Geologic Publications for Mount Rainier
Geomorphic assessment of significant sediment loading in Tahoma Creek
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Scott W. Anderson
, Paul M. Kennard
, John Pitlick
Mount Rainier National Park
Glaciers through out the world have been retreating as the earth warmed out of the last glacial maximum, around 12,000 years ago. As these glaciers retreat, they leave behind massive amounts of unconsolidated sediment stored in terminal and lateral moraines. This material is readily entrained into stream channels when heavy rains or glacial outburst floods trigger debris flows.
In Tahoma Creek, a glacial stagnation event in the late 1960's initiated a period of very rapid glacial retreat, numerous outburst floods, and consequently, a high volume of debris flows. This material caused significant damage to the West Side Road, and resulted in reduced or restricted access to much of the west side of the park. This material also has a downstream impact - the increased sediment inputs appear to be causing the elevation of the river beds to rise, or aggrade. Given that much of the infrastructure of Mount Rainier National Park lies along the valley floors of these streams, aggradation could pose a significant threat to park operations. This issue was illustrated by the massive 2006 flood event - while damaging in it’s own right, aggraded streams have less flood conveyance, and so are more likely to spill water overbank, and are also more laterally dynamic, shifting their course with potential to attack previously stable areas. The damage at Longmire and the destruction of Sunshine Point campground illustrate these issues. On Tahoma Creek, concern mostly lies in the fate of the Tahoma Creek Bridge, seen in figure 1. With only modest clearance between the river and the span’s base, even moderate aggradation could wash out this structure.
The goal of this research is to assess the processes and rates of aggradation within this valley to help guide management decisions regarding the bridge, as well as to gain a more detailed understanding of the broader dynamics at play. While this study is focused, the issue of river response to a changing climate is a broad one, with impacts through out the Park, as well as for downstream communities.
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In Text Citation:
Anderson and others (2013) or (Anderson et al., 2013)
Anderson, S.W., P.M. Kennard, and J. Pitlick, 2013, Geomorphic assessment of significant sediment loading in Tahoma Creek: Science Brief, Mount Rainier National Park, 2 p..