This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Saturday, June 18, 2011

Why old dams are dangerous: Martis Creek Dam, Polaris fault, and Reno

Martis Creek Dam and reservoir in winter
Photographer Michael Nevins
U.S. Army Corps of Engineers
public domain image
Martis Creek Dam is in Nevada County, California, about 6 kilometers east of Truckee, about 56 km upstream from Reno.  The lake is next to the Truckee-Tahoe Airport (runway in left of photo). The highway in the foreground is California State Route 267.  This winter scene shows the lake in winter when it is fairly full.

This dam is one of 10 dams in the U.S. that has been judged to have "urgent and compelling" safety concerns according to the U.S. Army Corps of Engineers. The dam, which was completed in 1972, has significant leakage and was believed to lie close to two fault zones. If the dam fails, potentially parts of Reno could be flooded.

The dam is an earthen embankment, underlain by glacial outwash. It has a history of excessive seepage during reservoir test fillings, including sand boils through the downstream toe, and seepage along stratigraphic contacts adjacent to the spillway. These concerns, along with the two known faults, have prevented it from being used at its design level. (Note: a post here about sand boils, and an update on that post: the levee did fail and the town of Hamburg is now in danger of flooding.)

The plot has now thickened: this month, Hunter et al. reported in the Bulletin of the Seismological Society of America that Lidar work there revealed a new fault, now named the Polaris fault.  It's 35 km long and has the potential to generate a magnitude 6.4-6.9 earthquake. It exhibits "youthful and laterally continuous tectonic geomorphic features" along its full length. It represents a significant seismic hazard to the greater Truckee-Lake Tahoe-Reno-Carson City area.

Reference: Hunter et al., LiDAR-Assisted Identification of an Active Fault near Truckee, California, Buletin of the Seismological Society of America, vol. 101 (3), p. 1162-1182, June 2011.


Thesis Writing said...

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Tara @ Stancliffe Stone said...

This is really concerning. Great post.