Rim of Fire

Black molten ash covers the sky, searing rocks and hot winds devour homes like fire consuming paper. "I suddenly heard a loud bang," says 47-year-old Toshiaki Irie, describing the sound from a pyroclastic explosion shooting 1000 meters (3200 ft) into the sky from the mouth of the Unzen Volcano; "then a heat wave enclosed my home," says the displaced farmer.

Active volcanoes linked in a chain encircling the Pacific Ocean basin continue their natural geological course which began before the land was ever inhabited; volcanoes know no man.

Several months after the eruption of the Unzen the people of Shimabara were able to return to their homes. A wet breeze from the Pacific Ocean cools Irie's face as he tends to his vegetable garden. Standing amidst the tobacco leaves he can see the rest of Shimabara: a small farming town on a peninsula in the Kyushu prefecture in southeast Japan.

Hot springs allure tourists to this beautifully rich area. Perhaps the best sight of this peaceful town is atop Mount Unzen, if this symmetrical mass had eyes it could see this small town growing upon its flanks.

"The fields may look beautiful from a helicopter, says Irie, but "at ground level the devastation is beyond imagination."

In 1991, what was left of the town was covered with a blanket of volcanic ash that accumulated to a catastrophic degree. Irie and 10,000 people were forced to evacuate. The event became known as one of Japan's worst disasters.

That same year, south of Japan in the Philippines 56,000 people-including 14,500 U.S. servicemen-evacuated areas near Mount Pinatubo days before the volcano cataclysmically erupted on June 15.

September 1995, even farther south of Japan and east of the Philippines, Mount Ruapehu in New Zealand exploded glowing hot clouds of ash as far as 7.5 miles into the sky every 15 to 45 minutes. All roads and airfields are closed from the thicket of volcanic ash, according to the New Zealand Herald.

It is not coincidental that these active volcanoes are exactly like the stratovolcanoes lined up along the west coast of the United States like Mount Shasta, Oregon, and Mount St. Helens, Washington.

These patterns of volcanism share more than their destructive nature. They are linked to a chain of volcanoes encircling the Pacific ocean, called the Pacific "Ring of Fire."

This fiery ring functions as proof of plate tectonics. This geographical theory states that the earth's outer crust or lithosphere, consists of about twenty segments called plates. The Pacific plate, the crust of land under the Pacific Ocean, is the largest.

These plates are always in motion, driven by an internal thermal engine a result of the unequal distribution of heat within the earth.

However, all twenty plates usually move in different directions at different times. This can create convergent plate boundaries: subduction zones, causing the oceanic sea floor to be pushed underneath continental plate boundaries. This process creates the most violent, and picturesque, of volcanoes: stratovolcanoes, also called composite volcanoes.

Stratovolcanoes are violent because of explosively ejected pyroclastic materials like hot ash, chunks of lava and microscopic bits of glass from deep within the earth's mantle. Another destructive quality is an avalanche moving down the slopes of a volcano at approximately 100 miles per hour in the form of a glowing cloud of ash and mud called nuee ardente, destroying all objects in its path. Nothing is left but a bed of volcanic ash settled upon the town.

Dr. Robert Dundas, Geology professor at San Francisco State University says the effects of pyroclastic eruptions are devastating. However, the effects of ash can be good or bad for the environment.

"In areas with minor traces of ash, it can release nutrients for plants, like fertilizer," Dundas says, "However, too much volcanic ash can destroy crops and other organic and inorganic structures by burying and crushing them with the weight of the fallen ash."

Meanwhile, Irie tries to clear the rocks and ash from his garden of tobacco and vegetables and wonders if they will ever flourish the way they once did.

Dundas says that it takes at least a decade to recover from the type of recurring destruction upon these farmlands. "Will the government ever rebuild my homeland?" Irie asks.

It does not seem prospects are positive for restoring the chief farming town of Kyushu. This ideology is dominant because of possible eruptions of volcanoes in the future, as well as the damage from the past volcanic activity.

In the past several months seismic activity has been increasing underneath the Unzen. Also increasing is the tiltmeter of the volcano-when the flanks of the volcano lift due to the uprising of magma, according to Volcanologist Setsuya Nakada, Kyushu University's Seismological Observatory.

Hideaki Nishikawa of the city's Disaster Restoration Department sympathizes with the evacuees. But he said the city, still lives under the constant threat of floods and volcanic avalanches.

"In most cases, they (evacuees) have refused to move into the places we have prepared because they say they are inconvenient or expensive. It's not that they don't have any place they could go," Nishikawa says.

Despite the uncertainty, most farmers are reluctant to abandon the ravaged farmland they inherited from their fathers.

Irie sighs, "Fortunately, our lives were somehow saved, but the farmland which is our life-blood was destroyed."

Dr. Dundas says there is a good indication an erruption could occur when steam vents from the volcano, and there is increased seismic activity. "But there is no way to predict the exact time when a volcano can erupt," Dundas says. Unfortunately, there is not much farmers or businesses can do to prevent the damage of property.

[ Prism Online November 1995 Homepage ]

[ Top of document ]