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Northwest Geology Field Trips, by Dave Tucker, is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 United States License. You can use what you find here, repost it with attribution to the author, "remix" it for your own purposes, but may not use it with the intent of making money off of it.
EDUCATORS: Please feel free to use anything you find here that is useful to your mission educating people about Earth science. E-mail me if it would help to have a larger or higher-resolution version of any of the images. tuckerd at geol dot wwu dot edu
Mazama O and Baker BA ash on the Damfino Trail.
I just posted my geology field trip guide to the Damfino Lakes Trail, reaching Excelsior Pass from the Canyon Creek road to the north- and a much shorter hike than the Excelsior Trail.
The rock exposures aren’t all that great, but there is a small and lovely exposure of Mazama ‘Layer O’ volcanic ash and Mount Baker BA ash sitting right on top. And of course the flower meadows and the views.
Filed under: News and notes |
Your scribe the cat mattress.
Dave, I did a short trail run up and down Cowap Peak today off the Boundary Trail. Nice! There are many granodiorite erratics near the top. Tons of flowers right now. About 8 cars when got there at 10, about 25 when Ieft at noon! Every single trailhead is full beyond capacity! Cowap…look it up on NWHikers
On Wed, Aug 12, 2020, 1:28 PM Northwest Geology Field Trips wrote:
> magmatist posted: ” I just posted my geology field trip guide to the > Damfino Lakes Trail, reaching Excelsior Pass from the Canyon Creek road to > the north- and a much shorter hike than the Excelsior Trail. The rock > exposures aren’t all that great, but there is a small and ” >
Thanks Doug, I know Cowap. Interesting to hear of the erratics, gives credence to the idea that ice eventually overtopped these ridges from the north. A complex sequence of events. I am trying to visualize them. I wonder what it was like when the first bit of ice pushed through, say, Gold Run, and began to inch down the south side into Swamp Creek. Then down into the Nooksack. Before eventually Swamp creek was filled and ice flowed over Goat. Good thought experiment.
I am leaving for Ozette in a couple days, camping. Take care.
DT
To still be as thick as they are after all these years, erosion and compression from other soil is amazing. How could you estimate the number of inches that fell in that area based on this modern day soil record?
Jim,
Ash falling out of the atmosphere sifts down onto vegetation, snow if present, and onto bare ground. Ash certainly compacts with time, but I don’t really don’t know to what extent. The main usefulness of these ash layers to a volcanologist is to constrain the area covered by the past eruption; the thickness of the ash in the soil is a relative measure. Volcanic ash on vegetation must first be washed or blown off the leaves and branches or twigs before it gets into the ground. Ash on protruding rock surfaces such as boulders and small outcrops is also flushed off. In our wet environment this may not take very long. So ash thicknesses in a soil layer are only a proxy for the initial, probably uneven, fall layer. Its hard to quantify the initial thickness. If you take a look at my Excelsior Trail post, you will see the photo of Mazama Layer O ash. It is very think in one location, and only a few meters away in the same trail cut is not preserved at all. So to have any idea of the original amount of ash, I look for flat surfaces, and take multiple samples. I didn’t have my soil sampling gear with me when I hiked the Damfino trail, so I only have that one fortuitous trail-side exposure to go on. I may go back sometime with my soil probe and see how thick the BA tephra [my primary interest] is in other places in the flats crossed by the trail. It is an obvious place to look for relatively undisturbed BA thickness.
Dave