The Pacific “Ring of Fire” is living up to its name again. After some rumblings in October, Mount Sinabung on the island of Sumatra (Indonesia) erupted with ash falls and lava flows last week. Five-thousand people were forced to flee the surrounding areas.

The volcano is only 230 miles west of Kuala Lumpur (Malaysia), illustrating the risk that modern megacities in Southeast Asia are facing. Just a few years ago, in 2010, the eruption of Mount Merapi erupted on the island of Java, which is part of Indonesia like Sumatra. Merapi is 265 miles from Jakarta, Indonesia’s capital and home to 10 million people.

The past decade has brought enormous growth to business centers like Jakarta, Kuala Lumpur and Singapore. But it also resulted in dozens of millions of people now living in the vicinity of dangerous volcanoes.

On the U.S. side of the Ring of Fire, things have been relatively quiet. No large volcanic eruption has occurred since Mount St. Helens blew its top in May 1980, killing campers and residents and covering towns like Yakima and Castle Rock, Wash. with ash.

Nearby, Mount Rainier is quiet, although it produces medium-strength earthquakes on a regular basis. Given the fact that Rainier is only 50 miles from Tacoma and 60 miles from Seattle, Wash., this puts roughly 3.5 million Americans at risk, should Rainier erupt again this decade. The same applies to Mount St. Helens, 100 miles south of Seattle.

The difficulty with volcanic eruptions of the explosive sort is that they occur on a geologic time scale, where 1,000 years are just a short tick on the clock. Cities operate on a human scale, though, and a 33-year period with no volcanic activity, as we’ve had with Mount St. Helens, lets people forget about the fragile nature of the earth’s crust.

Another well-known place, not part of the Ring of Fire but also in a geologically volatile part of the globe, is Naples, Italy. The 79 A.D. eruption of Vesuvius, obliterating the cities of Pompeii and Herculaneum, has long since acquired museum status. But in the same area, as little as 10 miles from the slopes of the active volcano, Naples (there called Napoli) and Ercolano have grown into large urban centers.

Attempts to forecast eruptions with more than a few hours’ notice have not been successful so far, and the geologic clock keeps on ticking.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.