Shallow water. Powerful currents.
Water reaches the lower part of a car. Even a modest depth can carry debris into objects and buildings.
Japan Meteorological Agency · Tsunami questions · NOAA / National Weather Service · About tsunamis
A ScaleTrip science chapter
Tsunami. A different scale of water.
A car. A house. A whole water column. Stay in the same scene and watch the scale change.
Start with what the height means2011 TOHOKU · FROM CAUSE TO LESSON
How did one disaster lead to another?
From moving plates beneath the sea to the loss of cooling at Fukushima. Pause across 12 scenes and follow each cause and consequence.
Loading the scenes. The full illustrated transcript below is already available.
HISTORICAL EVENT · JAPAN STANDARD TIME2011.03.11 · JAPAN
One earthquake. Cascading failures.
On 11 March 2011, a huge earthquake struck off northeastern Japan. Follow the links from movement beneath the sea to inundation on land, and then to the loss of cooling at Fukushima Daiichi.
The 128-second running time is authored for teaching; the actual events unfolded over minutes to days. Coast and plant images are generated illustrations. Flood boundaries, debris paths and reactor cutaways are conceptual, rather than exact geography or an engineering simulation.
Watch the continuous film · English-captioned MP4 2:08 · 720p
A silent educational film with on-screen explanations. Full-screen viewing is available.
Download film · Informed by JMA, USGS, IAEA and NRC sources
Read all twelve scenes and their sources
- 01
One earthquake. Cascading failures.
2011.03.11 · JAPAN
On 11 March 2011, a huge earthquake struck off northeastern Japan. Follow the links from movement beneath the sea to inundation on land, and then to the loss of cooling at Fukushima Daiichi.
Look for the cause first, then the function that failed.
- 02
Moving plates. A locked boundary.
BEFORE · 2011.03.11
Earth’s outer shell is divided into moving plates. At the Japan Trench, the Pacific Plate descends beneath the plate carrying Japan. Friction can hold part of that boundary while the surrounding rock slowly deforms.
Think of a ruler held bent in your hands. Rock also stores energy as it deforms.
- 03
The fault slipped. The seabed moved.
2011.03.11 · 14:46 JST
A large slip on the plate boundary caused the earthquake. Rapid vertical movement of the seabed displaced the water above it, sending long waves outward. JMA reports magnitude 9.0; USGS reports 9.1 using its assessment.
Imagine lifting a broad part of a bathtub floor. The water above it must move too.
- 04
Shutdown stopped fission, not all heat.
2011.03.11 · 14:46 → 14:49 JST
Units 1–3 shut down after the earthquake. Emergency diesels started when off-site power failed. Radioactive decay in the fuel continued producing heat. JMA issued its first tsunami warning at 14:49.
Switching off a stove does not instantly cool the pan. A reactor also continues generating decay heat after shutdown.
- 05
Deep ocean to shallow coast.
2011.03.11 · WAVES TRAVEL
A tsunami differs from a short wind wave. A very long disturbance travels across the ocean. In shallower water its propagation slows, while local depth and coastal shape alter wave height and flow.
Picture a long body of water advancing, rather than a single thin breaking wave.
- 06
Sea water entered everyday places.
2011.03.11 · COASTAL INUNDATION
After overtopping the coast, water spreads across low terrain. In one surveyed part of the Sendai Plain, it reached about 4.5 km inland. That is a horizontal distance, not the depth of the water.
About 45 lengths of a 100 m school field. This observation belongs to a surveyed area; the pictured coast is fictional.
- 07
Water carried debris with it.
2011.03.11 · FLOW AND RETURN
Depth alone does not determine damage. Flow pushes and lifts objects; trees, vehicles and building debris can strike other structures. Returning water also carries debris away. Later waves may be larger, so the first wave ending is not an all-clear.
Still water and fast, debris-filled flow can act very differently at the same depth.
- 08
Flooding disabled linked safety functions.
2011.03.11 · 15:27 / 15:35 JST
Waves reached Fukushima Daiichi at 15:27 and 15:35. Flooding damaged generators, electrical distribution and seawater systems. Multiple units lost power and cooling functions; surviving equipment and response time differed by unit.
Backups cannot fully protect one another if the same flood disables them together.
- 09
Heat needs a path out.
2011.03.11 → 15 · HOURS TO DAYS
Cooling carries heat from fuel into water and then out of the system. If that path cannot be maintained, water heats and evaporates. Without adequate replacement, the level falls and exposed fuel can overheat.
This cutaway shows the principle. Units 1–3 had different systems and accident timelines.
- 10
Fuel in Units 1–3 was severely damaged.
2011.03.11 → 15 · UNITS 1–3
Units 1–3 suffered severe fuel damage and melting. Radioactive releases and evacuation extended the disruption to people’s lives. Unit 4 was undergoing maintenance, with all its fuel in the spent fuel pool.
The core is the fuel region inside the reactor. Damage to Unit 4’s building does not mean a Unit 4 core meltdown.
Japan MOE · Accident sequence · IAEA · Accident report, Vol. 1
- 11
Hydrogen explosions were chemical.
2011.03.12 / 14 / 15
Hot zirconium fuel cladding reacted with steam to produce hydrogen. Building explosions occurred at Unit 1 on 12 March, Unit 3 on 14 March and Unit 4 on 15 March. Hydrogen from Unit 3 is understood to have entered Unit 4 through shared vent connections.
Hydrogen reacting with oxygen is a chemical explosion, not an atomic-bomb-like nuclear detonation.
NRC · Fukushima lessons · Japan MOE · Accident sequence · IAEA · Accident report, Vol. 1
- 12
Prepare people and systems in layers.
LESSONS · PREPARE IN LAYERS
Connect strong or long coastal shaking and official warnings to evacuation action. Protect diverse supplies of power, water and heat removal from a common hazard. Learn local evacuation routes and wait for official return guidance.
One wave ending, one barrier or one backup supply is not the end of preparedness.
Historical and accident sources checked 31 October 2026. Current decommissioning status and dose projections are outside this film’s scope.
Start at the ground to measure flood depth
A classroom floor can sit above sea level. If water covers that floor, the depth above the floor differs from the water’s elevation above sea level. Always mark where the ruler starts.
Work it out, one step at a time
Use the same reference level
water: 5 m; ground: 2 m
Both elevations begin at the same reference sea level.
Subtract to find local depth
5 − 2 = 3 m
Three metres is water above this patch of ground, not a universal tsunami height.
Words made simple
- Runup
- The elevation above reference sea level at the inland limit reached by the water.
Think about it: Two locations have the same water-surface elevation. Must their flood depths match?
No. Different ground elevations produce different local depths. For a real tsunami, follow local warnings and evacuation instructions; these pictures cannot determine safety.
Where the numbers come from: IGN. The illustration and worked model are made for this lesson; assumptions are stated above.
One coast. Seven depths.
Illustrated teaching model
Water above local ground
Scale comparison
Interactive controls become available when the model loads. The explanation and data remain readable below.
A fictional debris-rich scene informed by observations of the 2011 Japan tsunami. Earthquake magnitude and local flow depth describe different quantities. Object release, paths and debris density are authored illustrations. NOAA debris transport · USGS field evidence
Twice the depth. Four times this load.
Isolate the force of still water on one side of a vertical wall. The animation adds visual motion; this calculation considers only the hydrostatic component.
Reproduce the calculation- Gauge pressure at the base
- kPa
- Force per 1m wall width
- kN/m
- Static force versus 1m depth
- ×
“3 metres” can mean three different things.
This chapter controls flow depth above local ground. The diagram separates it from coastal wave height and runup.
- Coastal tsunami height
- The tsunami-related rise above the sea level that would otherwise occur at the coast.
- Ground-level flow depth
- Water above the local ground at a particular inland point. This is the slider’s quantity.
- Runup elevation
- The elevation, relative to reference sea level, at the landward limit reached by the water.
Instituto Geográfico Nacional · Tsunami measurements · Japan Meteorological Agency · Tsunami questions
Scale, exposure, and possible damage
These depths are teaching choices, not official alert levels. The accounts describe possible mechanisms and past observations, not a universal collapse threshold.
The street becomes a waterway.
Doorways and the lower floor are immersed. Construction type matters: JMA describes partial damage to some wooden homes around this inundation depth.
A different scale of structural stress.
JMA reports severe destruction of wooden homes around 2m of inundation in past cases, with large differences between structures and locations.
Japan Meteorological Agency · Tsunami questions · USACE HEC-RAS · Hydrostatic and momentum forces
Look beyond the crest.
A 3m water column reaches a notional storey height. Moving water, buoyancy, debris and erosion act together.
NOAA / National Weather Service · About tsunamis · USACE HEC-RAS · Hydrostatic and momentum forces
Water takes over the lower levels.
Much of the small house lies below the waterline. The same depth can have very different effects on different coasts.
NOAA Ocean Today · Tsunami debris transport · USGS · 2011 tsunami field observations
The house becomes a size reference.
The selected water depth exceeds the height of the 8m house model. A taller building makes the vertical scale visible.
An extreme scale, in one continuous view.
The selected depth approaches the top of the 24m building model. This is a fictional extreme-depth comparison, not a reconstructed event.
A calculation you can check
These are the complete assumptions behind the numerical readouts.
pbase = ρgD
F / b = ∫₀ᴰ ρgz dz = ½ρgD²
D is flow depth in metres; b is wall width. Assume constant density ρ = 1,025 kg/m³ and g = 9.81 m/s², a vertical wall extending through the full depth, still water on one side and a dry opposite side. Readouts subtract atmospheric pressure.
At D = 1m: p ≈ 10.06 kPa and F/b ≈ 5.03 kN/m. At 2m: the static force is ≈ 20.11 kN/m, four times larger. This is not the total loading on a real building: flow speed, impacts, buoyancy, erosion and water inside also matter.
Engineering Statics · Fluid statics · USACE HEC-RAS · Hydrostatic and momentum forces
How the scene is made
A fictional flat street and generated artwork illustrate the mechanisms. Reference heights are chosen model dimensions: person 1.7m, car 1.5m, house 8m and taller building 24m. Vertical sizes use one scale, while horizontal placement is arranged for readability.
The 14s inflow/return and 56s depth journey are presentation clocks. They do not calculate a tsunami travel time, inundation distance, current velocity, building fragility, or a safe elevation. The buildings stay visible as scale references.
In a real event, follow real warnings.
Strong or long shaking, a sudden sea-level change, or a loud ocean roar can be a natural warning. Move to high ground or inland when safe to do so, and follow local officials. Later waves can be larger; return when authorities say it is safe.
NOAA / National Weather Service · During a tsunami · Korea Meteorological Administration
Sources and editorial scope
Sources reviewed for this chapter on 25 October 2026. The physics readouts are reproducible teaching calculations; generated artwork supplies the atmosphere and object textures.
- Japan Meteorological Agency · Tsunami questions
- NOAA / National Weather Service · About tsunamis
- Instituto Geográfico Nacional · Tsunami measurements
- NOAA Ocean Today · Tsunami debris transport
- USGS · 2011 tsunami field observations
- Engineering Statics · Fluid statics
- USACE HEC-RAS · Hydrostatic and momentum forces
- NOAA / National Weather Service · During a tsunami