The Philippines make the world news regularly with reports of destructive storms. More frightening, due to being less predictable, are their local events related to plate tectonics. This means earthquakes and volcanic eruptions. Both occur suddenly and with little or no warning. A typhoon (hurricane) moves very slowly and there’s time to evacuate the most critical areas before disaster hits. But there are no warning signs of an earthquake until the moment the ground starts shaking violently.
Such was the case on January 21 when a quake occurred in the ocean halfway between the Philippines’ Mindanao Island and the Maluku Islands in Indonesia. The magnitude of the shake was a heart-stopping 7.0, enough to wreck a city and maybe produce a devastating tsunami. The hours that followed were particularly scary in Davao City, Philippines, a modern business hub with a population approaching 2 million. The town is located at the north end of Davao Gulf, which is 32 miles wide at its mouth. At the outskirts of Davao, it narrows to 10 miles. A tsunami, the set of waves produced by the shaking of the sea floor, could press into this gulf. Finding less and less space, the waves would pile up and finally break violently upon reaching the shoreline. It’s those breakers that cause the horrendous damage in tsunami events. A lucky break for the Philippines and Indonesia was that the January 21 quake was deep-seated and didn’t produce a tsunami or significant damage.
At the root of these troubles is the structure of the earth’s crust. The theory of Plate Tectonics, known since the 1960’s, explains how the globe resembles a raw egg with a highly cracked shell. The shell fragments are tectonic plates. Places in the center of such fragments tend to have no volcanoes and little or no earthquake activity. This is the case for Georgia, with no likelihood of Peachtree Center collapsing in a quake or Savannah getting washed away by a tsunami. It’s the borders of tectonic plates where trouble lies. The rubbing and grinding of the moving plates causes the vibration that we feel as earthquakes and the rips in the crust allowing lava to spew out in an eruption. A complicated network of “cracks in the eggshell”, or tectonic plate borders, near the Philippine islands ensures that more future activity is likely.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.