Tides in the atmosphere ― working much like ocean tides ― can trigger an episode of movement in an ongoing landslide. The study, published online this week in Nature Geoscience, found that episodic sliding of land near Slumgullion pass in Colorado, USA, tends to occur during the daily atmospheric low tide.

William Schulz and colleagues compared hourly measurements of the slip speed of the landslide over nine months with equally frequent observations of local atmospheric pressure. The scientists found a significant correlation between both time series. The effect could be caused by an upward movement of air and water molecules in the soil during periods of low atmospheric pressure, which reduces the friction that usually holds the landslide in place.

The researchers suggest that atmospheric pressure could trigger other geological phenomena that involve sliding surfaces, such as earthquakes, volcanic eruptions and glacier movement.