Monday, June 3, 2013
A Dam Big Dam and a Dam Big Bridge...And a Dam Frightening Problem
The dam was built during the height of the Great Depression between 1930 and 1935, and just two years after the catastrophic failure of St. Francis Dam in California that killed around 600 people. Lessons learned from the failure of St. Francis led to modifications of Hoover Dam which presumably make it more or less indestructable.
Just the same, it is amazing how many faults are exposed in the canyon walls adjacent to the dam. The rocks forming the abutments are Miocene volcanic tuff, which doesn't dissolve or crumble in water (a major factor in the St. Francis event). But the rock is highly faulted, and it is a great place to explain slickensides, the scratch marks that occur when blocks of rock slide past each other. The rock is literally polished.
And that's dam frightening.