What does an A bomb explosion look like...

[Incubus]

…when detonated deep under water? I know they did some tests in the Bikini Atoll using nuclear weapons at sea, but I couldn’t tell how deep underwater the thing was when it went off. If we were to set one off in the Marianas trench, mad-scientist style, would the flash be visible on the surface? I know the blast is extremely bright, but water absorbs a lot of light (not to mention heat and energy in general). I’m wondering if you could see a bright glow from the surface when it went off.

…from space? What does an A bomb look like on the surface if you were in space when it went off? Have these kinds of observations ever been done?

…IN space? Without gravity, or air for that matter, I imagine the blast would look very different. Would it simply be an expanding, glowing ball that gradually fades out? How much bigger (or smaller?) would the blast effects be without any atmosphere to push around or provide a shock wave?

[pan1]

No light would be visible from the surface of a bomb exploding in the deepest parts of the ocean. Maybe a little flash at the instant of explosion. You’ll even have a little bit to move out of the way of the huge ball of steam that going to leap through the surface. By the time it gets to the surface it may only be a mile or two across. But everything for several miles at the ocean floor would be killed by the shockwave. The shockwave should beat the steam to the surface - meaning a dome of water before it erupts. There are other mechanisms at play here too. I’m sure someone will give better details.

From space. it looks like a flash of light surrounded by a puff of smoke. the light doesn’t last very long.

A nuclear explosion in space would be much both smaller and bigger. The effects would be lesser in any given direction but would be spherical. Again the light wouldn’t last long. I don’t know how the shockwave would propogate without atmosphere. It would, space is not empty, its just sparse,so I don’t know the magnitude. The actual atoms spreading from the explosion would travel a great distance, far more than if it were in an atmosphere. And there would be no dust cloud - just the debris from the non fissile portion of the bomb - mostly in the form of vapor.

[Ranchoth]

@Incubus

…IN space? Without gravity, or air for that matter, I imagine the blast would look very different. Would it simply be an expanding, glowing ball that gradually fades out? How much bigger (or smaller?) would the blast effects be without any atmosphere to push around or provide a shock wave?

It’d look something like this. Purdy.

I can dig up relevant technical details later, if needed.

[mlees]

Operation Wigwam, a US Navy nuclear weapon test, detonated a 30kton device at a depth of 2000 feet.

http://www.dtra.mil/newsservices/fact_sheets/fs_includes/pdf/Wigwam.pdf (3 page PDF)

Operation Wigwam - Wikipedia (Has photo of air bubble rising to surface.)

No statements in either source as to how it looked at the moment of explosion. The water does not appear “lit”. The PDF states that it took ten seconds for the steam bubble from the explosion to reach the surface, and gives dimensions for the water plumes.

It’s possible that at the moment of explosion, there might have been a small flash bulb effect underneath the suspended cable, but that is a completely wild guess on my part.

I guess water really absorbs light. Sunlight only penetrates the top 200 meters or so, I think.

[Polycarp]

The following is a passage from a story written by a nuclear-Navy veteran describing a subsurface nuke explosion (ASROC nuclear depth charge) used by the U.S.S. Long Beach against a flotilla of Soviet subs that had damaged her when the Cold War turned hot in the story’s universe:

“Fire ASROC.” I said, surprised at the way my voice lurched. On the O-1 level amidships, the launcher fired and a rocket streaked away from the ship.

At six miles, a small explosive bolt fired, and the warhead separated from the now-empty rocket. A small parachute retarded the fall of the warhead as it hit the water and began to sink. While this was happening, the ship turned back to the east and accelerated to our maximum speed. With the damage, we could only reach forty knots, but that would have to be enough.

Under the water, four subs passed the spot where the depth charge had hit the water, unaware that their doom was now descending to five hundred feet. They were a mile past that point by the time the depth bomb had reached five hundred feet. Another six subs had closed to within two miles of that point as well as they joined the hunt for our fleeing ship. None of them had any more than a moment’s warning as the depth charge exploded at the prescribed depth.

In the flash of an eye, two square miles of ocean were evaporated in nuclear fire. Ten of the attacking subs were vaporized in that explosion, their crews never even knowing what happened to them. We would later find out that there were another ten submarines in the area. They were all destroyed by the pressure change as the ocean rushed in to fill the hole left by two square miles of evaporated ocean. A tidal wave formed and raced out in all directions.

We were running fast and hard, but not fast or hard enough. The wave had subsided to twenty feet in height by the time it hit us. The stern of the ship was pushed under water and the entire ship shook with the impact. For a moment, I thought we were going to break apart, but we emerged unscathed, although for a moment, eighty percent of the ship had been underwater.

A side effect was that most of the fires in the forward superstructure were put out, but we lost sixteen crewmembers overboard. (from chapter 39 of Do Over, © by Daniel R. Kirk Jr. Considering the length of the full story and the purpose of posting this excerpt, I certify that its use satisfies “fair use” criteria.)

I don’t guarantee the accuracy of it, but it’s probably relatively close to an accurate description of what might happen in such a situation.

[Machine_Elf]

If one were detonated in the Marianas Trench at depths of around 35,000 feet, I have some doubts as to whether the steam bubble would survive the ascent. The initial large steam bubble would break up into smaller bubbles, and in fairly short order would cool enough to condense back into liquid water at those high pressures (~15,000 psi at depth). Hot liquid water might continue to rise, but over the course of the seven-mile ascent it’s likely a lot of mixing would take place that might cool the whole mess down enough so that no steam bubbles would appear at sea level.

Things might change if one moves from a 50-kiloton device (Hiroshima was I think 10-20 kT) to a 50-megaton device (largest ever tested was a USSR-made device that was 58 MT).

[Ranchoth]

@mlees

No statements in either source as to how it looked at the moment of explosion. The water does not appear “lit”. The PDF states that it took ten seconds for the steam bubble from the explosion to reach the surface, and gives dimensions for the water plumes.

From Trinity and Beyond: The Atomic Bomb Movie (which I heartily recommend for anyone following this thread), we have this footage.

No flash that I can see there, and I don’t remember seeing one in the similar French nuclear tests back in the 90s, but if you look carefully at the footage of Bikini Baker—only the third test and fifth nuclear detonation overall—you can see what looks like a flash of light above the surface. However, considering how shallow that test was conducted (only 90 ft underwater), that’s really not surprising, and I would assume it’s the fireball itself breaching the surface.

[kferr]

@Polycarp's quote

In the flash of an eye, two square miles of ocean were evaporated in nuclear fire.

This makes me doubt the writer’s technical knowledge. The effect of an underwater explosion should be measured in cubic units.

[mlees]

@Ranchoth

From Trinity and Beyond: The Atomic Bomb Movie (which I heartily recommend for anyone following this thread), we have this footage.

No flash that I can see there, and I don’t remember seeing one in the similar French nuclear tests back in the 90s, but if you look carefully at the footage of Bikini Baker—only the third test and fifth nuclear detonation overall—you can see what looks like a flash of light above the surface. However, considering how shallow that test was conducted (only 90 ft underwater), that’s really not surprising, and I would assume it’s the fireball itself breaching the surface.

The lagoon was pretty shallow, too. I’m sure that has an effect as well. Wiki says that a lot of irradiated seabed sand got dumped on the test/target ships that were not capsized by the blast. Decontaminating the ships after the shallow water balst proved to be more difficult than anticipated.