The easy answer that you're going to hate? Because there hasn't been enough pressure built up to breach the structure of the volcanic edifice and cause an eruption. That's it.
It's part of the Cascadia volcanic zone, same as Mt. Shasta and Mt. St. Helens. Like Rainier and Shasta, it just hasn't had a reason to erupt recently.
In fact, it's not been just 1,000 years... the last major volcanic event of any kind was a lava flow that goes back roughly 3,500 years!
So... I wish that I had a more detailed answer, but that *is* the detailed answer. Without looking into the movement of magma inside its central conduit? That's the answer.
Right now, the only evidence of continuing volcanic activity are fumaroles on its flanks outgassing small amounts of steam and hydrogen sulfide up in the crater area.
It's part of the Cascadia volcanic zone, same as Mt. Shasta and Mt. St. Helens. Like Rainier and Shasta, it just hasn't had a reason to erupt recently.
In fact, it's not been just 1,000 years... the last major volcanic event of any kind was a lava flow that goes back roughly 3,500 years!
So... I wish that I had a more detailed answer, but that *is* the detailed answer. Without looking into the movement of magma inside its central conduit? That's the answer.
Right now, the only evidence of continuing volcanic activity are fumaroles on its flanks outgassing small amounts of steam and hydrogen sulfide up in the crater area.