Thanks jamesf for the welcome and the advice, I appreciate it. I can improve at the patience part, so that when someone says something so blatantly and demonstrably wrong like "stratification (of ash) only forms in water" I won't be short with them.
Just wanted to welcome you here. I found the above comment a very accurate summary. I hope you can stay around. You seem to have an excellent background in geology (and better than mine). However, you will have to be very patient with people here. As you state, many of their arguments directly contradict each other but as far as I can tell, they either don't understand the basic logic or simply refuse to acknowledge this.
The rivers incised in basalt have fascinated me for years. For instance,
A large portion of the pacific northwest is overlaid with a huge basalt field called the Columbia River Basalt. Conventional geology thinks this field formed between 14-16 MYA from the massive volcanic activity driven by plate tectonics
Over time, several major rivers (Columbia, Snake) and their tributaries have managed to erode deep winding meanders into the solidified basalt. A good example is the Powder River in Oregon
THE GEOLOGY OF THE LOWER HALF OF THE POWDER RIVER CANYON BETWEEN THIEF VALLEY RESERVOIR AND THE LOWER POWDER VALLEY, BAKER COUNTY, OREGON
Science Department, Badgley Science Center, Eastern Oregon University
Abstract: The Powder River between Thief Valley dam and the Lower Powder Valley is the deepest (244 m; 800 ft) and the gradient of the river is steepest (~9 m/km; 48 ft/mi) where the river cuts across faults that mark the margins of uplifted and tilted fault blocks. These sections of the river are the site of three large landslides that formed because steep slopes created by rapid river down-cutting, structural failure of tuff beds underlying the thick olivine basalt flows in the area, and, possibly, earthquakes activity. Two large-scale meanders in the course of the river appear to be related to geologic structures in the metamorphic bedrock. If uplift rates in the Powder River Canyon area were similar to those to the north between Telocaset and the Grande Ronde Valley over the past 9 million years, then the Powder River began carving the canyon between Thief Valley dam and the Lower Powder River at ~2 million years ago, the same time as when Lake Idaho drained out through Hells Canyon. The high river gradients, the abundance of landslides, and the occurrence of a magnitude 3.6 earthquake in 1969 along one of the faults in the area adjacent to the river suggest that uplift is continuing in the area and indicate that the river is still adjusting to the rotation and tilting of the fault blocks in the area.
Introduction: The Powder River and its principal tributaries originate on the east and west flanks of the Elkhorn Mountains of Baker County, Oregon. The river enters the Baker Valley at Baker City, flows northward to a point a few miles east of the town of North Powder, and enters a canyon that is deeply incised into the Powder River Volcanic Field and the underlying Mesozoic volcanic arc sequence (Bailey, 1990). The river flows through the canyon southeastward approximately 32 km (20 miles) across a series of uplifted fault blocks that tilt toward the east before exiting into the broad Lower Powder Valley syncline (Brooks and others, 1976). Below Thief Valley Reservoir, the Powder River flows through a rugged gorge that is more than 244 m (800 ft) deep from rim to riverbed, yet often less than half a mile wide. The river elevation drops from 950 m (3100 ft) at the upstream end of this stretch to 850 m (2800 ft) at the outlet of the canyon. This part of the Powder River Canyon includes huge landslides, entrenched meanders, precipitous cliffs and rock outcrops, and other features of geologic interest (Fig. 1).
source, read more here
Again, here we have incised (entrenched) meanders cutting down through over 800 ft. of solid basalt. Similar things are found in the other rivers in the area too, like the Snake River shown here
Maybe someday I'll get the detailed YE explanation for how these rivers formed in the basalt.