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A geyser is a special kind of hotunderground spring. It periodically ejects streams of hot water and steam intothe air. Geysers are very rare because they require a unique combination ofgeology that exists in only a few places earth. Only about 1,000 can be foundtoday, with half of them in Yellowstone National Park in the United States. Hotsprings are formed when surface water seeps down though the ground until itreaches rock that has been heated by magma, which is volcanic melted rock. Thehot water rises up to the surface through spaces between the underground rocklayer. The water becomes part of a geyser if the rising water is constrictedinto a narrow passageway that connects the underground water to the surface.
The water cools as it escapes to thesurface, causing it to exert downward pressure on the hotter water below. Thehot water has no place to go, being blocked by the solid layer of undergroundrock. As a result, the pressure and heat rises on the water, superheating it totemperatures around 95.6 degrees Celsius.
The boiling water surges through the ventleading to the surface. This escape reduces the pressure on the water below,causing the superheated water to burst out the vent into the air, resulting ina spray that we see as the end product of the geyser. The spray may continuefor several minutes.
Eventually, this release in pressure causesthe remaining water to cool below the boiling point, and the eruption ends,with the groundwater again seeping back into the ground. The cycle repeats itselfat predictable intervals. There are two type of geysers. Fountain geysers eruptfrom pools of water, usually in a series of violent bursts. Cone geysersemanate from mounds of mineral deposits known as geyserite. They form steadysprays lasting from a few seconds to several minutes. The most famous geyser isa cone geyser at Yellowstone National Park known as Old Faithful. It derivesits name from its regularity.
It erupts about every 74 minutes onaverage. Each eruption lasts between 1.5 and 5 minutes. The height of theeruption varies between 100 and 180 feet. The rarity of geysers is attributableto the unusual conditions necessary to produce them. The volcanic rock must bedissolved in order to form mineral deposits that line and strengthen the wallsof the passageway leading to the surface. Any interference with the vent candestroy the geyser. For example, many geysers have died from litter and debristhrown into them by people. And others have succumbed when nearby power plantshave diverted water away from them.
Passage summary
A hot (1) ________ that shoots (2) ________ into theair
Are only (3) ________ in the world
Hot springs
-form by (4) ________ going down to (5) ________
-water then rises to (6) ________ because of (7) ________
-becomes very (8) ________ and shoots up in the air
Two types of geysers
-fountain geysers
- (9) ________
Old Faithful
-(10) ________ geysers
-found in (11) ________
-erupts every (12) ________
参考答案：
•cone geysers – 9
•heated rock – 5
•hot water – 2
•hot – 8
•1,000 – 3
•most famous – 10
•pressure– 7
•surface water– 4
•the surface – 6
•underground spring – 1
•Yellowstone National Park – 11
•74 minutes – 12
Questions for general comprehension
Question 1
According to the paragraph 1, which of the followingis true about geysers?
1.
They are common in the United States.
2.
3.
They are underground springs.
4.
5.
There are about 1,000 in Yellowstone National Park.
6.
7.
They are parts of volcanoes.
8.
Question 2
According to the paragraph 6, the author’sdescription of why geysers are rare mentions which of the following?
1.
The passageway is strengthened by litter.
2.
3.
Power plants heat the water.
4.
5.
Hot water dissolves the rock.
6.
7.
The vent is opened by volcanic eruption.
8.
Question 3
The word constricted in the passage isclosest in meaning to
1.
heated
2.
3.
lowered
4.
5.
compressed
6.
7.
accelerated
8.
Question 4
The word them in the passage refers towhich of the following
1.
geysers
2.
3.
litters and debris
4.
5.
people
6.
7.
power plants
8.
参考答案：
答案1：B
解析：文章 Part 1 当中的第一句话(S1)当中明确提到了 A geyser is a special kindof hot underground spring.所以是B. 喷泉是rare，所以common是错的，排除A. 1000个喷泉是在全世界范围内，在美国黄石公园是500，排除C. 文章第一段没有提到volcanoes,排除D.
答案2：C
解析：根据文章 Part 1 当中的第三第四句话(S3S4)The rarity of geysers is attributable to the unusual conditions…然后补充道thevolcanic rock must be dissolved in hot water….也就是说这样的条件难形成，所以选C. A.和B.都是喷泉不能形成的原因。D.在文章中完全没有提到。
答案3：C
解析：constrict 既可以做动词表示“压缩”heat 表示“加热”lower 表示“降低”accelerate 表示“加速”，只有 compress 表示“压缩，压紧”的意思，与 constrict 意思最为接近。
答案4：A
解析：them所在原文是And others have…away from them. 这里的others可以通过前一句话的many geysers推出是喷泉。句意是当附近电厂从喷泉里把水引导离开时，另外一些喷泉就枯死了。
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