历年GRE考试真题精选系列十七
Scattered around the globe are more than onehundred regions of volcanic activity known as hot
spots. Unlike most volcanoes, hot spots are rarely
found along the boundaries of the continental and
oceanic plates that comprise the Earth’s crust; most
hot spots lie deep in the interior of plates and are
anchored deep in the layers of the earth’s surface.
Hot spots are also distinguished from other volcanoes
by their lavas, which contain greater amounts of
alkali metals than do those from volcanoes at plate
margins.
In some cases, plates moving past hot spots have
left trails of extinct volcanoes in much the same way
that wind passing over a chimney carries off puffs of
smoke. It appears that the Hawaiian Islands were
created in such a manner by a single source of lava,
welling up from a hot spot, over which the Pacific
Ocean plate passed on a course roughly from the east
toward the northwest, carrying off a line of volcanoes
of increasing age. Two other pacific island chains—
the Austral Ridge and the Tuamotu Ridge—parallel
the configuration of the Hawaiian chain; they are also
aligned from the east toward the northwest, with the
most recent volcanic activity near their eastern
terminuses.
That the Pacific plate and the other plates are
moving is now beyond dispute; the relative motion of
the plates has been reconstructed in detail. However,
the relative motion of the plates with respect to the
Earth’s interior cannot be determined easily. Hot
spots provide the measuring instruments for resolving
the question of whether two continental plates are
moving in opposite directions or whether one is sta-
tionary and the other is drifting away from it. The
most compelling evidence that a continental plat is
stationary is that, at some hot spots, lavas of several
ages are superposed instead of being spread out in
chronological sequence. Of course, reconstruction of
plate motion from the tracks of hot-spot volcanoes
assumes that hot spots are immobile, or nearly so.
Several studies support such an assumption, including
one that has shown that prominent hot spots through-
out the world seem not to have moved during the past
ten million years.
历年GRE考试真题精选系列十七
Beyond acting as frames of reference, hot spotsapparently influence the geophysical processes that
propel the plates across the globe. When a continental
plate comes to rest over a hot spot, material welling
up from deeper layers forms a broad dome that, as it
grows, develops deep fissures. In some instances, the
continental plate may rupture entirely along some of
the fissures so that hot spot initiates the formation
of a new ocean. Thus, just as earlier theories have
explained the mobility of the continental plates, so
hot-spot activity may suggest a theory to explain their
mutability.
20. The primary purpose of the passage is to
(A) describe the way in which hot spots
influence the extinction of volcanoes
(B) describe and explain the formation of the
oceans and continents
(C) explain how to estimate the age of lava
flows from extinct volcanoes
(D) describe hot spots and explain how they
appear to influence and record the
motion of plates
(E) describe the formation and orientation of
island chains in the Pacific Ocean
21. According to the passage, hot spots differ from
most volcanoes in that hot spots
(A) can only be found near islands
(B) are active whereas all other volcanoes are
extinct
(C) are situated closer to the earth’s surface
(D) can be found along the edges of the plates
(E) have greater amounts of alkali metals in
their lavas
22. It can be inferred from the passage that evidence
for the apparent course of the Pacific plate has
been provided by the
(A) contours of the continents.
(B) dimensions of ocean hot spots
(C) concurrent movement of two hot spots
(D) pattern of fissures in the ocean floor
(E) configurations of several mid-ocean island
chains
23. It can be inferred from the passage that the
spreading out of lavas of different ages at hot
spots indicates that a
(A) hot spot is active
(B) continental plate has moved
(C) continental rupture is imminent
(D) hot spot had been moving very rapidly
(E) volcano contains large concentrations of
alkali metals
历年GRE考试真题精选系列十七
24. The passage suggests which of the followingabout the Hawaiian Islands, the Austral
Ridge, and the Tuamotu Ridge?
(A) The three chains of islands are moving east-
ward.
(B) All the islands in the three chains have
stopped moving.
(C) The three islands chains are a result of the
same plate movement.
(D) The Hawaiian Islands are receding from
the other two island chains at a relatively
rapid rate.
(E) The Austral Ridge and the Tuamotu Ridge
chains have moved closer together
whereas the Hawaiian Islands have
remained stationary.
25. Which of the following, if true, would best
support the author’s statement that hot-spot
activity may explain the mutability of
continental plates?
(A) Hot spots move more rapidly than the
continental and oceanic plates.
(B) Hot spots are reliable indicators of the age
of continental plates.
(C) Hot spots are regions of volcanic activity
found only in the interiors of the
continental plates.
(D) The alignment of hot spots in the Pacific.
Ocean parallels the alignment of Pacific
Ocean islands.
(E) The coastlines of Africa and South
America suggest that they may once
have constituted a single continent that
ruptured along a line of hot spots.
26. The author’s argument that hot spots can be
used to reconstruct the movement of continental
plates is weakened by the fact that
(A) hot spots are never found at the boundaries
of plates
(B) only extinct volcanoes remain after a plate
moves over a hot spot
(C) lava flow patterns for all hot spots have not
been shown to be the same
(D) the immobility or near immobility of hot
spots has not been conclusively proven
(E) the changing configurations of islands
make pinpointing the locations of hot
spots difficult
27. The author’s style can best be described as
(A) dramatic
(B) archaic
(C)esoteric
(D) objective
(E) humanistic
20.D 21.E 22.E 23.B 24.C 25.E 26.D 27.D
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