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火山是当熔岩或岩浆从地球表面的裂缝中逸出，然后在这些裂缝周围凝固时形成的陆地形态。

Volcanoes are the landforms created when molten rock, or magma, escapes from vents in the Earth's surface and then solidifies around these vents.

在任何一年中，地球上大约有50座活火山会喷发——通常会有一些预警。

In any given year, roughly 50 of Earth's active volcanoes erupt—usually with some warning.

在喷发之前，它们通常会震动、膨胀、升温，并喷出各种气体。

Before they blow, they typically shake, swell, warm up, and belch a variety of gases.

来自火山灾害援助计划（VDAP）的科学家——隶属于美国地质调查局，位于华盛顿州温哥华的美国地质调查局喀斯喀特火山观测站——随时待命，一旦接到召唤，就能立即赶往世界上任何一座苏醒的火山；他们配备了最新的激光器、地震仪和其他监测设备，可以评估火山的潜在破坏力并预测其可能喷发的时间。

Scientists from the Volcano Disaster Assistance Program (VDAP)—part of the U.S. Geological Survey and based at the U.S. Geological Survey's Cascades Volcano Observatory in Vancouver, Washington—are always on call, ready when summoned to rush at a moment's notice to an awakening volcano anywhere in the world; armed with the latest in lasers, seismometers, and other monitoring devices, they can assess the volcano's potential for violence and predict when it might ignite.

地质学家在喷发阶段开始后专注于特定火山时，在预测单个喷发事件方面取得了相当的成功。

Geologists have enjoyed fair success in predicting individual eruptive episodes when they concentrate on a specific volcano after an eruptive phase has begun.

这些监测工作包括仔细测量火山表面温度的变化，观察其坡面最轻微的膨胀，并跟踪区域地震活动。

These monitoring efforts involve carefully measuring changes in a volcano's surface temperature, watching for the slightest expansion in its slope, and keeping track of regional earthquake activity.

西雅图华盛顿大学的一个实验室全天24小时有人值守，监测圣海伦斯火山的震动。

A laboratory at the University of Washington in Seattle is staffed 24 hours a day to monitor the rumblings of Mount St. Helens.

然而，即便有了当今技术的进步，火山预测的艺术仍未完全掌握。

Even with the advances brought by today's technology, however, the art of volcano prediction has not been fully mastered.

尽管一大群配备最新预测技术的科学家密切监视着圣海伦斯火山，美国地质调查局仍未能预测到1980年的爆发。

The U.S. Geological Survey missed the call on Mount St. Helens' 1980 blast despite the fact that the mountain was being watched closely by a large team of scientists armed with the latest in prediction technology.

它成功预测了菲律宾皮纳图博火山的喷发，在1991年5月17日火山强烈喷发前，疏散了25公里（15英里）范围内的几乎所有人。

It did successfully predict the eruption of Mount Pinatubo in the Philippines, evacuating virtually everyone within 25 kilometers (15 miles) before the volcano's powerful blast on May 17, 1991.

在火山喷发之前，炽热的岩浆向地表上升，因此任何局部升温现象可能预示即将发生的事件。

Before a volcano erupts, hot magma rises toward the surface, so any local manifestation of increasing heat may signal an impending event.

持续的调查可以识别新的地表温泉，并测量现有温泉中水和蒸汽的温度。

Ongoing surveys can identify new surface hot springs and take the temperature of the water and steam in existing ones.

如果逸出的蒸汽温度仅略高于水的沸点，那么地表水可能正渗入山体，被地下热岩石加热，暂时一切正常。

If the escaping steam isn't much hotter than the boiling point of water, then surface water is probably seeping into the mountain and being heated by contact with hot subsurface rocks, and all is well for the time being.

如果蒸汽过热，温度高达500°C（900°F），那么它可能来自浅层富水岩浆，这是喷发可能正在酝酿的迹象。

If the steam is superheated, with temperatures as high as 500°C (900°F), then it probably derives from shallow water-rich magma, a sign that an eruption may be brewing.

随着岩浆上升，火山锥本身开始升温。

As magma rises, the volcanic cone itself begins to heat up.

火山锥的整体温度可以通过配备红外热传感器的轨道卫星进行监测，以探测表面温度的微小变化。

The overall temperature of a volcanic cone can be monitored from an orbiting satellite equipped with infrared heat sensors to detect the slightest change in surface temperature.

这种高空技术为地球上大约600座活火山提供了同时的早期预警系统。

This high-altitude technology serves as a simultaneous early-warning system for most of Earth's 600 or so active volcanoes.

即将发生的喷发还可以通过上升岩浆释放的气体增加来预测。

Impending eruptions may also be predicted by increased gas emissions from rising magmas.

因此，火山学家持续监测潜在活火山的二氧化硫和二氧化碳排放。

For this reason, volcanologists continuously monitor sulfur dioxide and carbon dioxide emissions from potentially active volcanoes.

活火山随着下方新岩浆的供应而体积膨胀。

Active volcanoes expand in volume as they acquire new supplies of magma from below.

因此，火山坡度增加或隆起可能预示即将喷发。

As a result, an increase in the steepness or bulging of a volcano's slope may signal an impending eruption.

为了探测火山锥的膨胀，使用倾斜仪，一种类似于木匠水平仪的设备。

To detect the inflation of a volcanic cone, a tilt meter, a device like a carpenter's level, is used.

随着岩浆上升，它推开裂缝岩石，移动时扩大裂缝。

As magma rises, it pushes aside fractured rock, enlarging the fractures as it moves.

因为这种裂缝会导致地震，喷发常常伴随着一种独特的地震活动模式，称为谐波震颤，一种持续的节奏性隆隆声。

Because this type of fracturing causes earthquakes, eruptions are often preceded by a distinctive pattern of earthquake activity called harmonic tremors, a continuous rhythmic rumbling.

监测这些震颤发生位置的敏感设备可以测量上升岩浆的高度增加。

Sensitive equipment that monitors the location where these tremors occur can measure the increased height of rising magma.

岩浆上升的速率提供了喷发可能发生时间的估计。

The rate at which the magma rises provides an estimate of when an eruption may occur.

事实上，这是科学家准确预测圣海伦斯火山近期喷发的主要手段。

Indeed, it served as the principal means by which scientists accurately predicted recent eruptions of Mount St. Helens.

然而，当我们不知道一个地点的火山潜力时，预测喷发的努力会受挫。

Efforts to predict eruptions are thwarted, however, when we are unaware of a site's volcanic potential.

偶尔，新火山会突然且出乎意料地出现，如1943年，帕里库廷火山在墨西哥米却肯州（墨西哥城以西320公里/200英里）一夜之间形成。

Occasionally, a new volcano appears suddenly and rather unexpectedly, as was the case in 1943, when the volcano Paricutin developed literally overnight in the Mexican state of Michoacán, 320 kilometers (200 miles) west of Mexico City.

周围地区因其地质带而被认为是火山地区，但无法预测火山会在这个特定地点出现。

The surrounding area was known to be volcanic because of its geologic zone, but it was not possible to predict that the volcano would appear at this particular site.

我们预测火山喷发的能力持续改进，但仍未达到我们所需的准确度。

Our ability to predict volcanic eruptions continues to improve but is not yet as accurate as we need it to be.

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

The fact that "The U.S. Geological Survey missed the call on Mount St. Helens’ 1980 blast" supports which of the following points?

Why does the author mention the successful prediction of "the eruption of Mount Pinatubo"?

The word "manifestation" in the passage is closest in meaning to

According to paragraph 3, why is superheated steam in a surface hot spring a sign that an eruption may be developing?

The word "principal" in the passage is closest in meaning to

In paragraph 4, the mention of the accurate prediction of recent eruptions of Mount St. Helens serves to

According to paragraph 5, each of the following features of the appearance of the volcano Paricutin was a surprise to scientists EXCEPT

Look at the four squares  that indicate where the following sentence could be added to the passage. These additions often cause the volcano to bulge out sideways.  Where would the sentence best fit? Click on a squareto add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Predicting Volcanic Eruptions Volcanoes are the landforms created when molten rock, or magma, escapes from vents in the Earth's surface and then solidifies around these vents. In any given year, roughly 50 of Earth's active volcanoes erupt —usually with some warning. Before they blow, they typically shake, swell, warm up, and belch a variety of gases. Scientists from the Volcano Disaster Assistance Program(VDAP)—part of the U.S. Geological Survey and based at the U.S. Geological Survey's Cascades Volcano Observatory in Vancouver, Washington—are always on call, ready when summoned to rush at a moment's notice to an awakening volcano anywhere in the world; armed with the latest in lasers, seismometers, and other monitoring devices, they can assess the volcano's potential for violence and predict when it might ignite. Geologists have enjoyed fair success in predicting individual eruptive episodes when they concentrate on a specific volcano after an eruptive phase has begun. These monitoring efforts involve carefully measuring changes in a volcano's surface temperature, watching for the slightest expansion in its slope, and keeping track of regional earthquake activity. A laboratory at the University of Washington in Seattle is staffed 24 hours a day to monitor the rumblings of Mount St. Helens. Even with the advances brought by today's technology, however, the art of volcano prediction has not been fully mastered. The U.S. Geological Survey missed the call on Mount St. Helens' 1980 blast despite the fact that the mountain was being watched closely by a large team of scientists armed with the latest in prediction technology. It did successfully predict the eruption of Mount Pinatubo in the Philippines, evacuating virtually everyone within 25 kilometers (15 miles) before the volcano's powerful blast on May 17, 1991. Before a volcano erupts, hot magma rises toward the surface, so any local manifestation of increasing heat may signal an impending event. Ongoing surveys can identify new surface hot springs and take the temperature of the water and steam in existing ones. If the escaping steam isn't much hotter than the boiling point of water, then surface water is probably seeping into the mountain and being heated by contact with hot subsurface rocks, and all is well for the time being. If the steam is superheated, with temperatures as high as 500° C (900°F), then it probably derives from shallow water-rich magma, a sign that an eruption may be brewing. As magma rises, the volcanic cone itself begins to heat up. The overall temperature of a volcanic cone can be monitored from an orbiting satellite equipped with infrared heat sensors to detect the slightest change in surface temperature. This high-altitude technology serves as a simultaneous early-warning system for most of Earth's 600 or so active volcanoes. Impending eruptions may also be predicted by increased gas emissions from rising magmas. For this reason, volcanologists continuously monitor sulfur dioxide and carbon dioxide emissions from potentially active volcanoes. Active volcanoes expand in volume as they acquire new supplies of magma from below. As a result, an increase in the steepness or bulging of a volcano's slope may signal an impending eruption. To detect the inflation of a volcanic cone, a tilt meter, a device like a carpenter's level, is used. As magma rises, it pushes aside fractured rock, enlarging the fractures as it moves. Because this type of fracturing causes earthquakes, eruptions are often preceded by a distinctive pattern of earthquake activity called harmonic tremors, a continuous rhythmic rumbling. Sensitive equipment that monitors the location where these tremors occur can measure the increased height of rising magma. The rate at which the magma rises provides an estimate of when an eruption may occur. Indeed, it served as the principal means by which scientists accurately predicted recent eruptions of Mount St. Helens. Efforts to predict eruptions are thwarted, however, when we are unaware of a site's volcanic potential. Occasionally, a new volcano appears suddenly and rather unexpectedly, as was the case in 1943, when the volcano Paricutin developed literally overnight in the Mexican state of Michoacán, 320 kilometers (200 miles) west of Mexico City. The surrounding area was known to be volcanic because of its geologic zone, but it was not possible to predict that the volcano would appear at this particular site. Our ability to predict volcanic eruptions continues to improve but is not yet as accurate as we need it to be.