Definition of atom. 1  1a : the smallest particle of an element that can exist either alone or in combination an atom of hydrogenb : the atom considered as a source of vast potential constructive or destructive energy â¦ a largely forgotten legacy of this country's conquest of the atom.
The mountain, a part of the Cascade Range, is a volcano that has not erupted for 2,000 years. It is also the highest mountain in the state of Washington. English explorer George Vancouver named Mount Rainier in honor of another navigator, Peter Rainier. Some people, however, prefer to call the mountain by its Indian name, Mount Tacoma.
The Eruption History of Mount Rainier. Around 500,000 years ago, Mount Rainier started to grow atop the eroded remains of an earlier ancestral Mount Rainier that was active 1-2 million years ago. The modern edifice grew as a series of four alternating stages of volcanic activity, averaging a little more than 100,000 years duration.