At Oregon Caves National Monument in southwestern Oregon, resource managers are using a survey method called Visitor Impact Mapping to better understand where and how visitors have affected the condition of the marble cave that is the park’s centerpiece attraction.
Recreational use has significantly impacted the public caves in our national parks. Visitors can damage cave resources in a wide variety of ways, almost all of which come under the general headings of physical damage and secondary effects.
Some physical damage is obvious, such as graffiti (including old initials sketched with charcoal or carbide), directional symbols left on rocks by cave explorers (see photo), trodden earth, broken cave deposits, rock surfaces that have been darkened and polished by touching, and rock damaged when constructing pathways, building stairways, installing lighting, and constructing various safety and convenience features for cave visitors.
Some safety and convenience features are very large, such as this recently constructed tower and stairs at Mammoth Cave National Park or the elevator and natural entrance stairs at Carlsbad Caverns National Park.
Less obvious kinds of physical damage include lint deposition, sediment compaction and translocation in streams and pools, and the displacement of animal bones and fossils.
There are also secondary effects from cave development and use. Altered air flow from enlarged passages or entrances can change temperature and humidity conditions (the “cave climate”), which can in turn impact cave biota. Algae may flourish in the vicinity of tour path lighting and in other places where artificial lighting is provided (as when cave formations are backlit to enhance their appearance).
Though seldom a problem in public caves these days, food particles and human waste left behind by cave visitors can dramatically alter the chemical and nutritional environment in isolated areas of caves.
Having large numbers of humans pass through a cave alters it even if no one does anything but walk and breathe. Each person gives off about as much heat as a 100-watt light bulb, exhales copious amounts of carbon dioxide and water vapor, and leaves behind vast numbers of shed skin cells. Over time, even these seemingly innocuous additions to the isolated cave environment can have negative impacts.
Over the years, damage to physical and cultural resources can become quite serious. Caves don’t tend to heal themselves quickly – if at all -- and even seemingly minor changes can eventually accumulate to alarming levels.
Unfortunately, visitor impacts on cave resources tend to be difficult or even impossible to repair or reverse.
Resource managers must use appropriate means to address existing or potential problems. In some cases, improved signage, public education, tour leader training, and related tactics are sufficient to keep problems within bounds. In other cases, it may be necessary to bar visitor access to some areas, conduct cleanups, do some minor repairs, or even perform some minimal restoration.
A fundamental managerial need is to know what kinds of damage have occurred where. However, caves being what they are, surveying and monitoring physical damage and secondary effects can be a very daunting task.
At Oregon Caves National Monument, resource managers decided to employ Visitor Impact Mapping to gather vital information about visitor impacts. A three-year VIM project initiated in 2005 is scheduled for completion later this year.
Here is what the Visitor Impact Mapping program at Oregon Caves entails:
• Hazard-Fragility Assessment: All passages in the cave are classified according to the potential hazard they pose to the visitor and the potential impact of the visitor on the resources in that passage. These classifications are criteria-based and create an index for the cave that defines the system for obtaining permits to enter off-trail areas. Hazard-fragility assessment map, 507 KB pdf
• Fixed-Point Photomonitoring: There are 19 fixed-point photomonitoring stations in and just outside the cave. Year after year, high-resolution digital photos can be retaken from the exact same angle by using a special camera mono-rod that locks into a stainless steel sleeve.
• Photo Inventory: Any cave features or locations of noteworthy fragility, value, or impact are documented with digital photos, described, and geographically linked based on the nearest survey marker.
• Impact Inventory: Using survey markers in the cave for a reference, the presence and severity of 29 kinds of impacts are mapped in heavily traveled corridors of the cave. Some of these impacts include sediment compaction and translocation, broken cave formations, lint deposits, and wiring.
• Paleo Survey: A major characteristic of Oregon Caves is its collection of bone deposits. Many of the bones are bat and rat, the most common cave mammals, but some are of paleontological value, including grizzly bear, salamander, and jaguar bones. Human disturbance to these sites is a significant impact, so bones and animal remains are surveyed, photographed, described, and flagged for protection when necessary.
• Sediment Compaction Assessment: Foot traffic increases the bulk density of sediments on the cave floor. This may affect microbial activity and biodiversity, water infiltration rates, and amount of runoff. With the assistance of a National Park Service soil scientist, resource management staff will assess the sediment compaction along corridors of the off-trail route.
• Vandalism Survey: Cave formations that were broken by human activity are unobtrusively marked with a UV fluorescing compound as a way to monitor vandalism. After all formations have been marked, resurveys in the following years will reveal the newest damage in the cave, if there is any.
• Algae Mapping: Algae growth is mapped annually along the tour path based on a GIS layer of tour path lights.
• Monitoring Conductivity Levels in Cave Pools: Total ionic concentrations in cave pools may be affected by visitation, so pools near and far from the main path are monitored monthly.
By gathering and systematically recording these data, Oregon Caves officials intend to accomplish three main objectives: creating baseline datasets; developing impact monitoring protocols that may be used for other caves;, and revealing spatial patterns that will allow resource managers to focus cave cleanup efforts, understand the nuances of specific kinds of impacts, understand how visitor impacts change in the short-, intermediate-, and long term future.
In recent years Oregon Caves National Monument has averaged about 80,000 visitors. It’s a wonder the park gets that many visitors, considering how difficult it is to get there. The park is a good 20 miles from Cave Junction, and the last 10 miles are very narrow, steep, and winding, with loads of blind curves (not to mention wildlife hazards). Many drivers take 30 minutes to drive the last seven miles. That’s in good weather. Snow can complicate access from November through March. While on the monument property, motorists are cautioned to drive no faster than ten miles per hour.
By all accounts, the trip is worth it. Most visitors wax enthusiastic after taking the 90-minute general cave tour. Be forewarned that it is mildly strenuous. The half-mile route includes more than 500 steep and uneven stairs, and there are many places where visitors need to bend while walking.
Cave tours are available only on a seasonal basis beginning the third week of March and ending December 1. Visitors are cautioned that early arrival is recommended on the day of visit. No reservations are accepted (tickets are sold only on a first-come, first-served basis) and no self-guided tours are permitted. Off-trail caving tours and candlelight tours are offered in the summer only