National Park Service Logo
PEPC Planning, Environment & Public Comment
PEPC Home Documents by Park Policy/Links Park Planning Search Documents

Olmsted Point Perform Avalanche Monitoring And Hazard Analysis

Yosemite National Park » Olmsted Point Perform Avalanche Monitoring And Hazard Analysis » Document List

Opening Tioga Road is critical to providing access for recreational opportunities in Yosemite. El Nino predictions this winter may result in a heavy snow pack next spring, delaying the opening of Tioga Road and possibly risking employee safety without pertinent data on avalanche conditions. Installing a temporary weather station and automated remote camera to monitor snow and melt conditions at the Olmsted avalanche zone would provide the best data on avalanche conditions.

This project proposes to install a temporary weather station and time lapse camera to monitor avalanche conditions, inform snow removal strategies, and maximize worker safety. Specifically, this equipment will monitor a glide avalanche zone on Tioga Road near Olmsted Point. This glide avalanche path has damaged two tractors, killed one employee, and continues to threaten snow removal operations.

Glide avalanches occur when the entire snowpack slides as a unit on the ground, similar to a glacier. Glide occurs because melted water lubricates the ground and allows the overlying snowpack to slowly "glide" downhill. Research has shown that glide rates increase exponentially before a glide avalanche releases; thus monitoring changes in glide rates is essential for avalanche forecasting.

The installation of a portable, temporary weather station will provide data on air temperature, relative humidity, wind speed and direction, solar radiation, and snow depth. These measurements will be used in energy balance simulations to estimate the timing of snowmelt arrival at the base of the snowpack, which has been shown to trigger glide avalanches.

The temporary, remote camera will use time-lapse imaging to record all types of avalanche activity; this technique is especially useful for monitoring glide crack opening. From analysis of these measurements, consultants will identify meteorological conditions associated with rapid glide rates and provide recommendations for structural mitigation and spring road opening operations.

The weather station (approximately three meters tall) and camera (potentially strapped to a tree) will be temporarily placed shortly before the road closes in the fall and removed during spring opening, so impacts to the viewshed are minimized. While no major excavation is planned, stakes would be driven into soil or gravel to anchor the installations. Temporary anchors (straps/clamps) may also be placed in adjacent trees to secure monitoring equipment. The camera would be accessed remotely through a cellular satellite network or during winter field excursions. The system requires a high oblique angle to adequately monitor the Olmsted avalanche zone and the best camera location to achieve this requirement is in designated wilderness. The effectiveness of the installation will be reevaluated annually.