El Morro National Monument in New Mexico is the home of archaeological sites and inscriptions ranging in date from the 13th to 19th c., and a dramatic landscape characterized by Zuni Sandstone cliffs that rise 200 feet from the valley floor. Use of the site began in the late 1200s when ancestors of Zuni Indians moved onto the outcropping, building two pueblos–Atsinna and North Atsinna–above the cliffs. Later, from the early 1600s to the early 1900s, Spaniards and Americans passing through the area added inscriptions to the soft sandstone cliff face, in an area now called Inscription Rock. Today the National Monument extends over 1,276 acres, protecting the over 2500 inscriptions, archaeological sites, and cultural landscape.
Zuni Sandstone is very soft, making it easy to inscribe and swift to erode. In an effort to better understand how this sandstone erodes, site managers began the El Morro Inscription Preservation Project (EMIPP) in the 1980s to monitor the cliff’s condition. The EMIPP has been able to document that most major impacts (spall, delamination, efflorescence, ect.) were caused by moisture in the sandstone. In combination with condition assessments, researchers can use climate data extrapolated from tree-rings to explain past erosion events. For example, in 1979, El Morro rangers noted that up to 15 inscriptions were lost due to natural forces. Tree-ring data shows that the late 1970s to the early 1990s “had the highest rainfall of any 15-year period in over 2100 years” (Vanishing Treasures, 2010), and it is therefore likely that the high rainfall led to high moisture content in the sandstone and caused the inscription-loss in 1979.
Today, moisture continues to affect El Morro inscriptions, and in spite of prevailing drought conditions in the San Juan Basin, this year’s late season monsoon rains have been near record (Baumann 2013, personal communication). While we cannot be sure whether this extreme precipitation events will continue in El Morro, as there is considerable uncertainty about future precipitation in the southwest, documentation of material loss from high moisture content at El Morro gives us an idea of what could happen to Inscription Rock if extreme precipitation events do become more regular.
1. Baumann, Steve, Email to the author, September, 2013.
2. Baumann, Steve and James W. Kendrick. “Climate Change and the Deterioration of Cultural Resources: El Morro and El Malpais National Monuments in West-Central New Mexico.” Vanishing Treasures Fiscal Year 2010 Year-End Report, (2010): 17-21.
3. National Park Service (NPS). “El Morro: History and Culture.” Last accessed September 17, 2013, http://www.nps.gov/elmo/historyculture/index.htm.
4. United States Global Change Research Program (USGCRP). “Regional Climate Trends and Scenarios: The Southwest U.S.” 2013, http://scenarios.globalchange.gov/sites/default/files/NCA-SW_Regional_Scenario_Summary_20130517_banner.pdf.