The ‘bathtub effect’ – How a landslide turns into a tsunami
Using computer technology, it is now possible to predict the size of a potential tsunami wave and which areas it would affect.
By Rasmus Balle Hansen
Do you know the feeling when you’re trying to lower yourself into a bathtub, and suddenly the water starts moving left and right, causing a big puddle on the bathroom floor. Or, in another scenario, you’re walking with a cup full of hot coffee, trying to balance it without spilling.
These two small-scale examples demonstrate what happens when a landslide occurs and its impact on the water below.
Due to the long and narrow fjord systems, tsunami energy can become trapped, resonating, or sloshing like water in a bathtub. The result is tsunami waves that can be very large and last for many hours while moving through the fjord systems. This is known as the ‘bathtub effect’.
Increased attention on landslides
In 2017, a large landslide in the Karrat fjord caused a tsunami that, at its peak, measured 90 meters and could be detected 140 kilometers from the actual landslide. Since then, the Greenlandic authorities have worked to increase surveillance of potential landslides.
“Most importantly, we try to predict how big the tsunami will be when it reaches settlements.”
– Patrick Lynett
Patrick Lynett, Professor of Engineering from the University of Southern California, is working together with a team of geologists from the Greenlandic authorities to map out potential landslide areas and assess how large potential tsunamis triggered by a landslide could be.
“We try to understand how large tsunamis can be and to predict how they will evolve throughout the fjords, which allows us to estimate how far inland the tsunami will go, for example, in Uumannaq Fjord.”
Predicting disasters
Using data from previous landslides, like the one in 2017, geologists are now able, with the help of computer technology, to predict how big a potential tsunami would be and how it would evolve.
“With these models, we’re able to create movies and animations that show how long it takes for a tsunami to reach different settlements and which way it will travel,” says Patrick Lynett.
The models show how the tsunami moves through the fjords and how the bathtub effect increases the energy of the tsunami.
“The tsunami can sometimes loop around islands and come from an unexpected direction. Most importantly, we try to predict how big the tsunami will be when it reaches settlements.”
Future safety to the settlements
The model here shows how a tsunami moves through the fjord system. The tsunami is largest at the landslide location and then gradually decreases. But midway, the tsunami increases in size, which is called the bathtub effect.
“Because of these interesting fjord structures, which tend to be long and narrow, the tsunami energy can get trapped inside these fjords and resonate or slosh like a bathtub for many hours after the landslide. This energy will then leak out slowly, creating a tsunami that can last for many hours throughout the fjord.”
With the new computer technology, we’re better equipped to understand the tsunamis created by landslides. This new insight gives us the opportunity to develop more effective contingency plans, which will bring more safety to the settlements in the future.
Hear Patrick Lynett tell more in this video here.