Mount Pinatubo

Pampanga, Luzon


Mount Pinatubo is an active stratovolcano located on the island of Luzon, near the tripoint of the Philippine provinces of Zambales, Tarlac, and Pampanga. It is located in the Tri-Cabusilan Mountain range separating the west coast of Luzon from the central plains, and is 42 km (26 mi) west of the dormant and solitary Mount Arayat. Before 1991, the mountain has no recorded historical eruptions. 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 Aeta, who had fled to the mountains from the lowlands during the Spanish conquest of the Philippines.

The volcano's Plinian / Ultra-Plinian eruption on June 15, 1991 produced the second largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in the Alaska Peninsula. The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tonnes (10 cubic kilometres) of magma, and 20 million tons of SO2, bringing vast quantities of minerals and metals to the surface environment. It injected large amounts of aerosol into the stratosphere – more than any eruption since that of Krakatoa in 1883.

Mount Pinatubo's summit was 1,745 m (5,725 ft) above sea level, but only about 600 m (2,000 ft) above nearby plains, and about 200 m (660 ft) higher than surrounding peaks, which largely obscured it from view. It is a part of a chain of volcanoes which lie along the western side of the edge of the island of Luzon (West Luzon volcanic arc) specifically referred to as the Tri-Cabusilan Mountain Range which consists of Mt. Cuadrado, Mt. Negron, Mt. Tayawan and Mt. Pinatubo.

Several mountains near modern Pinatubo are old satellite vents of ancestral Pinatubo, formed from volcanic plugs and lava domes. Some nearby peaks are also remnants of ancestral Pinatubo, formed from erosion-resistant parts of the old mountain slopes left behind when the less resistant parts were eroded by weathering.
The eruptive activity of ancestral Pinatubo was much less explosive than modern Pinatubo, and probably ended about 45,000 years ago. After a long period of dormancy, modern Pinatubo was born in eruptions beginning about 35,000 years ago.

Peaks like Mt. Negron, Mt. Cuadrado, Mt. Dorst, Mt. Tayawan and Mt Donald are believed to have been part of the volcano's original peak. Despite becoming heavily silted with mud deposits, rivers like Tarlac River and Abacan River still flow through the mountain's summit area.  Scientists estimate that the most recent eruption before 1991 happened about 450 years ago, and after that, the volcano lay dormant. Its slopes became completely covered in dense rain-forest and eroded into gullies and ravines.