On March 22nd, 2014, a massive landslide occurred along the north bank of the North Fork of Stillaguamish River, just east of Oso, Washington. The event killed 43 people in the Steelhead Haven community, making it one of the most deadly landslides in US history. The deposits dammed the river, causing it to pool until it overtopped the material. The river then began to cut a new channel through the deposit, taking a course directly through the hummocky terrain.
The USGS Washington Water Science Center was tasked with monitoring this new channel, both for local stability and with an eye towards the impact of the newly eroded sediment downstream. As part of that effort, we are making use of photogrammetric techniques (structure from motion) that allow us to produce detailed topographic maps from aerial photographs. By comparing sequential terrain maps, we are able to quantify the volumes of sediment that have been eroded out of the new channel. In addition, we are able to stitch together the images to create a seamless aerial mosaic of the landslide. Those are the images you see here. Each consists of several hundred photos, taken using a Ricoh GR camera mounted into the wing of a Cessna 205 flying ~500-1000' above the slide.
The sequential images show that the channel has been stable over the first months of the flood season. The channel has widened, as expected, but at a relatively sedate pace. More subtle changes on the deposit surface are also visible, as various pools fill and connect and steep slopes slump towards an angle of repose. We will continue to monitor the channel over the course of the flood season, posting images as they become available.
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Jan 07, 2015
environmental, geology, landscape, nature