When: April 26, 2016 6:30 pm – 8:30 pm
Where: Fernbank Science Museum – Auditorium
767 Clifton Rd
Atlanta, GA 30307
Cost: There is no charge for attendance, but donations and membership support are welcomed!
Atlanta Geological Society
Please arrive early to guarantee entry. Only 178 seats are available for the presentation.
The presentation will be ~ 1 hour and will start between 7 and 7:15pmThere is no fee requirement to attend the event but donations and memberships for the Atlanta Geological society are available for those who wish to support their good work and the creation of similar future events for the public. AGS membership is only $10 for students and $25 for the general public, AGS membership provides a range of benefits including Professional Geologist training classes. You do not need to be a member to attend our social at 6:30 at Fernbank.
Terminal Ice Age Megafloods
Abstract: Since the early 1920s and the work of J Harlen Bretz, evidence has been growing that the termination of the Wisconsin Ice Age was extremely rapid and involved meltwater floods of extraordinary magnitude. The most well-known of these are the so-called Missoula Floods that swept over the Pacific Northwest contemporaneous with the Bolling-Allerod/Younger Dryas climate transitions, in the process producing the anastomosing plexus of erosional forms in SE Washington State known as the Channeled Scablands. However, major flood events occurred in numerous other locations around North America as well. The Bonneville Flood resulting from the catastrophic overflow of Lake Bonneville, of which Great Salt Lake, Utah, is a remnant, is also fairly well known. Many massive “superlakes” formed and drained catastrophically during the period of glacial retreat. All major North American rivers that rise in formerly glaciated regions are underfit streams, occupying outsized valleys formed by enormously augmented meltwater flows. A variety of geomorphic forms such as coulees, tunnel valleys, debris fans, boulder fields, drumlin swarms, over-deepened lake basins, and macro-scale bedforms may be attributed to terminal Pleistocene megafloods. The exact relationship and timing of these events has yet to be established with precision and a number of controversies have arisen in recent decades as to the number of floods, their causes and geographic distribution.
In regards to the Missoula Floods the prevailing causal theory holds that a large proglacial lake broke through its impounding glacial dam in northern Idaho, producing a massive jökulhlaups, or outburst flood, with discharges possibly exceeding 20 million m3/sec-1. Studies of slackwater depositional facies have resulted in the assumption that this process took place dozens of times, perhaps as many as 80 or 90 times. There are certain problems inherent in this model, both theoretical and empirical. Evidence supports the conclusion that the Missoula Floods were part of a much more extensive phenomenon of accelerated glacial melting over the whole Cordilleran-Laurentide ice complex. Depositional hiatuses suggest the melting occurred in several discrete pulses separated by longer periods of decelerated melting. Questions regarding the energy requirements for the tempo of glacial retreat have not been satisfactorily addressed. The general timing of these megafloods suggest a correlation with oceanic meltwater pulses, the interruption of the North Atlantic thermo-haline convection current, the extreme Bolling-Allerod/Younger Dryas/Preboreal climate oscillations, rapid meltdown of the Fennoscandian ice sheet, disappearance/disruption of the North American Clovis culture and the terminal Pleistocene megafaunal extinctions. The question of ultimate cause, or causes, of these dramatic global change events remains open.
Randall Carlson is a professional builder and co-owner of Archetype Design/Build Inc. He is a native of rural Minnesota where he developed a love for geology early in life. He majored in geology at Dekalb College where he was awarded outstanding geology student of the year for 1993. He has continued his interest in geology as an avocation with a primary interest in discontinuities and catastrophes in the geological record. Over the past two and a half decades he has logged approximately 40-thousand road miles of travel over North America to hundreds of sites, studying the effects of the Late Wisconsin Ice Age and its rapid termination ca 11 to 14 thousand years B.P. along with other phenomenon associated with extreme events such as impact craters, volcanic eruptions and Late Pleistocene megafaunal death assemblages. His focus has been directed primarily at the evidence for catastrophic megafloods associated with the recession of the vast Laurentide/Cordilleran ice complex, and is currently working on a book to detail these studies.
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