A. Choose the letter of the

best answer.

Pre-Assessment

1. Which characteristic of magma

mainly determines its explosiveness?

a. color

b. amount

c. temperature

d. silica content

2. Which of the following characteristics

of a volcano depends on its magma

emission?

a. age

b. size

c. shape

d. location

3. Which of the following factors

associated with huge volcanic

eruptions may cause the decrease in

the Earth’s average temperature for a

few years?

a. heat

b. light

c. acid rain

d. volcanic ash

4. A thick layer of volcanic ash can be

heavy enough to collapse the roofs of

buildings because ash ________.

a. is solid.

b. cannot be blown by winds.

c. becomes heavier as it cools.

d. consists of tiny fragments of rocks

that becomes heavy as they file up.

5. Which of the following is an active

volcano in the Philippines?

a. Apo in Davao

b.Bud Datu in Sulu

c.Isarog in Camarines Sur

d.Kanlaon in Negros Oriental

B. Answer the following questionsbriefly.

6. Aside from Mayon Volcano, nameanother Philippine volcano that haserupted recently.

7. What causes a shield volcano to beshaped like a broad dome?

8. By what process can a volcaniceruption affect temperatures aroundthe world?

9. Give one positive effect and one

negative effect of volcanic eruptions.

10. How is energy from volcanoes

tapped as source of electricity?

VOLCANOES

Classification of volcanoes

• Active volcanoes are those that have a recordof eruption within the last 600 years or thosethat erupted 10, 000 years ago based onanalyses of their materials.

• Inactive volcanoes, on the other hand, arethose that have not erupted for the last 10,000 years and their physical form is beingchanged by agents of weathering and erosionthrough formation of deep and long gullies.

• According to PHIVOLCS, our country hasmore than a hundred volcanoes as of2013. Twenty-three are active while therest are inactive.

List of Some Volcanoes in the Philippines

Volcano Latitude Longitude No. of historical eruptions

Latest eruption or

activity

Cabaluyan 15⁰ 42’ 120⁰ 19’ 0 -

Cocoro 10⁰ 53’ 121⁰ 12’ 0 -

Iraya 20⁰ 29’ 124⁰ 01’ 1 1454

Kanlaon 10⁰ 24’ 123⁰ 7’ 26 June 2006

Mayon 13⁰ 15’ 123⁰ 41’ 49 May 2013

Pulung 7⁰ 55’ 124⁰ 38’ 0 -

Smith 19⁰ 32’ 121⁰ 55’ 6 1924

Taal 14⁰ 120⁰ 59’ 33 1977

Tamburok 11⁰ 33’ 124⁰ 26’ 0 -

Urot 5⁰ 59’ 121⁰ 15’ 0 -

Summit

Slope

Base

• Summit is an opening which mayeither be a crater or caldera. Crater isa funnel-shaped opening at the topof a volcano while caldera is formedwhen a part of the wall collapsesfollowing an explosive eruption.

Crater Caldera

Primary factors affecting the volcanoes’ eruptive style:

• Magma’s temperature

The higher the temperature of magma is,the lower is its viscosity.

• Chemical composition

Magmas with high silica content are moreviscous than those with low silica content.

• Amount of dissolved gases it contains

Gas dissolved in magma tends toincrease its stability to flow.

Types of Volcanic Eruptions

a. Phreatic 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 of a large eruption.

Taal Volcano

b. Phreatomagmatic– is a violenteruption due tothe contactbetween waterand magma. As aresult, a largecolumn of veryfine ash and high-speed andsideway emissionof pyroclasticscalled base surgesare observed.

c. Strombolian

– a periodic weak toviolent eruptioncharacterized byfountain lava justlike the IrazuVolcano in CostaRica.

d. Vulcanian –characterized by tall eruption columns that reach up to 20 km high with pyroclastic flow and ash fall tephra like that of Paricutin Volcano in Mexico.

e. Plinian

– excessivelyexplosive type oferuption of gasand pyroclasticsjust like ourPinatuboVolcano inZambales.

Three Volcanic Cones1. Shield volcanoes are

formed by theaccumulation of lavathat oozes out from thevolcano. Since non-viscous lava can flowfreely, a broad, slightlydomed structure thatresembles a warrior’sshield is formed asshown in the figure. Anexample of this type isthe Mauna Loa inHawaii.

2. Cinder cones arebuilt from ejectedlava fragments.They have a steepslope, wide craterand are the mostabundant of thethree major volcanotypes. One exampleof this type is theParicutin in Mexico.

3. Composite cones orstratovolcanoes arelarge, nearly perfectsloped structureformed fromalternatesolidification of bothlava and pyroclasticdeposits. One perfectexample of this typeof cone is ourMayonVolcano.

• Geothermal energy - heat from the interior of the Earth.

- Geothermal power plants and geothermal heat pumps

- Used to generate electricity

- Places in the Philippines that uses geothermalpower plants as source of electricity are Tiwi(Albay), Kidapawan (North Cotabato), Calaca(Laguna), Tongonan (Leyte), Bago City ( NegrosOcc.), Valencia (Negros Or.), and Bacon(Sorsogon).

How do volcanic eruptions affect the society?

• Negative effects

- Lose of lives and properties

- Decreased in the Earth’s surfacetemperature

Can you name some?

Fig. Above: The Aftermath of Pinatubo Volcano Eruption (Photo credits: USGS)

• Positive Effects

- Spectacular scenery

- Production of very rich soil forfarming

- Making earthenware out of the ashfall

Signs of an impending volcanic eruption:

1. Increase in the frequency of volcanicquakes with rumbling sounds;occurrence of volcanic tremors.

2. Increased steaming activity; changein color of steam emission fromwhite to gray due to entrained ash.

3. Crater glow due to presence of magma at ornear the crater.

4. Ground swells (or inflation), ground tilt andground fissuring due to magma intrusion.

5. Localized landslides, rock falls and landslidesfrom the summit area which may notattributable to heavy rains.

6. Noticeable increase inn the extent of dryingup of vegetation around the volcano’s upperslopes.

7. Increase in the temperature of hot springs,wells (e.g., Bulusan and Canlaon) and craterlake (e.g., Taal) near the volcano;

8. Noticeable variation in the chemical contentof springs, crater lakes within the vicinity ofthe volcano;

9. Drying up of springs/wells around thevolcano; and,

10. Development of new thermal areas and/orreactivation of old ones; appearance ofsolfataras.

QUIZ…

1. Which among the following volcanoes is formed from:

a. cinders and ash?

b. mostly lava?

c. alternate solidification of lava and cinders?

1

2

3

2. Which of the following are active volcanoes?

I. Mayon in Albay

II. Taal in Batangas

III. Vulcan in Camiguin

IV. Kanlaon in Negros Or.

a. I and II only b. II and III only

c. I, II and III only d. I, II and IV only

3. Which of the following characteristics ofmagma mainly affect the explosiveness of avolcanic eruption?

a. color

b. amount

c. temperature

d. silica content

4. How does the eruption of a volcano lowerthe atmospheric temperature?

5. Give one positive effect and one negativeeffect of volcanic eruption.

6. Describe the shape of the volcanic cone formed from the following types of volcanic emission:

a. high temperature magma

b. low amount of gas magma

c. high silica content magma

The End…