Model Answer
0 min readIntroduction
Tsunamis, derived from the Japanese words ‘tsu’ (harbor) and ‘nami’ (wave), are a series of powerful ocean waves caused by large-scale disturbances. While often mistakenly called ‘tidal waves’, tsunamis are unrelated to tides. The Indian Ocean Tsunami of 2004, triggered by a 9.1-9.3 magnitude earthquake off the coast of Sumatra, Indonesia, tragically highlighted the devastating impact of these waves, causing over 230,000 fatalities across 14 countries. Understanding the characteristics of tsunami waves is paramount for effective hazard assessment, early warning systems, and mitigation strategies.
Tsunami Wave Characteristics
Tsunami waves exhibit unique characteristics throughout their lifecycle, which can be broadly categorized into three phases: generation, propagation, and inundation.
1. Generation Phase
Tsunamis are most commonly generated by underwater earthquakes, particularly those occurring at subduction zones where one tectonic plate slides beneath another. Other causes include volcanic eruptions, landslides (both submarine and coastal), and, rarely, meteorite impacts. The vertical displacement of the seafloor is the primary driver of tsunami formation. The amount of displacement directly correlates with the initial wave height.
2. Propagation Phase
Once generated, tsunami waves propagate outwards in all directions from the source. Several key characteristics define this phase:
- Wavelength: In the deep ocean, tsunamis have extremely long wavelengths, often exceeding 200 kilometers. This is significantly larger than typical wind-generated waves.
- Wave Height (Amplitude): In the deep ocean, wave height is relatively small, typically less than one meter. This makes them difficult to detect by ships.
- Speed: Tsunami speed is directly related to water depth. In the deep ocean (depth ~4000m), they can travel at speeds exceeding 800 kilometers per hour, comparable to a jet aircraft. The formula for tsunami speed (v) is v = √(g*d), where g is the acceleration due to gravity and d is the water depth.
- Energy: Despite their small height, tsunamis carry immense energy due to their long wavelength and high speed.
3. Inundation Phase
As a tsunami approaches the coastline, the water depth decreases. This causes several changes:
- Speed Reduction: The wave slows down due to the decreasing water depth.
- Wavelength Decrease: The wavelength shortens as the wave approaches the shore.
- Wave Height Increase: Crucially, as the wave slows and its energy is compressed into a smaller volume, the wave height dramatically increases. This process, known as shoaling, can result in waves reaching heights of 30 meters or more.
- Run-up: The maximum vertical height above sea level reached by the tsunami wave is called the run-up.
The impact of a tsunami on a coastline is also influenced by:
- Coastal Topography: Bays and inlets can focus tsunami energy, leading to higher run-up heights.
- Bathymetry: The underwater topography (shape of the seafloor) influences wave refraction and energy distribution.
- Vegetation: Coastal vegetation, such as mangrove forests, can provide some degree of protection by dissipating wave energy.
| Characteristic | Deep Ocean | Near Shore |
|---|---|---|
| Wavelength | >200 km | < 20 km |
| Wave Height | < 1 m | > 30 m (can be much higher) |
| Speed | > 800 km/hr | < 50 km/hr |
Conclusion
Understanding the characteristics of tsunami waves – their generation, propagation, and inundation – is vital for developing effective early warning systems and mitigation strategies. The dramatic changes in wave behavior as they approach the coast highlight the importance of accurate bathymetric data and coastal vulnerability assessments. Continued research and international collaboration are essential to minimize the devastating impact of future tsunamis, particularly in vulnerable regions like the Indian Ocean and the Pacific Ring of Fire.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.