介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[12:21.38]The last reading.
[12:24.08]Volcanoes
[12:26.17]A volcano is an opening in a planet's surface or crust,
[12:30.88]which allows lava, ash and gases
[12:33.96]to escape from the place below the surface.
[12:37.72]It is dramatic evidence of the powerful ...

介绍： 版权归原作所有，仅供此学习，若有侵权请告知删除。
[12:21.38]The last reading.
[12:24.08]Volcanoes
[12:26.17]A volcano is an opening in a planet's surface or crust,
[12:30.88]which allows lava, ash and gases
[12:33.96]to escape from the place below the surface.
[12:37.72]It is dramatic evidence of the powerful forces at work inside the Earth.
[12:43.41]Volcanoes are generally found
[12:45.44]where plates are moving apart or coming together.
[12:49.42]Erupting volcanoes can pose many hazards.
[12:53.57]And the most deadly volcanoes are usually those tall and conical ones
[12:58.56]built up by many layers of eruptive materials.
[13:02.62]They can destroy entire cities and kill large numbers of people.
[13:09.02]Nevertheless, volcanoes also add nutritious substances to soils,
[13:14.37]creating perfect conditions for many crops.
[13:18.22]Besides, some types of volcano make new sections of the plates
[13:22.62]that make up the Earth's surface.
[13:25.49]Without volcanoes and our planet's plates,
[13:28.70]the dry land we live on would not be renewed,
[13:31.74]and weathering and erosion by water, wind and ice
[13:35.90]would eventually carry it all into the oceans leaving Earth a water world.