Mount Natib is a stratovolcano type of volcano topped by a 6-by-7-kilometre (3.7 by 4.3 mi) acorn-shaped Natib Caldera that is open to the northwest. East of its caldera is the smaller 2-kilometre (1.2 mi) wide Pasukulan Caldera.[4] The highest peak of Mount Natib has an elevation of 1,253 metres (4,111 ft) asl and is at the point of convergence of the two calderas. The caldera complex has an overall base diameter of 26 kilometres (16 mi).[5]
Volcanic activity
There are no historical eruptions within the Natib caldera complex. Studies in 1991 (Panum and Rayem) indicate that the last eruptive activity was probably Holocene to upper Pleistocene.[1] An earlier study in 1971 (Ebasco Services) dated the eruptive products between 69,000 +/- 27,000 years old.[1] A recent study by Dr. Kevin Rodolfo of the Department of Earth and Environmental Sciences at the University of Illinois at Chicago, had Mount Natib's latest eruption between 11,000 and 18,000 years ago after studying a prehistoric pyroclastic flow from the volcano that entered Subic Bay in Zambales province.[6]
Current activity on Natib is through five thermal areas. The hot springs in the Natib caldera are Asin,[1] Mamot, Tigulangin, Uyong, and Paipit springs. The hot springs have temperatures ranging from 30-56 °C, with low flows, and a neutral to slightly alkaline water discharge.[5]