On March 22, 2014, a rainfall-triggered landslide near Oso, Washington, sent muddy debris spilling across the North Fork of the Stillaguamish River. The debris swamped numerous homes, resulting in the deaths of at least 24 people, according to news reports. As of March 25, dozens of people were still missing.

The landslide created an earthen dam that blocked the river, causing a barrier lake to form. The Operational Land Imager (OLI) on Landsat 8 acquired this image of landslide debris and the barrier lake on March 23, 2014. An image of the same area on January 18 is shown for comparison. Turn the comparison tool on to see how the landscape changed. To see aerial views of the landslide, read this blog post.

As water backed up, local authorities expressed concerns about a potential flash flood. On March 23, water began to flow around the north side of the dam. On March 26, a National Weather Service flood warning remained in effect for areas on the Stillaguamish River east of the blockage.

According to Durham University geologist Dave Petley, the landslide was a reactivation of an earlier landslide that caused problems in 1988 and 2006. The Seattle Times has reported that retired US. Geological Survey geologist Daniel Miller warned the hillside had the “potential for a large catastrophic failure” in a report filed with U.S. Corp of Engineers in 1999.

NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland.