<p>When comparing the sizes of the two craters, you are confusing how erosion works.</p>

<p>Erosion did not <em>shrink</em> the original crater to from 43 miles to 430 meters. The crater was 43 miles across and was completely erased: Nothing of it remains, neither the rim nor the central uplift. In fact, erosion has even erased the rocks into which the crater was blasted. This is what erosion over 2 billion years does. The only thing that is left are remnants <em>under</em> the central uplift, and these are 430 meters across.</p>

<p>On the other hand, the Manicouagan is as large as it has always been. Erosion has simply not leveled its outer ring yet. But when it does, it will still have the same diameter. Erosion isn't going to <em>shrink</em> it, it's just going to level it.</p>

CC BY-SA 4.0
2020-01-24T06:06:15.690Z
2020-01-24T06:06:15.690Z
Wolfgang Bangerth
<p>The 2.25 billion-year-old Yarrabubba crater in Western Australia has recently been identified as the world's oldest impact crater. It is said to be 43 miles (69 km) in diameter, yet the photo which accompanies the news item shows a circular structure about 430 metres across, hardly more than quarter of a mile. I realise there has been massive erosion since the crater was formed, but erosion to this extent is hard to believe.</p>

<p>The Manicouagan crater in Quebec has a clearly visible diameter of 62 miles (100 km). which is its official diameter. Its age is 214 million years. Erosion to the same extent as is claimed for the Yarrabbuba crater would give Manicouagan an original diameter of about 10,000 miles (16,000 km)! Clearly this is impossible, so being only about a tenth the age of the Australian example it has eroded far less. But that is not the same as no erosion at all.</p>

<p>Can anyone give an approximate diameter of Manicouagan at the time it was formed?  Another peculiarity of the Yarrabbuba crater is that in the photo it appears to be slightly domed rather than sunken. Is this an artefact of the photograph, a sort of optical illusion, or is it really raised?</p>

CC BY-SA 4.0
2020-01-22T16:06:52.557Z
What photo? What news item?
Jean-Marie Prival
CC BY-SA 4.0
2020-01-22T16:56:05.300Z
No, it was a photo, easily found on the internet. Lots of sites have it.
Michael Walsby
CC BY-SA 4.0
2020-01-23T13:17:49.770Z
The Vredefort Crater in South Africa is almost as old as Yarrabbuba,and has left an easily recognisable crater 190 miles across. It would be interesting to know how big it was when first created, over 2 billion years ago. It also has a central dome, so the one at Yarrabbuba is probably not an optical illusion.
Michael Walsby
CC BY-SA 4.0
2020-01-27T09:40:03.633Z
You can't ask the site to comment on a photo but refuse to provide the photo! Voting to close as unclear.
Semidiurnal Simon
<earth-history><erosion><asteroids><impact-craters>
Original Diameter of Ancient Impact Craters
Michael Walsby
# Original Diameter of Ancient Impact Craters

(Asked by: username_0 on 2020-01-22)

The 2.25 billion-year-old Yarrabubba crater in Western Australia has recently been identified as the world's oldest impact crater. It is said to be 43 miles (69 km) in diameter, yet the photo which accompanies the news item shows a circular structure about 430 metres across, hardly more than quarter of a mile. I realise there has been massive erosion since the crater was formed, but erosion to this extent is hard to believe.

The Manicouagan crater in Quebec has a clearly visible diameter of 62 miles (100 km). which is its official diameter. Its age is 214 million years. Erosion to the same extent as is claimed for the Yarrabbuba crater would give Manicouagan an original diameter of about 10,000 miles (16,000 km)! Clearly this is impossible, so being only about a tenth the age of the Australian example it has eroded far less. But that is not the same as no erosion at all.

Can anyone give an approximate diameter of Manicouagan at the time it was formed? Another peculiarity of the Yarrabbuba crater is that in the photo it appears to be slightly domed rather than sunken. Is this an artefact of the photograph, a sort of optical illusion, or is it really raised?

**Tags:** earth-history, erosion, asteroids, impact-craters

> **Comments:**
> **username_1**: What photo? What news item?  
> **username_0**: No, it was a photo, easily found on the internet. Lots of sites have it.  
> **username_0**: The Vredefort Crater in South Africa is almost as old as Yarrabbuba,and has left an easily recognisable crater 190 miles across. It would be interesting to know how big it was when first created, over 2 billion years ago. It also has a central dome, so the one at Yarrabbuba is probably not an optical illusion.  
> **username_2**: You can't ask the site to comment on a photo but refuse to provide the photo! Voting to close as unclear.  

---

## 1 answers

### Answer by username_3 on 2020-01-24. Score: 3

When comparing the sizes of the two craters, you are confusing how erosion works.

Erosion did not *shrink* the original crater to from 43 miles to 430 meters. The crater was 43 miles across and was completely erased: Nothing of it remains, neither the rim nor the central uplift. In fact, erosion has even erased the rocks into which the crater was blasted. This is what erosion over 2 billion years does. The only thing that is left are remnants *under* the central uplift, and these are 430 meters across.

On the other hand, the Manicouagan is as large as it has always been. Erosion has simply not leveled its outer ring yet. But when it does, it will still have the same diameter. Erosion isn't going to *shrink* it, it's just going to level it.


---

