The Physical Environment of Mt. Pangasugan, Leyte, Philippines

Geology

Mt. Pangasugan is generally built up by andesitic and basaltic pyroclastic rocks (referred to as Pangasugan formation) which are mostly of Quaternary and Tertiary origin. This rock formation is characterized by weak consolidation, lithologic discontinuities, abundance of rock outcrops, and shearing due to the occurrence of the Philippine fault line approximately at the center of the mountain range. Minor earthquakes are relatively frequent in the area. All these geological characteristics indicate that the area is unstable.

Geomorphology

The morphology of Mt. Pangasugan is largely the result of the combined effects of volcanism, erosion, faulting and tectonic uplift. Mt. Pangasuagn rises abruptly from the narrow alluvial coastal plain along the Camotes Sea into a vertical wall-like rock mass with a maximum height of about 1100 m above sea level (asl). The air distance between the sea level and the peak of the mountain is less than 3 km. This short distance suggests extremely high erosion energy potential which is visible in the form of waterfalls particularly during periods of high rainfall. The west-facing slope of the mountain is deeply dissected by several short parallel streams that empty into the Camotes Sea. The V-shaped valleys, which indicate youthful stage, coupled by the unconsolidated nature of the rock material, cause widespread landslides during typhoon periods.

Climate

The climate of the area is a humid tropical monsoon climate with no pronounced maximum rain period and no dry season (Type 4 of the Coronas climatic classification). It has an average annual rainfall ranging from 2600 mm in the coastal lowland, to more than 3000 mm at higher elevations. Average temperature in the plain is 27 degrees Celsius which decreases by an average of 0.6 degree Celsius per 100 m rise in elevation (i.e. at 500 m elevation, the average temperature is 24 degrees Celsius). Two types of monsoon winds tremendously influence the over-all climate of the area. From June to October, a southwest monsoon (Habagat) occurs which enhances rainfall in the area (western side of mountain). From November to February, the northeast monsoon (Amihan) follows which generally coincides with cyclonic disturbances thereby bringing plenty of rain particularly to the eastern side of the mountain range.

Pedology

The soils of the mountain can be grouped into four: the old soils in the mountain footslopes (approximately below 200m asl), the mature soils in the mountain midslopes (approximately between 200 and 400m asl), the young soils in the upper slopes (approximately above 400m asl) and the undeveloped soils in very steep slopes.The old soils (Ultisols) are deep, clayey, acidic and infertile. They are relatively stable although landslides may occur. The mature soils (Alfisols) are generally fertile and productive. The young soils in the upper slopes (Andisols) result from the fast weathering of andesitic rocks. They have excellent physical condition but are acidic and generally low in phosphorus. Because of their weak profile development and amorphous clay mineralogy, these soils are unstable and prone to landslides and erosion. The undeveloped soils on steep slopes (Inceptisols and Entisols) have low productivity due to their shallow profile, abundance of rock fragments and steep slopes. They are also prone to erosion.

References

Asio V.B.1996. Characteristics, weathering, formation and degradation of soils from volcanic rocks in Leyte, Philippines. Hohenheimer Bodenkundliche Hefte 33, Stuttgart, Germany, 290pp.

Quimio, J.M., V.B. Asio, J.M. Alkuino, B.B. Dargantes and P.S. Muga. 1997. Initial Environmental Examination of the Leyte-Mindanao Interconnection Project. NPC, Quezon City, 151pp.