Headed to the Northshore with alumni grad student par excellence @CarieAnnLau to check out the effects of Thursdays pineapple express. Lots of sediment in Mosquito Creek. @NVanDistrict working on removing it before the next storm comes in tonight. #SFUNaturalHazards
Lots of great, new sediment capture basins in @NVanDistrict. Idea is to stop culverts from getting plugged and causing diverting of flow and flooding. This one has a dip in the trail in case it does plug, it will keep the water in the right place. #SFUNaturalHazards
Small debris slide Upper Mosquito Creek just downstream of the debris retention netting. Still waiting to see this netting capture the next debris flow! Maybe tonight? Seem to be hiting the peak of the storm right about now.#SFUNaturalHazards
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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