求教 TT GWD-20-25 关于火山那篇

Q22 to Q25:

      Earth’s surface consists of rigid

            plates that
are constantly shifting and

            jostling
one another.  Plate 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.

Q25:

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

1. An
        untapped reservoir of hot rock in the base of the mantle
2. Volcanic
        activity at the edge of a plate
3. Solid
        mantle rock under tremendous pressure
4. The
        occurrence of a phenomenon unique to the Pacific plate
5. A
        plume of hot mantle rock originating near Earth’s core