Hundreds Trapped in Mexico Mudslide

There was a hill that was about 650 ft wide that collapsed on a town in Southern Mexico this morning.  They estimated that 300 homes were affected, but they are unsure of the death toll at this point.  They are guessing that it could reach to the 1,000's.  I am not sure of the cause of the mudslide but I am confused on why the people were not alerted earlier because a 1,000 people should not die from a natural hazard like this.  Mudslides are normally triggered by a different event, but they did not say what it was, but the looks of the video it looks like a flood caused it.  This town sits on a hillside so I was amazed to see all the water still tanding, because I figured it would continue down the stream.