Normally the tell-tale sign of a volcano that is preparing to erupt, and which volcanologists are interested about, is what they call the seismic signature. As molten magma moves through rocks, making its way to the surface, it causes small earthquakes. These are called harmonic tremors and are different from earthquakes created along fault lines. Also, there could be a continuous plume of ash and/or steam being blown up in the air.
The fact that Mayon volcano did not show any signs of seismic activity, which means that its pattern of behavior as an inactive volcano has remained the same all these times, the place continued to be open to tourists for viewing.
Supposedly a six-kilometer (3.75 mile) radius “permanent danger zone” has been enforced around the volcano. But, it looks like this instruction has been waived, as it is normally done by authorities, when Mayon is calm and no abnormalities are observed, thus, allowing people to climb up nearer to the crater.
What happened a few days ago could only be described as a freak accident when Mayon made a deadly eruption in what volcanologists described as a 73-second “steam-driven minor explosion” that was not expected to be repeated anytime soon.
Chief state seismologist Renato Solidum said the explosion was triggered when rainwater made contact with hot ash deposits on the crater mouth.
But what a lethal reaction it made, when Mayon, unexpectedly, spewed a giant ash cloud and a hail of rocks that eventually cascaded down where a number of foreign tourists were stationed, crushing some to death.
An Austrian survivor was quoted, saying, “It rained like hell with stones!”
“The rocks that came crashing down on them were as big as dining (table) sets,” a local tour operator said.
The reality about active volcanoes, like Mayon, is that, while predicting its eruption remains an important goal by any volcanologist, the fact remains that it is not an easy task to achieve.
But, barring unforeseen events that trigger its sudden eruption, like what happened to Mayon, the practice of monitoring active volcanoes can always help minimize death tolls, property losses and other economic upheavals.