SZO Seminar Notes – May 21, 2015: Geomorphology/landscape
evolution in
subduction zone settings
Discussion Leader: Alison Duvall
Faccenna,
C.,
P. Molin, B. Orecchio, V. Olivetti, O. Bellier, F. Funiciello,
L. Minelli,
C. Piromallo, and A. Billi (2011),
Topography of the Calabria subduction zone (southern Italy):
Clues for the
origin of Mt. Etna, Tectonics, 30, TC1003,
doi:10.1029/2010TC002694.
Personius, S.F. (1995), Late
Quaternary stream incision and uplift in the forearc of the
Cascadia subduction
zone, western Oregon, J. Geophys. Res., 100, 20193-20210.
Main take-home-message: any good subduction
zone observatory
should have surface process folks involved.
Today, will highlight some examples where
surface processes
and landscape studies contribute. More than landslides: includes
topography, river
incision, hillslopes (seismically induced landslides)....
Paper: Faccena et al. Calabrian subduction
Topography (amplitude and wavelength of
features) constrains
models of processes going on at depth. Some subduction processes
would lead to
uplift other might lead to sinking. Paper tests 4 models using
fault data,
tomography. Conclude that deformation is sustained dynamically by
Toroidal flow
around the edges of the slab.
----------
Paper: Kelsey et al., Topographic form of the
Coast
Ranges—coastal uplift and subduction. Anomalous
uplift rates at S and N ends of Cascadia. Possibly due to buoyancy
of younger
subducting plate? Perhaps larger point is that nowadays this type
of analysis could
be done easily anywhere with GIS.
-----------------
Paper: Personius. Stream incision and uplift.
Strath
terraces (bedrock stream terraces caused by erosion rather than a
terrace
formed of deposited riverbed material) record times of low
incision rate. Then
when a river starts incising you can
measure the difference between thalweg (?) elevation and terrace
elevation. Assuming
you can date the strath surface
formation, you can bound-or estimate-the incision rate. The
distribution of
incision rate can then be interpreted in terms of uplift (but may
be due to
base level drop).
-----------------
Paper: Paer VanLaningham et al (2006) looked at
other
metrics using modern techniques: Stream-profile (Slope-Area)
Analysis. Applied
to Oregon coast ranges. Bedrock lithology has an impact, too. Illustrated need to
characterize the rocktype
as well as other parameters. A complex signal indeed!
-----------------
Hillslopes above Subduction Zones (Earthquake
Induced
Landslides, Springer 2012).
A huge hazard. But also provides clues about
topographic
processes.
Alison pointed out: Seismically induced
landslides have
secondary major impacts (e.g. blocking access to recovery workers,
landslide
dams and flooding due to their failure, erosion & flooding,
destabilized
hillslopes) that can impact a region for a long time after an
earthquake.
So...the basic question for these studies, and
should be
part of a subduction zone observatory, is: what is retained in the
topography
that reflects the underlying subduction process?