Great chunks of the ice crust, which has covered the mountains through the winter, break off and drop heavily into the thawing sea beneath.
冬日里覆盖着山脉的大块冰壳开始破裂开来，重重地跌落到山脚下正在融化的海水里。
2
By 2011 scientists aboard a Japanese deep-sea drilling ship called Chikyu hope to start drilling through a thin piece of oceanic crust to reach Earth's mantle.
This is part of the system of mid-ocean ridges that form as the tectonic plates of the Earth's crust move apart-a process known as sea floor spreading.