If you are planning to watch the Leonid Meteor Showers in mid-November, you may want to consider what came out of the sky and landed in mid-Missouri in past eons.
Missouri is the location of three craters, or impact sites, along the N. 38th parallel, which bisects the state. Two — Decaturville and Crooked Creek — are confirmed to have been caused by meteors, and the one south of Osceola, known as the Weaubleau Impact Structure, is listed as probable.
It’s the discovery of Dr. Kevin Evans of Missouri State University, who was in Osceola last week to speak at the monthly meeting of the St. Clair County Historical Society. His topic was the Ozark Uplift, which created the Ozark Highlands in the southern half of Missouri, northwest Arkansas and southeast Oklahoma — mapping the geology of the state caused by its numerous side-slip faults being one of his current research projects. But the discussion veered back to the meteorite strike when a woman in the audience asked what the round rocks were that she and her sons kept finding. She thought they were geodes, she said, but when they crack open the balls, they find sand, not crystals.
The balls are called Weaubleau eggs, Dr. Evans explained, which were formed when a meteorite 1.2 miles in diameter struck the Earth just south of Osceola. He discovered the craters in 2003, when he was preparing digital elevation models (DEMs) of the area and put four quadrants of DEMS together, revealing the circular areas of rock deformation, the impact area and the larger circle of area affected by the impact, which would have been a quarter of mile across, Dr. Evans said, as it would be if struck by a meteor.
With an inner ring of 5.5 miles and the outer ring of larger than 11 miles to the rim, the Weaubleau Structure is one of the largest-known impact structures in the United States, and the largest exposed impact structure in the country. The size ranks the Weaubleau Structure in the middle range of impact sites. But it is mostly exposed, while larger impact sites are at the bottom of Chesapeake Bay or under glaciers in Idaho.
The good news — the meteors fell in the mid-Mississippian Period, 330 million years ago, named from the age of rocks exposed in the upper Mississippi River valley. The area was covered by a shallow sea that provided habitat for long-stemmed plants, seaweeds, corals and snails, with reptiles and ferns just starting to appear on land. The impact of the meteor was well below the threshold to generate mass extinction, and came from the west, hitting the water at angle and sending up a column of water and pieces of rock two miles high, Dr. Evans said.
Thomas Beveridge was the first to observe in 1951 that the rock layers in the area south of Osceola had undergone severe deformation and brecciation, meaning the rocks were broken into angular fragments. The impact sites along Missouri’s 38th parallel also resemble a pattern caused by a series of meteor strikes on the planet Jupiter, which were observed in 1994.
In all, there are seven craters of rock deformation on or just below the 38th parallel, including two more in Missouri. The others in Missouri turned out not to be caused by meteors, Dr. Evans said.
Geologists have not been able to drill down through the breccia to find the core of the meteor that fell near Osceola, which is estimated to be 1,000 feet deep. But Dr. Evans said that the tiny grains of shock quartz found in the breccia are a “smoking gun” for an impact.
In 2004, Dr.Evans and three other geologists reported on the geology of the site at the 50th annual meeting of Missouri Department of Natural Resources, including Weaubleau eggs. There are examples of the round rocks at the St. Clair County Historical Museum, and also Weaubleau eggs and fossils found in the area in a display case at the county library, across the street from the museum. Weaubleau eggs can be as large as basketballs, Dr. Evans said, adding that he has a collection at the university and also 60 of them in his yard at home.
If you look, you can see the layer of rock deformation in road cuts on Highway 13 south of Osceola. The outer ring of the Weaubleau Structure touches Osceola on the north. The small ring is southeast of the Ash Grove Aggregates Quarry, and encompasses the community of Gerster. Dr. Evans said he plans to conduct more research by boat along Weaubleau Creek and Truman Lake this summer.
That meteors would fall to earth like they did on Jupiter seems unlikely, according to some astronomers, as Earth’s gravitational pull is less than Jupiter’s. On the other hand, the moon has less gravitational pull than the Earth, but has sites where serial meteorite impacts created craters.
Just something to consider when you are driving down Highway 13 past Osceola, or are looking up at the night sky this fall for meteor showers. The Leonid Meteor Showers occur from Nov. 3 to Dec. 2, peaking on Nov. 18, and are best seen between midnight and dawn. They are created by ice and debris left in the trail of the 55P (for periodic) Temple -Tuttle comet, a small comet that circles the sun every 33 years, and will next appear in 2031.
They are called Leonid because they appear to eminate from the constellation of Leo, whose stars form a backwards question mark for the mane, a trapezoidal lion’s body and a triangular tail. It can be found by locating the Big Dipper and looking along a line formed by the pointer stars of the Dipper, the two on the outside edge of the cup, which point to the North Star on one side and to Leo in the opposite direction. For best viewing, sit in a dark place, lean back and when your eyes adjust to the dark, look all around the sky, astronomers advise.
Jay Manifold of the Kansas City Astronomical Society foreshadowed the Weaubleau Structure discussion when he opened last week’s meeting with a brief presentation on upcoming astronomical events. He noted the Geminid Meteor Showers will peak in mid- December, and are best seen at an earlier time in the evening — between sunset and 9 p.m. before the moon rises. He is also looking forward to Dec. 7, when the moon will cross, or occult, Mars about 9 p.m., a rare event made more special because Mars will be oppositional, meaning in the best viewing position. Manifold is already planning where he will go to view the solar eclipse in April of 2024.
For more information about the Weaubleau Structure and the forces that shaped Missouri geology, go to Ozarks Public Television for Dr. Evans’ appearances on Ozarks Watch.
