Volcanic ash and pumice blanketed the countryside. Huge avalanches of searing hot ash, gas and pumice fragments, called pyroclastic flows, roared down the flanks of Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as feet meters thick.
The eruption removed so much magma and rock from beneath the volcano that the summit collapsed to form a small caldera 1. If the huge volcanic eruption were not enough, Typhoon Yunya moved ashore at the same time with rain and high winds. The effect was to bring ashfall to not only those areas that expected it, but also many areas including Manila and Subic Bay that did not.
Fine ash fell as far away as the Indian Ocean, and satellites tracked the ash cloud as it traveled several times around the globe. With the ashfall came darkness and the sounds of lahars rumbling down the rivers. Several smaller lahars washed through Clark, flowing across the base in enormously powerful sheets, slamming into buildings and scattering cars as if they were toys.
Nearly every bridge within 18 miles 30 km of Mount Pinatubo was destroyed. Several lowland towns were flooded or partially buried in mud. The volcanologists at the Dau command post watched monitoring stations on Pinatubo fail, destroyed by the eruption. They watched telemetry go down but then come back up — a sign that a pyroclastic flow was headed down valley and temporarily interfering with the radio links.
They moved to the back of a cinderblock structure to maybe provide a little more protection from hot gas and ash; there was nowhere else for them to go. Fortunately, the flow stopped before it reached the building. The post-eruption landscape at Pinatubo was disorienting; familiar but at the same time, totally different. Acacia trees lay in gray heaps, trees and shrubs were covered in ash.
Roofs collapsed from the tremendous stresses of wet ash and continuing earthquakes. No matter which way one turned, everything looked the same shade of gray. Most of the deaths more than people and injuries from the eruption were from the collapse of roofs under wet heavy ash. Many of these roof failures would not have occurred if there had been no typhoon. Rain continued to create hazards over the next several years, as the volcanic deposits were remobilized into secondary mudflows.
Tiny aerosol droplets reflected sunlight away from Earth causing cooling at the surface. Scientists observed a maximum global cooling of about 1. Sunsets and sunrises were more brilliant because of the fine ash and gases high in the air. In addition, the aerosols from the eruption had a chemical effect that reduced the density of the ozone layer in the stratosphere.
Until the ozone reforms, it cannot shield that portion of Earth as effectivelyfrom the sun. By June 9, officials had ordered 25, people out of the area.
On June 10, American officials made the call to evacuate more than 14, service members and their families from Clark Airbase. The suddenly empty airbase was just one more source of pressure for the scientists, who took the opportunity to move their base of operations to the side of the base farthest from the steaming volcano.
They wouldn't have to wait long. At a. As Hoblitt and Ewert watched the volcano blow, they felt relief. Their admonitions — and the evacuation of more than 60, people — had not been in vain. But the relief was followed by concern, as after the initial minute eruption, Pinatubo started rumbling again.
The volcano was just getting warmed up. Over the next three days, the volcano spit out three more vertical eruptions and 13 smaller eruptions that produced pyroclastic flows molten mixtures of ash, gas and rock that can sweep over the landscape at more than 60 miles km per hour.
And then, on June 15, Pinatubo really let loose. Sometime around p. Chunks of pumice the size of golf balls fell at Clark Airbase. Ash spewed higher than it ever had before, and lahars, or mudflows, rushed down the slopes in a clatter of banging boulders. Maximum temperatures of the fumarole were close to boiling, It looked like some recent pyroclastic-flow deposits observed on Augustine, with rounded pumice clasts maximum size.
These cones resulted from the activity of large steam fumaroles. A water sample filtered from this stream showed a high chloride content compared to other streams and rivers travelling down the volcano table 3. Many old tracks of other mudflows were observed on the surface of the pyroclastic flow deposit. Bernard, A. Geological Summary. Prior to Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located km NW of Manila with no records of historical eruptions.
The eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2. Caldera formation lowered the height of the summit by more than m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities.
Widespread lahars that redistributed products of the eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in Information Contacts: R. Report on Pinatubo Philippines — July
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