Wetumpka Impact Crater

Wetumpka Impact Crater. Chronological Sequence of Crater Formation. A shallow offshore area of the ancient Gulf of Mexico eventually became the land upon which downtown Wetumpka was built and through which today's Coosa River flows. This area also was the site of Alabama's greatest natural disaster and the "bull's eye" of a great explosion caused by the impact of a huge object from outer space. , During the "Age of Dinosaurs" in Alabama, (late Cretaceous or about 85 million years ago) a meteor the size of a large college football stadium blasted 2,000 feet deep into local bedrock and exploded under the shallow sea. At the time of impact, marine reptiles, fish, and turtles inhabited the sea, and dinosaurs lived on nearby lands. The meteor impact created a 2.6 billion-ton TNT explosion causing heavy damage and death, affecting both land and sea. , The Wetumpka Impact Crater (4.7 miles in diameter) is the only confirmed impact crater in Alabama and one of only about 200 other recognized craters. Its age is based on fossils found in the youngest disturbed deposits in the crater and atomic age-dating of impact-affected crystals. , The arc of hills east of the Coosa River and downtown Wetumpka are the eroded remains of the Wetumpka Impact Crater's rim. , The Cliffs of the Wetumpka Impact Crater today. Photograph by Barry Chrietzberg , 85 Million Years Ago. [1] At the time of impact, North America was divided by an interior seaway, and Central Alabama was located along the shoreline. Dinosaurs roamed the land; giant sea reptiles, turtles, and fish inhabited the ocean., When a Meteor Hits the Earth. [2] There are three stages of impact crater formation that occur in the first few minutes: , 1 Contact and Compression-Energy forces rocks down; some melt or are shocked by intense pressure. , 2 Excavation-Material is thrown out (ejected) as crater gets larger. , 3 Modification-Crater is created and center rebounds (rises several hundred feet)., Use these murals to understand how the Wetumpka Impact Crater formed., Meteor Approaches Earth. [3] A very large stony meteor (1,200 feet in diameter) approaches Earth from outer space., Meteor Enters Atmosphere. [4] The meteor enters Earth's atmosphere, traveling approximately 43,000 miles per hour. It heats up, creating a blinding light, a tail of fire, and a sonic boom., Contact and Compression. [5] After burning through the atmosphere, the meteor makes contact (impact) in a shallow sea (100 feet deep). The blast travels about 2,000 feet deep, compressing bedrock and sending shock waves into the Earth. Crater begins forming., Excavation and Ejection of Rock Debris . [6] The explosion which occurs upon impact causes a blast of rock debris to fly from the shallow sea into the atmosphere. Some of the debris reaches low Earth orbit., Excavation and Earthquake. [7] Excavation results in a 9.0 (Richter scale) earthquake. Flash fires occur along the nearby shore, and rocks begin to fall on land and into the sea., Hurricane Force Winds. [8] Wind blasts more powerful than a violent hurricane extend out in excess of a 15 mile radius and affect the nearby shore., Falling Rocks. [9] During the first three minutes after the explosion began, ejected rocks fall within a thirteen mile radius causing injury and destruction of life., Modification and Trans-Crater Slide. [10] Located within the crater formed by the meteor impact, "The Cliffs" area is composed of layers of rock that slide across the crater floor and collide with the rim during the modification stage. Disturbed and folded layers can be seen in the walls of "The Cliffs" today., Modification and Tsunami. [11] At this point, the crater has sides up to 1,000 feet high except where the south side collapses. A tsunami wave from the impact moves outward and then comes back, bringing sea-floor sediment (chalk) from the south., Later the Crater Becomes a Terrestrial Island. [12] As life begins to return, an ecosystem develops on the crater island. The crater remains in the sea (Gulf of Mexico) for millions of years until the sea level recedes., Crater Buried in Sediment. [13] As the sea recedes, the crater, which was eroded and buried in sediment, becomes dry land. When the Coosa River develops, it flows over the buried crater., Wetumpka Impact Crater Revealed . [14] Over time, the sediment that buries the crater is eroded away. The Coosa River ceases to flow across the crater and changes its course to bend around the crater rim as seen today. The rocks in the Coosa River are part of the crater rim.