Releases in Nettleslide (Behrends path) & Last Chance
Goatwatching in winter leads inevitably to fascination with avalanches. Yesterday, Feb 12, 2022, with CBJ’s advisory forecasting level-4-high risk, 6 goats foraged slowly uphill across Nettleslide. Yikes! Careful out there, Jánwu! Personally, I didn’t dare film from any closer than the highschool.
We’ve had several avalanches above our Highlands neighborhood already this winter. Each time, when weather permitted, I shot aerial video. Nadir passes (camera straight down) allow stitches that can be georeferenced for reasonably accurate outlines of the runouts. While I was at it, figured it’d be interesting to compare this winter’s activity with extent of the Waterfall Creek avalanche in April, 2021 (pale blue) and the one in 2017 (lavender) that touched the gate on Judy Lane. Be aware that these runouts only show the ‘cemented’ deposits—what I call the ‘bedload.’ Full impact extends much farther. Kanaan Bausler pointed out a snapped red alder on Maintenance Road, more than 100 feet beyond the jan-2 deposits. It was knocked over by wind blast that could have killed a person.
Nettleslide avalanches mapped from drone passes. Trails in yellow. Pale ‘blobs’ are tallest trees, from 2013 CBJ LiDAR. Darker, unforested zone is mostly rubbery-stemmed slide-alder and more open ladyfern tussocks, maintained by steady barrage of snowslides. Extent of 1985 slide from Dan Bishop oblique, below.
A few days after the ‘big one’ in 1985, my friend Dan Bishop took aerials of the runout, here in Nettleslide and also over White subdivision to the northwest. My map above shows extent of these deposits as a pale white overlay.
Raven’s eye oblique, shortly after the second slide down Strikegully runout, on jan-21. Deposits typically fan out into ‘fingers’ near the bottom. Darker jan-02 deposits are from a dry avalanche that left finer material. The jan-21 slide—black dashed outline on map above—was wetter, forming bigger iceblocks. Stopped short of Maintenance Road in center, but at top, over-ran it, continuing toward Judy Lane gate like the one in 2017.
Meanwhile, back in Last Chance basin, there were snow- and rockslides during the same storms that blasted Nettleslide. Here’s a map showing 2 of them, and a powder plume witnessed by Eran Hood on the same day as our first avalanches around the corner on the channel.
On feb-01, I flew the runouts above Last Chance basin. Thick white lines are hydrologic ‘goatsheds,’ named for Bill Glude’s avalanche starting zones.
The Sunshine runout from jan-21, flown on feb-01. Cemented debris tinted pink. Basin Road at bottom. A faintly visible cross-slope miner’s road, yellowlined here, converges with Perseverance Trail. It’s a century old, which suggests pretty slow accretion of colluvium on this cone; otherwise no traces would remain. I take that to mean that high snowslide frequency and rock/mudslide frequency do not always coincide.
