--- title: "Why the Maine Coast Is Smooth in the South and Jagged in the East" description: "South of Portland, Maine has long sandy beaches. East of it, the shore breaks into a maze of rocky headlands, narrow peninsulas and long thin islands. A NASA Earth Observatory feature explains that the line between the two was drawn partly by the rock beneath and partly by the ice that once sat on top of it." category: "Science" category_url: https://newsparlor.com/category/science author: "Maya Coleman" published: 2026-07-21T04:33:19.000Z updated: 2026-07-21T04:33:19.000Z canonical: https://newsparlor.com/article/why-the-maine-coast-is-smooth-in-the-south-and-jagged-in-the-east tags: ["geology", "coasts", "nasa", "maine"] --- # Why the Maine Coast Is Smooth in the South and Jagged in the East South of Portland, Maine has long sandy beaches. East of it, the shore breaks into a maze of rocky headlands, narrow peninsulas and long thin islands. A NASA Earth Observatory feature explains that the line between the two was drawn partly by the rock beneath and partly by the ice that once sat on top of it. Look at a map of the Maine coast and it appears to be two different coastlines stitched together. To the south of Portland the shore is smooth, with long sandy beaches. To the east it dissolves into promontories, headlands and narrow peninsulas, fringed by long, thin islands. A [NASA Earth Observatory feature](https://science.nasa.gov/earth/earth-observatory/why-maines-sandy-shorelines-turn-jagged/), built around an image captured by the Landsat 9 satellite on August 31, 2025, sets out why. The short answer is that two separate causes happen to reinforce each other along the same line. ## The rock beneath The first cause is geology, in the most literal sense: the rock the coast is made of changes as you move east. Southern Maine, the feature explains, has headlands of erosion-resistant granite. East of Portland, the bedrock is largely metamorphic, rock that has been transformed by heat and pressure. Different rock resists the sea differently, and that difference alone begins to explain why one stretch wears into smooth curves and another holds its jagged edges. But bedrock is only half of it, and on its own it would not produce the striking pattern of long fingers of land and water running out to sea. ## The ice on top The second cause is the ice age, and this is the part that gives the eastern coast its distinctive shape. Over long stretches of geological time, the feature notes, the Saco River carried weathered material down from the White Mountains, building the arch-shaped, embayed beaches that characterise the south. Then came the glaciers. During the last ice age, they scoured and widened the coastal valleys that already existed. When the ice retreated and sea levels rose, the sea flooded into those deepened valleys. The high ground between them remained as ridges; the drowned valleys became the inlets and channels. The result is a coast of parallel fingers, land and water alternating, with the tops of the old ridges surviving offshore as the long, narrow islands the region is known for. That is the mechanism in one sentence: the sea did not carve the eastern coast so much as move into a landscape the ice had already shaped, and then fill it. ## Why it is more than scenery There is a practical dimension to this, which the feature notes and which is worth drawing out. The same drowned-valley geography that makes the eastern coast look complicated also makes it useful. The protected rocky inlets and estuaries of the midcoast are where much of Maine's lobster and oyster industry concentrates, because sheltered water with a rocky bottom is good habitat and good working ground. The shape of the coast is not just a matter of appearance; it determines where a particular kind of livelihood is possible. ## What a satellite adds None of the underlying science here is new. Geologists have understood drowned river valleys, called rias, for a very long time, and the researchers quoted in the feature, from the Maine Geological Survey and the University of Maine, work with this landscape directly. What the satellite view adds is the ability to see the whole pattern at once. From the ground, the transition from sandy south to rocky east is a series of local observations. From orbit it is a single, legible image: two kinds of coast meeting along a line, each the product of a different rock and a shared history of ice. It is a good example of a small thing satellite imaging does well, which is to make a large-scale pattern visible enough that the explanation for it becomes an obvious question to ask. ## Sources - [Why Maine's sandy shorelines turn jagged](https://science.nasa.gov/earth/earth-observatory/why-maines-sandy-shorelines-turn-jagged/)