LANDSCAPE HISTORY AND LAKE LEVEL CHANGES IN SOUTHWEST ALASKA

Current research in Lake Clark National Park and other Southwest Alaskan parks combines landscape history, paleoecology, and lake system history in order to understand the formation of the present ecosystem, and its vulnerability to climatic change, geologic change, or disturbance. Landscape-scale studies (that include timing of deglaciation, volcanic history, lake level history, vegetation change, and change in drainage patterns through the Holocene) compliment ongoing studies on the archeology and salmon history of these lake systems. Lake level histories around Lake Clark and other large southwest Alaska lakes were determined using sediment cores obtained from kettle ponds located within the paleoshorelines of the larger lakes. These small lakes act as ‘isolation basins' recording the change from large, glacial fed lake to small isolated pond as the lake level drops below its threshold. Studies to date show that Lake Clark gradually dropped at approximately 20 meters between deglaciation ~14,000 yBP and the early Holocene ~7,000 BP. Differences in the beach ridge profiles (gradient, and shape of profile) between the SE shore of the lake and the NW shore suggest some differences in drainage patterns and possibly indicate Holocene tectonic movement. Further radiocarbon dating may help determine the rate and nature of this difference. Kukaklek Lake and Naknek Lake (Katmai National Park and Preserve) show evidence of early Holocene lake level drop, however Nonvianuk Lake (located between the two) does not. This suggests the regional pattern of lake level change is not synchronous and most likely related to outlet changes instead of regional tectonism or isostatic rebound. Kukaklek Lake, does however, show evidence for recent (last several decades) lake level rise at it's western end, and possible regression indicated by the formation of beach ridges at it's eastern end. Continued studies at lakes surrounding Naknek Lake are expected to help us better constrain the degree and timing of lake level change in relation to salmon history, lake isolation, and archeological sites in the region.