Clastic dikes of the Pasco Basin, Southeastern Washington. Final report

• Main Author: Black, R.F.
• Language: unknown
• Published: 2012
• Subjects: 58 GEOSCIENCES; WASHINGTON; DIKES; FRACTURES; GEOLOGICAL SURVEYS; GEOLOGY; PETROGENESIS; FAILURES; GEOLOGIC STRUCTURES; NORTH AMERICA; PACIFIC NORTHWEST REGION; SURVEYS; USA; Pacific; Pasco; permafrost; wedge*
• Online Access: http://www.osti.gov/servlets/purl/7096853; https://www.osti.gov/biblio/7096853; https://doi.org/10.2172/7096853

Clastic dikes are planar features, commonly wedge shaped in cross section, with their apices mostly downward. They are filled with clastic sediments from clay to gravel in size. Three days were spent in the Pasco Basin examining clastic dikes in 10 localities. It was clear from the field observations, summarized in the text, that the features called clastic dikes are multigenetic. Previously proposed theories of origin of the initial fractures, involving earthquakes, desiccation, deep frost cracking, thermal contraction cracking of permafrost, and upward injection of groundwater are not considered primary modes of formation of most initial cracks observed. However, the mechanism of cracking is not yet fully understood. The bulk of material filling most observed fractures came from above during aperiodic and repeated widening and concurrent filling (under an aqueous environment). No evidence for horizontal compression of the dikes or their margins was observed, as from thermal changes or wetting and drying. A loading hypothesis from catastrophic scabland floods is outlined as a possible cause for many typical clastic dikes.