25 April 2023
The 22 April 2023 landslide in Draper in Utah
Last week, the State Geologist of Utah, Bill Keach, warned of landslides in Utah this year. He made a prescient observation:
“We hope our engineering is better. But our urban sprawl has pushed us into areas where we weren’t built before.”
A few days later, on 22 April 2023, his warning came to pass when a landslide occurred in the town of Draper in Utah, destroying two houses. The event was captured on video that has been posted to Youtube:-
The landslide occurred on the Hidden Canyon Subdivision. There is some good drone footage of the aftermath of failure. KUTV has a good gallery of images, which includes this view of the upper-reaches of the landslide:-
And this image looking down the landslide track:-
The second image shows a quite mobile landslide, presumably associated with the fine grained soils and the steep terrain.
The two destroyed houses were completed in December 2021 by a developer. Problems emerged in early 2022, as described in a news report on KSL TV from December 2022, which highlights the development of cracks in the structure and in the surrounding ground. Attempts were made to stabilise the properties, but in October 2022 the owners were forced to vacate the buildings. The same report has a video about the site, which includes this still:-
It appears that the location of the landslide is [40.486, -111.824]. The image above appears to show cracking of the engineered slope, most notably on the left hand side at the top of the slope. Google Earth imagery from 2020 hints at the reason for this slope – it appears to suggest that a large amount of fill has been emplaced to create the platform for the houses:-
Whilst the time of the Draper landslide might indicate that the snowmelt has played a role, the underlying cause will lie in the slope itself. There are two obvious possibilities – first, that the failure has developed in the fill slope itself; second, that the materials upon which the fill has been emplaced, which is likely to have had a volcanic origin, have failed.
Looking at the shape of the landslide I would tend towards the latter explanation, but a proper investigation is needed to verify the cause.
Clearly, this is a devastating event for the owners of the lost houses, and for the owners of the other two that have been evacuated. They are entirely blameless.