Practice these TOEFL iBT listening tests to help you score high in the TOEFL Listening Section. Check the correct answers and audio transcripts below. This video is in the series of NEW TOEFL iBT Preparation: https://www.youtube.com/playlist?list=PL2jvSGmpWX1UMjbc8Onae7i-R6Z8VcPbU.
Questions 23 through 28. Listen to a lecture in a geology class.
(professor) Good morning, class. Today, we're going to look at the three basic cave structures: sea caves, lava caves, and solution caves. As you may’ve guessed by the names, the cave structures’re named for the process that formed them.
(student 1) Excuse me, Professor, but can you please repeat that? I didn't quite get it.
(professor) You bet. I don’t want you to miss it because it's important. What I said was that we'll be talking about the three basic cave structures and that the names of the different types of caves are actually derived from the process that formed them. You'll see what I mean after I finish talking about different types of caves and how they’re formed.
(student 1) OK, thanks.
(professor) No problem. Now, let’s look at this picture of a sea cave. Sea caves are found along rocky shores. Sea caves are formed when pounding water washes away areas of rock, creating a cave. The cave in this picture is one of the most famous sea caves, the Blue Grotto on the Isle of Capri. Have any of you ever been there? . . . None of you? . . . Oh, that’s too bad. It’s gorgeous.
OK, now let’s look at a lava cave. Lava caves form during volcanic eruptions when the outer surface of flowing lava cools and the lava underneath remains hot. The hot lava below continues to flow and leaves a lava tunnel or lava cave underneath. This picture shows one of the approximately 300 lava caves in Lava Beds National Monument. . .. What does it look like to you? ... Have you ever seen any place that looks like this? It certainly looks like volcanic areas of Hawaii, and you might expect to find this monument on the volcanic islands of Hawaii, but it’s not there. It's actually in northern California.
OK, now ... let me go back to my main point for just a moment. Remember I said that cave structures are named for the process that formed them. Have you understood this in terms of the first two types of caves, the sea cave and the lava cave? Well, the same concept applies to the last type of cave structure I'm going to talk about now.
Here's a solution cave, which is the most complicated type of cave structure. You can see that this kind of cave has the stalagmites and stalactites that most people picture when you talk about caves. Now what does this picture show? Does anyone recognize it? Yes?
(student 2) It looks like Carlsbad Caverns.
(professor) That’s exactly right. This picture shows the Carlsbad Caverns in New Mexico, and this is one of the most famous American solution caves. A solution cave is formed in areas with a large amount of limestone, marble, or dolomite. Surface water works its way into tiny cracks in the rock. As the surface water trickles through soil, a mild acid is formed, and this mild acid is a solution that creates this type of cave. Over thousands of years, this acid solution dissolves the limestone or similar rock. And what do you think happens as a result? . . . Well, this causes passages and chambers to form underground. If the water table drops, or an earthquake lifts the cave up, the water drains out. Rainwater then continues the process by seeping through cracks into the rocks. At this point, the dripping or flowing water begins to form the marvelous structures found in solution caves, and entrances may develop. These caves usually have very few entrances. An earthquake can lift the cave to the surface, opening the cave. Sometimes land over a solution cave collapses to create a sinkhole entrance.
A solution cave can also develop an entrance as soil erodes from a hillside or as a spring flows from the cave. Now what’s very important to understand from all this is that this type of cave is a very complicated cave structure, and I think you see that. I think you also see that it’s called a solution cave because it’s an acid solution that forms it.
OK, that’s all for now. Next week we’ll discuss speleothems, the beautiful structures that form from various crystal deposits in solution caves. The most famous of these are, of course, the stalagmites and stalactites. See you next week.
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Correct Answers:
23. B
24. C
25. Blue Grotto: Sea cave
Carlsbad Caverns: Solution cave
Lava Beds National Monument: Lava cave
26. C & D
27. Lava caves: Created during volcanic eruptions
Solution caves: Created by weak acids dissolving rock
Sea caves: Created by erosion
28. D
