Dr. Anastasia Steffen Discusses Forest Fire Effects on Obsidian Artifacts in the Jemez Mountains

During Tuesday’s presentation at PEEC, Dr. Anastasia Steffen explains that patterns in the fracture face determine whether an obsidian rock fracture was caused by fire or man. Photo by TK Thompson/ladailypost.com
PEEC Co-founder and board member Becky Shankland addresses the audience at Tuesday’s talk. Photo by TK Thompson/ladailypost.com
Staff Report:
Dr. Anastasia Steffen of the Valles Caldera National Preserve presented a night Tuesday evening at the Pajarito Environmental Education Center (PEEC) in Los Alamos.
The topic of her talk was the effects of forest fires on the obsidian artifacts in the Jemez Mountains. Obsidian will turn from its normal glassy black look to a bubbly white material somewhat like puffed rice cereal upon being subjected to a very hot fire, she said.
The small amount of entrapped water in the obsidian (~0.5-1.0 percent) turns to steam and explodes in the molten rock creating the bubbly texture.
Another thing about obsidian that’s quite amazing is that obsidian, pumice, bandelier tuff and the gray Jemez rhyolitic rocks all have the same chemical composition.
What causes the difference in appearance is the time and temperature formation differences in the volcano before eruption and the eruption and molten rock cooling conditions.
Dr. Anastasia Steffen talks about fire caused fractures in obsidian. Photo by TK Thompson/ladailypost.com
Dr. Anastasia Steffen talks with community members and PEEC staff and board members after her presentation Tuesday. Photo by TK Thompson/ladailypost.com
Dr. Anastasia Steffen brought many samples of obsidian to exhibit at her talk at PEEC. Photo by TK Thompson/ladailypost.com

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