Reading Passage
Read the passage and answer Questions 1–20.
Many islands in the open ocean originated as volcanoes. Unlike continental islands, which are often fragments of larger landmasses or areas separated by rising sea levels, volcanic oceanic islands are built upward from the seafloor by repeated eruptions. Over time, lava accumulates until the volcanic structure rises above the ocean surface and forms a new landmass. Once exposed, the island may continue to grow if eruptions persist. In this early stage, construction by volcanic activity is more important than erosion.
One well-known mechanism for forming such islands involves hotspots, relatively fixed sources of magma located beneath moving tectonic plates. As a plate travels over a hotspot, magma may break through the crust and create a volcano. If the volcano grows large enough, an island appears. As the plate continues to move, the island is gradually carried away from the hotspot, volcanic activity declines, and a new volcano may begin forming above the hotspot itself. In this way, a chain of islands can develop, with older islands lying farther from the active volcanic source. The Hawaiian Islands are often cited as a classic example of this process.
Once an island is no longer actively supplied with lava, destructive processes become more prominent. Rain, waves, wind, and streams begin to wear away exposed rock and soil. Valleys may deepen, cliffs may retreat, and the general height of the island may slowly diminish. At the same time, the crust beneath the island can subside, or sink gradually, as it cools and adjusts to the weight of the volcanic mass. Because of both erosion and subsidence, the land surface may become lower even without any sudden catastrophe. [■] Once volcanic activity ceases, however, processes of reduction often become more important than processes of construction.
In tropical waters, another process may influence this transformation: the growth of coral reefs. Corals can build limestone structures in shallow, sunlit marine environments around the edges of volcanic islands. If reef growth keeps pace with subsidence, a fringing reef may become separated from the island by a lagoon, forming a barrier reef. If the central island continues to sink or erode away while the reef remains near sea level, an atoll may result. In that case, the original volcanic island may disappear entirely above the surface, yet a ring-shaped reef still marks the location where land once existed.
Not all volcanic islands follow exactly the same trajectory. Climate, wave energy, reef development, island size, and geological setting all affect how quickly change occurs. Some islands remain high and rugged for long periods; others are reduced relatively quickly. In cooler waters, where reef growth is limited, the later stages may differ from those in tropical regions. Even so, the long-term pattern is clear: volcanic islands are temporary landforms shaped by both constructional and destructive forces. Their ultimate form depends on the balance between eruption, movement, erosion, subsidence, and, in some settings, biological growth.
1. According to paragraph 1, the passage is mainly concerned with
A) why coral reefs grow faster in warm water B) how tectonic plates are measured C) how volcanic islands form and change over time D) why most islands are found near continents
2. The word emerge in paragraph 1 is closest in meaning to:
A) break through the ocean floor after repeated eruptions B) cool into smooth layers C) drift toward continental margins D) separate into smaller land masses
3. Why does the author mention the Hawaiian Islands in paragraph 2?
A) To show that volcanic islands form only in shallow seas B) To argue that all island chains are the same age C) To explain how coral atolls first develop D) To provide an example of a volcanic island chain built over a hotspot
4. According to paragraph 2, once an island is no longer above the hotspot, plate movement may
A) cause it to rise more rapidly B) move it away from the volcanic source C) stop all erosion immediately D) replace its volcanic rock with coral limestone
5. The word erosion in paragraph 3 is closest in meaning to:
A) wearing away exposed rock and soil B) hardening of newly formed lava C) displacement by earthquakes D) enrichment by biological growth
6. According to paragraph 3, why may an island become lower even if no dramatic event occurs?
A) Because reefs remove large amounts of rock B) Because ocean currents carry the island away C) Because the crust beneath it may cool and sink gradually D) Because magma chambers keep expanding upward
7. Why does the author discuss coral reefs in paragraph 4?
A) To show that reefs always prevent island erosion B) To explain why volcanic rock is rich in nutrients C) To compare island volcanoes to continental volcanoes D) To explain how reef growth can continue around a subsiding island
8. The word encircling in paragraph 4 is closest in meaning to:
A) lying beneath B) having a circular shape surrounding a central lagoon C) splitting apart from D) gradually replacing
9. Which of the following best expresses the essential information in the highlighted sentence in paragraph 4?In this way, land that originally rose through volcanic construction may eventually disappear while still leaving evidence of its former presence.
A) Volcanic islands may pass through several recognizable stages. B) Volcanic islands are usually destroyed before reefs can form. C) Reefs can only grow where volcanic rock remains above sea level. D) Submerged volcanoes are easier to detect than exposed islands.
10. The word trajectory in paragraph 5 is closest in meaning to:
A) location beneath the sea B) chemical composition of lava C) overall path of development over time D) temporary interruption in reef growth
11. Why does the author mention climate and wave action in paragraph 5?
A) To show that most islands remain unchanged after formation B) To indicate that island development varies according to environmental conditions C) To prove that erosion matters more than volcanism D) To explain why only tropical islands form reefs
12. Look at the four squares [■] that indicate where the following sentence could be added to the passage.Once volcanic activity ceases, however, processes of reduction often become more important than processes of construction.
A) Paragraph 1 B) Paragraph 2 C) Paragraph 5 D) Paragraph 3
13. Which of the following can be inferred from paragraph 3?
A) The crust beneath an island may sink gradually after volcanic activity declines. B) Island erosion stops completely when reefs begin to form. C) All volcanic islands remain above sea level for millions of years. D) Subsidence occurs only when earthquakes break the ocean floor.
14. Why are volcanic islands described as temporary landforms in paragraph 5?
A) because they are quickly replaced by continental crust B) because they are too small to resist tectonic motion C) because erosion and subsidence may alter or remove them over time D) because reef growth always covers them within a few centuries
15. The word obliterated in paragraph 5 is closest in meaning to:
A) measured precisely B) destroyed completely by storms C) isolated from marine life D) stabilized by reef limestone
16. According to paragraph 4, one possible final stage in the development of a volcanic island is that it may
A) rise again through renewed uplift B) become part of a continent C) split into several independent volcanoes D) leave a ring-shaped reef after the central land disappears
17. What can be inferred from the passage as a whole?
A) The passage explains a sequence of geological changes affecting oceanic islands. B) Reef growth is more important than volcanism in creating islands. C) All volcanic islands eventually become atolls. D) Most island chains form along continental shorelines.
18. The word hotspot in paragraph 2 refers to
A) an area of unusually warm ocean water near coral reefs B) a chain of extinct volcanoes beneath a tectonic plate C) a relatively fixed source of magma beneath the moving plate D) a region where earthquakes occur without volcanism
19. According to paragraph 2, which of the following is true of island chains associated with hotspots?
A) The youngest islands are usually farthest from the hotspot. B) The islands farthest from the hotspot are usually older. C) All islands in the chain form at the same time. D) Only one island in the chain can remain above sea level.
20. What is the main idea of the passage?
A) Coral reefs determine where volcanic islands first appear. B) Hotspots create islands only where tectonic plates move rapidly. C) Most volcanic islands survive because reef growth protects them. D) Volcanic islands are shaped by eruption, motion, erosion, sinking, and reef growth.
