Narrator: I am here at the U.S. Geological Survey debris-flow flume near Eugene, Oregon,
to talk to Kate Allstadt, a research geophysicist with the USGS. Kate is studying the dynamics
of debris flows using the vibrations they generate.
Kate Allstadt: Okay, so one of the focuses of this year's debris-flows experiments is
to understand how debris flows generate seismic signals.
So we actually have 48 seismometers-we have two arrays of 12 instruments, each on either
side of the flume that are of different sizes to look at different frequencies.
Using the arrays, we can actually track moving masses, we can see the direction changing
over time.
We are hoping to figure out how to get quantitative information about the debris flow from the
seismic signals.
Andy Lockhart: And so he is putting that seismometer there.
And the seismometer will very accurately give us the timing of the seismic signal as the
flow comes downhill.
Kate Allstadt: Another thing we're trying to understand is the signals that are generated
when a large mass of material starts to accelerate.
So this would apply to both landslides and debris flows.
So we have some instruments directly below the hopper of debris at the top as well as
some broadband seismic instruments that are close to it as well.
We are also trying to understand the physics of what is generating the different frequencies
that we see.
Whether it is the front of the debris flow and how that moves.
We're trying to figure out if that is the strongest part of the signal.
Is that generating signals at different frequencies than maybe the tail of the flow which is made
up of finer material and moves in a different way?
So we're just trying to basically understand what's generating the seismic waves.
Narrator: In addition to the seismometers, researchers use a special hammer that measures
the forces impacted on the ground.
The hammer strikes generate seismic waves that are recorded on the entire network.
It gives researchers information about the subsurface and how seismic waves move away
from the flume.
Precise timing is extremely important for seismology so they use GPS to ensure all the
sensors are synced to satellites.
It takes about a day to do one experiment so everything is carefully planned, set up
and calibrated.
Each experiment is documented by cameras, force plates, seismometers and other instrumentation.
It's all done before the dirt is loaded into the hopper.
Narrator: The experiments are set up in a debris-flow flume, 95 meters long, 2 meters
wide and about 1.2 meters deep.
It slopes at 31 degrees, an angle typical of terrain where natural debris flows originate.
Researchers dump up to 10 cubic meters (about 20 tons) of sediment behind a steel gate at
the head of the flume, saturate it with water and then release it, collecting data as
it flows.
The results of the debris-flow flume experiments help us to understand flow dynamics and develop
improved technologies for mitigating their destructive effects.
Kate Allstadt: ...and then test methods for detecting and tracking moving masses that
we can apply to much larger debris flows in a natural setting, such as at volcanoes, where
you get very large lahars, that are basically the same thing, only way bigger.
And we're hoping that eventually we can use techniques such as what we are testing here,
to detect lahars before they reach populated areas so people can have some warning time
to evacuate and get out of the way of these lahars.
Voice: okay, let's clean up.
CREDITS: Thanks to USGS scientists Kate Allstadt, David
George, Richard Iverson, Jason Kean, Chris Lockett, Andy Lockhart, Matt Logan, Joel Smith,
Kelly Swinford and Dan Tebo Annotated video courtesy of CalTech researcher
Maxime Farin.
The USGS debris-flow flume is located at the HJ Andrews Experimental Forest, near Eugene,
Oregon.
The Andrews Forest is administered cooperatively by the USDA Forest Service's Pacific Northwest
Research Station, Oregon State University and the Willamette National Forest.
See more debris-flow flume experiments at pubs.usgs.gov/of/2007/1315/
Research June 15-16, 2016 Video produced by Liz Westby
July 2016 USGS
2