Is the Slide Still Moving?

The landslide engineers, geotechnical engineers, and geologists have all said that there is a possibility that the West Broadway Landslide could move given the right conditions. The landslide is still moving as evident from the monitoring of inclinometers in the bore holes, extensometers at the scarp, and topographic surveys.

Survey & Technology Letters

If there was a condition where there was rain on frozen ground that allowed significant water to flow into the scarp and the slide slip plane, as occurred in 2014, a very raining period and/or an earthquake that disrupted the friction that is resisting the slide movement there could be substantial movement of the slide. The United States Geological Survey (USGS) Letter (PDF) predicted that slide debris form a secondary slide would flow onto Broadway. The Landslide Technology Letter (PDF) stated that the possibility of debris flow from a secondary slide reaching Broadway was low probability, but high consequences.

Landslide Movement

Given the relative risks and potential consequences, the Town through its consultants are monitoring the slide with instruments and periodic site inspections to manage safety concerns. Over the past one and a half years, the slide has been creeping at rates between 0.1 and 0.2 inches per month with occasional increases to 0.5 inches during wet periods. These rates and magnitudes of movement are relatively small and indicate a very low risk to safety. The probability of the slide failing catastrophically is very low due to the granular nature of the slide materials and that the slide movement in April 2014 resulted in a more stable geometry.

Show All Answers

1. Shouldn’t Walgreens Pay to Fix This Slide?
2. Is the Slide Still Moving?
3. What Has Been Done to Stop This Slide?
4. What Might Happen if the Slide Reached the Town’s Water Main Line?
5. What Are the Potential Risks if the Slide Reaches Broadway and the Main Water Line?