Thread by @SquigglyVolcano

Okay—an eruption has begun at La Palma, the most northwesterly island in the Canary Island archipelago in the Atlantic Ocean. It was announced (somewhat amusingly) in All Caps by @involcan just moments ago.

So: should we be worried? A thread, by me.

https://twitter.com/involcan/status/1439599283733413888

La Palma, an island not far off the shoes of Morocco, is administered by Spain. It's also one made of volcanoes—two large ones, specifically, an older northern one and a younger southern one. The younger one, Cumbre Vieja (CV), is known to be very active. volcano.si.edu/volcano.cfm?vn…

CV is about 125,000 years old. That's young for volcanoes. This elongated volcano erupts in a variety of ways, but often this involves fissures opening up in the ground and lava spilling and fountaining out, ~like the flank eruption on Kīllauea in 2018. nytimes.com/2018/12/12/sci…

Volcanoes, though, are like cats. No two are alike, they behave differently in the run-up to a paroxysm, and when they do erupt, each is somewhat different from the last.

So what does CV's history tell us about the current eruption?

CV has erupted a lot in the past 7,000 years, again according to the @SmithsonianGVP (the Library of Alexandria for the world's active volcanoes). Most of those involve lava flows and minor explosions—so yeah, definitely more like Kīlauea than anything Vesuvius-esque.

Its lava flows are its primary hazard; they have threatened populated areas and infrastructure on the island several times in the past few centuries; the lava flows have reached the sea on at least five different occasions.

The last eruption at CV was way back in 1971.

Earthquakes are common on La Palma. Any geologically active area is expected to have seismic activity. What's interesting is not whether something is rumbling, but whether that rumbling diverges from the area's usual seismic symphony.

In the last month or so, La Palma changed its tune. In September, there were thousands of earthquakes, several of which were powerful enough to be felt by people on the island.

So what was causing them?

Earthquakes can be caused by myriad geologic phenomena. But was put volcanologists on notice was that these earthquakes were not only frequent, but they were shallow. They also coincided with significant inflation of the land around CV.

That suggested magma was being injected at a shallow depth. Worth noting that most intrusions don't lead to eruptions; the magma cools and can't escape to the surface.

But sometimes, it does. A serpent of magma spent a few weeks trying to erupt in Iceland back in March before succeeding.

Looks like another intrusion succeeded on La Palma today!

nationalgeographic.com/science/articl…

In the last few days, scientists have been scurrying around the island and adding seismometers to its network. They were trying to listen for volcanic tremor, the tell-tale seismic signal of magma moving to the surface. The eruption sort of beat them to it

https://twitter.com/involcan/status/1439568373214502914

But the authorities were kept up to date and, based on ominous data, people around CV were evacuated with the help of the Spanish military. Good thing too, as the eruption began later that day. reuters.com/world/europe/p…

The eruption has just begun. It could suddenly stop, or persist for days, weeks or even months. If so, expect a lot of lava flowing across the island's south.

Sounds like a local hazard, right? So why should anyone off La Palma even care?

Well...

There is a history of giant landslides happening on the island. Part of the island in the north dumped 200 cubic km of a collapsing volcano into the sea 560,000 years ago, likely generating a large tsunami. blogs.agu.org/landslideblog/…

Today, the south of the island is where all the activity is at. It has been suggested that the haphazardly built CV could also partly collapse into the sea one day, perhaps after a big eruption—and possibly create a tsunami.

But wait: it's not that simple.

In 2001, a pair of scientists published a scary paper: one that suggested a catastrophic collapse of the CV volcano's flank could drop up to 500 cubic km of rock into the sea, creating a tsunami that would reach the Americas and rise to 25m.

Eeep.

agupubs.onlinelibrary.wiley.com/doi/abs/10.102…

But such an apocalyptic scenario has since been considered to be unlikely by other scientists. Dave Petley, a landslide expert at Sheffield University, summarised this work on a blog back in 2017, and it's well worth a look: blogs.agu.org/landslideblog/…

He's been to La Palma and he can't find convincing evidence that a *large* section of the CV volcano is unstable. He also notes that, during the 1971 eruption, no such collapse of any significance took place.

But that doesn't mean a flank collapse is impossible.

That 2001 represented a very unlikely worst-case scenario. There's no evidence that a flank collapse of that size could currently occur. If enough magma did intrude into CV volcano, it could make part of it slide off into the sea—but the resulting tsunami would be smaller.

This 2015 paper uses more realistic measures to simulate a possible volcano-triggered tsunami, and it found that if 80 cubic km of CV volcano fell into the sea, it could create a tsunami that would hit the eastern seaboard...but one only 2m high.

link.springer.com/article/10.100…

Ideally, this doesn't happen either. The salient point, though, is this: you do not have to worry about an apocalyptic tsunami destroying New York City because of what's happening on La Palma.

Volcano-triggered tsunamis are a real concern though. The tsunamis caused by the 1883 eruption of Krakatau killed tens of thousands of people. Anak Krakatau - the baby cano rising from its debris - collapsed in 2018, also creating a lethal (but smaller) tsunami.

There's a real worry that, one day (far from now, but hey), Mount Etna could undergo a flank collapse that could cause a tsunami to drown the shorelines of the eastern Mediterranean. That would be truly awful. nationalgeographic.com/science/articl…

But the current eruption at La Palma? It's very, very likely to remain a local hazard. So don't buy into any fearmongering.

Listen to @involcan and volcanologists/geo-experts in the know. And, hopefully, I'll get to write this up for NatGeo too (cc: @jaywbennett) soon-ish.

In the meantime, I'll keep an eye on things and share updates from official and trusted scientific sources should they arise.

End!

cc @BuzzFeedStorm @janinekrippner @NatGeo @jessphoenix2018 @SamLMontano et al for any potential signal boost.

And thanks for the continual updates, @involcan! :)

Huge thanks too to @davepetley for that great blog post from 2017. (You can bet we'll be talking if I get to write this all up formally!)

oh and cc @USGSVolcanoes for good measure

Okay, @NatGeo explainer coming tomorrow! :)

Hey @davepetley—can we have a quick chat about this tomorrow morning for a NatGeo explainer? DM me your email if you can. :)

Wow.

https://twitter.com/involcan/status/1439683225476124677

Glad to see this thread is helping so many people out! I don't have a Soundcloud to share, but I do have a book on the beauty and power of volcanoes coming out in November! You can pre-order it here if you'd like: amazon.com/Super-Volcanoe…

https://twitter.com/SquigglyVolcano/status/1439735202880888832?s=20