Volcanic craters are fissures in the Earth that release heat and gases. Volcanoes are cone-shaped mountains formed when magma and other hot materials from deep within the Earth are erupted through cracks in the Earth's crust and erupt out of the ground. It is also known as a volcano in earth science. There are active volcanoes and extinct volcanoes. Active volcano that is recorded in human history often or periodic eruptions of the volcano; dead volcano that is recorded in human history has not erupted in the volcano, but no one can not know when they will suddenly wake up in their sleep.
There are 2 largest belts of volcanic activity on Earth: the Pacific Rim Volcanic Belt and the Mediterranean Volcanic Belt. There are more than 850 active volcanoes in the world (more than 700 on land and more than 100 under the sea), 3/4 of which are located in the Pacific Rim Volcanic Belt, which has become the "Ring of Fire" worn by the Earth. Active volcano eruption is no regularity can be found, he seems to be an unlimited power of God's Rex, the outbreak of the power generated by people can not imagine. 1980 May 18, the United States, Washington State, St. Helens volcano eruption, the satellite photographed precious photographs, after analysis, the eruption of a volcanic shockwave through the 200-kilometer-thick atmosphere, the release of the equivalent of the United States put into Hiroshima in that year, 500 atomic bombs of the energy. The energy of more than 500 atomic bombs dropped on Hiroshima by the United States. The hot gushing magma destroyed houses, bridges, highways, forests, people and animals.
At least 20 cities around the world were instantly and completely destroyed by erupting volcanoes. One of the earliest records is from ancient Greece in 1470 BC, when the bustling ancient city of Knossos was flattened by the sudden eruption of the Santorin Island volcano, which sent 50-meter-high waves sweeping across the islands and coasts of the eastern Mediterranean Sea, instantly destroying the center of the Minoan civilization, as well as the island of Crete, 130 kilometers away.
Vesuvius in Italy in 79 A.D., which in an instant will be nearby Pompeii, Stabia, Gerculalum, Opolonji four prosperous for a while of ancient castles buried under the volcanic eruption. These have left human civilization with eternal regrets. Also makes mankind realize that our so-called brilliant civilization in front of the might of nature is so pale and powerless, and volcanic eruptions bring disaster is so irresistible. Volcanic eruptions in addition to the direct destruction of all, but also triggered a series of disasters - fires, tsunamis, mudslides, floods, the formation of crater lakes that may break at any time, the ash is very small, with the wind to fly to distant places or rise to the heights of the long-term diffusion, resulting in reduced visibility, leading to air accidents, traffic accidents, and even make the climate change! The Asama volcano erupted in 1783, causing "cold summers" in Japan and even freezing in the northeast. Volcanic eruptions: carbon dioxide, sulfur dioxide, hydrogen, chlorine, hydrogen sulfide, etc. can also pollute the air, forming acid rain and creating a greenhouse effect.
Volcano ignited a fire: January 7, 1977 Nyiragongo volcano erupted in Africa, burning Zaire, Rwanda, the two countries 430 square kilometers of tropical rainforest.
Volcano triggered a tsunami: August 27, 1883 in the Strait of Utah, Indonesia, Krakatoa erupted, triggering the largest tsunami ever recorded by mankind, setting off waves as high as 30 to 40 meters high, engulfing all the ships in this sea area, Java Island, Sumatra Island, the coast of the houses, vehicles, people and animals were all swept into the rough sea. Indonesia alone has 36,000 people killed in this tsunami, the economic loss is incalculable.
Volcanoes cause mudslides: In February 1943, Mexico's Palikona volcano erupted, and nearby slopes were covered with sixty to seventy centimeters of ash. When hurricane-force rains swept through Mexico, mudslides formed, instantly burying three villages and dozens of villagers below the mountain and destroying more than 600 square kilometers of farmland.
Volcano triggered floods: November 13, 1985 Tolima Province, Colombia, is located in the 5,000-meter plateau of the Luis volcano erupted, the thousands of years of snow instantly melted, flash floods, flooding more than 30,000 square kilometers, so that 25,000 people lost their lives, 130,000 people homeless, 150,000 livestock deaths, more than 200 square kilometers of farmland, orchards were destroyed, the direct economic losses more than 5 billion dollars.
Types of Volcanoes
Volcanoes are diverse and can be categorized as extinct, dormant and active according to their activities. A dead volcano is a volcano that has erupted in prehistory but has never been active in recorded history. Such volcanoes have lost their ability to be active. Some volcanoes still maintain a complete volcanic form, some have suffered weathering erosion, only the remains of the volcano is incomplete, China's Shanxi Datong Volcanic Group in a radius of about 50 square kilometers, the distribution of two isolated volcanic cone, which Wolf Wo mountain volcanic cone height of nearly 120 meters. Dormant volcano, refers to the history of once erupted. But for a long time in a relatively static state of the volcano. Such volcanoes are well preserved volcanic form, still has the ability of volcanic activity, or can not be concluded that it has lost the ability of volcanic activity. Such as China's Baitoushan Tianchi, had in 1597 and 1792 two eruptions, before that there are many activities. At present, although there is no eruptive activity, but from the slopes of some unfathomable jet holes continue to spew out high temperature gas, it can be seen that the volcano is currently in a dormant state. Active volcanoes are those that are still active or periodically erupt in modern times. This type of volcano is in the peak period of activity. Such as claw spit on the island of melapi volcano, this century, the average interval of two two years to continue to erupt a period of time, China's recent volcanic activity in Taiwan island datun volcano group of the main peak of the seven star mountain is most famous. On the mainland, only in 95 years in Xinjiang Kunlun Mountains western section of the Yutian Caldasi volcanic group has eruption records. The eruption formed a flat-topped volcanic cone with a summit elevation of 4,900 meters, a cone height of 145 meters, a diameter of 642 meters at the base of the cone, a diameter of 175 meters at the top, and a crater depth of 56 meters.
It should be noted that there are no strict boundaries between these three types of volcanoes. Dormant volcanoes can be revived, dead volcanoes can be "resurrected" are not static. In the past, it has been thought that Italy's Mount Vesuvius is a dead volcano, at the foot of the volcano, people built many towns and vineyards on the slopes of the volcano, but in 79 A.D. Mount Vesuvius suddenly erupted, the high temperature of the volcano's eruption took over the unsuspecting Pompeii and Herculaneum, the two ancient cities, the two cities and their inhabitants were all destroyed and lost their lives.
When a volcano erupts, the exit where gases, magma, solids, and other materials are discharged outward is called a crater. Generally, there is only one crater at a time for a central eruption, but the vast majority of volcanoes have multiple eruptions. Some of the subsequent eruptions are from the original crater, but more often they erupt on its side, thus forming new craters called parasitic craters. In addition to central eruptions there are also fissure eruptions, in which erupted material is ejected from a fissure in the earth's crust. The craters it forms are more numerous. For example, in the Laki eruption in Iceland, lava flowed continuously from 105 craters lined up in a 32-kilometer-long fissure. Craters are mostly circular in shape and are generally divided into five categories: symmetrical craters, asymmetrical craters, fissure craters, craters with no visible craters, and sunken craters. There is a more specialized category of volcanic craters called broken craters. It is because the volcanic eruption is too violent, a huge amount of magma at once will be the volcanic neck and the surrounding rocks rushed away, this eruption caused by the caldera, often more than 5 kilometers in diameter, violent eruption in addition to the formation of broken caldera, but also to make the volcano's height is greatly reduced. For example, the Tambora eruption produced a crater 12 kilometers in diameter, and the altitude was reduced by 1400 meters.
Earthquakes
The vibration of the Earth's surface caused by the sudden release of slowly accumulating energy within the Earth is called an earthquake. Due to the constant movement and change of the earth, different parts of the earth's crust are subjected to forces such as extrusion, stretching, spinning and twisting, gradually accumulating energy, and in certain vulnerable parts, rock layers are prone to sudden rupture, causing fractures and misalignments, and so earthquakes are triggered.
Several basic concepts about earthquakes;
Earthquake source: the place where a rupture occurs directly within the earth;
Earthquake epicenter: the place on the ground directly opposite the source of the earthquake;
Earthquake depth: the distance from the source of the earthquake to the epicenter;
Earthquake epicenter distance: the distance from the epicenter of the earthquake to any one of the observation points on the ground;
Extreme seismic region: the region of the earthquake with the most serious degree of damage.
Extreme seismic region: the region with the most serious damage after an earthquake.
Magnitude is a measure of the size of an earthquake, based on how much energy it releases, and is expressed as a "magnitude".
Magnitude is calculated from the records of seismic instruments, and the stronger the earthquake, the greater the magnitude. A magnitude difference of one degree results in an energy difference of about 30 times.
The classification of earthquakes according to magnitude:
Weak earthquakes: earthquakes with a magnitude less than 3;
Sensed earthquakes: earthquakes with a magnitude equal to or greater than 3, or less than or equal to sung 5;
Medium-strength earthquakes: earthquakes with a magnitude greater than sung 5, or less than sung 6;
Strong earthquakes: earthquakes with a magnitude equal to or greater than 6. An earthquake with a magnitude greater than or equal to 8 is also called a major earthquake.
The intensity of an earthquake is the degree of damage to the ground and buildings by the earthquake, expressed in degrees. China classifies earthquakes as having an intensity of 12 degrees.
Earthquake magnitude and intensity are two completely different concepts, the magnitude is only related to the amount of energy released by the earthquake, is expressed in the size of the earthquake metrics, so an earthquake is only a magnitude; while the intensity of the ground by the extent of the damage caused by earthquakes, but different places, but there is only one epicenter of the intensity of the earthquake.
In general, the greater the magnitude, the higher the intensity. The same earthquake, the epicenter of the different distances from the intensity of the place is not the same (in general, the epicenter of the region by the highest degree of damage, the intensity of the value is called the epicenter of the intensity, with the increase in the distance from the epicenter of the earthquake caused by the gradual reduction of the damage). The size of the intensity in addition to the magnitude, epicenter distance, but also with the depth of the epicenter, geological structure and rock properties and other factors.
Volcanoes are diverse, according to their activity can be divided into three categories: extinct, dormant and active volcanoes. Dead volcano, refers to the prehistoric eruption, but has not been active in history of the volcano. Such volcanoes have lost their ability to be active. Some volcanoes still maintain a complete volcanic form, some have suffered weathering erosion, only the remains of the volcano is incomplete, China's Shanxi Datong Volcanic Group in a radius of about 50 square kilometers, the distribution of two isolated volcanic cone, which Wolf Wo mountain volcanic cone height of nearly 120 meters. Dormant volcano, refers to the history of once erupted. But for a long time in a relatively static state of the volcano. Such volcanoes are well preserved volcanic form, still has the ability of volcanic activity, or can not be concluded that it has lost the ability of volcanic activity. Such as China's Baitoushan Tianchi, had in 1597 and 1792 two eruptions, before that there are many activities. At present, although there is no eruptive activity, but from the slopes of some unfathomable jet holes continue to spew out high temperature gas, it can be seen that the volcano is currently in a dormant state. Active volcanoes are those that are still active or periodically erupt in modern times. This type of volcano is in the peak period of activity. Such as claw spit on the island of merapi volcano, this century, the average interval of two two years to continue to erupt a period of time, China's recent volcanic activity in Taiwan island datun volcano group of the main peak of the seven star mountain is most famous. On the mainland, only in 95 years in Xinjiang Kunlun Mountains western section of the Yutian Caldasi volcanic group has eruption records. The eruption formed a flat-topped volcanic cone with a summit elevation of 4,900 meters, a cone height of 145 meters, a diameter of 642 meters at the base of the cone, a diameter of 175 meters at the top, and a crater depth of 56 meters.
It should be noted that there are no strict boundaries between these three types of volcanoes. Dormant volcanoes can be revived, dead volcanoes can be "resurrected" are not static. In the past, it has been thought that Italy's Mount Vesuvius is a dead volcano, at the foot of the volcano, people built many towns and vineyards on the slopes of the volcano, but in 79 A.D. Mount Vesuvius suddenly erupted, the high temperature of the volcano's eruption took over the unsuspecting Pompeii and Herculaneum, the two ancient cities, the two cities and their inhabitants were all destroyed and lost their lives.
When a volcano erupts, the exit where gases, magma, solids, and other materials are discharged outward is called a crater. Generally, there is only one crater at a time for a central eruption, but the vast majority of volcanoes have multiple eruptions. Some of the subsequent eruptions erupt from the original crater, but more often they erupt on its side, resulting in the formation of a new crater, called a parasitic crater. In addition to central eruptions there are also fissure eruptions, in which erupted material is ejected from a fissure in the earth's crust. The craters it forms are more numerous. For example, in the Laki eruption in Iceland, lava flowed continuously from 105 craters lined up in a 32-kilometer-long fissure. Craters are mostly circular in shape and are generally divided into five categories: symmetrical craters, asymmetrical craters, fissure craters, craters with no visible craters, and sunken craters. There is a more specialized category of volcanic craters called broken craters. It is because the volcanic eruption is too violent, a huge amount of magma at once will be the volcanic neck and the surrounding rocks rushed away, this eruption caused by the caldera, often more than 5 kilometers in diameter, violent eruption in addition to the formation of broken caldera, but also to make the volcano's height is greatly reduced. For example, the Tambora eruption produced a crater 12 kilometers in diameter and a consequent reduction in altitude of 1,400 meters.
On our planet, volcanism generally occurs in unusual geologic settings, most of which are at the boundaries of the massive plates that make up the lithosphere. About 80 percent of Earth's active volcanoes and their associated volcanism occur where two plates come together and one subducts beneath the other. The subducting plate, on the one hand, is locally pressurized by compression and, on the other hand, melts itself into magma; at this point, if cracks or weaknesses appear in the compressed plate above it, the extremely pressurized magma erupts out of these places, forming volcanoes. There is a different situation, on the axis of mid-oceanic ridges, where magma emerges from the mantle and separates to the sides of the ridge, forming a new ocean floor. This type of volcanism actually occurs underwater.
Volcanic eruptions volcanic eruptions
The nature of the magma, the pressure of the underground magma reservoir, the shape of the volcanic channel, the eruption of the environment (land or underwater) and other factors, so that the form of eruption is very different, there are generally some of these classifications:
1, fissure-type eruption
Magma along the crust of the earth's huge fissure spills over to the surface, known as the fissure eruption. fissure eruption. This type of eruption is not a strong explosive phenomenon, the ejected material is mostly basal lava, condensation tends to form a wide area covered by lava terrace. Such as the distribution of China's southwest Sichuan, Yunnan and Guizhou provinces in the junction area of the Permian Emeishan basalt and Hebei Zhangjiakou north of the Tertiary Hannaoba basalt are fissure type eruption. Modern fissure eruptions are mainly distributed in the ocean floor at the mid-ocean ridge, only Iceland on the continent can be seen in this type of volcanic eruption activity, so it is also known as Iceland-type volcanoes.
2, the center of the eruption
Underground magma through the tubular volcanic channel out of the surface, known as the center of the eruption. This is the main form of modern volcanic activity, and can be subdivided into three kinds:
Tranquility: volcanic eruption. Only a large number of hot lava from the caldera quiet overflow, along the mountain slopes flow slowly, as if the boiling rice soup from the rice pot boiling out of the same. Overflow to the base of the lava is mainly, lava temperature is high, viscosity is small, easy to flow. Containing less gas, no explosive phenomenon, the Hawaiian volcanoes as its representative, also known as Hawaii type. This type of volcano people can enjoy.
Explosive; volcano eruption, resulting in violent explosions, while spewing out a large amount of gas and volcanic debris material, spewing out of the lava to the acidic lava is mainly. 1902 December 16, the West Indies Pele volcano eruption shook the whole world. It spewed out viscous magma, as well as large quantities of pumice and fiery ash. The eruption, which killed 26,000 people, was of this type, also known as the Pele type.
Intermediate: belongs to the quiet type and explosive eruption between the transitional type. This type of lava eruption in the base of the main. If there is an explosion, the explosive force is not large. Can be a few months, or even years, long-term smooth eruption, and characterized by intermittent outbursts. Near the west coast of Italy on the Liparic Islands Strombolian volcano as a representative. The volcano erupts about every 2-3 minutes, at night in 50 kilometers away from the volcano can still be seen in the eruption of the light flame, so known as the "Mediterranean lighthouse". Also known as Stromboli style. Some people believe that China's Heilongjiang Province Wudalianchi volcano belongs to this type.
3, melt-through eruption
Magma melt through the crust of the earth overflowed a large area of the surface, known as melt-through eruption. This is an ancient form of volcanic activity that no longer exists in modern times. Some scholars believe that during the Archaic period, the crust was thinner and the heat of the underground magma was greater, often resulting in melt-through magma eruption activity.
Determine the form of volcanic eruption is mainly determined by two aspects: one is the nature of the magma, and the second is the eruption of solid, gas, liquid ratio of the three. Magma according to how much silica it contains, can be divided into basal magma and acidic magma. Basal magma viscous small, fluidity, also known as basaltic magma, by this magma triggered by volcanic activity less eruption, magma can be in the ground for a longer distance flow, and the formation of peculiar landscape. Acidic magma is viscous, poorly fluid, and the resulting volcanic activity is violent and intense. In addition, gas-based eruption is the strongest, known as the "explosion"; solid-based eruption is second, known as the "ejecta"; liquid-based weakest, known as the "flow"; All three are stronger, called "jet".
There are many volcanoes in the world, and more than 500 active ones have erupted in the past 400 years. Although the number of volcanoes is large, their distribution is very regular. People divide volcanoes into four belts: the Pacific Rim Volcanic Belt, the Atlantic Volcanic Belt, the Mediterranean Volcanic Belt and the East African Volcanic Belt. The Pacific Volcanic Belt includes both the east and west coasts, like our country Taiwan is in this volcanic belt. El Salvador, known as the "Land of Volcanoes", is also in this volcanic belt, and the world's highest active volcano - Chile's Yuyeyako Volcano, with an elevation of 6,723 meters; and the highest extinct volcano - Chile's Aconcagua Volcano, with an elevation of 6,964 meters, are also in this belt. The most striking undersea eruptions and the consequent formation of volcanic islands are found in the Atlantic Volcanic Belt. There, you can sometimes see the strange spectacle of a submarine volcanic eruption, where an island can emerge from what used to be a vast ocean in a matter of days. Because the newly formed volcanic island material is still relatively loose, can not resist the impact of the waves, so often like magic and suddenly disappeared. The Mediterranean Volcanic Belt is known for its high level of volcanic activity, and the world-famous Mount Vesuvius is located in this belt. Many of the volcanoes on this belt are still active today, such as Mount Etna on the island of Sicily, which has never stopped erupting since more than 6,000 years B.C. until today. The African continent by the two sides of the pulling force and the formation of faults, called the East African Rift Valley, this is also very active volcanic activity. Rift Valley on both sides, towering a volcano, the dead volcano still have water vapor spewing out, hot springs gushing, active volcano is hot, smoky. Two world-famous volcanic wonders are here: the second largest broken crater - Ngorongoro Ngorongoro Crater, and the lava lake of Nyiragongo Volcano. Africa's first peak-Mount Kilimanjaro and the second peak-Mount Kenya, the summits of these two extinct volcanoes are beautifully covered with snow all year round.
China's volcanoes, about 660, the vast majority of which are extinct. Active and dormant volcanoes are mainly found in Taiwan Province, the Kunlun Mountains region, Heilongjiang Province, Changbai Mountains and Tengchong in Yunnan Province. There are more than 230 of them in Heilongjiang and Jilin***, among which the famous ones are Wudalianchi and Baitou Mountain. Inner Mongolia is the region with the largest number of volcanoes in China, ****there are more than 270 of them, and the largest in China, containing a cluster of more than 100 volcanoes, is located here, including the Dali Volcanic Cluster, which has as many as 56 volcanoes. Taiwan Province is located right in the middle of the Pacific Rim Volcanic Belt, which is the place in China with the most intense volcanic activity. The Penghu Islands, the Fiery Islands, and the Diaoyu Islands are all volcanic islands formed by undersea volcanic eruptions. Taiwan's most famous volcano group, the Datun Volcano Group, is in the northern part of the island and consists of more than 10 volcanoes about 1,000 meters above sea level.
Earthquakes:
1. Prophets and thinkers of all nationalities have offered various explanations for the causes of earthquakes, and China's contribution to this field is unrivaled. As far back as 2,700 years ago in the Western Zhou Dynasty, Bo Yang father that "Yang ambush and can not come out, Yin forced and can not steam, so there are earthquakes." This is the philosophical "yin and yang theory".
2, since ancient times, mankind because of scientific backwardness, has been the earthquake disaster attributed to God God's natural forces. Many peoples believe that the earth is supported by a number of animals, these animals move, a will produce earthquakes. For example, some tribes in India believe that turtles standing on several elephants carrying the earth, elephants move earthquake will occur. Japan widely rumored that earthquakes are due to the underground big catfish turn over, suppress the catfish is the world peace. Ancient Greek legend has it that when Poseidon was angry, he took his trident and struck the bottom of the sea, thus causing earthquakes and tsunamis.
3, since the sixties of this century, scientists gradually put forward the theory of plate tectonics. The lithosphere of the earth's surface consists of several huge plates. These plates either separate from each other or collide and subduct. Plate boundaries are often seismic. Volcanic activity is particularly active zone. But the principle of earthquake occurrence within the plate is not yet clear.
4, 1996, the United States, San Francisco, a strong 8.3 magnitude earthquake, serious damage. After the earthquake found that: the west coast of North America, San Andreas rupture up to 430 kilometers long a section of both sides of the wrong movement. Through the study, the United States seismologist Ruide put forward the doctrine of elastic rebound. This doctrine that, due to seismic movement of the rock deformation, when the deformation exceeds a certain level, the rock breaks and misalignment, after the deformation of the rock rebound to restore the original state, which is the process of the earthquake. The picture shows the San Federico Fracture, the nest of earthquakes.
Modern science explains the causes of earthquakes as follows:
Because of the Earth's constant movement and change, gradually accumulated a huge amount of energy, in some vulnerable areas of the Earth's crust, resulting in the sudden rupture of the rock layer, or triggered the original fault fault fault, which is an earthquake.
The vast majority of earthquakes occur in the Earth's crust.
Earthquakes*** are divided into four types: tectonic earthquakes, volcanic earthquakes, trapped earthquakes, and induced earthquakes.
Tectonic earthquakes refer to the role of tectonic movement, when the local stress reaches and exceeds the strength limit of the rock layer, the rock layer will suddenly produce deformation, and even rupture, the energy will be released at once, which will cause the earth to shake, this type of earthquake is called tectonic earthquakes, accounting for more than 90% of the total number of earthquakes.
Volcanic earthquakes are earthquakes that occur after a volcanic eruption due to the loss of a large amount of magma, a reduction in underground pressure or deep underground magma to replenish the cavity, causing the fracture or collapse of the overlying rock layers. The number of such earthquakes is small, accounting for only about 7% of the total number of earthquakes.
Trapped earthquakes are localized earthquakes caused by underground cavities or the subsidence of mining areas. Trapped earthquakes are the result of gravity, small in scale and even fewer in number, accounting for only about 3% of the total number of earthquakes.
Artificial earthquakes and induced earthquakes are earthquakes caused by artificial blasting, mining, military construction and underground nuclear testing. Due to human production activities triggered by certain fault activity, caused by the earthquake called induced seismicity, mainly reservoir earthquakes, deep well pumping and water injection induced earthquakes, nuclear testing triggered earthquakes, mining activities, irrigation, etc. can also induce earthquakes. China's Xinfengjiang Reservoir in Guangdong Province has recorded 337 earthquakes as of 1987 since it was completed and filled with water in October 1959, including a 6.1-magnitude quake in 1962, which created an 82-meter-long crack in the concrete dam.
Respondent volcanoes are diverse and can be categorized into three main groups based on their activity: extinct, dormant and active. A dead volcano is a volcano that has erupted in prehistory but has not been active since recorded history. Such volcanoes have lost their ability to be active. Some volcanoes still maintain a complete volcanic form, some have suffered weathering erosion, only the remains of the volcano is incomplete, China's Shanxi Datong Volcanic Group in a radius of about 50 square kilometers, the distribution of two isolated volcanic cone, which Wolf Wo mountain volcanic cone height of nearly 120 meters. Dormant volcano, refers to the history of once erupted. But for a long time in a relatively static state of the volcano. Such volcanoes are well preserved volcanic form, still has the ability of volcanic activity, or can not be concluded that it has lost the ability of volcanic activity. Such as China's Baitoushan Tianchi, had in 1597 and 1792 two eruptions, before that there are many activities. At present, although there is no eruptive activity, but from the slopes of some unfathomable jet holes continue to spew out high temperature gas, it can be seen that the volcano is currently in a dormant state. Active volcanoes are those that are still active or periodically erupt in modern times. This type of volcano is in the peak period of activity. Such as claw spit on the island of merapi volcano, this century, the average interval of two two years to continue to erupt a period of time, China's recent volcanic activity in Taiwan island datun volcano group of the main peak of the seven star mountain is most famous. On the mainland, only in 95 years in Xinjiang Kunlun Mountains western section of the Yutian Caldasi volcanic group has eruption records. The eruption formed a flat-topped volcanic cone with a summit elevation of 4,900 meters, a cone height of 145 meters, a diameter of 642 meters at the base of the cone, a diameter of 175 meters at the top, and a crater depth of 56 meters.
It should be noted that there are no strict boundaries between these three types of volcanoes. Dormant volcanoes can be revived, dead volcanoes can be "resurrected" are not static. In the past, it has been thought that Italy's Mount Vesuvius is a dead volcano, at the foot of the volcano, people built many towns and vineyards on the slopes of the volcano, but in 79 A.D. Mount Vesuvius suddenly erupted, the high temperature of the volcano's eruption took over the unsuspecting Pompeii and Herculaneum, the two ancient cities, the two cities and their inhabitants were all destroyed and lost their lives.
When a volcano erupts, the exit where gases, magma, solids, and other materials are discharged outward is called a crater. Generally, there is only one crater at a time for a central eruption, but the vast majority of volcanoes have multiple eruptions. Some of the subsequent eruptions are from the original crater, but more often they erupt on its side, thus forming new craters called parasitic craters. In addition to central eruptions there are also fissure eruptions, in which erupted material is ejected from a fissure in the earth's crust. The craters it forms are more numerous. For example, in the Laki eruption in Iceland, lava flowed continuously from 105 craters lined up in a 32-kilometer-long fissure. Craters are mostly circular in shape and are generally divided into five categories: symmetrical craters, asymmetrical craters, fissure craters, craters with no visible craters, and sunken craters. There is a more specialized category of volcanic craters called broken craters. It is because the volcanic eruption is too violent, a huge amount of magma at once will be the volcanic neck and the surrounding rocks rushed away, this eruption caused by the caldera, often more than 5 kilometers in diameter, violent eruption in addition to the formation of broken caldera, but also to make the volcano's height is greatly reduced. For example, the Tambora eruption produced a crater 12 kilometers in diameter and a consequent reduction in altitude of 1,400 meters.
On our planet, volcanism generally occurs in unusual geologic settings, most of which are at the boundaries of the massive plates that make up the lithosphere. About 80 percent of Earth's active volcanoes and their associated volcanic activity occur where two plates meet and one subducts beneath the other. The subducting plate, on the one hand, is locally pressurized by compression and, on the other hand, melts itself into magma; at this point, if cracks or weaknesses appear in the compressed plate above it, the extremely pressurized magma erupts out of these places, forming volcanoes. There is a different situation, on the axis of mid-oceanic ridges, where magma emerges from the mantle and separates to the sides of the ridge, forming a new ocean floor. This type of volcanism actually occurs underwater.
Volcanic eruptions volcanic eruptions
The nature of the magma, the pressure of the underground magma reservoir, the shape of the volcanic channel, the eruption of the environment (land or underwater) and other factors, so that the form of eruption is very different, there are generally some of these classifications:
1, fissure-type eruption
Magma along the crust of the earth's huge fissure spills over to the surface, known as the fissure eruption. fissure eruption. This type of eruption is not a strong explosive phenomenon, the ejected material is mostly basal lava, condensation tends to form a wide area covered by lava terrace. Such as the distribution of China's southwest Sichuan, Yunnan and Guizhou provinces in the junction area of the Permian Emeishan basalt and Hebei Zhangjiakou north of the Tertiary Hannaoba basalt are fissure type eruption. Modern fissure eruptions are mainly distributed in the ocean floor at the mid-ocean ridge, only Iceland on the continent can be seen in this type of volcanic eruption activity, so it is also known as Iceland-type volcanoes.
2, the center of the eruption
Underground magma through the tubular volcanic channel out of the surface, known as the center of the eruption. This is the main form of modern volcanic activity, and can be subdivided into three kinds:
Tranquility: volcanic eruption. Only a large number of hot lava from the caldera quiet overflow, along the mountain slopes flow slowly, as if the boiling rice soup from the rice pot boiling out of the same. Overflow to the base of the lava is mainly, lava temperature is high, viscosity is small, easy to flow. Containing less gas, no explosive phenomenon, the Hawaiian volcanoes as its representative, also known as Hawaii type. This type of volcano people can enjoy.
Explosive; volcano eruption, resulting in violent explosions, while spewing out a large amount of gas and volcanic debris material, spewing out of the lava to the acidic lava is mainly. 1902 December 16, the West Indies Pele volcano eruption shook the whole world. It spewed out viscous magma, as well as large quantities of pumice and fiery ash. The eruption, which killed 26,000 people, was of this type, also known as the Pele type.
Intermediate: belongs to the quiet type and explosive eruption between the transitional type. This type of lava eruption in the base of the main. If there is an explosion, the explosive force is not large. Can be continuous for months, or even years, long-term smooth eruption, and characterized by intermittent outbursts. Near the west coast of Italy on the Liparic Islands Strombolian volcano as a representative. The volcano erupts about every 2-3 minutes, at night in 50 kilometers away from the volcano can still be seen in the eruption of the light flame, so known as the "Mediterranean lighthouse". Also known as Stromboli style. Some people believe that China's Heilongjiang Province Wudalianchi volcano belongs to this type.
3, melt-through eruption
Magma melt through the crust of the earth overflowed a large area of the surface, known as melt-through eruption. This is an ancient form of volcanic activity that no longer exists in modern times. Some scholars believe that during the Archaic period, the crust was thinner and the heat of the underground magma was greater, often resulting in melt-through magma eruption activity.
Determine the form of volcanic eruption is mainly determined by two aspects: one is the nature of the magma, and the second is the eruption of solid, gas, liquid ratio of the three. Magma according to how much silica it contains, can be divided into basal magma and acidic magma. Basal magma viscous small, fluidity, also known as basaltic magma, by this magma triggered by volcanic activity less eruption, magma can be in the ground for a longer distance flow, and the formation of peculiar landscape. Acidic magma is viscous, poorly fluid, and the resulting volcanic activity is violent and intense. In addition, gas-based eruption is the strongest, known as the "explosion"; solid-based eruption is second, known as the "ejecta"; liquid-based weakest, known as the "flow"; All three are stronger, called "jet".
There are many volcanoes in the world, and more than 500 active ones have erupted in the past 400 years. Although the number of volcanoes is large, their distribution is very regular. People divide volcanoes into four belts: the Pacific Rim Volcanic Belt, the Atlantic Volcanic Belt, the Mediterranean Volcanic Belt and the East African Volcanic Belt. The Pacific Volcanic Belt includes both the east and west coasts, like our country Taiwan is in this volcanic belt. Known as the "country of volcanoes" in El Salvador is also in this volcanic belt, the world's highest active volcano - Chile's Yuyeyako