Volcanism refer s to the ejection of molten materials from a volcano. A volcano is a mountain or a hill in a restricted vent in the earth’s crust. Through this vent, gases and other hot materials are expelled. These ejected materials accumulate around the vent and form volcanic cone forms. The top of the volcano is called the crater.

According to the Philippine Institute of Volcanologist and Seismology, there are 32 volcanoes in the Philippines. The most famous and beautiful of these volcanoes is Mt. Mayon in Albay Province. Volcanologists fear that this eruption has changed the perfect cone shape of the volcano.

Volcanic Products Volcanic products are materials that come out of

a volcano. These eruptive products are a mixture of gaseous, liquid and solid materials

Fragmental Material The fragments of magma quickly solidify and for

pyroclastic( meaning fire-broken) fragments. When the fragments are from 2 to 64mm in size, they are called lapilli. When they are smaller than 2mm, the fragments are called ash. It refers to tiny, powderlike fragments.

Gases The most abundant are water vapor, carbon dioxide, sulfur dioxideand hydrogen sulfide.

Volcanic GasesSample from present day volcanoes indicate the 50% to 80% of all volcanism gases are water vapor, with lesser amounts of carbon dioxide, nitrogen, sulfur gases, especially sulfur dioxide and hydrogen sulfide.

Formation of LavaMelting of solid rock to form magma is controlled by three physical parameters: its temperature, pressure, and composition.

The surfaces produced by lavaflows often reflect their internal movement in relation to their congealing crust.  Sheet- and pahoehoe lava flows result in continuous surfaces.  Aa- and block flows result indiscontinuous surfaces.  The terms "pahoehoe" and "aa" are Hawaiian words.

Pahoehoe lavas are thin.  They flow smoothly and are often formed by small volumes of hot, fluid basalt.  The higher the volume of lava emitted the faster the current.  Pahoehoe flows move forwards in tongues or lobes and are characterized by a glassy, plastic skin.  They may embrace obstacles at a rate of about 50m an hour.  When the pahoehoe lava flow cools, it often solidifies to a smooth surface.

Sheet lavas emerge from fissure systems forming flows commonly ranging between 10m and 30m in thickness.  They flow out so fast that vast volumes of basalt are discharged over an enormous area.  Featurelesslava plateaus are formed.  During the eruption of Roza, Oregon, 14 million years ago, 1500km3 of sheet lavas were produced in about a week.

 Aa flows are emitted from the vent at high rates ranging to 50km an hour, often with much lava fountaining.  They are characteristic of viscousmagmas.  Aa flows are animated with sporadic bursts of energy.  They may push down houses, walls and forests.  However, the hallmark of aa lava flows is the very rough surface it produces when it cools and solidifies.

The different parts of a Volcano

Magma - Molten rock beneath Earth's surface.

Parasitic Cone - A small cone-shaped volcano formed by an accumulation of volcanic debris.

Sill - A flat piece of rock formed when magma hardens in a crack in a volcano.Vent - An opening in Earth's surface through which volcanic materials escape.

Flank - The side of a volcano.Lava - Molten rock that erupts from a volcano that solidifies as it cools.

Crater - Mouth of a volcano - surrounds a volcanic vent.

Conduit - An underground passage magma travels through.

Summit - Highest point; apexThroat - Entrance of a volcano. The part of the conduit that ejects lava and volcanic ash.

Ash - Fragments of lava or rock smaller than 2 mm in size that are blasted into the air by volcanic explosions.

Ash Cloud - A cloud of ash formed by volcanic explosions.

Ten largest volcanoes in the world1.Mount Mazama/Crater Lake, Oregon-Over 6,000 years ago Mount Mazama (posthumously named) erupted. Before the explosion the mountain was 12,000 feet high; when it was over it had been replaced by a 1,900-foot deep crater. Crater Lake, famed for its intense blue waters, was made a National Park in 1902. Volcanic activity occurred some time after the Mount Mazama explosion, creating Wizard Island in the middle of the lake. See Crater Lake National Park

2. Mount Etna, Sicily-Although Mount Etna (or Aetna) is the highest active volcano in Europe, its renown comes from its role in Greek legends and in ancient works by writers such as Hesiod, Pindar and Aeschylus. According to Greco-Roman mythology, the giants -- the enemies of the gods -- were buried beneath Mount Etna. In their efforts to break free, the Giants caused frequent earthquakes around the mountain. The most recent eruption, in the Bove Valley section of Etna Volcano Park, occurred in December 1991. © 1998 Parco dell'Etna

3. Mount Vesuvius, Italy-Vesuvius' eruption in 79 A.D. covered the cities of Pompeii and Herculaneum, preserving them for generations to come. But this eruption also holds a place in history because of its documentation. Pliny the Younger left a detailed description of the event in two letters to Tacitus. A type of eruption -- the Plinian type -- is named for Pliny the Elder who died in the catastrophe. The volcano is still active and has had several eruptions -- the most deadly being in 1631. Check out this Mount Vesuvius page. Picture: UPI/Corbis-Bettmann | 

4. Mount Tambora, Indonesia-The largest eruption during the last two centuries, as well as the deadliest volcano in recorded history, Mount Tambora exploded April 10-11, 1815. It killed an estimated 92,000 people. Almost 80,000 of the victims died of starvation brought on by the agricultural devastation in the volcano's wake. The eruption and the resulting massive clouds of dust and ash affected most of the Northern Hemisphere, causing unusually cool temperatures and failed crops in 1816 -- sometimes referred to as "the year without a summer."

5. Mount Krakatau, Indonesia-On August 27, 1883, Mount Krakatau exploded with such force that it was heard in Australia, over 2,000 miles away. The force of the eruption triggered a series of tsunamis that reached the Hawaiian islands and the coast of South America, killing more than 36,000 people. The five cubic miles of ejecta covered the surrounding areas in darkness for over two days and caused a series of dramatic sunsets around the world throughout the following year. The explosion and subsequent collapse of the volcano left only a remnant of the island above sea level. By 1928, another small island had emerged from a rising volcanic cone. Visit Krakatau, Indonesia.

6. Mount Pelee, Martinique-The eruption on May 8, 1902, killed 29,000, destroying the port town of Saint-Pierre four miles away. Almost all the deaths were caused by the resulting pyroclastic flow -- a deadly, fast-moving cloud of hot gas and dense liquidized volcanic particles.Only two residents of the town survived the flow. Volcanology (also called Volcanism) was at best a primitive science in 1902, and the existence of pyroclastic flows was unknown. After this disaster a "new" type of eruption was named after Mount Pelee - the Pelean-type eruption. See Mount Pelee eruption.Photograph of the remains of St. Pierre by Heilprin, 1902.

7. Parícutin, Mexico-In February 1943, a pile of ash began to rise from a corn field near the town of Parícutin, Mexico. A mountain began to emerge from the earth, reaching a height of 1,200 feet in one year. Although the ensuing nine-year eruption resulted in the destruction of the town of Parícutin, it presented the modern world with a remarkable opportunity to see the birth of a volcano. Only three people died, all by lightning associated with the eruption.

8. Mount St. Helens, Washington-One of the more highly publicized and studied volcanic explosions, Mount St. Helens erupted on May 18, 1980. The volcano, which had been dormant since 1857, began erupting steam after a series of earthquakes in March 1980. The 1978 prediction of the U.S. Geological Survey that violent and intermittent volcanic activity would begin, "within the next 100 years, and perhaps even before the end of this century," had come true. Luckily, close study of St. Helens prevented a major loss of life. Even so, 60 deaths resulted from the May 18 eruption. Learn more about Mount St. Helens.

9. Nevada del Ruiz, Colombia-Although the eruption of Nevado del Ruiz (or Mount Ruiz) on November 13, 1985, was relatively small, the ensuing mudslides caused by melting ice and snow resulted in the the death of 23,000 people and the destruction of the town of Armero. Most of the residents would have survived had they moved to higher ground. This eruption brought attention to the fact that growing numbers of people live within the danger zones of the world's volcanoes. A larger eruption of Ruiz in 1845 killed about 700 people. VisitNevada del Ruiz.

10. Mount Pinatubo, Philippines-Killing almost 800 and leaving an estimated 100,000 homeless, Mount Pinatubo's eruption in June 1991 was 10 times larger than the Mount St. Helens' eruption and one of the biggest of the 20th century. It emitted a cloud of smoke and ash over 19 miles high. The evacuation of more than 70,000 people and the volcanic event were broadcast worldwide, making Pinatubo (in)famous throughout the world. Learn more about Mount Pinatubo.

Signs that a volcano is going to erupt.

The temperature of rocks in the volcanic cone increase.Changes in shape of the volcanic cone. Most of the time the cone starts to swell or bulge just before a eruption.A number of increases in small earthquakes or tremors around a volcanoEmission of gas and steam from a volcano.

The disadvantages of living near a volcano

When the volcano erupts it can do many things such as: -Kill people -Destroy crops and plantation -Suffocate people from the ashes 

The benefits of living near volcanoes- AgricultureVolcanic ash makes extremely fertile soil. Grape vines particularly grow extremely well in volcanic ash-soil, aside from other regular crops. The Ancient Romans realised this, which is the reason a lot of Roman vineyards are surrounded by volcanoes. Today, grapes grown in volcanic regions produce the best-rated wine on the globe. Crops can grow very well in volcanic soil, even if water isn't so common! - MaterialVolcanic Tuff, Pozzolona, Ignimbrite, Obsidian, Volcanic Glass, Pumice and so on. These are different rock variations formed by volcanoes and lava. Pozzolona for example is even tougher than concrete, and was used in many official and royal buildings throughout the Roman and Greek Empires. Pumice was, and still is today, used for personal hygiene. There is archaeological evidence that prehistoric man used volcanic rock to produce stronger weapons and tools than standard stone. - Geothermal EnergyFree, renewable, infinite energy and heat. In Iceland, a quarter of the country's electricity is produced by harvesting geothermal energy from its many volcanoes. It's also used to heat water for heating and hygiene. the Vikings, Romans and Greeks in particular harvested geothermal heat from volcanoes, usually for public baths. The Romans used geothermal heat to invent the worlds first central heating, by channelling the geothermal heat through complex plumbing underneath houses to provide underfloor-heating(however that would mean the settlement has to be really close to the source otherwise the heated water would run cold again. City of Pompeii anyone?).

- JobsVolcanoes erupt and adventurers get lost in volcanic mountains. This provides jobs for local people, as specialist rescue experts would need to be on hand at all costs. 

- AestheticsVolcanic mountains and volcanic islands are amongst some of the most beautiful places on Earth. They provide a peaceful, serene and relaxed scenery for all to enjoy (until it erupts of course). Tahiti and Bora Bora, islands surrounded by volcanoes, are considered to be paradise locations. 

- TourismPretty much the same as Aesthetics. The stunning scenery attracts tourists. Tourists bring money. Volcano country gets rich. 

- ScienceVolcanoes help us understand how Earth was born, the stages which it developed through, the magnetic field and so on. Wherever there's an active volcano, a scientists facility will be nearby. Of course aside from contributing to science, the scientists can also predict when eruptions will occur, providing locals with enough time to evacuate.