Tsunamis
A tsunami is a wave event associated with a displacement of a large volume of water in either an ocean or a sizeable extension of it (such as a sea, bay, or sound); infrequently, tsunamis can also happen on very large lakes. These displacements occur as a result of earthquakes, following a rift or shift in the ocean floor that causes the whole vertical water column to move and create a wave at the surface. Because tsunamis can travel quickly over a long distance on the open ocean, the people who are often most in danger of a tsunami are far away from the epicenter of the earthquake and have no idea a tsunami was even generated. Thanks to advances in technology and earthquake monitoring globally, scientists can now predict tsunamis and issue warnings with much greater accuracy and lead time than ever before. Let's look at how and where tsunamis form and the mitigations and warning systems that have been developed to mitigate their deadly potential.
First, log in to BBLearn and complete "Assignment 7.3: Tsunami." This assignment uses an interactive animation demonstrating how tsunamis originate, where they occur, and how remotely sensed satellite imagery has been used to measure their destruction.
First, log in to BBLearn and complete "Assignment 7.3: Tsunami." This assignment uses an interactive animation demonstrating how tsunamis originate, where they occur, and how remotely sensed satellite imagery has been used to measure their destruction.
Tsunami Prediction and Monitoring
In 1946, a strong earthquake (estimated at 8.3 on the Richter scale) hit the Aleutian Islands of Alaska. Nearly five hours later, a multi-wave tsunami hit the Hawaiian islands, resulting in widespread destruction and 159 deaths. In the aftermath of this event, the Pacific Tsunami Warning Center was established to monitor earthquakes and issue tsunami warnings in the Pacific Ocean. This center now relies on two types of data:
1) Seismographs from around the world that help pinpoint the location and magnitude of an earthquake immediately after it happens, and
2) A system of ocean sensors that measure wave energy as it passes across the floor of the Pacific and transmits that information to land via satellite.
After the 2004 tsunami that originated off the coast of Indonesia killed nearly one-quarter of a million people around the Indian Ocean who had no real warning before the tsunami struck, the sensor monitoring system was expanded to the Indian Ocean basin.
1) Seismographs from around the world that help pinpoint the location and magnitude of an earthquake immediately after it happens, and
2) A system of ocean sensors that measure wave energy as it passes across the floor of the Pacific and transmits that information to land via satellite.
After the 2004 tsunami that originated off the coast of Indonesia killed nearly one-quarter of a million people around the Indian Ocean who had no real warning before the tsunami struck, the sensor monitoring system was expanded to the Indian Ocean basin.
Tsunami danger mitigation
While humans cannot mitigate the potential of a tsunami happening, they can mitigate its impacts on lives and infrastructure. As part of the tsunami warning system, most coastal cities around the Pacific Ocean have established tsunami evacuation routes that direct people to the nearest higher ground in the event of a tsunami (below left). They also develop evacuation zone maps to help residents identify whether they are in an area they would need to evacuate from (below right). These maps also help builders in determining where they need to build stronger, reinforced homes that can better withstand the power and wave action associated with tsunamis.
This type of planning has likely saved hundreds of thousands of lives in recent decades. An excellent example of this is the March 2011 Tohoku earthquake off the coast of Japan. This magnitude 9.0 earthquake was the largest in recorded history for Japan, and the tsunami that hit the coast shortly afterward exceeded every model prediction for maximum wave height. As a result, nearly 20,000 people were killed in Japan, many because they thought they were safe behind sea walls that ended up being overtopped by the unprecedented wave heights. But hundreds of thousands more were able to immediately evacuate to high ground when the tsunami sirens sounded, and very few fatalities occurred around the rest of the Pacific Ocean, despite significant structural damage to coastal buildings and roads in Papua New Guinea, Hawaii, Russia, California, and Chile.