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Physical Environment


Physical Characteristics

Bicol is the fifth administrative region under the Integrated Reorganization Plan (IRP), which was implemented through Presidential Decree No. 1 in 1972.  Generally located at the midsection of the country or at the southern tip of Luzon, Bicol lies within coordinates 122 to 124.5 degrees longitude and 12 to 14.5 degrees latitude.  It is bounded northwest by Quezon Province, east by the open seas of the Pacific, southeast by Samar Sea and southwest by Sibuyan Sea.

The region is composed of four mainland provinces and two island  provinces.  It has a total of seven (7) cities and 107 municipalities subdivided into 3,471 barangays.  Politically, 14 congressional districts subdivide the region.

Land Area

The region’s land area of about 1.8 million hectares is roughly 6.04 percent of the country’s 30 million hectares.  Around 69 percent or two-thirds of the region’s land area is part of mainland Luzon while the rest is the combined land area of the island provinces of Masbate and Catanduanes.

Camarines Sur has the largest land area with 548,60 hectares or 30 percent of the regional area while Catanduanes has the smallest with 149,216 hectares or 9 percent.

As to municipal areas, Labo in Camarines Norte has the largest municipal land area of 58,936 hectares followed by Milagros in Masbate with 56,530 hectares.  In contrast, Camaligan and Gainza both of Camarines Sur, have the smallest land areas of 468 and 1,475 hectares respectively.  Among the seven cities in the region, Sorsogon City is the largest with 27,611 hectares followed by Ligao City (24,675 hectares) and Masbate City with 18,800 hectares.


The region’s topography may be generally described as ranging   from slightly undulating to rolling and from hilly to mountainous. Bicol is endowed with numerous mountains and volcanoes.  The most famous, Mt. Mayon in Albay, has the highest elevation at 2,462 meters above sea level.  Other volcanoes and mountains dominating the countryside and their corresponding elevations include:  Mt. Malinao (1,548 meters), Mt. Masaraga (337 meters) and Mt. Catburawan (473 meters) in Albay; Mt. Isarog (1,966 meters) and Mt. Iriga (1,143 meters) in Camarines Sur; and Bulusan Volcano (1,560 meters) in Sorsogon.

In Camarines Norte, a rolling to rugged terrain surrounds the plains of Labo, Talisay, Vinzons and Daet.  This rugged topography stretches from Mt. Labo to the Camarines Norte-Camarines Sur boundary and thence to a rolling strip along the western coast of Camarines Sur, Albay and Sorsogon.  The rugged landforms of Eastern Bicol, Cordillera in the northeast extending from Calinigan Mountain (Caramoan Peninsula) to Mt. Mayon, on the other hand, separates the plains of Lagonoy, San Jose, Goa, Tigaon and Sangay from Bicol Plains.  The Bicol Plains, a main physiographic feature in the region, is a wide depression that trends northwesterly from the western slopes of Mt. Mayon and stretches across the central part of Camarines Sur.  Three lakes–Buhi, Baao and Bato—are located within this valley.

Small patches of plains that are utilized for lowland farming intermittently break the rolling terrain in the western coasts of Albay and Sorsogon.   In Sorsogon, the most noted physiographic feature is the fertile Irosin-Juban Valley, which is surrounded by rough terrains of Bulusan Volcano in the southeast and Mts. Juban and Batuan in the southwest. This valley is also noted as schistosomiasis and filiariasis outbreak areas.  Such water and mosquito-borne diseases pose a big threat to public health in the area.

In the islands of Masbate, the relief conditions are almost similar in all three islands (Ticao, Burias and Masbate).  The terrain ranges from slightly undulating to rolling and from hilly to mountainous.  In each island, rugged topography is concentrated on the north and gradually gives way to hills and rolling areas in the south, southeast and southwest.  The highest point in the province is the conical peak of 700 meters above sea level located in Masbate, Island.

A rugged topography in its central core generally characterizes the island of Catanduanes.  Along its coastal regions, narrow strip of plains are found. A narrow depression both in the northern and southern cores.breaks the rough terrain of the island in its midsection.

Coastal Area

The region’s coastal area is deeply embayed.  This is   characterized by the presence of numerous bays and gulfs.  These are:  the Ragay Gulf, San Miguel Bay and Lagonoy Gulf outlining the coasts of Camarines Norte and Camarines Sur; Albay Gulf and Sorsogon Bay in Albay and Sorsogon.  In addition, the region is endowed with natural harbors, which serve as refuge for ships during heights of weather disturbances in the vicinity.

Volcanoes, Faults and Earthquake Zones

The distribution of faults, volcanic and earthquake belts in the region is shown in Figure 3.03.  A parallelism between the Bicol Volcanic Belt, the Philippine Fault Zone and the deep Philippine trench can be noticed.

The Bicol Volcanic Belt or Chain spans a total of 240 kilometers from Camarines Norte in the north down to Sorsogon in the south.  A total of sixteen volcanoes approximately 24 kilometers apart, lie along the 200 kilometer chain which runs parallel to and west of the Philippine Trench.

There are three active volcanoes, which have erupted within the past 600 years) and their last recorded eruptions are:  Mt. Mayon (2001); Mt. Bulusan (1988) and Mt. Iriga (1628).

Most famous among the active volcanoes is the majestic Mt.Mayon with its near perfect symmetry, fiery outbursts and destructive mudflows.    It consists of deposits formed basically by four major volcanic activities:  airfall disposition, pyroclastric flows, rain triggered debris flows and lava flows.

Mt. Iriga, with a peak of 1,143 meters above sea level, is likewise, of the stratovolcano type.  The main historical event for Mt. Iriga was a large volume debris avalanche in 1628 AD, which dammed the Barit River and created Lake Buhi presently known as the habitat of the smallest edible fish in the world, the sinarapan.

Bulusan Volcano, located near the central part of Sorsogon province, peaks at 1,550 meters above sea level.  Its last eruption was in 1988.

Associated with non-active volcanoes are geothermal fields. Tapped for power generation, these fields operate geothermal power plants in Tiwi and Bacon-Manito area in Albay and Sorsogon, respectively, for a combined Total Generating Capacity of 512.574 MW and 317.67 MW dependable capacity.  Sources of geothermal power are Mt. Malinao in Albay and Pocdol Volcano in Sorsogon.

In addition to its location along the volcanic belt, the region lies near the center of the Philippine Fault Zone (PFZ), which is a major earthquake generator in the Philippine Archipelago.  The zone, about 1,300 kilometers long, is characterized by a bundle of parallel to sub parallel active faults confined with a narrow zone trending north-northwest and south-southwest. It is characteristic of an active fault, like the PFZ, to generate potentially destructive tremors since those are shallow-seated or occur near the earth’s surface (less than 80 kilometers deep).

Another major source of earthquake in the region is the Philippine trench.  A trench is defined as a long, narrow and generally steep-sided very deep depression in the ocean floor.  The axis of a trench marks the position of a subduction zone, where old oceanic lithospheric plates begin their descent into the earth’s interior.

A study conducted by Efren A. Uy and Benito T. Punsalan published in 1987 indicated that the Bicol Region is prone to earthquakes of Intensity V from the above-cited source zones.

Climate and Weather Disturbances

Based on the Modified Corona’s climate classification system, three climate types occur over the Bicol Region, as shown in Figure 3.04. Type II is experienced over the eastern coasts of the region directly facing the Pacific Seas including the island of Catanduanes and the whole of Camarines Norte.  These areas are characterized by the absence of dry season with a very pronounced maximum rain period generally in the months of December and January. There is not a single dry month in these areas.  A dry month is defined as a month with less than 50 mm of rainfall.  A month with more than 100 mm can still be considered as dry if it is preceded by three or more very dry months.

A Type III climate is characterized by not very pronounced maximum rain period, with a short dry season occurring either in winter or spring.  Places under this type include the western coast of Mainland Bicol along Burias Pass, Burias Island and Mainland Masbate.  The rest of the region, i.e. the western part extending from Camarines Sur to the southwestern tip of Sorsogon belong to Type IV climate.  Rainfall in these areas is more or less evenly distributed throughout the year with exception of the occurrences of tropical cyclones in the vicinity, which can cause rainfall abnormalities.


Recent studies conducted by the Philippine Atmospheric and Geophysical Sciences Administration (PAGASA) showed that majority of the average rainfall in the country is due to the occurrence of tropical cyclones in the vicinity.  The southwest and northeast monsoons each contribute 7 percent while the remaining 39 percent is attributed to the combined effects of the Inter Tropical Convergence Zone, shearlines, easterly waves and other rainfall-causing weather patterns. The average annual rainfall in the region ranges from 1,900 to 3,500 millimeters.

Wind Velocity/Directions

The highest normal wind speed observed is 4 meters per second which passes the region northeasterly.  This occurs especially in the months of October to April when northeast monsoon is dominant air stream over the country.


The hottest months are May and June while the coldest months are January and February.  Higher temperatures are observed in the island provinces particularly in Masbate.


The annual average humidity is about 82 percent, almost equal to the country’s average relative humidity.

Inland Waters, Rivers and Lakes

The region’s inland waters consist of an intricate network of rivers, streams and lakes. This network serves as the natural drainage system especially in the mainland provinces.  The Bicol River is the largest river in the region and is considered as the main drainage way for the 3,771 hectares major basin area of the Bicol Plains.  It originates from streams in the southern and western parts of Camarines Sur and from the southwestern slopes of Mt. Isarog.  It meanders generally on a northwest direction from Lake Bato and joins Sipocot River at a point around seven kilometers from its mouth before discharging to San Miguel Bay, Sipocot River which is a principal tributary of the Bicol River orginates from the northern part of the province and trends southeasterly until it joins the Bicol River.

In Camarines Norte, drainage is provided by two minor rivers: Labo and Basud.  Both rivers drain areas of 913 and 270 hectares, respectively, towards the Philippine Sea.  For Sorsogon, a network of seven (7) minor rivers consist the province’s natural drainage system.  These rivers and their corresponding catchment or drainage areas are:

The narrowness and topography of the two island provinces, contribute    largely to the occurrence of numerous short minor rivers that serve as the drainage channels for ten basin areas in Masbate and three for Catanduanes.

Lakes consist another vital inland water resource for the region, environmentally and economically.  There are numerous lakes, but most have small volume water impounding capacities.  The more important freshwater ponds in the region are:  Lakes Bato, Baao and Buhi in the Bicol Plains and Bulusan and Aguingay in Sorsogon.

Lake Buhi is located at the eastern side of Mt. Iriga about 105 meters above sea level and is surrounded by hills more than 300 meters high.  It is well known for the smallest edible fish called tabios or sinarapan. The lake is believed to have been formed during Mt. Iriga’s large volume avalanche in 1628 AD, which dammed Barit River. Located at the southwestern boundary of Camarines Sur and Albay is Lake Bato.  This serves as the discharge area for numerous small rivers and streams from a large portion of Albay’s third congressional district.  The lake has an outlet waterway that runs from its northern shore towards Balatan finally discharging to Burias Pass.  The waterway is joined by another outlet channel from Lake Baao, which is located north of Bato Lake.

Bulusan Lake, on the southeastern side of Bulusan Volcano, is 635 meters above sea level.  The lake occupies the depression between two lava flow lobes abutting a hill on the southeast slope of the volcano.  With a depth of 33 meters, the lake covers an area of 16.5 hectares and has a circumference of 2,000 meters.  The intermittent Lake Aguingay is situated at a higher elevation about 1,100 meters above sea level.  This lake appears and disappears depending on the weather condition and even expands to three times the area of Bulusan Lake during extreme rainfall depths.


Slope greatly affects the use and management of the land.  It determines to a large extent the appropriate use and the optimum management practices to be adopted to prevent and/or minimize its rapid degradation.

About 56 percent of the region’s total land area is nearly level to moderately sloping lands (0-18 percent).  These are mostly the alluvial plains, mountain footslopes, floodplains and valleys.  The remaining 44 percent are mostly hilly and mountainous (above 18 percent slope) which includes the ranges of hills on the western and eastern section and some mountain peaks on the central part of the region (Figure 3.05).

Camarines Norte, Camarines Sur and Masbate have more level to gently sloping lands than hilly to mountainous areas (Table 3.03).  This physical characteristic is one major contributory factor to Camarines Sur’s achieved status as the region’s rice granary.  The suitability of this level to gently sloping areas for wetland farming is considerably high. In the case of Camarines Norte and Masbate, though they have higher percentages of level lands compared to the other slope categories, both provinces have not exhibited marked rice production figures due mainly to the limiting role of water in rice farming.  Either they lack irrigation facilities or their water supply is so minimal that it cannot sustain submerged farming practices.  Thus, other uses for this level to gently sloping lands have been found, i.e. pineapple production for Camarines Norte and livestock farming for Masbate.

In contrast, the provinces of Albay, Catanduanes and Sorsogon have more sloping lands than level areas.  This could be the main reason why abaca and coconut have become the principal crops grown in these provinces.  These crops are more or less suitable for the above terrain provided some other factors are present.


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