1994 Volume 47 Issue 2 Pages 52-60_2
The June 15, 1991 eruption of Mount Pinatubo, one of the largest eruption of this centry in the world, produced remarkable volumes of pyroclastic flow and fall deposits. The volumes of pyroclastic flow deposits on the mountain slope was estimated at 5 to 7 km3. The major piracies of river basins occurred a few times in the eastern slope of Mount Pinatubo, and new drainage systems were rapidly re-established within the pyroclastic flow deposits-filled river valleys. While, Lahars which are generated by rain falling on erodible pyroclastic flow deposits pose continuing and grave danger to human lives and property in low-lying area. Among the river basins surrounding Mount Pinatubo, Sacobia/Bamban and Abacan rivers possess a great danger to the outlying areas currently used for residential, commercial and industrial areas. The area of lahar deposition in Sacobia/Bamban and Abacan rivers was estimated at about 15, 000 ha with an average thickness of 2 to 3 m as of the year of 1993.
Upon the official request of the Government of the Philippines, the Japan International Cooperation Agency (JICA) organized a study team in November, 1993 to conduct a study for flood and lahar control works in the rivers. The Study Team proposed urgent rehabilitation works which should be undertaken before the onset of the rainy season in June, 1994.
