At a Glance

Air pollution may have played a role in a deadly 2009 landslide in China, researchers say.Toxic rain created by harmful pollutants in the air eroded a portion of the Jiweishan Mountain.Layers of shale and limestone underneath the land weakened over time due to the rain.

Researchers are rethinking what factors can cause a landslide after a study suggested air pollution played a role in a devastating 2009 landslide in China.

Seventy-four people were killed by the Jiweishan Mountain landslidethat seemingly came out of nowhere, as no earthquake activity or heavy rainfall , according to the January research. The scientists' findings suggest acid rain eroded a layer of shale in the peak, weakening the land over time.

Rainwater has been dissolving the mountain's limestone over millions of years, carving cracks and potholes into the peak’s landscape, according to the researchers.

The image above shows the slide area of the June 2009 Jiweishan landslide that killed 74 in China. Researchers believe air pollution might have played a role in triggering the avalanche.

(Earth and Planetary Science Letters/Yin et al., 2011)

“,” study co-author and China University of Geosciences geoengineer Ming Zhang told Earth Magazine.

China’s rain has become toxic from . Pollutants such as sulfur dioxide and nitrogen dioxide are released into the air, where they’re picked up by both rainand snow as it falls to the Earth's surface.

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The scientists tested their theory by placing a shale sample in diluted hydrochloric acid, where it dissolved and left behind a frail rock filled covered with tiny holes. They also found hundreds of microbes inside the shale, including onescapable of decomposing its organic matter and making it even weaker.

“Without calcite and organic material, the basal shale at the Jiweishan rock avalanche is composed largely of detrital talc,” wrote the researchers. They believe this saturated layer of talc allowed the land to slide out of place.

“It’s a whole new way of thinking about what might start a landslide,” Colgate University geochemist Richard April, who was not involved with the study, told Earth Magazine.

Mining underneath the slide area may have also played a role. Abandoned drains on the mountain could have spilled water from an aquifer above them onto the shale layer, the scientists suggest. The sudden rush of water combined with the acid may have worked together to trigger the slide.

The researchers say the next step of their research is to figure out how fast acid rain can penetrate limestone and reach the shale, and how much of the shale needs to be dissolved in order to destabilize the rock layers.

“I would like to see a lot more fieldwork – collecting rainwater, groundwater and rock samples,” said Zhang. Additionally, “more modeling and calculations about how much acid rain has fallen on this region will give a much better idea of whether this is a feasible means of initiating a landslide.”