The Park Service posted a video on its Web site taken from a security camera in the observation deck near the top during the quake. It shows debris falling from the ceiling, the entire structure shaking violently, and terrified visitors falling and running for safety.
Mall superintendent Bob Vogel said there were no injuries.
In addition, officials said, the elevator was damaged, possibly by its counterweights, and would need to be repaired. Vogel said the elevator was only partly functional.
Another Park Service official said the elevator could reach only the 250-foot level of the 555-foot-tall monument.
The Park Service had preliminarily said the quake caused some cracks in the stone, which resulted in water leaks when Hurricane Irene came through Washington a few days after the quake.
A team of engineers planned to start a block-by-block inspection of the exterior Tuesday while suspended by ropes. An inspection of the interior is finished, Vogel said.
He said the worst damage happened in the pyramidium, the pyramid-shaped top of the structure, where cracks up to 11
4 inches wide developed in the mortar and stone. “Daylight is visible at a number of the vertical joints where mortar is missing,” he said.
As a result, a substantial amount of water has been getting into the monument, which could cause more damage.
It is the extent of damage to the exterior that must now be assessed, he said.
The engineers, from Wiss, Janney, Elstner Associates’ “difficult access team,” are specially trained and equipped to rappel down the four sides of the monument. They will examine each of the marble exterior stones for damage.
Officials said the rappelling operation, in which engineers are harnessed in small seats hung from ropes, would last about five days. They hoped to have a more in-depth assessment of the monument by next month.
To assist the engineering team, the Park Service has brought in Brandon Latham, a mountaineering and rope-rigging ranger, from Denali National Park in Alaska.
Dan Gach, 35, one of the rappelling engineers, said each engineer will take one side. He said the team has a detailed description of each stone, which was compiled during the 1999 rehabilitation project.
He said the engineers have drawings of each of the marble exterior stones so they can compare its 1999 condition with the present one. Each stone is numbered.
The engineers also have small hammers they can use to test the soundness of the stones, he said.
“You can tap it lightly, and the stone density will make a definitive sound,” he said. When you tap a weak spot, “that area will just sound dead.”