Station P349

Questions for John Wahr

How did you become a scientist/engineer?

I had always taken it for granted that I would become a scientist. In fact, I wanted specifically to be a physicist back when I was a little kid and well before I even knew what that word meant. My father was a research physicist for the Dow Chemical Company, and my mother's father (my grandfather) was a physics professor at the University of Michigan. Whatever a physicist was, that`s what I wanted to be. It wasn't until I was in graduate school at the University of Colorado that I had to decide what field of physics I would go into. My tentative plan was to go into some sort of esoteric, strongly mathematically oriented field. But during my second year in graduate school, Professor Pete Bender, who I was working with on a one-year research project, introduced me to geophysics, and told me about a young geophysicist on campus named Martin Smith who was doing interesting work. I went to talk to Martin about what he was doing, and it sounded great, and so I went into geophysics, working with Martin on my PhD.

Crustal Loading from Lake Shasta

Lake Shasta is the largest man-made lake in California. Water flowing out through the dam is used for irrigation and to produce electricity, and the ability to let water out through the dam at a controlled rate allows water managers to reduce the dangers of downstream flooding. The lake level rises and falls both because of seasonal and long-term changes in rainfall, and because of controlled releases through the dam. When the lake level rises, there is more pressure on the surface of the underlying Earth, and the Earth's surface beneath the lake and in the surrounding region gets pushed downwards. Conversely, when the lake level falls, the Earth's surface rises.

Figure 3 shows, in black, how the lake level has varied between 2006 and 2011. There are large seasonal variations, as well as a prolonged dip between mid-2007 and mid-2010, which coincided with a serious drought in northern California. The orange line is a smoothed version of the black points, included to emphasize the dip. Figure 4 shows, in black, measurements of the vertical position of the ground observed by a GPS receiver (P349) located 2 km south of the lakeshore. Again, the orange line is a smoothed version of the black points. Figure 4 shows a positive bump between mid-2011 and mid-2010, corresponding to the dip in the lake level: when the lake level fell, the ground rose; and vice versa. In fact, a careful comparison of the two figures shows that this anti-correlation between lake level and ground motion occurred even for the large seasonally varying terms: the lake goes up, the ground goes down; and vice versa.

Spotlight Questions