Tsunami
A tsunami is a series of long-wavelength, high-speed ocean waves generated by the sudden displacement of large volumes of water, most commonly caused by undersea earthquakes, volcanic eruptions, submarine landslides, or meteorite impacts. In the open ocean, tsunamis travel at speeds of 500–900 km/h with barely noticeable wave heights, but as they approach shallow coastal waters, they slow down and dramatically increase in height through shoaling, sometimes reaching heights of 30 meters or more. Tsunamis are among the most destructive natural hazards, responsible for widespread coastal flooding, loss of life, and infrastructure damage.
Key Formula
tsunami speed v = sqrt(g * d)
LaTeX: v = \sqrt{gd}
| Symbol | Meaning | Unit |
|---|---|---|
| v | Tsunami wave speed | m/s |
| g | Acceleration due to gravity (9.81) | m/s² |
| d | Ocean depth | m |
Worked Example
Problem
An earthquake off the coast of Sumatra generates a tsunami in water 4000 m deep. Calculate the wave speed. How long would it take the tsunami to travel 2500 km to Sri Lanka?
Solution
Step 1: Calculate wave speed using shallow-water wave formula: v = √(g × d) v = √(9.81 × 4000) v = √39240 v = 198.1 m/s v = 198.1 × 3.6 = 712.9 km/h Step 2: Calculate travel time: Distance = 2500 km Time = Distance / Speed Time = 2500 / 712.9 = 3.508 hours ≈ 3 hours 30 minutes
Answer
Tsunami speed ≈ 198 m/s (713 km/h). Travel time to Sri Lanka ≈ 3.5 hours.
Major Historical Tsunamis and Their Parameters
| Event | Year | Cause | Max Wave Height | Deaths |
|---|---|---|---|---|
| Indian Ocean Tsunami | 2004 | Mw 9.1 Sumatra earthquake | 30 m | ~230,000 |
| Japan Tohoku Tsunami | 2011 | Mw 9.0 Japan earthquake | 40 m | ~20,000 |
| 1960 Chile Tsunami | 1960 | Mw 9.5 Valdivia earthquake | 25 m | ~1,655 |
| 1964 Alaska Tsunami | 1964 | Mw 9.2 Good Friday quake | 67 m | ~139 |
| 1883 Krakatoa Tsunami | 1883 | Volcanic eruption | 37 m | ~36,000 |
| 1958 Lituya Bay Megatsunami | 1958 | Landslide into bay | 524 m | 2 |
Interactive Tools
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Related Terms
Ocean Wave
An ocean wave is a periodic disturbance at the sea surface in which energy is transferred through the water without the net transport of water itself — water particles move in circular or elliptical orbits as the wave passes. Most ocean waves are generated by wind transferring energy to the water surface through friction and pressure, with wave size depending on wind speed, duration, and fetch (the distance over which wind blows). Ocean waves are critical to coastal erosion, sediment transport, navigation safety, and marine ecosystems.
Tide
A tide is the periodic rise and fall of sea level caused by the gravitational forces exerted on Earth by the Moon and the Sun, combined with Earth's rotation. The Moon's gravity creates a tidal bulge on the side of Earth nearest to it and another on the far side, resulting in two high tides and two low tides in most locations every approximately 24 hours and 50 minutes. Tides are essential for coastal ecosystems, navigation, fishing, and are a significant source of renewable tidal energy.
Coastal Upwelling
Coastal upwelling is an oceanographic phenomenon in which wind-driven surface water is pushed away from the coast, causing cold, nutrient-rich water from deeper ocean layers to rise and replace it at the surface. This process is driven by the combined effects of prevailing winds blowing parallel to the coastline and the Coriolis effect, which deflects the surface water offshore — a process described by Ekman transport. Coastal upwelling regions are among the most biologically productive ocean areas on Earth, supporting major fisheries such as those off Peru, California, and West Africa.
From Japanese "tsu" (harbor, port) and "nami" (wave), literally "harbor wave" — so named because these waves are often unnoticed at sea but become devastating as they enter coastal harbors. The term entered English usage in the late 19th century after major Pacific tsunami events.