[求助]gwd7-22-25

remona9t

      Earth’s surface consists of rigid

           plates that are constantly shifting and

           jostling one another.  late movements

Line          are the surface expressions of motions

  (5)         in the mantle—the thick shell of rock

that lies between Earth’s crust and its

metallic core.  Although the hot rock of

the mantle is a solid, under the tre-

mendous pressure of the crust and

(10)         overlying rock of the mantle, it flows like

a viscous liquid.  The mantle’s motions,

analogous to those in a pot of boiling

water, cool the mantle by carrying hot

material to the surface and returning

(15)         cooler material to the depths.  When

the edge of one plate bends under

another and its cooler material is con-

sumed in the mantle, volcanic activity

occurs as molten lava rises from the

(20)         downgoing plate and erupts through the

           overlying one.

                 Most volcanoes occur at plate

boundaries.  However, certain “mis-

placed” volcanoes far from plate

(25)         edges result from a second, indepen-

dent mechanism that cools the deep

interior of Earth.  Because of its prox-

imity to Earth’s core, the rock at the

base of the mantle is much hotter than

(30)         rock in the upper mantle.  The hotter the

mantle rock is, the less it resists flow-

ing.  Reservoirs of this hot rock collect

           in the base of the mantle.  When a

reservoir is sufficiently large, a sphere

(35)      of this hot rock forces its way up

through the upper mantle to Earth’s

surface, creating a broad bulge in the

topography.  The “mantle plume” thus

         formed, once established, continues to

(40)       channel hot material from the mantle

base until the reservoir is emptied.

The surface mark of an established

plume is a hot spot—an isolated

region of volcanoes and uplifted terrain

(45)         located far from the edge of a surface

plate.  Because the source of a hot

spot remains fixed while a surface

plate moves over it, over a long period

of time an active plume creates a chain

(50)         of volcanoes or volcanic islands, a

track marking the position of the plume

relative to the moving plate.  The natural

history of the Hawaiian island chain

clearly shows the movement of the

Pacific plate over a fixed plume.

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Q22:

The passage is primarily concerned with discussing

                     

the composition of Earth’s mantle

how the Hawaiian Islands were created

what causes Earth’s surface plates to move

two different mechanisms by which volcanoes are formed

why most volcanoes occur at plate boundaries

Answer:

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Q23:

It can be inferred from the passage that a chain of volcanoes created by a mantle plume would most likely be characterized by

                     

a curved outline

constituent volcanoes that differ from each other in age

occurrence near a plate boundary where one plate bends under another

appearance near many other volcanic chains

rocks with a wide range of chemical composition

Answer:

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Q24:

The author’s reference to the Hawaiian Islands serves primarily to

                     

provide an example of a type of volcanic activity that does not occur elsewhere

identify the evidence initially used to establish that the Pacific plate moves

call into question a theory about the source of the volcanoes that created the Hawaiian Islands

illustrate the distance from plate edges at which volcanoes typically appear

provide an example of how mantle plumes manifest themselves on Earth’s surface

Answer:

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Q25:

According to the passage, a hot spot on Earth’s surface is an indication of which of the following?

An untapped reservoir of hot rock in the base of the mantle

Volcanic activity at the edge of a plate

Solid mantle rock under tremendous pressure

The occurrence of a phenomenon unique to the Pacific plate

A plume of hot mantle rock originating near Earth’s core

Answer

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