2. 职称英语
  3. Scattered around the globe are more than 100 small regions of isolated volca

Scattered around the globe are more than 100 small regions of isolated volca

游客2025-04-07  34
问题     Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots.Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth’s surface; on the contrary, many of them lie deep in the interior of a plate.Most of the hot spots move only slowly, and in some cases the movement of the plates past them has left trails of dead volcanoes.The hot spots and their volcanic trails are milestones that mark the passage of the plates.
    That the plates are moving is not beyond dispute.Africa and South America, for example, are moving away from eath other as new material is injected into the sea floor between them.The complementary coastlines and certain geological features that seem to span the ocean are reminders of where the two continents were once joined.The relative motion of the plates carrying these continents has been constructed in detail, but the motion of one plate with respect to another cannot readily be translated into motion with respect to the earth’s interior.It is not possible to determine whether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it.Hot spots, anchored in the deeper layers of the earth, provide the measuring instruments needed to resolve the question.From an analysis of the hot spot population it appears that the African plate is stationary and that it has not moved during the past 30 million years.
    The significance of hot spots is not confined to their role as a frame of reference.It now appears that they also have an important influence on the geophysical processes that propel the plates across the globe.When a continental plate come to rest over a hot spot, the material rising from deeper layer creates a broad dome. As the dome grows, it develops seed fissures (cracks); in at least a few cases the continent may break entirely along some of these fissures, so that the hot spot initiates the formation of a new ocean.Thus just as earlier theories have explained the mobility of the continents, so hot spots may explain their mutability (inconstant). [br] The hot spot theory may prove useful in explaining______.
选项 A、the structure of the African plates
B、the revival of dead volcanoes
C、the mobility of the continents
D、the formation of new oceans
答案 D
解析 本题可参照文章的第3段。从中可知，热点区的重要性并不仅在于它们所起到的参照物作用；现在看来，它们还对推动板块在地球上移动的地球物理学的过程也产生了重大影响；当大陆板块漂移到热点区上方时，地壳深处涌出的物质会形成一个巨大的穹项；随着穹顶不断增长，它会出现深深的裂缝；如此作用几次后，大陆可能会沿着这些小裂缝完全裂开，这样热点地区就导致了新大洋的诞生。于是，该热点便开始形成一个新海洋；因此，正如早期的理论解释了大陆的移动那样，热点或许可以解释大陆的易变性。据此可知，热点理论可以用于解释大陆的不稳定性，即热点可以
转载请注明原文地址:http://tihaiku.com/zcyy/4031114.html
相关试题推荐
随机试题
最新回复(0)