I enjoyed Capt. David Bacon’s recent column about our confusing coastline, which makes us feel turned around. I would like to follow up a bit on just how this happened many years ago.
So why do the northern Channel Islands, the Santa Ynez Mountains and our local coastline trend east-west while the rest of California’s coastline and mountains trend closer to north-south?
And why is this important?
The answer lies in their origin, and how their present position and orientation affects winds and ocean currents. A bit more than 10 million years ago, what is now Santa Barbara, the northern Channel Islands and the Santa Ynez Mountains were deep underwater off the coast of northern Baja and what is now San Diego.
They started moving north with the Pacific plate along the San Andreas Fault. About 6 million years ago, they began to rotate clockwise, just like a big ball bearing stuck between two objects sliding past each other.
In this case, the two big objects were the Pacific and North American plates, and the ball bearing caught between them was the Santa Ynez-Santa Barbara-northern Channel Islands region. This region rotated more than 90 degrees clockwise as it continued to slide to the northwest (this is based on years of paleomagnetic work by UC Santa Barbara professor emeritus Bruce Luyendyk and his students).
During this time, large cracks opened in the sea floor that allowed magma from miles deep to come up and erupt, adding volcanic ground to some of the islands. During the rotation, the two big plates squeezed this region up vertically many thousands of feet, and well above sea level.
The northern Channel Islands continue to rise slowly, less than a tenth of an inch per year, while Santa Barbara and the Santa Ynez Mountains continue to rise rapidly, nearly a half-inch per year — about the same rate as the highest and fastest-growing mountains in the world, the Himalaya!
The uplift of these mountains and islands, and their east-west orientation, affects the ocean currents and wind patterns in a very big way, making the Santa Barbara Channel a major bio-geographical boundary of global importance. To the north lies cold water currents and cold water species, and to the south we have warmer ocean currents and warm water species. In the channel, these warmer and colder waters mix, and both types of species can thrive at various times.
The east-west trending mountains and islands act like a giant wall or barrier, interrupting the regional north to northwest winds and ocean currents. This in turn produces abundant upwelling in the channel’s waters (the details are complicated). This upwelling brings up nutrients from deep in the ocean, to the shallow, sunlit surface waters where plant plankton reproduce abundantly and create the base of a rich food chain.
So the unusual east-west orientation of the islands and mountains, produced by geologic forces starting millions of years ago, has created a Santa Barbara Channel that has extraordinary biodiversity (cold and warm water species), as well as an area of high biological productivity.
These productive and food-rich waters make it very inviting for many marine mammals, including sea lions, dolphins, porpoises and whales — more than 30 species in all. In fact, the largest animal to ever roam the Earth, the magnificent blue whale, chooses the Santa Barbara Channel as one of its favorite dining places.
Another consequence of the geologic history of the Channel Islands is its isolation from the mainland. Remember that the islands did not uplift to become islands, rising above sea level, until they were separated far from the mainland. This isolation allowed for species of plants and animals to evolve in a unique and protected environment; more than 140 species are “endemic,” occurring only here and nowhere else in the world!
This is why these islands are often referred to as the Galápagos Islands of the north, because like the Galápagos, the Channel Islands rose up from the deep sea floor and have remained isolated from the very beginning, allowing for many unique species to evolve and survive in the absence of mainland predators (well, until people and shipwrecks introduced some of these predators).
UCSB professor emerita Tanya Atwater, a geophysicist and the world’s expert on the plate tectonics of western North America, has produced some excellent and accurate animations of these processes. Click here to view the animations.
— Ken Macdonald is an oceanographer and professor emeritus in UC Santa Barbara’s Department of Earth Science. He has been affiliated with Woods Hole Oceanographic Institution and Scripps Institution of Oceanography, and has led deep-sea dives up to 15,000 feet in the submersible Alvin. He is a naturalist for Channel Islands National Park and the Channel Islands National Marine Sanctuary. Click here to read previous columns. The opinions expressed are his own.