According to a news article, on 22 January tourists noticed that the usually blue-to-green water in Pinatubo's crater lake was very dark brown. Scientists from the Pinatubo Volcano Observatory excluded renewed volcanism as the source of the discoloration due to the lack of increased seismicity, and an absence of new emissions in the crater or any increase in the water's temperature. They believed the change in water color was due to near-surface processes, such as biogenic activity or a steady supply of nutrient rich soil from landslides that have entered the crater since its formation after the June 1991 eruption. Visitors were warned against swimming in or consuming the water in the lake.

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.

Source: ABS-CBN News