Slope Stability
along Incised Fluvial Valleys
Morris, Alan P.1, David A.
Ferrill1, Ronald N. McGinnis1, Ben A. Abbott2
(1) Southwest Research Institute®, San Antonio, TX (2) Southwest Research
Institute®, San Antonio,
The Snake River and its tributaries in
southern Idaho have incised valleys
through Tertiary basalt into underlying clay-rich sediment. Incision has
destabilized valley walls causing landslides. The valleys are analogous to lowstand channels cut through competent strata into less
competent strata. Salmon Falls Creek, a tributary of the Snake River, flows through a
relatively narrow canyon (~130 m deep, ~375 m wide). Ten kilometers south of
its confluence with the Snake River, landslides originating
from the canyon wall widen the canyon to 1.3 km. Several landslides have
periodically dammed the creek. The most recent slide (1998, Bluegill Lake or Salmon Falls slide) is still active,
and previous workers interpret it as a rotational slide detaching within
sediments beneath the plateau-capping basalt. Bluegill Lake slide consists of a
vertical headscarp; zones of large, precariously
stacked boulders, and rotated, intact basalt pavements; a toe consisting of
boulders, clay-rich strata, and fluvial sediments; and a northern strike-slip
boundary. Landslides and their associated slope processes are important analogs
for evaluating hydrocarbon potential of subaerial and
submarine landslide deposits. We use a new high-resolution wireless sensor and
node-based, displacement-monitoring network and detailed mapping, together with
techniques of cross-section construction, to measure displacements and infer
the internal structure of the slide. Failure mechanics within a strong capping
layer above a weaker substrate are common to a number of environments including
continental margin gas hydrate accumulations and lowstand
systems of any age. Our new high-resolution displacement-monitoring network has
wide applications to natural and anthropogenic earth surface processes.