The Weaubleau structure, formerly known as the Weaubleau-Osceola structure, is a crater nineteen kilometers wide in St. Clair County, Missouri, centered near the community of Vista. It is believed to have been caused by the impact of 1,200-feet meteor about 335 million to 340 million years ago.
The Weaubleau Structure is one of the fifty largest known impact craters on earth and the fourth largest in the United States. The three larger ones in the U.S. either have been glaciated and buried, submerged under water, or deformed by tectonic movement. Therefore, the Weaubleau structure is the largest exposed impact crater in the U.S. that has not been deformed or misshapen.
Surrounding the impact area are spherical rock formations of varying size, called the Missouri rock balls, which probably formed at the time of the impact. Nearly perfectly round, they are also sometimes referred to locally simply as "geodes," "round rocks," or "Weaubleau eggs." The round rocks may have formed when the impact threw shale away from the center of the crater and silica-saturated waters subsequently formed silica around the shale fragments.
The Weaubleau structure is one of a series of known or suspected impact sites along the 38th parallel in Illinois, Missouri, and Kansas. The others include the Hicks Dome in Hardin County, Illinois; the Avon crater in Ste. Genevieve County, Missouri; the Furnace Creek volcanics in Washington County; the Crooked Creek structure in southern Crawford County; the Hazelgreen volcanics near the Laclede-Pulaski county line; the Decatur dome in southern Camden County; and the Rose dome in eastern Kansas. The effects of the impact on the surrounding topography at the Decatur dome can be seen in a road cut that runs along Highway 5 about sixteen miles north of Lebanon.
Because all of these structures are located roughly along the same latitude, one theory holds that all of them were the result of a serial meteorite strike. However, scientists consider such a serial impact a highly unlikely event on earth. The difficulty in dating all of the structures as having originated from the same period also casts doubt on the serial impact theory. In addition, there is evidence that at least some of the structures, such as the Hicks dome, resulted from volcanic eruptions rather than from meteorites. Only the Crooked Creek structure and the Decatur dome have been confirmed as having resulted from impacts.
5 comments:
You say that the crater is 19 kilometers wide, but that's not quite right. The impact structure -- the range of the surface that was altered by the impact -- is 19 kilometers wide, but the crater itself is much smaller and centered just south of Vista.
Thanks for the additional info. I've never actually seen the Weaubleau Structure and never been to Vista.
Actually its a bit ambiguous to refer to it as a "crater", as the topography of the area is a vast mixture of of hills and valleys. With regard to the "round rocks", there is an old homestead several miles north of Weaubleau, MO on Bear Creek. Apparently while digging a pond there many years ago, utterly hundreds of the nearly perfect round rocks ranging from baseball to basketball size were found. Since these are commonly found over a wide area it seems highly unlikely that they only occurred near an impact rim.
I've hunted the mile square property for decades
Ed P
Thanks for the additional info, Ed, from someone who is familiar with the area. I've never actually visited the place.
I live of 1/3 of an acre property in Osceola, MO.
I have a bunch of these round ball rocks in my yard.
From the size of a golf ball to a bit bigger than a soft ball.
Seems I can't dig without finding them. Also allot of large
rocks with Sea type fossils in them.
I love living here.
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