[meteorite-list] Re: possible impact crater -- Nicaragua, Chad, Algeria

[Jason Utas]

Hello Sterling, All,
I do realize that the 'craters' that I found were not, indeed, holes in the
ground.   However, the 'craters' that I found, would not be depressions as
you described.  Each consists of features well over ~15-20km across, the
diameter necessary to create a complex crater, and would therefore consist
of a central uplift with a series of concentric (raised) ridges.

In order to view mine correctly, try zooming out to forty miles or so and
having a look from up there.  A much larger circular feature can be seen
about the central uplift of my favorite candidate. (Visible at   21 17'10.89"N
19 20'35.61"E   ) This would be the area around the uplift that was shocked
and melted to some degree and also somewhat displaced.

The other consists of a large uplift and a single upraised ring about it,
making it appear  very similar to the large impact feature recently
discovered near the Egypt-Libya border.

The features that you describe -- a hole in the ground with a raised rim
-- apply only to simple craters (which cannot, in most cases, at least here
on Earth, exceed the limit of approximately 15-20km in diameter).  Stefan's
feature, measuring in at approximately nine miles across, appears to be a
rather large example (if it is actually a meteorite crater) of a simple
crater.

Here's an informative site that you might want to read, as it has some
rather good information on the subject.

http://www.lpi.usra.edu/publications/slidesets/impacts.html

also, try this:

http://www.solarviews.com/eng/tercrate.htm

Regards,
Jason


On 5/3/06, Sterling K. Webb <sterling_k_webb at sbcglobal.net > wrote:

>

> Hi, Stefan, List

>

>    I think you got a crater there! The most impressive view

> is to set your altitude around 30 or 40 miles up, orient yourself

> to the NE of the crater, looking to the SW, then tilt the view

> until your eye level is at about 4 miles up, and zoom in slightly.

> Wow! That is a classic crater. That view alone is convincing...

> almost. It needs to be seriously investigated.

>

>    Google Earth's view can be deceptive. I always trace the

> "rim" and "cavity" of what appears to be a crater and read off

> the altitudes to see it actually has a crater's geometric shape.

> Parts of the Nicaraguan crater's rim are half a kilometer or

> more above the floor.

>

>    Jason Utas' candidate in Chad is an example of the

> deceptiveness of visual features. Knowing the shape of a

> crater, we interpret the dark areas in the "floor" of what

> looks like a crater as depressed and the bright features

> as central uplift and rim, but the dark features are actually

> as high or higher than the bright ones. When you tilt the view

> you see that the whole feature is elevated, like a squashed

> mountain. Oddly, it seems to be set in a square embayment.

> Very strange. It doesn't look entirely volcanic but it doesn't

> look much like a crater, either.

>

> Kevin Forbes' Algerian feature is essentially flat and consists

> of concentric rings of contrasting materials. Its appearance

> reminds me a lot of the much larger Richat Dome in Mauritania,

> whose crater or not status has been argued over for a long time.

> Currently, we don't think the Richat is a crater, but a domed,

> layered structure sliced off flat to reveal its layers. His "less

> probable" structure looks more like a crater in the tilted view,

> but it is too battered to tell much. The Sahara is not kind,

> even to rocks...

>

>

> Sterling K. Webb

>

> -------------------------------------------------------------------------------

> ----- Original Message -----

> From: "Stefan Brandes" < brandes at gmx.at >

> To: "Meteorite-list" <Meteorite-list at meteoritecentral.com >

> Sent: Sunday, April 30, 2006 1:21 PM

> Subject: [meteorite-list] meteorite-list] possible impact crater

>

>

> > Hi list,

> >

> > has anybody heard about an impact crater in Nicaragua at coordinates :

> > 13°21' N / 85° 57' W

> > It´s about 12km in diameter and the town of Las Praderas lies directly

> in

> > the center.

> > It´s very good to see in Google Earth.

> > As far as I know it´s definitely no volcano.

> >

> > Any ideas?

> >

> > Thanks

> > Stefan

> >

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>

>

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