Wednesday, June 4, 2014
It's a Dam Big Reservoir, But There Are Some Dam Scary Things About It.
In any case, this is a dam big reservoir. It's Hoover Dam, the first of the gigantic mega-dams constructed in the U.S. back in the 1930s during the height of the Great Depression. Thousands of hungry unemployed men came from all over the country to work in the construction, and in the dangerous conditions, more than one hundred of them died. It's 726 feet high, which at the time was the highest dam in the world (it's the 18th highest now). It holds back about 30 million acre-feet of Colorado River water, equivalent to more than two years of normal stream-flow. At least, what was normal thirty years ago.
Still, there are some dam frightening things about visiting Lake Mead and Hoover Dam. First and foremost, the dam is missing something. Water. It's missing a lot of water. It's sitting at the lowest level ever seen since the dam's floodgates closed in the 1930s. It hasn't been full as far as I know since the flooding in 1983, and prospects are not good for changing this situation in the face of ongoing drought and climate change.
Before I started researching the field seminar that I'm currently conducting, I assumed that Hoover Dam was anchored in ancient stable metamorphic and plutonic rocks. That is the kind of rock that is exposed in Black Canyon downstream from the dam. A close look at the rocks reveals a different composition: they are rhyolitic volcanic rocks, and according to the guides and the maps, they are Neogene in age, from around maybe 15 million years ago.
The dam morning was almost over, so we hit the road. We were headed towards the Grand Canyon, a much better place to appreciate the Colorado River.