Dammit.
Tsunami can be generated by ANY large disruption of the ocean. Usually that’s earthquakes, but it can be eruptions, landslides, impacts, or calving glaciers.
Tsunami in Indonesia always have a big death toll.
Tsunami can be generated by ANY large disruption of the ocean. Usually that’s earthquakes, but it can be eruptions, landslides, impacts, or calving glaciers.
Tsunami in Indonesia always have a big death toll.
Q: If tsunami can be triggered by anything, what exactly are they?
A: Tsunami are large-wavelength displacement waves, like the nastier cousin of a ripple.
Since the wavelength is so huge, they behave as shallow-water waves even in open ocean. Yay simpler physics?
A: Tsunami are large-wavelength displacement waves, like the nastier cousin of a ripple.
Since the wavelength is so huge, they behave as shallow-water waves even in open ocean. Yay simpler physics?
Q: Wait, does that mean tsunami are monsters in open ocean?
A: Nope!
All waves shoal in shallow water: slow down, bunch together, & spike up.
In open ocean, tsunami are centimeters spread over hundreds of km traveling at jet-airliner speeds. We detect them by pressure changes.
A: Nope!
All waves shoal in shallow water: slow down, bunch together, & spike up.
In open ocean, tsunami are centimeters spread over hundreds of km traveling at jet-airliner speeds. We detect them by pressure changes.
The physics of water waves are all the same, but with wildly different wavelengths (λ), period (P), height (H), & speed.
Tides: λ~15,000km, P~12hrs, H~0-15m
Tsunami: λ~10-500km, P~10min-1hr, H~0-30m
Wind waves: λ~0.1-100m, P~5-20sec, H~0-30m
More: onlinelibrary.wiley.com/doi/full/10.10…
Tides: λ~15,000km, P~12hrs, H~0-15m
Tsunami: λ~10-500km, P~10min-1hr, H~0-30m
Wind waves: λ~0.1-100m, P~5-20sec, H~0-30m
More: onlinelibrary.wiley.com/doi/full/10.10…
Some people call tsunami tidal waves. This is a misnomer of hazy origin.
Tides are caused by the gravitational pull of the Sun & Moon. They’re huge wavelength (½ the planet), slow (½ the day), and we literally define the coast to match where they cover.
Tsunami are... not that.
Tides are caused by the gravitational pull of the Sun & Moon. They’re huge wavelength (½ the planet), slow (½ the day), and we literally define the coast to match where they cover.
Tsunami are... not that.
Q: What’s the different between deep- & shallow-water waves?
A: Water waves move in orbitals. These orbitals shrink with depth until they fade out.
Orbitals don’t touch bottom? Deep-water wave.
Orbitals flattened? Shallow-water waves.
A: Water waves move in orbitals. These orbitals shrink with depth until they fade out.
Orbitals don’t touch bottom? Deep-water wave.
Orbitals flattened? Shallow-water waves.
If a wave reaches bottom or not is related to wavelength (L in figure) & water depth.
We use different math for deep-water vs shallow-water waves. (The transition in between is messy & awful.)
Tsunami wavelengths are so long the entire ocean is shallow.
We use different math for deep-water vs shallow-water waves. (The transition in between is messy & awful.)
Tsunami wavelengths are so long the entire ocean is shallow.
It’s HARD to predict how tall a tsunami will be when it comes on shore.
But wave travel speed doesn’t depend on height. For shallow water waves, it doesn’t depend on the wave at all, just depth! (v=√gd)
This means we can predict WHEN a tsunami will come onshore really well.
But wave travel speed doesn’t depend on height. For shallow water waves, it doesn’t depend on the wave at all, just depth! (v=√gd)
This means we can predict WHEN a tsunami will come onshore really well.
But Indonesia is hard in best circumstances.
Low public knowledge on IDing tsunami & triggers or how to respond (run to high ground!)
Incomplete, broken, & poorly maintained warning system
LOTS of local sources that can trigger tsunami with little reaction time
Little trust
Low public knowledge on IDing tsunami & triggers or how to respond (run to high ground!)
Incomplete, broken, & poorly maintained warning system
LOTS of local sources that can trigger tsunami with little reaction time
Little trust
Aside from the tsunami, Krakatau (Krakatoa) is a NASTY volcano.
In 1888, Keakatau erupted so loudly, they heard it in Perth. It’s the “crack heard round the world,” estimated loudest sound in historic times. It triggered a mini ice age. Its tsunami hit ships in South Africa.
In 1888, Keakatau erupted so loudly, they heard it in Perth. It’s the “crack heard round the world,” estimated loudest sound in historic times. It triggered a mini ice age. Its tsunami hit ships in South Africa.
Krakatau’s 1888 eruption had huge cultural influence.
Frankenstein: theparisreview.org/blog/2016/10/2…
The Scream: smithsonianmag.com/science-nature…
A Christmas Carol: theguardian.com/news/2012/feb/…
All of them influenced by the Year With No Summer.
Frankenstein: theparisreview.org/blog/2016/10/2…
The Scream: smithsonianmag.com/science-nature…
A Christmas Carol: theguardian.com/news/2012/feb/…
All of them influenced by the Year With No Summer.
But here’s the thing:
THAT Krakatua is not THIS Krakatua. Same place, different volcano.
Yeah.
This one is Anak Krakatau, child of Krakatau.
Old-Krakatau blew out, emptying magma chamber & collapsing into a caldera. New-Krakatau emerged from its ashes.
THAT Krakatua is not THIS Krakatua. Same place, different volcano.
Yeah.
This one is Anak Krakatau, child of Krakatau.
Old-Krakatau blew out, emptying magma chamber & collapsing into a caldera. New-Krakatau emerged from its ashes.
*Errata. Some of the art was influenced by 1815 Mount Tambora, a nearby volcano of the same eruptive style.
Info in links is accurate, I just jumbled them together.
Info in links is accurate, I just jumbled them together.
Q: Is this new volcano as terrifying as it’s name-shared predecessor?
It’s in (exactly) the same place, so similar magma geochemistry, thus similar eruptive style. It has potential to be very, very nasty.
But... it’s been erupting since June.
Details: volcano.si.edu/volcano.cfm?vn…
It’s in (exactly) the same place, so similar magma geochemistry, thus similar eruptive style. It has potential to be very, very nasty.
But... it’s been erupting since June.
Details: volcano.si.edu/volcano.cfm?vn…
(*1883. sigh)
Krakatau has been under yellow alert for months: magma.vsi.esdm.go.id/img/varshare/K…
But...
Even a relatively small, young volcano in a relatively tame eruptive sequence can still produce deadly tsunami.
Which this one did.
Dammit.
Krakatau has been under yellow alert for months: magma.vsi.esdm.go.id/img/varshare/K…
But...
Even a relatively small, young volcano in a relatively tame eruptive sequence can still produce deadly tsunami.
Which this one did.
Dammit.
Post-disaster social media Best Practice notes:
1. Stay off disaster hashtags unless you’re impacted or an official news source.
2. Be careful boosting traumatic imagery & try to make it opt-in (quote-a-quote tweet, no-preview link).
3. Beware recycled/mislabeled imagery.
1. Stay off disaster hashtags unless you’re impacted or an official news source.
2. Be careful boosting traumatic imagery & try to make it opt-in (quote-a-quote tweet, no-preview link).
3. Beware recycled/mislabeled imagery.
Post-disaster communications rule of thumb:
The less we hear, the worse it is because infrastructure is too damaged or people are in too much immediate danger for posting updates, videos, pix, or even pleas for help.
Silence is terrifying.
Any news is better than silence.
The less we hear, the worse it is because infrastructure is too damaged or people are in too much immediate danger for posting updates, videos, pix, or even pleas for help.
Silence is terrifying.
Any news is better than silence.
Q: Would even the best, perfectly-maintained tsunami early warning system help with a local non-earthquake-triggered tsunami?
A: Not really.
Tsunami (DART) buoys measure pressure changes on the ocean floor. They verify tsunami were generated & track spread for distant warnings.
A: Not really.
Tsunami (DART) buoys measure pressure changes on the ocean floor. They verify tsunami were generated & track spread for distant warnings.
Q: Some articles say the tsunami was triggered by a landslide, others by the volcano, which is it??
A: Landslides on the volcano’s flanks.
Volcanoes are sloppy heaps of poorly-glued-together rocks all slanted downhill. It doesn’t take much for pieces to slip off.
A: Landslides on the volcano’s flanks.
Volcanoes are sloppy heaps of poorly-glued-together rocks all slanted downhill. It doesn’t take much for pieces to slip off.
Before/after satellite imagery. Even above water, it’s pretty clear that a lot of material moved quickly in the last day.
NOTE: images are May/Dec, not yesterday/today.
We can’t pinpoint that large dark flow to too recent using just this imagery (not ID it as the tsunami trigger), but it’s clearly relatively fresh.
We can’t pinpoint that large dark flow to too recent using just this imagery (not ID it as the tsunami trigger), but it’s clearly relatively fresh.
Before/After pairing bracketing the tsunami shows a partial summit collapse (top part of the volcano destabilizing; not unusual).
It’s going to be a while before anyone can take the time for detailed fieldwork, but everything is consistent so far.
?
It’s going to be a while before anyone can take the time for detailed fieldwork, but everything is consistent so far.
?
Q: Could another tsunami happen?
A: Yes
Q: Soon?
A: Maybe. It’s possible but not certain
Q: Will the next one have a warning now we know what’s going on?
A: Not likely. It’s hard to identify landslide-triggered tsunami, especially quickly enough to issue useful warnings
A: Yes
Q: Soon?
A: Maybe. It’s possible but not certain
Q: Will the next one have a warning now we know what’s going on?
A: Not likely. It’s hard to identify landslide-triggered tsunami, especially quickly enough to issue useful warnings
Q: Uh... so, what would you do?
A: Local officials are recommending staying away from local beaches until Krakatau calms down. That‘s a Very Good Idea.
If you do live nearby and absolutely MUST spend time on the shore, keep an eye on the water.
Details:
A: Local officials are recommending staying away from local beaches until Krakatau calms down. That‘s a Very Good Idea.
If you do live nearby and absolutely MUST spend time on the shore, keep an eye on the water.
Details:
