Seasons The climate in Irosin belongs to the Type II of the Corona System, the classification of Philippine climates. It must be noted that the climate is mainly influenced by the proximity of the place to a great body of water and the effects of elevation and mountain barriers. In this regard, Irosin’s topographical shape and its proximity to the China Sea to the west and Pacific Ocean to the east makes the climate fall under the Tropical Wet with short dry season of the Tropical Rainy Climate as classified under the world climate. In the northeast and southeast section of the municipality where the remaining forest cover are still continue reading : Climate

Water Resources

Water resources are abundant in Irosin. They flow down to the valley floor from rivers, creeks and streams coming from springs at the slopes of the surrounding mountains. There are 35 water tributaries with an approximate gross length of 45 kilometers. Cadac-an River is the biggest and longest river and has four main tributaries and sixteen collateral feeders covering a length of 35 kilometers. This river originates from the slope of the Bulusan Volcano to the Maraot Banwa Mountain ranges and stretches to the valley floor of Irosin and Juban before it flows out to Sorsogon Bay. The average water flow volume is 752.7 gallons per second.

Land Resources

Land Classification Land resources of the municipality are categorized into protection lands and production lands. Protection lands in the municipality are those peaks and mountainous areas with remaining forest cover and considered as critical watershed, these are the section of Bulusan Volcano Natural Park (BVNP) proclaimed as a protected area under the National Integrated Protected Area System (NIPAS) Act, Mount Jormajan and the mountain ranges in Cawayan and Tabon-tabon. Mount Jormajan and the mountain ranges in Cawayan and Tabon-tabon were classified as alienable and disposable lands however the existing primary and residual forest vegetation in the area rationalizes forest the protection. The total area of protection lands including the easements continue reading : Land Resources


Rock Formation Irosin’s basal soil and rock formation and composition are primarily of volcanic origin. The greater geologic formation at the plains of the valley floor is sedimentary rocks, alluvium and river deposits. In the northwest and southwest sectors is of recent alluvial plain deposit, igneous rocks, tuff, pumice and tuffaceous clastic rocks. The north is composed of undifferentiated Bulusan volcanic debris and mudflow deposits, pyroclastic flow deposits, lava dome deposits, recent alluvial plain deposit and Pre-Bulusan caldera deposits. At the southeast are mostly volcanic flows, mostly andesitic in composition. Mount Jormajan and Tulong Pansod the two prominent peaks have volcanic deposits as well as the areas surrounding the Bulusan continue reading : Geology


Terrain Irosin has a very irregular terrain characterized by the plain on the valley floor, secluded plains and valleys on the mountaintops, undulating hills and mountain peaks. The valley of which Irosin is famous is located at the floor of Irosin caldera. It is a contiguous zone extending from the south to the northeast occupying a quarter or 25.85% of the gross land area with 5 kilometers and 8.3 kilometers at the narrowest and widest point respectively. Also it is where the geographic center of the municipality where the 5 urban barangays are located.