Chiara Vercellone|USA TODAY
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The claim:Experts predict La Palma eruption to create tsunami that would reach the U.S.
A decades-old theory has resurfaced online afteravolcanic eruption on a Spanish island thatcaught the world's attention.
On the island of La Palma, in the Canary Islands, a volcano eruptedin the afternoon of Sept. 19 after a weeklong buildup of seismic activity.
Days later, the lava continued to flow through the four mouths of the volcano toward the island's western coast. By Sept. 20it had already forced the evacuation and relocation of over 5,000 residents.
As the latest developments areshared online, many social media users are also sharing a longtime theory thatthe eruptioncould cause a tsunami that would reach the East Coast of the United States.
"The things I've read they are expecting it to erupt and a piece of land would slide into the ocean and it would cause a tsunami for the USA east coast!" the post says. "They have been predicting this for years."
The accompanying image is a map of the eastern part of the United States. Text laid over it claims that a "50 meter tsunami after Canary Island volcano eruption and landslide puts THIS under water." Florida, New York, Washington, D.C., Boston, and parts of southern Texas andLouisiana are among the areas that would be purportedly affected by the tsunami, according to the image.
The image has spread widely on social media. Another version, posted on Facebook on Sept. 19, accrued more than 800 shares in two days before it was deleted.
Nick Knowles, an English television presenter, also shared a version of the claim on Twitter, where he has almost 160,000 followers.
While the theory being shared exists, social media users are presentingit as if it isa likely scenario or represents an expert consensus of some kind.
In reality,it's a hypothesis that both American and Spanish officials have debunked,saying the conditions required for a tsunami big enough to submerge part of the country's coastsare extremely unlikely to happen.
More: Volcano erupts on Spanish island La Palma forcing thousands of evacuations
USA TODAY reached out to the users who shared the image for comment.
Volcanic eruption not big enough to create tsunami
As of Sept. 21, two days after the initial spew of lava, the Cumbre Vieja volcanic eruption had covered around 254 acres and destroyed 166 buildings, according to the Canary Islands Volcanology Institute, which has been sharing news and analysis onthe eruption.
The chances of acid rain and toxic clouds remain low,though the volcanic ash in the air could pose a risk to residents of the island.
And there's a vastly lowerchance of a landslide causing a tsunami big enough to reach the coast of the United States.
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The theoryhas been around since 2001,whentwo college professors– Steven Ward from University of California, Santa Cruz and Simon Day from University College in London– published a study about the possibility of a tsunami originating in the Canary Islands later reaching American coasts and other parts of the world.
The four-page paper saidthat "during a future" eruption of theCumbre Vieja volcano, a landslideof between 150 and 500cubic kilometers, which could trigger a tsunami with waves between 10 and 25 meters high hitting North America around nine hours after the hypothesized volcanic eruption.
Spanish and American officials have pushed back onthe theory, however.
After announcing the eruption on Twitter on Sept. 19, the U.S. Geological Survey said the tsunami threat remained local, debunking users' claims that a purported "mega-tsunami" would happen.
That same day, the U.S. National Tsunami Warning Center posted on Facebook that the eruption did not pose any tsunami risks to the East Coast.
The islands' volcanology institute has assured that extreme conditions would have to occur for the theory to become a reality.
For instance, the volcano would have to grow by 1,000 meters over its current height, which the institute told Spanish national TV station Antena 3 would take another 40,000 years.
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Another way a "mega-tsunami" could occur is if an earthquake of "exceptionally high magnitude" and a high magnitude volcanic eruption were to take place at the same time. Those twophenomena together could lead to a landslide of the Cumbre Vieja flank, which is what Ward and Day's theory hypothesized.
None of these conditions have occurred, however.
'Mega-tsunami' theory resurfaces with seismic activity in La Palma's
The "mega-tsunami"theory often resurfaces with news of a volcanic eruption or seismic activity in the Canary Islands.
In 2016, the Daily Star, categorized by Media Bias Fact Checkas a "questionable source" of news based onits "routine publication of conspiracy theories,"published an articleon the theory. In response, geographer and earth scientist Dave Petley debunked the theory on his blog, "The Landslide Blog."
Petley,whose research at the University of Sheffield in the United Kingdomfocuses on landslides , said no previous volcanic flank collapse in the world has led to a tsunami of the magnitude Dayand Ward describe. Additionally, he wrote, submarinedeposits from volcanic flank collapses suggest they don't happen as one big collapse, like Day and Ward hypothesize.
Rather, they happen in a series of slides, which would make the resulting tsunami "much less significant."
"It really is time that this eventwas presented for what it is, which is an absolutely extreme scenario based on a very highly unlikely combination of events that is without precedent," Petley wrote.
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While the last volcanic eruption in La Palma happened 30 yearsbefore Ward and Day's study was published in 2001, the island is of volcanic nature, and seismic activity is often considered normal.
In the last two decades, there has been extensive seismic activity similar to the smallearthquakes seen prior to the eruption, according to Spain's National Geographic Institute. This activity waswithin normal parameters for the area and didn't"present any risks to the residents." Many of the earthquakes registered aren't even felt by residents, as they happen kilometers under the surface.
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In October 2017, aftermore than 100 seismic events were registeredwithin one weekin La Palma, the islands' volcanology institute debunked the theory– again.
"Although it's been more than 10 years since this theory,the hypothesis that gaveway (to the idea)ofa collapse of the Cumbre Viejais still being considered," the institute said,according to the Spanish online newspaper El Diario.
The institute saidthe probability of a highly explosiveeruption happening at the same time asa largeearthquake– which isrequired for the theory to be true–is "extremely remote, according togeological records of this type of event on the island."
"The Cumbre Vieja is stable even under the effects of eruptions similar to those that have occurred in the last tens of thousands of years," it said.
Our rating: False
Based on our research, we rate FALSE the claim that experts have predicted the eruption in La Palma will cause a tsunami that would reachthe U.S. Spanish and American officials have said the volcanic eruption doesn't present any risks to the United States.Experts have thoroughly debunked it, saying thehypothesis is based on unprecedented events and assumptions of a massive landslide. Experts said such a landslide is extremely unlikely.
Our fact-check sources:
- USA TODAY, Sept. 19, Volcano on Spanish island erupts for first time in 30 years; lava destroys homes and forces evacuations
- The Guardian, Sept. 20, Canary Islands: 5,000 evacuated as La Palma volcano eruptions continue
- Nick Knowles, Sept. 21, Tweet(archived)
- Involcan, Sept. 21, Tweet
- Antena 3, Sept. 21, Is there a risk of acid rain and toxic clouds when the lava from La Palma's volcano reaches the sea?
- University of California, June 27, 2001, Cumbre Vieja Volcano -- Potential collapse and tsunami at La Palma, Canary Islands
- Spain National Geographic Institute, accessed Sept. 22, "New seismic activity localized in the south of the island of La Palma"
- USGS, Sept. 19, Tweet
- National Tsunami Warning Center, Sept. 19, Facebook post
- Antena 3, Sept. 20, Is there a risk of a tsunami after the volcanic eruption in La Palma?
- Media Bias Fact Check, Feb. 7, 2020, Daily Star UK
- Daily Star, July 20, 2019, MEGA-TSUNAMI hell feared as killer wave could 'hit UK at ANYTIME'
- University of Sheffield, accessed Sept. 22, Professor Dave Petley
- The Landslide Blog, Sept. 20, 2016, A science story that just won't die: the Canary Island Megatsunami scare rears its head once more
- El País, Sept. 19, Teneguía, 1971: This was the last terrestrial volcanic eruption in Spain
- Spain National Geographic Institute, accessed Sept. 22, "Earthquake Swarm in the island of La Palma (09-10-2017 and 14-10-2017)"
- El Diario, Oct. 19, 2017, The Involcan assures the volcanic building of Cumbre Vieja is 'stable' and it's landslide is very remote
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