Geology topics
Robert Kayen
Publications and source records attributed to Robert Kayen.
The internal structure of sand bars on the Colorado River, Grand Canyon, as determined by ground-penetrating radar
High-resolution, subsurface imagery from ground-penetrating radar (GPR) has revealed the internal structure of sand bars at seven sites on the Colorado River, Grand Canyon. Based on reconnaissance-level surveys, we recognized three stratigraphic units and several intervening unconformities. Unit A, which exhibits hyperbolic reflections and always occurs at the base of the section, is interpreted as bedrock and/or talus. Unit B is a commonly observed sand deposit that overlies unit A and is characterized by reflections that gently dip down toward the river axis. Unit C is a sand deposit up to 2 m thick that always occurs at the top of the section and may represent a flood deposit from 1983. This study demonstrates the utility of GPR for non-destructive investigation of sand-bar thickness and the stratigraphic record of flood events in the Grand Canyon.
Evaluation of landslide hazards with ground-penetrating radar, Lake Michigan coast
Ground - penetrating radar (GPR) and boreholes were used to investigate a landslide -prone bluff at Sleeping Bear Dunes National Lakeshore on the northeastern coast of Lake Michigan . Based on borehole observations, sediment underlying the area is homogeneous, consisting of well-sorted, medium to coarse sand. GPR penetrated up to 20 m deep in these sediments , revealing the late Quaternary stratigraphy in great detail. We define four units, or radar facies, based on criteria similar to those used in seismic stratigraphy. Directly beneath a landslide at Sleeping Bear Point (and nowhere else in this survey) is a deeply incised, channel-fill deposit that intersects the shoreline at a high angle. The buried channel is at least 10 m deep and 400 m wide, and it might be a subglacially carved feature of Pleistocene age. A prominent, planar unconformity marks the upper surface of the channel deposit, which is overlain by stratified beach and dune material. Several crosshole GPR surveys were performed in the vicinity of the landslide: 1) a constant offset profile (COP), 2) a multiple offset gather (MOG), and 3) a vertical radar profile (VRP). Tomographic analysis of these data determined the velocity structure of sandy sediment that underlie the failed bluff. Because GPR velocity is dependent on electrical properties, we use it as a proxy for geotechnical properties of the soils. Our working hypothesis is that the hidden channel may act as a conduit for pore water flow between upland regions and Lake Michigan, and thereby locally reduce soil strength and promote slope failure.
Popular beach disappears underwater in huge coastal landslide — Sleeping Bear Dunes, Michigan
In February 1995, a 1,600-foot stretch of popular beach at Sleeping Bear Dunes National Lakeshore suddenly slid into the waters of northeastern Lake Michigan. The National Park Service (NPS) immediately requested the assistance of the U.S. Geological Survey (USGS) in evaluating the hazard at the lakeshore. To protect the public, USGS and NPS scientists are conducting studies that will help predict when the landslide-prone area will move again.