Tsunami - Wikiparency

# Tsunami A tsunami is a shallow-water wave no matter how deep the ocean, because its wavelength — often hundreds of kilometres — dwarfs any [[Ocean_current|ocean]] depth, a [[Dimensionless_quantity|ratio]] argument rather than a size one. That single fact explains everything odd about it: it crosses a basin at jetliner speed, passes under a ship almost unnoticed, and then rears up catastrophically at the shore — one wave, three [[Fluid_dynamics|regimes]]. ## Microsim — p5.js Sidecar: `Tsunami.p5.js` · route leaf: `microsim/p5js/Tsunami__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `depth slider` | ocean basin depth | | `shelf slider` | how abruptly the coast shallows | | `[space]` | launch a wave | *What to watch:* Fire the wave and watch it race across the deep basin at speed with almost no height — then slow and rear up as the shelf shallows. Speed and amplitude trade against each other the whole way. ## Speed, then height In the shallow-water regime, speed is set by depth alone, c = √(gh). Over four kilometres of ocean that is roughly 700 km/h; in twenty metres of coastal water it drops to about fifty — [[Gravity|g]] and depth, nothing else. The wave slows, the energy has nowhere to go but upward, and the front piles into itself — shoaling. Amplitude in the open ocean may be under a metre spread across a wave hundreds of kilometres long, which is why it is invisible at sea and why deep pressure [[Sensor|sensors]], not eyewitnesses, are the detection network. ## Not a wind wave [[Wind_wave|Wind waves]] carry motion in a shallow surface layer and their orbits die away with depth. A tsunami moves the entire [[Water|water]] column from surface to seabed, which is why it carries so much [[Energy]] and why it arrives as a prolonged flood rather than a breaking crest. Most are generated by seafloor displacement in an earthquake — a [[Force|impulse]] applied to the whole column; landslides and volcanic collapse produce rarer, locally larger ones — a [[Density]]-driven displacement rather than a tectonic one. The withdrawal of [[Water|water]] before the first arrival is the trough leading — a warning that has saved lives where people knew to read it. **Reads with:** *Introduction to Physical Oceanography (Robert H. Stewart, 2008)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/introduction-to-physical-oceanography) · [download](https://github.com/introocean/introocean-en/releases/tag/v20200229) · CC BY-NC-SA. Section 7 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Wind_wave]] · [[Ocean_current]] · [[Tide]] · [[Geophysical_fluid_dynamics]] · [[WT!Thury_Hydrodynamics_Compendium]].  *Linked from the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]], section 34, Waves and tides.*   **Microsim — three.js (Wikitube framework):** *Tsunami* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Tsunami.html" data-title="Tsunami"></div> *Built from `MICROSIM_GUIDE/specs/variants/Tsunami.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Tsunami) : [Wikitube](https://en.wikitube.io/wiki/Tsunami) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*