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Grade 9 Module 1, Lesson 1.1: Volcanoes (Teacher's Guide for Discussion)

A PowerPoint Presentation for Grade 9 teachers. This presentation is ONLY suggested guide for teachers to assist them on the discussion after the activities as suggested in the Learner's Module were performed. Please feel free to add comments and suggestions. Thanks!

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Grade 9 Module 1, Lesson 1.1: Volcanoes (Teacher's Guide for Discussion)

  1. 1. VOLCANOES Grade 9, Module 3 Lesson 1.1 (Teachers’ Guide for Discussion) Author: MA. RACHEL B. ESPINO Teacher I, Science Buhatan NHS, Sorsogon City
  2. 2. What is a volcano? • A volcano is a mountain where lava (hot, liquid rock) comes from a magma chamber under the ground. A volcano usually has a summit, a slope and base. • Most volcanoes have a volcanic crater at the top. When they are active, materials pour out of it. This includes lava, steam, gaseous compounds of sulphur, ash and broken rock pieces. • Volcanoes erupt when magma and pressure come together, and the pressure blows off the top of the solid rock, and the magma pours out.
  3. 3. Types of Volcanoes: SHIELD VOLCANOES • Shield volcanoes are built out of layers of lava from continual eruptions (without explosions). Because the lava is so fluid, it spreads out, often over a wide area. Shield volcanoes do not grow to a great height, and the layers of lava spread out to give the volcano gently sloping sides. Shield volcanoes can produce huge areas of basalt, which is usually what lava is when cooled. • Even though their sides are not very steep, shield volcanoes can be huge. Mauna Kea in Hawaii is the biggest mountain on Earth. If it is measured from its base on the floor of the sea, Mauna Kea is even taller than Mount Everest, the tallest mountain on land.
  4. 4. Types of Volcanoes: STRATOVOLCANOES • A stratovolcano, also known as a composite volcano, is a tall, conical volcano. It is built up of many layers of hardened lava, tephra, pumice, and volcanic ash. • Unlike shield volcanoes, stratovolcanoes have a steep profile and periodic eruptions. The lava that flows from stratovolcanoes cools and hardens before spreading far. It is sticky, that is, it has high viscosity. The magma forming this lava is often felsic, with high-to-intermediate levels of silica, and less mafic magma. Big felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).
  5. 5. Types of Volcanoes: CALDERA • A caldera is what is left when a huge stratovolcano blows its top off. It leaves a crater where the top of the volcano was before. Krakatoa, best known for its catastrophic eruption in 1883, is much smaller now.
  6. 6. How are volcanoes formed? There are two main processes. • Volcanoes are made when two tectonic plates come together. When these two plates meet, one of them (usually the oceanic plate) goes under the continental plate. This is the process of subduction. Afterwards, it melts and makes magma (inside the magma chamber), and the pressure builds up until the magma bursts through the Earth's crust. • The second way is when a tectonic plate moves over a hot spot in the Earth's crust. The hot spot works its way through the crust until it breaks through. The caldera of Yellowstone Park was formed in that way; so were the Hawaiian Islands.
  8. 8. Classification of Volcanoes A traditional way to classify or identify volcanoes is by its pattern of eruptions. Those volcanoes which may erupt again at any time are called active. Those that are now quiet called dormant (inactive). Those volcanos which have not erupted in historical times are called extinct.
  9. 9. ACTIVE VOLCANOES • An active volcano is currently erupting, or it has erupted in the last 10,000 years. An example of an active volcano is Mount St. Helens in the United States (US).
  10. 10. DORMANT VOLCANOES • A dormant volcano is "sleeping," but it could awaken in the future. Mount Rainier in the United States is considered dormant
  11. 11. EXTINCT VOLCANOES • An extinct volcano has not erupted in the past 10,000 years. Edinburgh Castle in Scotland is located atop an extinct volcano.
  12. 12. What determines the nature of eruption? • There are many primary factors affecting the volcanoes eruptive style, namely: the magma’s temperature, its chemical composition, the amount of dissolved gases it contains. These factors can affect the magma’s viscosity in different way.
  13. 13. VISCOSITY • VISCOSITY is the property of the material’s resistance to flow. It is also described as the liquid’s thickness and stickiness. The more viscous and thicker the material is, the greater is its resistance to flow.
  14. 14. Effect of Magma’s Temperature to Viscosity • The viscosity of the magma decreases with temperature. The higher the temperature of magma is, the lower is its viscosity. As lava flows, it cools and begins to harden, its ability to flow decreases and eventually stops.
  15. 15. Effect of Magma’s Composition to Viscosity • Magma’s with high silica content are more viscous than those with low silica content . The magma that contains less silica is relatively fluid and travels far before solidifying.
  16. 16. Effect of the Amount of Gases Contained in Magma to Viscosity • Gas (mainly water vapor) dissolved in magma tends to increase its ability to flow. Therefore, in near-surface environments, the loss of gases makes magma more viscous a dome or a columnar.
  17. 17. Lava with low amount of gas as it rises has high viscosity that piles up at a vent resulting into a dome. Lava with less silica content is too viscous to travel far, and tends to break up as it flows Lava with less silica content has less silica content has low viscosity that it can travel a great distance, fow=rming a thin sheet
  18. 18. Volcanic Eruption • Eruption of Mayon Volcano last 2006 in Albay, Philippines • Eruption of Mt. Kilauea in Hawaii, USA
  19. 19. Types of Volcanic Eruption • PHREARIC OR HYDROTHERMAL - is a stream-driven eruption, as the hot rocks come in contact with water. It is short lived characterized by ash columns but may be an onset for a larger eruption. Example is Taal volcano eruption in Batangas (as shown on the right)
  20. 20. Types of Volcanic Eruption • PHREATOMAGMATIC - is a violent eruption due to the contact between water and magma. As a result, a large column of very fine ash, high speed and side-way emission of phyroclatics called based surges are observed. Example is the eruption of Mt. Fukutoku-Okanoba in Bonin Islands, Japan
  21. 21. Types of Volcanic Eruption • STROMBOLIAN - a periodic weak to violent eruption characterized by fountain lava. Example is Mt. Irazu Eruption in Costa Rica
  22. 22. Types of Volcanic Eruption • VULCANIAN - characterized by tall eruption coulmns that reach up to 20 km high with pyroclastic flow and ash fall tephra. Example is Mt. Paricutin in Mexico.
  23. 23. Types of Volcanic Eruption • PLINIAN - excessively explosive type of eruption of gas and pyroclastics. Example is Mt. Pinatubo in Zambales.
  24. 24. Examples of Volcanoes found in the Philippines
  25. 25. Suggested Videos • Naked Science: Volcanoes (it provides discussion about the formation of new volcanoes in Yellowstone National Park, USA) • BBC: Iceland Volcanoes Erupts (it shows eruption of Iceland volcanoes, its effects and how people in Iceland adapts and survive along the volcanic areas)

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A PowerPoint Presentation for Grade 9 teachers. This presentation is ONLY suggested guide for teachers to assist them on the discussion after the activities as suggested in the Learner's Module were performed. Please feel free to add comments and suggestions. Thanks!


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