- Mount Rainier is an active volcano located in Washington state that last erupted in the 1840s. - Past eruptions have involved explosions of lava and rock from the top of the mountain, as well as mudslides and flooding caused by melted snow and ice. - Nearby cities like Ashford, Wilkeson, and Greenwater could face threats from landslides or mudflows if a large eruption occurred, though population levels are currently low in the surrounding areas.