How are Tsunamis Formed/What Causes Tsunamis
Tsunamis are generally secondary hazards caused by main hazards which occur underwater or close to the coast. Tsunamis are commonly caused by earthquakes and infrequently by landslides and volcanic eruptions.
This Dynamic Earth: the Story of Plate Tectonics; Historical Perspective Source: Image: Kious & Tilling, USGS
The Caribbean lies in a tectonic setting where the North American plate is sinking beneath the Caribbean plate giving rise to earthquakes and volcanic activity.
In this setting, earthquakes that rupture the earth’s crust may generate tsunamis and volcanic eruptions and landslides may also generate tsunamis. As a consequence, the entire arc may be considered a potential source for tsunami generation.
Very rarely a large meteorite impacts the ocean and this disruption may also cause a tsunami to be formed. (See Artist Impression of Cosmic Body at the right)
Large earthquakes occurring beneath the ocean floor or close to the shore can cause the water to be displaced and generate tsunamis.
Do all earthquakes cause Tsunamis?
All earthquakes do not cause tsunamis. There are four conditions necessary for an earthquake to cause a tsunami:
- The earthquake must occur beneath the ocean or cause material to slide into the ocean.
- The earthquake must be strong, at least magnitude 6.5 on the Richter Scale
- The earthquake must rupture the Earth’s surface and it must occur at shallow depth – less than 70km below the surface of the Earth.
- The earthquake must cause vertical movement of the sea floor (up to several metres).
Volcanic eruptions occurring close to the coast can result in tsunamis as fast-moving debris crashes into the sea and causes the water to be disturbed.
Underwater volcanic eruptions emit large volumes of volcanic material which can displace the ocean and generate tsunami waves in the immediate area.
Can an eruption from the Kick 'em Jenny submarine volcano generate a tsunami?
Kick ‘em Jenny is a submarine (underwater) volcano located 9 km northwest of Grenada in the Caribbean. Currently, scientists consider that there is a very small chance that an eruption of the volcano would trigger a tsunami. Any tsunamis triggered by underwater eruptions are a potential hazard for neighbouring islands.
A landslide which occurs along the coast can force large amounts of water into the sea, disturbing the water and generate a tsunami. Underwater landslides can also result in tsunamis when the material loosened by the landslide moves violently, pushing the water in front of it.