Sulawesi’s complicated shape resembles the accented Spanish letter n, as in Niño. The result is a multitude of ocean bays.
The Sept. 28 quake hit northern Sulawesi with a massive 7.5 magnitude. In terms of its violence, that’s more powerful than the 1989 Loma Prieta quake in California, which made a freeway collapse in Oakland. It’s half a notch below the enormous 1985 Mexico City quake.
The tremor shook the ocean water of the Makassar Strait, and ripples, called a tsunami, spread rapidly. While on the open ocean, tsunamis aren’t dangerous. They resemble common wind-driven ocean waves. But when they enter a bay, water suddenly piles up as the space narrows. The wave topples over where the bay bottom rises beneath it. Finally, a devastating series of splashes, dozens of feet tall, sweeps away buildings, cars, people and everything else in its path. The main victim this time was Palu, a city of 335,000 at the southern end of the 20-mile long bay.
On the map, facing northwest into the Makassar Strait, the narrow stretch of water leading to Palu resembles an upside-down Chesapeake Bay. Where Chesapeake narrows near Annapolis, Maryland it’s 4 miles wide. But that’s the maximum width of the bay leading to Palu, diminishing to 3 miles before it ends at the city’s shore. The curved shoreline had plenty of buildings in harm’s way when the waves came.
Tsunamis are more vicious than even the devastating storm surges we’ve seen in hurricane Florence last month. Wind systems like hurricanes, typhoons or tropical storms are visible in satellite images and can be tracked before they hit land. This is impossible with earthquakes. In spite of expensive research spanning decades, earthquakes can’t be forecast.
Consequently, tsunami warnings become possible only when the waves are already on their way toward land, moving at the speed of an airplane. Due to the complicated make-up of the earth’s crust in the western Pacific, Indonesia’s islands are the most vulnerable area in the world.
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.