IT'S only a five minute descent to the bottom of the Sacobia River Canyon, but it seems like a journey to the beginning of time.Not a breeze stirs in the silent canyon. The pungent scent of sulfur hangs in the air. Plump clouds of steam and ash, rolling soundlessly heavenward as if in a time-lapse film, are just visible over the steep canyon walls, indicating that Mt. Pinatubo is still erupting 10 miles to the west. A steamy, gray tongue of ash and volcanic debris, yards thick, a third of a mile wide, and as long as a river lies on the floor of the gorge like a giant loaf of newly baked bread cooling on a rack. This is the new river bottom, only days old. Already, tender green shoots of grass defy the thick sludge blanketing the old river bank. A mysterious fluorescent orange powder coats logs left by the flood of sand, pumice, and gas which roared down the mountain's slope at 125 miles an hour, changing the course of rivers and reshaping the foothills in its path. "Stick your arm in there - it's like an oven," says Lt. Col. Ron Rand, spokesman for Clark Air Base as he pulls a couple of light-weight pumice stones about the size and temperature of baked potatoes from a hole along the bank Meanwhile, the 20th century is only a few miles away. At the top of the canyon are the walls and sentry post of Clark Air Base, one of the largest United States military installations in Asia. Inside a sturdy air-conditioned building, US and Filipino scientists huddle over computers and watch the flimsy wands of seismographs dancing nervously over rolling cylinders, recording every quiver. In another room, a US military weather forecaster sits in front of a green radar screen behind a blue curtain recording the height of the volcano's plumes. A half dozen soldiers next door crowd around a portable television to watch a replay of the Mike Tyson-Razor Ruddock fight. While the computer room looks impressive, the simmering mountain, dormant for 600 years, is in command. On July 7, Mt. Pinatubo shot ash nine miles into the air. Vulcanologists predict that eruptions could continue for months or even years. No one can say with certainty whether the mountain will erupt again. All the scientists can do - as they did three weeks ago - is tell people when to run.
Ash circles the world In recent eruptions, bridges splintered like toothpicks as mudflows called lahars passed by. Volcanic ash created a thick blanket near the mile-wide gash ripped in the summit of the mountain by the explosion. The ash, which is now circling the globe, fell like snow across much of the Philippines, and lightly dusted locations as far away as Cambodia. "This is one of the largest eruptions of the century," says Jim Mori, a US Geological Survey seismologist. Mr. Mori says the readouts from the four seismometers located near the volcano were furious scribbles before becoming straight lines June 15, the day of the most powerful eruption, indicating the instruments had been buried. That is when the scientists made a break for it. They were among the last to leave Clark, which had been evacuated a week earlier. When they returned half a day later the printout of the one instrument that survived was solid black. Volcanic eruptions are accompanied by pyroclastic flows and lahars. A pyroclastic flow is dry, and hot - up to 476 degrees F.; it is accompanied by suffocating gas and moves at up to 435 miles an hour. A lahar is wet and not necessarily hot. It flows at up to 90 miles an hour, and can occur even after an eruption, and is often triggered by rain or smaller volcanic quakes. Before Mt. Pinatubo erupted, Philippine and US scientists undertook the risky job of flying over the slopes of the quivering, 4,592-foot volcano and bumping along hundreds of miles of roads criss-crossing foothills in order to plot previous pyroclastic flows and lahars on a "hazard" map. Because the volcano was "well behaved" and obeyed old flow patterns, Mori says, the scientists were able to make accurate predictions, and the government was able to evacuate villagers in the path of debris flows.
High-explosive volcano Mt. Pinatubo's eruption was termed a Plinian eruption - characterized by very high, vertical eruptive columns. Plinian eruptions were named after the Roman scientist and historian Pliny the Elder. He died during the eruption of Mt. Vesuvius in 79 A.D., but his written account of the eruption survived. The more common image of a peaked mountain propelling steam and stones into the air, while red hot lava flows down the side is just one type of eruption called a Hawaiian eruption. The magma of Mt. Pinatubo had a different chemistry and was more explosive because it had more gas than the "liquid" volcanos of Hawaii. Little lava flowed from Mt. Pinatubo, but pyroclastic flows have filled an entire valley with steamy material. From a few miles away, the debris looks like a mystical, white glacier. Despite its beauty, scientists say the debris from pyroclastic flows and lahars now poses the greatest danger. Rains will trigger further lahars. The Philippine typhoon season is just beginning, which means more villages and roads could be destroyed. Already, a quarter of a million villagers have fled their homes - the biggest evacuation from a volcano in history. About 350 persons have died. Damage to bridges, roads, schools, crop lands, and other assets is estimated at $US180 million, according to Finance Secretary Jesus Estanislao. He cautions that the assessment may exceed the US$5 to US$6 billion estimated damage caused by last year's earthquake. It will be several more weeks before an official estimate is made, but the preliminary estimate of damage to Clark Air Base and Subic Naval Station, both US military installations, is US$300 million according to Foreign Affairs Secretary Raul Manglapus. The Philippine government called a donors' meeting last week, attended by representatives of 50 countries. Among the priority requests from Filipino officials were two-way radios to be used for lahar warning systems and heavy equipment to dredge water ways, clear roads, and deep-till ash into the soil of crop lands.