The jagged shorelines of Maine's sandy beaches and rocky promontories are a captivating sight, but they tell a story of geological forces and natural processes that have shaped the state's coastline over millennia. While the Wabanaki people have creation myths explaining the rocky coastlines of Downeast Maine and Acadia National Park, the scientific explanations of coastal geologists are equally fascinating. The sharp contrast between the sandy shoals and beaches south of Portland and the rocky shoreline of promontories, headlands, and narrow peninsulas to the east is a result of differences in the underlying bedrock and the distribution of sediment left behind by the last glacial maximum. Southern Maine has broad deposits of sand, much of it sourced from rivers, which have weathered and broken down the White Mountains, with material transported to the coast largely by the Saco River. Waves and tides have reworked these soft sediments over time, sculpting them into the arch-shaped embayed beaches and sprawling salt marshes found around Saco Bay and the broader region. While erosion-resistant granite juts from the sandy shorelines in southern Maine to form rocky headlands, metamorphic bedrock becomes the dominant surface feature east of Portland. There, whole ridges and valleys made of rock layers transformed by exposure to high pressures and temperatures define the landscape. During the last ice age, glaciers scoured and widened many of these coastal valleys, which later flooded as the Laurentide Ice Sheet melted and sea levels rose. Around Casco Bay, these ridge-and-valley systems, combined with the drowning of the shoreline, produce the jagged, highly indented shoreline and many long, narrow islands seen today. The tortured folds of these old landscapes also set up a sharp directional preference for erosion to exploit, leading to the eye-catching difference in the orientation of the islands and necks that dominate Casco Bay compared with those to the northeast. The various forms that coastlines take fascinate geologists, but they also carry everyday implications for the economies of Maine's coastal communities. While tourists flock to the sandy beaches of communities like Saco and Kennebunkport, the state's iconic lobster fisheries are concentrated in Midcoast Maine. The crustaceans thrive in the cold waters of the region's many rocky, protected inlets, turning communities such as Harpswell into leaders in lobster landings. The state's oyster farms are also concentrated in this region. Casco Bay and the Damariscotta Estuary, sheltered from winds and waves, offer waters that farmers can easily access without large boats. These waters provide a range of temperatures, salinities, and other characteristics that create numerous microclimates where oysters can grow quickly and take on a variety of tastes, known as merroir. NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland. The jagged shorelines of Maine's sandy beaches and rocky promontories are a captivating sight, but they tell a story of geological forces and natural processes that have shaped the state's coastline over millennia. While the Wabanaki people have creation myths explaining the rocky coastlines of Downeast Maine and Acadia National Park, the scientific explanations of coastal geologists are equally fascinating. The sharp contrast between the sandy shoals and beaches south of Portland and the rocky shoreline of promontories, headlands, and narrow peninsulas to the east is a result of differences in the underlying bedrock and the distribution of sediment left behind by the last glacial maximum. Southern Maine has broad deposits of sand, much of it sourced from rivers, which have weathered and broken down the White Mountains, with material transported to the coast largely by the Saco River. Waves and tides have reworked these soft sediments over time, sculpting them into the arch-shaped embayed beaches and sprawling salt marshes found around Saco Bay and the broader region. While erosion-resistant granite juts from the sandy shorelines in southern Maine to form rocky headlands, metamorphic bedrock becomes the dominant surface feature east of Portland. There, whole ridges and valleys made of rock layers transformed by exposure to high pressures and temperatures define the landscape. During the last ice age, glaciers scoured and widened many of these coastal valleys, which later flooded as the Laurentide Ice Sheet melted and sea levels rose. Around Casco Bay, these ridge-and-valley systems, combined with the drowning of the shoreline, produce the jagged, highly indented shoreline and many long, narrow islands seen today. The tortured folds of these old landscapes also set up a sharp directional preference for erosion to exploit, leading to the eye-catching difference in the orientation of the islands and necks that dominate Casco Bay compared with those to the northeast. The various forms that coastlines take fascinate geologists, but they also carry everyday implications for the economies of Maine's coastal communities. While tourists flock to the sandy beaches of communities like Saco and Kennebunkport, the state's iconic lobster fisheries are concentrated in Midcoast Maine. The crustaceans thrive in the cold waters of the region's many rocky, protected inlets, turning communities such as Harpswell into leaders in lobster landings. The state's oyster farms are also concentrated in this region. Casco Bay and the Damariscotta Estuary, sheltered from winds and waves, offer waters that farmers can easily access without large boats. These waters provide a range of temperatures, salinities, and other characteristics that create numerous microclimates where oysters can grow quickly and take on a variety of tastes, known as merroir. NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.
