Mount Rainier is an episodically active composite volcano, also called a stratovolcano. Volcanic activity began between one half and one million years ago, with the most recent eruption cycle ending about 1,000 years ago. Over the past half million years, Mount Rainier has erupted again and again, alternating between quiet lava-producing eruptions and explosive debris-producing eruptions. The eruptions built up layer after layer of lava and loose rubble, eventually forming the tall cone that characterizes composite volcanoes. At one time, lava flows on opposite sides of the mountain probably projected more than 1,000 feet (305 meters) above the present summit at Columbia Crest which rises 14,410 feet (4392 meters) above sea level on the rim of the recent lava cone. The upper portion of the volcano's cone was likely removed by explosions and landslides. Mount Rainier's extensive glacier system then carved the volcano's cone into its current craggy form.