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National Geodetic Survey

National Mall — National Park Service

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Surveying on the National Mall

National Geodetic Survey Measures if Monuments Shifted Due to 2011 Earthquake, Part of a Larger Survey of Downtown Washington, D.C.

March 29, 2012
  • Surveyors near the Washington Monument

    Geodetic technician Davey Crockett, foreground, prepares to take height measurements near the Washington Monument. The measurements will determine if the monument experienced any significant up or down movement as a result of a 2011 earthquake in the region.

  • Dave Doyle, chief geodetic surveyor, National Geodetic Survey

    Dave Doyle, chief geodetic surveyor and 40-year NGS veteran, is leading the surveying effort on the National Mall. Learn more about this effort from our March 2012 podcast interview with Doyle.

  • Surveyors measured heights along the Tidal Basin on the National Mall.

    The leveling survey wrapped around the Tidal Basin on the National Mall. In total, the survey will cover nearly 12 kilometers (7.4 miles) of ground. However, NGS staff will walk twice that distance since all measurements will be taken two times to ensure the best possible data is collected.

  • close-up of a geodetic control disk

    This geodetic control disk, or bench mark, was one of many control points used during the leveling survey. A geodetic control disk is a location where a very accurate height has been previously measured and recorded.

  • This 12-foot-tall underground replica of the Washington Monument is a geodetic marker

    This 12-foot-tall underground replica of the Washington Monument is a geodetic marker that few people get to see! The 'mini obelisk' is located under a manhole cover close to the actual monument.

  • Surveyors near the Washington Monument

    Geodetic technician Eric Duvall (foreground) holds a graduated rod that looks like a giant yardstick on top of the control point known as the 'mini obelisk.' In the distance, geodetic technician Davey Crockett uses a level to take careful height measurements from the rod.

  • National Park Service employee Ned Wallace prepares to remove a protective covering to reveal a hidden geodetic control disk adjacent to the Washington Monument. Geodetic technician Clyde Dean looks on.

    National Park Service employee Ned Wallace prepares to remove a protective covering to reveal a hidden geodetic control disk adjacent to the Washington Monument. Geodetic technician Eric Duvall looks on.

  • NGS Geodesist Davey Crockett

    Davey Crockett, a geodetic technician with 47 years of service to NGS, prepares to take height measurements using a level set upon a sturdy tripod. The high-tech level is capable of measuring height differences at the sub-millimeter level.

  • Surveyors prepare to take height measurements near the Washington Monument.

    Surveyors prepare to take height measurements near the Washington Monument. From left to right, Clyde Dean, cartographic technician; Davey Crockett, geodetic technician; Jeff Olsen, geodesist; and Eric Duvall, geodetic technician.

  • Eric Duvall, cartographic technician, holds a leveling rod in position near the Tidal Basin in Washington, D.C.

    Clyde Dean, cartographic technician, holds a leveling rod in position near the Tidal Basin in Washington, D.C. The rod is used to measure differences in height. The National Mall is built largely on landfill and is slowly settling over time.

Making Waves

Audio Podcast: This month, NOS's National Geodetic Survey is conducting a study on the National Mall to help the National Park Service understand the settling and shifting of the ground underneath the monuments on the National Mall, particularly after the August 2011 earthquake. Tune in to our interview with Dave Doyle, NGS chief geodetic surveyor, to learn more. (13 minutes)

Listen to our latest podcast

A rare 5.8-magnitude earthquake near Washington, D.C., on August 23, 2011, shook the nation's capital with enough force to crack stones and loosen mortar in the Washington Monument. But not all effects of the earthquake are visible to the naked eye.

What if the ground underneath the Monument shifted because of the quake?

What if the ground underneath the Monument shifted because of the quake?

Experts from NOAA’s National Geodetic Survey (NGS) are nearing completion of a leveling survey that will help answer this question. This is the first phase of a planned longer-term effort to assist the National Park Service (NPS) by regularly surveying the grounds of the National Mall.

While preliminary analyses indicate that the earthquake did not cause significant vertical motion in the Washington Monument, even slight changes could affect plans for repairing the stone obelisk.

A map of the survey area. The yellow lines indicate the paths of the NGS leveling survey. In total, the surveyors will cover nearly 12 km (7.4 miles). Click for a larger view.

The survey is initially focusing on whether any abnormal displacement of the Monument resulted from the earthquake. Later this year, NOAA surveyors will also take GPS measurements from the top of the Washington Monument to determine if the stone obelisk tilted due to the quake. Engineering firms under contract to NPS will use the survey results in the planned $15 million restoration efforts to repair the stone structure.  

Beyond determining the effects of the earthquake, NGS surveyors are concurrently collecting miles of leveling data in the downtown DC area that they expect to update every three to five years. The National Mall is built largely on landfill and is slowly settling over time, causing ongoing maintenance concerns with many of the heavy monuments in the area. This long-term effort will provide the Park Service with better information to help in the preservation of historical structures, while providing a low-cost field training opportunity for NGS personnel.

NGS and its predecessor agency have conducted periodic surveys of National Park Service sites around Washington since 1884.

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