The Process of Mountain Formation

Have you ever stood in wonder before the towering peaks that define our planet's landscape and pondered, 'how do mountains form?' These natural wonders encapsulate the dynamic and powerful forces that have shaped Earth's history, revealing a narrative carved into rock by the relentless movements of nature.

How Are Mountains Formed?

Annually, around 2 to 3 million individuals strap on their hiking boots and embark on a journey along the Appalachian Trail. The breathtaking views are unparalleled. Spanning 2,200 miles (3,540 kilometers), this trail is named after a mountain range renowned for its lush forests and rugged terrain, attracting outdoor enthusiasts. If you ever choose to ascend one of the Appalachian peaks, be prepared for a challenge. The 10 tallest mountains east of the Mississippi are all situated within this ancient range. By a narrow margin, the highest is North Carolina's Mount Mitchell, towering at 6,684 feet (2,037 meters).

However, it's unlikely to grow any taller. Geologically speaking, the Appalachians have experienced little growth for a long time. Since the age of the dinosaurs approximately 225 million years ago, this range has been gradually eroded by natural forces. In contrast, other mountains around the world continue to rise annually. So why aren't the Appalachians doing the same?

Their age plays a crucial role. Mountains are formed through various processes, but most arise from the collision of tectonic plates. For the uninitiated, tectonic plates are the shifting segments of the Earth's lithosphere, the planet's outer shell. It's important to note that not all plates are the same.

Continental plates are relatively lightweight, whereas oceanic plates are denser. When two plates collide, the oceanic plate is forced beneath the continental one, a process known as "subduction." This action pushes magma to the surface, forming volcanic mountains such as Japan's Mount Fuji or Washington State's Mount Saint Helens. The tectonic pressure at these subduction zones can also create non-volcanic mountains like Alaska's Mount Denali, which — according to NASA — is growing by 0.04 inches (1 millimeter) each year.

But what occurs when two continental plates collide? When this happens, the Earth's crust at their boundary is displaced and pushed upward, giving birth to a new mountain range.

Understanding Geological Formations: The Appalachians

These two geological processes played a pivotal role in the formation of the Appalachians. Approximately 480 million years ago, an oceanic plate was subducted beneath the eastern edge of North America, leading to the creation of volcanic mountains in the region. Later, around 180 million years afterward, significant uplift occurred when the continent collided with western Africa.

However, the Appalachians ceased their growth over time. For the past 200 million years, North America and Africa have been moving apart. The eastern coastline of North America is no longer colliding with another landmass, and currently, no oceanic plates are being subducted beneath it. As a result, the Appalachian region is tectonically inactive. Without the collision of tectonic plates, the mountains have not grown taller in the last 200 million years.

All mountain ranges undergo continuous erosion, which gradually reduces their size. Mountains that are tectonically active can counteract this erosion through new growth and uplift. However, since the Appalachians are no longer growing, they cannot counteract the effects of wind and precipitation. Consequently, they are gradually diminishing in size.

Mountain Ranges in the Himalayas

The situation in the Himalayas is quite different. For the past 50 million years, India has been colliding with Asia. Geologically speaking, the Himalayas, which lie along this boundary, are relatively young. Additionally, they remain tectonically active, allowing the entire range to continue growing despite the persistent effects of erosion.

As author John Green aptly put it, "the truth resists simplicity." Not all mountains within a range grow or shrink uniformly. At times, one section of a mountain chain may rise while another section simultaneously declines.

This phenomenon was observed in Nepal in 2015 following a catastrophic 7.8 magnitude earthquake. In the aftermath, scientists found that some of the taller peaks in the Himalayas lost up to 23 inches (60 centimeters) in height within the first five seconds of the quake. Conversely, a few of the shorter mountains actually increased in height. The impact of the 2015 earthquake on Mount Everest, the world's tallest peak, remains uncertain, as Nepal's government is currently re-measuring its summit.

Other Ways Mountains Form

It’s worth noting that tectonic collisions aren’t the sole method of mountain formation. The Adirondack range, located in upstate New York, is a prime example. Geologists are particularly intrigued by this region because, unlike the shrinking Appalachians, the Adirondacks are still growing. Estimates suggest they are rising at a rate of 0.08 to 0.11 inches (2 to 3 millimeters) annually. The likely cause? A hotspot of molten magma beneath the Earth’s crust is believed to be pushing the region upward.

Currently, the Adirondacks are experiencing uplift faster than erosion can wear them down. However, geological history suggests that this balance won’t last forever. On a planet where landscapes are always evolving, change remains the only constant.