AGS Monthly Meeting

Speaker: Randall Carlson

Topic: Ice Age Megafloods, Hypervelocity Impacts and the Energy Paradox

Speaker bio: Growing up in the glacially sculpted landscapes of rural Minnesota, Randall Carlson developed a fascination with natural history at an early age. Regular outings to places like the Wisconsin Dells and the St. Croix wild and scenic river with its collection of giant potholes stimulated an interest in geology and the forces that created such unique features. A summer after high school hiking and camping across the American west confirmed his interest in Earth history and he subsequently embarked on a lifelong avocational study of the geological sciences. Following in his father’s footsteps as a builder he learned that geological knowledge aided his professional endeavors in many ways such as understanding the properties of building stone, groundwater hydrology, soil properties and so on. o increase his knowledge, Randall enrolled in Dr. Pamela Gore’s geology program at Perimeter College in the early 1990s and somehow managed to earn Outstanding Geology Student of the Year Award. After that his geological interests intensified and he spent all his spare time studying the literature and going on field excursions, often with professionals in the field. He became especially interested in the evolving insights of catastrophic geology and traveled extensively investigating such things as megafloods, glacial geomorphology and the effects of hypervelocity impacts. He now leads geologically oriented tours and hosts a podcast Kosmographia.com where he shares his love of Earth history.

Abstract: Since the 1920s and the work of J Harlan Bretz, there has been a growing realization that colossal megafloods have been part of the Earths geological story. Such floods are closely associated with the phenomenon of glaciation as rapidly melting glacial ice is the primary source for the copious volumes of water comprising these floods. Following the advent of radiocarbon dating, it became apparent that the deglaciation processes occurred much faster than previously assumed. This led to a realization that the known energies available to effect deglaciation were inadequate and hence led to the still unresolved “energy paradox.” Since the 1980s there has been a growing realization that hypervelocity impacts of cosmic bodies have played a critically important role in Earth history. There has also been a growing awareness that the end of the most recent ice age ca. 12 to 14 thousand years ago involved catastrophic climate changes in addition to megaflooding and a severe mass extinction of late Pleistocene megafauna. The most extreme of these climatic shifts is called the Younger Dryas and for decades presented a major challenge to workers to explain. In 2007 it was proposed that a major cosmic impact event occurred at the lower Younger Dryas boundary ca 12,900 BP, and since then a considerable amount of evidence has continued to accumulate supporting this interpretation. In this lecture and presentation Randall will present updated evidence that a major impact event occurred, likely involving multiple pieces of a fragmenting comet and that at least several of these pieces impacted the great ice sheets of both North America and northern Europe directly, with calamitous consequences.