New Method for Counting the Missoula Floods

Boise State University
Meridian, Idaho
Earth Science
Open Access
Raised of $3,500 Goal
Ended on 3/15/15
Campaign Ended
  • $2,157
  • 62%
  • Finished
    on 3/15/15

About This Project

Sheeted clastic dikes offer geologists a new way to count the Missoula floods. The dikes formed coincident with flooding and grew larger with each flood event. Each flood is preserved as one or more fill bands in dikes. Each subbasin preserves a different flood count. Here we test whether clastic dikes grew larger in basins visited by more floods by documenting the number of fill bands in dikes at 300 sites throughout the Columbia Basin.

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What is the context of this research?

Clastic dikes are sediment injection structures that form in response to perturbation by earthquakes or rapid loading. In this case, the dikes appear related to floodwater loading. The dikes number in the tens of thousands and are composed of multiple vertical fill bands. Each fill band represents a pulse of injected sediment and an increment of dike widening. Fill bands vary in number from place to place around the Columbia Basin, thus should offer a high resolution record of flood routing through the seven main subbasins; lower elevation tracts received more floods. Our preliminary survey of 200 dikes indicates more fill bands do indeed occur at lower elevations. Fill bands counts are an elegant and quantitative way to increase our spatial understanding of flooding basin by basin.

What is the significance of this project?

The Missoula floods are some of the largest to occur in Earth's history. The floods repeatedly inundated a region some 30,000 km2 in size. Through time, the floodway shifted and waters followed a variety of different tracts. Flood sediments, preserved in off-channel slackwater areas, preserve a record of flooding within individual subbasins. However, Missouls flood sediments are notoriously difficult to age-date and fingerprint geochemically. The result is an unclear picture of anastomosing floodway through time. Basic flood routing questions remain unanswered. We seek to provide new data on what floods were in which basins at what times during the ~3000-year Missoula flood cycle. PLEASE SEE OUR FIELD PHOTOS.

What are the goals of the project?

1.) Document fill band counts at at least 300 locations where clastic dikes are exposed throughout the entire Columbia Basin (Rathdrum Prarie to Willamette Valley). How do fill band counts vary spatially throughout the Missoula floodway?2.) Compare our results to variable-volume 3D hydrologic models of Missoula flooding built previously by the USGS (Denlinger & O'Connell, 2010). Does correlations exist between dike width, fill band count, flood depth, and flood velocity?3.) Present our results at the upcoming Geological Society of America meeting and other regional gatherings.4.) Prepare a manuscript for publication in relevant academic journals. We will target Geomorphology, Geology, GSA Bulletin, PLOS, and Quaternary Research.


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We have a singular focus: Collect accurate fill band counts from several hundred locations along the 500 km-long flood route through the Columbia Basin (Lewiston, ID to Albany, OR). We have planned our stops in advance and secured the necessary landowner permissions in order to maximize travel efficiency.

The funding we seek directly supports field data collection, including the travel and spartan accommodations (tent camping).

Our study area is vast. Getting to all of our sample sites is our primary challenge. We provide our own excavation tools, sample-collection supplies, camping equipment, and vehicles so no new equipment will be purchased.

This is bare-bones, old-school field work like you probably did back in the day.

Meet the Team

Skye W. Cooley
Skye W. Cooley

Team Bio

I am passionate about field work, especially when it involves new discoveries. Clastic dikes in Missoula flood basins represent an exciting new path for research into the flood story, one popularized by film and books, but incomplete and lacking field data. Clastic dikes are intricate and extremely well-preserved sedimentary features that have much to tell us about past climate, local tectonics, flood physics, and sedimentation. My approach is quantitative, regional in scale, and data-focused. The dikes offer an excellent chance for discovery.RELEVANT PUBLICATIONSCooley, SW, 2014, Field guide to exposures of large clastic dikes in Columbia Basin of WA-OR-ID, Northwest Geology v. 43 Cooley, SW, 2008, Clastic Dikes: Indicators of climate during late-glacial Missoula flooding? GSA Ann. Mtg. Abs w/ Progs v. 40Cooley et al., 1996, Timing and emplacement of clastic dikes in late Pleistocene Missoula flood deposits, Walla Walla Valley WA, GSA Cordilleran Section Mtg. Abs w/ Progs v. 28

Additional Information

A typical clastic dike in Missoula flood deposits. Each vertical fill band represents an increment of filling and dike widening driven by flood loading. Each band represents one outburst flood event.Some dikes grew very large. This one is 2m wide. Many show evidence of reinjection over time, consistent with the 2000-3000 year Missoula flood cycle. The left-most fill band in the photo above intrudes from the bed just above and left of the trowel. On the right, many fill bands intruded later and were sourced in the overlying beds. One way we can tell the dikes intruded downward from the surface is by the composition of their fill. Whatever sediment was available at the surface at the time of injection was forced downward. In this case, light-colored silty sediment was injected into ancient river gravels.Once in awhile you get lucky and catch the dikes in the process of formation. These examples show how mobilized sediment cuts across sedimentary layering, but was only able to reach this stratigraphic level.If you excavate away the sandy fill material to expose a dike's wall, you will see this. The silt walls are lined by upward-pointing features called "flute casts". Flute casts are unambiguous indicators of fluid flow direction. Sediment entered the dikes from above.The dikes have clear relationships to flooding. Here, downward-tapering dikes originate from the base of a high-energy backflood channel confined in a narrow bedrock canyon.The dikes cut straight through layers of varying grainsize and strength routinely. This dike, thicker at its top, originates in tan colored flood sediments at the top of the outcrop and penetrates downward through older layers of sand, silt, and gravel.Reinjection of younger fill bands into older ones is common. Here, a smaller dike (right) joins a larger one (left), utilizing the pre-existing plane of weakness.In several locations around the Columbia Basin, silt-sand dikes intrude bedrock. This example shows a 15cm-wide dike intruding several meters into pillow basalts of the Columbia River Basalt Group. The dike is sourced in flood sediment atop deposited atop the basalt (out of frame). Cross-cutting relationships like this leave little room for traditional explanations that attribute the dikes to liquefaction and upward escape of fluidized sediment. Clastic dikes in the Columbia Basin are unusual in the geologic record. Fieldbook for scale.Floodwater loading appears to explain best the large soft-sediment deformation features preserved in shoreline exposures near the mouth of the Sanpoil River. The Sanpoil is located 200km north of Wallula Gap and the major through-going fault zone, the OWL. Here, clay-rich sediment of Glacial Lake Columbia was mobilized by Missoula floods that overtopped them, forming a contorted, dike-like body.One way to visualize the formation of clastic dikes by floodwater loading is with this debris flow analog from Black Dragon Canyon, Utah. The photo shows red clastic dikes forced downward into light-colored sediment from the base of a heavy, over-riding debris flow. Debris flows are rapidly-deposited and can be quite voluminous, thus impose heavy loads. Missoula floods also arrived very quickly and were, in places, more than 100m deep. Slackwater lakes in back-flooded valleys stood atop valley fill sediment for several weeks prior to draining.Some dikes in the Columbia Basin are lithified. These dikes are finer grained and generally constructed of a much thinner set of fill bands. Lithified dikes are older than the more common Missoula flood-age dikes, which are late Pleistocene in age. Lithified dikes are early to middle Pleistocene in age, a period sometimes referred to as "pre-late Wisconsin". These dikes also formed during a glacial period and under climate conditions similar to that during Missoula flooding. This older set of dikes intrude flood-related deposits in the Walla Walla and Pasco subbasins. We see this older set as further link between clastic dikes and outburst floods. Thin sections have been made from several dikes and the petrographic analysis of the fill bands and micro-scale cross-cutting relationships is currently underway.

Project Backers

  • 22Backers
  • 62%Funded
  • $2,157Total Donations
  • $98.05Average Donation
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