2013年雅思阅读必读文章：Runaway Devils Lake

　Devils Lake is where I began my career as a limnologist in 1964, studying the lake's neotenic salamanders and chironomids, or midge flies. Back then, the lake covered about 80 square kilometers, had a maximum depth of about 3 meters and held about 130,000 acre-feet of water. The lake has since risen 13 meters, from a surface elevation of 430 meters above mean sea level to 443 meters. Estimated lake volume is now 4.1 million acre-feet, or about 32 times greater than it was in 1964, and about 370 times greater than it was in 1940 when the lake stood at a record low elevation of 427 meters.

　　The Devils Lake Basin is an endorheic, or closed, basin covering about 9,800 square kilometers in northeastern North Dakota. The basin is at the epicenter of an unprecedented wet period in the lake's modern-day history going back to 1867, when the lake's surface elevation was first measured. Basin climate has become substantially wetter since 1990, with the years 1990 through 2009 ranking as the wettest 20-year period in more than a century. The National Weather Service has referred to this trend as "the new climate" for the Devils Lake region, cautiously predicting that the current weather pattern may continue for several decades and possibly intensify. Indeed, the agency has warned that the region faces the strong possibility of an "unprecedented fourth consecutive major spring flood threat in 2012."

　　Rising lake waters have flooded much of the region, engulfing hundreds of homes and farmsteads, more than 650 square kilometers of productive farmland, major highways and bridges, state parks, Native American tribal lands, historical landmarks and more than half a million trees. Submerged too is the North Dakota Biological Station, a two-story limnological facility established in 1909 to study the lake's unusual ecology and biogeochemistry. Portions of U.S. Highway 281 are now underwater, which has forced the relocation of this principal north-south highway several kilometers to the west. Other roads and highways are either extremely hazardous or simply impassable because of encroaching floodwaters. Amtrak and the BNSF Railway may have to reroute their trains over more southern lines as rising waters threaten to wash out roadbeds and bridges. The small town of Minnewaukan, once located 13 kilometers west of the lake, is now partly underwater, and many of its 300-plus residents have been forced to abandon their homes. Only a handful of people remain in Churchs Ferry and nearby Penn, communities established more than a century ago. The city of Devils Lake, North Dakota's eleventh largest city with about 7,000 residents, sits behind a U.S. Army Corps of Engineers levee that protects the community from storm-generated waves that reportedly reach 2 meters or more in height. Without the levee, 3 to 4 meters of water would now cover parts of the city. To date, efforts by federal, state and local governments to control flooding and protect communities exceed $1 billion, a cost that is rising as fatefully as lake waters.

　　Ancient Lake Minnewaukan

　　Devils Lake owes its existence to a continental glacier that covered much of North America during the Pleistocene Epoch. Carving a basin as it advanced over the landscape, the glacier deposited excavated materials along its leading edges, leaving terminal moraines marking the farthest extent of glacial ice sheets. Near the end of the Pleistocene, roughly 11,000 years ago, the glacier began its retreat. As the glacier withdrew, glacial meltwaters poured into the basin, creating a vast proglacial lake dammed by morainal deposits. Native Americans called this lake Minnewaukan, meaning, among other possible interpretations, Bad Spirit Water. Recent flooding has perhaps given credence to a legend told by those Native Americans, claiming that the lake once overflowed and flooded the entire world.