It was a devastating landslides, burying Oso, Washington in March 2014 and setting a record for the deadliest landslide ever in the history of the United States — and more may be coming.

New research by geologists at the University of Washington have analyzed debris bured in past landslides and then used it to map the history of landslide activity in the area. And what they found was disturbing: these landslides happen a lot more often than we thought, according to a Washington Post report.

The landslide last year killed 43 people in the north Seattle suburb. And the study shows that rather than happening every thousand years or so, these landslides actually happen every 140 years, and they have been accelerating this past millenium.

The researchers found evidence of landslides just a few hundred years old, including the Rowan slides, which was massive — five times that of the Oso slide — and happened between 300 and 700 years ago.

That might mean people aren’t in imminent danger of lots of landslides in the near future, but considering how surprisingly often they happen, future land-use decisions will have to take that into account in that region. Logging will need to be examined as it can increase the rate of instability and potentially trigger deadly landslides.

The next step for researchers will be to determine whether earthquakes in the area may help to drive landslides, which may help determine which areas are most susceptible to a landslide triggered by a quake.

“The soil in this area is all glacial material, so one hypothesis is the material could have fallen apart in a series of large landslides soon after the ice retreated, thousands of years ago,” said corresponding author Sean LaHusen, a UW doctoral student in Earth and space sciences, in a statement. “We found that that’s not the case — in fact, landslides have been continuing in recent history.”

The findings were published in the journal Geology.