Word: karst
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...carbonic acid, which is produced when water reacts with carbon dioxide. The weak acid slowly dissolves bedrock. An underground stream forms, and an elaborate network of chambers like those found at Mammoth Cave in Kentucky takes shape. The unusual limestone terrains where this process occurs are known as karst, named for one such region in Slovenia that is famous for its caves. About 15% of the earth's terrain is karst. By studying and dating the old subterranean waterways, researchers can tell how wet or dry past climates have been...
...underground. In most parts of the U.S., the ground is solid and compact and water flows down through it at a rate of less than 30 m (100 ft.) a year. But about 20% of the U.S.'s fresh water flows through the myriad cavities and pores of limestone karst, often traveling 1 km (0.6 mile) overnight, taking unpredictable turns and sometimes bubbling up to the surface through a spring. Containment of a toxic spill in such terrain is virtually impossible. Even ordinary garbage that is dumped in a sinkhole can contaminate groundwater miles away...
...potential for disaster is only beginning to be appreciated. For years residents and businesses around Bowling Green, Kentucky, pumped or buried solvents and wastes in the ground, heedless of the fact that the city of 40,000 sits on karst. In effect, they turned the underlying caves into a toxic sewer. Twice during the 1980s, benzene and other chemicals rose up from the caves into homes and elementary schools, endangering people's lives...
...their knowledge of how water flows through caves to trace the source of the fumes and put a stop to the contamination. They plan to map out more of the underground caves and passageways in order to better understand which areas are at highest risk. Communities built on karst in Tennessee, West Virginia, Florida and Missouri may someday follow suit...
Early on Oct. 6, photographer Davis and I, accompanied by a translator from the Foreign Ministry press center, set off from Hanoi on a seven-hour, 150- mile drive through the scenic karst valleys of Son La province to Phu Yen district. Before the last two-hour leg of the journey, the driver warned that we would not be able to stop until we reached the hamlet of Phu Yen because even a brief halt in daylight might leave us prey to the bandits who operate in the area...