Earth’s surface may look solid—after all, we walk on it and construct buildings on it—but in fact it is a constantly moving puzzle of interlocking pieces. These pieces, known as tectonic plates, are giant sections of Earth’s crust whose edges interact with one another by either colliding or moving apart. The plates of the lithosphere float on top of the malleable asthenosphere in Earth’s interior. The movement of these plates is called plate tectonics, and scientists have studied this field since the 1950s. While the movement of tectonic plates is usually slow—typically just a few centimeters per year—plate tectonics are linked to several kinds of natural disasters, namely earthquakes, volcanoes, and tsunamis.
On the afternoon of March 11, 2011, a large earthquake struck off the northeastern coast of Japan. This event, which would prove to be deadly, was caused by a specific type of plate movement: subduction. Subduction occurs when one tectonic plate—the one that is older and denser—sinks or is pulled under another tectonic plate. This process does not proceed smoothly, however—tectonic plates can shift and grind against each other, snagging on each other due to friction. Once plates overcome this friction and move past each other, the energy released leads to earthquakes. Near Japan, the Pacific Plate is subducting under the North American Plate. Although it may seem impossible, parts of Japan actually sit above a portion of the North American Plate.
In the 2011 Tohoku Earthquake—so named for the part of northeastern Japan that was struck hardest by the quake—a submerged section of the North American plate jolted upward in the Japan Trench. This undersea valley is located roughly 130 kilometers (81 miles) from the main island of Japan. The magnitude 9.0 earthquake produced by the upward movement of this plate—one of the most powerful quakes in recorded history—hoisted a wall of seawater.
That huge upwelling of water created a series of waves—a tsunami— that moved outward in all directions from the earthquake’s epicenter, both toward and away from Japan. The waves moved at speeds of up to 800 kilometers (500 miles) per hour, roughly the speed of a jet airliner. When those waves rolled up on the eastern shore of Japan, the tallest measured more than 10 meters (33 feet) high. The waves that rushed toward the east eventually struck Hawai'i and then the western coast of the United States, though with much less force.
The tsunami that hit Japan was far higher than the seawalls that had been built to protect the Japanese coastline from such inundations. The water rushed inland in a great flood, carrying with it ships, sweeping away cars, and destroying buildings. About 20,000 people were killed. Images captured on the day of the earthquake, as well as the days that followed, revealed a shattered landscape full of debris. The environmental impact of the 2011 earthquake and tsunami has been enormous; researchers studying soil samples have detected pollution from industrial chemicals and pesticides that leaked from the wreckage. That is not surprising given the amount of destruction caused by the disaster: oil refineries in flames, sewer and gas lines broken, and chemical plants damaged.
The tsunami also crippled the Fukushima Daiichi Nuclear Power Plant near Sendai, Japan. Ocean waves caused flooding that cut off the plant’s electrical power, making it impossible to cool the plant’s nuclear reactors. As a consequence, three of the plant’s four reactors overheated, causing the uranium fuel rods to liquefy. The melted rods burned through the steel walls meant to contain them, releasing uranium and other radioactive materials into the air and sea. The airborne radioactive particles blanketed houses, crops, and schools. Over 100,000 people were forced to evacuate from their homes. The Japanese government expected to spend the equivalent of more than 200 billion U.S. dollars (and perhaps as much as 600 billion dollars) cleaning up radioactive contamination and dismantling the power station, a task that could take 30 years or more. A lot has been accomplished already, however: 1,500 fuel rods from the Fukushima Daiichi Nuclear Power Plant have been removed and radioactive topsoil and vegetation from the surrounding area have been placed in bags for long-term storage.
This earthquake also had far-reaching effects: tsunamis rolled up on distant shorelines in places as far away as Chile, and the intense ground shaking might have even changed the rotation rate of Earth, shortening the length of the day by about 1.8 microseconds.
Earthquakes and tsunamis are powerful natural disasters capable of wreaking extreme havoc. For that reason, scientists are interested in being able to predict when and where these events will occur. By installing sensors capable of measuring ground movements, researchers can monitor earthquakes, even tiny ones, worldwide. This data allows scientists to assemble global maps of earthquakes to look for patterns in their locations. Researchers have also placed buoys in the ocean to detect tsunami waves traveling toward land. Detecting a tsunami before it floods a shoreline and issuing an alert can save many lives.
