Geologic Map of Baranof Island, Southeastern Alaska Now Online

Posted: 10 Aug 2015 10:00 AM PDT

Summary: In the 20th century, Baranof Island in Southeastern Alaska has drawn attention for its gold, chrome and nickel deposits, timber industry, potential activity of the dormant Mount Edgecumbe volcano, and for numerous commercially developed hot springs. In addition, Baranof Island is known for its outstanding scenic fjords, pristine rainforests, and prolific fishing grounds

ANCHORAGE, Alaska — In the 20th century, Baranof Island in Southeastern Alaska has drawn attention for its gold, chrome and nickel deposits, timber industry, potential activity of the dormant Mount Edgecumbe volcano, and for numerous commercially developed hot springs. In addition, Baranof Island is known for its outstanding scenic fjords, pristine rainforests, and prolific fishing grounds.

A new map from the U.S. Geological Survey updates the geology of Baranof Island based on field studies, petrographic analyses of minerals, fossil ages, and isotopic ages for igneous, metamorphic, and sedimentary rocks. These new data provide constraints on ages of rock units and the structures that separate them, as well as insights on the regional tectonic processes that affected the rocks on Baranof Island. This work provides stratigraphic, geochemical, and structural evidence that ties Baranof Island geologically to Vancouver Island and Haida Gwaii rather than other islands in southeast Alaska.

"This report is a modern synthesis of new work and many years of topical investigations," said USGS geologist Susan Karl. "Pulling together all of this information in one product is a benefit to scientists working on similar or related studies, and is of interest to the general public for explanations of local geologic features such as the Mount Edgecumbe volcano, the Fairweather, Chatham Strait, and Peril Strait Faults, gold deposits, and hot springs."

A pamphlet complements the map and includes a geologic overview of the results of USGS studies and detailed rock unit descriptions. The map is available at the USGS Alaska Science Center website.