The Cumbre Vieja volcano on the Spanish island of La Palma has occasionally twitched, convulsed, and rumbled, but no lava has emerged since 1971. That changed this weekend. At 3:12 p.m. local time on September 19, rising magma tore open several fissures on its western flanks, and an extravagant eruption began.
From afar, it looked spectacular. Vertiginous fountains of lava almost 2,000 degrees Fahrenheit screamed skyward, reaching heights of up to 5,000 feet—nearly twice that of the Burj Khalifa, the world’s tallest skyscraper. Below, braided rivers of molten rock poured from the fissures like blood from open wounds.
Sitting 300 miles west of Morocco’s shores in the Atlantic Ocean, La Palma only exists because a volcanic hot spot built land above the waves long ago, forming the archipelago known as the Canary Islands. That long-lasting, superheated blowtorch within the underlying mantle created eight main islands that have delightfully varied ecosystems, from subtropical forests to deserts. On La Palma, high mountains provide ideal conditions for cloud-free star-gazing, which is why the island hosts a major European observatory.
But as this new eruption demonstrates, “the price and privilege of living on a beautiful little island is, in this case, its geological history,” says Helen Robinson, a geoscientist at the University of Glasgow who worked as part of the monitoring team for Cumbre Vieja in 2015.
Cumbre Vieja is a highly active volcanic edifice, and in the past 7,000 years, a plethora of eruptions have taken place on a north-south orientated ridge—a battle-scarred axis dotted by fissures, cones, craters, and vents. Since the 15th century, multiple lava flows have damaged buildings and crawled into the sea. They often erupt from fissures, a style common to many volcanoes around the world, from Hawai‘i’s Kīlauea to the ongoing eruption in Iceland’s Reykjanes peninsula.
As of the afternoon of September 20, the latest eruption shows no signs of slowing down. According to Pedro Hernández, a volcanologist at the Volcanological Institute of the Canary Islands (INVOLCAN), lava continues to cascade slowly downslope and venture westward toward the sea. Most of the island remains unaffected, but 5,000 people in the path of the fiery streams have been evacuated. “More than 20 houses have been destroyed,” says Hernández. Reuters reports that more than 500 tourists had to leave their hotels, and about 360 were evacuated from a local resort to the nearby island of Tenerife.
How long the lava will remain a threat is tricky to estimate. Eruptions on La Palma can last from a few weeks to several months. “The only way to know is to know the total volume of eruptible magma under Cumbre Vieja,” says Pablo J. González, a physical volcanologist at the Spanish National Research Council on Tenerife. “That piece of information is unknown.”
The changing shape of the volcano and the seismic soundtrack of its quakes may reveal an answer to this all-important query. But even under intense scientific interrogation, Cumbre Vieja is unlikely to give up its secrets easily.
The rising threat
La Palma, the most northwesterly of the Canary Islands, is a volcanic chimera: a mishmash of various volcanic edifices big and small. In the south you can find Cumbre Vieja, or “Old Summit,” and despite its name it’s one of the younger siblings, dating back a mere 125,000 years. The volcano’s last eruption was from a small cone called Teneguia back in 1971. But that doesn’t mean Cumbre Vieja has been quiet since.
According to Itahiza Domínguez Cerdeña, a seismologist at the National Geographic Institute, on Tenerife, nine earthquake swarms—hundreds of rumbles happening in the same area in close succession—have occurred some 18 miles below the volcano since October 2017.
Just a week ago, these earthquakes were happening only seven miles deep, and in the last few days, quakes were emanating from just below the surface. From September 10 to 19, a staggering 25,000 quakes, most of them imperceptible to people, had been recorded. This ascending cacophony was the sound of the crust being pushed aside and deformed. The cause? The “pressure of the magma intruding in the crust,” says Cerdeña.
By this past weekend, the ground there had inflated by six inches, suggesting a moderate volume of magma had recently infiltrated the shallow crust.
Most intrusions of magma don’t lead to eruptions; they cannot punch through the solid rock above, so they cool down and ultimately stop rising. But it’s always possible for a greater volume of molten rock to gather under an intrusion, and that can potentially fuel a prolific, prolonged eruption.
Volcanologists were alarmed by the mountain’s deformation and its seismic clangor, and on September 13, the authorities raised the alert level, warning the southern section of the island and its 35,000 residents that an eruption may follow.
On September 18 scientists began deploying additional seismometers in the region to better identify types of quakes and to track their migration with more precision, while others conducted flybys in helicopters to discern if the ground was heating up. Just before midday on September 19, a potent magnitude-4.2 quake shook the volcano.
Out of an abundance of caution, Spanish soldiers helped evacuate 40 people and their farm animals from several villages around the volcano.
Later that afternoon, lava exploded out of the forested hills on the volcano’s western flank. The lava set trees and farmland aflame, crossed a highway and destroyed eight isolated houses. That night, the government announced that 5,000 people potentially in harm’s way had been evacuated.
Although its lava has not yet punched through the more built-up parts of the nearby El Paso municipality, it “is sort of creeping toward quite a densely populated area,” says Robinson. The hope is that the flow will avoid that area on its journey to the sea, but even if it doesn’t, the area has been evacuated, significantly reducing the odds of fatalities.
Ash, astronomy, and tsunamis
Fortunately, no matter how long the eruption lasts, it shouldn’t damage the multitude of astronomical telescopes at the island’s Roque de los Muchachos Observatory. Juan Carlos Pérez Arencibia, the observatory’s administrator, says that the facilities are 11 miles north of the eruption site. Also, the observatory is located 7,900 feet above sea level, while the lava is emerging at 2,000 feet.
“The ash might mean that the telescopes remain closed for several days without observing, but the observatory itself should be unharmed,” says David Jones, an astronomer at the observatory.
And despite fears swirling on social media sparked by a highly speculative 2001 paper, there’s almost no chance that the Cumbre Vieja eruption could create a mega-tsunami that would slam into America’s eastern seaboard, says Dave Petley, a landslide expert at the University of Sheffield in England.
Flank collapses of volcanoes are a genuine concern, and it’s true that several flank collapses on La Palma’s shores took place many thousands of years ago. But a study from 2015 found that under realistic modeling conditions, the most severe collapse could cause no more than a six-foot tsunami along western Atlantic coastlines.
Although such an eventuality would still be decidedly unwelcome, INVOLCAN notes that it would take an incredibly powerful earthquake and an astoundingly explosive volcanic eruption happening simultaneously for any sort of flank collapse to transpire. Cumbre Vieja is structurally sound at present, and there is no indication that such a confluence is even remotely possible.
Make no mistake: the lava flows are the real hazard here. Fortunately, the residents of La Palma are being protected by a vanguard of volcanologists and a shield of seismologists. The long-term efforts by geoscientists on the island ensured that it was clear that something wicked was brewing long before serpentine lava flows crept out of Cumbre Vieja’s hillside.
“If they didn’t do such intense monitoring,” says Robinson, “they wouldn’t understand their volcanoes as well as they do.”