Sunday, June 4, 2017

The Airliner Chronicles: The San Francisco Peninsula and the San Andreas Fault

Crystal Springs Reservoir is on the upper left, while San Andreas Reservoir is on the lower right
As has been no doubt obvious, I was in Hawai'i last week, and there have already been several posts about some of my adventures. I started through the many pictures in a more chronological manner, and realized there were some neat things I saw before I even left California. I always notice on a flight that some people do such things all the time and are not particularly impressed that they are in a large metal tube traveling at hundreds of miles an hour at 35,000 feet. Others have a sense of history, realizing that for the first few million years of hominid existence, this was an unnatural thing to be doing. I don't get to fly all that often, so I tend to fall into that second category. As soon as we are off the ground, the camera that I surreptitiously placed at my feet swings into place and I start snapping pictures as if I were the first human being ever to see such incredible sights. My photo habit led to my first blog series in 2008, the Airliner Chronicles. Consider this a new entry...

It is the geologist's perspective that provides some insight as to the nature of the landscape below. We left from Oakland Airport and flew over the north end of the San Francisco Peninsula, which provided an outstanding view of the San Andreas fault. Often such faults are indicated by linear valleys owing to the ease with which crushed rock in the fault zone erodes. But on the peninsula the fault is even easier to pick out because of the presence of two reservoirs filling the linear valley, Crystal Springs reservoir, and San Andreas reservoir.
It's quite a coincidence, the fault and the lake both being called "San Andreas", so the question naturally arises, which was named first? The fault may be more famous to most people, but the lake came first. It was constructed in 1868. In 1895, the geologist Andrew Lawson was mapping in the area and discovered the fault, which he named after the lake. He had no idea that the fault was 600 miles long, or that it was particularly active, or that it was the boundary between the Pacific and North American tectonic plates. And he most certainly didn't know that it would shift in 1906 in a most tragic way.
The city has grown in the years since 1906, to say the least. We know a great deal more about fault zones and earthquakes, and thus we have a better understanding about the threats of future quakes in the Bay Area. Both by law and by subsequent experience (Loma Prieta in 1989 and the Napa Valley in 2014), the cities of the peninsula are better prepared for large earthquakes, but no matter how ready they may be, the next large earthquake will cause major damage on the peninsula and many will die or be injured. Seeing the proximity of the fault and the cities from above provides a stark reminder of the need to be prepared.

We flew out over Half Moon Bay, and soon land was left behind. There was more than 2,000 miles of open ocean ahead of us, a five hour flight. I settled in and thought of how the islands were inaccessible to humans of any kind until only a thousand or so years ago, and even a hundred years ago it took weeks or months to cross the ocean. How even more wondrous the number of bird and insect species that survived the journey over the millennia.