Knut Foppe, left, Darin Oestmann, center, with the National Park Service and Thorsten Mowes, right, rappel a scuplture of Thomas Jefferson's face to begin power washing Mount Rushmore National Monument, Thursday, July 7, 2005, near Keystone, S.D. (AP Photo/Doug Dreyer)
After more than 60 years of being exposed to the elements, the presidents of Mount Rushmore are getting a facial.
Park rangers armed with hand-held power washers begin rappelling down the faces of George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln on Saturday to blast away the dirt, grime and lichen that has collected on the granite surfaces.
Lichen eats away at granite and over time can cause cracks and pockmarks. If left for long enough, they could eventually cause the 60-foot tall (18 meter) statue to crumble.
"This is the first time the faces have been washed," said Judy Olson, Mount Rushmore's chief interpreter.
"To the ordinary visitor who comes to Mount Rushmore they probably won't notice a difference, but the lichen have been growing and invading the rocks and this high pressure very hot water will get rid of them."
Olson said the National Park Service has been wanting to do something about the lichen for several years but didn't have the expertise or room in the budget to hire someone.
Rangers armed with silicon putty check the sculpture for cracks every fall but were unable to chip away at the black and green lichen that was spreading across the surface.
Then a German cleaning equipment company offered to foot the bill and train the rangers.
Alfred Karcher GmbH and Co. has cleaned a number of monuments, including the Statue of Christ in Rio de Janeiro, the Brandenburg Gate in Berlin and the Statue of Liberty in New York.
The project is expected to take three to four weeks.
Construction on the South Dakota monument began in 1927 with the face of George Washington. Designed by Gutzon Borglum, 90 percent of the 500-foot-wide sculpture was carved using dynamite. It was completed in 1941, seven months after Borglum died.
More than 2 million people visit the monument every year.
facial: a treatment for the face, usually consisting of a massage and the application of cosmetic creams（美容，面部治疗）
ranger: a warden employed to maintain and protect a forest or other natural area （国有森林员，保护森林等自然地貌的看护员）
lichen: a fungus, usually of the class Ascomycetes, that grows symbiotically with algae, resulting in a composite organism that characteristically forms a crustlike or branching growth on rocks or tree trunks（青苔，地衣，苔藓）
crumble: to fall into small fragments or particles; disintegrate（碎裂，破碎）