Cuatro Islas in Leyte: The pristine tropical paradise

 Protected Landscape/Seascape 

The four islands collectively known as the Cuatro Islas—Apid, Digyo, Himokilan, and Mahaba—were proclaimed on April 23, 2000, as a protected landscape/seascape under the NIPAS Act of 1992 by President Joseph Ejercito Estrada through Proclamation No. 270. The protected area is under the administrative jurisdiction of the municipalities of Inopacan and Hindang, Leyte.

Location of Cuatro Islas off the coast of Inopacan and Hindang, Leyte

 Geologic Origin 

The Cuatro Islas are believed to be remnants of a barrier reef system located off the coast of Inopacan and Hindang in Leyte. In a study conducted during the International Tropical Ecology Workshop in 1999 organized by the ViSCA-GTZ Tropical Ecology Program, we proposed that these coral reef islands are underlain by a volcanic basement connected to the extinct Mt. Sacripante on the Leyte mainland (Grenz et al., 1999). Geological evidence suggests that the islands formed during the Upper Pleistocene epoch of the Quaternary period, as indicated by the presence of coralline limestone of Quaternary age. During the Last Glacial Maximum, approximately 15,000 years ago, sea levels across Southeast Asia dropped by about 100 to 150 meters. This significant decline exposed large portions of the continental shelf, creating conditions favorable for coral growth in newly formed shallow tropical marine environments. In addition, ongoing tectonic uplift in Leyte and other parts of the Philippines further facilitated reef development, as corals thrive in shallow, sunlit warm waters. This combination of falling sea levels and gradual tectonic uplift contributed to the emergence and present configuration of the barrier reef system. Similar uplifted coral reef formations can also be found in the northwestern and southwestern regions of Leyte Island (Grenz et al., 1999). 

Digyo Island, a pristine tropical paradise

 Digyo, the Jewel of the Cuatro Islas 

 Among the four islands, Digyo stands out for its relatively flat, low-lying topography, rising only about 2 to 3 meters above the present sea level. It suggests that Digyo is geologically younger than the other islands, having formed more recently. Its crystal-clear turquoise water and fine white sand, derived from coralline limestone and the shells of marine organisms, make Digyo a favorite destination for tourists. Many people call it the jewel of the Cuatro Islas. 

The stunning white sandbar 

 Digyo Soils are Sandy and Undeveloped 

 The soils of Digyo Island are dominated by sand (largely calcium carbonate) and show no signs of pedogenesis. Roots of coconut trees, the main vegetation on the island, hold the sandy soil but contribute little humus. The soils belong to the Entisols order in Soil Taxonomy, and Arenosols in the World Reference Base (WRB). 

The young, sandy, & undeveloped soil of Digyo Island showing roots of coconut trees

Photo credit: All photos were taken by V.B. Asio on 25 April 2026

 

Reference 

Grenz, J., Zukunft, S., & Asio, V. B. (1999). Geomorphology and soils of Apid Island, Inopacan, Leyte, Philippines. Annals of Tropical Research, 21, 1-8.

The rock formation along the highway in San Jose, Dulag, Leyte

Have you ever wondered about the rock along the highway in San Jose, Dulag, Leyte? Especially where the road runs close to the sea, travelers see a striking, dark-colored rock formation exposed by the ongoing road widening. 

The andesite rock along the highway in San Jose, Dulag, Leyte

Formed by volcanism between 2.6 and 23 million years ago during the Miocene and Pliocene epochs, this rock in Dulag is known as andesite. Andesite is an intermediate type of volcanic rock, with silica (SiO2) content ranging between 52% and 63%, commonly found in areas with past or present volcanic activity. 

The Dulag andesite belongs to the Pliocene-Miocene intermediate rocks (Jahn & Asio, 2006)

Andesite got its name from the Andes Mountains in South America, where it is abundant. It is also widespread in volcanic regions around the world, especially along the Pacific Ring of Fire, where many volcanoes produce this type of rock. It is an extrusive (volcanic type) and the most widespread igneous rock in the Philippines. 

Andesite typically appears fine-grained, sometimes with small visible crystals embedded in it called phenocrysts. These crystals are often made of minerals like feldspar and dark-colored minerals such as pyroxene or biotite. Because of this, andesite can look gray, pinkish, or slightly dark, depending on its composition. 

Mineral composition of the andesite in Abuyog: Amp- amphibole; Cpx- clinopyroxene;
Opq-opaque minerals; Pl-plagioclase feldspar

Laboratory examination of thin sections using a petrographic microscope (above photo) revealed that the andesite in Dulag, Leyte, consists primarily of plagioclase feldspar (45% of the mineral content), clinopyroxene (20%), and amphibole (5%), along with minor amounts of secondary minerals. It is darker in color compared to the younger andesite rocks (Quaternary volcanics) in the central highlands of Leyte.

The typical andesite rock in the central highlands of Leyte formed by volcanism during the Quaternary period (2 million years ago up to the present). The sample comes
from Cabintan, Ormoc at an elevation of 900 m above sea level.

Acknowledgement

I thank the National Institute of Geological Sciences (NIGS) at UP Diliman for conducting the thin section analysis of my rock samples.

References

Britannica Editors. "andesite". Encyclopedia Britannica, 5 Jul. 2015, https://www.britannica.com/science/andesite. Accessed 3 April 2026.

Jahn, R., & Asio, V. B. (2006). Climate, geology and soils of the tropics with special reference to Southeast Asia and Leyte (Philippines). In Proceedings of the 11th International Seminar-Workshop on Tropical Ecology (pp. 21-25).