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Re: Hell Creek (long)


MariusRomanus@aol.com wrote:

Then why is it that most all very large impact craters throughout the solar system are essentially (nearly) circular?  (jrc)
 Graydon pretty much explained that one for you..... Thanks Graydon
Yes, that was a retorical question I already knew the answer to.  And I agree with Graydon.
> For the most part, it all has to do with the time the object is  passing through the atmosphere... regardless if it is large or
> small....

Not entirely.  It also has to do with the diameter of the impacter versus the effective depth of the atmosphere.

 Yes...... as I said..... Pretty much the time the object is passing through the atmosphere...
The diameter of the object doesn't have anything much to do with the time it spends traversing the atmosphere.  The leading side will spend about the same amount of time in the atmosphere whether the object is 100 meters in diameter or 100 miles in diameter.
I'll leave that as an excercise for you, if you're interested.
Nice try..... But no thanks.... :-)  I have nothing to prove here...... Those were nice computations though....... I vaguely remember doing things just like it in Mechanics class when we were toying with Orbital Dynamics and when I was doing papers on this subject..... The nightmares are coming back......
I'll pass too, for the same reason -- though I don't really see it as a nightmare, just a waste of my personal time.
Objects a few miles in diameter will likely survive to reach the ground since they are a substantial fraction of the effective depth of the atmosphere.
Large objects generally don't have time to vaporise substantially prior to impact.  Shearing affects mostly intermediate sized objects on a near-grazing trajectory and large objects on a grazing trajectory. Large objects don't slow substantially due to aerodynamic drag (not enough displaced mass in the  traversed atmosphere to be truly significant to a really large impactor).
 Your comments such as these 2 really didn't have to be made.... I guess I needed to completely clarify things when I was talking in general about impactors?????......  I mean really?..
I made them because it seemed to me that you appeared to have been arguing both sides of the coin on several issues.
.. Do you seriously think I don't realize that a huge body would survive to hit the ground???.... regardless of trajectory angle or composition????? Let alone one that can extend into the upper atmosphere????..... I don't think you did... Which makes me wonder why you needed to write what you wrote.........
See my comment immediately above.
So, I didn't make this up........
Never thought you did.
Quite right.  Some of them are elliptical.  But the big ones are pretty much circular.
Graydon answered the why of that one too......
Yes, and his response was contrary to your initial statement that crater shape is dependent upon impact angle no matter what the size (mass....kinetic energy) of the impactor.  My original point (as his) was that craters become more circular with increasing impact energy, so that effects of approach angle become subordinate with increasing energy.
I notice that we're describing the melt sheet and ground impact, but Chicxulub impacted in water......
Yup...... and I touched that a bit in another post. Sandia did a simulation ..... The blast force was hundreds of magnitudes larger then that of the oblique asteroid impact..... a ridiculous 400 gigatonnes or something like that..
Pretty small compared to Chicxulub, which would likely have been measured in teratons.
.. Really amazing stuff...... And these results fit oh so nicely with my post to Rob about the dust cloud.

Nice to know that you are interested in the hydrology after the fact.... I've never read anything about it before.

I make my living working as an expert witness on litigations in the fields of hydrology, hydraulics, and fluid mechanics and occasionally teach courses in them at a couple of the local universities.  I'm very interested in hydrology.   Re paleontology, I'm somewhat interested in the effects of the excess water added into the hydrologic cycle by the impactor as it would affect the flight mechanics of the pterosaurs which survived the immediate blast effects.  My major paleontological interest is in the flight mechanics of the azhdarchidae.
> It's not the size of the body that dictates the crater's shape  (circular or elliptical)..... It's the angle of attack..

For small, slow objects, that's true.  For large, fast ones, apparently not quite so true.

 Well, refer back to what Graydon and I have said....... then you can take it up with the astrophysical community I guess..... :-)
Well, Graydon agreed with my initial position.  Initially, you didn't.  Glad to see you've changed your mind.
Excuse me, but you have just said that the craters will be circular for all but very low impact angles, and if I'm following you correctly, that appears to be contrary to what you have been saying previously.
 Gettin a bit testy at this point huh?....

I hope not.  It ain't like I'm all that wound up in this.

I notice that you say that Chicxulub is only slightly elliptical, though the impact trajectory was very flat (substantial zenith angle).  To me, only slightly elliptical translates as pretty near circular.
 Well, this is the only thing you got me on.........
So, I'm not making this up......
Again, never thought you were.
Well...... if you post the rest of what I said......... "This doesn't make sense if you throw a rock in mud.
Chicxulub wasn't directly comparable to tossing a rock in mud.  I think we've beaten this particular horse into the ground.  I've found it enlightening though.All the best,