Lesson 1: Distribution of Active Volcanoes

• The Philippines is one of the countries in the world with high disaster risk index. It means that we are vulnerable to different natural hazards like storms, floods, and most of all seismic activities.
• Several earthquakes occur everyday but most are weak and generally cannot be felt by people.
• Volcanoes and mountains are the most common landforms in the archipelago.
• Each landform has unique legendary stories on its origin but scientiests argue that its formation is because of the movement of Earth's crust.
• According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), there are 23 active volcano and more than 400 mountains in the country.
• There are four different layers consisting Earth.
• The crust consists of tectonic plates that according to the theory of plate tectonics, change shape and position over time due to convection currents beneath the plates.
• Heat fluctuation at the Earth's mantle produces the convection currents.
• The ocean floors are spreading from the center, sinking at the edges, and being regenerated.
• The constant movement of the plates forms ocean basins, mountain ranges, islands, volcanoes, and earthquakes.
• The Philippines is an archipelago blessed with beautiful natural landforms that include dormant and active volcanoes. Alongside with the aesthetics value provided, howeever, is the high risk of disaster.
• Earthquakes due to volcanic activities are very common it the country. It is likely that volcanoes are present in every region.
• Earth's surface is composed of major and minor tectonic plates
• These tectonic plates overlying the semi-solid, plastic-like asthenosphere are in constant motion. It tends to move towards or away from each other, thus, forming mountains or volcanoues.
• In the course of volcanic formation, molten rocks or magma makes its way up to the surface and fill the spaces between the two colliding plates.
• The Philippines is in a zone within the Pacific ocean that covers a collection of moving plate edges forming a "ring" of volcanoes that cause earthquakes. This region is called the Pacific Ring of Fire or the Circum-Pacific Belt.
• The Pacific Ring of Fire is a 40,000-kilometer, horshoe-shaped basin that is associated with oceanic trenches, volcanic arcs, and plate movements.
• The Pacific Ring of Fire includes several volcanoes from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, into New Zealand, and even closed by several active and dormant volcanoes in Antartica.

  • Around 75% of the world's active and dormant volcanoes can be found in this region.
• The Philippines is an archipelago surrounded by subducting plates that provide the ideal condition for volcanic formation resulting to highly active seismicity and volcanism in the country.
• Tectonic activity in the Philippines is one of the most active in the world characterized by a number of earthquakes and active volcanic activities. This is due ot the interaction of tectonic plates comprising the archipelago.
• Most active volcanoes in the Philippines are found in volcanic arcs.
• Volcanic arcs are chains of volcanoes formed by subducting plates. It is formed through the subduction of an oceanic tectonic plate under another tectonic plate.
• There are five distinct volcanic arcs in the Philippines, where the volcanically active region can be found, namely: the Luzon Volcanic Arc, the East-Philippine Volcanic Arc, the Negros-Panay Arc, the Sulu-Zamboanga Arc, and the Cotabato Arc.
• Emission of gases, flowing of lava outside the surface and sudden violent explosive bursts are some of the chracteristics that describe a volcanic activity.
• Buoyant molten rock also known as magma rises towards the surface, eventually forming a magma chamber.
• Some of these molten materials may ascend to the Earth's surface and are extruded as lava during a volcanic eruption.
• Active volcanoes are those that erupted within the last 10,000 years. This can be indicated by historical reports or radiometric dating.
• As of 2008, PHIVOLCS listed 23 active, 26 potentially active, and 281 inactive volcanoes.
• Out of 23 active volcanoes, 21 had historic eruptions. This number may still increase depending on future tectonic activites.
• Most volcanoes in the country are subduction-related although there are few exotic types.
• Mayon Volcano, located in Albay, is the most active volcano in the country. It is famous because of its almost perfect cone shape. It is a stratovolcano with an elevation of 2.46 kilometers and a base diameter of 20 kilometers.
• A stratovolcano is one of the three types of volcano commonly characterized by a conical shape, nearly symmetrical structure with a steep summit and more gradually sloping sides. Its latest eruption activity was a lava dome growth on January 2018.
• Another active volcano being monitored by PHIVOLCS is Taal Volcano in Batangas. It is a volcano caldera composed of several active volcanic landforms making it a complex type of volcano.
• A caldera is a volcanic landform associated with depression in a circular form and has a diameter exceeding one kilometer. Its crater lake is 1.9 kilometers in diameter and located 4 meters above sea level.
• It is a popular misconception that the crater that can be in Tagaytay is the Taal volcano itself. It is the parent volcano of Taal called Binintian Volcano.
• The Taal caldera is 25 kilometers across and within it is Taal Lake, which has an area of 267 km2 and located 2 meters above sea level.
• There are a total of 47 craters and four maars in Taal Volcano Island. The most recent activity of this volcano was noted last April 2011.
• Kanlaon Volcano is another active stratovolcano located in Negros Oriental. It is 2.435 kilometers in elevation with a base diameter of 30 kilometers. Its latest activity was on June 18, 2016, according to PHIVOLCS.
• Located in the province of Sorsogon is Bulusan Volcano. It is a stratovolcano formed inside a caldera. It has several craters and fractures along with four different hot springs adjacent to it. It is 1.599 kilometers in height and has a base diameter of 15 kilometers. Its latest activity was March 2, 2017.
• Potentially active volcanoes do not have any historical record of any eruption but are considered as morphologically young. There are also suspected seismic activity and documented local ground deformation.