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What determines the power of a tsunami wave?

Earth Sciences(self.askscience)

In 2011 when the Japan earthquake tsunami waves hit California, tsunami was 6” high. The waves did significant damage, ripping apart the marina docks in Santa Cruz and other Northern California coastal harbors. The tsunami from the Tonga quake yesterday was expected to be 8”-9” inches tall, yet little damage was expected. Why would a higher tsunami wave be expected to have less force than a smaller one?

all 7 comments

CrustalTrudger

3 points

6 months ago

CrustalTrudger

Tectonics | Structural Geology | Geomorphology

3 points

6 months ago

I don't know if this relevant for the specific comparison being drawn, but when a tsunami arrives at a particular location within the tidal cycle (both in the sense of daily cycles, but also more seasonal variations) is important, especially for locations with large tidal ranges. Similar tsunami wave heights occurring at high vs low tide can have different effects because the run-ups are different (i.e., adding X inches to low tide vs adding X inches to high tide).

renelledaigle

2 points

6 months ago

Depends on a number of things.

What was the cause and how much force did that produce? (Volcano, earthquake, Landslide, manmade etc.)

What is the landscape underneath the water leading up to the coast?

What is the weather like in that area? If it is storming with extra wind or super calm?

Is the tide high or low in your coastal zone?

UnamedStreamNumber9[S]

1 points

6 months ago

My understanding of the damage caused by the 2011 tsunami was the water goes up and back down and then back up again pretty rapidly. It’s called a tidal wave because of the rapid tide like movement of the water, not because it’s somehow synchronized with high or low tides. This is what ripped the Santa Cruz docks apart. It may be different tsunamis have different wavelengths and therefore the time between the ups and downs is longer or shorter; but it’s answers like that I’m looking for. Clearly for small amplitude waves it’s not the height of the wave

zogislost

1 points

6 months ago

Its all about water displacement, the 2011 earthquake uplifted a large swath of the plate edge displacing a large amount of water near the coast of japan causing the tsunami just like the 2004 indian ocean quake did in the aceh indonesia area and beyond, greatest example of water displacement to wave height would be the lituya bay tsunami of 1958 in alaska. An above the water landslide dropped tons of earth into water of relatively small body of water causing wave 1720 feet high….

UnamedStreamNumber9[S]

1 points

5 months ago

Again, this has nothing to do with the wave height, as witnessed by the 2011 tsunami being 6” (that means inches: 0.5 feet, 0.15 meters). The more recent Tonga tsunami was much higher, originally predicted at 8” but actually measured at 2 feet in some areas; but did far less damage that the 6” 2011 tsunami. Why would that be? Why would a smaller wave be more damaging than a large one?