- January 17, 2022
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Subject – Disaster Management
Context – Tsunami threat recedes after undersea volcanic eruption in Pacific
- The word “tsunami” comprises the Japanese words ”tsu” (meaning harbour) and “nami” (meaning wave). A tsunami is a series of enormous waves created by an underwater disturbance usually associated with earthquakes occurring below or near the ocean.
- Volcanic eruptions, submarine landslides, and coastal rock falls can also generate a tsunami, as can a large asteroid impacting the ocean. They originate from a vertical movement of the sea floor with the consequent displacement of water mass.
- Tsunami waves often look like walls of water and can attack the shoreline and be dangerous for hours, with waves coming every 5 to 60 minutes.
- The first wave may not be the largest, and often it is the 2nd, 3rd, 4th or even later waves that are the biggest.
Causes of Tsunami
- It can be generated by movements along fault zones associated with plate boundaries. The region where two plates come in contact is a plate boundary, and the way in which one plate moves relative to another determines the type of boundary:
- spreading, where two plates move away from each other;
- subduction, where two plates move towards each other and one slides beneath the other;
- transform where two plates slide horizontally past each other.
- Most strong earthquakes occur in subduction zones where an ocean plate slides under a continental plate or another younger ocean plate.
- 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 the material to slide into the ocean.
- The earthquake must be strong, at least magnitude6.5 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 seafloor (up to several meters).
- A landslide that 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.
- Volcanic Eruption
- Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.
- According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion, by a volcanos slope failure, or more likely by a phreatomagmatic explosion and collapse/engulfment of the volcanic magmatic chambers.
- One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia.
- Extra-terrestrial Collision
- Tsunamis caused by extra-terrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence. Although no meteor/asteroid induced tsunami has been recorded in recent history, scientists realize that if these celestial bodies should strike the ocean, a large volume of water would undoubtedly be displaced to cause a tsunami.
- Scientists have calculated that if a moderately large asteroid, 5-6 km in diameter, should strike the middle of the large ocean basin such as the Atlantic Ocean, it would produce a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States.