How much and how powerful would a "phlebotinium" bomb launched from orbit be to create an artificial sea? [closed]

Question

I am writing a setting for an unspecified goal, whether I will end up doing a video game or a novel out of it all, but I am still working on the worldbuilding aspect.

Lore-introduction, (you can skip it)

In my setting: [please refer to the context links if you are interested]

After the Apocalypse that happened in 2009, renamed the First Apocalypse, a (civil) war has raged on for decades (since after the end of the world, thanks to the surviving pockets of mankind and an untouched, and disproportionately advanced technologically civilization that came from the future (the technology has been lost since*).

It is a civil war between the two major powers, and in as a last-ditch effort by the "Federalist" forces in their war against the "Republicans". The winning guys at the end managed to hack a pre-War orbital bombing platform using said "phlebotinium" (renamed "Nex-Reginium" for a region in space where it is the only place where it appears naturally). For context, the Civil War started in 2040, while the Apocalypse happened in 2009. Two factions within the Federation existed and were rock-solid, the Commandery (which became the "Republicans") and IDS (which became the "Federalists").

Contrary to the three of these warheads used to destroy much of the world, they are minified, and are used to destroy large swaths of territory instead of almost entire continents and without disrupting much of Earth, except where it is detonated.

The Federal forces have lost countless troops, and forces, because the Republican forces foresaw the advance of the Federal forces, as it rallied the pockets of mankind in inhabitable pockets, mainly in Europe - close to London and Great Britain.

The reason behind the use of that "phlebotinum" weapon, which was the last functioning one on the platform Erlösung-6

Spoiler Alert [heh, always wanted to say that], the Federal forces wins thanks to the relatively large alliance made with the pockets of civilizations).

The question

If you refer to this map you can see much of London and its surrounding were obliterated thanks to the Erlösung-6 strike - a Dimensional Weaponry which uses Nex-Regniumum (the name for "phlebotinum" in the setting). It has been completely banned from warfare, it is a war crime, but was done due to aforementioned reasons.

How much TNT-equivalent/ whatever unit of measure would this mean? How much would be the destruction?

*Here are additional questions branching from the same:

• I am also looking for how far the shockwave would travel and even more info. as I am not smart at all about these sort of things. Could you please explain me (in detail if possible, what would advene after this detonation please?*

Here are useful links:

For context

• The [First] Civil War, from 2040 to 2086
• The Archipelago;
• The "Sea of London" - the image

Less relevant context but still relevant:

• The orbital platform that put an end to the [First] Civil War
• "The Republicans" (Incomplete and full of mistakes)
• The "Federalists" (Incomplete and full of mistakes)

PS: The reason for the war crime being committed against the laws put in place after the apocalypse: An enormous mech, capable of launching ICBMs, armed with artillery, anti-infantry, anti-tank, and much other types of weaponry has been discovered in London, as the last trump card of the Commandery. After bloody massacres after bloody massacres from civilians and military alike, the region war quickly overwhelmed and retreat was the only option, as they regain much of the British Peninsula.

Answer 1

10,000 GT TNT

So, it looks like your crater is maybe 100 km radius. (It should really be more circular than you have shown.) I found this article for estimating crater size from near-surface nuclear explosions. For very large explosions, the equation $0.5 V^{0.41} < R < 0.6 V^{0.41}$ appears on page 39 relating volume and radius of the crater. That suggests a crater volume of 300000 km^3, which is about 10^16 ft^3 (the paper deals in ft^3). Now, the paper talks about "cratering efficiency" which is the ratio of crater volume to ton TNT yield of the explosion. This depends on height of burst, which can be negative. Cratering efficiency reaches a maximum of about 10000 for a sufficiently deep underground burst, which for this crater would be about 2 km deep. See figure 16. Let's suppose that the bomb was not somehow exploded 2 km under London, but was rather a surface burst. In that case cratering efficiency is about 1000. So, 1000 ft^3/ton * (yield) = 10^16 ft^3. It follows that yield = 10^13 ton TNT, which is 10,000 gigatons. For those who like SI units, that's 4 * 10^22 J, about 1/1000 or 1/10000 of Chicxulub. Chicxulub had a 90 km radius crater, by the way, smaller than this, but of course Chicxulub was not a surface burst. Of course, this answer may vary several orders of magnitude, depending on the height of burst and the difficulties in extrapolating the paper's crater estimates to such a large explosion.

Answer 2

We have a handy geological example at hand

About 66 million years ago, a large-ish asteroid (about 10 kilometers or 6 miles in diameter) hit the Earth with a velocity of about 20 kilometers per second (12 miles/second). The impact energy was about 72 teratonnes of TNT (72,000,000 megatonnes). It created a crater about 180 km (112 miles) across.

The crater was not the most important effect of the impact; in fact, it was a minor effect. The big problem is all that rock which was suddenly vaporized to make the crater; part of it ignited everything in the world which could be ignited, and the other part of it blocked the sunlight for decades before it finally came down to rest on the ground. As the Fount of All Knowledge says:

• "The impact, expansion of water after filling the crater, and related seismic activity spawned megatsunamis over 100 meters (330 ft) tall, with one simulation suggesting the immediate waves from the impact may have reached up to 1.5 kilometers (0.93 mi) high."

• "The waves scoured the sea floor, leaving ripples underneath what is now Louisiana with average wavelengths of 600 meters (2,000 ft) and average wave heights of 16 meters (52 ft), the largest ripples documented."

• "A cloud of hot dust, ash and steam would have spread from the crater, with as much as 25 trillion metric tons of excavated material being ejected into the atmosphere by the blast. Some of this material escaped orbit, dispersing throughout the Solar System, while some of it fell back to Earth, heated to incandescence upon re-entry. The rock heated Earth's surface and ignited wildfires, estimated to have enveloped nearly 70% of the planet's forests."

• "This global dispersal of dust and sulfates would have led to a sudden and catastrophic effect on the climate worldwide, instigating large temperature drops and devastating the food chain. [...] he emission of dust and particles could have covered the entire surface of Earth for several years, possibly a decade, creating a harsh environment for living things. [...] Photosynthesis by plants would also have been interrupted, affecting the entire food chain."

And, of course, it killed all the large dinosaurs, allowing the small furry mammals to take over the world, and, in the fullness, post questions of Worldbuilding Stack Exchange about such large explosions.