One of the things I find especially appealing about this area is the way the inorganic pillars and the trees echo each other. The Pinnacles are described as the remains of fumaroles, where hot gasses escaping from the tuff altered the surrounding rock, cementing it better and making it more resistant to erosion than in areas farther away from such vents.
The compositional difference between the upper and lower portion of the tuff at The Pinnacles is particularly obvious in this photo, due to the dramatic lighting. I mentioned yesterday that for years, I had understood this compositional change to be due to magmatic segregation in the enormous Mazama magma chamber. But in retrospect, and thinking a bit more carefully, magmatic segregation occurs not by felsic and mafic components separating in molten form- they are not immiscible liquids. Segregation occurs as higher melting/freezing temperature minerals crystallize out of the solution, leaving the liquid portion of lower melting/freezing compositions behind, commonly by settling, or being "sieved" out. The resulting more felsic melt might also be pressed out, leaving the more mafic solids behind. In other words, magmatic segregation does not form two different compositions of melt, it forms a molten portion and a (mostly) solid portion of two compositions. Multiple episodes of cooling could form three or more distinct compositions.
What we're seeing here is clearly two different compositions of melt.
Now, I've not read any scholarly papers on this, but I did read an article in Scientific American in the mid-80's, and discussed the ideas therein pretty thoroughly with Ed Taylor. To the best of my recollection and understanding, what this represents is an injection of mafic composition into the bottom of a felsic melt. (Note, I do not know the true compositional names of these- is the felsic portion rhyolite, dacite, rhyodacite, etc? So I'll just refer to them as mafic and felsic.) The higher temperature of the additional melt may have triggered a massive convective overturn in the overlying felsic pool, which had previously been stable. The cooler (less thoroughly volatile saturated?) upper felsic magma was replaced with hotter (more volatile saturated?) lower felsic magma. Like LakeNyos in Cameroon, this disruption led to runaway gas exsolution from the magma (though the primary gas was certainly water, not CO2)- in other words, a catastrophic eruption.
So in shortest form, what we're seeing here is not only the result of the eruption, but also the trigger for the eruption. And that blows my mind, in a caldera-forming sort of way.
As spectacular and awe-inspiring as the caldera and lake are, The Pinnacles, to me, is the most illuminating geological feature at Crater Lake National Park. The story told in these deposits is awe-inspiring in its own right. When I was an undergraduate, I was under the impression (I don't recall whether I was told or pieced together my own knowledge and assumptions) that this represented magmatic segregation , with the felsic component on top, and the mafic component on the bottom. This sequence was then subsequently inverted as the magma erupted from the top down when the magma chamber was breached during the catastrophic eruption. There is, however, a serious problem with that conjecture: that's simply not how magmatic segregation works! I'll talk a little more about that and the theory that emerged in the 1980's that may help explain the trigger for this and other large eruptions, tomorrow.
Standing on Dutton Ridge, looking to the south-southeast, across Kerr Valley and Sand Creek, we're looking from the Cascade Range out into Basin and Range. The typical "range and basin" topography of the latter province isn't well expressed in the photo, mainly because the enormous Klamath Basin dominates the distance. But if you look carefully at the scarps on the far side of that basin, their form is unmistakeable.
From Dutton Ridge, looking across Kerr Valley, Mount Scott dominates Crater Lake's southwestern horizon. This ridge between Kerr and Sun Valleys- both glacially modified- is deeply buried in Mazma tephra, which can easily be seen in the foreground. The excellent drainage this creates can make it difficult for perennial plants to get established, and results in vast, beautiful meadows with single and small clusters of trees standing out here and there. Additionally, the fact so much water simply goes into the ground means it has to come out somewhere, and springs are abundant around the area. One in particular that I visited once, Anderson Springs, was quite impressive. It was like a whole hillside gushing water. There was no trail, I just walked off the road. I don't know if the park either encourages or discourages this kind of bushwhacking, but I had the time and opportunity to do so, and felt well-rewarded.
In this location, I think Vidae Creek is best thought of as a hanging valley. It's coming down from a high platform, and here, it's falling off the edge of the Sun Notch glacial valley. The lake itself is the big draw in this park, but many of the lesser-known and unsung features are worth one's time, too.
With Dana Hunter in the foreground, this is the view northward from Sinnott Memorial Overlook. It provides a good view of the caldera and lake, but also has a small museum of sorts, with artifacts from early to modern study of the lake, as well as some interpretive geology exhibits. Another memorable feature is the raised relief model of the park area, which provides a perspective you simply can't get from the ground. Llao Rock and Wizard Island make cameos in the distance. There are many spots with good views, but there's only one spot like this.