Mount Pinatubo erupted on June 15, 1991, after 600 years of dormancy, lasting for 9 hours and claiming 800 lives. Locals were unaware it was a volcano, as it was shrouded in dense forest. Thousands of indigenous people, known as the "Aeta," evacuated ahead of the eruption, saving many lives. It was the second-largest eruption of the last century, causing widespread devastation exacerbated by Typhoon Yunya. The eruption, combined with rain, led to extensive destruction of nearby villages and altered river systems. The Lahar field it created is the world's largest. Its impact was global, with the resulting ash reducing global temperatures by 0.5 degrees. The formation of a hot, highly acidic crater lake followed the eruption. In 2001, concerns about crater stability led to a 25 percent drainage of the lake.