Since its initial construction in 1860, Alcatraz Island has been a “star attraction” located in the San Francisco Bay area. This major historical site and tourist destination makes the effects of ongoing geologic hazards and erosion on cultural features and public safety a long-term concern.
Over the last 150 years, many natural and manmade changes have occurred on the island. Completing the island’s first comprehensive geologic and geotechnical hazards assessment required both detailed historical review and modern-day on-the-ground geologic investigation on, above, below, and around the island’s circumference. It also required using a variety of investigative methods, including surface mapping, historical aerial photograph interpretation, and cliff mapping by boat.
Kleinfelder utilized its team of nationally recognized engineering geologists to identify the geologic conditions and the existing and potential geologic hazards that affect cultural resources and the public. The geologic data was presented in a form the related the various probabilities of hazards that may occur to the existing cultural features and to general public safety.
This study provided the National Parks Service with the first ever Geologic Risk Assessment Zonation map that easily identifies problem areas and provides recommendations, on a relative-rated risk basis, for areas needing immediate study and mitigation as well as for future, phased mitigation studies. The study also summarized the impacts on the island and improvements resulting from future sea level rise.