The Jeffers Petroglyphs Conservation Project

Petroglyph obscured by lichen

Preservation Challenges
The Jeffers Conservation Project began in 2006 to address environmental and preservation challenges affecting the Jeffers Petroglyphs and to ensure long-term preservation.

The biggest difficulty in recent years has been the spreading growth of several lichen species on the rock face. Lichen are a combination of a fungus and a plant that needs sunlight, such as algae. It obscures the petroglyphs by creating a varnish on the surface and increasing the rate of deterioration.  Lichen tendrils grow into surface cracks and fracture the rock over time.  This allows water to enter into the rock and increase fractures during freez-thaw cycles.  The spreading vegetation and turf, in and around the quartzite outcrop, has also affected the visibility and integrity of the carvings.

Lichen removal process

Conservation
The first phase of the conservation project removed the lichen from the rock face and cleared vegetation and turf from cracks and along the edges of the quartzite outcrop.
To remove the lichen using the least intrusive method, a synthetic rubber membrane was placed over the rock face for 5-12 months, depriving it of sunlight and the photosynthesis process, causing the lichen to die. When the covering was removed, the dead lichen was removed with water and a soft brush. By removing the lichen, more than 3,000 new petroglyphs were revealed, doubling the number of carvings identified.

Plant and Soil Accumulation on Rock Face
Vegetation growing in cracks of the rock face "catches" fine soil and dust deposits, resulting in a growing mat of vegetation that slowly covers the rock face. The soil and plant material accelerates the freeze-thaw cycle that fractures the surface. The fine dust and soil material also serves as a growth medium for lichen. In order to prevent further growth, vegetation was removed from all cracks throughout the outcrop.

Quartzite dust from a nearby quarry was also contributing to the accelerated growth of vegetation and lichen by acting as a binding agent that held windblown dust fertilizer.  Site manager Tom Sanders worked with the gravel quarry to significantly reduce the amount of quartzite dust it produced. In addition, MNHS purchased 80 acres adjacent to the site’s southern border, where 120 species of local ecotype prairie plants were planted to reduce the amount of agriculturally-produced, nitrogen-laced windblown dust.

3D white-light scanner

Documentation
MNHS partnered with the University of Minnesota's Evolutionary Anthropology Lab to conduct white light scanning of the Sioux quartzite outcrop at the Jeffers Petroglyph Historic Site. White light scanning creates a precise image while having zero impact on the rock surface. The baseline documentation provides first-time records of individual carvings, their condition following conservation treatment, and a point from which to measure any future changes.

The scanning produces a three-dimensional model of individual carvings, which create new possibilities for both viewing and analyzing petroglyphs. Light conditions can make viewing petroglyphs challenging; with digital reproductions, the intensity and direction of light can be altered to recreate the experience of seeing petroglyphs at different times of the day and year, improving their visibility.

This supplemental method of viewing the petroglyphs aids the visitor's experience and allows for publishing images online, making the glyphs located in rural Southwestern Minnesota more accessible. View over 2,000 3D models of individual carvings in Collections Online.