Bilderback, "Hillslope response to climate driven river incision"

Start Date/Time: Thursday, March 08, 2012, 3:30 PM
Ending Date/Time: Thursday, March 08, 2012, 4:30 PM
Location: JHN 102

***Applied Geosciences Colloquium***

Speaker: Mr. Eric Bilderback
Title: Landscapes on the edge: Hillslope response to climate driven river incision, East Coast North Island, New Zealand

Quantifying hillslope response to the interplay between tectonic uplift and climate change is fundamental to understanding the evolution of landscapes during glacial, inter-glacial cycles. The non-glacial Waipaoa River catchment on the east coast of the North Island of New Zealand, vividly illustrates this interplay. Parts of the catchment have been incised up to 120 m since the last glacial coldest period (LGCP). Dramatic changes in upland erosivity provide a mechanism for linking climate with aggradation and incision by replacing bed load over-capacity with under-capacity. New high resolution topographic data sets (lidar and photogrammetry) combined with field mapping and tephrochronology in the upper Waipaoa indicate that hillslopes adjusted to this rapid incision through the initiation and reactivation of deep-seated landslides.

The ages of tephra cover beds determined by electron microprobe analysis show that after an initial several thousand year time lag, hillslope adjustment started between the deposition of the ca. 13,600 cal. yr BP Waiohau tephra and the ca. 9,500 cal. yr BP Rotoma tephra. Tephrochronology further shows that many slopes have continued to adjust to channel incision into the late Holocene. The signal of rapid incision and landslide response appears to be near synchronous from the headwaters to the mainstems. Hillslope response in the catchment can include the entire slope from river to ridgeline, with some ridges between incising sub-catchments dramatically modified through ridgeline retreat and/or lowering. The combination of geomorphic mapping and tephrochronology helps to describe the spatial and temporal response of hillslopes to climate change in the Waipaoa over the last glacial, inter-glacial cycle.