Mount Pinatubo is a stratovolcano. Stratovolcanoes are the most deadly type of volcano, and they are recognizable by their sharp rise and steep slopes.
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.