The most spectacular sight on earth is the eruption of volcanoes, which erupt with huge pillars of fire soaring into the sky (Fig. 3-1). More than 1,500 volcanoes have been active on earth in the last 10,000 years, mostly under the sea. The countries with more volcanoes are Indonesia, Japan, Italy, New Zealand, America and China.
Fig. 3-1 Spectacular sight of volcanic eruption
What are volcanoes?
Volcanoes are deposits formed by magma and other high-temperature substances deep in the earth passing through cracks in the crust and erupting from the ground.
Magma is melted rock under the ground, there is a lot of hot magma inside the earth， because magma is warmer and less dense than surrounding rocks, it upwells to the surface and melts some of the rocks during the lifting process. Once magma finds a way to reach the surface, it immediately erupts from the surface, which is a volcanic eruption, the erupted lava condenses and forms a volcano.
Volcanic eruption is the way of releasing energy from magma, when the magma energy inside the earth accumulates to a certain extent, it will erupt to the surface along the weak area of the crust under strong pressure, forming a spectacular volcanic eruption phenomenon. Craters are the gaps where the earth releases heat and gas, the channels where magma erupts from the ground.
Volcanoes occur in the fault zone of the earth's crust. Volcanoes are concentrated in the Pacific Rim and Indonesia northward through Myanmar, the Himalayas, Central Asia Minor to the Mediterranean, where 99% of the active volcanoes on the earth are located today.
Volcanic eruption can cause huge losses to human life and property in a short time. It is a catastrophic natural phenomenon. But it also brings many benefits, volcanic eruptions can provide abundant land, heat and many types of mineral resources, as well as tourism. Many gems are formed by volcanic eruptions; volcanic eruptions can also expand the land area, the Hawaiian Islands were formed by volcanic eruptions; some volcanoes can also become tourist attractions to promote tourism development, such as Mount Fuji in Japan, Hawaii Islands in the United States, Yellowstone National Park, Changbai Mountain in China, Tengchong and other places are volcanic tourism resources.
On the one hand, volcanoes provide fertile soil, air, minerals, building materials, energy and other resources for mankind; on the other hand, they often bring disasters and sufferings to us. Volcanic eruptions, such as volcanic ashes, lava flows, pyroclastic flows and volcanic debris flows, earthquakes and tsunamis associated with volcanic eruptions, can cause huge disasters, even long-term disaster consequences, cause global climate change, and lead to large regional disasters and famines. Since the 1920s, in order to prevent and mitigate volcanic disasters, many countries have carried out monitoring and research on volcanic activities, predicted volcanic disasters and adopted corresponding countermeasures for disaster prevention and mitigation.