Did obsidian come out of mt st Helens?

Answer 1

Interesting question. After the explosive eruption, the gas content of the rhyolitic magma should have decreased enough to allow obsidian to form. It is the right kind of lava. However, most of the lava dome in the Mount St. Helens caldera is dacite, which is "grainier" than obsidian, indicating that it cooled too slowly to have a "glassy" appearance. Obsidian flows must cool quickly to prevent crystal formation. It is possible that some obsidian was formed, but subsequently covered by dacite. I have not been able to find any reports that mention obsidian recovered from the Mount St Helens lava dome.

So the answer is a qualified no, we don't have any evidence of obsidian flows from Mount St Helens.

Incidentally, there are individuals and companies selling products they call "helenite" or "St Helens Obsidian", which is a synthetic material created by fusing volcanic ash (which may or may not have come from Mount St Helens).