Hydrothermally altered andesite from Bumpass Hell at the Loomis Museum




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Sulfur-containing andesite from Bumpass Hell

Sulfur-containing andesite from the geothermal Bumpass Hell area displayed in the Loomis Museum
Sulfur-containing andesite from the geothermal Bumpass Hell area
displayed in the Loomis Museum

Andesite occurs in volcanic regions around the world; for example, in regions belonging to the margin of the Pacific Basin—like South America's Andes, after which this family of extrusive igneous rock is named. In North America, Lassen Volcanic is such a region. There, andesite and dacite rocks erupted from Lassen Peak in 1915: dark andesite and light dacite mixed to form banded pumice. Park visitors can see and touch a banded pumice specimen at an interpretive outdoor exhibit and compare its texture with that of other volcanic rocks that during eruptions tumbled down the northeast slopes of Lassen Peak as hot lava rocks and “created” the Devastated Area.

Andesite is typically black or gray colored. But the Bumpass Hell andesite, which is shown above and displayed at the Loomis Museum, has a yellow-sulfur appearance. The museum panel explains that the hot water and sulfurous steam of the hydrothermally active Bumpass Hell area decomposed the rock.