A new book on the Clastic Dikes of the Columbia Basin of Washington, Oregon, and Idaho will soon be published. It is the culmination of some 20 years of field work throughout this vast inland region (>25,000 km2). The book offers a complete treatment of the dikes, including detailed descriptions, measurements, original maps, dozens of new figures, charts, and clear photographs showing many of the key aspects of these intriguing structures.
Excerpt #1 - Unusual features in an unusual landscape Clastic dikes in the Columbia Basin differ markedly from earthquake-related liquefaction and water escape structures that make up the majority of features described in the geologic literature over the past 150 years. The vast majority of clastic dikes here taper downward (per descensum) and lack connection to a source layer at depth. The dikes are v-shaped injection structures that formed by hydrofracture triggered by repeated loading beneath Pleistocene megafloods and the weight of slow-draining slackwater lakes...
Excerpt #2 - Hydrofracture mechanism
Hydrofractures propagated downward and outward into the substrate, following trajectories consistent with pressurized fluid injection along pre-existing subvertical fractures and horizontal bedding planes. Fluid pressures commonly exceeded O3 (dikes) and occasionally O1 (sills). The fractures were filled forcefully from the top with sediment sourced in bottom-hugging currents. Dike fills preserve a sedimentary record consisting of both far-traveled "exotic" sediment sourced in scabland tracts to the north and east as well as materials derived from local hillslopes and valley bottoms...
Excerpt #3 - Temporal constraints The dikes formed only during the Pleistocene, not before or since. Neogene and Holocene clastic dikes are rare in Eastern Washington and almost completely absent beyond the margins of Ice Age floodways...
Excerpt #4 - Spatial constraints
The Columbia Basin was coursed repeatedly by glacial outburst floods and is the only place in North America where great numbers of wedge-shaped, sheeted clastic dikes, some as large as 2m wide and 50m deep, are found. Either the floods themselves or an outside driver coincident with repeated megaflooding caused the dikes to form here and only here, in a region located hundreds of kilometers inland of the Cascadia margin. Adjacent areas, including the Snake River Plain, East slope of the Cascades, and LaGrande basin, had climates similar to the Columbia Basin at LGM, but were not visited by outburst floods. Neighboring areas are cut by faults, also active since the Miocene, are underlain by similar bedrock (mostly flood basalt), and contain similarly-thick basin fill sediments and loess. None contain clastic dikes in any significant number...
Excerpt #5 - Consistent patterns observed in the field
A rule of thumb pertinent to field work in Pleistocene sediments of the Columbia Basin: If flood deposits, then dikes. Size and abundance depend primarily on silt content and flood count...
Field Data from a Vast Inland Region The scientific foundation for the book is field data collected on thousands of dikes at hundreds of locations in the Columbia Basin - from Hunters, WA to The Dalles, OR and from White Swan, WA to Lewiston, ID. Rather than an elegant study of a few key locations, the typical approach in megafloods research, I chose instead to employ the "brute force" approach, one that involved systematic documentation of dike size and abundance throughout the region in which they occur. The dataset is unique, as is the regional perspective.
I also dive deeply into the evidence for and against the 4 proposed origins and resolve several existing controversies using field evidence and clear illustrations. I tackle intrusion direction (up or down?), the expression of 3D features in 2D outcrops, dike age, how sills and dikes relate, the role liquefaction played in dike formation, water holding capacity and cementation, and origin. Reinjection and truncation - the keys to understanding how and where dikes grow - are covered in detail.
TABLE OF CONTENTS
2.) Field Work in a Vast Inland Region
3.) Proposed Origins
4.) Description of Clastic Dikes Intruding 12 Geologic Units
5.) Fill Bands, Flute Casts & Taper Direction
6.) Truncation, Source Beds, Cross-cutting Relationships & Age
7.) Flood Routing, Sedimentation & Controls on Dike Size & Abundance
8.) New Data: Measurements on >3000 Dikes at >300 Locations in WA, OR, ID
9.) Maps & Spatial Analysis
10.) Hydrofracture, Pressure, Propagation, Hall Plots & Oil Industry Analogs
11.) 2D/3D Geometry & Common Misconceptions
12.) Floodwater Loading, Slackwater Lakes & Analogs from Other Geological Settings
14.) Field Guide to Clastic Dikes in the Columbia Basin
15.) Annotated Literature Review of 75 Articles on Columbia Basin Dikes
Format & Availability
The book will be published in hardcopy format. It will be available for purchase online and through select retail book stores in the Pacific Northwest.