Once A Geothermal Prospect

Introduction

    People have been fascinated with the prospect of harnessing energy beneath the surface of the earth. The prospect has become a reality as the development of geothermal energy technology has seemed to progress from the stage of exploration projects.

    Geothermal energy can be best defined as the natural heat of the earth which is captured in the form of fluids trapped in rock formations beneath the earth’s surface. The primary source of heat is the molten rock known as "magma" which lies of depth for its energy to be useful.

    The Philippines has eventually emerged as the second largest geothermal power user for power generation in almost half a decade now. The country’s total installed power capacity to date from the said energy source riches 781 megawatts (Mge) which has been surpassed only by the Geysers of California with more than 900 megawatts output.

    Today, some 25 geothermal sites have been identified for exploration and development in the country from which Mt. Arayat has become one of the geothermal energy prospects.

    Several brief reconnaissance geological, geophysical surveys of Mt. Arayat and its vicinities had been carried out in the past by numerous geoscientists and engineers who were interested in the possible natural potential of the volcano. The different aspects of the survey were conducted intermittently from February to June of 1983. Its objective was to locate for geothermal manifestations and to determine the geothermal potential of this volcanic edifice.

Geology

    Mt. Arayat (1026m), located strategically near the boundaries of the provinces of Pampanga & Nueva Ecija, is an is an isolated quarternary basaltic volcano characterized by a basal diameter of about 7 kilometers. The central plain of Luzon from which Mt. Arayat rises is an intermontane basin approximately 10 kilometers deep filled with tertiary and possibly cretaceous sedimentary deposits covered by relatively thin veneer of quarternary fluvial deposites and volcanics.

    The rocks that comprise Mt. Arayat porphyritic dark colored basaltic lavas having a crystaltine groundmass. Olivence occurs as the primary mineral constituent of the rock together with puroyene. The groundmass mineralogy includes plagioclass, magnetite and care borblende crystals as large phenocrysts. No hystoric eruption has been recorded for Mt. Arayat, but present radiometric data (ABASCO 1977) confirmed the young age of the volcanic cone as deduced from its morphology and the presence of glass in some of the rock samples colected during the survey. Two rocks dated by potassium-argon method, yielded ages of 0.65 to 0.53 millions of years which, therefor, has become suggestive that the age of Mt. Arayat is with in the aforementioned figures.

Structures

    Two (2) parallel almost east-west normal faults are prominent flanks. The faults are about 1 kilometer apart but they appear to merge near the summit of the cone to form an oval-shaped collapse structure. Another pair of parallel normal faults trending north - south are seen along the northern, flank. The vertical displacement in both pairs can be observed clearly from a distance, but the sense of movement is qiute default to establish. The structures have been noted to form a radial fault pattern very common among mountains like Mt. Arayat.

Glossary

By Rizalito G.Lapuz