The highest level of ultraviolet radiation ever recorded on the Earth's surface has been measured in the Andes mountain range in South America by researchers from the United States and Germany.

The extraordinary UV bursts, observed 1,500 miles from the equator, are far above levels typically considered harmful to life in or out of water, according to a news release.

The readings were taken in the southern hemisphere during that area's summers of 2003 and 2004, with instruments developed for the 33-station European Light Dosimeter Network, which "measure[s] radiation in three biologically relevant wavelength bands."

The results appear in the open-access journal Frontiers in Environmental Science.

NASA's Ames Research Center and the SETI Institute were focusing on the South American mountain range as part of an investigation of "high-altitude Andean lakes as part of an astrobiology study of Mars-like environments," according to the release.

Dosimeters were placed on the summits of Chile's towering Licancabur volcano, which is 5,917 meters (19,413 feet) high, and nearby Laguna Blanca in Argentina, which is 4,340 meters (14,239 feet) high.

"The combination of a midday sun near the zenith," high elevation and naturally low ozone produced high irradiation levels.

Regardless, research team leader Nathalie A. Cabrol explained, the 280- to 315-nm-wavelength UV-B radiation intensities were unprecedented. (A nanometer is a millionth of a millimeter.)

"These record-setting levels were not measured in Antarctica, where ozone holes have been a recurring problem for decades," Cabrol said in the news release. "This is in the tropics, in an area where there are small towns and villages."

A UV index of 11 is considered extreme in most places, although some locales have reached 26 in recent years, Cabrol said. "But on December 29, 2003, we measured an index of 43. If you're at a beach in the U.S., you might experience an index of 8 or 9 during the summer, intense enough to warrant protection. You simply do not want to be outside when the index reaches 30 or 40."

The intense radiation in the Andes "coincided with other circumstances that may have increased the UV" exposure levels, including "ozone depletion by increased aerosols from both seasonal storms and fires in the area," the release states.

Additionally, a large solar flare occurred just two weeks before the highest UV readings. Then, ultraviolet spikes continued to occur at lower intensities during the solar instability and ceased after.

"Evidence linking the solar event to the record-breaking radiation" is circumstantial, but the highly energetic particles from such flares affect atmospheric chemistry and could have sped the rate of the earth's ozone depletion.

"While these events are not directly tied to climate change, they are sentinels of what could occur if ozone thins globally," Cabrol said. "The thinner and more unstable the ozone, the more prone we will be to this kind of event," so "while this unsettling record might be the result of a 'perfect storm' of events, it could happen again, because the factors that caused it are not rare."

Study of the Andean UV event "is an excellent example of how astrobiology -- which includes understanding the atmospheres of other planets -- is germane to contemporary concerns here on Earth," said David Black, president and CEO of the SETI Institute.