A mother lode of obsidian nodules has been discovered at Ptarmigan Lake (Alaska), near the headwaters of the Nabesna and White rivers. Mass spectrometer analysis has revealed that the Ptarmigan Lake site was a major source of tools for prehistoric Alaskans, especially those that lived along the Tanana River. Obsidian – a black volcanic glass – was highly prized by ancient peoples, who broke apart the larger ‘bulbs’ to make tools and weapons with razor-sharp cutting edges. Obsidian fields were therefore a major resource, both for local consumption and for trade.
     Over the past 30 years archaeologist John Cook, now retired from the Bureau of Land Management, has found obsidian artefacts throughout Alaska. Some years ago Cook stumbled across a field of obsidian on the Indian River, near Hughes. Chemical analysis proved that Indian River obsidian was traded throughout Alaska between 10,000 and 2,000 years ago. But there are other places in Alaska, notably the upper Tanana River, where obsidian tools had a different chemical signature. Cook embarked on a quest to find the source of the upper Tanana material so that he could learn more about the people who used it.
     Paul Layer, head of geology and geophysics at the University of Alaska and director of the Geophysical Institute’s geochronology lab, used laser and spectrometer technology to determine that the upper Tanana obsidian was formed after a volcanic eruption 20 million years ago. It is known that Indian River obsidian is 40 million years old, so the findings confirmed that the Tanana material originated from a different source. Layer’s further research into the vulcanology of the Wrangell-St. Elias mountains revealed that the further to the east, the older the eruptions. Layer pinpointed an area close to the Nabesna and White river headwaters where the eruptions date back only 20 million years.
     Cook enlisted the help of a U.S. Geological Survey geologist and other archaeologists from the Bureau of Land Management and the National Park Service. Together they discovered the Ptarmigan Lake deposits. Samples were sent to Layer, who confirmed that their age and chemical composition was the same as the obsidian from upper Tanana archaeological sites.

Source: Anchorage Daily News (28 September 2003)