GWEN IFILL: Finally tonight, a national landmark shuttered indefinitely by last month's East Coast earthquake.
Ray Suarez tells the story.
RAY SUAREZ: High atop the Washington Monument today, engineers rigged ropes so they can rappel down the sides of the structure. Tourists watched as they used a hatch at the pinnacle 555 feet up and windows on the observation deck just below to gain access.
U.S. Park Service Ranger Gordy Kito was one of those watching the delicate operation.
GORDY KITO, National Park Service: What they will do is, they will rig the ropes from the upper part of the pyramid on swings that are up there. The evaluators will then exit out of the windows that are below the pyramid. They will ascend the ropes to the upper part of the pyramid, switch their rigging over to a lower system, and then lower themselves down while doing the evaluation of the exterior.
RAY SUAREZ: The engineers are members of the Difficult Access Team from Chicago engineering and architectural firm Wiss, Janney, Elstner, their mission, to make meticulous checks for cracks and other damage to the monument's marble exterior from the earthquake that shook the nation's capital last month.
Bill Line is also with the National Park Service.
BILL LINE, National Park Service: We're going to literally, by eyeball, the human eyeball, have to determine whether there are any small cracks or shards of stone or shawls (ph), is what the terminology is, that could expand into larger cracks in three years, five years, 15 years, 20 years from now, and make a determination as to whether those individual cracks need to be repaired.
RAY SUAREZ: Yesterday, for the first time, the public got a look at what it was like inside the monument as the quake hit. The Park Service released video from a surveillance camera in the observation deck. It captured the entire structure shaking violently, as terrified visitors fled for safety from debris falling from the ceiling.
Nikolette Williams was the ranger inside the observation deck that afternoon.
NIKOLETTE WILLIAMS, National Park Service: The biggest indicator was that the metal apparatus for the elevator began to shake. It was moving before the building was even shaking. And I had never seen that done before, obviously.
And then I began to feel the floor under my feet shaking. My first thought was that: I'm going to run. I'm going to get out of here. And then I realized that I'm responsible for the 20 lives that are around me right then. And so my next thought is, I don't know if it's an attack, if it's an earthquake. Whatever it is, we need to be at the bottom. That is going to be the safest place.
RAY SUAREZ: When the ground started shaking back in August, it posed some pretty big challenges to one of the world's best-known buildings. More than 130 years old, it wasn't built to any modern seismic code. It's many times taller than it is broad at the base, so swaying was going to be a problem. And the exterior is marble, most of the interior granite, two materials not known for their flexibility.
On Monday, National Mall Superintendent Bob Vogel said first indications are the damage was relatively slight.
BOB VOGEL, National Park Service: The good news, the monument is structurally sound and is not going anywhere. It is a testament to the original builders that the monument has withstood not just this earthquake, but an even larger one in the late 1800s. They obviously knew what they were doing. The better news, none of our visitors were hurt during the earthquake.
RAY SUAREZ: Just the same, the monument has been closed since the earthquake hit and will stay closed indefinitely, leaving more than a few visitors disappointed.
WOMAN: So, to see a kid come up here, and with their family, and me explaining it to the kids, it's kind of heartbreaking, you know?
RAY SUAREZ: The Park Service says it's all in the interest of public safety.
And Stephanie Meeks, president of the National Trust for Historic Preservation, agrees safety has to come first.
STEPHANIE MEEKS, National Trust for Historic Preservation: The other thing that I would hope that comes out of this is just sort of a re-awareness on behalf of all Americans about these significant structures that we all sort of take for granted -- they're in our backyards here in Washington, D.C. -- the really important national monuments across the country, and remember that they are vulnerable to natural occurrences like this and that they need our very best care and support.
RAY SUAREZ: The rappelling operation is expected to last about five days. Park Service officials hope to have an in-depth assessment of the damage by next month.
But, for now, there's no timetable for completing repairs and reopening the Washington Monument to the public.