World Tsunami Awareness Day (WTAD) is observed every year on November 5 to promote tsunami awareness and preparedness worldwide. Established by the United Nations, this day focuses on educating communities, reducing disaster-related risks, and enhancing global resilience. The observance aims to bring together experts, government bodies, and communities to spread knowledge about the causes, impact, and prevention strategies related to tsunamis. The theme for World Tsunami Awareness Day 2024 centers around “Building Resilient Communities,” which emphasizes community-based approaches to preparedness and resilience-building.
Understanding Tsunamis: Nature and Impact
Tsunamis are long, high sea waves generated primarily by underwater earthquakes, volcanic eruptions, or landslides. These massive waves can travel across entire oceans, often hitting coastlines with devastating force. Unlike typical ocean waves, tsunamis have long wavelengths, making them particularly dangerous and capable of flooding vast inland areas.
Some key features of tsunamis include:
- Speed: Tsunamis can travel at speeds up to 800 km/h in deep water, decreasing only slightly as they approach shore.
- Height: While they may appear as small waves in open water, they can rise dramatically near coastlines.
- Impact: Tsunamis can lead to extensive flooding, loss of life, destruction of infrastructure, and environmental changes in affected areas.
Famous tsunamis, like the 2004 Indian Ocean tsunami and the 2011 Tōhoku tsunami in Japan, remind us of the catastrophic potential of these natural disasters.
History of World Tsunami Awareness Day
World Tsunami Awareness Day was established by the United Nations in 2015, inspired by Japan’s historical experiences with tsunamis. Japan has a long history of suffering from tsunamis and has also developed advanced preparedness techniques over the years. November 5 was chosen to commemorate the story of “Inamura-no-hi” (The Burning of the Rice Sheaves), in which a Japanese villager set fire to his rice stacks as a warning to his neighbors, saving their lives from an impending tsunami. This story has become a symbol of community-driven preparedness, a core principle of World Tsunami Awareness Day.
World Tsunami Awareness Day 2024 Theme
This year’s World Tsunami Awareness Day theme aligns with the International Day for Disaster Risk Reduction, and the Summit of the Future, focusing on “youth and future generations.” The activities planned for the observance aim to commemorate the 20th anniversary of the Indian Ocean Tsunami by passing on its lessons to a new generation of children and youth.
What are tsunamis?
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. After one wave inundates, or floods inland, it recedes seaward often as far as a person can see, so the seafloor is exposed. The next wave then rushes ashore within minutes and carries with it many floating debris that were destroyed by previous waves.
What are the causes of tsunamis?
Earthquakes
It can be generated by movements along fault zones associated with plate boundaries.
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 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 sea floor (up to several metres).
Landslides
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.
Volcanic eruptions
Although relatively infrequent, violent volcanic eruptions also represent impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.
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. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36,417 people.
Extraterrestrial collisions
Tsunamis caused by extraterrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence. Although no meteor/asteroid-induced tsunamis have 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.
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