice calving, all of which can lead to tsunamis.

In the Liquiñe-Ofqui Fault Zone (LOFZ) of Chile, instrumental and historical data remain limited. But scientists have observed that seismic swarms occur repeatedly in this area, generating landslides and subsequent tsunamis.

Take November 21, 1927. A magnitude 7.1  earthquake occurred 100 kilometers (62 miles) north of Aysén Fjord. Two other significant events were the Aysén earthquake that took place on April 21, 2007 and the Chaitén volcano eruption that occurred in 2008. 

Between January 23 and mid-June 2007, over 7,200 seismic events were recorded by a local seismic network. Its associated swarms provided an excellent opportunity to study the seismotectonic structure. However, Chile is not the only region with steep slopes and seismic hazards.

Slopes, landslides, and tsunamis

In southern Chile, particularly south of the junction of three tectonic plates (called the triple junction), tsunamigenic geohazards remain poorly studied. This is mainly due to the lack of enough geophysical data and the inaccessibility of the area.

Chile is geologically significant because it includes more than half of the subduction zone along South America’s western margin.

In addition, over 42 percent of Chile’s mainland coastline consists of Patagonian fjords, making the region uniquely suited to studies of landslide-generated tsunamis.

Southern Chile is not alone. In regions like eastern Canada and western Norway, fjords were formed by frequent ice ages or Pleistocene glaciations.

These processes have created steep slopes that make the areas prone to landslides which can, in turn, trigger tsunamis.

And when these natural forces coincide with deep water, the result can be massive and fast.

Giant waves leave clues behind

Avalanches, landslides and rockfalls in steep mountain regions often trigger tsunamis that can be highly destructive.

These waves can reach heights of several hundred meters, unlike earthquake-generated tsunamis. In 1948, a landslide-generated tsunami in Lituya Bay, Alaska, reached up to 524 meters (1,720 feet).

Landslide-generated tsunamis often recur in the same area. In Lituya Bay alone, historical records show several significant events. These recurring disasters remind us that landslide-generated tsunamis are not rare.

Understanding these unique hazards is important for disaster planning and for improving early warning systems.

The full study was published in the journal Coasts.

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