This is a picture of my house.  And of a landslip that happened this winter during a severe downpour.  The picture makes it look like the house is at risk, but the house is at least 30 meters back from the edge.  The soil here is alluvial loess, which means dust particles from the river valley blew on the wind and built up over the millinea.  Those particles are rounded, making them slippery like ball bearnings rather than grippy, so the soil is subject to slacking and dispersion.  You'll see slips like this all over this region of New Zealand.  The popular and willow trees were planted to help contain these slips.  Still I may want to build a retaining wall to keep it from moving backwards towards the house because I don't want a smaller yard.