Mount Mayon (My Backyard Volcano)
Why is a Volcano Here?
Mayon Volcano stands 150 miles south of Manila, the Philippine capital, and looms above the bustling city of Legazpi. More than 2400 meters (~8,000 feet) tall, Mayon is the most active of the numerous volcanoes dotting the Philippine Islands. The volcanoes of the Philippines, in turn, are part of a much longer chain of volcanoes, called the Ring of Fire, that encircles the Pacific Ocean from South America up to Alaska, across to Russia, and down through Japan and Indonesia.
The Ring of Fire. Intense tectonic activity occurs all around the perimeter of the Pacific Ocean. Along this length, the Pacific Plate and various smaller oceanic plates collide, scrape and subduct, or sink below, one another and the adjacent continental plates. This subduction - actually a string of subduction zones - generates the chain of volcanoes known as the Ring of Fire. The Philippines, part of the Ring of Fire, lie at the meeting point of at least three tectonic plates: the Eurasian, the South China Sea, and the Philippine plates.
The squeeze is on. The Philippine Islands are all that remain of a narrow - and gradually disappearing - oceanic plate. This "microplate" is wedged against the Eurasian and South China Sea plates to the west. Meanwhile, the Philippine plate is slowly advancing from the east. The microplate is caught in the middle. As a result, the islands are bounded by trenches, laced with faults, and are rife with seismic stress; earthquakes and volcanic eruptions are common events. The squeezing has been going on for 20 to 30 million years.
Stuck in the middle. The Philippines sit on a microplate that is caught between two subduction zones. The eastern zone, called the Philippine Trench, marks the boundary of the advancing Philippine plate. This zone gives rise to the Bicol Arc, a string of volcanoes that includes Mayon. The western subduction zone, called the Manila trench, occurs where the microplate meets the South China Sea plate. This zone feeds another string of volcanoes: the Bataan Arc, which includes Mount Pinatubo, the source of the biggest eruption of the 20th century.
Why does subduction cause volcanoes? When two tectonic plates collide, the heavier plate subducts, or descends, beneath the other, into the mantle below. Water in the descending plate is pressed out and rises into the mantle above. This water causes the mantle to partially melt.The melted rock, called magma, is more buoyant than the rock around it. The magma rises to the Earth's surface and forms a volcano. In fact, magma rises along the entire length of the subduction zone. The result is usually a string, or arc, of volcanoes.
A continent grows. For geologists, the Philippines offer an opportunity to watch new continental crust take shape - a process that is poorly understood. Subduction along the western margin of the Philippines is slowly pinning the islands against the Eurasian continent. In effect, the islands are being bulldozed into an ever-growing pile. The Philippines are being added to the landmass of the Eurasian Plate - and a large continent is becoming even larger.
Dying gasps. Volcanic activity in the Philippines is slowly changing. The archipelago is pinned against the Eurasian plate; it can't move any farther. As a result, subduction along the western zone (the Manila Trench) is slowing and eventually will stop. And when subduction stops, the volcanoes above (including Mount Pinatubo) become extinct. The eastern subduction zone, however, will grow: it will extend northward and join the Ryukyu Trench as the Philippine plate continues to sink below the Eurasian plate. So Mayon and the eastern volcanoes will keep on erupting.
The Recent Eruptions
In mid-February, a series of small earthquakes signalled to scientists that Mayon might soon erupt. On February 28, just before dawn, the drama began: explosive eruptions of lava, sulfurous ash and superheated steam. Fourteen explosions were recorded by late afternoon. The fiercest sent ash several kilometers into the air. Dr. Ronaldo Arboleda, of the Philippine Institute of Volcanology and Seismology, saw Mayon eject rocks "as big as houses." By late evening, lava trailed several kilometers down the volcano's flank.
Mayon remained active well after its initial outburst. For days, the volcano emitted clouds of superhot steam and ash that darkened skies and cascaded down the mountainside. These pyroclastic flows, powered by volcanic gases within them, reached temperatures in excess of 450 degrees centigrade (850 degrees Fahrenheit) and traveled as fast as 80 km (50 miles) per hour, incinerating everything in their path.
Lately Mayon has quieted down. Small tremors still occur, and the occasional puff of ash and steam is released. By early April, volcano experts had downgraded Mayon's status from Alert Level 5 ("Alarming") to Alert Level 2, which means that the probability of another explosive eruption at this point is minimal. Officials warn that mudslides and landslides still present a danger, particularly with the onset of the rainy season in the autumn. The 6 kilometers (4 miles) immediately surrounding the crater, however, remain permanently off-limits to people.
Will it happen again?
Mayon is the most active volcano in Philippines. And because so many people live on Mayon's slopes, Mayon's eruptions have often wrought calamity. More than 2,000 villagers perished in 1814, during Mayon's most violent eruption, when volcanic mudflows buried two nearby towns. To avert such tragedies, and to improve their own understanding of how volcanoes work, scientists at the Philippine Institute of Volcanology and Seismology constantly monitor Mayon for signs of new activity.
Although scientists didn't know exactly when Mayon would rewaken, they knew eventually it would. "The volcano had been quiet since 1993 and we all knew it would be erupting again one of these years," says Chris Newhall, a geologist with the U.S. Geological Service who has studied volcanoes in the Philippines extensively. The volcano showed renewed signs of unrest last June, when it began billowing steam and ash. Earthquakes and further ash releases in February, just days before the latest eruption, warned experts of the coming explosion.
By studying volcanoes like Mayon, scientists understand better than ever how to tell whether a major volcanic eruption is pending. The warning signs include:
Seismic activity. As magma rises toward Earth's surface, it displaces the rock around it, causing earthquakes. The frequency, intensity and location of earthquakes in turn can tell scientists how close the magma is to the surface, how fast it's moving - and roughly how soon it might erupt.
Ground tilt. As magma rises, but before it erupts, it wells to form a lava dome at or near the surface. By measuring the tilt of the ground at various points around the dome, and by monitoring how quickly the tilt increases or decreases, scientists can gauge how quickly magma is moving into the uppermost part of the volcano - and how soon it might erupt.
Gas emissions. The magma in subduction volcanoes is rich in dissolved gases, particularly sulfur dioxide. As the magma rises toward Earth's surface, the pressure exerted on it by the surrounding rock decreases. The decrease in pressure permits the dissolved gas to escape, like bubbles escaping from a newly opened soda can. When a volcano begins emitting more sulfur dioxide than usual, that's often a sign that fresh magma is on the move towards the surface.
Scientists have found that Mayon's eruptions are usually preceded by ground tilting and an increase in earthquakes and gas emissions. Also, the crater may begin to glow, or the volcano may give off audible rumbling sounds. What do these events add up to? Sometimes nothing at all happens, and the volcano returns to normal. Sometimes the volcano emits a minor puff of ash, as it did last June. And sometimes the volcano in fact erupts - if not within days, then within a few months.
Will Mayon erupt again? Without a doubt. Mayon's history, recent behavior and active tectonic setting suggest that the volcano will continue to erupt for thousands, or even hundreds of thousands of years to come. From a human perspective, however, there is good news: the number of Mayon's fatalities has dropped significantly in the past hundred years, even as the population of the surrounding area has grown. Mayon will never be completely safe - but volcanologists will continue to get better at forecasting its activity.
Eruptions aren't the only danger. An eruption produces tons of ash and debris, which settle loosely back to earth. Subsequent earthquakes (common around volcanoes) can jolt the debris free, causing deadly landslides. Heavy rains can cause lahars, or mudslides. Fortunately, Mayon's recent eruption happened during the Philippine dry season. But the danger is ever-present. In 1766, 2,000 people died when rivers of hot mud, set loose by rains months after one of Mayon's eruptions, swept over surrounding villages.
Volcanoes and Climate
A single volcano can dramatically alter weather patterns around the world. This was made clear in 1991, when Mount Pinatubo, a volcano in the western Philippines, erupted with astonishing force. 800 people were killed, and dust and gas were blasted more than 18 kilomters (12 miles) into the air. The debris formed a thin veil in the upper atmosphere, preventing some of the Sun's heat from reaching Earth's surface. In the following months, temperatures around the world dropped by several tenths of a degree. Could Mayon have the same effect?
Whether a volcano affects climate depends in large part on what it ejects. The key compound is sulfur dioxide. In the upper atmosphere, sulfur dioxide reacts with water molecules to form chemical compounds called aerosols. Aerosols scatter sunlight back into space, effectively cooling the earth; in fact many man-made pollutants create aerosols. During the eruption on June 15, 1991, Pinatubo emitted 18 to 20 megatons of sulfur. Mayon, in contrast, emitted 5,000 to 9,000 tons a day during its recent eruption - too little to have a global impact.
To affect global temperatures, a volcano must loft sulfur dioxide and dust particles very high into the atmosphere. The Pinatubo eruption of 1991 sent gases and debris 20 kilometers (12 miles) high, enough to reach the upper atmosphere. Here the sulfur dioxide molecules reacted with OH to form aerosols. High-altitude winds then carried the dust and aerosols around the globe. Mayon's eruption in February sent debris only about 13 kilometers (8 miles) up - that's high, but it's not stratospheric. In the end, it looks like Mayon won't have the cooling effect that Pinatubo did.
A monster eruption. Legend has it that "Frankenstein" was born, indirectly, from a climate-cooling volcano. In 1815, the Indonesian volcano Tambora erupted violently. 90,000 people were killed, and millions of tons of debris were blasted into the stratosphere. The following year was cold and dark in Europe; it became known as "the year without summer." That summer, Shelley and her husband Percy were holed up at the house of their friend Lord Byron; to amuse themselves, they wrote ghost stories. Mary's effort eventually became the classic story we know today.
Life Around Volcanoes
Mayon has erupted more than 40 times, several times with fatalities, since historians began keeping track in 1616. And yet a million people live within 14 kilometers (8 miles) of the volcano; tens of thousands live on the volcano itself. Worldwide, tens of millions of people live within close proximity of an active volcano. Why would a person choose to live on or near a volcano?
Why do people live near volcanoes? Because volcanic soils are especially fertile. To a farmer, a thin blanket of volcanic ash is free fertilizer from above - though it may take months for rain and weathering to release the ash's nutrients. The world's best coffee is grown on volcanic soil. The region around Naples, Italy, one of the richest farming areas in the world, is built in part on volcanic ash from nearby Vesuvius. The lower slopes of Mayon are covered with rice fields and coconut plantations; tomatoes and other vegetables grow further uphill.
Farming the soil of an active volcano is inherently risky. For poorer residents, however, it is often the only livelihood available. Mayon's eruption in 1993 killed 75 people - all of them tomato farmers in the Bonga Valley, one of the ravines declared off-limits by the government. Today nearly 20,000 locals live and farm within Mayon's Permanent Danger Zone. Half of these farmers refused to evacuate during the most recent eruption. Others returned surreptiously to tend their fields and animals: without their crops, they risked starvation.
Researches and Studies about Mayon
Chris Newhall, a geologist with the U.S. Geological Service, has been studying Mayon for 30 years. "I joined the Peace Corps in 1970," Newhall says. "I wanted to apply my geology training to humanitarian projects. They offered me a spot in a science-teacher training program in the Philippines. After a few months I began teaching Geology 101 in a small college at the foot of Mayon. It was perfect: I could study Mayon on weekends, and I managed to interest a few of my students in doing the same."
"Volcanoes in the Philippines are typical of volcanoes in the Ring of Fire," Newhall says. "One can study their magma to learn about the underlying mantle. Or one can focus, as I do, on the processes in the uppermost 10 kilometers (6 miles) or so, in shallow magma reservoirs and conduits. I'm interested in determining what leads to explosive eruptions, and how we can forecast when and how big such eruptions will be. This knowledge is critical for people who live at the foot of volcanoes."
Mayon Volcano stands 150 miles south of Manila, the Philippine capital, and looms above the bustling city of Legazpi. More than 2400 meters (~8,000 feet) tall, Mayon is the most active of the numerous volcanoes dotting the Philippine Islands. The volcanoes of the Philippines, in turn, are part of a much longer chain of volcanoes, called the Ring of Fire, that encircles the Pacific Ocean from South America up to Alaska, across to Russia, and down through Japan and Indonesia.
The Ring of Fire. Intense tectonic activity occurs all around the perimeter of the Pacific Ocean. Along this length, the Pacific Plate and various smaller oceanic plates collide, scrape and subduct, or sink below, one another and the adjacent continental plates. This subduction - actually a string of subduction zones - generates the chain of volcanoes known as the Ring of Fire. The Philippines, part of the Ring of Fire, lie at the meeting point of at least three tectonic plates: the Eurasian, the South China Sea, and the Philippine plates.
The squeeze is on. The Philippine Islands are all that remain of a narrow - and gradually disappearing - oceanic plate. This "microplate" is wedged against the Eurasian and South China Sea plates to the west. Meanwhile, the Philippine plate is slowly advancing from the east. The microplate is caught in the middle. As a result, the islands are bounded by trenches, laced with faults, and are rife with seismic stress; earthquakes and volcanic eruptions are common events. The squeezing has been going on for 20 to 30 million years.
Stuck in the middle. The Philippines sit on a microplate that is caught between two subduction zones. The eastern zone, called the Philippine Trench, marks the boundary of the advancing Philippine plate. This zone gives rise to the Bicol Arc, a string of volcanoes that includes Mayon. The western subduction zone, called the Manila trench, occurs where the microplate meets the South China Sea plate. This zone feeds another string of volcanoes: the Bataan Arc, which includes Mount Pinatubo, the source of the biggest eruption of the 20th century.
Why does subduction cause volcanoes? When two tectonic plates collide, the heavier plate subducts, or descends, beneath the other, into the mantle below. Water in the descending plate is pressed out and rises into the mantle above. This water causes the mantle to partially melt.The melted rock, called magma, is more buoyant than the rock around it. The magma rises to the Earth's surface and forms a volcano. In fact, magma rises along the entire length of the subduction zone. The result is usually a string, or arc, of volcanoes.
A continent grows. For geologists, the Philippines offer an opportunity to watch new continental crust take shape - a process that is poorly understood. Subduction along the western margin of the Philippines is slowly pinning the islands against the Eurasian continent. In effect, the islands are being bulldozed into an ever-growing pile. The Philippines are being added to the landmass of the Eurasian Plate - and a large continent is becoming even larger.
Dying gasps. Volcanic activity in the Philippines is slowly changing. The archipelago is pinned against the Eurasian plate; it can't move any farther. As a result, subduction along the western zone (the Manila Trench) is slowing and eventually will stop. And when subduction stops, the volcanoes above (including Mount Pinatubo) become extinct. The eastern subduction zone, however, will grow: it will extend northward and join the Ryukyu Trench as the Philippine plate continues to sink below the Eurasian plate. So Mayon and the eastern volcanoes will keep on erupting.
The Recent Eruptions
In mid-February, a series of small earthquakes signalled to scientists that Mayon might soon erupt. On February 28, just before dawn, the drama began: explosive eruptions of lava, sulfurous ash and superheated steam. Fourteen explosions were recorded by late afternoon. The fiercest sent ash several kilometers into the air. Dr. Ronaldo Arboleda, of the Philippine Institute of Volcanology and Seismology, saw Mayon eject rocks "as big as houses." By late evening, lava trailed several kilometers down the volcano's flank.
Mayon remained active well after its initial outburst. For days, the volcano emitted clouds of superhot steam and ash that darkened skies and cascaded down the mountainside. These pyroclastic flows, powered by volcanic gases within them, reached temperatures in excess of 450 degrees centigrade (850 degrees Fahrenheit) and traveled as fast as 80 km (50 miles) per hour, incinerating everything in their path.
Lately Mayon has quieted down. Small tremors still occur, and the occasional puff of ash and steam is released. By early April, volcano experts had downgraded Mayon's status from Alert Level 5 ("Alarming") to Alert Level 2, which means that the probability of another explosive eruption at this point is minimal. Officials warn that mudslides and landslides still present a danger, particularly with the onset of the rainy season in the autumn. The 6 kilometers (4 miles) immediately surrounding the crater, however, remain permanently off-limits to people.
Will it happen again?
Mayon is the most active volcano in Philippines. And because so many people live on Mayon's slopes, Mayon's eruptions have often wrought calamity. More than 2,000 villagers perished in 1814, during Mayon's most violent eruption, when volcanic mudflows buried two nearby towns. To avert such tragedies, and to improve their own understanding of how volcanoes work, scientists at the Philippine Institute of Volcanology and Seismology constantly monitor Mayon for signs of new activity.
Although scientists didn't know exactly when Mayon would rewaken, they knew eventually it would. "The volcano had been quiet since 1993 and we all knew it would be erupting again one of these years," says Chris Newhall, a geologist with the U.S. Geological Service who has studied volcanoes in the Philippines extensively. The volcano showed renewed signs of unrest last June, when it began billowing steam and ash. Earthquakes and further ash releases in February, just days before the latest eruption, warned experts of the coming explosion.
By studying volcanoes like Mayon, scientists understand better than ever how to tell whether a major volcanic eruption is pending. The warning signs include:
Seismic activity. As magma rises toward Earth's surface, it displaces the rock around it, causing earthquakes. The frequency, intensity and location of earthquakes in turn can tell scientists how close the magma is to the surface, how fast it's moving - and roughly how soon it might erupt.
Ground tilt. As magma rises, but before it erupts, it wells to form a lava dome at or near the surface. By measuring the tilt of the ground at various points around the dome, and by monitoring how quickly the tilt increases or decreases, scientists can gauge how quickly magma is moving into the uppermost part of the volcano - and how soon it might erupt.
Gas emissions. The magma in subduction volcanoes is rich in dissolved gases, particularly sulfur dioxide. As the magma rises toward Earth's surface, the pressure exerted on it by the surrounding rock decreases. The decrease in pressure permits the dissolved gas to escape, like bubbles escaping from a newly opened soda can. When a volcano begins emitting more sulfur dioxide than usual, that's often a sign that fresh magma is on the move towards the surface.
Scientists have found that Mayon's eruptions are usually preceded by ground tilting and an increase in earthquakes and gas emissions. Also, the crater may begin to glow, or the volcano may give off audible rumbling sounds. What do these events add up to? Sometimes nothing at all happens, and the volcano returns to normal. Sometimes the volcano emits a minor puff of ash, as it did last June. And sometimes the volcano in fact erupts - if not within days, then within a few months.
Will Mayon erupt again? Without a doubt. Mayon's history, recent behavior and active tectonic setting suggest that the volcano will continue to erupt for thousands, or even hundreds of thousands of years to come. From a human perspective, however, there is good news: the number of Mayon's fatalities has dropped significantly in the past hundred years, even as the population of the surrounding area has grown. Mayon will never be completely safe - but volcanologists will continue to get better at forecasting its activity.
Eruptions aren't the only danger. An eruption produces tons of ash and debris, which settle loosely back to earth. Subsequent earthquakes (common around volcanoes) can jolt the debris free, causing deadly landslides. Heavy rains can cause lahars, or mudslides. Fortunately, Mayon's recent eruption happened during the Philippine dry season. But the danger is ever-present. In 1766, 2,000 people died when rivers of hot mud, set loose by rains months after one of Mayon's eruptions, swept over surrounding villages.
Volcanoes and Climate
A single volcano can dramatically alter weather patterns around the world. This was made clear in 1991, when Mount Pinatubo, a volcano in the western Philippines, erupted with astonishing force. 800 people were killed, and dust and gas were blasted more than 18 kilomters (12 miles) into the air. The debris formed a thin veil in the upper atmosphere, preventing some of the Sun's heat from reaching Earth's surface. In the following months, temperatures around the world dropped by several tenths of a degree. Could Mayon have the same effect?
Whether a volcano affects climate depends in large part on what it ejects. The key compound is sulfur dioxide. In the upper atmosphere, sulfur dioxide reacts with water molecules to form chemical compounds called aerosols. Aerosols scatter sunlight back into space, effectively cooling the earth; in fact many man-made pollutants create aerosols. During the eruption on June 15, 1991, Pinatubo emitted 18 to 20 megatons of sulfur. Mayon, in contrast, emitted 5,000 to 9,000 tons a day during its recent eruption - too little to have a global impact.
To affect global temperatures, a volcano must loft sulfur dioxide and dust particles very high into the atmosphere. The Pinatubo eruption of 1991 sent gases and debris 20 kilometers (12 miles) high, enough to reach the upper atmosphere. Here the sulfur dioxide molecules reacted with OH to form aerosols. High-altitude winds then carried the dust and aerosols around the globe. Mayon's eruption in February sent debris only about 13 kilometers (8 miles) up - that's high, but it's not stratospheric. In the end, it looks like Mayon won't have the cooling effect that Pinatubo did.
A monster eruption. Legend has it that "Frankenstein" was born, indirectly, from a climate-cooling volcano. In 1815, the Indonesian volcano Tambora erupted violently. 90,000 people were killed, and millions of tons of debris were blasted into the stratosphere. The following year was cold and dark in Europe; it became known as "the year without summer." That summer, Shelley and her husband Percy were holed up at the house of their friend Lord Byron; to amuse themselves, they wrote ghost stories. Mary's effort eventually became the classic story we know today.
Life Around Volcanoes
Mayon has erupted more than 40 times, several times with fatalities, since historians began keeping track in 1616. And yet a million people live within 14 kilometers (8 miles) of the volcano; tens of thousands live on the volcano itself. Worldwide, tens of millions of people live within close proximity of an active volcano. Why would a person choose to live on or near a volcano?
Why do people live near volcanoes? Because volcanic soils are especially fertile. To a farmer, a thin blanket of volcanic ash is free fertilizer from above - though it may take months for rain and weathering to release the ash's nutrients. The world's best coffee is grown on volcanic soil. The region around Naples, Italy, one of the richest farming areas in the world, is built in part on volcanic ash from nearby Vesuvius. The lower slopes of Mayon are covered with rice fields and coconut plantations; tomatoes and other vegetables grow further uphill.
Farming the soil of an active volcano is inherently risky. For poorer residents, however, it is often the only livelihood available. Mayon's eruption in 1993 killed 75 people - all of them tomato farmers in the Bonga Valley, one of the ravines declared off-limits by the government. Today nearly 20,000 locals live and farm within Mayon's Permanent Danger Zone. Half of these farmers refused to evacuate during the most recent eruption. Others returned surreptiously to tend their fields and animals: without their crops, they risked starvation.
Researches and Studies about Mayon
Chris Newhall, a geologist with the U.S. Geological Service, has been studying Mayon for 30 years. "I joined the Peace Corps in 1970," Newhall says. "I wanted to apply my geology training to humanitarian projects. They offered me a spot in a science-teacher training program in the Philippines. After a few months I began teaching Geology 101 in a small college at the foot of Mayon. It was perfect: I could study Mayon on weekends, and I managed to interest a few of my students in doing the same."
"Volcanoes in the Philippines are typical of volcanoes in the Ring of Fire," Newhall says. "One can study their magma to learn about the underlying mantle. Or one can focus, as I do, on the processes in the uppermost 10 kilometers (6 miles) or so, in shallow magma reservoirs and conduits. I'm interested in determining what leads to explosive eruptions, and how we can forecast when and how big such eruptions will be. This knowledge is critical for people who live at the foot of volcanoes."
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