Geology Makes the Mayon Volcano Visually Spectacular—And Dangerously Explosive

Update January 22, 2018: The Philippine Institute of Volcanology and Seismology raised the alert status for Mount Mayon to a 4 on a scale of 5, which means "hazardous eruption is imminent." Officials strongly discourage civilians from going within 5 miles of Mayon's summit.

Last weekend, the Philippines' most active—and attractive—volcano, Mount Mayon, roared back to life. The 8,070-foot volcano began releasing spurts of incandescent molten rock and spewing clouds of smoke and ash into the sky, causing over 30,000 local residents to evacuate the region. By the morning of January 18, the gooey streams of lava had traveled almost two miles from the summit.

Though the images of Mount Mayon are startling, the volcano isn’t truly explosive—yet. The Philippine Institute of Volcanology and Seismology (PHIVolcs), which monitors the numerous volcanoes of the island chain, has set the current warning level at a 3 out of 5, which means that there is "relatively high unrest." At this point, explosive eruption is not imminent, says Janine Krippner, a volcanologist and postdoctoral researcher researcher at Concord University. If the trend continues, however, an eruption is possible in the next few weeks.

Located on the large island of Luzon, Mount Mayon is known for its dramatically sloped edges and picturesque symmetry, which makes it a popular tourist attraction; some climbers even  attempt to the venture to its smouldering rim. "It's gorgeous, isn't it?" marvels Krippner. But that beauty isn’t entirely innocuous. In fact, Krippner explains, the structure’s symmetrical form is partly due to the frequency of the volcano's eruptions.

"Mayon is one of the most active volcanoes—if not the most active volcano—in the Philippines, so it has the chance to keep building its profile up without eroding away," she says. Since its first recorded eruption in 1616, there have been roughly 58 known events—four in just the last decade—which have ranged from small sputters to full-on disasters. Its most explosive eruption took place in 1814, when columns of ash rose miles high, devastated nearby towns and killed 1200 people.  

Many of these eruptions are strombolian, which means the cone emits a stuttering spray of molten rock that collects around its upper rim. (Strombolian eruptions are among the less-explosive types of blasts, but Mayon is capable of much more violent eruptions as well.) Over time, these volcanic rocks "stack up, and up, and up," says Krippner, creating extremely steep slope. That’s why, near the top of the volcano, its sides veer at angles up to 40 degrees—roughly twice the angle of the famous Baldwin street in New Zealand, one of the steepest roads in the world.

17 January 2018 Mayon Volcano aerial photos pic.twitter.com/0bUUEzgbGL

— PHIVOLCS-DOST (@phivolcs_dost) January 18, 2018

So why, exactly, does Mayon have so many fiery fits? It’s all about location.

The islands of the Philippines are situated along the Ring of Fire, a curving chain of volcanism that hugs the boundary of the Pacific Ocean and contains three-fourths of all the world's volcanoes. What drives this region of fiery activity are slow-motion collisions between the shifting blocks of Earth's crust, or tectonic plates, which have been taking place over millions of years. The situation in the Philippines is in particularly complex, explains Ben Andrews, director of Smithsonian's Global Volcanism Program. "It's a place where we have a whole bunch of different subduction zones of different ages that are sort of piling together and crashing together," he says. "It gets pretty hairy."

As one plate thrusts beneath another, the rocks begin to melt, fueling the volcanic eruption above. Depending on the composition of the melting rock, the lava can be thin and runny, or thick and viscous. This viscosity paired with the speed at which the magma rises determines the volcano's explosivity, says Andrews: The thicker and quicker the lava, the more explosive the blast. Mayon produces magma of intermediate composition and viscosity, but it differs from eruption to eruption.

Think of a volcanic eruption like opening a shaken bottle of soda, says Andrews. If you pop off the cap immediately, you're in for a spray of sugary carbonated liquid to the face, just like the sudden release of gas and molten rock that builds under a plug of viscous magma. But if you slow down and let a little air out first—like the gases that can escape from liquid-y magma—a violent explosion is less likely.

News outlets have been reporting on an “imminent explosion,” warning that Mayon will erupt within days. But given its activity so far, it’s not yet clear if, or when, Mayon will erupt. Volcanoes are extremely hard to predict as the magma is constantly changing, says Krippner.

Since the volcano began belching, small pyroclastic flows—avalanches of hot rocks, ash and gas—have also tumbled down its flanks. Though dangerous, these pyroclastic flows have the potential to be much more devastating. Previously at Mayon, says Krippner, these flows have been clocked in at over 60 meters per second. "They're extremely fast and they're extremely hot," she says. "They destroy pretty much everything in their path."

If the eruption continues, one of the biggest dangers is an explosive blast, which could produce a column of volcanic ash miles high. The collapse of this column can send massive, deadly pyroclastic flows racing down the volcano's flanks. The last time Mayon burst in an explosive eruption was in 2001. With a roar like a jet plane, the volcano shot clouds of ash and molten rock just over six miles into the sky.

Also of concern is the potential for what are known as lahars, or flows of debris. The volcanic rumblings have been actively producing volcanic ash, a material that’s more like sand than the kind of ash you see when you burn wood or paper, notes Krippner.  A strong rain—as is frequent on these tropical islands—is all that’s needed to turn these layers of debris into a slurry and send it careening down the volcano's slopes, sweeping with it anything that gets in its way. Mayon's steep sides make it particularly susceptible to these mudflows.

Residents suffered the full potential for destruction of Mayon's lahars in November of 2006 when a typhoon swept the region, bringing with it heavy rain that saturated built up material. A massive lahar formed, destroying nearby towns and killing 1,266 people.

Both Krippner and Andrews stress that local residents are in good hands under PHIVolcs' careful watch. The researchers have installed a complex network of sensors that monitor Mayon's every tremble and burp and are using their vast amounts of knowledge garnered from past events to interpret the volcano’s every shiver.

And as Krippner notes, "it's still got two more levels to go." If PHIVoics raises the alert level to a 4 or 5, she says, "that could mean something bigger is coming."

Maya Wei-Haas | | READ MORE

Maya Wei-Haas is a freelance science writer who specializes in geology of Earth and beyond. Her work has been featured in National Geographic, News from Science, and AGU’s EOS.