GEOLOGIC HAZARD EVALUATION ALONG THE DENALI PARK ROAD

The 92-mile Denali National Park Road has a long history of landslides and debris flows causing disruptions to traffic and public safety. The road is a major conduit for approximately 500,000 visitors to the park each year and is also the only access for several lodges located in Kantishna (mile 92). The park, and therefore the road, is a major economic engine for the region. Most visitation is during summer months, which is also when landslides are likely because seasonally-frozen ground is thawed. Much of the road traverses areas of permafrost, which is regionally known to be thawing; this trend may be contributing to greater frequency of events.

The Denali Park Road has experienced numerous landslides through history. The most dramatic occurred in October 2013 when a 180-m-long, 35-m-wide debris slide blocked the road near mile 38. Blocks of permafrost-frozen, unconsolidated debris up to 5 m thick slid on slippery, unfrozen clay. Fortunately, this event occurred after the road was closed for the season. If it had occurred during visitor season, it may have resulted in fatalities/injuries as well as economic losses for the entire region. Many less dramatic events have blocked traffic, undermined road surfaces, and caused damage to vehicles. Numerous individual slides are monitored along the road and this event could have seriously endangered visitor safety; therefore a risk analysis must be completed to identify the highest risks so they can be properly mitigated before future events occur.

National Park Service (NPS) staff are partnering with the Federal Highway Administration (FHWA) to complete a comprehensive risk analysis of the road. The risk analysis will include five parts: (1) inventory maps and linked database that illustrate spatial/temporal distribution of geohazards, their relative activity, and geomorphic attributes; (2) alpha/beta testing of the new Unstable Slope Management Program rating criteria; (3) susceptibility maps and linked database that illustrate spatial distribution of geohazards in an area and their probability of occurrence; and (4) geohazard risk maps and linked database that illustrate where landslides and other geohazards may initiate, and probability and consequences of occurrence. The NPS and FHWA will use results to mitigate those areas identified in the highest risk categories.