Glaciers erode rocks, but exactly how this process occurs remains largely unexplained. Scientists are currently working to understand its mechanisms through rock profiles, climate data analysis and an innovative tool.
Abrasion is an essential component of glacial erosion, but only under certain conditions. Two other processes include plucking and freeze-thaw weathering which also play an integral part.
What is a glacier?
Glaciers are huge bodies of ice that move down mountain valleys like rivers. Their weight allows them to transport rocks and dirt along their journey, scraping away at bedrock below before breaking them up into fine particles called rock flour.
Glacier erosion often appears as long scratch-shaped depressions in the underlying rock surface known as glacial striations striations striations that point in the direction that the glacier was moving.
Other hallmarks of glacial erosion include cirques (bowl-shaped depressions), hanging valleys (U-shaped valleys), and horns (pointy mountain peaks created when multiple glaciers erode all sides of a mountain). This process, known as glaciation, and its study is known as glaciology. Glaciers typically erode bedrock by either plucking or abrading it; freeze-thaw weathering also plays an integral part in this process.
What is ice?
Ice itself is not particularly effective at erosion; rather, the rock fragments embedded within its depths cause most of the destruction. To visualize this effect, think of rubbing paper over wood; nothing significant happens, while using sandpaper can produce considerable abrading effects.
Glacier erosion gives rise to several features: aretes: sharp ridges that separate U-shaped valleys; cols: low points along aretes that serve as passes between glacial valleys; horns: pointed mountain peaks and cirques: round basins cut into mountain slopes. Other formations result from the erosion of ice deposits: drumlins (winding ridges of sand and gravel); moraines (accumulated debris on glacier bed surfaces), and talus (deposited boulders and cobbles from melting).
What is abrasion?
Abrasion occurs when glaciers rub and scrape against rocks beneath them, creating telltale landforms such as striations lines, grooves and glacial pavements. Abrasion also produces fine-grained material known as rock flour which gives glacial streams their characteristic milky color.
Glaciers are highly efficient erosion machines. They move large stones such as boulders and sand across land masses before depositing them on valley sides as moraines or even scraping away mountain faces altogether.
As glaciers generally consist of rock particles of similar size and strength, they tend to create similar types of features when erosion takes place. If they encounter harder rock however, different landforms will result.
What is plucking?
Glaciers often collect large chunks of rock and sediment as they flow, known as plucking.
Process of glacial erosion and deposit are at their peak when glaciers are moving down valleys; this type of glacier is known as a valley glacier and, as it moves along its course, creates distinctive landforms along its route.
These features include stoss-and-lee topography and glacial striations – long parallel scratches which mark where glaciers moved.
Plucking is responsible for creating features known as horns. Horns form when glaciers erode mountain sides, producing hanging valleys and moraines as well. Geologists use these features as indicators of where and how a glacier has eroded certain regions.
What is freeze-thaw weathering?
Glaciers are powerful forces of erosion, creating landforms such as U-shaped valleys, U-horned horns, hanging valleys and glacial striations. Furthermore, glaciers leave deposits called moraines behind when retreating glaciers retreat – piles of rocks, dirt and other debris left behind from an retreating glacier’s retreat.
Rain can have an indirect effect on glacier erosion. When percolated through its base, rainfall can lubricate the interface between ice and rocks to accelerate its destruction faster.
Plucking and abrasion are the two principal processes of glacial erosion, creating distinctive landforms like horns, hanging valleys, cirques and moraines that reveal where and how far glaciers advanced.