一、在地球上从古到今,从海到陆,火山活动从未停止过现今世界的活火山约有400—500多座。这主要是指大陆、岛屿以及曾经露出过水面或在水面下不深的火山,深海中的火山大部不包括在内。因为在深海中活动的火山,由于水压、跃层(具有特殊温度、盐度或密度的水层)和声波折射、散射的影响,一般常不易被人觉知。 First, on Earth, from ancient to present, from sea to land, volcanic activities have never stopped. There are about 400-500 active volcanoes in the world today. This mainly refers to the mainland, islands and volcanoes that once appeared or were not deep beneath the surface of the water. Most of the volcanoes in the deep sea are excluded. Because of volcanic activities in the deep ocean, the effects of water pressure, thermocline (water layer with special temperature, salinity or density) and acoustic refraction and scattering are generally not easily known.