Quaternary Science is the multi-disciplinary study of geological, biological, climatological and human systems of the past two million years (the Quaternary Period), and the evolution of these systems into present conditions on Earth. The Alaska Quaternary Center (AQC) is committed to the promotion of interdisciplinary research and the enhancement of interdisciplinary instruction in Quaternary sciences.
VISITING SPEAKER - Friday 23rd Sept.
AQC invited speaker, Dr. James McCalpin
Talk title: The Mountains Are Falling Apart; A Spectrum of Mass Failures from Landslides through Deep-Seated Gravitational Spreading ( Sackung ), to “Unfolding” of Folds
Talk time: 3:00 - 4:00pmMurie Auditorium, Murie Building, UAF
Recent geologic mapping in mountainous areas of Alaska, California, Colorado, and Utah, supplemented by LiDAR DEMs , has revealed an abundance of young scarps, graben , bulges, and other geomorphic anomalies. Some landforms are sackungen formed by deep-seated gravitational spreading (called by Doug Morton of USGS “half-a-landslide”). Gravitational spreading results in detachment of large masses of bedrock from mountain flanks, causing lateral bulging and vertical collapse of the crest. Detached blocks do not display hummocky topography because they are not rubble, as are landslide deposits. Instead, stratigraphy and structure within the blocks is relatively undisturbed, so geologic maps show these areas as unfailed bedrock, and do not hint that the block margins are sites of recent deformation with engineering significance. As local relief in mountains increases (often due to valley glaciation in the Pleistocene) and active tectonism increases, the types of different failure styles and number of failures increase. In southern Alaska the combination of high relief and seismic shaking has even led to the Quaternary “toppling-unfolding” of pre Quaternary folds, due to gravitational spreading and development of extensional flexural-slip faults. Lower-relief areas in Colorado show similar swarms of young scarps related to unfolding of Cretaceous folds by evaporite dissolution in underlying rocks. Taken together, the landforms now known represent a nearly continuous spectrum of mass failures, ranging in scale from small landslides that we would all be able to recognize, to incipient landslides, to large detached parts of mountains, to deep-seated gravitational spreading that looks almost tectonic in nature. In mountain areas that contain active faults, it is difficult to separate the tectonic seismogenic structures from the gravitational-non seismogenic structures, but these two types have different hazard significance for engineering geologists. This talk is based on my research into sackungs since 1994, and on trenching evaporite scarps since 2010. The talk draws on examples from Colorado, Europe, California, Utah and Alaska.