Mount Pinatubo is an active stratovolcano in the Cabusilan Mountains on the island of Luzon, near the tri-point of the Philippine provinces of Zambales, Tarlac, and Pampanga. Before the volcanic activities of 1991, its eruptive history was unknown to most people. It was heavily eroded, inconspicuous and obscured from view. It was covered with dense forest which supported a population of several thousand indigenous people, the Aetas, who fled to the mountains during the Spanish conquest of the Philippines.