[ghsc-seminars] GHSC Seminar, Thurs. 3/21 @ 10am - Christian Mohr: Post-eruptive landsliding

[Mirus, Benjamin]

*Post-eruptive landsliding and the organic carbon footprint of explosive
volcanic eruptions*

*Dr. Christian Mohr*
*University of Potsdam, Germany *

Fjord landscapes sustaining old-growth temperate rainforests not only
feature some of the most spectacular topographic relief; they are also
major sinks of organic carbon. Prior work has focused on the effects of
past glacial processes in these landscapes, but we still have much to learn
about contemporary rates of erosion and the involved organic carbon. In
this context, the role of episodic disturbances—particularly volcanic
eruptions—in mobilizing sediment and highly organic soils and vegetation
mats is largely unknown.

Following two recent explosive volcanic eruptions in Chile, erosion and
organic carbon entrainment rates by shallow landslides and floodplain
erosion in forests smothered by thick tephra layers were at least one order
of magnitude higher than in undisturbed forests nearby. A distinctly
clustered distribution of landslides is consistent with slope-stability
models that capture opposing trends of root decay after deforestation and
successive regrowth. These competing trends indicate a window for maximum
hillslope instability somewhere between four to six years after the
eruptions.

Given an recurrence interval of roughly 275 years for major explosive
eruptions in the Andean Southern Volcanic Zone, the combined long-term
annual carbon release from hillslopes and floodplains into the fjords is
around 3-13 tC/km2. Yet, this average does not capture the pulsed nature of
sediment and biomass flushing observed in the first few years following the
eruptions. Therefore, Patagonian temperate rainforests may tip from carbon
sinks to carbon sources, if impacted by tephra cover. In this context, soil
burial plays the decisive role. Explosive volcanic eruptions may be
previously overlooked generators of terrestrial organic carbon pulses into
the Patagonian fjords, and the delayed hillslope response to these
eruptions adds to the portfolio of protracted geomorphic hazards.


*Thursday, March 21st**, 2019*
*Presentation: 10-11a*
*m*
*  (Mountain Time)*
*USGS, 1711 Illinois Street, Golden, CO*
*Entry Level Seminar Room (204)*

*Note: Please arrive *~5 minutes early* and *bring photo ID* for
airport-style security measures now in place at the USGS building.

Thank you,
GHSC Seminar Committee

Ben
Mirus - bbmirus at usgs.gov
Josh Rigler - erigler at usgs.gov
Oliver Boyd - olboyd at usgs.gov <oboyd at usgs.gov>
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