Listening audioscript

21. ACCORDING TO THE CONVERSATION, WHAT DEVELOPMENT MADE THE 
NEW DISCOVERY ABOUT THE PARTICULAR SPECIES OF SQUID POSSIBLE? 
 
 

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22. LISTEN AGAIN TO PART OF THE CONVERSATION. THEN ANSWER THE 
QUESTION. 
 (Professor)
It is really impressive; in the video it shows several squid attacking their 
prey and they reach speeds of up to nine kilometers per hour, which 
doesn’t really sound that fast, but you have to remember that the water 
pressure is pretty strong deep in the ocean. 
WHY DOES THE PROFESSOR SAY THIS?
 (Professor)
Which doesn’t really sound that fast, but you have to remember that the 
water pressure is pretty strong. 
 
Page 524
[ mp3 260-261] 
Questions 23 through 28. 
Listen to a lecture in a geology class. 
(Professor)
Okay, so we’ve been discussing the three basic cave structures: sea 
caves, lava caves, and solution caves. As you remember the 
names…um… the cave structures are named for the process that formed 
them. So as we said, sea caves are found along rocky shores. Sea 
caves are formed when pounding waves erode, or wash away areas of 
rock, creating a cave. The Blue Grotto on the Isle of Capri off the coast of 
Italy is one of the most famous sea caves. Sea caves form along a crack 
in a rock in areas where the rock is soft, typically sandstone or limestone. 
It is pretty rare to find sea caves formed in harder rock such as granite. 
We also talked about lava caves. Lava caves form during volcanic 
eruptions when the outer surface of flowing lava, which is molten rock, 
cools and the lava underneath remains hot. As lava flows down a slope, 
it forms a channel and in the middle of that channel the lava flows faster 
than the lava on the surrounding edges, just like a river or stream has a 
channel of faster moving water over the deepest point. The slower 
moving lava along the edges of the channel cools first, leaving a stream 
of flowing lava near the center. As the edges cool and solidify, a tube 
forms that surrounds the flowing lava and traps in heat which allows the 
lava in the center of the channel to continue flowing. When the flow of 
lava from the underground sources ends, the remaining lava in the tube 
flows out, leaving a hollow tube. These kinds of caves can be seen all 
over Hawaii, as you might expect. The longest lava cave is Kazumura 
Cave in Hawaii, a cave system that is almost 30 miles long.
Okay, so today I want to focus on solution caves. Remember I said that 
cave structures are named for the process that formed them? 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 imagine when you talk about caves. This 
picture shows the Carlsbad Caverns in New Mexico, and this is one of 
the most famous American solution caves, which are formed primarily by 
rainwater and snowmelt, and are by far, the most numerous of all cave 
types. 
There are a few prerequisite conditions needed for the formation of 
solution caves. First, solution caves are created when a mild acid, or 
solution, reacts with limestone or a rock containing 80 percent or more 

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calcium carbonate, which is characteristically found in, um, limestone, 
dolomite, or similar types of rocks. Also, the rock needs to be fractured 
so the water can seep through these cracks and be relatively close or at 
the surface. The fourth requirement is a relatively moderate annual 
rainfall, around 18 inches per year. Finally, vegetation cover—vegetation 
enhances cave formation by producing more available acids. Now, we 
aren’t going to discuss this in detail today, but there are a few other 
variable factors that also play an important role in the development of a 
cave such as humidity, temperature, and airflow through a cave. Oh… so 
where was I? 
Oh yes, solution caves are usually formed in areas with a large amount 
of limestone or dolomite. Surface water works its way into tiny cracks in 
the rock. As the surface water trickles through soil, it combines with 
calcium carbonate to create a weak acid called carbonic acid. …Um, I 
should note here that recently it was discovered that sulfuric acid formed 
beneath the Earth’s surface was the acid responsible for some solution 
caves, including Carlsbad Caverns. …Well, once this weak acid comes 
in contact with limestone, it will begin to dissolve the limestone. This 
process slowly creates larger and larger cracks and over thousands of 
years, this acid solution dissolves the limestone or similar rock and 
causes magnificent passages and chambers to form underground. 
Eventually, if the water table drops, or an earthquake lifts the cave up, 
the water drains out, and 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.
Oh sorry, let me backtrack a bit, as I was saying, once the passages and 
chambers of the cave have formed, marvelous structures particular to 
solution caves begin to evolve. The most common formations are 
stalactites, stalagmites, and columns. Stalactites are dagger-like 
formations that hang from the ceiling of a cave. Stalactites are formed by 
drops of water containing small amounts of dissolved limestone that have 
been acquired from seeping through the cracks in the rock. Once this 
drop is suspended from the ceiling of the cave, some carbon dioxide 
escapes this small hanging drop of water. Because carbon dioxide is 
escaping, the water can’t retain all the limestone in it, so a thin ring of 
limestone is formed on the ceiling of the cave. After the drop falls, the 
small ring is left on the ceiling of the cave. This process is repeated 
numerous times over thousands of years at the same spot, and this 
eventually forms a hollow stalactite called a soda straw. After countless 
drops of water have dripped through the soda straw, it can become 
plugged by increasing deposits of dissolved limestone. This results in 
cone shaped stalactites. On average, stalactites grow about an inch 
every 200 years, a very slow process indeed.
Stalagmites are formations that are created from the ground up. These 
formations form from the drops that have fallen from stalactites on the 
ceiling of a cave. Even though some of the dissolved limestone from the 

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drops of water was used in the formation of the stalactite, there is some 
remaining limestone in the water that drops to the floor of the cave. As 
drops of this water fall from the ceiling and hit the bottom of the cave, the 
drops of water are dispersed, which allows for more carbon dioxide to be 
released and another formation on the cave floor starts to form. After 
many drops have landed on the exact same spot, a stalagmite develops. 
Columns form after thousands if not millions of years of stalactite and 
stalagmite growth. When both of these two formations finally grow into 
each other, a column is formed.