New bedrock geology map of Mount Desert Island

Braun, Duane

From the abstract: "The map of the Bedrock Geology of Mount Desert Island has finally been completed in 2018, a project that began with field work primarily in 2012 through 2015. The map is published at a scale of 1:30,000 with twice or more detail than on the previous 1:50,000 scale Mount Desert Island map published in 1988. Geologic features on the present map are much more accurately located thanks to GPS technology than on the previous map. The map has a legend with a detailed description of each of the 33 different rock units that have now been identified on the island. There are also two cross-sections showing the interpretation of how the rock units project underground to a depth of three kilometers (two miles), one running north to south across the island and the other running west to east across the island. In addition there is a text giving a concise synopsis of the geologic history of the island. The map helps to confirm other research since the early 1990s that Mount Desert Island was a super volcano 420 million years ago. The area at that time was a large volcanic caldera 15 km (10 mi) across that had a number of major eruptions from several different pulses of magma that were intruded below the caldera surface. Since that time 3 km (2 mi) of rock has been eroded from the area. The present land surface exposes the deep interior of the volcanic magma chamber - all the different granites, diorites, and gabbros that form most of the island."