Do you want to hike on the remnants of the most powerful volcanic eruptions known in Whatcom County? Many of you already have, possibly without knowing it, if you have hiked the popular branch trail from Hannegan Pass up to Hannegan Peak.
This caldera, essentially a large volcanic crater formed by huge explosive eruptions with subsequent edifice collapse, was only discovered as to its formation less than twenty years ago.
More technical detail is here
The eruptions have been dated at about 3.7 million years before present. You won't see a large 'hole' such as at Crater Lake due to details for original shape and also due to extensive post- caldera collapse erosion. Another even less obvious but younger caldera is the 1.15 m.y. old Kulshan caldera, which is closer to Mt. Baker. If you have hiked out on Ptarmigan Ridge you have traversed the rocks of that caldera (more detail here).
The Hannegan Pass trailhead is not accessible by vehicle due to a significant washout, but the good news is that you can park only about 200 yards short of the road end. I believe that the washout is partly due to a large rockfall event that occurred about 3 years ago from the adjacent steep slope on the south toward Mount Sefrit. This rockfall, which stopped just short of one of the campsites, diverted Ruth Creek toward the road, significantly aiding the erosion during a recent flood of Ruth Creek.
not easy to repair. The diverting rockfall is visible on right, former road end on left.
source of the 3 year-old rockfall is cliff in upper right. Sorry about the underexposed pic.
The trail to Hannegan Pass is in fantastic condition....brushed out, no logs, and at present the tread is quite dry. Water for drinking is present in several places before the pass. There is one large log across the branch trail to Hannegan Peak but it is easily climbed over.
Mt.Sefrit. When I climbed it in 1967, we crossed Ruth Cr. here (1/2 mi. along trail), climbed the slabs next to the stream in center, then ascended up and left to the ridge. Summit is on right.
nice work by a trail crew
still some color
bird food: mountain ash.(Bear food too! Link to photo on trail on 10/27 by Steph Abegg).
down Ruth Cr.valley
flaming slopes high on Hannegan Peak. Sefrit beyond.
Ruth. I wish I had a picture of it to show you from the 1960s....much larger glacially-covered area then!
rhyolite ash-flow tuff of Hannegan caldera on Hannegan Peak
There were at least 18 people in small groups coming up as I descended. The weather was cloudy but the cloud base was generally around 8,000' so views were good.
Ruth Creek Valley
"Ruth Glacier" has crevasses.
Ruth, with Blum (immediate left), Jagged Ridge (right) behind
Upper Chilliwack River Valley
tiny pond high on Hannegan Peak...water source for camping up top.
dikes in the walls of the caldera
gray rock is rhyolitic tuff
wall rock of the caldera, with dikes and even some intra- caldera collapse breccia blocks. Hannegan Peak upper left.
Copper lookout (tiny square on ridge top) with Redoubt in distance
Popular destination for October midweek day. 1 other car when I arrived, 11 when I left..
-------------- Passing rocks and trees like they were standing still
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