A tsunami crossing an ocean is a single thing.
One displacement of the seafloor sends out one train of waves, and by the time that train has run several thousand miles it is remarkably uniform.
Arriving at a coastline, it stops being one thing at all.
Gauges a short distance apart report numbers that have almost nothing in common, and the differences are far larger than any measurement error.
That is not the ocean being inconsistent. The pulse reaching each of them is identical.
What differs is what receives it.
A harbor has a note it wants to ring at
Any enclosed body of water has a natural period, meaning a rhythm at which it sloshes back and forth if disturbed and left alone.
That period is set by the length of the basin and the depth of the water in it, the same way the length of a pipe sets the note an organ plays.
A tsunami is not a single wave but a series arriving over hours, and if the spacing of that series lands near the basin’s own period the energy accumulates instead of dispersing.
Each arriving crest adds to a motion already underway, and the water inside the harbor ends up moving far more than the water outside it.
Miss the period and the opposite happens. The arriving waves fight the existing motion and the basin damps the whole thing down.
Resonance is the entire explanation.
The shape that keeps topping the list
The harbor at the center of this is a long shallow rectangle open toward the north, dredged square and walled on three sides.
That geometry gives it a period that sits close to the spacing of a typical distant tsunami, which is why it has done this before.
It is the place in the islands that routinely records the maximum, event after event, regardless of which ocean the quake happened in.
Harbors a short flight away behave completely differently. Deeper approaches, curved shorelines and open exposures all shed the energy rather than storing it.
A reading of a foot at one of those and a reading of eleven at this one are not in conflict.
They are two different instruments.
Eleven point four four feet and a first ever
The source was a magnitude 8.8 rupture off the Kamchatka coast on July 29 of 2025, one of the largest earthquakes recorded anywhere.
The gauge in the Maui harbor logged a maximum of 11.44 feet from trough to crest, and the water reached 4.49 feet above the normal high tide mark.
That second figure is the one the agency flagged, because it is the highest ever documented at that station.
Elsewhere the same pulse produced 7.42 feet at a northern California harbor, which was the largest anywhere on the continental coast.
Further out it gave 6.25 feet in American Samoa and 2.86 feet in the Aleutians.
The network bought the mainland 8 to 12 hours.
What a gauge reading is not
Peak to trough is a measurement of how far the water surface moved at one fixed point, and it is routinely mistaken for something larger.
It is not run up, which is how high the water climbs on land, and it is not inundation, which is how far inland it goes. Those depend on the slope and the ground and are often several times the gauge figure.
Nor is a gauge guaranteed to survive the event it is recording, in the way that a widely quoted price or a single headline figure gets repeated without the conditions attached.
The largest number in the islands therefore means the largest number a working instrument reported, which is not the same as the largest wave.
Observers at the same harbor described the water drawing down by something closer to fifteen feet at one point, which the record does not carry.
Gauges report what they can.
Why one number cannot run an evacuation
The practical consequence is that no single reading tells a coastline what to expect.
A harbor forty miles away is not a forecast for the harbor you are standing in, and a small first wave says nothing about the size of the fourth or the seventh, which are frequently larger.
What the network does is different and more useful. Each gauge that reports narrows the model as the wave crosses, so the estimate handed to a coast still hours away gets better while the water is still travelling.
That is the argument for maintaining instruments that spend decades recording nothing, as the agency account of the event sets out.
The Maui harbor did not get a bigger tsunami.
It got the same one.
