Scientists are increasingly pointing to storms as a trigger for earthquakes and mudslides. That's raising questions about the effects that climate change might have on one of the world's deadliest natural catastrophes, and to what extent, if any, insurers and governments could be adapting to the interplay between atmosphere and earth.

So far, those answers are as mysterious as the timing of earthquakes, a question that has baffled humans -- and killed them -- for generations. But recent findings suggest that some linkage exists to increasingly powerful storms.

The Slumgullion Landslide in the San Juan Mountains of Southwest Colorado is named after a lumpy stew of ages past because of its colored and chunky landscape. The mix of mountain mass is nearly 2.5 miles long and 1,000 feet wide. It has been creeping downhill since the Black Plague ravaged Europe in the 14th century. On most days it descends by 1 tiny centimeter, but there are a few when it speeds into a lurching plunge of about 10 feet.

New evidence (pdf) shows that atmospheric low pressure systems can prompt the landslide to lurch downward. Pressure drops when warm daytime air results in low "tides," or when fast-moving storms race onto the scene. The effect on landslides and earthquakes only occurs when the pressure plummets suddenly, causing underground water and air to shoot toward the surface.

That reduces friction between grinding subterranean plates, or under a landslide that's been held immobile by abrasive dirt and rocks.

"Slides, earthquakes, glaciers, volcanic eruptions -- all of these things involve soil sliding on soil, or rock sliding on rock," explains William Schulz, a research scientist at the U.S. Geological Survey and the author of a study published this month in the journal Nature Geoscience. "And sliding is resisted primarily by one thing, and that's friction."

Typhoons can make plates slip

The same conclusion was reached by scientists in Taiwan this June. A study (pdf) published in the journal Nature described how low pressure accompanying typhoons sparked small earthquakes along the fault between the Philippine Sea Plate and the Eurasian Plate. The scientists note that they make "a definitive connection between fault slip and changes in atmospheric pressure."

Importantly, both studies say weather impacts can accelerate an earthly act that was bound to happen sooner or later. In other words, low pressure is not the cause of an earthquake, just the trigger.

The findings follow warnings about strengthening thunderstorms related to higher levels of atmospheric greenhouse gases. Heavier downpours are already being observed in the United States, said Jerry Meehl, a climatologist with the National Center for Atmospheric Research.

"The lower the pressure, the more intense the storm would be," he said. "One idea is that the warmer air is holding more moisture, and when you have a storm start up, it has more moisture source, and moisture source can provide energy to the storm, and it can make it a bit more intense."

Meehl noted that the evidence is limited. He added, however, that wintertime storms in mid-latitude regions, areas about halfway between the equator and the poles, are "definitely associated with lows -- low-pressure systems."

"In summer, it's more just convection, where the ground heats up and you get vertical motion and you get the afternoon thunderstorms," he added.

Last week, there were 750 U.S. quakes

It's a guess whether climate change will result in more earthquakes. But that's a bet Schulz, who wrote the Slumgullion article, seems willing to take.

"Storm systems are supposed to become more numerous and more severe," Schulz said. "One can assume, then, if you've got more severe storms, or storms with, say, more extreme pressure changes, then the effects [on seismic activity] could be more pronounced in the future."

That assertion comes as natural catastrophes are rising worldwide. In the 1950s, two mega-disasters, defined by the United Nations as killing thousands of people and uprooting hundreds of thousands more, would occur annually. Now, that number routinely reaches six a year, and often more, according to Munich Re, a reinsurance company that tracks disasters.

Earthquakes are especially fatal. They account for six of the 10 most deadly natural disasters since 1980, killing about 470,000 people.

The damage inflicted by the San Francisco earthquake of 1906 has not been eclipsed in the United States, though smaller tremors happen all the time. In the last week, more than 750 earthquakes have occurred in the United States, according to the U.S. Geological Survey.

So how will insurers react to the idea that storms can spark earthquakes?

Insurer: no 'earthquake weather'

Peter Hoeppe, head of Munich Re's Geo Risks Research unit, said in a statement that weather can be the "final straw" in prompting a seismic event. While that is significant, he suggested, it won't affect the way the industry prices earthquake risk or models the probability of earthquakes' occurrence.

"Weather is only one or one of many possible triggers," Hoeppe added. "For risk-assessment purposes, the question is purely academic: there are neither more nor fewer earthquakes or landslides because of the weather and there is no such thing as 'earthquake weather.'"

That is yet to be seen, scientists involved in the studies suggest. There might be more small earthquakes if more low-pressure systems occur in the future, said Schulz. That might even be good news for people who live along faults, and for insurers, because the small slips could relieve underground pressure before a big shift occurs.

"If anything, you might be reducing the magnitude of earthquakes by having more frequent events," Schulz said.

One insurance regulator whose state is above the New Madrid fault line, which runs through the Midwest and shook the Corn Belt with a tremor that could be felt in Chicago last year, thinks insurers might be keen to explore the new science.

"My expectation is that if the science supports the conclusion [that weather can affect earthquakes], that insurers will look or consider that information perhaps when evaluating or pricing earthquake coverage," said Michael McRaith, Illinois' insurance regulator.

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