Definition of Mount St Helens from the Oxford Advanced Learner's Dictionary

 

Mount St Helens

 
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a volcano (= a mountain from the top of which melted rock and gases can explode with great force) in the Cascade Range of the US state of Washington. It exploded in 1980 for the first time in 120 years killing about 60 people, and causing damage to the surrounding area. The explosion also reduced the height of the mountain by over 1 000 feet/300 metres. There have been several weaker explosions since.