火山喷溢的物质来源于地壳下部的地幔,它由炽热高温、高压的粥状岩浆构成。当岩浆沿着地壳的某些裂隙作为通道喷溢出地表或大洋底,就形成火山的喷溢(图①见封2、封3,下同)。南大西洋中的特里斯坦—达库尼亚群岛为四个火山岛所组成,它曾发行4枚火山邮票均为火山岛的剖面图,可见呈层状堆积,说明该火山岛是多次喷溢而形成的(图②)。喷溢时的喷出物 Volcanic material from the lower crust of the mantle from the hot, hot, high pressure of porphyritic magma composition. When magma along the crust some of the fissures as a channel spilled from the surface or the ocean floor, the formation of volcanic spurt (Figure ① see seal 2, seal 3, the same below). The Tristan da Cunha in the South Atlantic consists of four volcanic islands. It issued four volcanic stamps, each of which is a cross-section of a volcanic island. It can be seen that the volcanic island is sprayed repeatedly Overflow formed (Figure ②). Ejector when sprayed