Unit 2 Tsunamis of the Past

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

2.1 Ways of Knowing


Overview

This unit discusses different ways to learn about tsunamis of the past. Accessing and valuing different knowledge systems or ways of knowing can enrich a learner’s way of looking at and understanding the world. Increasing the diversity of how information is presented helps make knowledge acquisition an active and creative process.

  • Knowledge about tsunamis is passed down through oral traditions that include stories and chants containing important information that explains natural phenomena.
  • Interviews with survivors and written accounts of survivor’s experiences are cultural artifacts that help us remember to heed natural and official warnings.
  • Breakthroughs in science help us learn about tsunamis of the past by giving us tools to analyze and date layers of soil and deposits left behind, even in areas where there is no living memory of tsunamis having ever occurred.

Essential question: What are effective ways to learn about tsunamis?
Enduring understanding: People can learn about tsunamis of the past by studying tsunami legends, survivor stories and physical evidence. Cultural knowledge passed down through stories and chants conveys tsunami wisdom gathered over centuries. In some coastal areas, residents believe tsunamis will not affect them because there is no living memory of tsunamis; however, physical evidence can show tsunamis have occurred in the past.

Explore Native Ways of Knowing
and Western Science


 


2.2 Hawaiian Tsunami Legends


Two Ways of Looking at Tsunamis

Click on the Multimedia Below to Learn About Hawaiian Tsunami Mythology and Indigenous Knowledge

 

 

 

 

 

 

A long time ago people were taught to pay attention to what is usual and what is out of the ordinary in the natural world. In Hawai‘i, people were taught to be aware of unusual behavior in the ocean as a message or warning from kūpuna, or ancestors
(ha‘ailona).

Deities and their stories are one way tsunami science is taught in Native Hawaiian culture. Many deities are tied
to and said to embody specific physical phenomena. Some Native Hawaiian deities represent how tsunami waves behave,
for example.




2.3 Local Tsunamis


Tsunamis can be generated locally or at a great distance. Locally generated tsunamis happen quickly.The earth shaking and other natural warnings may be the only signs to evacuate the coast and move to high ground.

In 1975, a large earthquake off the southeast coast of Hawai‘i Island caused a tsunami that resulted in two casualties and 19 injuries at Halapē, a secluded cove used by campers south of Hilo. Some of the campers moved closer to the shoreline following a foreshock that caused rock falls, and all were engulfed by the tsunami created by the major quake that followed just over an hour later.

1975 Earthquake and Tsunami Survivor Stories

 

Listen to a 1975 Tsunami Survivor Story

In 1975, two earthquakes off the southeast coast of Hawai‘i Island caused a tsunami that resulted in two casualties and 19 injuries at Halapē, a secluded cove used by campers along the coast of Hawai‘i Island, south of Hilo. The campers had very little time to react between a second quake and the subsequent tsunami.


 


2.4 Teletsunamis


Generally, teletsunamis, or ocean-wide tsunamis from far away, are more hazardous than locally generated tsunamis. Major subduction zone earthquakes release great amounts of energy that displace water, creating tsunamis that travel all the way across the ocean, potentially causing damage along many coasts.

 

Hawai‘i at the Center

Tsunamis generated in Russia, Japan, Alaska, and as far away as Chile
have all caused damage somewhere in Hawai‘i.



April 1, 1946 Tsunami

Often called the April Fool’s Day tsunami, the 1946 tsunami generated
in Alaska caused extensive damage and loss of life in Alaska and Hawai‘i.
In Hawai‘i 159 lives were lost. The Big Island suffered the greatest
damage and loss of life. Ninety-six lives were lost in Hilo and 24
students and teachers died in Laupāhoehoe that day. Many survivor
stories describe natural warnings that people did not know how to
interpret. The tragedies of this day and those from later tsunami
events underscore the need for education and warning systems.




2.5 Paleotsunamis









Buried Evidence

Tsunami deposits from long ago provide opportunities to better understand future tsunami dangers. Large tsunami waves transport and deposit marine sediment and debris far inland. Over time, natural processes bury these sediments and preserve them in the geologic record that can be investigated.

Research Tool

One tool researchers use to investigate evidence of past tsunamis is a soil profile pit, a large hole with straight sides to allow for layer comparisons. Tsunami deposits lack decomposed organic matter and are lighter in color than many soil types, resulting in alternating black and white bands clearly visible in the soil profile.

How Old?

If the soil above or below the tsunami deposit contains organic material, scientists may use radiocarbon dating to estimate the age of the event. In locations lacking organic soils, evidence of past tsunamis may be observed as marine rocks and corals that have been transported beyond the range of storm surges. These clues are used by scientists to estimate when the tsunami occurred and the distance the tsunami traveled inland.

How Large?

Scientists also investigate the size of tsunami waves by studying the size of sediment deposited by tsunamis. Tsunami waves lose energy as they move inland and elevation increases. As wave velocity decreases, large debris such as boulders or cobbles fall out of the water column sooner than small sediment such as sand or silt. Because of this, large debris layers are found closer to the ocean than sand or silt layers. By measuring the size and distance of transported sediment, scientists learn about the velocity and height of past tsunamis.

Why Study Paleotsunamis?

Studying past events allows communities to make informed decisions when building homes and infrastructure to mitigate effects from future tsunamis. Evidence of inundation, run-up and frequency of past tsunamis allows researchers to estimate the severity of future events.


2.6 Past and Present


A Tsunami Chant How can science, survivor stories, legends and chants help students pass on what they learn to their families and communities about what to do before, during and after a tsunami?

Carrying the memory of lessons learned is made easier with the tools of science and culture that help us to understand and remember. The tools of science can be used to understand the physics of tsunami generation, propagation and inundation. Lessons can be learned from the experience of survivors and the knowledge passed down through oral traditions.

Studying the tsunamis of the past, both recent and distant, through historical records that include the stories in the sediment, legends and chants and survivor interviews will allow individuals and communities to make informed decisions on how to plan for and respond to tsunamis.

  Download the Chant



2.7 Review


Take the following practice quiz to review content covered in Unit 2.

  1. What characteristic(s) do indigenous knowledge and western science knowledge systems share?





  1. How can Hawaiian deities and legends help teach tsunami science?
    Certain deities explain why tsunamis occur.




  1. What is a Hawaiian word that describes the flooding or inundation from a tsunami?





  1. Why did some communities survive devastating tsunamis even though there was no official tsunami warning system in place?





  1. Why should residents of Hawai'i be aware of geologic activity along the coasts of Chile, Russia, Alaska and Japan?





  1. Approximately how long does it take the first wave from a tsunami generated in Alaska to reach the Hawaiian Islands?





  1. What is a teletsunami?





  1. What is a feature of locally generated tsunamis?





  1. What is one way scientists differentiate tsunami deposited sediment from organic soil?





  1. Why is it useful to study past tsunamis?