JJ18确认是否为原文？考友们，叩谢！！！

goxong

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 tremendous
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 consumed
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 “misplaced”
volcanoes far from plate
(25) edges result from a second, independent
mechanism that cools the deep
interior of Earth. Because of its proximity
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 flowing.
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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betty_chang

这个是gwd题嘛