“[Mayon’s eruptions] will not be in the scale of Pinatubo’s,” Dr. Renato Solidum, director of the Philippine Institute of Seismology and Volcanology (Phivolcs), said in a phone interview when asked how Mayon would behave in an event it blows up.
The two volcanoes are different in several ways.
Mayon, as andecite volcano, is acidic and thus, contains white rocks, less thick magma and lower amount of gas. Pinatubo, on the other hand, is a dacite volcano, meaning it has grayish stones, thick magma and explosive gases like sulfur.
Pinatubo was more explosive. It spewed out seven billion cubic meters of pyroclastic debris or everything that rose up from the belly of the earth—gases, rocks, magma (molten rocks), ash and sand. Considered the second biggest eruption in the 20th century after Nuvarupta in Alaska, Pinatubo’s 1991 bang was still not the biggest compared to its ancient and modern eruptions.
In contrast, Mayon had released 20 to 150 cubic meters of pyroclastic materials since its 1844 eruption. Yet, it showed it was capable of violent explosions 1814 and 1897 when eruptions happened in a few days or weeks.
“This is quite different from the present activities where you have slow lava flows,” Solidum observed.
Mayon was first monitored to be acting up on July 10. Then it had ash explosion on Sept. 15, Oct. 28, Nov. 11, Dec. 11 and 14, Phivolcs data showed.
RISKS HIGH
But what makes Mayon potentially dangerous is that human settlements are very close to the crater.
“They’re within the six-km radius of the crater,” Solidum said, raising concern for the safety of some 10,000 people within that area. “The risks to people are high because they’re near [the crater] and the amount of deposits [there] are different.
The hazards are ash falls, lava flows, hot pyroclastic debris and secondary explosions. Lahar, which can bury entire communities or people alive, can be conveyed by rains to the lowlands because there are many rivers around Mayon, he said.
At the advice of Phivolcs, the local governments have evacuated around 70 percent of the residents in harm’s way.
In Pinatubo, which straddles the provinces of Pampanga, Tarlac and Zambales, over three million people were concentrated outside the 20-km radius. The Negrito tribe of Aeta, counting over 50,000 before the 1991 eruption, occupied the upper and middle flanks of the volcano.
Pinatubo did not create much lava domes because it took only nine weeks before it blew its top.
Magma rose so fast, releasing so much gasses and volcanic debris.
SHIFT TO EXPLOSION
Mayon has taken its sweet time to create two lava domes on the crater. Here’s the danger: Because these domes are plugging the vent on the crater, the pressure is building up from below. “It can be gathering more momentum,” Solidum noted.
According to him, Mayon’s magma is known to carry big boulders. The ash fall can reach as far as Camarines Norte.
“Our problem us when the scenario changes. It can shift to explosion. You can have a tall eruption column and pyroclastics. The current episode most likely would lead to an eruption. But the ascent of magma is slow,” he explained.
The best move, he said, is to evacuate to safety.
Simple folks can monitor eruptions to be underway by watching out for their signs: Heavy smell of sulfur, earthquakes, changes in the color, volume and height of ash, drying of river, wilting of vegetation, rumblings from the ground and unusual behavior of animals that escape the hot environs of the volcano.
WELL-WATCHED
Mayon is well-watched by the Phivolcs from its center in Quezon City and on the ground. It has six staff on Mayon including volcanologist July Sabit who has active in Pinatubo’s response.
The United States Geological Survey, which was involved in Pinatubo’s study, is not present yet in Mayon’s observation, Solidum said.
The agency has installed equipment on Mayon including seismographs that measure earthquakes, tilt meters that check ground deformation, a fly speck that rates the amount of gas in steam plumes.