December 2003 Hubas River Debris Flow Pintuyan, Panaon Island, Southern Leyte

Carlo D. Dayanghirang

MSc. Quaternary Geology
EMB Accredited Environmental Professional

Abstract

Panaon Island was brought to national attention by the multiple slides which killed scores of residents in December 2003. Unnoticed, the high precipitation that initiated the multiple slides also triggered a debris flow, a seldom recognized mass wasting hazard. The debris flow occurred at Hubas River, which drains the western flanks of Mt. Nelangkapan, a Quaternary Volcano at the southern end of Panaon Island.

The December 2003 debris flow has 3 distinctive morphologies namely: (a) 3.5-4 meters high snout composed of boulders with varying diameters; (b) side ridges of lateral deposit at both sides of the channel mainly of boulders left behind by the passage of the snout; and (c) medial depression left within the channel, ed by the ridges of the lateral deposits, composed of boulders and gravel supported by a loose sand matrix. The flow also left behind boulders perched on the ridges of lateral deposits of earlier debris flow.

The debris flow deposited an estimated 83,000 m³ of loose materials and terminated at the river mouth at the coastline forming a fan shaped lobe. The velocity of the flow had sufficient momentum to deposit 2 to 3 meters diameter boulders 20-25 meters offshore.