USGS has published a summary observations on the large landslide near Oso, Washington.
“The slide took place along the edge of a plateau about 600 feet high composed of glacial sediments. The volume of the slide is estimated to be about 10 million cubic yards, and it traveled about 0.7 miles from the toe of the slope. This travel distance is about three times longer than expected based on published information regarding previous slides of this height and volume worldwide. If the landslide had behaved in the expected range, it would have likely blocked the river and possibly destroyed a few houses. Instead it led to tragic loss of life and destruction of property.” Quoted from the USGS summary.