Thursday, March 23, 2006

Glossary: Zambales Mountains (Sambal)

Zambales is the name of a mountain range and corresponding biogeographic zone along the eastern edge of Zambales Province in the Central Luzon region of the Philippines.

The Philippine islands are located between the northward-moving Philippine Sea Plate and the relatively stationary Asian region. The Zambales Mountains are formed at the subduction of the Asian plate at the Manila Trench. Mt. Pinatubo is the most well-known peak in this range.

An exposed area of ocean crust and mantle known as an ophiolite is found in Zambales. The Zambales Ophiolite boundary can easily be distinguished as the differing rock types of the ocean crust and mantle bring about contrasting vegetation. Two differing blocks within the ophiolite, the Coto and Acoje blocks, and evidence of lava mixing, give the Zambales area a highly heterogeneous geochemistry.

"We suggest that the array of geochemical data from the Zambales ophiolite can be explained in terms of processes observed in present-day convergent plate margins, such as the Marianas or Lau Basin in the western Pacific. Complicated plate boundaries which have existed for long periods of time, including closely opposing and changing subduction systems, the rifting of arcs, and the formation of backarc basins may result in the superposition of one lava type on another or may produce many small domains in the upper mantle sources for subduction-related lavas, some of which become extremely depleted or secondarily enriched. Magmas derived from such a heterogeneous mantle will display ranges in geochemical characteristics, possibly similar to those observed in the Zambales ophiolite." (Evans et al., 1991)

Mt. Pinatubo's 1991 eruption produced dacite lava consisting of a mixing of Zambales ophiolite melt with sub-arc mantle melt.

High variance in the geological makeup might help account for region's rich mineral resources. The area was known in early times for its magnetic iron deposits. More recently the Coto block of the ophiolite has become the world's largest producer of refractory chromite, and also a good source of platinum. Nickel and chromite are found at the Acoje block.

Dizon mine near the border with Pampanga is noted for its copper-gold-silver deposits. Non metallic minerals such as sandstones, Zambales jade, serpentine, pumice, white clay, rock aggregate, salt, stones, cobbles, boulders, and silica quartz are found in abundance.

Non-pumicitic lahar is a component of concrete mixes, while non-magnetic lahar is the primary component of fired "Lahar Porcelain."

Pinatubo's eruption expelled large quantities of sulfur dioxide into the atmosphere, the most ever recorded and nearly three times that of El Chinchon, its nearest competitor. Pumices in the area often have very high sulfur content. The source of all this sulfur is a matter of dispute. Some believe the sulfur may have been contained in remnants of previous sulfur-rich eruptions.



Despite it's relatively small land area, the Zambales Mountains have long been known for their natural beauty and biological diversity.

Although studies in this area are preliminary at best, some 61 endemic plants species have been found, of which 39 are endemic to Mt. Pinatubo alone.

About 50 species of moss thrive in the thick moss forests that were once considered inpenetrable. These forests have long been famed for their valuable tropical hardwoods, and today produce some of the most prized orchids in the international flower trade.

At one time, the area abounded in native deer species but these were wiped out during the colonization period due to deerskin trade with Japan and China. Now, the principal mammal species are monkeys, bats, including the Luzon pygmy fruit bat, and various rodents including a newly-discovered member of the tweezer-beaked Rhynchomys family.

Southern Zambales near Subic is the largest roosting refuge for bats in the world.

The town of Balincaguin in eastern Zambales, now known as Mabini, means "Home of Bats" in the native Sambal language.

The two largest bats in the world, the Golden-crowned Flying Fox (Acerodon jubatus) and the Giant Fruit Bat (Pteropus vampyrus), find their most important roosting ground in southern Zambales near Subic.

As might be expected in a rainforest region, Zambales is home to a dazzling variety of insects including many rare butterflies. At Subic, a tourist spot known as the "Butterfly Garden" showcases an enclosed butterfly farming exhibit.

While some areas of the vast Mt. Pinatubo watershed are still biologically sterile, most regions have recovered since lahar flows stopped in 1997. Aquatic ecosystems including fish, vegetation, insects, algae, crustaceans and the like have returned.

The greening of Mt. Pinatubo

With standing freshwater swamps and pools, Zambales is a paradise for reptiles and amphibians. At one time, frogs and snakes constituted the most important source of protein for some indigneous peoples living here.

Zambales western seacoast is an important marine conservation area with sea turtle nesting areas and mangrove forests. To the east, just south of the sister volcano Mt. Arayat are the Candaba wetlands, a major nesting area for migratory birds in the Philippines.

Indigenous peoples

The two indigenous peoples of the Zambales Mountains are the Ayta and Sambal. The Sambal live mostly in the northern part of the province while the Ayta live around Pinatubo.

Many Ayta were displaced after the 1991 eruption, but slowly some have been returning to the region. While most now practice root agriculture, they still have a fondness for hunting, and gathering honey, fruits and wild plants.

The Sambal, like the Ayta, fiercely resisted the Spanish invaders. Their conversion to Christianity was only accomplished through the rare implementation of the Inquistion in the Philippines. The Sambal priests continued to practice their old ways even after outwardly taking on Catholic practices.

Paul Kekai Manansala


Brown, R. M., J. W. Ferner, R. V. Sison, P. C. Gonzales, and R. S. Kennedy. 1996. Amphibians and reptiles of the Zambales mountains of Luzon Island, Philippines. Herpetological Natural History 4:1-17.

Evans, Cynthia A.; Casteneda, Gerry; Franco, Helen. "Geochemical complexities preserved in the volcanic rocks of the Zambales Ophiolite, Philippines," Journal of Geophysical Research, Volume 96, Issue B10, 1991, p. 16251-16262.

The Greening of Mt. Pinatubo,

Yumul, G.P., Jr., 1996. Rare earth element geochemistry of a supra- subduction zone ophiolite: The Zambales Ophiolite Complex. Tectonophysics 262, 243-262.