Naguilian Cave - Fuga Island - Philippines
Fuga Island is the most southerly of the Babuyan group of islands which lie off the north of the main Philippines island of Luzon. Working recently as part of an Anglo-American team drawing up a master plan for the development of the island as a resort, I was able to spend some time exploring the island and its cave.
Fuga is about 22km long by 6km wide, privately owned and wholly undeveloped. The local population of about 1500 survive through subsistence farming and fishing. Geologically the island is composed entirely of sediments of Pliocene age which consists of thick beds of coral limestones interbedded with softer beds of brown marine siltstone; possibly of volcanic origin. The limestone is well exposed in the cliffs around the island but inland it is lost beneath a gently rolling terrain with little or no karst features.
The only cave known by the natives on the island is at Naguilian, a village on the south side which was once the site of a large Spanish mission; the impressive ruins of which remain to this day. Other caves probably exist, particularly around the coastal cliffs and a concerted search might reveal other sites. However, the only sea caves investigated by the author are of no significant size.
Naguilian village lies on a terrace about 60m above the sea created by an outcrop of a coral limestone bed . The cave was visited on 30th January 1996 and lies to the east of the village. It is entered by a shallow gully in coral limestone which opens out into an impressive cave entrance about 6m square. The cave floor descends steeply to a mud block age after 20m. Our guide told us that it is normally possible to slide down a hole in the floor to further large chambers beyond.
The main chamber contains impressive flowstone deposits which encrust all of the floor and walls of the cave; the roof being of classic ogee shape with a small fault guiding the alignment. Closer inspection revealed that whilst the roof was in a bed of limestone the calcite covered walls were in a soft brown siltstone; possibly volcanic tuff. The mode of formation of the cave would therefore seem to have been by the downward development in the floor of a small cave originally formed at the base of the limestone bed. A complex mechanism of mechanical erosion and collapse may have been at work here.
The chambers beyond the end of the cave may well be in another bed of limestone. The entrance gorge is evidently formed by the collapse of the thin cave roof
The only other sites of speleological interest on Fuga are a number of tunnels dug by the Japanese during the second word war when they occupied the islands. These are to be found near the village of Mudoc at the west end of the island. They are of limited extent and little more than hideouts and storage sites. The 1:50000 survey sheet of Fuga shows a tunnel about 1km long near Mudoc. As far as can be ascertained his is a fantasy of the surveyors imagination.
