Fissure eruption
Magma overflows surface along huge cracks in the crust, called fissure eruptions. This kind of eruption has no strong explosion phenomenon, the ejections are mostly alkaline molten slurry, after condensation often form a wide coverage of lava platform. For example, the Permian Emei mountain basalt distributed in the border area of Sichuan, Yunnan and Guizhou provinces in southwestern China and the Tertiary Hannuoba basalt north of Zhangjiakou in Hebei Province, both belong to fissure eruption. Modern fissure eruptions are mainly distributed in the mid-ocean ridges of the ocean floor, such volcanic eruptions can been seen only at Iceland on the mainland, so they are also called Icelandic volcanoes.
Central eruption
Underground magma erupts from the surface through tubular volcanic channels, called central eruptions. This is the main form of modern volcanic activity, which can be divided into three types:
When a quiet volcano erupts, only a large amount of hot lava flows quietly from the crater and slowly along the hillside, as if boiled rice soup is boiling out of a rice cooker. The overflow is mainly alkaline slurry with high temperature, low viscosity and easy flow. Less gas, no explosion. Hawaiian volcanoes are its representative, also known as the Hawaiian type.
When an explosive volcano erupts, it produces a violent explosion, at the same time, it erupts a large number of gases and pyroclastic materials, the erupted slurry is mainly medium-acid slurry. The eruption of Mount Pelee in the West Indies on 25 June 1568 was one of these, also known as the Pelean type.
The intermediate type is the transitional type between the quiet type and the explosive type. This type is dominated by moderate alkaline lava eruption. If there is an explosion, the explosive force is not great. It can erupt smoothly for several months or even years, characterized by intermittent eruptions. It is represented by the Strombard volcano, near the Lipari Islands on the west coast of Italy, which erupts every 2 to 3 minutes, and its flame can still be seen 669km away at night.
Penetration eruption
Magma penetrates the crust and overflows the surface in a large area, which is called penetration eruption. This is an ancient way of volcanic activity, which has not existed in modern times. Some scholars believe that in Archaean era, the crust was thinner and underground magma was more thermodynamic, which often resulted in penetrating magma eruption.
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