GEOHAZARDS EVALUATION OF MASS MOVEMENTS IN GRAND CANYON NATIONAL PARK, ARIZONA

Grand Canyon National Park has never been extensively surveyed for the documentation and assessment of geologic hazards. The Grand Canyon is a constantly eroding system not only subjected to the Colorado River incision, but also to physical weathering processes. The objective of the project was to develop a database for all known documented events. Data was procured from the National Park Service press releases, historic photographs and from personal accounts of sources within the park.

Detailed examination of documented and potential sites was conducted between June 3^rd and August 3^rd, 2013. A total of 45 documented events were entered into the database with 35 of the events having exact dates. Pertinent causes were verified using weather data for those 35 events. Accordingly, erosive agents such as precipitation, root wedging and freeze-thaw processes coupled with gravity led to undercutting inevitably causing slope failures.

Initial findings suggested that mass movements are likely to occur during the winter to early spring and summer monsoon seasons. Of the 35 events with exact dates, 21 of those events occurred in winter to early spring, indicative of prolonged effects of residual snow cover lasting from late November to early March. The remaining 14 summer events were most probably initiated by the short bursts of rain characteristic of the monsoon season spanning from mid-July to early September. Temperature fluctuations preceded certain events; however no definite link in temperature propagating mass movements has been ascertained. The North Kaibab Trail was identified as the most active corridor trail resulting in 18 of the 45 documented events. Further analysis established that an average of 3 to 4 documented events have occurred per year.

Mass movements have repeatedly caused damage to the trans- canyon pipeline which is the park’s only source of potable water. Erosionally active areas pose a significant threat to human life and park infrastructure. The findings of this project will be handed over to park management to improve infrastructural planning and prepare mitigation measures for high risk areas.