Landslides
Definition of Landslide : the massive flow of earthen debris and rock, caused by seismic motions in the Earth's crust. Landslides can also be caused by solifluction, the downslope of waterlogged soil.
The picture below was taken near coast of Isla Mocha, an island just north of Valdivia. Massive landslides can be seen in the backround, where the light brown and green colors are seperated. These particular landslides occurred after the earthquake, the soils reacted to the seismic waves, gravity took over and debris fell. Luckily there were no structures in their paths! ( The ship in the middle was wrecked by the tsunami. )
(Source : http://www.ngdc.noaa.gov/seg/hazard/slideset/45/45_thumbs.shtml )
In the city of Valdivia landslides occurred after the initial shock of the Earthquake. Once the massive piles of debris and rock slid off the banks and into the rivers, the result was a dam-like effect. Residents watched as their town was being flooded. Floods waterlogged the soil in ground fill areas designated for residential housing. The soil slid so much, due to solifluction, that it caused the houses in the picture below to fall apart, as you can see the damage was devastating!
(Source : http://www.ngdc.noaa.gov/seg/hazard/slideset/45/45_slides.shtml )
Residents were determined to prevent further flooding, they dug trenches allowing some water to flow through the landslide debris that blocked the rivers path. Eventually the river water moved all the sediment out into the Pacific ocean, if it weren't for the trenches that allowed water to start moving again, major floods could have damaged even more of the cities structures further up stream.