Mount Pinatubo was dormant for 400 years before it erupted in 1991. Its eruption was the second largest in the 20th century, and it came as a complete surprise to both residents of the area and scientists. Before its eruption, Mount Pinatubo was a little known volcano that didn't pose a threat to the people of the Philippines. It stood about 5,725 feet tall, and scientists believed it began forming around 1 million years ago.
Stratovolcanoes are sometimes called composite cones, and there are several well-known stratovolcanoes all over the world. Besides Mount Pinatubo, Japan's Mount Fuji and Hawaii's Mount Saint Helens are also stratovolcanoes.Learn more about Volcanoes