How Tectonic Plates Can Cause Earthquakes, Volcanoes and Tsunamis
On a snowy Saturday in November 1966, my family flew from JFK in New York to Los Angeles. I had accepted a postdoctoral research position in the physics department of the University of California campus in Riverside. We took a helicopter from the Los Angeles airport to the small airport in Riverside, fifty miles east into the desert. Then we took a cab to our motel.
We went to sleep and the next morning I awakened early and walked out of our cabin. A man opened the door of the neighboring cabin and said, “That was really something last night!” “What do you mean?” I asked. “The earthquake. Didn’t you feel it? It knocked my son right out of bed.” “You must be joking,” I said with a nervous laugh. He replied, “Don’t you know that you are standing on the San Andreas fault? And that it runs through Riverside?”
Well, I didn’t know that. I might not have accepted the position at the university if I had known that it was in an earthquake zone. “I’m okay with hurricanes, but not earthquakes. How dangerous are these earthquakes?” I asked. He said, “Usually they are very small and frequent. That’s good because it relieves the stress on the fault line. But this year we’re supposed to have the 100-year quake. It’s going to be a big one. Welcome to Southern California!”
The Drifting Continents
In 1912, Alfred Wegener, a geophysicist and meteorologist, proposed that the Earth’s continental land masses “drifted” across the Earth, sometimes plowing through oceans and crashing into each other. Wegener used fossil records from geology, plant and animal biology to support his theory. It also explained why look-alike animal and plant fossils, and similar rock formations, are found on different continents.
Wegener constructed a map of the continents that showed how they fit together as in a jigsaw puzzle. He called the resulting supercontinent “Pangea.” We now know that there were many such supercontinents before Pangea, and that this latest one began to break apart approximately 200 million years ago.
Wegener’s theory ran into opposition, primarily because he could not suggest a mechanism that would cause the continents to move. But 50 years later his theory was supported by evidence of the drift from an unexpected source: the seafloor of the Atlantic Ocean.
In the 1960s, magnetic maps of a structure called the North Atlantic rift showed that the pattern of ridges on one side of the ridge exactly mirrored that on the other side. The researchers had discovered convincing evidence that the Atlantic Ocean was spreading.
This led to the conclusion that the continents were riding on moving rock formations, which they named “tectonic plates.” This was a late vindication of Wegener’s theory, which has been proven correct.
The discovery of seafloor spreading inspired geophysicists to construct a new dynamic picture of the Earth: a planet with a liquid metal core surrounded by a mantle of heavy rock and an outer crust of lighter material divided into plates, on which the continents rested.
If the Earth were the size of a cherry, the pit would represent the liquid core. The meat of the cherry would be the mantle and its skin the crust. And the tectonic plates have the ability to move on the surface of the mantle.
The Atlantic sea floor is a gigantic tectonic plate. It is made of basalt, a dense rock. The continents, which ride as passengers on the plate, are made of lighter granitic, sedimentary and metamorphic rocks.
In the process of seafloor spreading, molten rock rises from the Earth’s mantle and creates new seafloor (oceanic crust) to the edges of the old. It occurs mainly at underwater mountain ranges known as mid-ocean ridges. As the new seafloor emerges, the continents on opposite sides of the ridge move away from each other. The continents of America and Europe are continually separating at 2.5 centimeters (1 inch) per year.
The Ring of Fire
Plate tectonics has a huge influence on the weather and air quality. It can also cause mass deaths, earthquakes, volcanoes, tsunamis and the creation of deserts. These disasters are the result of the movement and collision of tectonic plates.
Most of the earth’s volcanic and earthquake activity occurs at plate boundaries. Perhaps the most dramatic is the “ring of fire” which surrounds the Pacific plate. The map below shows earthquakes that occurred from 1900 to 2013.
One of the most devastating occurred in 2011 and devastated a portion of Japan’s coast. Its magnitude was 9.0 earthquake making it the fourth most powerful since records were kept.
It struck in the Pacific Ocean off the northeast coast of the Tōhoku region of Japan’s Honshu island on March 11, 2011. It created a massive tsunami (erroneously called a tidal wave) more than 100 feet high that flooded more than 200 square miles of coastal land, causing deaths and extensive property damage. It destroyed a major nuclear power plant, releasing radioactive material. As a result of this event, the Japanese island of Honshu moved 8 feet east.
The San Andreas Fault
The San Andreas Fault is the boundary between the North American plate and the Pacific plate. Los Angeles is on the Pacific plate, and San Francisco is on the north American plate. The Pacific plate is moving north. The part of California on the Pacific plate includes the city of Los Angeles.
Ever so slowly, Los Angeles is moving northward up the coast of California. And some day, it will be at the same latitude as San Francisco. As the North American plate dives under the Pacific plate, a process called “subduction,” it melts. That boundary is where earthquakes and volcanoes occur.
Plate Tectonics Can Provide Cheap Energy
There is a bright side of plate tectonics for humanity. We can use it to generate cheap electricity.
Here’s how electricity is produced: a coil of copper wire is rotated in a magnetic field. The wire become electrically charged. The resulting current can be stored in batteries or shipped directly to consumers. There are many ways to rotate the coil. Water falling over a dam can turn the coil. Steam from a nuclear power plant can rotate it. Steam generated from geothermal energy can also turn a coil of wire, nearly without cost.
The boundaries of tectonic plates are regions where magma can come to the surface, as in a volcanic eruption There is plenty of available thermal energy in these locations. We can drill holes to harness this geothermal heat, which can power a steam engine and produce electricity.
How Iceland Benefits from Plate Tectonics
Iceland straddles the Mid-Atlantic Ridge, where divergent tectonic plates release heat and magma close to the earth´s surface. It sits on one of the largest sources of geothermal energy on the planet. These enormous and boundless geothermal resources make Iceland nearly energy self-sufficient.
And the energy is very inexpensive to produce. Icelandic scientists and engineers have drilled dozens of deep holes to tap into the magma-driven heat needed to produce electricity. As a result, Iceland has become the world leader the production of this eco-friendly, sustainable and renewable power. Even its sidewalks and some highways are heated by geothermal energy, and the lamp posts at its international airport are lit by electricity generated from geothermal sources.
Our Never-Ending Journey
About five years ago, I became a frequent traveler to northern California to visit my daughter and her family. On my first ride from San Jose airport to the town of Aptos, about 50 miles south, I noticed a huge trench to the right of the highway. It was roughly 200 feet wide and 40 feet deep, and it went on as far as I could see. Of course, it was the San Andreas fault, which runs for 750 miles in California.
I stopped my car and got out to look at it. I was overwhelmed by the knowledge that I was gazing at the boundary between the North American and Pacific plates. I was standing on the North American plate, which was moving to the west. The land on the western side, the Pacific plate, was moving north.
It was said of James Hutton, the father of geology, that he could sit on a mountainside and feel the rain eroding the rocks. In the mid-1700s, he argued that the Earth was dynamic, not static as everyone else thought.
Unlike Hutton, I tried unsuccessfully to feel the westward movement. It was too subtle. Yet I knew that if I stood there long enough, I would be subducted into the fault and would disappear into the Earth’s interior. I would be, as I always was, riding on the westward flowing continent with all its inhabitants, human and otherwise. My life is just a small part of the immense journey that has been taking place long before humanity existed.
