English name: volcano Definition: Magma activity passes through the crust, reaches the ground or ejects the ground with water vapor and ash, forming mountains with special structure and conical shape. Subject: geography (first-class subject); Geomorphology (two disciplines) There is a "liquid zone" under the crust from 100 to 150 km, in which there are molten silicate substances containing gas volatiles at high temperature and high pressure, that is, magma. Once it rushes out from the weak part of the earth's crust, a volcano is formed. Volcanic eruptions can spew out all kinds of substances. Volcano is a blazing window to the center of the earth and the most explosive force on the earth. There are about 2000 known "extinct volcanoes" on the earth. A total of 523 "active volcanoes" were discovered, including 455 land volcanoes and 68 underwater volcanoes. Volcanoes are unevenly distributed on the earth, and all appear on the fault zone in the crust. Around the world, volcanoes are mainly concentrated in the Pacific Rim and Indonesia's route to the Mediterranean through Myanmar, Himalayas, Central Asia and West Asia. Today, 99% of the active volcanoes on the earth are distributed in these two belts. Volcano has a long history. Some volcanoes have erupted before human history, but they are not active now. 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". There is a "liquid zone" between 100 and 150 km under the crust. In this liquid zone, there is a molten silicate substance containing gas volatiles at high temperature and high pressure, that is, magma. Once it rushes out from the weak part of the earth's crust, a volcano is formed. There are about 2000 known "extinct volcanoes" on the earth; A total of 523 "active volcanoes" were discovered, including 455 land volcanoes and 68 underwater volcanoes. Volcanoes are unevenly distributed on the earth, and all appear on the fault zone in the crust. Worldwide, volcanoes are mainly concentrated around the Pacific Ocean and Indonesia, passing through Myanmar, Himalayas, Central Asia and the Mediterranean Sea to the north. Today, 80% of the active volcanoes on the earth are distributed in these two belts. Volcanic activity can eject a variety of substances, and among the ejected 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 can sometimes kill people, or make power and instruments fail, resulting in plane and ship crashes.