TC

Tsunami Study Notes

Environmental & Geologic Hazards

Topic 6: Tsunamis

Chapter 4: Tsunamis

Professor: Dr. Pat Harris
This section discusses the phenomenon of tsunamis, focusing on their generation, historical impacts, and preventive measures.

1. Definition of Tsunami

A tsunami is defined as a large harbor wave, which can cause significant destruction when it reaches land.

2. Tsunami Generation

2.1 Causes of Tsunamis

Tsunamis can be generated by several natural events which include:

  • Earthquakes: Responsible for 73% of tsunamis.

  • Volcanoes: Account for 27% of tsunamis, which may also include undersea eruptions.

  • Landslides: Large landslides, either underwater or from the shore, can also trigger tsunamis.

  • Meteorological events: Certain weather phenomena can generate local tsunamis.

3. Historical Case Study: The 2004 Indian Ocean Tsunami

3.1 Overview

On December 26, 2004, a magnitude 9.2 earthquake (the 3rd largest recorded) struck 155 miles southeast of Banda Aceh, Sumatra, Indonesia. This earthquake generated a devastating tsunami.

3.2 Impact of the 2004 Tsunami

The resulting tsunami caused widespread destruction across multiple countries, including:

  • Indonesia

  • Thailand

  • Sri Lanka

  • India
    The tsunami resulted in a catastrophic loss of life, with approximately 230,000 fatalities recorded.

4. Characteristics of Tsunamis Approaching Land

As a tsunami approaches land, the water column height increases. This occurs because the wave runs out of accommodation space below the water's surface, leading to significant elevation of the wave.

  • Specifically, the tsunami generated from the 2004 earthquake was about 10 meters high when it made landfall.

5. Key Questions Regarding Tsunami Events

Several questions arise concerning the 2004 tsunami:

  • Why did it cause destruction over the entire Indian Ocean?

  • Why did it occur where it did?

  • Could people have been warned effectively?

  • What are the chances of a similar event occurring again?

  • What are the chances of it happening in the Gulf of Mexico?

6. Post-tsunami Analysis

6.1 Shift in Land Levels

Following the tsunami, Banda Island exhibited significant changes:

  • The northwestern coast of Sumatra experienced 1 to 2 meters of subsidence as a direct consequence of the earthquake and tsunami.

6.2 Follow-up Events

On July 29, 2025, a separate magnitude 8.8 earthquake occurred in Kamchatsky, Russia.
Questions persist regarding potential tsunami effects from this region.

7. Tsunami Hazards

Many modern, heavily populated cities are located along coasts that are at risk for tsunamis, including:

  • Australian Coast

  • Chilean Coast

8. Minimizing Tsunami Hazard

8.1 Early Warning Systems

To mitigate the impact of tsunamis, various strategies have been implemented, including:

  • The establishment of tsunami buoys linked to the Pacific Tsunami Warning Station. These buoys are designed to detect wave heights and provide timely warnings to at-risk areas

9. Conclusion

Understanding tsunamis involves studying their causes, historical impacts, and ongoing efforts to minimize future risks. Continuous advancements in detection and warning systems are critical to reducing potential casualties occurred by tsunami events.