Science 9 Unit 15 Volcanoes Study Guide PDF

Unit 15 Understanding Volcanoes Table of Contents Introduction 3 Essential Questions 4 Review 4 Lesson 15.1: Volcanoes...

Unit 15 Understanding Volcanoes Table of Contents Introduction 3 Essential Questions 4 Review 4 Lesson 15.1: Volcanoes 5 Objective 5 Warm-Up 5 Learn about It 6 Key Points 12 Web Links 12 Check Your Understanding 13 Challenge Yourself 14 Lesson 15.2: Types of Volcanoes Based on Structure 15 Objectives 15 Warm-Up 15 Learn about It 17 Key Points 20 Web Links 21 Check Your Understanding 21 Challenge Yourself 22 Lesson 15.3: Active and Inactive Volcanoes 23 Objective 23 Warm-Up 23 Learn about It 24 Key Points 30 Web Links 30 Check Your Understanding 31 Challenge Yourself 31 1 Lesson 15.4: Volcanic Eruption 32 Objective 32 Warm-Up 32 Learn about It 33 Key Points 39 Web Links 40 Check Your Understanding 40 Challenge Yourself 41 Lesson 15.5: Materials Emitted from Volcanic Eruptions 42 Objectives 42 Warm-Up 42 Learn about It 43 Key Points 50 Web Links 50 Check Your Understanding 50 Challenge Yourself 51 Lesson 15.6: Harnessing Volcanic Energy 52 Objective 52 Warm-Up 52 Learn about It 53 Key Points 57 Web Links 57 Check Your Understanding 58 Challenge Yourself 59 Laboratory Activity 60 Performance Task 61 Self Check 62 Key Words 63 Wrap Up 65 Photo Credits 66 References 67 2 GRADE 9 | SCIENCE Unit 15 Understanding Volcanoes Whether they are towering cones or long fissures, undersea ridges or enormous calderas, volcanoes allow us a glimpse into our planet’s fiery interior. They play a significant role in maintaining the Earth’s internal energy balance and are among the most dynamic and spectacular representations of geologic processes. There are many types of volcanoes, and some of them do not exhibit volcanic activity anymore. How are volcanoes classified? How do these impact human society? Understanding volcanic characteristics and occurrence is essential to geology, allows us to better prepare for volcanic hazards, and helps us harness volcanoes for energy. There are established ways that are currently being practiced for this to be possible. How do humans harness volcanic energy? 3  Essential Questions At the end of this unit, you should be able to answer the following questions. describe the different types of volcanoes; differentiate between active and inactive volcanoes; explain what happens when volcanoes erupt; and illustrate how energy from volcanoes may be tapped for human use. Review Plate tectonics theory states that the lithosphere is broken into plates which move independently. Their interactions at their boundaries result in different processes and landforms. Plate boundaries include divergent boundaries where they move apart; convergent boundaries where they move toward each other; and transform boundaries where they slide past one another. Magma is defined as subsurface molten rock material produced by partial melting of the uppermost mantle and crust. It contains melt (liquid rock ions), dissolved volatiles, crystals, and rock fragments. Lava is magma that is erupted onto the surface. 4  Lesson 15.1: Volcanoes Objective In this lesson, you should be able to: understand why and how volcanoes form. In 1991, central Luzon became ground zero for one of the largest volcanic eruptions in history: Mt. Pinatubo. What processes could cause an erstwhile quiet mountain to eject 10 km3 of material into the atmosphere? The local Aetas believe the mountain houses their deity Apung Pinatubu, who hurls rocks when angered. Geologic studies, instead, indicate that volcanoes erupt where magma rises to and emerges at the surface. What processes and settings are used to define a volcano? Warm-Up Volcano in a Beaker You can recreate a very simple volcanic eruption using household items. This activity will show you how. Materials beaker water stove or hot plate candle wax sand Procedure 1. Place a 1-inch cube of candle wax inside a beaker. Place around 3 inches of sand to cover the candle wax. Fill the beaker with enough water to submerge the sand with around 2 inches of extra water on top. 2. Allow the sand to completely settle. 3. Heat the beaker using a hot plate. Observe what happens to the wax. 5 Guide Questions 1. Why did the wax bubble to the surface? 2. Would the results be the same without sand? Learn about It Volcanoes Volcanism is the process in which magma, which is buoyant against rock, rises to the surface and becomes lava. Any vent or built-up mountain where lava, pyroclastic materials, and/or gases erupt is called a volcano. Note that this definition is not restricted to mountainous landforms erupting lava, but includes such phenomena as fissure eruptions, solfataras, etc. Fig. 2. Global distribution of volcanoes and plate boundaries. 6 Geologic Settings of Volcanism The location where volcanism occurs largely dictates the types of magma generated, and thus the style of volcanism. The Plate Tectonics theory states that tectonic processes (which include volcanism) are directly influenced by plate interactions at their boundaries. Indeed, most eruptions occur along plate boundaries, while a smaller number occur at intraplate hot spots. Divergent boundaries At divergent boundaries, volcanism manifests as ridges or fissures where lavas erupt. Here, melted rocks are produced by decompression melting or the anatexis (partial melting) of the hot asthenosphere due to decreased lithostatic pressure exerted by the thinned overlying lithosphere. Decompression melting occurs when portions of Earth’s mantle moves to an area of lower pressure, and this is usually because of movements going in an upward direction. This results in the melting of rocks into magma. Fig. 3. Rocks start to melt even with low temperature due to difference in pressures. 7 Divergent boundaries mostly occur between two oceanic plates, and the volcanism at these boundaries manifest as mid-ocean ridges. Mid-ocean ridge (MOR) volcanism accounts for the production of a new oceanic crust that covers 70% of the Earth’s surface. MOR volcanoes develop along the parallel fractures formed during rifting, giving rise to an elongated volcanic chain parallel and proximal to the plate boundary, or ridge axis. These volcanoes erupt basalt which forms into rounded pillow lava due to the surrounding pressure. Water is heated as it circulates near the volcanoes, and is erupted through hydrothermal black smokers. Divergent boundaries occurring within continental plates are known as continental rifts where diverse manifestations of volcanism can occur. This is due to the anatexis of both the crust and the mantle, creating complex blends of basaltic fissure eruptions, linear chains of tephra cones, rhyolite domes, and alkalic stratovolcanoes erupting rare carbonatite (e.g. Ol Doinyo Lengai). Convergent Boundaries At convergent boundaries, volcanism is restricted to convergence involving an oceanic plate (i.e. involving subduction); volcanism will cease once collision occurs. Subduction causes flux melting (volatile-induced) of the mantle wedge between the subducting plate and the overlying plate. Flux melting occurs once substances like volatiles and water are added to rocks, resulting in melting into magma. It is the rock in the upper layer of the mantle that melts if this happens in an area of subduction. Fig. 4. Rocks melt as a result of the addition of volatiles. 8 A portion of the magma rises and reaches the surface, resulting in curving volcanic chains called arcs, which follow the shape of trenches. Arcs growing on the oceanic crust are called island arcs (e.g. most Philippine volcanoes) while those growing on continents are called continental volcanic arcs (e.g. the Cascades, the Andes). These arcs surround the Pacific Ocean (including the Philippines), forming a 40 000 km horseshoe-shaped region of high volcanism and seismicity known as the Pacific Ring of Fire. Fig. 5. Schematic of convergent continental-oceanic subduction, forming a continental volcanic arc. Convergent boundaries typically produce the basalt, andesite, dacite, rhyolite (BADR) suite of magmas, which are silica-saturated and mafic-depleted. Volcanoes here commonly form composite cones such as Mt. Mayon and Mt. Fuji and account for most of the subaerial volcanoes on the planet. Intraplate Volcanism Intraplate volcanism occurs due to the ascent of mantle plumes to the base of the lithosphere. This creates a region of abnormally high temperature known as a hot spot, which triggers anatexis of the overlying oceanic or continental plate. Hot spot volcanism manifests as a chain of extinct volcanoes similar to a conveyor line, with only the youngest volcano being active. This is due to the fact that hotspots are stationary relative to an overlying plate; a volcano forms above the hotspot, and as the plate moves, the volcano is robbed of its magma source and becomes extinct. Meanwhile, a new volcano forms at the location of the plate which is present above the hot spot, and so on. 9  Fig. 6. Formation of an ocean island chain by the motion of a tectonic plate over a fixed mantle plume. Hot spots underlying an oceanic plate erupt ocean island basalts, and form chains of volcanic islands. The best example is the Hawaiian Island-Emperor Seamount Chain. The Hawaiian Islands are the younger subaerial volcanic islands (one of which is active); the orientation of the islands forms a track, which represents the recent movement of the Pacific Plate. Northwest of the Hawaiian Islands is the submarine Emperor seamount chain, which was produced by the same hot spot as Hawaii. It follows a different direction from the Hawaiian Islands, marking the shift in the Pacific plate’s direction of movement ~40 Ma. 10  Fig. 8. The Yellowstone Caldera chain, an example of continental intraplate volcanism. Hot spots are also found beneath continental plates, where they can erupt more diverse magmas like rhyolite. Continental hot spots are typically explosive and produce large deposits and enormous calderas. An example is the Yellowstone Caldera, which is the youngest in a chain of massive calderas running across the mid-western USA. Under specific circumstances, mantle plume volcanism can produce huge sheets of lava flows known as flood basalts. These can be built up over time, and many successive flood basalt eruptions can form a plateau of lava flows known as a large igneous province (LIP). Examples of LIPs include the Deccan Traps in India, the Siberian Traps of Russia, and the Benham Rise under the Philippine Sea. 11  Key Points Volcanism is the process in which magma, which is buoyant against the rock, rises to the surface and becomes lava. Volcanic activity varies and not always seen in the form of a mountainous landform spouting lava. At divergent boundaries, the manifestation of volcanism is in the form of ridges or fissures where lava erupts. At convergent boundaries, volcanism is restricted to convergence involving an oceanic plate. Intraplate volcanism occurs due to the ascent of mantle plumes to the base of the lithosphere. Continental hot spots are typically explosive and produce large deposits and enormous calderas. Web Links For further information regarding this lesson, see the video links below: Supervolcanoes produce much more emissions than normal volcanoes. For more information, watch “The colossal consequences of supervolcanoes - Alex Gendler”: TED-Ed. 2014. ‘‘The colossal consequences of supervolcanoes”’ https://www.youtube.com/watch?v=hDNlu7Qf6_E How do Large Igneous Provinces Form? To learn more, watch “Large Igneous Province Formation” by OceanDrilling: TED-Ed. 2012. ‘‘The wacky history of the cell theory”’ https://www.youtube.com/watch?v=MKmf9BUukC0 12  Check Your Understanding A. Identify the term being described by the statements below. 1. Any vent or built-up mountain where lava, pyroclastic materials, or gases erupt is known by this term. 2. This term refers to the volcanoes found at the divergent boundaries occurring between two oceanic plates. 3. Divergent boundaries occurring within continental plates are known by this term. 4. These are arcs growing on the oceanic crust. 5. Arcs growing on continents are known by this term. 6. Convergent boundaries usually produce this suite of magmas. 7. Intraplate volcanism creates a region of abnormally high temperature. This region is known by what term? 8. Mantle plume volcanism can produce huge sheets of lava flows known by this term. 9. Many successive flood basalt eruptions can form a plateau of lava flows known by this term. 10. MOR volcanoes erupt basalt, and the surrounding pressure forms this type of lava. B. Identify if the statement is true or false. 1. The Benham Rise is an example of a LIP. 2. The Yellowstone Caldera is an example of an ocean island basalt. 3. The Plate Tectonics theory states that tectonic processes are directly influenced by plate interactions at their boundaries. 4. At divergent boundaries, volcanism manifests as ridges or fissures where lavas erupt and produce flux melting. 5. At convergent boundaries, subduction causes decompression melting. 13  Challenge Yourself Answer the following questions. 1. Is volcanism possible without high amounts of heat? 2. Why are most Philippine volcanoes part of island arcs? 3. How do volcanoes form? 4. What is the difference between lava and magma? 5. Scientists believe that LIP volcanism has caused mass extinctions in the past. Why is this so? 14  Lesson 15.2: Types of Volcanoes Based on Structure Objectives In this lesson, you should be able to: differentiate between volcanic architectures and why they form; and describe the different types of volcanoes. The different settings and processes of anatexis produce diverse magmas, each with specific properties and behaviors. This diversity ensures that once they reach the surface and erupt, they will form equally diverse types of vents, conduits, and debris. In other words, the diversity of magmas leads to the different structures of volcanoes. What are these volcanic structures, and how are they formed? Warm-Up Shaping Volcanoes Volcanoes may be classified based on the type of mound that they have. This activity will help illustrate some of these mound types. Materials: brown and red clay illustration board Procedure: 1. Use a piece of illustration board as a base. Use the brown clay to represent the mound, and red clay to represent lava. 2. Shape one volcano to be at least 5 inches high. The volcano is supposed to have a steep edge. You may pattern it after the photo below. Place a piece of red clay at the crater. 15 3. Shape another volcano to be dome-shaped, no more than 2 inches high. Make sure that it is wide. You may pattern it after the photo below. Place a piece of red clay at the crater. 4. Shape your last volcano as a small cone no more than 2 inches high. Make sure that the edges are steep. You may pattern it after the photo below. Place a piece of red clay at the crater. 16 Guide Questions: 1. Based on the models above, what are the differences in slope between the volcano types? 2. Do all volcanoes have mounds? Learn about It The Parts of a Volcano There is a common misconception that the interior of the Earth is a frothing sea of molten magma, filling up an otherwise empty and enormous cavern. Apart from the outer core, which is a molten iron and nickel alloy, the rest of the Earth is solid. As discussed previously, melting occurs only at specific geologic settings near the surface; melting can never occur deeper into the Earth due to great lithostatic pressures. Fig. 9. Cross-section of a typical volcano, with labeled parts. Magma is thus always surrounded by rock which is denser. This allows the magma to rise buoyantly, but not always directly to the surface. Typically, magma accumulates underground in an open space or an area of a highly fractured 17 substrate, known as a magma chamber. Some of this trapped magma will crystallize into intrusive rock, but some will rise to the surface through conduits, or openings, and erupt, forming a volcano. Conduits may take the form of a central vent (shaped like a vertical pipe), a flank vent (smaller conduits issuing from a central vent), or an elongated crack, called a fissure. Dikes are rock sheets that can form from magma when they seep into cracks in rocks. Sills are beds of rocks that form as a result of rock formation between layers of older materials. Over time, solid volcanic debris accumulates around a conduit, forming a mound or cone. The end of a pipe-like conduit at the top of the mound is the crater; eruptions issuing from the crater are summit eruptions. Eruptions issuing from flank vents can produce parasitic cones around a mound. During especially large eruptions, a mound may be blown apart, or the magma chamber may be sufficiently drained such that the mound collapses under its own weight due to the suddenly empty space beneath. In either case, a caldera forms, which is a large circular depression with steep walls and is at least 1km wide. Taal Lake is an example of a collapsed caldera. Classifying Volcanoes Based on Mound Structure In terms of mound structure, geologists distinguish between three types. Note that this only applies to subaerial volcanoes. Table 1. Comparing the Different Types of Volcanoes Height Shape Slope Examples Small (up to Circular Lava dome around 200 mound or Steep Didicas meters high) dome-shaped Very tall (up to Like a shield Gentle slope, Shield volcano around 9,000 set on the Mauna Kea ~10° meters high) ground, broad Composite Tall (up to Roughly volcano 8,000 meters symmetrical Steep Mayon (Stratovolcano) high) mound Small (up to Roughly Taal’s Pyroclastic around 400 symmetrical Steep Binintiang cone meters high) mound Malaki 18 Lava Domes Lava dome mounds are roughly circular. These domes form when viscous lava cannot flow too far due to the viscosity and cools into a mound. Lava domes are usually smaller compared to the other types of volcanoes as a result. An example of a lava dome volcano in the Philippines is the Didicas volcano in Cagayan. Shield Volcanoes Shield volcanoes are broad gently-sloping mounds shaped like a soldier’s shield. They encompass the largest area of the three subaerial volcanoes. They form when low-viscosity basaltic lava is allowed to flow freely from a vent; over time, these flows stack upon each other, forming the volcano. An example is the Hawaiian mountain Mauna Loa. Composite Volcanoes Composite volcanoes, also known as stratovolcanoes, are tall, steep, conical mountains. They form by the accumulation of various successive erupted materials; differing layers of pyroclastic flows and lava flows. Occurring at subduction zones, stratovolcanoes commonly erupt the more viscous lavas. This is why most catastrophic eruptions are produced by stratovolcanoes. An example is Mt. Mayon in the Bicol Region. 19 Pyroclastic Cones Pyroclastic cones are small, steep mounds composed of tephra or volcanic fragments formed by explosive eruptions. They usually occur as groups in volcanic fields. Depending on the size and nature of the comprising fragments, pyroclastic cones may be further classified into scoria cones, tuff cones, or cinder cones. An example of a pyroclastic cone is Binintiang Malaki, the largest flank volcano of Taal. Pyroclastic cones are often (but not always) monogenetic, meaning they form over one eruptive event. Other commonly monogenetic landforms are tuff rings and maars. These form during shallow phreatomagmatic eruptions which will be discussed in subsequent lessons. Examples of maars are the Seven Lakes of San Pablo, Laguna. Key Points Volcanoes have distinct parts. These include the crater, magma chamber, conduits, dikes, sills, and the vents which could be a central vent, flank vent, or fissure. Volcanoes may also be classified based on mound structure. 20  ○ Lava domes are roughly circular. These domes form when viscous lava cannot flow too far due to the viscosity and cools into a mound. ○ Shield volcanoes are broad gently-sloping mounds shaped like a soldier’s shield. ○ Composite volcanoes, also known as stratovolcanoes, are tall, steep, conical mountains. ○ Pyroclastic cones are small, steep mounds composed of tephra or volcanic fragments formed by explosive eruptions. Web Links For further information regarding this lesson, see the video links below: For more information about the types of volcanoes, watch “Volcano types: Cinder cone, composite, shield, and lava domes explained - TomoNews”: TOMONews US. 2017. ’ https://www.youtube.com/watch?v=y2Yd-XzMcO4&t=5s For more information about how volcanoes form, watch “Volcanoes 101” by National Geographic: National Geographic. 2015. ‘‘Volcanoes 101”’ https://www.youtube.com/watch?v=yDy28QtdYJY&t=5s Check Your Understanding A. Identify if the statements are true or not. Write true if it is, and false if otherwise. 1. The mound of earth surrounding the crater is called a caldera. 2. Shield volcanoes form when low-viscosity basaltic lava is allowed to flow freely from a vent. 3. Composite volcanoes are small, steep mounds composed of tephra or volcanic fragments formed by explosive eruptions. 4. Pyroclastic cones are tall, steep, conical mountains. 5. Magma accumulates underground in an open space or an area of highly fractured substrate known as a flank vent. 21 B. Identify the parts of a volcano. Challenge Yourself Answer the following questions. 1. Why does magma tend to rise above the ground? 2. How do calderas form? 3. How can low-viscosity lava form shield volcanoes? 4. How is it possible to form multiple pyroclastic cones from one eruptive event? 5. Why is there a need to classify volcanoes? 22  Lesson 15.3: Active and Inactive Volcanoes Objective In this lesson, you should be able to: differentiate between active and inactive volcanoes. The hazard posed by volcanoes in society necessitates a monitoring system that facilitates disaster risk reduction and provides a warning system. In the Philippines, volcano monitoring is conducted by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). Under the government’s Department of Science and Technology, PHIVOLCS has a nationwide network of monitoring stations, equipment, and teams of geologists that continuously monitor volcanic and seismic hazards. What system does PHIVOLCS use to monitor and reduce volcanic hazards? Warm-Up Mapping Active and Inactive Volcanoes Materials: internet-connected device red and black pins map of the Philippines (physical copy) Procedure: 1. Refer to the sites below for more information on active and inactive volcanoes of the Philippines. 2. Use the information in the sites to pin the province of the active volcanoes using a red pin, and inactive volcanoes with black pins. 3. The following are the volcanoes that you are supposed to pin: Mayon, Taal, Arayat, Lake Palakpakin, Talinis, Isarog, and Lake Pandin 23  4. Use the sites below: Active Volcanoes of the Philippines PHILVOLCS. n.d. List of Active Volcanoes. https://web.archive.org/web/20180119150540/http://www.phivolcs.dost.gov.ph/html /update_VMEPD/vmepd/vmepd/active.htm Inactive Volcanoes of the Philippines PHILVOLCS. n.d. List of Inactive Volcanoes. http://web.archive.org/web/20180422002134/https://www.phivolcs.dost.gov.ph/html /update_VMEPD/vmepd/vmepd/inactive.htm Guide Questions 1. Based on the number of volcanoes in the sites, do you think there is a high amount of volcanic activity in the Philippines? 2. Why do almost all Philippine provinces have volcanoes? Learn about It Due to its unique geologic setting, the Philippines has no shortage of volcanism and seismicity. While round-the-clock monitoring is effective, PHIVOLCS cannot monitor every one of the hundreds of volcanoes in the country. Hence, they use a classification system to single out the most dangerous volcanoes, in order to maximize their efforts. The classification system is based on volcanic activity. It is similar to activity classifications by USGS and other national agencies. Active Volcanoes Active volcanoes have eruptive histories; there has been a recorded eruption in historical times. Alternatively, dateable erupted materials confirm that they erupted within the last 10,000 years. There are currently 23 active volcanoes being monitored by PHIVOLCS. 24 Fig. 15. A PHIVOLCS map detailing the distributions of Philippine volcanoes and their designations. 25 The four most active volcanoes are Mt. Kanlaon, Mt. Bulusan, Taal Volcano, Mayon Volcano. Mt. Kanlaon Mt. Kanlaon’s last eruption was in 2016, with a total of 30 eruptions; The highest mountain in the Visayas is a complex stratovolcano with several flank vents around the spectacular summit crater. Fig. 16. A photo of Mount Kanlaon. Mt. Bulusan Mt. Bulusan’s last eruption was in 2017, with a total of 18 eruptions; Mayon’s often overlooked neighbor, Bulusan is part of the Irosin Caldera, a complex volcanic field spanning most of Sorsogon. Fig. 17. A photo of Mount Bulusan. 26 Taal Volcano Taal Volcano’s last eruption was in 2020, with a total of 34 eruptions; A geologically complex region, Taal Lake represents a collapsed caldera covering 267 km2. Volcano Island is the main activity region, surrounded by several parasitic pyroclastic cones. Mayon Volcano Mayon Volcano’s last eruption was in 2018, with a total of 52 historical eruptions; The famous “perfect cone” signifies Mayon’s structure as a stratovolcano, dominating the plains of Albay. Potentially Active Volcanoes Potentially active volcanoes, similar to dormant volcanoes, have no eruptive histories and no recent dateable materials, but are morphologically recent (i.e. un-eroded) and in some instances present signs of activity or remnant heat. PHIVOLCS lists 26 potentially active volcanoes. Some of the most prominent are Mount Apo, Cuernos de Negros, Mount Isarog: Mount Apo Mount Apo is the country’s highest peak, which still showcases sulfuric steam and in fact, hosts a geothermal plant. Mount Apo is a stratovolcano and is considered a national park. Fig. 18. A photo of Mount Apo. 27 Cuernos de Negros Cuernos de Negros is also known as Mount Talinis. Dominating southeast Negros Island, this range exhibits areas of geothermal alteration and steaming, and will soon host a geothermal plant. Mount Talinis is a popular tourist spot due to the Balinsasayao Twin Lakes National Park. Fig. 19. A photo of Mount Talinis. Mount Isarog Isarog is located in Camarines Sur. It is a stratovolcano famous for its rich and unique biodiversity. Fig. 20. A photo of Mount Isarog. 28 Inactive Volcanoes Inactive volcanoes have no eruptive histories, are heavily weathered, and will never erupt again. PHIVOLCS lists 281 inactive volcanoes, with several being unnamed peaks. Some notable inactive volcanoes in the Philippines include Mount Arayat, Seven Lakes of Laguna: Mount Arayat This volcano is located in Pampanga, on the island of Luzon. Mount Arayat’s hiking trails are well-known, and there is a rich history of folklore and superstition surrounding the mountain. Fig. 21. A photo of Mount Arayat. Seven Lakes of Laguna Also known as the Seven Lakes of San Pablo. These lakes are the following: Lake Calibato, Lake Palakpakin, Lake Muhikap, Lake Sampaloc, Lake Yambo, Lake Pandin, and Lake Calibato. All of these are inactive crater lakes found in San Pablo, Laguna. 29  Key Points PHIVOLCS uses a classification system to track the activity of Philippine volcanoes. Active volcanoes have eruptive histories; there has been a recorded eruption in historical times. Potentially active volcanoes have no eruptive histories and no recent dateable materials but are morphologically recent. Inactive volcanoes have no eruptive histories, are heavily weathered, and will never erupt again. The Philippines is situated in the Ring of Fire, meaning that there is a significant amount of volcanic activity in the country. Web Links To see a video of some of the most active volcanoes on Earth, watch “The Most Active Volcanoes in the World”: The Richest. 2014. ’The Most Active Volcanoes in the World’ https://www.youtube.com/watch?v=MoDrrEb1Tf0 To see a feature on two of the Seven Lakes of San Pablo, watch “Discover the Twin Lakes in San Pablo City, Philippines called Pandin Lake and Yambo Lake” by ABS-CBN News: TV Patrol. 2015. ‘‘Discover the Twin Lakes in San Pablo City, Philippines called Pandin Lake and Yambo Lake”’ https://www.youtube.com/watch?v=Njy0N78twa4 30  Check Your Understanding A. Answer the questions below. 1. What are the three classifications of volcanic activity according to PHIVOLCS? 2. Give an example of each. 3. Name the four most active volcanoes in the Philippines. 4. Name two of the seven lakes of San Pablo. 5. What is the tallest volcano in the Philippines? B. Identify if the statements are true or false. 1. Active volcanoes have the potential to still erupt. 2. Mayon is an inactive volcano. 3. Potentially active volcanoes have no eruptive histories. 4. Active volcanoes erupted within the last 10,000 years. 5. Inactive volcanoes have the potential to erupt. 6. Lake Palakpakin is a stratovolcano. 7. Lake Muhikap and Lake Sebu are part of the seven lakes. 8. The seven lakes is an active volcano. 9. All of the Philippines’ inactive volcanoes are named peaks. 10. Potentially active volcanoes do not give off traces of heat. Challenge Yourself Answer the following questions. 1. Why are active volcanoes the ones being monitored by PHIVOLCS the most closely? 2. Why should potentially active volcanoes also be monitored? 3. What are extinct volcanoes? 4. What are dormant volcanoes? 5. Why is a classification system necessary for volcanic activity? 31  Lesson 15.4: Volcanic Eruptions Objective In this lesson, you should be able to: explain what happens when volcanoes erupt. On March 7, 1978, an incandescent flow of hot lava erupted from the summit of Mayon, covering its flanks over the summer. However, by 1984, the summit of Mayon exploded and expelled a gigantic column of hot ash and gases. There are clearly many different types of eruptions, evidenced by two distinct types occurring at the same volcano. How are eruptions classified? Warm-Up Differences in Eruptions This activity will modify the eruptions that you did in Lesson 1. Try to observe the differences between the eruptions based on what will be modified. Materials: beaker candlewax sand water stove/hot plate Procedure: 1. This activity will modify the warmup in Lesson 1. All the sand and water amounts will be the same as in Lesson 1. The modifications for wax are detailed below. 2. For the first setup, use a 1-inch cube of wax. Use 3 pieces of 1-inch cubes for 32  the second. Use a 3-inch cube for the third setup. For the fourth setup, pre-melt some candle wax and lay it down as a layer on the bottom of the beaker before covering it with sand. Make sure the wax layer is 0.5 inches thick. 3. Heat the beakers and record the time it takes for the wax to bubble out. Also, observe the quality of the eruption. Record all observations below. Setup Time Observations 1 2 3 4 Guide Questions: 1. Which setup bubbled out fastest? Which one bubbled out the slowest? 2. What accounts for the differences in time? 3. Which setup had the widest eruption? Learn about It Eruptions are classified based on their eruptive style (or underlying process), explosivity, the volume of debris, and the height of the resulting eruption column. Fig. 22. Effusive and explosive eruption 33 The most general classification is based purely on the type of debris erupted. Eruptions are considered effusive when they produce lava flows exclusively. This generally applies to low-viscosity lavas, which can flow in sheets or shoot up like fountains. On the other hand, explosive eruptions produce pyroclastic debris due to the sudden release of built-up pressure. Gas expansion caused by decompression, flash boiling of water, etc., is the main source of the pressure behind explosive eruptions. Eruptions are then further classified according to their eruptive style, then the height of the eruption column. Magmatic Eruptions These are driven by the thermal expansion of the dissolved gases in lava. As magma rises, the lithostatic pressure is reduced, allowing gases to expand. The viscosity of the melt and other factors such as blockages in the conduit determines the explosivity of the eruption; more contained gases result in more explosive eruptions. Fig. 23. Different eruption types Plinian Eruptions Plinian eruptions result from the extreme buildup of gases in the magma chamber and conduit (which become as much as 75% gas). The pressure is released once the blockage or even the flank of the volcano itself fails. The result is an immense eruption column higher than 10 km, scattering debris over thousands of square kilometers. Nuée ardente is also a common occurrence similar to Vesuvian and Ultra Plinian. An example is the 1991 Pinatubo eruption. 34  Fig. 24. An Ultra Plinian eruption from Pinatubo Peléan Eruptions Peléan eruptions are very similar to Vulcanian eruptions, except that they are of greater magnitude. These eruptions are characterized by nuée ardente or “glowing avalanches,” which result from the collapse of the eruption column into an incandescent pyroclastic flow. Fig. 25. A Peléan eruption from Mayon 35 Vulcanian Eruptions Vulcanian eruptions result from more viscous lava which slows down bubble formation and clogs up conduits. The pressure then builds up until the volcano explodes, releasing large volumes of pyroclastic debris and an eruption column 5-10 km high. Fig. 26. A Vulcanian eruption from Mayon Icelandic Eruptions Icelandic eruptions are sustained fissure eruptions, producing curtains of basaltic lava. Prolonged eruptions produce large igneous provinces (LIPs). Fig. 27. An Icelandic, or fissure, eruption 36 Strombolian Eruptions Strombolian eruptions are the result of the bursting of clumps of gas bubbles at the surface, throwing up clots of lava. Incandescent lava flows accompany high concentrations of pyroclastic debris. The eruption column is less than 5km. Fig. 28. A Strombolian eruption in Stromboli Hawaiian Eruptions Hawaiian eruptions produce low-viscosity basaltic lava flows and fountains. It evolves from Icelandic eruptions. Over time, Hawaiian eruptions produce shield volcanoes. Fig. 29. The 1950 Mauna Loa eruption is an example of a Hawaiian eruption. 37 Surtseyan Eruptions A Surtseyan eruption occurs in a shallow body of water, and are usually characterized by strong explosions as a result of magma coming in contact with water. Fig. 30. A Surtseyan eruption from Kavachi. Phreatomagmatic Eruptions These eruptions are driven by the violent thermal contraction of magma when it interacts with water, resulting in an explosion. The best example is a Surtseyan eruption, caused by shallow-water lava interaction at sea or with an aquifer. It is the equivalent of a “wet” Strombolian eruption. Phreatic Eruptions These are purely steam-driven, caused by the expansion of water into steam when heated by a nearby magma chamber or volcanic source. The water flash boils and explodes, fracturing surrounding rock and even tearing off debris. 38 The Volcanic Explosivity Index Volcanic eruptions have the potential to be destructive. This is why scientists have devised a way to measure the explosive force of eruptions. If earthquake magnitudes are measured using the Richter scale, the volcanic counterpart of this scale is the Volcanic Explosivity Index (VEI). Much like the Richter scale, a higher numerical value for an eruption indicates a more powerful explosive force. Eruption types may also be classified according to the VEI. Fig. 31. Volcanic Explosivity Index (VEI) Key Points Eruptions are classified based on their eruptive style (or underlying process), explosivity, the volume of debris, and the height of the resulting eruption column. Eruptions are considered effusive when they produce lava flows exclusively. Explosive eruptions produce pyroclastic debris due to the sudden release of built-up pressure. Eruptions can either be magmatic, phreatomagmatic, or phreatic. If earthquake magnitudes are measured using the Richter scale, the volcanic counterpart of this scale is the Volcanic Explosivity Index (VEI). 39  Web Links For more information, check the following weblinks: To see some of the deadliest eruptions in history, watch “5 Deadliest Volcano Eruptions In Human History”: Tech Insider. 2017. ’5 Deadliest Volcano Eruptions In Human History’ https://www.youtube.com/watch?v=u-ha1K9jj9E To see a feature on the eruptions of Mayon volcano, watch “Red Alert: Mayon Volcano” by ABS-CBN News: Red Alert. 2018. ‘‘Red Alert: Mayon Volcano”’ https://www.youtube.com/watch?v=ywovuS_4KNk Check Your Understanding A. Fill in the blanks in the statements below. 1. Eruptions are considered ________ when they produce lava flows exclusively. 2. __________ eruptions produce pyroclastic debris due to the sudden release of built-up pressure. 3. __________ eruptions are sustained fissure eruptions, producing curtains of basaltic lava. 4. __________ eruptions produce low-viscosity basaltic lava flows and fountains. 5. __________ eruptions are the result of the bursting of clumps of gas bubbles at the surface 6. __________ eruptions result from more viscous lava, which slows down bubble formation and clog up conduits. 7. __________ eruptions result from the extreme buildup of gases in the magma chamber and conduit 8. __________ are purely steam-driven, caused by the expansion of water into steam when heated by a nearby magma chamber or volcanic source. 9. Over time, Hawaiian eruptions produce __________ volcanoes. 10. Prolonged Icelandic eruptions produce __________. 40 B. Identify if the statements are true or false. 1. Eruptions are classified based on the mound type of the volcano. 2. Gas expansion caused by decompression is the main source of the pressure behind explosive eruptions. 3. Magmatic eruptions are driven by the thermal expansion of the dissolved gases in lava. 4. Vulcanian eruptions have potentially higher eruption columns compared to Strombolian eruptions. 5. The 1991 Pinatubo eruption is a Plinian eruption. Challenge Yourself Answer the following questions. 1. What are the differences between effusive and explosive eruptions? 2. What are the sources for the force behind explosive eruptions? 3. How does the amount of gases affect the force of the explosion in magmatic eruptions? 4. How does the blockage in a Plinian eruption result in a large eruptive column? 5. How do Phreatic eruptions occur? 41  Lesson 15.5: Materials Emitted from Volcanic Eruptions Objectives In this lesson, you should be able to: explain what happens when volcanoes erupt; and describe the materials released by volcanoes when they erupt. In essence, volcanoes represent how molten Earth materials from beneath react and behave when exposed to surface conditions. They also serve as release valves, when forces bring up subsurface material. Notably, we have learned that volcanoes diversify based on the process of formation and structure. Thus, it follows that the same diversity exists for volcanic products. What are the different materials erupted by volcanoes? Warm-Up Differences in Eruptions This activity will modify the eruptions that you did in Lesson 1. Try to observe the differences between the eruptions based on what will be modified. Materials: shoebox pebbles stratovolcano model gray paper yarn brown, red and yellow clay glue Procedure: 1. This activity will use the model of a stratovolcano from Lesson 3. Lay a shoebox on its side, and set down a layer of yellow clay on the inside. Lay down a layer of brown clay above it. 2. Cut the stratovolcano in half, lengthwise. Set it down on the edge of the 42  brown clay. 3. Remove a small part of the brown clay under the volcano. Place a small amount of yellow clay to replace it, and add a column of yellow clay going upwards until you reach the crater of the volcano. 4. Plug the top with red clay. Simulate a lava river flowing from the crater by using red clay. 5. Stick some pebbles to yarn and stick them on top of the shoebox, near the crater. 6. Use the gray paper to represent smoke coming from the crater and fumaroles. Guide Questions: 1. What do the red and yellow clays represent? What is the difference between them? 2. What do the pebbles represent? Learn about It Lava The primary products of eruptions are lavas which are molten rock materials that have made it to the surface. They are derived from anatexis of the crust and mantle at specific conditions and include liquid mineral ions, solid crystals and glasses, and dissolved volatiles. Magma (subsurface melt) is typically subject to the processes of magmatic differentiation, which alters the compositions of melts, providing diversification. Once exposed to surface conditions, lava cools quickly, which restricts the growth of crystals in the melt. As such, lavas crystallize into fine-grained volcanic rock (e.g. basalt, andesite, rhyolite). Surfaces of lava exposed directly to the air, water, or ground may freeze instantaneously, in a process called quenching. This prevents any crystals from forming at all and results in a non-crystalline mineraloid called volcanic glass (e.g. obsidian, palagonite). 43  Basalt, a fine-grained volcanic rock. Obsidian, a felsic volcanic glass Fig. 32. Basalt and obsidian The composition of lavas, along with temperature, determines their physical properties, most notably their viscosity. This property dictates how lavas behave, and what they will produce, given certain conditions. Viscosity is best measured against the silica content of the lava, with more siliceous or silica-rich melts being more viscous. Lava is extruded as a lava flow, or a moving stream of lava, and flows are classified based on silica content. Fig. 33. The character of a lava flow depends on its viscosity. 44 Basaltic Flows Basaltic flows are silica-depleted and very hot, and thus have a very low viscosity when erupted. Basaltic lava is capable of fast movement on steep slopes, and some flows may reach up to 500 km from their source. The parts of the flow in contact with the ground and the air cool rapidly; this may produce an insulating crust, allowing the interior of the flow to remain hot and molten. These conduits within flows are called lava tubes. The surface texture of basaltic flows indicates the viscosity and temperature of the lava upon freezing. Pahoehoe is a low-viscosity flow with wrinkled, billowing, or ropey surfaces. More viscous flows produce a’a’ or broken, rubbly, spiny surfaces. Both flows may occur from the same volcanic source, with pahoehoe evolving into a’a’ with increasing viscosity as it cools. Pahoehoe lava flow. a’a’ lava flow. Fig. 35. The surface texture of basaltic flows Interiors of basaltic flows cool more slowly and may contract into well-formed hexagonal columns perpendicular to the flow. This is known as columnar jointing. 45 Basaltic flows erupted underwater are squeezed into blobs, or pillows, due to rapid surface cooling and water pressure. These are known as pillow lavas. Fig. 36. Columnar joints. These joints form perpendicular to the direction of flow. Andesitic Flows Andesitic flows are said to have an intermediate viscosity, and cannot flow as easily as basaltic lava. Andesitic lava tends to form a mound when first erupted, before slowly flowing. The speed of movement allows a large part of the flow’s surface to solidify into large angular blocks. Andesitic flows do not typically move further than 10 km. Rhyolitic Flows Rhyolitic flows are the most silica-enriched and have the lowest temperatures. The extremely low viscosity they exhibit results in a blocky, bulbous mass of a flow that does not move very far from the source. Lava domes, or blister-like inflated areas above the vent, contain accumulated rhyolitic and dacitic lava. Sometimes rhyolitic magma solidifies inside a conduit and is pushed 46 through the surface as a spire-like column called a spine. Spines and lava domes act as stoppers, preventing rising materials from exiting a vent. This leads to a pressure buildup; the collapse of these two features can produce catastrophic pyroclastic flows. Volcanoclastic Deposits During eruptions, volcanoes eject large quantities of fragmental igneous debris, which accumulate into volcanoclastic deposits. These include fragments of frozen ejected lava, fragments of pre-existing volcanic rock blasted apart by an explosive eruption, and debris from a volcano's flank carried down by mass wasting. Pyroclastic debris is any volcanic fragments produced directly by eruptions. Basaltic lava’s low viscosity allows dissolved volatiles to easily form and burst at the surface. This ejects drops and clumps of lava into the air, and the pressure may be enough to form fountains of melt; once airborne, the lava quenches into glassy fragments. These become streamlined as they fly, resulting in fragments with relatively smooth, rounded surfaces. Lava fragments 2-64 mm in size (pea- to plum-sized) are called cinders or lapilli, while larger fragments are called bombs. During flight, droplets may trail thin lava strands, which freeze into glass filaments called Pelé’s hair; glass droplets are also called Pelé’s tears. Erupting lava fountains eject blobs of spatter, which can accumulate into spatter cones and spatter ramparts around a vent or fissure. Fig. 39. Pele’s tears. Dime as scale. 47  Fig. 40. Lava fountain. Explosive eruptions produce a buoyant eruption column or vertical plume of fragments and hot gases. The airborne materials fall back down according to density, with the densest fragments falling first and closest to the vent. These air fall deposits vary in size and composition. The first to deposit are generally blocks, which are large (>64 mm) angular fragments tore off the volcano or blasted apart by the explosion. The finest fragments consist of ashes (