
The Underappreciated Threat of Volcanic Tsunamis - pseudolus
https://blogs.scientificamerican.com/rosetta-stones/the-underappreciated-threat-of-volcanic-tsunamis/
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btilly
Simple picture for those who do not understand what makes a tsunami a tsunami.

Gravity waves have a direct relationship between wavelength, the depth of the
wave, and its speed. There is no such relationship with the height of the
wave. You get a tsunami whenever a very tall column of water moves all at
once, whether it is rising a little bit or a lot. The result is a very deep
wave, with a correspondingly long wavelength, that travels at about the speed
of a jetliner.

As a wave approaches land, it begins to rise and then break when the bottom of
the wave hits the sea floor. It can then carry a volume of water inland
determined by its overall size. This applies to all waves, but since tsunamis
are so much deeper they rise more and carry much more water for their height.
Hence they bring water in "like a tide". Thus the alternate name "tidal wave".

Most tsunamis are caused by earthquakes. They shake the sea floor, moving the
entire column of water above, and off the tsunami goes.

They can also be caused by underwater mudslides, eruptions, or (rarely) large
meteors - anything that moves the entire water column will do. And those
causes often involve much larger vertical displacements, leading to a much
taller wave and a lot worse tsunami.

Therefore the very largest tsunamis are caused in these alternate ways. See
[https://en.wikipedia.org/wiki/Megatsunami](https://en.wikipedia.org/wiki/Megatsunami)
for information on some of the largest.

~~~
arethuza
We recently went for a walking holiday on El Hierro - which is a small
volcanic island in the Canaries not far from La Palma where Cumbre Vieja is
located.

El Hierro, in addition to being generally lovely, has a particularly
spectacular feature - a big chunk of the island is missing leaving behind El
Golfo (The Gulf) - which is where a 150–180 km3 landslide(s) occurred leaving
behind a flat bottomed area with a surrounding 1000m escarpment. The old paths
up this escarpment make for interesting walking...

[https://en.wikipedia.org/wiki/El_Hierro#Landslides_and_tsuna...](https://en.wikipedia.org/wiki/El_Hierro#Landslides_and_tsunami)

~~~
throwaway5752
[https://blogs.agu.org/landslideblog/2013/12/13/canary-
island...](https://blogs.agu.org/landslideblog/2013/12/13/canary-islands-
tsunami/)

Sounds like an amazing site to have visited, but just to be clear, this is not
the kind of volcanic tsunami the linked article is talking about and the
threat of them is exaggerated.

~~~
arethuza
The article does mention "Flank failures and sector collapses" \- which sounds
like El Hierro to me? (Mind you, there is no evidence that the El Golfo event
actually caused any tsunamis).

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rad_gruchalski
> Caldera collapse, like the catastrophic conclusion of Krakatau's 1888
> eruption,

Wasn’t the eruption in 1883?

~~~
oska
It most definitely was.

It's bizarre seeing such an error in a _Scientific American_ article. Was it
the author's own error or some sort of transcription process during
publication?

The dating error is repeated under the tsunami travel times chart at the top
of the article too.

------
everdev
The article ends with:

> Next, we'll explore regions at risk, determine the geologic factors that
> signal potential volcanic tsunami hazards ...

Where's part 2 of this article?

~~~
fwip
It's only been a week since it was published.

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MPSimmons
Oh, hi there Anxiety! There wasn't enough going on in the world, so we brought
you volcanic tsunamis. Enjoy!

