GIS Plays Growing Role in Monitoring and Limiting the Impact of Visitors
Protecting Oregon Caves
By Elizabeth Hale, U.S. Department of the Interior, National Park Service, Oregon Caves National Monument
Nature has filled Oregon Caves with many wonders to see. But visits by 48,000 people a year to the national monument, located 50 miles south of Grants Pass, Oregon, significantly impact the natural resources in the "Marble Halls of Oregon." Damage can include broken cave formations, darkened and polished rock caused by touching, and lint deposits. Cave sediments and animal bones also get disturbed.
GIS technology is playing a growing role in helping the National Park Service protect the cave and its resources. In the past two years, the most basic GIS layers of the cavesurvey stations (points), survey shots (lines), and cave walls (polygons)have been the starting point for developing datasets and maps to help visualize the cave's hazardous and fragile areas, protect paleontological resources, manage a growing collection of photos, and develop a new public off-trail caving tour. The National Park Service at the Oregon Caves National Monument used GIS software for its project, along with COMPASS, a cave survey management software package and extension to ArcView software.
Implementing a Fair System for Issuing Caving Permits
A complete cave map provides some information about potential safety hazards and the cave's vulnerability to human impact via labels for ceiling heights and pit depths and symbols for slopes and delicate cave formations. But this information can be viewed and synthesized in many ways, leading to varied conclusions about how hazardous or how fragile a particular area is.
To eliminate this kind of subjectivity when determining whether to issue caving permits, GIS was used to produce hazard and fragility maps from a criteria-based assessment to clearly and objectively display the hazardous and fragile areas of the cave.
ArcPad mobile GIS software on a Pocket PC in a rugged case was used to conduct the hazard-fragility assessment. Based on the GIS line layer of survey shots, cave passages were attributed with a rating for hazard and fragility. Factors considered for a hazard rating included potential falls, loose ceiling rock, mazy passages, and required caving gear. Fragility was assessed as the average of four equally weighted ratings: resource condition, proximity to fragile resource, resource value, and density of breakable formations. To design hazard and fragility maps with ArcGIS Desktop (ArcMap) software, the GIS layer of cave walls was divided into polygons to represent areas encompassed by individual survey shots, as the assessment was conducted on a shot-by-shot basis.
Combined hazard and fragility ratings were used to categorize areas of the cave into caving zones. Permits to enter areas of the cave beyond the tour path are now issued based on the requirements of the caving zone being visited, as defined by the monument's subsurface management plan.
Keeping Track of Paleontological Resources
Oregon Caves contains hundreds of animal bones, some of which are very old or fragile yet well preserved in the cool and dark passages of the cave. Bones were inventoried in a nonspecific way in the 1990s, resulting in a rough map of where they were found throughout the cave. More recently, a site-by-site paleontology survey was undertaken to compile precise locations and descriptions of bones.
In the subterranean passages of Oregon Caves where GPS cannot be used, survey station markersoften a labeled strip of aluminum or piece of surveyor's tapeserve as points of reference. Paleontology sites were surveyed from the nearest survey marker with a laser distance meter, compass, and inclinometer. Additionally, sites were described systematically, photographed with an object for scale, and flagged when in danger of being disturbed. COMPASS was used to create a GIS layer of paleontology sites from survey measurements. Attribute data is managed in a table that can be queried, sorted, and joined to the GIS layer.
As of mid-March 2008, more than 180 paleontology sites had been documented. The staff at Oregon Caves works with professional paleontologists to identify and study these paleontology sites. Approximately 30 vertebrate species have been identified.
Managing and Retrieving Photos for Monitoring
Photo monitoring is perhaps the most common approach to keep track of the impact of visitors to the cave. Photo monitoring involves repeatedly photographing a site from the same distance and angle to detect changes in its condition. There are 19 sites along Oregon Caves' tour routes that are photo monitored from fixed-point stations. However, many other sites and features of interest or concern have been photo documented casually (without a specific distance and angle), which has resulted in a larger set of photos that can become unwieldy without naming conventions and methods for retrieval.
To make the cave photo collection more usable, old and new photos were sorted by location and a GIS layer was prepared so that a wide range of photos can be retrieved by selecting any area of the cave. To do this, the photos were named according to a specific format and organized by the closest survey station marker. The GIS layer of cave walls was divided into polygons to represent areas defined by their proximity to survey station markers. Then a text field in the attributes table was set up so that when hyperlinks are enabled for this layer, photo sets can be accessed with the hyperlink tool.
GIS layers for photo-monitoring stations and paleontology sites were also set up so that photos could be hyperlinked from individual stations and sites.
Planning Low-Impact, Off-Trail Tours
In summer 2007, the National Park Service offered a public, off-trail caving tour in Oregon Caves for the first time. Data on the off-trail tour route was gathered from cave-resource and visitor-impact inventories, as well as the hazard-fragility assessment and paleontology survey. These datasets helped identify every hazardous area and fragile resource so that each could be addressed with protective flagging, rerouting, and/or training for tour guides. The visitor-impact inventory was analyzed to predict how the caves would be affected by visitors who take the tours.
The polishing and darkening of rocky surfaces caused by touching was one expected impact. As there are many tight passages along the off-trail route, this is largely unavoidable, though all visitors wear gloves. Photos were taken to monitor polishing and darkening of several areas along the route.
Accumulation of hair was also expected to occur. People who visit the caves all leave behind some skin flakes, hair, or lint, which can build up and create unnatural deposits of organic material. These deposits, besides being unsightly, can have an ecological impact.
Survey Station Markers Key
Survey station markers were an important component of the approach that Oregon Caves took to use GIS to help monitor and limit visitor impacts. Otherwise, a completely different scheme would have been needed to reference assessments, surveys, and photos to physical locations. The efforts described here can be applied at other caves and carried out even when staff members have only a basic knowledge of GIS.
About the Author
Elizabeth Hale is a physical science technician with the Resource Management division at Oregon Caves National Monument. Her duties include monitoring cave processes and fauna, managing GIS data, and coordinating cave cleanup and restoration.