A hanging valley is a geological formation where a smaller valley meets a larger, main valley at a significantly higher elevation. It appears as though the tributary valley is “hanging” above the floor of the primary valley. These features are found in mountainous regions that have experienced extensive glaciation, formed by the powerful erosive forces of ancient ice sheets.
How Hanging Valleys Form
Hanging valleys primarily form due to the differential erosive power of glaciers during past ice ages. A larger, more massive glacier flowing through a main valley possesses immense force, enabling it to carve out a deep, broad trough. This main glacier effectively deepens and widens its valley through processes like abrasion and plucking. Over thousands of years, this action transforms a pre-existing river-carved V-shaped valley into a characteristic U-shaped glacial valley.
Concurrently, smaller tributary glaciers flow into this main glacial valley from the sides. These tributary glaciers, having less ice volume and therefore less erosive capability, cannot cut down into the landscape as deeply as the main glacier. Consequently, their valleys are eroded at a slower rate, remaining at a higher elevation relative to the rapidly deepening main valley. When the ice eventually melts and retreats at the end of a glacial period, the tributary valley is left suspended high above the main valley floor, creating the “hanging” appearance.
Identifying Features
Hanging valleys have several distinct characteristics. The most striking feature is the abrupt elevation difference where the tributary valley terminates high above the main valley. This often results in a steep cliff or a pronounced drop-off from the mouth of the hanging valley to the main valley floor. Waterfalls are a common indicator of a hanging valley, as streams or rivers flowing from the higher tributary valley cascade down into the lower main valley.
Both the main valley and the hanging valley typically display a U-shaped cross-section, a clear signature of glacial erosion. This U-shape, characterized by steep, often near-vertical sides and a flat or rounded bottom, distinguishes them from the V-shaped valleys carved by rivers. The presence of these parallel U-shaped profiles, with one positioned significantly higher than the other, helps confirm the glacial origin of the landform.
Notable Examples Worldwide
Hanging valleys are found in many glaciated mountainous regions across the globe. Yosemite National Park in California is known for its numerous hanging valleys and the waterfalls they produce. For instance, Yosemite Falls, one of North America’s tallest waterfalls, plunges from a hanging valley into the main Yosemite Valley. Bridalveil Fall is another prominent example, cascading from its own hanging valley into the larger glacial trough.
The fjords of Norway also provide examples of hanging valleys, which often contribute to the scenery with waterfalls plunging into the deep, U-shaped inlets. These narrow, steep-sided fjords, such as Sognefjord and Geirangerfjord, were carved by massive glaciers that extended to the sea. The Alps, spanning several European countries, also feature numerous hanging valleys formed by extensive past glaciation, contributing to the region’s rugged landscapes.