Overnight, a sinkhole swallowed a pond on Mark Korb's property in Newcastle, Calif.

When he went to bed Saturday night, the pond was there. On Sunday, March 17 it was gone.

How does that happen?

While northern California is no where near as prone to sinkholes as Florida (see USGS sinkhole map), one clue might be the fact that the pond was man-made.

While sinkholes don't need a human trigger, changes in drainage due to construction or agricultural irrigation have been known to activate mass outbreaks of sinkholes in Florida and other parts of the country. As The Christian Science Monitor reported earlier this month after a Florida man was swallowed in his bed by a sinkhole, "Drought followed by heavy rains can also instigate sinkholes as heavy, water-logged earth presses down on limestone caves suddenly devoid of buoyant water. The two previous deaths attributed to sinkholes both involved professional well drillers whose activities cracked the top of limestone caverns, causing collapse."

"Humans can [destabilize karst landscapes] by drawing down water tables or irrigate too much, increasing the weight of the mass of materials that sits on top of the void," says Jonathan Martin, a geologist at the University of Florida, in Gainesville. "Humans can modify the environment" enough to cause sinkholes.

The US Geological Society echoes this idea:

"Sinkholes can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created. The substantial weight of the new material can trigger an underground collapse of supporting material, thus causing a sinkhole."

So, it's possible that when Korb built his pond, he may have disturbed the local geology.

Another theory for the swallowing of Korb's pond was put forward by Sierra College Professor of Geology Alex Amigo. He also points to a human cause: gold mining.

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This part of California is dubbed "Gold Country," for its long history of mining. "There was such a lot of mining activity going on in this area in the past, that we never know when there was a man-made cavity underground," Amigo told KCRA-TV.

Korb is now looking into how to deal with the sinkhole and doing research on the history of his property to see if there has been any gold mining on or near the property in the past.