6．How the Hawaiian Is lands Were Built

Volcanoes have been erupting on the earth for millions of years．More than five hundred still erupt today．These are called active volcanoes．Volcanoes are located in belts or chains．They are found where the earth's crust is weak．The weak spots let the hot rock escape when the volcano erupts．

Many volcano belts are mountain ranges along the edges of continents．One belt runs along the western coast of South America up through the western part of the United States．Other volcanoes are found in ocean basins．

About three－fifths of all active volcanoes in the world are in the Pacific Ocean．Many of these volcanoes erupt under the water．The Hawaiian Islands were built by volcanoes that began erupting under water and finally reached the surface of the ocean．

6．夏威夷群岛是怎样形成的

火山在地球上喷发已有几百万年的历史。有500多座火山至今还在喷发，这些火山叫做活火山。火山呈带状或链状分布，它们一般位于地壳脆弱的地段。火山喷发时，灼热的岩浆便从脆弱的地点流出。

许多火山带是一些大陆边缘的山脉。有一个火山带沿南美洲的西海岸向北，穿过美国的西部。另一些火山位于海洋盆地中。

世界上大约有3／5的活火山在太平洋，这些火山中有许多在水下喷发。夏威夷群岛便是由从水下喷发、最终达到洋面的火山而形成的。