Can the October 8 full moon trigger Mayon’s eruption?

Pia Ranada

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Can the October 8 full moon trigger Mayon’s eruption?
At least 3 Mayon eruptions happened during a full moon. The October 8 full moon will be accompanied by a 'blood red' total lunar eclipse. Should we worry?

ALBAY, Philippines – Some of Mayon’s past eruptions happened when a full moon lit the sky. With Mayon within weeks of eruption, can the full moon on Wednesday, October 8, be a sign that a hazardous eruption will happen at last?

It’s possible, but only under certain conditions, said a Philippine Institute of Volcanology and Seismology (Phivolcs) geodetic expert. (READ: Mayon ‘relaxing before full-blown explosion’)

“It has a very small effect on a volcanic eruption. But if the volcano is on the verge of an eruption, it could be a trigger. It’s like the straw that breaks the camel’s back,” Phivolcs science research specialist Edgardo Villacorte told Rappler on Saturday, October 4.

He explained that during a full moon, the moon’s gravitational pull on the Earth is at its strongest.

The pull causes small undulations in the Earth’s crust, a phenomenon called “earth tide.” It is similar to how the moon’s gravitation pull causes ocean tides, but instead of causing ocean waters to rise or fall by meters, the change in the earth’s crust is only in millimeters or centimeters. 

The undulations may lessen the confining pressure currently keeping the volcano from explosively erupting. This confining pressure may be coming from older magma that has hardened, from the earth’s crust, or from the lava dome and magma clogging  the conduit leading to the crater.

Meanwhile, gas pressure inside the volcano, increasing with every new magma rising to the higher chambers, is pushing against the confining pressure.

“Those undulations might lessen the confining pressure by a small degree. When the gas pressure exceeds the confining pressure, that’s when an explosive eruption may happen,” said Villacorte. 

Only significant at alert level 4

But the effect of the undulations will only be significant if the volcano is already on the verge of an eruption.

At the time of the interview, Mayon was under alert level 3, meaning a hazardous eruption could happen in weeks or months.

It would take an elevation to alert level 4, which means “imminent hazardous eruption,” for the full moon or earth tide effect to be of any significance. 

So if Mayon does not reach alert level 4 by October 8, it won’t make a big difference on whether or not the volcano erupts. 

While there is no sure way of predicting when Mayon will reach alert level 4, based on most recent data on its behavior, it looks like it may be weeks to months before it will happen. 

Villacorte, who is in Albay to help the local Phivolcs experts gather data, said the magma is still around 5 kilometers from the crater and is rising at a speed of one meter per hour. But even this speed could change depending on gas build up or flow of new magma from the volcano’s lowest chambers. 

They estimate that around 70 million cubic meters of magma is inside the volcano. Of this, 2 million cubic meters – equivalent to 80,000 10-wheeler trucks – continue to rise to higher chambers.

But technically, Mayon already erupted on August 15, when Phivolcs hoisted alert level 2 on the volcano, said resident Mayon volcanologist Ed Laguerta.

The lava dome spotted that day means that magma was expelled from the crater (“lava” refers to magma outside the crater) in what may be called a “silent eruption.” 

What everyone is waiting for now is a hazardous eruption, an explosive eruption that could expel ash, lava bombs, volcanic rock, and lahar from the crater.

Mayon and the full moon 

Laguerta, who has been watching over Mayon since 1993, confirmed that the full moon has become closely associated with Mayon eruptions because many of its past eruptions happened during the phenomenon.

Based on records, at least 3 of its 49 eruptions, including those in 2000 and 2001, occurred during a full moon. 

But the full moon on October 8 is special. It will be accompanied by a “blood red” total lunar eclipse. The phenomenon is predicted to happen from around 6:30 pm (Philippine time) to 7:30 pm. 

But according to scientists, the occurrence of a lunar eclipse has no measurable significant effect on the gravitational pull of the moon on the earth. –

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Pia Ranada

Pia Ranada is Rappler’s Community Lead, in charge of linking our journalism with communities for impact.