For the final act of a story I'm building, I'm planning a scene that involves the sudden appearance of fog, along with a small Tsunami, affecting part of the city.

To ask this question, I am going to pose a simplified scenario. Let's say that in the sea we have a submerged object, which I will call Joflu (this is an improvised name at the last minute, don't give it importance). Imagine the Joflu as a sphere 15 meters in diameter, the exact nature of which is irrelevant. Previously in the story, Joflu was exposed to an emission of 12552000 Gigajoules (equivalent to 3 Megatons of TNT), of which it is expected to have absorbed up to 1%, that is to say 125520 GJ, however, we are going to limit it to 0, 25%, so our Joflu stores 31380 GJ. With this said, we establish that Joflu has access to a large amount of energy, but it is not unlimited. It should be noted that you cannot release all this energy together either, but you can do it gradually. Continuing the argument, let's assume that the Joflu has the ability to adapt to harness the energy stored in its body. With this premise, let us establish that when Joflu began his adaptation, the release of energy increased, from a minimum level, to a medium and stable release. However, during the first half of the adaptation process, the release of energy spiked, either due to a higher energy requirement, or due to system failures. I avoid going into details about what form of energy the stored energy belongs to, and the energy released, including the spikes, to give space for more response options.

Finally the stage I wanted to reach. Joflu is submerged at a point with a depth of 55 feet (~17 meters), located 5.4 nautical miles (~10 kilometers) from the coast, and from the coast inland, we have two kilometers of land to the place Where is the observer of this scene? In this extension, we have some obstacles, such as streets, trees, the gradual elevation of the terrain, and small buildings, but in general it is an open terrain. Our observer is in an avenue, at an altitude of 10 meters above sea level. The man is driving his car, on a day like any other, except for his interest in the news of the moment -the previous events in history-, which for him are nothing more than news, like the ones he hears on the radio in that moment, ignoring that the Joflu is 12 kilometers from his location. Simultaneously, the Joflu is adapting to take advantage of its reserves, and has a peak of energy release, 37 seconds later, in the avenue the first effects are felt. Our observer's car shakes slightly but rhythmically, when a rumble, a weak shock wave, reaches the avenue, and the same happens to the other vehicles. Out of a mixture of curiosity and fear of crashing or overturning, he decides to stop his car and get out to look. When doing so, he checks that the noise persists, but the shock wave became a gust of humid wind that carries water vapor. The man does not know what is happening, so he decides to wait a few minutes, during which the blast persists. Eventually, he hears shouts and horns coming from the streets closest to the coast, and as if responding to his doubts, a layer of warm water appears, partially boiling, with a height of no more than 20 centimeters, which, driven by the wind, it is washed inland from the sea, forming what appears to be a small tsunami. Suddenly, in the same way that the event began, the gust of wind stops, leaving a dense layer of fog, which covers several neighborhoods of the city, making visibility difficult.

Since magic does not exist in my story (at least, not that magic), I would not want this phenomenon to happen without a plausible explanation being possible in the real world. One idea I had to explain it was that the energy peak implied the release of heat, with the consequent increase in temperature, causing the evaporation of water. The problem with this is that the releases of large amounts of energy into the sea (for example, a nuclear explosion), at least under normal conditions, do not produce this effect. Another idea I had was a chain reaction, where the spike of energy produced the breaking of the hydrogen bonds of the surrounding water, together with the ignition of the hydrogen. The sudden release and combustion of hydrogen results in an explosion, which apart from breaking a few more hydrogen bonds, boils water, and propagates the steam in the form of shock waves. The second explanation seems to me a little more plausible than the first, but I find some problems with it.

My question, assuming this event isn't too fantastic, is how plausibly could such an event be explained? Alternatively, what changes should I make to make it more plausible?

  • $\begingroup$ Just in case, I would like to point out that I wrote all this in Spanish, and I translated it with Google Translate. Please excuse any grammatical errors. $\endgroup$ Commented Dec 2, 2022 at 21:10
  • $\begingroup$ "how plausibly could such an event be explained" - how this can be physically explained given what you said about Joflu, or what natural explanation a scientist could have come up with? $\endgroup$
    – Alexander
    Commented Dec 2, 2022 at 21:28
  • $\begingroup$ 31,380 GJ is equivalent to 7,500 tonnes of TNT. 10 kilometers is not so very far away. For an idea about the effects of 7,500 tons of TNT going off, you may want to reasearch Operation Big Bang, when, in 1947, the enlightened United Kingdom detonated 6,700 tonnes of ammunitions on the island of Heligoland, as a sort of PR demonstration event. "The tremors could still be felt in Cuxhaven, 70 kilometres away. The mushroom cloud rose about nine kilometres [...] into the air." (Wikipedia.) $\endgroup$
    – AlexP
    Commented Dec 2, 2022 at 21:38
  • $\begingroup$ I wonder how would a wave with a height of 20cm be a "Tsunami" ? If noticed at all, your boiling water wave would crawl up the beach for a few meters, then flow back quickly, cooling down. Maybe I don't understand your text... $\endgroup$
    – Goodies
    Commented Dec 3, 2022 at 2:03
  • $\begingroup$ Alexander: My fundamental idea is to know if this scenario that I thought of for my story makes any sense, if it is plausible from a physical point of view. Within the story, this event is not going to have a direct explanation, there is not going to be a scientist explaining what happened, but I would like what is represented to be plausible in the real world, so that someone can see the work. , and find a natural explanation for this phenomenon, instead of assuming that it just happened. $\endgroup$ Commented Dec 3, 2022 at 5:44

3 Answers 3


Ultrasonic Jittering.

Bear with me...

Ultrasonic sound generated underwater is often used in ponds and water-features to generate surface mist.

It's tricky to find a non-commercial picture or link, so here's a DIY pond-mister project page, and a video demonstration: https://youtu.be/Lxvt25Ke2OI

The high-energy ultra sonics have a secondary effect, they dislodge a large mass of rock in the ocean, perhaps a boulder, perhaps a stratum that's been undermined over time by having softer rock eroded from beneath leaving a shelf.

This rock falling under gravity causes the tsunami - much as was feared might happen on a much larger scale in La Palma, Spain (now thankfully debunked)

  • $\begingroup$ I hadn't thought to explain it with ultrasonics, and had no idea they were used to generate steam in ponds, but within the context of my story, it's a very interesting explanation, even opening the door for a dramatic charging sound. The explanation of the eviction of the stone from the bottom, as the origin of the Tsunami, I should investigate, but I think it is also a good explanation. $\endgroup$ Commented Dec 3, 2022 at 5:47

Move Joflu to just off shore.

mission bay

For example, Mission Bay here in San Diego.

It is a big ask for a 20cm high tsunami of boiling water to start 10 km off shore and still be much of anything once it makes landfall. Consider the energy released by this frisky orb out at sea will itself be spherical and once it is on top of the water, radiate out as a circle, like a ripple. That is a circle with a 10 km diameter and a lot of regular ocean to cool it off as its thinning perimeter moves landward.

You want Jofs to be as close as possible to the observer to maximize the effect it creates. If you had these events take place in the confined, shallow water of Mission Bay, Joflu could very much boil the water and send (at least!) a boiling 20cm ripple in all directions. What you call fog would actually be steam.

Also in favor of Mission Bay is that the dogs of Fiesta Island dog park could be recruited to help deal with the trouble. Along with Shamu.

  • $\begingroup$ For somewhat allegorical reasons, I am using a certain place in the real world, taking the story to another place, particularly in this scene, would cause problems with that meaning. I say this because originally, the real object that I am represented with the Joflu, was located next to the coast when doing this, but after consulting some Nautical Charts, I had to move it. Apart from that, the conditions that I describe are those that can be perceived where the observer is, they do not represent the totality of the phenomenon. $\endgroup$ Commented Dec 3, 2022 at 5:47
  • $\begingroup$ Then again, I probably need to reimagine the Tsunami part, but that's another topic. $\endgroup$ Commented Dec 3, 2022 at 5:47

Underwater nuclear test seems comparable?

I appreciate that you are writing allegorical fiction! I was thinking about blasts 10km off shore. I found this.


wahoo blast

I found this footage of the Wahoo blast which was a nuclear test in open water in the Pacific. Unfortunately the camera pans up and so you cant see how big the waves are. Now that I see this I think 20 cm waves are not outrageous. This footage shows how good such a blast would be for your desired fog. I found this description of the fog or "base surge".


THE VISIBLE BASE SURGE 2.72 As the column (or plume) of water and spray fell back into the lagoon in the BAKER test, there developed a gigantic wave (or cloud) of mist completely surrounding the column at its base (Fig. 2.68). This doughnut-shaped cloud, moving rapidly outward from the column, is called the "base surge." It is essentially a dense cloud of small water droplets, much like the spray at the base of Niagara Falls (or other high water-falls), but having the property of flowing almost as if it were a homogeneous fluid.

2.73 The base surge at Bikini commenced to form at 10 or 12 seconds after the detonation. The surge cloud, billowing upward, rapidly attained a height of 900 feet, and moved outward at an initial rate of more than a mile a minute. Within 4 minutes the outer radius of the cloud, growing rapidly at first and then more slowly, was nearly 3 1/2 miles across and its height had then increased to 1,800 feet

You are not specific about the energy release but the main driver of these undwerwater blast phenomena is the thermal energy. The linked discussion also considers radioactivity as that is what makes the fog etc dangerous at a distance but a non-nuclear energy release should do all the same things as regards movements of water and steam at sea.

I think Wahoo was a fair bit closer than 10 km. I would be interested to read estimates anyone might have after watching the video. When I watch the video the test ships are on the far side of where the blast comes up. It made a wave. I found this account by a cameraman filming the test.


After the shot, it seemed to be a couple of minutes or so before the first wave came in, not very high, and up to that time the water had been quite calm at the beach,” says Bradley. “The first wave came in, then receded. The second wave came in, and a little higher, and also retreated. And the third wave came in, was the highest, and completely covered the island in about 4- to 6-feet high. And after about 10 minutes the water subsided, we could get down out of the tree

A 2 meter wave at (?)5 km could be a 20 cm wave at 10 km I think./ Close enough for fiction!

  • 1
    $\begingroup$ That video changes my perspective. The recordings of nuclear tests at sea that I consulted, showed the steam as a relatively small effect, which was lost within the mushroom cloud, but this video, I suppose thanks to the angle of the camera, shows a lot of steam activity, surprisingly similar to what I have in mind for my story. The fact that the steam "expands" with the second explosion, gives me the idea of chaining a series of peaks, to amplify and extend the effect. I'm thinking of a couple of options for combining the ultrasonics with a series of water boils mimicking the Wahoo Explosion $\endgroup$ Commented Dec 4, 2022 at 23:29

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