I've been trying to find a name for the peak on the left-middle skyline; at 6200 feet plus, it must have a name. However, I've been unsuccessful. The rubbley and shaded area on the left is the quarry northeast of, and the base of, Hogg Rock, and TFJ is the peak on the right. My sense, when I was there, was that we were looking at the transition between an icefield and a valley glacier in terms of the valley landforms, and the Google topo map below seems to support that somewhat. The black dot is the approximate location where the above panorama was taken. The patch of blue on the map's lower left edge, above Route 20, is the east end of Lost Lake.
Directly south of Hogg Rock, and not pictured, is Hayrick Butte, another tuya, and Hoodoo Butte, a post-glacial cinder cone, and the closest ski area to the mid-valley region.
From a quarry on the north side of Hogg Rock, the view to Three Fingered Jack is excellent. Three Fingered Jack is described on OSU's Volcano World page as a stratovolcano in the leading basic information, then in the first sentence as "a deeply eroded basaltic shield volcano." I don't know which it is, but I guess I'd lean toward shield rather than stratovolcano. The Oregon Cascades were heavily glaciated during the Pleistocene, and the fact the volcano is so deeply incised shows that it hasn't been active- or at least hasn't had any major lava-producing eruptions- since the end of the ice age. Mt. Jefferson, the next major peak north of it, shows the same style of faceted glacial erosion.
Route 20 winds around the west and south side of Hogg Rock, a tuya (a sub-glacial eruptive landform, where the lava erupted under ice), much too close to get any decent photos, and the rock here in the quarry seemed too nondescript to bother with. The best photo of Hogg Rock on this trip was the one I took at Lost Lake. As noted in the post at that link, the pass area burned a few years ago, killing many, many trees.
I'd say the hole is about 4-5 feet across, less than the 6 foot diameter reported in most of the stories I've read, and 2-3 feet deep. As I mentioned in the first post about this location, the layers of ash and lapilli are probably responsible for creating a tough and poorly permeable lake bed. It does seem likely to me that this is some kind of sinkhole, but I don't have any sense of what might have created the void that the rock collapsed into. The mafic lava flows in the area have enormous amounts of void space in their rubbly surfaces, and I don't feel that a lava tube is a necessary conclusion, though it might be the correct one. Perhaps someday we'll find out.
To put this in a broader context, if you're traveling across Santiam Pass, and you have a little time, this is well worth the rugged, pot-holey drive in (I'd say okay for smaller cars, just take it slow.) at least once. It's not something I'm going to feel I need to do every summer, but I'd like to visit in the late spring sometime, and given the new hole, it might be worth stopping every few years or so, to see if the area evolves further.
Drain, Oregon is an actual town off I-5, south of Eugene. But these two holes actually help drain Oregon. With Gary for scale, you can get a sense of how large the holes are, and their relationship to each other.
Looking more or less west from its newest "drain hole." The old one is just out of the frame to the right. It's an odd spot, even without the drains: the basin was almost certainly covered in glaciers during the Pleistocene, but more recent volcanic activity blocked the outlet. As I mentioned on Friday, much of this area is covered with very permeable lava flows. Rain and snow melt goes directly into the ground, to re-emerge as springs at Clear Lake and elsewhere along the Upper McKenzie River. Here, apparently, the tephra seen in Fridays post, and the lacustrine sediments visible in the sides of the hole above, create a less permeable cap and impounding the lake's water. I can't say what portion of the lake's summer water loss goes down these holes, and what infiltrates directly through the lake bed and into the underlying bedrock, but I doubt the holes account for all of it. That is, I expect the lake bed isn't entirely impermeable.
Route 20 runs through the notch in the horizon on the left, and along the south side of the lake.
The sediment forming the edge of the second hole appears to be more like lake mud and silt than the ash and lapilli in the first, older, hole. However, I didn't look all that carefully at the stratigraphy here- the same mud and silt (which appears to be more easily eroded) may have been removed over the years since the original hole opened up. In other words, given a few years of erosion, this hole may come to look the same as the old one.
Also, as you can see, this hole is still draining the lake in early September. We had our first significant rain of the season yesterday and this morning, and I'd bet the pass area got much more rain than we did down here in the valley. While the next week is forecast to be dry and very pleasant, it won't be too long before both holes are submerged again.