From Atmospheric Rivers to Rivers of Debris:
Will climate warming increase the risk of debris flows
from Cascade volcanoes?
Background
A major warm rainstorm in November 2006
produced damaging debris flows from Cascade
volcanoes, resulting in major damage to Mt Rainier
National Park (MRNP), and closing of mountain
roads throughout the region. Similar debris flow
events earlier in the decade prompted concern that
the risk profile for Cascade volcanoes may be
changing.
Climate may impact debris flow frequency by:
• Changing intensity/frequency of forcing events
• Promoting continued glacial retreat/fragmentation
• Increasing length of snow free period
This study focuses on cool wet season events only
(not glacial outburst floods).
Gordon Grant, USDA Forest Service; Anne Nolin, Stephen Lancaster,
Beth Copeland, Lauren Parker, Oregon State University; Paul Kennard,
National Park Service, Mt. Rainier; Ian Delaney, Whitman College
1) Are there characteristic meterological conditions
associated with debris flow events?
10/31-11/7/06
a) lots of rain
b) strong SW flow
Mount Rainier
i.e. Pineapple Express /
Atmospheric River (PE/AR)
2) Where have recent debris flows
initiated with respect to modern
glaciers and previously glaciated
terrain?
Mt Rainier
NASA Earth
Observatory image
Cascade volcanoes with debris
flows initiated by Nov 2006
storm. Data presented is
primarily from Mt. Rainier.
Figure courtesy
Richard Iverson
c) high freezing levels
d) little antecedent
snow cover
Mt Rainier peak
elevation
A debris flow is PE/AR related if a PE/AR event occurred
on the same or prior day as a debris flow.
2001-2006
debris flow
initiation sites
Glacier Extent
1913
2008
non PE/AR event
PE/AR event
2006 debris flow damage, Mt Rainier National Park: photos NPS
• Atmospheric events producing debris
flows come in different flavors
• Apparent recent increase in debris flows,
but record is incomplete and potentially
biased
• Initiation sites located immediately below
active glaciers or ice cored snowfields
• Consistent pattern of aggradation within
Mt Rainier National Park (MRNP)
• No consistent aggradation in larger rivers
Acknowledgements
Funding for this research has been provided
by USFS, NPS, NSF and the Mazamas.
Poster design: Sarah Lewis
3) Is there a change in the pattern of downstream disturbance due to
historical and recent debris flow and floods?
1951
post 2006 storm
1960
1000.0
Recent Aggradataion Rates (cm/yr)
Initial Findings
Pineapple Express (PE) events (Dettinger, 2004) and Atmospheric Rivers (AR)
(Neiman et al., 2008); Debris flow data from Driedger, Walder, Kennard
from Beeson,
1) Data
Evidence
for2007
widespread
aggradation
100.0
Sunshine
Point
10.0
1989
2) Higher than
long-term
average in last
decade
White
River
1.0
Longmire
1997-2006
0.1
1978
Lower Van
Trump
0.1
1.0
10.0
100.0
> 100yr Flood
• In areas exposed by recent
(5-10 yr) glacier retreat
• Near glacier termini or
debris-mantled stagnant ice
• At heads of steep-walled
gullies flanked by steep
debris-mantled slopes
• No clear evidence for mass
movement (below)
2006
1000.0
Long term (1910-2006) Aggradation Rates (cm/yr)
Tahoma Creek
Historical widening of
channels greatest for those
with highest frequency of
recent debris flows
Debris flow channels within
MRNP show recent increase in
aggradation rates (above)
Larger channels outside MRNP
show both aggradation and
degradation (right)
Christopher Magirl, USGS
Photo: NPS
The Cascade Periglacial Debris Flow Project
Mt Rainier
Fire Hose Effect? (above) water is
concentrated in sub- or supraglacial channels. Flow directed
toward unstable, sediment mantled
slopes below or adjacent to glaciers.