Mount Rainier is the most dangerous volcano in the United States - and its deadliest threat needs no eruption, gives no warning, and cannot be outrun.
It's called a lahar: a wall of wet concrete moving up to 50 mph.
5,600 years ago the Osceola Mudflow buried the ground beneath Kent, Auburn, and Tacoma and poured into Puget Sound.
Today more than 150,000 people live and work on top of old Rainier mudflows.
This is the lahar nobody can outrun - and the 40 minutes that stand between a sleeping mountain and the cities in its shadow.
