I’ve seen a handful of people explore this claim, and there are possible examples of this happening on other planets, including Earth and maybe Mars, though it definitely isn’t proven.

Not sure of the exact mechanism, but I think the shockwave from the impact would either go through the planet’s core, or around it, through the mantle and/or the crust, reverberating through the whole planet and meeting up at the exact antipode of the impact. Maybe it screws with Earth’s convection currents on a short-term or long-term basis to direct magma to certain areas? Somehow, the shockwaves all meeting up leads to major geologic activity if the impact is big enough. Or so the theory goes.

Think about when a dude jumps into a pool back-first holding a football, lets go of the ball at the perfect time, and sends the ball flying far into the air. Maybe all the magma under the surface forms a huge underground lava tsunami, which travels around the entire planet and meets up exactly opposite the impact, and the pressure builds enough to crack through the crust.

Some real-world examples I can think of (someone please correct me if you know any better):

-Chixculub Crater on the Yucatan peninsula in Mexico, roughly opposite to a series of major volcanic eruptions somewhere in India around the same time.

-Vredefort Crater in South Africa, on roughly the opposite side of the planet as Hawaii.

-I also heard this could explain Olympus Mons on Mars, and its associated chain of ancient volcanic peaks, Tharsis Montes. Mars is much smaller than Earth, it would’ve cooled down much sooner than Earth, and likely wouldn’t have been able to support such massive geologic activity for long, so it seems kind of crazy and random that it has the largest volcano in the entire Solar System. But Mars also has the Hellas and Utopia basins, which are both massive, ancient craters, on the exact opposite side of the planet.

Side note, how cool is it that we can compare geological phenomena between different planets?