IELTS Reading 練習火山如何形成（含題目+詳解）

How Volcanoes Form

IELTS · 雅思備考 · 12 min read · 2026-04-25

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主題: How volcanoes form
文章重點: Volcanoes are produced by at least three different geological settings — subduction zones, mid-ocean ridges and hot spots — and despite better instruments, the precise timing of eruptions is still impossible to predict reliably.
難度: 中等 · Intermediate
建議時間: 18 分鐘

重要單字

molten — made liquid by very high heat / 熔融的
subduction — the sinking of one tectonic plate beneath another / 隱沒（板塊）
magma — hot liquid rock below the Earth's surface / 岩漿
silica — a mineral that makes magma sticky / 二氧化矽
plumes — rising columns of hot material / 上升熱柱
seismic — relating to earthquakes and ground vibrations / 地震的

30 秒快速理解 30-second summary

A volcano is an opening through which molten rock reaches the surface. The most common setting is a subduction zone, where wet sinking rock makes sticky, gas-rich magma and explosive eruptions. Mid-ocean ridges produce gentle underwater eruptions that account for most volcanic activity by volume. Hot spots, plumes from deep in the mantle, create isolated chains like Hawaii. Forecasting eruptions remains unreliable.

逐段練習 Read paragraph by paragraph

1 段落 1 — What a volcano is

A volcano is, in the simplest sense, an opening through which molten rock from inside the Earth reaches the surface. The processes that drive these openings are extraordinarily varied, however, and modern geologists distinguish at least three principal mechanisms. Each is linked to the slow movement of the rigid plates that make up the outermost shell of the planet.

本段重要單字 (3)

molten — made liquid by very high heat / 熔融的
mechanisms — ways in which something works / 機制
rigid — stiff and not bending / 僵硬的

Quick Check · 隨堂小測

According to the paragraph, what links all three volcano-forming mechanisms?

A. They are all caused by ocean currents.
B. They are all linked to the slow movement of tectonic plates.
C. They all occur only on continents.

看答案 · Show answer

答案：B — B. They are all linked to the slow movement of tectonic plates.

The text states that each mechanism "is linked to the slow movement of the rigid plates that make up the outermost shell of the planet".

2 段落 2 — Subduction zones and explosive eruptions

The most common setting is the subduction zone, where one tectonic plate slides beneath another. As the descending plate sinks into the hotter mantle, water locked inside its rocks is released, lowering the melting point of the surrounding material. The resulting magma is comparatively rich in dissolved gas and silica, which makes it sticky. When this magma rises and reaches the surface, the trapped gas often expands violently, producing the explosive eruptions characteristic of volcanoes such as Mount St Helens or Mount Pinatubo.

本段重要單字 (3)

subduction — one plate sinking beneath another / 隱沒
magma — molten rock beneath the surface / 岩漿
silica — a mineral that makes magma sticky / 二氧化矽

Quick Check · 隨堂小測

Why are subduction-zone eruptions often explosive?

A. The lava is unusually low in silica and very runny.
B. The magma is sticky and rich in dissolved gas, which expands violently as it rises.
C. The plates collide head-on without sliding.

看答案 · Show answer

答案：B — B. The magma is sticky and rich in dissolved gas, which expands violently as it rises.

The paragraph says the magma is "comparatively rich in dissolved gas and silica, which makes it sticky" and that "the trapped gas often expands violently".

3 段落 3 — Mid-ocean ridges

A second setting occurs at mid-ocean ridges, where two plates pull apart. As the plates separate, hot rock from below flows upward to fill the gap and partially melts as the pressure on it drops. The lava produced here is generally low in silica, runs easily and erupts gently. Because most mid-ocean ridges lie thousands of metres below sea level, these eruptions usually go unseen, but they account for the majority of volcanic activity on Earth by volume.

本段重要單字 (3)

ridges — long raised strips, here on the ocean floor / 海脊
lava — molten rock that has reached the surface / 熔岩
volume — the total amount of something / 總量

Quick Check · 隨堂小測

Why do most mid-ocean ridge eruptions go unnoticed?

A. They are too small to detect on any instrument.
B. They occur thousands of metres below sea level.
C. They produce no lava at all.

看答案 · Show answer

答案：B — B. They occur thousands of metres below sea level.

The paragraph states "most mid-ocean ridges lie thousands of metres below sea level, these eruptions usually go unseen", although they account for the majority of volcanic activity by volume.

4 段落 4 — Hot spots far from plate edges

A third, more puzzling setting is the so-called hot spot. Here, plumes of unusually hot rock rise from deep within the mantle, possibly from as far as the core-mantle boundary. They burn through the overlying plate to produce isolated volcanoes far from any plate boundary. Hawaii is the classic example: as the Pacific plate drifts north-westward over a stationary plume, a chain of progressively older, extinct islands trails behind the active volcanoes.

本段重要單字 (3)

plumes — rising columns of hot material / 熱柱
overlying — lying or being on top of / 上方覆蓋的
extinct — no longer active / 死火山的、已熄滅的

Quick Check · 隨堂小測

How does the Hawaiian island chain illustrate hot-spot activity?

A. The hot plume moves while the Pacific plate stays still.
B. The Pacific plate drifts over a stationary plume, leaving a chain of older, extinct islands behind.
C. All Hawaiian islands are exactly the same age.

看答案 · Show answer

答案：B — B. The Pacific plate drifts over a stationary plume, leaving a chain of older, extinct islands behind.

The text says "the Pacific plate drifts north-westward over a stationary plume, a chain of progressively older, extinct islands trails behind the active volcanoes".

5 段落 5 — Why prediction is still hard

Forecasting eruptions remains difficult. Although seismic instruments now track the movement of magma in unprecedented detail, the precise moment when a volcano will erupt — and how violently — is still beyond reliable prediction.

本段重要單字 (3)

forecasting — predicting future events / 預測
seismic — relating to earth tremors / 地震的
unprecedented — never done or known before / 前所未有的

Quick Check · 隨堂小測

What does the paragraph imply about volcano prediction today?

A. We can now predict the exact moment and force of any eruption.
B. Despite better instruments, the timing and violence of eruptions still cannot be reliably predicted.
C. Seismic instruments are no longer used.

看答案 · Show answer

答案：B — B. Despite better instruments, the timing and violence of eruptions still cannot be reliably predicted.

The text says instruments give "unprecedented detail" but "the precise moment when a volcano will erupt — and how violently — is still beyond reliable prediction".

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閱讀前先看 Before you read

30 秒快速理解 30-second summary

逐段練習 Read paragraph by paragraph

1 段落 1 — What a volcano is

2 段落 2 — Subduction zones and explosive eruptions

3 段落 3 — Mid-ocean ridges

4 段落 4 — Hot spots far from plate edges

5 段落 5 — Why prediction is still hard

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