Sedimentary history of Crater Lake caldera, Oregon

Barber, J; Nelson, Charles

"Reflection seismic and sedimentologic studies reveal an evolution of depositional styles in Crater Lake caldera that reflects waning volcanic and seismic activity during a 7000-year history. Rapid construction of the volcanic edifices (central platform, Wizard Island, and Merriam Cone) divided the caldera floor into three basins. A hummocky acoustic basement is recognized in seismic records and probably represents the surface of syncollapse deposits. This irregular surface forms the caldera floor upon which subaerial and lacustrine sediment has accumulated. The deepest acoustic unit contains both flat-lying and chaotic reflectors that may reflect subaerial sheet-wash and mass-wasting. It is followed by subaerial debris flows that are recognized by their chaotic acoustic signature and wedge-shaped geometry and appear to be a response to seismicity associated with post-caldera volcanism. Among these is a major landslide wedge off the southern margin of the lake. Subaerial conditions may have prevailed only a short time (hundreds of years?) following the formation of the caldera, because hemipelagic lake sediment on the central platform dates almost as old as the caldera itself, indicating subaqueous deposition over most of the caldera history. Basin-margin sediment wedges evolving to flat-lying, parallel, basin-wide acoustic reflectors, a decease in mean grain size from basin edge to basin center, and graded sand beds indicate that lacustrine deposits consist of base-of-slope aprons and basin-filling turbidites. A change from high- to low-amplitude acoustic reflectors may be related to a reduction in turbidite sedimentation about 4,000 years ago that resulted from waning volcanism and seismicity."

Sedimentary history of Crater Lake caldera, Oregon

Part of