When The Hills Flow

Huge earthflows dominate parts of the landscape in the rapidly eroding Eel River catchment in Northern California. These spectacular clay-rich ‘earth glaciers’ can be up to 3 miles long, and can move at rates in excess of 1 meter per year. In addition to causing problems for landowners and transport corridors, the earthflows are of significant scientific interest due to the controls they exert on the long term evolution of this “melting ice-cream” landscape.

Ben Mackey studies these slow moving landslides, focusing on issues including how the earthflows influence the height and morphology of hills, and how earthflows interact with channels and gullies. Ultimately, we hope to quantify the long term earthflow-driven sediment flux from the hillslope to the river.

The primary tool for analyzing the earthflows is an extensive high resolution LiDAR dataset along the Eel River Canyon, which (once the vegetation has been filtered out), allows an unprecedented view of the topography (see figure to the left). Aided by a suite of statistical tools that measure the surficial roughness and other characteristics of earthflows, Ben uses LiDAR-derived Digital Elevation Models (DEM’s) to map the multiple generations of late Pleistocene-Holocene earthflow activity adjacent to the Eel River. Traditional field surveying techniques, analysis of historical orthorectified aerial photographs, and some innovative geochemical techniques illustrate where the earthflows are currently active and provide both recent and longer term movement rates.

Interestingly, some earthflows are visibly active, whereas others appear long dormant or ‘deflated’. Ben will determine whether the earthflow activity is either naturally episodic, or influenced by river incision propagating through the landscape. Alternatively, the earthflows may largely reflect the legacy of different climatic conditions from the last glaciation.