Due to the threat of Pinatubo's crater lake overflowing during draining procedures, Philippine officials plan to evacuate ~40,000 residents of the town of Botolan 40 km NW of Pinatubo's crater to higher ground on 5 September. The crater lake is ~2.5 km wide, and contains ~210 million cubic meters of water. According to a Guardian news article, water in the crater rose to ~80 cm below the lowest point of the crater rim on 3 September. In comparison, water was 1.5 m below the rim on 31 August, and 4.5 m below it 5 weeks earlier. On 6 September workers plan to remove a 5-m-large portion of the crater's wall that will cause the water to be released towards the N.

Geological Summary. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 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 1991 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 1991.

Sources: ABC News - Australian Broadcasting Corporation, The Guardian News, Agence France-Presse (AFP)