New Map Shows Where You’re Most Likely to Encounter Landslides in the US

If you see your reflection in the snow covered hills, it might be time to check out a new map from the United States Geological Survey. The map reveals that a surprisingly large part of the country is at risk for landslides.

Landslides are often deadly and can cause costly damage. Previous maps only highlighted areas with a high risk of landslides, but the new map, as described in a new paper published in AGU Advances, draws on an extensive database of past incidents and a high-resolution elevation model to assess the threat across the entire U.S. In total, 43% of the contiguous U.S., Hawaii, Alaska, and Puerto Rico is considered “susceptible terrain” under the new calculations, but not all locations are equally at risk.

Previous maps were limited due to several factors. Data for polar regions was scarce, leading to the frequent exclusion of Alaska, despite its significant areas prone to landslides. The data that was used was often fairly low-resolution, which affected accuracy. According to the USGS, previous attempts at creating a comprehensive susceptibility map also underestimated the hazards present in areas with moderately sloping terrain, despite those areas being more likely to be densely populated.

The USGS was able to partially solve this problem thanks to the increasing availability of high-resolution topographic data, which allowed them to more accurately calculate things like the angle of mountain slopes. Also included in their calculations is a database documenting over 600,000 landslides.

“This new national landslide susceptibility map addresses an important but difficult question: which areas across the entire U.S. are prone to landslides?” said Ben Mirus, a research geologist at the USGS who led the effort to create the new map, in a press release. “We are excited that it is now publicly available to help everyone be more prepared–to be a more hazard-ready nation.”

The end result is a colorized map, in which white represents fewer landslides and dark red means more landslides. It’s important to note that the map doesn’t necessarily take into account the severity of landslides, only the risk of a high number of them occurring in a geographic area.

According to the new map, there are some notable problem areas. Almost the entire west coast carries high levels of risk, as does a considerable portion of Idaho. Essentially the entire island of Puerto Rico is high risk, as is much of Alaska. Another problem area is in the Rust Belt area, from the southwestern tip of Pennsylvania, all the way down to northern Georgia.

But there’s good news for the heartland: A long alley of minimal risk stretches from North Dakota all the way down to Texas. Florida has essentially no risk of landslides anywhere, which is good, because Florida has its own problems.

The purpose of the map isn’t to freak people out who live in landslide-heavy areas, but to “potentially support state and federal agencies in their efforts to determine if landslides are a concern for areas of interest and whether site-specific analyses may be warranted,” the USGS geologists wrote in the study.

While the officials touted the new map as a big leap forward in landslide risk assessment, they acknowledged in the study that it’s not perfect. Topography and geology alone aren’t perfect predictors, they wrote. Landslides can even occur in areas with few or no steep slopes. The geologists expressed confidence that continued efforts to make more accurate maps could help improve their models in the future. Which is good, because thanks to the effects of climate change, there are signs landslides could be becoming more frequent.