Interesting Geology

[Turtle]

Originally Posted by Racoon

Me and a buddy went hiking along the Columbia River Gorge.. There are so many interesting geologic formations!

and so may great hikes available to explore.
We did the Wygant on the latest excursion.. a pretty rough trail and rather difficult.

The Columbia River - Mitchell Point, Oregon

this image is from racoon san's link.



on first seeing it and some of the other photos there, i thought they were photos rac took himself. so apparently not but perhaps he will favor us with some if he has them.

so, to the interesting parts at a turtle's pace! . . . there exist on continents today fewer than half-a-dozen such rock formations as those of the columbia plateau & gorge. it is a standing joke among some friends that i drove up the gorge with years ago to say "what kind of rock is that", and then all shout in unison, "BASALT!" you might well imagine what it might be like to be confined with me in a small space for several hours if the joke is not apparent enough.

so it's all basalt and one gigantomundous set of eruptions of lava along seams miles long, rather than erupting vents as in my nearby green mountain which lies less than 20 miles wnw of the terminus of the columbia basalts in the columbia river gorge. here we go thens.

Flood basalt - Wikipedia, the free encyclopedia

Originally Posted by wikack

A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales (large igneous provinces) in prehistory, creating great plateaus and mountain ranges. Flood basalts have erupted at random intervals throughout geological history and are clear evidence that the Earth undergoes periods of enhanced activity rather than being in a uniform steady state....

The Columbia River flood Basalt Province : Current status

Originally Posted by P. R. Hooper

Résumé / Abstract
The Columbia River flood basalt province is smaller by an order of magnitude than the Deccan, Karoo, Paraná, and Siberian continental flood basalt provinces. Its smaller size, relative youth (17-6 Ma), excellent exposure, and easy accessibility have allowed development of a flow-by-flow stratigraphy in which ' many flows can be traced across the Columbia Plateau, often linked directly to their strongly oriented feeder dikes in the southeast quadrant. The detailed stratigraphy provides a precise record of the changes in magma composition and volume with time and demonstrates more clearly here than in other provinces that single fissure eruptions had volumes in excess of 2,000 km3 and flowed across the plateau for distances up to 600 km with negligible changes in chemical or mineralogical composition. Current evidence suggests that the Columbia River flood basalts resulted from impingement of a small mantle plume, the Yellowstone hotspot, on the base of the lithosphere near the Nevada-Oregon-Idaho border at 16.5 Ma and that the main focus of eruption then moved rapidly north to the Washington-Oregon-Idaho border from where the main eruptions occurred. ...

note: there is some new evidence that the siberian flood basalts resulted from antipodal focussing of a very large meteor impact, the crater of which now lies beneath the antarctic ice, and that interesting story is in one of our "impact" threads here.

[Turtle]

Originally Posted by Turtle

note: there is some new evidence that the siberian flood basalts resulted from antipodal focussing of a very large meteor impact, the crater of which now lies beneath the antarctic ice, and that interesting story is in one of our "impact" threads here.

so doing some outside reading i came across some of the material i mentioned about antipodal focussing and discovered that it is considered a possibility that the columbia flood basalts were initiated by a large impactor.

so what the rock is antipodal focussing? funny you should ask.

Shock Dynamics: Antipodal effects


so here is the bit, an abstract only, mentioning the possibility of an impact triggering the columbia flood basalts. note that at the necessary position, the antipode, no impact crater evidence is yet found. (boldenation mine.) . . . .

Energy Citations Database (ECD) - - Document #10197028

Originally Posted by mark boslough et al

We suggest that the most likely result of the focusing for a sufficiently large impact, consistent with features observed in the geological record, would be a flood basalt eruption at the antipode followed by hotspot volcanism. A direct prediction of this model would be the existence of undiscovered impact structures whose reconstructed locations would be antipodal to flood basalt provinces. One such structure would be in the Indian Ocean, associated with the Columbia River Basalts and Yellowstone; another would be a second K/T impact structure in the Pacific Ocean, associated with the Deccan Traps and Reunion.

[Turtle]

i earlier misspoke when i put the terminus of the columbia flood basalts 20 miles ese of green mountain; in fact the basalts extend all the way to the coast. here is a map & some explanatory material.

CVO Website - Columbia River Flood Basalts - Map


i also plotted the antipode of the columbia flood basalts, starting from the more-or-less geometric center of gravity of the flood basalts extent shown on the map above; centered near Umatilla. i used this mapping tool: >> Antipodes Map - Antipodal location for any map point
mind that it takes a veeeerrry large asteroid to have the energy for antipodal focussing to result in volcanism. the crater under the ice in Antartica suspected of initiating the Siberian flood basalts is on the order of 300 miles across. >> Meteor Impact Crater Discovered Under Antarctic Ice
i say Winston!