Lassen Peak became a national park in 1916 because of its significance as an active volcanic landscape. Lassen Peak began erupting in 1914 and had the most significant activity in 1915. It was the most recent volcanic activity in the lower 48 states until the explosive eruption of Mt. St. Helens in 1980.

OK, is this like Jeopardy where you give us the answer and we have to ask the question? LOL

OK, I'll bite...
"After 200 years of calm, what U.S. volcano let loose in 1914- 1916?"

You're right!

And I see that you have met my challenge. I have to throw in a few twists to make it interesting!

That was a "quick save" on your part!
Glad I met your "challenge"