Understanding the complex evolution and hazard susceptibility of karst landscapes remains a challenge in the Philippines. Rapid development due to the booming tourism industry poses a
threat to the fragile karst environment. The Climate-responsive Karst Management for Sustainable Tourism (PhilKarst) Program of the Mines and Geosciences Bureau (MGB) aims to understand the effects of natural and anthropogenic factors in the development and degradation of karst systems in key tourist destinations of the country. This paper discusses the detailed geomorphological analysis of notable karst terrains in Palawan (El Nido) and Siargao Island, Surigao del Norte (General Luna and Del Carmen).
Using topographic maps and Interferometric Synthetic Aperture and Radar (IfSAR) Digital Elevation Model (DEM), sinkholes were delineated, and morphometric parameters such as slope, relief, topographic position index (TPI), and sinkhole morphometry (e.g. density, percent area, circularity index, eccentricity index) were calculated through ArcGIS 10.6.1. Inventory of karst features (i.e. caves, sinkholes, towers, cone hills), landslides, and hydrogeological features (i.e. springs, wells) were also conducted through field surveys.
Results show contrasts in geomorphometric parameters among the study sites indicating their different stages in karst evolution. To date, there are 54 sinkholes identified in El Nido that are distributed mainly in the karst tower-valley zones of the Permian and Jurassic limestone, while there are 281 sinkholes in the cockpit and reef terrace zones of Miocene and Plio-Pleistocene limestone in Siargao Island. Sinkhole occurrence also increases near lineaments (100 – 500 m) and natural streams (40 – 80 m). While dissolution of limestone is the primary process that drives karstification in the two sites, tectonic evolution, geologic structures, and hydrological processes also affect the development and spatial distribution of different karst features. In addition, land conversion and heavy development can exacerbate the subsidence hazard and environmental problems in karst tourism areas.
KEVIN L. GARAS1,2*, ROSS DOMINIC D. AGOT1,3, LIZA SOCORRO J. MANZANO1,
NOELYNNA T. RAMOS3, JETHRO B. CAPINO1, NICOLE JEAN L. MERCADO1, AQUILA KRISTIAN B. ESMERALDA1 AND JAN CEDRIC G. SISRACON1
1Lands Geological Survey Division, Mines and Geosciences Bureau, Philippines 2Graduate School of Science, Hokkaido University, Japan
3National Institute of Geological Sciences, University of the Philippines Diliman
*Corresponding author email address: This email address is being protected from spambots. You need JavaScript enabled to view it.