|Are the mountains here in Santa Barbara growing and how much do they grow per year?|
|Question Date: 2020-05-08|
Yep. The mountains here are growing. But, they are not growing constantly. Every few thousand years or so there is a large earthquake that lifts up the mountains and all of Santa Barbara by several feet. So, to build the mountain, it takes a very long time, like tenths of millions of years.
Even though the mountain doesn't go up every year. We can still express its growth as a yearly rate by taking the total amount of growth and dividing by the number of years it has taken to get to its current position. The rate ends up being about 2mm (0.08 inches) per year. For reference, 2mm is about the thickness of a nickel!
In between earthquakes, the mountain is actually shrinking because pieces of rock are breaking down and being transported by streams to the ocean.
So, there is this competition between breaking down and transporting pieces of the mountain to the ocean (erosion) and building it up through large earthquakes (uplift). In Santa Barbara and Ventura, uplift is winning, and at rates that are some of the fastest in the world!
The mountains here in Santa Barbara are part of the Western Transverse Ranges (see below map from Hammond et al. 2018)!
Santa Barbara mountains.
Our mountains ARE growing! This happens because we live in a special part of the plate boundary where there is both side-to-side movement (where the two sides of the earth move in opposite directions) AND a squeezing movement (where parts of the earth move towards each other). Because of this squeezing, our mountains grow pretty fast - about 2 mm/yr.
That might not seem like much, but if you were to make a stack of paper 20 sheets tall, that's how much taller our mountains get every year. That's quite a lot for a mountain!
The Western Transverse Range, which includes the Santa Ynez Mountains that we can see from town, are rising at about 2 mm (0.079 inches) per year. This has been measured with GPS units and satellites. More locally speaking, the Santa Ynez Mountainslowly, about 1 mm per year. This growth is caused by the Pacific tectonic plate pushing into the North American plate. This produces faults, including the Santa Ynez fault, that pushes up the Santa Ynez Mountains.
How fast mountains are growing kind of depends on how long you're looking at them. It's a bit like a car trip. Sometimes you might be on the highway and going quickly, and sometimes you might be at a gas station and not moving at all! If someone calls you and asks you how fast you're going, then you could say the average over the whole time, but if you're at a gas station you could have a speed of zero.
Movement on faults that can cause mountains to rise is like a trip. Sometimes the fault is "locked," and won't move or will actually cause the land to flex up or down like a ruler, but sometimes the faults may be moving. So the mountains are growing 1-2 mm/year, and that's about 3 feet/ thousand years if you look at an average over thousands of years (the whole trip). But over short times some sensors show the land moving down, which probably is from flexing on locked faults (although sometimes areas can move down from pumping groundwater, but it looks like that isn't the case here).
The answer seems to be about two millimeters each year. However, this is still an area of research.
Good question! The mountains here in Santa Barbara ARE still growing. Growing 12 inches per 100 years.
The following article says the mountains in Santa Barbara are growing 1-2 millimeters each year. But the mountains also move down about a centimeter every winter because snow and rain push them down, and then they move up about a centimeter in the summer when it's dry.
One  inch = 2 1/2 centimeters = 25 millimeters.
Humans causing California's mountains to grow.
"In addition to these seasonal variations — on the order of a centimeter up and down — the team found year-over-year trends in the stations’ average vertical positions. In the mountains around the edges of San Joaquin Valley, these trends showed elevation increases of roughly 1 to 3 millimeters annually, meaning the seasonal ups have been outpacing the downs, and that the mountains there are growing."
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