Duane and Ruth Braun will share the history of the geology of Mount Desert Island when they speak at the Southwest Harbor Public Library on June 20. PHOTO COURTESY OF DUANE BRAUN

Brauns to talk about geological evolution of MDI

SOUTHWEST HARBOR — Geologists Duane and Ruth Braun will talk about the geological makeup of Mount Desert Island at the Southwest Harbor Public Library on Tuesday, June 20, at 5:30 p.m.

At the end of the talk, there will be a book signing for their “Guidebook to the Geology of Mount Desert Island and Acadia National Park.” Proceeds will benefit the library.

The talk will begin around a billion years ago when MDI was attached to the supercontinent Gondwana. It split from Gondwana and eventually attached itself to North America. MDI itself experienced three major geologic events, which resulted in the formation of 10 different rock units that now make up MDI. The oldest of these formations is the beautifully crenulated Ellsworth schist. Most of the rock on MDI formed around 420 million years ago as alternating intrusions of pink granite and gray gabbro magma fed a huge volcanic caldera the size of MDI. Two miles of rock have been eroded since then to form the present landscape. Over the last 2.5 million years, glaciers have repeatedly covered the island with up to 5,000 feet of ice. When the glaciers retreated, they left behind a number of different deposits and landforms, helping to create a beautiful and striking landscape.

Ruth Braun earned her master’s degree from Johns Hopkins University. Over the years, she has taught science, math and geology courses in various high schools and universities.

Duane Braun earned his doctorate from Johns Hopkins University. He was the geosciences professor at Bloomsbury University. He also mapped the glacial deposits of a 9,000-square-mile area of northeastern Pennsylvania for the Pennsylvania Geology Survey.

The Brauns both have taught about the geology of MDI for Acadia Senior College and have written a new guidebook to the geology of MDI. Duane Braun has revised the geologic maps of MDI for the Maine Geologic Survey. The Surficial Geology (glacial deposit) map of MDI is presently available as a free PDF download, and the Bedrock Geology map should be available later in the year.

As seating is limited, reservations are required. Call the library at 244-7065.

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