Read the following passage.
A. A volcano is an opening, or vent, in the Earth's surface where lava, small rocks called tephra and steam erupt. Below ground, molten rock is known as magma; once it erupts it is called lava. Magma is lighter than the solid rock around it, so it is driven upward toward the surface. Most volcanic activity happens along the boundaries of tectonic plates or above hotspots. There are about 1,350 potentially active volcanoes worldwide, not counting those under the oceans. The best-known types are cinder cones, composite volcanoes and shield volcanoes, and lava domes are often described alongside them.
B. Cinder cones are the simplest type, and they are the most common volcano in the world. They form when gas-charged lava is blown violently into the air from a single vent. The lava breaks into small pieces that harden and fall as cinders, piling up into a round or oval cone with a bowl-shaped crater on top. A cinder cone usually erupts only once, and the eruption is often brief: half of all historic cinder cone eruptions lasted less than 30 days. In 1943 one began growing on a farm in Mexico and destroyed the town of San Juan.
C. Shield volcanoes are the largest volcanoes on Earth, yet they do not form steep peaks. They are built almost entirely of very fluid lava, which pours out from vents at the summit or from cracks on the flanks called rift zones. Thousands of these flows spread over great distances and cool as thin sheets, so the volcano grows into a broad, gentle dome shaped like a warrior's shield lying flat. Shield volcanoes are much wider than they are tall: the base of Mauna Loa in Hawaii is about 160 kilometres wide. Mauna Loa, the largest active volcano on the planet, has erupted 34 times since 1843.
D. Composite volcanoes, also called stratovolcanoes, are tall, steep cones made of layers of lava, ash and rock, such as Mount Fuji in Japan. Lava domes form when lava is too thick to flow far, so it piles up over and around the vent, often inside the crater of a composite volcano. As a dome grows from within, its cooler outer surface can shatter and send hot rock and gas down the mountain. In 1980 a huge landslide removed the top 400 metres of Mount St. Helens. Mount Rainier is considered the most dangerous volcano in the lower 48 states, and its greatest hazard is destructive mudflows called lahars.
E. Not given in any of the above paragraphs.
Decide which paragraph, A to D, has the information given in each statement below. Select E if the information is not given in any of the paragraphs.
AI explanationShows the answer. Tap to open.
Correct Answer: B
Why this is correct: Paragraph B says cinder cones are the most common volcano in the world. It also says half of all historic cinder cone eruptions lasted less than 30 days. Thirty days is about a month, so half of these outbursts ended within a month.
Passage Reference: A cinder cone usually erupts only once, and the eruption is often brief: half of all historic cinder cone eruptions lasted less than 30 days.
Tips: First work out which kind of volcano is 'the most common'. Then check how long half of its outbursts went on, and compare that with a month.
Why the other options are wrong:
- A: Paragraph A lists cinder cones among the best-known types but says nothing about how long any eruption lasts.
- C: Paragraph C counts 34 eruptions of Mauna Loa since 1843, which tells how often, not how long.
- D: Paragraph D describes explosive composite volcanoes and growing domes. No eruption length is given there.
- E: The figure of less than 30 days for half of historic cinder cone eruptions sits in Paragraph B.
Correct Answer: C
Passage Reference: They are built almost entirely of very fluid lava, which pours out from vents at the summit or from cracks on the flanks called rift zones.
Why this is correct: Paragraph C talks about the fluid lava of a shield volcano. It pours out from vents at the summit or from cracks on the flanks called rift zones. The summit is the top and the flanks are the sides.
Tips: Find where shield volcanoes are described. Check how their lava gets out, and whether it comes from more than one place.
Why the other options are wrong:
- A: Paragraph A defines a vent in general terms, but it does not say where lava leaves any particular type of volcano.
- B: The second paragraph says a cinder cone erupts from a single vent, which is the opposite of several openings.
- D: Look at paragraph D: it says a lava dome piles up over its vent, but it names no cracks along the slopes.
- E: Vents at the summit and cracks on the flanks of shield volcanoes are both described in Paragraph C.
Correct Answer: E
Passage Reference: Mauna Loa, the largest active volcano on the planet, has erupted 34 times since 1843.
Why this is correct: Paragraph C gives one count: Mauna Loa has erupted 34 times since 1843. The passage never compares how often shield volcanoes erupt with cinder cones or composite volcanoes. So this ranking is not given.
Tips: A count for one volcano is not a comparison between types. Look for words like 'more often than'.
Why the other options are wrong:
- A: Paragraph A counts potentially active volcanoes around the world, but it does not rank the types by how often they erupt.
- B: Notice that paragraph B says a cinder cone usually erupts once, yet it never says another type erupts most often.
- C: Mauna Loa's 34 eruptions are listed in Paragraph C, but that is one volcano, and no other type is measured against it.
- D: Notice that paragraph D describes dangerous eruptions and Mount Rainier, with no comparison of how frequent each type is.
Correct Answer: A
Passage Reference: Below ground, molten rock is known as magma; once it erupts it is called lava.
Why this is correct: Paragraph A says that below ground molten rock is known as magma, and once it erupts it is called lava. Melted rock has one name underground and another name after it comes out.
Tips: Find where 'melted rock' is named. Check whether its name changes once it 'comes out of the ground'.
Why the other options are wrong:
- B: Look at paragraph B: it describes lava blown into the air as cinders. But it does not explain that the rock changes name.
- C: Very fluid lava on shield volcanoes is what paragraph C discusses, not the words magma and lava.
- D: In paragraph D, the writer describes lava that is too thick to flow, which is about texture rather than naming.
- E: The two names, magma underground and lava after an eruption, are explained in Paragraph A.
Correct Answer: E
Passage Reference: A cinder cone usually erupts only once, and the eruption is often brief: half of all historic cinder cone eruptions lasted less than 30 days.
Why this is correct: Paragraph B says cinder cones are the most common volcano and that a cinder cone usually erupts only once. It gives this as a fact but offers no cause, and nothing is said about the vent being plugged afterwards.
Tips: The most common kind is the cinder cone. Check whether Paragraph B explains why it goes quiet, or only says that it does.
Why the other options are wrong:
- A: Notice that paragraph A explains why magma rises, not why a cinder cone stops erupting.
- B: The single eruption of a cinder cone is noted in Paragraph B, but the passage never explains what causes it.
- C: The third paragraph describes shield volcanoes built by thousands of flows, with no mention of blocked vents.
- D: Look at paragraph D: it says lava can pile up over a vent in a dome. That is a different type, and it says nothing about cinder cones.
Correct Answer: D
Passage Reference: As a dome grows from within, its cooler outer surface can shatter and send hot rock and gas down the mountain.
Why this is correct: Look at paragraph D: it says lava domes form from lava too thick to flow far. As a dome grows from within, its cooler outer surface can shatter and send hot rock and gas down the mountain. Swelling is growing from within, and breaking apart is shattering.
Tips: The word dome appears in Paragraph C too. There it only describes a shape.
Why the other options are wrong:
- A: Notice that paragraph A names lava domes only in its list of types, with no description of how they behave.
- B: The second paragraph describes lava breaking into cinders in the air, not a swelling mound that bursts.
- C: Look at paragraph C: it uses the word dome for the broad shape of a shield volcano. That shape is gentle and does not shatter.
- E: The shattering surface of a growing lava dome is described in Paragraph D.
Correct Answer: C
Passage Reference: Mauna Loa, the largest active volcano on the planet, has erupted 34 times since 1843.
Why this is correct: In paragraph C, the writer says Mauna Loa has erupted 34 times since 1843. Thirty-four is more than thirty, and 1843 falls in the 1840s.
Tips: Look for the name Mauna Loa and a count of eruptions.
Why the other options are wrong:
- A: The first paragraph counts about 1,350 volcanoes around the world, which is not the history of one mountain.
- B: Look at paragraph B: it dates a cinder cone in Mexico to 1943, not an eruption record for Mauna Loa.
- D: Look at paragraph D: it gives a date of 1980 for Mount St. Helens and does not mention Mauna Loa.
- E: The count of 34 eruptions since 1843 closes Paragraph C.
Correct Answer: A
Passage Reference: There are about 1,350 potentially active volcanoes worldwide, not counting those under the oceans.
Why this is correct: In paragraph A, the writer says there are about 1,350 potentially active volcanoes worldwide, not counting those under the oceans. Potentially active means they could erupt, and 1,350 is more than a thousand.
Tips: Find where the number of volcanoes in the world is given. Check that it is over a thousand, and which volcanoes it leaves out.
Why the other options are wrong:
- B: Look at paragraph B: it says cinder cones are the most common volcano, but it gives no total number.
- C: The third paragraph gives a size and an eruption count for Mauna Loa, not a count of volcanoes.
- D: Look at paragraph D: it names three mountains in Japan and Washington, with no world total.
- E: The world total of about 1,350 potentially active volcanoes is stated in Paragraph A.
Correct Answer: C
Passage Reference: Shield volcanoes are much wider than they are tall: the base of Mauna Loa in Hawaii is about 160 kilometres wide.
Why this is correct: In paragraph C, the writer says shield volcanoes are much wider than they are tall. The base of Mauna Loa is about 160 kilometres wide. Spreading out means width, and rising means height.
Tips: Notice that paragraph D also talks about shape. Make sure the type is the shield volcano.
Why the other options are wrong:
- A: The first paragraph names shield volcanoes as a well-known type but describes neither their width nor their height.
- B: Look at paragraph B: it describes a round or oval cinder cone, which is a different type of volcano.
- D: Notice that paragraph D calls composite volcanoes tall and steep, which is the opposite shape.
- E: The comparison of width and height for shield volcanoes is made in Paragraph C.
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