Mount St. Helens has erupted multiple times throughout history. Its most recent eruption occurred on May 18, 1980. This was a major eruption that caused significant damage and loss of life.

However, it's important to note that Mount St. Helens has erupted numerous times before 1980 and continues to be an active volcano. Here are some of the other notable eruptions:

* 1857: A significant eruption

* 1903: Another period of volcanic activity

* 1980-1986: A series of eruptions, culminating in the devastating 1980 event

* 2004-2008: A period of smaller eruptions and dome building

So, depending on the context, you could say Mount St. Helens erupted in 1980, or you could say it erupted most recently in 2008.