New York
The view from the top of Panther Peak, in the High Peaks Wilderness, near the center of the Adirondack Mountains dome.
Most of North America’s mountain ranges run north and south, with a few oriented east and west. But the Adirondack Mountains in upstate New York have a unique geometry. Seen from the air, the range is shaped like a circular dome, 160 miles in diameter and about a mile high. Mountain ranges usually form along plate boundaries, as the result of collisions, extensional stresses, or volcanic activity. But the Adirondacks were uplifted by entirely different forces working deep in Earth’s mantle.
The rocks that make up the Adirondacks are among the oldest on the planet. Dating back as many as 2 billion years, to the Precambrian Era, these rocks were originally laid down as fine sediments at the bottom of an ancient sea. At the time, this sea was located near the equator and the sedimentary rocks were likely once rich in fossils from the earliest life-forms.
The Adirondacks form a round mountain range just east of Lake Ontario. Lake Champlain is visible on the northeast corner of the range.
As the first continents began to form and move into new positions via plate tectonics, the precursor continent to North America (Laurentia) collided with the oceanic plate underlying the seafloor sediments. The heat and pressure generated by this collision changed the sedimentary rocks into metamorphic rocks, erasing most of the ancient fossils in the process. Around 10 million years ago, hundreds of millions of years after the Appalachian Mountains had formed, the seafloor rocks that make up the Adirondacks began to be uplifted into a dome shape. The driving force of this uplift is not well understood, but some geologists think it’s the result of a hot spot deep in Earth’s mantle.
So far, the dome has been uplifted nearly 7000 feet and continues to rise about two millimeters per year. Earthquake swarms up to magnitude 5 tend to strike around Blue Mountain Lake—one of the region’s many lakes—located near the center of the dome, suggesting these uplifting forces are centrally located and still active. This unique source of uplift means the Adirondack Mountains are wholly separate from the Appalachian Mountains geologically, even though the two are close neighbors.
You might fly over the Adirondacks on your way to Portland, Maine; Boston, Massachusetts; or New York City. Look for a circular mountain range to the north and west of the elongated Appalachian range.
