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At the Mountain’s Underbelly

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Biologist Klaus Stiefel goes deep into Mabinay, the Caving Capital of the Philippines, to explore the dynamics between the creatures of the night and the subterranean.

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Carmen del Prado
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The island of Negros is bisected between the politics of Negros Oriental and Occidental, and the linguistics of Bisaya and Hiligaynon. Even beneath its surface, this division is mirrored in the Negros volcanic arch and the Visayan basin that make up the western and eastern half of the island. When you go from end to end, you travel from one world to another.

In the west, the municipality of Valencia thrums with geothermal activity—rivers run red with iron while rock walls covered in yellow volcanic sulfur emit odorous fumes. Three hours away, the mountainous heart of the island is composed of elevated limestone. The dissolution of the rock has birthed the caving capital of the region, Mabinay.

On the road, Negros may seem like an endless expanse of sugarcane, the economic basis in this part of the country, but it features a distinct topography you cannot find, say, in parts of Europe, as Dumaguete-based Austrian scientist Klaus Stiefel points out. From the east of France to the west of Austria, you will find alps, and then even more alps—landscapes formed by near identical geological forces. 

“In contrast, the geology of the Philippine archipelago is extremely varied, and that's still the case within individual islands. The reason for this exciting geological situation is the unusual plate tectonic setup in the region.” The surface of the planet is made up of tectonic plates, gigantic slabs of rock that independently move around. For most of the world, tectonic plates are the size of large nations, like India, or whole continents, like South America. Not so in the Philippines, where an armada of clan-territory-sized mini-plates moves about, each heading in its own direction.

Geologists call this constellation of tectonic plates the “Philippine Mobile Belt.” Although scientific literature has yet to reach a consensus on its precise age—another sign of how complicated the geology of the central Philippines is—there is an understanding that the mountain range formed by the Canloan volcano at the north of the island is dated about two and a half million years ago, around the beginning of the Ice Age. This is the youngest part of Negros.

This active geological situation has brought heaven and hell to the country. Tectonic activity is the cause of deadly catastrophes, like volcanic eruptions and earthquakes. But without these micro-collisions, neither would a labyrinth of bays, trenches, ocean straits, and basins that allow the immensely biodiverse fauna of the country to thrive. 

Cave fauna are special because of their isolation from animals thriving out in the open. It is as if the caves of the Philippines are islands within islands.

The Art of Dripping Water

The unusually rich biodiversity of the Philippines is what brought Klaus to the country eight years ago. In the mid-2010s, he had been in search of the most fascinating habitat he could study as a biologist. While he had been initially drawn to the coral reefs and fish fauna of Batangas and Tubbataha, Klaus found a home studying the terrestrial biodiversity in Negros. He now teaches fish and coral reef biology at Siliman University.

But, this sense of wonder is not shared by too many. Whenever Klaus visits the Mabinay caves, he would only run into locals. On his last visit in March, there had only been high school students looking to help market the caves as an ecotourism destination. The caves hold untapped potential for socio-economic benefits, including providing a source of revenue for local communities and augmenting funds to support the management of protected areas.

Caves are a sleeping beauty of natural wonders—but it is also an exercise of your physical and mental abilities. It can be suffocating to explore the underbelly of a mountain. Lying under the earth’s surface is a subterranean maze of precipitous drops, tight crawl spaces, and underwater passages. However, the caves of Mabinay make for a great place to start, where you can enjoy its beauty without being clipped to miles of rope that spelunkers have rigged or having to navigate through the dark.

When rain mixes with carbon dioxide in the atmosphere, it picks up more of the gas as it’s absorbed into the soil. As National Geographic explains, the acidic water seeps through cracks and fissures underground, creating a network of passages like a plumbing system. In karst landscapes, as more water seeps down, these passages widen over time as rocks dissolve in the solution. It takes hundreds of thousands of years for these caves to grow enough to make room for a human.

Locals claim there are 400 caves in Mabinay, but only a quarter of them are known—half of which were explored and identified in 1989 by a team of Dutch-Belgian cavers. But even prior to this discovery, its underground passages had once given shelter to locals hiding during the Japanese occupation.

In the interest of environmental protection, only three of the caves are open to the general public, fitted with floodlights and steel walkways for better accessibility. Other caves, such as Mambajo and Odluman, require rappelling down the entrance or swimming through an underground river and are reserved for experienced spelunkers.

To get to these caves, visitors can take a Ceres bus bound for Bacolod from the Dumaguete bus terminal and get off at Bulwang caves. Upon paying the fee for the entrance and an accredited guide at the cave visitor center, equip yourself with a helmet and light before embarking. Klaus also recommends hiking boots for the two-hour expedition.

The first stop is the Panligawan cave, whose name translates to courtship. In the past, this is where the Ati, the indigenous peoples of Negros, would profess their love to receive blessings from the nature spirits that inhabited the cave. In this geological cathedral, the collapsed ceiling allows light to enter from above—illuminating rock sculptures from different angles, while vegetation grows underneath the large window.

In such chambers, water dripping from the ceiling deposits tiny amounts of limestone with every drop, forming drooping stalactites. With every drop that hits the cave floor, another tiny amount of limestone is deposited, forming corresponding upward-facing stalagmites. Both are continuously in reach of one another, and a column forms where stalactites and stalagmites meet. By and by, columns merge like sheets of a waterfall frozen in time.

The next stop is the highlight of the Mabinay caves, the Gasidlak or Crystal cave wherein the limestone has formed a crystal structure that partially reflects light. When the guide directs his flashlight onto it, the rock gleams—as if it were fiberglass, the crystal rock formation conducts light along its surface. 

Like the other caves, Gasidlak is alive, or as alive as a rock can be: There are limestone sculptures still forming. But this means they can be stunted by a touch of a finger. The oil left behind by our hands can create a barrier that prevents minerals dissolved in the water to be deposited. Though they take a millennium to form, rocks can be paradoxically fragile.

Creatures of the Night

For many animals, the end of the day is the start of theirs. Many inhabitants of perpetually dark environments have foregone their sense of sight and instead, use their other enhanced sense organs to map their surroundings, stay safe from predators, and hunt.

The final destination, Pandalihan cave, is home to a menagerie of creatures of the night. While its vast chambers and breathtaking rock sculptures are reason enough to visit the Mabinay caves, the intriguing nature of cave fauna is the source of Klaus’ fascination.

Their guide spots pseudoscorpions and crickets crawling along the crevices of the cave. Similar to the anatomy of nocturnal creatures, both possess antennae used to orient themselves with a heightened sense of touch and smell, sensitive to small movements of air and vibrations from prey. The arachnid also has powerful pincers that they use to clasp onto the legs of flying insects and hitch a ride to a new habitat.

The cave is also the nesting ground of a population of bats. These flying mammals have evolved a fine-tuned sense of echolocation as seen in the smaller bat species' large, unusually shaped ears. Aside from navigating their environment, the call of the bat plays a role in their social life, containing information like sex, age, or even individual identity. The sound waves they emit are so highly pitched that, for the most part, humans can’t hear them except for the low-frequency components. This is the very subtle tweeting that cavers hear in Pandalihan. 

The Mabinay Caves posit that mother nature is not the immutable force fiction makes it out to be. 

Klaus’ primary research interest is the biology and behavior of gobies, a family of small marine and freshwater fishes. In the caves of Negros, Samar, and elsewhere in Mindanao, a blind goby was discovered having lost its vision in the dark habitat. He had hoped to find the blind goby just as he had once caught sight of it on a previous visit. But that day, the small fish had eluded him. Nonetheless, the fascinating ecosystem of cave dwellers still has much to offer to the scientist.

A Man vs. Nature conflict arises when a character is faced with the elements, but Mabinay posits that mother nature is not the immutable force fiction makes it out to be.  The environment is affected in the same way that the subterranean bends creatures to its will and causes its occupants to adapt. Caves are living organisms in themselves, with vessels that contract and expand, taking in organic matter that passes slowly through their systems. Thus, the ever-changing Mabinay caves contain countless biological secrets, waiting to be explored by scientists and travelers alike, as does the multitude of terrains the country is home to.

“The fractured geography of the Philippines contributes to its amazing biodiversity: New species evolve more rapidly when different populations of animals are separated from each other,” Klaus remarks.

 “Just as the Philippines is special in terms of biodiversity because its land fauna is isolated from that of mainland Asia, so are the caves special as their fauna is isolated from the animals thriving out in the open. [It is as if the caves of the Philippines are] islands within islands.”

A labyrinth of bays, trenches, ocean straits, and basins that allow the immense biodiversity of the Philippines to thrive.

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