Unit 1 Introduction to Tsunamis

1 Introduction to
2 Tsunamis of
   the Past
3 Plate Tectonics
4 Tsunami Generation
5 Tsunami Propagation
6 Tsunami Inundation
7 Tsunami Aftermath
   and Response

1.1 Introduction to Tsunamis



In this unit, find out what a tsunami is, what causes a tsunami, and signs and forewarnings of an impending tsunami.

Knowledge of tsunamis can be shared at school, through legends,
stories, and experiences. When the experience of past tsunamis is remembered, loss of life and property can be prevented.

  • Essential question: What is a tsunami?                                                                  Click image to enlarge
  • Enduring understanding: A tsunami is a series of waves caused by a massive displacement of water most often caused by an undersea disturbance, such as an earthquake, landslide or volcanic eruption. Tsunami education will increase understanding of Earth’s geologic processes and help prevent loss of life and property.





1.2 What's in a Name?

A scientist defines the word tsunami

Tsunami, a Japanese Word

“Tsunami” is Japanese for harbor (tsu) wave (nami). Japanese writing is made with characters that symbolize ideas and others that symbolize sounds. The word tsunami is made with characters that symbolize ideas. The term is appropriate, because a tsunami, a series of waves caused by an undersea disturbance, such as an earthquake, landslide or volcanic eruption, can cause great destruction along low-lying coastal areas. Historically tsunamis often have been called “tidal waves.” However, tsunamis are not caused by the tides.

Hawaiian Words for Tsunami

In the United States, indigenous people in coastal communities have had long histories with tsunamis. Hawai‘i’s native language and legends contain many terms for sea, ocean, waves, tsunamis, floods, and even different parts of a wave are identified and embodied by specific deities.

In the Native Hawaiian language, kai means ocean, and there are several terms that describe tsunamis. Some Native Hawaiian terms for tsunamis include kai a Pele (literally, sea of Pele); kai e‘e, a term for giant tsunami waves; manawahua kai ko‘o, anther term for tsunamis that also describes the agitation of the sea with wind blowing in the opposite direction of the sea current kai mimiki or kai mihi refers to the withdrawal of water before the wave strikes; mimiki also refers to the collision of one returning wave with another.

A kai ho ‘e‘e, or “mounting” sea, is a term used if the sea rises and then withdraws. If the land is covered by the sea, it is kaiakahinali‘i (the sea caused by Kahinali‘i, or the sea that made the chiefs, or ali‘i, fall down, hina). Another flood from mythological times, described in a chant and different from kaiakahinali‘i, is called the kai o Kahulumanu or kai a ka hulumanu.

Click image to enlarge

1.3 What Causes a Tsunami?


Click below to learn more



A tsunami is a series of waves caused by an undersea disturbance. The most common source of a tsunami is an earthquake or landslide. Less frequent sources include undersea and near-ocean volcanic activity. 


Undersea earthquakes often result when tectonic plates collide.
One plate is forced below another or subducted, this area is
called a subduction zone and is usually marked by a deep ocean trench. If one plate gets dragged downward with the other plate,
an earthquake can be produced as the subducting plate bounces back upward. A great volume of water can be displaced, producing massive tsunami waves.



Tsunamis may be produced by land sliding into the ocean from above
sea level or by landslides occurring completely under water. The large volume of water that is suddenly displaced produces a tsunami.



    Volcanic activity can generate local tsunamis in three ways:
1.) an undersea explosion;
2.) production of pyroclastic flows, dense clouds of heated gases and
    debris, which displace ocean water; and
3.) collapse of an undersea caldera, or mouth of a volcano.


Other Causes

Other causes of tsunamis are more rare.
They include but are not limited to:

· Meteorite impacts from space of sufficient size and force
· Human-caused explosions

1.4 Where Do Tsunamis Occur?

Click on the map to see where
tsunamis occur


Low-lying Coastal Areas are Vulnerable

Tsunamis can occur in any low-lying coastal area at any time of day or night. Most tsunamis are produced in the Pacific Ocean as the result of geologic activity. Worldwide, an average of two tsunamis per year inflict damage near the source. About every 15 years, a destructive,
ocean-wide tsunami occurs.

1.5 Tsunami Warning Signs

Play the Tsunami Warning Signs Game


Is there any way to know a tsunami is about to occur? Observing sudden
changes in the environment, especially the ocean, can indicate an impending tsunami. Additionally, warning systems are designed to alert people of possible danger. In the event of these warnings, take
immediate action, and move to higher ground.

Examples of Tsunami Warning Signs

  • An earthquake: swaying buildings and trees or trembling ground
  • Water suddenly surging inland
  • An unusually low or receding waterline
  • Eerie silence along a coast instead of the usual sound of surf
  • Sucking, hissing, bubbling and boiling may be heard as rocks, pebbles and water are drawn out to sea
  • Unusual bubbles in the water
  • Exposed seafloor for hundreds of feet
  • Warning broadcast from a low flying aircraft
  • Warnings from Emergency Broadcast Systems
  • Sirens
  • Telephone calls
  • Text messages
  • Radio alerts
  • Television alerts


1.6 Tsunami Education

Education combined with natural or official warnings helps people know what to do in the event of a tsunami. Here are two survivor stories that tell how people took heed of a tsunami warning and knew what to do, because they had studied tsunamis in school and practiced evacuations.

Reading the Signs

Click to enlarge

  • Principal Evacuates Students, Saves Lives
       Tutuila Island, American Somoa
  • Itai Lilo, the High Talking Chief, or tulafale sili, the acting ambassador to those visiting his village, Poloa, tells of the local school principal’s decision to quickly evacuate students after an earthquake instead of eating breakfast. The tsunami waves destroyed the school, but the students were saved.

    The take-home message is that education is necessary for natural or official tsunami warnings to be effective. When a warning is given, take action!

  • Ancient Stone Markers Save Lives
  • Ancient stone markers along the coast of Japan are tsunami warnings carved by the ancestors of local residents. Some were carved 600 years ago. People tend to forget the lessons learned from past tragedies, so the markers were made to help people remember. Makers of the stone marker system made the best use of technology available at the time. One tsunami stone reads, “If an earthquake comes, beware of tsunamis.”

    In Aneyoshi, Japan, residents were prepared for the tsunami that struck after the March 11, 2011 earthquake. Yuto Kimura, age 12, spoke to the Associated Press and guided a recent visitor to the tsunami stone that protected his village. “Everybody here knows about the markers. We studied them in school,” he said. “When the tsunami came, my mom got me from school and then the whole village climbed to higher ground.”

    The stone slab in Aneyoshi reads, “High dwellings are the peace and harmony of our descendants. Remember the calamity of the great tsunamis. Do not build any homes below this point.”

    1.7 Review

    Take the following practice quiz to review content covered in Unit 1.
    1. What are the most common cause(s) of tsunamis?

    1. Which geologic process is responsible for creating the most powerful tsunamis?

    1. Where do most earthquake-generated tsunamis originate?

    1. When can tsunamis occur?

    1. Water along the coast may recede before an approaching tsunami, exposing the ocean floor. Select the answer that best describes the above statement.

    1. Given the fact that tsunamis are comprised of multiple waves, what is important to remember in the event of a tsunami?

    1. Knowledge from past tsunamis can help us remember what to do in the event of a tsunami. Select the answer that best describes something that might help reduce casualties in the event of a tsunami.

    1. Select the answer that best describes what causes a tsunami.

    1. Knowledge about past tsunamis can be transmitted to serve as a warning for future generations. Why are methods like telling stories and the placement of stone markers with carved warnings helpful? Select the answer that best answers the question.

    1. What does a tsunami warning system need to be combined with to be successful at saving lives? Select the best answer.