Friday, August 29, 2008

First insights from the Grand Canyon

Probably the most striking aspect of my recent trip down the Grand Canyon is the stark contrasts of the intracanyon lava flows and related response of the river there with those of the Owyhee.
  • The lava stratigraphy in the GC is notably more complicated than the Owyhee.
  • In GC the variability in lava textures and the facies variability of related volcaniclastic deposits is much greater. Some GC volcaniclastic deposits are downright bizarre looking to me.
  • In several circumstances, there is strong evidence supporting the occurrence of catastrophic flooding in conjunction with the incursion of lava into the Grand Canyon (note photo above); whereas on the Owyhee, there is no clear evidence of this.
  • In GC, there are few to no really good examples of lava deltas. The Owyhee has world class examples.
  • In GC, the intracanyon flows are not associated with large-scale (post-emplacement) mass wasting processes. The Owyhee has some spectacular post-emplacement landsliding of lava flow remnants and, thus, continue to plague the river for 1000s of years.
Bottom line is that there is great evidence in the Grand Canyon for lava dam failure and related catastrophic flooding. There is weak to no evidence in the Grand Canyon for effective, relatively long-lived damming of the river. In contrast, there is weak to no evidence on the Owyhee River to support catastrophic flooding related to lava dams. There is great evidence on the Owyhee that substantiates effective, relatively long-lived damming of the river by lava.

Obvious questions: Why the profound differences? Why is the Owyhee so much easier to dam with lava than the Colorado?

1. Volume of lava vs. volume of water
2. Mode of entry: canyon rim cascade vs. tributary valley route
3. Severity of topography (vertical and lateral trajectory of lava incursion)
4. Proximity of volcanic vent to the canyon; abundance of pyroclastic material.

I am pretty sure it involves aspect of each of these factors. Stay tuned for more maunderings and some more details on the points above.

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