Extreme weather

Tsunamis – top 10 misconceptions

This blogpost outlines top 10 common misconceptions about Tsunamis. Tsunamis are dangerous events that require effective investment strategies, in order to mitigate damages.

1. Tsunamis are a single huge wave travelling across the sea.

People often have the misconception that tsunamis are a singular wave with a huge crest. They think that Tsunamis come plunging in and destroying nearby infrastructure as it crashing in onshore.

This way of visualizing a tsunami is wrong in many different ways. For instance, the tsunami amplitude is typically overestimated. The problem is not the amplitude, but that the wave keep rushing in with water. This means that the amplitude provide the means, while the water provides the method of destruction.

As an example of this effect consider the video below of the 2004 tsunami hitting the shores of Sri Lanka.

Video 1: 2004 Tsunami of Hitting Sri Lanka

2. Tsunamis travel underwater before arising up near the coast.

Another common misconception is that Tsunamis travel underwater. People think of them as an intermittent wave with high amplitude that is unnoticeable due to the deep water.

That is wrong. Water is very nearly incompressible. This means that waves at the sea surface can be felt at the bottom off the ocean. Large amplitude waves are therefore not possible to hide deep under the water without influencing the surface.

Deep water misconception on tsunamis

We would therefore have the opportunity to measure the wave amplitude of the tsunami without needing deeper measurements.

3. Tsunamis only occurs due to earthquakes

This misconception is a simplification of the reality. Often times tsunamis are caused by earthquakes, However that is not the only explanatory event.

In reality, tsunamis can be caused by multiple effects such as; landslides above and below water, tilting icebergs, subduction holes, volcanic eruptions and meteor impacts. This is only to mention some of the most significant events.

4. Tsunamis are ‘deep’-water waves.

First of all let’s answer some common questions like; what is a deep water wave? What is a shallow water wave? And what’s the difference between a deep and shallow water wave?

In short: a deep water wave have almost circular particle orbits whose diameter Shriners with depth until a minuscule radii.

A shallow water wave is a wave whose particle orbits are approximately horizontal straight lines. This means that matter is transported back and forth during a wave period. The transport distance is approximately equal and non-varying with water depth.

The difference between a shallow and deep water wave is that the bottom is almost unaffected by deep-water waves while shallow water waves influence the bottom of the sea-floor. The main characteristic defining what type of wave is considered is the period.

The nature of a tsunami is that is a shallow water wave, meaning that it has a long period and high amplitude, thus the water keeps rushing in and although it is present at several thousand meters of depth, it is still considered a shallow water wave due to the long period of often multiple minutes.

5. Tsunamis are most dangerous due to a high wave crest

Similar to an earlier question the amplitude of the wave is dangerous in the sense that inundation is governed by the amplitude and terrain of the shoreline. However the combination of the high amplitude and long period is really what makes the tsunami dangerous.

The high amplitude enables the long period wave of water to keep rushing inwards destroying and inundating large areas of inland area.

This means that the amplitude in and of itself is not dangerous without the large volume of water which accompanies it.

6. Tsunamis are only dangerous due to the incoming wave

Tsunamis are dangerous because of the large volume of water which keeps rushing inwards, however as tsunamis consists of wave-trains there are typically multiple instances of flooding during a tsunami events where water draws back before rushing back in.

This way of water pulling debris and people back towards the sea is another aspect of the tsunami event that proves quite damaging and dangerous.

7. Tsunami impact areas cannot be predicted

In previous times, it was impossible beforehand to accurately estimate the impacts and inundation areas of potential tsunami waves. With the advent and innovation of modern computers and computational fluid dynamics this becomes feasible to create storm floods and inundation maps.

The inundation maps created based on high-fidelity hydrodynamic simulations allows engineers and scientists to test difference approaches towards mitigation of potential tsunami events. From these studies it is therefore feasible to predict the damages before the catastrophic events such as tsunami flooding.

GIF of an incoming tsunami

8. Tsunamis only hit in warm places

As tsunamis can be caused by landslides, volcanic eruptions, subductions and iceberg tilting they can occur on places where waters and temperatures are cold.

As an example of cold weather tsunamis consider the Alaskan tsunami event of Lituya Bay, see Figure 1, believed to be caused by an enormous landslide event resulting in what is considered the largest recorded Tsunami on the planet.

Figure 1: Lituya Bay Tsunami caused by a landslide. The white areas on the picture show the inundation of the Tsunami, scraping away vegetation as it travelled down the fiord.

The height of the tsunami in the valley was devastating to the local wildlife, biodiversity and tree life. The amount of damages from the tsunami event was recorded in the water level where trees where cut down due to the tsunami.

9. Tsunamis are fully understood phenomena

Although much documentation, theoretical considerations and measurements have been utilized in an effort to understand and describe tsunamis radical nature.

Presently, it is not a fully understood phenomena and to this day there is still undergoing state-of-the-art research especially considering the development of numerical weather prediction tools providing early warning to these events.

Some of the questions which need to be understood in more detail are: What are the main mechanisms behind the creation of tsunamis, what amplitudes are created and how are the periods created during earthquake and landslide events.

Complete understanding of phenomena’s

10. Tsunami catastrophes cannot be mitigated

There exist multiple measure to try and counteract the terribly powerful destructive forces which tsunamis bring forward.

Shoreline flooding walls provide the much needed cover of tsunami events and will provide the users

Bonus: You can’t do anything to protect yourself against Tsunamis

Although the technology to accurately predict and stop Tsunamis before they hit shores doesn’t exist, you can still do something in order to mitigate the impacts of an incoming Tsunami.

The number one rule when trying to survive a Tsunami attack is seek shelter high up and act fast! Tsunamis are dangerous and hit within minutes of the alerts. This means that every second is precious when trying to escape and thus easy access to high terrain is critical when seeking shelter from the incoming danger.

The signs that a Tsunami is underway is explained in this blogpost, in summary some of the signs are: A receding coastline, a recent nearby earthquake, volcanic eruption or landslide.

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