Ritzy Edmonton houses slide down ravine

It's a real estate slump like no other. Some families in Edmonton are watching their stately homes slide into a valley along the North Saskatchewan River.

One house, worth about $500,000, tumbled into the ravine on the weekend as horrified residents of the upscale neighbourhood watched.

The owners have known for about two months that their 15-year-old house was collapsing, but that didn't make the final plunge any easier.

The couple moved out about two weeks ago, when the place became too structurally unsound.

At least six other posh residences appear headed for the same fate, perhaps as early as Monday.

Police have blocked off the area, and evacuated about 18 homes as a precaution.

Workers used backhoes and jackhammers in a frantic effort to cut off the gas, water, and electricity to the entire street.

Some people were worried the vibration caused by the utility companies would be enough to push more homes down the embankment.

Engineers are not sure why the ground is crumbling.

They've begun drilling holes and removing test samples to figure out what is causing the slide.