| Abstract |
The breaching of natural dams consequent to the breakout of large reservoirs generates some of the world's largest floods and lahars (Schuster and Costa, 1986; Costa and Schuster, 1988; Costa, 1988; Catane and Gabinete, 1995; King and others, 1989; Walder and O'Connor, 1997; Waythomas, 1996; 2000; Plaza-Nieto and Zeballos, 1999). A similar and lingering threat to Botolan, Zambales (pop. ca. 40,000) emanates from Mount Pinatubo's summit caldera lake, a condition that peaked last year when the lake rose critically close to the caldera rim's lowest point, the Maraunot Notch (ca. 960 m asl; Figure 1). The lake had risen by 40m between May 1998 and July 2001, the period within which the Philippine Institute of Volcanology and Seismology (PHIVOLCS) had monitored the Maraunot freeboard. Its surface stood at 955m asl, 5 m below the notch, by July 2001. Recorded lake rise increments warned of definite overflow at the notch, or "overtopping", in the last quarter of 2001, an event fraught with grave possibilities of triggering a breach at Maraunot and the ultimate breakout of Pinatubo's crater lake. |