The Tsunami of Hawaii Five-0 “Kai e’e”

I am in no way affiliated with Hawaii Five-0, but as a disaster specialist and instructor of a university course on tsunami, I can’t refrain from commenting on season 1, episode 15: “Kai e’e”, where the science of tsunami and the functioning of the Pacific Tsunami Warning Center play a central role to the plot.

My attempts to discover if the writers did their own research or got some help from a science consultant are thus far unsuccessful so I don’t know who to credit, but I’m overall impressed. The basics are good, the level of accurate detail is downright impressive, and the scientific mis-steps are mostly acceptable within the context of entertainment. A few details stand out as downright strange, but the level of science is high enough that I’m considering using scenes to promote student discussion my natural catastrophes course.

Tsunami Science

A tsunami is generated by some form of displacement of the water column. This can be subduction earthquakes (moving the sea floor), landslides (under or into water), meteor impacts, or anything else that moves a lot of water rapidly. Like ripples from a stone tossed in a pond, the tsunami will spread from the source in multiple waves. A tsunami consists of multiple waves, both crest and trough.

Warnings and Prediction

Watchstanders at the Pacific Tsunami Warning Center

Watchstanders at the Pacific Tsunami Warning Center

The Pacific Tsunami Warning Center is the central coordination point for detecting and evaluating tsunami hazards for the Pacific Rim, with a secondary center is in Alaska. The center is manned 24 hours a day, 7 days a week, by two scientists (watchstanders) who must make a decision on if an event has likely triggered a tsunami within seconds of the event.

The warning center has pre-generated tsunami propagation models for many trigger scenarios (commonly for subduction earthquakes along the ring) so that when an event is detected, it can be rapidly evaluated for probable risk. Not every eligible event actually triggers a tsunami: the existence of a tsunami is verified by data from the DART buoy system. This data is also used to update arrival times, adjusting models to a particular event.

It is relatively easy to predict tsunami speed, thus arrival times, and incredibly difficult to predict tsunami height. Although we only care about large tsunami, it is possible for a tsunami to come on shore only a few centimeters tall. Wave height can only be verified when a tsunami first comes on shore.

Tsunami at the Shore

Tsunami have wavelengths so large that they act as a shallow-water wave even in deep ocean, so it doesn’t break as it comes onshore. A single wave consists of both crest and trough: in shallow water, this looks like the ocean pulling back exposing sea floor (the trough) and a rapidly rising tide (the crest). The odds are 50/50 that the crest or trough will arrive first. A tsunami consists of multiple waves; the first wave may not be the largest.

Tsunami shoal, slowing down, decreasing in wavelength, and increasing in height as the water gets shallower. In open ocean, a tsunami has a wave height of only a few centimeters, and travels as fast as a jet. Near shore, the waves increase to tens of meters in height, slowing down to freeway-car speeds. The period stays constant, with anywhere from minutes to an hour between crests.

Damage from 1946 seiche in Hilo, Hawaii. Image credit: NOAA

Tsunami can be amplified in semi-enclosed water bodies forming a seiche: waves growing from constructive interference when the wavelength matches the resonance frequency. This means that tsunami damage is often worse in harbours and bays than it is along straight coastlines.

The order of preferred actions for surviving a tsunami are 1. to evacuate inland and uphill, 2. to seek out vertical refuge (getting to the top of a strong, tall structure, or when desperate, climbing a tree), and when all else is impossible, 3. to cling to something that floats.

Science in Fiction

The episode successfully communicated the existence, location, and purpose of the warning center, and did a good-enough-for-entertainment explanation of the tools used and the challenges of tsunami prediction. The only bit that made me sigh in mild exasperation was the plot-necessary one-and-only be-all/end-all key specialist required to interpret wonky data. In reality any pair of watchstanders is totally capable of dealing with inconsistent data (and even accepting only inexperienced graduate students were on-call, all the data could be analyzed remotely by far-away experts). Redundancy and resiliency in all things, including personnel, is a basic part of emergency planning; it’s ridiculous to think that the center would fall to pieces with one person missing.

The chaos in the response room bent plausibility for me. Emergency response experts drill for these moments, and everyone has clearly-defined jobs. Operations centers are places of stress with focused, intense concentration. A more credible portrayal would mirror that of mission control during shuttle launches in space-rocket movies, and I think it’d make for a more striking dramatic background.

I really liked that the tsunami trigger was attributed to a submarine landslide, as that would be something that cannot be directly detected by the existing sensor network (unlike earthquakes, where global seismographic data would need to be falsified).

Steve McGarrett, the locally-raised and tsunami-aware hero character, protests a lack of draw-down proceeding a tsunami as evidence of Something Wonky, which is 50/50 good science and dangerously bad science. Teaching that draw-down = “Run for your life!” can and has saved lives, but a mistaken belief that lack-of-draw-down = safe could conceivably cost lives. Still, considering how many lives have been lost to people curiously exploring suddenly-exposed sea floor and the potential a few viewers might now instead run for high ground, I’ll count it as overall positive.

That ships are safe from tsunami in open ocean (where the wave height is centimeters) was inconsistently conveyed; the navy moved its ships to open ocean yet even with hours of warning the harbour stayed fully occupied with pleasure craft. Considering Hilo’s historic problems with seiche (the 1946 tsunami is a textbook example of the phenomena) I don’t buy that boat owners would leave their property in such risk with so much warning time. This is one of those moments where reality is more compelling than fiction: the shock of an empty harbour would be dramatic on par with a silent space scene. …but it’d probably be budget-bustingly expensive, and filming at waterfront non-harbour locations would be less visually diverse as most episodes already feature a beach scene.

The episode did incredibly well with casual conversation, with the local (and thus presumably tsunami-aware) hero talking about the “first wave” with the implication that a tsunami consists of a series of waves. I was also impressed that the non-local hero Danny “Danno” Williams was both unaware of tsunami characteristics (relative speeds mentioned by his daughter and by the warning center personal) yet took the time to learn local hazards by recognizing that when you have insufficient time to evacuate inland, vertical refuge (flee up a strong, tall building) is a very good idea. I was a bit peeved that the emergency response routes during the frantic driving around town did not feature the appropriate signage, since that would be a nice lesson in “this sign means Authorized Personnel Only during disasters!”, but I would’ve been shocked with the attention to detail if it had.

Having a local refusing evacuation on the premise that they’d survived previous tsunami and thus would survive this one just fine is an excellent representation of one of the common issues with ordering evacuations. This problem is exacerbated when false positives become common, thus why tsunami warnings step up in intensity as the events are first verified and first come on shore.

The use of sandbags to protect against a tsunami just baffled me, although it was a plot-necessary device. Yes, a tsunami appears more like a rapidly-rising tide than it does a perfect surfing crest (because of its incredibly long wavelength, a tsunami is a shallow-water wave even in deep ocean), but a few sandbags really isn’t going to hold it back.

Overall, the episode is a very fun and accurate hook to trigger discussion tsunami science and mitigation.

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