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Mesa Verde National Park will attempt to stabilize the overhanging rock arch above the popular Spruce Tree House cliff dwelling to remove the risk of it collapsing and damaging the ruins below./ Courtesy of National Park Service
Total collapse Mesa Verde faces big task to save prized cliff dwelling by Jonathan Romeo
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t’s not going to be easy: Mesa Verde National Park is about to try and stop a massive slab of sandstone from collapsing and destroying one of the most prized cliff dwellings in the park, Spruce Tree House. In October 2015, park officials were forced to close Spruce Tree House to visitors after a series of rock falls made it too dangerous for people to enter the iconic alcove. Mesa Verde is home to some of the most notable and best-preserved cliff dwellings in the world, but Spruce Tree House, the thirdlargest cliff dwelling in the park, is by far the most visited because of its easy access. The ancestral Puebloan people built these massive and thriving communities between the years 900-1250 in protected alcoves – large, arched recesses in the cliff wall. But, over the years, park officials have been concerned the rock structures above and around the alcoves are increasingly at risk of erosion and other geological forces. For the past six years, Mesa Verde has undertaken an exhaustive effort to figure out how best to stabilize the failing sandstone above Spruce Tree House – not just to make it safe for the public, but also to save the cliff dwelling underneath. Those plans are coming together, said project manager
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Allan Loy, but there’s still a ways to go. Preserving the past Most national parks receive such a designation because of natural beauty and sweeping landscapes. Mesa Verde, on the other hand, was the first national park established specifically for the preservation of the “works of man” – i.e. the ancestral Puebloan’s civilization. For more than 700 years, the region around Mesa Verde was a robust and thriving community, with hundreds of villages and more than 22,000 people (almost the same population as today). Around 1250, however, the region was mostly abandoned, likely due to climate issues and/or social disruptions. In the 1870s, the first white settlers discovered and started to understand the complexity of the vast network of ruins throughout the deep canyons and mesas of the high desert. (Of course, the Ute people were actively living in the region at the time, but did not inhabit the ruins, believing them sacred). Subsequent research expeditions revealed more amazing truths about Mesa Verde, but also brought on a disturbing amount of looting and destruction of sites. By the end of the 19th century, it was apparent the region needed federal protections. The park was established in June
1906, protecting more than 4,300 cultural sites, including 600 cliff dwellings, within the 52,000-acre national park. Crumbling curio From the beginning, archaeologists were alarmed about the imminent risk of rock fall to Spruce Tree House, with the first concerns documented as early as 1908. Spruce Tree House is home to 130 rooms and eight kivas, and lies within a natural sandstone alcove that’s 216 feet long and 89 feet deep. The issue at hand is water draining between the arch of sandstone overhanging the alcove, which causes erosion and poses the risk of the arch breaking off and collapsing right on the ruins. Early archeologists tried fixing this by blasting a trench in the sandstone to direct water to the sides of the structure, to no avail. Attempts in the 1960s did accomplish temporary relief after the southern half of the arch was stabilized by rock bolts, anchoring the arch to the alcove. The crack was then cleaned and plugged with burlap and concrete. This was effective, for a time, until natural elements once again started eating away at the rock structure, resulting in the rock falls in 2015. Park officials originally thought it would take two years to come up with a fix. But the complexity of the problem, as well as continued rock fall, has required more time
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for study. Mesa Verde hired one of the best geo-tech engineering firms in the world, Loy said, which has generated an incredible amount of research and study. Three-dimensional modeling, high-resolution Lidar, photogrammetry, on-site inspections, material testing – you name it, the park has done it, Loy said. The most vexing problem, according to studies, is how to fill the significant gap between the alcove face and the arch to prevent water from entering Spruce Tree House. It appears the fix is going to be multipronged. The park will likely use rock bolts again, but this time, installed at offset angles, which would increase strength (think of the root structure of a tree). And, new material, likely a type of metal, will be used to fill the crack to stop water from entering. “And we’ve been using a number of models to see where failures could happen in our designs,” Loy said. “And then we ensure our design compensates for it.” The crown jewel Spruce Tree House has always been the centerpiece of Mesa Verde, said Fort Lewis College professor and historian Andrew Gulliford. Centrally located in the park, and surrounded by facilities like a museum and the superintendent’s house, the cliff dwellings are also relatively easy to get to compared to other sites. As a result, the
