Fumarole at Sulphur Works

Old fumaroles at Sulphur Works

Here we are, back at Sulphur Works in Lassen Volcanic National Park, having walked across the road to view the current state of fumaroles (as of about 3 weeks ago. The shadowed, small holes above the large indented or concave area, approaching the top of the triangular upper face is where numerous fumaroles have been active during many of our previous visits to the area (visits by MOH and I, only one visit on this blog, with photos from October, 2006).

A couple videos on YouTube (2007, 2010) show the old vent steaming away, and the first one shows just how pockmarked that little hill was with fumaroles!

Active fumarole surrounded by large orange circle

Now we've moved down the road from the viewing area, to get a clearer view of the fumarolic vent that was steaming, that pock-mark in the center of the large orange circle. I suspect the circle may be formed not only by iron oxides, but possibly some jarosite, a sulfate mineral, and some native sulfur.

Close up of the active fumarole

Here we've zoomed in on the active fumarole, a small hole in the ground emanating steam that is no doubt adding to the pervasive, sulfurous stink of rotten eggs.

My video of the active fumarole

One interesting thing about the location of Sulphur Works, including this fumarole and the boiling mud pot across the road: Sulphur Works is near the center of ancient Mount Tehama (or Brokeoff Volcano, as it is sometimes known), a large stratovolcano that was active between about 600,000 and 400,000 years ago.

More Reading:

“Hot Water” in Lassen Volcanic National Park—Fumaroles, Steaming Ground, and Boiling Mudpots - U.S. Geological Survey

Explore the Hydrothermal Areas - Lassen Volcanic National Park