What are Tsunamis? How and where are they formed? What are their consequences? Explain with examples. (Answer in 150 words)

How to Approach

The approach for this 10-mark, 150-word question must be highly structured and concise. Start with a precise definition of a Tsunami. The body must clearly segregate and address the 'how' (mechanism) and 'where' (geographical context) of formation, followed by the 'consequences'. Conclude by citing specific, impactful examples to meet all parts of the demand within the strict word limit. Focus on keywords like 'seismic activity', 'plate boundaries', and 'Ring of Fire'.

Model Answer

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Introduction

Tsunamis, derived from the Japanese meaning 'harbour wave', are a series of colossal ocean waves caused by the rapid, large-scale displacement of a significant volume of water. This phenomenon is a major natural hazard, often resulting from sudden geological events beneath the ocean floor, setting the stage for widespread coastal destruction.

Tsunami Formation: How and Where

Tsunamis are primarily generated by sudden vertical displacement of the seafloor, most commonly due to:

Submarine Earthquakes: Megathrust earthquakes (usually $>7.0$ magnitude) at convergent plate boundaries (subduction zones) are the main trigger.
Other Causes: Large underwater landslides, volcanic eruptions, or meteorite impacts.

They occur most frequently along the **Pacific 'Ring of Fire'** due to its high concentration of active subduction zones. In the deep ocean, the waves travel at jet-plane speeds but have low height; as they approach the coast, friction with the rising seafloor causes them to slow down, leading to a massive increase in wave height (shoaling effect).

Consequences and Examples

The consequences are catastrophic:

Massive coastal inundation, loss of life, and destruction of infrastructure.
Salinization of freshwater sources and agricultural lands.
Severe coastal erosion and destruction of marine ecosystems like coral reefs and mangroves.

Examples: The devastating **2004 Indian Ocean Tsunami**, triggered by a megathrust earthquake off Sumatra, affected 14 countries. Similarly, the **2011 Tōhoku Tsunami** in Japan highlighted the need for robust coastal defence mechanisms.

Conclusion

Tsunamis represent a critical geophysical hazard, demanding comprehensive mitigation strategies. While geological causes cannot be prevented, the scale of devastation can be significantly reduced through the implementation of advanced, multi-hazard early warning systems, strict adherence to coastal zone regulations, and continuous community-level disaster preparedness drills.

Answer Length

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Additional Resources

Key Definitions

Shoaling Effect

The phenomenon where the speed of a tsunami wave decreases as it enters shallower water, causing its wavelength to shorten and its amplitude (height) to increase dramatically.

Megathrust Earthquake

The largest type of earthquake, resulting from the sudden slip and release of accumulated strain between two tectonic plates along a subduction zone.

Key Statistics

The 2004 Indian Ocean Tsunami is estimated to have killed approximately 230,000 people across 14 countries, making it one of the deadliest natural disasters in recorded history. [cite: N/A - General Knowledge]

Source: Historical Records

The 2011 Tōhoku earthquake and tsunami registered a magnitude of 9.1, making it the most powerful earthquake ever recorded in Japan and the fourth most powerful in the world since modern record-keeping began in 1900. [cite: N/A - Geological Survey Data]

Source: USGS/Global Seismological Data

Examples

2004 Indian Ocean Tsunami

Caused by a magnitude 9.1–9.3 earthquake off the west coast of northern Sumatra, Indonesia. The wave travelled across the Indian Ocean, causing destruction as far away as the east coast of Africa.

Pacific Tsunami Warning Center (PTWC)

Established in Hawaii, it monitors seismic activity across the Pacific basin to issue timely warnings to member states regarding potential tsunami threats.

Frequently Asked Questions

▶Are tidal waves the same as Tsunamis?

No. Tidal waves are caused by the gravitational pull of the Moon and Sun (tides), while Tsunamis are caused by sudden geological displacements.

Topics Covered

GeographyEnvironmentDisaster ManagementTsunamisOceanographyNatural DisastersGeology

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