【小站出品】雅思阅读机经真题解析-探测陨石湖

A

As the sun rose over picturesque Lake Bosumtwi, a team of Syracuse University prepared for another day of using state-of-the-art equipment to help unlock the mysteries hidden below the lake bottom. Nestled in the heart of Ghana, the lake holds an untapped reservoir of information that could help scientists predict future climate changes by looking at evidence from the past. This information will also improve the scientist’s understanding of the changes that occur in a region stuck by a massive meteorite.

B

The project, led by earth sciences professor Christopher Scholz of the College of Arts and Sciences and funded by the National Science Foundation (NSF), is the first large-scale effort to study Lake Bosumtwi, Earth’s surface. The resulting crater is one of the largest an most well-preserved geologically young craters in the world, says Scholz, who is collaborating on the project with researchers from the University of South Carolina, the University of Rhode Island, and several Ghanaian institutions. “Our data should provide information about what happens when an impact hits hard, pre-Cambrian, crystalline rocks that are a billion years old”, he says.

C

Equally important is the fact that the lake, which is about 8 kilometers in diameter, has no natural outlet. The rim of the crater rises about 240 meters above the water’s surface. Streams flow into the lake, Scholz says, but the water leaves only by evaporation, or by seeping through the lake sediments. For the past million years, the lake has acted as a tropical rain gauge, filling and drying with changes in precipitation and the tropical climate. The record of those changes is hidden in sediment below the lake bottom. “The lake is one of the best sites in the world for the study of tropical climate change,”Scholz says. “The tropics are the heart engine for the Earth’s climate. To understand global climate, we need to have records of climate changes from many sites around the world, including the tropics.”

D

Before the researchers could explore the lake’s surface, they need a boat with a large, working deck area that could carry eight tons of scientific equipment. The boat-dubbed R/V Kilindi-was built in Florida last year. It was constructed in modules that were dismantled, packed inside a shipping container, and reassembled over a 10-day period in late November and early December 1999 in the rural village of Abono, Ghana. The research team then spent the next two weeks testing the boat and equipment before returning to the United States for the holidays.

E

In mid-January, five members of the team-Keely Brooks, an earth sciences graduate student; Peter Cattaneo, a research analyst; and Kiram Lezzar, a postdoctoral scholar, all from SU; James McGill, a geophysical filed engineer; and Nick Peters, a Ph.D. Student in geophysics from the University of Miami-returned to Abono to begin collecting data about the lake’s subsurface using a technique called seismic reflection profiling. In this process, a high-pressure air gun is used to create small, pneumatic explosions in the water. The sound energy penetrates about 1,000 to 2,000 meters into the lake’s subsurface before bouncing back to the surface of the water.

F

The reflected sound energy is detected by underwater microphones-called hydrophones-embedded in a 50-meter long cable that is towed behind the boat as it crosses the lake in a carefully designed grid pattern. On-board computers record the signals, and the resulting data are then processed and analyzed in the laboratory.” The results will give us a good idea of the shape of the basin, how thick the layer of sediment are, and when and where there were major changes in sediment accumulation,” Scholz says, “we are now developing three-dimensional perspective of the lake’s subsurface and the layers of sediment that have been laid down.”

G

Team members spent about four weeks in Ghana collecting the data. They worked seven days a week, arriving at the lake just after sunrise. On a good day, when everything went as planned, the team could collect data and be back at the dock by early afternoon. Except for a new relatively minor adjustments, the equipment and the boat worked well. Problems that arose were primarily non-scientific-tree stumps, fishing nets, cultural barriers, and occasional misunderstandings with local villagers.

H

Lake Bosumtwi, the largest natural freshwater lake in the country, is scared to the Ashanti people, who believe their souls come to the lake to bid farewell to their god. The lake is also the primary source of fish for the 26 surrounding villages. Conventional canoes and boats are forbidden. Fishermen travel on the lake by floating on traditional planks they propel with small paddles. Before the research project could begin, Scholz and his Ghanaian counterparts had to secure special permission form tribal chiefs to put the R/V Kilindi on the lake.

I

When the team began gathering data, rumors flew around the lake as to why the researchers were there. “Some thought we were dredging the lake for gold, others thought we were going to drain lake or that we had bought the lake,” Cattaneo says, “But once the local people understood why we were there, they were very helpful.”

体裁

论说文

题目

陨石湖底回声探测

结构

A段： 利用陨石湖底回声进行探测的时间和地点。

B段：利用陨石湖底回声进行探测的重要条件。

C段：为了更好地研究全球气候，人们需要收集全世界很多不同地方的气候变化的记录，包括热带。

D段：研究者们建造了一艘名为R/V KIlindi的船来探索博苏穆图湖的表层。

E段：众多学者通过地震反射成像来收集湖面表层的数据。

F段：学者在实验室通过处理和分析收集到的数据可以帮助研

究盆地的形状，湖底沉积物的厚度，以及在沉积物积累

的过程中这些主要的变化时在什么时候什么地方发生的

G段：收集数据的过程以及碰到的一些问题。

H段：研究者们需要从部落的首领那里获得特批才能把R/VKilindi船放入博苏穆图湖中进行探测。

I段：大家对在博苏穆图湖中行驶的R/VKilindi船众说纷纭。