托福阅读材料：LAVA
托福考试中阅读一块最是考察大家的英语综合能力。想要提高英语阅读能力，除了词汇量的积累，也需要在积累阅读背景知识，同时多做题目提高阅读速度。下面是查字典出国留学网()托福频道小编为大家整理的关于LAVA的阅读材料，希望对大家有所帮助!
Lava is magma that breaks the surface and erupts from a volcano. If the magma is very fluid, it flows rapidly down the volcano’s slopes. Lava that is more sticky and less fluid moves slower. Lava flows that have a continuous, smooth, ropy, or billowy surface are called pahoehoe (pronounced pah HOH ee hoh ee) flows; while a a (pronounced ah ah) flows have a jagged surface composed of loose, irregularly shaped lava chunks. Once cooled, pahoehoe forms smooth rocks, while a a forms jagged rocks. The words pahoehoe and a a are Hawaiian terms that describe the texture of the lava. Lava may also be described in terms of its composition and the type of rock it forms. Basalt, andesite, dacite, and rhyolite are all different kinds of rock that form from lava. Each type of rock, and the lava from which it forms, contains a different amount of the compound silicon dioxide. Basaltic lava has the least amount of silicon dioxide, andesitic and dacitic lava have medium levels of silicon dioxide, while rhyolitic lava has the most.
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