Tsunamis Part 1

Week 6 Overview

  • Focus on tsunamis, a major natural hazard caused primarily by underwater earthquakes.
  • Review video lectures on Canvas covering the following topics:
  • Wave characteristics: amplitudes, height, and differences between tsunami waves and regular waves.
  • Mechanisms leading to tsunamis, specifically how earthquakes cause them.
  • Wave speed and behavior as tsunamis approach land.
  • Safety precautions to take during a tsunami event.

Exam Preparation

  • No reflection assignment this week, focus time on reviewing material and preparing for the exam next week.
  • Check the syllabus for specific details about the exam format, timing, and accommodations.
  • Detailed announcements will be released alongside lectures. Read them carefully for all necessary information.
  • A study guide for the exam will be available on Canvas by Wednesday.
  • Teacher will be available for questions via email or in-person on Monday from 2 to 3 PM in Penny Hall.

Understanding Tsunamis

  • A tsunami is a series of water waves caused by a large displacement of water, typically due to underwater earthquakes.
  • The term "tsunami" originates from Japanese:
  • "Tsu" means harbor
  • "Nami" means wave
Formation of Waves in Water
  • Ocean Waves:
  • Caused primarily by wind; the friction between wind and water creates waves.
  • Waves have a crest (highest point) and a trough (lowest point).
  • Definitions:
    • Wave Height (h): Vertical distance from crest to trough.
    • Wavelength (l): Distance between two consecutive crests.
  • Factors influencing wave size:
    • Wind velocity
    • Duration of wind blowing
    • Size of the water surface affected by the wind
    • Consistency of wind direction
  • Energy from the wind creates circular motion in water, but water itself doesn't travel with the wave.
Behavior of Waves in Shallow Water
  • As waves approach land and enter shallower water:
  • The wave slows down, and its wavelength decreases.
  • Energy gets concentrated, increasing wave height.
  • Waves break when the height-to-wavelength ratio reaches about 1.7.
  • Sea Swells:
  • Produced when waves from different storms interfere with one another.
  • Constructive and destructive interference can lead to larger or smaller swells.
  • Rogue Waves: High waves formed by synchronized smaller waves, can be extremely dangerous.

Differences Between Tsunami Waves and Regular Wind Waves

  • Regular Wind Waves:
  • Speed: 10 - 20 mph
  • Height: Approximately 10 feet
  • Wavelength: About 300 feet
  • Tsunami Waves:
  • Speed: 450 - 650 mph (much faster)
  • Height: 20 inches to 1.6 feet
  • Wavelength: Long, exceeding 316,800 feet.
  • Wave Period:
  • Tsunamis have longer wave periods, meaning the time between crests can exceed one hour due to their long wavelengths.
Summary of Tsunami Characteristics
  • Tsunamis have long wavelengths, high speed, and can travel great distances across oceans.
  • Understanding the mechanics and differences of wave behavior is crucial for effective preparation and safety during tsunami events.