They were discovered by a glider pilot, Wolf Hirth, in 1933.[6] These waves reach heights much greater than the original obstruction and so can permit gliders to climb to the stratosphere. Pilots use supplementary oxygen to avoid hypoxia because gliders do not have pressurized cockpits. This lift is often marked by long, stationary lenticular (lens-shaped) clouds lying perpendicular to the wind.[7] A mountain wave was used to set the record for highest altitude by a glider when Steve Fossett and Einar Enevoldson, wearing pressure suits, soared to an altitude of 50,699 feet (15,453 m) on August 29, 2006 over El Calafate, Argentina in their modified DG-505.[8] The current world distance record of 3,008 km (1,869 statute miles) by Klaus Ohlmann (set on 21 January 2003)[9] was also flown using mountain waves in South America.