Duane and Ruth Braun. The Brauns will speak about the geology of Mount Desert Island at the Southwest Harbor Public Library on Sept. 5. PHOTO COURTESY OF DUANE BRAUN

Brauns to talk about 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, Sept. 5, at 5:30 p.m.

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

The Brauns will take us on a geologic history tour starting 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 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 Mount Desert Island.

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 a variety of 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.

Both Duane and Ruth Braun have been instructors for Acadia Senior College, teaching about the geology of MDI. They have written a new guidebook to the island’s geology. 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.

Call the library at 244-7065 to reserve a seat.


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