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Thin section of lava from the Cobweb Lava Flow, erupted from Aniakchak Peak ~400 years ago. The name "Cobweb" comes from B.R. Hubbard (1932), who called it the "Avernian Cobweb." According to Wes Hildreth (USGS), "The poisonous vapors of Avernus, Italy, killed many birds, and Hubbard witnessed the same at Aniakchak, which seems why he adopted this name." The video shows 3-5 mm wide aggregates of crystals suspended in a finer-grained groundmass of tiny crystals. The minerals under the cross-polarized light are plagioclase (gray/white), clinopyroxene (blues/reds/oranges), orthopyroxene (pale yellow-gray), and FeTi oxide minerals like magnetite and ilmenite (black). Most of the tiny minerals in the groundmass are plagioclase. They formed when the magma ascended to the surface and solidified as a lava. The larger minerals formed under higher temperatures (~850 C) deep underground.

Date: Oct 27th, 2020
Volcano(es): Aniakchak
Photographer: Browne, Brandon
Image courtesy of the AVO/ADGGS.
Please cite the photographer and the Alaska Volcano Observatory / Alaska Division of Geological & Geophysical Surveys when using this image.
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