High-Altitude Asteroid Impact

Question

66 million years ago, the dinosaur empire was in its death throes when its final nail in the coffin came hurtling down from the sky. A clump of rock the size of Mount Everest smashed into the Gulf of Mexico, bringing about the end of 70-75% of all species. How?

1. The impact tossed out about 500 billion tons of debris into the atmosphere, some of which escaped into space.
2. The atmospheric temperature rose to the extent of provoking multiple spontaneous combustion, merging together into global forest fires.
3. The impact melted the surrounding rock.
4. The asteroid couldn't have landed at a worse place on Earth. The Gulf of Mexico was rich in sulfur and carbon, which many scientists believed compounded and even prolonged the fall of the dinosaur empire. From the sulfur, the first few years of the catastrophe saw a five-degree-Celsius drop in temperature before spiking up to a 20-degree rise that persisted for millennia, thanks to the carbon.
5. The impact left behind a crater 93 miles wide and 12 deep.

Now let's say that the Chicxulub asteroid landed today in a different spot--the top of the Tibetan Plateau (last I checked, nil amounts of sulfur and carbon.) Should an asteroid the size of Mount Everest slam into the heart of Tibet, far above sea level, would the aftermath of a high-altitude asteroid impact be different from the below-sea-level impact of our timeline?

Answer 1

The impact tossed out about 500 billion tons of debris into the atmosphere, some of which escaped into space.

The difference in altitude from the perspective of the meteor would be utterly irrelevant. It's like suggesting there's a difference between stepping on a hardwood floor, and a piece of paper on the hardwood floor. The same 500B tons of debris would go into the atmosphere — but it is 4.5 Km higher off the sea floor, which means there is a difference in how the debris would be distributed initially in the atmosphere. Frankly, it would probably distribute faster due to lower gas density. But that's a bit of a guess on my part.

Conclusion: No difference.

The atmospheric temperature rose to the extent of provoking multiple spontaneous combustion, merging together into global forest fires.

Same force, but at 4.5 Km altitude the air is thinner. Would it have been thinner enough to make a difference? To reduce the compression wave that wove around the world?

500B tons of mass thrown into the sky....

Conclusion: No difference.

The impact melted the surrounding rock.

This is perhaps the most important observation. If this site is to be believed, the Chicxulub impact was all ocean. No land. The maximum Gulf of Mexico depths today (ignoring all the disputes) are about 13,000 feet deep. Even if we assume half that (1.25 miles or 2 Km), it's a whole lot of water to boil away to get to that 500B tons of material thrown into the sky. And yet the surrounding rock is known to have melted.

Have you ever seen a stone thrown into a hot mudpit? It doesn't leave a crater. In fact, for a moment, the area the stone entered is higher than the surrounding mud pit. There are a lot of reasons for this effect (not the least of which is the extra mass represented by the stone), but the result — if you could freeze it — is a plateau. Which is actually what we got. Compared to the depths of the Gulf of Mexico, the Yucatan Peninsula exists and the ocean around Chicxulub is shallow.

When you get to that level of force, the thin layer (2 Km at least) of water is almost if not completely meaningless. So, yeah, molten rock.

Conclusion: No difference.

The asteroid couldn't have landed at a worse place on Earth. The Gulf of Mexico was rich in sulfur and carbon, which many scientists believed compounded and even prolonged the fall of the dinosaur empire. From the sulfur, the first few years of the catastrophe saw a five-degree-Celsius drop in temperature before spiking up to a 20-degree rise that persisted for millennia, thanks to the carbon.

This, on the other hand, may be the most debatable condition. Carbon is a part of everything on this planet. The idea that there was more of it 65M years ago at Chicxulub than elsewhere on the planet sounds frankly daft to me. 500B tons of mass were thrown up in the air. The volumes we're talking about were astronomical. So, unless someone can prove Chicxulub 65M years ago was all diamond (500B tons of it), the amount of carbon was irrelevant.

The sulfur might be an issue. But the rock melted. The forests burned world-wide. 500B tons of mass. All of which might be irrelevant because there's a giant sulfur deposit on the Eastern Tibetan Plateau.

Conclusion: No difference.

The impact left behind a crater 93 miles wide and 12 deep.

This issue might actually be irrelevant.

Conclusion: I don't believe there would have been a significant difference in the final timeline. Oh, maybe something other than the alligators would have survived and the alligators themselves wouldn't, but when considering the timeline as a whole: no, nothing would have changed.

Answer 2

You are still going to experience an extinction level event, only the details will vary slightly. That asteroid, regardless of where it hits, is still a kinetic energy bomb. Hitting in the Tibetan Plateau is going to send a percentage of its energy (depending on where ground zero is) down into the division between the Eurasian and Indian tectonic plates. That energy is going to cause massive plate shifting all around the globe which will set off a series of (secondary) earthquakes, volcanos, and tsunamis. The initial impact is also going to vaporize and/or displace tons of material. Those particles are going to block sunlight affecting plants and planet temperature until they settle out of atmosphere. If you say some debris escaped out into space at sea-level, at this altitude much more will reach escape velocity possibly enough to have a second (much smaller) moon/satellite orbiting Earth or sent into an orbit where it will re-enter the atmosphere at a later date. The rock, dirt and dust that got ejected but didn't reach escape velocity is going eventually land somewhere possibly choking rivers and disrupting local ecologies far from the impact site. Then those secondary eruptions are going to spew ash and add to the atmospheric dust. The impact might also displace enough material to affect the wobble.