Why did Mt. Saint Helen almost self-destruct instead of erupting like we know most volcanoes to?

Question

I didn’t know about Mt. Saint Helen today, and watching the videos, it feels almost unreal. What’s the science behind it?

In: Geology

Answer 1

There was a huge amount of carbon dioxide and sulfur dioxide gasses under a huge amount of compression in the lava before it erupted. When it erupted the gasses fizzed the lava like a shook up soda bottle. Those gasses when they came out of compression exploded the molten lava, which resulting in all the ash.
This type of volcano is called a composite volcano.