Volcanoes 605t1x

Learning Competencies/Objectives In this module, the Learner should be able to: 1. differentiate active and inactive volcanoes; 2. describe the different types of volcanoes; 3. explain what happens when volcanoes erupt; and 4. illustrate how energy from volcanoes may be tapped for human use.

 The Philippines is located along the Ring of

Fire. As a result, it is a home to many volcanoes. The most famous among our volcanoes is the Mayon Volcano that has erupted last May 7, 2013 while a group of hikers were exploring its beauty.

-A volcano is cone-shaped. - It has an opening at the top (or in some case, on the sides) - Hot thick cloud of gas, molten rocks, ash forming a cauliflower shaped-cloud comes out of its opening.

Volcanoes in the Philippines Minor  Volcanoes are found in the differentUrsa locations in the Philippines  Mayon volcano has the most number of eruptions while Iraya volcano has the least number of eruptions. The following volcanoes have no record of eruption: Cabaluyan, Ursa Major Cocoro, Pulung, Tamburok and Urot.

CLASSIFICATION OF VOLCANO  Active

- volcanoes that have a record of eruption within the last 600 years or those that erupted 10, 000 years ago based on analyses of their materials.  Inactive volcanoes,-are those that have not erupted for the last 10, 000 years and their physical form is being changed by agents of weathering and erosion through formation of deep and long gullies.  According to PHIVOLCS,our country has more than a hundred volcanoes as of 2013. Twenty-three are active while the rest are inactive.

PROCESSES INSIDE THE VOLCANO • Magma inside the volcano has high temperature. As the

magma is continuously heated, it goes up. As it rises, gas bubbles are developed. The gas bubbles are trapped and expand causing the molten material to swell also, resulting in a gradual increase in pressure within the volcano. When the pressure exceeds the strength of the overlying rock, fracturing occurs. The resulting breaks lead to a further drop in confining pressure, which in turn causes even more gas bubbles to form. • Lava may appear to be the primary material ejected from a volcano, but this is not always the case. Aside from lava, broken rocks, lava bombs, fine ash and dust are also ejected.

VOLCANIC LANDFORMS AND ERUPTIVE STYLES

 A volcano usually has a summit, slope, and

base. At the summit, there is an opening which may either be a crater or a caldera. A crater is a funnel-shaped opening at the top of a volcano while a caldera is formed when a part of the wall collapses following an explosive eruption.  A volcano can have one crater, like Mayon Volcano, or more than one, like Taal Volcano that has 47 craters.

 Volcanic activity can be very fascinating. After an explosive

eruption, a scenic cone-shaped structure may be produced or changes on its slope can be observed. The emissions of a volcano provide us with clues on what materials are found inside the Earth. Some eruptions are very explosive, while many others are not.  There are primary factors affecting the volcanoes’ eruptive style, namely: the magma’s temperature, its chemical composition, and the amount of dissolved gases it contains. These factors can affect the magma’s viscosity in different ways. 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.

FACTORS AFFECTING THE VISCOSITY OF MAGMA a. Temperature

- The viscosity of 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 it stops.

b. Composition of Magma - Magmas 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.

c. The amount of gases contained in the magma - Lava with low amount of gas and high silica content is very viscous and does not flow out at all as it rises forming, a columnar plug in the vent.

TYPES OF VOLCANIC ERUPTIONS a. Phreatic or hydrothermal – is a stream-driven

eruption as the hot rocks come in with water. It is short lived characterized by ash columns but may be an onset of a larger eruption. b. Phreatomagmatic – is a violent eruption due to the between water and magma. As a result, a large column of very fine ash and high-speed and sideway emission of pyroclastics called base surges are observed.

c. Strombolian – a periodic weak to violent eruption characterized by fountain lava just like the Irazu volcano in Costa Rica d. Vulcanian – characterized by tall eruption columns that reach up to 20 kms high with pyroclastic flow and ashfall tephra like that of Paricutin volcano in Mexico

 e. Plinian – excessively explosive type of

eruption of gas and pyroclastics, just like our PinatuboVolcano in Zambales.

Effects of Volcanic Eruptions in the Society  Loss of lives and properties

 As the lava flows or pyroclastic materials are ejected in the air, they can destroy anything in their way  Caused the decrease in the Earth’s surface temperature or measurable cooling of the Earth’s surface

Effects of Volcanic Eruptions in the Society  Production of Sulfuric Acid

- combination of sulfur dioxide and water in the atmosphere - as it circulates, it may block the sunlight causing a decrease in the earth’s temperature - contributed in the thinning of the ozone layer

Positive Effects of Volcanic Eruption  created spectacular scenery in its wake (Mt.

Pinatubo’s eruption)  Produced very rich soils for farming (Musuan Volcano eruption in Bukidnon)  people became creative by making earthenware out of the ashfall

Signs of Impending Volcanic Eruptions 1. Increase in the frequency of volcanic quakes with rumbling sounds; occurrence of volcanic tremors; 2. Increased steaming activity; change in color of steam emission from white to gray due to entrained ash; 3. Crater glow due to presence of magma at or near the crater; 4. Ground swells (or inflation), ground tilt and ground fissuring due to magma intrusion;

Signs of Impending Volcanic Eruptions 5. Localized landslides, rockfalls and landslides from the summit area which not attributable to heavy rains; 6. Noticeable increase in the extent of drying up of vegetation around the volcano's upper slopes; 7. Increase in the temperature of hot springs, wells (e.g., Bulusan and Canlaon) and crater lake (e.g., Taal) near the volcano; 8. Noticeable variation in the chemical content of springs, crater lakes within the vicinity of the volcano;

Signs of Impending Volcanic Eruptions 9. Drying up of springs/wells around the volcano; and, 10. Development of new thermal areas and/or reactivation of old ones; appearance of solfataras.

Preparing for Volcanic Eruptions  Before

- Prepare an evacuation plan - Prepare an emergency kit - Renovate the parts that need fixing

- Clear the area surrounding your house

- Anticipate possible earthquakes and secure all breakable items

Preparing for Volcanic Eruptions  During

- Evacuate if needed - Proceed with precautions - Wear face mask or gas mask

- Tune in to the radio or tv for the latest news

- Stay in the safest place

Preparing for Volcanic Eruptions  After

- Check for damages - Wear face mask and clean your surrounding - Clean accumulated ash over electricity and

communicative lines - Check the potability of drinking water - Stay away from areas with volcanic ashfall