London, November 2 (ANI): In a new research, scientists have found out that atmospheric tides are responsible for causing landslides.
According to a report in Nature News, the research was carried out by William Schulz of the United States Geological Survey in Denver, Colorado, and colleagues, who took as their subject case the four-kilometre-long Slumgullion landslide in the San Juan Mountains of southwestern Colorado.
At its centre, soil and weathered rocks creep downhill at an average speed of half a millimetre per hour.
The movement of the landslide accelerates during the spring snowmelt period. And, puzzlingly, it is generally faster during the night than in the day.
The team of researchers set out to investigate the landslide's mysterious movements.
Over a period of nine months they monitored the landslide at two spots, taking hourly measurements of slide speed, the water pressure inside pores in the soil, and weather conditions.
They discovered that the movements of the rubble were in sync with 'atmospheric tides' - daily highs and lows in atmospheric pressure that are excited by changing exposure to the Sun's rays and by the Moon's gravitational pull.
The team found that during nightly hours of low atmospheric pressure, the landslide moves fastest. When air pressure increases during the day, the flow slows down or stops.
The scientists suspect that changes in air pressure alter the frictional forces that hold the landslide in place.
During periods of relatively low atmospheric pressure, air and water particles contained in sediment pores in the soil tend to move upwards to areas of lower pressure, easing frictional forces, they believe, and allowing easier sliding.
According to the researchers, their mathematical model of the basic physical forces driving landslide movement shows that their proposed mechanism is plausible.
"We do know that heavy rainfall is the most common trigger mechanism," said Falk Lindenmaier, a landslide expert at the University of Karlsruhe in Germany. "But this must not lead us to ignore other processes at play," he added.
Schulz and his team suspect that atmospheric tides could be involved in other phenomena that involve sliding surfaces, including earthquakes, volcanic eruptions and glacier movement. (ANI)