The Ever Changing Earth

Chapter 9

The Ever Changing Earth

A quick look on the earth’s surface would reveal that it is mostly made of rocks. These rocks appear to be solid and could not be moved at all by any force. However, you have learned that the surface of the earth constantly changes. Wind, water, man and animals can bring about these changes.

In this chapter, you will learn more about other forces that could bring about changes on the earth. These changes could be devastating, destructive and create tremendous effects on man and other living things. What are these forces? Why do they happen? Can man do something to predict or overcome these forces?

The Structure of the EarthLesson 1

The Structure of the Earth

The earth has three major parts – the land part or lithosphere, the water part or hydrosphere and the air part or atmosphere. The lithosphere is the surface on which you live. It is also the earth’s solid sphere consisting mainly of massive rock. The massive rocks form large land masses called continents and small island groups. Different land forms such as mountains, hills, valleys plateaus and plains make up the lithosphere.

The hydrosphere includes all water forms such as oceans, seas, rivers, lakes and groundwater found beneath the earth.

Geologists or scientists who specialize on the history and composition of the earth study carefully these two major parts of the earth. They study the different layers of the earth and what each layer is made of.

You see only the surface of the earth – the oceans, seas, rivers, rocks and soil. They cover the earth just like the thick peeling of a pomelo or orange fruit. When you cut open the pomelo, you see layers of pulp inside it. If the earth were cut open, you would see that it is made of three main layers. They are the crust, mantle and core.

The topmost layer of the earth is the crust which is made of solid rock. It is thicker under the continents, approximately between 11 to 35 kilometers. But under the oceans, it can be 5 to 12 kilometers thick only. At the lower boundary of the crust is the Mohorovicic discontinuity or Moho; named after its discoverer Yugoslav geologist Andrija Mohorovicic. The Moho separates the crust from the next layer beneath it – the mantle.

The mantle is about 2,900 kilometers in depth or thickness. Just like the crust, it is also made of solid rock. But because of extreme heat and pressure, some of these rocks may even flow very, very slowly.

The core is the innermost part of the earth which is about 3,400 kilometers in thickness. It is divided further into two: the outer core which behaves like liquid and the inner core which is believed to be solid. The ore is mostly iron with lesser amounts of nickel and silicon.

Crustal rocks that are parts of the earth’s crust are of two types – granite and basalt. Most of the rocks under the ocean’s basins are basalt which is similar to the rocks at the upper mantle. Beneath the continents, the crust is made up mostly of granite. Granite is lighter than basalt so continents float high on the heavier mantle.

Remembering Science Facts

• The earth has three layers – the crust, the mantle and the core.

• Crustal rocks which are parts of the earth’s crust are basalt and granite.

Make a Cross-section of the Earth

Materials: Styrofoam ball, knife, colored pens

1. Cut the Styrofoam ball lengthwise like cutting a pomelo. Make sure the interior part of the ball is exposed.

2. Mark the inside part of the ball with colored pentel pens to show the different layers of the earth. Use assorted colors to distinguish layers.

Forces that Change the Earth’s Surface

Lesson 2

Forces that Change the Earth’s Surface

The earth’s surface has been constantly changing since the world began. Some changes may be so slow that you hardly can notice it. But over millions of years, mountains rise and are worn down. What forces change the earth’s surface?

What change can you see?

There are two kinds of forces that are at work to constantly change the earth’s surface. They are

tectonic forces and gradational forces.

Gradational Forces

Gradational forces are caused by wind, ice, moving or flowing water and other living organisms. Weathering causes rocks to be broken down into smaller pieces or fragments. Erosion carries away or transports these eroded rocks into the rivers and oceans as sediment. Seas creep in over the land and rise, making new land. Glaciers roll down the mountains and form valleys. Erosion and weathering are gradational forces; they come from outside or beyond the earth.

Tectonic Forces

Tectonic forces come from inside the earth. There are two groups of tectonic forces- diastrophism and volcanism. Diastrophism refers to all movement of the solid parts of the earth as in earthquakes. Volcanism or volcanic eruptions make new landforms when lava hardens. Earthquakes and volcanic eruptions cause sudden changes on the earth’s surface. They may bring about the rise or fall of surface rocks.

Remembering Science Facts

• Gradational and tectonic forces bring about changes on the earth’s surface.

• Erosion and weathering are gradational forces. They bring about slow changes on the earth’s surface.

• Diastrophism and volcanism are tectonic forces. They bring about sudden or rapid changes.

Identify the word being described.

1. It is the outermost layer of the earth.

2. They make up the crustal rocks found beneath the oceans.

3. Separates the crust from the mantle.

4. All movements of the solid parts of the earth.

5. The process by which rocks are worn down into fragments.

6. Forces that come from inside the earth and cause sudden changes on the surface.

7. A gradational force which carries away broken pieces of rocks.

8. Crustal rocks found beneath the continents.

9. Can make new landforms when lava hardens.

10. The innermost layer of the earth.

Movements on the Earth’s CrustLesson 3

Movements on the Earth’s Crust

Some changes on the earth’s surface are caused by the movements of the crust. Geologists found out that the crust is made up of six large plates, forming the continent and a number of smaller plates. Each plate holds land masses and ocean regions. These are called crustal tectonic plates.

These plates continuously move which may result in warping, folding and bending of rock layers.

The present appearance of the earth is the result of millions of years movement of the earth’s crustal tectonic plates. There are three main types of plate boundaries. These are ridges, trench or subduction zones and transform faults.

Ridge

When crustal tectonic plates move slowly with a sliding motion, two neighboring plates may move apart. A crack opens between the plates wherein hot, molten rock from the earth’s interior spreads through to form a new ocean crust called ridge. The mid-Atlantic ridge is an example.

Trench or Subduction Zone

In another place, two plates may collide head on causing one plate to be forced under the other. A trench or subduction zone results. Examples are the trenches around the Pacific Ocean. Great mountains such as the Appalachian and Alps Mountains are also believed to be formed from this collision.

Transform Faults

Transform faults such as the San Andreas fault of California is formed when two plates slide slowly past each other, scraping their edges and then causing the plates to press together. Continuous pressure may cause rocks to slip which may change the position of rock layers. This is called a fault.

These movements of the crustal plates are sometimes grouped according to the direction they take. An uplift is rising of the earth’s crust while subsidence is the sinking of the earth’s crust or land areas. The sideways movements of rock layers is called thrust.

Folding is the bending of rock layers due to strong pressure or strong temperature exerted on their sides. Sometimes, folding occurs over a wide area wherein the upfold or anticline becomes a folded mountain and the downfold or syncline becomes a valley.

Rock layers may also produce cracks or joints which may later break or split due to continuous pressure. This causes rocks to slip or slide along the crack and form a fault. When faulting occurs over a wide area on the earth’s crust, block mountains are formed.

Remembering Science Facts

• The earth’s crust is made of tectonic plates which hold land masses and ocean regions.

• The three main types of plate boundaries are ridge, trench or subduction zones and transform fault.

• The continuous movement of the earth’s crustal tectonic plates may result in the warping, folding and bending of rock layers.

True or False? If false, change the underlined word to correct the sentence.

1. Movements on the earth’s crust cause the formation of mountains, ridges and valleys.

2. The syncline is the raised portion of a fold.

3. Each tectonic plate holds land masses and ocean regions.

4. The Appalachian and Alps Mountains are examples of folded mountains.

5. The sideways movements of rock layers is called uplift.

6. A fault is formed when the rock layers slip or slide along a crack.

7. Folding is the bending of rock layers due to extreme pressure and temperature.

8. When two neighboring tectonic plates move apart, a ridge is formed.

9. Gradational forces come from inside the earth.

10. Block mountains are formed when faulting occurs over a wide area.

Causes and Kinds of Earthquakes

Lesson 4

Causes and Kinds of Earthquakes

Do you remember that day when the earth moved and shook many buildings last July 16, 1990? People ran to the streets for fear that their houses might collapse. Do you know the intensity of that earthquake? What is an earthquake? What causes it? Can scientists predict the occurrence of an earthquake?

Rock layers on the crust and mantle are pushed by some forces within the earth and by movements of the crustal plates. The blocks of rocks adjust by bending or slipping against each other quietly. However, the pressures or forces may become so tremendous or intense that sometimes the plates may stick. Then, the rock snaps or jumps leaving a crack or fault. This part of the crust may remain like this for a long time until it snaps again along the fault. Then, earthquakes occur. Earthquakes are vibrations or tremors produced in the earth’s outer layer or crust. The vibrations can be barely noticeable to catastrophically destructive. There are three general kinds of earthquakes. They are tectonic, volcanic and artificially produced. Tectonic earthquakes are most devastating and difficult to predict.

Tectonic quakes are produced when rocks slip along fault lines. These usually occur at the boundaries of the tectonic plates wherein a rock layer may slide up, down or sideways in relation to another layer. Tectonic quakes are concentrated along the so-called Ring of Fire. The Ring of Fire is a narrow band about 38,600 km long that stretches along the Pacific Ocean. The world’s destructive seismic events or earthquakes and 75 percent of the earth’s seismic energy are produced in this region. Geologists believe that quakes are a symptom of forces tearing apart the earth’s crust.

The earthquake which occurred last 1990 shook the whole island of Luzon. It was 7.2 intensity in the Richter scale! A small slip of even only a centimeter along the fault can send vibrations which move outward in all directions. This, this earthquake was felt.

Volcanic earthquakes are seldom very large or destructive. These tremors or vibrations are often produced to signal an upcoming volcanic eruption of a volcano in that vicinity. Such quakes originate as magma, molten rock from a layer in the earth’s mantle called the asthenosphere, is working its way up the volcano. As many as 1,000 small quakes a day may be produced before an eruption occurs.

Artificially produced earthquakes may be caused by a variety of man’s activities. Filling of new reservoirs, the underground detonation of atomic explosives or the pumping of fluids deep into the earth through the wells are examples of such activities. Landslides over a wide area may also produce landslips.

Remembering Science Facts

• Earthquakes are tremors or vibrations produced in the earth’s outer layer or crust.

• Earthquakes may be tectonic (caused when a rock slips or slides along a fault), volcanic and artificially produced.

Earthquake BeltsLesson 5

Earthquakes frequently occur in the Philippines. On January 17, 1994, an earthquake struck Northern Los Angeles, California. The following year, January 16, 1995, another earthquake severely damaged Kobe, Japan which lasted for 20 seconds. On May 28, 1995, a devastating earthquake struck Neftegorsk, Russia, located at the far eastern part of the country. Why do earthquakes often occur at these places?

Earthquakes do not occur in all parts of the world. They are limited to certain areas or belts called earthquake belts. The Philippines, Japan, California, Chile and other countries lie near the Pacific Ocean. These countries have been identified by seismologists to have weak earth’s crust. They belong to the Circum Pacific Belt or the Pacific Belt of Fire.

The second belt stretches from China to Southeast Asia to the Mediterranean areas of Africa and Europe. These include countries like Italy, Portugal, Monaco and Russia. The third earthquake belt is the long ridge that lies under the Atlantic Ocean. Geologists believe that these ridges and similar ridges under the oceans are made of hot lava from the mantle that bursts up through the ocean floors. This causes a gradual spreading of the ocean floor.

Deep Earthquakes

By studying these earthquake belts, seismologists have been able to determine why many earthquakes occur where they do. However, about 10 percent of each year’s quakes are a puzzle to scientists. These quakes could not be located in any of these quake belts. These are the so called deep earthquakes. They do not occur at the surface of the earth but occur deep down in the earth as much as 750 km below the surface. These quakes do not leave cracks at the earth’s surface since the fracture is some distance underground. Deep earthquakes are also felt over a wider area than a surface quake.

Remembering Science Facts

• Earthquakes occur only to certain areas called earthquake belts.

• The earthquake belts are the Pacific Belt of Fire, Mediterranean Belt of Firs and the Atlantic Ocean Ridges.

Detecting and Predicting Earthquakes

Lesson 6

Imagine this scenario- the ground moves suddenly; then, it moves again and again, strongly and sharply. Buildings sway and some even collapse. Concrete bridges and fly-overs collapse. Falling debris trap people in the streets.

Hundreds of earthquakes occur every year. Most earthquakes do little harm, but a few have killed thousands of people and cause enormous destruction. Man has had to endure earthquakes throughout history. Can earthquakes be detected or predicted? How is this being done?

The study of earthquakes is called seismology; seismos means earthquake and logos means study. Seismologists, experts on the study of earthquakes, observe seismic waves sent out by earthquakes in seismic observatories.

When a pebble is dropped in a pond, you see ripples or tiny waves spreading outward in ever widening circles. The pebble pushes the particles of water nearest it. This pushes the nearby water particles in all directions creating what is called a wave. A wave is the push that moves out in all directions. An earthquake also sends out seismic waves in all directions similar to waves produced in water.

In the same way, the rock surface that moves forward pushes the rock particles ahead of it. These in turn push the rock particles ahead of them which create tremors and is felt throughout the earth. This is called a push wave or compression wave. It travels faster at an average of 8 km per second but its speed increases with depth. Since a push wave travels fast, it arrives first. Seismologists call it primary wave or P wave.

An earthquake also sends out a secondary wave or S wave. With a pencil between your hands, when you slide one palm of your hand forward over the other palm, the pencil rotates or twists. In the same way, rock particles between the slipping surfaces are twisted. These send a torsion wave or twist wave throughout the earth. It travels more slowly at about 5 km per second. Seismologists all this an S wave.

Earthquakes are detected by an instrument called a seismograph. A seismograph determines place of origin of the shock called focus. The point or line on the earth’s surface directly above the focus of an earthquake is called the epicenter. The difference between the speeds of the P waves and S waves is useful to seismologists. It tells how far away from the observatory an earthquake is. The observatory seismograph registers each wave and records the exact time of its arrival. Observatories in other parts of the world have recorded the same earthquake. These observatories pool their information to determine where the earthquake occurs.

In practice, several hundred seismographs are kept in continuous operation all over the world. Daily information is received by the Division of Seismology of the US Coast and Geodetic Survey in Washington, DC. It issues the official location of each earthquake that occurs after feeding the received information into a computer. Now, calculations on the location of the earthquake and its depth below the earth’s surface are done in a few seconds.

Remembering Science Facts

• Seismology is the study of earthquakes.

• Seismologists are scientists who specialize in the study of earthquakes.

• Earthquakes produce seismic waves which can be detected by an instrument called a seismograph.

Reaching Out

Now-a-days, a seismograph is made up of two instruments: a seismometer which detects ground vibrations, and a recorder which makes these vibrations visible on a permanent record.

The picture shows a photographic seismograph recorder. Built into it is a second, much smaller coil and magnet device called galvanometer. When current from the first coil flows through the galvanometer, the second coil moves a little piece attached to a tiny mirror.

The mirror reflects a light beam into a sheet of photographic paper. During an earthquake, the back and forth ground motion produces a series of back and forth currents that move the mirror. The mirror’s motions record zigzag lines on the photographic paper.

Intensity and Magnitude of Earthquakes

Lesson 7

Earthquakes can cause a great loss of life and property. They may destroy structures such as buildings, bridges and dams. They can also trigger devastating landslides. Seismic sea waves cause tidal waves or tsunamis. These towering walls of water strike populated coastlines which can wipe out the entire town.

Earthquakes are recorded in terms of their destructive effect on people and other structures on the earth’s surface. How is the power or strength of an earthquake measured?

Seismographic recorders help seismologists locate earthquakes. They also calculate how powerful the quake is. The strength of an earthquake is known as its intensity. The power or magnitude of an earthquake is the amount of energy released at the focus of the quake. It is based on the amplitude of seismic waves radiated by the earthquake.

Richter Scale

Seismologists have devised two scales of measurement to describe the intensity and magnitude of an earthquake. One is the Richter scale named after American seismologist, Charles Francis Richter who developed it. The scale runs from 1 to 10. Each number on the Richter scale indicated a magnitude 10 times as great as the number below it. Thus, an earthquake with a magnitude of 6 is 10 times as great as an earthquake with a magnitude of 5. Very small tremors are rated up to 2.5 on the scale while quakes up to 5 can cause some minor damage. Those of magnitude 6 and higher are major quakes that can cause widespread damage.

Mercalli Scale

Italian seismologist Ginsepjoe Mercalli devised the Mercalli scale. It measures intensity of shaking or tremors with gradations from I to XII. Intensity I shows that quake is barely felt or felt by very few people while intensity XII shows a catastrophic event that causes total destruction. Mercalli’s intensities II to III are roughly equivalent to quakes of magnitude 3 or 4 on the Richter scale while XI to XII will be magnitudes of 8 to 9 on Richter’s. PAGASA uses the Richter scale.

Remembering Science Facts

• Intensity is the strength of an earthquake while magnitude is the amount of energy released at the focus of a quake.

• Richter and Mercalli scales are used to measure the intensity and magnitude of an earthquake.

Identify the word being described.

1. The scale used by PAGASA to measure the intensity of an earthquake.

2. Experts on the study of earthquakes.

3. Tells the amount of energy released at the focus of a quake.

4. An instrument used to measure tremors or vibrations on the earth’s surface.

5. A kind of seismic wave that travels fast and increases its speed with depth.

6. The place of origin of the shock.

7. Tidal waves caused by seismic sea waves.

8. The point or line on the earth’s surface directly above the focus of an earthquake.

9. Earthquakes that cause widespread damages or loss of lives.

10. A scale which measures intensity of shaking or tremors with gradations from I to XII.

Safety Measures During and After Earthquakes

Lesson 8

Have you experienced a major earthquake? What will you do during a quake? Why is it important for you to have presence of mind during an earthquake?

Surface quakes may run as high as 100 in a month. The number of earthquakes may vary from month to month. The extent of the disaster in an earthquake depends on many factors. If a building is well constructed and built on solid ground, it will withstand an earthquake.

Most deaths in earthquakes have been due to faulty building construction or poor building sites. But the most serious factor is panic. When people rush out into narrow streets or push one another into the nearest exit of a building, more deaths result from trampling and suffocation.

Here are some things you should remember to do during and after an earthquake. When first tremors are felt, do not panic. If you are inside a building, turn off electric appliances at once. Seek shelter under a table until tremors have stopped. If you are near the doors, walk fast to an exit of the building. Avoid carrying things that may slow down your movements. Avoid standing near light posts, trees or any tall object that may fall or collapse. Stay away from glass windows also. Avoid touching loose electrical wires. Watch out for fires which may be caused by damaged electrical wires.

Remembering Science Facts

• Always have presence of mind during an earthquake. Do not panic.

Check the right things to do during and after an Earthquake.

1. You should get nervous since earthquakes signal the end of the world.

2. Seek shelter under a table.

3. Stand near tall objects that may fall.

4. Stay away from glass windows which may break due to extreme vibrations.

5. Have presence of mind; do not panic.

6. Avoid pushing one another to the nearest exit.

7. Watch out for fires that may be caused by damaged electrical wires.

8. Call PAGASA at once to know the intensity of the earthquake.

9. Turn off electric appliances the first time you feel the tremors.

10.Stay out in the open fields during an earthquake.

VolcanoesLesson 9

Have you heard of the eruption made by Mount Pinatubo in 1991? The destruction brought about by this volcanic eruption is tremendous. Many towns in Tarlac, Pampanga and Zambales were buried in lahar. The people living near volcanoes still feel the same threat. Volcanoes have always terrified people. But today, volcanoes fascinate people, especially geologists. Do you know why? Geologists study volcanoes to learn more things about the earth’s interior. The materials which come from the earth’s interior can only be seen when they come out of the volcanoes.

What is a volcano? How is a volcano formed? What are the different kinds of volcanoes?

A volcano is a cone-shaped mountain which has an opening called a crater or a volcanic vent. It has a slope which may either be gentle or steep. Through the crater or vent, gas and rock fragments from inside the earth pass or come out into the earth’s surface. Molten or melted rock called magma sometimes flows out quietly. At other times, expanding gases cause explosion and throw pieces of rocks high into the air to shower around the vicinity of the volcano. This is called volcanic eruption. Magma pouring out gently forms streams of molten rock called lava flows. Gas rushing out of the crater may carry with it fragments of solid and liquid rocks. These fall back to the ground to form pyroclastic rocks, such as obsidian, basalt and rhyolite. Besides earthquakes, volcanic eruptions can cause sudden change on the earth’s surface. This force is called volcanism.

Volcanoes are sometimes called smoking chimneys. They are classified according to the type of volcanic cones or slope they have. Lava cone or shield cone volcanoes usually have a wide base and a gentle slope. These volcanoes are formed when lava flows out of the crater quietly and moves far down the slope. They usually have the quiet type of eruption or flood eruptions. Thus, these are also called oozing volcanoes. Volcanoes Kilauea and Mauna Loa in the Hawaiian Islands are examples of shield volcanoes.

Mauna Loa

A cinder cone volcano has a steep slope and a narrow base. It is formed when steam ashes and liquid rocks are thrown up high into the air and harden rapidly before they can spread down. Cinder cone volcanoes usually have the explosive volcanic eruption. They are destructive and violent. Before the eruption, minor earthquakes and loud rumblings could be felt. Mt. Krakatau in Indonesia and Mt. Paricutin in Mexico are examples of this type of volcano. Many cinder cones are found on the sides of bigger volcanoes.

Mt. Krakatau

A composite or stratovolcano is formed by alternate layers of lava and cinder. It has the intermediate type of volcanic eruption. Many volcanic cones erupt only once. But some world’s famous volcanoes are composite. Mount Mayon in Lagazpi, Albay; Mount Egmont in New Zealand; Mount St. Helens in Washington, USA and Mount Fuji in Japan are some examples.

Mt. St. Helens

Remembering Science Facts

• A volcano is an opening where gas and rock from inside the earth come into the surface.

• Volcanism or volcanic eruption is another force that changes the earth’s surface.

• Magma is molten rock.

Reaching Out

Volcanoes are sometimes grouped according to their volcanic activity/eruptions. Some volcanoes erupt after a short period of time or have recently erupted. They also show seismic activity from time to time. These are active volcanoes. Some active Philippine volcanoes are Mayon Volcano, Mount Pinatubo, and Taal Volcano. Mount Fuji, Mount Etna and Mount St. Helens are other active volcanoes of the world.

Some volcanoes are dormant since they have not erupted for quite some time. A dormant volcano may become active again. Mount Pinatubo was a dormant volcano for more than a hundred years until its last eruption in 1991. Mount Apo and Mount Santo Tomas are dormant volcanoes. When a volcano has remained dormant for a long time, it becomes and extinct volcano. Mount Data is an example. Use a map of the Philippines to locate other volcanoes and find out if they are active, dormant or extinct.

Volcanic ProductsLesson 10

Volcanic Products

Disasters like the eruption of Mount Pinatubo are unforgettable. Gray, powdery ash drifted down like snow as far as Southern Luzon. Mud flowed swiftly down the mountainside and buried several villages or barangays. When rain came, mudflows mixed with loose cinder and ash formed lahar. It did great damage to many agricultural fields. Up to now, these lands are rendered useless.

Besides lahar and ash, what are the other products of volcanic eruption?

Some volcanoes have expelled as much as five tons of volcanic products or materials in a single day. Volcanic explosions throw out several kinds of materials like the following:

Fragmental or Pyroclastic Materials

Fragments the size of sand and dust are called volcanic ash. These ashes are not the result of burning; they form when rock is blown apart by expanding gas. Loose volcanic ash becomes cemented together to form a hard rock called tuff. Bits of liquid lava may be puffed up by gases and become lapilli or cinder. Large, thick rock materials are called volcanic bombs such as pumice. True pumice will float in water.

pumice

Gases and Vapors or Steam

Clouds of gases are dark gray or black at daytime. But at night, their heat makes them glow red. These “smokes” are clouds of steam and other gases rising from gas vents or fumaroles. Sulfur, hydrogen, helium, carbon monoxide, ammonia and hydrochloric acid are gases emitted from a volcano.

Lava

Molten rock or magma which reaches the earth’s surface and turns into a solid rock is called lava. Magma usually contains the crystals of minerals that are forming in it. Magma which cools quickly forms obsidian, a kind of natural glass. Lava rock is made up of tiny crystals of glass or both. Magma pouring out gently forms streams of molten rock known as lava flows. They solidify into igneous rocks such as basalt, rhyolite and granite.

In Iceland, volcanoes sometimes erupt beneath glaciers. They melt the ice and cause floods of water mixed with cinder and ash. At other volcanoes, the water of a crater lake may be thrown out by explosions. This mixes with loose pyroclastic material on the side of the mountain such as the ones from Mount Pinatubo and Mount Mayon.

A lot of damage and threat to the lives of people living within the kilometer radius of danger are expected during volcanic activity. Safety precautions/measures should be taken to avoid or minimize loss of lives. Philvolcs issues bulletins at even the first sign of seismic activity to alert the people. Listen to these bulletins aired over the radio or television. If necessary, evacuate or go to a safer place or resettlement home. Stay calm; do not panic when tremors become more frequent.

Remembering Science Facts

• The products of volcanic eruption are pyroclastic materials, gases or steam and lava.

• Fumaroles are gas vents or openings where different gases come out.

• Safety measures should be taken during a volcanic eruption.

Reaching Out: Identify the word

1. A kind of natural glass

2. Openings where gases escape from inside the earth

3. Igneous rocks which float in water

4. Hard rock formed from loose volcanic ash cemented together

5. Fragments with the size of sand and dust

6. Sometimes called smoking chimneys

7. Mayon Volcano is this type of volcano

8. A type of volcano which usually has a wide base and gentle slopes

9. The government agency which issues bulletins at even the first sign of seismic activity to alert people

10. Gas vents wherein clouds of steam and other gases rise

Importance/ Benefits from Volcanoes

Lesson 11

A volcanic eruption releases a huge amount of heat energy which is greater than the most powerful nuclear bomb. This heat could be an important source of geothermal energy to generate electricity such as that in Tiwi, Albay. Volcanic steam and gases are used to produce chemicals such as boric acid and sulfuric acid. Ammonia is used in the production of fertilizers. Helium is used in dirigibles, filling balloons and smelting. Methane is used for fuel.

Volcanic products such as lava and ash make fertile soil. Volcanoes bring to the earth’s surface many of the minerals that plants need to grow well.

Igneous rocks such as basalt and granite are used in constructing roads. Pumice is used for grinding and polishing. Tuff is used in building walls and fences. Mayon and Taal Volcanoes make beautiful scenic landscapes which attract tourists and other visitors.

Taal

But volcanoes also have their harmful effects. Eruptions have sometimes killed many people and done great damage to property and agricultural products. During the eruption of Krakatau in Indonesia, most o the island and parts of nearby islands were destroyed. Floating pumice covered the surrounding ocean. These posed hazards or dangers to navigating ships. Tsunamis or huge waves waters swept into the shores drowning thousands of people. Mount Pinatubo’s explosion in 1991 blew fine ash high into the upper atmosphere. This dust drifted slowly around the earth and caused brilliant red sunsets as far away as England. It also caused a change in weather and climate patterns around the world.

In 1914, a mudflow from Mayon Volcano completely buried the town of Cagsawa and all its people.

Remembering Science Facts

• Volcanoes are an important source of geothermal energy which can generate electricity.

• Lava and ash make the soil fertile.

• Volcanic eruptions have caused changes to the climate patterns of the world.

FOR YOU TO REMEMBER

• The earth has three layers – the crust, the mantle and the core.

• Crustal rocks which are parts of the earth’s crust are basalt and granite.

• Gradational and tectonic forces bring about changes on the earth’s surface.

• Erosion and weathering are gradational forces. They bring about slow changes on the earth’s surface.

• Diastrophism and volcanism are tectonic forces. They bring about sudden or rapid changes.

• The earth’s crust is made of tectonic plates which hold land masses and ocean regions.

• The three main types of plate boundaries are ridge, trench or subduction zones and transform fault.

• The continuous movement of the earth’s crustal tectonic plates may result in the warping, folding and bending of rock layers.

• Earthquakes are tremors or vibrations produced in the earth’s outer layer or crust.

• Earthquakes may be tectonic (caused when a rock slips or slides along a fault), volcanic and artificially produced.

• Earthquakes occur only to certain areas called earthquake belts.

• The earthquake belts are the Pacific Belt of Fire, Mediterranean Belt of Firs and the Atlantic Ocean Ridges.

• Seismology is the study of earthquakes.

• Seismologists are scientists who specialize in the study of earthquakes.

• Earthquakes produce seismic waves which can be detected by an instrument called a seismograph.

• Intensity is the strength of an earthquake while magnitude is the amount of energy released at the focus of a quake.

• Richter and Mercalli scales are used to measure the intensity and magnitude of an earthquake.

• Always have presence of mind during an earthquake. Do not panic.

• A volcano is an opening where gas and rock from inside the earth come into the surface.

• Volcanism or volcanic eruption is another force that changes the earth’s surface.

• Magma is molten rock.

• The products of volcanic eruption are pyroclastic materials, gases or steam and lava.

• Fumaroles are gas vents or openings where different gases come out.

• Safety measures should be taken during a volcanic eruption.

• Volcanoes are an important source of geothermal energy which can generate electricity.

• Lava and ash make the soil fertile.

• Volcanic eruptions have caused changes to the climate patterns of the world.