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Background:

  • A peak-ring crater is a sub-type of complex crater (an impact crater in which the impact wave rebounded from the rim of the crater and pushed up a mountain in the middle) where, instead of the rebound forming a central peak, it instead formed a ring-shaped plateau similar to one large, continuous, circular mountain.

Let's say that, 2 million years prior to the present day, a meteor impacts roughly in the middle of the Strait of Gibraltar. It is large enough and strikes at sufficient velocity to create an impact crater 100 kilometers in diameter, which completely destroys the land on either side of the Strait and generally turns it into a gigantic crater that's a lot less of a strategic chokepoint.

  • Would such an impact produce a peak-ring crater, or at least a central peak, that would still be around 2 million years after the impact?

  • If so, what would its elevation be?

  • If it's a peak-ring crater, would it form atolls?

I'm asking because I'm working on an alt-history scenario where this occurs and the mountain/mountains/land/etc. that poke up out of the crater are highly strategically important up until their equivalent of the modern age (when long-range missiles become available, letting countries control the passage without controlling the islands); up until then, whoever plants artillery and establishes ports on these islands controls passage through the waters near them.

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  • $\begingroup$ Long-range missiles don't in themselves let you control a strait. You also need sensors to detect targets. For surface ships, that's radar, and you either need to maintain radar aircraft over the strait full-time, or put your radars on the islands. For submarines, that's sonar, and you need to hold the islands to provide power to the sonars and receive their signals. Both have to be done via cables. $\endgroup$ Aug 2, 2021 at 11:35

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It would produce a crater determined by the mass and velocity and impact angle of the asteroid.

It is unlikely that any peak ring would survive today, erosion would reduce it to hill sized mounds. The Chicxulub peak ring is the only one on earth, your asteroid is not likely large enough to leave one.

It is possible for your asteroid to widen the strait, or to obstruct it, depending on the impact angle and center. You can use any scenario you wish in your plot.

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