GMAT 考满分题库

     Everest and Jengish Chokusu, two of the tallest mountains on earth, are both products of collisions between continental plates and other tectonic forces. Ojos del Salado and Llullaillaco are somewhat shorter and the product of volcanic forces. The formation of these mountains can be compared to that of the planets in our solar system, in which the original stellar material congealed to form multiple celestial bodies with wildly varying sizes, compositions, and physical characteristics. The mountains of Earth are, however, more identifiable than the materials from which they originally formed: mountains are formed from the same rocks and minerals that have existed on Earth for billions of years. Everest, for example, is largely composed of limestone and marble, Jengish Chokusu consists primarily of crystalline and sedimentary rocks, and though Ojos del Salado and Llullaillaco are both different types of volcanic peak, both have similar metamorphic compositions.

     The distinction between volcanic and tectonically formed peaks has behavioral ramifications. Ojos de Salado remains an active volcano, and Llullaillaco is dormant at present but has been active in the past. Everest and Jengish Chokusu were formed from a tectonic plate collision millions of years ago, so they exhibit no volcanic activity. Because of that, the appearances of Everest and Jengish Chokusu are permanent, more or less; tectonic changes occur more slowly than volcanic changes and those two mountains will change but very gradually. On the other hand, the appearances of Ojos del Salado and Llullaillaco might change rapidly and with little warning, as dormant volcanoes have been known to become active and volcanic eruptions can radically reshape mountains in a matter of moments.