A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
地球上的火山之所以能出现，是因为地球的地壳是由17块巨大的板块构成的。这些板块漂浮在地幔中的一层更热、更软的物质上。因此，在地球上，火山一般发生在板块分离或聚合的地方，并且绝大多数火山都发生在水下。比如，一个中洋脊（例如大西洋中洋脊）会出现因分离板块而产生的火山，而环太平洋火山带则有一些因聚合板块而产生的火山。火山也可能会在板块延伸并变薄的地方出现。这种类型的火山现象属于“板块假说”火山现象。Earth\'s volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust\'s plates, e.g., in the East African Rift, the Wells Gray-Clearwater volcanic field, and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism.convergent boundary volcanoesdivergent boundary volcanoes远离板块边缘的火山是由地函热柱（mantle plume)产生的。这些火山被称为"hotspot"。例如，夏威夷群岛就是由源自地表以下3000千米的地心深处涌起的岩浆所形成的。Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example, Hawaii, are postulated to arise from upwelling diapirs with magma from the core-mantle boundary, 3,000 km deep in the Earth.本话题必备专业词汇：volcano 火山