国家地理:Killer Lakes 　杀人湖

（单词翻译）

Volcanic¹ gases escape from the magma. They percolate² through the earth crust and into the atmosphere. Professional geologist³, Charles Watson, investigates the risks at Horseshoe Lake close to Mammoth⁴'s main resort. There is a quiet, silent killer⁵ that's lurking⁶ about in the trees, along the lake's edge.

In the early 1990s, trees began to die in the area north of the lake. The cause, high concentrations of carbon dioxide. Scientists have discovered that around 100 tons of the gas escapes around Horseshoe Lake each day, raising the level of carbon dioxide in the soil up to 95 times normal levels. A simple test at the lakeside shows what this means in practice. Carbon dioxide is heavier in the air, so what we've done is we dug a hole and the carbon dioxide is gonna fill that up and displace the oxygen out and extinguish this butane lighter⁷. Fire needs oxygen to burn. Starved of this, the flame dies. It won't even relight. High concentrations of carbon dioxide can kill a butane flame in seconds and it can have a deadly effect on humans.

The usual concentration of carbon dioxide in air is only 0.035 percent. At a concentration level of around one percent, it causes dizziness, headaches and hallucinations. Above 17 percent, unconsciousness and death happens in a matter of seconds.

At Mammoth Lakes, wind usually disperses⁸ the carbon dioxide safely. But in 2006 investigators⁹ confirmed that a lethally¹⁰ high concentration of the gas killed three ski patrollers who fell into a snow cave on Mammoth Mountain and there was no volcanic eruption¹¹.


magma: 【地质学】The molten rock material under the earth's crust, from which igneous¹² rock is formed by cooling. 岩浆
percolate: (v.) To drain or seep¹³ through a porous¹⁴ material or filter. 过滤
butane: 丁烷
hallucinations: (n.) False or distorted perception of objects or events with a compelling sense of their reality, usually resulting from a mental disorder¹⁵ or as a response to a drug. 幻觉