What will happen if there is an explosive eruption of Mount Mayon in the Philippines?

The Philippines’ most active volcano Mount Mayon, located on the large island of Luzon, continues to spew lava and ash from its summit after it began erupting at the weekend.

Tens of thousands of people have been evacuated from ashfall-hit villages in the Philippines, as a danger zone has been issued around the volcano. 

Volcanologists have warned a hazardous eruption could happen “within weeks or days” and said the volcano was in the grip of a non-explosive magmatic eruption. 

Red hot lava has been seen flowing down the sides of Mount Mayon and pictures show a red glow at the top of the 8,077 foot-tall volcano. 

Professor of Planetary Geosciences at the Open University David Rothery said a “lava dome is growing” at the top of summit and there are lava flows and pyroclastic flows (PDCs) travelling 3km from the summit.

Residents and tourists have been told to stay outside of a 6km Permanent Danger Zone (PDZ) and an extended 7km Extended Danger Zone (EDZ) around Mount Mayon. 

The extended danger zone has been put in place because of the “danger of rockfalls, landslides and sudden explosions or dome collapse” which could “generate hazardous volcanic flows.”

Phivolcs raised the alert level for Mount Mayon from level 2 to level 3 on Sunday which means a “hazardous eruption is possible within weeks or even days.”

The Phivolcs website stated: “Alert Level 3 remains in effect over Mayon Volcano, which means that it is currently in a relatively high level of unrest as magma is at the crater and hazardous eruption is possible within weeks or even days.”

Professor Rothery said: “Phivolcs is concerned about a lava dome that is growing inside the crater, which may become too steep so that it might collapse, sending pyroclastic flows mainly down the southern side of the volcano.

“If that happens, there will be an ash column too, which will rain ash downwards in the downwind direction – this is less hazardous to people on the ground than a pyroclastic flow.”

The over-steepened lava dome is formed by lava oozing out and piling up to form the dome.

Within the last 24 hours, volcanologists have recorded one volcanic earthquake, 48 rockfall events and two PDCs.

There have not been enough volcanic earthquakes to prompt scientists to raise the alert level to four, which would indicate an explosive eruption may be imminent. 

If the alert was upgraded to level four then a hazardous eruption would be possible “within days or even hours,” Phivolcs chief volcanologist Dr Renato Solidum said in an interview with Rappler Talk.

Professor Rothery explained it is hard to predict what would happen in the event of an explosive eruption.

He said: “Unlike earthquakes, which usually happen suddenly, at least a volcano usually builds up gradually towards a major eruption, so there is some warning. Sometimes, activity subsides again, sometimes it keeps getting stronger,” he said.

“It is all do to with movement of magma (molten rock) and the gas escaping from the magma, that is rising upwards beneath a volcano.

“We can monitor, but there are so many variable factors that it is rarely possible to predict with certainty what will happen.” 

However he added that Mount Mayon was not “due” for eruption.

He said: “It erupts quite often, and volcanoes that erupt frequently tend to have smaller eruptions than those that erupt less frequently.”

The largest and most destructive eruption of Mount Mayon was in 1814 and measured four on the Volcanic Explosivity Index (VEI), all other eruptions have measured 1-3 on the scale.

It caused an ash column to rise 10-25km above the summit of the crater and killed more than 1,200 people and devastated several towns.

The Philippines sits in the Ring of Fire – a line of seismic faults surrounding the Pacific Ocean – where a large number of earthquakes and volcanic eruptions occur. 

Phivolcs continues to closely monitor the activity of Mount Mayon.