---
source: https://iinventedlight.com/library/notes/how-tsunamis-form.md
title: "How tsunamis form (and why they are not tidal waves)"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NOAA, What is a tsunami?, US government work, public domain; NOAA, U.S. Tsunami Warning Centers, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: earth and ocean science"
tags: science, ocean, tsunami, earthquakes
sources:
  - id: S1
    title: "What is a tsunami?"
    publisher: NOAA
    url: https://oceanservice.noaa.gov/facts/tsunami.html
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "U.S. Tsunami Warning Centers"
    publisher: NOAA
    url: https://www.tsunami.gov/?page=tsunamiFAQ
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# How tsunamis form (and why they are not tidal waves)

## Short answer
A tsunami is a series of waves caused by a large, sudden shove of the ocean, most often an undersea earthquake, but also undersea volcanic eruptions and other disturbances. It has nothing to do with tides, so "tidal wave" is the wrong name. [S1][S2]

## Key points
- The word comes from Japanese for harbor (*tsu*) and wave (*nami*). [S2]
- Scientists cannot predict when the next one will strike, but warning centers know which earthquakes are likely to cause one and send alerts. [S2]

## Claims
- id: C1
  claim: A tsunami is a series of waves caused by earthquakes or undersea eruptions.
  source: S1
  evidence: "A tsunami is a series of waves caused by earthquakes or undersea volcanic eruptions."
- id: C2
  claim: Tsunami comes from Japanese characters for harbor and wave.
  source: S2
  evidence: "comes from the Japanese characters for harbor (“tsu”) and wave (“name”)"
- id: C3
  claim: Calling a tsunami a tidal wave is incorrect.
  source: S2
  evidence: "it is incorrect to call a tsunami a tidal wave"

## Sources
- [S1] What is a tsunami?. NOAA. https://oceanservice.noaa.gov/facts/tsunami.html . License: US government work, public domain. Accessed 2026-11-04.
- [S2] U.S. Tsunami Warning Centers. NOAA. https://www.tsunami.gov/?page=tsunamiFAQ . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).