On August 29 examined some active layer detachment slides Near Arch and Quill creeks, SW Yukon. Around 25-30 slides occured on August 17, the same time the Alaska Highway was blocked by debris flows. A thread of these. This is the slides near where we landed. 1/10
Landed on the deposition zone of one of the landslides and flew the drone. Helicopter indicated for scale. 2/10
This is part of Crey Ackerson’s MSc thesis supported by Kristy Kennedy from the Yukon Geological Survey. 3/10
Finally some pictures of the Koidern Landslide. Start with some aerial pictures and then some more details. Some really interesting mollards, and some have remobilized! It is a long thread as it was a really cool landslide! 1/10
Looks like several phases. Initial failure crossed the small valley and then turned the corner. Then remobilization with a more fluid flow down the valley, blocking the larger stream. Then a smaller failure from the headscarp, where we first landed the helicopter. 2/10
Margin of the slide with lots of mollards. Nice streaking of the bedrock. 3/10
Spent a beautiful Friday at Point Grey (aka Wreck Beach) looking at the stratigraphy. He we have two advance sub-units below the till. The lower is interstratified sand and silt with peats, with ages from 26-24 ka, the upper, cross stratified sand. 1/
These advance sediments are called Quadra Sands and some diatoms in the lower sub-unit sediments indicate marine incursion. The upper sands show tidal influence. With eustatic sea level at this time, indicates >100 m of isostatic depression! 2/
The accumulation of ~70 m of Quadra sands indicates significant accommodation space. The two sub-units are exposed all along the escarpment. 3/
Friday’s Seymour valley fieldtrip examined the stratigraphy of the thick valley fill. The base is 42-29 ka MIS 3 gravel, sand and peat, indicating warmest climate at the base and progressively cooler to the top. 1/9
The MIS 2 Fraser Glaciation, has two advance stades. These are advance glaciolacustrine sediments of the older Coquitlam Stade, a mix of laminated to finely bedded silt and sand and diamicton. 2/9
Indicates ice blocked the mouth of the Seymour valley, forming this lake. There is wood in these advance sediments, dating to around 21 ka. Implies there is a spruce-fir forest in the area as ice advanced. 3/9