Quarter 3 Module 1: Volcanoes PDF

# What Is It ## What Are the Different Types of Volcanoes? ### Classification of Volcanoes The term volcano generally refers to an opening or vent on a planet's crust from which molten rock and ash (pulverized rock and pumice) may come out. You may also think or associate volcanoes with earthquake...

# What Is It ## What Are the Different Types of Volcanoes? ### Classification of Volcanoes The term volcano generally refers to an opening or vent on a planet's crust from which molten rock and ash (pulverized rock and pumice) may come out. You may also think or associate volcanoes with earthquakes. This is because when a volcano erupts, it generates enough energy to cause earthquakes or tremors. While it is true that earthquakes can be caused by volcanic activities, not all earthquakes are triggered by them. With that, you can now proceed to learning the different classifications of volcanoes. There are many types of volcanoes and they can be grouped based on the different classifications. This module has three classifications for volcanoes. These are: * Frequency of Eruption * Volcanic Features * Locations Taal Volcano in Batangas is one of the several active volcanoes found in the Philippines. ### Based on Frequency of Eruption Volcanoes are classified as active or inactive depending on the frequency of their eruption. If you encounter the term dormant, it also refers to inactive volcanoes. Many scientists consider a volcano active if it has erupted within the last 10,000 years. This definition would include approximately 1500 active volcanoes worldwide. But others would only like to consider volcanoes active if it has erupted in recorded history. Based on this definition there could only be more than 500 active volcanoes on Earth. There are also volcanoes referred to as extinct. They consider a volcano as an extinct volcano if it has not erupted in historical times. However, there are volcanoes that have long been thought to be extinct but suddenly resumed eruption lately. An example of this is the Four-peaked Volcano in Alaska, which has been considered extinct for 10,000 years but erupted in the year 2006. In this case, the term dormant or inactive is more applicable than extinct. An example of an inactive volcano is Mt. Batulao in Batangas. It has not erupted for more than 10,000 years. What scientists consider as extinct are only those that are not likely to erupt again because their supply of magma has been depleted. The question is, how sure are we that a volcano has no more magma supply? And so, scientists now prefer the terms active and inactive only, being most cautious with the term extinct. The term active is used when the volcano shows signs of activity like earthquakes and gas emissions. ### Volcanic Features Contrary to the common idea of how a volcano looks like, a "volcano" may just be a simple crack or opening in the ground from which lava and gases come out. The picture below shows the parts of a volcano. Keep in mind that what is shown below is an erupting volcano. * Magma * Ash and steam cloud * Crater * Lava * Secondary vent * Main vent * Layers of lava and ash * Magma chamber ### Composite Volcanoes Composite volcanoes or stratovolcanoes represent your idea of what a volcano is. It is a tall mountain with a crater on top from which pyroclastic (or "fire-broken") materials, gases, and lava escape. It is in fact the most common type of volcano. Its height is explained by the volcanic materials that eventually cool and harden after eruption, piling on top of another with subsequent eruptions. Its magma has a high content of silica, making the lava thick or viscous and capable of reaching great heights. Some of the composite volcanoes are known for their violent eruptions. ### Shield Volcanoes The profile of a shield volcano is very different from that of a composite volcano. A shield volcano is almost flat and broad like a warrior's shield. Its magma has a lower percentage of silica and is thus less viscous than that of a composite volcano. During an eruption, its lava flows easily and reaches a great distance from the crater. Mauna Loa, Kilauea, and other Hawaiian volcanoes are shield volcanoes. As of today, there are no shield volcanoes discovered in the Philippines. This might be because of the viscosity of the magma in the Philippines. ### Cinder Cone Volcanoes The last classification is the cinder cone. Cinder cone volcanoes are usually small. They are made up of pyroclasts or fragments of volcanic rocks that form steep slopes around their wide crater. They often form in groups near a large volcano. Most of them erupt only once. ### Based on Location The Earth is 71% water and although we may be familiar with continental volcanoes, the land part of the earth is only about 29%. This means that it is possible that there are many volcanoes that are located under the sea. Volcanoes which can be found on land are referred to as continental volcanoes. However, there are volcanoes that lie beneath the ocean and high-latitude countries like Iceland. Most of the volcanoes that you know in the Philippines like Mt. Pinatubo, Mt. Apo, Mayon Volcano, and Taal Volcano are continental volcanoes. Submarine volcanoes are underwater vents on certain zones of the ocean floor from which magma can erupt. An example of a submarine volcano in the Philippines is Ibugos, which is located near the island of Ibugos at the southernmost end of Batanes Islands. On the other hand, subglacial volcanoes are located either underneath a glacier itself or under the water which is inside a glacier. These volcanoes have different shapes compared to the other types of volcanoes. # What Happens When Volcanoes Erupt? ## Volcanic Eruption Hazards When a volcano erupts, there may be lava flows, poisonous gases, and lowering of atmospheric temperatures. Extremely hot lava flows burn and destroy everything on its path. Lahar, a mudflow that includes all debris along its path, which is usually a river valley, is composed of a very thick slurry pyroclastic material, rock debris, and water. It can wash out towns near the volcano. While lava flow is made up of molten rock from the volcano, lahar is a fast-moving muddy water with pyroclastic material from the volcano. Other damages from the volcano include volcanic ash fall, which can be abrasive, acidic, and odorous. This can eventually cause lung damage in infants, the elderly, and those who have respiratory illnesses. This acidic ash can also damage electrical and mechanical equipment. It can also mix with rain and collapse roofs. A single eruption can cause damage hundreds of kilometers away from the volcano. Other hazards include earthquakes, flash floods, landslides, acid rain, and fire. ## Benefits from a Volcanic Eruption Volcanic eruptions are one of the most dangerous natural phenomena that occur on Earth. The poisonous gases, pyroclastic materials, and earthquakes are dangerous to human settlement near volcanoes. However, there are also a lot of benefits that are brought by the eruption of the volcano. Every eruption is an event that brings a fresh supply of nutrients to the soil through breakdown and chemical decomposition of rocks. This was observed in Mt. Pinatubo's eruption in 1991 and Taal Volcano in 2020. Another beneficial outcome of volcanic eruptions is formation of landforms. New islands can be formed from explosions of submarine volcanoes in shallow waters. Similarly, continental volcanoes close to shore widen the land when their lava flow reaches the sea and harden when cooled by seawater. One of the most dangerous hazards of volcanic eruptions is the lahar flow. This is particularly dangerous when it comes from the slopes and gets washed toward communities at the foot of the volcano. One of the greatest damages caused by lahar was observed when Mt. Pinatubo erupted in 1991. During the eruption of Mt. Pinatubo, typhoon Diding, was also passing through the country. The typhoon brought in rain, caused lahar to flow and damaged a large portion of Pampanga.