What does a volcano mean?
[Edit this paragraph] The name of the volcano originated in ancient Rome. When people saw the eruption of the volcano, they attributed the burning of the mountain to the anger of SHEN WOO Carr, so the Vulcano volcano in the Ribari Islands in the southern Italian Mediterranean was named after it, and it also became the English name of the word volcano. [Edit this paragraph] Overview of Volcanoes The blazing window of the center of the earth is the most explosive place on earth: volcano volcano.
There are about 2000 known "extinct volcanoes" on the earth; A total of 523 "active volcanoes" have been discovered, including 455 land volcanoes and 68 underwater volcanoes. Volcanoes are unevenly distributed on the earth, and they all appear on the fault zone in the crust. As far as the world is concerned, volcanoes are mainly concentrated in the Pacific Rim and Indonesia's northward passage through Myanmar, Himalayas, Central Asia and West Asia to the Mediterranean Sea. Today, 99% of the active volcanoes on the earth are distributed in these two belts.
Volcano has a long history. Some volcanoes erupted before human history, but they are no longer active. Such a volcano is called an "extinct volcano"; However, some "extinct volcanoes" will suddenly erupt with the change of the earth's crust, which is called "dormant volcano"; Volcanoes that erupt from time to time in human history are called "active volcanoes".
Volcanic activity can spew out various substances. Among the spewed solid substances, there are generally rocks, debris and volcanic ash crushed by blasting. Among the ejected liquid substances, there are generally lava flows, water, various aqueous solutions and mud flows mixed with water, debris and volcanic ash. Among the ejected gas substances, there are usually water vapor and oxides of carbon, hydrogen, nitrogen, fluorine and sulfur. In addition, in volcanic activities, visible or invisible light, electricity, magnetism, sound and radioactive substances are often ejected, which sometimes kill people, or cause power and instruments to fail, leading to the crash of planes and ships.
The intensity of volcanic eruption is related to the nature of lava. The eruption time is long or short, ranging from a few hours to thousands of years. According to the active degree of volcanoes, volcanoes can be divided into three categories: active volcanoes, extinct volcanoes and dormant volcanoes. Among them, dormant volcano refers to the eruption in human historical records, but its activity has not been seen since then. There are about 500 active volcanoes in the world.
Volcanic eruption will cause great losses to human beings, lives and property in a short time. This is a catastrophic natural phenomenon. However, after the volcanic eruption, it can provide abundant land, heat energy, various mineral resources and tourism resources.
Many books describe the volcanic eruption in detail. For example, in Biography of Heilongjiang, the eruption of two volcanoes in Wudalianchi Volcano Group in Heilongjiang Province is described. "In the southeast of Mulgen (now Nenjiang), one day a fire broke out underground, stones soared and the sound shook the fields. The more days the fire goes out, the land becomes a pond. This is the fifty-eighth year of Kangxi. "
Volcanic formation
What are volcanoes made of? Below the surface, the deeper the surface, the higher the temperature. At a depth of about 32 kilometers from the ground, the temperature is enough to melt most rocks.
When rocks melt, they expand and need more space. In some parts of the world, mountains are rising. The pressure under these rising mountains is decreasing, and a pool of lava (also known as "magma") may form under these mountains.
This substance rises along the cracks caused by the uplift. When the pressure on the lava dome is greater than the pressure on the top of the rock above it, a volcano will form outward.
When erupting, hot gas, liquid or solid substances suddenly emerge. These substances piled up around the opening, forming a conical hill. "Crater" is a depression at the top of the volcanic cone, and its opening leads to the surface. This cone-shaped mountain is the product of volcanic formation. The material ejected by the volcano is mainly gas, but it also ejects a lot of volcanic rocks and solid materials, such as slag and ash.
In fact, volcanic rocks are magma erupted by volcanoes. When the magma rises to the height close to the surface, its temperature and pressure begin to drop, and physical and chemical changes take place, and the magma becomes volcanic rock.
Volcanic formation
The formation of volcanoes involves a series of physical and chemical processes. At a certain temperature and pressure, the rocks in the crust and upper mantle are partially melted and separated from the parent rocks, and the molten body moves upward through pores or cracks, and gradually enriches in some parts to form magma sacs. With the continuous supply of magma, the excess pressure of magma in the magma sac gradually increases. When the strength of the crust cover is not enough to stop the magma from moving upward, the magma will rise to the surface through the weak zone. In the process of rising, the volatiles dissolved in magma gradually dissolve out and form bubbles. When the volume fraction of bubbles exceeds 75%, the bubbles trapped in the liquid will be released quickly, leading to explosive eruption. After the gas is released, the viscosity of magma drops to a very low level and the flow becomes turbulent. If the viscosity of magma is low or there are few volatiles, it will only overflow quietly. The difference of a series of physical and chemical changes from partial melting to eruption has formed various volcanic activities. [Edit this paragraph] Volcanic resources Although volcanoes often bring great disasters to mankind, they are not useless. The utilization of volcanic resources can also bring joy and convenience to our lives. Generally speaking, volcanic resources are mainly reflected in their tourism value, geothermal utilization and volcanic materials. Volcano and geothermal are twin brothers. Where there are volcanoes, there are geothermal resources. Geothermal energy is a cheap and pollution-free new energy, so it has been widely used. Now, from medical treatment, tourism, agricultural greenhouses and aquaculture to civil heating, industrial processing and power generation, we can see the application of geothermal energy. People have calculated the geothermal energy in the volcanic area of Camet, where there are thousands of natural steam and hot water vents, which generate 20,000 cubic meters of hot water and steam every second on average, and can bring out 40 trillion calories from the earth's interior in a year, equivalent to 600 million tons of coal. Iceland is located in a zone with frequent volcanic activities. The exploitable geothermal energy is 45 billion kWh, and the annual power generation can reach 7.2 billion kWh. People there make good use of this resource. Although only 7% of it has been developed at present, it has brought many benefits to the local people. Among them, three geothermal power stations around Reykjavik provide hot water and electricity for150,000 Icelanders, and 85% of Iceland's residents use geothermal energy for heating. Geothermal resources are clean and hygienic, which greatly reduces the import of oil and other energy sources. The air quality in Iceland has been greatly improved since 1975. Icelanders are also good at improving the utilization efficiency of geothermal resources, including planting vegetables and flowers in greenhouses, building all-weather outdoor swimming pools, and laying hot water pipes under sidewalks and parking lots to speed up the melting of snow in winter. At present, more than a dozen countries in the world are using geothermal energy to generate electricity. Yangjiao, Tibet, China established the largest geothermal test base in China, and achieved good results.
Volcanic activity can also form various minerals, the most common being the formation of sulfur ore. Natural copper and calcite are often crystallized from basalts erupting on land, and basalts erupting from submarine volcanoes can often form huge iron and copper deposits. In addition, we are familiar with diamonds, and their formation is also related to volcanoes. Basalt is the most widely distributed volcanic rock and a good building material. Melted basalt is called "cast stone" and can be made into various plates and utensils. The biggest characteristics of cast stone are hardness, wear resistance, acid resistance, alkali resistance, non-conductivity and thermal insulation materials. [Edit this paragraph] Volcanic geysers are natural phenomena in the later period of volcanic eruption. After the underground high temperature heats the underground water to a certain pressure, water and steam will rush out of the nozzle, and then stop spraying after the pressure is reduced and enter the next process. The geysers in Yellowstone National Park in the United States are very famous, some of which can spray to a height of 100 meters, and their stormy roar is amazing. For example, the water column of Old Faithful Spring can reach about180m, and the steam from boiling water hangs in the blue sky like white clouds. It sprays for 5 minutes every hour, which is very punctual, hence the name.
Some craters have magma lakes at the bottom, just like a pot of boiling porridge. Kilauea crater on Hawaiian island is over 4000m in diameter and130m deep. At the bottom of this "cauldron", there is a magma lake more than ten meters deep, and sometimes a lava fountain as high as several meters appears on the lake.
There is an "underground forest" in Heilongjiang Province, China, which evolved from seven dead craters. Because the volcanic eruption has weathered to form fertile soil, some plants have settled in this pit. This kind of underground forest is rare.
Some craters are masterpieces of nature. For example, the Ngorongoro volcano, known as the "eighth wonder of the world", is more than 600 meters deep, with a diameter of 18 km above, an area of 254 square kilometers and a bottom area of 260 square kilometers, just like a giant well going straight up and down. In this well, there are many animals, such as lions, giraffes, buffaloes and zebras, just like a lively zoo.
The largest crater in the world is Yasu volcano on Kyushu Island. This crater is 17 km long from east to west, 25 km long from north to south, and its circumference exceeds 100 km. From its scale, we can imagine the great power that broke out at that time. [Edit this paragraph] Volcanic types
According to the classification of volcanic activity
1 active volcano
Refers to a volcano that is still active or erupts periodically in modern times. This volcano is in its heyday of activity. For example, since this century, Mount Merapi on Zhaotu Island has erupted every two or three years on average. The recent volcanic activity in China is most famous in Qixing Mountain, the main peak of Datun Volcano Group on the island of Taiwan Province Province. On the mainland, only six years ago, the Caldarcy Volcano Group in Yutian, the western part of Kunlun Mountain in Xinjiang, recorded volcanic eruption. The volcanic eruption formed a flat-topped volcanic cone. This volcano has lost its ability to move. Some volcanoes remain intact, while others have weathered and eroded, leaving only incomplete volcanic remains. Within about 50 square kilometers of Fiona Fang, there are two isolated volcanic cones, of which the height of the Langwoshan volcanic cone is nearly120m.
2. extinct volcano
Refers to a volcano that erupted in prehistoric times, but it has never been active in history. This volcano has lost its ability to move. Some volcanoes remain intact, while others have weathered and eroded, leaving only incomplete volcanic remains. There are 99 isolated volcanic cones in the area of about 123 square kilometers in Fiona Fang, among which the height of the volcanic cone of Langwoshan is nearly 1900 meters.
3. dormant volcano
Refers to a volcano that has erupted in history but has been relatively static for a long time. This kind of volcano has preserved the complete volcanic male form, and still has volcanic activity ability, or it cannot be concluded that it has lost its volcanic activity ability. For example, Tianchi Lake in Baitoushan, China broke out twice in 1327 and 1658, and there were many activities before that. Although there is no eruption activity at present, high-temperature gas is continuously ejected from some unfathomable blowholes on the hillside, which indicates that the volcano is currently in a dormant state.
It should be noted that there is no strict boundary between these three types of volcanoes. Dormant volcanoes can be resurrected, and dead volcanoes can also be "resurrected", and they are not static with each other. In the past, Mount Vesuvius was always considered as an extinct volcano. At the foot of the volcano, people built many towns and opened vineyards on the hillside of the volcano. However, in 79 AD, Vesuvius erupted suddenly, and the high-temperature volcanic eruption in Attack and Capture created two unsuspecting ancient cities, Pompeii and Heragonom. Cities and residents were destroyed and killed.
② types of volcanic eruption
Volcanic eruption types can be divided into fissure eruption and central eruption according to the passage of magma.
Fissure eruption is also called Icelandic volcanic eruption. Magma overflows the surface along the fault zone in the earth's crust. The eruption is mild and quiet, and the ejected magma is basic basaltic magma with low viscosity, and there is almost no debris and gas. After the basic lava overflows, a wide and thin lava blanket or basalt plateau is formed. Lava cones are arranged in a straight line along the fault zone.
The magma erupted from the center gushed out of the ground along the volcanic throat. According to the intensity and activity of ejecta, they can be divided into the following categories, and their names are named after representative volcano names or place names and names.
① Hawaiian magma is basically dissolved rock, containing a small amount of gas and volcanic ash. Lava overflows from the crater, and the cone of the volcano is shield-shaped. There is a fiery lava lake in the top bowl-shaped crater, and there is a lava "fountain" on the lake.
② Stromboli-type magma is relatively viscous, intermediate-basic, gas-rich and explosive with moderate intensity. The ejecta are mainly volcanic bombs, volcanic slag and old fragments, and lava flows. Volcanic cones are clastic cones or layered cones.
(3) the violent eruption of hourquin type. Viscous or solid angular lava blocks are thrown together with a large amount of volcanic ash to form a "smoke column". There is little or no lava flow. Forming a debris cone or a layered cone.
④ Pei Lei-type magma is thick, moderately acidic, gassy, explosive and volcanic ash flows fast. Volcanic cone is a clastic cone with steep slope, and the top of the cone is a rock dome. After weathering and denudation, volcanic neck stands out from the ground.
⑤ Purini-type viscous magma forms a "plug" in the volcanic channel. Once the lava breaks through the plug, the explosion will be particularly strong, leading to towering luminous volcanic clouds and volcanic ash streams. A crater with a conical top damaged by violent explosion.
⑥ Super Hour Quinnuotype usually has no magma ejection, and the ejecta are mainly cuttings, volcanic ash and gas, with a small number and a low crater.
⑦ Steam jet groundwater is gasified by magma, and gas is continuously or periodically ejected. [Edit this paragraph] The influence of volcanoes
The most powerful and spectacular volcanic eruptions often occur in subduction zones. The volcano here may erupt again after hundreds of years of silence, and once it erupts, its power is particularly fierce. Such volcanic eruptions often bring disasters to mankind.
1 Affect the global climate
When a volcano erupts, a large amount of volcanic ash and gas will have a great impact on the climate. Because in this case, dark days, storms and even mud rain will haunt local residents for months. Volcanic ash and gas are sprayed into the sky, and they will spread to far places with the wind. These volcanic materials will block the sunlight and cause the temperature to drop. In addition, they will filter out some wavelengths of light, making the sun and the moon look like they are covered with rings or have strange colors, which can form strange natural landscapes, especially at sunrise and sunset.
Step 2 destroy the environment
A large amount of volcanic ash ejected by volcanic eruption combined with heavy rain to form debris flow, which can destroy roads and bridges, flood nearby villages and cities and make countless people homeless. Mud formed by soil and rock fragments can flood the whole city.
Although the rocks are covered by volcanic ash clouds, huge rocks can still be seen spraying into the air when the volcano just erupts.
Step 3 rejuvenate
Volcanic eruption has a far-reaching impact on the natural landscape. Land is the most precious resource in the world, because it can breed all kinds of plants to support everything. If volcanic eruption can cover farmland with less than 20 cm thick volcanic ash, it is really good news for farmers, because these volcanic ash are rich in nutrients and can make the land more fertile.
After the lava disintegrated, weeds and money began to appear.
Pteridophytes grow on slopes where rope-like lava flows.
Volcanic ash enriches the surrounding land, and local grapes harvest every year. [Edit this paragraph] Volcanic eruption presents a crazy side of nature. An erupting volcano may spew a hot red lava flow, or a lot of volcanic ash and volcanic gas. Such natural disasters may cause thousands of casualties, but most volcanic eruptions will only cause minor damage to life and property. Volcanic eruption is a natural disaster that may occur all over the world, but it occurs frequently in some areas.
The interior of the earth is full of hot magma. Under great pressure, magma will break through the crust from weak places and spew out, triggering volcanic eruption.
Volcanoes can be divided into active volcanoes, extinct volcanoes and dormant volcanoes. The Tambora volcano mentioned above and the volcano on the Hawaiian Islands are still active. This is an active volcano. An extinct volcano refers to a volcano that has been active in prehistoric times, but there is no record of eruption in history. Most of the more than 600 volcanoes in China have been extinguished. Some volcanoes have recorded activities in history, but they have been inactive since then. This kind of volcano is called dormant volcano. A dormant volcano may suddenly "wake up" and become an active volcano.
Violent volcanic eruption will devour and destroy a large area of land and burn a lot of lives and property to ashes. Surprisingly, however, volcanoes are often located in densely populated areas, such as Nasu volcano and Fuji volcano in Japan. It turns out that the volcanic ash ejected from the volcano is a good natural fertilizer, and the mulberry trees in Mount Fuji grow very well, which is conducive to sericulture. Vesuvius is rich in grapes. Volcanic areas often become tourist attractions because of their peculiar scenery.
Before people can control volcanic activity, strengthening prediction is the only way to prevent volcanic disasters. Scientists' research on volcanic eruptions often benefits from some sudden changes in animals and plants. Many animals often flee before the volcano erupts, as if a disaster of knowledge is coming. There is a strange plant in Java, Indonesia, which will bloom before the volcano erupts. Local residents call it "volcano warning flower".
Volcanic eruption may be an important cause of global warming.
"There are about 50 volcanic eruptions of different scales on the earth every year, which may be an important cause of global warming," said Liu Jiaqi, chief scientist of the Antarctic scientific expedition in China Antarctic Village and academician of the China Academy of Sciences, after inspecting volcanoes and geology in the Antarctic region. Academician Liu Jiaqi also stressed that this conclusion needs further exploration and research by scientists.
Academician Liu Jiaqi is a researcher at the Institute of Geology and Geophysics of China Academy of Sciences and an internationally renowned expert in volcanic geology and Quaternary geology. He has participated in many scientific expeditions and research in China's Antarctic and Arctic regions, and has traveled all over the world. When talking about the Antarctic expedition, Academician Liu, as the chief scientist, said excitedly that the Antarctic expedition spanned a latitude of 30 degrees. In addition to the Great Wall Station in China, it also reached the Antarctic scientific research stations of other four countries and more than a dozen islands in the Antarctic region, and collected relevant samples, which obtained more data and basis for further study of geological evolution, crustal movement and climate and environmental changes in the Antarctic region.
When talking about the relationship between volcanic activities in the Antarctic region and global climate and environmental changes, Academician Liu Jiaqi said: The Antarctic continent is an ancient continent with the highest average altitude and the coldest and driest climate. In the late 1960s and early 1970s, there were many large-scale volcanic eruptions in Antarctica, each of which produced hundreds of thousands of tons of sulfur dioxide, carbon dioxide and other substances, indicating that the dormant volcano in Antarctica has entered an active period.
Academician Liu Jiaqi emphasized that volcanic eruption and crustal movement are manifestations of life on earth. At present, only Earth's satellites and Jupiter (Io 1) have such large-scale volcanic and crustal movements. On the earth, there are about 50 volcanic eruptions of different sizes every year. Academician Liu Jiaqi pointed out that volcanic eruption may be an important cause of global warming. But these problems need further exploration and research by scientists.
Academician Liu said frankly: There are still many things in nature that have not been discovered and recognized by human beings. The cognitive ability of human beings to nature is inevitably limited by the times and history, especially the means, methods, tools and human cognitive ability. There is still a long way to go for China's polar scientific exploration, especially because of the traffic conditions, it is impossible to conduct scientific research in a wider area and radius of Antarctica. If one day a mountain or an island in the Antarctic region is named after an explorer or scientist in China, it will be the pride of China people.
"A country's polar scientific research level is actually the embodiment of a country's comprehensive strength. Although China started late, it has developed rapidly in polar scientific research and investigation, such as Antarctic and Arctic. The polar expedition can be said to be a powerful symbol of a country. " When talking about human polar scientific research, Academician Liu Jiaqi added: Since the establishment of the Great Wall Station in China Antarctic 20 years ago, China's polar scientific research has opened a new chapter. China is a powerful country. At present, more than 50 countries in the world have established scientific research stations in Antarctica. The Antarctic Treaty stipulates that countries cannot claim resources and territories in the Antarctic region, but the Antarctic Treaty has a time limit. At present, all countries in the world are stepping up the implementation of the Antarctic strategy. Because Antarctica is rich in mineral resources, energy, biological resources and fresh water resources, it has become an important choice for all countries in the world to expand their living space. Antarctica is the fifth continent in the world, accounting for 70% of the world's fresh water resources. However, due to the unique geographical location and complex environment of the Antarctic and the Arctic, it is much more difficult and dangerous for human beings to engage in scientific investigation and research in the polar regions than in other regions, and the cost is also greater. Academician Liu pointed out that although China's polar scientific research started late, it has made many scientific achievements, some of which are still in the forefront of the world.
A volcano is not a mountain spewing "fire", but a high-temperature and viscous substance called magma. The scene when the volcano erupted was spectacular. Usually, magma is tightly wrapped in the earth's crust. Because of its extremely high temperature and great pressure from the earth's crust, whenever cracks appear in the thin earth's crust, magma will violently rush out of the ground.
When the volcano erupts, with the earth-shattering roar, stones fly and roll, and fiery magma spews out of the ground like a fierce dragon, devouring everything around. At the moment, Fiona Fang is shrouded in dense fog for dozens of miles. Sometimes, due to volcanic eruption, a high mountain can be erected on flat land in an instant, such as Kilimanjaro and Kotopak West Mountain near the equator. Sometimes, it can devour whole villages and towns in an instant.
Volcanoes form below the surface, and the deeper the place, the higher the temperature, about 20 miles deep, which is enough to melt most rocks.
When volcanoes erupt and rocks melt, they expand and need more space. This material melted by high temperature will rise along the cracks caused by the uplift.
When the pressure in the lava tank is greater than the pressure of the rock above it, it will explode outward to form a volcano. [Edit this paragraph] Since the establishment of plate tectonics theory, many scholars have established a global volcano model based on plate theory. They believe that most volcanoes are distributed on the plate boundary and a few volcanoes are distributed in the plate. The former constitutes four major volcanic belts, namely, the Pacific Rim volcanic belt, the mid-ocean ridge volcanic belt, the East African Rift Valley volcanic belt and the Alps-Himalayan volcanic belt. The significance of plate theory in volcanic research lies in that it can combine many seemingly isolated phenomena into an organic whole, but the volcanic activity model established by this theory is not perfect, such as why there is no volcanic belt in ring the atlantic; The intraplate volcano is not on the plate boundary, so it seems that the basis for explaining its origin with mantle plume is not sufficient. Recently, another scholar (Li Hongye, 1993) put forward the theory of bipolar compression, revealing the mystery of the development of the earth. He believes that under the action of bipolar compression, the equatorial axis of the earth expands to form meridional tension and latitudinal compression, and global volcanoes are mainly distributed in meridional and latitudinal structural zones. The following picture shows the distribution map of global volcanoes and strong earthquakes. In the picture, the red is Holocene volcano, and the data is taken from Smithsonian Institute, while the white is strong earthquake with magnitude above 7, which is drawn according to the catalogue of China Seismological Network.
The first is the Pacific Rim volcanic belt.
The Pacific Rim volcanic belt starts from Cordillera Mountains in South America in the south, turns to Aleutian Islands and kamchatka peninsula in the northwest, and continues to extend to the southwest with Kuril Islands, Japanese Islands, Ryukyu Islands, Taiwan Province Island, Philippine Islands and Indonesian Islands, with a total length of more than 40,000 kilometers, showing a ring-shaped structural system opening to the south. The Pacific Ring of Fire is also called the Pacific Ring of Fire. There are 5 12 active volcanoes, including more than 30 active volcanoes in the southern segment of the Andes in South America, 16 active volcanoes in the northern segment, and llullaillaco in the middle segment is 6723 meters above sea level, making it the highest active volcano in the world. Further north to the Caribbean, there are famous volcanoes along the Pacific coast, such as Chiriki volcano, Izu volcano, Santa Ana volcano and Mount Humar volcano. There are more than 90 active volcanoes in North America. Famous are Mount St. hellens, Mount Larsen, Mount Rainier, Mount Shasta, Mount Hood and Mount Sanford. The most famous Aleutian Islands are Katmai Volcano and Ilyamna Volcano. There are often Criou Chev volcanoes in kamchatka peninsula, which have attacked the island arcs of the Kuril Islands and the Japanese archipelago. Famous volcanoes distributed in Japanese archipelago, such as Asayama, Iwateyama, Shishengyuan, Asu Mountain and Sanyuan Mountain, are active volcanoes that have erupted many times. There are many volcanic islands from Ryukyu Islands to Taiwan Province Island, such as chiwei yu, Diaoyu Island, Pengjiayu, Penghu Island, Qixingyan, Lan Yu and Huoshao Island, all of which were formed since Cenozoic. The most active volcanic activities can be classified as those from the Philippines to Indonesia, such as Krakato volcano, Pinatubo volcano, Tayun volcano, Tambora volcano and Pere volcano in the Lesser Antilles, which have erupted many times in modern times.
In the Pacific Rim, volcanic activity is frequent. According to historical data, 80% of the world's volcanoes erupted in modern times, mainly distributed in North America, kamchatka peninsula, Japan, the Philippines and Indonesia. Indonesia is called "the country of volcanoes", and Sumatra is located in its south. There are nearly 400 volcanoes in the arc-trench system formed in Java Island, of which 129 are active volcanoes. During the five years of 1966- 1970, 22 volcanoes erupted here, and submarine volcanic eruptions also occurred frequently, resulting in some new volcanic islands exposed to the sea.
Volcanic rocks in the Pacific Rim volcanic belt are mainly the products of neutral magma eruption, forming calc-alkaline series rocks. The most common volcanic rock type is andesite. On the land150-300km away from the trench axis, andesite is distributed in an arc parallel to the trench, which is called "andesite line". Another feature is that the rocks from the trench to the land have obvious horizontal zonation, and generally distribute in turn as tholeiite series rocks, calc-alkaline series rocks and alkaline series rocks with the increase of the distance from the trench. Most of the volcanoes here erupt at the center, and the intensity of volcanic eruption is relatively high. If they occur in densely populated areas, they often cause serious volcanic disasters.