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What Causes Tsunamis and Earthquakes?

Tsunamis and earthquakes are both natural events that can cause massive destruction. The two phenomena are often related, as the motion of earthquakes can cause tsunamis. While not all earthquakes cause tsunamis, if they occur near the ocean and shift large masses of water, tsunamis can result.

Shifting Tectonic Plates
- Tectonic plates are the moving pieces of Earth's crust and outer mantle, which cover the entire planet. These plates are in constant, slow motion, and sometimes bump and slide past one another along boundaries known as "faults." Earthquakes occur when two plates shift suddenly against one another along a fault surface. When earthquakes happen at the bottom of the ocean, they can cause tsunamis. In order to cause a tsunami, the seafloor must move enough to displace a large amount of water, generating a series of large waves.
Volcanic Eruptions
- Just as underwater earthquakes can cause tsunamis by disturbing large water masses, volcanic eruptions can have the same effect. A powerful volcanic eruption that occurs underwater can lift up the water column, causing a tsunami. Volcanic activity can trigger tsunamis through other mechanisms, including volcanic earthquakes, landslides and airwaves from large volcanic explosions. In 1883, the most violent volcanic tsunami on record was triggered by the eruption of Krakatoa, which killed 36,000 people.
Landslides
- Whether they originate above or below the water, landslides can move enough water to trigger tsunamis. Submarine landslides, which can be caused by earthquakes or volcanic activity, can redistribute sediment and rock on the bottom of the ocean floor. If this motion disturbs enough of the water above, a tsunami can result. When debris from landslides that occur on land hits the ocean, its momentum is transferred into the water. If the momentum is great enough, it can generate a tsunami.
Cosmic-body Impacts
- Meteorites and asteroids, like supermarine landslides, transfer their momentum into the water when they strike the ocean. While these types of impacts generally don't cause the same long-traveling tsunamis generated by strong earthquakes, scientists have found evidence of a prehistoric, asteroid-generated tsunami that would have destroyed most life on Earth. This tsunami, which occurred 3.5 billion years ago, would have swept around the Earth, changing coastlines and sweeping across continents.

Nature